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

• Interaction of select MAX phases with pure molten sodium is reported for first time.
• Samples sealed in 316 stainless steel filled with Na and heated to 750 °C for 168 h.
• Using SEM, EDS, and XRD, we conclude samples did not react with Na.
• For Ti3AlC2, Na appears to attack the grain boundaries, with no Na signal detected.

Herein we report on the interaction of the Mn+1AXn 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 °C or 750 °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 h at 750 °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.