Process dependent Microstructure and Electrical/Protective Performances of Plasma Sprayed MCO coatings in SOFCs

Manganese cobalt spinel (Mn_1.5Co_1.5O₄, MCO) coatings were prepared by air plasma spray process to protect from Cr-poisoning of cathode side in solid oxide fuel cells. Spray parameters were manipulated in terms of hardware, gas contents, mass flow rate, and power to find optimum process condition. These various spray conditions were mapped on 2-dimensional thermal and kinetic energies space via diagnosing particle temperature and velocity in plasma plume. Dense MCO coating was generated by high thermal and kinetic energies, but low temperature and velocity used coatings contain microcracks and pores that lowered coating residual stress. As-sprayed coatings contain CoO and Mn_xCo_3-xO₄ due to rapid quenching and preferential vaporization of manganese and oxygen. Post annealing process can recover oxygen in the coatings as well as allow phase transition from trapped rock salt to spinel which were demonstrated by TGA/DSC and XRD. Also, coatings with high density show excellent conductivity and protection characteristics.