Spray-graphitization as a protection method against corrosion by molten nitrate salts and molten salts based nanofluids for thermal energy storage applications

Nanoscale science rapidly enters nearly every field of technology providing perspectives of new advanced applications. In the area of thermal energy storage (TES) doping molten salts with small amounts of nanoparticles represents tremendous interest due to the perspective of pronounced enhancement of their thermophysical properties. This is particularly important for the concentrated solar power (CSP) technology where a considerable decrease of investment costs is required. However, the information about materials degradation in direct contact with molten salts based nanofluids is practically absent. In this work, the compatibility of carbon steel A516.Gr70 with NaNO3-KNO3-Ca(NO3)2 (15-43-42 wt%) molten salt known as HitecXL doped with SiO2 nanoparticles was evaluated under thermal cycling conditions. We demonstrate that the presence of nanoparticles in the salt considerably increases the corrosion rates even for carbon steel protected by spray-graphitization method – the anti-corrosion method capable of reducing the corrosion rates for nanoparticles-free-HitecXL under similar conditions.