High-temperature oxidation of the Crofer 22 H ferritic steel with Mn1.45Co1.45Fe0.1O4 and Mn1.5Co1.5O4 spinel coatings under thermal cycling conditions and its properties

The aim of the presented study was to deposit protective-conducting Mn1.45Co1.45Fe0.1O4 and Mn1.5Co1.5O4 spinel coatings on the Crofer 22 H ferritic steel by means of electrophoresis and to evaluate their physicochemical properties after high-temperature oxidation under thermal cycling conditions. When the Crofer 22 H steel – whether uncoated or coated with the two spinels – was oxidized in 48-h cycles involving a temperature of either 750 or 800 °C, its oxidation kinetics approximately obeyed the parabolic rate law. The oxidation rate observed for uncoated steel was higher than that for the studied coating/steel systems. The Fe-doped spinel coating material improved the oxidation resistance of steel to a higher degree than the undoped spinel coating. The obtained bulk spinels exhibited a regular phase composition and high electrical conductivity, while the Mn1.45Co1.45Fe0.1O4 and Mn1.5Co1.5O4 coatings were dual-phase, compact, and exhibited good adhesion to the metallic substrate. The area-specific resistance values measured for the steel/coating systems indicate that the coatings significantly improve the electrical properties of the studied ferritic steel, especially at 800 °C. The conducted research confirmed the suitability of the Mn1.45Co1.45Fe0.1O4 and Mn1.5Co1.5O4 spinels as coatings on the Crofer 22 H ferritic steel to be applied in the production of interconnects used in intermediate-temperature SOFCs.