Synthesis and characterisation of nanostructured Ni–Co alloy Part 2: Co 3 O 4 reduction kinetics

Abstract

This work is the second 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 oxide reduction was studied in the range from 200 to 500°C. This paper is then related to the production of isolated Co3O4 from Co(NO3)2·6H2O dissociation followed by its hydrogen reduction, which showed a good agreement with the topochemical model. The apparent activation energy was found to be 33·7 kJ mol⁻¹. Transmission electron microscopy (TEM) has been used to observe the morphology and size of the cobalt oxide. This material is composed by particles having a 40 nm average size. The cobalt in oxide and metallic form was both analysed by X-ray diffraction in which the presence of these crystallised species was confirmed.