Electrochemical impedance spectroscopy (EIS): An efficient technique for monitoring corrosion processes in molten salt environments in CSP applications

This study assessed the behaviour of a constructive material in CSP plants, namelyferritic-martensitic steel, withmoltenNaNO3/KNO3(60/40 wt%), also known asSolar Salt. To this end, EIS is presented as a suitable technique to evaluate and monitor the resistance of this material to Solar Salt at 580 °C. Tests were performed up to 1000 h and results were also supported by gravimetric and microstructuralcharacterisationof the samples andchemical analysisof the salt. According to the EIS results, adiffusion-controlled reactionoccurred during contact, which indicates that the corrosion process follows aporous layermechanism. The results also indicated variations in corrosionlayer thicknessand instability of the salt during the whole test. The EIS results were also used for determining thecorrosion rate, this being estimated at ~300 µm year−1. Results obtained by EIS were in line with the behaviour of P91 steel as measured by gravimetric, morphological and chemical analysis. Thus, the results confirm the suitability of EIS for monitoring corrosion processes in real-time of constructive materials in CSP plants.