Molten salt synthesis and formation mechanisms of ternary V‐based MAX phases by V–Al alloy strategy

Abstract V 2 AlC and V 4 AlC 3 are obtained in much milder conditions by a new facile approach using low‐cost V–Al alloys and carbon black with the assistance of molten salts. Density functional theory (DFT) calculations show that our strategy is feasible and thermodynamically superior to the traditional method, with the following X‐ray diffraction and Scanning Electron Microscopy fully revealing the phase and morphology evolutions of both reaction processes. Unreported formation mechanisms are revealed for the first time. Al 8 V 5 transforms directly into V 2 AlC with both lattices perfectly overlapped due to the existence of multiple parallel planes between V 2 AlC and Al 8 V 5 with consistent interplanar spacings, which leads to the overlapped phenomenon of the diffraction spots as well. For V 4 AlC 3 , an embedded structure of V 2 AlC–VC is first formed through an aluminum removing behavior in V 2 AlC layers, causing the increase of the VC content, and V 4 AlC 3 is transformed by the embedded V 2 AlC–VC structure through diffusion and interface migration with a possible climb behavior of Frank partial dislocation.