Evaluation of Ni-Fe base alloys as inert anode for low-temperature aluminium electrolysis

Isothermal oxidation behaviors of Ni–Fe (wt.%) and of the same alloy with additions of 10 and 15%Cr alloys in the air at 800 °C and 900 °C and their anodic behaviors in aluminum electrolysis system at 800 °C were evaluated. The composition morphologies of oxide scales were characterized by XRD, SEM, and EDS. Results show that the scales formed on Ni–Fe alloy at both temperatures consisted of an inner (Ni,Fe)3O4 layer and an outer Fe2O3 layer. For Ni–Fe–10Cr alloy, an external (Ni,Fe)3O4/Fe2O3 layers and an internal oxidation zone were formed at 800 °C, while a continuous Cr2O3 layer forms at the internal oxidation zone/substrate interface at 900 °C. A multilayer structure oxide of Cr2O3/(Ni,Fe,Cr)3O4/(Ni,Fe)3O4/Fe2O3 was formed on Ni–Fe–15Cr alloy at 800 °C, while at 900 °C the Fe2O3 becomes discontinuous disperses in the (Ni,Fe)3O4 layer close to the surface. Increases in oxidation temperature or Cr content for Ni–Fe–Cr alloys promote the growth of the inner Cr2O3 layer and simultaneously reduce Fe2O3 content. After 4 h of electrolysis at an anode current density of 0.25 A cm−2, the oxidation resistance of Ni–Fe–15Cr anode is superior to the Ni–Fe anode.