Comparison of Titania particles between oxidation of titanium tetrachloride and thermal decomposition of titanium tetraisopropoxide

Thermal decomposition of TTIP was compared with oxidation of TiCl4 in morphology and primary particle size of produced TiO2 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 1000degreesC for TiCl4 oxidation and from 492 to 579degreesC 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 TiCl4 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 1.09x10(-6) to 1.09x10(-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 TiCl4 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 TiO2. The loss of precursor to the wall was greater with TiCl4 oxidation. The particle size was, however, larger by 20% with TiCl4 oxidation. By replacing the straight reaction tube with a concentric tube, the loss could be reduced, thereby increasing the amount of TiCl4 available for particle formation significantly; the particle size was similar, however. With the straight tube a mixture of TiCl4 and oxygen entered the reactor and the reaction occurred over the gradual increase from 650degreesC to a reactor set temperature of 900degreesC. 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, TiO2 particles from both routes were nearly nonporous, showed anatase peaks in majority, and contained no appreciable volatiles.