Polarization corrosion of the iron-nickel alloy in Na3AlF6-based system molten salts

Fe-Ni (with different wt.%) alloys were prepared by powder metallurgy process and used as anode for aluminum electrolysis. Electrolysis polarization of these anodes was conducted for 12 hours at 850 degC in a Na₃AlF₆-based molten salt. The anodic current density was 0.75 A/cm2. At the initial stage, the corrosion rate decreased with increasing ratio of Fe to Ni in the alloy, when the ratio of Fe to Ni was 1.42, the lowest value of the corrosion rate with 21 mm/a was obtained. Then corrosion rate increased with increasing ratio of Fe to Ni. The analysis of Electron Probe Micro-analyzer and X-ray diffraction showed that the film formed on the anodic surface consisted of iron oxide as outer layer, and nickel oxide and nickel ferrite spinel as inner layer. The metal anode presented good performance in terms of anti-oxidation and corrosion resistance, and the purity of the produced aluminum was 98%.