High temperature oxidation behaviour of Ni–Fe–Co anodes for aluminium electrolysis

The oxidation behaviour of ternary NixFeyCoz alloys (where x/y (wt) = 1 and 1.85; z = 0, 10, 30 and 50 wt.%) was studied in air at 800 °C. Alloys were found to follow complex oxidation kinetics, with the highest oxidation rates observed for alloys having 50 wt.% Co. Significant improvements in oxidation resistance were achieved by addition of 10 and 30 wt.% Co to the Ni–Fe system. The decrease in oxidation rate was associated with suppression of Fe2O3 formation in preference for (Co,Ni)xFe3−xO4 growth. The results were discussed in light of the materials requirements for inert anodes for aluminium electrolysis.

► Oxidation behaviour of Ni–Fe–Co alloys studied at 800 °C in air. ► Oxidation found to follow complex kinetics. ► Alloys with 30–50 wt.% Co produced multi-layer scales containing Co3O4, CoO, NixCo3−xO4 and CoxFe3−xO4. ► Alloys with 0–10 wt.% Co produced multi-layer scales containing Fe2O3, NixFe3−xO4, NiO. ► Decrease in oxidation rate of binary Ni–Fe system achieved with addition of 10 and 30 wt.% Co.