Preparation And Heat Treatment Of Nanometer γ-Al₂O₃ Powders With Low Cost

Nanometer Al₂O₃ , one of new types of functional materials with volumetric effect, quantum size effect, surface effect and macroscopic quantum tunnel effect, obtains a series outstanding performance in optics, electricity, magnetism, thermodynamics, chemistry and mechanical industry and has broad application and development prospects in structural ceramics, catalyst carrier, catalytic agent, fine ceramics and so on. In this paper, the γ-Al₂O₃ and hydrated alumina were analyzed with the cost control, factors affecting nanometer Al₂O₃ fabricated using sol-gel method, the adhesive solvents, the surface active agents and heat treatment technology.At present, the preparation of nanometer alumia powders has the disadvantages of high cost and industrialization difficulty. It is hard to produce the high purity and narrow size distribution powders because the fineness, purity and shape are easily influenced by the equipment and technological conditions. In this paper, remelting aluminum ingot and isopropanol were used to prepare aluminium alkoxide. The study shows that the aluminium alkoxide with impurities separation was similar to the product produced by pure aluminum ingot while its price was much lower.The aluminium alkoxide was used as raw materials to prepare hydrated alumina with sol-gel method. The experiments show that the water content, hydrolysis temperature and ageing time had the influence on the crystallinity, dispersibility and particle size distribution. High pure hydrated alumina with good dispersibility and uniform particle size about 30⁴0nm was prepared when the ratio of aluminium alkoxide and water was 1:3 and the hydrolysis temperature was 80 ℃.The characteristic of alumina and hydrated alumina powders was greatly influenced by adhesive solvents with different species, content and pH value. When the ratio of ammonium bifluoride and water was 0.02, the y- Al₂O₃ powders was well dispersed with high purity and uniform particle size about 8¹0nm.The surface active agents have certain influence on the dispersibility and particle shape with different species and molecular weight. The experimental data shows that the aggregation could be better improved with longer molecular chain, larger molecular weight. The powders was well dispersed with sphere shape and uniform particle size about 8¹0nmadding oleate as surface active agents while the powders had much better dispersibility with no aggregation adding PEG 1000.The heat treatment conditions, one important factors on powder characteristics were arranged by orthogonal design with a L9 (34) array. The experimental results show that the degressive order of the influence of heat treatment conditions on the average size and pattern is the calcination temperature, the holding time at the calcination temperature and the holding time at 300°C. By contorting heat treatment conditions, spherical y—AI2O3 powder was fabricated with desired size, morphology and good dispersion. For obtaining 8 nm spherical y —AI2O3 powder, the optimal calcination temperature is 900 °C, soaking 4 hours at that temperature without soaking any time at 300 °C.