Synthesis Of Porous Alumina Spherical Particles By Quasi-gaseous State Reaction

Aluminia materials possess high strength and hardness, excellent corrosion, high temperature, oxidation resistances, and other characteristics. Aluminia powder is the raw materials of preparing Aluminia materials such as catalyst and its carrier, dental materials, special ceramics. Porous spherical Al2O3 particles not only serve as an excellent catalyst and its carrier, drug delivery/controlled release, but also can used less due to its low density, therefore lower production costs of Aluminia materials. Besides, spherical Al2O3 particles are favourable to forming of bulk Al2O3 densified. In this thesis, a novel quasi-gaseous state reaction method, for the first time, was used for preparation of a new porous alumina spherical particles.Firstly, porous alumina prescursor spherical particles were synthesized using aluminum chloride solution and high-purity ammonia gas as starting agents. Effects of AICl3 solution concentration, vacuum, and NH3 gas flow rate on precursor particle morphology, size and microstructure have been investigated, and optimum synthetic conditions have been attained:AICl3 solution concentration—25wt%, vacuum—-0.01MPa, NH3 gas flow—50L\h. Precursor particles synthesized with optimum synthetic conditions are:average size—6.705μm, standard deviation—3.224μm, well sphericity, solid or hollow microstructure.Secondly, the drying and calcination processes and the control of agglomeration were studied for alumina precursor spheres. Effects of dryings in the oven, at room temperature, and with microwave on the performance of the precursor have been investigated, also the effects of calcination temperatures at 500℃,800℃,1000℃and 1200℃on the performances of alumina spheres have been studied. The results show that a proper drying and calcining process for alumina precursor spheres synthesized by using optimum conditions is:first drying with microwave of "low fire" for 12 min., then calcining at 1200℃for 2h. Porous alumina particles, obtained through above drying and calcining processes, have the average diameter 2.68μm, spherical shape, solid and hollow microstructures, andα-Al2O3 crystalline type.Finally, effects of molecular weight and concentration of polyethylene glycol(PEG), added in collection bottle in quasi-gas reaction synthesis and drying process, repectively, on particle clusters have been investigated. The results show that for any one of two adding ways, using 3.0wt% of PEG 6000 can effectively prevent the clusters formation, and adding in drying process is better than doing in collection bottle.Therefore, porous alumina spherical particles can be prepared using quasi-gas reaction process, and a proper process is:AICl3 solution concentration—25wt%, vacuum—-0.01MPa, NH3 gas flow rate—50L\H, drying with "low fire" microwave for 12min., and calcining at 1200℃for 2h. The porous alumina spheres prepared by above process possess average size 2.68μm, spherical shape, well dispersion, solid and hollow microstructures, crystalline structure of the monoclinicα-Al2O3...