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Solar Salt (60 wt% NaNO3, 40 wt% KNO3), used in Concentrated Solar Power (CSP) Thermal Energy Storage (TES) technology, can decompose into various products at elevated temperatures, with oxide ions being one of the known corrosive byproducts. The study mimics Solar Salt aging by intentionally adding sodium peroxide (Na2O2) and sodium oxide (Na2O) at concentrations of 0.005–0.33 wt% to investigate their role in the corrosion of austenitic stainless steel at 600 °C in typical operating conditions. Salt chemistry (nitrite, nitrate, oxide ions, and metal cations) was analyzed every 24 h, and steel corrosion after 168 h was assessed by weight change, corrosion rate, phase analysis, and cross-sectional morphology. Results reveal that at or above 0.135 wt% added Na2O2/Na2O leads to a quasi-steady-state equilibrium of oxide ions in the salt. Interestingly, at these concentrations, the presence of steel further decreases oxide ion concentration. Furthermore, above 0.135 wt%, the corrosion rate increases significantly, along with increased spallation, porosity and disintegration of the corrosion layer, forming a non-protective layer. This study highlights the critical role of oxide ions in the corrosion process.
Concentrated solar power (CSP) systems commonly use solar salt as a high temperature heat transfer and storage medium. This study examines the effect of oxygen (O2) and nitrogen oxide (NO) gas concentrations on solar salt thermal stability and 310N stainless steel corrosion at 600°C up to 1224 h. The impact of the gas atmosphere (5–80 vol% O2 , 400–600 ppm NO) on salt chemistry, including nitrate, nitrite, oxide, and chromate ions, was analyzed, and corrosion behavior was evaluated through weight change, corrosion rate, and microstructural analysis. The results show that introducing NO gas concentrations ≥ 400 ppm with at least 5 vol% O2 stabilizes salt decomposition by controlling nitrite and oxide ion formation and promotes the development of a protective corrosion layer on the steel surface. Once this protective layer is formed, variations in oxygen concentration (5–80 vol%) in the presence of ≥ 400 ppm NO gas have a minimal long‐term effect on the corrosion behavior of stainless steel in solar salt. These findings underscore the importance of maintaining minimum O2 and NO levels to optimize salt chemistry that effectively mitigates steel corrosion in solar salt systems.
