Suspension plasma spray deposition of CoxNi1-xO coatings

Suspension Plasma Spray (SPS) process was used for the deposition of cobalt-nickel oxide solid solutions as potential coatings for inert anodes in primary aluminum production. The effects of SPS process parameters (plasma power, standoff distance, gas mixture, and substrate temperature) on the structure and composition of coatings were investigated. X-ray diffraction measurements, coupled with Rietveld refinement analysis, and scanning electron microscope (SEM) coupled with energy-dispersive X-ray spectroscopy (EDX) analyses were performed. It was shown that substrate temperature is the single most important parameter affecting the nature of the coating, and that uniform, adherent and non-porous CoxNi1-xO coatings made of a single solid solution phase are obtained when the substrate temperature is above 950 degrees C. Metallic Ni is observed in coatings prepared at lower temperatures and, in that case, the composition of the solid solution phase deviates from that of the starting materials. This work also discusses possible causes for the formation of metallic nickel during spraying.