Synthesis of functional oxides through plasma spraying

Thermal spray coatings have become an important part of modern industry, offering customized surface properties for a variety of industrial applications, e.g. thermal barrier coatings, wear resistant coatings, erosion resistant coatings and functional coatings. Although the usage of thermal spray coatings has increased dramatically, the scientific research of these coatings has lagged behind. Good understanding of thermal spray processes can provide the optimistic combination of operation parameters to obtain high quality of coating, improve service life of the product, and lower cost of the system.; The research presented in this dissertation focuses on the synthesis of functional oxide coatings through plasma spraying techniques. The materials studied in this research are: yttrium aluminum garnet (YAG) which can be the thermal barrier coating and environmental barrier coating; doped YAG as phosphor; yttrium iron garnet (YIG) applied in telecommunication and data storage; aluminum substituted YIG for biomedical applications; and zirconium substituted yttrium titanate pyrochlore in developing solid oxide fuel cells (SOFCs). The synthesis processes, phase formation, microstructure, and physical properties of above materials have been investigated in a comprehensive and integrated way.; The precursor powders or solutions were prepared via different chemical routes. The experiments suggest that formation of phase-pure oxides occurs through different phase evolution pathways and depending on the reaction conditions. Chemically derived precursors and/or powders were used as feedstock in plasma spray to form functional oxide coatings. Due to its rapid heating and cooling features, plasma spraying techniques provide a novel opportunity for functional oxides to transfer from amorphous into crystallized structure at a relatively low temperature in a single step. The properties of assprayed and post-heated coatings strongly depend on their microstructure and phase content.