Preparation Modification And The Control Of α-Phase-Transformation Of Ultrafined Al₂O₃ Powder

A new precursor of Al2O3 has been synthesized by precipitation method, using NH4A1 (SO4) 2 and NH4HCO3 as raw materials. Some research work has been done on the preparation process. The phase transformation behavior during heat-treatment has been studied. The results show that the a -phase-transformation of pure AACH can be completed by heating at 1200 癈 for two hours. But under this temperature, the alumina particles will be sintered together, which can lead to the formation of bough-like structures. And these bough-like structure will make the powder difficult to be dispersed.To resolve this problem , TiO2, MgO, ZnO have been used as doping materials. The results show that these three kind of materials are effective to reduce the a -phase-transformation temperature and accelerate the a -Phase-Transformation process. No bough-like structure was found in the doping production of heat-treatment.As far as alumina powder is concerned ,on the contrary, the excellent thermal stability is needed as catalyst carrier. The effects of SiO2 and ZrO2 on the thermal stability of alumina powder has been studied. The. results show that SiO2 is effective to stablize Al2O3 powder, which can be drawn from the fact that the particle size of the sample with 5%Si02 doped can be kept around 10nm after calcined at 1200℃ for two hours.