On the interactions of Ti2AlC, Ti3AlC2, Ti3SiC2 and Cr2AlC with pure sodium at 550 °C and 750 °C

Herein we report on the interaction of the M(n+1)AX(n) phases - Ti2AlC, Ti3AlC2, Ti3SiC2 and Cr2AlC - with static, pure molten sodium. The MAX phases were sealed in 316 stainless steel tubes filled with Na that, in turn, were heated to 550 degrees C or 750 degrees C for 168 h. Based on scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) of post-exposed samples we conclude that even after exposure for 168 hat 750 degrees C, Ti2AlC, Ti3SiC2 and Cr2AlC did not react with Na. In the case of Ti3AlC2, exposure to molten Na alters both the grains and the grain boundaries, despite the fact that no Na signal was detected in the post-exposed samples. These chemical alterations were observed in TEM and manifested themselves by a change in the hardness values of the exposed surfaces. (C) 2016 Elsevier Ltd. All rights reserved.