Phase relations in the SiC-Al₂O₃-Pr₂O₃ system

Phase relations in the Si-Al-Pr-O-C system, including the SiC-Al₂O₃-Pr₂O₃, the Al₂O₃-Pr₂O₃-SiO₂ and the SiC-Al₂O₃-Pr₂O₃-SiO₂ subsystems, were determined by means of XRD phase analysis of solid-state-reacted samples fabricated by using SiC, Al₂O₃, Pr₂O₃ and SiO₂ powders as the starting materials. Subsolidus phase diagrams of the systems were presented. Two Pr-aluminates, namely PrAlO₃ (PrAP) and PrAl₁₁O₁₈ (β(Pr) β-Al₂O₃ type) were formed in the SiC-Al₂O₃-Pr₂O₃ system. SiC was compatible with both of them. Pr-silicates of Pr₂SiO₅, Pr₂Si₂O₇ and Pr_9.33Si₆O₂₆ (H(Pr) apatite type) were formed owing to presence of SiO₂ impurity in the SiC powder. The presence of the SiO₂ extended the ternary system of SiC-Al₂O₃-Pr₂O₃ into a quaternary system of SiC-Al₂O₃-SiO₂-Pr₂O₃ (Si-Al-Pr-O-C). SiC was compatible with Al₂O₃, Pr₂O₃ and the Pr-silicates. The effect of SiO₂ on the phase relations and liquid phase sintering of SiC ceramics was discussed.