The oxidation of ferritic stainless steels has been studied under solid oxide fuel cell (SOFC) interconnect "dual" exposure conditions, i.e. simultaneous exposure to air on one side of the sample, and moist hydrogen on the other side. This paper focuses on the oxidation behavior of ferritic stainless steels during cyclic oxidation in the dual environment. It was found that scales grown on the airside under these dual exposure conditions can be significantly different from scales grown on samples exposed to air on both sides. After only three cycles from room temperature to 800°C (with a dwell time of 100 hours for each cycle), a-Fe2O3 hematite phase nucleated inhomogenously and grew into thick nodules on the airside of the dual exposure stainless steel coupons, leading to localized metal loss or attack. For coupons cycled to 850°C, the scale on areas both with and without nodules tended to develop a stratified structure, causing increased metal loss. The accelerated oxidation and growth of hematite nodules which was observed in thermally cycled samples (as compared to samples which were not cycled) was tentatively attributed to an increased concentration of defects in the scale resulting in enhanced transport of iron cations through the scale.
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