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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 8C, leading to a sharp temperature rise at $ 1400 8C. During prolonged heating at the Ti melting point (1670 8C), 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.

We report a compact microgravity flight apparatus for characterization of high-temperature chemical reactions in single particle systems. The apparatus employs an infrared CO(2) laser to ignite 1-5 mm samples while video images, thermocouple measurements, laser on/off status, and XYZ accelerometer signals are synchronously recorded. Different operating modes permit preignition quenching, ignition, and combustion experiments to be performed. The apparatus was successfully utilized during microgravity experiments on board NASA research aircraft.

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