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Materials Science and Engineering Laboratory 

CERAMICS 


NAS-NRC 
Assessment Panel 
April 21-22, 1994 


NISTIR 5313 

U.S. Department of Commerce 
Technology Administration 
National Institute of Standards 
and Technology 



— QC— 
100 
.056 
1994 
//5313 


Technical Activities 
1993 


Machining can constitute a significant proportion of of the cost 
of production of a ceramic component. Diamond wheel 
grinding, as depicted in the cover schematic drawing, is the 
most widely used method of surface finishing in the advanced 
ceramics industry. The Ceramics Division program in grinding 
addresses the development of both an understanding of the 
process and a database on the effect of process parameters on 
material properties. The latter effort is conducted as a 
NIST/industry/university consortia. 


HSEL 


Materials Science and Engineering Laboratory 

CERAMICS 


S. W. Freiman, Chief 
S. J. Dapkunas, Deputy 


NAS-NRC 
Assessment Panel 
April 21-22, 1994 

NISTIR 5313 

U.S. Department of Commerce 
Technology Administration 
National Institute of Standards 
and Technology 


Technical Activities 
1993 



U.S. DEPARTMENT OF COMMERCE 
Ronald H. Brown, Secretary 

TECHNOLOGY ADMINISTRATION 

Mary L. Good, Under Secretary for Technology 

NATIONAL INSTITUTE OF STANDARDS 
AND TECHNOLOGY 
Arati Prabhakar, Director 




TABLE OF CONTENTS 

Page 

OVERVIEW 1 

TECHNICAL ACTIVITIES 5 

I. Data Technologies 7 

II. Powder Characterization and Processing 15 

III. Surface Properties 33 

IV. Mechanical Properties 63 

V. Electronic Materials 89 

VI. Optical Materials 107 

VII. Materials Microstructure Characterization 123 

RESEARCH STAFF 141 

OUTPUTS AND INTERACTIONS 151 

Technical Publications 153 

Patents 165 

Conferences and Workshops Sponsored 169 

Standard Reference Materials 171 

Technical/Professional Committee Leadership 175 

Industrial and Academic Interactions 179 

FACILITIES 201 

APPENDIX 

Organizational Chart 

National Institute of Standards and Technology 

Organizational Chart 

Materials Science and Engineering Laboratory 

Organizational Chart 
Ceramics Division 







OVERVIEW 


In 1993 the Ceramics Division continued to emphasize a technical program directly relevant to 
the needs of U.S. industry. This program is made up of tasks which involve standard materials 
development, construction of evaluated databases, and laboratory research focused on topics that 
address the dominant issues affecting commercialization of advanced ceramics, namely, 
processing costs and reliability. 

In accord with the strategic plan laid out by the Materials Science and Engineering Laboratory, 
the Ceramics Division is continuing to expand its direct involvement with industrially related 
research issues. For example, during this past year a new consortium which will address the 
intelligent processing of ceramic powders and slurries was formed with six industrial members. 
The Ceramic Machining Consortium, established in 1992, and consisting of 17 members from 
industry and academia, is already generating data which will help companies to optimize their 
manufacturing processes. Other direct programs with industry have been conducted over the 
past year with Itek Optical Systems, a division of Litton Industries, and one with Norton/Saint 
Gobain. The Division is also increasing collaborative research activities with other Federal 
laboratories, e.g., Sandia National Laboratories and the Oak Ridge National Laboratory. 

Another important role that the Division continues to play is to bring together U.S. industrial 
representatives to obtain firsthand knowledge of their research priorities. As examples, 
workshops were conducted on Measurement Issues in Diamond Films, Lubrication for Advanced 
Engine Materials, and Machining of Advanced Materials. 

The output of the Ceramics Division program is made available to U.S. industry and the 
ceramics community through a number of avenues including presentations, publications, and 
direct collaborations with companies and universities. During this past year the research 
program produced 125 publications, 133 presentations, and three invention disclosures. Five 
new Cooperative Research and Development Agreements (CRADAS) were signed with 
companies and universities. 

Standard materials and data activities continue to represent an important portion of the Division’s 
program. Three new Standard Reference Materials were developed this year, and an evaluated 
database on high T^, superconducting materials was begun in collaboration with a Japanese 
laboratory. 

A major effort over the past few years has involved the NIST leadership of the International 
Energy Agency ceramic powder characterization program. During the past year powder analysis 
techniques developed on this program were released to standards organizations in the U.S., 
Japan, and Europe. 

The Division’s program on high T^, superconducting materials has continued to focus on research 
relevant to the production of bulk products such as superconducting wires and magnets. We are 
working closely with the Department of Energy and U.S. companies to develop the data, 
measurement procedures, and understanding needed for wire development. NIST recently 


1 


became a member of the Wire Development Group, a partnership between the Oak Ridge 
National Laboratory, Argonne National Laboratory, Los Alamos National Laboratories, and the 
University of Wisconsin to enable the American Superconductor Corporation to commercialize 
superconducting products. 

Work on the use of nanosized materials is being expanded. As examples, research on the 
development of magnetic nano-composites for use in refrigeration has continued in collaboration 
with the Metallurgy Division. A study is being carried out on the issues of scale-up of the 
process for producing silicon nitride from nanosized starting powders. Finally, Division 
personnel are investigating the preparation of Bi 2 Te 3 composites which are of interest as 
components in thermoelectric refrigerators. 

In 1993, both funding and staff levels remained relatively constant. The relatively high 
percentage of funds from other government agencies continues to be a concern, but we are 
optimistic about the future support of the NIST laboratory program through the Congressional 
budget process. 

Finally, during the year. Ceramics Division personnel were significantly involved with the NIST 
Advanced Technology Program (ATP). S. J. Dapkunas and J. A. Carpenter served as members 
of the ATP Source Evaluation Board for competitions held in 1993, and a large percentage of 
Division personnel participated in the ATP review and program monitoring processes. 

Stephen W. Freiman 
Chief, Ceramics Division 


2 


TECHNICAL ACTIVITIES* 


Certain trade names and company products are mentioned in the text or identified in illustrations 
in order to adequately specify the experimental procedure and equipment used. 

In no case does such identification imply recommendation or endorsement by the National 
Institute of Standards and Technology, nor does it imply that the products are necessarily the 
best available for that purpose. 


3 




TECHNICAL ACTIVITIES* 





>■ 





DATA TECHNOLOGIES GROUP 


I. 


S. J. Dapkunas 


The objective of the Data Technologies Group is to develop and facilitate the use of evaluated 
data bases for the materials science and engineering communities. 


Both research and application directed organizations require readily available evaluated data to 
take advantage of the large volume of materials information developed on public and privately 
sp)onsored programs. This information, particularly numeric data, is available in an ever 
increasing number of publications published worldwide. The necessity to consolidate and allow 
rapid comparison of properties for product design and process development underlies the 
database projects in the Ceramics Division. 


The Data Technologies Group activities extend from traditional data compilation to data transfer 

protocols and the development 

of interactive tutorials on the use of materials data. 


Specific projects include (1) the traditional Ceramic Phase Equilibria Program conducted in 
cooperation with the American Ceramic Society; (2) the Structural Ceramics Database developed 
with support of the Gas Research Institute; (3) the High Temperature Superconductor Database 
recently initiated in cooperation with the Japanese National Research Institute for Metals; (4) 
implementation of STEP protocols for international exchange of materials data under the 
auspices of the ISO 10313 activity and; (5) the development of a phase equilibria tutorial 
utilizing digital-video-interactive technology. 

Significant Accomplishments: 

• The Ceramics Division and the Standard Reference Data (SRD) Program completed 
negotiations with Japan’s National Research Institute for Metals to establish a 
collaborative, international effort to develop a computerized database of evaluated 
materials properties for high-temperature superconductors (HTSC). 

• The Ceramics Division and the SRD Program have initiated a program with the Russian 
Research Center for Standardization, Information, and Certification of Materials to 
establish evaluated property data for selected oxide and carbide structural ceramics from 
worldwide sources. The data will become part of the NIST Structural Ceramics Database 
which is distributed by the NIST SRD Program. 

• An assessment of the corrosion of silicon carbide and silicon nitride ceramics was 
completed under funding from the Department of Energy’s Pittsburgh Energy Technology 
Center. These materials are candidates for use in coal-fueled heat exchanger applications 
in which the temperature exceeds 1000 °C and the environments are often complex 
gaseous and particulate mixtures. Included in the study are atmospheres of dry and moist 
oxygen, mixtures of hot gaseous vapors, molten salts, molten metals, and complex 
environments pertaining to coal ashes and slags. 


7 


High-Temperature Superconductors 

R. G. Munro, and J. R. Rumble, Jr.^ 

^ NIST Standard Reference Data Program 

High-Temperature Superconductors (HTSC) comprise one of the most intensely studied classes 
of materials currently available. Since their discovery in 1986, more than 35,000 reports on the 
processing, characterization, and properties of these materials have been published in the open 
literature. This prolific publication rate is evidence of the intense interest in the potential 
applications of these materials. Developing commercial applications, however, requires the 
fabrication of HTSC materials into useful forms such as films on non-HTSC substrates or as 
wires. The fabrication of such forms is highly dependent on the thermal, mechanical, and 
chemical properties of these materials because HTSC materials are brittle and often reactive with 
the relevant substrate materials under processing conditions. While extensive bibliographic 
databases of titles and abstracts of reports are maintained by several public and private agencies, 
there has been no systematic compilation, evaluation, and computerization of the numeric data. 
As a result, there are three major information barriers confronting materials researchers and 
application designers who would like to use HTSC materials: (1) the quantity of reports; (2) the 
reliability of the data; and (3) the currency of the results. These barriers are best resolved 
through the use of evaluated computerized databases. 

In 1992, NIST initiated the development of a computerized database of evaluated materials 
properties for HTSC materials to fulfill this critical need. The project aimed to provide a 
comprehensive source of information about HTSC materials. Included in the project design were 
details about processing and measurement methods, chemical composition, crystal structure, a 
full range of thermal and mechanical properties, and the critical characteristics of high- 
temperature superconductors. 

To ensure the most comprehensive coverage of these rapidly developing results, NIST in the 
U. S. and the National Research Institute for Metals (NRIM) in Japan established an agreement 
to collaborate on this effort. NRIM has agreed to provide data not only from Japanese language 
publications, but also from a special long-term experimental research effort sponsored by Japan’s 
Science and Technology Agency (STA). In the STA project, a master batch of material is 
prepared by a selected industrial material manufacturer. Samples from the master batch are then 
sent to numerous laboratories to provide complementary characterization and property 
measurements. The result is a detailed collection of data from a single batch. At the present 
time, there does not appear to be any other effort comparable to this STA project anywhere in 
the world. Under the NIST-NRIM agreement, the STA data will become accessible through the 
NIST database project. 

The first release of the computerized HTSC database is expected to be ready near the end of 
fiscal year 1994. The program will run on IBM-compatible personal computers under a 
Windows environment. 


8 


Structural Ceramics Database 


R. G. Munro, J. R. Rumble, Jr., and S. J. Dapkunas 

The potential applications of advanced structural ceramics have been widely appreciated for 
several decades. Characteristics such as strength retention at high temperature and chemical 
stability have held forth tantalizing possibilities for more efficient engines, heat exchangers and 
recuperators, and for more durable chemical processing components. The Structural Ceramics 
Database (SCD) provides evaluated data for the properties of the primary candidate ceramics for 
such applications. 

The original scope of the database, materials for gas-fueled heat exchangers, has been greatly 
expands! . Efforts are now underway to include thermal, mechanical, and chemical property 
data for all types of nominally monolithic structural ceramics. One goal of this new effort is 
to include data from worldwide sources, especially data that are generally considered by U. S. 
industries to be inaccessible in practice. Towards that end, cui agreement has been established 
with the Russian Research Center for Standardization, Information, and Certification of 
Materials. The Russian group will use the NIST SCD Data Entry Software to provide evaluated 
data for AI 2 O 3 , B 4 C, TiC, and Zr 02 . The data records will include text entries for material 
processing and specification information, text entries for descriptions of measurement methods, 
and numeric data for the thermal, mechanical, and chemical properties. 

In a special effort, the Ceramics Division has completed a review of the corrosion of two 
important classes of structural ceramics, silicon carbides and silicon nitrides. When any load- 
bearing material is used in a corrosive environment, the primary concerns are the survival of 
the material and the retention of its strength. While the corrosion rates for ceramics can be 
relatively small, surface pitting and an overall increase in the surface flaw populations generally 
cause the strength of the material to be decreased and the mechanical lifetime to be reduced. 
The effects, however, depend significantly on the compositions of the materials, the impinging 
environment, the exposure history, and the thermal and mechanical characteristics of the 
application. The NIST review examined the effects of corrosion on material properties, 
performance, and durability in diverse environments, usually at temperatures of 1000 ®C or 
higher. The environments included dry and moist oxygen, mixtures of hot gaseous vapors, 
molten salts, molten metals, and complex environments pertaining to coal ashes and slags. The 
quantitative results from this study will be incorporated into the next version of the Structural 
Ceramics Database. 

Phase Equilibria Information System Incorporating Digital Video Interactive Technology 

E. F. Begley and C. G. Lindsay 

In materials research, the phase diagram is a critical processing tool describing the relationship 
between temperature, chemical composition, and gaseous environment to the crystalline phases 
that should appear. The phase diagram can be considered a "blueprint" for processing materials 
such as ceramics. The Ceramics Division has initiated the development of innovative, 
distributable, multimedia software incorporating digital video interactive (DVI) technology to 


9 


assist in the understanding and use of these diagrams. This new software will complement phase 
diagram work that has been part of almost 60 years of cooperation between NIST and the 
American Ceramic Society. 

Two stages have been planned for this project. The first stage will concentrate on developing 
an application that will enable individuals to learn or review how to interpret and use unary, 
binary, ternary and quaternary phase equilibria diagrams. This is a necessary precursor to the 
second stage which will concentrate on the implementation of an application that will provide 
instruction in developing phase diagrams. The goal of this latter stage is to capture in an expert 
system the relevant expertise of Dr. R. S. Roth, a nationally recognized scientist with forty years 
of experience and integrate it with digital video and audio clips of Dr. Roth in action. In this 
way, the expertise, particularly the laboratory techniques and insights which do not appear in 
technical publications, would be preserved for future generations and, furthermore, would be 
widely distributable. 

The software will make extensive use of DVI technology which allows motion video and audio 
signals to be digitally compressed and integrated with traditional software. Motion video and 
audio allow the user to visualize technical content to an extent not possible with a textbook, this 
would be particularly helpful in presenting crystallization sequences in ternary systems. 
Textbook presentations of this principle are often difficult to follow because they necessarily rely 
on printed words and still pictures to convey the concepts. The ideas are easier to grasp when 
the sequence is seen to develop in a moving picture accompanied by an audible explanation of 
what is being shown. As a simple example, a user who does not understand the concept 
embodied in the term "phase" could ask the software for an explanation. Rather than responding 
with simple text, the software would show a short video of an expert explaining the concept by 
actually pointing out the distinct interfaces between phases and demonstrating the separability 
of two phases. 

The target audiences for the software are U.S. industrial scientists and engineers as well as 
university students in geology, petrology, and materials science programs. Consequently, an 
essential consideration in selecting and arranging the content of the software is the breadth of 
occupational and educational levels of the intended audience. Students being exposed to this 
materials for the first time need to have the full range of pertinent information available for their 
study, practice, and review. Definitions of terms and concepts must be complete and accurate, 
but should be incorporated in a way that the main part of the presentation, phase diagram 
interpretation, does not suffer from too much detail. Professionals reviewing the materials are 
more likely to want immediate answers to a few questions about phase diagram interpretation 
without having to wait through extended presentations of supporting concepts. However, in 
seeking the answers to these few questions, the need occasionally arises to review a supporting 
concept as well. Therefore, as much detail as practicable will be included and arranged in 
segments that can be called by the user as desired. 

At this point, the components required to develop this software have been acquired and several 
of the important concepts and definitions have been identified. Video and audio segments have 
been incorporated into interactive software and the demonstration system was presented to the 
American Ceramic Society Technical Review Committee in November 1992. We are working 


10 


to establish a cooperative relationship with the University of Maryland to develop the academic 
or classroom perspective needed to identify areas troublesome to students, the knowledge of 
cognitive issues important to learning, and a testbed of students to check the quality and 
effectiveness of the tutorial. 

STEP Materials 


J. A. Carpenter, Jr. and J. R. Rumble, Jr.^ 

^ NIST Standard Reference Data Program 

STEP is the STandard for Exchange of Product Data Model, the now-emerging world standard 
for computerized exchange of data on manufactured parts. ISO is the International Organization 
for Standardization and IPO is the IGES/PDES Organization, the organization primarily 
responsible for the development and promulgation of STEP in the United States. 

In this period, J. A. Carpenter, Jr. assumed leadership of the ISO/IPO STEP Materials 
Committee. That committee refined and issued ISO 10303 Part 45 Materials as a CD 
(committee Draft), which is currently in ballot by participating ISO countries to determine if it 
shall advance to a DIS (Draft International Standard). 

Meetings were held with staff of the Semiconductor Research Corporation (SRC) and the 
Microelectronics and Computer Technology Corporation (MCC) resulting in both organizations’s 
serious consideration of adopting STEP in various developmental CAD/CAM projects. These 
interactions also resulted in identifying the materials-related information needed in those projects. 

Additional meetings were held with staff of the Society of Plastic Industries (SPI) and certain 
of its member companies toward the adoption of STEP in the exchange of data from the testing 
of materials, the initial focus being on polymers. 


11 



CERAMIC PHASE EQUILIBRIA PROGRAM 


S. W. Freiman, M. A. Clevinger, T. R. Green\ K. M. Hill\ 

N. Swansong E. Hayward^ C. L. Cedeno^’ and H. M. Ondik 

^American Ceramic Society Research Associates 

The Ceramic Phase Equilibria Program continues to provide the ceramics user community with 
evaluated phase equilibria data covering all non-alloy, inorganic systems. This past year has 
been the eigth full year of operation of the Ceramics Phase Diagram Data Center under the 
expansion plan sponsored cooperatively by NIST and the American Ceramic Society (ACerS). 
Over $2,500,000 was raised by the ACerS from industry and universities for the support of the 
program. 

Examination, evaluation, and digitization of diagrams for inclusion in Volume 10 of Phase 
Diagrams for Ceramists (now entitled Phase Equilibria Diagrams) has been completed. This 
topically-oriented hardcover volume contains boride, carbide, and nitride systems of interest to 
the structural ceramics community. It will be available for distribution in April 1994. Volume 
1 1 , focusing on oxides, particularly those of interest for electronic applications will be completed 
early in 1995. 

An updated and expanded database system for use on DOS-based personal computers (PC) will 
soon be ready for marketing by NIST and the ACerS. The original version has undergone 
extensive revisions based upon comments received when demonstrated at meetings, and advice 
from the Standard Reference Data Program staff. The system provides for search and 
manipulation of both textual and graphics information. 


13 





II. POWDER CHARACTERIZATION AND PROCESSING 


Subhas G. Malghan 


The US advanced structural ceramics industry is continuing to focus on the demonstration of 
cost-competitive ceramics production. Though several components such as machining have a 
large influence on total cost, the powders and their processing to green and sintered state is 
another major factor. In addition, the industry is moving toward the production and application 
of lower cost materials such as reaction bonded silicon nitride for heat engine applications or 8 % 
Y 2 O 3 containing zirconia for thermal barrier applications. Since most of these processes start 
with fine-size powders as the starting materials, their characterization and processing play a 
significant role in deciding cost-effective manufacturing. Some issues affecting cost-effective 
manufacturing are synthesis of novel powders that have tailored properties, repeatability and 
reproducibility in the measurement of powder properties, procedures in the characterization of 
secondary properties, and powder-aqueous environment interactions. 

Our program on ceramic powders characterization and processing is designed to address some 
of these significant issues. The primary focus of our program is on improvement of 
measurement quality in ceramic powders processing. This is accomplished by providing the 
US ceramics community the ability to control ceramic powder properties so that cost-effective 
manufacturing can be achieved. The program is continuing to emphasize structural ceramics 
with applications of silicon nitride to automotive engines and zirconia to coatings for use in 
aircraft engines. The specific elements of the program are the development of: 

• Ceramic powder characterization techniques measurement science, standard 

methods, and standard reference materials; 

• Powder processing science to understand interrelationships between powder 
characteristics, and their processing environment; and 

• Novel synthesis methods as applied to nano-size and ultra-pure powders for processing 
studies. 

The major components of the powders characterization program have been the development of 
standard procedures, standard reference materials, improving the scientific basis of powder 
dispersion measurements in slurries, overall improvement in measurement accuracy, and 
leadership in national and international standardization activities. The powder characteristics of 
interest include physical and surface chemical properties, and phase composition. In powder 
processing, our efforts have been focussed around nano-size silicon nitride powders processing, 
high energy agitation milling of powders, and microstructure modeling as applied to the behavior 
of particles under stress fields such as in injection molding. The powder synthesis activities aiQ 
directed toward synthesis of novel precursors and powders for ferrites use as thick films in 
microwave applications, bismuth telluride-based powders as thermoelectric materials, and 
magnetic nano-composites for magnetic refrigeration. 

Four new efforts were initiated during the year: 1. A joint NIST-industry consortium on 
intelligent processing of powders and slurries; 2. Extension of international cooperation activity 
on the development of procedures for secondary properties of powders under the auspices of the 
International Energy Agency; 3. Characterization of powders used as thermal barrier coatings; 


15 


and 4. Modeling and powder-processing interrelationships in injection molding. The consortium, 
based on our past four years of research, is primarily directed toward developing electroacoustics 
as a sensor for on-line dispersion monitoring. This effort is expected to be expanded in the 
future to include other sensors, and models development. The second and third efforts are 
attempting to develop powders specifications by expanding the range of properties that have 
relevance to powder response during processing. In the fourth effort, our major activities will 
be to model the behavior of particles under stress fields as applied to injection molding, and to 
enhance the characterization of powders and green bodies, as applied to injection molding. 

Our future activities are expected to focus on improved understanding of surface chemical 
interactions between powder and gel-forming chemicals, physical and chemical barriers 
preventing high green density compaction of nano-powders, near-net-shape forming to decrease 
the need for machining, and novel methods of coating oxide and non-oxide powders. 

Significant Accomplishments: 

• The final report on Subtask 6 , a powders characterization project under the auspices of 
the International Energy Agency (IE A), was released to participants. In addition, the 
report was approved for release to the standards setting bodies in Japan, Europe, and the 
US. This step is expected to speed up the standardization programs in the participating 
countries. This is considered to be a significant decision since a number of procedures 
in this report are ready for standardization, and their unavailability has been a barrier to 
commercialization in the past. 

• A follow-up to the powders characterization project under the IE A program was initiated. 
The primary emphasis of this project is to focus on secondary properties of powders that 
potentially have a major influence on the behavior of powder during processing. These 
procedures are expected to play a significant role in the development of powder 
specifications. Two additional countries (Norway and Belgium) have joined this activity 
that brings the total to six, and the number of participants to 44. 

• A NIST-industry consortium to address intelligent processing of powders and slurries was 
initiated. This project, in the initial stages, will focus on the development of 
electroacoustics for on-line measurement of dispersion during aqueous processing of 
powders, and on the nuclear magnetic resonance for developing improved understanding 
of homogeneity in slurries and green ceramic. Six industrial organizations have joined 
this consortium. 

• The data on compaction and pressureless sintering of nano-scale silicon nitride and 
alumina powders show that the green density has a significant influence on the amount 
of final densification. Cryogenic compaction of 3 mm diameter samples yielded a 
maximum random packing which resulted in green densities of 64% and 74% for 
amorphous silicon nitride and 7 -alumina, respectively. Sintering results on these green 
compacts showed that increased interfacial contact between the particles in silicon nitride 
are required for improved densification. 


16 


• In the development of a silicon nitride standard reference material (SRM) for phase 
composition analysis, time of flight neutron analysis data has been obtained to enhance 
the accuracy to the order of 0.1%. The x-ray diffraction for certification of this SRM 
was carried out by using Rietfeld method. The SRM will contain two powders that have 
either a high alpha or beta phase composition. 

• In a collaborative study with Pennsylvania State University on alumina green compacts, 
improved capabilities of solid state nuclear magnetic resonance were demonstrated. The 
distribution of a three component binder was mapped in three dimensions using the 
measurement of proton nuclear spin-spin relaxation times (T 2 ) of binders. In addition, 
a mobile proton species produced during injection molding was detected by the T 2 study. 

• Experimental studies involving electroacoustics, adsorption, and dispersion measurement 
on a number of powders showed that there is a unique way to describe the parameters 
for dispersion of powders in water. The effective pH at which the particles carry a net 
zero charge and the pH of dispersion are the most important parameters that define 
dispersion using polyelectrolytes in aqueous environment. Using this information, one 
can develop dispersion parameters for most powders of interest to structural ceramics. 

• In the electroacoustic analysis of silicon nitride powders, the studies on influence of 
inorganic salts and organic polyelectrolytes have concluded that the measurement of 
electrokinetic sonic amplitude (ESA) has the potential to provide data on powders in 
concentrated suspensions. These studies have formed the basis for the proposed NIST- 
industry consortium. A workshop was organized at NIST to identify issues in the 
measurement of surface chemical properties of the powders in aqueous and non-aqueous 
environments. 

International Interlaboratorv Comparison of Powders Characterization 

S. Malghan and L. Lum 

As the structural ceramics industry is progressing toward commercialization, the need for 
developing commonly acceptable procedures for measurement of powder properties is more 
important then ever. Some of the reasons for this continuing need are the use of submicrometer 
powders as the starting materials in the manufacture of ceramic components, and nature of 
international trade involved in the production and use of fine powders. The powders used in the 
production of structural ceramics continue to be produced and used in different countries. 

This is a continuing project under the auspices of the International Energy Agency (IE A) in 
which six countries are now participating. The overall goal of the project is to develop pre- 
standardization procedures for characterization of powders. In 1993, Subtask 6 was completed, 
and the final report on the project was released to participants. In addition, a highlight of the 
accomplishments was the decision by the Executive Committee to release the report to the 
standards setting bodies in the participating countries. As a result, ASTM, CEN, and JSA will 
be able to use the round-robin data and procedures for developing their standards. Eventually, 
this effort is expected to speed up the development of international standards. The ASTM C- 


17 


28.05 subcommittee has already initiated efforts to draft procedures based on this report. 

During the year, a technical plan for Subtask 8, a continuation of Subtask 6 powder 
characterization project, was developed. Subsequently, the plan was approved by the 
participants, technical leaders, and the lEA Annex 2 Executive Committee. The overall goal 
of this project is to develop pre-standardization procedures for characterization of secondary 
properties of powders such as those for the measurement of slurry pH, green density, and 
porosity of green ceramic. In addition, several procedures for the measurement of physical, 
bulk chemical, and surface chemical properties will be examined to improve the quality of data. 
This is an ambitious project involving a number of very important parameters of powders that 
have the potential to provide practical guidelines to develop powder specifications. Japan, 
Germany, Sweden, Norway, Belgium, and the US are participating in this project with the total 
number of participants at 44. Now, we are developing procedures, collecting powders, and 
validating the procedures. All three activities require extensive experimental investigations since 
only a small amount of data are available in the open literature. The samples and procedures 
are expected to be sent to participants in the next six months. 

Standard Reference Materials for X-Ray Diffraction fXRDl 

J. P. Cline 

Standard Reference Materials (SRMs) for powder diffraction serve to increase the accuracy and 
precision of measurements by providing a range of materials that exhibit certified or model 
diffraction properties. SRMs allow the user to trace the results of their measurements to 
fundamental physical constants, or to values decided through round-robin studies conducted in 
conjunction with the International Centre for Diffraction Data (ICDD). Quantitative analysis 
SRM powders are selected for phase purity and freedom from microstructural characteristics that 
may induce errors in diffraction intensity measurements. A brochure that discusses the range 
of NIST SRMs for powder diffraction is available from the Office of Standard Reference 
Materials (OSRM). The following is a brief description of the XRD projects. 

We have undertaken a project in collaboration with the Quantum Metrology Division to develop 
new, high accuracy line position SRMs using an optically-based wavelength/crystal-spacing 
scale. The fundamental basis is the wavelength of an iodine-stabilized HeNe laser operating near 
633 nm that is the most accessible current embodiment of the length standard. The strategies 
available to us for powder lattice normalization include: continuation of the use of an x-ray line 
profile as a transfer standard; generation of a effectively narrower profile (likely extracted from 
a synchrotron radiation continuum) by using a monolithic crystalline monochromator as a 
transfer standard; or devising a comparator scheme by which a powder spacing may be related 
to the lattice period of a single crystal. For any of these procedures, we are restricted to parallel 
beam optics to fit the single crystal characteristics and to gain immunity from penetration effects 
in the powder specimen. 

In parallel with the efforts to assure adequate linkage of the powder spacing scale to basic length 
standards, another part of this effort is aimed at assuring more optimized and stable materials 
for distributable line position SRMs. In this aspect, we are examining the effect of crystallite 


18 


size on the observed lattice spacings and the stability of the sample d-values with respect to 
aging and environmental degradation. Of particular significance to this component of the effort 
is the application of fabrication techniques aimed at producing a narrow range of crystallite sizes 
and particle morphologies. 

A new line profile SRM that displays profiles broadened by crystallite size effects is presently 
in development. Two methods of pattern deconvolution are being evaluated for use as a 
certification method. The first consists of the Williamson-Hall approach which requires that the 
sample broadening be modeled by a specific profile shape function. The second approach 
involves a Fourier analysis of the diffraction profiles. This method is prone to noise in 
diffraction data unless analysis excludes the tail region of the diffraction peaks. The four 
candidate alumina powders considered for use as the material for SRM 676, an alumina SRM 
certified for quantitative analysis, were analyzed for crystallite size and micro-strain using these 
techniques. TTie accurate characterization and modeling of broadening due to the instrument was 
found to be critical to the accuracy of the results from both methods. 

The certification measurements for SRM 656, a quantitative analysis SRM for the two phases 
of silicon nitride, were completed. The preferred powders for quantitative analysis SRMs 
consist of phase pure materials of single crystal, isometric particles between 0.5 and 1.0 ^m 
range. The particle size of such powders permits a minimum specific surface area for a material 
that is free from the effects of extinction. Other factors held constant, the surface of crystal is 
a region of disorder and, therefore, minimization of surface area will reduce "amorphous" or 
surface phase contamination. Single crystal particles of isometric morphology would not impart 
the effects of microabsorption or preferred orientation to subsequent measurement data. The 
SRM consists of two powders, one containing a large amount of the a phase, while the other 
is high in jS. 

The quantification of amorphous content requires a material that is considered to be absolutely 
phase pure for a baseline and measurements that are free of systematic bias. Such a bias is 
expected to affect x-ray measurements to a greater extent than the neutron data due to the 
manifestations of the more complex x-ray optics; neutron measurements have been accurate to 
within 1 % while x-ray measurement errors are typically several times this value. The spectrum 
of radiation used in neutron time-of-flight (TOF) experiments permits the measurement of 
extinction effects. Thus, the former of the two approaches may be pursued with x-ray 
diffraction measurements, while the latter two may be pursued with neutron TOF measurements, 
with the aid of phase pure standards. Both x-ray powder diffraction and neutron TOF analysis 
have been used to obtain the accuracy required for analysis of amorphous content to the range 
of 0.1 % for certification of SRM 656. 

Particle Size Distribution Standards 

J. Kelly, L. Lum, and S. Malghan 

The measurement of particle size and particle size distribution of the starting powder as well as 
powders during processing is important for achieving the desired properties and microstructure 
from the final product. The ceramic industry produces ceramic components of both non-oxide 


19 


and oxide materials. NIST had developed and certified SRM 659 as a silicon nitride powder 
particle size distribution standard. Subsequently, the need for an oxide SRM was identified. 
In addition, the ability to measure accurately and reproducibly the size distribution of powdered 
materials is a critical need of the ceramics and glass industries as well as other industries using 
powders or granular materials. An important element in achieving this capability in industrial 
analytical laboratories and quality control programs is the availability of appropriate SRMs of 
similar composition to those being processed. 

The certification of a silicon nitride powder as SRM 659 for x-ray sedimentation type of 
equipment was completed in 1992. While SRM 659 provides a standard in the one micrometer 
range, the requirements for standards in larger size ranges are satisfied by several SRMs using 
spherical glass beads. One of the objectives of this year’s effort was to determine the size 
distribution of two glass bead SRMs that are used for evaluation and calibration of particle size 
measurement instrumentation. Toward that end we have developed a sample preparation 
protocol using successive stage riffle-splitting for obtaining representative 6 mg subsamples of 
the particles from 25 g bottles. The glass beads are imaged by optical and scanning electron 
microscopy and digital image files created by optical scanning of photographs. A computer 
program using commercially available software has been written to analyze the digital image 
files. The computer program calculates the projected area of the glass beads and the equivalent 
sphere diameter for each of approximately twenty thousand particles taken from several samples 
of the powder. These data were used to generate the measured size distributions and calculated 
cumulative weight distributions for SRM certification. The production and certification have 
been completed for glass bead SRMs 1003b and 1004a. 

In another effort, SRM 1978 was developed to provide a standard material in the one micrometer 
range for use in zirconium oxide powder processing using gravitational sedimentation 
instruments. This SRM was developed by an interlaboratory comparison study to establish the 
certified values by four laboratories in the U.S., Japan and Sweden. The experimental 
procedure developed for this SRM is similar to that for SRM 659. The uncertainty in the 
certified value at the 50th percentile, 0.98 fxm, is 0.04 fxm based on all data. 

These reference materials are now available through OSRM. Close communication with the 
industrial end-users of NIST SRMs is maintained through active participation in the ASTM 
committees relating to ceramics, glass, and particle size standards. 

Standards for Mobility Measurements 

S. G. Malghan, R. S. Premachandran, and V. A. Hackley 

The dispersion characteristics of ceramic powders and other particulate materials depend on the 
zeta potential of the powder in suspensions. Generally, a high zeta potential or electrokinetic 
mobility is required for a better dispersion. Though these measurements are carried out in a 
large number of industries including ceramics, minerals, solid and liquid waste processing, and 
biological, no standards are available to assure reproducibility and accuracy. Based on an 
extensive round-robin conducted under a DOE sponsored project during 1988-92, we selected 
goethite as an ideal material for developing an SRM. 


20 


SRM 1980 is being developed by NIST for calibration of electrokinetic mobility measurement 
instruments that are commonly used. This SRM was produced by synthesizing a goethite, 
FeO(OH), powder at NIST. The goethite sample is packaged as a 50 mg/L suspension, 
dispersed in 5 x 10'^ M NaC 104 and 100 micromole/g KH 2 PO 4 . The certification was carried 
out by a round-robin of five participants. The uncertainty in the certified value for positive 
electrophoretic mobility, 2.55 /im*cm/V*s, is 0.12 /im*cm/V*s, based on all data. At least 
four different types of instruments were used by the participants which indicated that the data 
are not affected by the instrument type. A second SRM being certified has a negative mobility 
in the same range. 

Surface Chemistry of Silicon Nitride Powders 

V. A. Hackley and S. G. Malghan 

With the recent arrival of electroacoustic methods we Ccin now characterize ceramic powder slips 
containing solid loadings approaching 40% by volume. The measurement of electrokinetic 
properties is based on the measurement of electrokinetic sonic amplitude {esa). The esa signal 
and phase information are used to measure the electrophoretic mobility and zeta potential of the 
particles. We have applied this technique to investigate the surface chemical reactions of Si 3 N 4 
powders in aqueous processing of slurries. 

The control of reactions at the solid-solution interface is critical in ceramic powder processing. 
Interfacial electrochemical properties can be significantly affected by the presence of surface 
impurities or secondary components added to the suspension. For non-oxide materials such as 
silicon nitride, the presence of oxygen in the surface region is known to modify the electrical 
double-layer properties in a predictable manner. The isoelectric point {iep), or pH of zero 
electrokinetic charge, of Si 3 N 4 decreases linearly with increasing surface oxide thickness. The 
iep is the single most important variable that decides the rheological and dispersion properties 
of slips. We have examined the role of dissolved ions on the surface chemistry of Si 3 N 4 
powders, and the implications for the effects of impurities, contaminants and additives in 
processing. We find that most simple univalent electrolytes behave indifferently toward the 
Si 3 N 4 surface, with the exception of fluoride that specifically adsorbs and may form a strong 
complex with the surface silicon. Oxy-anions such as sulfate and carbonate adsorb specifically 
on the Si 3 N 4 surface, but the interactions are weaker than previously observed on metal oxides. 
The alkaline-earth cations, common impurities in commercial powders, exhibit a similar weak 
specificity over the normal pH range. In the presence of hydrolyzable transition metal cations 
such as Fe"^^, powder surface chemistry is controlled by the adsorption of hydroxy metal 
complexes and by the solubility of a surface-precipitated metal hydroxide phase. In this case, 
multiple iep's are possible, and the primary iep may be shifted several pH units from the native 
value. These observations suggest that the so called heterogeneous precipitation could be used 
as a method for adding inorganic sintering aids and nitriding agents more uniformly and 
efficiently compared to the use of secondary powder phases. 

We have also measured the ionic contributions to the electroacoustic signal for a series of 
electrolytes. In many cases the electrolyte background signal is significant compared with the 
powder signal, and must be corrected for in order to avoid serious problems with measurement 


21 


artifacts. We have examined the accuracy of applying a simple subtraction procedure to remove 
background signal, and have generated the necessary data to predict whether a background signal 
will be significant for a given ion pair in aqueous solution. 

Weak-acid polyelectrolytes, such as poly (acrylic acid) (PAA), are added to slips to control 
particle dispersion and rheology during processing. These polymers impart stability through 
electrosteric mechanisms that are poorly understood. In the past year, we have begun an 
investigation of the electrochemical interaction of PAA with Si3N4 using electroacoustic analysis 
coupled with adsorption measurements and potentiometric titration. Preliminary results show 
a complex interaction mechanism between the polyelectrolyte and Si3N4 surface. Electroacoustic 
measurements correlate with adsorption data as a function of solution pH and polymer 
concentration. The PAA adsorbs strongly in an acidic medium and reduces the surface potential, 
as illustrated in Figure 1 , that leads to severe agglomeration. In an alkaline medium, the 
polyelectrolyte is weakly adsorbed as a result of repulsive electrostatic interactions with the 
particle surface. A range of behaviors is possible between these two extremes, including particle 
charge reversal. Dispersion properties appear to improve under alkaline conditions, suggesting 
that free polymer may play an important role in the enhancement of slip properties. Some of 
the major findings in this projects are: 

• The role of dissolved ions in the surface chemistry of Si3N4 powders was resolved. This 
work has implications for the effects of impurities, contaminants and additives in aqueous 
processing of Si3N4 powders. 

• The contribution of electrolytes to the measured ESA was obtained for a wide range of 
ion pairs. These data are vital for predicting and evaluating the background signal 
correction necessary in the electroacoustic analysis of aqueous suspensions. 

• The electroacoustic properties of Si3N4 slips in the presence of polyacrylic acid 
dispersants was correlated with polymer adsorption and the degree of ionization as a 
function of solution pH and molecular weight. The potentially significant role of free 
polymer in slip dispersion and rheology was identified. The mechanism of interaction 
and dispersion of these polymeric additives is presently not understood, and yet of critical 
importance to the powder processing industry. 

Consortium on Intelligent Processing of Powders 

S. G. Malghan, V. A. Hackley, and P. S. Wang 

A NIST-industrial consortium on intelligent processing of ceramic powders and slurries was 
initiated in September 1993 . The participants are from the ceramic powder synthesis and 
processing industry (Cercom Inc., Eaton Corporation, Kerr-McGee Corporation, Golden 
Technologies Company, Inc., and St. Gobain/Norton Industrial Advanced Ceramics), and the 
powder measurement industry (Matec Applied Sciences). This consortium addresses critical 
powder processing issues identified by industry and builds upon the measurement, 
characterization and analysis capabilities developed at NIST. 


22 



Figure 1. The ESA of silicon nitride powder, SNE-10, in the presence of a 5000 MW 
polyacrylic acid at three pH values of the suspension. 

Reproducible processing is recognized as a vital component in the achievement of cost-effective 
manufacture and reliable application of advanced ceramics, particularly silicon nitride, for a wide 
variety of automotive and industrial components. The consensus opinion of a recent workshop 
held at NIST to identify powder related issues that limit reproducibility of ceramic processing, 
was that the ability to measure subtle powder characteristics and characterize the behavior of 
powders in slurries would further the understanding and process control required to improve 
reproducibility. 

Recent advances in electroacoustics and NMR technology have provided a means for improved 
in situ and on-line characterization of slurry processing at various stages from powder to slurry 
to green body. The application of multiple frequency analysis of the electrokinetic sonic 
amplitude and phase shift, in conjunction with recent breakthroughs in electroacoustic theory. 


23 


allows simultaneous determination of both agglomerate size and particle charge in dense 
suspensions approaching 40% by volume solids. Using this technique, the electrochemical 
properties of powders in suspension, and the interaction of slurry components, can be studied 
and quantified for application in intelligent processing (Figure 2). The distribution of organic 
in a slurry is a critical parameter in deciding homogeneity of slurry components and agglomerate 
formation. NMR imaging is a unique diagnostic technique that can provide internal mapping 
of material distribution. ^^Si magic angle spinning NMR spectroscopy is a powerful technique 
for determination of phase composition of powders. Nuclear spin relaxation times can be used 
to examine the interaction of polyelectrolyte dispersants with the solid\solution interface. 

Our research will focus on Reaction Bonded Silicon Nitride (RBSN) and Sintered Reaction 
Bonded Silicon Nitride (SRBSN) systems. RBSN/SRBSN routes begin with low-cost metallic 
silicon powders that are dispersed in an aqueous environment with several secondary components 
(dispersants, binders, nitridation catalyst and sintering-aids). A green body is produced by a 
shape forming process such as slip-casting. The shape is then nitrided to form porous silicon 
nitride with least dimensional change, followed by sintering to an acceptable density. 

The objectives of this project are: (1) develop improved surface chemical understanding of 
aqueous slurry processing of ceramic powders; (2) develop the electroacoustic technique for 
slurry characterization and on-line measurement applications; (3) develop NMR spectroscopy and 
imaging techniques for the characterization of powders, slips and green bodies. 

Nuclear Relaxation NMR Imaging of Green Ceramics 

P. S. Wang 

Development of proton nuclear magnetic resonance (^H NMR) analysis at 400. 159972 MHz has 
been initiated to evaluate the binder in injection molded alumina green compacts. The nuclear 
spin-spin relaxation times (T 2 ) of protons in the binder components (paraffin wax, 
polypropylene, and stearic acid) were measured to allow comparison with those in the injection 
molded green compacts. nuclear spin echo signals were observed by a multiple pulse 
sequence. Block’s equations were used to calculate the spin-spin relaxation times from these 
echo intensities. The T 2 for paraffin wax and polypropylene were in the 30 to 33 ^sec range 
and their intensity decay behaviors were very similar. However, the T 2 value for stearic acid 
was found to be only 17 /xsec and its echo signal intensity decays more rapidly than those for 
paraffin wax and polypropylene. Injection molded alumina green compacts containing 
polypropylene/ wax/stearic acid from Prof. R. German’s laboratory at Pennsylvania State 
University were examined for binder distribution by proton nuclear magnetic resonance (^H 
NMR) imaging. The solid imaging technique of nuclear spin-spin relaxation time (T 2 ) weighted 
imaging at 400. 159972 MHz was used for this study. Two- and three-dimensional images were 
constructed from the intensities of these nuclear echo signals. 

Binder content variations in three green compacts molded from the same nominal blend 
composition were detected. The spatially-resolved two-dimensional images obtained by 
application of the T 2 technique indicated that the green compacts fabricated from the same 
nominal binder composition did not have the same content as expected. This observation agrees 


24 



Figure 2. Schematic of (Proposed) On-Line ESA Measurement for Intelligent Processing of 
slurries. The results obtained in this program will help us design such a system. 

well with our previous conclusion drawn from nuclear spin echo studies by Hahn’s pulse 
sequence. A three-dimensional imaging revealed that the binder distribution inhomogeneity and 
internal imperfection do exist at certain parts of the samples. A binder-rich folding line was also 
detected in one of these green compacts. 

Analysis of the molded compacts also showed the presence of a specie with a T 2 value near 300 
fxsec. This species may be the result of a reaction during processing or the presence of 
moisture. The width of RF-pulses used to measure echoes did not have a significant effect on 
relaxation times, but it should be considered in calculation of echo intensities at equilibrium and 
hence binder composition. This technique development is expected to allow analysis of both 
binder content and distribution in molded components with application in process models. 


25 


Kinetics of Si 3 N^ Oxidation Using Auger Electron Spectroscopy 
P. S. Wang 

One of the major technical issues in the processing of silicon nitride ceramic materials is 
sinterability of silicon nitride starting powders. One piece of relevant data to define the 
sinterability is to develop data on the formation of oxide layer on the surface of the powder 
particles at sintering temperatures. Thus, information on oxidation kinetics will be useful in 
evaluating sinterability. In addition, the oxidation kinetics can define surface reactivity of 
powders. 

Surface techniques such as XPS and/or Bremsstrahlung-excited Auger electron spectroscopy 
(AES) have been used to measure oxidation kinetics of silicon carbide whiskers, silicon carbide 
platelets, and silicon nitride powders. With the silicon nitride powders, a difference in activation 
energy was observed between powders manufactured by direct nitridation and by pyrolysis of 
silane and ammonia. The silicon nitride powder used in this study was obtained from Union 
Carbide Coatings Service Corporation. This powder was synthesized by pyrolysis of silane and 
ammonia. Mean particle size in this powder was 0.2 ^m. The powder was vacuum heat-treated 
to remove chemically-bound hydrogen. The powder prepared by pyrolysis of silane and 
ammonia was found to contain chemically bound hydrogen. Since this hydrogen is evolved at 
about the same temperatures that the oxidation begins, this was believed to be the reason for the 
difference in oxidation kinetics. In the present study, the silicon nitride powder containing 
chemically bound hydrogen was heat-treated in vacuum to remove hydrogen. The oxidation 
kinetics of these powders were studied using Bremsstrahlung-excited AES. 

The Si KLL peaks for Si02 and Si 3 N 4 were observed at 1609 and 1612 eV, respectively. This 
is in good agreement with previously reported results. The increase of Si02 component with 
heating time is a clear indication that surface oxidation increases as a function of heating time 
and temperature. The average oxide thickness on the surface of the Si 3 N 4 particles can be 
measured from the Si KLL data using the methods developed previously. 

The oxide thickness on the vacuum heat-treated Si 3 N 4 powder before oxidation was 0.8 nm. 
Average oxide thickness data for the vacuum heat-treated Si 3 N 4 powders as a function of heating 
time at 850°, 900°, 950°, and 975 °C show that at each temperature, the oxidation followed a 
linear rate law. The activation energy for linear oxidation was measured to be 195+26 kJ/mol 
(47+6 kcal/mol). This is significantly different from the value of 104 ±22 kJ/mol measured for 
the untreated powder. The gas evolution measurements show that more hydrogen is evolved 
during the oxidation of untreated Si 3 N 4 powders than from the treated sample. It is this 
evolution of hydrogen that apparently has inhibited the oxidation of untreated powders. 

