Synthesis Of High-purity Alumina And Aluminium Hydroxide From Aluminium Isopropoxide

High-purity alumina and aluminium hydroxide are widely used in industrial fields such as advanced ceramics, trichromatic phosphor, long afterglow phosphor, substrate of light emitting diode, high pressure sodium lamp, synthetic sapphire and et al. Besides these, high-purity pseudoboehmite is highly desired in petrochemical industry.Currently, main technique in our country to produce alumina and aluminium hydroxide is based on inorganic aluminium salt, which leads to considerable amount of contamination and thus limits its applications. However, in the worldwide, aluminium isopropoxide hydrolysis approach is extensively adopted to produce alumina and aluminium hydroxide. According to the requirement from industry, the author’s group have comprehensively investigated the industrial amplification conditions of aluminium isopropoxide hydrolysis technique. Based on the aluminium isopropoxide hydrolysis method, this dissertation studies the property variation of alumina and aluminium hydroxide with response to the change of hydrolysis conditions. In details:1. Synthesis of pseudobohmite from aluminium isopropoxide. Pseudobohmite was obtained from hydrolysis of aluminium isopropoxide. Hydrolysis conditions including ratio of water to aluminium isopropoxide, ratio of water to isopropoxide in the hydrolysis solution and dry temperature are found to be key factors in determining quality and property of pseudobohmite. Pure phase pseudobohmite can be acquired at different hydrolysis and dry environments. The ratio of water to isopropoxide in the hydrolysis solution shows little effect on the final product. Increasing the ratio of water to aluminium isopropoxide could enlarge the packing density and decrease the surface area and pore volume. Elevated temperature will increase the content of alumina with little influence on other properties.2. Synthesis of porous alumina from aluminium isopropoxide. Porous alumina was acquired from annealing pseudobohmite, which come from hydrolysis of aluminium isopropoxide. Hydrolysis conditions described above also could impact porous structure of the alumina. The results show that the pore volume will increase and specific surface area will decrease during the phase transition process from pseudobohmite to alumina. Larger amount of water will lead to smaller surface area and pore volume. Meanwhile, no obvious changes are found with the variation of water to isopropoxide ratio and dry temperature. 3. Synthesis of gibbsite microcrystals by introducing additive to aluminium isopropoxide hydrolysis process. In order to increase the packing density of gibbsite, various additives have been introduced to the hydrolysis system. Higher concentration of D solution and longer hydration time are found to be preferable. The quantity of aluminium isopropoxide and drying method have little influence on the phase of product. With the hydrolysis additive, the packing density of aluminium hydroxide is enhanced from0.23g/cm3to0.9g/cm3, saving three quarter of the sintering energy.