Mullite-Zircon Thermal Barrier Coating Production by Plasma Spraying Process

Zircon (ZrSiO₄) is a technologically important oxide ceramic material known for its high refractoriness and chemical stability. It shows excellent thermal shock resistance as a result of its very low thermal expansion coefficient and a low heat conductivity coefficient. Plasma spraying is a convenient method to produce large area coatings with high growth rates, necessary for many applications. ZrSiO₄ is among the least expensive spraying materials for refractory applications. In this study, a single-step process was used to prepare mullite/zirconia ceramic composites by plasma spraying zircon/alumina mixtures. Mixtures of ZrSiO₄ and Al₂O₃ powders with Al₂O₃ to SiO₂ molar ratios of 3:2 were milled for 2 h in a zirconia medium using a ball mill. The as–milled powders were dried in the furnace and sintered at 1300 and 1350 °C for 2h then crushed to a size less than 100 μm. The powders were sprayed by an atmospheric plasma spray gun (Metco 3MB) using C/C+SiC ceramic matrix composite substrates. Scanning electron microscopy (SEM) was used to analyze the microstructures of the powders and plasma coatings. The phase composition analysis of the powder showed the presence of alumina and zircon. After plasma coating, alumina, zircon, and zirconia phases were determined.