Formation of titania nanoparticles by vapor phase reactions of titanium tetraisopropoxide in oxygen/ozone containing atmospheres

Crystalline TiO2 particles were produced in a tubular flow reactor by chemical vapor reactions using titanium tetraisopropoxide as a starting material. The principal mechanism of formation of particles is decomposition of the precursor; generation of TiO2 nuclei by collision of intermediate Ti-containing species with O-containing species and growth of the particles. Small particles require a high nucleation and a small growth rate of the particles. The reactions of particle formation are kinetically controlled by Arrhenius relationships. The reaction constants and activation energies are dependent on the reactants. We used oxygen and oxygen/ozone mixtures as the reaction atmosphere over a wide range of temperatures. Ozone as a highly oxidizing gas was believed to change the kinetics for the particle formation mechanism with regard to pure oxygen atmospheres. The resulting powders were characterized by x-ray diffraction, TEM and BET-surface area measurements. Ozone was found to decrease the particle size and the crystallite size by a factor of two and to increase the surface area of the particles. Fine anatase monocrystals were prepared which showed a surface area of 80 m(2)/g. (C) 1997 Acta Metallurgica Inc.