Synthesis and oxidation of V2AlC and (Ti0.5, V0.5)2AlC in air

In this paper we report on the synthesis and oxidation behavior of the layered ternary carbides V2AlC and (Ti-0.5,V-0.5)(2)AlC. The oxidation kinetics were studied thermogravimetically in air in the 500 to 700degreesC temperature range. The oxidation of V2AlC is governed by the inward migration of O, and possibly the outward migration of V; the Al atoms are essentially immobile. At 500 and 600degreesC, the oxide layers formed were layered and protective up to at least 24 h. The outermost layers were VO2 at 500degreesC, and V2O5 at 600degreesC; the inner layer compositions were myriad solid solutions of V, Al, and O in varying ratios. The average oxidation state of the V ions decreased from +4 or +5 at the air/oxide interface to +3 at the substrate/oxide interface. The oxides that form on (Ti-0.5,V-0.5)(2)AlC are amorphous or nanocrystalline, and are not protective, which implies the maximum-use temperature in air of the solid solution will have to be <500 degrees C. The oxidation occurred exclusively by the inward migration of O; the cations were oxidized in situ. For both ternaries, some of the oxides formed at 700 degrees C were molten which resulted in poor oxidation resistance. (C) 2004 The Electrochemical Society.