fundamental research needs in ceramics

Fundamental Research Needs In Ceramics 1

NSF Workshop Report:

FUNDAMENTAL RESEARCH NEEDSIN CERAMICS

April 1999

NSF Grant #DMR-9714807

Workshop Chairs:

Yet-Ming Chiang Karl JakusMassachusetts Institute of Technology University of Massachusetts

Cambridge, MA 02139 Amherst, MA 01003

Fundamental Research Needs In Ceramics2

Executive Summary ............................................................................................................ 3

The Process ......................................................................................................................... 5

"Piezoceramics are getting smarter" ................................................................................... 6

I. Structural and Electromechanical Ceramics ....................................................................... 8

"Better portable power" .................................................................................................... 13

"Phone home with microwave ceramics" ......................................................................... 15

II. Electrical and Chemical Ceramics .................................................................................... 16

"The detector material for the 21st century" .................................................................... 21

III. Glass and Photonic Materials ........................................................................................... 22

"Rapid prototyping speeds up design and production" .................................................... 27

IV. Ceramics Processing ......................................................................................................... 29

"Building better bones with ceramics" ............................................................................. 34

V. Integration of Ceramics with Dissimilar Materials .......................................................... 36

"Teaching the wonders of science through ceramics" ...................................................... 41

VI. Education in Ceramics ...................................................................................................... 42

VII. Role of NSF in Supporting Collaborations with Industry and Other Sectors .................. 43

Acknowledgements .......................................................................................................... 44

Appendix: Workshop Speaking Program ........................................................................ 45

Participants ....................................................................................................................... 46

Table of Contents


EXECUTIVE SUMMARY

Ceramics are one of the most important materials in human civilization. Their socioeconomic impact is asimportant today as it has been throughout history. In the 1990’s alone, advances in ceramic materials haveenabled several technological breakthroughs of truly global impact. The incredible growth in wirelesscommunications would not have been possible without the miniaturization permitted by oxide ceramicmicrowave filters and resonators. Scanning-tunneling and atomic-force microscopy, medical ultrasoundtechnology, autofocus cameras, and the vision-correction system of the Hubble Telescope all rely on piezo-electric ceramics. The exponential rate of commercialization of lithium rechargeable batteries over thepast several years was enabled by the development of new oxide electrode materials. Repair, reconstruc-tion, and replacement of the hard tissues of the body, bone and teeth, are largely possible today due to thedevelopment of bioceramics. These and other examples are elaborated upon in the body of this report.These milestones in advanced technology could not have occurred without the continuous support of ce-ramics fundamental research by government agencies and industry.

Ceramics are a class of materials broadly defined as inorganic, nonmetallic solids, which arguably providethe broadest range of functions of all known materials. They are synthesized as glasses, polycrystals, andsingle crystals, and in many forms dictated by their end use, including fine powders, monoliths, thin films,and composites. They are also frequently integrated with other materials in advanced structures and de-vices. Their commercial impact can be appreciated by the fact that in 1998, the 150 largest ceramicscompanies worldwide had a combined revenue of $175B.

Because of ceramic materials’ scientific and technological importance, ceramic research spans many fieldsincluding electronics, chemical engineering, mechanical and aerospace engineering, biomaterials, con-densed matter physics, and solid state chemistry involving a significant portion of the world’s scientificmanpower. The membership of ceramics-focused science and engineering professional societies world-wide numbers over 75,000 at present.

This Workshop Report represents an attempt to capture the consensus view of a representative cross-section of the ceramics field as to the most promising directions for fundamental ceramics research in thefirst decade of the new millenium. The workshop “Fundamental Research Needs in Ceramics,” was heldat the National Science Foundation (NSF) on June 10-11, 1997, with the goal of identifying and prioritiz-ing basic research needs in ceramics. The participation was limited to a total of 40 people, invited forrepresentation by field, institute type, and geographic locale.* The five research areas reported on hereinwere identified by the workshop participants as the most vital and promising areas for future research.While past successes of the discipline are also discussed, our primary charge was to identify the mostpromising areas for the future.

Several main conclusions can be drawn from this study. Firstly, basic research in ceramics is characterizedby diversity. This field engages in fundamental research ranging from the design of new materials (com-pounds) at the atomic level, to the understanding of basic physical phenomena, to chemical synthesis andprocessing science, to the design and characterization of complex microstructures, to novel forming meth-ods aimed at components of microscopic-to-macroscopic length scale.

Secondly, despite such diversity, there are several broad needs that rise to the top and cut across the variouschapters: 1) It is clear that some of the most exciting recent developments have been in the design and


discovery of new ceramics. Examples include ultrahigh-strain single crystal piezoelectrics, new high-frequency dielectrics, phosphors, intercalation compounds, ductile layered structural ceramics, andthermoelectrics. Activities focused on the (rational) search for, and design of, new materials should beencouraged. 2) Processing science remains a key focus of this field, for the simple reason that it is thecornerstone of manufacturing technology. However, it must be recognized that ceramics processing hasevolved from primarily the study of powder-based materials, to now include thin film device processing atone limit, and macroscopic (e.g., solid free-form) fabrication at another. Continued innovation requiresthat we avoid a narrow view of what constitutes ceramics processing. 3) Some of the greatest new chal-lenges and opportunities lie in the integration of ceramics with other materials. Examples include theincorporation of ceramic sensors and actuators in silicon-based MEMS, polymers/ceramic composites inelectrochemical devices and structural materials, and interactions between ceramics and the human bodyin biomaterials and drug-delivery systems. Successful integration will require fundamental research intothe properties of surfaces and interfaces, the chemistry and reactivity of dissimilar materials, and the physi-cal properties of composites at various length scales. 4) Computational modeling, as applied to ceramics,has reached a new level where clear examples exist of the a priori prediction of crystal properties and ofmicrostructural optimization. Looking forward, synergistic modeling/experimental efforts may best beable to reduce the cycle time for scientific discovery.

Finally, the organizers and participants alike feel that this workshop must be regarded as just a beginning.We strongly recommend that NSF provide the support necessary to continue the effort of identifying thescientific and technological potentials of fundamental ceramic research. A number of workshops with amore specific focus on the subdisciplines within ceramics could be highly productive.

* 81% of the participants were from academic institutions, 12% from industry, and 7% from national laboratories. This

report represents the opinions of those who participated, and not the views or policies of NSF. Furthermore, while NSF andthe organizers have aimed for a representative cross-section of the ceramics field, it is unlikely that the views of every interestgroup in ceramics is represented in this report. Liselotte J. Schioler, Ceramics Program Director, Division of MaterialsResearch, sponsored the workshop and presided as the NSF representative.


THE PROCESS

To initiate this review, an electronic mail survey was conducted in the spring of 1997 to solicit input fromthe ceramics community (U.S. only) as to the most important present and future areas of basic research.The responses to this survey were distributed (without identifying the respondents) to the participants priorto the workshop.

The workshop opened with seven overview presentations (Appendix). These were intended to stimulatediscussion rather than to comprehensively review the field. A general discussion of the workshop goalsand format followed, from which five Working Groups were formulated with the goal of providing ad-equate representation for all significant areas of ceramics research. Each Working Group was charged withdiscussing critical needs in their respective areas during the remainder of the workshop, and drafting areport which addresses the following:

• Why is this topic important and timely?• What does Ceramics bring, as a field, to this field of endeavor?• What are the most exciting present opportunities?• What steps should NSF take?

A summary session was then held in which each Working Group presented their draft report for discussion.Program managers from other government agencies were invited to the closing session. The reports of thefive Working Groups follow, each edited by the workshop Chairs for consistency of format. We alsosummarize in two separate sections Collaborations with Industry and Other Sectors and Education in

Ceramics. A majority of the participants contributed to the discussions of these subjects during the work-shop.


Piezoceramics are getting smarter

Given the many productapplications for piezoelectricceramics or piezoceramics, it isno wonder that the market isvery large. Globally, the marketfor such products is around $11billion, and in the UnitedStates, the market is estimatedat $1.5 billion. Industry expertspredict the market will enjoy acompound growth rate of 20 to25% over the next several years.Piezoelectric actuators are used

in a wide range ofapplications, includingoptical modulators,microtransducers andcertain types of resonantacoustic sensors andcellular radio controlelements.

A piezoelectricmaterial produces anelectric charge whenpressure is applied, ordeforms when electricallycharged. Strains areproduced that are linearlyproportional to an ap-plied electric field. Theamount of deformation orcharge is dependent onthe composition. Thus,by altering the composi-tion and part dimensions,the piezoelectric proper-

ties can be designed for veryspecific product applications.For instance, compositions basedon the modified lead perovskitesystem are potential candidatesfor high strain actuators withlarge thermal stability and lowhysteresis.

One major advantage ofpiezoelectric actuators is theability to produce displacementsof 10 micron in a time as shortas 10 microseconds, even whenthe transducer is subjected tohigh (about 100 MPa) opposingstresses. Thus, actuators havebeen developed for fuel injectionsystems, ink-jet printers, andcameras, among others. In

autofocusing movie cameras, forexample, actuators produceprecise rotational displacements.Other applications that requireaccurate positioning includeplacement of circuits duringfabrication of semiconductorchips and adjusting lenses andmirrors in optical equipment.

Piezoelectric transducers havealso shown great promise for useas acoustic actuators in activenoise and vibration controlsystems for low frequency rangeapplications. A high displace-ment magnitude is usuallydesired to generate sufficientsound pressure for effectivecancellation of low frequencynoise. An air acoustic actuatorhas been designed for suchapplications. This design incor-porates a double amplifierconfiguration that uses twoparallel lead-zirconate-titanateceramic plates clamped at oneend with a curved cover platebonded at the other end. Thisconfiguration enables ratherlarge surface displacementamplitudes, a large driving force,a high sound pressure and goodcoupling to the air loading.

Another actuator of noveldesign is the Rainbow (reducedand internally biased oxidewafer) actuator, which has adome-shaped configuration.Such a configuration featureshigh displacement and goodload-bearing capability, betterthan conventional designs.

x1

x2

x3

PolingDirection

Top Etched Copper/Kapton Electrode

Bottom EtchedCopper/KaptonElectrode

FiberPolymer

Flexible “active fiber composites” usepiezoelectric ceramic fibers of PZT tocreate a robust, conformable, sensing/actuation device. Courtesy of Dr. AaronA. Bent, Continuum Control Corpora-tion, Cambridge, MA.


Displacements have beenroughly 30 to 40% higher than aflat unimorph actuator type,which uses a single ceramic platebonded to a metal plate. Amonomorph design has alsobeen proposed, which solves theproblems of traditional bimorph(two plate) actuators, includingshort life times and displacementdrift. This design uses a singleplate of uniformly-doped piezo-electric ceramic (lead zirconatetitanate containing zinc borate)that is semiconductive.

With further improvementsin design, new applications forpiezoelectric ceramic transducersand sensors will continue toemerge. However, difficulties inreducing manufacturing costshave limited several high-volume applications of piezo-electric actuators, especiallymulti-layer actuators used infuel-injection systems. On theother hand, demand is expectedto grow for applications in thebiomedical and aerospace indus-tries, which can tolerate therelatively high cost of piezoelec-tric ceramic components.

The promise of developing“smart” materials, providingboth sensing and actuatingfunctions, has also increased thefocus on development of piezo-electric, electrostrictive (thesematerials exhibit a quadraticrelationship between inducedstrain and applied voltage) andother active materials for use as

precision positioners, miniatureultrasonic motors and adaptivemechanical dampers. Multilayerstructures are receiving the mostattention because of their lowdrive voltage, high energydensity, quick response and longlifetime.

A current smart applicationof piezoelectric ceramics is thesuspension system in high-endluxury cars. Other smart applica-tions involving piezoelectricceramics, in combination withother materials, are underdevelopment to meet U.S.military needs. For instance,ceramic microresonators in theform of plates and cantileversare being investigated formicroelectromechanical(MEMS) structures.

