Metal Anode Performance in Low-Temperature Electrolytes for Aluminum Production

An investigation has been undertaken into the performance of metal alloy anodes used to produce aluminum via an electrochemical method. Alumina was electrolyzed in NaF/AlF₃ and KF/AlF₃ electrolytes and mixtures thereof with copper-nickel-iron (Cu:Ni:Fe) alloy anodes and titanium diboride (TiB₂) cathodes. The operating temperatures of the electrochemical cells ranged from 973 K to 1123 K (700 °C to 850 °C), with an anode current density of 5000 A/m². Cells ranged in current capacity from 10 to 300 amperes, with oxygen gas formed at the anode and molten aluminum collected from the cathode. Posttest anodes were sectioned, and elemental maps were performed to characterize the distribution of the chemical phases, including the metal electrodes, bath phases, and aluminum metal production, which were used to determine the reaction mechanisms of the cell. The metal alloy slowly corroded and formed an adherent, electronically conducting nickel ferrite plus copper scale during the operation of the cell. The proposed mechanisms of the anode performance are described herein.