FACTORS AFFECTING PREPARATION OF α-Al_2O_3 POWDER AT LOW TEMPERATURE BY HYDROTHERMAL METHOD

The hydrothermal method was used to prepare α-Al2O3 powders using industrial grade Al(OH)3 as a starting material with the addition of seeds and mineralizers. The effects of solid content, particle size of the starting material, hydrothermal temperature, hydrothermal holding time, addition of seeds and kinds of mineralizers on the productivity of α-Al2O3 and on the morphology of the product were investigated. The results show that the productivity of α-Al2O3 increases and then decreases with the increase of the solid content. The smaller the particle size (16 μm to 2.5 μm) of starting material, the more the productivity of α-Al2O3, but further decreasing the particle size exhibits little influence on the productivity. The productivity of α-Al2O3 increases and the crystal structure develops well with elevating hydrothermal temperature, prolonging hydrothermal holding time and addition of seeds. The nucleation activation energy of α-Al2O3 decreases with the addition of seeds. The well-developed α-Al2O3 crystal is a hexagonal prism with {0001} and {11 2 0} crystal face appearance. The processing parameters are a solid content of 5% (in mass),temperature of 390 ℃ , holding time of 2 h, the addition of 5%(in mass) seeds, a filling factor of 40% (in volume) and mineralizer of 0.5 mol/L KBr.