KINETICS OF SYNTHESIZING PROCESS OF MICRON NICKEL POWDER BY HYDROGEN REDUCTION FROM OXIDE COMPOUND UNDER NON-ISOTHERMAL CONDITIONS

Abstract

In this work the kinetics of the process of obtaining micron nickel powder by hydrogen reduction of the oxide compound under non-isothermal conditions were studied. The hydrogen reduction process of micron NiO powder with hydrogen under non-isothermal conditions was carried out in the linear heating mode at a rate of 10°C/ min in the temperature range of 20-450°C. The study of crystal structure and composition of the powder samples was performed by XRD phase analysis. The specific surface area S of the powders was measured using BET method by low-temperature nitrogen adsorption. The average particle size D of powder samples was determined via the measured S value. The size and shape of the particles were investigated by scanning electron microscopic method. The calculation of kinetic parameters of the reduction process of nickel oxide in nonisothermal conditions was carried out by the differential-difference method using the data of thermogravimetric analysis and the equation for non-isothermal kinetics. It was revealed that the hydrogen reduction process of micron NiO powder in non-isothermia occurs in the temperature range of 270-335°C with a maximum specific rate of 9.667·10-8 kg/s recorded at 316°C. The dependence of the degree of conversion during reduction process was determined by mathematical statistics method and can be well described by the expression y=0.0001e0.0168·x with the coefficient of determination R2=0.9739. The activation energy of hydrogen reduction processes of the micron NiO powder under non-isothermal conditions was found to be ~43 kJ/mol, which indicates a mixed reaction mode. In this mode, a rational way to accelerate the process is both increasing the temperature and eliminating the diffusion layer of the reduction product by intensive mixing. It is shown that an increase in temperature to 316ºС can effectively increase the rate of the overall process of hydrogen reduction of micron NiO powder while guaranteeing the quality of the reduction product. The obtained micron Ni particles are highly porous material, while the Ni particles are collected in large porous aggregates up to 10 μm in size.