Long term study of Cr evaporation and high temperature corrosion behaviour of Co coated ferritic steel for solid oxide fuel cell interconnects

• Published in: Journal of power sources Vol. 220; pp. 217 - 227
• Main Authors: Froitzheim, J., Canovic, S., Nikumaa, M., Sachitanand, R., Johansson, L.G., Svensson, J.E.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.12.2012; Elsevier
• Subjects: Applied sciences; Coating; Corrosion; Cr volatilization; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; Interconnect; SOFC; TEM; Interconnect; Cr volatilization; Coating; Corrosion; TEM; SOFC; Oxidation test; Microanalysis; High temperature; Coatings; Long term; Solid oxide fuel cell; Coated material; Time resolution; Transmission electron microscopy; Interconnection; Chromium oxide; Spinels; Ferritic steel; Oxidation; Comparative study
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2012.06.092

The oxidation behaviour of the uncoated ferritic Fe-22Cr steel Sanergy HT is compared with an 640 nm Co coated version of the same material. The materials have been subject to corrosion and Cr volatilization measurements in air for up to 3000 h at 850 °C. Oxidation tests have been carried out both isothermal and discontinuously. The volatilization measurements were carried out using a recently developed denuder technique, which allows to quantify Cr evaporation in a time resolved manner. The oxidation process is studied from very initial phases (>15 s) to long term behaviour (3000 h). The formed oxide scales are analysed by XRD, SEM/EDX as well as TEM/EDX. The results show that both materials form an oxide scale with an inner layer of Cr2O3 and a spinel layer on top. In the case of the uncoated material, the spinel layer is of (Cr,Mn)3O4 type while in the presence of a Co coating a (Co,Mn,Fe)3O4 is formed. The Cr evaporation measurements show that despite the fact that the Co coating is very thin (640 nm) it effectively blocks Cr evaporation for at least 3000 h. This is in line with TEM analysis showing that after 3000 h there is only a low Cr content in the outer oxide scale. This long term stability indicates the suitability of the coated material as solid oxide fuel cell (SOFC) interconnect. ▸ Continuous Cr evaporation measurement for 3000 h. ▸ 640 nm Co coating showing no sign of degradation over 3000 h. ▸ Detailed TEM analysis of oxide scale/coating development from 15 s to 3000 h.