Combustion of levitated titanium particles in air

Combustion of titanium particles in air is of interest for applications to pyrotechnic countermeasures against chemical or bacteriological pollution, synthesis of nanoscale titania, and fire/explosion safety in metallurgical and SHS technologies. In this work, combustion of single titanium particles is studied using electrodynamic balance (levitation) and laser ignition. High-speed digital video recording and a photomultiplier are used for diagnostics. Based on the obtained data, empirical formulas are proposed for the dependence of the burning time on the initial particle size. Thermodynamic calculations are made to support the conclusions based on experimental data. The particle burning time is estimated using a simplified mathematical model for diffusion-controlled combustion. Comparison of the estimates with the experimental results suggests that oxygen diffusion in the gas phase plays a major role in the combustion mechanism of 100-mu m or larger titanium particles in air, while kinetics become more important for smaller sizes. (c) 2007 The Combustion Institute. Published by Elsevier Inc. All rights reserved.