Corrosion behavior of aluminide diffusion coatings in low temperature molten carbonate electrolysis environments

Interest on low‐temperature molten carbonate electrolysis processes (T < 600 °C) for advanced energy conversion and storage applications appears to be progressively growing in literature. However, the corrosion of metallic materials in molten carbonate salts in equilibrium with the acidic CO2‐rich electrolysis gas atmospheres has been scarcely studied. In this work, the corrosion stability of a low‐activity FeAl aluminide diffusion coated 316 L stainless steel has been tested in a ternary carbonate eutectic mixture Li2CO3‐Na2CO3‐K2CO3 by 48 h‐immersion tests at 500 °C under CO2 atmosphere. Before the corrosion testing, the coated steel samples were pre‐oxidized in air at 750 °C in order to generate a protective thin alumina film on the aluminide coating surface. The salt immersion results indicate that FeAl aluminide coatings are not stable in acid molten carbonate environments due to rapid transformation of the pre‐existing alumina film into a non‐protective mixed Fe‐Al oxide crystalline layer. Corrosion degradation has been found to consist of both general and localized forms of attack. Factors affecting FeAl aluminide coating corrosion have been analyzed and discussed in detail.