However, improving theperformance and reliability ofpiezoelectric ceramics is requiredto expand applications evenfurther. The mechanical behav-ior of these materials must becompletely understood, espe-cially the stresses developedunder application of electricfields, chemical gradients andthermal gradients in multilayerstructures. Though work hasalready started in this area, itmust continue so that theseunique ceramic devices can bedeveloped to their full potential.v


I. STRUCTURAL AND ELECTROMECHANICAL CERAMICS

David J. Green, Pennsylvania State University (Chair)Michel Barsoum, Drexel UniversityI-Wei Chen, University of MichiganYet-Ming Chiang, Massachusetts Institute of TechnologyVinayak P. Dravid, Northwestern UniversityAnthony G. Evans, Princeton UniversityKatherine T. Faber, Northwestern UniversityNesbitt W. Hagood, Massachusetts Institute of TechnologyJohn W. Halloran, University of MichiganArthur H. Heuer, Case Western Reserve UniversityKarl Jakus, University of Massachusetts, AmherstNitin P. Padture, University of ConnecticutDennis W. Readey, Colorado School of MinesBrian W. Sheldon, Brown UniversitySusan E. Trolier-McKinstry, Pennsylvania State UniversityEric D. Wachsman, University of Florida, GainesvilleKenneth W. White, University of Houston

The very title of this working group reflects a growing belief that the historically separate structuralceramics and functional ceramics sectors of our field have many common scientific issues, and that greatopportunities lie at the interface of the two. The working group began its discussions by summarizingthe most notable technological achievements which have been made possible by research in the me-chanical behavior of ceramics. These include:

Commercial Successes• Remarkable improvements in toughness, hardness and strength of non-oxide ceramics, coupled

with advances in processing, have led to:- More than 1 million ceramic turbochargers on the road with zero failure- Ceramic bearings in both military and civilian turbomachinery surviving loss of coolant with

zero failure.- Development of cutting tools and forming dies with extreme hardness, chemical resistance, and

adequate toughness, which now permeate the infrastructure of manufacturing.• Zirconia ceramics with improved strength, toughness, corrosion resistance, and wear resistance

have saved $millions in paper manufacturing and other industries.• Thermally shock resistant insulation tiles enabled the Space Shuttle.• Ceramic thermal barrier coatings extending the upper use temperature of superalloy components

are commercially successful, as well as being the focus of much current basic and applied research• The following areas are examples of primarily electronic applications in which attention to me-

chanical reliability has been important to commercial success:- High purity silica fibers for fiber optics with ultrahigh strength and minimum variability.- Microwave magnetic ceramics used in radar systems.- Ceramic packaging for microelectronics.- Ceramic insulators used in electrical power delivery systems.- Microwave dielectrics for the wireless communication industry.


Innovative New Applications in Which Mechanical Performance is Critical:• Electromechanical active systems for sensing, active control, and actuation.• Microelectromechanical Systems (MEMS).• Biomedical imaging devices.• Solid state/electrochemical power generation, now at the pilot plant demonstration level.• Si

3N

4 turbine blades and vanes, now being evaluated in land-based gas turbine generators.

• Numerous ceramic matrix composite (CMC) applications, which have resulted from research inmechanical behavior and the development of new fibers

- The first CMC aircraft exhaust system flaps and seals, in the F/A 18 E/F.- Ceramic matrix composites for rocket nozzles, hot gas filters, and chemical industry process

components.- Ceramic matrix composite combustor liners in land-based gas turbine generators.

From the ensuing discussions, the following fundamental research areas were identified as being par-ticularly timely and relevant.

1. Predicting and Improving the Mechanical Properties of Active Ceramics

Electronically and chemically functional ceramics are used as the active components in applicationssuch as actuators, memory devices, fuel cells, and sensors. These applications require operation underextremes of electric fields, chemical gradients, and thermal cycling. The basic mechanical behaviorunder these conditions are not well understood.

The ceramics field has historical strength in this area. Ceramists can contribute to the understandingand technological development of these devices with fundamental research on the mechanical propertiesof active ceramics, and the stresses developed under application of electric fields, chemical gradients,and thermal gradients in multilayer structures.

The mechanical behavior of piezoelectric/electrostrictive ceramics is one such research opportunity.Fundamental questions include the following. Are domain-switchable ferroic materials inherently weak,or can they be made more mechanically robust without sacrificing electromechanical activity? How canmechanical constitutive behavior be described for non-linear coupled systems? What are themicromechanical mechanisms involved in crack propagation in ferroics, including electric field effectsand the interaction of the crack-tip process zone with the domains and the polarization? What are themicrostructure-property relationships for coupled materials? How is the reliability of electroded activeceramics influenced by defects and high drive conditions?

2. Enhancing the Electromechanical Properties of Active Ceramics

Piezoelectric and electrostrictive materials present outstanding research opportunities. Improvedunderstanding of the mechanisms of deformation which can be exploited for controlled motions isrequired to develop high strain, active materials. Research is also needed on new processing methods toproduce these materials in the forms desired for active composites (e.g. thin films, fibers, and multilayerstructures).

Recent observations of unusually high strain in single crystal relaxor piezoelectrics (S.-E. Park and T.R.


Shrout, J. Appl. Phys., 82[4], 1804 (1997) have created new opportunities for research on the preparationof high-quality single crystals with controlled composition and engineered domain structures, as well asthe fabrication of devices from the single crystals. The origin of the high coupling coefficients, highstrain, and the behavior under mechanical load must be determined. Since implementation would befacilitated by the availability of low-cost specimens, textured polycrystals should be examined to deter-mine whether the exceptional properties will also be observed in such materials. Can this effect can begeneralized to other systems, particularly lead-free materials?

Most electrically-actuated ceramics are implemented as polycrystalline ceramics. The ability to predictthe electromechanical properties of polycrystals from those of the single crystals, including the piezo-electric coefficients, the coupling coefficients, and the achievable strains, is currently limited. Thisscientific problem requires understanding of the intrinsic crystalline anisotropy, coupling across grainand domain boundaries, and the distribution of electrical polarization and stress. Fundamentally, animproved understanding of the behavior of nonlinear, hysteretic materials is required.

3. Understanding the Effects of Interfacial Chemistry on Adhesion and Fracture

Research on metal/ceramic and ceramic/ceramic interfaces will impact a variety of structural applica-tions. In particular, the integration of dissimilar materials requires the resolution of interfacial issues. Inthe case of metal/ceramic interfaces, potential applications include (but are not limited to): coatings onmetals (e.g., thermal barrier coatings), metal-ceramic joining, and composites containing both metal andceramic phases. Ceramic/metal interfaces are also critical in electronic, optical, and magnetic applica-tions. Ceramic/ceramic interfaces in monoliths and composites dictate key properties and are oftencritical factors in the performance of these materials. There are also important challenges in solid oxidefuel cells, where interfaces involving multicomponent oxides are thermally cycled. With this in mind,fundamental research on the structure, formation, and properties of both metal/ceramic and ceramic/ceramic interfaces are a key research need.

Advances in both computational and experimental methods make it possible to investigate the atomic-scale structure of interfaces. It is important to continue these types of efforts on relatively simple sys-tems. Work on more complex systems also offers a number of exciting challenges. This includessystems with a larger number of chemical components (e.g., impurity effects, etc.) and systems whereinterfacial reactions and phase transformations create more complicated interfacial structures. Complex-ity is particularly inherent in dynamic processes such as fracture. Kinetic effects also introduce com-plexity during processing (i.e., interface formation) and during service (i.e., chemical reactions). Inmost of these cases, this complexity can not be addressed with purely atomistic approaches. Thus,important advances in treating dynamic processes at interfaces can be made by bridging the atomic andcontinuum length scales.

4. Understanding the Deformation Mechanisms of New Layered Carbide and Nitride Ceram-ics

The unique set of properties exhibited by a newly identified family of ternary layered hexagonal car-bides and nitrides (e.g., Ti

3SiC

2, Ti

2AlC, Ti

2AlN, and related compounds) warrants further research. As a

family, these compounds are malleable at room temperature, deform plastically at elevated temperatures,and appear to possess at least one operative slip system at all temperatures. The fundamental questions


that need to be addressed include: What is the basic deformation mechanism? How is the strain accom-modated during deformation at high temperatures? Can they be strengthened by traditional metallurgi-cal processes such as solid-solution and precipitation hardening? Other aspects that are not understood,let alone measured, are the creep resistance and fatigue properties of these compounds.

5. Developing a Mechanical Design Methodology for Ceramic-Based MEMS and OtherMicrosystems

A recent report (A.H. Epstein and S.D. Senturia, Science, 276, 1211, 23 May 1997) assesses the feasibil-ity of high temperature ceramics for high power density micro-turbines. The report suggests that themicro-turbine as part of a 1 cm3 turbine generator could deliver as much as 50W of electric power. Theproblems that have normally plagued monolithic ceramics for large scale structural application, notablythermal shock, are no longer present due to the sizes involved. Conventional Weibull extrapolationwould also suggest that requisite strengths are achievable on the micro scale. Nonetheless, numerousresearch challenges remain.

Firstly, the fracture mechanics-based design approaches may not be appropriate for the micro scale.Secondly, the applicability of scaling laws for lifeline production to microstructures which approach thecomponent dimension may prove problematic. Thirdly, design validation will require a new set ofmechanical testing methodologies both in monotonic, cyclic and thermo-mechanical loading.

6. Marrying Descriptions of Fracture and Deformation at Different Length Scales

Fracture and deformation are generally considered in terms of three length scales. Macroscopic andmicroscopic behavior are treated from a continuum viewpoint with a mixture of physical and phenom-enological models. At the atomic level, deformation and fracture is treated from discrete atomisticapproaches. A fundamental issue in the understanding of deformation and fracture concerns consolida-tion of these three "scale viewpoints" into a unified approach. Such a consolidation would lead to realpredictive capability of bulk mechanical behavior as it relates to structure at any length scale withassociated opportunities for materials design. This effort is timely due to recent advances in computa-tional methods and capability as well as experimental tools to study and characterize mechanical re-sponse and structure at different length scales. Such capability in theory and experiment will allow trueexamination of concepts to develop a unified description of deformation and fracture. The opportunityto develop the foundation of unified approach to deformation and fracture in the context of ceramics iswelcome. The level of understanding mechanical properties of ceramics at the three individual lengthscales is arguably more complete than for other classes of materials. The role of a priori design ofceramic microstructures for specified properties is also more integrated in ceramic systems than othermaterials systems and the potential benefit to the design of ceramics from a unified fracture viewpoint issignificant. The following lists a few specific areas of fracture and deformation that would benefit forma unified view of fracture:

• Design of ceramics for mechanical reliability.• Environmental influenced fracture.• Lubrication in tribology.• Understanding extensive damage development (Quasi-ductility) in ceramics.


The most significant research barriers require implementation of process zone and cohesive elementtechniques into finite element methods and the connection between continuum finite element methodsand molecular dynamics and other atomistic descriptions of fracture. Experimental issues include thestudy of process zone mechanisms and crack-tip chemistry.

7. Ceramics in Tribological Applications

Ceramics are uniquely suited for contact loading, which may be in the form of rolling contact, scratch-ing contact or quasi-static contact. However, the fundamental understanding of contact behavior ofceramics is not very well understood. There is a need for fundamental research in the areas of theoreti-cal and experimental contact behavior of various length scales, from the atomic to the continuum, in away which integrates the complex phase assemblages and microstructures present in real ceramic mate-rials. Basic understanding of effects of microstructures and surface-modification on contact behavior isneeded.

How lubrication, used to alleviate the contact severity, works in these situations is not very well under-stood at all. There is a need for lubrication at elevated as well as near-room temperatures. What are theuseful lubricants? How do they work? How do they degrade? This topic would appear to overlap withinterests of programs within the Divisions of Civil and Mechanical Systems and Chemistry at NSF.

