Synthesis and oxidation resistance of V₂AlC powders by molten salt method

Abstract

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°C, NaCl melts to form ionic liquid environment for the formation reaction of V2AlC, which starts at the temperature above 1050°C. The existence of NaCl in starting mixture results in the synthesis of V2AlC at 1050°C. And following annealing at 1400°C can remove the impurities of Al23V4 and C to synthesize pure V2AlC. Without NaCl, V2AlC cannot be synthesized at 1050°C and V2AlC synthesized at 1400°C is not pure. For the purpose to measure oxidation resistance of V2AlC samples, as‐synthesized V2AlC powders were pressed to cylinder shape (Φ10 mm×2 mm) and the cylinders (relative density of 82.7%) were heated in air. At temperature below 400°C, the oxidation was not obvious. At 650°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°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.

Synthesis Protocols of the Most Common Layered Carbide and Nitride MAX Phases

“…After heating, the V 2 AlC can be obtained, but it will have some impurities like C and Al 23 V 4 as these following reactions occur at 1050 °C …”

“…Afterward, a plateau at 1050 °C occurs for the reaction to happen. Finally, a plateau at 1400 °C is done to get rid of the impurities . First, while heating, V 8 C 7 is formed …”

“…The furnace is heated at a rate of 10 °C min −1 for 1 h at 1050 °C. [41] Results: After heating, the V 2 AlC can be obtained, but it will have some impurities like C and Al 23 V 4 as these following reactions occur at 1050 °C [41]…”

“…Finally, a plateau at 1400 °C is done to get rid of the impurities. [41] First, while heating, V 8 C 7 is formed…”

“…This mix is then ball‐milled for 12 h. Then, the powders are placed in an alumina crucible before going in a furnace. The furnace is heated at a rate of 10 °C min −1 for 1 h at 1050 °C …”