Fabrication and Characterization of Nickel Ferrite Based Inert Anodes for Aluminum Electrolysis

Nickel ferrite-based cermets and their relevant composites have been widely used as inert anodes for aluminum electrolysis due to the good combination of chemical resistance, thermal, and mechanical stability. In this study, various NiO/NiFe₂O₄ composites consisting 5, 10, and 15% NiO in conjunction with Cu/NiFe₂O₄ cermets containing 5, 10, and 15% Cu have been prepared by powder metallurgy method. The degradation resistance of developed inert composites has been evaluated under hot corrosion conditions by plunging the samples in the molten electrolyte at 1,000 °C for various holding times. The strength, toughness, hardness, relative density, microstructural observation, phase analysis, and electrical resistivity have been investigated in details by the 3-points bending test, Vickers hardness test, Archimedes method, scanning electron microscope, x-ray diffraction, and conventional direct current four-probe technique, respectively. The experimental results for NiO/NiFe₂O₄ composites show that a significant improvement of toughness and degradation resistance occurred in conjunction with a moderate decrease in strength by adding NiO content from 5 to 15%, while the relative density has been increased only up to 5%NiO content and then decreased. Moreover, increasing of Cu content from 5 to 15% in the cermet samples, all of the mentioned engineering properties such as strength, toughness and electrical conductivity have been improved considerably, but the degradation resistance has been decreased.