COMPETITION BETWEEN GAS-PHASE AND SURFACE OXIDATION OF TICL4 DURING SYNTHESIS OF TIO2 PARTICLES

The effect of TiCl4 surface reaction on the size of product TiO2 parti cles is quantitatively investigated over a wide range of process condi tions (temperature and reactant concentration) that are typically empl oyed in industrial and research facilities. A model for titania aeroso l dynamics is developed accounting for the simultaneous gas phase and particle phase (surface) oxidation rate of TiCl4. Using this model, th e implications of these two chemical pathways on the size of product t itania particles are elucidated. It is shown, for the first time, that TiCl4, oxidation on the surface of freshly formed titania particles i s most important at high TiCl4 concentrations. A design diagram is pre sented mapping the significance of surface and gasphase oxidation of T iCl4 in terms of process temperature and initial TiCl4 mole fraction. The model predictions are compared with experimental results and confl icting interpretations of the mechanism of titania formation by TiCl4 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. (C) 1 998 Elsevier Science Ltd. All rights reserved.