8. Other Areas In Which Understanding of Mechanical Behavior can Make Major Contribu-tions

The following topics were also discussed in lesser detail by the panel:

• Corrosion of Structural Ceramics in Severe Environments• Evolution of Stresses During Processing of Bulk and Thin Film Ceramics• High Temperature Stability of Heterogeneous Materials• Porous and Cellular Materials


Better portable power

First-principles calculations provide insightinto the role of atomic species in oxidesused as lithium battery electrodes, leadingto the design of new materials. This imageshows the change in electron density inLiCoO

2, a cathode oxide, when lithium

ions are removed and inserted, corre-sponding to the charge/discharge process ofa battery. The bright areas are regions ofhigh electron transfer, and shows thatoxygen has an unexpectedly large role.Courtesy of Gerbrand Ceder, Massachu-setts Institute of Technology, Cambridge,MA.

All manner of portable elec-tronic devices used for comput-ing, communications, andentertainment require electricpower. The ideal portable powersource would provide an infiniteamount of energy, weigh noth-ing, take up no space, lastforever, and cost nothing.While this goal cannot berealized without repealingcertain physical laws, recharge-able lithium battery technologyhas come closer to this ideal

than any that haspreceded it. Thespecific energydensity of lithium-ion batteries used inlaptop computersand cellular tele-phones now exceeds100 Wh/kg, a valuenearly 3 timesgreater than that oflead-acid batteriesand twice that ofnickel-cadmiumrechargeables.

Lithium rechargeables are safe,have a useful lifetime of at leastseveral hundred charge-dis-charge cycles, and show nomemory effects. So attractive isthis new technology that world-wide sales of rechargeablelithium batteries have grownfrom $120M per year in 1995 toapproximately $3B per year in1998, the latter being more thandouble the market value ofnickel-cadmium and nickel-metal hydride batteries com-bined. Some have projectedthat for applications in portableelectronics alone, the worldwidemarket will easily reach $10B bythe year 2002. This growthestimate excludes the potentialimpact of exciting new applica-tions such as hybrid and electricvehicles, and new designs suchas thin-film batteries and flex-ible solid-polymer batteries.

Batteries are an advanced

materials technology whichrequires the thoughtful integra-tion of metals, polymers, andceramics. However, it is theceramic oxide cathode morethan any other material that hasrevolutionized lithium batterytechnology. The electrodes of abattery are the active compo-nents which, by storing chargeand setting the voltage of thebattery, determine the theoreti-cally achievable energy density(product of specific chargecapacity and voltage). All othercomponents such as the electro-lyte, separator, current collec-tors, and packaging are necessaryto allow the electrodes to dotheir work, but are minimizedwherever possible. Lithiumcobalt oxide (LiCoO2) has beenthe preferred cathode for re-chargeable lithium batteries dueto its high voltage and stability.When used as the cathodeagainst a carbon anode, theresulting cell has a nominalvoltage of 3.6V (inspection of atypical lithium battery packusing multiple cells shows avoltage that is a multiple of thisvalue). The primary disadvan-tage of LiCoO2 based batterieshas been the relatively high costof cobalt as a raw material, butalready a number of alternativeceramic compounds based onlithium nickel oxide and lithiummanganese oxide are in thedevelopment pipeline. Newmaterials will lower the cost and


broaden the applications inwhich lithium rechargeablebatteries can be used.

Lithium cobalt oxide and otheroxide cathodes are intercalationcompounds, having crystalstructures containing layers orchannels of lithium ions that areeasily removed and re-inserted atroom temperature during batterycharging and discharging. Acritical need for the develop-ment of improved battery tech-nology is the design and synthe-sis of new compounds for bothelectrodes. Some of the mostexciting new anodes that arecontenders to replace carbon arealso oxides, such as tin-oxidebased glasses that undergoelectrochemical reduction in use(Fuji Photo Film Company,Dalhousie University). A recentbreakthrough in the design ofnew electrode compounds usesfirst-principles computationalmethods (Massachusetts Insti-tute of Technology, NationalRenewable Energy Laboratory)to predict the voltage andstructural stability of hypotheti-cal compounds that may nothave yet been synthesized.Combined with vigorous experi-mental programs at numerousuniversities, government labora-tories, and companies world-wide, a steady stream of innova-tion in battery materials seemsassured.

These new ceramic electrodes,when integrated with innova-tions in thin film battery materi-als and construction (Oak RidgeNational Laboratory) or solidpolymer electrolytes, seemdestined to expand the bound-aries of battery design. Form isthe new frontier; thin credit cardbatteries have recently reachedcommercialization, and beforelong, we may find that thebattery that powers portableelectronic devices has all butvanished from view, beingintegrated into the devicehousing, or even being worn inthe user’s clothing. ❖


Phone home with microwave ceramics

13 GHz linear amplifier used forsattellite link. The ceramic dielectricdisc in the circular opening is based onBa

2 Ti

9 O

20 oxide. Courtesy of Dr.

Terrell A. Vanderah, NIST,Gaithersburg, MD.

Though the first cordlessphones were introduced in the1970s, it was not until the mid-1990s that consumers had accessto an industrial technology thatincreased the range of thesephones tenfold. In 1983, the firstregular U.S. cellular phonesystem using microwave trans-missions went into operationafter two years of testing. Thissystem was the size and weight ofa small brick; it was not until1996 that cellular phones be-came pocket-sized. At the end of1997, nearly 40% of all U.S.household had a cellular phone.

Cordless and cellular phonesare just two segments of thehuge wireless communications

market. This market is one ofthe fastest growing markets ofthe global electronics industry,currently at an estimated rate of50% per year. The U.S. wirelesscommunications market alone(including services) is expectedto grow from $42 billion to $70billion by 2001.

Ceramics have made wirelesstechnologies possible – everymodern system in actual use orin development today –whetherit be portable or cellular tele-phone systems, portable personalcomputers, data communica-tions or global positioningsystems – incorporates oxideceramics with unique electricalproperties. Cellular phones salesin the U.S. have reached over$2 billion and the global marketfor mobile satellite earth stationsis forecast to increase by almostten orders of magnitude by 2001.

Such ceramics are used asfilters, oscillators and resonatorsfor storing, filtering or transfer-ring electromagnetic energy incircuits that operate at micro-wave frequencies (0.4-30 GHz).Ceramics enable these devices tooperate at minimal loss and withminimal frequency drift underchanging temperature condi-tions. Microwave ceramics inthe 1-4 GHz range have alsopermitted size reductions in cellsite transmitters and receivers,hand set transceivers and satel-lite communication filters.

Unfortunately for this coun-

try, most new developments inthis area of microwave ceramicsare coming from overseas,especially Japan. Without anincrease in effort, the U.S. riskslosing a leadership position inboth research and technology.More research is needed todevelop a fundamental under-standing of the relationshipsbetween chemistry, structure,composition and dielectricproperties of these materials,which in turn will help lead tothe discovery of new composi-tions that will achieve furthersize reduction. The country thatis successful in discovering thesenew materials is expected toreap enormous economic ben-efits. ❖


II. ELECTRICAL AND CHEMICAL CERAMICS

David R. Clarke, University of California, Santa Barbara (Chair)Sheik A. Akbar, Ohio State UniversityI-Wei Chen, University of MichiganYet-Ming Chiang, Massachusetts Institute of TechnologyAlexis Clare, Alfred UniversityHimanshu Jain, Lehigh UniversityDavid W. Johnson, Jr., Lucent TechnologiesJennifer A. Lewis, University of Illinois, Champaign-UrbanaPaul McIntyre, Stanford UniversityPatricia Morris-Hotsenpiller, Dupont CompanyGregory S. Rohrer, Carnegie Mellon UniversityThomas M. Shaw, IBMSusan E. Trolier-McKinstry, Pennsylvania State UniversityTerrell A. Vanderah, National Institute for Standards and TechnologyEric D. Wachsman, University of Florida, Gainesville

Electroceramics are responsible for scientific and technological innovations which have contributedimmeasurably to modern society. The zirconia oxygen sensor and 3-way automotive catalyst haveenabled vast improvements in air quality; piezoelectric ceramic actuators have enabled technologiesranging from advanced sonar to scanning probe microscopies to the Hubble Telescope repair; ceramicspackaging and multilayer device technology have facilitated the continuing miniaturization of electron-ics, and microwave dielectrics enable present-day wireless communications.

These applications are based on electrical, electromechanical, dielectric, electrochemical, and chemicalfunctions. The science involved is inherently multidisciplinary. What has distinguished the contributionof Ceramics is the recognition that the performance of real materials is determined not only by intrinsicstructure and composition, but also by defects, interfaces, and often-complex microstructures, eachinfluenced by processing.

The Working Group discussed a number of areas in which historically close ties between electronicceramics and device technologies exist. A specific technology focus is warranted for some areas (e.g.,wireless communications) due to the size of the field and the potential impact. In other areas, the re-search opportunities cut across many fields of application. As discussed further in the section Role ofNSF in Supporting Collaborations with Industry and Other Sectors, teaming between university re-searchers and industry is particularly recommended where ceramics for electronics are concerned, inorder to facilitate the informed selection of basic research projects for technological impact.

It was also found that in several major technologies, ceramics are enabling materials, yet have nothistorically enjoyed the widespread participation of the ceramics community. Examples include hetero-geneous catalysis and photocatalysis, in which the active materials are frequently semiconductingoxides, and lithium ion battery technology, in which oxides are the active cathode materials. Theserepresent areas where ceramics can and should have a major impact in the future.


The following topics were discussed in greater detail as examples where fundamental research is par-ticularly needed.

1. Size Effects in Electroceramics

Electroceramics are used as thin films, single crystals, and bulk polycrystals. In device technologies,trends towards miniaturization and integration with silicon has resulted in an increasing focus on theproperties and processing of thin films. The properties of thin film ceramics, often oxides, can deviateremarkably from those of their bulk counterparts. The understanding of such properties is an importantneed and opportunity. A specific example discussed during the Workshop concerns high permittivityceramics used in DRAM’s, where it is found that in very thin films, dielectric properties can be domi-nated by interfacial rather than bulk capacitance. Predictors of performance based on bulk properties areconsequently of limited validity.

Chemical and electrochemical applications also use thin film (e.g., fuel cells, sensors) and fine powderceramics (e.g., catalysts). Size effects can be equally important in these applications.

Research in this area is therefore generally concerned with understanding properties under severe sizeand shape constraints. Properties and phenomena of interest include:

• Dielectric response of thin films and interfaces• Nonstoichiometry and point defects in thin films and small crystallites• Phase stability and phase transitions• Electronic and ionic transport• Reliability; mechanisms of device degradation• Electromechanical response of thin films

It is anticipated that improved fundamental understanding in this area will have a fairly direct impact onmicroelectronics and communications technologies, in which ceramics are used in conductive, magnetic,and optical applications.

2. Ceramics for Wireless Communications

Communication technologies and in particular, wireless communication technologies, are one of themost important growth businesses in the global electronics industry. Ceramic requirements; specificallyfor filters, oscillators and resonators; are critical and represent the single largest cost and size driver ofthe end devices. Most new ceramics enabling significant advances are coming from research doneoverseas. Without an increase in effort, the US risks losing a leadership position in both the researchand technology.

Ceramics contributes to this technology in several ways. There are several classes of microwave ce-ramic dielectrics which offer the combination of relatively high permittivity (ε

r = 20 - 100), low loss (Q

= 1000 -20,000) and low temperature coefficient of frequency (τf ≅ 0), all at microwave frequencies (1 -

4 GHz). These materials have permitted size reductions in cell site transmitters and receivers, hand settransceivers and satellite communication filters. Also, high temperature ceramic superconductors arefinding their first large scale commercial uses in very low loss microwave resonators for wireless com-


munications. These very low loss resonators allow the manufacture of multipole filters with very highfrequency selectivity and very low insertion loss for application in environments where nearby fre-quency interference causes performance problems.

