ROLE OF SURFACE-REACTION IN AEROSOL SYNTHESIS OF TITANIUM-DIOXIDE

The role of surface reaction in the synthesis of titanium dioxide from TiCl4 in aerosol reactors was studied theoretically using a one-dimen sional log-normal model in which particle growth occurred by coagulati on and surface reaction. The surface reaction kinetics were obtained f rom chemical vapor deposition studies of TiO2 from TiCl4 reported in t he literature and the gas-phase kinetics from data for aerosol reactor s. The effect of surface reaction rate on the TiO2 particle size distr ibution was studied for different axial temperature profiles and for l aboratory and industrial conditions. Within the inlet TiCl4 concentrat ion range of 4.7 x 10(-8)-5.5 x 10(-6) mol cm(-3) and gas velocities o f 30 cm s(-1)-20 m s(-1) at atmospheric pressure, surface reaction did not affect the average TiO2 particle size or the spread of the distri bution. Two dimensionless quantities were identified which enable the determination of the significance of surface reaction in aerosol synth esis of particles. In general, for any system where homogeneous gas-ph ase reaction directly forms particles, and particle growth occurs by s urface reaction and coagulation, it is not possible in practice to obt ain a final particle size distribution with a geometric standard devia tion less than the asymptotic geometric standard deviation determined by the coagulation kinetics (e.g. 1.32 for spherical particles with a log-normal size distribution in the continuum regime (Lee, 1983), whic h is the value determined by coagulation kinetics). Copyright (C) 1996 Elsevier Science Ltd