Microstructure and DC electrical conductivity of spinel nickel ferrite sintered in air and nitrogen atmospheres

In recent years, the development of inert anode materials has gained considerable attention because such materials are capable of producing only environment-friendly O₂ and saving energy during aluminum electrolysis. Nickel ferrite was prepared by a solid-state reaction as the inert anode in this study and its microstructures and direct current conductivities were analyzed in detail regarding the effects of different sintering atmospheres. A single-phase spinel structure was confirmed for all samples by X-ray powder diffraction. The grain sizes and the relative densities of the samples sintered in nitrogen increased by over 7 μm and 10.8%, respectively, compared to those sintered in air. The direct current conductivities of the samples sintered in nitrogen showed a drastic increase compared to those sintered in air, believed to be due to the effects of increased Fe²⁺ ion concentration at octahedral sites and the increase of the relative density.