Research opportunities abound in this field. Several top materials R & D issues have already beenidentified by U. S. Industries [published in J. Res. Natl. Inst. Stand. Technol., 101, 797 (1996)]. Theseare, in prioritized order:

• Develop a fundamental understanding of the relationships between chemistry, structure (includingtexture), and dielectric properties of microwave ceramic dielectrics.

• Development of phase diagrams of pertinent ceramic systems which are accurate and reliable.• Research directed toward the discovery of new ceramic compositions with ε

r > 150, τ

f ≅ 0 and high

Q at microwave frequencies.• Understanding of the reaction kinetics during reactive sintering.

Beyond this, the Working Group identifies the following basic issues:• Development of a basic understanding of the physical basis to stretched exponential decay times

responsible for higher polarizabilities than those expected from ionic contributions.• A “microscopic” understanding of the dielectric constant and conductivity (loss factor, Q) at high

frequencies. Recent new models have been proposed for the losses in glasses in terms of multi-atom (jelly fish) movements. Similar models may apply to crystalline ceramics, and should atleast be tested as a starting point for understanding the underlying phenomena.

• Understanding the role of composition on Q, εr and τ

f. This includes an understanding of the effect

of dopants on polarizability and its coupling to high frequencies.

3. Integrated Functions in Electronic Ceramics

The electronic ceramic industry has derived tremendous value from the integration of metals and insula-tors (multilayer ceramic packages); metals and high e ceramics (multilayer ceramic capacitors); andmetals and piezoelectric or electrostrictive ceramics (actuators). Other multifunctional electronic ce-ramic devices and systems can benefit from the economies of manufacturing cost and size reductionprovided by integration. A few actively pursued examples include:

• high ε dielectrics, metals and magnetic inductors (LC circuits)• high ε dielectrics, metals and cofired resistors (RC circuits)• insulators, high µ magnetics and metals (small surface-mount inductors and transformers).

The technological potential in this field is very high. Examples of new devices include combinedsensors and actuators, power supplies integrated on silicon chips, and biomedical systems.

Ceramics as a class of materials is critical to most of these electronic functions since it offers the broadarray of properties needed, including high magnetic permeability, high dielectric permittivity, high orlow dielectric constant, tailorable resistivities (including superconductivity), hermaticity, low dielectricor magnetic loss, electooptic functionality, high piezoelectric or magnetrostrictive strain, and outstand-ing magnetoresistive properties.

The greatest opportunities in this area lie in understanding how to process dissimilar materials while


achieving the desired integration of functions. Co-fired devices are an example where the ceramics fieldhas made the seminal contributions in the past. Current needs in this area include:

• Identifying systems of dissimilar dielectric magnetic, resistive and piezoelectric ceramics whichcan be co-sintered in the 800 to 1000 °C range with acceptable properties. This includes resolvingissues of interdiffusion and thermomechanical properties mismatch as well as controlling sinteringshrinkage as a function of time and temperature.

• Developing forming methods to accomodate disparate shrinkage during firing. The advantagesprovided by the ductility of metals will not be present in co-sintering of many multifunctionalelectronic ceramics.

4. Chemically and Electrochemically Active Ceramics

Chemically active ceramics are widely used in chemicals production, sensing, and energy production,conversion, and storage. Specific examples include:

• Solid oxide fuel cells for energy production.• Intercalation compounds in rechargeable Li-ion batteries.• Ceramic gas sensors for monitoring O

2, CO, NO

x, and hydrocarbon emissions.

• Titania for the photocatalytic remediation of waste water.• Mixed metal oxides for the synthesis of chemical intermediates.• Perovskites for gas separation membranes (e.g., (La

1-xSr

x)(Fe

1-yCo

y)O

3).

• Zeolites and clays for petroleum refining.• Alumina catalyst supports and ceria oxygen buffers in the 3-way automotive catalyst.

Core topics in ceramics basic research such as defects, electronic and ionic transport, crystallography,microstructure, surfaces, and interfaces all have impact on this class of materials. In some areas such asheterogeneous catalysis, photocatalysis, and lithium battery technology, the field of ceramics has beensurprisingly underrepresented, given that the active materials are ceramics. These are areas in which thematerials science approach can have important impact.

The Working Group found that many of the most exciting opportunities are concerned with surfaceactive materials. Broadly speaking, the key goal of researchers in this area is understanding how tocontrol the chemical activity and selectivity of ceramic surfaces and interfaces by manipulating theirstructure and composition. A few specific topics include:

• Understanding how second phases and hetero-interfaces influence the selectivity of sensors. Forexample, why does the addition of Y

2O

3 to TiO

2 (anatase) make it selective for CO while the

addition of Al2O

3 makes it selective for H

2?

• Understanding the mechanisms controlling catalytic anisotropies and using this phenomenon toinfluence chemical functionality. For example, why is the (100) facet of vanadyl pyrophosphateactive for the oxidation of n-butane to maleic anhydride while the others are not?

• Stabilizing high surface area materials against phase transformations and consolidation. Forexample, how are γ-alumina supports stabilized against transformation to a-alumina in automotivecatalysts?


• Understanding how surface electrochemical potential influences catalytic activity and selectivity.Examples include the enhanced catalytic oxidation of hydrocarbons and CO by using an electri-cally biased solid electrolyte such as Y

2O

3-ZrO

2.

• Improving the efficiencies of photcatalytic reactions on metal oxide surfaces. For example, whatintrinsic or defect properties of TiO

2 influence the efficiency with which photo-generated charge

carriers are transferred from the surface to adsorbed reactants?

Another particularly timely area is the efficient design of new materials, by computational and/orexperimental approaches. This includes the discovery of new compounds as well as the design ofcomposites and integrated systems. Examples include:

• Design of improved intercalation compounds for lithium ion batteries and electrochromic devices.For instance, what are the microscopic mechanisms of cycling fade in Li-ion batteries, and canthey be circumvented through crystal chemical or microstructural engineering of the activematerials?

• Design of composites for electrochemical systems. For example, can the composite which bestsatisfies the multiple demands placed on fuel cell components of thermomechanical compatibil-ity, thermodynamic stability, and gas-phase and solid-state transport, be designed from basicprinciples rather than by empiricism?

Chemically active ceramics is, like electronic ceramics, a highly interdisciplinary field, being studiednot only by ceramists but also by electrochemists, solid state chemist, catalytic chemists, chemicalengineers, and surface scientists. The uniqueness of the ceramics field has been its emphasis on pro-cessing-structure-property relationships, which is not present in (for example) surface physics or crystalchemistry. For greatest impact, the ceramics community should attempt to strengthen its interactions(both through interdisciplinary research, professional societies, and funding agencies) with these alliedfields.


The detector material for the 21st century

Computer tomography scanner that usespolycrystalline ceramic scintillator as theprimary x-ray sensor. Courtesy of Dr.Steven Duclos, General ElectricCompany,Schenedtady, NY.

Computed tomography (CT)is a medical imaging techniquethat has become an importantmedical diagnostic tool over thelast 15 years. This techniquereconstructs cross-sectionalimages of the body and head byscanning the patient with X-rays. Body tissues and bonesintersected by the X-ray beamcan be imaged. In addition tomedical applications, CT isbeing used for industrial inspec-tion of aircraft engine compo-nents.

At the heart of a CT systemis the detector, consisting of anumber of scintillator elements.A scintillator is made out of asolid state luminescent materialthat converts high energyradiation (such as X-rays) intouseful visible light. When thislight strikes another device

called a photodiode it isconverted into electricalsignals that are used toproduce the image afterbeing digitized.

To be effective, ascintillator materialmust have certainproperties. These in-clude high absorptionefficiency (the percent-age of X-ray energyabsorbed), high scintil-

lation efficiency (the ratio ofemitted light energy to theabsorbed X-ray energy) lowafterglow (produced by theoutput signal after the X-raysource is turned off) and excel-lent stability (the ability toretain performance despitecontinued exposure to X-raysand temperature). In addition,geometric efficiency is impor-tant, which is defined as thepercentage of x-ray energyexiting the patient that is inci-dent on the cells of the detector.

Another critical property istransparency. A transparentmaterial allows light to betransmitted with very littlescatter. Transparency results inhigher light output, better signalto noise, and reduced radiationdamage. Another advantage oftransparency is that detectionuniformity along the length ofthe body (from head to foot) isimproved. Good uniformity willeliminate artifacts during imag-ing of the skull, which is espe-cially critical when scanning the

small heads of infants andchildren.

A unique ceramic materialbased on a combination of rareearth oxides (Eu3+ doped yttria/gadolinia — (Y, Gd)2 O3:Eu) hasbeen developed that meets theserequirements. In addition tobeing transparent, the materialhas an absorption efficiency of99%, a scintillation efficiencythree times that of conventionaldetector materials, excellentstability, and a geometric effi-ciency of 80% in all modes ofscanning. This material’s verylow afterglow properties resultsin crisp edge definition that ismaintained between acquiredviews during scanning.

These properties are neces-sary in order to producesmoother , sharper images andsuperior low contrast detectionwithout the risk of increasedradiation dose to the patient.Thus, a more accurate and saferdiagnosis can be made.

Further research will lead toceramic scintillators with higherX-ray stopping power, fasterspeeds and lower costs that canbe tailored to specific applica-tions. Whether used for imagingthe human body or aircraft parts,such improvements can onlyresult in more saved lives. ❖


III. GLASS AND PHOTONIC MATERIALS

Steve W. Martin, Iowa State University, Ames, Iowa (Chair)James H. Adair, University of Florida, Gainesville, FloridaAlexis Clare, Alfred University, NYS College of Ceramics, Alfred, New YorkJohn Gruber, San Jose State University, San Jose, CaliforniaHimanshu Jain, Lehigh Univeristy, Bethlehem, PennsylvaniaDavid W. Johnson, Jr., Lucent Technologies, Murray Hill, New Jersey

Glass is one of the most ubiquitous of all ceramic materials and impacts nearly all segments of residen-tial, commercial and technology markets worldwide. The tremendous range of compositions, properties,and processing techniques enables glass to be tailored to applications ranging from consumer tableware,to large area sheet glass, to telecommunication optical fibers. One of the great advantages of glass is ourunique ability to continuously vary the structure and properties through composition. Many if not all ofthe technological breakthroughs made possible by glass have been achieved through compositionaloptimization to achieve desired performance. Glass is the most widely manufactured of all ceramicmaterials. Such wide applications and range of properties have enabled glass to dramatically impact thequality of life through such technologies as the following:

• Fiber optics are a critical technology in revolutionizing the telecommunication industry and creat-ing the Internet and Information superhighway

• Glass (photonic) devices may move computer performance into the next century• Glasses are now being used for the safe disposal of high level nuclear waste• Glass fibers have revolutionized surgery in the US• Thermally efficient window glass are used in nearly all buildings and automobiles• Glass fiber reinforced composites are used in structural applications ranging from aircraft to auto-

mobiles to sporting goods• Glass fiber insulation is used in millions of homes worldwide• Glass makes up nearly half of the entire market of the ceramics industry in the US

Research in glass and optical materials has had, and continues to have, impact across the broader mate-rials research community. A hallmark of glass research is the need to synthesize and characterize ther-modynamically unstable materials. Critical issues in the manufacture of glass remain achieving perfor-mance goals and reliability as well as maintaining the homogeneity associated with glass. Glass re-searchers have long recognized the implications of thermodynamic instability, and have developedsophisticated and complex synthetic techniques for this class of materials. As a result, many new bulkand thin film synthetic techniques have developed from the glass and optical materials research commu-nity. In addition, the characterization of glasses and optical materials has required the development oftheoretical and experimental tools which have benefited many other materials areas. These include theability to understand and model the chemistry, structure, and property relationships of complex aperiodicsolids.

