Microscale spherical TiO2 powder prepared by hydrolysis of TiCl4 solution: Synthesis and kinetics

Hydrolysis of TiCl4 solution is capable of preparing microscale TiO2 particles. This research studied the synthesis of microscale spherical TiO2 powders and the hydrolysis kinetics. The effects of the flow field generated by different agitators and baffles in the crystallizer, the initial free acid concentration, the initial equivalent TiO2 concentration, and the temperature on the hydrolysis progress and powder morphology were systematically studied. The results show that the flow field in a crystallizer can significantly affect the morphology and particle size of the powders, and the axial flow can improve the sphericity of the powders. The increased free HCl and equivalent TiO2 concentrations in the pregnant solution inhibit the forward hydrolysis reaction, prolong the time to reach equilibrium, and reduce the yield. An appropriate temperature matching the compositions of the pregnant solution is crucial for the powder morphology and size. Powders with sizes ranging from around 5 μm–40 μm can be tuned under controlled flow field, solution compositions, and temperature conditions. In addition, the Cheng and Wunderlich modified Avrami equation was used for the crystallization kinetic modeling. The effects of the free HCl concentration, equivalent TiO2 concentration, and hydrolysis temperature are reflected in the reaction rate constant and active nuclei reduction index. Increasing the free HCl and equivalent TiO2 concentrations will reduce the reaction rate constant and accelerate the deactivation of the active nuclei, thus increasing the final powder size, while increasing the temperature will lead to the opposite results.