Chemical inhomogeneity in commercial alumina powders and its effect on abnormal grain growth during sintering

Chemical inhomogeneity in four commercial alumina powders and its effect on the abnormal grain growth (AGG) during sintering have been investigated. Classification and chemical analyses revealed that relatively small portions of coarse particles in all the powders contained a significantly higher concentration of impurities than their corresponding large portions of fine particles. Hot pressing showed that AGG occurred for all the coarse portions whereas there was no significant indication of AGG for the fine portions. AGG also occurred for all unclassified powders during sintering at the interfaces of bilayer specimens fabricated by repeated centrifugal casting, which could also be attributed to the coarse particles mass-segregated during centrifugal casting. Results of this investigation indicate that coarse particles in commercial purity alumina powder generally contain high concentration of impurities and thus can cause AGG during sintering. Particle aggregates were attributed to the high concentration of impurities in the coarse portions.