Corrosion and depassivation of a chromia-forming Ni-based alloy in the 0.75Na2O-B2O3-2.75SiO2 melt

Abstract Corrosion resistance of nickel based alloys in molten silicates is linked to the temperature. Above a certain temperature, the protection of the alloy by a chromia layer is no more ensured: this depassivation phenomenon leads to active corrosion. Electrochemical methods were used for in situ characterization, and Scanning Electron Microscopy (SEM) and Scanning Electron Transmission Microscopy (STEM) were used in order to measure the oxide thickness after immersion. Corrosion tests with increasing temperature showed that above a certain temperature, the oxide thickness decreased homogeneously leading to the depassivation of the alloy. The different steps of this phenomenon are discussed here.