Competition between gas phase and surface oxidation of TiCl 4 during synthesis of TiO 2 particles

Abstract

The effect of TiCl 4 surface reaction on the size of product TiO 2 particles is quantitatively investigated over a wide range of process conditions (temperature and reactant concentration) that are typically employed in industrial and research facilities. A model for titania aerosol dynamics is developed accounting for the simultaneous gas phase and particle phase (surface) oxidation rate of TiCl 4. Using this model, the implications of these two chemical pathways on the size of product titania particles are elucidated. It is shown, for the first time, that TiCl 4 oxidation on the surface of freshly formed titania particles is most important at high TiCl 4 concentrations. A design diagram is presented mapping the significance of surface and gas-phase oxidation of TiCl 4 in terms of process temperature and initial TiCl 4 mole fraction. The model predictions are compared with experimental results and conflicting interpretations of the mechanism of titania formation by TiCl 4 oxidation in the literature are reconciled. This model can be used to investigate the significance of surface growth in gas-phase synthesis of fumed silica as well as other ceramic and metallic particles.