Corrosion resistance of Cr/Ni alloy to a molten carbonate salt at various temperatures for the next generation high-temperature CSP plants

Abstract

The corrosion behaviour of a commercial HR3C steel in a molten eutectic ternary Li2CO3-Na2CO3-K2CO3 mixture was studied by isothermal immersion tests at 700 °C and 800 °C for 2000 h. It was found that in both cases the corrosion products were arranged in a multilayer structure, with LiFeO2, LiCrO2, NiO and FeCr2O4 as the main compounds. Similar results to those obtained at 700 °C were reached in the tests performed at 800 °C but 1000 h earlier, which seems to indicate that the process was accelerated at higher temperature. Furthermore, regarding the superficial crystalline phase formed and according to the XRD and SEM examinations, it was found that on increasing the test temperature, a continuous transformation occurred from the rhombohedral to the cubic phase of the LiFeO2 oxide layer. This transformation took place at both temperatures when the tests proceed and it was also accelerated by increasing the temperature from 700 to 800 °C. Thus, the process seems to be slower at 700 °C, which complicates the use of HR3C at 800 °C in the molten eutectic ternary Li2CO3-Na2CO3-K2CO3 salt mixture. These results suggest that the use of protective coatings should be assessed and that this material should be tested at 700 °C under more aggressive conditions, such as flowing salt, in future studies.