The melting and oxidation behavior of in-flight particles and their effects on the splat formation are studied. An order-of-magnitude analysis and one-dimensional thermal resistance analysis are employed to investigate the heat and mass transport from the plasma flame to the particle. Two dimensionless parameters, "melting index" and "oxidation index" are derived to characterize the melting status and the oxide content of the in-flight particles, respectively. These two indice are correlated with experimentally measurable parameters, such as particle size, velocity, temperature and spray distance. Numerical simulations and experimental results are discussed to validate the analytic solutions. Effects of particle size on the melting and oxidation behavior are also investigated. (c) 2005 Elsevier Ltd. All rights reserved.