Synthesis and characterisation of nanostructured Ni–Co alloy Part 3: NiO and Co 3 O 4 coformed reduction kinetics

Abstract

This work is the third part of an investigation dedicated to produce a Ni–Co nanostructured 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 in order to evaluate the viability of the process as well as to select experimental conditions for the individual reductions. The oxides reduction was studied in the range from 300 to 500°C. This paper is then related to the production of NiO–Co₃O₄, from a solution containing both Ni(NO₃)₂.6H₂O and Co(NO₃)₂.6H₂O, followed by its hydrogen reduction, which showed a good agreement with the topochemical model. The apparent active tion energy was found to be 29·7 kJ mol⁻¹. Transmission electron microscopy has been used to observe the morphology and size of the obtained materials (Ni–Co co-oxides and Ni–Co alloy). These materials were also analysed by X-ray diffraction in which was confirmed the presence of the crystallised species. Such analyses showed that coformed oxides particles could already be found in the range from 10 to 50 nm while the average particle size of the alloy was ∼40 nm with the smallest ones of ∼20 nm.