Study of Cu-Ni-Fe Alloys as Inert Anodes for Al Production in Low-Temperature KF-AlF₃ Electrolyte

Cu-Ni-Fe-based alloys are considered as promising O₂-evolving anode materials for CO₂-free Al production. In the present study, biphased (as-cast) and monophased (postcasting homogenized) Cu₆₅Ni₂₀Fe₁₅, alloys, and monophased Ni₆₅Fe₂₅Cu₁₀ alloy (in wt pct) are evaluated as O₂-evolving anodes for Al production in potassium cryolite at 700 °C. The produced Al purity is 99.6 wt pct, and the erosion rate is estimated at 0.4 cm year⁻¹ for both Cu₆₅Ni₂₀Fe₁₅ anodes compared to 95.2 wt pct and 3.2 cm year⁻¹ for the Ni₆₅Fe₂₅Cu₁₀ anode. The compositions, and morphologies of the surface oxide layer and the metal fluoride layer present at the oxide/alloy interface are compared for the three anodes. The deleterious impact of electrolyte infiltration on the surface oxide building is highlighted.