Oxidation of Zr₂[Al(Si)]₄C₅ and Zr₃[Al(Si)]₄C₆ in air

The oxidation behavior of Zr₂[Al(Si)]₄C₅ and Zr₃[Al(Si)]₄C₆ in air has been investigated. The oxidation kinetics of bulk Zr₂[Al(Si)]₄C₅ and Zr₃[Al(Si)]₄C₆ at 900–1300 °C generally follow a parabolic law at a very short initial stage and then a linear law for a long period with the activation energy of 237.9 and 226.8 kJ/mol, respectively. The oxide scales have a duplex structure, consisting of mainly an outer porous layer of ZrO₂, Al₂O₃, and aluminosilicate/mullite, and a thin inner compact layer of these oxides plus remaining carbon. The oxidation resistance of Zr₂[Al(Si)]₄C₅ and Zr₃[Al(Si)]₄C₆ has been improved compared with Zr₂Al₃C₄, and is much better than ZrC due to larger fraction of protective oxidation products, Al₂O₃ and aluminosilicate/mullite.