Mechanically Alloyed Cu-Ni-Fe-O Based Materials as Oxygen-Evolving Anodes for Aluminum Electrolysis

Abstract

A series of compounds with the general formula (Cu65Ni20Fe15)100-xOx, with x = 0.3, 1.4, 3.3 and 7.2 were prepared by high energy ball milling and evaluated as oxygen-evolving anodes for aluminum electrolysis. In a first step, elemental Cu, Ni and Fe powders were milled together to form a face-centered-cubic (fcc) phase (γ-phase). Then, the milling operation was resumed in presence of the desired amount of oxygen. Upon heat-treatment at 1000°C during the subsequent powder consolidation, the added oxygen reacted with Fe to form Fe2O3. Aluminum electrolyses conducted for 20 h in low-temperature (700°C) KF-AlF3 electrolyte at an anode current density of 0.5 A cm−2 showed that the electrode stability and aluminum purity are strongly dependent on the amount of oxygen added. The best results were obtained for x = 1.4. In that case, the cell voltage was stable at ca. 4.0 V and the Cu, Fe and Ni contaminations of the produced Al and electrolyte were minimal, resulting in an anode erosion rate of 0.8 cm year−1. In this case, the size, dispersion and concentration of Fe2O3 precipitates in the consolidated powder were optimal to give rise to the formation of a protective NiFe2O4-rich layer.