Lifetime prediction for manganese cobalt spinel oxide coatings on metallic interconnects

To prevent chromium poisoning of cathodes in solid oxide fuel cells, metallic interconnects are coated with protective oxides. One commonly used coating is manganese cobalt spinel oxide (MCO). Although MCO acts as a barrier to oxidation of interconnects, formation of native oxide scales on interconnects still occurs. As a result of native scale growth during fuel cell operations, the strength of the MCO interface will degrade. In addition, the spallation is generally driven by the temperature coefficient of expansion mismatch between the native scales and the MCO. Thus MCO spallation is likely to be dependent on the thicknesses of the different layers and is most likely to occur when cooling the fuel cell from high operating temperatures. In this study, the effects of the native scale thickness on MCO spallation are explored. To obtain interfacial fracture energy as a function of native scale thickness, room temperature, four-point bend experiments are performed on coated interconnects with various native scale thicknesses. By comparing the evolving interfacial fracture energy from experiments with the interfacial fracture energy obtained from an analytical model, coating lifetime is predicted.