Cold-Sprayed Cu-Ni-Fe Anodes for CO2-Free Aluminum Production

Cu-Ni-Fe-coated and bare aluminum bronze materials are evaluated as O-2-evolving anodes for Al production in low-temperature (700 degrees C) potassium-based cryolite. The Cu-Ni-Fe coating (similar to 0.8 mm thick) is obtained by cold spraying of mechanically alloyed Cu65Ni20Fe15 (wt.%) powder and presents a biphase Cu-rich/Ni-Fe-rich structure. The composition and morphology of the scale formed on both anodes are characterized after different electrolysis times (3 to 50 h). In both cases, the formed surface oxide is porous with significant electrolyte infiltration. However, for the Cu-Ni-Fe-coated anode, there is formation of an inner NiFe2O4-rich layer limiting the outward Cu diffusion at the anode surface. As a result after 50 h of electrolysis, a lower anode wear rate (0.37 versus 3.8 cm year(-1)) and a higher produced Al purity (98.8 versus 95.4 wt.%) are observed with the Cu-Ni-Fe-coated anode compared to the uncoated aluminum bronze anode.