Self-adaptive MgAl2O4 spinel layer for enhanced corrosion resistance of alumina-forming alloy in molten chloride salts

Abstract

Molten chloride salts are promising heat-transfer and storage media for next-generation energy systems but pose severe corrosion risks to metallic structural materials. Here, we present a novel corrosion mitigation strategy for FeCrAl alloy by constructively leveraging the molten salt environment to induce a spinel protective layer on the metal surface. Porous alumina is initially engineered through selective anodization of FeCrAl, which facilitates Mg²⁺ incorporation and effectively relieves volumetric expansion stress during molten NaCl–MgCl₂ exposure. Consequently, the porous alumina is transformed into a compact and chemically robust MgAl₂O₄ spinel barrier. Corrosion testing at 700 °C for 700 h reveals nearly an order-of-magnitude less chromium depletion in the anodized FeCrAl (∼22 μm) compared with the bare alloy (∼171 μm). Comprehensive characterization, along with measurements of dissolved Cr concentration and mass loss, further support the enhanced corrosion resistance. This scalable strategy offers a viable pathway for long-term materials durability in next-generation nuclear power, concentrated solar power and thermal energy storage systems.