Compatibility of SiC–and MAX phase-based ceramics with a KNO ₃ -NaNO ₃ molten solar salt

In this work, several ceramic materials were exposed together with two reference structural materials (i.e., 316 L stainless steel and Inconel 600) to a molten solar salt (40 wt% KNO ₃ and 60 wt% NaNO ₃ ) for 1000 h at 600 °C to investigate their compatibility with the molten salt medium, thus assessing their potential use in concentrated solar power (CSP) applications. The exposed ceramics included different SiC grades (solid state-sintered, liquid phase-sintered, and silicon-infiltrated) and MAX phase-based materials (Maxthal ^® 211 & 312 (nominally, Ti ₂ AlC & Ti ₃ SiC ₂ , respectively), Cr ₂ AlC, Nb ₄ AlC ₃ , (Nb,Zr) ₄ AlC ₃ , and a cermet comprising 40 vol% Fe and 60 vol% (Nb,Zr) ₄ AlC ₃ ). All SiC grades were chemically stable in the molten salt, whereas all Nb-containing MAX phase ceramics were severely oxidized. Comparing the two Maxthal ^® grades showed that the 312 was chemically more stable than the 211, and both grades formed a Na-based oxide scale. Interestingly, Cr ₂ AlC showed practically no interaction with the molten salt during the performed exposure, forming a stable, sub-micrometre-thick Cr ₇ C ₃ scale. Hence, it may be considered as promising structural/coating material candidate for the targeted CSP application.