Investigating the Corrosion Behaviors of Fe-Ni-Cr Anode Material for Aluminum Electrolysis

Abstract

Corrosion resistance in cryolitic melts is the most important property for inert anode used in aluminum electrolysis. Ni-Fe-Cr alloy anodes were prepared with a protective layer on their surface through a pre-oxidation procedure, and corrosion tests were carried out in a laboratory aluminum electrolysis cell at 950 °C. The microstructures of the anodes before and after the electrolysis were inspected using XRD and SEM techniques. It is found that a starting protective layer formed after 10 – 20 hour pre-oxidation could be sufficient to make the anode maintaining function during the corrosion tests. A corrosion layer with varying thickness on the metal anodes at a current density of 0.75 A/cm2 was formed in aluminum electrolysis in the cryolitic melts, where various metal fluorides were involved in the surface reactions. Detailed analysis revealed that the chemical compositions of the corrosion-oxide protective layers on the metal anodes varied due to selective corrosion and migration of Fe, Ni, Cr, and O crossing the interface. The results may provide useful technical data for materials design and process development for metal inert anode that can maintain the function through a dynamic oxide protective layer during aluminum electrolysis.