Synthesis of non-aggregated titania nanoparticles in atmospheric pressure diffusion flames

Flame aerosol synthesis has been employed to synthesize nanoscale titania (TiO2) particles by oxidation of titanium tetraisopropoxide (TTIP) vapor. The influence of reactant mixing and flow rates on particle morphology, size and phase composition has been studied for two different diffusion flame configurations using transmission electron microscopy, X-ray diffraction and photon correlation spectroscopy. Spherical, loosely agglomerated powders with a minimum secondary particle size of 90 nm and a rutile content of up to 35 w % were obtained at low oxygen flow rates in the double diffusion flame, while large anatase-rich aggregates formed at high oxygen flow rates. It is shown that the degree of aggregation of the as-synthesized particles is represented better by the ratio of dPCS3/dTEM3, than by the ratio of dBET3/dXRD3 commonly used in literature. The differences observed in particle morphology and phase composition can be explained by considering their time–temperature history as a function of flame configuration and gas flow rates.