High-temperature chemical stability of Hf₆Ta₂O ₁₇ ceramic for thermal barrier coatings

High-temperature chemical stabilities of Hf₆Ta₂O ₁₇/Al₂O₃, Hf₆Ta₂O ₁₇/YSZ and Hf₆Ta₂O₁₇/Sm ₂Zr₂O₇ were studied for thermal barrier coatings (TBCs). The mixed powders of Hf₆Ta₂O ₁₇/Al₂O₃ and Hf₆Ta₂O ₁₇/YSZ were annealed at 1600°C for 8 hours in air, and the mixed powders of Hf₆Ta₂O₁₇/Sm₂Zr ₂O₇ were annealed at 1200°C for 8 hours in air. The phases of the mixed powders after annealed were observed by X-ray diffractometry (XRD). The sample of Hf₆Ta₂O₁₇/Al ₂O₃ mixed powder was molded and sintered at 1600°C for 8 hours in air, and the microstructures of the sintered sample were investigated by scanning electron microscopy (SEM). The XRD results revealed that the crystal structure of Hf₆Ta₂O₁₇ had no remarkable changes in the mixed powders of Hf₆Ta₂O ₁₇/YSZ and it had changes in the mixed powders of Hf ₆Ta₂O₁₇/Al₂O₃. The monocline HfO₂/ZrO₂ phases were found in the mixed powders of Hf₆Ta₂O₁₇/Sm₂Zr ₂O₇. The SEM results showed that the boundaries of Hf ₆Ta₂O₁₇ and Al₂O₃ crystals were clear. The element composes in crystals were analyzed by energy dispersive spectrometer (EDS), and the EDS results showed that a little amount of Al diffused into Hf₆Ta₂O₁₇ crystals.