This Small Business Innovation Research Phase I Project aims to establish the feasibility of improved copper-base alloys as inert, oxygen evolving anodes for aluminum electrowinning from molten cryolite-alumina. The search for an inert anode has previously focused mainly on ceramic oxides, cermets and in situ formed ceramic oxides. The most serious problems with these materials are, (a) dissolution into the cryolite with subsequent contamination of the product aluminum, and (b) mechanical fracture. An alternative approach is to use a material which actually thrives in the hostile molten salt/O2 environment. This concept was demonstrated recently using metal anodes. This work included experiments with binary Cu-Al alloys. Under oxygen evolution conditions, these alloys should form stable, protective Al2O3-based films. However, the alloys exhibited only partial stability and suffered periodic film failure. This problem will be solved by using ternary and/or quaternary alloying additives to a Cu-Al base. Retrofitting US aluminum smelters with inert anodes could reduce energy consumption significantly. Eliminating carbon anode use would also avoid formation of the perfluorocarbons CF4 and C2F6, greenhouse gases with lifetimes of greater than many thousands of years in the atmosphere. U.S. aluminum producers have committed to reduce emission of these gases significantly by the year 2000.