Low-Temperature Fabrication of Transparent Silicon Nitride 

W. Chen and S. Malghan 

The production of nano-size particles has recently enabled the synthesis of a new class of 
ultrafine-grained materials by using non-con ventional compaction and sintering. In the present 


26 


research, we are studying the feasibility of producing a nano-phase Si 3 N 4 with nanostructure and 
transparent to visible light without the use of sintering-aids. Our basis for this study has been 
the use of cryogenic compaction of amorphous silicon nitride powders. 

To study the cryogenic or other lubricant compaction process in more detail, we designed and 
constructed a novel system. The new equipment is capable of producing 3 mm disk-shaped 
samples under vacuum or in a variety of controlled conditions such as surrounding gaseous or 
liquid environments, and temperatures in the range from liquid nitrogen to 28°C, and pressures 
up to 3 GPa. In addition, during powder compaction, continuous measurements of sample 
volume, applied force, and frictional force between the sample and the die wall are performed. 

A maximum random packing density (about 64% of theoretical) for nano-size amorphous Si 3 N 4 
was achieved by compacting at 2.5 GPa under liquid nitrogen temperature. At room 
temperature, dry compaction of the same powder at 2.5 GPa resulted in a green density of 57%. 
These results show that cryogenic compaction is an efficient technique to obtain a high packing 
density and small-scale porosity. The green body showed transparency under visible light 
indicating uniform nano-scale porosity. Our attempts to further densify cryogenic-compacted 
green bodies by sintering and hot-isostatic pressing up to 1500°C have not been successful. We 
are exploring various alternatives for densification of silicon nitride green compacts. 

Because full density may not be obtained without the addition of sintering-aids, we plan to 
measure the maximum density achievable with the nano-powders with the expectation that the 
small pore size and associated defects may not drastically reduce mechanical properties. 
Cryogenic or other lubricant compaction techniques will be used to produce dense compacts 
(65% or higher density at 2.5 GPa) from amorphous nano-size silicon nitride powder. 
Following this, the dense compacts will be hot-pressed to increase contact area between particles 
at 1.0 GPa and 1000°C. Finally, the compact will be pressureless sintered at 1400°C. This 
process is expected to promote a strong bonding at the contact area due to solid-state surface 
diffusion. The density of the new microstructure of silicon nitride ceramic with nano-scale 
porosity and grain size is expected to be between 65 - 80% of theoretical with enhanced optical, 
electrical, and mechanical properties. These data will not only help develop a new class of 
materials but also will have broad implications in the development of nano-powders processing 
technology. 

Computational Models of Microstructural Development 

W. C. Carter, A. Roosen^, J. Cahn^ and J. Taylor^ 

^ Metallurgy Division, NIST 
^ Metallurgy Division, NIST 
^ Mathematics Department, Rutgers University 

A number of issues are being addressed with a common theme of using mathematical tools to 
develop an improved understanding of particulates behavior in processing and microstructure 
design. An example is presented on the development of methods and software to calculate the 
evolution of fully feceted particles for surface and vapor diffusion. This represents the first time 
such diffusion processes have been exactly analyzed for such faceted crystals that are commonly 


27 


found in nature. The results identify visual clues for materials processors and experimentalists 
to decide which diffusion mechanisms are active during microstructural evolution. This effort 
also represents the first rigorous approach to calculations of interface evolution in anisotropic 
systems and will be the cornerstone to future advances in the computational materials science 
of microstructural development. 

Novel mathematical techniques and software were developed to study microstructural 
development in anisotropic materials and particles. The development of these methods is 
important in studies of many technological processes including sintering and powder processing. 
The techniques are also applicable to the study of material behavior at high temperatures and the 
results are useful to engineers in materials processing design. 

Tracking of the evolution of an continuous interface during diffusive transport is a notoriously 
difficult problem. Modeling interface growth and shape changes is fundamental to the study of 
microstructural evolution. Methods were recently developed to calculate the time evolution of 
highly anisotropic two-dimensional interfaces for two cases of diffusive transport; surface 
diffusion and interface attachment limited vapor diffusion. These two independent diffusive 
mechanisms are extreme cases of volume conserving flows. In surface diffusion, mass flux is 
along the interface. In interface attachment limited vapor diffusion, evaporation or growth takes 
place by attachment of mass at the interface from some ambient (vapor) phase where diffusion 
is considered to be infinitely fast compared to the attachment kinetics. 

Recently developed sharp interface or "crystalline" methods have shown that computations of 
interface growth can be greatly simplified when the Wulff shape of the underlying crystal is 
completely faceted. An interface must be completely faceted at any orientation which 
corresponds to either a facet in the Wulff shape or to missing orientations (edges or comers) in 
the Wulff shape— in which case the anisotropic analogue to the isotropic mean curvature, called 
weighted mean curvature (wmc), has a particularly simple form. The average chemical potential 
along a facet is proportional to wmc (the analogue of Gibbs-Thomsen) and is likewise simple 
to calculate. The evolution of those interfacial orientations which are not faceted can be 
approximated in the crystalline method by replacing differentiable Wulff shape with one of many 
facets. In the case where growth is proportional to the local mean curvature, the crystalline 
methods appears to converge to isotropic flow, but has not been proven. 

The results have practical utility. Typically, scaling laws are applied to some set of stereological 
measures. Values are plotted on a log-log plot and exponents are used to identify the active 
diffusive mechanism in the process. Such averaging is open to misinterpretation and conclusions 
are often equivocal. From visual inspection of our results which show a marked distinction in 
the interface development depending on the active diffusive mechanism, the dominant diffusive 
mechanism can be discerned by comparing experimentally observed microstructures to computed 
results. A video is available and a publication is in progress. Local removal of gradients in 
wmc is indicative of surface diffusion; long-range coarsening is indicative of interface-limited 
vapor diffusion. Of course, there are mixed cases where neither process is dominant and 
calculations of such cases are in progress. 


28 


Synthesis of Nanostructured Materials 

J. J. Ritter 

A new class of materials comprising nano-scale (< 100 nm) particulates is being considered for 
advanced applications. There are increasing numbers of recent reports that point to the potential 
for greatly enhanced mechanical, electrical and magnetic properties from these materials. While 
the field is still embryonic, obvious benefits can be readily appreciated from factors such as 
reduced flaw size producing substantial increases in strength and special functional properties 
arising from a high density of interfaces. 

The initial task is to identify procedures to generate nano-structured materials in a controlled and 
reproducible manner. The following are examples of some novel approaches to the synthesis 
of nanostructured ceramic materials being developed. 

Ferrite Materials: These materials are used for miniaturization of microwave communications 
components. A CRADA has been signed with Trans-Tech, Adamstown MD. Novel chemical 
syntheses of thick-film microwave ferrite materials will be explored based on the NiFe204, 
Y3Fe50i2 and BaFei20i9 families of compounds. 

Initial studies using modified metal nitrate solutions and a novel sequential dip and cure 
procedure has shown that good quality, well-adhered NiFe204 films can be deposited on a 
dielectric substrate. It is hypothesized that the beneficial mechanical properties arise from the 
controlled deposition of material in 5 nm-thick layers. While this research is in its early stages, 
the prospects for producing a variety of well-formed magnetic materials in film form is very 
encouraging. 

Thermoelectric Materials: These materials are intended for use for modular thermoelectric 
refrigeration as an alternative to CFC systems. Chemical synthesis procedures are being 
developed for Bi2Ti3 and related materials that are projected to lead to improved thermoelectric 
performance. Two routes for chemical synthesis of fme-particulate bismuth telluride-based 
powders were developed. One of these routes gives plate-like particles that may be amenable 
to orientation. Procedures for the inclusion of nano- size second phases into these materials have 
been developed and we have observed that sintered samples compacted between 1.5 and 2.0 GPa 
show an increased Seebeck coefficient and a lowering of thermal conductivity by a factor of 3 
to 5 in these sintered compacts. This latter effect is believed to be due to phonon scattering by 
nano-porosity generated during sintering. Unfortunately, the processing techniques used to date 
give samples that exhibit high electrical resistivity. Thus, an improved figure-of-merit has not 
yet been realized. 

Magnetic Nano-composites: These materials are intended for magnetic refrigeration in the 7 to 
80 K range. Chemical synthesis of garnet materials of the type Gd2.j^Mj^0^2 where M = Fe is 
being pursued in this project. 

Measurements on the GdGaFeO(GGIG) system shows an enhancement in magnetocaloric effect 
by a factor of about 3.4 over the best currently-used magnetic refrigerant, gadolinium gallium 


29 


gamet(GGG), at temperatures around 15K. Moreover, GGIG exceeds the performance of GGG 
by a significant margin for temperatures in the 10 to 80K range, allowing for the design of 
magnetic refrigerators that can operate well above the current maximum of 20K, In addition, 
GGIG does not possess a remanent magnetization and therefore exhibits no hysteresis losses 
during field cycling, an important factor to be considered in magnetic refrigerant selection. 
Experimental evidence suggests that the improved magnetocaloric performance of GGIG arises 
from the presence of nano-sized magnetic regions throughout the material. 

High Energy Agitation Milling of Silicon Nitride Powders 

D. B. Minor, P. T. Pei and S. G. Malghan 

Since most structural ceramics are manufactured from ceramic powders as starting materials that 
are highly agglomerated due to the van der Waals attractive forces between the primary 
particles. Shape-forming from fine powders constitutes slurry-based processing and milling is 
often used to achieve particle size reduction, deagglomeration, and/or homogeneity of the slurry. 
This project is on the development of high energy agitation milling of silicon nitride powders 
by the addition of yttria as a sintering-aid. Specifically, we have been studying the factors 
responsible for repeatability improvement, preparation of high density suspensions, and 
application of electrokinetic sonic amplitude (ESA) measurement for characterization of milled 
slurries. 

We have carried out a series of experiments under a set of fixed milling conditions to assess 
factors affecting milling process responses such as particle size distribution, specific surface 
area, ESA, and the pH at the iso-electric point. Preliminary analysis of these results have shown 
that variability in the data associated with the measurement error is not a factor. However, 
material and process variabilities have a strong influence. The material variability is associated 
not only with batch-to-batch variation as well as microstructural variations due to agglomeration 
of primary particles and bonding between the particles in as-received powders. In addition, the 
yttria powder has a strong influence on the variability of milling response. The yttria powders 
undergo hydrolysis as milling proceeds and interact with the silicon nitride powder. Another 
significant variability is due to operator influence during milling such as the rate of addition of 
powder and rate of build-up of solids concentration as milling proceeds in the initial period. 
These variabilities are being examined so that overall repeatability can be enhanced. 

The preparation of high density silicon nitride suspensions is being studied as a collaborative 
project with the St. Goblin-Norton Company. We have been able to prepare suspensions 
containing solids loading between 75-79% by weight. These suspensions have been evaluated 
in both laboratories by slip casting and iso-pressing. In addition, the green bodies have been 
densified by hot isostatic pressing. The results show that the green densities are considerably 
higher (about 2.2 g\cm^) than those obtained by using slurries from vibratory milling. However, 
the green bodies are brittle since they do not contain binder. Additional hurdles to overcome 
are green body cracking and decrease of specific surface area of milled powders from 12 to 
approximately 10 m^/g. 


30 


In a separate study, we are studying the application of ESA measurement techniques to monitor 
surface chemistry changes in the slurry and to optimize milling conditions. The ESA of milled 
slurries was found to have a strong correlation with the green density of compacts prepared by 
slip casting the slurries. This is not surprising since improved dispersion should result in higher 
green densities due to the presence of larger number of fine particles and their ability to fill 
interstitial voids. 


31 




III. SURFACE PROPERTIES 


Stephen Hsu 


The ability to control the surface and interface properties of advanced materials such as 
ceramics, coatings, and composites is a key issue in achieving cost-effective and successful 
application of these materials. 

Surface properties such as elastic modulus, hardness, friction, shear strength, and chemical 
reactivity control the materials’ performance and durability under a variety of environmental 
conditions. These properties are dependent on the surface texture, microstructure, surface 
contaminants, defects, and the physical and chemical nature of the molecules at and near the 
surface. The exact relationship between these parameters and performance is not known. 

The objectives of the group are: (1) to develop new measurement techniques to characterize the 
physical and chemical properties of ceramic surfaces and interfaces under static and dynamic 
contact conditions; (2) to understand the relationship between microstructure, chemical 
compositions of the surface and interface, and the micro-mechanical and tribological properties 
of ceramics and other materials; (3) to develop the science and technology for the control of 
surface properties by lubrication and surface texture design, and to develop basic design 
principles for optimum combination of materials and lubricants; (4) to provide data, reference 
materials, and design guidelines for the introduction of new materials in industrial applications. 

Significant Accomplishments: 

• A series of wear maps has been updated and published for silicon nitride, silicon carbide, 
and zirconia as a function of speed and load. These maps provide design guidelines for 
industrial designers in considering ceramics for applications. 

• The chemically assisted machining of ceramics technology has been demonstrated on a 
surface grinder. A family of chlorinated compounds has been developed that 
significantly reduce cutting time and at the same time, reduce surface roughness of the 
as-machined surface, reducing the cost of ceramic components. 

• The advanced lubrication technology developed under DOE sponsorship was validated 
by the Cummins Engines Co. Eight lubricants were selected for testing and only two 
were able to finish the 200 hour endurance test. One of the two was the technology 
developed at NIST. 

• An industrial workshop on lubrication technology needs for transportation industries was 
held at Northwestern University, Evanston, IL on Sept. 21-23, 1992. A consensus on 
research needs and prioritized areas was reached. A report was prepared and has been 
released by ASME for distribution in 1993. This is the first time that lubricant, 
automotive, and diesel industries have come together with component suppliers, national 
laboratories, universities, and government personnel to discuss a single topic and arrive 
at some consensus. 


33 


• We have initiated a joint research program on ceramic valve inserts used in the 
Caterpillar 3500 series gas engines for cogeneration in conjunction with Caterpillar, GRI, 
Eaton, Norton, and SWRI. The goal of the project is to develop life prediction 
methodology for such ceramic components. 

• We have demonstrated that silicon nitrides and silicon carbides can be lubricated by a 
new generation of lubricant chemistries, such as oxygenates and sulfonates. An effective 
lubricating film can lower the stress intensity at asperity contacts, thus protecting the 
surface. Successful development of this knowledge could pave the way for wide-spread 
use of ceramics in engines. 

• A new method, the ball on inclined surface, to measure surface quality (surface strength 
as related to the defects size and population) of as-machined ceramic surfaces has been 
developed. The location of the first tensile crack in the wear track indicates the stress 
at which a preexisting crack on the surface propagates to form a tensile crack. The 
stress level has been demonstrated to correlate with the quality of the surface. 

• Nanoindentation and low load instrumented scratching techniques have been applied to 
measure hardness and scratch properties of copper and molybdenum oxide films with 
thicknesses in the range 100-600 nm and to nickel/nickel oxide plasma spray deposited 
coatings. Techniques developed in this research permit determination of mechanical 
behavior and adhesion of films placed on ceramic and other substrates to improve wear 
performance. 

• A detailed study of the mechanisms of wear of Si-based ceramic over a range of speeds 
and loads reveals that there are multiple mechanisms at work. Results suggest that wear 
of ceramics can be classified into three levels: a mild wear region where hardness and 
surface roughness dominate the process; a severe wear region where fracture dominates; 
a failure region where ftacture and thermal shock combine to cause rapid deterioration 
and failure. 

• A computerized ceramic wear database has been successfully developed. The database 
contains friction and wear data of ceramics in an user-friendly software package. This 
and other databases jointly developed between ACTIS Inc. and NIST form the most 
comprehensive collection of design codes, data bases, and information software in 
Tribology in the world today. 

Wear and Wear Mechanisms for Si-based Ceramics 

T. N. Ying^ Y. S. Wang^ M. Shen^, and S. M. Hsu 

^ PhD Candidates, Materials Science, University of Maryland 

^ Post-doctoral Fellow, University of Illinois at Chicago 

Advanced ceramics are increasingly being considered for tribological applications such as engine 

components, bearings, cutting tools, pump seals, etc. However durability is a concern and wear 


34 


life and wear mechanisms of Si-based ceramics are not well understood. This research attempts 
to present a systematic view of how ceramics wear, the dominant mechanisms under which they 
wear, and the models available to describe the wear processes. 

The materials studied included a hot-isostatically-pressed silicon nitride, a hot pressed silicon 
nitride, and two silicon carbides. The microstructure of the silicon carbide samples is different; 
one with a duplex structure, one with an equiaxed grain structure. Wear experiments were 
conducted by using a ball-on-three-flats wear tester. Both the ball and the flats were made out 
of the same ceramic material. 

Wear maps of Si3N4 and SiC under dry sliding conditions are shown in Figure 1 . The overall 
wear characteristics of the silicon nitride and silicon carbide shown in the maps are similar in 
shape with wear transition, defined as a sudden increase in wear due to a small change in either 
load or speed, observed in both materials. Such transitional behaviors are mainly due to 
dislocation build up in the grains due to repeated asperity contacts. These eventually lead to 
intergranular cracking producing large wear particles, which cause gross fracture due to high 
intensity loading. The location of such transitions as a function of load and speed has an 
obvious significance in engineering applications. In addition, for a given material pair, the 
transition location is influenced by the lubrication environment. 

Figure 2 a which utilizes mean Hertzian pressure to directly compare the materials shows the 
wear transition boundary, the location at which the wear transition occurs, in Si3N4 and SiC 
under dry sliding and paraffin oil lubricated cases. The existence of the three regions implies 
that there are different wear mechanisms operating in each of the regions. The diagrams have 
two key features: the location of the transition boundary and the functional dependence of the 
transition boundary on speed and pressure. 

At low speeds, the transition boundary is shown to be independent of speed, implying that 
critical stresses for both Si3N4 and SiC are responsible for such transitions. As speed increases 
beyond 0.01 m/s, this boundary starts to bend toward lower contact pressures, suggesting the 
onset of the temperature influence due to speed increase. The transition boundary between 
regions B and C represents the wear transitions from severe to ultra-severe wear. The shape of 
the boundary line indicates that the transition is the result of the combined effect of contact 
pressure and speed. These results suggest that surface temperatures due to the frictional 
dissipation of heat play a significant role in the occurrence of wear transitions. 

The major effect of adding a lubricant such as the purified paraffinic oil to the wear system is 
the elimination of high surface temperatures. Under paraffinic oil lubricated condition, as shown 
in Figure 2 b, the wear transition line moves to much higher pressures and speeds. Furthermore, 
only a mild-to-severe wear transition is present for both Si3N4 and SiC. Also, the shape of the 
transition line is altered suggesting more speed dependence at high pressures and more pressure 
dependence at high speeds. Both the location and the functional dependence in this case 
resembles the boundary transition line separating region B and C in Fig. 2 a. This similarity is 
probably due to the flash temperature induced transition. 

The mechanism of wear can be examined in terms of the different wear regions. The silicon 


35 



Figure 1. Three-dimensional wear maps of (a) SNl and (b) SCI under dry sliding conditions. 


36 




TJ 

0^ 

Q) 

a 

m 

CJO 

a 

•pH 

in 



A 

B 

C 


o SiC 

• SiaN, 

mild wear 
severe wear 
ultra-severe wear 


mean Hertzian pressure (GPa) 


(b) 



mean Hertzian pressure (GPa) 


mild wear 
severe wear 


Figure 2. Wear transition diagrams of SNl and SCI under (a) dry sliding and (b) paraffin oil 
lubricated conditions. 


37 


nitride surface from region A as shown in Fig. 3a, reveals a polished surface with wear debris 
in the form of rolls which are perpendicular to the direction of sliding. This is primarily due 
to the presence of water which reacts with the silicon nitride surface forming silicon hydroxides. 
The presence of such large particles inside the contact changes the stress distribution which 
causes the onset of transition. In this region, the pressures at the asperity tips are controlling 
the wear action. There is not sufficient compressive stress due to normal loading to cause 
substantial fracture. Therefore, we see abrasion by the asperities and grooves appear on the 
surface. 

The SiC worn surface shown in Fig. 3b displays polished and grooved surface features. The 
width of the grooves is on the order of 2-3 ^m. The micrograph suggests that wear in this 
region is similar to silicon nitride and is dominated by deformation-controlled processes. After 
transition to region B in Figure 2a, wear is much more rapid and severe. Brittle fracture has 
become the predominant wear mechanism in this region after the mild-to-severe wear transitions. 
Under ultra-severe wear conditions, region C in Fig. 2a, a severely fractured surface covered 
by large quantity of debris is observed for Si 3 N 4 , while the worn surface of SiC displays a 
mostly intragranularly fractured surface. Brittle fracture is still the dominant wear mode in 
region C. However, the extent of brittle fracture in this region is evidently more severe than 
in region B. Overall, the dominant wear mechanism for Si 3 N 4 and SiC under dry sliding 
conditions changes from plastic deformation in mild wear regimes to brittle fracture in severe 
wear regimes. 

Under paraffinic oil lubricated condition, there are only two regions, mild and severe wear. 
For mild wear, polishing is the dominant wear mode. Hence, plastic deformation and asperity 
abrasion are the dominant wear mechanism. After transition, the surface morphology is rough 
and full of fracture and grain pull-outs. Observation using transmission electron microscopy 
(TEM) was conducted showing transgranular dislocations in the sub-surface grains. For SiC, 
intergranular cracking is present in addition to the dislocation pile-ups. One can conclude that 
dislocation pile-ups, plastic deformation, and brittle fracture (mostly intergranular cracking) are 
the predominant wear mechanisms for Si-based ceramics under paraffin oil lubrication 
conditions. 

In addition to the wear mechanisms discussed so far, 3rd-body effects due to the presence of 
different wear debris are important. The wear level of this case is in region B, i.e., post- 
transition wear dominated by fracture. The wear scar is found to be covered by a thick layer 
of loosely bound wear particles. The sizes of these particles are mostly sub-micron. The size 
and shape of the wear particles are distinctly different from the normal particles where abrasion 
by the few large particles cause damage. This large amount of submicron particles serves as a 
form of solid lubrication redistributing the contact stresses. 

A series of simple tests was carried out to examine the wear of ceramics from the perspective 
of the materials’ response to stresses. In order to simulate the stress field encountered in the 
sliding contacts, a ball indenter is used to apply stress on a flat surface. Fig. 4a shows a Si 3 N 4 
flat sample indented by using a diamond indenter with a spherical tip. The average contact 
pressure is estimated to be — 20 GPa. Hertzian cone crack and radial cracks appear from the 
circumference of the indentation. Subsurface damage can be observed from the cross-section 


38 



' Figure 3. Representative worn surface morphology in mild wear under dry’ sliding conditions 

i (region A in Fig 2(a)): (a) SNl and (b) SCI. 

I 


39 





shown in Fig. 4b. A lateral crack is observed propagating parallel to the surface. Crack 
initiation appears at about 10 kg, which corresponds to a mean Hertzian pressure of about 15 
GPa. The test results suggest that compressive stress induced tensile cracks are primarily 
dependant on the mean critical pressure in the contact and the asperity pressure is not a factor 
here. Very little shear stress is involved in indentation, but the results show considerable 
compressive stress would be required to initiate damage. 

To examine the role of shear force on ceramic damage, a ball-on-inclined plane test was used. 
The test configuration consists of a ball sliding on an inclined flat plane. The test is designed 
to measure in a single sliding the various stages of fracture of the ceramic in response to a 
continuously increasing force. The ball used is a diamond indenter, the flat sample is SNl 
silicon nitride, and the incline angle of the flat is 1.1°. The friction coefficient during the 
scratch test increases from 0.1 at the beginning of the test to 0.4 at the end of the test. Fig. 5 
shows the morphology of the wear track. One can see that initially there is a plastically 
deformed region, followed by tensile crack region, and then the cracks propagate outside the 
wear track. At the end of the sliding, gross fracture occurs coupled with delamination revealing 
sheet detachment. Considerably lower pressure is required to cause tensile cracks, 5-8 GPa as 
compared to 15 GPa estimated from indentation. 

To simulate more realistically the contact conditions between two silicon nitride surfaces, a two 
ball collision test was used to study the deformation and wear processes. The apparatus is the 
same one used in the ball-on-inclined plane test, except here two silicon nitride balls are collided 
together and the forces are measured continuously by force transducers. Video pictures are also 
taken to record the sequence of events. The test was conducted in the absence of any liquid 
lubricant. The contact configuration dictates an increasing load followed by a decreasing load. 
A high level of friction, 0.6-0.8, was measured for this test. In Fig. 6, it can be seen that the 
two surfaces come together and many fine debris are exploding out of the contact zone. This 
is the first time such event has been recorded in ceramic tribology. When an element of the 
subsurface volume is under high hydrostatic pressure, a sudden appearance of a crack creates 
a free surface and the volumetric element breaks into many fine particles and practically 
explodes out of the contact. Such cracks could be caused by a secondary tensile crack or a shear 
crack. This explains the mechanism and the source of the sub-micron wear particles discussed 
previously. 

Instrumented Scratch Testing and Nanoindentation 

A. W. Ruff and H-J. Shin^ 

^ Post-doctoral Fellow, University of Maryland 

The NIST^ instrument for controlled load/depth scratching and nanoindentation of materials has 
been used to characterize the behavior of several ceramic materials. The instrument measures 
instantaneous load and indenter penetration continuously, with or without simultaneous specimen 
motion. The data can be used to determine hardness, elastic modulus, ductility, toughness, and 
resistance to scratching damage. The techniques developed are particularly appropriate for 
characterizing ceramic coatings, a new NIST technical initiative area for FY94. They are also 


40 



(b) 



surface 


cross-section 


Figure 4. Silicon Nitride (SNl) flat sample after indentation by using a diamond indenter 
(spherical tip radius: 0.2 mm) under 30 kg load and 15 seconds duration: (a) indentation 
impression, and (b) impression and cross-section. (C=cone crack, R=radial crack, L=lateral 
crack) 


41 






tensile crack sheet detachments 



42 


(b) cross-section of the wear track. 


top ball 

moving direction 



stationary ball 



Figure 6. (a) Side-view of a two-ball collision showing numerous fine particles expelled from 
the contact zone, (b) Wear scar on a ball sample of NS 1 . 


43 



critical to developing an improved understanding of proper surface grinding and finishing 
methods to be used by industry in preparing ceramic materials for products. This work has been 
done jointly with staff in the NIST Manufacturing Engineering Laboratory , the Lawrence 
Livermore Laboratory, the Naval Research Laboratory, the University of Mary and, at a private 
sector firm, and at the Thermal Spray Laboratory, Stony Brook University Y). 

Controlled scratching and indentation studies were done on CVD silicon carbide, silicon nitride, 
and a composite alumina-titanium carbide material. Both a diamond pyramid and a single point 
diamond turning tool were used, in either air or several different fluid environ nents. Detailed 
studies of the Al 203 -TiC material showed that surface damage caused by scratching was 
localized within one or two grains distance from the scratch track. Damage consisted of "grain 
spalls" at the bottom or edge of the scratch (Figure 7a), probably caused by crack growth within 
the grain boundary regions due to tensile stresses forming behind the indenter during scratching. 
Observation showed intergranular fracture at spalling sites which is believed to be due to weak 
grain or interphase boundaries. Another type of damage was "shear cracks" formed 
perpendicular to the scratching direction inside the scratch track. These shear cracks appeared 
to be associated with plastic plowing that is atypical for a ceramic material even when confine 
to local regions. The lateral extent of surface damage from scratching was studied by maldng 
two closely spaced parallel scratches in sequence using increasing load values. The second 
scratch appeared not to be influenced by the first scratch until the distance between the two 
scratches reduced down to about one half of the scratch width. Once they were close enough 
to each other, heavy spalling of material between two scratches occurred to an extent not 
observed in single scratches at even the largest load used in this study on polished surface. 

Substantial differences in damage to the material were found by scratching in different fluids. 
Figure 7b shows results from controlled scratching at loads of 145-172 mN in mineral oil. The 
changes in the scratch-resisting force curve and in the relative scratch depth curve are the result 
of severe edge and sub-surface cracking and the associated surface uplifting. This damage 
occurs sporadically along the scratch and appears to involve some damage accumulation process, 
possibly elastic strain build-up in the material. The area marked A in (a) that contains 
considerable scratch edge cracking damage is also marked in (b) with an arrow, where both 
scratch force and penetration decrease suddenly. Studies are planned to continue to further 
clarify damage mechanisms, critical load effects, and the importance of different test and 
material conditions. 

Nano-indentation techniques using small spherical diamond tips were also further developed to 
measure elastic properties of materials and coatings. The method involves low load elastic and 
plastic indentation of surfaces, while acquiring continuous displacement data. Several models 
exist for extracting elastic modulus values from those results, although some uncertainty remains 
concerning the effect of indenter shape on the results. The method can be used for coatings or 
layers as thin as 1(X) nm. Results were obtained on nickel/nickel oxide plasma deposited 
coatings, and showed the effect of coating anisotropy and processing conditions. Techniques 
developed in this research permits determination of mechanical behavior and adhesion of films 
placed on ceramic and other substrates to improve wear performance. Such results are needed 
for development of more durable industrial products, particularly for applications in extreme 
environments of temperature and chemical reactivity. 


44 



(b) 



Figure 7. (a) Scanning electron micrograph of scratching damage in alumina-titanium carbide 
material from a test at loads of 145-172 mN in mineral oil. The area marked A contains 
considerable edge cracking damage, (b) From the same test, the changes in the scratch 
(resisting) force curve and in the scratch depth curve are the results of severe sub-surface and 
edge cracking and the associated surface uplifting. The region marked with an arrow in the 
graph corresponds to the region marked a in the photograph. 


45 



Tribological Films and Coatings 

A. W. Ruff, L. K. Ives, H-J. Shin^ N. Vinod^, and M. B. Peterson^ 

^ Post-doctoral Fellow, University of Maryland 
^ Graduate Student, University of Maryland 
^ Guest Scientist, Wear Sciences, Maryland 

Friction and wear properties of alloys at high temperatures are controlled by their tribologically 
generated oxide films, in the absence of other intentional lubrication or surface contamination. 
However detailed knowledge is lacking on what alloy compositions produce suitable films, and 
what properties of the oxide films are critical. Studies have been underway at NIST on several 
pure metals, alloys, and oxides, mainly of copper and molybdenum, in the form of either metal 
films or powders. These studies have provided valuable information on the process of oxide 
lubrication in those systems up to temperatures of 800® C, and could also provide insight into 
improved friction and wear behavior for oxide ceramics. Such information would assist in 
expanding industrial use of hard, wear resistant ceramics. This research has been done jointly 
with scientists at the Naval Research Laboratory. 

Studies over the past year have been concerned with tribo-chemical solid state reactions of 
molybdenum, copper, and their oxides. It has been possible to generate low friction films in 
situ during sliding at temperatures in the range 300 - 800°C. Metal and metal-oxide films and 
powders have been studied on glass and AI 2 O 3 substrates in sliding. Friction coefficients have 
been as low as 0.3 for copper oxide and 0.2-0. 3 for copper-molybdenum oxide. 

Some insight has been gained into the mechanisms involved with these thin (up to 500 nm) 
tribologiczd films. Techniques of nanoindentation and instrumented scratching have been used 
to measure film hardness and plasticity. Based on numerous sliding tests over a range of 
temperatures, two general situations seem to occur: in one the film remains continuous during 
sliding, in the other the film becomes broken into discrete regions or patches. Continuous films 
with adequate flow and cohesive properties can provide low friction and wear if sufficiently thick 
compared to surface roughness, and if sufficiently adherent to the substrate. Discrete, patchy 
films cannot in general provide continuing low friction and wear performance, although they 
may constitute the final stage of continuous film performance. 

In this research, nanoindentation hardness measurements have been made using a 55 deg. 
trigonal diamond indenter on the copper - copper oxide, molybdenum-molybdenum oxide, and 
ion-beam mixed copper-molybdenum-oxide films, about 100 to 500 nm thick, formed by vapor 
deposition on aluminum oxide and glass substrates. Both as deposited/oxidized films and 
wom/ in situ oxidized films were examined. The indentation hardness values actually refer to 
the film-substrate combination; extracting a film-only hardness value is dependent on correctly 
adjusting for substrate effects, particularly for very thin films ( < 100 nm thick). Results for the 
copper-oxide films (comparing at loads of 0.02 N, equivalent to depths of 150-200 nm) indicated 
the presence of a soft film (H 02 = 4-6 GPa) on either a glass substrate (where H 02, substr. “ 
7-8 GPa) or an alumina substrate (where Hq 2, substr. ~ 15-30 GPa). The as-oxidized copper 
oxide film structure consisted of small cryst^lites with considerable porosity. In contrast, the 


46 


copper oxide films that were formed during sliding at 600 °C showed a smooth, continuous 
structure and had considerably higher hardness (H 02 = 30-45 GPa). It was clear that the film 
in the wear track was very different in morphology and properties than the unworn films. 
Studies of actual sliding contacts for the copper oxide films on alumina showed nominal, average 
pressures of about 0.6 GPa, much less than measured film hardnesses. This indicates that stress 
concentration within the contact area could be tolerated by these films, up to factors of 10-50 
times. 

Scratching studies were also conducted on the films and they showed that the copper oxide film 
adhesion was poor. Scratching at light loads (down to 10 mN) caused complete film 
detachment. Thus while the copper oxide films showed some cohesion and reasonable hardness 
(for carrying contact loads), poor substrate adhesion was a serious failing in terms of good wear 
performance. 

By comparison to these results, molybdenum-oxide films showed significantly higher hardnesses; 
Ho ,2 = 8-10 GPa on glass and H 02 = 30-45 GPa on alumina. Further, the ion-beam mixed 
molybdenum-copper-oxide films also had similar, higher hardnesses. Both of these types of 
films also exhibited low friction and wear in the 300-600 °C range. Preliminary scratching data 
suggests that adhesion to alumina substrates may also be improved over that of the copper oxide 
films. 

Wear Models for Ceramics 


M. C. Shen\ O. B. Bogatine^, and S. M. Hsu 

^ Post-doctoral Fellow, University of Illinois at Chicago 
^ Visiting Scholar, Institute of Non-Metallic Materials of Russian Academy of 
Science at Yakutsk 

There are several wear models for ceramics in the literature. Each of the models was developed 
based on a set of assumptions and fitted with a set of experimental data. In this effort, the wear 
data available were used to test these models. The first model examined was the lateral crack 
model. This model was developed for grinding of ceramics and the basis was that materials 
were primarily removed by lateral cracks. The prerequisites of the lateral crack model are: 1) 
the applied load is higher than the threshold load for lateral crack initiation; and 2) the material 
is assumed to be homogeneous. The model neglects the effect of friction and temperature in the 
material removal process. 

The second model examined assumes that the mild-to-severe wear transition is caused by tensile 
cracking. The effects of microstructure and coefficient of friction are incorporated in the model. 
Considering the heterogeneous nature of polycrystalline ceramics and the increasing propensity 
of fracture due to high friction, this model appears to be more realistic for modeling wear of 
ceramics. 

These models were tested against the silicon nitride wear data. Fig. 8 shows the results of the 
data fit using the lateral crack and the tensile crack models. The experimental wear data are 


47 



10 “* 10 ’* 10 '^ 10 "’ 10 ** 10 *‘ 10 ® 10 ‘ 


Theoretical prediction (mm*) 



Figure 8 . Results of correlation by using (a) lateral crack model and (b) tensile crack model. 
The experimemtal data were obtained from a Si3N4 under dry sliding wear tests of progressive 
loads and various speeds. 


48 


silicon nitride sliding on itself under dry sliding conditions of progressive loads and speeds at 
room temperature. To use the tensile crack model, the critical damage-induced stress crj^ for this 
Si 3 N 4 was determined experimentally to be ~ 1.4 GPa. The two models predict reasonably well 
for wear volumes in the range of 10"^ to 10‘^ mm^. The experimental observations revealed that 
wear was dominated by brittle fracture in this regime. Brittle fracture was also the predominant 
wear mechanism in the high wear regime, where wear volumes were beyond 10"^ mm^. Both 
models underestimate the wear volumes in this high wear regime. Since the wear data collected 
in the high wear regime were under high speeds, thermal stresses due to frictional heating may 
present additional stresses causing an ultra-severe wearing condition. The critical velocity model 
confirms that the criterion of V > is satisfied in this high wear regime. This suggests that 
thermal shock induced damages are probably responsible for the ultra-severe wear in Si 3 N 4 . In 
the mild wear regime, where wear volumes are mostly lower than lO"^ mm^, the two fracture 
mechanics models provide significant overestimates. Wear in this regime was found 
experimentally to be dominated by micro-cutting and plastic deformation. The difference in the 
predominant wear mode seems to explain why the two fracture models fail to correlate with the 
experimental data in this regime. 

The third model examined is pertinent to the thermal shock induced fracture. Due to their 
relatively poor thermal diffusivity, PSZ materials are prone to suffer thermal shock induced 
brittle fracture. A critical velocity criterion has been developed to examine the susceptibility 
to thermal shock induced surface damage in PSZ materials. When the operating velocity V is 
faster than i.e., V > thermal shock induced surface damages will occur. 

The transitional phenomenon from mild to severe wear in ceramics has been consistently 
observed experimentally. Although many studies have demonstrated the presence of such 
phenomena, the mechanism of wear transition is still not well understood. One plausible 
hypothesis is that wear damages cause changes in surface geometry when two surfaces are in 
sliding contact. As rubbing continues, changes in surface geometry may increase local stress 
intensities, which in turn cause further damages. Thus, damages are accumulated and the 
process repeats itself leading to a wear transition. So far the relationship between the surface 
geometry changes and damage accumulation process has never been determined. Hence, the 
purpose of this task is to examine how surface geometry changes are to influence the damage 
accumulation process. 

A mathematical method has been developed to determine the subsurface stress field in the 
vicinity of a cavity of small depth located inside of a hertzian contact. The defect is assumed 
to be located at the center of the Hertzian contact. The Hertzian contact has a radius of a, and 
the defect is a circular hole with a radius of r. Besides the normal load, tangential force is 
included in the analysis to reflect the effect of friction. Fig. 9 shows the distribution of surface 
stress cr^ for different defect sizes and a coefficient of friction f = 0.5. The direction of the 
frictional force is from left to right, and is the stress component parallel to the direction of 
frictional force, ere conducted for a wide range of defect sizes, r/a = 0.0005 to 0.6. 

Without the defects, the stress component at the surface is compressive (negative) around 
the center of the hertzian contact, even under the condition of a friction coefficient of 0.5. The 
the right edge. The presence of such a sharp maximum compressive is thought to be 


49 


ff* = o-„aVP 



x/a 


Figure 9. Distribution of the surface stress in hertzian contact with surface defect of size 
of r/a = 0.6, 0.5, 0.4, 0.3, 0.2, 0.15, 0.1, 0.07 and 0.04, labeled from 1 
through 9. (f= coefficient of friction, P=load, lim 1 = limit of the influence form another edge, 
lim 2=limit of plasticity, lim 3=limit of defect size) 

caused by overlapping the negative stress, due to the presence of the left edge of the defect, and 
positive stress, due to the presence of the right edge. When the defect size is small, the 


50 


maximum compressive at the left edge is relatively small. As shown in Fig. 9, the local 
maximum compressive increases with increasing defect size, and may be an order of 
magnitude greater than the in an undamaged hertzian contact. The dotted lines in Fig. 9 
represent the envelope of those local maxima. This envelope reaches an extreme value 
somewhere around x/a = 0.6. Consequently, limit 1 in Fig. 9 represents a limit of the influence 
from the right edge. Because of the substantial increase in the compressive stress in the 
vicinity of a defect, even a safe initial contact stress distribution may exceed some dangerous 
limit such as a limit of plastic yielding or fracture. This kind of limit, shown in Fig. 9 as limit 
2, should certainly be considered in estimates of the tendency of direct fracture in a damaged 
surface. Finally, the limit 3 in Fig. 9 reflects the decrease in with the decrease in the defect 
size. Certainly, this limit approaches the value of of an undamaged surface as the defect 
size reaches zero. 

The results shown in the above clearly suggest that, after a few defects are initiated on the 
surface, they would act as nucleators to accelerate surface microfracture locally. Further 
development of such defects seem to follow two possible routes. The first is through an increase 
in the number of defects and the second follows increases in the size of the defects. Based on 
the envelope curves shown, the second possibility would eventually prevail. 

Numerical Simulation of Sliding Contact Over a Half-Plane 

Y.-M.Chen*, L. K. Ives and J. W. Dally^ 

^ Graduate Student, University of Maryland 
^ Professor, University of Maryland 

A number of models have been developed to describe wear processes. Typically, they are 
largely, if not entirely, empirical in nature. Most often these models determine a wear rate 
value for a particular exposure condition without identifying an actual mechanism or utilizing 
relationships based on fundamental materials properties. In this study a two-dimensional finite 
element analysis code, EPIC II, that had been developed to model the displacement of material 
resulting from the impact of a projectile with a ductile target was adapted to describe material 
displacement in a tribological contact. Other finite element analysis approaches have been 
employed to simulate deformation at sliding contacts, however, they have been limited to strains 
that are much lower than those known to occur during extended sliding under real contact 
conditions. The EPIC II code is able to simulate the large deformations, large strains, and high 
strain rates that can occur in sliding contacts. Experiments were conducted to test the validity 
of the behavior simulated by the modified EPIC II code and the results were found to be in good 
agreement. 

The experiment consisted of a cylinder with a very large length to diameter ratio loaded against 
and forced to slide perpendicular to its axis along the flat surface of a thick OFHC copper plate. 
The symmetry of this geometry permitted an accurate two dimensional simulation. At the 
completion of the sliding experiment an automated profilometer system was used to map the 
surface topography of the OFHC copper plate surface. 


51 


Utilizing parameters describing the elastic and plastic properties of the OFHC copper material 
and other conditions of the experiment, the simulation shown in Fig. 10 was obtained. 

Future investigations are being considered in which the deformation and flow in a thin ductile 
film on a hard surface will be simulated in order to model a solid lubricating film. 

Such films are important in many tribological applications and currently may have application 
with respect to reducing the head to disk spacing in hard disk drives, thereby increasing 
substantially the drive storage capacity. 

Microstructural Design of Wear Resistant Silicon Nitride Ceramics 

H. Liu\ V. Nagarajan^, and S. M. Hsu 

^ Post-doctoral Fellow, University of Illinois at Chicago 
^ Visiting Scientist, Indian Institute of Science, Bangalore, India 

The goal of this project is to optimize wear resistance of silicon nitride by tailoring 
microstructure. Fracture induced wear is controlled by localized stresses at the surface and near 
surface. Monolithic Si3N4 ceramics normally have no effective ways to release stress and 
energy except fracture. A multilayer architecture is proposed to adsorb strain energy and thus 
to improve wear resistance. A surface layer with fine grains is preferred because the fine grained 
structure has high resistance to short cracks. The layer beneath the surface layer is desired to 
have coarse, equiaxed grains with weak grain boundaries. The weak layers with large grains are 
likely to adsorb more energy. In order to test this concept, multilayer Si3N4 with this structure 
has been prepared by a tape-casting, lamination and hot-pressing as shown in Fig. 11 . 
Preliminary wear tests suggest that this material has the same wear resistance as that of the best 
commercial bearing. 

Another approach is to introduce surface compressive stress by making a sandwich structure. 
The surface layer has fine, elongated Si3N4 grains, and small amount of SiC particles are added 
to the bulk Si3N4 matrix. Because SiC has higher thermal expansion coefficient than Si3N4, 
compressive stresses build up during cooling after the hot-pressing. Wear of this material is up 
to 40 % lower than that of NBD -100 under high load. This suggests that surface compressive 
stresses can be effective in reducing wear. 

Another approach is to engineer the grain boundary interfaces. The crack arresting/deflecting 
mechanisms in Si3N4 often depend on the ratios of toughness and strength that exists between 
the grain, grain boundary and the solid solution phases. Hence this approach mainly 
concentrates on the tailoring of the microstructures through the chemistry at the grain boundaries 
(such as the nature of secondary phase, thickness of the grain boundary phase, formation of solid 
solutions). The chemical processing routes adopted in this approach ensure a uniform 
distribution of the additive glassy phase and hence a uniform microstructure after densification. 
Our preliminsuy results on ( 1 ) Si3N4 (lOGl) hot pressed with a novel glass additive (10 wt%) 
and ( 2 ) Si3N4 (SNAl) prepared by solution-mixing of the additives are very encouraging. The 


52 


(a) t = 6.0 fis, depth = 52 /im, distance - 120 fim, average velocity = 63.8 m/s 






Figure 10: Deformations at several times during the sliding contact. 


53 






Figure 11. SEM micrographs showing (a) side view of a multilayer Si 3 N 4 bending bar: crack 
propagation along weak layers and crack bridging (x 100); (a) top view of scratch damage on 
a multilayer Si 3 N 4 : large, equiaxed grained weak layer (left) and fine, elongated grained strong 
layer (right) (x 3 k). 


54 






lOGl material indicates a fine-elongated (grain size < 0.5 microns; Aspect Ratio >7) 
microstructure which is desirable for reducing the contact damage during wear. The wear 
volume estimated from the wear scar diameters in lOGl as a function of load suggests that the 
designed morphology with appropriate grain boundary engineering can result in high wear 
resistance. The SNAl material shows a better wear resistance than the commercial bearing 
material, NBD 100, at high loads. Furthermore, the crack patterns observed during a Ball-on- 
Inclined-plane scratch test suggest that the crack-resisting capability of lOGl and SNAl may 
be high. It is expected that further optimization of the microstructure should lead to potential 
high wear resistance materials. 

Effect of Grain Boundary Phase on Wear of Zirconia-alumina composite 

Chuan He^ and S.M. Hsu 

^ Ph. D. candidate. Materials Science Department, University of Maryland 

Composition and strength of a grain boundaries play a vital role in the properties of ceramic 
materials. Although the effect of grain boundary phase on the bending strength has received 
much attention, the effect of grain boundary phases on wear is often neglected. This project 
investigates the effect of grain boundary phase in zirconia-alumina composites on wear 
resistance. The effect of various contents of silica were examined in a Zr02-15 v% AI2O3 
composite. 

Three compositions of Zr02-Al203 with different levels of Si02 were fabricated: AZSO (0 v% 
Si02), AZSl (1 v% Si02), and AZS2 ( 10 v% Si02). It should be noted that even in AZSO, 
a certain amount of Si02 is inevitable from contamination. This "intrinsic" Si02 is estimated 
to be 0.1 v%. The composition and microstructural parameters of those materials are listed in 
Table 1. It can be seen that the major difference among these three materials are the grain 
boundary glassy phase content. Most of the Si02 exists in the grain boundary. However, some 
of the Si02 in AZS2 was found to form mullite ( 3Al203.2Si02). This suggests that not all Si02 
in AZS2 is in the grain boundary glassy phase and there is certain amount of crystalline mullite 
in the grain boundary. 

The hardness of AZSO, AZSl, and AZS2 were measured from room temperature to 1(X)0°C in 
vacuum with a Nikkon High Temperature Microhardness Tester. The hardness of the different 
materials is quite similar below 400°C. This is to be expected because Si02 is brittle at low 
temperatures. When the temperature is above 600°C, the hardness varies among the three 
materials. AZS2 has the highest hardness while AZSl has the lowest. The fact that AZS2 has 
higher hardness than AZSO at temperatures above 400°C may be explained by the crystallization 
process of the grain boundary glassy phase in AZS2. The crystallization process occurs during 
the cooling in the sintering process and during the hardness test. Crystallization of grain 
boundary glassy phase has been a very successful technique to improve the high temperature 
properties of Si3N4 materials. It should be noted that although crystallization gives AZS2 higher 
hardness over AZSO, the hardness still decreases rapidly with higher temperatures. 


