Controlled synthesis of nano-sized titania (TiO2) powder was performed by an improved design of a flame reactor

where titanium tetrachloride (TiCl4) was oxidized in vapor phase at high temperature conditions.By isolating the methane (CH4) flames from the injection of TiCl4

the formation of TiO2 occurred at a certain distance from the TiCl4 inlet

which accordingly avoided the scaling phenomenon often encountered in such processes.The particle diameter and its distribution could be effectively influenced by the operating conditions.The results showed that a lower precursor concentration and a higher carrier-gas flow rate benefited the production of smaller particles of TiO2.The increase of the carrier-gas flow rate resulted in the transition from laminar flow to turbulent flow and the decrease of flame length

and consequently the formation of smalle particles.With increasing flow rate of CH4

the flame

i.e.

the reaction zone

enlarged

causing larger particle size owing to the longer time for the formed TiO2 to stay in the flame.While

extra oxygen supply around the center nozzle of TiCl4 could effectively reduce the particle size of TiO2

which may be attributed to the better initial mixing of TiCl4 and oxygen.The nano-sized TiO2 particles ranging from 20 nm to 80 nm on average were obtained in most of the experiments.