Formation and structure of plasma sprayed manganese-cobalt spinel coatings on preheated metallic interconnector plates

Manganese-cobalt spinels are promising materials for protective coatings on metallic interconnector plates in solid oxide fuel cells. These protective coatings are used to prevent growth and evaporation of chromium oxide, chromium poisoning and ageing phenomena of the cathode side of the fuel cell. It is well known that chromium trioxide and chromium hydroxide on interconnector plate may easily evaporate at high temperatures and transform back to chromium oxide at the cathodes active area and cause degradation of the solid oxide fuel cell performance. In the present study, plasma spraying together with a substrate pre- and simultaneous heating was found to be an appropriate technique to control the formation and densification of the coating. When plasma spraying Mn-Co spinel powder for cold substrate, high cracking effect inside the splats and in the formed coating was noticed. When applying the molten drops to the substrate heated up to 450 °C amount of cracks in single splats and coatings could be mostly eliminated. The splats stayed in the liquid state longer, which effected for spreading properties and spinel structure could be better preserved by longer crystallize time.