Applying the protective CuMn2O4 spinel coating on AISI-430 ferritic stainless steel used as solid oxide fuel cell interconnects

Abstract

Ferritic stainless steels at high temperature and long operating time of solid oxide fuel cells (SOFC) face with some problems such as overgrowth and spallation of the surface oxide and cathode poisoning due to chromium evaporation. In the present work in order to improve the above-mentioned problems, the protective/conductive CuMn2O4 spinel coating was created on the AISI-430 ferritic stainless steel by means of pulse electrodeposition and subsequent heat treatment. Therefore, at first, the copper was applied to the substrate from a sulfate bath with an average current density of 48mA/cm2 and a deposition time of 4min. Subsequently, manganese was electrodeposited on the copper layer from a sulfate bath with an average current density of 125mA/cm2 and a deposition time of 8min. The frequency and duty cycle in the pulse electrodeposition of Cu and Mn Were considered100Hz and 80%, respectively. Then, to convert the metallic layers to spinel and also to evaluate its prevention of outward diffusion of Cr, oxidation was carried out at 750°C in the air for 24h and 100h. Microstructural evaluation of samples cross-section by scanning electron microscope (SEM) equipped with EDS indicated that the CuMn2O4 spinel layer acted as a barrier to outward diffusion of Cr effectively and the amount of Cr in the coating surface was zero. Also, coating layer had good adhesion to the substrate. By investigation of samples oxidation in the air for 0.5, 10 and 120min at 750°C, the results indicated that Mn was rapidly oxidized to MnO and Mn3O4, at the outset of the oxidation of the CuMn metallic coating. Gradually, the MnO and Mn3O4 disappeared and Mn2O3 was formed and the copper was oxidized to CuO. Finally, spinel phase of CuO and Mn2O3 was formed.