Study On Preparation Of Nano-AL₂O₃ Powder By Precipitation Methods

Adopting three methods (direct precipitation method,homogeneous precipitataion method and precursor pyrogenation method), nano-Al2O3 powder has been prepared in the present paper. In the process of preparing nano-Al2O3 powder by direct precipitation method, relatively cheap AlCl3 was used as raw material, NH3 H2O as precipitator, the process parameters including concentration of reactants,pH values of solutions and aging time were studied. Experimental results show that powder size, size distribution of granularity and the properties of nano-Al2O3 powder prepared in this way were not very well.In the process of preparing nano-Al2O3 powder by homogeneous precipitataion method, using AlCl3 and Al(NO3)3 as raw materials, hexametny lenetetramie as precipitator, process parameters including concentration of reactants, proportion of reactants, reaction temperature and reaction time were studied.It was indicated that steady and transparent A1(OH)3 geltum can be produced by using A1(NO3)3 as raw material under the condition of reactants concentration of 2.0mol/L and reaction temperature of 50 C in a water bath for 30mins, then 80~120nm and irregular sized nano- -Al2O3 powder can be prepared through calcining geltum at 1150C for 1h. This is a potential way to prepare nano-powder because of its characteristics such as relative simple technology, high purity, high efficiency and relative simple facilities requirement.In the process of preparing nano-Al2O3 powder by chemistry precipitation method, the technology of uniform sized NH4A1O(OH)HCO3 precursory preparation was studied. Research shows that technical factors including mixing mode of reactants , titration speed , proportion of reactants and pH value of solutions etc have a great influence on the formation of precursor. Adopting supercritical drying and feeze drying technology, these two kinds of precursor were pretreated, sintered at different temperature. XRD,DTA?TG,TEM,BET techniques were used to characterize the nano-Al2O3 powder, the results show that drop NH4A10(OH)HCO3 solution whose concentration is 0.2mol/L into NEUHCO3 solution whose concentration is 2 mol/L with the speed of 2 ~3ml/min, controlling the solution pH value is about 8.5 ~ 10.0, and the excess-ratio of matching NH4HCO3 to NH4Al(SO4) 2 is about 1.20~1.40, can get good-nature precursor of NH4AlO(OH)HCO3. through supercritical dried, 1200 C 60 min calcined, low agglomeration fiber-like nano- -Al2O3 power with the length of 100~200nm and the wideth of 5~ 10nm can be prepared.