Synthesis and oxidation resistance of V2AlC powders by molten salt method

Herein, ternary carbide V2AlC was synthesized by molten salt method from elemental powders with molar ratio of V:Al:C=2:1.2:1 and same mass of NaCl. According to thermal analysis of the starting mixture, at 800 degrees C, NaCl melts to form ionic liquid environment for the formation reaction of V2AlC, which starts at the temperature above 1050 degrees C. The existence of NaCl in starting mixture results in the synthesis of V2AlC at 1050 degrees C. And following annealing at 1400 degrees C can remove the impurities of Al23V4 and C to synthesize pure V2AlC. Without NaCl, V2AlC cannot be synthesized at 1050 degrees C and V2AlC synthesized at 1400 degrees C is not pure. For the purpose to measure oxidation resistance of V2AlC samples, as-synthesized V2AlC powders were pressed to cylinder shape (phi 10mmx2mm) and the cylinders (relative density of 82.7%) were heated in air. At temperature below 400 degrees C, the oxidation was not obvious. At 650 degrees C, a rough film composed of V2O5 and Al2O3 was formed and cover the surface of V2AlC. The film resulted in good oxidation resistance of V2AlC. At 800 degrees C, the rough film transformed to needle-like crystals, which were mainly composed of V2O5. The oxidation resistance became very bad. V2AlC can be completely oxidized to form V2O5 and Al2O3.