High-temperature oxidation process analysis of MnCo 2O 4 coating on Fe–21Cr alloy

Abstract

Even though the operation temperature of solid oxide fuel cells (SOFCs) stacks has been reduced (∼750 °C), stainless steel interconnect within the stacks still requires protection by high conductive coatings to delay the growth of oxide scales and reduce chromium evaporation. Manganese cobaltite spinel protective coating with a nominal composition of MnCo 2O 4 was produced on Fe–21Cr stainless steel. Electrical, microstructural and compositional analysis were performed to investigate the interfacial reaction of MnCo 2O 4 protective coating with the stainless steel substrate during 750 °C oxidation process. The spinel coating not only acts as a barrier to Cr outward transport, but also improves the electrical conductivity of the alloy interconnect during long-term oxidation. The coated alloy demonstrates good electrical conductivity with an area specific resistance (ASR) of about 5 mOhm cm 2 after oxidation for 1000 h at 750 °C, which is about 1/4 of the ASR of bare Fe–21Cr alloy. The reduction of ASR might be caused by the fact that Cr migrated from the steel substrate interact with MnCo 2O 4 coating and generated Mn–Co–Cr spinel phase, which has higher electrical conductivity than that of Cr 2O 3.