Unveiling the protection mechanism of LaPO₄ against CMAS attack

This work evaluated the resistance of LaPO₄ ceramics to CMAS attack at 1250 °C and explored their interaction mechanisms. The chemical reaction between molten CMAS and LaPO₄ involves two stages leading to formation of a continuous inner layer and outer polyhedron grains, which effectively prevents the infiltration of CMAS. The reaction layer in this study is formed by inter-diffusion between LaPO₄ and CMAS melt in the interface region, which involves a series of events including solution, substitution and recrystallization. The mitigating mechanism differs significantly from the typical 'dissolution-precipitation' process observed in rare-earth zirconate or alumina-based materials during CMAS attack. Because of this novel mechanism, the reaction layer has a crack-free microstructure and seals the surface of the underlying LaPO₄ ceramic, which consequently results in enhanced resistance to CMAS attack.