Formation of TiO2 aerosol from the combustion supported reaction of TiCl4 and O2

Abstract

The formation of particulate TiO₂ has been studied by the addition of small quantities (10^–5–10^–3 mol fraction) of TiCl₄ vapour to a lean CO + O₂+ N₂ flame with a maximum temperature of about 1400°C. Measurements of TiCl₄ concentration have been made as a function of height (residence time) by u.-v. absorption spectroscopy. The results demonstrate that chemical reaction is essentially complete 50 ms down stream of the CO flame-front, at which stage the TiO₂ particles have reached a diameter of 410 Å. Electron microscopic examination of samples of material from the flame shows that particle growth continues for a further 200 ms by a flocculation mechanism. This is a major factor determining the final particle size (630 Å). Agreement with theoretical flocculation predictions is reasonable both with respect to the development of the mean size and the size distribution. Results of sintering experiments carried out in the flame and of similar measurements carried out in the hot stage of an electron microscope demonstrate that the particles produced in this system exhibit a fusion temperature much below that of the bulk solid (1850°C). The occurrence of sintering in the flame is necessary to account for the form of the TiO₂ particles produced in this system.