55 


Table 1 : 


Composition and microstnictural parameters of AZSO, AZSl, and AZS 2 


Material 

AZSO 

AZSl 

AZS2 

Zr02 content, v% 

15 

15 

15 

Si02 content, v% 

0.1 

1.1 

10.1 

Relative density 

99% 

97% 

99% 

t/m Zr02 

ratio 

22/78 

36164 

23/77 

AI2O3 

^average ’ 

1.7 

2.0 

1.8 

grain size 

fim 






0.8 

0.9 

0.8 

Zr02 

^average » 

1.0 

1.1 

1.0 

grain size 

(xm 






0.3 

0.4 

0.3 


Wear transition loads of the composites as a function of Si02 content were determined. The 
transition load has a log-linear relation with Si02 content in the range of present study. Based 
on the present observation, small amounts of Si02 in the materials can improve the wear 
transition resistance. The most reasonable explanation is that the grain boundary glassy phase 
releases the residual stress during cooling in the sintering process. During the wear test it is 
possible that the flash temperature reduces the viscosity of the glassy phase which can absorb 
the strain energy by viscous flow. 

There were small spikes in the friction coefficient traces during pretransition sliding wear test 
suggesting localized surface disruptions during the test resulting from the generation of third 
body wear particles at the interface due to grain pull-out or localized fracture. The wear of 
AZSl and AZS 2 are both higher than AZSO. The dominant wear mechanism in the pretransition 
wear region is primarily plastic deformation with occasional grain pull-out or localized fracture. 
The difference in pretransition wear resistance between three materials cannot be explained by 
the difference in hardness alone and may be effected by residual stresses in the materials. For 
AZSl the addition of 1 % Si02 probably reduces the grain boundary residual stress, which would 
increase the wear resistance. The reason that AZS 2 has a higher pretransition wear rate than 
AZSO may be that part of the Si02 in AZS 2 reacts with AI2O3 to form mullite (2Si02*3Al203). 
It is believed that the crystallization of a grain boundary phase will introduce additional residual 
stress due to the volume change accompanying the crystallization process. 


56 


Chemically Assisted Ceramic Machining 

T. Ying\ J. Gu^, Y. Wang^, and S. M. Hsu 

^ Graduate Student, University of Maryland 
^ Post-doctoral Fellow, University of Maryland 

This project aims to increase the machining rate of ceramics using chemical reactions at the 
interface during diamond wheel grinding. The chemical reactions could change the hard ceramic 
surface into a softer material and hence reduce the contact stresses and damage. The reaction 
product layer produced could also change the conditions at the interface between the diamond 
abrasive and the ceramic surface reducing the wear of the diamond thus increasing the machining 
rate. Si 3 N 4 is the main material of focus, but other materials such as SiAlON or SiC will also 
be examined. 

Many halogenated compounds formulated in our laboratory have been proven effective in 
diamond wheel cutting in that cutting time and surface roughness are reduced compared to water 
or LEGO VC-50. The cutting rate of the new fluids is about five times than that of commercial 
fluids. Although cutting rates for most of the chemicals examined were found to be about the 
same initially, the experimental cutting fluids exhibited less decline in rate at longer times. 

Data were also generated on a surface grinder which has a constant feed rate control, with forces 
measured during the grinding by a force transducer. The normal and tangential forces were 
measured for commercial and experimental fluids. The tangential force (about 25 N) was found 
to be the same for commercial aqueous and experimental candidate fluids. The normal force 
increases to about 250 N for the experimental fluid, however. The high normal force during 
grinding may result in a higher residual compressive stress in the ground parts. 

Study will continue in next year to focus on basic mechano-mechanical analysis and technology 
development in conjunction with an industrial partner. 

High Temperature Liquid Lubricant for Advanced Diesel Engine 

H. Z. Hu^ and S.M. Hsu 

^ Post-doctoral Fellow, The Pennsylvania State University 
^ Post-doctoral Fellow, University of Maryland 

In this project, the important characteristics of high temperature liquid lubricants are explored 
by comparing the engine test data with laboratory simulating bench test results. The high 
temperature engine test was conducted at Cummins Engine Co. General phenomena observed 
in the engine test included excessive sludge formation, heavy deposit build-up in the top ring 
groove, but few deposits were found on the crownland. Filter plugging and turbocharger failure 
also have been observed frequently during the engine test. These problem could be mostly 
attributed to the sludge in the lubricant. Only a few of the specially formulated lubricants were 
able to finish the 200-Hr engine test. 


57 


A sequential thermogravimetric analysis (TGA) procedure was used to examine new and used 
lubricants from the engine test under both argon and oxygen environments. This method can 
tell the difference between conventionally formulated lubricants and high temperature liquid 
lubricants, it also can provide insight on the stability, deposit forming tendency, and oxidative 
volatility of the lubricants. The impact of engine test on a lubricant also can be detected by the 
TGA procedure. The TGA combined with engine data suggests that besides thermal and 
oxidative stability, the oxidative volatility of a lubricant plays a key role in its engine 
performance. 

Lubrication technology for engine particulate control 

R. S. Gates and S. M. Hsu 

The U.S. Congress has mandated a series of increasingly stringent limits on diesel exhaust 
emissions effective in 1994 and 1998. The new limits reduce the allowable hydrocarbon (HC), 
nitrogen oxides (NO^), and particulate matter emissions from diesel engines. Part of the 
particulate matter is organic and is derived from the lubricant present in the combustion chamber 
during operation. As the limit on the particulate level is reduced, the relative importance of the 
lubricant contribution to particulate increases. It is projected that the percentage lubricant 
contribution to total particulate will increase from the current 18-25% to about 35-50% for the 
1994 engines. 

Under the sponsorship of the Department of Energy, Office of Transportation Technologies, the 
Surface Properties Group has been conducting a research project to reduce the lubricant 
contribution to diesel particulate. The approach is based on developing an understanding of how 
lubricants contribute to diesel particulate. This is being accomplished through a combination of 
analytical method development, bench simulation test development, and examination of the 
effects of lubricant molecular structure on the formation of particulates. In conjunction with 
industrial partners, various novel lubricant structures are to be developed to reduce the lubricant 
contribution to particulates. This is the second year of a three year project. 

A rapid analytical technique (simultaneous TGA/DTA) was developed to characterize the organic 
fractions of the particulate. The lubricant contribution to particulate shows up in this organic 
fraction and can therefore be quantified. This analysis takes only a few hours resulting in 
substantial time savings when compared to the usual soxhlet extraction procedure that takes over 
24 hours. A recent comparison between supercritical fluid extraction (SEE) and soxhlet 
extraction of the diesel particulate has revealed that SEE offers several advantages over soxhlet 
extraction for the analysis of the organic portion of diesel particulate. SEE is more rapid, 
requiring only 1 hour versus 24 hours for soxhlet extraction. SEE uses carbon dioxide instead 
of methylene chloride. SEE is less prone to the light end losses attributed to soxhlet extraction. 
This is especially critical in analyses of diesel particulate with lighter, fuel-derived, organic 
components. 

Bench simulation tests have been developed to study the interaction between lubricants and 
carbonaceous material (soot) under a variety of conditions. This is important because the 
adsorption and/or reaction of the polar lubricant degradation products on the soot surface 


58 


eventually show up as the organic fractions. Experiments conducted using a commercial 
lubricant and samples of actual engine soot have indicated that surface reaction and not mere 
physical adsorption is an important phenomenon in lubricant-soot interactions. The simulation 
techniques that have been developed give us a means of studying the effect of lubricant 
structures on the lubricant-soot interaction. 

Lubricant solutions are being explored based on novel chemical structures that should have lower 
contribution to particulate. Much of the characterization, analytical development and engine test 
verification of being achieved through close collaboration with a variety of industrial and 
academic contacts. 

A Computerized Tribology Information System 

A. W. Ruff and S. M. Hsu 

The third phase of work on A Computerized Tribology Information System, ACTIS, has been 
completed. It involved development of a database on advanced ceramic materials of interest for 
tribological applications. The data sources were NIST research activities, selected published 
data, and national and international round-robin measurement programs. The database contains 
about 350 records covering 44 different ceramic materials. It becomes part of the ACTIS data 
and information system developed at NIST over the past 5 years. The previous materials 
database in ACTIS, Tribomaterials I, had only 39 records on ceramic materials, and this was 
felt to be insufficient in view of the high level of interest and need by industry for evaluated 
ceramic materials data. The new database focuses on ceramics with high industrial importance 
and for which data availability has been poor. Data areas include wear data, friction data, 
lubricated sliding data, and mechanical and physical design data. The new database represents 
the most extensive tribology database on ceramics presently available. Data evaluation was 
carried out both by NIST and by experts at Stevens Institute of Technology. The user interface 
was developed by a private sector contractor specializing in PC databases, and is the same as 
the interface used with the lubricant database in the ACTIS system. The Ceramic Tribomaterials 
Database can be used separately or as part of the complete ACTIS system. 

The ACTIS system now contains twelve different PC modules: the ceramic tribomaterials 
database, two rolling element bearing design modules, an advanced gear design module, a 
lubricant database, a lubricant expert system selector module, a numeric database on tribological 
materials, a design code for contact stress, a design code for lubrication conditions, a simple 
gear system code, and journal bearing design code, along with an improved central access 
module. The modules work together within one central PC system. 

The overall effort for the ACTIS system, following a plan developed at a workshop held at NIST 
in 1985, has been supported by NIST, other federal agencies (Department of Energy, Air Force 
Wright Aeronautical Labs, Army Belvoir Research and Development Center, National Science 
Foundation), and two professional societies (the Society of Tribologists and Lubrication 
Engineers, and the American Society of Mechanical Engineers). The ACTIS system is presently 
being marketed by a not-for-profit corporation, ACTIS, Inc. It is intended for use in the 


59 


educational sector for training , and by industrial designers who need the latest data on both new 
and traditional materials for product development purposes. 

Standards and Measurement Activities 


A. W. Ruff 

This project contributes to new ASTM standards, and involves chairmanship of the 
Computerization Sub-committee on Wear and Erosion in Committee G2, Two new standards 
have been completed this year: G-117 on wear data analysis methods, and G-118 on database 
formats for sliding wear data. The work has been coordinated with ASTM Committees E49 on 
Computerization of Material Property Data. These standards were developed jointly with 
representatives from numerous private sector firms, including Eastman Kodak, Carpenter 
Technology, Deere and Co., IBM, Westinghouse, General Motors, as well as from Oak Ridge 
National Laboratory, and Iowa State and Tennessee State Universities. 

Another on-going task involves the VAMAS Wear Test Method group in an effort to establish 
a uniform methodology for organizing wear test data. The work involves representatives from 
9 countries and over 35 laboratories around the world, and is the first attempt to reach an 
international consensus on the evaluation and dissemination of wear data. 

A task nearing completion concerns preparation of an atlas of worn surfaces. The work involves 
experts at NIST, Battelle Columbus Labs, and BAM in Germany. The wear atlas will consist 
of two parts; one a collection of data and micrographs of worn surfaces on a variety of materials 
under different exposure conditions. The second part will be a computerized database of over 
300 records drawn from publications from the International Conference on Wear of materials, 
over the period 1977-1991. The database will permit searching that literature source for 
particular tribology data and information. 

All of these activities will assist industry in acquiring needed information and data for new and 
improved product developments, particularly pertaining to applications involving rolling and 
sliding contacts. 

A Catalyst Package for Lubricant Oxidation Evaluation 

J. Sun^ and S. M. Hsu 

^ Post-doctoral Fellow, University of Maryland 

A research project was undertaken for the Office of Standard Reference Materials (OSRM) to 
develop a new lubricant oxidation catalysts package for the sequence III engine test. The old 
catalyst package was developed for HID engine test. When the engine test was changed to HIE, 
the chemistry and engine test conditions changed significantly that the correlation could not be 
maintained. The catalyst package was developed under the Recycled Oil Program and was the 
center-piece of a strategy to monitor the quality of re-refmed base oils. The catalyst package 
since its introduction, has sold all over the world. The new catalyst package will correlate with 


60 




the new HIE engine test (90% correlation coefficient). The new package will be distributed 
through OSRM. 



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61 



IV. MECHANICAL PROPERTIES 


Stephen W. Freiman (Acting) 


The use of ceramics in structural applications such as automotive engines, turbines for power 
generation, bearings etc. depends upon an ability to control and predict their mechanical 
reliability. The program of the Mechanical Properties Group has as its broad objectives: (1) 
the generation of new models and supporting data to elucidate fracture and deformation 
mechanisms in brittle materials at both ambient and elevated temperatures; (2) the investigation 
of ceramic microstructures and their relationship to mechanical behavior; (3) the development 
of standard test methods; and (4) the development of test methodology applicable to obtaining 
fracture, elastic property, and hardness data for ceramic films and coatings. The advanced 
ceramics industry’s needs for such a program are reflected in their extensive direct participation 
in NIST programs and the broad agenda and industrial participation in ASTM Committee C28 
on Advanced Ceramics. 

The projects being conducted by the Mechanical Properties Group are currently focussed in six 
major areas: 1) Long-term creep and creep rupture of silicon nitride at elevated temperatures, 
combining creep measurements, detailed microstructural characterization, and small angle x-ray 
scattering in order to elucidate the mechanisms of creep damage; 2) fracture resistance of silicon 
nitride with emphasis on understanding mechanisms of self-toughening and microstructural 
development; 3) Fracture and creep in fiber reinforced ceramic composites involving modeling 
and measurement development; 4) Machining of ceramics conducted jointly with the 
Manufacturing Engineering Laboratory and the Ceramic Machining Consortium, including the 
development of a database for industry as well as increased understanding that could lead to 
more economical machining methods; 5) Standards development emphasizing development of 
a standard reference material applicable to ceramic hardness measurements as well as 
international inter-laboratory efforst to develop a standard technique for fracture toughness; and 
6) A new program aimed at understanding the mechanical behavior of films and coatings whose 
goal is to develop test methods for the hardness, toughness, adhesion, etc. of films and coatings 
that can be used by U. S. industry. 

Significant Accomplishments: 

• Mr. George Quinn was elected Chairman of ASTM Committee C28 on Advanced 
Ceramics. This committee is developing ASTM standards of critical importance to U.S. 
industry. 

• A nano-indentation system was put into operation for use in determining the properties 
of films and coatings. 

• Working with Itek Optical Systems, NIST successfully completed a reliability 
assessment for large-scale glass aircraft windows using state-of-the-art fracture 
mechanics and statistical techniques. These are the first non-laminated glass 
windows approved for aircraft by the Federal Aviation Administration. 

• Computer simulations of thermal-expansion-anisotropy induced microcracking in 
brittle ceramics have been to elucidate the influence of thermal misfit- strain, grain 


63 


size, and Poisson’s ratio on microcrack density. Results provide insight into the 
nature of microcrack nucleation and propagation as influenced by microstructural 
parameters, such as grain-boundary toughness and grain size. 

• In joint research with the members of the Ceramic Machining consortium, it was 
found that under certain conditions grinding rates for silicon nitride can be 
increased by a factor of 60 over those currently used. 

• Two chemical compounds were found to increase the drilling rate of ceramics by 
more than 50% compared to either pure water or commercial cutting fluids. One of 
the compound, boric acid was effective in drilling of alumina, a second compound, a 
silicate, was effective in increasing the drilling rate of silicon, silicon nitride, 

and silicon carbide. 

• Using a newly developed indentation technique, three types of processes were 
identified for material removal in machining: 1) microfracture and chipping within 
the grains through crack propagation along the twin/slip boundaries, 2) intergranular 
fracture and grain dislodgement, and 3) formation of lateral, radial, and median 
cracks, leading to removal of large pieces. 

• A fracture mechanics formalism combined with a non-parametric statistical simulation 
of the empirical data was developed as a methodology to assess the reliability (i.e., 
lifetime) of brittle structural components which are subject to failure from time-dependent 
crack growth. The methodology was applied in a case study to the design of glass 
aircraft windows in collaboration with ITEK Optical Systems. 

• Computer simulations of thermal-expansion-anisotropy induced microcracking in brittle 
ceramics have been used with simulated, stochastic microstructures to elucidate the 
influence of thermal misfit-strain, grain size, and Poisson’s ratio on microcrack density. 
Results provide insight into the nature of microcrack nucleation and propagation as 
influenced by microstructural parameters, such as grain-boundary toughness and grain 
size. 

• To explore experimentally the role of internal residual stresses on the mechanical 
behavior of ceramic materials with complex and heterogeneous microstructures, one 
needs material’s microstructures with controlled thermal expansion misfit strains. Such 
microstructures with crystallographic textured were developed in a very anisotropic 
pseudobrookite material (iron titanate) by slurry processing in a strong magnetic field. 


64 


Fracture Behavior of Transformation Toughened Ceramics 

L, M. Braun and R. F. Cook* 

*IBM T. J. Watson Research Center 

Transformation toughened materials possess good thermal shock resistance, high toughness, and 
moderate strengths. The high toughness values for this class of materials, i.e., zirconia, is a 
consequence of the tetragonal-to-monoclinic phase transformation induced in metastable grains 
or precipitates by the enhanced stress field of a propagating crack. The phase transformation 
is accompanied by volume and shear strains which act to mitigate the tensile field, leading to 
an increase in fracture resistance or toughness (an R-or T-curve). 

The fracture behavior of transformation toughened ceramics is investigated using indentation 
radial cracking experiments on yttria stabilized tetragonal zirconia polycrystals (Y-TZP) with a 
range of grain sizes. For all materials investigated, two distinct types of cracks exist. Above 
a threshold indentation load, short cracks of variable length are observed, "trapped" in a 
compressive, contact-induced transformation zone. Above a second threshold, longer, "well- 
developed" cracks of more consistent length form, extend beyond the zone boundary. 

A fracture mechanics model for indentation cracking in phase- transforming materials has been 
developed, based on the competing interaction of the tensile residual-mismatch field and the 
compressive contact-induced transformation field. In addition to the usual subthreshold and well- 
developed cracking ranges, the model predicts the trapping of cracks at indentations, within the 
transformation zone. Therefore, the model explicitly addresses the experimentally observed 
trapping behavior. Although applied to phase-transforming materials, the principles of the model 
are generally applicable to systems with short-range, compensating stress fields competing with 
longer-ranged, dominant fields, leading to two discrete crack populations. 

Ceramic Matrix Composites 

L. M. Braun 

The retention of mechanical strength due to in-service damage is of vital importance in the 
industrial application of toughened continuous fiber ceramic composites (CFCCs). In order to 
assess the impact of the toughening achieved in CFCCs on their strengths and flaw tolerance (or 
damage resistance), it is important to determine the effect of crack size on strength and 
toughness on a scale comparable to the controlling microstructural features (e.g., fiber spacing). 
A technique whereby controlled size surface-cracks are introduced by Vickers indentations can 
be applied to evaluate the effect of crack size on the strength and toughness of CFCCs. 
Combined with studies of CFCCs with different fiber contents (and matrix microstructures), the 
application of the indentation-strength technique also allows one to examine the effects of a 
composites’s structure on its mechanical performance. In the present study, dense unreinforced 
Si 3 N 4 and dense Si 3 N 4 reinforced with 14 and 29 vol % SCS-6 SiC fibers were evaluated. 

The indentation-strength results allow for determination of fracture toughness curves K(c) 
(resistance curves) as a function of crack size. Fracture toughness curves, as represented by a 


65 


shaded band for each individual material, are shown in Figure 1. The fracture toughness curve 
for the unreinforced Si 3 N 4 is indicative of a material with single-valued toughness. A Kq = 
4.8 MPa.m^^^ was determined for this hot-pressed Si 3 N 4 . The toughness for the 14 volume 
fraction fiber composite increased from the initial value to 15 -ISMPa.m^^^; indicative of a 
material with a sharply rising resistance curve, consistent with the strength response. 

In summary, the indentation-strength technique was successfully used to study the mechanical 
properties of CFCCs. Failure mechanism transitions from catastrophic flaw-sensitive to non- 
catastrophic flaw-tolerant behavior were observed by increasing both the initial flaw size and the 
fiber volume fraction. This technique is a powerful tool that can be used to also determine 
temperature, environmental, and oxidation effects on CFCCs. The technique can also be used 
to evaluate damage and failure mechanisms in new materials and can be used to compare 
existing materials. 



Figure 1. Fracture toughness curves, as represented by a shaded band for each individual 
material. 


66 


Time-dependent Reliability for Silicon Carbide at 1400°C 

Tze-jer Chuang and Steve F. Duffy* 

*NASA Lewis Research Center, Cleveland, Ohio 

Advanced ceramic material systems have several mechanical characteristics which must be 
considered in the design of structural components. Focussing on laminated CFCMC the most 
deleterious of these characteristics are low strain tolerance and a large variation in ply failure 
strength specifically in the direction transverse to the fiber. Analyses of components fabricated 
from these types of advanced ceramics require a departure from the well-entrenched 
deterministic design philosophies currently utilized for metal and polymer based composites (i.e., 
the factor-of-safety approach). Although a diminished size effect in the fiber direction has been 
reported in the literature, the bulk strength of a unidirectional-reinforced ply will decrease 
transverse to the fiber direction as the size of the component increases. For this reason the use 
of a weakest-link reliability theory is advocated in the design of components fabricated from 
advanced ceramics. 

Reliability is defined as the probability that a component performs its required function 
adequately for a specified period of time under predetermined (design) conditions. Methods of 
analysis exist that capture the variability in strength of ceramics as it relates to fast fracture. 
However, creep rupture typically entails the nucleation, growth, and coalescence of voids 
dispersed along grain boundaries. A method to determine an allowable stress for a given 
component lifetime and reliability is presented for component service life dominated by creep 
rupture. This is accomplished by combining Weibull analysis with the principles of continuum 
damage mechanics. 

Fig. 2 depicts several time dependent reliability plots as a function of normalized time. Here 
normalized time. Here normalized time is defined as the ratio of real time (t) divided by the 
time to failure (?). In this figure four curves representing different applied stresses are shown. 
Note that the intercepts along the vertical axis would lie on a fast fracture curve (i.e., the time 
independent or inert strength curve). In addition as the applied stress is increased, the relative 
position of the curve shifts downward. For this particular set of material parameters the 
reliability curves are relatively stable beyond 0.8 normalized time. However, beyond this point 
reliability drops off rapidly, indicating that the material is becoming unstable. 


67 


Time-dependent Reliability 



Figure 2. A family of time dependent reliability curves demonstrating the effect of increasing 
applied stress. 


68 


Lifetime Prediction Methodology on Continuous Fiber Reinforced Ceramic Composites 

T.-J, Chuang, Ralph Krause and John Blendell 

Advanced high propulsion blades made of continuous fiber reinforced ceramic matrix composites 
to be used in the jet engine of a high speed civil transport vehicle in the 21st century have a 
target of 18,000 hours in design life under ultra-high temperature and high stress. At issue is 
how the reliability of the structure or component in question can be assured throughout the entire 
service life. Development of models for lifetime prediction for these advanced materials under 
service conditions is required. NIST is conducting a program to develop a methodology for 
lifetime estimation on these materials under long-term sustained loading conditions. Evidence 
collected from electron microscopy has indicated that advanced materials behave differently in 
long-term and short-term responses. For example, the failure mode in a typical elastic (short- 
term) strength and/or toughness test consists of macrocrack growth with fiber bridging and pull- 
out; whereas that in a typical (long-term) creep test consists of nucleation, growth and linkage 
of interfacial microcracks. Thus, enhanced strength/toughness often leads to deteriorated 
durability. The service life is the sum of times spent in each developmental stage. A time- 
dependent theory based on mass transport kinetics has been developed which is capable of 
predicting lifetime if temperature and external loads are given. 

A continuum damage mechanics approach is adopted in which constitutive creep laws 
incorporating damage are constructed based on micromechanical modeling. A model is 
established to take advantage of the periodic feature of the material. The model which entails 
two elements (one representing the fiber phase and the other the matrix phase) connected in 
parallel is subjected to a constant stress applied in the fiber direction. From the requirements of 
equilibrium and compatibility, a system of simultaneous differential equations was derived for 
the dependent variables: stress, strain and damage as functions of time, with the initial conditions 
given by the elastic state of the material. The results suggested that creep life is strongly 
dependent on applied stress, temperature and volume fraction of the fibers. 

Tensile Creep Test Equipment Development 

S.M. Wiederhom, D.E. Roberts, W.E. Luecke and R.F. Krause 

During the past five years, an inexpensive tensile creep test was developed in the Mechanical 
Properties Group. The equipment uses flat dog-bone specimens approximately 50 mm in length, 
with a gauge section of approximately 14 mm, and a cross section of «2 mm on a side. 
Displacements are measured with a commercial laser extensometer. The equipment is stable for 
test periods in excess of 1000 hr. This equipment is now being used to obtain creep and creep 
rupture data on ceramics in the temperature range 1000°C to 1500°C. The technique is also 
being used by six other laboratories nationwide. Many of these laboratories use a commercial 
version of the apparatus developed and sold by Applied Test Systems. The equipment developed 
is ideal for laboratory scale tests on experimental materials, and is used primarily to understand 
mechanisms of failure in structural ceramics at elevated temperatures. During the past two 
years, methods of measuring displacements were improved through the development of a new 
flag geometry and a new method of data analysis. This type of test technique is being 


69 


considered as part of an ASTM Standard as one of the methods for characterizing creep of 
ceramic materials. 

Creep Cavity Evolution 

W.E. Luecke, S.M. Wiederhom, B.J, Hockey and G.G. Long 

Substantial progress has been made in understanding mechanisms of creep in structural ceramics. 
Cavity formation has been shown to dominate the creep and creep rupture behavior of high 
temperature structural silicon nitride. Cavity formation was studied on several commercial 
grades of silicon nitride using transmission electron microscopy, small angle x-ray scattering and 
precision density measurements. The type of cavity to form depended on both the 
microstructure and the test temperature. The refractoriness of the vitreous phase that bonds the 
silicon nitride grains together determined whether isolated lenticular cavities, or crack like 
cavities are formed at grain boundaries. High temperatures, favored the formation of a third 
type of cavity, an irregular, non-planar type of cavity that formed at multigrain junctions. Small 
angle x-ray scattering was used to illustrate the nucleation of small —100 nm cavities at 
multigrain junctions, and their growth into much larger « 1/xm cavities. The formation and 
growth of these cavities are believed to account for the difference in creep behavior of silicon 
nitride in compression and tension. Precision density measurements showed that approximately 
85% of the deformation in one grade of silicon nitride (NT 154) can be accounted for by cavity 
formation. Based on the above data, a model of creep deformation is being developed for 
silicon nitride. 

A New Creep Theory based on Cavitation Damage 

Tze-jer Chuang 

Creep damage in a form of sporadic distribution of cavities at interfaces normal to principal 
tensile directions is a well-established phenomenon. As a result of cavitation, softening or 
degradation in stiffness is introduced together with permanent deformation or creep strain. A 
new creep theory is proposed here based on the assumptions that cavitation is a major 
contribution to the total creep strain and mass transport (notably surface self-diffusion and 
interfacial diffusion at the cavity apex) plays an important role in the damage process. The stress 
dependence on the creep rate is investigated and it was found that in the steady-state creep 
regime and at lower stresses, the cavity morphology retains equilibrium shapes and creep rate 
is linearly dependent on the applied stress, the same stress dependence as Coble creep or 
Nabarro-Herring creep (i.e. stress exponent of unity in the power-law creep equation). However, 
at higher stress regime, the cavity morphology becomes crack-like, and the dependence of creep 
rate on the applied stress can be cast in a power-law creep equation with stress exponent n 
equal to eight (8) or more. 


70 


Structural Reliability of Ceramics at Elevated Temperatures 

S.M. Wiederhom, G.D. Quinn and R.F. Krause 

Over the past few years, the tensile creep and creep rupture behavior has been characterized in 
an effort to assemble a data-base to establish the structural reliability of ceramics at elevated 
temperatures. Our main objective is the construction of fracture mechanism maps, which 
provide a means of assessing the structural reliability of ceramics at elevated temperatures. 
They can be used to summarize large quantities of data dealing with effects of load, temperature 
and environment on component lifetime. They also can be used to generate a design envelopes 
that defines stress allowables for a given application. During the past year, data was collected 
on a commercial grade of silicon nitride containing 6 weight percent yttria. Materials of this 
type will be used as components in high temperature turbines for power generation. The data 
was used to generate a fracture mechanism map that could be used for structural design. Figure 
3. As with other grades of silicon nitride, the map suggests three distinct regions of lifetime 
control: overload fracture at high stresses and low temperatures; subcritical crack growth at 
lower stresses and low temperature; and creep rupture at the lowest stresses and highest 
temperatures. The creep rupture regime involves cavity generation and their effect on crack 
nucleation and crack growth. Based on this data, a fracture mechanism map was generated and 
published as part of a recent ASTM proceeding. 


FRACTURE MECHANISM MAP 
Silicon Nitride (PY6) 



Temperature, C 

Figure 3. Fracture mechanism map for PY6 in air in tension. 


71 


Surface Forces Between Ceramic Materials 


D.T. Smith, A. Grabbe and J.-P. Chapel 

The surface force apparatus has been used successfully for more than a decade to make 
fundamental measurements of forces between molecularly smooth mica surfaces in a variety of 
liquid and vapor environments. Recently at NIST, a method was devised to extend these 
measurements to silica surfaces. This development greatly extends the range of possible studies 
that can be made with the apparatus, and in particular it has opened the way to investigating 
forces between dissimilar materials. Such forces play a vital role in areas such as intergranular 
fracture, the mechanical properties of composite materials, colloidal processing of mixed 
powders and composites, and the adhesion of coatings. 

In 1993, work on the surface force apparatus was focused primarily on forces between silica 
surfaces, which are used either as-prepared (using an oxy-hydrogen flame) or after being 
subjected to a surface treatment that chemically modifies the surface. Forces are measured both 
in "symmetric" systems, where the two silica surfaces are identical, and in "dissimilar" systems, 
where opposing silica surfaces have received different treatments. 

Work in symmetric systems has been directed at the hydration forces between as-prepared silica 
surfaces separated by aqueous salt solutions. These forces play a key role in understanding the 
stability of silica-based colloidal suspensions. It was found that these surfaces almost always 
display a hydration repulsion, but that the strength and range of the interaction depended both 
on the cation concentration and its radius (cations investigated included Li'^, Na"*", and 
Cs'*'). It was also discovered that under very specific circumstances the hydration repulsion was 
absent. When the force was measured immediately after initial contact with a relatively strong 
(0.1 M) NaCl solution, several minutes were required for the repulsion to develop, raising 
interesting questions about the dynamics of the formation of the hydration layer that as yet 
remain unanswered. 

In dissimilar material systems, work has focused primarily on the adhesion between silica and 
mica and between silica surfaces with different surface treatments. Of particular interest is the 
phenomenon of charge transfer between the two materials, which results in a strong interfacial 
adhesion and a strong electric field in the gap as the materials are separated. This field is high 
enough (approaching 10^ V/m) that discharges occur across the gap during separation. 

Additional work in dissimilar material adhesion has been performed in collaboration with the 
Eastman Kodak Co. Adhesion and charge transfer between untreated silica surfaces and mica 
sheets that have received two different surface treatments has been studied. One treatment 
covers the surface with methyl groups that passivate the surface and reduce adhesion and 
charging. The other treatment is a coating of a gelatin used in photographic emulsion. This 
surface shows stronger adhesion and charging than the methyl surface, but not as strong as that 
seen with bare mica. The goal of the work is to better understand tribocharging effects in film 
manufacture and handling. 


72 


In 1993, several significant improvements to the surface force apparatus were completed. First, 
it is now possible to slide one surface over the other to study tribocharging, friction and shear 
behavior on the molecular scale. Second, interferometry is no longer necessary to measure the 
force between the surfaces, removing the restriction that the surfaces studied be thin and 
transparent. 

Nanoindentation Studies 


D.T. Smith 

In 1993, a new instrumented indentation facility was established in the Ceramics Division. The 
facility consists of a Nano Indenter II indentation machine, manufactured by Nano Instruments, 
Inc., and related computer and optical components, as discussed in the Facilities section of this 
report. The machine is capable of measuring the hardness and Young’s modulus of materials 
by continuously recording load and displacement information during an indentation cycle. 
Reliable data can be obtained from surface impressions as shallow as 20 nm, allowing results 
to be obtained for sample volumes as small as 10“^^ m^. 

To date, most of the work performed in the new facility has been related to setup, calibration 
and modification of the equipment to meet the specific research needs of the Division, but 
several experimental studies have been begun. Of particular interest are studies of ceramic 
films, coatings and multilayers on a variety of substrates, to understand both the mechanical 
properties of the films themselves and strength of the film-substrate interface. For example, the 
hardness of BaTi03 films prepared for the Electronic Materials group was measured as a 
function of indentation depth. Films with thicknesses in the 200-300 nm range, and with either 
(100) or (111) crystallographic orientation relative to the substrate, were deposited on ((X)l) Si 
with a 25 nm intermediate bond coat of (111) Pt. It was observed that the (lOO)-oriented 
BaTi03 films were twice as hard as (111) films. Other systems currently of interest include 
AI2O3/YSZ ceramic multilayers from Pratt and Whitney, and Al/Cu and AI/AI2O3 multilayers 
prepared by a group at the University of Virginia. A collaboration is also under way with 
DuPont to study the mechanical properties of individual particles in the 10-50 fim size range, 
to better understand attrition problems in powder conveyance. 

In addition to studying specific systems of technological interest, the facility will also be used 
to advance standardization within the field of instrumented indentation. There is a need for both 
standard reference materials and standard data analysis techniques to aid in the comparison of 
results from different machines and different laboratories. 

Microstructural Development in Situ Reinforced Silicon Nitride 

Jay S. Wallace and James F. Kelly 

The extraordinary mechanical properties of in situ reinforced silicon nitride materials are related 
to development of rod-shaped 6-silicon nitride grains during sintering, producing a composite- 
like, fibrous microstructure. Understanding microstructural development and the role of 


73 


microstructure in the mechanical properties has been complicated by the inability to accurately 
characterize microstructures such as these in situ reinforced Si3N4 materials with acicular grains. 

A unique approach is being taken to analysis of microstructure and the factors controlling 
microstructural development. First, a technique has been developed for dissolving the oxynitride 
grain boundary phase without attacking the Si3N4 grains. When this grain boundary phase is 
dissolved, the Si3N4 grains are liberated and dispersed for accurate microscopic characterization 
of size and shape. From these measurements the evolution of populations of grain size and 
shape are made. 

Development of these microstructural analysis techniques allows study of the factors which either 
promote or inhibit production of the elongated grains which are responsible for the superior 
mechanical properties of in situ reinforced Si3N4. Microstructural observations suggest that 
impingement of growing grains on other grains of similar and larger size restricts further 
growth. This is supported by measurements of samples for which the volume fraction of Si3N4 
in the oxynitride phase is varied. Over a wide range of low Si3N4 volume fractions, where the 
growth is not restricted by impingement, the mean size is independent of volume fraction. When 
the separation between growing Si3N4 grains is decreased by increasing the volume fraction of 
Si3N4, their growth is restricted by impingement and the mean size decreases. Microstructural 
evaluation has shown that impingement limits growth only when the grain inhibiting further 
growth is nearly the same size or larger than the growing grain; smaller grains are not able to 
restrict growth of larger grains. This results in the production of multiple grain size populations 
in a single sample where the largest grains are free to grow while growth of the finer grains is 
limited by impingement on nearest neighbors. This behavior is contrasted to those samples with 
low Si3N4 volume fractions; where impingement does not occur there is only one grain size 
population. 

These characterization techniques are now being used to determine the effect of microstructure 
on creep properties of Si3N4 materials. 

Fracture Toughness Round Robin 

George Quinn 

An international round robin for fracture toughness testing based on the controlled surface flaw 
method was successfully concluded. This exercise, which was organized by NIST under the 
auspices of VAMAS, had twenty four participating labs. Results were surprisingly consistent 
(Figure 4 ) despite the need for participants to perform fractographic analysis. Many refinements 
to the test method were made. A result of this project is that the method will be advanced for 
standardization in ASTM Committee C- 28 , Advanced Ceramics. 


74 


Fracture Toughness (MPa 


8.0 -I 


7.0 - 


E 6.0 - 


5.0 - 


4.0 - 


3.0 - 


2.0 - 


1.0 - 


0.0 


NC-132 Hot-pressed Silicon Nitride 


71 


5 ? 


7 7 


37 5 5 


6 3 . 


-t-TI- 

A. 




-^11 


107 


* SEM 
o Optical 


+ Data revised. 

? Data not verified by photos. 


~\ I I I I I i I I I \ I I \ I I I I I I I I I I 

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 


Laboratory 


Figure 4. Fracture toughness results for hot pressed silicon nitride as measured by the surface 
crack in flexure method. Twenty laboratories returned results in this VAMAS round robin. 
Mean, standard deviation and number of specimen tested are shown for each lab. 


75 


Hardness SRM Program 


George Quinn 

Prototype hardness standard reference materials (SRM’s) were prepared to meet a desperate need 
to improve testing practices for Vickers and Knoop hardness characterization of ceramics. A 
round robin verified the suitability of the prototypes. Subjectivity in the interpretation of optical 
images of hardness impressions contributes to very high scatter in hardness readings. NIST is 
preparing certified SRM’s with diagonal measurements made by a calibrated scanning electron 
microscope. These SRM’s will enable users to refine their optical measurement techniques 
which will improve measurement accuracy and precision. 

Coordination of the VAMAS Technical Working Area #3. CERAMICS 

George Quinn 

Mr. Quinn as chairman managed the activities of TWA #3. In this year three international 
round robins on advanced ceramics characterization were completed. Mr. Quinn and Mr. 
Gettings of NIST in cooperation with Mr. J. Kiibler of Swiss Federal Research Labs in 
Switzerland conducted, finished, and documented within one year a twenty four laboratory round 
robin on fracture toughness testing by the controlled surface flaw method. Mr. Quinn 
collaborated with Mr. J. Swab of the U.S. Army Research Laboratory to also set up, perform, 
and finish within one year a fractographic analysis round robin with eighteen labs in North 
American and Europe. The high-temperature fracture toughness round robin, organized by the 
Japan Fine Ceramic Center, was also completed this year. 

A Fracture Mechanics Approach to the Design of Glass Aircraft Windows: A Case Study 

Stephen W. Freiman, Edwin R. Fuller, Jr., George D. Quinn, Janet B. Quinn\ and W. Craig 
Carter, and John Pepi^ 

^ Guest Scientist 
^ITEK Optical Systems 

In the simultaneous presence of tensile stresses and moisture, flaws in glasses and ceramics 
grow, leading to time-dependent structural failures of components made of these materials. The 
basic concepts of this phenomenon were developed via a fracture mechanics perspective to assess 
the reliability (i.e., lifetime) of dual-pane glass aircraft windows. The analysis is based on two 
principles: (1) a statistical distribution of window strengths; and (2) moisture-assisted, time- 
dependent growth of defects, or "cracks", under stress. 

The strength distribution originates from a distribution of defects on the window surfaces and/or 
edges, the most severe of which determines the strength of the window. These strength-limiting 
defects arise from a variety of sources. For a "protected" inner window they typically result 
from the window preparation procedures, such as grinding and polishing procedures for the 
center of the pane and similar procedures with subsequent etching for the window edges. The 


76 


outer windows additionally can incur various types of in-service "damage", such as, scratches 
from cleaning and handling, and dust or sand impact damage from environmental or in-flight 
conditions. Strength distributions for these types of surface conditions were evaluated by rapidly 
loading biaxial flexure specimens in an inert environment. Data were analyzed as three- 
parameter Weibull distributions using a maximum likelihood algorithm to determine the 
estimated Weibull parameters. 

When subjected to in-flight stresses from pressure and thermal gradient across a window 
assembly, defects in the glass pane can grow subcritically due to moisture-assisted crack growth 
until a critical defect size is reached, and failure occurs. The growth rate depends strongly on 
the relative humidity. Crack growth parameters for this process were measured with a 
procedure known as dynamic fatigue, wherein the strength of laboratory specimens are measured 
as a function of stressing rate. These tests were conducted with idealized, indentation-produced 
cracks, rather with "natural" flaws, to control the residual stress state associated with the flaws 
and to reduce experimental variability. Asa worst case scenario, these tests were conducted in 
water at room temperature. 

Using a fracture mechanics formalism, the strength and crack growth data can be integrated to 
obtain an estimate of the window lifetime, or reliability. A question which is not typically 
considered in such calculations is the confidence level of the prediction. Since this is of utmost 
importance for a real structural component, and since a previous procedure, developed at NBS 
in the mid 1970’s, was determined to be inappropriate by current understanding, an alternative 
procedure was developed. In this alternative procedure a simulated distribution of lifetimes is 
generated from the empirical data via a Monte Carlo technique. This so-called, non-parametric 
bootstrap procedure was used to estimate the lifetime at a 95% confidence level for survival 
probabilities of 90% and 99%. Various window configurations and damage types were 
considered. 

Computer Simulations of Thermal Expansion Anisotropy (TEA) Induced Microcracking in Brittle 

Ceramics 


Edwin R. Fuller, Jr., Narayanaswamy Sridhar^, and David J. Srolovitz^ 

^The University of Michigan 

Fracture processes in brittle, granular materials, such as fine ceramics, are profoundly influenced 
by grain-boundary properties and microstructure. Microcracking in single-phase ceramics, 
resulting from the intrinsic thermal expansion anisotropy (TEA) of the grains, is such a process. 
Typically, a phenomenon such as this is modelled by an extension of linear-elastic fracture 
mechanics, either with an idealized micro-mechanics model, i.e., a "regular array" of 
microstructural features, or from a "continuum perspective." Indeed, such models have 
contributed to many advances in understanding in recent years. However, an important aspect 
of the fracture process is ignored by these models, namely, the stochastic nature of the 
microstructure. Such considerations are crucial to the development of new and improved 
materials and to structural design with these materials. Knowledge about stochastic aspects is 
most readily attained from computer simulations: using statistically generated microstructures 


77 


and micro-mechanical descriptions of the toughening mechanisms to relate grain-boundary 
properties and their distributions to processing variables and structural performance. Mimicking 
physical phenomena with simplistic algorithms, these simulations elucidate the stochastic 
influence of complex microstructural phenomena, such as thermal-expansion-anisotropy, 
microcracking, crack deflection and crack bridging, on strength and fracture toughness, 

A two-dimensional, micro-mechanics model was developed in collaboration with N. Sridhar and 
Prof. David Srolovitz of The University of Michigan to simulate TEA-induced microcracking 
and TEA-influenced crack propagation in microstructural simulations of polycrystalline ceramics. 
It consists of a two-dimensional, triangular network of springs upon which a polycrystalline 
microstructure is mapped. The energy of each spring (or bond) has both a bond-stretching and 
a bond-bending component. The total energy of the system is a sum over all the bonds. 

The simulation is periodic in a direction parallel to the applied tensile axis and has free surfaces 
in the transverse directions. It thus simulates a sample with an effectively infinite gage length. 
The network is stressed by applying a fixed strain over the gage length and relaxing the node 
positions with a double-precision conjugate gradient algorithm to minimize the total energy. 
Bond rupture is affected via a critical bond-strain-energy criterion, and thus mimics a critical 
strain-energy-release-rate or fracture surface energy criterion for failure. (Bulk and grain- 
boundary bonds are assumed to have different critical strain energies.) When a bond fractures, 
the system is re-equilibrated at the existing applied strain, and additional bonds are allowed to 
fracture, if required, before applying a further strain increment. 

Polycrystalline aspects of the ceramic microstructure are introduced into the spring network 
models by "overlaying" a random, "digitized" ceramic microstructure on the spring network. 
Accordingly, different spring elements with different constitutive properties and breaking 
strengths are used to represent various microstructural features, e.g,, transgranular versus and 
intergranular properties. 

TEA effects are introduced into the simulation by randomly selecting a high-expansion direction 
in each grain and initially contracting the network spring in this direction. This contraction was 
applied gradually, thereby simulating cooling from elevated temperatures. At each (misfit) strain 
step the system is tested for localized fracture (microcracks). 

Initial studies have examined the influence of the size of the misfit strain, the grain size, and 
Poisson’s ratio on microcrack density. Qualitatively, microcracks preferentially form at grain 
boundaries and propagate either along grain boundaries or into the grains, depending on the 
relative toughness of the grain boundaries to that of the grain interiors. The influence of TEA- 
induced microcracking on grain size depends on the damage measure employed. Although 
microcracking is first initiated in the large-grain microstructures, small-grain microstructures for 
most of the TEA misfit strain regime have more total microcrack length per area of cracking. 
Large grain-size microstructures, however, undergo a more detrimental strength degradation as 
a result of larger microcrack sizes compared to those in small grain samples. Unlike in 
unconstrained samples, when a sample is constrained during a temperature excursion, the stress 
created by the overall thermal expansion can directly lead to fracture of the entire sample. 


78 


Development of Textured Microstructures with Lar 2 e Thermal Expansion Anisotropy 

S. W. Paulik^ K. T. Faber^, and E. R. Fuller, Jr. 

^Guest Scientist, Northwestern University 
^Northwestern University 

Mechanical properties of single-phase polycrystalline ceramics with large thermal expansion 
anisotropy have been shown, both experimentally and theoretically, to depend strongly on grain 
size. This dependence is directly related to the residual stresses, or strains, which are generated 
in the microstructure during cooling from the fabrication temperature. These stresses are created 
from the thermal expansion misfit strains that result between neighboring grains with different 
crystallographic orientations. Crystallographic texture, thereby, provides a means of controlling 
and tailoring these internal stresses. Our ultimate objective is to examine the role of residual 
stresses on various toughening mechanism proposed for advanced ceramics with complex and 
heterogeneous microstructures. 

This phenomenon was studied in iron titanate (Fe 2 Ti 05 ), a pseudobrookite material which 
exhibits a high degree of anisotropy in both its thermal expansion and paramagnetic 
susceptibility. Anisotropy in the paramagnetic susceptibility allows a crystallographically 
textured microstructure to be developed by slurry processing in a strong magnetic field. Using 
a simple measure of crystallographic texture, sintered samples with magnetically-assisted grain 
alignment have a b-axis alignment approximately three times that of randomly-oriented samples. 
This texturing reduces the large residual stresses generated from the large thermal expansion 
anisotropy between the b-axis (16.3 x 10'^ K'^) and the c-axis (0.6 x 10'^ K'^), as evidenced by 
reduced microcracking and morphological texturing of the aligned microstructure. 

