INVESTIGATION OF THE INFLUENCE OF ELECTROMAGNETIC FIELD AND ENERGY-MECHANICAL PROCESSING ON THE PRODUCTION OF METALLIC COBALT NANOPOWDER BY HYDROGEN REDUCTION

Nanopowders (NP) based on cobalt have significant prospects for use in various fields of science, engineering, industry and medicine.In this work the authors have studied the kinetics of the production of metallic cobalt nanopowder by hydrogen reduction of oxide material Co₃O₄ in an electromagnetic field, and with an energy-mechanical processing (EMP) in eddy layer created by ferromagnetic bodies subjected to such field.Cobalt oxide Co₃O₄ NP was obtained by thermal decomposition of the hydroxide compound Co(OH)₂ chemical-precipitated from 10  % aqueous solutions of nitrate cobalt Co(NO₃)₂ and sodiumhydroxide NaOH under the conditions of pH  =  9 and t  =  20  °C. The production of metallic cobalt nanoparticles by the hydrogen reduction of Co₃O₄ NP was carried out on the apparatus of eddy layer (AED) of UAP-3 model modified with an internal heating furnace and a flow reactor. The amplitude value of induction of magnetic field inside the reactor was 0.16  T. The experimental temperatures of the reduction process were chosen based on the result of a thermogravimetric analysis (TGA) of the initial cobalt hydroxide sample. The kinetic parameters of hydrogen reduction processes under linear heating and in isothermal conditions were calculated using the Freeman-Carroll and McKewan models, respectively. The authors have found a decrease in the rate of obtaining Co nanopowder in the electromagnetic field (up to 14  % at 250  °C) due to the decrease in the adsorption ability of hydrogen atoms on the surface of the formed metallic nanoparticles. EMP in the eddy layer leads to an increase in the reduction rate by 4  –  5 times due to the effect of mechanical activation of the material. The properties of the initial material and the obtained products were investigated using the methods of thermogravimetry, X-ray diffractometry, electron microscopy and measurement of the specific surface area by low-temperature nitrogen adsorption. It was shown that reduction of the samples in the electromagnetic field facilitate the formation of more finer-dispersed Co nanoparticles, than in the case without the field. The EMP in the eddy layer leads to the aggregation of the formed metallic nanoparticles and the formation of granules of micron size.

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