Kinetics of cobalt nanopowder obtaining process by hydrogen-reduction method under non-isothermal conditions

Metallurgy and Material Science

Nanotechnologies and nanomaterials


Nguyen T. H.1*, Nguyen V. M.2**, Le H. N.2***, Nguyen H. 2****

1. Le Qui Don State Technical University, Quoc Viet street, Hanoi, 100000, Vietnam
2. Institute of Technology, Hanoi, 100000, Vietnam



The article presents the studies of the process kinetics of obtaining nanopowder of metallic cobalt by hydrogen-reduction method under non-isothermal conditions, as well as properties analysis of the initial material and obtained products. Cobalt nanopowder was being obtained by hydrogen reduction of cobalt hydroxide nanopowder in the linear heating mode at a rate of 15°C/min within the temperature range from 25 °C to 500 °C. The Co(OH)2 nanopowder was synthesized in advance by chemical precipitation from aqueous solutions of cobalt nitrate Co(NO3)2 (10 wt. %) and alkali NaOH (10 wt. %) under conditions of continuous stirring, control of the T = 20 °C temperature and pH = 9 acidity. Kinetic parameters of the hydrogen reduction process under non- isothermal conditions were calculated by the differential-difference method using the data of thermo-gravimetric analysis and non-isothermal kinetic equation. The phase composition and structure of the samples were analyzed by the X-ray method. The specific surface area and average particle size of the powder samples were determined using the Brunauer–Emmett–Teller (BET) method by the low-temperature adsorption of nitrogen. The morphology and size of the nanoparticles were studied by scanning and transmission electron microscopy. It has been established that the process of non-isothermal hydrogen reduction of Co(OH)2 nanopowder occurs within the temperature range from 180 °C to 310 °C with a maximum rate 222.34·10-5 s-1 at a temperature of 280 °C. The dependence of the degree of conversion on еру temperature during the Co(OH)2 reduction process has been determined in the form of a mathematical function y = 0,0756·e0,0248x. The value of activation energy for the Co(OH)2 nanopowder reduction process was found to be ~45 kJ/mol, which indicates a mixed reaction mode. It was revealed that the Co(OH)2 hydroxide reduction at a temperature of 280 °C allowed to accelerating the process while ensuring the required properties of the product. The obtained metallic cobalt nanoparticles have a spherical shape with a nanometer size (about tens of nanometers) and are in a sintered state. Each of them herewith is connected to several neighboring particles by isthmuses.


kinetics, cobalt nanopowder, hydrogen-reduction, non-isothermal condition, difference-differential method


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