Thierry Poirier

Deposition of nanoparticle suspensions by aerosol flame spraying: Model of the spray and impact processes

Aerosol flame spraying (AFS) combines the atomization of a colloidal suspension with the lateral injection of the aerosol in a flame. The aerosol droplets are partially dried when crossing the flame and then deposited as a coating onto a substrate. Afterwards, the coating is consolidated by heat treatment without extensive grain growth. In this paper a model of the trajectories, acceleration and vaporization of the droplets is used to predict the impact conditions of the in-flight dried droplets, as well as their size and water content when they impinge onto the substrate. From these calculations and the hydrodynamic properties (viscosity, surface tension, contact angle) of the suspensions, the morphology and size of the lamellae deposited on the substrate are determined by using classic impact models. In spite of the complexity of the mixing of the suspension spray with the flame and the diversity of the thermal histories of the droplets, the observation of the latter after impact shows that the results of the model are quite consistent with measurements. The relationship between droplet impact parameters and coating formation is discussed.

Laser Ablation in the Synthesis of Zirconium Oxide

Results of an experimental study of the oxidation of a zirconium plasma generated by laser ablation of a metallic target under low pressures of oxygen are presented. The crystallographic identification of the collected product by electronic diffraction shows metastable ZrO cubic phase. The oxidation phenomena are interpreted by thermochemical simulation suggesting a model in accordance with other cases of synthesis of metastable oxides at high temperatures, such as plasma reactors.

Colour Matching in Decorative Thermally Sprayed Glass Coatings

Coloured coatings were obtained on steel by plasma spraying without severe in-flight alteration of pigments, taking profit of the low thermal conductivity of the glassy matrix of glaze particles. Colour matching was studied by mixing 3 different glazes, comparing Grassmann and Kubelka-Munk based algorithms. Results suggest that the latter method should be preferred upon Grassmann method, particularly when the light absorption/dispersion ratios of coloured feedstocks are very different.

Influence of Laser Glazing on the Characterization of Plasma-Sprayed YSZ Coatings

In this study, 8xa0wt.% yttria-stabilized zirconia powder was deposited on the substrates by atmospheric plasma spray. The coatings were post-treated by laser glazing under different parameters in order to densify them. The characterization of the laser molten pools under different laser treatment conditions was studied. Preheating processes were also employed. Scanning electron microscopy observations of the surface and cross section of as-sprayed and laser-glazed coatings were carried out to investigate the influence of laser glazing on the microstructure on laser-glazed coatings. The results show that preheating processes improve the coating in terms of deepening the laser-glazed layer, reducing the number of vertical cracks and surface density of cracks and widening the molten pool. Finally, the influences of linear energy density on the characterization of the glazed layer are discussed.