Electrolysis and post-testing of inert cermet anodes

Stoichiometric nickel ferrite cermet anodes with 17% copper metal added, constituting a cermet, were electrolyzed for 50 hours in an alumina-saturated cryolite-based bath. Bath samples were frequently withdrawn from the cell and analyzed with respect to the anode constituents. Steady-state concentrations of iron and copper were below their solubility concentrations, while the nickel concentration was a little higher. Precautions had to be taken to avoid unwanted precipitation of solid alumina and cryolite at the cathode. Post-tests of the anodes showed that copper was depleted in the outer zone of the anode, and the composition of the copper-rich alloy (Cu-Ni-Fe) was changing from the interior toward the surface. However, the metaldepleted surface seemed to be dense, and no voids/pits from the lost metal grains were found in this region.