On the Mechanisms of Titanium Particle Reactions in O2/N2 and O2/Ar Atmospheres

Combustion of titanium particles in air may potentially be used for the in situ synthesis of nanoscale TiO2 particles, which can photocatalytically degrade chemical and biological air pollutants. The knowledge of Ti particle reactions in O-2-containing atmospheres is required to develop this method. In the present work, large (similar to 3 mm) single Ti particles were heated by a laser in O-2/N-2 and O-2/Ar environments. High-speed digital video recording, thermocouple measurements and quenching at different stages of the process were used for diagnostics. Analysis of the obtained temperature-time curves and quenched particles does not show a significant influence of nitrogen oil the oxidation of solid Ti. In all experiments. noticeable surface oxidation started at temperatures between similar to 850 and similar to 950 degrees C, leading to a sharp ternperatLire rise at similar to 1400 degrees C. During prolonged heating at the Ti melting point (1670 degrees C), a liquid TiO2 bead formed and, after an induction period, ejected fragments. It was shown that this phenomenon may result from an excess of oxygen ill the liquid bead. Fragment ejection in O-2/N-2 atmospheres was more intense than in O-2/Ar, indicating that N-2 accelerates the oxidation of liquid Ti.