The present paper describes the electrochemical results and the post exposure microstructural characterization by means of SEM/EDS of a four layer SOFC stack after 34,000 h operation under load at 700 °C, showing low voltage degradation rate less than 0.3% per 1,000 h. Emphasis was put on the behavior of the ferritic interconnect steel and its interaction with glass sealants as well as contacting and coating materials. The interconnect steel had formed thin protective chromia scales. Gas distributing steel foils of 200 µm showed in some locations breakaway type oxidation. It was related to local overheating caused by locally occurring combustion of a defective cell. The interaction of the steel with the glass sealant showed good adhesion. Interdiffusion at the joint between nickel contact and steel interconnect at the anode side resulted in minor oxide formation on the Ni wires and in austenite formation in the steel without formation of σ‐FeCr formation at the steel/austenite interface. The steel showed excellent compatibility with the Manganese‐Cobalt‐Ferrite (MCF) chromium retention coatings. Chromium enriched phases were found near the interface between MCF coating and perovskite contact layer. Excess glass sealing material interacted with the contact layer without showing obvious detrimental effects.
NiCr, NiCrAl and FeCrAl based Oxide Dispersion Strengthened (ODs) high temperature alIoys possess far better oxidation resistance than dispersion free alloys of the same base composition. The presence of yttria dispersions leads to excellent scale adherence and a very selective oxidation of the scale forming element. Most of the observed differences in microstructure and protective properties between oxide scales on ODs and non-ODs alloys can be explained by differences in scale transport mechanisms. Although other dispersions have been found to have a positive effect on oxidation behaviour similar to that of yttria, they seem to possess no major advantage, provided that the yttria content is properly adjusted to the actual alloy system.
Since the mid-nineties several generations of SOFC stacks have been designed and tested incorporating the anode substrate-type cells developed in Jülich. The 6 th generation, the so-called F-design stacks, with metallic interconnect has been the 'work horse' used for testing materials, cells and manufacturing processes in cell and stack development since its introduction in the year 2001. Stacks with up to 60 layers have been operated in recent years, delivering up to 13 kW of electric power. The ferritic parts are made of the commercial steel type CroFer22APU. This paper summarises the current developments at FZJ and presents some recent results obtained with new materials.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.