The objective of this study is to establish relationships between the optical properties of yttria-stabilized zirconia (YSZ) plasma-sprayed coatings and their microstructure to improve YSZ thermal barriers. So, coatings with significant microstructural differences were manufactured and their hemispherical reflectance and transmittance were investigated over the 0.25-20µm wavelength range. However as plasma-sprayed coatings are heterogeneous materials, they exhibit optical properties different from those of homogeneous ones. Indeed, the pores and grain boundaries act as scattering centers and cause modifications in optical properties that are closely linked both to intrinsic properties of materials and microstructural characteristics. Therefore, the extinction coefficient which describes the decrease in light intensity due to the light absorption and diffusion processes in the matter, was determined by using the Kubelka-Munk two-flux model. The absorption and diffusion coefficients were infered from the comparison between the experimental data and model predictions of reflectance and transmittance.

Relationships between the electrical properties of thermally sprayed titania coatings and their microstructure have been investigated. As far as possible, a broad range of microstructures was produced by using various processes of plasma spraying with different powder size ranges and variations of the plasma operating parameters. The two spraying processes consisted of DC plasma spraying and RF plasma spraying. Physical properties of plasma-sprayed coatings are generally influenced by their microstructure. But the electrical properties of plasma-sprayed titania coatings are known to be strongly influenced by their stoichiometry. It is the reason why coatings with identical stoichiometry were compared. It was found that electrical resistivity was directly linked to the quality of the contact between the splats and their density through the titania plasma-sprayed coatings.