Investigation of the early stage corrosion characteristics of molten (nitrate) salt – oxide – metal interfaces, and the links to interfacial thermo-mechanical stress

This paper investigates the early-stage corrosion behaviour of 4 alloys in solar-salt under air and argon at elevated temperatures for 7 days. The multi-layered interfacial corrosion oxides were observed to consist of an inner Cr-rich oxide and an outer Na/Fe-rich oxide. The inner tensile stress between the interfacial oxide layers were observed to correlate to the spallation of the porous outer Na/Fe-rich oxide layer. The combination of chemical aggression of molten salt, high temperature and argon atmospheres, acts in synergy to increase the kinetics of formation of Na/Fe–rich outer oxide layer, and it’s tendency to degrade by spallation due to an inner tensile stress.