Chemical stability of (Sm_1-xLa_x)₂Zr ₂O₇ and Al₂O₃ at high temperature

Due to its high melting point, low thermal conductivity, and good phase stability at high-temperature, rare earth zirconates material (A ₂B₂O₇) will be one of the candidate materials used for the thermal barrier coating. At high temperature, the chemical stability between rare earth zirconates and TGO layer (mainly Al ₂O₃) affects much the performance of coating, so the study of the chemical stability is of great significance. In this paper, (Sm _1-xLa_x)₂Zr₂O₇(x=0, 1) were prepared by the co-precipitation method and the chemical stability between (Sm_1-xLa_x)₂Zr₂O₇(x=0, 1) and Al₂O₃ was investigated at the temperature of 1 200 °C, 1 300 °C, 1 400 °C, 1 500 °C, 1 600 °C respectively for 8 h and 24 h. The microstructures were analyzed by scanning electron microscope (SEM) and the crystallographic phases were determined by X-ray diffraction (XRD). The results showed that the chemical reaction occurred between Sm2Zr2O7 and Al₂O₃ above 1 200 °C producing SmAlO₃. With the heating temperature increased, the content of SmAlO₃ increased. The chemical reaction between La₂Zr₂O ₇ and Al₂O₃ began at 1 200 °C producing LaAlO₃ and ZrO₂. LaAl₁₁O₁₈ appeared at 1 300 °C. As the increase of heating temperature, the content of LaAlO₃ and ZrO₂ with tetragonal phase reduced gradually in the heated samples, and the content of LaAl₁₁O₁₈ and ZrO₂ with monoclinic phase increased gradually in the heated samples. With the increase of heating temperature, the doping amount decreases in ZrO₂ with tetragonal phase, the structure of ZrO₂ with tetragonal phase tend to be more complete. So ZrO₂ with tetragonal phase transformed to ZrO₂ with monoclinic phase in cooling process easily, which leads to the increase of ZrO₂ with monoclinic phase in the heated samples. As the time of heating temperature prolonged, the kinds of reaction products didn't change, but the amount of reaction products increased.