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 20 vol% 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 2400 rpm. 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 theisothermal sintering, the samples used a heating rate of20 ◦C min−1 to reach the desired temperature and were heldfor different times. For nonisothermal sintering, four heating rates of 3, 5, 10, and 20 ◦C min−1 were used to reach thedesired temperature without holding. The green density wasmeasured by the geometric method, and the sintered densitywas measured by the Archimedes method with deionizedwater. The value 3.986 g cm−3 was used as the theoreticaldensity.