Thermal stability of bulk Zr2Al4C5 ceramic at elevated temperatures

Thermal expansion analysis is applied to the study of phase segregation of Zr₂Al₄C₅ at elevated temperatures (20-2000 °C) under flowing argon. Such information would be useful for the detection of phase decomposition temperature and thermal stability of materials. The detected phase-decomposition temperature of Zr₂Al₄C₅ is approximately 1900 °C. The presented thermal expansion analysis results are in good agreement with the X-ray diffraction (XRD) and SEM results. The results indicate that Zr₂Al₄C₅ is susceptible to decomposition through sublimation of high vapor pressure of Al and weaker covalent bonds between ZrC slabs and Al₄C₃ layers. Thus, minimal amounts of Al, Zr₂Al₃C₅, Al₄C₃ and ZrC form on the surface layer. Zr₂Al₃C₅ further decomposes to ZrC_1 − x and Al₄C₃ at 2000 °C. However, the amount of decomposing phase slowly increases, and the structural shape of bulk Zr₂Al₄C₅ ceramic is always kept stable during heat treatment.