Galvanic corrosion of pure metals in molten fluorides

• Galvanic corrosion of the couples Ni/Cr, Fe/Cr and Ni/Fe occurs in molten (Li,Na,K)F.
• Galvanic corrosion effects are obviously greater than 1, with the largest value of 80.97 observed for the couple Ni–Cr.
• Anodes Cr coupled with Ni or Fe, and Fe with Ni are dissolved to form metal ions which then are reduced on cathodes.

The corrosion of structural materials is a great challenge for the development of a molten salt reactor using molten fluorides as fuel or coolant. The corrosion of materials in molten fluorides occurs mainly through the dissolution of alloying elements into the melt. In the present investigation, the galvanic corrosion behavior of pure Ni, Fe, and Cr as the common alloying constituents in an eutectic LiF–NaF–KF melt at 700 °C has been investigated. The experimental results indicate that the corrosion potential of the three metals decreases significantly by the order of Ni, Fe and Cr, with the largest potential difference observed between Ni and Cr. Their great potential differences lead to the occurrence of significant galvanic corrosion. The galvanic corrosion effects of the couples Ni/Cr, Ni/Fe and Fe/Cr are significantly larger than 1, with the most remarkable effectiveness obtained for the couple Ni/Cr, then Fe/Cr and Ni/Fe.

Galvanic corrosion of the couples Ni/Cr, Ni/Fe and Fe/Cr in an eutectic (Li,Na,K)F melt at 700 °C. Anode: M→Mn++neM→Mn++ne, Cathode: Mn++ne→MMn++ne→M, Cr(galvanic effect = 80.97)Ni, Cr(galvanic effect = 70.65)Fe, Fe(galvanic effect = 55.94)Ni. Significant galvanic corrosion.Figure optionsDownload as PowerPoint slide