Abstract: Pre-oxidation is a common surface treatment approach to enhance the corrosion resistance of metals, which suffers from slow ion diffusion kinetics, bad oxide scale adhesion, and weak compactness. Herein, we propose an electrochemical oxidation approach in molten carbonate to improve the oxide scale growth and adhesion via electrochemically regulating ion diffusion in the formed oxide scale. An anodic polarization applied at the metal substrate enlarges the chemical potential gradient of oxygen and offers a favorable electric field across the metal/oxide interface to the oxide scale/molten salt interface, thereby speeding up the oxide scale growth rate in terms of increasing the diffusion rate of metal cations and oxygen ions through the oxide scale. At the same time, the oxide scale adhesion is remarkedly improved because the metal vacancies at the oxide/alloy interface are filled by the newly formed oxide. After being treated by electrochemical oxidation, the corrosion rate of the Ni-16Fe-4Mo alloys in molten Li₂CO₃-Na₂CO₃-K₂CO₃ decreased ten-fold. Overall, electrochemical oxidation enables the rapid formation of an adherent and corrosion-resistant oxide scale on the metal substrate, offering a general and effective way to fabricate corrosion-resistant films to survive in various aggressively corrosive media.

Key words: Molten salt, High-temperature oxidation, Anodic polarization, Corrosion protection, Inert anode