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In comparison with the typically worm-like α-Al 2 O 3  powders formed from an unground Al(OH) 3  precursor calcined at 1450°C, spherical α-Al 2 O 3  powders with ~1 μm in size were prepared by the calcination of a ground Al(OH) 3  precursor with 5 wt.% [NH 4 ] + BF 4  −  under the same calcination conditions. The influence of a high-energy ball milling pretreatment as well as of the additives on the morphological evolution of α-Al 2 O 3  powders was studied using the commercial precursor Al(OH) 3  as raw material. The results indicate that the morphology of α-Al 2 O 3  powders is closely related to the morphology of the Al(OH) 3  precursor and to the introduction of different additives. The refinement of the Al(OH) 3  precursor in aggregate size and of the primary crystal size by high-energy ball milling has effectively suppressed the neck growth of α-Al 2 O 3  grains. In contrast to the findings made previously with the introduction of 5 wt.% [NH 4 ] + Cl − , the morphology of the α-Al 2 O 3  particles could be significantly improved from a ground Al(OH) 3  precursor with the addition of 5 wt.% [NH 4 ] + BF 4  − , which resulted in the formation of spherical α-Al 2 O 3  powders with 1 μm size at 1450°C.

Influence of high-energy ball milling and additives on the formation of sphere-like α-Al 2 O 3 powder by high-temperature calcination