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A ferritic alloy interconnect was studied through solid oxide fuel cell ͑SOFC͒ stack operation at intermediate temperatures. Certain pretreatment of the alloy surface proved to be effective for controlling initial degradation of the stack performance, presumably by the formation of stable and conductive oxide scale. Evidences were found that glass sealant containing alkali metals affected the oxidation behavior of the alloy surface not in contact with the cathode material. A thick scale rich in iron tended to be formed at the air side in the vicinity of the glass sealant, while a thinner scale rich in chromium was preferably found in the other. Alkali metal components were found in that thick oxide layer. At the interface between the alloy and the cathode current collector, a strontium chromate, which might cause chromium poisoning at the cathode/electrolyte interface, was formed, and that was found to be distributed over the current collector away from the interface. A thermodynamic equilibrium calculation using a thermodynamic database revealed that the chromium component is highly reactive with alkali or alkali earth metals and forms stable chromates. Some of those chromates are very stable and may hinder the formation of stable oxide scale such as Mn-Cr-O spinels or Cr 2 O 3 , and may cause the severe oxidation of the alloy.

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Oxide scale formation was examined on the modified Fe-Cr alloys (Si and Al reduced concentrations) in H2-H2O or CH4-H2O atmospheres to simulate SOFC fuels. The formed oxide scales were characterized by surface and depth profile analyses. The oxide scale was composed of the following oxide phases from surface to inner oxide scale: Mn-Cr-(Fe) spinel layer, Cr2O3 layer, and Si-rich interface, and Al2O3 internal oxide. Although the scale formation mechanism is similar between modified and conventional alloys, the oxide scale growth rates were decreased in the modified Fe-Cr alloy. The electrical conductivity of oxidized Fe-Cr alloys was improved in the modified Fe-Cr alloy due to thinner oxide scale thickness and less distribution of insulating Si and Al internal oxides.