Drying and Condensation of Sol-Gel-derived Ceramics
J. Kieffer,* E. Guilbert
National Science Foundation, CTS 94-07958

During sol-gel processing, structural developments occur as a result of network condensation. Consequently, the rigidity of the structure and the resistance it offers to the escaping solvent increase. Pressure gradients build and the gels risk fracture. Using Brillouin light scattering in the course of the drying process, we monitor the complex mechanical modulus, characterizing the dynamic response of these gels on a molecular scale. This yields information concerning the change of elastic properties and viscous dissipation, as controlled by chemical composition and drying rates.

Engineered Nanoporous Materials
J. Kieffer*
University of Illinois

The ability to design and manufacture materials with controlled pore structures, with sizes between nanometer and micron, requires understanding the relationships between processing conditions, structure, and properties of these systems. This understanding is derived from multiscale computer simulations of the processes involved in structural assembly and evolution. We perform large-scale molecular dynamic simulations that incorporate length and time scale bridging features, including acceleration algorithms, scaling, coarse graining, and overlap matching with continuum modeling techniques, such as cellular automata and phase field models, to generate accurate models of porous materials.

Fundamental Interactions in Colloidal Suspensions- Depletion Effects in Charged, Binary Collodial Systems
J. A. Lewis,* V. Tohver
NSF Presidential Faculty Fellow Award; National Aeronautics and Space Administration

We are carrying out rheological measurements (stress viscometry and oscillatory measurements) to probe the effects of charged depletant species on the stability of concentrated collodial dispersions. Our observations have highlighted the importance of depletion stabilization in such systems. Novel crystallization phenomena have been observed. Currently, we are investigating using this materials system as feedback for photonic band gap applications in collaboration with P. Braun (U of I) and P. Wiltzius (Lucent Technologies).

Fused Deposition of Ceramics-Development of Feed Materials and Sintering Processes
A. Zangvil,* W. A. Ellingson,* S. Pekin
U.S. Department of Energy, DE-FG02-96ER45439; Argonne National Laboratory (In cooperation with the Materials Research Laboratory)

Solid free-form fabrication enables the production of prototypes and parts directly from CAD files, without the need for hard tooling, and is presently explored for the production of ceramic components. Our objectives are to develop the polymer/ceramic mixtures suitable for controlled fused deposition of specific ceramic materials and to investigate the debinding, sintering, and microstructure development processes in components produced by this technique.

Gelation Behavior of Aqueous Ceramic Suspensions
J. A. Lewis,* J. Zysk, J. Smay, M. Janet
Sandia National Laboratories

Gel casting is a near-net shape-forming process suitable for complex 3-D components. We are studying the gelation behavior of aqueous suspensions that contain high solids volume fraction in the presence of low molecular weight polymeric additives (e.g., polyvinyl alcohols). Such systems are environmentally benign and produce consolidated bodies with low organic content facilitating subsequent debinding processes. In collaboration with Sandia National Laboratories, we are developing a novel solid free form (SFF) fabrication route which utilizes gel-based precursors for component build sequences. The coupling of gel-casting with SFF routes is being undertaken for the first time to produce components with impaired handling strength and macrostructural uniformity.

Microcomposite Fast Ion Conductors Derived from Coated Powders
J. W. Bullard,* D. R. Diercks
University of Illinois

Stabilized zirconia is a fast oxygen conductor and as such is widely used in solid oxide fuel cell applications. Microstructural defects like grain boundaries raise the ac impedance in this material. We are investigating the effects on electrical properties of placing a second oxygen-conducting phase at the grain boundaries, which we attempt to achieve by coating zirconia powders with that phase prior to consolidation. The goal of the work is to tailor the temperature-dependent oxygen conductivity by adjusting the type and thickness of this secondary phase.

Microdesigning Model Material Systems to Probe Dissipative Interface Motion in Heterogeneous Ceramic Microstructures
J. W. Bullard,* M. Menon
National Science Foundation CAREER Award

We are experimentally examining the energetics and kinetics of microstructure evolution in heterophase systems by patterning simple, controlled-geometry microfeatures of ceramic phases onto crystalline substrates. By exploring the influences of the initial geometry and heteroepitaxy on equilibrium morphology and on coarsening and coalescence rates, we should be able to derive quantitative data on relative interfacial energies and on the rate-controlling mass transport mechanism governing the evolution. Such information is crucial to understanding the processing of materials ranging from thin ceramic layers to structural composites.

Microstructural Engineering in the Al2O3-ZrO2 Eutectic System
M. Berg,* P. Yang
W. R. Grace & Co.

This research is being conducted to examine the relationship between microstructure and mechanical performance in the Al2O3-ZrO2 eutectic system. The study will concentrate on densification processes, thermal instability associated with phase distribution of zirconia in this eutectic composite. The effect of processing on the microstructural-mechanical properties will be evaluated.

Processing of Metal Foams
Y. Q. Sun,* Y. R. Chen
University of Illinois

The goal of this research is to engineer the density of metallic materials by foam processing. Two processing methods will be investigated for the production of stable and castable liquid foam structures. One is based on using an in situ surfactant to stabilize the liquid foam structure. The other method is to foam liquid alloys possessing a wide solidification range, with the viscosity being controlled by controlling the relative content of the liquid-sold two-phase mixture.