Advanced Ceramics for Building Construction
G. P. Wirtz,* C. Dry,* J. R. Wylder, M. W. Anderson, T. Park, J. Biggars, D. Griffin
University of Illinois

Modern ceramic fabrication techniques are being applied to inexpensive raw materials to produce strong lightweight building panels. Emphasis is on common clays, fly ash, bottom ash, and diatomaceous earth as raw materials. Lignin sulphonate, a by-product of the paper industry, is used as a foam-stabilizing agent in fabricating foamed ceramic construction materials. Sol incorporation and gellation, with careful control of pH and rheology, is similarly being evaluated in fabrication, as is phosphate bonding. Combustible additives, such as sawdust, and expansive additives, such as vermiculite, are also being studied as means of decreasing density. Extruded honeycomb structures will be produced and evaluated.

Crystallization Kinetics of Amorphous Mullite and YAG Fibers
W. M. Kriven,* B. R. Johnson
U.S. Air Force Office of Scientific Research Science and Technology Transfer (STTR) (In collaboration with Containerless Research Inc., Evanston, Ill.)

Amorphous fibers synthesized by laser-heated, containerless methods are being tested to develop a process to convert them into single-crystal fibers. These fibers are projected to have important applications for reinforcing ceramic matrix composite materials. The kinetic parameters of the crystallization process have been determined using differential thermal analysis (DTA). The measured kinetic parameters were then used to determine rates of crystallization as a function of temperature and time. Additionally, the crystallinity of the fibers and their microstructure have been evaluated using various spectroscopic techniques including TEM, optical microscopy, and SEM. Strength values of the fibers have been measured using tensile testing techniques.

Defects and Diffusion in Ceramic Materials
R. S. Averback,* C. P. Flynn* (Physics)
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Basic aspects of diffusion and radiation-induced defects in model ceramic oxide materials are investigated. Specimens especially grown by MBE methods, tailored to specific experiments, ion beam analysis, and x-ray diffraction and SIMS comprise the methods of study.

Determination of the Elastic Tensor of 2:1 Mullite and YAG as a Function of Temperature
W. M. Kriven,* J. Palko
Hertz Fellowship

An important step in the development of ceramic matrix composites is the modeling of the mechanical behavior of the reinforcing phase. The anisotropy can have a great effect on the stresses applied on the reinforcement, which is critical in determining the crack propagation properties of the composite. Of particular interest is the temperature dependence of the elastic tensor in the range of possible service temperatures. Such modeling requires complete specification of the elastic tensor for the single-crystal phase. This research utilizes laser Brillouin spectroscopy to determine the elastic constants of candidate reinforcement phases from measured sound velocities. 2:1 mullite (2A12O3.SiO2 and yttrium aluminum garnet (Y3Al5O12) are being studied at temperatures ranging from room temperature to 1500?C.

Ion Beam Modifications of Materials
R. S. Averback*
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Basic aspects of ion beam modifications of materials are being investigated. These studies include ion beam mixing, defect production, radiation-enhanced diffusion, and ion beam-assisted film growth. The work combines molecular dynamics computer simulation with experimental studies using MBE grown films and 1 keV to 3 MeV ion beams and various surface analysis methods. Metals, intermetallic compounds, oxide ceramics, and compound semiconductors are of interest.

Mechanism of Oxidation of SiC-AlN Solid Solutions
A. Zangvil,* R. Ruh,* Y. Xu
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with AFWAL/MLLM and the Materials Research Laboratory)

We are investigating mechanisms of high-temperature oxidation of hot-pressed SiC-AlN compositions. The dense materials are either composites or solid solutions, depending on processing conditions. The oxidation is strongly affected by the formation and further reaction of several layers found at the outer surface, such as SiAlON and mullite, and by microstructural factors. High-resolution and analytical TEM, as well as SEM and XRD, are used in the investigation.

Microcharacterization of Microcrystalline Fibers and Matrices from Organic Precursors
A. Zangvil,* S. Pekin, P. Mogilevsky
Dow Corning Corp. (In cooperation with the Materials Research Laboratory)

Detailed microstructural and microchemical investigation of polymer-derived fibers and matrices is being performed. In particular, the amorphous/crystalline nature of the materials and the presence of second phases are being studied. The effect of various processing conditions and exposure to various environments on fibers and fiber/matrix interfaces is being investigated using a variety of microanalytical techniques.

Structure and Properties of Nanoparticles
R. S. Averback,* J. M. Gibson*
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

The structure of nanoparticles and their interactions with one another and with substrates are examined on an atomic scale using high-resolution transmission electron microscopy and molecular dynamics computer simulations. Sintering of small assemblies of nanoparticles, epitaxial relationships between the particles and substrates, and the dependence of size on alloy phase stability are investigated.

Structure and Properties of Nanophase Ceramics
R. S. Averback*
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

Nanophase processing is a novel technique by which metallic and ceramic materials can be produced in the form of ultrafine powders with sizes in the range of 5 to 50 nm. The resulting powder particles, called nanophase or nanocrystalline powder, can be cold compacted at or near room temperature to near theoretical density. The novel microstructure of ceramics thus produced can impart several useful engineering properties. Ongoing research on these nanophase ceramics includes sintering kinetics, fracture strength and toughness, and superplastic deformation. The goal of the research program is to identify useful engineering properties of the nanophase ceramics and to understand their structure and property relationships.

Transformation Weakening by Cristobalite in Mullite-Cordierite Laminates
W. M. Kriven,* S.-J. Lee
U.S. Air Force Office of Scientific Research

This research involves preparation of chemically stabilized b-crystobalite powders synthesized by the solution polymerization technique employing Pechini resin and PVA solution as a polymeric carrier and consideration of mullite-cordierite composites with b-cristobalite interfaces showing the optimum phase transformation weakening behavior at the laminate/matrix interface. We are investigating grain size effects on the b?a transformation of cristobalite and fabricating laminate structure by the tape-casting process including the control of thermal and co-firing conditions between them.