On the Mechanisms of Titanium Particle Reactions in O 2 /N 2 and O 2 /Ar Atmospheres

Combustion of titanium particles in air may potentially be used for the in situ synthesis of nanoscale TiO 2 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 (∼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 on the oxidation of solid Ti. In all experiments, noticeable surface oxidation started at temperatures between ∼850 and ∼950 °C, leading to a sharp temperature rise at ∼1400 °C. During prolonged heating at the Ti melting point (1670 °C), a liquid TiO 2 bead formed and, after an induction period, ejected fragments. It was shown that this phenomenon may result from an excess of oxygen in 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.