What are the greatest research opportunities?

The research opportunities in glass can be divided into three broad categories: New Behavior, New


Materials, and New Systems and Devices. These research opportunities are related and will therefore bediscussed synergistically as well as individually. Particular research areas of opportunity are discussedbelow.

1. Ion Dynamics and Transport in Glass and Optical Materials

Many of the useful properties of glasses and optical materials hinge on ion dynamics, at low and highfrequencies, and over short and long length scales. Ion motion determines the utility of glassy solidelectrolytes, electrochromic windows, sensors, durable nuclear waste forms, and low- as well as high-dielectric constant glasses for microelectronics. In general, the ion dynamics and transport – propertyrelationships in glasses are not well understood. Different constituents in a glass have very differentresponses; historically, the movement of alkali ions has been of great concern. Depending on the prop-erty of interest, and the temperature and frequency scale, the movement of ions can be a simple diffu-sional process or a complex collective movement of a group of atoms. The latter is very poorly under-stood at present. There is little understanding of how the composition and structure of glass affects thesevarious aspects of ion dynamics. For optimization of glass properties it is important to establish afundamental understanding of ion dynamics related phenomena. Both modeling and experimentalstudies can contribute to this understanding.

This research opportunity is closely allied with fundamental studies of glass structure and properties.The modeling and characterization of glass structure, particularly at the intermediate-range order level,and the study of crystallization in glass-forming systems remain important research areas. However,there is a need for these studies to become truly predictive. For example, models of glass structureshould predict properties, rather than just accurately reproducing partial radial distribution curves, andstudies of crystallization should aim to develop new glasses and glass forming systems.

Research priorities:

• Fundamental understanding of ion motion in glasses under broad ranges of frequency andtemperature.

• Development of glasses of very high and very low dielectric constant.• Detailed understanding of the correlation between ionic transport and the structure and

composition.• Intermediate range order characterization and correlation to physical properties.• Implications of the homogeneity of glass - what are the consequences to properties?

2. Phosphors and Luminescence Materials

Phosphors for luminescent displays are commonly used in the form of powders. However, the role ofparticle size, shape, and crystallographic habit on excitation, quenching and emission is not understood.Fundamental studies which examine the fundamental luminescent characteristics of model particlesystems of controlled purity, size and shape are necessary. Better understanding of issues such as con-centration and impurity quenching, and of the effects of composition, crystal structure, and size scale,can enable development of tailored particles for optical applications.

The optical properties of nanometer size particles are not well understood even in common applications


such as photochromic and colloid colored glasses. The use of newly developed nanometer-scale particlesynthesis methods to produce particles of controlled size, shape, and composition, in both isotropic andanisotropic systems, can provide model systems heretofore not available. The needs for passive opticalmaterials are similar to those for active optical systems (e.g. electroluminescent materials).


• Better understanding of excitation, emission, and quenching.• Detailed understanding of concentration and impurity quenching.• Luminescence processes in fine particles, including nanometer-scale structures.• Optical properties of glass-ceramics and composite materials.

3. New UV/VIS/IR Glasses and Optical Materials

Pushing the limits of transparency in ceramic materials further into both the UV and the IR is of ex-treme importance in many applications. At the UV end of the spectrum, there is a need for UV laseroptics and optical fiber delivery systems. UV lasers are being widely applied in technologically impor-tant areas such as lithography, surgery, materials processing, cutting and welding. One of the mostcritical issues is optical damage caused by impurities and defects, which can be ameliorated eitherthrough new materials and processing techniques, or by using dopants to mitigate the effects of theoptically induced defects.

At the IR end of the spectrum, IR-transparent ceramics and glasses tend to be based on weak bondingand heavy elements. Applications include long wavelength laser light delivery, communications andsensing. While materials with desirable optical properties have been discovered and manufactured, theirinferior mechanical, chemical and thermal durability makes them impractical for many applications.These problems may be overcome by either the development of new materials or the use of transparentprotective coatings. High purity processing is important for IR-transparent materials due to the negativeeffects of impurities such as oxygen which absorb in the region of interest.


• Development of doped, high silica glasses for optical applications.• Discovery of new materials with better IR/UV transparency.• Radiation-hard ceramics and glasses (short wavelength systems).• Characterization of and improvement in chemical, mechanical and thermal durability.• Innovative protection systems for materials with desirable optical properties.

4. Optical Coatings and Thin Films

Coatings for optical materials can serve to protect non-durable materials with desirable optical proper-ties (including non-ceramics, e.g., liquid crystals), but can also serve additional functions. Ceramics areideal for transparent electrodes because of their transparency and durability, combined with electronicconductivity. The technological shift from tubes towards flat panel displays provides additional oppor-tunities for the development of ceramic optical coatings with multiple functionality. Other applicationsinclude electrochromic devices, and smart coatings for architectural glass which provide IR/visiblespectrum light management, while adapting to daily and seasonal conditions. For large-scale applica-


tions in particular, there is an important need to develop low cost, low temperature processes for ceramicoptical coatings.

Research Priorities:

• Low-cost processing of optical thin films.• Developing ceramic optical films with multiple functionality.• Smart optical coatings (responsive to light environment).• Long-term durability and reliability of optical gratings.• Glass thin films with bulk glass optical properties.

5. Integration into New Systems and Devices

Integration of glasses and optical materials into hybrid systems and devices will become increasinglyimportant in the technological drive to achieve ever greater performance in ever smaller volumes and atlower costs. This group strongly felt that some of the greatest future advances in our area will comefrom research directed at glass and photonicoptical materials systems and devices. Among the opportu-nities is the integration of ferrolectric materials into photonic systems based upon electrooptic effectsand second harmonic generation. Some of the most critically needed systems, and components whichwill enable new systems, include:

• Amplifiers: high quantum efficiency 1.3 µm and 1.55 µm optical amplifiers• Integrated ferrolectric photonic devices based on the electrooptic effect and second harmonic

generation.• Fibers: mechanically robust IR fibers, improved fiber gratings• Frequency converters: higher efficiency and selectable frequencies• IR/VIS/UV/X-Ray Materials and Glasses• Lasers: glass-based lasers to reduce cost, wider range of lasers with complete tunability of wave-

length• Lenses and GRIN Lenses: lower cost systems with broader optical ranges• Phosphors, Fluorescent and Scintillating Ceramics and Glasses

6. Processing

Development of new glasses and optical materials, and new systems and devices, requires paralleladvances in processing. Bulk processing remains important, while many of the new device applicationsrequires processing in thin film configurations. Planar grids are taking on increasing importance inintegrated photonic systems. Processing techniques exist for simple systems such as silica. However,thin film techniques via chemical vapor deposition and sol-gel need to be developed for doped (e.g.,with rare earth elements) materials and multicomponent glasses for integrated photonic applications.The following are amongst the most important and exciting new processing approaches for this class ofmaterials:

• Development of CVD thin film techniques for doped high-silica materials and rare earth-dopedmulticomponent glasses.

• Low temperature bulk and thin film processing methodologies. Is room temperature processing of


ceramic thin films feasible?• Low-cost, high performance planar waveguide processing.• Template-based and self-assembly-based processing for new thin film materials and structures.• Template-based processing to control domain structures, such as in ferroelectrics and nonlinear

optical materials.


Rapid prototyping speeds up design and production

Sintered alumina samples fabricated bylayered gelation of suspensions.Courtesy of Dr. Suresh Baskaran,Pacific Northwest Material Laboratory,Richland, WA.

With global competition onthe increase, it is even morecritical to drastically reduce thetime between conceptual designand component production,especially for advanced ceramics.Rapid prototyping (RP), whichis now being adapted for makingceramic components, is onepossible solution to achievingthis goal. This technology makesdimensionally-accurate threedimensional models directlyfrom computer-aided design fileswithout using hard tooling,molds or dies. It is also calledsolid freeform fabrication (SFF)or layered manufacturing since itbuilds an object layer by layerusing two-dimensional sections.RP is currently being improvedso that fully functional parts canbe directly constructed fromceramics and other engineeringmaterials.

A number of RP systems are

commercially avail-able that are beingapplied to ceramics.These includesterolithography,laminated objectmanufacturing, fuseddeposition modeling,selective laser sinter-ing, and ink-jet or

three dimensional printing.Other RP or SFF methods underdevelopment specifically forceramics include robocasting(Sandia National Laboratories),selected-area-gelation of slurrylayers (Pacific Northwest Na-tional Laboratory), and com-puter-aided manufacturing oflaminated engineering materials(CAM-LEM, Case WesternReserve University). Complexparts have been made with manyof these techniques, with proper-ties similar to conventionallyprocessed materials. Robocastingcan also fabricate parts of largethicknesses that are unobtain-able using slip casting.

There has been rapid progressin several of these RP methods,including three-dimensionalprinting (3DP, MassachusettsInstitute of Technology). Thisprocess – which uses ink-jetprinting nozzles to depositbinder onto layers of powdermaterial to form green bodies –is now being used to produceceramic filters for hot gas filtra-tion, investment casting shellsand cores, slip casting molds and

other ceramic parts. Alumina,zirconia-toughened alumina andsilicon nitride parts have dem-onstrated flexural strengths of400, 670 and 570 MPa, respec-tively. Such prototype parts canbe designed and manufactured ata fraction of the time of conven-tional processes.

The ink-jet printing conceptcan be implemented further tocreate solid components withspatially controlled compositionor in other words, functionallygraded materials. Various addi-tives, in addition to binder, canbe deposited onto the powderbed in a controlled fashion byusing multiple nozzles. Thisapproach has been used to makezirconia-toughened aluminawith controlled residual stressdistributions by varying thedopant concentration withposition. Graded microstructuresof high aspect ratio beta-siliconnitride grains and equiaxed beta-silicon nitride grains have alsobeen obtained.

Another 3DP application isthe fabrication of drug deliverydevices with spatially arrangedmicro-reservoirs, each loadedwith varying composition andconcentration of drugs. Highlyreproducible release profileshave been achieved with 3Dprinted pharmaceutical oraldosage forms. Orthopedic im-plants with complexmacrotextured surface andsuperior surface finish on


untextured areas can also beproduced with 3DP. This in-volves 3D printing texturedceramic inserts, integrating theminto investment casting waxtooling, and injecting wax insidethe mold and textured insert.

Modifications to existingequipment continue to take fulladvantage of these processes. Forinstance, 3DP systems have beenredesigned to include a widerrange of operating speeds, bothdrop-on-demand and continuousjet nozzles for greater flexibility,and increased resolution of therastering axis for improvedprinting accuracy. Laminatedobject manufacturing (LOM),which uses a series of laminationand laser cutting steps to form apart, has recently been modifiedto fabricate curved parts ofcontinuous-fiber ceramic matrixcomposites. These LOM com-posites maintain their fibercontinuity in the plane ofcurvature to achieve optimummechanical performance.

Though 3DP has traditionallyused a dry powder system, aslurry-based process has alsobeen developed so that parts ofhigh green density (65%) can bedirectly fabricated. This ap-proach deposits the powder bedby spraying a dispersed slurry ofthe component material onto apiston. A rigid unbound powdermatrix is produced, which isremoved from the part byredispersion in water. Surface

finish of printed parts is im-proved over the standard 3DPprocess since layer heights canbe substantially reduced.

