Improvement of the corrosion properties in ternary molten nitrate salts for direct energy storage in CSP plants

• Addition of Ca(NO3)2 reduces the corrosion ability in molten nitrate salts.
• A1 steel is not recommend for its use in CSP plants containing lithium ternary molten salts.
• 2 wt.% Cr improve significantly the corrosion produced in carbon steels.

The corrosive effects of a molten nitrate mixture composed by 20% LiNO3 + 28% NaNO3 + 52% KNO3 were appraised at 390 °C on a low-Cr alloy steel (T22) and a carbon steel (A1). The corrosion rates were determined using gravimetric analysis, which measures the weight gain over 2000 h in order to identify the corrosion products with scanning electron microscopy (SEM) and X-ray diffraction (XRD).The observed behavior was compared with the corrosion ability produced by 58% KNO3 + 11% Ca(NO3)2 + 31% LiNO3 mixture. The results shown improved behavior in the ternary molten salt with calcium nitrate content due to the reduction of chloride ion levels and the superior diffusion and formation of protective spinels, such as MgCr2O4 and FeCr2O4, which were detected in ternary molten salt with Ca(NO3)2 content.The formation of certain stable compounds with salt impurities, such as carbonates and sulfates, was also observed.