Electrolytic Production of Aluminum Using Mechanically Alloyed Cu-Al-Ni-Fe-Based Materials as Inert Anodes

Cu92-xAlxNi5Fe3 materials with x varying from 0 to 20 (wt %) were prepared by mechanical alloying. For x <= 10, the as-milled Cu92-xAlxNi5Fe3 was made of an alpha-phase, whereas lambda-Cu9Al4 was formed at x = 20. Upon consolidation, a small amount of kappa Ni/Fe-rich Al phase with a B2 structure is formed for x = 6 and 10, whereas no new phase is formed in the other compounds. Aluminum electrolysis tests conducted at an anode current density of 0.5 A cm(-2) for 20 h in a low temperature (700 degrees C) KF-AlF3 electrolyte showed that the electrode stability and aluminum purity are strongly dependent on the alloy composition. The lowest values of cell voltage (4.1 V) and Cu contamination (0.8 wt %) were obtained for x = 10 wt %. This relatively lower contamination is due to the formation of a dense and adherent CuAl2O4 oxide scale between the outermost Cu2O oxide layer and the substrate. In comparison, a hot-rolled C63000 commercially available alloy with the same composition but lower chemical/microstructural homogeneity gave a higher Cu contamination level (1.4 wt %). (c) 2010 The Electrochemical Society. [DOI: 10.1149/1.3482156] All rights reserved.