Corrosion behavior of Ni-based alloys in molten NaCl-CaCl2-MgCl2 eutectic salt for concentrating solar power

Abstract

In this work, the corrosion behavior of Ni-based alloys including Inconel 625(In625), Hastelloy X(H X) and Hastelloy B-3(H B-3) alloys were investigated in a molten salt NaCl-CaCl2-MgCl2 by gravimetric methods. The corrosion test was conducted at 600°C for a maximum immersion time of 3 weeks. The corrosion behavior was determined by measuring the mass loss of samples at different time intervals. The corrosion products and morphology were investigated in detail via X-ray diffraction (XRD) and scanning electron microscope (SEM). The microscopic area element analysis in corrosion surface and the mapping diagram of element distribution from corrosion profile were carried out by energy dispersive spectroscopy (EDS). The results show that In625 alloy resists corrosion better than H X and H B-3 alloys in molten salt NaCl-CaCl2-MgCl2 in the presence of air. The corrosion profile in In625 and H X alloy show a poor Cr zone in the inner corrosion layer, probably caused through the outward diffusion of CrCl4(g) which is forecasted the formation by thermodynamic calculation. MgCr2O4 attached to the In625 and H X alloys specimens surface formed a compact protective layer and thus resist corrosion well. Thin and uniform corrosion layer was observed from profile in H B-3 alloy after immersed in NaCl-CaCl2-MgCl2 molten salt when air was present, however there is not a poor Cr zone in corrosion profile of H B-3 alloy. From above, the corrosion rate of Ni and Mo in alloy dominates the corrosion rate. Certain amount of Cr in the nickel-based alloys enhanced its corrosion resistance in molten salt NaCl-CaCl2-MgCl2, even if Ni and Mo in nickel-based alloys shows more stable performance in the corrosion test in chloride molten salt.