Study of the corrosion of different alloys in molten carbonate salts by electrochemical impedance spectroscopy

In the present work the corrosion behavior of different alloys (AISI 304, AISI 430 and TiAl6V) in molten carbonates at 650EC are compared. By using the Electrochemical Impedance Technique different corrosion parameters such as the corrosion rate and the oxyde concentration and others features of the different layers of corrosion products are "in situ" determined. Take into account, the corrosion product characterization by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Electrochemical impedance Spectroscopy (EIS) a corrosion mechanism for every tested alloy is proposed. In all cases, the corrosion mechanisms during the first hours are similar to a high temperature oxidation mechanism. When the equilibrium is established, the lithiation began by the formation of different double-layers on the surface of Li-metal oxydes. At the end of the corrosion process, one or two inner layers of metallic oxydes and one or two outer layers of Li-metal oxydes were formed. The corrosion mechanisms of the stainless steels (AISI 304 ans AISI 310S) are a function of their chromium contents. TiAl6V alloy showed the best behavior against the corrosion of molten carbonates by the formation of a protective layer of mixed Li-Ti oxydes.