CHARACTERIZATION OF CERAMIC PARTICLES: ANALYSIS OF ALUMINA BY DIELECTRIC MEASUREMENTS.

Abstract : The purpose of the study was to determine if dielectric behavior can be a useful tool for characterizing ceramic particulates. A qualitative examination was made on four commercial aluminas ranging in particle size from 0.3 micro to 45 micro. The surface chemistry and environment of these powders were varied. Pronounced dielectric effects were found at frequencies below 100,000 Hz and were attributed to surface conductance. The conductance results from the diffusion of ionized species along the surface, and is aided by adsorbed water which allows electrolytes to form and which serves as a vehicle for diffusion. The surface conduction causes individual particles to become polarized when a field is applied. Also, some conduction occurs from particle to particle, causing an electrode polarization effect. The contribution to dielectric effects due to the local and continuous conduction mechanisms have been separated experimentally. These results indicate that dielectric measurements appear useful for monitoring the level of ionic impurities and adsorbed water on particulates and as a tool for ceramic processing studies. (Author)