Corrosion assessment of 9Cr-1Mo steel in molten LiCl-KCl eutectic salt by electrochemical methods

Abstract

Ferritic chromoly steels are being considered for the process crucibles for the electrorefining of the pyrochemical reprocessing of spent metallic fuels in India. Pyrochemical reprocessing uses molten LiCl-KCl salt at 500–600 °C under an inert argon atmosphere for the electrorefining. The corrosion assessment of the 9Cr-1Mo steel in LiCl-KCl molten salt at 500 °C under inert argon atmosphere has been attempted using electrochemical measurements such as open circuit potential (OCP), linear polarization resistance and electrochemical impedance spectroscopy (EIS). The OCP of the sample was shifted towards noble direction during the total duration of 98 h. The linear polarization resistance, measured at regular intervals of exposure of 9Cr-1Mo steel to molten salt, increased with the increase of the exposure duration. The electrochemical impedance technique has been used to evaluate and monitor the molten salt-corrosion processes of the base metal. The EIS results showed the formation of a large semi-circle, with the characteristics of double loops capacitance attributed to the nature of intermittent oxide film over the surface. The surface oxide films are mostly composed of iron and chromium oxides confirmed by XRD and SEM-EDS analysis. It is also evident from the EDS analysis that depletion and enrichment of Cr and Mo across the surface of the 9Cr-1Mo steel. This work indicated that the electrochemical techniques show considerable promise for the monitoring of high-temperature molten salt corrosion processes.