Effect of crystallite size of boehmite on sinterability of alumina ceramics

Alumina ceramics were prepared by heating γ-Al₂O₃ powders obtained from boehmites with a variety of crystallite sizes to elucidate effect of the crystallinity on the sinterability of alumina derived from boehmite. Boehmite powders were prepared both by precipitation and by hydrothermal treatment of a commercial boehmite powder. The crystallite sizes of these boehmites were ranged from 0 (in a gel) through 2.9 to 24.4 nm while those of the γ-Al₂O₃ powders formed by heating the boehmites at 600 °C for 1 h were 4.0, 4.6 and 8.0 nm, respectively. The powders were ground in a planetary mill to 1.4-1.5 μm and their sinterability was examined by forming them into pellets and heating at 1400-1600 °C for 3 h. The sinterability increased in the γ-Al₂O₃ from boehmite of larger crystallite size. The difference in sinterability is suggested to originate in the difference in agglomeration hardness of fine boehmite particles.