Electrochemical Degradation Mechanism of a Cermet Anode for Aluminum Production

Abstract

Tests on (Ni x Fe y O 4 - Ni 1? x Fe x O)/(Cu x Ni y Fe z ) cermets, considered as promising anode for the aluminium production, were performed under electrolysis at 0.8 A·cm -2 in molten mixture of cryolite at 960°C. In order to predict phase compositions, a thermodynamic study was performed and experimentally verified by SEM-EDS analysis. The metallic phase oxidation leads to the formation of different phases such as FeF 2 , Ni 0.90 Fe 0.10 O, NiF 2 and Cu 2 O phases, while Ni x Fe 3-x O 4 spinel is continuously enriched up to x = 0.90, the thermodynamically stable nickel composition. When the cermet material is fully oxidized, metallic and oxide phases are converted into soluble or non-conductive phases, leading to the end of anode service life.