With these and other devel-opments, RP methods promiseto revolutionize ceramics manu-facturing. ❖


IV. CERAMICS PROCESSING

Richard E. Riman, Rutgers University (Chair)James H. Adair, Pennsylvania State UniversityRajendra K. Bordia, University of WashingtonKeith J. Bowman, Purdue UniversityMichael Cima, Massachusetts Institute of TechnologyJennifer A. Lewis, University of Illinois, UrbanaPaul C. McIntyre, Stanford UniversityNitin P. Padture, University of ConnecticutBrian W. Sheldon, Brown University

Research in ceramics processing is extremely diverse, and encompasses all activities which contribute tothe science and technology of fabricating ceramic materials in a useful form. With the exception ofglass, ceramics manufacturing has historically been based primarily on powder processes. In terms ofsheer volume, this remains true today. The basic fabrication steps in producing such a ceramic compo-nent consist of powder synthesis, powder forming, and sintering. An important role of basic research isto address the chemical and physical phenomena involved in each of these steps. However, ceramicsprocessing research also addresses the needs of applications that are not powder based, including micro-electronics, single-crystal products, thermal barrier coatings, and fiber-reinforced composites. Ceramicsprocessing research therefore also includes the formation of thin-film and bulk materials from the liquidphase or by physical and chemical vapor deposition, and crystal growth. The control and developmentof desirable microstructures in any ceramic material, whether it is a thin film, polycrystal, or singlecrystal, is also a mainstay of the ceramics processing field.

Some notable recent achievements in ceramics processing include:

• Use of colloidal chemistry techniques to develop ceramic components such as multilayer capacitorswith active ceramic layers as thin as 2.5 microns, and with drastically improved dielectric break-down strengths and increased reliability.

• Ceramic rolling elements for hybrid bearings, now used in advanced turbine engines and rocketmotors such as those in the Space Shuttle.

• The application of nucleation and seeding techniques to control phase and microstructure. Singlecrystal magnetic ferrites are now commercially produced by recrystallization in the solid state.

• The development and application of piezoelectric materials for a wide range of acoustic applica-tions, such as real-time ultrasound and shock wave lithotripsy for elimination of kidney stoneswithout intrusive surgical intervention.

• Processing of biomaterials including alumina acetabula and femoral heads for total hip prosthesesand replacement roots for teeth.


• Increases in the mechanical strength of alumina, zirconia, and silicon nitride functional ceramicsfrom 200 to 300 MPa in the mid-1980’s to over 1000MPa today, with typical Weibull moduliincreasing from 5 to 15.

• Rapid prototyping of ceramic components by a variety of methods, enabling the evaluation ofsimple and complex ceramic components with minimal investment rather than by conventionaltrial and error techniques.

• Development of predictive sintering models to guide firing processes.

This Working Group identified four major areas of focus for ceramics processing in the coming decade:1) Particle Synthesis and Processing; 2) Forming and Fabrication of Ceramic Components; 3) CeramicThin Films and Coatings; and 4) Sintering and Microstructure Development. Below, the goals andresearch priorities of each are summarized.

1. Particle Synthesis and Processing

Powder processing remains the fabrication scheme of choice for the vast majority of ceramic materials.The driving forces behind this approach are primarily economic. Many ceramic compounds are mosteasily prepared in a powder form. Powder-based processing allows the fabrication of ceramics at tem-peratures that are hundreds of Celsius degrees lower than is possible by the melt processes often used formetals and polymers. If properly performed, powder processing also results in ceramic componentswith microstructures that are ideal for particular applications. The densities achievable with powderprocessing can be widely varied; applications of controlled-porosity ceramics range from low-density,high-temperature filters for molten metals, to fully-dense materials used in the majority of structural andelectronic applications.

One of the primary limitations of ceramic powder processing, as practiced by industry throughout theworld today, is that it remains primarily an art rather than a science. This is slowly changing. Bothchemical and morphological control of many advanced ceramic powders have been achieved at thecommercial level, for compounds including aluminum oxide, tetragonal zirconia polycrystals, silica,silicon nitride, and barium titanate. The integration of powders of controlled size and shape with han-dling procedures based on principles of colloid and interfacial science has permitted the development ofnew powder processing paradigms. For example, the improvement in mechanical properties of struc-tural ceramics has been enabled by better powders and more thoughtful processing to avoid the deleteri-ous effects of aggregates. However, the applications that have benefited from these developmentsremain relatively few in number.

Among the greatest future challenges is the development of processing paradigms for the ever-finerpowders being developed. Powders with particle sizes on the nanometer scale have the potential forfurther decreasing firing temperatures, and thereby developing new applications. These will includemany in which refractory ceramics are integrated with dissimilar materials. The development of newtools suitable for nanoscale particles such as computational chemistry and improved understanding ofcolloidal behavior at the nanoscale are required. Furthermore, there is a need to develop processingschemes that utilize more environmentally-benign aqueous systems rather than organic solvents.



• Development of synthesis routes for specific ceramic powders that yield particles of controlled sizeand shape, particularly anisometric particles.

• Development of schemes to synthesize and process nano-size powders into useful articles.• Development and experimental verification of theories to predict colloidal behavior of nanoscale

particles.• Development of more environmentally benign aqueous processing for ceramics, many of which are

water-sensitive.• Development of polymer systems specific to aqueous processing.

2. Forming and Fabrication of Ceramic Components

Performance in a ceramic component demands control of the structure over many length scales, rangingfrom the grain size level to the macroscopic dimensions of the component. Thus research in the formingand fabrication of ceramics ranges broadly from the control of interparticle forces in a dense suspension,to novel assembly techniques for large components. Two examples of new materials designs that requirecontrol at a range of length scales include functionally-graded ceramics in thermal-barrier and structuralapplications, and ceramic components within microelectromechanical systems (MEMS). A number ofnew microscopic and macroscopic forming technologies have recently emerged within the field knownas solid free-form fabrication, as is discussed in the article on rapid prototyping. Ceramics basic re-search has traditionally underestimated the value of shape; these and other new forming technologiescan have a profound impact on ceramics manufacturing.


• Forming on a small scale (MEMS, mm length scale structures).• Point-wise, parallel manufacturing technologies with control of single particles.• Development of process models that relate particle-pair interactions to dense suspension behavior.• High speed chemical-mechanical machining of ceramics.

3. Ceramic Thin Films and Coatings

Ceramic thin films are presently used in, and will continue to be developed for, a multitude of devicescritical to electronics and communications technology. Ceramic coatings are also becoming increasinglyimportant for thermal, chemical, and tribological applications. The processing of thin-film ceramicsdiffers from that of many other materials due to the complex microstructures and defect structures thatcan arise in complex ionic and covalent compounds. For instance, heteroepitaxy with large strains iscommon in ceramic systems. The fundamental knowledge base necessary for understanding and pre-dicting the orientation and microstructure of ceramic thin films does not now exist. The nucleation andgrowth mechanism of ceramic compounds in thin film form is also poorly understood, as are the me-chanical strains that accompany film formation, and the surface morphologies of ceramic thin films.

Furthermore, many applications of thin film ceramics require deposition at very low temperatures. The


successful integration of crystalline ceramic films with polymer substrates, for example, can enable newtypes of integrated electronic, optical, and electrochemical devices (e.g., batteries and displays). Therole of nonthermal sources of energy in determining ceramic film microstructure is emerging as a fasci-nating area for future research, as is the processing of low density (microporous) ceramic films for theirdielectric and optical properties.


• New tools for direct observation and property characterization of ceramic thin films at the atomicscale.

• Fundamentals of crystal growth in thin films of complex compounds.• Evolution of thermal and densification stresses upon processing of thin films (for electronics) and

thicker coatings (e.g., for thermal barrier coatings).

4. Sintering and Microstructure Development

A largely qualitative understanding of sintering and microstructure development has evolved over recentyears, leading to successful control of the sintered microstructure of many structural and functionalceramics. Examples include translucent aluminas for sodium lamps and orthodontic fixtures, self-reinforced Si

3N

4 for ball bearings and internal combustion engine valves, toughened zirconia for wear

parts and other structural applications, and many types of co-fired multilayer ceramic devices andpackages for microelectronics.

However, the integrated processes of sintering and microstructure development in a crystalline com-pound are so complex that even after 50 years of research, it is not possible to predict quantitatively thesolid-state sintering behavior of a “simple” single-phase crystalline material. This is true even if thefundamental characteristics of the powder are known. Most ceramics are significantly more complex,involving more than one component, more than a single phase, particles of complex morphology, andgradients in chemical composition, temperature, stress, and density. In contrast to crystalline ceramics,successful models have been developed for the viscous sintering of glasses and polymers. In thesematerials, sintering behavior can be predicted from knowledge of basic properties or from a limitednumber of experiments. A similar accomplishment should be envisioned for crystalline ceramics. Thehistorical record indicates that it is unlikely that models based on first principles will capture the com-plexity of real systems. Therefore, the models should incorporate both empirical and fundamentalparameters.


• Development of predictive models for sintering and microstructure development that are quantita-tive, efficient, and robust.

• Continued development of computational models capable of capturing the complexity of sinteringphenomena.

• Recent advances in characterization and instrumentation, such as tools for mapping texture in apolycrystalline solid, should be brought to bear on developing quantitative, pragmatic sintering


models.• There is a continuing need for the measurement of fundamental properties such as atom

diffusivities and interfacial and surface energies (including anisotropies). These measurementsshould be closely coupled to sintering studies.


Building better bones with ceramics

Bioactive glass granule after threemonths in a periodontal defect; thephysiological fluids eroded the granule,leaving an internal recess in which newbone formed (center circular regionwithin the dark annulus). Courtesy ofDr. Paul Ducheyne, University ofPennsylvania, Philadelphia, PA; andDr. Evert Schepers, University ofLeuven, Leuven, Belguim.

In recent years, bioceramicshave helped improve the qualityof life for millions of people.These specially designed materi-als – polycrystalline alumina orhydroxyapatite or partiallystabilized zirconia, bioactiveglass or glass-ceramics andpolyethylene-hydroxyapatitecomposites – have been success-fully used for the repair, recon-struction and replacement ofdiseased or damaged parts of thebody, including bone. For in-stance, alumina has been used inorthopedic surgery for more than20 years as the articulating

surface in total hipprostheses because ofits exceptionally lowcoefficient of frictionand minimal wearrates.

Clinical successrequires the simulta-neous achievement of astable interface withconnective tissue and amatch of the mechani-cal behavior of theimplant with the tissueto be replaced.

Microporous bioceramics basedon calcium phosphate, withpores >100 to 150 microns indiameter, have been used to coatmetal joint implants or used asunloaded space fillers for boneingrowth. Ingrowth of tissue intothe pores occurs, with an in-crease in interfacial area be-tween the implant and thetissues and a resulting increasein resistance to movement of thedevice in the tissue. As innatural bone, proteins adsorb tothe calcium phosphate surface toprovide the critical interveninglayer through which the bonecells interact with the implantedbiomaterial.

Although good bone bondingis achieved to the calciumphosphate coatings currently inuse, poor adhesion between thecalcium phosphate coating andthe metal implant can occur.Research is continuing to de-velop new coatings that can be

chemically bonded directly tothe implant material, similar tooxide layers that readily form onsome metal surfaces, rather thaninterlocked mechanically to theimplant surface, as in the currentapproach.

Such a coating must induceappropriate protein adsorptionbehavior, such that bone celladhesion will occur and promotebone formation at the junctionsite. The ability to controlprotein adsorption throughengineering of ceramic surfacestructures could also be appli-cable to the use of ceramics asvaccine adjuvants and in drugand DNA delivery.

Resorbable biomaterials havealso been designed to degradegradually over time, which arethen replaced by the naturalhost tissue. Porous or particulatecalcium phosphate ceramicmaterials (such as tricalciumphosphate) have been success-fully used as resorbable materialsfor low mechanical strengthapplications, such as repairs ofthe jaw or head. Resorbablebioactive glasses are also re-placed rapidly with regeneratedbone.

Bioactive materials produce aspecific biological response atthe interface of the material,which results in the formation ofa bond between the tissues andthe material. The surface forms abiologically activehydroxycarbonate apatite layer


that provides the bondinginterface with the tissues. Awide range of bonding rates andthickness of interfacial bondinglayers are possible by changingthe composition.

Bioactive materials includeglass and glass-ceramics based onsilica-phosphate systems con-taining apatite, dense synthetichydroxyapatite and polyethyl-ene-hydroxyapatite composites.Applications include orthopedicimplants (vertebral prostheses,intervertebral spacers, bonegrafting), middle-ear bonereplacements and jawbonerepair.

