(Co,Ni)O solid solutions as protective coatings for inert anodes in aluminum electrolysis

The substitution of consumable carbon anodes that emits CO₂ with inert (O₂-evolving) anodes in the primary production of aluminum would considerably reduce the emissions of carbon dioxide and perfluorocarbons of this industry. It would eliminate about 6 Mt of CO_{2 eq} produced annually by Canadian aluminum smelters, which is equivalent to the amount of CO₂ generated annually by about 2 million cars. However, the design of inert anodes is a major challenge because of the severe Al electrolysis conditions that requires materials with excellent resistance to corrosion and thermal shock, as well as adequate electrochemical properties. Cu-Ni-Fe based alloys are promising inert anode materials for Al production, however, they need to be protected by a layer to improve their long-term corrosion resistance.

In this context, Co-Ni-O protective coatings were deposited on Cu-Ni-Fe inert anodes by High Velocity Oxy Fuel (HVOF) thermal spraying. The morphological and microstructural characteristics of the coating were investigated as a function of the deposition conditions. The behaviour of the coated inert anodes under air and argon at high temperature as well as under Al electrolysis conditions were studied.