Influence of Solar Salt Chemistry on Corrosion Evolution of SS316L

Kurzfassung

The increasing demand for renewable energy sources subsequently led to the development of new energy storage solutions. Thermal Energy Storage (TES) systems that use molten Solar Salt (60 wt.% NaNO3/40 wt.% KNO3) as storage medium and heat transfer fluid are one of the most promising solutions regarding scalability to the GWh-scale, economics and intrinsic compatibility with a multitude of thermal processes. Despite their implementation, long term corrosion studies, especially under controlled salt decomposition, are not available. Hence, the impact of molten salt ageing on the lifetime of the TES system is mostly unknown. In this work a unique approach is used to identify the critical concentration of oxide ion species and to compare the corrosive properties of oxide and peroxide ions in Solar Salt. For this purpose, various concentrations of Na2O and Na2O2 ranging from 0.005 to 0.2 wt.% were added to synthetic Solar Salt with AISI 316 L steel samples inside at 600 °C for 7 days under air purged gas atmosphere. The salt analysis was carried out every 24 hours using ion chromatography (IC) and titration, the corrosion scale thickness was analysed using scanning electron microscope (SEM) and Energy dispersive X-ray (EDX), in addition mass gain and mass loss were also recorded for comparison.