Effect of SiO₂ nanoparticles concentration on the corrosion behaviour of solar salt-based nanofluids for concentrating solar power plants

Recently, corrosion of nanoparticles molten salt-based nanofluids studies have emerged as Concentrating Solar Power plants provide a low carbon alternative to produce electricity. Enhancing the heat capacity and thermal conductivity of molten salts by using inorganic nanoparticles has been targeted as a strategy to decrease the overall investment cost of CSP systems. However, there is scarce and insufficient information about their effect on the corrosion behaviour of nanofluids, whether the nanoparticle content increases it or have no significant effect. The scatter data found show no clear agreement and the measurements are done under different conditions (temperature, time, impurities, nanoparticle's chemical nature and concentration, metal and alloy composition, testing method). In this context, the authors evaluated the effect of SiO₂ nanoparticles concentration in an industrial-grade Solar Salt in contact with four different alloys; AISI 1045, 304H, 316L and Inconel 600 by isothermal tests, 500 °C up to 2160 h. The effect of nanoparticles, 0.5% and 1% wt., was evaluated in comparison with Solar Salt industrial grade. The corrosion rate of the samples decreased in the following order AISI 1045 > 304H > 316L > Inconel 600 and nanoparticles increased in general and to a different extent the corrosion rate of the alloys. The one that experiences the highest nanoparticle effect is stainless steel 304H, followed by AISI 1045 and Inconel. For 316L, no significant differences can be seen. The applicability assessment carried out has shown that molten salt nitrate-based nanofluids can be used with Inconel 600, 304H and 316L in long-term service high-temperature applications such as CSP.