Corrosion properties of a ternary nitrate/nitrite molten salt in concentrated solar technology

The enhancements in the storage systems developed by solar thermal power plants have provided to renewable energy a considerable increase in efficiency. Thermal Energy Storage (TES) using HITEC mixture could be used as Heat Transfer Fluid (HTF) in concentrated solar linear technology. In this research, the corrosive effects of HITEC mixture composed by 40 wt% NaNO2 + 7 wt % NaNO3 + 53 wt% KNO3 were assessed at 390 degrees C on a carbon steel (A516) and on low-Cr alloy steels (T11 and T22). The corrosion rates were determined by gravimetric tests, measuring the weight gain during 2000 h, identifying the corrosion products via scanning electron microscopy and X-ray diffraction. T22 steel shows a corrosion layer of 6.05 microns, with a protective layer formed in the inner zone to the material, identified through DRX as the K2CrO4 protective spinel. Fe2O3 and MgO were the others important products found on the tests performed at 390 degrees C, being observed also the formation of some stable compounds with the impurities of the salt, as carbonates. The use of the HITEC mixture in solar technology would provide a less aggressive behaviour for materials in contact with it, providing an increase in operational life cycles in current solar technology. (C) 2015 Elsevier Ltd. All rights reserved.