Research Interests in Ceramic Processing and Ceramic Materials
Binder Removal by Thermal Methods
During the processing of ceramics from powders to sintered parts, binder is often added to aid in the handling and processing of the green components. The thermal removal of the binder is often a very slow process requiring days and the yield losses can be high. We have been using a combined modeling and experimental approach to predict rapid binder removal cycles without causing defects in the green body.
Supercritical Extraction of Binder
Supercritical extraction of binder has been used as an alternative processing strategy to rapidly remove binder from green bodies without causing defects in the components. With this methodology, about half of the binder can be removed in as little as three hours.
Synthesis and Processing of Ceramics for Capacitor Applications
To obtain well-defined chemical homogeneity, crystallinity, and porosity, ceramic powders are synthesized by a number of routes, a general attribute of which is that atomic level mixing occurs early in the synthesis process. Powders prepared by these chemical synthesis routes are being evaluated for the application of ceramic capacitors. We have recently synthesized perovskite-type materials having greater than 1000 V/mil (40 V/μm) breakdown strength for use as high-energy density, high voltage capacitors.
Sintering of Ceramics and High Temperature Reactions
The kinetics accompanying the high-temperature sintering of ceramic materials are investigated using combined dilatometry and mass spectrometry. The objective of this work is to develop models for the reaction networks occurring at high temperature and to provide insight into the development of microstructure that occurs at high temperature during sintering.
Lamination, Adhesion Strength and Gas Permeability of Green Ceramic Tapes
In the fabrication of multilayer ceramic capacitors, green sheets are first tape cast and then laminated. To obtain good adhesion between the green tapes, the variables of lamination temperature, pressure, and time can be selected. We have examined in detail the effects of the lamination conditions on the microstructure, adhesion strength, and gas-phase permeability of multilayer green bodies.
Strain Mismatch in Ceramic Processing
We have recently developed a method to shape thin ceramic components at high temperature, without the application of external pressure. To cause this deformation, a coating of a ceramic is applied to a substrate and the strain mismatch which occurs at high temperature leads to curvature in the body. The strain mismatch may arise from cation size effects, phase changes, and differential shrinkage during sintering. The mechanics models which describe the deformation may also have some applicability for describing unwanted deformation in the processing of, for example, LTCC components.
The motion of ceramic particles in a fluid during the forming processes of slip casting, injection molding, and extrusion plays a key role in the development of the microstructure of the body. Both experiments and models are used to probe the role of particle size, size distribution, surface charge, and particle velocity on the evolution of the microstructure during the casting process. We have recently showed how the effects of particle velocity and cake compressibility lead to strain mismatch, and hence bending, in ceramic bodies formed by slip casting. The degree of strain mismatch can be adjusted by modifying the solids loading, the dispersant concentration, or the binder concentration used in the slurry.
We have recently completed quasi-elastic neutron scattering study of the dynamics of ethylene and ethane in microporous silica membrane material. These adsorbates diffuse in a continuous fashion with rotation playing a role in their mobility in the confined pore space.