Contact Damage and Fatigue in Tough Ceramics 

Brian R. Lawn, Nitin P. Padture Hongda Cai Fernando Guiberteau Marion Stevens 
Kalceff Lanhua Wei ^ 

^ Guest Scientist, Lehigh University 
^ Guest Scientist, Lehigh University (now at ORNL) 

^ Guest Scientist, Universidad de Extremadura, Badajoz, Spain 
^ Guest Scientist, University of Technology, Sydney, Australia 
^ Guest Scientist, Wayne State University 

Ceramics are limited in their use as practical materials by a low toughness and, correspondingly, 
a lack of ductility to absorb mechanical energy. Of the various mechanisms that have been 
advocated for imparting toughness to ceramics, the most widespread and practical is that of 
"bridging” in which frictional pullout of interlocking grains and second-phase particles retards 
crack-wall separation. Toughness then becomes a rising function of crack size (so-called 
resistance-curve behavior). A most important element in enhancing bridging is the controlled 
introduction of weak interfaces on the microstructural scale, so as to deflect the primary crack 
and thereby generate a more effective interlocking structure. Bridging is also enhanced by 


79 


coarsening and elongating the grain structure and by incorporating internal mismatch stresses. 
Thus to gain toughness in ceramics one builds in microstructural heterogeneity. However, the 
toughness is improved only in the "long-crack” region. In the "short-crack” region, built-in 
weakness can enhance fracture at the microstructural level, reducing laboratory strength and 
increasing the susceptibility to wear. 

In view of this tendency to countervailing interrelations in toughness properties, surprisingly 
little effort has been made to understand the seemingly deleterious short-crack properties of 
heterogeneous ceramics. This despite the obvious relevance of these properties to engineering 
design — in most ceramic components it is the evolution of microstructural-scale flaws that 
determines the failure characteristics. Our program has adopted a new approach, using an old 
testing methodology, to determine the essential short-crack properties of tough ceramics. 

Our method uses the Hertzian test, in which a hard sphere is loaded onto the specimen surface. 
The test procedure is uncommonly simple and economical. It samples the test surface over a 
small area, and generates a relatively high stress. The ensuing damage is controlled and 
localized, and is readily amenable to examination by a variety of observational techniques. The 
spherical indenter can be loaded repeatedly, to simulate cyclic fatigue, or translated laterally, 
to simulate wear damage. We have developed a special specimen configuration, consisting of 
two polished rectangular half-blocks bonded together with thin adhesive, that allows us to obtain 
section as well as surface views of the contact damage. Indentations are placed symmetrically 
across the surface trace of the bonded interface on the top surface. After indentation, the 
adhesive is dissolved and the half-blocks separated to reveal the subsurface damage. The top 
and side surfaces of a given half-block are then coated with gold, and viewed in Nomarski 
illumination. 

Several ceramic systems have now been evaluated using this procedure. Our first experiments 
have been conducted on alumina, the prototypical "model” ceramic. In fine microstructures, 
a classical Hertzian cone fracture is formed outside the contact circle, typical of ideal 
homogeneous brittle solids. In coarse alumina, however, the damage is totally different, 
consisting of a dense zone of intergranular microfractures immediately below the contact. 
Stress-induced intragrain twins appeared to act as crack precursors in the alumina by 
concentrating stresses at the weak grain boundaries. The subsurface multiple microfracture 
damage zone expands dramatically with increasing load, producing a quasi static "plastic” 
impression. It also increases with cyclic loading, indicating a pronounced "fatigue” 
characteristic. 

Tests have also been conducted on a machinable mica-containing glass-ceramic from the Coming 
Company. In this system, the microstructure is readily varied by simple heat treatments, so the 
influence of microstructure can be studied in a controlled manner. We find a similar 
"brittle-ductile” transition from classical cone crack to distributed subsurface damage as more 
second phase mica flakes are crystallized from the glass. The weak mica-glass interfaces 
provide easy paths for microcracking in the subsurface zone. It is this tendency to enhanced 
local microcracking that accounts for the machinability of the mica glass-ceramic. A 
collaborative program with Dr. K. Chyung and Dr. D. Grossman at Coming has been 
established to continue these studies. 


80 


Further work has been conducted on some of the harder ceramics currently used in bearing and 
machine tool applications, notably silicon carbide and silicon nitride. Recent advances in 
producing tougher silicon-based ceramics, by growth of elongated grains using in situ processing 
methodologies, have aroused considerable interest. We find that such microstructural 
modifications again result in a brittle-ductile transition. Surface and section views of the 
damage patterns in (A) fine grain and (B) coarse and elongate grain silicon carbide materials are 
shown in figure 5. The implications concerning prospective damage modes in bearing and wear 
applications are profound. We are collaborating with Dr. R. Yeckley at Norton/TRW on 
optimization of silicon nitride microstructures for various applications. 

Detailed evaluations are currently being carried out on the subsurface damage. Dr. Lanhua Wei 
at NIST has used thermal wave imaging to map out the subsurface distributions of microfractures 
in silicon nitride specimens. This work is of special relevance to the potential use of 
nondestructive evaluation techniques for evaluating contact and machining damage in bearing 
materials. In addition, theoretical models, using conventional fracture mechanics and the newest 
computer simulations are being formulated, in collaboration with Dr. Edwin Fuller and Dr. 
Craig Carter. 

The implications of this work are far reaching. The formation of a single cone crack is highly 
degrading to strength properties. A distributed subsurface damage zone is less deleterious to 
strength, but on the other hand enhances wear. The design of ceramics is therefore a matter of 
compromise: microstructures needs to be tailored according to specific applications. 

Machining of Advanced Ceramics 

S. Jahanmir, L. K. Ives, T. Strakna*, H. Liang*, H. S. Ahn**, L. Wei***, H. Xu*, T. 
Hwang*, X. Dong*, G. Zhang* 

*Guest Scientist, University of Maryland 

**Guest Scientist, Korea Institute of Science and Technology 

***Guest Scientist, Wayne State University 

The ceramic machining research is being conducted under the auspices of the NIST Ceramic 
Machining Consortium, which has been established to provide measurement methods, data, and 
mechanistic information needed by industry to develop innovative cost-effective methods for 
machining advanced structural ceramics. Currently, the consortium has 17 members: Ceradyne, 
Cincinnati Milacron, Coming, Dow Chemical, Eaton, Eonic, Ford Motor Company, GE 
Superabrasives, General Motors, Norton, SAC International, Stevens Institute of Technology, 
Texas A&M University, Tower Oil and Technology, University of Maryland, W. R. Grace & 
Company, and West Advanced Ceramics. Current projects include: Grinding Optimization for 
Advanced Ceramics, Ceramic Machinability Database, Characterization of Machining Damage, 
Nano-precision Grinding of Silicon Nitride Bearing Materials, Chemomechanical Effects in 
Drilling and Grinding of Ceramics, and Characterization of Ceramic Grinding Process. 
Consortium members participate in these projects by providing materials, testing, advice, and 
other in-kind contributions. Highlights of these projects are described below. 


81 



Figure 5. Half-surface (top) and section (bottom) views of Hertzian contact damage in silicon 
carbide, from a tungsten carbide sphere of radius r=3.18 mm at load P=2000 N: (A) 
Homogeneous fine-grain form showing well-defined cone crack; (B) Heterogeneous coarse-grain 
form showing distributed subsurface damage. 


82 


Grinding Optimization for Advanced Ceramics 


The goal of this project is to produce and collect data on the effects of grinding parameters on 
properties and performance of ceramics. This project has been planned in two phases. In phase 
one, the participating consortium members were asked to use their experience in selecting 
grinding conditions to be used in the study. Each participant machined one set of flexure test 
bars (28 to 30) of each material, which were then tested and characterized at NIST for surface 
integrity and fracture strength. The surface roughness was determined by a 3-D stylus surface 
profilometer; and the surfaces were examined by scanning electron microscopy to evaluate the 
surface condition. The test bars were subjected to four-point bend tests according to the ASTM 
Standard C 1161. The fracture strength data were analyzed using Weibull statistics. Two types 
of silicon nitride materials, reaction-bonded (RBSN) and sintered-reaction-bonded (SRBSN), 
were used for this study. The results shown in Figure 6 indicate that the grinding conditions 
used had no effect on the fracture strength of the samples ground in the longitudinal direction; 
but the fracture strength was reduced when grinding was performed in the transverse direction 
to the tensile axis of the flexure bars. The extent of strength reduction was somewhat 
proportional to the material removal rate used in grinding. These results suggest that the 
material removal rate in grinding can be increased by a factor of 60 over the rate currently used 
in practice, as long as grinding is performed in a direction parallel to the major tensile stress 
direction experienced by the component in the intended application. 


800 

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£ 600 

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0 400 
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1 300 

2 200 
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0 500 1000 1500 2000 

Volumetric Removal Rote (mm 3/ min) 


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O SRBSN Longitudinal Ground 
A RBSN Trenavarto Ground 
Q SRBSN Tronavoraa Ground 


H 

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32* 


Figure 6. Characteristic fracture strength as a function of removal rate in grinding for two types 
of silicon nitrides ground in two directions with respect to the tensile axis of the four-point bend 
bars. 


83 


In phase two of this project, a statistical design of experiments is being employed to 
systematically analyze the effect of various grinding parameters. The aim of this study is to 
achieve high removal rates while maintaining an acceptable level of surface roughness and 
strength. It is also planned to identify the material removal mechanisms as a function of 
grinding parameters, and to use fractography to identify fracture initiation sites. A factorial 
design of experiments has been developed for this study, which will be performed on three types 
of silicon nitride materials: reaction-bonded (RBSN), sintered reaction bonded (SRBSN), and 
sintered silicon nitride (SSN). 

Ceramic Machinability Database 

The objective of this project is to develop a PC-based database containing evaluated 
machinability data for ceramics. The Ceramic Machinability Database developed jointly with 
the Standards Reference Data Program, will provide easy access to machinability data for 
different types of ceramics and will help users such as manufacturing engineers, tooling 
managers, and machinists develop machining plans for cost-effective production of ceramic 
parts. For example, the manufacturing engineer may have already selected the material to be 
used for the part and the necessary machining operations, but does not know what machining 
parameters to use. The database will provide this information for the selected material. 

Characterization of Machining Damage 

The objective of this project is to evaluate and compare thermal wave measurements, ultrasonic 
methods, and X-ray diffraction for detection and characterization of machining damage in 
ceramics. In general, microcracks generated in ceramics by grinding can be classified into three 
types: lateral cracks (parallel to the surface), median and radial cracks (perpendicular to the 
surface), and small intergranular and transgranular microcracks. In the following experiments, 
well-defined crack systems were introduced in glass by indentation in order to evaluate the 
capability of ultrasonic method and thermal wave measurement technique for the detection of 
each crack system. 

The geometry of a pair of Vickers indents on glass is shown in Figure 7 (a). The median\radial 
cracks emanating from the comers of the indents and the lateral cracks seen as the bright areas 
are apparent in the optical reflection micrograph. The geometry of the upper indent is 
schematically shown in Figure 7 (b). The echo-amplitude contour plot of the upper indent is 
shown in Figure 7 (c). A 50 MHz transducer was used to transmit and receive the normal 
incident ultrasonic signals using a 30 fim beam width. The sample was moved in 5 /xm steps 
in both X and y directions. The indent geometry is also shown in the contour map in Figure 7 
(c) identifying the location of the indent with respect to the echo-amplitude signal. It is noted 
in the figure that the vertical cracks (i.e., median/radial) with their planes parallel to the incident 
compressional wave are not discemable. The lateral cracks, however, are detected. 

The same indent was evaluated with the thermal wave measurement technique. In order to 
detect the median/radial cracks emanating from the comers of the indent, the transverse 
component of the deflected probe beam (parallel to the sample surface) was used, since this 
component detects the thermal waves with preferential propagation along the surface and 


84 




Figure 7. (a) Optical reflection micrograph of Vickers indents in a glass specimen, (b) 

schematic drawing of the upper indent and the vertical cracks, (c) ultrasonic echo-amplitude 
contour plot of the upper indent, and (d) thermal wave image of the surface using the transverse 
component of the deflected probe beam (the scan area is 200 x 200 ^m). 


85 


perpendicular to the vertical crack plane. An image of a ra'^ter scan on the specimen is shown 
in Figure 7 (d), using a step size of 5jum in both x and y dir :ion. The scan area covers a 200 
X 200 nm region, giving approximately the same scale as n Figure 7 (b). The modulaiion 
frequency used was 20 Hz, corresponding to the thermal diffusion length of lOO/im ir; the 
material. In the image, the darker areas indicate a lager signal corresponding to higher 1 cal 
temperatures on the specimen. In these high temperature regions, the heat flow is disturb^ by 
the existence of a defect or a crack. The Y-shape of the vertical cracks can be clearly st in 
Figure 7 (d). This indicates that the signal corresponds to the median/radial crack systen out 
not to the lateral cracks. Also, the signal is unaffected by the depression of the indent, t is 
important to note that only the vertical cracks located along the probe beam are sensed t iris 
technique. The cracks along the x direction are located in a plane parallel to the eat 
propagation direction and do not disturb the heat flow, and therefore are not detected. 

Ductile-Regime Grinding of Silicon Nitride Bearing Materials 

The objectives of this project are to develop guidelines and recommendations for ductile regime 
grinding of silicon nitride bearing materials and to identify the effects of grinding parameters 
and the role of microstructure in obtaining damage-free bearing surfaces. "Ductile regime" 
grinding is defined as an ultra-precision grinding process where the material is removed from 
the surface by a plastic deformation process rather than a brittle fracture process. In order to 
achieve the conditions necessary for ductile regime grinding, a stiff and high-precision grinding 
machine is used with an extremely small depth of cut in the order of nanometer. The results 
of this project, which is being carried out jointly with the Precision Machining Research Facility 
have been very positive, and show that ductile regime grinding can produce a high quality 
surface with a roughness in the nanometer range. In addition to the fine surface finish obtained 
by ductile regime grinding, the results show that the fracture strength is increased compared with 
the strength of flexure bars ground with conventional grinding methods. 

Because of the small depth of cut used in ductile regime grinding, the ceramic microstructure 
is expected to control the material removal process. Recent results obtained on several silicon 
nitride materials with various microstructures have confirmed this point. The results are being 
analyzed currently to develop a correlation between mechanical properties and microstructure 
with the propensity for ductile regime grinding. 

Chemomechanical Effects in Drilling and Grinding of Ceramics 

The goal of this project is to determine the effects of grinding fluid chemistry on material 
removal rate in order to selected most promising additives for cutting fluids used with ceramics. 
Interactions between chemical compounds added to cutting fluids and the workpiece surface in 
the cutting zone can have pronounced effects on the material removal process during abrasive 
machining. The influence of chemical compounds in machining is complex and may involve 
non-stoichiometry reactions accelerated by the mechanical energy involved in machining. 

Experiments were conducted on sapphire, polycrystalline alumina, silicon, silicon nitride, silicon 
carbide, and silica glass to evaluate the chemomechanical effects of several chemical compounds. 
The tests were performed on a precision drill with metal-bonded diamond core-drills. Following 


86 


the experiments, the drilled surfaces, and the diamond particles in the drills were examined by 
scanning electron microscopy to elucidate the material removal process. Two chemical 
compounds showed promising results in increasing the drilling rate by more than 50% compared 
to either pure water or commercial cutting fluids. The following test sequence was used to 
reduce the experimental uncertainties due to the differences in the condition of the drills, i.e., 
the number and distribution as well as sharpness of the diamond particles engaged in cutting. 
First, alumina was drilled for 15 s using distilled water, and the hole depth was measured at the 
completion of the test cycle. This was followed by a second cycle in which a boric acid solution 
was substituted for water in drilling the same hole for another 15 s. The hole depth was 
measured after each cycle. The sequence of drilling alternating between water and the boric acid 
solution was continued for a total of 180 s. Figure 8 shows the drilling rate against the drilling 
time for a number of cycles alternating between water and boric acid solution; the drilling rate 
increases on replacing the distilled water with the boric acid solution. The results indicated an 
average increase of drilling rate by over 100%. Similar tests on sapphire and silicon based 
materials provided no significant benefit for the boric acid solution. Based on the results it is 
postulated that boric acid interacts with the amorphous grain boundary phase in polycrystalline 
alumina promoting intergranular fracture; thereby, increasing the drilling rate. 



Figure 8. Drilling rate of polycrystalline alumina in alternating test cycles between distilled 
water and boric acid solution. 

A second compound was found that increased the drilling rate of silicon-based ceramics. This 
compound which is based on a silicate chemistry did not work with glass nor the alumina 
surfaces. However, it increased the drilling rate of silicon, silicon nitride, and silicon carbide. 


87 


Currently, tests are being conducted to evaluate the mechanisms by which the silicate compound 
interacts with the silicon-based ceramics during drilling. 

Characterization of the Ceramic Grinding Process 

The objectives of this project are to determine the fundamental mechanisms involved in material 
removal during ceramic grinding and to explore effects of material properties, grinding fluids, 
and process parameters. An instrumented surface grinder was used to measure the grinding 
forces in grinding of several types of silicon nitride. These forces were then used to calculate 
the specific grinding energy, which is defined as the energy used in removing a unit volume of 
material from the surface. It was found that the specific grinding energy varies with the 
grinding parameters and depends on the material type. In a similar experiment with different 
commercial grinding fluids, it was found that the specific grinding energy also depends on the 
type of cutting fluid used during grinding. Therefore, the specific grinding energy is not an 
intrinsic material property, but it is an extrinsic property, since it depends also on the grinding 
parameters. An attempt was made to correlate the specific grinding energy to the material 
properties such as hardness and fracture toughness of the silicon nitride materials. It was 
concluded that the specific grinding energy cannot be correlated with these "bulk" properties. 
Recent results obtained in scratch testing have shown that the material removal rate is related 
to the short-crack toughness, as opposed to the long-crack toughness (i.e., a "bulk" property). 


88 


V. 


ELECTRONIC MATERIALS 


Grady White 


The Electronic Materials Group research during the past year has continued in the three 
categories which have driven Group efforts in the previous few years: phase equilibria studies 
of high T^. superconductors, development of measurement techniques, and expansion of modeling 
capabilities. This year has witnessed, however, an increased number and degree of our 
interactions with other government agencies and with private industry. 

The phase equilibrium program underway has focussed on two aspects of high T^, materials: 
the Pb-Bi-Sr-Ca-O system and further investigations of the liquidus Ba-Y-Cu-O phase diagram. 
This work builds upon recent high T^, phase diagram advances made by the Ceramics Division. 
The significance of this work and of the reputation of NIST for phase equilibria studies is 
emphasized by the fact that the DoE has chosen NIST as its source for phase diagram expertise 
in high T^, materials. 

The second thrust of the Electronic Materials Group is the continued development of 
measurement techniques to determine critical materials properties. The Group has experience 
in measuring mechanical, thermal, and dielectric properties of bulk materials. These 
capabilities are being extended to include measurements of effects of cyclic loading, interactions 
between electric field and mechanical loads, thermal properties of films, and thermoelectric 
power (Seebeck) coefficients. In addition, the ability to measure grain texture, i.e., the degree 
of grain orientation, has been achieved for both bulk and film geometries. Finally, the capability 
to measure residual stresses quantifiably over distances of a few micrometers is being developed. 
While these capabilities are valuable for a wide range of applications and materials, they have 
been acquired specifically to evaluate ferroelectric actuator materials, which undergo cyclic 
strains and large electric fields, ferroelectric films, whose properties (electronic or optical) can 
be enhanced by appropriate texturing of the grains, and bismuth telluride based ceramics for 
thermoelectric power applications, whose efficiencies depend upon both thermal and electrical 
conductivities as well as degree of grain alignment. Thermal measurement capabilities have been 
greatly enhanced with thermal diffusivity measurements being made as a function of microcrack 
density, machining processes, grain size, and film thickness in a variety of ceramic systems. 

The Electronic Materials Group has also expanded capabilities in modeling. First principles 
calculations are being used to predict phase diagrams in ferroelectric systems. This type of 
calculations has previously been made only in simpler, non-ceramic systems. Molecular orbital 
(MO) calculations are being used to evaluate how environments interact with strained ceramic 
bonds; this effort could result in the ability to predict different ceramics will survive under load 
in different environments. Finally, surface energy models relating grain growth and faceting to 
the presence and composition of glassy phases at grain boundaries could have an important 
impact on the development of processing techniques to design particular textures into ceramic 
components. 


89 


Significant Accomplishments: 

• Measurements of Raman peak shifts have demonstrated that internal stresses at specific 
depths in transparent materials can be detected. In addition, peak shifts in Raman-active 
coatings have been correlated with the stresses applied to substrate suggesting that 
stresses applied to materials with no Raman signature might be determined by the 
application of a Raman-active coating. 

• The source of microcracking in cyclically loaded PZT has been traced to the presence 
of second phases at triple points and along grain boundaries, implying that mechanical 
properties of PZT might be substantially improved by elimination of second phases. 

• The height of the energy barrier to the reaction of water with silica has been determined 
as a function of strain of the Si-0 using ab initio molecular orbital calculations; in 
addition, a physical interpretation for the decrease of the barrier with strain has been 
obtained. 

• For the first time, First-Principles calculations were used to predict a phase diagram 
forcomplex oxide system. 

• For the first time, phase equilibria studies of the bismuth cuprate superconductors have 
demonstrated that addition of excess bismuth promotes formation of the "2223" (T^. * 
110 K) phase. For the lead-containing members, an essentially single phase "2223" 
region between the approximate limiting compositions Bi^ YPbo. 4 Sr 2 Ca 2 Cu 302 and 
Bi 2 jPbo 4 Sr 2 Ca 2 Cu 30 z has been located. 

PHASE DIAGRAMS 


Phase Equilibria and Crystal Chemistry in Ceramic Systems 

C. G. Lindsay, S. Bernik^ and R. S. Roth^ 

^Guest Scientist, Institute "Jozef Stefan", The Viper Group 

Experimental phase equilibria and solid state chemistry of oxide ceramic systems, a long- 
standing program at NBS/NIST, continued to concentrate on the y 2 Bi 203 ;SrO:CaO:CuO 
(BSCCO) system this system is known to contain at least three high-temperature superconducting 
phases. The system was expanded this year to include extensive examinations in the five 
component system V 2 Bi 203 :PbO:SrO:CaO:CuO (BPSCCO). The objective has been to 
characterize the phase relations involving the phase with highest critical temperature (Tp): 
nominally Bi 2 Sr 2 Ca 2 Cu 30 z or (Bi,Pb) 2 Sr 2 Ca 2 Cu 30 z (2223). 

The primary objective in studying the BSCCO and BPSCCO systems is to attempt to find a 
single-phase 2223 stability region in each system. Part of this objective is to determine whether 
or not it is possible to form the 2223 phase without Pb. Additionally, we want to determine the 
phases in equilibrium with 2223 in each system. We have made Pb-free 2223, though not as 


90 


a single phase, using excess Bi (starting composition Bi2 581^ 9Ca2 iCu30^. Indications of the 
presence of 2223 by x-ray diffraction (XRD) become stronger (possibly suggesting larger 
amounts of 2223) with more Bi (starting composition Bi2.75Sri 9Ca2 1CU3O2); but strong XRD 
indications of CuO are also found. Experiments are now underway in which Bi is increased and 
Cu decreased in the starting compositions. Excess Bi seems to contribute to the stability of 
single-phase 2223 in the BPSCCO system as well. When Bi + Pb = 2 in Bij^PbySr2Ca2Cu302, 
at least 10 mol% Bi must be substituted by Pb to obtain any 2223. When Bi -I- Pb > 2, 2223 
can be formed with less than 10 mol% substitution of Pb for Bi. We have obtained single-phase 
2223 within XRD detection limits with starting compositions Bij^Pbg 4Sr2Ca2Cu302 (1.7 < x < 
1.9). 

Study of the y2La203:y2Al203:y2Nb205:Ti02 system, containing microwave dielectric materials, 
continued this year as well. Lanthanum titanate (La2/3"^^03)’ ^ defect perovskite structure 

and a dielectric constant nearly invariant with temperature, but is apparently unstable without 
small amounts of Al. Unfortunately, A1 also reduces the dielectric constant. We chose to 
examine Nb as an alternate dopant based on the isostructuralism between La2/3Ti03 and 
La2/3Nb03. Our early research in the y2La203'*/2Al203:y2Nb205-Ti02 system showed no 
La2/3Ti03“La2/3Nb03 solid solution series, but last year, nearly single-phase perovskite-like 
materials were made with approximate composition Lao.63"*"^o.90^o.io^3 
L%).67'^^0. 80^0.10^^0. 10O3 . It is also known that a single perovskite-like La^ +x)Ti(i.x)Alx03 

phase can be formed for x ^ 0. 10. The results obtained last year suggest that the 'Lai 2 i 3 ^^^ 3 ~' 
LaA103 phase field can be extended to at least some degree toward Lay3Nb03. This year, 
efforts have been directed toward producing large samples of La^ 63Tio .9oNbo. 10O3 and 
L^.67"^io.80^o. lO'^^O. J0O3 for dielectric measurements. It has proven very difficult to obtain 
^^.63"^^0.90^0. jo03 without either monoclinic LaNbTiOg or 1^2^1207 a secondary phase. 
Efforts are continuing both toward obtaining dielectric measurements and toward finding the 
stability fields for perovskite-like compounds. 

Superconducting Ceramic: Crystal Chemistry and Meltin£ Studies of the Ba-Y-Cu-0 System 

W. Wong-Ng, L. P. Cook and B. Paretzkin^ 

^Guest Scientist 

In the past year, efforts to study the liquidus phase diagram of the Ba-Y-Cu-0 system continued. 
Since compositional data of the liquid is important for constructing a quantitative phase diagram, 
we continued to use a procedure designed in our laboratory two years ago which involved a 
combination of experimental methods to circumvent experimental difficulties. This procedure 
includes (1) calcination and materials handling in special furnace and dry box assembly, (2) 
DTA/TGA studies to obtain indication of thermal events, (3) annealing of samples with porous 
wick materials in order to capture the liquid formed, (4) fast quenching of samples in a liquid 
nitrogen cooled environment for preserving the oxygen stoichiometry, (5) powder x-ray 
characterization of solid phases present, (6) SEM studies and x-ray mapping to study the 
microstructure of the quenched materials, (7) quantitative SEM/EDX analysis of the composition 
of melts, and (8) hydrogen reduction to obtain the oxygen content. 


91 


The main effort in the past year was concentrated on the completion of the quantitative liquidus 
diagram of the Ba0-y2Y203-Cu0 system near the high phase Ba2YCu306^x 
as determination of the effect of oxygen partial pressure on the minimum melting of the system. 
The resulting liquidus diagram indicates that the primary phase field of Ba2YCu306^.x is narrow, 
with < 1 mole% y2Y203; therefore stoichiometry must be precisely controlled to maximize 
yield of Ba2YCu305+x single crystal growth technique. Low temperature melts have low 
yttrium, indicating the growth rate and the size of single crystals may be restricted. Loss of 
oxygen accompanies melting, indicating the melt needs adequate oxygen during crystallization, 
and as a result, P02 can be used as a control variable during melt processing. 

A pressure-temperature phase diagram for the composition Ba27_gY5 5CU65 was constructed. 
It was found that, as the oxygen partial pressure decreases, the eutectic melting temperature 
decreases. The eutectic melting reactions in the oxygen partial pressure region 0.0015 < P02 
< 1 atm and at the more reduced region of 0.0009 < P < 0.0015 atm, were found to be 

Ba2YCu306+x BaCu024.x — > L 

Ba2YCu306+x + CU2O + BaCu202 — > L 

respectively. Also, depending on the composition used and oxygen partial pressure, the 
topological sequence of reaction at higher temperature is different. The Y content of the melt 
decreases as the oxygen partial pressure decreases (ie. from « 0.45% in 1 atm to 0.08% in 
0.0015 atm O2), but there is not a substantial difference between that in air and in oxygen. 
These results imply that there will probably not be a substantial increase of the Y content or the 
expansion of the primary phase field of Ba2YCu305+x at 1 atm oxygen partial pressure. Figure 
1 is the pressure temperature dependence of the phase equilibria of the eutectic composition of 
the Ba-Y-Cu-O system. 

Research in the A-R-Cu-0 systems, where R=lanthanides and yttrium, and A=Ba, Sr and Ca 
continued. For example, the effects on compound formation of two important factors, the 
progressively decreasing size of the lanthanides and different oxidation state stability of these 
elements, continued to be studied. Collaborative efforts were conducted with the International 
Center of diffraction Center (ICDD) towards the preparation of powder x-ray patterns of 
compounds in these systems in order to provide standards for the high T^, community. 

In addition to the above activities, two reviews have been completed, one on the crystal 
chemistry and crystallography of the Ba-Cu-O system and another one on the Sr-Nd-Cu-O 
system. These two systems are of interest to researchers in the high T^. area. The crystal 
chemistry of the Ba-Cu-O system provides an essential basis for study of the complex barium- 
and copper-containing high T^. phases such as Ba2RCu305+x, Ba2Tl2Cajj.iCuOx, and Ba2TlCaQ. 
^CUjjOx- The crystal chemistry of the compounds in the Sr-Nd-Cu-0 system, which contains the 
high T^, superconductor phase Sr^.^NdxCu02, was found to be very complicated. An 
understanding of the non-stoichiometry of oxygen which leads to different possible distributions 
of anionic vacancies in the pervoskite layers provides further understanding of the possible role 
oxygen plays in the superconductors. 


92 


1000 


I 


! 


I 




93 


Figure 1. Pressure-temperature dependence of the phase equilibria of the eutectic composition; unit of oxygen partial pressure used 
in 10-^ Pa. 


Single Crystal X-ray diffraction Studies 

W. Wong-Ng and R. S. Roth\ Y. S. Dai^, and, M. Mathew^ 

^Guest Scientists, The Viper Group, Smithsonian Institute 
^Polymer Division 

Crystallographic structural characterization has been shown to be essential for understanding 
phase equilibria. During the research of potential microwave materials, it was found that recent 
devices on the international market utilize ZnO as an additive to counter balance the negative 
dielectric temperature coefficient of barium titanates BaTi409 and Ba2Ti902o- Phase equilibrium 
and single crystal study of the Ba-Zn-Ti -0 system is therefore important to understand the effect 
of Zn on the crystal chemistry of barium titanate compounds. Last year, we reported the 
structures of three new ternary oxides with formulas Ba4ZnTij2027, BaZn2Ti40ii and 
Ba2ZnTi50i3. We have continued our effort to determine the crystal structure of a related 
fluoride, Ba2Zn7.^TixF^g.yOy by using single crystal X-ray diffraction method. Most crystals 
were found to be twinned. The twinning direction has been determined. Similar to the three 
oxides mentioned above, this compound consists of a 3 -dimensional comer-shared 
interconnecting network of octahedral (Zn,Ti )06 groups. Substitution of Zn by Ti and F by O 
was found in some sites. 

In the area of structural characterization of high T^. superconductors, collaboration has been 
extended to outside research laboratories with Bai-Hao Chen of IBM, Bryan Eichgom of 
University of Maryland and Phillip E. Fanwick of Purdue University. Structures of two more 
members of a newly discovered series of compounds of Ba^j^. jAjjS3jj 4.2, where A = Hf and Zr 
have been determined. Ruddlesden-Popper type stmctures play an important role in high T^ 
superconductor series, i.e. in the Bi and Tl containing compounds of 

(Tl,Bi)m(Ba,Sr) 2 Cajj.iCUjj 02 ii+iii+ 2 ’ where m = l or 2 for the Tl system and m =2 for the Bi 
system. To our knowledge, only compounds with n < 3 have been reported and well 
characterized. In this new series of compound of Bajj+2^QS3jj+i, n has been observed as high 
as 5 . Our collaborative results also showed a progression of symmetry of these compounds from 
tetragonal to more distorted orthorhombic as n increases. The reason of the absence of 
superconductivity in these compounds and the possibility of inducing superconductivity by 
doping is currently under investigation. 

MEASUREMENT TECHNIQUES 

Cyclic Loading of PZT 

M. D. Hill, G. S. White, C-S. Hwang^ 

^Guest Scientist, Seoul National University 

The effect of mechanical cycling (four point bend) and electrical cycling (ac excitation at the 
longitudinal resonance frequency) on the degradation of the mechanical properties of PZT bars 
was examined. 


94 


TEM of cycled specimens revealed microcracks which originated from second phase material 
located at triple junctions. EDX showed that this second phase material contained Pb, Ti and 
Fe but no detectable Zr. 

High intergranular microcrack densities were observed for mechanically cycled samples and 
samples electrically cycled at temperatures < 80 °C, Electrically cycled samples allowed to 
heat, via internal friction to a steady state temperature of 180 °C showed much lower crack 
densities. d 33 measurements revealed that depolarization occurs in the 180 °C electrically cycled 
samples but not in mechanically cycled material nor in the 80 °C electrically cycled material. 
Also, samples heated in a furnace to 180 °C in the absence of extemed stress showed no 
evidence of depolarization. It appears that at lower temperatures (< 80 °C), electrical and 
mechanical cycling leads to microcracking while at elevated temperatures (—180 °C), domain 
reorientation competes with microcrack formation. 

An S-N Curve for indented PZT specimens was generated by mechanical cycling in four point 
bending at different stress amplitudes. Theoretical S-N curves were derived by numerical 
integration techniques assuming that slow crack growth is the sole mechanism for crack 
extension and, ultimately, sample failure. These theoretical models took into account the effects 
of the residual stress field from the indentation The slope of the theoretical S-N curves were 
different from that of the experimental S-N curve, suggesting that a mechanism other than slow 
crack growth is responsible for the behavior observed for mechanically cycled PZT. 

Thermal Wave Measurements in Ceramic Systems 

L. Wei^ and G. S. White 

^Guest Scientist, Wayne State University 

Through our contract with Wayne State University, both the hardware and software of the 
thermal wave system at NIST were upgraded to the current state-of-the-art. The hardware 
improvements now allow measurements to be made at — 100 KHz, which improves the depth 
resolution of the system by almost xlO. This improvement makes it possible to investigate the 
thermal diffusivity of ceramic films less than a micrometer thick. The software improvements 
allow much more precise determinations of thermal diffusivity to be obtained, due to the 
improved 3-D model of heat flow incorporated into the programs. 

The improved thermal wave system has been used to detect damage resulting from machining 
of Si 3 N 4 (in collaboration with Said Jahanmir, Mechanical Properties Group) and from cyclic 
(ball on flat) loading of alumina (in collaboration with Brian Lawn, Laboratory Scientist). In 
the latter case, damage attributed to microcracks was clearly seen in thermal wave images. The 
system has also been used to measure thermal diffusivity in the oxide layers on Si as a function 
of film thickness. In all cases, experiments are continuing and models describing the heat flow 
in terms of the specimen characteristics, i.e., microcrack density and film thickness and 
adherence, are being developed. 


95 


Intergranular Wetting in AI 2O3 

J-H. Choi^ B. J. Hockey^, C. A. Handwerker^, S. M. Wiederhom^, J. E. Blendell 

^Guest Scientist, Seoul National University 
^Mechanical Properties Group 
^Metallurgy Division 
"^MSEL 

Many of the properties of advanced ceramics are critically dependent on the nature and 
distribution of thin intergranular films. The idea that a second phase will either completely wet 
or be completely isolated is based on the assumption that the interfacial energy between the two 
phases is isotropic. It is known that ceramics exhibit pronounced surface energy anisotropy as 
exhibited by the faceted crystal faces commonly observed. Thus it is expected that wetting of 
grain boundaries by a second phase will depend both on the anisotropy of the solid-liquid energy 
and on the anisotropy of the grain boundary energy. 

Low-angle tilt boundaries ( 7 ° about < 10 l 0 >) were produced by annealing a layer sample 
containing tape-cast AI2O3 between two near basal ( 0001 ) plane sapphire crystals. The AI2O3 
tapes contained 4 % anorthite glass. As the sapphire grew and consumed the polycrystalline 
tapes, a liquid layer was formed at the boundary. At long times a low-angle tilt boundary was 
formed. It was found that boundary structures containing both wetted and non- wetted regions 
were stable, in contrast to the isotropic model where it is assumed that the glass either 
completely wets the surfaces or a dry grain-boundary is formed. The orientation of the 
boundary relative to the sapphire crystal structure determined what type of boundary was stable. 
Based on these observations, we have developed a method for determining the shape of a 
partially wetted interface. Using the equilibrium shape of a crystal in contact with the liquid (the 
Wulff shape), the shape of a fully wetted interface can be determined. The shape of the fully 
wetted interface can be combined with the Wulff shape of the grain boundary (which can be 
calculated for low-angle boundaries) to give the shape of the partially-wetted interface. This 
shape can then be used to predict when wetting will occur and to what degree. 

However, the Wulff shape for anorthite glass-filled pores in AI2O3 is not known with enough 
accuracy for a determination of the wetting conditions. We have attempted to measure the Wulff 
shape by examining the shape of glass inclusion formed by infiltrating cracks. Cracks were 
formed either by thermal shock or by indentation. The cracks were then infiltrated by anorthite 
glass and allowed to heal during a high temperature anneal, resulting in glass pockets at different 
crystallographic orientations completely inside single crystalline AI2O3 . Pores of various sizes 
formed; the shapes were measured as a function of time and size to determine when the 
equilibrium shape was reached. 

The implications for improving the properties of advanced ceramics are clear, in that using the 
shape of a partially wetted grain boundary, the degree of texture needed to either prevent or to 
allow wetting is known. Thus, some of the properties of ceramics can be tailored by controlling 
the orientation of the boundaries in the samples. Also, this technique has allowed us to 
determine the surface tension of AI2O3 in a direct method, with the only assumption being the 


96 


ratio of the surface energy of the basal plane to the rhombohedral plane surface energy. Based 
on observations of when the boundaries are fully dewetted and knowledge of the Wulff shape 
of the crystals, the surface tension can be determined. For the basal plane of AI 2 O 3 in contact 
with anorthite, the surface energy was found to be 0.9J/m^ (assuming that the ratio was 1.4). 
This is in good agreement with the estimates of the surface energy from a variety of other 
studies. The determination of the exact Wulff shape for this system will allow a better 
measurement of the surface energy of AI 2 O 3 . 

Thermoelectric Refrigeration using Thermogenic Materials 

J. J. Ritter and C. K. Chiang 

Theoretical projections indicate that an improved thermoelectric flgure-of-merit, Z, for bismuth 
telluride-based thermogenic materials could be achieved through a decrease in thermal 
conductivity in these materials. This effect becomes apparent from an inspection of the 
expression for the figure-of-merit, Z = S^/pK, where S is the thermopower (Seebeck 
coefficient), p, the electrical resistivity and K, the thermal conductivity. It is believed that the 
introduction of nanoporosity or a nanosized second phase, being of the order of the wavelength 
of phonons, could serve as phonon scattering sites, and thus decrease thermal conductivity. Two 
chemical synthetic procedures amenable to the production of bismuth telluride-based materials 
with nano-inclusions as a second phase have been developed. 

The first of these procedures involves the coprecipitation of bismuth and tellurium oxides. The 
mixed-oxides are chemically reduced to give equiaxed particulates approximately 25nm in size. 
Thermoelectric measurements on sintered specimens compacted at IGPa or less exhibit very low 
Seebeck coefficients. When compaction pressures are raised to 1.5GPa and higher, sintered 
specimens exhibit substantially increased Seebeck coefficients as well as a reduction in thermal 
conductivity by factors of 3 to 5. The latter effect may arise from phonon scattering by 
nanoporosity generated as a second phase during sintering. Unfortunately, these samples 
concomitantly exhibit low electrical conductivities. As a result, an improved figure-of-merit has 
not yet been realized. 

An alternative chemistry for bismuth telluride synthesis involves the complexation of bismuth 
and tellurium ions with a poly functional organic acid. The resultant metal-organo complexes 
are thermally processed to a mixed-oxide precursor. Hydrogen reduction of the precursor gives 
plate-like particles of bismuth telluride. Thus, an important option for processing this 
polycrystalline material arises from the particle morphology. It may be possible to texture 
bismuth telluride platelets to take maximum advantage of the anisotropic nature of their 
thermoelectric properties with respect to the crystallite axes. 

Both approaches allow the introduction of second phases as nanosized inclusions in bismuth 
telluride. Second phases successfully introduced to date include Fe, Ni, Si 02 , and C. The 
metal-organo route readily permits the synthesis of bismuth telluride alloy systems such as Bi-Sb- 
Se-Te. Evaluations of the thermoelectric properties of these more complex materials are 
pending. 


97 


Ferroelectric Thin Films by Pulsed Laser Deposition 


L. P. Cook, B. W. Lee\ C. K. Chiang, W. Wong-Ng, P. K. Schencl^, C-S. Hwang\ 

P. S. Brody^ and K. W. Bennett 

^Guest Scientist, Hanyang University, Seoul National University 
^Metallurgy Division 

^Army Research Laboratory, Adelphi, Maryland 

During the year, work on pulsed laser-deposited thin films was completed in three principal 
areas: 1 ) crystallization of amorphous BaTi03; 2 ) preparation and characterization of PbTiOj - 
Pb(MgQ 5 Wo_ 5 ) 03 ; and 3 ) preparation and characterization of Nb-doped PZT. 

Barium titanate films are of interest because of their high dielectric constant, giving it potential 
application as thin film capacitors at a great saving in space for a given charge storage capacity. 
Studies of the crystallization of amorphous laser deposited BaTi03 concentrated on 
microstructural investigation of the crystallization process and the relation of the microstructure 
to the crystallization kinetics. TEM examination of the amorphous as-deposited material 
indicated that the films had columnar structure and confirmed their lack of crystallinity. In spite 
of the columnar nature of the initially amorphous deposits, post-depositional isothermal 
crystallization resulted in essentially random orientation of crystallites —5 nm in diameter. 
Crystallization was essentially complete at 650 °C, with no detectable second phases. The 
BaTi03 crystallization kinetics are consistent with a simple model involving rapid, dense 
nucleation, followed by unimpeded growth, with a change in growth Idnetics occurring at the 
point where the growing crystals unpinge upon one another. A major challenge in processing 
the amorphous BaTi03 is the elimination of voids associated with shrinkage produced during the 
crystallization process. The shrinkage voids tend to reflect the columnar structure by forming 
channels parallel to the columns. Unfortunately these voids have prevented measurement of the 
dielectric constant. Another issue important in the crystallization of BaTi03 is related to the 
apparent cubic nature of this material. To investigate this, an estimate of residual stress was 
obtained by x-ray line profile analysis. The stresses estimated on this basis may be sufficient 
to cause substantial change in the temperature of the ferroelectric phase transition, possibly 
explaining why no tetragonality was observed in these materials. 

(Mg,W)- doped PbTi03 is of interest because of possible applications in imaging and image 
storage. The advantage of this material over pure PbTi03 is that it is less tetragonal, and hence 
the material can be cooled through the ferroelectric phase transition without microcracking. 
During the year, efforts were concentrated on preparing single phase perovskite and minimizing 
the troublesome occurrence of the pyrochlore phase. A processing diagram indicating the 
regions of optimum film growth in terms of background oxygen pressure and substrate 
temperature was developed. The crystallographic orientation of these films, if crystallized 
during deposition (rather than by post annealing amorphous films) is strongly controlled by 
preferred orientations in the underlying Pt substrates. It has not proved possible to control the 
orientation of the deposited film independently of texturing in the substrate. The crystallographic 
orientation of the film has a marked effect on the ferroelectric properties. To optimize the 
remanent polarization on (lOO)-oriented Pt substrates, a random orientation of the film was 


98 


successfully produced by a novel two- stage deposition process in which a thin layer of 
amorphous material was deposited on Pt, then crystallized, with the remaining material deposited 
at a higher temperature. These films had the highest remanent polarizations. 

Degradation of ferroelectric properties with time (fatigue) has been a longstanding issue in the 
development of ferroelectric thin film memory devices. However it was noted that PZT films 
with Nb seemed to undergo much less fatigue. To investigate this possibility further, PZT 
targets containing 0.5, 1.0 and 1.5 wt% Nb were prepared, films were deposited, and fatigue 
properties were measured. Results to date indicate that Nb doped samples show substantially 
less fatigue out to at least 10^^ cycles than non-doped material. 

Until recently, much of our effort was devoted to preparing ferroelectric thin films of nominal 
phase purity. However, for practical application in which laser deposition of ferroelectric thin 
films is integrated with device manufacturing procedures, it will be necessary to produce, not 
only ferroelectric properties, but also quality surface smoothness with freedom from particulates, 
pinholes, and other flaws. Experiments to date have shown that the background pressure during 
deposition has a large effect on surface smoothness; generally films deposited at higher oxygen 
pressures (e.g. PO 2 = 40 Pa) are characterized by higher surface roughnesses. Substrate 
temperature may also play a role, with geometrical factors and the nature of the laser target 
surface also having an effect. A major challenge in the further development of these materials 
is the improvement of surface smoothness and the elimination of pinhole and particulate defects. 

Stress Measurements Using Micro-Raman Spectroscopy 

G. S. White, L. M. Braun^, G. J. Piermarini, M. R. Gallas^, and Y. Chu^ 

^ Mechanical Properties Group 

^ Guest Scientist, Institute de Fisica da Ufrgs, Howard University 

The ability to measure stress on a local scale has important implications for the design of 
modem materials and, because of the catastrophic fracture characteristics of brittle materials, 
particularly for ceramics. The capability to determine residual stresses resulting from processing 
techniques as well as the potential ability to map out stress distributions resulting from the 
presence of defects, e.g., cracks, pores, or inclusions, or from material modifications, e.g., 
reinforcing fibers or electrode layers, would permit the generation of models which could, in 
turn, optimize design and manufacturing procedures for enhanced material applications. With 
these goals in mind, we have continued our investigation of using the micro-Raman technique 
to determine stresses in ceramic materials. 


99 


Measurements of stresses in polycrystalline 
alumina and in single crystal sapphire have 
been made during the past year by correlating 
shifts in the sapphire peaks with a known 
applied load. The loads were generated in a 
biaxial fixture described last year which 
produced a uniform tensile load on one side 
of disk shaped specimens and a uniform 
compressive load on the other side. In situ 
measurements demonstrated that stresses 
approximately 10% of the strength of the 
material could be detected reliably. In 
addition, measurements of transparent 
material (sapphire) showed that the signal for 
the Raman spectrum is predominately 
controlled by the material at the focal plane 
of the microscope in the micro-Raman 
system. 


Figure 2 is a plot of the shift in an alumina peak position as a function of applied load for a 
sapphire specimen. The surface of the sapphire was originally in a state of uniform 
compression, due to the sawing and polishing associated with the sample preparation. The data 
in the figure which are shifted to lower wavelengths with externally applied load represent the 
fact that the residual compressive stress on the top surface of the specimen is decreasing. In 
contrast, the remaining data were taken by focussing the microscope at the bottom of the 
specimen and represent the increasing compressive stress at that point of the specimen. This 
figure demonstrates that: 1) stresses well below the strength of the material can be determined 
by this technique 2) both tensile and compressive stresses can be measured, and 3) the technique 
is sensitive to the focal plane of the measurement and is insensitive to the remaining optical path 
through the material. 

Experiments made on polycrystalline alumina have demonstrated that measurements within 
individual grains can be made; due to the focal spot size of the laser, the grain size has to be 
on the order of several micrometers. 


1.002 


c 

O 1.001 

'ot 

o 

Q- 

"O 1.000 

(D 

N 


• 0.999 


0.996 


i; 

T -- 


5C 

ir T 

^ i i[ 


- 0.10 


0.30 0.70 

Load (mV) 


t r I I I I I 

1.10 1.50 


Figure 2 Peak position, 
formalized by initial position as a 
function of applied load for the top 
surface (bottom curves) and the bottom 
surface of a sapphire disk. 


