Preparation Of Nano Al₂O₃

Alumina ultrafine powder is an important feedstock in preparing catalyst carrier and special ceramic products.There are diversified methods for its preparation,and the sol-gel method is widely used,which generally uses cheaper inorganic materials,simpler equipment and technical processes, meanwhile,the powder product is of high purity,small particle size and narrow size distribution.Hence,liquid preparation method is practical and quite competitive.Supercritical drying method is a very effective drying method,which has been widely used in7 organic synthesis and new advanced materials' preparation.Using aluminum nitrate as raw material,citric acid as dispersant and anhydrous ethanol as solvent,nanosized AlOOH products were prepared by the combination of sol-gel and supercritical drying method.Upon calcination at 500-900℃,nanoγ-Al₂O₃ was obtained.Because sol-gel method always use water as solution,during the supercritical drying process there company with filtration and washing process.This dissertation mainly discusses use ethanol as solvent to avoid filtration process.The effect of the ammonia dripping speed and whip speed,the sort of solvent,the pH of the solution,the ageing temperature,and the ratio of aluminum nitrate to citric acid on the particle size of AlOOH as well as the calcination temperature on the particle size ofγ-Al₂O₃ were investigated.The morphology,particle size and structure of the products were characterized by TEM,IR and XRD analyses.Test results indicated that,the pH of the solution during the preparation of the sol-gel and additions of citric acid significantly affect the morphology and size of AlOOH.When pH=3 and n(citric acid):n(aluminum nitrate)=1:2,fibrous nano AlOOH(a diameter of 1-10nm and a length of 30-40nm)could be prepared.Calcination of thus obtained nano AlOOH at 500-900℃converted it into fibrous nanoγ-Al₂O₃ with a diameter of 1-10nm and a length of 30-70nm.At the same time design the orthogonal experimental test to determine the influence of the add amount of citric acid and ammonia,ageing temperature,the concentration of aluminum nitrate to the BET of the AlOOH.Discussed the major influence factors during the supercritical drying method such as pressure,constant temperature time and pressure reliefing speed to the result.