In the next century—as abetter understanding of theinteractions of bioceramics withorganic components is achievedon the molecular level – it willbe possible to tailor the physicaland chemical properties of thematerial with the specific bio-logical and metabolic require-ments of tissues or disease states.The ability to develop newmaterials that have comparablebioactivity but improved bond-ing strength to the materialscurrently in use – in combina-tion with other biotechnologyadvances – should lead to arange of products and applica-tions never before imagined. ❖


V. INTEGRATION OF CERAMICS WITH DISSIMILAR MATERIALS

John E. Ritter, University of Massachusetts, Amherst (Chair)Stephen J. Bennison, DuPont CompanyKeith J. Bowman, Purdue UniversityVinayak P. Dravid, Northwestern UniversityLorraine F. Francis, University of MinnesotaCarol A. Handwerker, NIST, Gaithersburg, MarylandAlan Lesser, University of Massachusetts, AmherstAndy Szweda, Dow Corning, Midland, Michigan

This Working Group focused primarily on the integration of ceramics with organic materials, in the contextof ceramic/polymer hybrids and ceramic/biological interfaces, while recognizing that ceramics are alsowidely integrated with metals and semiconductors in structural and electronic functions. Discussion of thelatter systems appears in reports from Working Groups I and II.

Ceramic/polymer interfaces have importance to a great many current and future technologies. A largefraction of consumer polymers such as filled polymers, high-performance composites for civilian andmilitary transport, exterior finishes for architectural and transportation media, and synthetic fibers forapparel, all contain ceramic phases as passive or active components. Inorganic/organic hybrid materialsoffer potential for tailored properties in new applications such as contact lens materials and abrasionresistant coatings. The latest combinatorial chemistry approaches to the synthesis of bio-chemicals forlife sciences, such as specific drugs for human and animal treatment and compounds for agricultural use(herbicides, fungicides, fertilizers, etc.) rely on the development of selective screens and separationmedia that are often ceramic-based. The development of bioceramics for uses as prosthetic devices,drug delivery systems, and structural scaffolds for bone regeneration are an essential component offuture health care strategies and treatments. Exciting innovations in cancer therapy use ceramics for insitu radio therapy, delivery of heat at tumor sites, and as substrates for extracting and replacing geneti-cally-modified tumor cells that result in self-destruction of tumors. Ceramic/polymer and ceramic/biological interfaces are a field in which scientific understanding is relatively immature, yet critical tothe development of a broad range of new technologies.

The following subjects were discussed as areas of particularly great opportunity.

1. Characterization of Ceramic/Organic Interfaces

Enormous progress has been made in recent years in the study of ceramic free surfaces, grain bound-aries, and ceramic/metal interfaces. High resolution TEM, analytical electron microscopy, scanningprobe microscopies, and surface and interface spectrocopies are amongst the tools which have contrib-uted greatly to developing an atomic level understanding of such phenomena as intergranular filmformation, crystalline surface anisotropy, wetting, and heterogeneous chemical reactions. Modeling ofinterfacial atomic structure and the thermodynamics/kinetics of interfaces has proceeded synergisticallywith the development of these experimental tools. These tools and approaches should now be brought tobear on ceramic/polymer and ceramic/biological interfaces.

It is our view that frequently, in past research on such interfaces, the ceramic surface has been generally


treated as chemically and structurally simple, while the polymer and biological molecules are analyzedand treated with great skill. To continue to ignore the complexity of ceramic surfaces will ultimatelylead not only to major gaps in fundamental knowledge but also lost opportunities for the creation ofinteresting and technological breakthroughs. The ceramics field has the background and capability tomake major contributions in this area, and should seize the opportunity.

2. Ceramic/Polymer Hybrid Materials

The science and engineering of ceramic/polymer hybrids is rich with fundamental questions related tothe synthesis, fabrication, and characterization of physical and mechanical properties. The synthesisapproaches and the materials produced can perhaps be conceptually separated according to the size scaleof the microstructure produced. At one limit are organic/inorganic interpenetrating networks in whichthe inorganic regions are produced in-situ, and are of nanometer scale. These are true hybrid materialsin which properties are determined by local structure and bonding, rather than by interactions betweendiscrete inorganic and organic regions. The second general class of materials are microcomposites inwhich discrete ceramic particles are typically formed by sol-gel routes in a matrix of organic polymer.Here, surface adsorption and self-assembly of the polymers, and adhesion between the phases determinethe physical and mechanical properties. Both of these synthesis routes are producing exciting newmaterials that can be utilized in the areas of fire-resistant materials, bioceramics, and electronic materi-als.

Fundamental studies addressing the effects that the ceramic interface morphology and topography haveon the adsorption and interaction with polymer materials and their self-assembly are needed. Surfacecharacterization tools are needed to describe the physical and mechanical properties of these particularinterfaces. Theoretical and modeling studies are also required to predict atomistic, microscopic, andmacroscopic characteristics of these interfaces.

Understanding the effects of the size and method of synthesis of ceramic particles on their surfaces andinterfaces with polymers will also lead to improved properties in composites and better handling ofnanosized particles. The inorganic regions generated in-situ in a polymer represent the smallest “par-ticle” and colloidal sized particles the largest. The chemical structure of the surface will depend on thesynthesis method; in-situ formed ceramic regions have strong bonds established in synthesis. Ceramicparticles generated by other means will have surface characteristics that depend on the synthesis. Onekey opportunity is to provide a control over the surface and hence interface with the polymer during thesynthesis of the particle. Another is to determine how the surface area to volume ratio affects thestrength of bonding.

3. Controlling Ceramic/Molecular Interactions Through Ceramic Surface Modification

The general view of a ceramic in ceramic-containing “hybrid” system is that it acts as an inertphase or filler. Research to date concerning the interaction of molecules and macromolecules withceramics has thus focused on molecular modification to control interactions and resulting system proper-ties. A few exceptions to this statement, such as the role of glass chemistry in the function of silanecoupling agents for adhesion control and the role of glass chemistry in reactions of macromolecules insolution with surfaces, are cited as evidence for the active nature of the ceramic phase.


We identify that there is great opportunity to study the role of the ceramic surface in ceramic-molecular interactions and associated system properties. Not only will such programs address a signifi-cant gap in understanding but the opportunities for new aproaches to the control of ceramic-molecularinteractions will arise from such studies. Specific ceramics-related issues related to modification in-clude:

• Adjustment of surface (atomic) structure.• Adjustment of surface chemistry and the use of coatings.• Adjustment of surface morphology (over several length scales).

The following areas are suggested as fruitful areas of research:

• Ceramic/polymer coupling for adhesion control for mechanical behavior.• Ceramic/inorganic liquid interactions for colloidal and rheological properties• Ceramic/bio-molecular coupling for bioengineering of the control of molecular functionality in life

sciences.• Ceramic/molecular interactions for combinatorial chemistry.• Molecular and nanoparticle interactions in nano-porous ceramics.

4. Ceramic/Polymer Adhesives

The influence of the ceramic on polymer adhesion has been largely ignored by both the ceramic andpolymer communities. Most of the experimental and theoretical research has concentrated on tailoringthe polymer adhesive to improve bonding. Little is known about the influence and role of the ceramic inthe bonding. Influence of the environment and cyclic stressing on the mechanisms controlling slowcrack growth at ceramic/polymer interfaces is largely unexplored. Computational modeling, coupledwith fundamental experiments, of adhesion as well as delamination is needed to gain a fundamentalunderstanding of these interfaces and how they may be improved.

5. Biological Interfaces

Compared to some other materials, such as polyethylene and surgical steel, ceramics currently enjoylimited use in the biological arena. When they are employed they are often generically described as“ceramic substrate” or “glass slide.” It is generally assumed by the biological community that thesurface is hydroxylated and therefore much the same regardless of the composition, microstructure orsurface structure. There are many materials issued within the biological community that have the dis-tinct potential for a much wider exploitation of ceramics, but in order to achieve this potential a muchbetter understanding of the interaction of biological molecules with the ceramic is essential. While somework with peptide, protein and even cell adhesion has been carried out by biologists, it has focused onthe organic components and hasn’t been carried out as a function of ceramic composition, microstructureor surface structure. In addition, the effects of the biological system on the ceramic are almost nevercharacterized. Ceramics have such a huge potential for impacting this field because of composition andprocessing flexibility, and surface chemistry modifications that can afford tailored responses bybiomolecules. Underlying this potential are fundamental studies in the interaction with increasingcomplex biological molecules with different functional groups as a function of the ceramic structure,composition and surface with an emphasis on complete surface characterization of the ceramic before


and after the interaction. However, in order to successfully implement this research the recommendationwould be to team with a biological group in a multidisciplinary research group.

For ceramics and ceramic-polymer composites used in dental restorative applications, the interface withthe oral environment as well as the interface with the remaining tooth tissue are critical to the perfor-mance and lifetime of the restoration. The key interfacial issues are adhesion and chemical interactionwith the oral environment. Degradation of highly filled ceramic-polymer composites for tooth-coloredfillings is partly linked to the attack of the bonds at the ceramic-polymer interfaces (typically based onsilanes) and at the interface between the restoration and remaining tooth. While ceramic-based crownsare less affected by interaction with the oral environment, strength degradation is observed and the bondwith the remaining tooth tissue must be designed to keep the crown in place and for effective loadtransfer to the supporting tissue (in the case of lower modulus restorations). Much of the research onceramic dental materials has originated from the dental community. While there has been input from theceramics perspective, more ceramics-oriented research is needed to gain a fundamental understanding ofthe structure and chemical interaction of these complex interfaces. Some of the key questions aresimilar to those discussed above: how does the structure and chemistry of the ceramic influence thechemical interaction with components in oral fluids? how can this interaction be characterized? Withknowledge gained from fundamental studies , new methods of bonding and new ceramics with improvedproperties can be developed. For example, can new ceramics be designed to resist plaque accumula-tion and staining, or to have improved bonding to tooth tissue? The need for understanding of ceramic-biological interfaces obviously extends to other applications of bioceramics (e.g., joint replacements,implants), although the specific needs are not addressed here. It should be stressed that collaborationwith those in the dental and medical fields is essential for effective research in these areas.

In a related but conceptually distinct arena, “biological ceramics”, i.e. heavily mineralized hard tissuesproduced by organisms ( teeth, bones, and shells), provide optimized biomineral/protein interfaces.Study of such hard tissue interfaces is relevant to the biomaterial issues just described, as well as toenhancing our knowledge of how such tissues are mineralized. Such “biomimetic” studies representexciting opportunities for ceramic researchers, as well as for interdisciplinary research with biologistsand polymer scientists.

6. Role of Ceramic-Polymer Interfaces in Processing

Polymer adsorption/desorption phenomena and ordering phenomena at ceramic interfaces are critical toan array of areas including ceramic processing. Specifically, a better understanding of how ceramicsurface chemistry and surface morphology and roughness affects such phenomena is needed. Polymerphysicists have explored explored polymer adsorption/desorption on smooth, model surfaces (e.g.,oxidized Si single crystal wafers); however, little attention has been given to complex surfaces (i.e.,those containing multications and multiphase, roughened, porous, etc.). New experimental and computa-tional efforts aimed at elucidating these effects should be initiated. In addition, ordering of small species(e.g., polymers, oligomers, even solvents) at ceramic interfaces have profound implications on structuralinteractions and hence, colloidal stability during processing. There is a need for direct measurement ofthese effects via the surface forces apparatus and atomic force microscopy, as well as characterization ofceramic surfaces (both chemistry and roughness and how these attributes evolve during processing andin the presence of the liquid phase).


