Compatibility of SiC--and MAX phase-based ceramics with a KNO3-NaNO3 molten solar salt

Abstract

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% KNO3 and 60 wt% NaNO3) 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, Ti2AlC & Ti3SiC2, respectively), Cr2AlC, Nb4AlC3, (Nb,Zr)4AlC3, and a cermet comprising 40 vol% Fe and 60 vol% (Nb,Zr)4AlC3). 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, Cr2AlC showed practically no interaction with the molten salt during the performed exposure, forming a stable, sub-micrometre-thick Cr7C3 scale. Hence, it may be considered as promising structural/coating material candidate for the targeted CSP application.