Electrochemical Behavior of Cr(III/II) in MgCl2-NaCl-KCl Melt and its Potential Application for Corrosion Inhibition of 316H Stainless Steel

Understanding the behavior of Cr(III/II) in molten salt environments is crucial for effective corrosion control. A systematic study is conducted on the redox behavior of Cr(III)/Cr(II) and Cr(II)/Cr in the MgCl2-NaCl-KCl (MNKC) melt, with electrochemical methods used to determine the redox mechanism, formal standard potential, and diffusion coefficients. The corrosion performance of 316H stainless steel (316HSS) is examined in H2-treated MNKC-CrCl2 and Cr-equilibrated MNKC-CrCl2 systems, revealing corrosion in the former and corrosion inhibition in the latter. This phenomenon is explained from a thermodynamic perspective, with a corrosion inhibition threshold condition of CCr(II) >= 32.05CCr(III)2/3. Both experimental and thermodynamic evaluation results suggests the viability of the Cr-equilibrated Cr(II) for corrosion inhibition in the MNKC melt. These findings highlight the intricate relationship between redox behavior and corrosion inhibition in molten salt systems, offering valuable insights for future research and practical applications. The redox of Cr(III)/Cr(II) with different coordination environments is investigated.The corrosion threshold is evaluated thermodynamically according to the determined formal standard potentials of Cr(III)/Cr(II) and Cr(II)/Cr.Corrosion tests agree with the thermodynamic evaluation results.