100 


In addition, the calibration of the pressure dependence of the Raman scattering peaks for a- 
alumina has been accomplished with the aid of a diamond anvil high pressure cell (DAC) 
specially modified with low fluorescence diamond anvils coupled with the ruby fluorescence 
method of pressure measurement. The calibration was made to 1750 MPa, exceeding the 
maximum strength of a-alumina crystals (1000 MPa) by a wide margin. From a least-squares 
linear fit to the data, the wavenumber shift with pressure was calculated to be 0.0022 ± 6.9x10' 
^ cm'^MPa'^ for a-alumina. In the case of a-alumina, residual stresses on the order of 5(X) to 
a maximum of 1000 MPa are expected before cracking occurs. 

Lifetime Predictions in InP 

G. S. White, L. M. Braun\ W. C. Carter^, and E. R, Fuller, Jr.^ 

^Mechanical Properties Group 

^Powder Characterization and Processing Group 

^Division Scientist, Ceramics Division 

Lifetime predictions have been made for single crystal InP. InP has important applications as 
a connector for optical fiber cables; therefore its reliability, particularly in inaccessible locations, 
is a matter of substantial industrial significance. The key points of concern were: 1) what is the 
susceptibility of InP to environmentally enhanced crack growth (i.e., the susceptibility of InP 
to crack growth for loads less than the ideal strength of the material as a result of attack of the 
stressed crack tip bonds by water molecules) and 2) once the susceptibility of water was 
determined, what could the lifetime be expected to be for a range of applied static loads? 

In addition to strength measurements made on the as-received material, dynamic fatigue 
measurements (measurements of breaking strength as a function of loading rate) were made on 
indented specimens in liquid water and in Ar gas at 50% relative humidity (RH). The dynamic 
fatigue measurements covered 5 orders of magnitude in velocities. InP is so insensitive to water 
enhanced crack growth, however, that even with this range of velocities, no precise measure 
of N (a parameter related to the efficacy of an environment at enhancing crack growth; the 
larger N, the less the tendency for environmentally enhanced fracture to occur) could be 
obtained. The best fit to the dynamic fatigue data resulted in N-values of 269 for the 50% RH 
environment and of 958 for liquid water. While these values could easily be off by a large 
amount, they do indicate that InP is not very susceptible to slow crack growth in either water 
or humid gas. Resultant lifetime predictions indicate that, if the material does not break 
immediately upon the application of a load, it will probably last for many years. This 
information suggests that, from a mechanical reliability standpoint, InP will function well as a 
fiber optic coupler. 

The large uncertainty remains a problem from a scientific standpoint, however. InP has the 
same structure as GaAs, which has been shown not to be susceptible to water-vapor enhanced 
fracture but to be susceptible to liquid water. The uncertainty in N does not let us draw any 
conclusions for InP. Therefore, we plan to conduct crack growth measurements of InP using a 
double cantilever beam geometry. 


101 


BaTiQ 3 Films on Pt Substrates 

M. D. Vaudin, C-S. Hwang^ , P. K. Schenck^ 

^ Guest Scientist, Seoul National University 
^Metallurgy Division 

Pulsed laser deposition (PLD) 

Fine-grained (<20 nm) thin films (100 to 500 nm thick) of BaTi 03 have been deposited on self- 
heated Pt/Ti/Si02/Si substrates using PLD. Observation of the films indicated that faceted 
hillocks of Pt formed on the surface of the substrate and the BaTi 03 film followed the Pt surface 
morphology and was itself rough; for current device applications of high dielectric thin films, 
particularly in the area of advanced DRAMs (>256 Mb), the surface of the film must remain 
planar to ±20 nm. To reduce the thermal processing time of the substrates and thus the Pt 
hillock formation, the method of heating the substrate has been changed from resistive self- 
heating (passing a current through the substrate) to a small BN resistive heater. 

The formation of the faceted hillocks (or "mesas") of Pt has been studied by annealing substrates 
at temperatures from 500 °C to 750 °C under various oxygen partial pressures for times up to 
15 minutes. The substrates were then observed with SEM, TEM and atomic force microscopy 
(AFM). Figure 3 is a bright-field cross-section TEM micrograph of a substrate which was 
annealed for 1.5 h at 750 °C in flowing N 2 with 20 ppm residual O 2 . The micrograph shows 
a Pt mesa, 100 nm high and 500 nm across, with a {llljpt top surface. 



Figure 3 Bright-Field cross-section TEM micrograph of Pt/Ti/Si02/Si substrate annealed 1.5 
h at 750 °C in 20 ppm O 2 . The Pt film thickness is 200 nm. The micrograph shows a Pt 
"mesa", 100 nm high and 500 nm across, with a (lll)pt top surface, and Ti02 grains in the 
center of the Pt film. 


102 


The light contrast regions in the center of the Pt film which are Ti 02 grains that forms when Ti 
diffusing from the interlayer along Pt grain boundaries to the surface reacts with oxygen 
diffusing down grain boundaries from the surface. This oxide formation results in a volume 
increase which is the driving force for mesa production. Before annealing, the substrates had 
been characterized by powder x-ray diffraction and the degree of < 1 1 1 > preferred orientation 
had been determined. After annealing, the crystallographic orientation of a number of mesas 
in selected samples was determined using backscattered electron Kikuchi patterns (BEKP) which 
showed that the mesas had a more pronounced < 1 1 1 > texture than the as-received substrate. 
Since Ti 02 production causes significant surface roughening, we plan to anneal substrates with 
a thinner Ti interlayer to investigate whether there is a critical Ti thickness below which this 
phenomenon does not occur. 

Nanosize Powder Processing 

G. J. Piermarini, M. R. Gallas^ A. Pechenik^, B. J. Hockey^ 

^Guest Worker, Institute de Fisica da Ufrgs 

^Guest Worker, Air Force Office of Scientific Research 

^Mechancial Properties 

A fundamentally new approach to the fabrication of ceramic materials is currently being studied 
at NIST. The method involves the production of nanometer size ceramics using cryogenic 
(liquid nitrogen) compaction of nanosize particles followed by pressureless heat treatments. 
Materials which are intrinsically transparent can be made into transparent green-state compacts 
by this process because the material does not scatter visible light. Transparent greenware 
produced by this method permits easy flaw detection during fabrication, hereby augmenting 
quality control. Required sintering temperatures are significantly lower than those used for more 
coarse-grained ceramics. Transparent ceramic compacts of cubic materials such as 7 -alumina 
and silicon nitride have been made by this process without requiring the addition of sintering 
aids. Transparent, bulk 7 -alumina ceramic with hardnesses in the 10 GPa range have been made 
for the first time. 

Innovative Processing of Sol Gel Derived Nanosize Powders 

G. J. Piermarini, M. R. Gallas^, J. J. Ritter^, B. J. Hockey^ 

^Guest Scientist, Institute de Fisica da Ufrgs 
^Powder Characterization and Processing Group 
^Mechanical Properties Group 

Gel shrinkage and crack formation during drying are problems encountered in the early stages 
of the processing of sol-gel nanosize particulates. In fact, these problems have prevented the sol- 
gels from being utilized in commercial ceramic processing methods. NIST is studying methods 
to minimize shrinkage and crack-formation by a novel approach of subjecting semi-cured gels 
to a series of controlled cyclic compactions to extrude and eliminate unwanted solvents, while 
simultaneously achieving a high-density green-state without cracking. Subsequent heat treatment 


103 


under a program of controlled pressure/temperature/environments to produce sintered bodies is 
then carried out. The compacts are evaluated for optical clarity, microstructure, microhardness, 
and fracture toughness. 

Amorphous silica was fabricated from the sol-gel material by the application of pressures up to 
3000 MPa at room temperature and also under liquid nitrogen. Heat treatments of the green 
bodies were carried out at both 400 and 800 °C for various time periods. The starting material 
is amorphous and in the form of a viscous gel. The gel cures into a very porous glass over a 
period of 7-10 days during which time it undergoes enormous shrinkage (about 50%) usually 
accompanied with cracking and an increase in viscosity (ultimately exceeding the glass 
transition, 10'^^ Poise). In our experiments, samples of the silica-gel were removed for 
processing each day during the cure period to determine if an optimum cure condition was 
relevant to the processing procedure employed. Indeed, this was found to be the case as our 
results show that the best compacts can be made starting with gel taken in the 4*^-to-7* day of 
cure, pressing it to clarity using only 3000-4000 MPa and sintering for 4 hr at 600 °C. Optically 
clear, dense, crack-free amorphous compacts were made with hardness values in the 10 GPa 
range. This value of hardness is significantly larger than the typical silica glass hardness of 6-to- 
8 GPa. In fact, 10 GPa is typical for crystalline silica. 

MODELLING 


Molecular Orbital Calculation 


W. Wong-Ng, G. S. White, S. W. Freiman, and C. G. Lindsay 

Efforts continued to investigate the interaction of environmental species such as water with 
silicon and with vitreous silica. Experimentally, it has been observed that water enhances the 
crack growth of silica but not silicon under externally applied strain. In the past year, ab initio 
molecular orbital calculations (MO) have been performed on both systems. Factors such as the 
size of crack tip (crack- wall), net charge on the crack-tip atoms as a function of strain were 
investigated for both systems. 

Si: 

Our results show that the unstrained crack tip opening is too small to accommodate 
environmental molecules; strain is necessary both to widen the crack tip and to attract and to 
orient the molecule. As tensile strain was applied along the Si-Si crack-tip bond, the net charge 
on both Si atoms increased (more positive) regardless of the manner the strain was applied (ie. 
with or without angle distortion, and whether the strain was distributed evenly in the 
neighborhood of the crack-tip bonds). This is different from the situation of silica in which 
when the crack-tip Si-0 bond is strained, the net charge of Si becomes more positive and O 
becomes more negative, which enhances the interaction with an environmental molecule 
containing atoms which both donate and accept electrons. 

The absence of chemical reaction in Si with environmental molecules is also demonstrated from 
the geometry optimization calculations of the system SigH^gO-l-H20. In the absence of strain, 
the water molecule is always about 5 A from the crack-tip Si [0(H20)...Si], whereas under 15% 


104 


strain (15 % elongation of the Si-Si bond), the molecule is able to move closer towards the crack- 
tip (still at a relatively great distance of 2.9 A, which is slightly less than the sum of the Van der 
Waal’s radii of Si (l.VA) and 0 ( 1 . 4A)). This separation suggests that no chemical reaction takes 
place. Therefore, despite strain widening the size of the crack-tip, the result of charge 
redistribution at the crack-tip does not favor chemical reaction. 

Silica: 

Reaction calculations between silica and water show that without the application of strain, the 
activation energy (difference in energy between reactants and transition complex) is «45 
Kcal/mole, and the reaction is slightly endothermic. With strain applied, this energy decreases 
to «22 Kcal/mole, due to the raise of the reactant energy, and the reaction becomes exothermic. 
The increase in the reactant energy was determined to be due to distortion of the silica tetrahedra 
and is insensitive to the specific environmental molecule present. 

First Principles Phase Diagram Calculations 

B. P. Burton, A. Pasturel\ G. Ceder^, S. Greiner^, and R. E. Cohen'^ 

^CNRS, Grenoble France 
^Massachusetts Institute of Technology 
^Allied Signal Research, Des Plaines II. 

^he Geophysical Laboratory, Carnegie Institute of Washington, D.C. 

Relaxor ferroelectrics are a technologically important class of solid solution materials in which 
the ferroelectric properties are sensitive functions of composition and quenched in cation order. 
The results of a first principles calculation of order-disorder phenomena in Pb(Sci/ 2 Sci/j )03 (PST) 
were reported at the Eighth International Meeting on Ferroelectrics and at the Calculation of 
Phase Diagrams (CALPHAD XXII) meeting. In addition, work continues on a first-principles 
phase diagram (FPPD) calculation for the relaxor solid solution system 
(1 -x)Pb(Sc,^Sc ,/^)03 -xPbTi 03 . 


In collaboration with Gerbrand Ceder and his student Patrick Tepish, we have done three 
different FPPD calculations for the system CaO-MgO. This was done to assess the relative 
merits of the three different techniques for calculating the formation energies of ceramic 
compounds with large unit cells. From these we obtained model Hamiltonians that were used 
as input for FPPD calculations. 

FPPD calculations were used to study stable and metastable bcc based ordering in the systems 
Fe-Be and Mg-Li. These calculations combine full potential electronic structure calculations (to 
obtain a model Hamiltonian) with a cluster variation method phase diagram calculations. In the 
Fe-Be system, both chemical and magnetic ordering were considered and it was demonstrated 
that: 1) Magnetic ordering is responsible for the observed B2 (CsCl structure) ordering in 
metastable bcc solutions (without magnetism B32 ordering would occur); 2) The energetic cost 
of mixing atoms of very different sizes is responsible for observed spinodal ordering/phase 
separation in metastable bcc solutions; 3) The DO 3 structure Fe 3 Be phase is predicted to be less 
stable than a mixture of ferromagnetic BCC Fe plus ferromagnetic B2. 


105 




VI. OPTICAL MATERIALS 


Albert Feldman 


The objectives of the Optical Materials Group are to provide data and their evaluation, 
measurement methods, standards and reference materials, concepts, and technical information 
on the fundamental aspects of processing, structure, properties, and performance of optical and 
photonic materials. The program supports generic technologies in crystalline, glassy, and thin 
film inorganic optical and photonic materials in order to foster their safe, efficient and 
economical use. Research in the group addresses the science base underlying advanced optical 
and photonic materials technologies together with associated measurement methodology. 

The principal activity of the Optical Materials Group is being directed toward materials for 
photonic technology related to data processing, storage, and display. Three aspects of this 
technology to be addressed are modulator materials, storage media materials, and material for 
compact short- wavelength radiation sources to increase storage density. In the area of modulator 
materials, we are evaluating new processing methods that would result in thin film materials with 
superior properties such as enhanced electro-optic modulator characteristics. In the area of 
storage media materials we are addressing the development of thin film photorefractive 
materials, in which the storage method involves modification of the refractive and absorptive 
properties upon exposure to optical radiation. Ferro-electric oxides (more specifically barium 
titanate) are the materials we are studying in the latter two aspects because they possess large 
electro-optic coefficients and a large photorefractive effect. 

In the area of materials for short wavelength sources, our studies are being directed toward 
crystalline materials with large band gaps. This is because a large bandgap is required if a 
material is to emit radiation at short wavelengths. We have been studying diamond, a wide 
band-gap material; we are extending this work to other wide band-gap materials that hold 
greater promise as optical sources, such as gallium-nitride, aluminum-nitride, zinc-selenide, and 
in the future, quantum well structures of these materials. Diamond possesses numerous superior 
properties make it an excellent material for a variety of photonic applications. In addition to its 
optical transparency, it has the highest thermal conductivity of any material at room temperature 
making it an excellent substrate material for solid-state semiconductor laser sources. 

Work on gallium-nitride and zinc-selenide is just beginning. A key issue in the research will 
be the characterization of defects to very low concentration levels (less than 10^^ cm‘^). 
Collaborations have been established for the purpose providing data that will allow 
manufacturers to improve the quality of the materials. Specimens of gallium nitride are being 
provided by Johns Hopkins Applied Physics Laboratory and specimens of zinc-selenide are being 
provided by Eagle Picher. NIST will be characterizing the defects in the material; feedback 
between processors and NIST may allow the producers to improve the quality of their materials 
to the point where viable, compact short wavelength laser sources can be produced. 

Significant Accomplishments: 

• Electro-optic thin film ceramics proposed for use in future photonic information 
technology systems must have great microstructural and compositional uniformity and yet 
must be fabricated by practical methods, such as metalorganic chemical vapor deposition 


107 


(MOCVD). Our MOCVD facility has been modified to improve the through-thickness 
uniformity of polycrystalline barium titanate (BaTi03) films. Films prepared in the 
modified system have shown improved microstructural and compositional uniformity as 
determined by cross-sectional transmission electron microscopy and by secondary-ion 
mass-spectroscopy (SIMS) depth profiling. 

Raman spectroscopy has been used to characterize the structure of MOCVD-grown 
BaTi03 films. The films were grown at NIST and at Advanced Technology Materials 
(ATM). The spectra showed features due to crystalline and amorphous phases suggesting 
the presence of material other than BaTi03. intensity of the impurity-phase features 
in the spectra varied from film to film. Lines due to tetragonal BaTi03, the phase 
required for photonic applications of the material, were identified in the spectra of the 
films with lowest impurity-phase content. The results demonstrate the usefulness of 
Raman spectroscopy for characterizing of the structure of BaTi03 complementing 
other techniques such as X-ray diffraction and electron diffraction. 

High-power high-speed electronics is projected to be an important application of chemical 
vapor deposited (C VD) diamond and doping with boron to produce p-type material would 
be a major component of this technology. A set of boron-doped diamond films grown 
by filament-assisted chemical vapor deposition was characterized by Raman spectroscopy. 
The peak of the diamond Raman line was observed to shift to lower wavenumber with 
increasing boron concentration and, in the most heavily doped films, to broaden in an 
asymmetric manner toward lower wavenumber shift. Our results indicate that Raman 
spectroscopy is a useful method for evaluating the effect of boron doping on the diamond 
microstructure and on the charged carrier density. 

Diamond cannot be used at temperatures significantly greater than 500 °C because it 
oxidizes in air. Reducing the oxidation rate might make it usuable at these high 
temperatures. We have found that the oxidation rate of CVD dimond in pure flowing 
oxygen at 700 °C can be significantly lowered if it is doped with boron. The oxidation 
rate, as measured by thermogravimetric analysis, of a CVD diamond film doped with 0.6 
% boron was one tenth the oxidation reate of undoped CVD diamond. 

Grain boundaries in high temperature superconductors can severely degrade critical 
current densities, J^., thereby preventing the use of these materials in high-power 
commercial applications such as motors and power-transmission systems. Understanding 
how grain boundaries affect the dynamics of flux penetration may allow us to develop 
materials with high J^,. A high-resolution magneto-optical imaging system has allowed 
us to quantitatively measure the flow of flux across grain boundaries in YBa2Cu307.x 
(YBCO) polycrystals. This is the first time such measurements have been made. Flux 
penetration of all high-angle grain boundaries (misorientation angle greater than 10®) 
occured at very low applied fields (1-2.5 mT). Flux penetration of small-angle grain 
boundaries (misorientation angle less than 10°) required higher applied fields; the smaller 
the misorientation angle, the higher the applied field required for flux penetration. 


108 


FERROELECTRIC OXIDE THIN FILMS FOR PHOTONICS 


Photonic devices made of ferroelectric oxide films that have large electro-optic coefficients are 
expected to have a major role in future information technology systems. U.S. dominance in 
these advanced technologies will be important for maintaining the future economic health of the 
nation. Pioneering new methods of materials fabrication and characterizing the materials 
produced is an important means of promoting U.S. dominance in these technologies. 

Metalorganic Chemical Vapor Deposition of Barium Titanate 

D.L. Kaiser, M.D. Vaudin, C.-S. Hwang, L.D. Rotter, L.H. Robins and G. Gillen^ 

^Surface and Microanalysis Science Division 

The ferroelectric oxide barium titanate (BaTi03) has excellent electro-optic properties that make 
it potentially very useful for many photonic applications such as electro-optic modulation and 
switching, holographic imaging and data storage, and frequency doubling to produce blue/green 
light. Commercialization of these processes for future information technology systems requires 
that high-quality, single crystal films be fabricated reproducibly by a practical processing 
technique such as metalorganic chemical vapor deposition (MOCVD). Furthermore, the 
preparation of films with optimal electro-optical properties can only be achieved through detailed 
studies of how defects affect critical properties and how defect concentrations and distributions 
can be controlled by processing. 

Our research has focused on the growth and microstructural characterization of polycrystalline 
films of BaTi03. Films were deposited at 600°C on fused quartz substrates in a research-scale 
MOCVD system with the precursors titanium isopropoxide (TIP) and barium B-diketonate 
[Ba(thd)2]. The microstructures of the films were characterized by several techniques. 
Crystalline phases were identified by x-ray powder diffraction (XRD) techniques and the 
presence of tetragonal BaTi03 was detected by Raman spectroscopy. Compositional 
homogeneity through the film thickness was determined by secondary ion mass spectroscopy 
(SIMS) depth profiling and structural uniformity was determined by cross-sectional transmission 
electron microscopy (TEM). Energy dispersive x-ray spectroscopy measurements revealed that 
the films contained approximately 2 mole % strontium. 

Initially, films that had appeared to be pure BaTi03 XRD had been found to be structurally 
and compositionally nonuniform through the film thickness. The titanium concentration was 
found to vary through the thickness and transition layers at the film/substrate interface had 
compositions that varied from film to film. To improve uniformity, the MOCVD system was 
modified by installation of: 1) an elevated pressure TIP bubbler to stabilize the TIP 
concentration in the process gas; and 2) a process-gas bypass apparatus to allow the gas 
composition to stabilize before deposition. A film prepared in the modified system was pure 
BaTi03 with a slight < 100 > texture as determined by XRD. (See Fig. 1.) The SIMS depth 
profiles, seen in Fig. 2, indicated good uniformity of the barium, strontium and titanium 
concentrations from the surface of the film (depth = 0) to the film/substrate interface (depth « 
1.2 ^m). The high ion counts at the surface of the film were an artifact of the SIMS 


109 


measurement; the gradual decrease in the silicon ion counts from the film/substrate interface into 
the film may indicate silicon diffusion into the film. A cross-sectional TEM image, seen in Fig. 
3, revealed a uniform, columnar microstructure with grain widths in the range 0.1 to 0.2 ^m. 
Lattice imaging studies showed that the white streaks between the grains in Fig. 3 were 
amorphous material. Raman spectroscopy measurements revealed that the films contained 
tetragonal BaTi 03 , the phase required for use of the material in photonic devices. 

The next phase of this project will be devoted to the goal of epitaxial growth of BaTi 03 on 
lattice-matched substrates, such as MgO and KTa 03 . The microstructures of these films will 
be characterized by the above techniques and by small angle neutron scattering. In addition, 
electrical, optical and electro-optical properties of the films will be measured and correlated with 
the defect structures. Results of these characterization studies will provide input for modifying 
the deposition process to further improve the quality of the films. 



Figure. 1. Conventional 6-26 XRD pattern for the film deposited in the modified MOCVD 
system. BaTi 03 peaks are indexed with the indices of the cubic phase. 


110 



Figure 2. SIMS depth profile data on the film deposited in the modified MOCVD system. 



Figure 3. Cross-sectional TEM micrograph of film deposited in the modified MOCVD system 
showing the substrate (S) and the BaTi 03 film (F). 


Ill 


Structure and electro-optic properties of barium titanate thin films 

L. H. Robins, L. D. Rotter, and D. Kaiser 

For use in practical photonic applications, films of BaTi03 of the tetragonal 

phase with negilible contamination by impurities and other structural phases. It is expected that 
single-crystal films, or highly oriented and poled polycrystalline films, will be needed to 
minimize optical scatter and maximize the strength of the electro-optic effect. Characterization 
methods that provide detailed information about the structure and compostion of the films are 
thus needed to provide feedback for improving the deposition process. 

Raman spectroscopy can provide structural information that is difficult to obtain by other 
methods even though it does not directly determine the crystal structure, such as is done by 
X-ray or electron diffraction. For example, the tetragonal axis in BaTi03, c-axis, is difficult 
to distinguish from the other principal axes by diffraction methods because of the small 
anisotropy in lattice spacing. However, Raman spectroscopy is very sensitive to the orientation 
of the c-axis in single-crystal BaTi03 because of the coupling of the Raman phonons to the 
electric dipole moment, which is par^lel to the c-axis. 

Raman spectra were obtained from a number of BaTi03 films grown by metal-organic chemical 
vapor deposition (MOCVD). These films had been grown at NIST and at Advanced Technology 
Materials (ATM). For comparison, the Raman spectra of a large single crystal and of a bulk 
ceramic specimen were recorded under conditions similar to those used to obtain the thin-film 
spectra. All the MOCVD specimens showed spectral features due to phases other than BaTi03. 
The intensity of the non-BaTi03 features differed significantly from film to film, and the most 
intense non-BaTi03 features in the ATM films differed from those in the NIST films. The 
Raman spectra of five specimens are shown in Fig. 4. From top to bottom, these are a NIST 
film with high impurity-phase content, designated N35, a NIST film with low impurity-phase 
content, designated N36, an ATM film with high impurity-phase content, designated A46, an 
ATM film with low impurity-phase content, designated A40, and the bulk ceramic specimen. 

Lines attributed specifically to the tetragonal phase occur in the spectra of the ceramic specimen 
and the films with lowest impurity-phase content: specifically, the narrow line at 305 cm'^ and 
the relatively narrow line at 710 cm'^ to 720 cm'^. Unlike some of the broad Raman lines, these 
narrow lines have been shown to vanish at temperatures above the tetragonal-to-cubic phase 
transition in single-crystal BaTi03, which occurs at about 135 °C. The presence of the narrow 
lines in the spectra of the purer BaTi03 films strongly suggests that the crystal structure of these 
films at room temperature is tetragonal rather than cubic. Additional measurements of the 
Raman spectra are planned to investigate the dependence of the various spectral features on 
temperature. 

Optically polarized Raman spectra from the large single crystal were found to be strongly 
dependent on the orientation of the crystal axes. The observed orientation dependence is in good 
agreement with previous results for single-crystal BaTi03. The results suggest that Raman 
spectroscopy should be useful in determining the orientation of the crystal axes in epitaxial 
single-crystal or highly oriented polycrystalline films. 


112 



Figure 4. Raman spectra of five BaTi03 specimens. The top four spectra are from 
MOCVD-grown films: N35, grown at NIST, high impurity-phase content; N36, grown at 
NIST, low impurity-phase content; A46, grown at ATM, high impurity-phase content; and A40, 
grown at ATM, low impurity-phase content. The bottom spectrum is from a bulk ceramic 
specimen. The narrow lines at 305 cm*^ and 710-720 cm‘\ in the spectra of N36, A40, and the 
ceramic, are attributed to tetragonal-phase BaTi03. 

Polarimetric Investigation of Barium Titanate Films 

L.D. Rotter, D.L. Kaiser, A. Feldman, L.H. Robins, M.D. Vaudin, C.S. Hwang 

The purpose of this project is to develop techniques to characterize currently grown BaTi03 
films. The films under investigation were grown by MOCVD at NIST and at Advanced 
Technology Materials (ATM). 

Most applications of BaTi03 thin films will require poled epitaxial films of the material in which 
the optic axis lies either in the plane of the film or perpendicular to it. This orientation allows 
us to make use of the largest electro-optic coefficient in the material, T 42 , for modulator 


113 


applications and to achieve maximum photorefractive gain. In a periodically poled film one can 
realize efficient second harmonic generation. 

However, truly epitaxial films of BaTi 03 are not yet available. The films tend to be 
polycrystalline with randomly oriented or partially oriented crystallites and the phases present 
are not entirely of the desired tetragonal phase; cubic and amorphous phases are usually present 
as well. 

We are developing optical techniques which, in conjunction with x-ray scattering and TEM, are 
expected to quantitatively determine the ratio of the tetragonal phase to the cubic plus amorphous 
phase volume ratio in thin films of BaTi 03 . The techniques employ polarimetry to investigate 
the linear birefringence (LB) and effective linear electro-optic coefficient (rgff). Both LB and 
r^ff are signatures of the tetragonal phase; in cubic and amorphous phases, LB and r^^^ would 
both be zero. In the following, we discuss LB; rgff will be treated in the future. 

The specimen and a photoelastic modulator (PEM) are placed between crossed polarizers and 
the throughput intensity of HeNe laser radiation (wavelength, 632.8 nm) is measured. The 
modulation frequency of the PEM is 50 KHz. If the beam possesses a large cross-sectional area, 
LB is found to be zero. However, by focussing the beam to a 2.6 fim diameter gaussian spot 
size, we obtain a signal indicating LB is present. If the specimen is translated across the beam, 
we find that the LB varies rapidly on the scale of the spot size. The peak throughput measured, 
however, is orders of magnitude smaller than what would be obtained for a single crystal 
specimen. It is found that the peak intensity values decrease as the spot size increases. 

It is known from TEM that the crystallite size in these films is about 10 to 100 nm. The film 
thickness as determined by a number of methods is usually in the range of 300 nm to 1.5 /xm. 
X-ray scattering shows random orientation in some films, partial orientation in others, and 
equivalent cubic <1(X)> orientation (i.e., cubic <100>, or tetragonal <100> or <001 > 
oriented) in others. However, the orientation of the optic axis is not known even in the < 100 > 
oriented films. Raman scattering shows some tetragonal phase exists, but not how much. 

We therefore arrived at the following hypothesis: The optic axis is randomly distributed among 
the equivalent cubic < 100 > directions. When the spot size is large the experiment averages 
over so many randomly oriented crystallites that the film looks isotropic, and the LB averages 
to zero. When the spot is decreased to several microns the number of crystallites over which 
the experiment averages becomes sufficiently small so that fluctuations from the mean value of 
zero become apparent. The smaller the spot size, the fewer the crystallites, and the larger the 
fluctuations. 

To test this hypothesis we have modelled the film as a dense array of stacks of linear retardation 
plates, each plate representing a single crystallite. If a plate represents a cubic crystallite or 
amorphous section of the film, the retardation of a plate is zero. The probability, P, that a plate 
will be cubic or amorphous is the volume fraction of the cubic plus amorphous phases. If a 
plate represents a tetragonal crystallite, the retardation is calculated from a random distribution 
of crystallite sizes and orientations. The objective then is to determine P. We note that a stack 
of linear retardation plates is equivalent to a single elliptical half-wave plate (i.e., a half-wave 


114 


plate where the eigenpolarizations are elliptical). We have written a computer program to 
simulate the LB experiment. It uses the Jones calculus to compute the equivalent elliptical 
waveplate of each stack and the ellipticity of the eigenpolarizations, and collects the values in 
an array representing the plane view of the film. It convolutes this array with a gaussian profile 
representing the laser beam power distribution. The probability distribution functions (PDFs) 
for orientation of the optic axis are obtained by considering the ratio of peak heights in the x-ray 
spectra. The PDF for the crystallite size can be estimated from TEM pictures. Preliminary 
simulated LB measurements qualitatively reproduce the experimental data. 

We are in the process of increasing the speed of the calculation which will allow us to examine 
the effect of different PDFs for the crystallite orientation and size, and different values of P on 
the LB. We will then be able to determine with what accuracy changes in P can be 
distinguished from changes in the PDFs. We will also examine the interplay between the spot 
size, the PDFs, and P to determine if we can estimate the crystallite size PDF in the absence 
of TEM data by collecting data with different spot sizes. Simultaneously, we are examining a 
number of films with different crystallite sizes and degrees of orientation. 

The technique developed here should be applicable to any film in which a single birefringent 
phase is mixed with isotropic phases. Thus, it should be a useful diagnostic tool for most 
ferroelectric oxides, as well as other anisotropic polycrystalline films. 

DIAMOND THIN FILMS 


Chemical vapor deposition of diamond will have a significant economic impact in the near future 
on a range of commercial products including durable cutting tools and heat dissipating substrates 
for electronics and opto-electronics. Diamond is an enabling technology because its economic 
impact will be greater than the market for the material itself, creating markets that might not 
otherwise develop. Thus, CVD diamond research at NIST is important for helping U.S. 
industry obtain a competitive edge. In addition to research on materials characterization 
methods, NIST has been making an significant impact by organizing standards related workshops 
at which representatives of U.S. companies come together to decide on generic issues important 
to diamond technology. 

Characterization of Boron-Doped CVD Diamond Films 
L. H. Robins, E. N. Farabaugh, and A. Feldman 

Raman spectroscopy is commonly used to characterize the crystalline quality of CVD diamond 
films. The first-order Raman spectrum of crystalline diamond consists of a single narrow line 
at 1333 cm*^ In undoped CVD diamond specimens, extra broad lines in the Raman spectrum 
indicate the presence of nondiamond carbon phases. The linewidth and change in peak position 
of the diamond line provides information about strain and disorder within the crystalline diamond 
phase. 

A set of boron-doped diamond films has been characterized by Raman spectroscopy. The boron 
concentrations, which were determined by secondary ion mass spectroscopy (SIMS), ranged 


115 


from 200 to 6300 ppm. Within the set of boron-doped films examined here, the boron 
concentration was found to have a strong effect on the form of the Raman spectrum. The peak 
of the diamond Raman line shifted to lower wavenumber with increasing boron concentration. 
In the most heavily doped films, the diamond line also broadened in an asymmetric manner. 
The width of the line on the low-wavenumber side of the Raman peak was greater than the width 
of the line on the high-wavenumber side of the Raman peak. The intensity of the broad 
nondiamond carbon lines at first decreased as the boron concentration increased, up to 1300 
ppm, but then increased with further increases in boron concentration. The Raman spectra of 
the boron-doped films are shown in Fig. 5. The peak position of the diamond line is plotted as 
a function of boron concentration in Fig. 6. 

Several factors may contribute to the dependence of the Raman spectrum on the boron 
concentration. The behavior of the broad nondiamond lines suggests that boron doping tends 
to suppress the growth of nondiamond carbon phases at low concentration, but enhances the 
growth of nondiamond carbon at high concentration (above 1300 ppm). The most interesting 
effect is the shift and broadening of the crystalline diamond line. One possible explanation for 
such a shift would be an increase in the average C-C bond length with increasing boron 
concentration; this would act to lower the frequencies of all of the lattice vibrations. However, 
X-ray diffraction results do not show an observable increase in the mean lattice constant with 
boron doping. We believe that the shift and broadening of the diamond line is due primarily to 
the interaction between the Raman-active phonon and the charge carriers (holes) introduced by 
the boron doping. Similar effects have been observed previously in heavily doped silicon and 
germanium. According to these researchers, the deformation of the lattice by the Raman-active 
phonon causes an energy splitting at the top of the valence band. Dynamic redistribution of 
carriers between the deformation-split bands causes a softening of the lattice and, hence, a 
downward shift of the Raman frequency^. 

Another effect occurs when the spin-orbit splitting between different valence bands is smaller 
than the optical phonon frequency, as in silicon and diamond. In this case, intervalence-band 
transitions can give rise to electronic Raman scattering. This scattering occurs in the same 
frequency range as the conventional Raman scattering due to optical phonons. Interference 
between these two types of Raman scattering can causes an asymmetric broadening the observed 
Raman line. This effect was observed by Cardona and co-workers in silicon that had been 
heavily doped with acceptor impurities. 

More work is needed to quantify these effects. In particular, measurements of both carrier 
concentration and boron concentration are needed to investigate whether it is only the charge 
carriers (holes) or whether it is the total impurity atom content that correlates with the shift and 
broadening of the diamond Raman line. Our results suggest it might be possible to use Raman 
spectroscopy to measure the carrier concentration in heavily boron-doped diamond. 

Raman spectroscopy may prove useful as an in situ noncontact nondestructive method of 
measuring the extrinsic carrier concentration during deposition of boron-doped films. This is 
because in diamond, the carrier concentration due to doping has been found to be larger than 
the intrinsic carrier concentration even at the temperatures necessary for CVD growth 
(~800°C). 


116 


>N 

"in 

c 

CD 

C 


C 

o 

E 

o 

cn 


1 000 1 200 1 400 1 600 1 800 

Raman shift (cm~ ) 



Figure 5. Raman spectra of boron-doped diamond films grown by filament-assisted CVD. The 
boron concentration in parts per million, as measured by SIMS, is shown for each film. Spectra 
are rescaled and offset to best display the lineshape variation. 

1334 i ' ' — ' ■ ' ■ ■ h 



1324 -I . ^ ^ ^ ^ ^ ^ h 

0 2000 4000 6000 8000 

Boron concentration (ppm) 


Figure 6. Peak shift of the diamond Raman line as a function of boron concentration in heavily 
boron-doped diamond films. Peak positions were obtained from the spectra shown in Fig. 5. 
The dashed line that connects the data points is purely empirical. 


117 


OXIDATION OF BORON DOPED DIAMOND FILMS 


E.N. Farabaugh and E. Johnson^ 

^Naval Air Warfare Center, China Lake, CA 

Diamond cannot be used at temperatures significatantly greater than 500 ®C because it oxidizes 
in air. Reducing the oxidation rate might make it usuable at these high temperatures. We have 
conducted oxidation rate experiments on chemical vapor deposited diamond to ascertain whether 
the oxidation rated can be significantly reduced by doping with boron. Previous studies had 
shown a reduced in oxidation rate of single crystal diamond doped with boron. 

Boron doped diamond films have been produced by the hot filament chemical vapor deposition 
(HFCVD) process by bubbling argon through a solution of B 2 O 3 in ethanol. This solution 
furnished both the carbon for the diamond film growth and the boron for doping. The argon 
gas was then mixed with hydrogen. This mixture served as the feed gas for doped diamond film 
growth. The highest growth rate for these boron doped diamond films was 0.7 /xm-h'^ The 
boron concentration in the films was controlled by changing the concentration of B 2 O 3 in the 
ethanol. The highest doping level, as measured by secondary ion mass spectrometry (SIMS), 
was 6300 ppm atomic. Raman spectroscopy and x-ray diffraction both confirmed the presence 
of diamond films. 

The oxidation rate of doped and undoped diamond films was measured by thermogravimetric 
analysis (TGA) at 700 °C in flowing high purity oxygen. The results the TGA work are shown 
in Table 1. We see a general trend of reduced oxidation rate with increasing boron 
concentration. The oxidation rate of a film with 0.6 % boron is 0.1 the oxidation rate of the 
undoped film. 

Auger analysis of these samples after oxidation was carried out to investigate the mechanism 
responsible for the reduced oxidation rate with doping. The spectra indicate that partially 
oxidized diamond films contain a layer of B 2 O 3 on the surface. It would seem that the B 2 O 3 
layer acts as a barrier to oxidation of the underlying diamond. 

The utility of boron doping in lowering the oxidation rate will depend on the intended use of the 
diamond. Thus, applications that are not deleteriously affected by the presence boron might 
benefit. On the other hand, optical applications and applications that require the material to be 
electrical insulating would not be able to use the doped material. 


118 


Table 1 . Rate of weight loss of boron doped C VD diamond due to oxidation in 


flowing oxygen at 700 °C. 


Boron 

Rate of 

atomic fraction 

weight loss 

ppm 

per cent/min 

0. 

1.1 

200.* 

0.65 

6300.* 

0.11 

* Measured by SIMS 



WORKSHOP ON CHARACTERIZING DIAMOND FILMS 


A. Feldman 

The second in a series of workshops was held at NIST on February 24th and 25th to discuss the 
characterization of diamond films and the need for standards in diamond technology. The 
audience targeted for this workshop were the producers and potential users of CVD diamond 
technology in the United States. Three technical topics that have relevance to applications of 
chemical vapor deposited (CVD) diamond were discussed: characterization of optical absorption 
and scattering for optical applications; characterization of electrical propierties and electrical 
contacts for electronic applications; and, standardization of thermal conductivity measurement 
for heat spreading applications. A particular accomplishment of the workshop was the formation 
of a working group to evaluate methods of measuring the thermal conductivity or thermal 
diffusivity of CVD diamond. A round-robin has been organized to compare different 
measurement techniques. A set of specimens prepared voluntarily by producers of CVD 
diamond have been circulated among experts in the measurement methodologies. NIST is 
coordinating the circulation of the specimens among the measurement laboratories and will 
collate the results of the measurements for presentation at the next working group meeting. 

HIGH T, SUPERCONDUCTING CRYSTALS 

Large scale commercial applications of high temperature superconductions will depend our 
ability to to produce material that can sustain high critical current densities (Jj,). Our ability to 
control a prime factor in promoting high flux pinning, is the motivation of the research 
discussed below. 


119 


Magnetization of YBa 2 Cu 30 -y Polycrystals 


D.L. Kaiser, M. Turchinskaya^ F.W. Gayle^, A. Shapiro^, A. Roytburd^, A. A. Polyanskii'^, 
V.K. Vlasko- Vlasov'^, L.A. Dorosinskii'^, and V.L Nitotenko*^ 

^Consultant 
^Metallurgy Division 
^University of Maryland 

“^Institute for Solid State Physics, Russian Academy of Sciences 

Many grain boundaries in high temperature superconductors act as weak links or regions of poor 
superconductivity, thereby lowering the critical current density (J^) and preventing the use of 
these materials in high-power electrical applications such as superconducting motors and power 
transmission systems. Understanding the underlying microstructural causes of this weak link 
behavior is critical to achieving high values. Although the role of grain boundaries in 
electrical transport in the high temperature superconductor YBa 2 Cu 307 .x (YBCO) has been 
studied extensively, there have been no detailed investigations of the effect of grain boundaries 
on microscopic flux flow during magnetization. In this study, we have used a high-resolution 
magneto-optical method to directly observe real-time flux flow in bulk-scale YBCO polycrystals 
containing [001] tilt grain boundaries of known misorientation angle, 0. 

The magneto-optical technique utilizes an yttrium-iron-gamet indicator film, having in-plane 
magnetic anisotropy, placed over the specimen. After cooling the specimen with liquid helium 
in zero magnetic field, an external field (HJ in the range of 0 to ± 65 mT is applied parallel 
to the common [001] axes of the grains in the specimen. Real-time dynamics of the magnetic 
flux as a function of temperature (7 to 50 K) and are viewed and recorded by means of a 
video system. Calibration of the indicator films allows the resulting images to be converted to 
quantitative magnetic induction maps. 

Flux flow was studied in polycrystals containing both high-angle grain boundaries (HAGB, 0 
> 10°) and low-angle grain boundaries (LAGB, 0 < 10°). At low temperatures (7 to 20 K), 
with increasing field, flux penetrated first along HAGBs, then along LAGBs, and finally into 
grains along the direction of twin boundaries. At higher temperatures (30-50 K), intergranular 
penetration occurred at lower fields than those required for penetration of LAGBs. The field 
required for initial penetration of a boundary was strongly correlated with misorientation 
angle as shown in Fig. 7. For LAGBs, increased strongly with decreasing 0, whereas for 
all HAGBs, was in the range of 1-2.5 mT. While flux penetrated instantaneously along the 
entire length of each HAGB at its H^^ value, the distance of penetration along LAGBs increased 
gradually with increasing fields above H^j. 

In the final stage of flux penetration, flux flowed into grains from HAGBs, from LAGBs and 
from the edges of the specimen. Flux flow always proceeded along the direction of twin 
boundaries. In general, the depth of flux penetration into a grain from a grain boundary was 
greatest when the twin boundaries in the grain were normal to the grain boundary. The 
penetration depth decreased with increasing angle between the grain boundary normal and the 
twin boundary. 


120 


Ha1 fmTesla] 



Figure 7, Dependence of the field required for initial flux penetration (H^j) on misorientation 
angle (0) in YBCO polycrystals at temperatures of 7 and 19 K. Hgi is strongly dependent upon 
0 for LAGBs; for all HAGBs, is in the range of 1-2.5 mT. 

In summary, flux motion in YBCO polycrystals in an increasing external magnetic field is highly 
nonuniform, and highly anisotropic due to the presence of grain boundaries and twin boundaries. 
The extent of flux penetration depends on the misorientation angle of the adjacent twin 
crystallites and the angular relationship between twin boundaries and grain boundaries. 


121 





VIL MATERIALS MICROSTRUCTURE CHARACTERIZATION 


Gabrielle Long 


The Materials Microstructural Characterization Group in the Ceramics Division operates two x- 
ray experimental beamports at the National Synchrotron Light Source, where researchers from 
NIST, industry, academia and other government laboratories carry out state-of-the-art 
measurements on ceramic, semiconductor, photonic, metallurgical, polymeric, and other 
materials of high scientific or technological interest. Measurement capabilities include ultra- 
small-angle x-ray scattering, x-ray topography, x-ray diffraction-imaging microscopy, x-ray 
absorption fine structure spectroscopy, standing-wave x-ray scattering, and reaction-kinetic 
surface science measurements. 

Another major area for this Group is a processing/microstructure program in ceramics at the 
Cold Neutron Research Facility at the NIST Research Reactor. This year, we have 
commissioned a ceramics furnace which fits onto the small-angle neutron scattering (SANS) 
instruments. The microstructure evolution of ceramics during sintering can now be examined 
quantitatively and without interruption as a function of processing variables. 

The range of scientific problems which have been addressed over the past year include sintering 
of commercial alumina powders, processing of nanophase ceramics, research on microwave- 
assisted reaction-bonded silicon nitride, icosahedral-phase AlPdMn, characterization of man- 
made and natural diamond, strain effects in homoepitaxial films on diamond, creep cavitation 
of silicon nitride, strain sensitivity in high-Tc superconducting tapes, and the determination of 
atomic-scale and molecular-scale structures at technologically-important surfaces and interfaces. 

In addition, as part of a national facility, time on the NIST instruments at the National 
Synchrotron Light Source is made available to qualified researchers based on peer-reviewed 
proposals. In the past year, researchers from chemical, aerospace, energy, materials production 
industries as well as from NIST laboratories, other government laboratories and universities have 
completed experiments that could not have been performed elsewhere in the United States. The 
long term goal of research at these facilities is to enable researchers to address basic issues so 
that U.S. manufacturers can provide superior materials based on structural information not 
available elsewhere. 

Significant Accomplishments: 

• A ceramics furnace, which fits into the small-angle neutron scattering instruments, has 
been commissioned. The new instrument permits in-situ measurements on materials 
during heat treatment. We have been able to investigate, non-interruptively, and for the 
first time, the effects of sintering parameters on microstructure during densification. 

• Small-angle neutron scattering has revealed how grain microstructure development in 
nanophase ceramics can be engineered by control of processing parameters. In 
particular, we have explored the influence of sintering temperature and environment in 
controlling grain growth, and the role of additives in suppressing potentially deleterious 
phase transitions. 


123 


An extended formulation for analysis and interpretation of multiple small angle scattering 
studies of advanced ceramics has been developed. The new formulation permits coarse 
plate-like or ribbon-like microstructures to be quantitatively characterized. The improved 
method provides a powerful new tool for probing the late stages of sintering in ceramics, 
2md for detecting the onset of incipient microcracking during processing. 

Studies of the microstructure development of silicon nitride during sintering has revealed 
significant morphological changes during the late sintering stages. As more sintering 
variables are probed, a generalized model for grain-pore evolution is emerging. 

The defect microstructure of thick homoepitaxial diamond films has been studied by x- 
ray diffraction imaging. For the first time, nearly-perfect man-made diamond was used 
as a substrate. The low defect density and the very low residual strain in man-made 
diamond allowed us to observe and measure changes caused by the deposited film. The 
surprising result was that the film induces a large strain in the substrate, with the film 
in tension and the substrate in compression. 

The successful application of ZnSe as a wide band-gap material depends critically on the 
availability of large high-quality crystals. X-ray diffraction imaging has been applied to 
the problem of characterizing defects in this material as a function of growth conditions 
in an effort to determine the parameters that suppress defect generation. Our studies of 
the subsurface microstructure of substrate wafers has led to the modification of wafer 
processing proceedures in the industry. 

X-ray transmission topographs of partially-twinned Ba2YCu307.x crystals and of 
thermomechanically-detwinned Ba2YCu307.x crystals reveal that the detwinning process 
leaves significant residual strain. 

Fluorescence-yield near-edge x-ray absorption measurements of a buried metal/polymer 
interface were used to determine the orientation of polymer aromatic ring planes in the 
interface region. This type of information is critical for predicting and optimizing 
adhesion at these technologically-important interfaces. 