As is evident from above, research on interfaces is by necessity multidisciplinary and collaborative. Thisrepresents an opportunity for the ceramics researcher to interact with researchers in a wide range ofother disciplines. This also plays an important role in the education of graduate students through work-ing in teams, learning new characterization techniques, and analytical methods. This research also couldprovide a mechanism of interaction with relevant industry reseachers for cross-fertilization of ideas,techniques and experiences.


Teaching the wonders of science through ceramics

Students testing the strength of ceramicspecimens as part of the Materials WorldModules activity at NorthwesternUniversity. Courtesy of Dr. RobertChang, Northwestern University,Evanston, IL.

In order to attract more highschool students to technicalfields, the educational commu-nity must find nonconventionalways to teach general topics likemath and science, instead ofsimply relying on boring text-books and dreary laboratoryexperiments. Materials engineer-ing is one field that offers a greatway to expose students to sci-ence since they can see, touchand make things used in every-day life. The ceramics commu-nity has been particularly proac-tive in such educational pro-grams. One of these programs,Materials World Modules, isfinding great success in makingscience an exciting topic tolearn.

“It’s a fun way to learn sci-ence” is how one high school

student dubs her experiencewith the MWM, whichwere developed with fund-ing from the NationalScience Foundation. Thesemodules include nineeducational kits that covertopics of interest in materi-als science by combininglessons in chemistry, math-ematics, biology and physicsthat last two to four weeks.

This teaching tool has not onlyproven to increase studentinterest in science and math butalso makes them more aware ofthe importance of materialsscience and engineering.

Part of a national programdesigned in conjunction withNorthwestern University ofChicago and local high schoolprograms, MWM are now in usein 80 high schools across thecountry. Each module provideshands-on experience designingwith materials and requirescollaboration between students,thus creating a real world envi-ronment. For instance, onemodule requires students toperform the same tests as engi-neers do.

The modules have flexibleformats, making it easy to fitthem into existing science andmath curricula. Each comes withteacher and student manuals, astudent journal, an interactivevideo support system and helpfuldesign simulation software.Another key feature of theprogram is that each school is

linked electronically to North-western University, providingaccess to user support servicesand online discussions withother teachers.

The ceramics module hasstudents design a prototypeceramic varistor capable ofprotecting a circuit from voltagesurges and its correspondingcurrent over loads. Students alsolearn the difference betweenceramics and other materials bytesting properties, explore theprocessing steps to make aceramic and fabricate the actualelectronic device. Other mod-ules cover biodegradable materi-als, composites, sensors andsports materials with similartasks.

The success of this programcan be extended to even morestudents by simplifying themodules for middle schoolstudents and translating theprogram into other languages.More programs like MWM canonly lead to a better understand-ing by both students and teach-ers alike on how ceramics andother materials impact society,with the additional benefit ofimproving math and scienceliteracy. Such an educationalapproach is also an excellentway to attract top talent toceramic science and engineer-ing. ❖


VI. EDUCATION IN CERAMICS

Katherine T. Faber, Northwestern University (chair)James A. Adair, Pennsylvania State UniversityMichael Barsoum, Drexel UniversityJohn Gruber, San Jose State UniversityHimanshu Jain, Lehigh UniversityJennifer A. Lewis, University of IllinoisKenneth W. White, University of Houston

NSF research grants in ceramics primarily support (and thereby educate) graduate students. However,education in our field is an important and broad topic that typically begins much earlier than the gradu-ate research degree and continues long after it is completed. Thus ceramics education needs to bediscussed with full participation by educators from primarily undergraduate institutions, and the indus-tries which represent the customer base for ceramics graduates, as well as the research communityrepresented by this group.

Nonetheless, within the discussion that took place at the workshop, several general goals were identi-fied. Firstly, ceramics is inherently interdisciplinary, both fertilizing and drawing from the fields ofchemical engineering, mechanical engineering, electrical engineering, aero/astro engineering, physics,and chemistry. Part of the educational mission of ceramics should be to reach out to these allied disci-plines on a ongoing basis, especially when new fields emerge in which ceramics can have an importantrole (e.g., biomedical engineering). Secondly, ceramics has historically enjoyed a comparatively highlevel of representation by women students at both graduate and undergraduate levels. However, minor-ity students have been underrepresented in our field, and a special effort by the Ceramics Program incollaboration with related educational initiatives at NSF must be encouraged. Thirdly, as discussed inVI., good planning for fundamental research in advanced materials requires an increasingly in-depthknowledge of the technologies that use them. Education of faculty as well as students through intern-ships in industry should be supported by NSF.


VII. ROLE OF NSF IN SUPPORTING COLLABORATIONS

WITH INDUSTRY AND OTHER SECTORS

To what extent should research problems should be driven by pure scientific curiosity, as opposed totechnological impact? Obviously, the two are not mutually exclusive, and differences in opinion on thispoint amongst the participants of the workshop, as well as the respondents to the Email survey, tended to beones of emphasis. Considerable support was given to the view that, while discovery is the goal of basicresearch, implementation is also necessary to justify further discovery.

However, NSF can take steps to facilitate greater impact of university basic research on technology. Oneparticular problem is that many advanced technologies are so complex and advance so rapidly that it isdifficult for university researchers to identify and address key fundamental issues in a timely manner. Apossible solution would be for NSF to promote the substantial immersion of faculty as well as graduatestudents in particular technologies for short periods of time. The level of immersion must be deeper thanhas been characteristic of university-industry collaborations in the past. National laboratory collaborationswith industry and universities would also benefit from this approach. NSF should solicit and supportcreative experiments along these lines.


ACKNOWLEDGEMENTS

The organizers thank the participants for their enthusiastic and thoughtful input during the Workshop.Special thanks are extended to James H. Adair, David R. Clarke, David J. Green, Carlo G. Pantano, andWilliam B. White for editing or writing portions of the final report, and to David Shum and Erin B. Lavikfor helping to ensure a smoothly run conference. Also, thanks are extended to Laurel Sheppard for writingexample sections; and to Pamela Stephan for preparing the report for the web.


APPENDIX: WORKSHOP SPEAKING PROGRAM

NSF Workshop

“Fundamental Research Needs in Ceramics”

June 10 and 11, 1997NSF, Arlington, VA

June 10, 1997 (Tuesday)

8:00 AM Welcome and Introduction (L.J. Schioler)8:10 Rationale, Objectives, and Format (Y.-M. Chiang)8:20 Overview: The Future of Ceramics Research (A.G. Evans)9:10 Composite Active Structures Utilizing Ceramics

(N.W. Hagood)10:00 - 10:20 Break10:20 Thin Film Oxides for Electronics (T.M. Shaw)11:10 Formulating Impact Driven Research in Ceramics

(M.J. Cima)

12:00 - 1:00PM Bag Lunch

1:00 Chemical Applications of Ceramics (G.S. Rohrer)1:50 Microstructural Tailoring of Structural Ceramics:

Challenges and Opportunities (N.P. Padture)2:25 Processing of Functional Ceramics (J.A. Lewis)3:00 - 3:15 Break3:15 Definition of Working Groups

5:00 - 7:00 Dinner

7:00 - 9:00 Working Groups, Round 1

June 11, 1997 (Wednesday)

8:00 Reports from 1st Round Working Groups9:00 Working Groups, Round 211:00 Reports from 2nd Round Working Groups

12:00- 1:00 Bag Lunch

1:00 Preparation of the Draft Report3:00 - 3:15 Break3:15 Closing Session (Summary of Conclusions)5:00 Adjourn


LIST OF PARTICIPANTS

Adair, James H.

Pennsylvania State University

University Park, PA

[email protected]

Akbar, Sheikh A.

Ohio State University

Dept. Mat. Sci. & Engr.

Columbus, OH

[email protected]

Barsoum, Michel

Drexel University

Dept. Mat. Engr.

Philadelphia, PA

[email protected]

Bennison, Stephen J.

Du Pont Company

Central R&D, Exp. Station

Wilmington, DE

[email protected]

Bordia, Rajendra K.

University of Washington

Seattle, WA

[email protected]

Bowman, Keith J.

Purdue University

Mat. & Electrical Engr.

West Lafayette, IN

[email protected]

Chen, I-Wei

University of Pennsylvania

Dept. Mat. Sci. & Engr.

Philadelphia, PA

[email protected]

Chiang, Yet-MingMassachusetts Inst. of TechnologyCambridge, [email protected]

Cima, Michael J.Massachusetts Inst. of TechnologyCambridge, [email protected]

Clare, AlexisAlfred UniversityNew York State College of CeramicsAlfred, [email protected]

Clarke, David R.University of CaliforniaMat. Engr. Dept.Santa Barbara, [email protected]

Dravid, Vinayak P.Northwestern UniversityDept. Mat. Sci. & Engr.Evanston, [email protected]

Evans, Anthony G.Princeton UniversityPrinceton, [email protected]

Faber, Kathy T.Northwestern UniversityDept. Mat. Sci. & Engr.Evanston, [email protected]

Francis, Lorraine F.University of MinnesotaDept. Mat. Sci. & Chem. Engr.Minneapolis, [email protected]

Green, David J.Pennsylvania State UniversityDept. Mat. Sci. & Engr.University Park, [email protected]

Handwerker, CarolNational Institute of Standards

of TechnologyGaithersburg, [email protected]

Gruber, John

San Jose State University

Inst. of Optics

San Jose, CA

Hagood, Nesbitt W.Massachusetts Inst. of TechnologyDept. Aero/Astro.Cambridge, [email protected]

Halloran, John W.University of MichiganDept. Mat. Sci. & Engr.Ann Arbor, MIjohn_halloran@

mse.engin.umich.edu

Harris, Michael T.University of MarylandDept. Chem Engr.College Park, [email protected]

Heuer, Arthur H.Case Western Reserve UniversityDept. Mat. Sci. & Engr.Cleveland, [email protected]

Jain, HimanshuLehigh UniversityDept. Mat. Sci. & Engr.Bethlehem, [email protected]

Jakus, Karl

University of Massachusetts

MIE Department

Amherst, MA

[email protected]


Johnson, David W. Jr.Lucent TechnologyMurray Hill, [email protected]

Johnson, D. LynnNorthwestern UniversityDept. Mat. Sci. & Engr.Evanston, [email protected]

Lesser, Alan J.University of MassachusettsPolymer Sci. & Engr.Amherst, [email protected]

Lewis, Jennifer A.University of IllinoisUrbana, [email protected]

Martin, Steve W.Iowa State UniversityDept. Mat. Sci. & Engr.Ames, [email protected]

McIntyre, Paul C.Stanford UniversityPalo Alto, [email protected]

Morris-Hotsenpiller, Patricia

DuPont, CR&D

Wilmington, DE

[email protected]

Onoda, George Y.National Institute of Standards

of TechnologyCeramics DivisionGaithersburg, [email protected]

Padture, Nitin P.University of ConnecticutStorrs, [email protected]

Readey, Dennis W.Colorado School of MinesDept. Met. & Mat. Engr.Golden, [email protected]

Riman, Richard E.Rutgers UniversityDept. CeramicsPiscataway, [email protected]

Ritter, John E.University of MassachusettsMIE Dept.Amherst, [email protected]

Rohrer, Gregory S.Carnegie MellonDept. Mat. Sci. & Engr.Pittsburgh, [email protected]

Shaw, Thomas M.IBMT. J. Watson Res. CenterYorktown Heights, [email protected]

Sheldon, Brian W.Brown UniversityDivision of Engr.Providence, [email protected]

Szweda, AndrewDow Corning CompanyMidland, [email protected]

Trolier-McKinstry, Susan E.Pennsylvania State UniversityUniversity Park, [email protected]

Vanderah, Terrell A.National Institute of Standards

of TechnologyCeramics Div.Gaithersburg, [email protected]

Wachsman, Eric D.University of FloridaDept. Mat. Sci. & Engr.Gainesville, [email protected]

White, Ken W.University of HoustonDept. Mech. Engr.Houston, [email protected]

fundamental research needs in ceramics

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