A new challenge in the field of Solid Oxide Fuel Cells (SOFCs) concerns the reduction of their operating temperature down to 700°C. Apatite ceramics are interesting alternatives for SOFC electrolytes due to their high ionic conductivity at this temperature. The present work reports on the manufacturing and characterization of La 9 SrSi 6 O 26.5 coatings obtained by atmospheric plasma spraying at two different plasma spray powders. The microstructure and the composition of the as-sprayed and heat-treated coatings were investigated by several techniques including X-Ray Diffraction, Inductively Coupled Plasma - Atomic Emission Spectroscopy as well as Scanning and Transmission Electron Microscopy. The porosity level of the coatings was evaluated by the Archimedean method and image analysis. The studies revealed that the as-sprayed apatite coatings were composed of an amorphous phase, a crystalline apatite phase and chemical heterogeneities due to Si volatilization in the high-temperature plasma. Furthermore, a heat treatment made it possible to obtain denser, fully crystallized apatite coatings and also improved their ionic conductivity.

This study investigates the feasibility of manufacturing lanthanum silicate coatings for solid oxide fuel cells by atmospheric plasma spraying. The coatings produced are cohesive, relatively dense, and contain no secondary phases. Test results show that the starting composition of the powder is maintained after spraying and that particle velocity depends primarily on the plasma gas mixture. Due to the relatively high melting temperature of the particles, dense apatite coatings with few microstructural defects are obtained.