Relationship among Process, 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 APS to protect from Cr-poisoning of cathode side in SOFCs. 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 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 can recover oxygen in the coatings and allow phase transition from trapped rocksalt to spinel which was demonstrated by TGA/DSC and XRD. Also, coatings with high density show excellent conductivity of 40S/cm at 800^oC and protection characteristics. Also, average CTE between 150-800^oC of 11x10^-6K^-1 is obtained.