Hot-corrosion studies of separator plates of AISI-310 stainless steels in molten-carbonate fuel cells

The corrosion behavior of a stainless steel 310S was investigated in a molten carbonate electrolyte at 650 degrees C. The LiFeO2 and LiCrO2 oxides were formed in contact with the eutectic 62mol% Li2CO3-38 mol% K2CO3 mixture. Despite the low solubility of these oxides, the presence of fissures in the LiFeO2, layer does not provide good protection of the metallic material. The electrochemical-impedance spectroscopy (EIS) technique has shown low values of polarization resistance up to 80 hr and an increase of the electrolyte resistance because of the dissolution of part of the scale after immersion. A mechanism for the corrosion of stainless steel 310S in molten carbonates is proposed between 0 and 80 hr, taking into account thermodynamic simulations, X-ray diffraction (XRD), scanning electron microscopy (SEM) characterizations, and ac-impedance (EIS) results. This mechanism confirms a high corrosion rate and nonprotective scaleformation during the first hours of in immersion. An external and discontinuous iron-rich oxide layer covered by a thin chromium-rich oxide layer and an intermediate chromium-rich oxide and an internal spinel layer were observed. Internal oxidation of the substrate also occurred to for (Fe, Cr)(2)O-3 oxide. The dissolution in the melt of a part of the scale has been detected by EIS.