Corrosion Behavior of Fe-Cr-Ni Alloys in Molten NaNO3-KNO3 Salt Mixture and Vapor

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The serious challenges for harvesting solar energy from solar power tower is the inherent intermittence caused by altering of day and night and by the weather event changes, posing a significant threat to the continuous supply of solar electricity. The most promising solution explored by the researchers during the last few decades would be integrating the thermal storage system with the Concentrated Solar Power Plant (CSP) to stabilise and provide the high-quality electrical energy at night or anytime without sufficient solar irradiance. Typical thermal energy storage system enables the CSP plants to store solar energy by heating the sensible storage medium, like molten nitrate salt in a hot tank.

Product Number: 51323-18909-SG

Author: Qingyang Liu, Frederick Pessu

Publication Date: 2023

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The corrosion behavior of two Fe-Cr-Ni alloys in eutectic nitrate (NaNO3/KNO3) salt and its vapor were investigated at 565˚C for 28 days. Results show higher corrosion rates in salt vapor than in liquid salt. In addition, the surfaces of samples exposed to vapor were severely corroded with spallation of the outer oxide layer. The oxide layer of the corroded alloys in molten salt exhibited lower Cr depletion in comparison with the surface exposed to the vapor salt. The alloy formed a loose double layer of Cr, Fe and Na oxide in molten salt vapor. The oxidation of material in the molten salt vapor contributed the most to the overall corrosion of the sample, and its Cr-depleted depth was nearly twice that of a sample immersed in molten salt. Alloy (chromium) dissolution from the metal into salt and selective oxidation at the salt/metal interface dominates the corrosion mechanism in liquid and vapor salt. This confirms the need to take into consideration the corrosion of alloy by salt vapor during practical material selection process for such applications.