Preparation and sintering pure nanocrystalline α-alumina powder

Seeding of aluminum nitrate solution with ≥0.5 wt.% of the 25 nm α-Al2O3 powder markedly accelerates the kinetics of α-alumina crystallization from the gel, the latter being formed in course of addition of ammonia to the solution. Depending on the amount of seeds and the way of their incorporation to the solution the complete transformation occurs from 800 to 930 °C. The resulting powder consists of 50–60 nm crystallites which, in turn, are agglomerated in 10–20 μm species, the size of crystallites being independent of the amount of seeds added. Grinding under mild conditions destroys agglomerates and leads to a nano-powder of which 95–99% dense bodies have been sintered at 1300–1400 °C.