Corrosion of Ni–Fe based alloy in chloride molten salts for concentrating solar power containing aluminum as corrosion inhibitor

Abstract

Chloride molten salt is extremely corrosive at high temperature. Thus, it is significant to study molten salt purification schemes to prevent structural materials from high-temperature corrosion. This paper performed corrosion tests of a Ni–Fe-based materials (HT700 alloy) in ternary chloride molten salt at 800 °C to identify the inhibiting effects of Al powder by using electrochemical methods which included impedance spectroscopy and potentiodynamic polarization, the morphologies and phase composition of HT700 alloy after corrosion tests were determined by scanning electron microscopy equipped with energy dispersive spectroscopy and X-ray diffraction. Addition of Al powder could reduce the corrosion current density of HT700 alloy in chloride molten salt, the Al2O3 layer was formed from the reaction of Al and impurities on the surface of the alloy, and the beneficial effects of Al powder increased with increasing Al content added in the chloride molten salt. There was a diffusion layer beneath the oxide scale resulting from the outwards diffusion of Cr in the alloy, addition of Al could hinder the outwards diffusion of Cr, thus prolong the lifetime of HT700 alloy in the chloride molten salt. Otherwise, a protective Ni3Al layer formed by the inwards diffusion of Al when the content of addition Al reached up to 10 wt%. Therefore, addition of Al powder in ternary chloride molten salt as corrosion inhibitor was feasible, but the content of added Al should be optimized to balance the corrosive and the thermal-physics properties of the chloride molten salt.