Impurity Effects in Surface Diffusion on Aluminum Oxide

Abstract

Surface diffusion on aluminum oxide was studied by measuring the growth rate of grain boundary grooves at high temperatures. Three materials were studied, high-purity aluminum oxide crystals containing low-angle subgrain boundaries and two grades of polycrystalline sintered alumina having different impurity contents. The rate of grooving on the higher-purity surfaces was! to i that on the lower-purity surfaces. The activation energy for surface diffusion on the high-purity crystals and on one of the sintered materials is about 130 kcal/mole, compared to 75 kcal/mole for the less-pure sintered material. Intentional impurity additions to the surfaces indicate that small amounts of impurities can appreciably change the rate of groove growth.