Standing- wave x-ray data on the Bi-Si(lll) interface were used to determine directly 
the position of the Bi atoms. The surface was proven to be a honeycomb array of Bi 
atoms, each located above a first-layer Si atom with no lateral reconstruction. This result 
resolves conflicting reports in the literature from STM studies, which variously found the 
structure to be monomer, trimer, and honeycomb reconstructions. The standing-wave 
data are supported by Rutherford backscattering results which determine the absolute 
coverage of Bi to be 2/3 monolayer. 

Crystal lattice deformation associated with optical fanning in photorefractive barium 
titanate has been observed directly for the first time. High resolution x-ray diffraction 
images display the strain pattern induced by laser beam fanning in a highly perfect 
barium titanate crystal. The observation provides a basis for refining models for fanning 


and thus for improvement of photonic devices that utilize photorefraction for ultra high 
capacity parallel information processing, such as self-pumped phase conjugate mirrors. 

• The first high resolution x-ray diffraction images of epitaxial bismuth germanium oxide 
layers on sapphire substrates have been obtained. Diffraction was observed 
simultaneously over a large fraction of the layer-substrate surface indicating a high 
degree of orientation over a large area. The degree of epitaxy thus displayed suggests 
that this economical approach to photorefractive oxide layer formation is technically 
promising for electrooptic elements for high capacity information processing. 

• Changes in the formation of periodic irregularities in strontium barium niobate that can 
be correlated with specific changes in growth procedures have been observed for the first 
time. These irregularities affect the uniformity of photorefractive response in 
photorefractive devices for high capacity information processing. On the basis of this 
study we anticipate that more effective control of the growth process can be exercised, 
leading to practical options for more rapid information processing. 

• Initial results of a study of the one of the boules of cadmium zinc telluride grown on 
space shuttle USML-1 indicate that the microstructure of the material grown in 
microgravity is substantially changed from that of similar material terrestrially grown. 
Whether this results in superior performance of infrared detectors made from these 
crystals remains to be determined. 

Microstructure Control in Nanophase Zirconia 

A. J. Allen, S. Krueger^, G. Skandan^, J. Parker^ and G. G. Long 

^Reactor Radiation Division 
^Rutgers Univeristy 
^Nanophase Technology Inc. 

Nanophase ceramic oxides, having grain sizes in the range 5-50 nm, are of technological 
interest because they enable the sintering of small grained, fully dense samples at substantially 
reduced temperatures (less than 1000° C). The resultant materials exhibit novel properties 
including plastic deformation by creep processes at low temperature. However, they also offer 
the prospect for combining advanced mechanical properties (e.g. high strength and wear 
resistance) with good formability during processing into components. In practice, however, it 
is difficult to obtain high density material without coarsening of the pore/grain microstructure. 
Therefore, we seek to obtain a better understanding of how the microstructure develops during 
sintering, and of how sintering parameters and additives can be used to improve the final 
microstructure. 

We have carried out an extensive characterization of nanophase zirconia, n-Zr02, for which 
small samples have been fabricated using a cold-finger gas-condensation technique, or 
alternatively a commercial continuous-flow technique. Specimens 0.5 - 1 mm thick and 5-10 
mm in diameter have been used in absolute-calibrated small-angle neutron scattering 


125 


experiments. Indeed, we are the first to carry out a completely quantitative non-destructive 
SANS characterization of the microstructure changes during sintering under different conditions. 
We have studied the effects of sintering temperature, pressure and time, air vs. vacuum 
conditions, and the use of yttria to stabilize the a-b transformation during sintering. Our 
measurements have established that, for samples less than 100% dense, the characteristic 
scattering of nanophase materials arises from the grain/pore interfaces, not from a supposed low- 
density disordered grain-boundary phase, as proposed in earlier studies. 

Figure 1 shows the radially-summed absolute-calibrated SANS data for n-Zr02 in the as- 
compressed state and after sintering in air for 20 minutes at 800° C. These data exhibit the 
characteristic hallmarks for SANS from nanophase materials: the coarsening of the grain size 
during sintering, as measured by the narrower profile, and the interparticle interference peak 
which develops during early densification. The fitted lines are based on a grain/pore 
microstructure model developed for nanophase ceramic systems. The primary scattering features 
are slightly oblate pores between the grains. In the as-compressed state, the excess scattering 
at low scattering wavevectors, Q (where Q = (4';r/X)sin(0s/2), X is the neutron wavelength and 
03 is the angle of scatter), is attributed to the presence of some coarser pores. Such coarser 
porses are probably associated with a small amount of grain agglomeration. The interparticle 
interference peak appears as soon as the sintering has imposed some ordering in the grain/pore 
morphology, and is caused by the relatively monodispersed grains separating discrete nearest- 
neighbor pores while there is still a high number density of such pores present in the system. 
The peak moves to lower Q and eventually disappears as full density is approached. 


•g 1000 

0 

>s 
<0 

1 10 

■O 

0 

k- 

1 0.1 

3 

o 

(A 

^ 0.001 

0.001 0.01 0.1 1 
Scattering wavevector, Q(A*’) 

Figure 1 . Absolute-calibrated SANS data for n-Zr02 in the as-compressed state (open circles) 
and after sintering in air for 20 minutes at 8(X) °C (solid triangles). 



126 


From our model a number of nanophase microstructure parameters can be quantified and 
followed through the sintering process: grain size and polydispersity, grain/pore surface area, 
porosity and coarse pore volume fraction, and the fractional closure and disappearance of 
pores along the grain boundaries. We have found that the most important microstructure- 
determining material variable is the relative density. Figure 2 illustrates this point by 
showing how the inferred grain diameter varies with the relative density of the material. 
Control of the grain size and ensuring cohesion of the grain boundaries as full density is 
approached are the major challenges for future work. 



Q I I I ■ I I ■ I I I I ■ I ■ I I I I I I I — I — I — I — I — I — I — I — I — I — 

40 50 60 70 80 90 100 


Fractional Density (%TD) 


Figure 2. Grain diameter of the nanoparticles as a function of the achieved density of the 
ceramic body. 


127 


Surface Sensitive X-ray Standing Wave Studies of Relaxation at Metal-Silicon Interfaces 


J.C. Woicik, T, Kendelewicz^, A. Herrera-Gomez\ K.E. Miyano^, P.L. Cowan^, C.E. 
Bouldin, P. Pianetta"^, and W.E. Spicer^ 

^Stanford Electronics Laboratory 

^Brooklyn College 

^Argonne National Laboratory 

"^Stanford Synchrotron Radiation Laboratory 

Combining the surface sensitivity of low-energy electron yield with the position sensitivity 
of the x-ray standing-wave technique, we have developed a new method for determining the 
position of surface atoms at clean semiconductor surfaces. Our structural determination for 
the clean InP(llO) surface now stands as a model test system for new diffraction techniques 
such as low-energy positron diffraction and chemical-shift low-energy photoelectron 
diffraction. 

Recent work has extended our studies to the examination of the degree of relaxation of 
semiconductor surfaces beneath metal overlayers. Although precise knowledge of these 
atomic positions is paramount for the testing of theoretical modelling of order at 
semiconductor surfaces, the prior amount of experimental knowledge relevent to subsurface 
distortion was scant; it had typically been assumed in the analysis of structural data that the 
substrate assumes its ideal bulk structure beneath the overlayer. For the In-terminated 
Si(lll) surface, however, there is a large body of theoretical work predicting that this 
interface is relaxed by as much as 0.3 @. Our study of the In-terminated Si(lll) surface has 
found that the In bonds to an ideal unreconstructed top layer of Si atoms. Further 
examination of this system with surface extended x-ray absorption fine structure 
spectroscopy, which measures the adatom-to-substrate near-neighbor bond lengths directly, 
confirms the standing-wave results and demonstrates that, in systems which deviate from 
tetrahedral geometry, large deviations in bond lengths from the simple sums of covalent 
radii can also be present. This data have corrected the long existing misconception that the 
stability of this geometry results from substrate relaxation; it has also revealed the limited 
accuracy of theory in predicting near-neighbor bond lengths at surfaces and interfaces. 

Figure 3 shows our structural determination for the Si(lll) a3xa3-In interface. The In 
atoms are bonded 1.71 @ above the top layer of an ideal, unrelated. Si double layer. 


128 


Si(111)"^3x^3'ln 



Figure 3. Structural model of the determined Si(lll) V3x\/3-In interface. 


129 


Fluorescence-Yield Near-Edge X-ray Absorption Fine Structure of a Buried Metal/Polymer 

Interface 

D.A. Fischer, B.M. DeKoven\ and G.A. Mitchell^ 

^Dow Chemical Corporation 

DVS bis-BCB (divinyl siloxane bis-benzocyclobutene) is used for dielectric layers in new- 
generation multilayer interconnect devices (multichip modules) [1]. For this application, it 
is important to understand the nature of the bonding and complexing which occurs as the 
metal/polymer interface. The depth sensitivity of about 200 nm, and the nondestructive 
nature of fluorescence yield, make it particularly useful in studying the buried interface 
between DVS bis-BCB coated with 10 to 100 nm of aluminum. In contrast, the relatively 
small depth sensitivity of traditional electron yield makes it useless as a probe of the buried 
interface since it would only measure within the outer 5 nm of the aluminum overlayer. 

We have measured fluorescence-yield carbon K near-edge spectra for the bare polymer, and 
for 50 nm aluminum on 50 nm DVS bis-BCB. Figure 4 shows the normalized spectra for 
normal and glancing-incident x-rays. To enhance the metal/polymer interface sensitivity, 
each panel shows a difference plot (coated polymer minus bare polymer). The C-C x* peak 
(at 286 eV) of the aromatic ring of DVS bis-BCB in the difference plots undergoes a 
dramatic enhancement in polarization dependence after the formation of the metal/polymer 
interface. This polarization enhancement at the interface region indicates that the aromatic 
ring planes of DVS bis-BCB are highly oriented towards the surface normal. This type of 
fluorescense-yield soft-x-ray data is extremely useful for the prediction and optimization of 
adhesion at metal/polymer interfaces. 

[1] T.M. Stokich, Jr., W.M. Lee and R.A. Peters, Proc. of the Materials Research Society 
227, 103 (1991). 

Microradiographv of In-situ Strained High Tc Superconductor Tapes 

R.D. Spal, C. K. Chiang, G. N. Riley, and A. Otto^ 

^American Superconductor Corporation 

Given the brittle nature of high temperature superconductors, it is difficult to fabricate them 
into wire which can tolerate strain and maintain high critical current. To understand critical 
current degradation with strain, and to improve strain tolerance, it is desirable to study the 
evolution of wire microstructure with strain. Toward these ends, NIST and American 
Superconductor Corporation (ASC) are collaborating in an x-ray microradiographic study 
of Bi2223/Ag metal matrix composite wire subjected to tensile strain. The wire, in the form 
of thin (typically 175 /xm) tape containing multiple superconductor filaments, is fabricated 
by ASC using either oxide-powder-in-tube (OPIT) or metallic precursor methods. The 
microradiography is carried out with synchrotron radiation, monochromated to 24 keV to 
give reasonable (about 10%) transmission, at NIST beamline X23A3 at NSLS, using a 


130 


asymmetric Bragg diffraction microscope developed and recently patented by NIST. This 
study is intended to complement optical and electron microscope studies carried out by 
ASC. Since microradiography is non-destructive, the evolution of microstructure with 
applied stress can be followed. Areas of a few mm^ can be examined at a spatial resolution 
of about 1 ^m, thereby obtaining both macroscopic and microscopic views. 


A preliminary experiment on pre-strained 19 filament OPIT tapes showed many high 
visibility cracks at 3 and 10% strain, one at 0.7%, and none at 0%. A second experiment 
concentrated on low strain, applied in-situ to a 19 filament OPIT tape. Digital images of 
a 0.5 mm long section of tape, covering nearly its entire 2.5 mm width, were taken at five 
strains from 0 to 1.34%. Cracks appear between 0.55 and 0.80% strain, but their visibility 
is low, partly due to overlapping of filaments. The images are being analyzed to obtain 
crack dimensions and strain maps. There are many instances of dark spots of various 
shapes which appear at some strain levels but not others. They are believed to be 
extinctions by individual crystal grains which accidently satisfy the Bragg condition. While 
currently a nuisance, in the future they could provide valuable information on crystal 
orientation. 


Defect Characterization of ZnSe bv X-rav Diffraction Imaging 

D.R. Black and H.E. Burdette 

The successful commercial application of ZnSe as a wide band-gap material depends on the 
ability to grow large, high-quality single crystals. To improve crystal perfection and the yield 
of device material, the relationships between the growth conditions and defect generation 
are under intense investigation. X-ray diffraction imaging, which is highly sensitive to lattice 
defects, is being used in a critical characterization program on the bulk ( — 0.5 fxm thick) and 
near-surface regions of substrate crystals, with spatial resolution of order one micrometer. 
The technique is sensitive to defects that change the local atomic spacing or the local 
crystallographic orientation such as: stacking faults, dislocations, voids, inclusions, 
inhomogeneous strain and the presence of additional phases. 

We have performed studies on several wafer-sized crystals as well on as-grown material. 
Long-range inhomogeneous strain, residual subsurface damage, and a complex dislocation 
network have been observed. In addition, a critical examination of the near-surface regions 
of substrates has revealed otherwise unobservable damage from cutting and polishing. This 
observation has led the crystal grower to modify the surface preparation techniques. 


131 



Figure 4. FY carbon K near edge spectra for evaporated aluminum coated (50 nm thick) 
DC VS bis-BCB (50 nm thick) as well as the identical bare polymer, upper and lower 
paneslshow spectra for normal and glancing incident x-rays respectively. In order to 
enhance the metal/polymer interface sensitivity each panel shows a difference plot (coated 
polymer minus bare polymer). 


132 


In Situ X-Ray Diffraction Imaging of Optical Interactions in Photorefractive Crystals 

Bruce Steiner, Mark Cronin-Golomb,^ Gerard Fogarty,^ John Martin,^ and Robert Uhrin^ 

^Electro-Optics Technology Center, Tufts University 
^Deltronic Crystal Industries, Inc. 

Increased signal processing capacity and speed may be facilitated by the development of 
optical approaches, which incorporate parallelism with relative ease. One promising 
technique for processing optical signals uses photorefractive crystals; however this is compli- 
cated by amplified optical scattering (fanning) in some materials such as barium titanate and 
by periodic irregularities identified as striations in other materials such as strontium barium 
niobate. In each case, the irregularities in signal processing response are traceable to 
crystalline disorder. The relative importance of various specific crystal irregularities is not 
yet known; nor are the role that they play in the crystal optics and their specific origins 
during growth understood. The development of a satisfactory understanding of these 
defects should lead to improvement in optical signal processing through growth of more 
satisfactory photorefractive crystals. We thus set out three years ago to address these issues 
through direct, in situ, observation of photorefractive crystals and optical interactions in 
them. 

This past year we succeeded for the first time in imaging the lattice deformation due to 
photorefractive fanning in barium titanate. The images obtained showed conclusively that 
the fanning is due to internal scattering and not to surface interactions. We have shown 
also that the sources of this scattering are smaller than one micrometer in dimension. 
Further progress in this direction would be facilitated by improvement in spatial resolution 
in these experiments. 

Moreover, we have now observed changes in the periodic irregularity observed in strontium 
barium niobate. These striations interfere in the establishment and reading of 
photorefractive gratings. The diffraction images can be correlated with recorded changes 
in growth conditions and thus are expected to lead to substantial improvement in the 
crystals grown and thus ultimately in the feasibility of high capacity photorefractive image 
processing. 

This work was made possible by funding from ARPA and from the NIST Advanced 
Technology Program. 


133 


Irregularities in Crystals Grown in Microgravity and Related Terrestrial Crystals: their 

Nature. Genesis, and Effects on Electro-Optical Device Performance 

Bruce Steiner, Lodewijk van den Berg,^ Heribert Wiedemeier,^ Yu Ru Ge,^ Ravindra Lal,^ 
and David Larson'^ 

^EG&G Energy Systems 
^Rensselaer Polytechnic Institute 
^Alabama A&M University 
“^Grumman Corporation 

Crystals grown in microgravity have previously been found to have properties superior to 
those of directly comparable terrestrial crystals. For example, the charge carrier mobility 
of X- and gamma-ray mercuric iodide detectors made from space-grown crystals was a least 
six times higher than for similar detectors made from ground-grown crystals. This 
superiority has naturally led to substantial interest in crystal growth in space. Neither the 
structural nature of the differences nor their origins in crystal growth had been determined 
prior to the initiation of the current program. Since both issues are important to the space 
crystal growth program and indeed to improvement in the effectiveness of crystal growth in 
general, we have established a collaborative program with commercial and academic crystal 
growers in NASA’s Microgravity Sciences and Applications Program. 

We have focussed this year on the two materials grown on space shuttle IML 1 in February 
1992: vapor-grown mercuric iodide and solution-grown triglycine sulfate; and on the 
observation of two of the four materials grown on space shuttle USML 1 in April 1993: 
mercury cadmium telluride layers grown by vapor transport on cadmium telluride substrates, 
and Bridgman-grown cadmium zinc telluride. 

In the initial ground-grown mercuric iodide crystals observed in high resolution diffraction 
imaging, more than one phase in the form of arrays of non diffracting inclusions was 
observed. These appeared to stiffen the lattice, imparting long range regularity to it. With 
the suppression of these inclusions, either through growth in microgravity or through the 
use of more highly purified starting material, the lattice was appreciably weakened. 

It has been unclear whether the long range changes in lattice orientation observed were 
characteristic of the growth process, or simply a result of the slicing and polishing process 
for what was now a very soft material. This past year we showed conclusively that the lower 
level of inclusions in superior material softens the resulting crystals, leading to the necessity 
for the development of new techniques for crystal handling in order to realize the superior 
long range order inherent in recent improvements in processing whether in microgravity or 
on the ground. The required new sophisticated crystal handling techniques have now been 
successfully developed and demonstrated to be effective in superior diffraction images. We 
anticipate that the result of these advances will be radiation detectors with substantially 
improved properties. 


134 


Through the immediate application of these new crystal handling techniques, we found that 
the mercuric iodide crystal vapor-grown on IML-1 had long range uniformity in lattice 
orientation a factor of 15 higher than that of comparable terrestrially grown material. 
Uniformity in intermediate range lattice orientation, i.e.on a scale comparable to the 1 mm 
thickness of the crystal slice, was found to be a factor 10-20 higher than a comparable 
crystal grown on the ground. 

This increased uniformity in the orientation of the lattice in the space-grown IML-1 crystal 
on a scale comparable to the charge carrier travel distance fulfills the principal expectations 
for this space crystal growth experiment. Mercuric iodide is extremely soft at crystal growth 
temperature and thus particularly susceptible to hydrostatic loading by gravity. Reduction 
of this loading by growth on IML-1 resulted as expected in more uniform lattice orientation 
than that achieved with comparable material on the ground. The expected improvement 
in the electrical parameters of radiation detectors made from other slices of these crystals, 
which are expected to be particularly sensitive to lattice regularity over the distance 
travelled by charge carriers, has been achieved. The superior electrical properties of these 
crystals result, in turn, in an increase in energy resolution for the detectors made from them. 
Moreover, these improved crystal handling techniques made possible the following 
observations, which themselves are expected to result in still further improvement in this 
technology. 

Single crystals of mercuric iodide recently grown on the ground from newly available more 
highly purified source material have demonstrated precipitation hardening in those regions 
that grew in the [110] direction, and its absence in those that grew in the [001] direction. 
This observation may lead to the terrestrial growth of superior crystals for radiation 
detectors as well. 

Anomalous x-ray diffraction through a mercuric iodide crystal in Laue geometry at 1 1 keV 
has been observed this year for the first time. The new level of crystalline order thus 
demonstrated is expected to lead both to understanding of the genesis of the inclusions and 
to further increases in the electrical properties of high energy radiation detectors made from 
this material. 

A triglycine sulfate crystal grown on IML-1 has been examined with high resolution 
diffraction imaging in order detect the interface between the terrestrially grown seed, which 
had been deliberately dissolved back in the early parts of the space-growth experiments, and 
that part of the crystal grown in microgravity. The precise location of this interface is 
important because it determines the regions of the crystal to be compared after their 
fabrication into infrared detectors. 

The layers of mercury cadmium telluride grown on cadmium telluride grown on USML-1 
provided preliminary evidence for a higher degree of long range order than that found in 
comparable terrestrial systems. Initial results of a study of the one of the boules of 
cadmium zinc telluride grown on USML-1 indicate that the microstructure of the material 
grown in microgravity is substantially changed from that of similar material terrestrially 


135 


grown. Whether these results lead to superior detector device performance remains to be 

determined. 

This work was funded by the NASA Microgravity Sciences and Applications Division. 

Defects in Epitaxially Layered Systems: Their Genesis and Effects on Semiconductor 

Device Performance 

Bruce Steiner, Joseph Pelegrino^ and Larry Sorenson^ 

^NIST Electronics and Electrical Engineering Laboratory 
^University of Washington 

Commercially available semi-insulating gallium arsenide and indium phosphide wafers, used 
in photonic device fabrication, have a very high density of severely strain-inducing 
crystallographic irregularities such as dislocations, anti-phase boundaries, low angle grain 
boundaries, stacking faults, etc. (> lO^cm"^ etch pit density). Epitaxial layers grown on the 
surfaces of these substrates contain defects, some of which propagate from the underlying 
wafers into the layers grown on them and vice versa. Moreover, other crystal defects are 
introduced by device fabrication and processing. We are examining the various factors that 
influence the generation of disorder in these layers. The diffraction imaging of layered 
semiconducting crystals over the past three years has resulted in the development of criteria 
for the nucleation and propagation of irregularities in layered systems. 

This past year we have focused on the influence of layer thickness around the critical 
thickness, i. e. the thickness above which pseudomorphic growth of a lattice-mismatched layer 
cannot be sustained. Our studies have addressed strained indium gallium arsenide layers 
on gallium arsenide substrates. High resolution x-ray diffraction also was performed to 
determine the lattice constant of the strained films. Initial results find the layers to be 
pseudomorphic and uniform below the critical thickness; however, above the critical 
thickness the layers are found to relax through a network of misfit dislocations, which 
propagate into the substrate. The density of these defects is found to be directly related to 
the thickness of the layer and hence to its degree of relaxation. These defects are found 
to have preferred nucleation around pre-existing defects in the substrate. 

Growth-Related Factors in the Optical Performance of KDP 

Bruce Steiner, James DeYoreo,^ and Chris Ebbers^ 

^Lawrence Livermore Laboratory 

Growth related factors are believed to limit the performance of potassium dihydrogen 
phosphate crystals in high performance systems for laser fusion. Therefore, we have 
initiated an exploratory program to observe whether the disorder visible in high resolution 
x-ray diffraction imaging is relevant, and, if so, how. Initial results are extremely 


136 


encouraging. We have observed strong evidence for strains associated with clearly visible 
faceted growth. 

Irregularities in Quartz Resonator Structures 

Bruce Steiner, Robert R. Whitlock,^ and Michael I. Bell^ 

^ Naval Research Laboratory 

The frequency stability of quartz resonators is believed to be determined by crystalline 
irregularities that are induced either during crystal growth or subsequent complex machining 
into delicate devices that are designed to vibrate independently of their attachment. We 
have initiated a study of the irregularities in devices and in the material from which they are 
made. Initial imaging proved successful in spite of the challenging suspension of these 
devices, which is an intrinsic part of their structure. 


137 




RESEARCH STAFF 




DATA TECHNOLOGIES 


Begley, Edwin F. 

Database management methods 

Engineering database structures 

Digital video interactive technology 

Carpenter, Joseph A., Jr. 

Functional ceramics applications 

Technical assessments 

Industrial liaisons 

Cellarosi, Mario 

Glass Standards 

Clevinger, Mary A. 

Phase diagrams for ceramists 

Computerized data 

Dapkunas, Stanley J. 

Structural ceramics applications 

Technical assessments 

Munro, Ronald G. 

Materials properties of advanced ceramics 

Data evaluation and validation 

Analysis of data relations 


POWDER CHARACTERIZATION AND PROCESSING 


Carter, Craig W. 

Materials thermodynamics 

Advanced mathematical and computational techniques 
Computation of materials processes 

Cline, James P. 

Standard reference materials 

High-temperature x-ray diffraction 

Microstructural effects in x-ray 
diffraction 

Rietveld Refinement of XRD data 

Kelly, James F. 

Quantitative scanning electron microscopy 

Image analysis 

Microstructure analysis 

Powder standards 

Lum, Lin-Sien H. 

Powder characterization 

Instrumental analysis 

Malghan, Subhas G. 

Powder and dense slurry characterization 

Colloidal processing and forming 

Interfacial and surface chemistry of 
powders 


141 


Standards development 


Minor, Dennis B. 


Pei, Patrick T. 


Ritter, Joseph J, 


Wallace, Jay S. 


Wang, Pu Sen 


Analytical SEM of ceramics and 
particulates 

Powder test sample preparation 
Powder characterization 

Spectroscopic and thermal characterization 
Chemical coating 
Powders characterization 

Chemistry of powders synthesis 
Specialty powders synthesis 
Powder preparation and compositional 
evaluation 

Processing and microstructure 
Silicon nitride densification 
Thermal analysis 

Solid state NMR 
Surface characterization by x-ray 
photoelectron and Auger electron 
spectroscopy 


SURFACE PROPERTIES 


Gates, Richzu'd S. • Tribo-chemistry 

• Surface chemical properties of ceramics 

• Machining of ceramics 

Hsu, Stephen M. • Ceramic wear mechanisms 

• Engineered ceramic surfaces 

• Lubrication and machining of ceramics 

Ives, Lewis K. • Wear of materials 

• Transmission electron microscopy 

• Mechanical properties 

Ruff, Arthur W. • Wear of materials 

• Microstructure effects 

• Mechanical behavior 


MECHANICAL PROPERTIES 


Braun, Linda 


Raman stress measurements 


142 



• 

• 

Ceramic matrix composites 
Toughening mechanisms 

Chuang, Tze-Jer 

• 

• 

• 

• 

Creep/creep rupture 

Fracture mechanics 
Finite-element modeling 
Lifetime predictions 

Cranmer, David C. 

• 

• 

• 

• 

• 

Ceramic and glass composite 
fabrication 

Composite test development 
Ceramic composite properties 
Glass viscosity 

Properties of glass 

Hockey, Bernard J. 

• 

• 

Electron microscopy 
High-temperature creep 

Jahanmir, Said 

• 

• 

Ceramic Machining Research 
Machining Data 

Kauffman, Dale A. 

• 

Glass melting 

Krause, Ralph F., Jr. 

• 

• 

• 

• 

Creep in flexure and tension 
Fracture mechanics 

Hot pressing 

Chemical thermodynamics 

Quinn, George 

• 

• 

• 

Mechanical Property 

Test Standards 

Standard Reference Materials 
Creep Testing 

Smith, Douglas T. 

• 

• 

• 

• 

Surface forces 

Charge transfer at interfaces 
Adhesion and friction 
Colloidal processing 


ELECTRONIC MATERIALS 

Blendell, John E. • Ceramic processing and clean-room 

processing 

• Sintering and diffusion controlled 
processes 

• Processing high T^, ceramic 
superconductors 


143 


Activation chemical analysis 




Burton, Benjamin P. • Calculated phase diagrams 

• Ferroelectric ceramics 

Chiang, Chwan K. • Electronic ceramics 

• Thermoelectric power measurements 

• Electrical measurements 

Cook, Lawrence P, • High temperature chemistry 

• Phase equilibria 

Hill, Michael D. • Mechanical properties of PZT 

• Ceramic processing 

Lindsay, Curtis G. • Phase equilibria of high dielectric ceramics 

• Phase equilibria of high ceramics 

• MO calculations of environmentally enhanced fracture 

Piermarini, Gasper J. • Ceramic processing and high pressure 

sintering 

• Pressure-induced transformation 
toughening 

• High pressure physical properties and 
structures 

• High pressure X-ray diffraction and 
spectroscopy 

Vaudin, Mark D. • Electron microscopy of ceramic 

superconductors and of ceramic- 

ceramic and ceramic-metal composites 

• Microscopy and diffraction studies of 
interfaces 

• Computer modelling of grain boundary 
phenomena 

• Dielectric Films 

White, Grady S. • Thin films 

• Nondestructive evaluation 

• Subcritical crack growth 

• Stress measurements 

• Cyclic fatigue 

Wong-Ng, Winnie • X-ray analysis 

• X-ray standards 

• Molecular orbital calculations 


144 


OPTICAL MATERIALS 


Farabaugh, Edward N. • Chemical vapor deposition of diamond 

• Structure and morphology analysis 

• Scanning electron microscopy 

• X-ray diffraction 

• Thin film deposition 

• Surface analysis 

Feldman, Albert • Chemical vapor deposition of diamond 

• Thermal properties 

• Modelling thermal wave propagation 

• Thin film optical properties 

Kaiser, Debra L. • Bulk single crystal growth 

• Phase equilibria 

• Physical properties and structures of high 
temperature superconductors 

• Interfaces in high temperature superconductors 

• Chemical vapor deposition of ferroelectric 
oxide thin films 

Robins, Lawrence H. • Defect identification and distribution in 

CVD diamond 

• Stress in ceramics 

• Cathodoluminescence imaging and 
spectroscopy 

• Photoluminescence spectroscopy 

• Optical properties 

• Raman spectroscopy 

• Scanning electron microscopy 

Rotter, Lawrence D, • Measurement of electro-optic coefficients 

• Photorefractive effect 

• Optical spectroscopy of thin films 

MATERIALS MICROSTRUCTURE CHARACTERIZATION 


Black, David R. 


Bouldin, Charles E. 


Defect microstructure in diamond 
Polycrystalline diffraction imaging 
X-ray imaging of photonic materials 

X-ray absorption spectroscopy 
Diffraction anomalous fine structure 
GeSi heterojunction bipolar transistors 


145 


Burdette, Harold E. 


Fischer, Daniel A. 

Lx)ng, Gabrielle G. 

Spal, Richard D. 

Woicik, Joseph C. 

DIVISION OFFICE 

Freiman, Stephen W. 

Fuller, Edwin, R., Jr. 


Steiner, Bruce W. 


• X-ray optics 

• X-ray diffraction imaging 

• Crystal growth 

• Instrumentation 

• X-ray absorption fine structure 

• X-ray scattering 

• Surface science 

• Small-angle x-ray and neutron scattering 

• Ceramic microstructure evolution as a 

function of processing 

• X-ray optics 

• X-ray optics 

• Diffraction physics 

• X-ray scattering 

• UV photoemission 

• X-ray standing waves 

• Surface and interface science 


Electronic ceramics 
Mechanical properties 
S uperconducti vity 

Influence of microstructure on fracture and other 
physical properties of materials 
Toughening mechanisms in ceramics and 
ceramic composites, and their relations 
to processing 

Interfacial fracture and toughening 
mechanisms in reinforced ceramic 
composites 

Processing/property relations and phase 
equilibria of high ceramic superconductors 

High resolution diffraction imaging 
Nature, genesis, distribution, and 
effects of irregularities in 
monolithic crystals and multilayers 
Non linear optical processes 


146 


GUEST SCIENTISTS AND GRADUATE STUDENTS 


Allen, Andrew 

University of Maryland 

Bell, Michael I. 

Naval Research Laboratory 

Bernik, Slavko 

University of Ljubljana 

Blackburn, Douglas 

Consultant 

Block, Stanley 

Consultant 

Brower, Daniel 

Optex Corporation 

Bogatin, Oleg 

Institute of Nonmetallic Materials 

Butler, Elizabeth 

Rutgers University 

Cedeno, Christina 

American Ceramic Society 

Chapel, Jean-Paul 

Ecole Normale Superieure, Paris 

Chen, Yung-Mien 

University of Maryland 

Chen, Wei 

Alfred University 

Dai, Yongshan 

Smithsonian Institute 

Dally, James 

University of Maryland 

Domingues, Louis 

Trans-Tech, Inc. 

Dong, Xiaoyuan 

University of Maryland 

Frederikske, Hans 

Consultant 

Gallas, Marcia 

Instituto de Fisica da Ufrgs 

Green, Thomas 

American Ceramic Society 

Grabbe, Alexis 

Postdoc (ex - University of 

North Carolina at Chapel Hill) 

Gu, Jia-Ming 

University of Maryland 


147 


Hackley, Vince 

University of Wisconsin 

Haller, Wolfgang 

Abbott Laboratories 

Harmer, Martin 

Lehigh University 

He, Chuan 

University of Maryland 

Hill, Kimberly 

American Ceramic Society 

Hong, William 

Institute for Defense Analysis 

Hwzing, CheolSeong 

Seoul National University 

Hu, Zu-Shao 

East China University 

Jemian, Peter 

Illinois Institute of Technology 

Kerch, Helen 

Johns Hopkins University 

Krebs, Lorrie 

Johns Hopkins University 

Kruger, Jerome 

Johns Hopkins University 

Laor, Uri 

Nuclear Research Center of the Negev 

Larsen-Basse, Jom 

National Science Foundation 

Lee, Byeong 

Hanyang University 

Lee, Hsien-Ming 

University of Maryland 

Lee, Soo Wohn 

University of Illinois 

Liang, Hong 

University of Maryland 

Liu, Hanyan 

Northwestern University 

McMurdie, Howard 

Joint Center for Powder 

Diffraction Studies 

Messina, Carla 

American Ceramic Society 

Ondik, Helen 

American Ceramic Society 

Pan, Yi-Ming 

Southwest Research Institute 


148 


Paretzkin, Boris 

Joint Center for Powder 

Diffraction Studies 

Paulik, Steven 

Northwestern University 

Pechenik, Alex 

Air Force Office of Scientific Research 

Perez, Joseph 

Department of Energy 

Peterson, Marshall 

Wear Sciences 

Premachandran, Ramannair Sarasamma 

Indian Institute of Technology, Madras 

Roth, Robert 

Consultant 

Russell, Thomas 

Naval Surface Warfare Center 

Sater, Janet 

Institute for Defense Analysis 

Shechtman, Dan 

Johns Hopkins University 

Shen, Ming 

University of Illinois 

Shin, Hung Hyangjae 

University of Maryland 

Smith, Wallace 

Office of Naval Research 

Sponner, Stephen 

Oak ridge National Laboratory 

Strakna, Timothy 

University of Maryland 

Sun, Jian-Xia 

Shanghai University of Science 
and Technology 

Swanson, Nils 

American Ceramic Society 

Vandiver, Pamela 

Smithsonian Institute 

Vinod, Natarajan 

University of Maryland 

Wang, Yushu 

University of Maryland 

Wei, Lanhua 

Wayne State University 

Xu, Huakun 

University of Maryland 


149 


Ying, Tsi-Neng 


Zhang, Guangming 
Zimmerman, Michael 


University of Maryland 
University of Maryland 
Northwestern University 


150 


OUTPUTS AND INTERACTIONS 







TECHNICAL PUBLICATIONS 


DATA TECHNOLOGIES 


R. G. Munro and S. J. Dapkunas, Corrosion Characteristics of Silicon Carbide and Silicon 
Nitride, J. Res. NIST 98 (5) 607-631 (1993). 

R. G. Munro and S. J. Dapkunas, Corrosion of Ceramics in Coal-Combustion Applications, 
Proceedings of the Ninth Annual Coal Preparation, Utilization, and Environmental Control 
Contractors Conference, pp. 202-209 (1993). 

R. G. Munro, submitted to ASTM, The Role of Corrosion in a Material Selector Expert 
System for Advanced Structural Ceramics. 

Begley, E.F. and Lindsay, C.G., "A Multimedia Tutorial on Phase Equilibria Diagrams," 
American Ceramic Society Bulletin, Volume 72, No. 12, pp. 103-104, 1993. 

John Rumble, Jr. and Joseph Carpenter, Jr., "Materials ’STEP’ into the Future," Advanced 
Materials and Processes , vol. 142, No. 4, October 1992, pages 23-27. 


POWDER CHARACTERIZATION AND PROCESSING 


Cline J. P., "Powder Diffraction SRMs", Brochure available from the SRMP office, January 
1994. 

Rosetti G. A., Cross E., and Cline J. P., "Structural Characteristics and Ferroelectric Phase 
Transition Behavior of Lanthanum-Substituted Lead Titanate" submitted to Journal of 
Materials Science, 1993. 

Kreider K. G., Tarlov M. J., and Cline J. P., "Sputtered Thin Film pH Electrodes of 
Platinum, Palladium, Ruthenium and Iridium Oxides" submitted to Sensors and Actuators, 
1993. 

Kalceff W., Cline J. P., and Von Dreele R. B., "Size/Strain Broadening Analysis of SRM 
676 Candidate Materials", submitted to Advances in X-ray Analysis, vol 37, 1993. 

Cline J. P., Handwerker C. A., Vaudin M. D., and Blendell J. E., "Texture Measurement 
of Sintered Alumina Using the March-Dollase Function" submitted to Advances in X-ray 
Analysis, vol 37, 1993. 

Cline J. P., "An Overview of NIST Powder Diffraction Standard Reference Materials," 
submitted to the Proceedings of The Third European Powder Diffraction Conference, 1993. 


153 


Wang P. S., Malghan, S. G., Dapkunas, S. J., Hens, K. F., Raman, R., "NMR 
Characterization of Injection Molded Alumina Green Compacts: I, Nuclear Spin-Spin 
Relaxation," submitted to the Journal of Materials Science, 1993. 

Wang P. S., Malghan S. G., Dapkunas S. J., Hens K. F., Raman R., "NMR 
Characterization of Injection Molded Alumina Green Compacts: 11. T 2 -Weighted Proton 
Imaging," submitted to the Journal of Materials Science, 1993. 

Wang P. S., Malghan S. G., Hsu S. M., Wittberg T. N., "An X-Ray Induced AES Study of 
the Effect of Chemically Bound Hydrogen on the Oxidation Kinetics of a Si 3 N 4 Powder," 
submitted to the Surface and Interface Analysis, 1993. 

Hackley V. A. and Malghan, S. G., "Polyelectrolytes as Dispersants in Colloidal Processing 
of Silicon Nitride Ceramics," Polymer Preprints, 34, 1024 (1993). 

Hackley V. A. and Malghan S. G., "Investigation of Parameters and Secondary Components 
Affecting the Electroacoustic Analysis of Silicon Nitride Powders," in Electroacoustics for 
Characterization of Particulates and Suspensions, NIST Special Publication 856, S.G. 
Malghan, Ed. (U.S. Department of Commerce, Technology Administration 1993) p 161. 

Hackley V. A., Wang P. S. and Malghan S. G., "Effects of Soxhlet Extraction on the 
Surface Oxide Layer of Silicon Nitride Powders," Mat. Chem. Phys., 36, 112 (1993). 

Hackley V. A. and Malghan, S. G., "The Surface Chemistry of Silicon Nitride Powder in 
the Presence of Dissolved Ions," submitted to 7. Mat. Sci. (1993). 

Shull R. D., McMichael R. D., Ritter J. J., Swartzendruber L. J. and Bennett L. H., 
"Nanocomposite Magnetic Refrigerants," Proc. 7^ International Cryocooler Conference, 
Santa Fe, NM, Nov. 1992. 

Shull R. D., McMichael R. D., Ritter J. J. and Bennett L. H., "Nanocomposites for 
Magnetic Refrigeration," Proc. MRS Conf., Dec 3, 1992, Boston MA. 

Ritter J. J., "A Chemical Synthesis of Bismuth Telluride and Bismuth Telluride Composite 
Thermoelectric Refrigerants," submitted to Chemistry of Materials. 

Shull R. D., Kerch H. M. and Ritter J. J., "Magnetic Properties of Colloidal Silica: 
Potassium Silicate Gel/Iron Nanocomposites," J. App’d Phys., 38^ Conf. on Magnetism and 
Magnetic Matl’s, Minneapolis MN, Nov. 15-19, 1993. 

McMichael R. D., Ritter J. J. and Shull R. D., "Enhanced Magnetocaloric Effect in Gd 3 Ga 5 . 
xFexOi 2 ," J.App’d Phys., 73, 6946-6948, (1993). 

Shull R. D., McMichael R. D., and Ritter J. J., "Magnetic Nanocomposites for Magnetic 
Refrigeration," Nanostructured Materials, 2, (1993), 205-211. Oct. 1992. 


154 


Deb K. K., Hill M. D, and Kelly J. F., "Pyroelectric Characteristics of Modified Barium 
Titanate Ceramics," Journal of Materials Research Vol. 7, No. 12, Dec. 1992. 

Chen W., Pechenik A., Dapkunas, S. J., Piermarini G. J., and Malghan S. G., "Novel 
Equipment for the Study of the Compaction of Fine Powders," accepted for publication by J. 
American Ceramic Society, October 1993. 

Cox B. N., Carter W. C., and Fleck N. A., "A Binary Model for Failure of Textile 
Composites," submitted to Acta Met., December 1993. 

Malghan S. G., Premachandran R. S., and Pei P. T., "Mechanistic Understanding of Silicon 
Nitride Dispersion Using Cationic and Anionic Polyelectrolytes, " accepted for publication by 
Powder Technology, September 1993. 

Premachandran R. S. and Malghan S. G., "Dispersion Characteristics of Ceramic Powders in 
the Application of Cationic and Anionic Polyacrylates," accepted for publication by Powders 
Technology, October 1993. 

Wang, P. S., Malghan, S. G., Hsu, S. M., and Wittberg, T. N., "Oxidation of Surface- 
Treated Q!-SiC Platelets Studied by XPS and Bremsstrahlung-Excited AES," Surface and 
Interface Analysis. . 20, 105-110, 1993. 


MECHANICAL PROPERTIES 

Lawn, B. R., Padture, N. P., Braun, L. M., and Bennison, S. J., "Model for Toughness- 
Curves in Two-Phase Ceramics: 1. Basic Fracture Mechanics," J. Am. Ceram. Soc., 76 [9] 
2235-40 (1993). 

Padture, N. P., Runyan, J. L., Braun, L. M., Bennison, S. J., Lawn, B. R., "Model for 
Toughness-Curves in Two-Phase Ceramics: 11. Microstructural Variables," J. Am. Ceram. 
Soc., 76[9] 2241-47 (1993). 

Braun, L. M. and Cook, R. F., "Effect of Stress on Trapped Cracks in Y-TZP," Science 
and Technology of Zirconia V, S.P.S. Badwal, M. J. Bannister, and R.H. J. Hannink eds., 
Technomic Publishing Company, Inc., Lancaster, PA 1993. 

"A Methodology to Predict Creep Life for Advanced Ceramics Using Continuum Damage 
Mechanics Concepts" T.-J. Chuang and S. F. Duffy to be published in ASTM STP 1201, 
1993. 


Chuang, T.-J., Chu, J.-L. and Lee, S., "High Temperature Crack Growth in Dissimilar 
Media," Proc. 8th International Conference on Fracture, Keiv, Ukraine, June 8-14, 1993. 

Krause, R.F. Jr., "Flat and Rising R-Curves for Elliptical Surface Cracks from 
Indentation and Superposed Flexure," (in press) J. Am. Ceram. Soc., 77 (1994). 


155 


Krause, R.F. Jr., and Wiederhom, S.M., "Tensile Creep of a Silicon Nitride Ceramic," 
Silicon Nitride 93 . Proceedings of the International Conference on Silicon Nitride-Based 
Ceramics, Stuttgart, Germany, Oct 1993, Trans Tech Publications Ltd., Switzerland, 1994, 
pp 619-624. 

Luecke, W.E., Wiederhom, S.M., Hockey, B.J. and Long, G.G., "Cavity Evolution during 
Tensile Creep of Si 3 N 4 ," Mat. Res. Soc. Symp. Proc. 287 467-472 (1993). 

Luecke, W.E. and Wiederhom, S.M., "Tension/Compression Creep Asymmetry in Si 3 N 4 ," 
Silicon Nitride 93 . Proceedings of the International Conference on Silicon Nitride-Based 
Ceramics, Stuttgart, Germany, Oct 1993, Trans Tech Publications Ltd., Switzerland, 1994, 
pp 587-592. 

Romero, J.C., Arsenault, R.J., and Krause, R.F. Jr., "Microstmctural Changes During 
Creep of a SiC/Af 203 Composite," Mater. Sci. and Eng. A., (1994). 

Wiederhom, S.M., Quinn, G.D., and Krause, R.F. Jr., "Fracture Mechanism Maps: Their 
Applicability to Silicon Nitride," Life Prediction Methodologies and Data for Ceramic 
Materials. ASTM STP 1201, C.R. Brinkman and S.F. Duffy, Editors, American Society for 
Testing and Materials, Philadelphia, 1993. 

Wiederhom, S.M., Quinn, G.C., and Krause, R.F. Jr., "High Temperature Stmctural 
Reliability of Silicon Nitride," Silicon Nitride 93 . Proceedings of the International 
Conference on Silicon Nitride-Based Ceramics, Stuttgart, Germany, Oct 1993, Trans Tech 
Publications Ltd., Switzerland, 1994, pp 575-580. 

Horn, R.G., Smith, D.T., and Grabbe, A., Nature 366, 442-443 (1993). 

Jahanmir, S., and Fischer, T. E., "Friction and Wear of Advanced Ceramics," Tribology 
Handbook . Vol 3, in press. 

Gangopadhyay, A., and Jahanmir, S., "Self-lubricating Ceramic Matrix Composites," 
Friction and Wear of Advanced Ceramics . S. Jahanmir (Ed.) Marcel Dekker, New York, 
NY, (1993) 163-198. 

Dong, X., and Jahanmir, S., "Wear Transition Diagram for Silicon Nitride," Wear . 165 
(1993) 169-180. 

Jahanmir, S., "Advanced Ceramics in Tribological Applications," Friction and Wear of 
AdvancedCeramics . S. Jahanmir (Ed.) Marcel Dekker, New York, NY, (1993) 3-13. 

Jahanmir, S. and Dong, X., "Wear Mechanisms of Aluminum Oxide Ceramics," Friction 
and Wear of Advanced Ceramics . S. Jahanmir (Ed.) Marcel Dekker, New York, NY, (1993) 
15-50. 


156 


Alexeyev, N. and Jahanmir, S., "Mechanics of Friction in Self-lubricating Composite 
Materials, Part 1. Mechanics of Second Phase Deformation and Motion," Wear 166 (1993) 
41-48. 


Alexeyev, N. and Jahanmir, S., "Mechanics of Friction in Self-lubricating Composite 
Materials, Part 2. Deformation of the Interfacial Film," Wear 166 (1993) 49-54. 

Jahanmir, S. and Dong, X., "Wear Transition Diagrams for Ceramics," Proceedings of the 
1st International Symposium on Tribology . Y. S. Jin (Ed.), International Academic 
Publishers, Beijing, PRC, (1993) 362-371. 

Jahanmir, S. (Ed.), Friction and Wear of Ceramics . Marcel Dekker, New York, NY 
(1993). 

Jahanmir, S. (Ed.), Machining of Advanced Materials . Proceedings of the International 
Conference on Machining of Advanced Materials, National Institute of Standards and 
Technology, Special Publication 847, Government Printing Office, Washington, DC (1993). 

