September 28, Rishi Raj, University of Colorado
Refreshments served at 2:45 PM
Field Assisted Sintering of Ceramics and Viscous Flow in Glass
Abstract: The application of DC electrical fields, of modest strengths, when applied to ceramics and glasses at elevated temperatures produce dramatic new effects: ceramics that normally require several hours at temperatures above 1400oC can be sintered in <5s at furnace temperatures of less than 1000oC. A glass that softens above 950oC is shown to flow with low viscosity at temperatures of about 500oC. These effects are accompanied by a sudden surge in electronic conductivity producing Joule heating, which, however, is insufficient to explain these unusual phenomena. Instead a mechanism based upon the nucleation of Frenkel pairs is proposed, and some experimental evidence for it is presented.
Biography: Rishi Raj has worked in high temperature processing-structure-properties relationships in ceramics for forty years, starting at the University of Colorado in 1971, then at Cornell University from 1975, finally returning back to Colorado in 1996. His work is distinguished by the way it molds fundamental concepts into closed form models that link parametric relationships to laboratory measurements. Often, the concepts are rooted in the structure, thermodynamic and kinetic properties of interfaces, and diffusion in the solid–state. This Feature summarizes his most recent work on the influence of electrical fields on grain growth, sintering, and superplastic deformation in ceramics. He is pleased that here, he is able to build on his undergraduate education in electrical engineering and doctoral education in engineering and applied sciences.
Faculty Host: Uday Pal
Student Host: Xiaofei Guan