Isothermal oxidation of bulk Zr(2)Al(3)C(4) at 500 to 1000 degrees C in air

The isothermal oxidation behavior of Zr(2)Al(3)C(4) in the temperature range of 500 to 1000 inverted perpendicular C for 20 h in air has been investigated. The oxidation kinetics follow a parabolic law at 600 to 800 degrees 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 ZrO(2) and Al(2)O(3). As indicated by x-ray diffraction and Raman spectra, the scales formed at 500 to 700 degrees C are amorphous, and at higher temperatures are alpha-Al(2)O(3), and t-ZrO(2) nanocrystallites. The nonselective oxidation of Zr(2)Al(3)C(4) can be attributed to the strong coupling between Al(3)C(2) units and ZrC blocks in its structure, and the close oxygen affinity of Zr and Al.