Thermal influence in corrosion properties of Chilean solar nitrates

•Impurities levels have influence in molten nitrate corrosion process.•A purification treatment was performed on the binary solar salt.•The proposed treatment decreases the corrosion ability of the energy storage salts. Chile’s Atacama Desert is one of the world’s premier locations for the study and application of solar power. The typical impurities present in Chilean nitrates are Mg, SO4− and Cl−, among others. Developing a heat treatment to eliminate impurities and optimise the quality of the salts from the solar flats of the Atacama Desert is one of the most important goals of the inorganic chemistry industry in northern Chile. In this study, a full characterisation of the binary solar salt 60% NaNO3+40% KNO3 was performed by studying the influence of the most important impurities on the thermal processes and corrosiveness at the storage temperatures of the most important solar thermal plants. Moisture is another parameter that is important for this technology. The corrosion test results improve after heat treatment. The corrosion characteristics were determined using gravimetric tests, measuring the weight gain of three alloy steels with low Cr contents at 390°C over 2000h and identifying the corrosion products using scanning electron microscopy (SEM) and X-ray diffraction (XRD). Fe2O3 and Fe3O4 were the most important corrosion products. Additionally, some stable compounds were formed from the impurities in the salt, such as magnesium ferrite (MgFe2O4).