Cai, Hongda, Faber, Katherine T., and Fuller, Edwin R. Jr., "Crack Bridging by Inclined 
Fibers/Whiskers in Ceramic Composites" J. Am. Ceram. Soc., 75 [11], 3111-3117 
(November 1992). 

Paulik, S. W., Faber, K. T., and Fuller, E. R. Jr., "Development of Textured 
Microstructures in Ceramics with Large Thermal Expansion Anisotropy," J. Am. Ceram. 
Soc., 77 [2], (1994). 


SURFACE PROPERTIES 

He, C., Wang, Y. S., Wallace, J. S., and Hsu, S. M., "The Effect of Microstructure on the 
Wear Transition of Zirconia Toughened Alumina," Wear . 162-164 . p. 314-321, 1993. 

Ying, T. N., and Hsu, S. M., "Asperity- Asperity contact mechanisms simulated by a Two- 
ball Collision Apparatus," To appear in Wear in 1993. 

Wang, J. C., and Hsu, S. M., "Chemically Assisted Machining of Ceramics," accepted for 
publication in J. of Tribology. 

Lee, S. C., Hsu, S. M., and Shen, M. S., "Ceramic Wear Maps: Zirconia," Journal of the 
ACerS, 76, [8], 1937-47, 1993. 

Zhang, P. Y., and Hsu, S. M., "Inhibition Mechanisms of Some Antioxidants in Lubricant 
Oxidation Using a Chemiluminescence Technique," submitted to J. of Lub. Sci. 

Hsu, S. M., Shen, M., Klaus, E. E., Cheng, H. S., and Lacey, P., "A Mechano-Chemical 
Model: Reaction Temperatures in a Concentrated Contact," submitted to Wear. 


157 


Ruff, A, W., "Multilayer Coatings for Tribological Applications," A. W, Ruff, Proceedings 
of a DOE Workshop on Coatings for Advanced Heat Engines, Monterey, CA, 1993, pp. IV- 
45 to 54. 

Ruff, A. W., and Peterson, M. B., "Wear of Self-lubricating Composite Materials vs. M0S2 
Films," Wear 162-164 . 492-497, 1993. (also in Wear of Materials- 1993 . pp. 492-497). 

"Standard on Calculating and Reporting Measure of Precision Using Data From 
Interlaboratory Wear or Erosion Tests," ASTM G-117 (93) (author: A. W. Ruff). 

"Standard Data Format for Computerization of Wear Test Data," ASTM G-118 (93) (author: 
A. W. Ruff) 

Ruff, A. W., and Bayer, R. G., Wear Test Selection for Design and Application , eds., 
ASTM STP 1199, Philadelphia, PA, 1993. 

Ruff, A. W., Shin, H., and Evans, C. J.,"Chemo-mechanical Damage During Diamond Tool 
Scratching of CVD Silicon Carbide," Proc. ASME Symposium on Contact Problems and 
Surface Interactions in Manufacturing and Tribological Systems, ASME, 1993. 

Chen, Y-M., Ruff, A. W., and Dally, J. W., "Numerical Simulation of the Micro- 
indentation Process," Proc. ASME Symposium on Contact Problems and Surface Interactions 
in Manufacturing and Tribological Systems, ASME, 1993. 

Chen, Y-M., Ruff, A. W., and Dally, J. W., "A Method for Determining Material 
Properties from Instrumented Micro-indentation Experiments," Y. M. Chen, A. W. Ruff, 
and J. W. Dally, J. Matls. Research, 1993, in press. 

Armstrong, R. W., Shin, H., and Ruff, A. W., "Elastic/Plastic Effects During Lx)w-load 
Hardness Testing of Copper," submitted to Acta Met. 1993. 


ELECTRONIC MATERIALS 


Rawn, C. J., Roth, R. S., Burton, B. P., Hill, M. D., "Phase Equilibria and Crystal 
Chemistry in Portions of the System Sr0-Ca0-y2Bi203-Cu0, Part V The System SrO-CaO- 
V2Bi203, accepted, Journal of the American Ceramic Society. 

Wong-Ng, W., Cook, L. P., Paretzkin, B., Hill, M. D., Stalick, J. K., "Crystal Chemistry 
and Phase Equilibrium Studies of the BaO-y2R203-CuOx System in Air. VI. R- 
Neodymium"; in press Journal Less Common Metals. 

Wong-Ng, W., Cook, L. P., "Eutectic Minimum Melting in the System Ba0-y2Y203-Cu0x 
in Air"; in press Journal of the American Ceramic Soc. 


158 


Burton, B. P., Pasture, A., "LMTO/CVM Calculations of BCC Based Phase Ordering in 
the System Fe-Be"; Proceedings of the NATO/ASI Statics & Dynamics on ordering in 
Alloys, 6/21/92-7/3/92, Rhodes, Greece, in press. 

Rhine, W. E., Hallock, R. B., Davis, W. M., and Wong-Ng, W., "Synthesis and Crystal 
Structure of Barium Titanyl Oxalate, BaTi(0)C204)2'5H20: A Molecular Precursor for 
BaTi03. Chemistry of Materials, 4, 1208, 1993. 

Hill, M. D., Blendell, J. E., Vaudin, M. D., and Chiang, C. K., "Effect of 
Processing Conditions on the Microstructure and Superconducting Properites of Sintered 
YBa2Cu306+x Superconductors; Journal of the American Ceramic Society, in press. 

Burton, B. P., Rawn, C. J., Roth, R. S., and Hwang, N. M., "Phase Equilibria 

and Crystal Chemistry in Portions of the System Sr0-Ca0-Bi203-Cu0, Part IV - The System 

Ca0-Bi203-Cu0; J. NIST, 98, 469-516, (1993). 

Smilgys, R. V., Hsieh, T. J., Robey, S. W., and Chiang, C.K., "Reactive Coevaporation of 
DyBaCuO Superconducting Films on MgO (100): The Effect of Substrate Annealing; J. 

Vac. Sci. & Tech. A 11(4), 1993. 

Freiman, S. W., and Hill, M. D., "Mechanical Reliability of High Tc Superconductors, 

Proc. of Fifth US-Japan Workshop on High Tc Materials. 

Wong-Ng, W., Mighell, A., and Karen, V., "Materials Research Society, Short Course on 
Crystallographic Databases for Chemical and Materials Analysis; Boston, Ma., Nov. 1992. 

Wiederhom, S. M., Hockey, B. J., Handwerker, C. A., and Blendell, J. E., "On the 
Wetting of Grain Boundaries in Aluminum Oxide", Journal of the American Ceramic Soc., 
in press. 

Sora, I. N., Wong-Ng, W., Roth, R. S., Rawn, C.J., and Burton, B. P., "X-Ray and 
Neutron Diffraction Study of CaBi204 " J. Chem. Mater., in press. 

Wong-Ng, W., "Structures and X-Ray Patterns of Compounds in the Sr-Nd-Cu-0 System", 
to be published in the Powder Diffraction Journal. 

Lee. H. M., Chuang, T. J., Chiang, C. K., Cook, L. P., and Scheck, P. K., "Crack 
Development in Pulsed Laser-Deposited PZT Thin Films, MRS Symposium Proceedings on 
Laser Deposition, eds. B. Braren, J. Dubowski, and D. Norton, J. Mat’ls. Soc., v. 285, 
409-413, 1993. 

Lee, B. W., Lee, H. M., Cook, L. P., Schenck, P. K., Paul, A., Wong-Ng, W., Chiang, 
C. K., Brody, P. S., Rod, B. J. and Bennett, K. W., "Preparation of PbTi03Pb 
(Mgo sWo 5)03 Thin Films Using Pulsed Laser Deposition, MRS, Symposium Proceedings 
on Laser Deposition. 


159 


Lindsay, C. G., Rawn, C. J., Roth, R. S., "Powder X-Ray Diffraction Data for 
Ba4ZnTiuji027 and Ba 2 ZnTi 50 i 3 ," Journal: Powder Diffraction, in press. 

Carpenter, J, A. Jr,, Piermarini, G. J., Dickens, B., Manning, J. R., Read, D. T., Mattis, 
K. G., Kreider, K, G., Mattis, R. L., Evans, R,,"NIST/NCMS Program on Electronic 
Packaging: First Update", to be published in the proceedings of the Symposium on 
Microelectronic and Optoelectronic Packaging, American Ceramic Society, San Franciso, CA 
Nov. 1-4, 1992. 

Russell, T. P., Miller, P. J., Piermarini, G. J., and Block, S., 

"Pressure/Temperature/Reaction Phase Diagrams for Several Nitramine Compounds", to be 
published in the Journal Proceedings of MRS Vol. 296, 119 (1993). 

Handworker, C. A., Blendell, J. E,, Interrante, C. G., and Ahn, T. M., "The Potential Role 
of Diffusion-Induced Grain-Boundary Migration in Extended Life Prediction", Proceedings 
MRS Mtg, Nov. 92. 

Gallas, M. R., and Piermarini, G. J., "The Bulk Modulus and Young’s Modulus of 
Nanocrystalline - 7 - Alumina", submitted to Journal of the American Ceramic Society. 

Lindsay, C. G., White, G. S,, Freiman, S. W., and Wong-Ng, W.,"A Molecular Orbital 
Study of the Environmentally-Enhanced Crack Growth Process in Silica, " submitted to 
Journal of Amer, Ceram. Soc. 1993. 

Pechenik, A., Piermarini, G. J., and Danforth, S. C,, "Low Temperature Densification of 
Silicon Nitride Nanoglass, " Proc. of 2nd International Conference on Nanostructured 
Materials, Cancun, New Mexico, Sept. 23, 1992. 

Chen, Bai-Hao, Wong-Ng, W., and Eichhom, B., " Structural Reinvestigation of Ba 3 Zr 2 S 7 
by Single Crystal X-Ray Diffraction". 

Wong-Ng, W., Roth, R. S., Sunshine, S., and Rawn, C. J., "Refined Crystal Structure of 
Willemite, Zn 2 [Si 04 ]." 

Wong-Ng, W., "X-Ray Diffraction Patterns for BaR 2 Pd 05 ." 

Mathew, M. and Wong-Ng, W., "Crystal Structure of a New Monoclinic Form of Potassium 
Diyhydrogren Phosphate Containing Orthophosphacidium Ion, (H 4 P 04 )‘^, Journal of Solid 
State Chemistry, in press. 

Meng, W. G., Vaudin, M. D., Bartholemeusz, M. F., and Wert, J. A., "Experimental 
Assessment of Crack Tip Dislocation Emission Models for an Ald67Crd8Tid25 Intermetallic 
Alloy," to be published in Met Trans A. 


160 


Bennett, K. W., Brody, P. S., Rod, B. J., Cook, L. P., Schenck, P. K., and Dey, S., 
"Dielectric Constant and Hysteresis Loop Remanent Polarization From 100 Hz to 2 MHz for 
Thin Ferroelectric Films," Ferroelectric Thin Films II, A. I, Kingon, ed., v. 243, 507-512, 
1993. 


OPTICAL MATERIALS 


Kaiser, D.L., Vaudin, M.D., Gillen, G., Hwang, C.-S., Robins, L.H. and Rotter, L.D., 
"Growth and Characterization of Barium Titanate Thin Films by Metalorganic Chemical 
Vapor Deposition (MOCVD)," J. Crystal Growth, in press, 

Kaiser, D.L., Vaudin, M.D., Gillen, G., Hwang, C.-S., Robins, L.H. and Rotter, L.D,, 
"Growth of BaTi 03 Thin Films by MOCVD," MRS Proceedings, Symposium on Metal- 
Organic CHemical Vapor Deposition of Electronic Ceramics, Fall, 1993, in press. 

Robins, L.H., Farabaugh, E.N. and Feldman, A., "Cathodoluminescence Spectroscopy of 
Free and Bound Excitons in Chemical-Vapor-Deposited Diamond" Physical Review B, in 
press. 

Robins, L.H. and Black, D.R. "Defect Mapping of a Synthetic Diamond Single Crystal by 
Cathodoluminescence Spectroscopy", Journal of Materials Research, in press. 

Jin, S., Fanciulli, M., Moustakas, T.D. and Robins, L.H,, "Electronic Characterization of 
Diamond Films Prepared by Electron Cyclotron Resonance Microwave Plasma", in Diamond 
Films ’93, Proceedings of the Fourth European Conference on Diamond, Diamond-like and 
Related Coatings, in press. 

Shechtman, D., Hutchinson, J.L., Robins, L.H., Farabaugh, E.N. and Feldman, A., 

"Growth Defects in Diamond Films", J. Mater. Res. 8 (3), 473-479, (1993). 

Shechtman, D., Feldman, A., Vaudin, M.D. and Hutchison, J.L., "Moire-Fringe Images of 
Twin Boundaries in Chemical Vapor Deposited Diamond", Appl. Phys, Letters 62, 487-489 
(1993). 

Feldman, A., Beetz, C.P., Klocek, P. and Lu G., "Workshop on Characterizing Diamond 
Films 11", NISTIR 5198, May 1993. 

Feldman, A., Beetz, C.P., Klocek, P. and Lu, G., "Workshop on Characterizing Diamond 
Films 11", Conference Report, J. of Res. NIST, 98 , 375-381 (1993). 

Feldman, A. and Frederikse, H.P.R., "Measuring the Thermal Diffusivity of Chemical 
Vapor Deposited Diamond" in Proceedings of the Applied Diamond Conference 1993, the 
Second International Conference on the Applications of Diamond Films and Related 
Materials, (MYU, Tokyo, 1993) pp. 261-268. 


161 


Turchinskaya, M., Kaiser, D.L., Gayle, F.W., Shapiro, AJ., Roytburd, A., Vlasko- Vlasov, 
V., Polyanskii, A. and Nikitenko, V., "Direct Observation of Anisotropic Flux Penetration 
in Twinned YBa2Cu307.x Single and Polycrystals," Physica C 216 , 205-210 (1993). 

Turchinskaya, M., Kaiser, D.L,, Gayle, F.W., Shapiro, A.J., Roytburd, A., Dorosinskii, 
L.A., Nikitenko, V.L, Polyanskii, A. A, and Vlasko- Vlasov, V.K., "Real-Time Observation 
of the Effect of Grain Boundaries on Magnetization of YBa2Cu307.x Polycrystals," Physica 
C, in press. 


MATERIALS MICROSTRUCTURE CHARACTERIZAITON 

Allen, A. J., and Jemian, P. R., "The Effect of the Shape Function of Small Angle 
Scattering Analysis by Maximum Entropy Method," J. of Applied Crystallography, (1993). 

Allen, A. J., and Berk, N. F., "Analysis of SAS Data Dominated by Multiple Scattering for 
Systems Containing Eccentrically-Shaped Particles or Pores, J. of Applied Crystallography, 
(1993). 

Black, D. R., Larson, D. L., Silberstein, R. P., DiMarzio, D., Carlson, F. C., Gillies, D., 
Long, G., Dudley, M., and Wu, J., "Compositional, Strain-Contour, and Property Mapping 
of CdZnTe Boules and Wafers," Semiconductor Science and Technology, (1993). 

Black, D. R., Kycia, S. W., Goldman, A. L, Lograsso, T. A., Delaney, D. W., Sutton, 

M., Dufresne, E., Bruning, R., and Rodricks, B., "Dynamical X-ray Diffraction from an 
Icosahedral Quasicrystal," Physical Review Letters, (1993). 

Black, D. R., and Robins, L. H., "Defect mapping in synthetic single-crystal diamond by 
cathodoluminescence spectroscopy," J. of Materials Research, (1993). 

Bouldin, C. E., Tan, Z., Heald, S. M., Rapposch, M., and Woicik, J. C., "Gold-Induced 
Germanium Crystallization," Physical Review B, (1993). 

Fischer, D. A., Moodenbaugh, A. R., and Xu, Y., "Oxygen K Near-Edge X-Ray 
Absorption Spectroscopy of La2_xMjjCu04(M=Ca, Sr, and Ba): x Dependence of Hole State 
Density," Physical Review B (1993). 

Fischer, D. A., Srivatsa, A. R., Borra, R. T., and Skotheim, T. A., "A Near Edge X-ray 
Absorption Study of Diamond-Like Nanocomposites, " Proceedings of the Third International 
Symposium on Diamond Materials. Honolulu. HI . May 16-21, 1993. 

Fischer, D. A., Purdie, D., Muryn, C. A., Crook, S., Wincott, P. L., and Thornton, G., 
"Potassium bond site in ZnO(0001)p(2x2)K," Surface Science Letters, (1993). 

Fischer, D. A., Davis, S. M., Meitzner, G. D., and Gland, J., "Studies of Fluorine in 
Catalysts with Ultra-Soft X-ray Absorption Spectroscopy," J. of Catalysis, (1993). 


162 


Fischer, D. A., Mitchell, G. E., DeKoven, B. M., Yeh, A. T,, Gland, J. L., and 
Moodenbaugh, A. R., "Ultra-soft X-ray Absorption Spectrocopy: A Bulk and Surface Probe 
of Materials," MRS Proceedings "Applications of Synchrotron Radiation Techniques to 
Materials Science" MRS Spring Mtg. San Francisco. CA . April 12-16, 1993. 

Fischer, D. A., Huang, S. X., and Gland, J. L., "Aniline Hydrogenolysis on the Pt(lll) 
Single Crystal Surface: Mechanisms for C-N Bond Activation," ACS Symposium on 
"Mechanism of HDS/HDN Reactions" Chicago. IL . August 22-27, 1993. 

Fischer, D. A., Hastie, G. P., Roberts, K. J., Adams, D., and Meitzner, G., "Investigating 
the Structural Chemistry at the Interface Formed Between Zinc Dialkyldithiophosphate 
(ZDDP) and Mild Steel Using Ultra-Soft X-ray Absorption Spectroscopy," Japanese J. 
Applied Physics, Proceedings 7th International Conference on X-rav Absorption Fine 
Structure. Kobe. Japan. (1993). 

Lx)ng, G. G., Jemian, P. R., and Weertman, J. R., "A Gradient Method for Anomalous 
Small- Angle X-ray Scattering," Journal of Applied Crystallography, (1993). 

Long, G. G., Krebs, L. A., Kruger, J., Ankner, J. F., Satija, S. K., Wiesler, D. G., and 
Majkrzak, C. F., "Neutron Reflectivity Studies of the Passive Film on Iron," Proceedings of 
Symposium on "Oxide Films on Metals and Alloys." ed. by Barry MacDougall. The 
Electrochemical Society, Toronto, October 11-16, 1992. 

Long, G. G., Krebs, L. A., Kruger, J., Wiesler, D. G., Ankner, J. F., Majkrzak, C. F., 
and Satija, S. K., "Passive Film Studies Using Neutron Reflectivity," Proceedings of the 
12th International Congress on Corrosion. Houston. TX . September 19-24, 1993. 

Long, G. G., Luecke, W., Wiederhom, S. M., and Hockey, B. J., "Cavity Evolution 
During Tensile Creep of Si 3 N 4 ," Materials Research Society Symposium Proceedings. 

Boston. MA . 287 , 467-472 (1993). 

Woicik, J. C., Kendelewicz, T., Miyano, K. E., Herrera-Gomez, A., Cowan, P. L., Karlin, 
B. A., Bouldin, C. E., Pianetta, P., and Spicer, W. E., "Structural Study of Sb Monolayers 
on Ga As(llO) with the X-ray Standing-wave Technique," Physical Review B, (1993). 

Woicik, J. C., Kendelewicz, T., Herrera-Gomez, A., Andrews, A. B., Kim Boong Soo, 
Cowan, P. L., Miyano, K. E., Bouldin, C. E., Karlin, B. A., Herman, G. S., Erskine, J. 

L., Pianetta, P., and Spicer, W. E., "Adatom Location on the Si(lll) 7x7 and Si(lll) 
V3xV'-In Surfaces by the X-ray Standing Wave and Photoemission Techniques," J. of Vac. 
Science and Tech., (1993). 

Woicik, J. C., Herrera-Gomez, A., Kendelewicz, T., Miyano, K. E., Pianetta, P., 
Southworth, S., Cowan, P. L., Karlin, B. A., and Spicer, W. E., "Determination of the 
Geometrical Configuration of Bi on GaAs(llO) by X-ray Standing Wave Triangulation," J. of 
Vac. Science and Tech. A, (1993). 


163 


Woicik, J. C,, Kendelewicz, T., Herrera-Gomez, A., Miyano, K. E., Cowan, P. L., Karlin, 
B. A., Pianetta, P., and Spicer, W. E., "X-ray Standing Wave Study of the 
Sb/GaAs(110) Interface Structure," J. Vac. Science & Tech. A, (1993). 

Woicik, J. C., Kendelewicz, T., Herrera-Gomez, A., Miyano, K. E., Cowan, P. L., 

Bouldin, C. E., Pianetta, P., and Spicer, W. E., "The Si(lll) VSKv/S-In Interface: An 
Unrelaxed T4 Geometry," Physical Review B, (1993). 

Woicik, J. C., Kendelewicz, T., Miyano, K. E., Herrera-Gomez, A., Cowan, P. L., 
Pianetta, P., and Spicer, W. E., "Structure of Sb Monolayers on Ge(l 11)2x1: A Combined 
Study Using Core Level Photoemission, X-ray Standing Waves, and Surface Extended X-ray 
Absorption Fine Structure," Physical Review B (1993). 

Steiner, Bruce, Tseng, Wen, Comas, James, Laor, Uri, Dobbyn, Ronald C., and Rajan, 
Krishna, "Defect Formation in Semiconductor Layers during Epitaxial Growth," J. Crystal 
Growth, 128, 543-549 (1993) 

Steiner, Bruce, Comas, James, Tseng, Wen, and Laor, Uri, "The influence of lattice 
mismatch on indium phosphide based high electron mobility transistor (HEMT) structures 
observed in high resolution monochromatic synchrotron x-radiation diffraction imaging," 
Proc. Mat. Res. Soc. 281, 127-132 (1993) 

Steiner, Bruce, Comas, James, Tseng, Wen, Laor, Uri, and Dobbyn, Ronald C., "Defects in 
III-V Materials and the Accommodation of Strain in Layered Semiconductors," J. Elect. Mat. 
22, 725-738 (1993) 


164 


CERAMICS DIVISION PATENTS 


1993 


Oxygen-Containing Organic Compounds as Boundary 
Lubricants for Silicon Nitride Ceramics (D) 

A Method of Obtaining High Green Density 
from Ceramic Powders (D) 

Method of Producing a Smooth Plate of Diamond (I) 


Asymmetric Bragg diffraction microscope (I) 

Method for Fabrication of Dense Compacts from 
Nanosize Particles Using High pressures and Cryogenic 
Temperatures (P) 

1992 


Novel Method of Bonding Materials Together - 
"Nanoglue" (P) 

Coprecipitation Synthesis of Precursors 
to Bismuth-Containing Superconductors (I) 

A Super Stable High-Temperature Liquid Lubricant 
Containing a Unique Antioxidant and Additive 
Solulubilizing Ternary System (D) 

A Chemical Assisted Process for Rapid Machining 
of Tough Ceramics (D) 

A Cutting Fluid Additive for Machining 
of Ceramics (P) 

Hydroxyl Containing Organic Compounds as Boundary 
Lubricants for Silicon Nitride Ceramics (D) 

A Process to Lubricate Titanium with Chlorinated 
Hydrocarbons (D) 

A Process to Machine Titanium Using Chlorinated 
Hydrocarbons (D) 


R. S. Gates 

S. M. Hsu 

S, G. Malghan 
R. S. Premachandran. 

A. Feldman 
E. N. Farabaugh 

R. Spal 

A. Pechenik 
G. J.Piermarini 


D. T. Smith 

R. G. Horn, A. Grabbe 

J. Ritter 


J. Perez, 

C. Ku, Y. M. Zhang 


J. Wang, 

S. M. Hsu 

S. Jahanmir, 
G. Zhang 

R. S. Gates, 

S. M. Hsu 

J. Wang, 

S. M. Hsu 

J. Wang, 

S. M. Hsu 


165 


Methods of Reducing Wear on SiC 
Ceramic Surfaces (P) 


D. E, Deckman 
S. M. Hsu 


Detergent and Dispersant Type Organic Compounds as R. S. Gates 
Boundary Lubricants for Silicon Nitride Ceramics (D) S. M. Hsu 

1991 


Diamond Coated Laminates and Methods of 
Producing Same (D) 

High Resolution X-Ray Microtomographic 
Detector (P) 


A Colloidal Processing Method for Coating 
Ceramic Reinforcing Agents (I) 

U.S. Patent No. 5,039,550, August 1991 

Process for the Fabrication of Ceramic 
Monoliths by Laser-Assisted Chemical 
Vapor Infiltration (I) 

A Method for Making Translucent High 
Purity Transparent Silicon Nitride (P) 


1990 


Novel Synergistic Additive Packages 
Containing High Molecular Weight 
Antioxidants for High Temperature 
Lubricants (P) 

Low Energy (Thermal) Neutron 
Absorbing Glass (A) 


Process for Elimination of Twins in 
Perovskite-Typie Superconducting 
Single Crystis (D) 


A. Feldman 
E. N. Farabaugh 

R. D. Spal 

R. C. Dobbyn 
M. Kuriyama 

S. Malghan 
C. Ostertag 


J. Ritter 


A. Pechenik 
G. Piermarini 
S. Block 
S. Danforth 


S. Hsu 
J. Perez 

C. Ku 

Y. Zhang 

D. Blackburn (Retired) 

C. Stone 

D. Cranmer 
D. Kauffman 
J. Grudl 

D. Kaiser 
F. Gayle 


166 


A Method for Fabrication of Materials 
from Nano-Sized Particles Using High 

Pressure and Cryogenic Temperatures (I) 

A. Pechenik 
G. Piermarini 

Aluminum Hydroxides as Solid Lubricants 

U.S. Patent 4919829, issued April 24, 1990 

R. Gates 

S. Hsu 

1989 


Ultraviolet Transmitting Glass for 308mm 

Ring Dye Laser (D) 

D. Blackburn 
D. Cranmer 
D. Kauffman 

Buffered Cell for Sintering of High T^. 

Thallium Containing Ceramics (D) 

L. Cook 

Polished Plates of Chemical Vapor 

Deposited Diamond (A) 

A. Feldman 

E. Farabaugh 

Additive Packages Containing High 

Molecular Weight Antioxidants for High 

Temp Lubricant (D) 

S. Hsu 

J. Perez 

C. Ku 

A Novel Fluid to Solubilize High Temperature 
Liquid Lubricant Antioxidants (D) 

J. Perez 

C. Ku 

S. Hsu 

A Process for the Controlled Preparation of a 
Composite of Ultra-Fine Magnetic Particles 
Homogeneously Dispersed in a Dielectric 

Matrix (P) 

J. Ritter 

R. Shull 

Optical Sensor: Molecular Orientation 
and Viscosity of Polymeric Materials (D) 

A. Bur 

R. Lowry 

R. Roth 

Elimination of Twins in Perovskite-Type 
Superconducting Single Crystals (D) 

F. Gayle 

D. Kaiser 

1988 


Stress-Free Sintering of Fiber- 
Reinforced Ceramic Composites (D) 

C. Ostertag 

Electrode Array for Analysis of Particles 
in Slurries (D) 

A. Dragoo 


167 


Quantitative & Qualitative Technique for 
Assessing Stresses During Densification (D) 

Process for the Preparation of Fiber-Reinforced 
Ceramic Matrix Composites (A) 


A Process for the Chemical Synthesis and 
Forming of BiPbSrCaCuO and BiSrCaCuO High 
Temperature Superconductors Materials (D) 

Low Temperature Chemical Synthesis of 
Precursors to BiCaSrCuO^ High 
Temperature Superconductor Powders (D) 

High Pressure Process for Producing 
Transformation Toughened Ceramics (I) 

Superconductor-Polymer Composite (D) 


(D) = INVENTION DISCLOSURE 
(P) = PENDING DECISION BY PATENT OFFICE 
(A) = INVENTION ALLOWED BY PATENT OFFICE 
(I) = PATENT ISSUED 


C. Ostertag 


W. Haller 
U. Deshmukh 


J. Ritter 


J. Ritter 


S. Block 
G. Piermarini 

A. DeReggi 
C. Chiang 
G. David 


168 


CONFERENCES AND WORKSHOPS SPONSORED 


A workshop was organized by S. G. Malghan on electroacoustics for characterization of powders 
and slurries. The workshop addressed recent developments in measurements, theory and 
application of the technique to inorganic and organic systems. 

Silicon Nitride 93: International Conference on Silicon Nitride-Based Ceramics University of 
Stuttgart, Stuttgart, Germany, October 4-6, 1993. E.R. Fuller Member, International Advisory 
Committee 

NISS-NIST Workshop on Statistics and Materials Science: Microstructure - Property - 
Performance Relations, NIST, Gaithersburg, MD, July 26-28, 1993. Co-Organized by Alan 
Karr, NISS, and E. R. Fuller, Jr., NIST 

Workshop on Crystallographic Data Bases, International Union of Crystallographic Congress Co- 
Organizer-Winnie Wong-Ng and Alan D. Mighells, Bejing, China, August 1993. 

Workshop on Characterizing Diamond Films II, A. Feldman, Organizer and Chairman, February 
24, 25 (1993). A NIST sponsored workshop for U.S. companies covering in depth issues 
related to applications of diamond and the need for standards. 

First meeting of the Technical Advisory Meeting Consortium for Commercial Crystal Growth 
organized by G. Long, May 20-21, 1993, at the National Institute of Standards and Technology. 


169 


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STANDARD REFERENCE MATERIALS 


The Division provides science, industries, and government a central course of well characterized 
materials certified for chemical composition of physical or chemical properties. These materials 
are issued with a certification and are used to calibrate instruments, to evaluate analytical 
methods, or to produce scientific data which can be referred to a common base. 


SRM 

DESCRIPTION NUMBER 


Abrasive Wear 1857 

Alumina Elasticity 718 

Alumina Glass Anneal Point 714 

Alumina Glass Anneal Point 715 

Alumina Melting Point 742 

Aluminum Magnetic Susceptibility 763-1 

Aluminum Magnetic Susceptibility 763-2 

Aluminum Magnetic Susceptibility 763-3 

Barium Glass Anneal Point 713 

Borosilicate Glass Composition 93(A) 

Borosilicate Glass Thermal Expansion 731L1 

Borosilicate Glass Thermal Expansion 731L2 

Borosilicate Glass Thermal Expansion 731L3 

Cadmium Vapor Pressure 746 

Calibrated Glass Beads 1003* 

Calibrated Glass Beads 1004a* 

Catalyst Package for Engine Simulation (HID) 1817 

Catalyst Package for Engine Simulation (HID) 1817b 

Catalyst Package for Engine Simulation (HIE) 8500 

Catalyst Package for Engine Simulation (HIE) 8501 

Catalyst Package for Engine Simulation (HIE) 8500a 

Chlorine in Base Oil 1818 

Container Glass Composition 621 

Container Glass Leaching 622 

Container Glass Leaching 623 

Copper Thermal Expansion 736L1 

Fused Silica Thermal Expansion 739L1 

Fused Silica Thermal Expansion 739L2 

Fused Silica Thermal Expansion 739L3 

Glass Analytical Standard 1835 

Glass Dielectric Constant 774 

Glass Electrical Resistance 624 

Glass Fluorescence Source 477 


171 


Glass Liquidus Temperature 

773 

Glass Refractive Index 

1820 

Glass Sand (High Iron) 

81A 

Glass Sand (Low Iron) 

165A 

Glass Stress Optical Coefficient 

708 

Glass Stress Optical Coefficient 

709 

Glass Viscosity Standard Renewal 

717 

Gold Vapor Pressure 

745 

High Boron Glass Viscosity 

717 

Intensity XRD Set 

674 

Lead Barium Glass Composition 

89 

Lead Glass Anneal Point 

712 

Lead-Silica Glass High Temperature Resistivity 

1414 

Lead Glass Viscosity 

711 

Line Profile 

660 

Liquids Refractive Index 

1823 

Low Boron Glass Composition 

92 

MNF 2 Magnetic Susceptibility 

766-1 

Mica X-Ray Diffraction 

675 

Neutral Glass Anneal Point 

716 

Nickel Magnetic Susceptibility 

772 

Opal Glass Composition 

91 

Palladium Magnetic Susceptibility 

765-1 

Palladium Magnetic Susceptibility 

765-2 

Palladium Magnetic Susceptibility 

765-3 

Particle Size Distribution Standard 

1978* 

Platinum Magnetic Susceptibility 

764-1 

Platinum Magnetic Susceptibility 

764-2 

Platinum Magnetic Susceptibility 

764-3 

Refractive Index Glass 

1822 

Respirable Cristobalite 

1879 

Respirable Quartz 

1878 

Ruby EPR Absorption 

2601 

Sapphire Thermal Expansion 

732 

Silicon X-Ray Diffraction 

640(b) 

Silicon Nitride Particle Size 

659 

Silver Vapor Pressure 

748 

Soda Lime Flat Glass Composition 

S620 

Soda Lime Float Composition 

1830 

Soda Lime Float Viscosity 

710 

Soda Lime Sheet Composition 

1831 

Soda-Lime-Silica Glass 

710a 

Sulfur in Oil 

1819 

Toluene 5 ML 

211c 

Total Nitrogen in Oil 

1836 

Tungsten Thermal Expansion 

737 


172 


Total Nitrogen in Oils 1836 

Wear Metals in Oil 1084a 

Wear Metals in Oil 1085a 

X-Ray Diffraction Instrument Sensitivity 1976 

X-Ray Diffraction Intensity 676 

X-Ray Diffraction Intensity Set 674a 

*New in FY-1993 


173 




SELECTED TECHNICAL/PROFESSIONAL COMMITTEE LEADERSHIP 


American Association for the Advancement of Science 
Physics Section 

B, Steiner, Representative of the Optical 
Society of America 

American Association for Crystal Growth 

D. L. Kaiser, Trustee 

American Ceramic Society 

Program and Meetings Committee 
S. Freiman, Chairman 
Glass Division 

Committee on Glass Standards Classification and 
Nomenclature 

M. Cellarosi, Chairman 
Editorial Committee 

S. Wiederhom, Subchairman 
Basic Science Division 

E. Fuller, Vice-Chair 
Editorial Committee 

B. Lawn, Chairman 

ASM International 
Energy Division 

S. Dapkunas, Past Chairman, Division Council Member 
Journal of Materials Engineering and Performance 
S. Dapkunas, Editorial Board 
Journal of Thermal Spray Technology 

S. Dapkunas, Editorial Board 
Washington D.C. Chapter Education Committee 
J. A. Carpenter, Jr., Chairman 

American Society for Engineering Education 
Postdoctoral Review Committee 
A. Feldman, Member 

American Society for Testing and Materials 
C14: Glass and Glass Product 

M. Cellarosi, Chairman 

C14.01: Nomenclature of Glass and Glass Products 
M. Cellarosi, Chairman 


175 


C28. Advanced Ceramics 

G. D. Quinn, Vice-Chairman 
C28.05: Powder Characterization 

S. Malghan, Working Group Chairman 
C28.07: Ceramic Matrix Composites 
D. C. Cranmer, Chairman 
D2: Petroleum Products and Lubricants 
E24.07: Fracture Toughness of Brittle Nanmetallic Materials 
G. D. Quinn, Member 

E29.01: Advanced Ceramics, Organizational Meeting 

M. Cellarosi 
E42: Surface Science 

G. G. Long, Member 

E49: Computerization of Material and Chemical Property Data 

R. G. Munro, E. F. Begley, Members 
FI: 02: Lasers 

A. Feldman, Subcommittee Editor 
G2.2.02: Solid Particle Erosion 

A. Ruff, Task Group Leader 
G2.4.04: Pin-on-Disk 

A. Ruff, Chairman 

G2.12: Computerization in Wear and Erosion, 

A. Ruff, Chairman 

American Society of Mechanical Engineers 

Journal of Tribology 

S. Jahanmir, Associate Editor 
Research Committee on Tribology 

S. Jahanmir, Member 
S. Hsu, Member 

Wear of Materials Conference Steering Committee 
A. Ruff, Member 

Applied Diamond Conference 

A. Feldman, Executive Committee 

Diamond Films and Technology 
Editorial Advisory Board 

A. Feldman, Member 

IEEE Lasers and Electrooptics Society 
Washington-Northern Virginia Chapter 

B. Steiner, Treasurer 


176 


International Center for Diffraction Data 
High Tech Materials Task Group 

W. Wong-Ng, Chairman 

International Energy Agency 

Task II - International Standards 

S. Hsu, Overall Task Leader on Powder Characterization 
Subtask 6 Powder Characterization Subgroup 
S. Malghan, U. S. Task Leader 

International Union of Crystallography (lUCr) 

Commission on Crystallographic Studies at Controlled 
Pressures and Temperatures 

G. Piermarini, Chairman 

Minerals and Metallurgical Processing Journal 
Editorial Board 

S. G. Malghan, Member 

National Materials Advisory Board, National Academy of Sciences 
Committee on Superhard Materials 

A. Feldman, Member 
Committee on High Temperature Coatings 

S. J. Dapkunas, Member 

National Synchrotron Light Source 
Housing Committee 

C. E. Bouldin, Member 
User Executive Committee 

G. G. Long, Member 
EXAFS Special Interest Group 

C. E. Bouldin, Chairman 
Proposal Study Panel 

D. A. Fischer, Chairman 

B. Steiner, Member 
Housekeeping Committee 

J. C. Woicik, Member 


NIST Cold Neutron Research Facility 

G. G. Long, Program Advisory Committee Member 

Optical Society of America 

Archie Mehan Prize Committee 
B. Steiner, member 


177 


Powder and Bulk Engineering Journal 

S. Malghan, Member Editorial Advisory Board 

Powder X-Ray Diffraction Data 

W. Wong-Ng, Consulting Editor 

Society of Photooptical Instrumentation Engineers 
Kingslake Award Committee 

B. Steiner, Past Chairman 

Society of Tribologists and Lubrication Engineers 
Annual Meeting Program Committee 
S. Jahanmir, Member 
Board of Directors 

S. Hsu, Director 

Ceramics and Composite Committee 
S. Jahanmir, Chairman 

Strategic Defense Initiative Organization Technology Applications Office (SDIO/TA) 

Materials and Electronics Panel 

J. A. Carpenter, Jr., Member 

Superconductor Applications Association 

E. Fuller, Jr., Member of Advisory Board 

U. S. Department of Energy, Office of Program Analysis 

Peer-Review Panel for Office of Basic Energy Sciences, "Structural Ceramics and 
Mechanical Behavior of Ceramics: Emphasis on Mechanical Behavior" 

E. Fuller, Jr., Chairman 

Versailles Project on Advanced Materials and Standards (VAMAS) 

Technical Working Area on Ceramics 

G. D. Quinn, U. S. Representative and International 
Chairman 

Technical Working Area on Wear Test Methods 

S. Jahanmir, U. S. Representative and International 
Leader 


178 


INDUSTRIAL AND ACADEMIC INTERACTIONS 


INDUSTRIAL 


ACTIS, Inc. 

An agreement has been signed between NIST and ACTIS, Inc. for a joint research and 
development activity related to comprehensive computerized tribology databases. These 
databases will be evaluated by NIST and marketed by ACTIS, Inc. Other participants in the 
program are DOE, U.S. Army, U.S. Air Force, ASME and STLE. 

Advanced Technology Materials 

Dave Black (NIST) and Dr. Nik Buchan of ATM are studying defects in 6H-SiC wafers. 

Advanced Technology Materials (G. Stauf and P. Van Buskirk) is collaborating with NIST 
(C.-S. Hwang, L. H. Robins, L. D. Rotter, M. D. Vaudin and D. L. Kaiser) to study the 
processing/ structure/property relationships in BaTi 03 films deposited by MOCVD. Films 

grown at ATM under various processing conditions have been characterized at NIST by 
transmission electron microscopy, Raman spectroscopy, x-ray diffraction and electro-optical 
measurements. These specimens are being compared with specimens prepared by NIST (D. 
Kaiser). The specimens are allowing us to develop methods of analyzing the defect structure 
of MOCVD ferroelectric oxide films. 

Specimens of silicon carbide single crystal provided by Advanced Technology Materials have 
been examined for defect content by cathodoluminescence (L. Robins) and X-ray diffraction 
imaging (D. Black). 

As part of the development of the thin film program in the Ceramics Division, several 
collaborations with ATM have been established. In this group, Cheol Seong Hwang is doing 
TEM characterization (planar and cross section) of thin films of BaTi 03 and Bai.xSrxTi 03 on 
single crystal MgO and Pt-based substrates. ATM has agreed to perform electrical 
characterization of thin films made at NIST. (Mark Vaudin) 

AKZO Chemical Co. 

A Cooperative Research and Development Program continues to utilize the NIST technology 
(S. M. Hsu, NIST; T. Marolewski, AKZO) in development of a high temperature liquid 
lubricant for evaluation in low heat rejection engines. 

Allied Signal Corporation 

A joint research program is underway to determine the role of impurities in superconducting 
ceramic powders on limiting the critical current density in the final product. Allied (A. Trivedi) 
is supplying superconducting powders containing various quantities of carbon and other 


179 


impurities. NIST (S. Freiman) is processing these powders and determining critical current 
densities. The work will be published as a joint paper. 

S. G. Malghan is conducting collaborative studies with B. Busovne and J. Pollinger of 
Garrett Ceramic Components (an Allied subsidiary) on the interactions of powder-binder- 
sintering aid in the processing of silicon nitride powders. Garrett intends to utilize the results 
developed at NIST. 

A collaborative effort between NIST (Benjamin Burton) and S. P. Greiner, Allied Signal has 
begun to conduct first principles phase diagram calculations of BCC based ordering in 
Ca-Mg-Li alloys. 

American Superconductor 

The preferred crystallographic orientation of 2223 BSSCO superconductor in Ag-swaged 
"wires" is being investigated using x-ray diffraction techniques (see above report). This is part 
of a project to investigate correlations between the mechanical and electrical properties of the 
BSSCO wire and the texture induced in the wire by the fabrication method. (Mark Vaudin). 

Study the effect of mechanical strain on the electrical properties of silver-sheathed bismuth 
superconductor (BSCCO-2223) tapes. (C.K. Chiang) 

American Xtal Technology, Inc. 

Collaboration in the characterization of gallium arsenide substrates grown with a greatly 
increased degree of regularity by a new commercial process: vertical gradient freeze is being 
carried out by Bruce Steiner, NIST, and Morris Young, President, AXT, Inc. 

Argonne National Laboratory 

Dr. Paul Cowan of ANL and Joe Woicik (NIST) are collaborating on the study of novel 
semiconductor structures and bulk semiconductor impurities. 

AT&T Bell Laboratories 

Dr. Clifford King of Bell Labs and Joe Woicik (NIST) are collaborating on the growth, 
characterization and the consequences of strain in SiGe and other group IV semiconductor 
quantum structures. 

Dr. Jim Patel of Bell Labs and Joe Woicik (NIST) are collaborating on standing-wave x-ray 
studies of Pb on Ge. 

In collaboration with AT&T, lifetime predictions for InP in water and in 50% RH were 
made. The results indicated that optical couplers made with InP would survive the chemical 
environment in which they were placed (G.S. White, L.M. Braun, W.C. Carter, and E.R. 
Fuller, Jr.). 


180 


Battelle Columbus Laboratories 


A joint activity is underway to prepare a wear atlas from selected literature and research 
findings at Battelle Columbus Laboratories, NIST, and the West German Bundesanstalt fur 
Materialprufung. Battelle (W. Glaeser) and NIST (A. W, Ruff) are evaluating publications in 
wear and friction to select authoritative findings that relate wear and friction with materials 
properties and surface morphology. 

Buffalo Medical Center 

Dr. George Detitta of Buffalo Medical Center is the co-investigator of the development of 
a standard reference material for the alignment of single crystal x-ray diffractometers. NIST 
(Winnie Wong-Ng). 

Catalyst Research Corp. 

D. Schrodt (CRC) has obtained laboratory procedures from J. Ritter for designing tests for 
Li-batteries. 

Caterpillar Company 

The Surface Properties Group at NIST is working with Caterpillar Company in several areas. 
F. Kelly is working with S. M. Hsu in the area of advanced lubrication, diesel particulate 
reduction and engine simulations. He is also working with A. W. Ruff to improve the wear 
resistance of tractor under-carriage linkage. S. M. Hsu is also working with K. Bruk, B. 
Hockman, and R. Nevinger on the design of ceramic valve seat inserts. 

As part of the DOE sponsored study on diesel particulates formation, S. M. Hsu and R. S. 
Gates at NIST is working with the CRC study group to jointly evaluate the effects of fuel type, 
engine design and service duty on diesel particulate formation. The study group consists of the 
major oil companies, engine manufacturers and component suppliers. Various particulate 
samples were received from the study group who is currently conducting various engine tests 
and full-scale field tests of different engine and fuel combinations. 

Crystacomm 

Characterization of defects in 7.62 mm (3 inch) diameter InP wafers is carried out in a 
collaboration between George Antypas of Crystacomm and Dave Black (NIST). 

Crystallume 

Dr. Mary Anne Plano of Crystallume is collaborating with Dave Black (NIST) in the 
characterization of strain and defect generation in thick CVD-grown homoepitaxial diamond 
films. 


181 


Cu mmi ns Engine Company 

S. M. Hsu is working with J. Wang, M. Naylor, and T. Gallant of Cummins Engine on the 
lubrication of new materials, evaluation of chemistries and development of advanced lubrication 
concepts for future engines. In conjunction with Akzo Chemicals Company under a DOE 
contract, new chemistries are being developed and these chemistries are being evaluated in 
prototype engines by Cummins. 

Deere and Company 

A collaborative research project is in progress between Deere and Company (P. A. Swanson) 
and NIST (L. K. Ives) to determine the influence of crystal structure on galling resistance of 
nitrided 4140 steel. 

Delco Products (Division of General Motors) 

Dr. V. Ananthanarayanan, Delco Products, has collaborated with S. Malghan in developing 
test procedures for evaluating the dispersion of strontium ferrite in aqueous environment. Two 
scientists spent two months at NIST to conduct experimental research. Based on these results, 
a development program is being carried out at the Delco Products production facility. 

Deltronic Crystal Industries 

Collaboration in the characterization of barium titanate and strontium barium niobate and 
correlation of the results with specific changes in crystal growth procedures are being carried 
out by Bruce Steiner, NIST, John martin and Robert Uhrin, Deltronic Crystal Industries, as well 
as by Mark Cronin-Golomb and Gerard Fogarty, Tufts University. 

DOW Chemical Company 

Gary Mitchell and Ben Dekoven of the Dow Chemical Company have begun a research 
collaboration with Dan Fischer (NIST) to study polymer surfaces and metal polymer interfaces 
using ultra soft x-ray absorption spectroscopy. The concentrations and orientations of functional 
groups have been characterized at and near the surface for a series of model polymeric 
materials. The materials studied include poly (acrylic acid), poly (butyl methacrylate), 
polystyrene, polycarbonate, poly(ethylene terephthalate), and model acrylic coatings. 

Eagle-Picher 

A collaboration has been initiated between Eagle-Picher Research Laboratory (G. Cantwell) 
and NIST (L. Robins and D. Black) to characterize defects and dopant impurities in zinc 
selenide single crystals. These crystals are being developed as substrates for laser/LED devices. 
Eagle-Picher currently has an ATP grant for this work. 


