When spraying ceramic particles with a low thermal conductivity such as zirconia using Ar-H 2 direct-current (d.c.) plasma jets where the heat transfer is important, heat propagation phenomena take place with the propagation of melting, evaporation or even solidification fronts. Most models neglect these heat propagation phenomena assuming the particle as a lumped media. This work is aimed at developing a model coupling the effect of heat propagation with the particle dynamic within plasma jets. It uses an adaptative grid in which the coordinates of the phase change fronts are fixed. It allows minimizing the calculation costs (approximately 10 seconds on PC under windows XP against 1hour with an enthalpy model). Such calculations are illustrated for dense and porous agglomerated zirconia as well as iron particles which evaporation in an Ar- H 2 (25 vol %) plasma is important.

Recently the research about technical ceramics knows a renewed interest. The synthesis process of nanopowders plays a significant role in the production of such materials. This work, concerns particularly the synthesis of the nanopowders by laser pyrolysis. A numerical model is developed in order to understand the influence of the heat transfers occurring in the reactor and around the reaction zone, for a better control of the process. The study highlights the importance of the thermal transfer in the cell. A simple one dimensional analysis enabled us to define a stability condition of the flame function of the precursor flow rate and the cell pressure. The extended 3D calculations underline the complex fluid flow and heat transfer developing in the synthesis reactor.

A numerical study has been conducted on yttria stabilized zirconia and molybdenum splat cooling taking into account the effects of various parameters. In particular, the effect of the splat thickness, the splat/substrate interface thermal resistance, the latent heat of solidification and the substrate initial temperature on the solidification occurrence and kinetics have been studied. A two-dimension model of heat transfer taking into account the phase change during rapid solidification with an enthalpy formulation has been used for these calculations.

The present work deals with numerical simulations based on a computational heat transfer model for spherical composite particles typically used under plasma conditions. Results describe heat transfer in mono and two layers steel/alumina particles immersed in an uniform infinite plasma. Time dependent behaviours interacting with phase change occurrence and taking into account the contact quality between the two layers are considered.

As underlined in 1981 by Mc Pherson, thermo-mechanical properties of plasma-sprayed coatings depend not only on the way particles flatten and resulting splats solidify and cool down, but also on the thermal history of particle layering at the same location. To illustrate what is our present knowledge in that field, plasma-sprayed alumina coatings will be considered through modelings and measurements. The first part of this paper discusses the phenomena linked with particle impact and splat formation: splashing, spreading, solidification and grain growth, angle of impact in conjunction with particle parameters at impact and substrate surface parameters (chemistry, phase structure and roughness, temperature). The second part examines splats layering. It addresses the influence of plasma jet heat flux, relative velocity torch-substrate, powder flow rate and deposition efficiency on splat time-temperature evolution and resulting quenching stress, coating adhesion/cohesion and microstructure. The shadow effect when spraying off normal angle is also discussed. The last part deals with the effect of the successive cooling and reheating of passes on coating properties, and condensation of the vapor issued from evaporating particles.