Influence of a Rotary Electromagnetic Field and Mechanical Stimulation on the Production of Cobalt Nanopowder by Reduction with Hydrogen

Аннотация

Cobalt nanopowder is very promising for use in science, engineering, industry, and medicine. The present study focuses on the kinetics of nanopowder production by the reduction of cobalt oxide with hydrogen in an electromagnetic field, under the action of a bed of ferromagnetic particles rotating in the electromagnetic field. Cobalt oxide (Co₃O₄) nanopowder is obtained by the thermal decomposition of cobalt hydroxide Co(OH)₂ deposited from 10% ionic solutions of cobalt nitrate Co(NO₃)₂ and sodium hydroxide NaOH at 20°C, with pH 9. Cobalt nanoparticles are produced from Co₃O₄ nanopowder in a modified UAP-3 vortical bed system with a built-in furnace and flow-through reactor. The amplitude of the magnetic induction within the reactor is 0.16 T. The experimental reduction temperature is selected on the basis of thermogravimetric analysis of the initial Co(OH)₂ sample. The kinetic parameters of hydrogen reduction with linear heating and in isothermal conditions are calculated on the basis of the Freeman–Carroll and McKewan models, respectively. The rate of cobalt- nanopowder production slows in an electromagnetic field (by up to 14% at 250°C), on account of hindrance to the adsorption of hydrogen atoms at the surface of the metallic nanoparticles formed. However, mechanical stimulation in a vortical bed increases the rate of the process by a factor of 4–5 as a result of activation. The properties of the initial material and the products are studied by thermogravimetric analysis, X-ray diffraction analysis, scanning electron microscopy, and measurement of the specific surface by low-temperature nitrogen absorption. In the reduction of the samples, smaller cobalt nanoparticles are produced in the presence of an electromagnetic field. Mechanical stimulation in a vortical bed results in aggregation of the cobalt nanoparticles and the formation of microgranules.