Corrosion behavior of Fe-37 wt% Ni in molten NaCl-MgCl2 and the effects of alloy element Sc on its corrosion resistance

As a solar energy storage medium or heat transfer medium at moderate-high temperature, the molten NaCl-MgCl 2 has the advantages of high stability and low cost. But a pipe and container material with Cr will be corroded badly in a molten chloride. Based on the founded corrosion resistance phase (Fe 0.64 Ni 0.36 ) in previous experiments, the corrosion behavior of a new alloy of Fe-37 wt% Ni with rare earth alloy element Sc in the molten eutectic NaCl-MgCl 2 at 520 °C was studied. The corrosion rate of the Fe-37 wt% Ni alloy is lower than that of the researched Fe-based superalloys (GH1035 and GH1140). After corrosion for 15 h, a porous structure with Ni-rich and Fe-depletion is formed at the local location on the Fe-37 wt% Ni surface. For the specimens with Sc (0.3 and 0.5 wt %), a compact protective MgO layer covers on the porous structure, which prevents further corrosion in the molten salt . It is speculated that the Sc is oxidized to Sc 2 O 3 directly or by the chlorination-oxidation reactions, which improves the adhesion strength between the MgO layer and the alloy matrix by the effects of inhomogeneous nucleation and pinning.