High-temperature corrosion study of alloys in molten MgCl₂-KCl eutectic salt
The MgCl₂-KCl molten salt has been proposed as one of the heat transfer fluids (HTFs) in the solar energy system because of its potential thermal properties. This research investigates the corrosion behavior and protection strategies of Haynes 230 (H230), Incoloy 800H (800H), and Stainless Steel 316 (SS316) in MgCl₂-KCl molten salt at high temperature. First of all, the corrosion rates of different alloys are determined by performing the long-term static corrosion experiments. The morphologies of the surface and corrosion depths are examined by scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometer (EDS). Secondly, the effect of Ni on the corrosion behavior of the alloys is studied in this research. When the alloy is connected with Ni, the corrosion rate is higher than that without connection in the same condition. Thirdly, the electrochemical tests of three alloys are also investigated in present research work. Tafel curves are plotted to calculate the corrosion potentials and corrosion rates of three alloys at different temperatures. Fourthly, two methods are proposed and studied to protect the alloys from severe corrosion in the MgCl₂-KCl molten salt: 1) adding a sacrificial anode into the salt, and 2) coating a high-corrosion-resistance alloy. Mn, Zn, and Zr are chosen as the sacrificial anode materials to protect the alloys from further corrosion. The result showed that additions of inhibitor into the molten salts decrease the corrosion rates of the tested alloy. Pure Ni, Al₂O₃, Ni-Al alloy, and Cr-Fe-Al alloy are chosen to coat the tested alloy. Long-term corrosion experiments, as well as electrochemical tests of alloys with and without different coatings, are studied in present work. The results demonstrated that all these coatings decreased the corrosion rates of the tested alloys. Finally, the diffusion models are constructed to predict the distribution of the Cr in the different alloys after corrosion. And the results are comparable to the experimental data. In conclusion, H230 showed the highest corrosion resistance in the MgCl₂-KCl salt proved by long-term corrosion test and electrochemical tests. Different inhibitors and coatings all improved the corrosion resistance of alloys in the molten salt.