Zircon is widely used as a refractory material, because of its excellent mechanical and chemical properties. Several studies on plasma sprayed zircon were reported since 70's, and it is known that zircon dissociate into silica and zirconia during the plasma spray process. Authors have been studied on plasma sprayed zircon for a protective coating application, and successfully obtained very dense coating with excellent adhesive strength by optimizing the spray parameter. However, it was also revealed that the coating had poor stability above 1500K. In this study, the effects of two different oxides additive (yttria and ceria) on the structure and stability of the plasma sprayed zircon coating above 1500K are evaluated. The addition of these oxides enhanced the amount of residual zirconia and decreased zircon after the heat treatments. Addition of yttria resulted in the coating composed of cubic zirconia and zircon, while monoclinic zirconia was formed by ceria addition.

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