Effect of surface impurities on the microstructure development during sintering of alumina

Microstructural evolution during sintering of alumina powder compacts prepared by cold isostatic pressing (CIP) was monitored. For CIP, rubber molds lubricated with silicone oil were used so that a very small amount of impurity was introduced to the surface of the powder compacts, During sintering at 1600 degreesC, grain growth in the surface region was inhibited up to sintering for 1 h, but subsequently abnormal grain growth occurred. in the inner region, however, the grains grew uniformly without abnormal grain growth. Impurities that initially drag the boundary migration but form liquid at the end are suggested to cause abnormal grain growth.