Interface reactions between electrically conductive ceramics and ferritic steel-I. The system Cr–22Fe–0.5Mn/Mn2O3/(La,Ca)(Cr,Co,Cu)O3

The interface between metallic components and ceramics play an important role in the long-term stability of solid oxide fuel cell stacks. In order to improve the contact resistance and durability of cathodes, contact coatings and protective layers, respectively, are applied between interconnects and cathodes. In this study, a ferritic steel with 22% Cr is used as an interconnect material. Mn2O3 and (La,Ca)(Cr,Co,Cu)O3 are applied as protective and contact coatings, respectively. Several stack tests are performed for different operation periods using these materials. Post-test analyses are carried out using X-ray diffraction and metallographic methods identifying the reactions between the steel and the ceramic materials. Microstructural and analytical results indicate a complex interdiffusion behaviour of several cations: Mn and Cr from the steel diffuse into the ceramic layers, Mn from the Mn2O3 diffuses into the perovskite-based contact layer, and Ca and Cu from the perovskite diffuse into the manganese oxide layer. Chemical equilibrium is established after about 2000 h of operation at 800 °C. Longer operation times only showed continuous scale growth of the formed reaction layers.