High temperature corrosion behavior on molten nitrate salt-based nanofluids for CSP plants

Recently, a number of theoretical and experimental studies have been performed to understand the effect of nanoparticles on thermal properties and heat transfer performance but there is a lack regarding their corrosion properties. In this work, an extended corrosion characterization (at central tower plant storage temperature (565 degrees C)) has been carried out in two different grades of solar salt (industrial and refined purity) doped with the addition of 1 wt% Al2O3 nanoparticles or 1 wt% SiO2 nanoparticles. Corrosion rates were determined in commercial stainless steel commonly used in CSP technology (347SS) by gravimetric tests, measuring the weight gain during 1000 h, identifying the corrosion products by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The lowest corrosion rate (0.007 mm/year) was obtained in the refined solar salt with the addition of 1 wt% Al2O3 nanoparticles. A protective layer was formed in the steel-salt interphase, identified through XRD as Al2O3. Additionally, hematite (Fe2O3) and magnetite (Fe3O4) were obtained as unprotective corrosion products throughout the test carried out with or without nanoparticles. In addition, the presence of impurities on the salts generated some stable compounds, as magnesium ferrite (MgFe2O4). (C) 2018 Elsevier Ltd. All rights reserved.