Preraration Of Alumina Ultrafine Powder By Utrasonic Precipitation Method

Alumina ultrafme powder is an important feedstock in preparing catalyst carrier and special ceramic products. There are diversified methods for its preparation, and the precipitation method is widely used which generally uses cheaper inorganic materials, simpler equipment and technological processes, meanwhile, the powder product is of high purity, small particle size and narrow size distribution. Hence, liquid precipitation method is practical and quite competitive. Ultrasonic cavitation is a unique property of ultrasound, which has been widely used in organic synthesis and new advanced materials' preparation. The aims of this dissertation are:1. Preparing ultrafme alumina powder of mean diameter smaller than l00nm with ultrasonic-precipitation method by using A1(NO3)3-(NH4)2CO3 and NaAlO2-CO2 as starting materials.2. Investigating the effects of ultrasound on the properties of the alumina ultrafme powder, especially on the particle size and distribution.For A1(NO3)3-(NH4)2CO3 system, the effects of aluminum nitrate concentration, the system temperature and PH, the reacting time, the amount of PEG added and the application of ultrasound on the powder properties have been studied, and arrived at the following conclusions. First, 9-Al2O3 ultrafine powder with mean diameter of 20nm can be prepared under alkaline condition and there were no obvious differences in the size and morphology among all the products when the reaction conditions are controlled in the following range: aluminum nitrate concentration 0.2-0.6mol/l , reaction temperature 15-45癈, PH 7.2-8.3, the amount of 10%(wt) PEG less than 4ml, reaction time 0.5-2.Oh, calcination of precursors at 1000 for Ih. This conclusion is further justified by scaling up the preparation to 2 times and 5 times without noticeable variation of particle size and morphology. Second, under acidic condition, when PH value is lower than 4.4, no precipitation can be formed. However, when PH is equal or higher than 4.5, precursor precipitation can be formed, which is transformed into corundum with mean diameter of 56nm after 1 hour calcination at 1000 . When PH is higher than 5.0, there are no noticeable differences among the calcinated products, and they are all Y -A12O3 with mean diameter of 20nm.For NaAlO2-CO2 system, the effects of NaAlO2 concentration, the system temperature and PH value, the flow rate of CO2, the amount of PEG added, the aging process and the presence of ultrasound on the apparent density and particle size of alumina ultrafme powder have been studied systematically. It has been found that among all the factors considered, the NaAlO2 concentration and reaction temperature had the most significant effect on the apparent density and the particle size of the products, and the succeeding factors are PH value and the flow rate of CO2. Although the effects of ultrasound, the amount of PEG added and the aging process on the apparent density is marginal, the effect of aging process on the particle size is not negligible. In addition, the optimum conditions for preparing ultraflne alumina powder with minimum apparent density and particle size have been found.In the two reaction systems studied, the effect of ultrasound on the particle size of alumina is marginal, however its effect on the distribution of particle size is noticeable.