Synthesis And Characterization Of Apatite-type Lanthanum Silicate (ATLS) Deposited By Atmospheric Plasma Spraying As A Novel Electrolyte At Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs)

In the field of electrical power generation, the development of solid oxide fuel cells (SOFCs) is limited because of their high operating temperatures. Two solutions are generally considered to decrease the temperature: reducing the thickness of the conventional yttria-stabilised zirconia (YSZ) electrolyte and / or using the new materials. The second option seems the most exploitable because novel apatite-type silicates are attracting considerable interest as a new family of oxide-ion conductors with potential use in intermediate temperature between 500 and 800℃. Among the many silicate ceramics that could be used for this application, lanthanum silicates are very promising candidates at the moment.The objective of this thesis is the synthesis and characterization of apatite-type lanthanum silicate (ATLS) as a novel electrolyte dedicated to SOFC at intermediate temperature (IT-SOFC).In a first step, this work is to synthesize La₁₀(SiO₄)₆O₃ powders via a solid-state reaction. Particular emphasis is placed on optimizing executive protocols. The control of synthesis parameters (nature reagents, co-grinding, sintering temperatures and residence times, etc.) can get the apatite phase in a sintering temperature between 1350℃and 1650℃. The calcined powders were used to prepare density coatings greater than 90%.La₁₀(SiO₄))₆O₃ coatings were thermally deposited by conventional atmospheric plasma spraying (APS). The influence of projection parameters on the microstructure of coatings has been studied. The effects of porosity on the electrical properties were also discussed.Improving the ionic conductivity is based on controlling the properties of developed coatings. For example, several sets of samples to be controlled stoichiometry have been synthesized and characterized. This study has enabled us to establish a correlation between the microstructure and conduction properties of the ceramics.