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)Olayer and an outer FeOlayer. For Ni–Fe–10Cr alloy, an external(Ni,Fe)O/FeOlayers and an internal oxidation zone were formed at 800 °C, while a continuous CrOlayer forms at the internal oxidation zone/substrate interface at 900 °C. A multilayer structure oxide of CrO/(Ni,Fe,Cr)O/(Ni,Fe)O/FeOwas formed on Ni–Fe–15Cr alloy at 800 °C, while at 900 °C the FeObecomes discontinuous disperses in the(Ni,Fe)Olayer close to the surface. Increases in oxidation temperature or Cr content for Ni–Fe–Cr alloys promote the growth of the inner CrOlayer and simultaneously reduce FeOcontent. After 4 h of electrolysis at an anode current density of 0.25 A cm, the oxidation resistance of Ni–Fe–15Cr anode is superior to the Ni–Fe anode.