Isothermal oxidation of bulk Zr₂Al₃C₄ at 500 to 1000 °C in air

The isothermal oxidation behavior of Zr₂Al₃C₄ in the temperature range of 500 to 1000 °C for 20 h in air has been investigated. The oxidation kinetics follow a parabolic law at 600 to 800 °C and a linear law at higher temperatures. The activation energy is determined to be 167.4 and 201.2 kJ/mol at parabolic and linear stages, respectively. The oxide scales have a monolayer structure, which is a mixture of ZrO₂ and Al₂O₃. As indicated by x-ray diffraction and Raman spectra, the scales formed at 500 to 700 °C are amorphous, and at higher temperatures are α-Al₂O₃ and t-ZrO₂ nanocrystallites. The nonselective oxidation of Zr₂Al₃C₄ can be attributed to the strong coupling between Al₃C₂ units and ZrC blocks in its structure, and the close oxygen affinity of Zr and Al.