182 


EG&G Energy Systems 

Collaboration in diffraction imaging of irregularities in terrestrial and space-grown mercuric 
iodide crystals, used or high energy radiation detectors, is underway by Bruce Steiner, NIST, 
and Lxxlewijk van de Berg, EG&G. 

Elxxon Research and Engineering 

George Meitzner and John Sinfelt of Exxon are collaborating with Dan Fischer (NIST) to 
study the electronic structure of adsorbed carbon monoxide and hydrocarbons on platinum- 
supported catalysts using near-edge spectroscopy above the carbon K-edge. 

Eaton 

S. M, Hsu is working with J. Edler and M. Leydet of Eaton to jointly evaluate ceramic 
material for gas-fuelled co-generation engines. NIST conducts wear tests and mechanistic 
studies and provides feedback to Eaton. This is part of the study sponsored by GRI. 

Eastman Kodak Company 

D. T. Smith (NIST) has been collaborating informally with Ravi Sharma of Kodak’s Polymer 
Research Laboratory to study the surface charging properties of thin insulating films of potential 
industrial interest in Kodak. 

E. I. DuPont de Nemours & Co. 

NIST (L. P. Cook) is collaborating with DuPont on their ATP thallium high T^, research on 
problems in processing and characterization, especially as related to the phase equilibria of these 
materials and their interaction with ferroelectrics in thin film devices. 

DuPont (D, Roach) has provided alumina and alumina-zirconia fibers to C. Ostertag for 
incorporation into ceramic, ceramic-metal, and glass matrix composites. 

C. Torardi of AT&T Bell Laboratories has assisted R. Roth and C. Rawn of NIST in 
determining crystal structures of calcium bismuth oxides that occur in the Bi-Sr-Ca-Cu oxide 
system. This system is currently of major interest as it contains important high-temperature 
superconducting materials. 

E^ge Technology Inc. 

Artificial diamonds to be used as machine tools were supplied to D. R. Black. Topographic 
examination of these crystals was correlated to optically observed defects for quality control. 

Ford Motor Company 

Ford Motor Company (K. Carduner and M. Rokosz) have been active in the application of 


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NMR spectroscopy and imaging to characterize ceramic materials. Collaborative effort with P. 
S. Wang involves data exchange of Si -29 CP/M AS NMR for phase composition determination 
of silicon nitride and carbide powders. In the future, we plan to exchange imaging capabilities. 

Gas Research Institute and Center for Advanced Materials, Pennsylvania State University 

The Structural Ceramics Database project was funded in part by the Gas Research Institute 
through the Center for Advanced Materials at Pennsylvania State University, as an important 
step towards the use of advanced ceramics in heat exchangers and gas-fueled engines. 

General Electric 

NIST has been collaborating with General Electric (W. Banholzer) to evaluate a 
single-crystal diamond wafer by spatially resolved CL spectroscopy (L. Robins) and X-ray 
diffraction imaging (D. Black). 

GE Corporate Research Center 

Dr. Donna Hurley of GE and Dave Black (NIST) are performing defect characterization on 
isotopically-controlled man-made diamond crystals. They are studying the relationship of defects 
to ultrasonic measurements on these materials. 

Geophysical Laboratory, Carnegie Institute of Washington, DC 

NIST (Benjamin Burton) has been working with R. E. Cohen, The Geophysical Laboratory, 
Carnegie Institute of Washington, D.C. on a first principles study of cation ordering in the 
relaxor ferroelectric system Pb(Sci^Tai/2)03-PbTi03. 

Grumman Corporate Research 

Dave Black (NIST), Hal Burdette (NIST) and G. Long (NIST) are collaborating with Dr. 
Dave Larson of Grumman on the characterization of earth-grown and space-grown CdZnTe 
crystals. 

GTE Laboratories, Inc. 

GTE (J. Baldoni) has provided whisker-reinforced and whisker-free silicon nitrides to S. 
Wiederhom and D. Cranmer for evaluation of creep and creep rupture, and changes in 
microstructure as a result of creep. 

Collaboration in diffraction imaging on irregularities in gallium arsenide. (Bruce Steiner, 
NIST, and David Matthiesen and Brian Ditchek, GTE) 

Hughes Research Laboratories 

Collaboration in the crystal growth of barium titanate. (Bruce Steiner, NIST, Mark Cronin- 


184 


Golomb and Gerard Fogarty, Tufts University, and Barry Wechsler, Hughes) 

IBM, Almaden Research Laboratory 

Interactions between NIST (W. Wong-Ng) and IBM (T.C. Huang) focused on the 
investigation of the X-ray property of PZT and BaTi03 films which were prepared at NIST 
using the laser deposition technique. 

Illinois Superconductor 

NIST (John Blendell) has collaborated with ISC in support of their ATP project. This has 
involved determining the reaction path form forming YBa2Cu306+x different atmospheres. 

International Centre for Diffraction Data (ICDD) 

As the Chairperson (W. Wong-Ng, NIST) of the Ceramics Subcommittee, efforts have been 
initiated to organize the inorganic materials of the X-ray Powder Diffraction File (PDF) into 
minifiles according to their functions, properties or structure. W. Wong-Ng also serves as a 
consulting editor for the PDF. 

ITEK Optical Systems 

A joint research program with ITEK Optical Systems was undertaken to assess the reliability 
of dual-pane glass aircraft windows. ITEK provided as-polished glass specimens from 

which both strength and crack growth properties were evaluated at NIST. These data were 
combined with a finite-element stress analysis by ITEK and a fracture-mechanics and statistically 
based methodology, developed at NIST, to determine pane lifetimes under various conditions 
at a 90 % survival probability to a 95 % confidence level. 

Johns Hopkins University Applied Physics Laboratory (JHUAPL) 

Dennis Wickenden of the JHUAPL is collaborating with NIST (L. Robins) in a project for 
characterizing defects and dopant impurities in thin films of gallium nitride and Al^^Ga^.^N by 
spatially resolved CL. These materials are being developed for short-wavelength laser and LED 
devices. The specimens, grown at JHUAPL, are being characterized at NIST. 

Kennemetal Inc. 

S. M. Hsu is cooperating with the machining group at Kennemetal (R. F. Upholster) on 
jointly developing chemically assisted technology of ceramics. Samples were exchanged and 
many discussions were held. Some of the more promising chemistries may be tested at their 
facility. Kennemetal is the largest US manufacturer of ceramic wear inserts. 

Kobe Steel Electronic Research Center 

Characterization of defects in natural diamond substrates and in doped homoepitaxial 


185 


diamond films is currently the subject of a collaboration between Dave Black (NIST) and Dr. 
Brad Fox of Kobe Steel. 

Lawrence Livermore Laboratories 

As part of a study with Pat Johnson of Lawrence Livermore Laboratories, of the cohesive 
strength of grain boundaries in Ni 3 Al as a function of grain boundary misorientation and 
symmetry, alloy stoichiometry and boron concentration, grain orientations in test bars have been 
measured at NIST (Mark Vaudin) prior to mechanical testing. 

Collaboration on the crystal growth of potassium dihydrogen phosphate for high power lasers 
is being carried out by Bruce Steiner, NIST, and James DeYoreo and Chris Ebbers, LLL. 

Matec Applied Sciences 

This cooperative research is related to the development of electrokinetic sonic amplitude 
measurement for dispersion of powders in dense slurries. Research at NIST under the direction 
of S. Malghan will be utilizing hardware and software developed by Matec Applied Sciences for 
on-line measurement of dispersion. 

Morgan-Matroc 

In collaboration with Morgan-Matroc, damage in PZT-8 due to cyclic loading has been 
investigated. Morgan-Matroc supplied the specimens and information regarding their 
piezoelectric properties and NIST (G.S. White, M. Hill, C. Seong) provided information on the 
mechanical response to loading. 

Nanophase Technology Inc. 

Dr. John Parker of Nanophase Technology is collaborating with G. Long (NIST) and S. 
Krueger (NIST) in the investigation of microstructure evolution during densification of 
nanophase ceramics. 

NASA Consortium for Commercial Development 

Cooperative research is aimed at understanding fundamentals of zeolite nucleation, growth 
of CdTe single crystals and strain development during growth of GaAs. G. G. Long, D. R. 
Black, H. E. Burdette, and S. Krueger (Reactor Radiation Division) are working with E. Coker, 
H. Wiedemeier and D. Larson on this research. 

National Institute of Statistical Sciences (NISS) 

A collaboration between NISS, the Ceramics Division, and the Statistical Engineering 
Division has explored cross-disciplinary applications of statistics and statistical concepts to 
materials science and the formulation of a research agenda leading to high-impact advances. An 
outgrowth of this collaboration was a workshop. Statistics and Materials Science: 


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Microstructure - Property - Performance Relations, which was held at NIST on July 26-28, 
1993. It was attended by fifty-two participants from industry, government laboratories and 
universities. The principal findings were (i) crucial problems in materials science are inherently 
statistical, so that statistics is an enabling technology for progress in materials science; and (ii) 
fulfilling industrial needs and goals demands cross-disciplinary collaboration between materials 
and statistical scientists. More detailed findings and recommendations are contained in a report. 
Statistics and Materials Science: Report of a Workshop, by Alan F. Karr (Technical Report #14, 
National Institute of Statistical Sciences, Research Triangle Park, NC, January 1994). 

National Renewable Energy Laboratory 

Carbon films deposited by solar methods at the National Renewable Energy Laboratory (R. Pitts) 
were examined for diamond content by Raman spectroscopy (L. Robins). 

National Research Institute for Metals (Japan) 

R. G. Munro and J. Rumble (SRD) are collaborating with S. Nishijima, Y. Asada and K. 
Hoshimoto on development of a comprehensive materials property data base for High T^, 
Superconductors. 

Naval Research Laboratory 

S. Lawrence and B. Bender (NRL) are collaborating with J. Wallace on the thermochemical 
treatment of polymer-derived SiC fibers and the degradation mechcmisms of these fibers during 
high temperature heat treatments. A joint publication is planned. 

NIST (Mike Hill and Grady White) is collaborating with Dr. Sadananda at the Naval 
Research Laboratory investigating cyclic fatigue of piezoelectric material. Mechanical properties 
are investigated at NIST and TEM will be done at NRL. 

Collaboration in a study of the role of crystalline irregularities on the performance on quartgz 
crystal resonators is being carried out by Bruce Steiner, NIST, Michael Bell, NRL, and Robert 
Whitlock, NRL. 

Naval Surface Weapon Center (NSWC) 

NIST (Winnie Wong-Ng) and I. Talmy of NSWC are in collaborating in the study of the 
phase diagram of barium and strontium feldspar solid solutions, (Ba,Sr)Al2Si20g. Revised phase 
diagrams and standard X-ray powder diffraction patterns were obtained based on these 
collaborations. 

Tom Russell, Naval Surface Warfare Center (NSWC) has been working with NIST (Gasper 
J. Piermarini) collaborating on the study of energetic materials and Buckminsterfullerenes at high 
pressure. 

A joint research project with D. R. Black has been developed to supply and characterize 


187 


copper single crystal substrates for use as substrates for heteroepitaxial growth of diamond films. 
Norton Company 

In one collaborative project V. Pujari and C. Willkens of Norton Company, and S, Malghan 
of NIST are studying the characteristics of agitation milled silicon nitride powders in aqueous 
environment. Norton Company has provided silicon nitride powder samples. Based on the 
results of first stage of collaboration, a second stage of research was initiated with an intent to 
compare the performance of agitation ball milling to large-scale processing by conventional 
methods. 

Thermal conductivity measurements are important for characterizing diamond films. 
Interaction with Norton (K. Grey) involved learning to use the NIST (A. Feldman and H.P.R. 
Frederikse) photothermal radiometry facility for the purpose of setting up such a facility at 
Norton. We plan to collaborate in the analysis of the data generated at Norton. 

Dr. Vimal Pujari is cooperating with S. M. Hsu on the effects of machining on tensile 
strength of silicon nitrides. Tensile bars were received from Norton and were subjected to 
chemical assisted machining. These bars are being tested. 

Norton/TRW (R. Yeckley) has provided a Y 203 -containing silicon nitride to S. Wiederhom 
and D. Cranmer for evaluation of creep and creep rupture, and changes in microstructure as a 
result of creep. 

S. M. Hsu is working with Brian McEntire at Norton-TRW to jointly evaluate ceramic 
materials for valve seat insert application. The program is a joint program with the Gas 
Research Institute (GRI), Caterpillar, and Southwest Research Institute (SWRI). A Full-scale 
engine test is being conducted at SWRI to evaluate different materials for the valve seat inserts 
in a gas-fuelled Caterpillar 3500 series engine. 

OPTEX Inc 

NIST, (Winnie Wong-Ng) in collaboration with an ATP funded company OPTEX (of 
Rockville, Maryland), conducted X-ray diffraction studies of undoped and doped optical SrS thin 
films (for optical data storage ) to characterize these films in order to correlate processing 
parameters. 

Research Triangle Institute 

A joint research project was developed with D. R. Black to study the microstructure of 
diamond substrates to be used for homoepitaxial growth of diamond films by chemical vapor 
deposition. 

Rockwell International 

A collaboration between NIST (A. Feldman) and Rockwell International (S. Holly) to 


188 


organize the Diamond Optics IV conference sponsored by the Society of Photo-Optical 
Instrumentation Engineers (SPIE). 

Russian Academy of Sciences Institute of Solid State Physics 

A collaborative program to elucidate the nature of disorder in oxide crystals has been 
initiated by Bruce Steiner, NIST, and Veniamin Shekhtman, Institute for Solid State Physics. 

Russian Research Center for Standardization, Information and Certification of Materials 

R. G. Munro and J. R. Rumble (SRD) are collaborating with A. D. Koslov to establish 
evaluated property data for selected oxide and carbide structural ceramics worldwide. 

Rotem, Inc. 

Collaboration in the characterization of sapphire substrates. (Bruce Steiner and Uri Laor, 
NIST, and Shlomo Biderman and Yezekiel Einav, Rotem) 

Russian Academy of Science 

Cooperative activities under the NIST-Russian Academy of Science Agreement have 
continued in the areas of tribology and materials science. Current emphasis is on a joint US- 
USSR book on tribology (A. W. Ruff and S. Jahanmir). Future benefits to NIST and the 
Division include exchange of tribology data, exchange of computer software for surface analysis, 
and future exchange of technical staff. 

A collaborative program between the Russian Academy of Sciences and NIST Ceramics (D. 
Kaiser) and Metallurgy Divisions is underway to map flux distributions in high temperature 
superconductors by a magneto-optical technique. 

Sanders Corporation 

Collaboration on the crystal growth of barium titanate single crystals (Bruce Steiner, NIST, 
Mark Cronin-Golomb and Gerard Fogarty, Tufts University, and Tom Pollack, Sanders) 

Schmidt Instruments 

A collaborative research project was initiated with D. R. Black to grow heteroepitaxial 
diamond films and characterize their crystal perfection. 

Southwest Research Institute 

Dr. Richard Page of SRI is collaborating with S. Kruger (NIST) and G. Long (NIST) on the 
microstructure evolution of alumina during densification. 


189 


Smithsonian Institute 


NIST (Winnie Wong-Ng) in collaboration with Y.S. Dai of the Smithsonian Institute has 
studied the twin structure of Ba-Ti-Zn-(F, 0 ) as well as the characterization of Na-doped 
Ba2YCu305^.^ superconductors. 

Trans-Tech, Inc. 

NIST (C. Lindsay and R. Roth) and Trans-Tech, Inc. (T. Negas), collaborate on microwave 
dielectric materials processing, phase equilibria and crystal structure data for these materials. 
Measurement of electrical properties is a joint effort between NIST and Trans-Tech. 

Ube Industries, Japan 

Ube Industries (T. Yamada) has collaborated with S. Malghan by providing powder samples 
for studying the high energy agitation milling of silicon nitride powders. The specific interest 
lies in the development of an understanding of morphological and surface chemical changes 
taking place to the milled powders. 

U. S. Army Research Laboratory 

NIST (Lawrence Cook, Mark Vaudin, and C. K. Chiang) has collaborated with the U. S. 
Army Research Laboratory on measurements of ferroelectric and dielectric properties of BaTi03, 
PZT and PbTi03 thin films, prepared by pulsed laser deposition. 

U.S. Bureau of Mines at Albany 

The goal of this collaboration between N. Gokcen of U.S. Bureau of Mines and W. Wong- 
Ng of NIST is to investigate the effect of high oxygen pressure on the structural and 
superconducting properties of the superconductors, Ba 2 RCu 306 +x R=neodymium and yttrium, 
and (Ca,Sr)Cu02 . 

Xsirius, Inc. 

Collaboration in the characterization of sapphire substrates for high temperature 
superconducting devices. (Bruce Steiner and Uri Laor, NIST, and William Graham, President, 
Xsirius, Inc.) 


ACADEMIA 


Alabama A&M University 

Collaboration on the crystal growth of triglycine sulfate in space and on the ground (Bruce 
Steiner, NIST, and Ravindra Lai and Ashok Batra, Alabama A&M) 


190 


University of Colorado/Joint Institute for Laboratory Astrophysics 

Collaboration in the surface treatment and characterization of barium titanate single crystals 
and their photorefractive interactions with laser beams is underway by Bruce Steiner, NIST, 
Mark Cronin-Golomb and Gerard Fogarty, Tufts University, and Dana Anderson, University 
of Colorado/Joint Institute for Laboratory Astrophysics. 

Auburn University 

A collaboration between NIST (A. Feldman) and Auburn University (Y. Tzeng) to organize 
the First International Conference on the Applications of Diamond Films and Related Materials, 
ADC ’91. 

Boston University 

L. Robins has collaborated with Boston University (S. Jin) to examine by cathodoluminescence 
spectroscopy the defect content of thin boron-doped diamond films grown by the electron 
cyclotron resonance microwave plasma assisted CVD method. The CL results were correlated 
with electrical and ESR measurements. This is part of a manuscript submitted for publication. 

Clemson University 

B. I. Lee is collaborating with S. Malghcui on surface chemical characteristics of silicon 
nitride powders in aqueous environment in the presence of organic surface active agents. 

Cleveland State University 

Professor Stephen Duffy is collaborating with T.-J. Chuang in the area of continuum damage 
mechanics on continuous fiber reinforced ceramic composites for high-temperature applications. 

Columbia University 

P. Somasundaran has been collaborating with S. Malghan on a research project to study basic 
parameters affecting the preparation of dense suspensions of silicon nitride powder containing 
sintering aids. 

Dartmouth College 

Real-time imaging of dislocation motion in pure and doped ice is currently underway between 
Dave Black (NIST) and Dr. Fuping Liu of Dartmouth. 

Drexel University 

This is a joint program between Drexel University (M. Barsoum) and NIST (D. Cranmer) 
to investigate and control the fracture behavior of ceramic and glass matrix composites. 


191 


East China University of Chemical Technology 

This is a joint effort to use finite-element techniques to analyze creep behavior of ceramic 
c-rings at elevated temperatures. ECUCT (D. Wu and Z-D Wang) is developing the finite 
element model for C-rings and a computational algorithm for creep and NIST (T.-J. Chuang) 
is providing a theoretical framework and experimental data to support the program. 

Professor D. Wu and Dr. Z Wang are collaborating with T.-J. Chuang in the area of finite 
element method and numerical analysis for mechanical evaluation of advanced ceramics. 

Florida State University 

A collaborative study between Florida State University (J. Schwartz) and NIST (D. Kaiser, 
F. Gayle) is underway to correlate microstructure with microscopic flux flow during 
magnetization of Bi2Sr2CaCu20g+x superconducting tapes by means of a magneto-optical 
imaging technique. 

Harvard University 

Professor Gene Golovchenko of Harvard and Joe Woicik (NIST) are collaborating on 
standing-wave x ray and scanning tunneling microscopy studies of Bi on Si(lll). 

Howard University 

Prof. George Walrafen, Chemistry Dept., Howard University and NIST, Gasper Piermarini. 
Long standing collaboration on study of materials at high pressures. Currently studying liquid 
state of H2O in the superpressed state at elevated temperatures and pressures. 

Iowa State University 

Characterization of defects in icosahedral AlPdMn is being performed by Dave Black 
(NIST), Dr. Alan Goldman and Stefan Kycia of Iowa State. 

Johns Hopkins University 

Professor J. Kruger and L. Krebs are collaborating with G. G. Long, NIST, and C. 
Majkrazak (Reactor Division, NIST) on in situ polarized neutron reflectometry studies of the 
nature and structure of passive films. 

Dan Shechtman of Johns Hopkins is collaborating with NIST (A. Feldman and E. Farabaugh) 
in the high resolution TEM anzdysis of CVD diamond nucleation and growth. 

Illinois Institute of Technology 

P. R. Jemian is collaborating with G. G. Long and S. Krueger (Reactor Division) on neutron 
and x-ray scattering by novel materials. 


192 


Lehigh University 

This is a collaboration to determine the effect of microstructure on the fracture resistance of 
monolithic ceramic materials. The materials under study have been manufactured at Lehigh 
University (H. Chan, M. Harmer) and are being characterized at NIST (B. Lawn). 

Massachusetts Institute of Technology 

Collaboration in diffraction imaging on the crystal growth of barium titanate (Bruce Steiner, 
NIST, and Mark Garrett, MIT) 

Interaction with R. Hallock and W. Rhine of MIT (W. Wong-Ng of NIST) was conducted 
to characterize the BaTi03 precursor material, BaTi(0)(C204)2 *51120 by x-ray diffraction 
method. 

National Tsing Hua University 

Professor S. Lee and Dr. J.-L. Chu are collaborating with T.-J. Chuang, NIST on creep life 
prediction. 

Northwestern University 

S. M. Hsu is collaborating with Prof. M. Fine on optimization of ceramic wear resistance 
by introducing compressive stress into the surface and interfaces. A previous study by Prof. 
Fine has demonstrated that introduction of a compressive surface layer increased the wear 
resistance of ceramic material significantly. 

Professor Katherine T. Faber and several students at Northwestern University are 
collaborating with E. R. Fuller, Jr. on a research project focused on the understanding and 
control of materials which undergo process-zone phenomena around propagating cracks. These 
phenomena occur in materials which possess large thermal expansion anisotropy, or for multi- 
phase materials, thermal expansion mismatch, or in materials which undergo crystallographic, 
martensitic phase transformations. In all instances, lack of microstructural control, such as 
exaggerated grain growth, causes the phenomenon to occur spontaneously. 

Profesor D.L. Johnson is collaborating with G. Long (NIST) and A. Allen (U. Md.) on 
microwave-assisted reaction-bonded silicon nitride. 

Oklahoma State University 

Collaborative research between OSU and NIST (R. Powell and D. Cranmer) is being 
conducted to investigate the properties of permanent, laser-induced refractive index gratings 
based on Eu-containing glasses. The end result of this effort will be a device for processing 
optical signals. 


193 


Pennsylvania State University 

S. M. Hsu is collaborating with Profs. Duda, Klaus, Philips, and Christen on a variety of 
projects. Duda and Klaus are working on lubrication, development of lubricants for alternative 
fuels and ceramic lubrication. Philips is working on synthesis of nano-sized particles of ceramic 
materials using a microwave assisted plasma reactor. Christen is working on computer 
simulation of grain growth. 

Purdue University 

NIST (Mark Vaudin) has interacted with Prof. K. Bowman on the measurement of texture 
in tape-cast AI2O3 samples. Bowman has determined x-ray pole figures for the same samples 
on which we have measured texture by BEKP analysis and by x-ray powder diffraction. 

Rensselaer Polytechnic Institute 

Collaboration on the diffraction imaging of semiconducting multilayers in order to determine 
the genesis and influence of disorder on photonic device performance is being carried out by 
Bruce Steiner, NIST, Heribert Wiedemeier, RPI, and Krishna Rajan, RPI. 

Rutgers University 

S. C. Danforth (Rutgers) has provided S. Malghan (NIST) with nano-sized Si3N4 powder. 
The powder is processed at NIST using cryogenic compaction. 

S. M. Hsu is collaborating with Profs. Niesz and Wachtman on microstructural design for 
wear resistance on silicon nitrides. Variation of grain size, shape and interface strength are 
being examined. The materials processed are evaluated both at NIST and at Rutgers. 

H. Han is collaborating with G. G. Long (NIST) and S. Krueger (NiST/Radiation Reactor 
Division), A. Allen and H. Kerch in the study of nanophase powders and processing. 

NIST (Linda Braun, Grady White, and Gasper Piermarini) has begun a collaborative effort 
with Roger Cannon to investigate toughening mechanisms in ceramics via micro-focus Raman 
spectroscopy measurements. 

Grady White of NIST has been interacting with Steve Garofalini at Rutgers University 
investigating environmental effects on crack growth in silica. 

Seoul National University 

NIST (John E. Blendell) is collaborating with Doh-Yeon Kim of Seoul National University, 
Korea on the wetting of grain boundaries in AI2O3. 


194 


Stanford University 

Professor William Spicer of Stanford is collaborating with Joe Woicik in the use of x-ray 
standing-wave studies, surface-EXAFS, and ultraviolet photoemission of metal/ semiconductor 
interfaces and semiconductor surfaces. 

State University of New York at Stony Brook 

Collaboration on the observation of four wave mixing and related optical phenomena in non 
linear optical crystals (Bruce Steiner, NIST, and Mark Cronin-Golomb and Gerard Fogarty, 
Tufts) 

Tufts University 

Collaboration on the observation of four wave mixing and related optical phenomena in non 
linear optical crystals (Bruce Steiner, NIST, and Mark Cronin-Golomb and Gerard Fogarty, 
Tufts) 

University of California at Berkeley 

Professor Andrea M. Glaeser is collaborating with T.J. Chuang, NIST, on microdesign of 
interfacial defects for creep crack growth experiments. 

University of California at Santa Barbara 

Joint experiments between University of California (J. N. Israelachvili, P. McGuiggan) and 
NIST (R. Horn and D. Smith) are being conducted to investigate frictional properties of silica 
surfaces under dry conditions and with a variety of thin (< 10 nm) intervening liquid films. 
University of Colorado/Joint Institute for Laboratory Astrophysics 

Collaboration in the surface treatment of barium titanate single crystals (Bruce Steiner, NIST, 
Mark Cronin-Golomb and Gerard Fogarty, Tufts University, and Dana Anderson, U. Col.) 

University of Dayton Research Institute 

Using UDRI’s x-ray photoelectron spectrometer (XPS) and Auger electron spectrometer 
(AES), T. Wittberg, UDRI, is conducting studies on surface structures and reactivities with P. 
S. Wang, NIST. A variety of powders and ceramic materials have been investigated and the 
results have been published. 

University of Florida 

B. Moudgil is studying the characterization techniques and structure of floes in dense slurries 
with G. G. Long and S. G. Malghan. Primary emphasis is placed on interfacial, rheological, 
and scattering (neutron and x-ray) techniques. 


195 


University of Grenoble 

NIST (Benjamin P, Burton) has been working with Prof. A. Pasturel, CNRS/University of 
Grenoble, to make first principles phase diagram calculations of BCC based ordering in Ni-Al- 
Ti and Fe-Be alloys. 

University of Illinois 

Prof. S. Danyluk is collaborating with S. M. Hsu on wear mechanisms of ceramic materials 
and the definition of surface quality in terms of strength as a result of machining damage. 

University of Illinois and Rockwell Science Center 

NIST (Grady White and Steve Freiman) has written a joint proposal with Dwight Viehland 
of the University of Illinois and Ratnaker Neurgaonkar of Rockwell Science Center to investigate 
mechanical and electronic properties of piezoelectric and electrostrictive materials for use in 
smart material applications. 

University of Maryland 

A collaborative study between the University of Maryland (A. Roytburd) and NIST (D. 
Kaiser, F. Gayle) involves theoretical aspects of the effect of twin boundary and grain boundary 
defects on flux flow during magnetization of high temperature superconductors. 

L. Chang (U. Md.) is collaborating with E. Begley and C. Lindsay (NIST) on appropriate 
instructional techniques for a computer-based tutorial in phase diagram interpretation. U. Md. 
will also provide a testbed of students for evaluation of the tutorial. 

Bai-Hao Chen and Bryan Eichgom of UM are collaborators in the structural investigation 
of possible new superconductor related single crystal materials (with W. Wong-Ng, NIST). New 
members of a Ruddlesten-Popper series of compounds Ban+iA^S3jj+i, where A = Hf and Zr 
have been successfully studied. 

Investigators at NIST (Mike Hill, Grady White, and Steve Freiman) are collaborating with 
Isabelle Lloyd investigating mechanical and electrical effects of cyclic loading of PZT. Mike 
Hill is using the research as partial fulfillment of requirements for a PhD in materials science. 

University of Michigan 

John Gland (University of Michigan) and Dan Fischer (NIST) are collaborating on the study 
of hydrogenolysis of aniline on the Pt(lll) surface. 

University of Michigan 

J. Schwank is carrying out specialized characterization of conductive ceramic powders by 
ESCA and Auger spectroscopy in collaboration with J. Ritter, NIST. These powders are 


196 


synthesized at NIST for NASA. 

University of Pennsylvania 

P. Davies of the University of Pennsylvania has been working with NIST (Robert S. Roth, 
Claudia J. Rawn, and Curtis G. Lindsay) on high-resolution transmission electron microscopic 
images of microwave dielectric materials. 

University of Virginia 

NIST (Mark D. Vaudin) and John Wert, University of Virginia, have been investigating the 
orientation of grains adjacent to a fracture surface in a brittle intermetallic (Al3Ti) as part of a 
project to test a model of fracture in these materials. 

University of Washington 

Professor Larry Sorenson (U.of W.) and Joe Woicik (NIST) are using diffraction anomalous 
fine structure measurements to study strained semiconductor layers and 123 semiconductors. 

Collaboration on strain relaxation in III-V photonic crystals is being carried out by Bruce 
Steiner, Joseph Woicik, and Joseph Pellegrino, NIST, and Larry Sorenson, University of 
Washington. 

University of Western Ontario 

A collaboration was initiated this year between H. H. Schloessin and R. A. Secco of the 
Geophysics Department and R. D. Spal, NIST, involving the study of geological samples by 
means of x-ray diffraction topography and the asymmetric Bragg diffraction microscope. 

University of Wisconsin 

V. Hackley, Water Chemistry Program, Civil Eng. Department at the University of 
Wisconsin is conducting joint research with NIST on the electrokinetic sonic amplitude (ESA) 
measurement technique for dispersion of powders. The results of this research are to be used 
for the application of ESA technique for on-line monitoring of ceramic slurry properties. 

A joint activity is underway between the University of Wisconsin (S. Babcock, X. Cai, D. 
Larbalestier) and NIST (D. Kaiser) to characterize the microstructural, magnetic and electrical 
transport properties of single crystals and bicrystals of superconducting YBa2Cu305+x. 

University of Washington 

David Castner, Buddy Ratner, and Dan Fischer (NIST) have used the polarization 
dependence of carbon and fluorine NEXAFS to understand the orientation of fluorocarbon 
groups and proteins on polymeric biomaterials used in medical implants. The orientation of 
surface species was shown to differ for various polymeric preparation techniques which also 


197 


correlated with protein film growth, an important consideration in bio compatibility of these 

materials. 


198 


FACILITIES 





FACILITIES 


POWDER CHARACTERIZATION AND PROCESSING 


High Temperature X-ray Diffraction - J. P. Cline 

The x-ray diffraction facility at NIST consists of a high temperature machine of theta-two theta 
geometry equipped with an incident beam monochrometer and a position sensitive proportional 
counter. The incident beam monochrometer removes the Kq! 2 radiation and results in diffraction 
profiles that are more sensitive to effects of sample character. The position sensitive detector 
allows for data collection at a rate two orders of magnitude faster than conventional detectors. 
The furnace is an enclosed high vacuum chamber capable of reaching 3000K, it is equipped with 
a mass flow controller for atmospheric control. This equipment is used for the study of high 
temperature phase equilibria, high temperature reaction kinetics, sintering of monolithic 
ceramics, and strain development during sintering of ceramic composites. Additional equipment 
consists of four automated and updated Philips diffractometers which are used for certification 
of standard reference materials (SRMs), studies on the effects of microabsorption and extinction, 
and the development of the Rietveld method for a conventional, sealed tube. 

X-ray diffraction equipment. 

Electroldnetic Measurements - V. A. Hackley and S. G. Malghan 

The Matec ESA-8000 system has the unique capability for measuring colloidal properties in 
dense slurries. The analytical capabilities of the ESA system include performance in the 
following modes: potentiometric titration, conductometric titration, time-series titration, and 
concentration series titration. In the selected mode, the equipment can monitor: electrokinetic 
sonic amplitude, zeta-potential, electrophoretic mobility, electrical conductivity, isoelectric point, 
surface charge density, and phase angle of the material with the specified experimental 
conditions. 

Slurry Rheology - S. G. Malghan and V. A. Hackley 

The RTI rheometer allows for viscosity as well as rheology characterization of ceramic slurries. 
Rheological measurements are more informative and flexible with respect to the various slurry 
properties: Newtonian, pseudoplastic, plastic, dilatant, and thixotropic. The modeling of these 
rheological properties as a function of sample treatment, surface chemical properties is 
paramount in developing and improving the slurry processing technology. 

Physical Properties Characterization Laboratory - L. Lum, D. Minor, P. Pei and S. Malghan 

The physical properties characterization laboratory is equipped with state-of-the-art techniques 
for the measurement of particle size distribution, specific surface area, specific gravity, tap 
density, and porosity. The particle size distribution is measured by three techniques — gravity 
sedimentation by Sedigraph, centrifugal sedimentation by Joyce-Loeble, laser diffraction by 
Horiba LA -900. The range of particle size distribution covered by these techniques is 0.01 


201 


micron to 200 microns. The specific surface area determination is carried out by nitrogen 
adsorption and the BET method. The porosity of powders and ceramics is measured by mercury 
intrusion. 

Colloidal Processing of Powders - S. Malghan, D. Minor and P. Pei 

The focus of this laboratory is to develop data and understanding of non-oxide powders 
processing in aqueous environment. The laboratory is equipped with instruments and equipment 
for studying deagglomeration, dispersion, suspension stability, slurry casting, and green body 
microstructure evaluation. 

Agitation Milling of Powders - D. Minor and S. Malghan 

High energy agitation milling of silicon nitride powders is carried out with a minimum 
contamination by the use of a specially designed milling system. This milling device allows for 
the size reduction of silicon nitride powder by milling at high slurry densities in approximately 
l/6th to 1/lOth of the time required by the conventional tumbling ball mill. The mill is lined 
with silicon nitride and the media are made of silicon nitride materials. Hence, external sources 
of contamination can be minimized. 

Nuclear Magnetic Resonance (NMR) - P. S. Wang 

The solid state NMR facility includes a Bruker MSL-400 NMR system capable of studying 
almost all NMR active nuclei in the periodic table in both solid and liquid states as well as 
performing NMR imaging in proton and carbon- 13 frequencies. Currently, the operation 
parameters for both states at proton, deuterium, carbon- 13, and aluminum-27 have been defined 
and proved by documented NMR spectra of organic and inorganic molecules. The equipment 
has been tun^ to Si-29, Cu-63, and Y-89. 

Scanning Electron Microscope/Image Analysis (SEM) Facility - J. F. Kelly 

This laboratory is equipped with an Amray 1830 digital scanning electron microscope with LaBg 
source and a Leitz optical microscope. The SEM is equipped with a solid state backscatter 
detector and an ultrathin window x-ray detector. A Kevex Delta V EDS x-ray analysis and 
image analysis system is interfaced to both the SEM and optical microscopes. Automated 
imaging capabilities enable rapid size and shape analysis of a variety of imaged features, 
including ceramic powder particles and second phase regions in composite structures. Fracture 
stages have been developed for real time observation and measurement of in-situ crack 
propagation in ceramic specimens. The addition of an interior mounted phosphore screen with 
video camera imaging provides the capability of imaging single grain electron backscatter 
diffraction patterns from bulk specimens. This permits the measurement of crystallographic 
orientation in ceramic specimens. 

Thermal Analysis Facility - J. Wallace and J. Blendell 

This facility includes equipment for measurement of behavior of ceramic materials in a wide 


202 


range of atmospheres and temperatures. The equipment is comprised of a computer-controlled 
differential pushrod dilatometer capable of measuring thermal expansion or sintering shrinkage 
in vacuum, inert, oxidizing or reducing conditions from room temperature to 1600°C. The 
atmosphere can be monitored using either a zirconia oxygen cell or an external mass 
spectrometer using its own associated computerized data acquisition system. 

The second major piece of equipment is a simultaneous thermal analysis (STA) system which 
is capable of performing simultaneous thermogravimetric and differential thermal analysis from 
room temperature to 17(X)°C. Atmospheres can be varied from vacuum to single and mixtures 
of gases using a four channel mass flow controller. The STA is also connected to the mass 
spectrometer system and it’s associated data acquisition system. The quadrapole mass 
spectrometer system has a capability of analyzing to 512 AMU. 

Chemical Laboratory Facilities - J. J. Ritter 

Chemical synthesis of powders is carried out in a well-equipped laboratory, which consists of 
controlled atmosphere glove boxes, preparative chemical vacuum systems, and a chemical flow 
reactor. A range of powders can be synthesized for exploratory purposes. 

Ceramics Powders Processing Laboratory - J. Wallace and J. Blendell 

A processing laboratory for processing and sintering well controlled ceramic powders has been 
assembled. This facility consists of: equipment for chemical powder synthesis routes; attrition 
mills; ball mill; jet mill; pressure slip caster; uniaxial presses; cold isostatic press; spray dryers; 
drying ovens; hot presses; air furnaces to 17(X)°C; controlled atmosphere furnaces with 
associated gas flow systems and oxygen sensors for temperatures to 1600°C; graphite furnace 
for temperatures to 2300 °C and a hot isostatic press/gas pressure sintering furnace capable of 
2300 "C and 200 MPa using graphite elements and insulation. 

Nano-Size Powders Processing - W. Chen and S. Malghan 

This is a new facility which consists of equipment for powder handling in inert environment, 
compaction of nano-size powders, and sintering under environment control. The compaction 
equipment was designed to facilitate the application of wide range of pressures (up to 5 GPa), 
temperatures (cryogenic to 1000°C) and environments. The size of green ceramic produced in 
this system is 3.0 mm diameter. 


SURFACE PROPERTIES 


Wear Tests - S. M. Hsu and S. W. Ruff 

A state-of-the-art friction and wear testing laboratory is available for the evaluation of materials 
under different applications and conditions. Contact geometries include pin-on-disk, cross 
cylinders, ball-on-flat, ball-on-balls, flat-on-flat, and ring-on-block. Various motions and 


203 


operating conditions are available to simulate many industrial applications. Environmental 
control includes temperature (room temperature to 1200°C), vacuum, and humidity. 

Surface Analysis - S. M. Hsu, R. S. Gates, and S. W. Ruff 

Many modem specialized instrumentation are available for the analysis of surface properties of 
materials. Mechanical property measurement include hot hardness tester, Vicker’s indenter, 
nano-indentor, scratch test, and controlled depth micro-scratch test. Chemical property 
measurement include time-resolved micro-Raman spectroscopy, FTIR microscopic spectroscopy, 
GC-MS, SEM with EDX analysis, IR and UV spectroscopies with API compound identification 
files. A specially designed organo-metallic specification facility is also available to detect 
surface reaction products at ppm level. Access to conventional surface analysis such as XPS, 
ESCA, AUGER, etc are also available through external contract. 

Hydrocarbon Oxidation Facility - S. M. Hsu 

Various oxidation apparatus are available to study the oxidation and degradation mechanisms of 
hydrocarbon mixtures. These include DSC, TGA, a simultaneous TGA/DTA, a specially 
designed chemiluminescence apparatus, hot tube, panel coker, micro-oxidation, TFOUT, and 
other engine simulation instruments. 

STM/AFM - S. M. Hsu 

A Digital commercial scanning tunnelling microscope (STM) and atomic force microscope 
(AFM) is available to measure surface properties at atomic level. 

Time-Resolved Micro-Raman - S. M. Hsu 

This versatile facility consists of a pulsed ND-YAG laser, a CW Ar-ion laser, a triple 
monochromator, and a gated intensified diode array detector. This facility, therefore, provides 
a wide variety of Raman analysis techniques in both time-resolved and continuous operation 
modes, using either visible or ultra-violet excitation sources for either operation mode. In 
addition, either bulk macro-Raman or 5 ^m resolution micro-Raman analysis is available. 


MECHANICAL PROPERTIES 


Surface Forces Laboratory - D. Smith 

The surface forces laboratory consists of a semi-clean-room preparation facility and a crossed- 
cylinders surface force apparatus. The crossed-cylinder apparatus permits measurements of 
atomic-scale forces between surfaces. It can be operated with a variety of liquid or gaseous 
environments, thus allowing investigations of the effects of chemical changes on the forces 
between two surfaces. The apparatus includes several unique features that were developed and 
built by the surface forces group. First, sensitive custom electrometer circuits were built into 
the apparatus to allow in situ measurements of surface charges resulting from contact 


204 


electrification. Second, the apparatus has been modified to permit the sliding of one surface 
over the other under constant applied load. 

Instrumented Indenter - D. Cranmer 

This apparatus is designed to enhance our ability to measure the properties of the fiber/matrix 
interface in ceramic matrix composites. The instrumented indenter permits us to measure the 
force on and displacement of a fiber directly during loading and unloading. Previous methods 
for examining these properties could only measure the maximum applied load and inelastic 
displacement. 

Analytical Electron Microscopy - B. Hockey 

Several transmission and scanning electron microscopes are available for analysis of the changes 
in microstructure as a result of creep. 

Glass Melting - D. Kauffman 

Extensive glass melting and annealing facilities for production of melts up to 1600 °C are 
available. Batch sizes up to about 2.5 -3 kg can be produced using this equipment. Special 
facilities for melts containing heavy metals such as thallium and lead are also available. 

Creep Apparatus — R.F. Krause, Jr. and S.M. Wiederhom 

The creep measurements laboratory possesses 19 controlled-temperature furnaces (800 to 
17(X)°C), 7 laser extensometers, 10 optical long-distance microscopic extensometers, 20 loading 
frames (14 pneumatically driven, 4 screw driven, and 2 direct weight). Among these loading 
frames 14 can be used in tension, 3 in tension or compression, 1 in flexure, and 1 as a sintering 
forge. 

Hot-Pressing Apparatus — R.F. Krause, Jr. 

A graphite heating-element furnace (23(X)°C max) which be can operated in vacuum or an inert 
gas atmosphere is mounted in a hydraulic loading frame (0.5 MN max). Ceramic powders can 
be hot pressed in graphite dies (50, 75, 100, and 125 mm diam). 

Nano-Indentation Facility - D.T. Smith 

The Ceramics Division nano-indentation facility consists of a Nano Indenter II indentation 
machine, manufactured by Nano Instruments, Inc., and related computer and optical 
components. The indenter, under computer control, is capable of measuring loading-unloading 
curves with displacement resolution better than 0. 1 nm and load resolution better than 200 nN. 
Nomarsi interference contrast (NIC) optics and translation stages with placement precision better 
than 1 ^m permit the measurement of material properties such as hardness and Young’s modulus 
in selected volumes as small as 10“^^ m^. 


205 


ELECTRONIC MATERIALS 


Level 10 Clean Room - J. Blendell 

A Level 10 Clean Room has been constructed for the processing of ceramics in a controlled 
environment where the presence of air low contaminants can seriously affect the final products 
properties. The room is provided with separated work stations to allow simultaneous conduct 
of experiments. 

Thermal Wave Analysis Facility - A. Feldman and G. White 

This facility is used for characterizations based on variations of thermal diffusivities. Equipped 
with both an Ar-ion and CO 2 laser, the facility permits analyses by infrared and Mirage 
methods. It is especially useful as a nondestructive method of detecting flaws in ceramics 
especially in near-surface regions. 

Single Crystal X-ray Diffraction - W. Wong-Ng 

Currently this research is primarily used to characterize single crystals in terms of crystal 
symmetry, lattice parameters and detailed structure. 


OPTICAL MATERIALS 


Optical Characterization - L. Robins and A. Feldman 

Facilities include a Cary spectrophotometer for measuring optical transmittance in the spectral 
range 0.2 fxm to 2.5 fim, optical spectrometers for measuring photoluminescence and Raman 
spectra, and an argon ion laser. 

Magneto-Optical Imaging of High Temperature Superconductors - D. Kaiser, F. Gayle, A. 
Shapiro 

The facility consists of a magneto-optical imaging system with attached video equipment. It is 
used to measure real-time flux distributions in high temperature superconductors as a function 
of temperature (7 -300 K) and applied magnetic field (0 to ± 65 mT). 

Electro-optic Thin film Characterization - L. Rotter 

The facility consists of a vibration isolated optical table, argon-ion and helium neon laser 
sources, polarizing components, lenses, optical stages, optical detectors, and electronic signal 
processing equipment for measuring the electro-optic coefficients and optical birefringence of 
thin ferro-electric films. 


206 


Metalorganic Chemical Vapor Deposition (MOCVD) System - D. Kaiser 

A specialized system was constructed for the deposition of oxide thin films from metalorganic 
precursors. It has been used to deposit BaTi 03 films on 1.5 cm x 1.5 cm substrates. 

Diamond Film Deposition - E.N. Farabaugh and A. Feldman 

Facilities consist of 3 hot filament CVD reactors and a microwave enhanced CVD reactor. The 
hot filament reactors can accommodate substrates up to 2.5 cm x 2.5 cm square. The 
microwave reactor can accommodate substrates up to 10 cm in diameter. The reactant gases are 
hydrogen, methane, oxygen, argon, and ethyl alcohol which contains boron of doping. Growth 
rates typically range from 0.1 to 0.6 ^m/h. 


MATERIALS MICROSTRUCTURE CHARACTERIZATION 


Synchrotron Radiation Beamlines - G. G. Long 

The Materials Microstructure Characterization Group operates two beamstations on the X23A 
port at the National Synchrotron Light Source at Brookhaven National Laboratory in New York. 
These two beamstations offer access to dedicated instrumentation for small-angle x-ray 
scattering, x-ray diffraction imaging (topography) and EXAFS. 

Small-angle x-ray scattering can be carried out in the energy range from 5 to 11 keV. The 
minimum wavevector is 4 x 10'^ nm'^ and the wavelength resolution is AX/X = 10"^, 
nomalous small-angle scattering with excellent resolution. Diffraction imaging of single crystals 
and powders is carried out with monochromatic photons between 5 and 30 keV. An energy- 
tunable x-ray image magnifier enables imaging of microstructure down to less than 1 ^m. 
EXAFS experiments are also performed over an energy range from 5-30 keV. 

Small-angle scattering measurements on ceramic and metallurgical materials are being used to 
characterize the microstructure in the 2 nm to 1 /^m size range as a function starting chemistry 
and processing parameters. Diffraction imaging is being used to study imperfections and strains 
in single crystals and powder compacts. EXAFS is being used to study the structure of strained 
semiconductor interfaces and metal multilayers. A combination of EXAFS and diffraction will 
provide a capability for site- specific local structure determination in crystals. 

SANS - Ceramics Furnace - G. Long 

The SANS-Ceramic furnace is a unique facility that is now coming together. This system will 
allow in-situ densification studies of ceramic powders and SANS application. The experimental 
system has been designed to carry out densification studies of oxide powders at temperatures up 
to 2000 °C. In addition, the furnace will be equipped with a dilatometer. 


207 


APPENDIX 






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