Phase diagram, thermal stability, and high temperature oxidation of the ternary copper-nickel-iron system

Due to the aluminum industry demands, a large effort has recently been devoted to the development of special alloys to be used as inert anodes for a newly designed aluminum reduction cell. The implementation of this new technology aims at the replacement of the graphite anodes that have been used for over 100 years in aluminum smelting, which would reduce fossil carbon consumption, and eliminate the emission of carbon dioxide and of perfluorocarbons. Ternary alloys containing copper, nickel, and iron have been the subject of the research activities.; The present research focused on the stability of the Cu-Ni-Fe alloys at high temperatures in oxidizing and fluoridating environments. The experimental methods included thermodynamic calculations of the phase diagram (Thermocalc), optical microscopy and microprobe microstructural and chemical investigations (EMPA), small-angle neutron scattering (SANS), differential thermal analysis (DTA), and air-oxidation studies.; The results have led to the optimization of the Cu-Ni-Fe ternary phase diagram and to an extensive study of the thermodynamics and kinetics of the spinodal decomposition and discontinuous reactions occurring during ageing as a function of alloy composition. The oxidizing reactions occurring in air at high temperatures at the surface of the alloys have been also discussed in terms of thermodynamic and kinetic laws. The phase formation in a fluorine containing environment as encountered in an aluminum electrolytic cell is predicted using principles of physical chemistry.