Comparison of Titania Particles Between Oxidation of Titanium Tetrachloride and Thermal Decomposition of Titanium Tetraisopropoxide

Abstract

Thermal decomposition of TTIP was compared with oxidation of TiCl 4 in morphology and primary particle size of produced TiO 2 particles in a tubular reactor 2.7 cm in diameter and 54 cm in length under equal rate constants. The reactor temperature was varied from 850 to 1000°C for TiCl 4 oxidation and from 492 to 579°C for TTIP decomposition. The lower and upper limits of decomposition temperature for TTIP were determined so that the rate constants become equal, at corresponding limits, between TiCl 4 oxidation and TTIP decomposition. In order to maintain constant concentration with variation of reactor temperature, the flow rate of dilution gas was adjusted to compensate for the volume change of gas with temperature. The precursor concentration at the reaction condition was in the range of 1.09 2 10 m 6 to 1.09 2 10 m 5 mol/L, and the residence time of 3.1 to 10.8 s was based on the reactor set temperature. Particles from TTIP were spherical, while those from TiCl 4 were polyhedral. A considerable fraction of the precursor admitted to the reactor was consumed on the tube wall by surface reaction to form a zone coated with TiO 2 . The loss of precursor to the wall was greater with TiCl 4 oxidation. The particle size was, however, larger by 20% with TiCl 4 oxidation. By replacing the straight reaction tube with a concentric tube, the loss could be reduced, thereby increasing the amount of TiCl 4 available for particle formation significantly; the particle size was similar, however. With the straight tube a mixture of TiCl 4 and oxygen entered the reactor and the reaction occurred over the gradual increase from 650°C to a reactor set temperature of 900°C. With the concentric tube, the reactants had been preheated separately and then brought into contact right at the set temperature. The difference in the history of temperature for reaction may have brought about a difference in nucleation rate and consequently yielded particles of similar size. By analyses of BET surface area, X-ray diffraction patterns, and thermogravimetric data, TiO 2 particles from both routes were nearly nonporous, showed anatase peaks in majority, and contained no appreciable volatiles.