A high-purity
-Al2O3 powder (>99.9

A high-purity
-Al2O3 powder (>99.995%, AKP-50, Sumitomo Chemical Co., Tokyo, Japan) was used in this investigation. The as-received powder had an average diameter of 0.24um. The classified powder had an average diameter of 0.21um and was produced from as-received powder using the centrifugal process. The centrifugal process for preparing classified powders started with a slurry of 20vol% solids dispersed in deionized water and stabilized at pH 4 with nitric acid. The dispersed slurry was centrifuged at 800 rpm for 30 min. Thereafter, the upper suspension solution of the slurry was used for further centrifugation at speeds up to 2400rpm. The classified powder was the final sediment in the slurry. The as-received and classified samples used for studying the sintering behavior and microstructural evolution were prepared by slip casting. The green density of these samples was about 62% theoretical density .Sintering was performed in air using a dilatometer. For the isothermal sintering, the samples used a heating rate of 20℃ min−1 to reach the desired temperature and were held for different times. For nonisothermal sintering, four heating rates of 3, 5, 10, and 20℃ min−1 were used to reach the desired temperature without holding. The green density was measured by the geometric method, and the sintered density was measured by the Archimedes method with deionized water. The value 3.986 g cm−3 was used as the theoretical density.