Synthesis of α-Al2O3 nanopowder by sol-freeze drying method

alpha -Al2O3 nanopowder was synthesized by a sol-freeze drying-calcination method using AlCl3 . 6H(2)O as precursor for the aluminum chloride solution. Boehmite precipitate was first prepared by reaction of the AlCl3 solution with a NH3 solution. The precipitate was converted into a transparent sol by peptizing with nitric acid under controlled heating at 80 degreesC. After freeze drying the sol, a white boehmite powder was obtained. Finally, alpha -Al2O3 nanopowder with an equivalent diameter of 42 nm was obtained by calcination of the boehmite powder in air at 1100 degreesC for 1 h.