A new observation on the phase transformation of TiO2 nanoparticles produced by a CVD method

Titania (TiO2) nanoparticles with primary diameters of less than 30 nm were produced by the thermal decomposition of TTIP and by the oxidation of TiCl4 in a cylindrical furnace reactor at 1200degreesC. Particle size, crystalline phase, and phase transformation were investigated as a function of precursor concentration and total flow rate by TEM, a DMA/CNC system, XRD, and TG-DTA. The results show that both particle size and number concentration were increased with increasing precursor concentration, and that the primary size could be controlled by changing the operating conditions. An anatase-to-rutile phase transformation occurred at TTIP concentrations above 7.68 x 10(-6) mol/l and this was enhanced with increasing precursor concentration. It is noteworthy that the transformation is independent of grain size but appears to be related to the presence of carbon impurities in the nanoparticles.