Bauxite-based \ Alumina Matrix Of ¦Á-al <sub> 2 </ Sub> O <sub> 3 </ Sub> Nanometer Powders

Preparation of α -Al₂O₃ nano powder with three methods a) calcining and decomposition directly from aluminum hydroxide, b) Sol-Gel method using industrial alumina Sol, c) hydrothermal method based bauxite with high alumina content was investigated. The effects of seed, phase transformation additive, synthesis temperature, synthesis time and dispersant on phase transformation temperature of alumina and grain size were discussed, and post-treatmentof powder prepared above was also studied. The results showed as follows:Method a) , phase transformation temperature of α -Al₂O₃ would be lowed to 950℃ withaddition of 1wt% seed ( α -Al₂O₃ nano powder) and 3wt% AlF₃ or 1wt% ZnF₂ and with milling 3h, and grain size of 30nm and 33nm respectively would be obtained for lh heat preservation. With same addition of seed and additives, sample A4 with dry milling and sample C2 with wet milling would be transformed to α -Al₂O₃ at 1100℃ and 950℃respectively, and the latter's phase transformation temperature would be lowered 150℃ than the former's. After post-treatment, the secondary particle size of powder is 168nm, and the size distribution was narrow; TEM showed that the morphology of α -Al₂O₃ grain was irregularly polygon and dispersed well.Method b) , α -Al₂O₃ nano powder with grain size of 26nm can be prepared at 800 ℃ with addition of lwt% grain seed ( α -Al₂O₃ nano powder) and 1wt% ZnF₂, and with PEG as dispersant and by using alcohol as milling medium. Increasing addition of ZnF₂ had little effect on the phase transformation temperature of α -Al₂O₃, but can increase the grain size of it; Increasing calcined temperature and reaction time can also result in increasing of grain size. At same condition, using alcohol as milling medium was good for uniformity of shrinking and solid phase reaction during calcinations. Powder's secondary particle size is 186nm after post-treatment; and TEM showed the morphology of α -Al₂O₃ nano powder prepared above was ball.Method c) , 28nm α -Al₂O₃ powder with a little mullite phase can be prepared at 380℃ X 2h with calcined slightly bauxite with high alumina as reactant and with 0.1mol.L^-1NaOH addition, and relative contents of α -Al₂O₃ and mullite in hydrothennal product were 86% , 9%, respectively; With the concentration of NaOH increasing the hydrothermal product's colour would become dark gradually, and hard dregs appeared, the size of powder also increased; At...