Molten carbonate corrosion of a 13-Cr ferritic stainless steel protected by a perovskite conversion treatment: Relationship with the coating microstructure and formation mechanism

Abstract

A feasibility study has been conducted to determine if a recently developed molten salt perovskite conversion coating process can be applied to protect an intrinsically low corrosion-resistant 13-Cr ferritic stainless steel in Molten Carbonate Fuel Cell (MCFC) demanding environments. The molten salt bath composition has been adapted to evaluate the influence of two different reaction mechanisms, namely dissolution-precipitation and precursor-template synthesis, on microstructure and MCFC corrosion resistance of the LaFeO3-based perovskite coatings. It has been found that the necessary strong basic/oxidizing chemistry conditions for the dissolution-precipitation mechanism to occur cause extensive substrate corrosion that contribute to coating porosity and poor MCFC corrosion protection. On the other hand, excellent corrosion protection of the 13-Cr steel is afforded by a perovskite conversion coating that had been produced via an iron oxide precursor-template route under milder basic conditions. The results show that a decreased salt bath basicity fully suppresses substrate corrosion, while promoting at the same a fine coating microstructure and virtual absence of coating through-porosity, thus markedly improving the barrier properties of coated 13-Cr steel against MCFC corrosion attack.