Oxidation and Electrical Behavior of Mn-Co-Coated Crofer 22 APU Steel Produced by a Pack Cementation Method for SOFC Interconnect Applications

Abstract

An issue associated with chromia-scale formation on ferritic stainless steels is an associated increase in electrical resistance over time, due to the oxide growth. Further, the migration of chromium via chromia-scale evaporation into solid oxide fuel cell (SOFC) cathodes can result in degradation in cell electrochemical performance. In this research, manganese and cobalt were deposited by the pack cementation method onto Crofer 22 APU ferritic stainless steel. Isothermal and cyclic oxidation was carried out to evaluate the role of coating materials during oxidation. Area-specific resistance (ASR) of the Mn–Co-coated substrates was also tested at 800 °C. The results demonstrate that the coating layer transforms to MnCo2O4, CoFe2O4, CoCr2O4, and Co3O4 spinels during oxidation. This scale is protective, and acts as an effective barrier against chromium migration into the outer oxide. Mn–Co oxide and cobalt oxides also cause a reduction in ASR, in comparison to that of bare steel.