Study On Preparation Of Nanometer TiO₂ Powders By Hydrolysis Of TiCl₄ Aqueous Solution

Nanometer TiO₂ powders have wide potential use in many fields such as coatings, cosmetics, waste water treatment and automobile industry, because of their excellent Ultra-violet screening property, high photo-catalytic activity, and peculiar frost effect. The low-cost process for preparing nanometer TiO₂ powders is the key technical problem that must be firstly overcome for studying nano-coatings. The thermal hydrolysis process of TiCl₄ aqueous solution is a promising liquid approach for low- costly preparing nanometer TiO₂ powders.The synthesis of hydrous TiO₂ particles by thermal hydrolysis of TiCl₄ aqueous solution has been studied. Based on fundamentals for generating particles from homogenous solution and hydrolysis property of TiCl₄, the formation mechanism of hydrous TiO₂ particles was proposed: Larger polymeric clusters are formed by further hydrolysis of [Ti(OH)_nCl_6-n]^2- and consequent condensation polymerization. When the polymer cluster grows to a certain size and reach critical nucleus size, TiO₂ particles generate. To prevent primary particles aggregating together, the initial Ti concentration does not ought to exceed 0.3mol/L. The suitable amount of HCl added to the hydrolysis system can increase the particle size, strengthen the electrostatic repulsive force between two primary particles, and facilitate the generation of rutile product. From 60℃to 102℃, with the increase of hydrolysis temperature, the rutile phase content is decreased, and the anatase content is increased. The soluble Ti consumption kinetics data at 80℃follow the first-order reaction model. When the stirring rate is too high, the shear force can result in the aggregation of primary particles. When the initial Ti concentration was 0.2mol/L, added HCl concentration was 0.76mol/L, and hydrolysis temperature and time was 80℃/2h, stirring rate was 300～400rpm, the hydrous TiO₂ powder which main crystalline phase is rutile , and particle size is 6～10nm was prepared. The effect of calcining temperature on the particle size and crystalline phase composition of TiO₂ powders has been studied. Because the thermal hydrolysis process of TiCl₄ aqueous solution can produce...