Synthesis and characterisation of nanostructured Ni–Co alloy Part 1: NiO reduction kinetics

Abstract

Nanostructured materials have been receiving distinguished interest in recent scientific investigations due to their particular properties, which may not be present in the same material in bulk. This work is part one of a whole investigation which presents an alternative route for the synthesis of nanostructured nickel–cobalt alloy. The route begins with the coprecipitation of the NiO–Co₃O₄ from dissociation of the respective nitrates followed by a hydrogen reduction of these oxides. Preliminary thermodynamic studies have been carried out to evaluate the viability of the process as well as to select experimental conditions for the individual reductions. The reduction reactions were studied in the range from 200 to 500°C. This work is then related to the production of isolated NiO from a Ni(NO₃)₂.6H₂O dissociation, followed by its reduction. The reaction showed an autocatalytic behaviour with E_a=28·7 kJ mol⁻¹. Transmission electron microscopy has been used to observe the morphology and size of the nickel oxide. This material presents some particles even smaller than 5 nm while its particle size distribution has an average of 20 nm. The obtained oxide and metallic nickel were both analysed by X-ray diffraction in which was confirmed the presence of these crystallised species.