Electrochemical Corrosion Studies in Molten Chloride Salts

Abstract

This study investigates corrosion of Fe-(Cr)-Ni model alloys in eutectic molten chloride salt mixtures that broadly simulate the heat transfer circuits of molten salt cooled nuclear reactors. The primary focus is impurity-driven corrosion and selective dissolution of electrochemically reactive element(s) (dealloying), which are known degradation modes for Fe- and Ni-based alloys in molten salts. This study demonstrates that a Mg rod performs close to a true Mg|Mg2+ reference electrode system in a MgCl2 containing mixture. Mg dynamic reference electrodes validated the performance of the ordinary Mg reference electrode. The residual moisture content in molten salts is measured by cathodic polarization of Pt, which showed that convection of molten salts, after step-wise heating, through a bundle of Mg ribbons dropped the moisture content by 30-fold. The effect of impurities in the molten salt mixture, moisture and NiCl2, on dealloying was also investigated at low homologous temperature. It was found that the universal parting limit for dealloying is decreased to a value of approximately 32 at.% Fe when Ni from the parent alloy is close to equilibrium with Ni2+ ions added to the eutectic molten salts. Results support the percolation/surface diffusion concept for dealloying in molten salts at low homologous temperature.

The Effect of Temperature on Dealloying Mechanisms in Molten Salt Corrosion

“…Electrochemical measurement of the moisture content supported the effectiveness of this purification procedure and was previously described in Ref. 51.…”

“…A schematic of the experimental setup and a detailed procedure was previously described. 51 The working electrode is the alloy of interest (see Materials and sample preparation section), and graphite was used as the counter electrode. Mg was used as a true Mg|Mg 2+ reference electrode (RE) for this study and was found to have a fast and stable potential in molten Cl salts when MgCl 2 was one of the constituents, which was ensured by calibration against "dynamic" Mg REs.…”

“…Mg was used as a true Mg|Mg 2+ reference electrode (RE) for this study and was found to have a fast and stable potential in molten Cl salts when MgCl 2 was one of the constituents, which was ensured by calibration against "dynamic" Mg REs. 51 A Pt wire was used as a pseudo-RE for experiments where LiCl-KCl was used, as described elsewhere. 52 All electrodes were connected to a software-controlled potentiostat (PARSTAT 2263, Princeton Applied Research).…”

The Effect of Atmospheric Chloride Ions on the Corrosion Fatigue of Metal Wire Clips in Power Grids

“…31-19.04 µg•m −3 in winter and 4.28-9.17 µg•m −3 in summer [17]. The Cl − penetrates the surface of the metal material into the substrate, causing the metal to undergo electrochemical corrosion and form unstable iron chloride compounds [18], and Cl − is absorbent and more likely to form an electrolyte of chloride, which is more aggressive toward metals [19]. Pitting occurs in metal under the Cl − corrosion environment, which can develop into cracks at low cyclic stress (well below the fatigue limit of pure mechanical fatigue), which eventually leads to the metal cracking and failing [20].…”

Evolution of micro-pores in Ni–Cr alloys via molten salt dealloying

“…As an alternative approach, molten salt has been demonstrated as a promising dealloying agent to fabricate porous structures 26,27 . Molten salt dealloying (MSD) was motivated by the salt-induced corrosive attack of metals and alloys in next-generation nuclear reactor system 28 , concentrated solar power plants [29][30][31] , and waste incineration plants 32,33 .…”