Consolidation of mechanically alloyed Cu-Ni-Fe material by spark plasma sintering and evaluation as inert anode for aluminum electrolysis

A Cu65Ni20Fe15 powder was prepared by mechanical alloying at semi-pilot scale to form a face-centered-cubic (fcc) phase (γ-phase). This powder was then consolidated by spark plasma sintering (SPS) to form a pellet. The crystallographic structure of the material is not affected by the consolidation process, although there is a slight increase of the crystallite size from 20 to 32 nm, and a slight decrease of the lattice strain from 0.5% to 0.2%. The relative density of the SPS consolidated sample is 95%. Thermogravimetric analysis confirms the good oxidation resistance of the SPS sample with a mass gain of only 0.4% after 20 h of oxidation at 700 °C, which is attributed to the rapid formation of a protective NiFe2O4 layer. The SPS sample was then evaluated as inert anode for Al electrolysis in low-temperature (700 °C) KF-AlF3 electrolyte. After 20 h of electrolysis at an anode current density of 0.5 A cm−2, the cell voltage reaches an unstable value of 5.0 V. The purity of the produced aluminum is 99.4% and the wear rate of the electrode is estimated at 1.8 cm year−1.