Electrochemical Monitoring of the Corrosion of Ni, Fe, and Their Alloys in Molten Salts Available to Purchase

Instantaneous rates of the corrosion of Ni, Fe, and their alloys were measured in molten alkali chlorides, carbonates, and sulfates at 973 K by the electrochemical polarization resistance method. The stability of the oxide films formed on the surfaces was evaluated from steady-state anodic polarization curves. The polarization resistances varied proportionally to the corrosion currents measured by weight loss in all of the melts and obeyed the Stern-Geary equation. From the polarization resistance measurements, it was found that alloying with Cr increased the corrosion resistances of Ni and Fe in all of the melts and especially in molten sulfates. Alloying with Mo increased the corrosion resistance in molten chlorides, but decreased that in molten carbonates and sulfates. These results correspond well with those obtained from anodic polarization curves. It is concluded that the polarization resistance method is useful for assessing the corrosion resistance of alloys in molten salts.