Morphological changes and kinetic assessment of Cu2O powder reduction by non-thermal hydrogen plasma

Abstract

Non-thermal hydrogen plasma is a novel reducing medium that can yield H2 derived species capable of improving the reduction efficiency of metallic oxides when compared to a conventional reduction by hydrogen gas. To analyze the morphological changes of the samples and evaluate the impact of the plasma hydrogen species on the kinetic process, this work performed Cu2O powder reduction by non-thermal hydrogen plasma and compared it to hydrogen gas reduction at the same experimental conditions. The experiments were conducted in a pulsed direct current glow discharge reactor at pressure of 533 Pa, varying temperatures between 250°C and 400°C and reduction time intervals from 5 to 120 min. The results show that hydrogen plasma reduction is a faster process, reaching a higher degree of metallization of the Cu2O powder than hydrogen gas process in any reduction condition. Hydrogen plasma promotes a higher sintering degree of the newly formed porous copper particulates than hydrogen gas processing. The kinetic assessment of experimental data shows that plasma process kinetics are best-fitted to Prout-Tompkins’ nucleation model at temperature range from 300°C to 400°C, and to Jander's diffusion model at 250°C. On the other hand, gas process kinetics are best adjusted to Prout-Tompkins’ and JMAEK's models at 400°C and 350°C, respectively. The calculated apparent activation energy of plasma reduction is 19.06 kJ/mol at temperature range of 300°C – 400°C; whilst for gas reduction is 73.79 kJ/mol at temperature range of 350°C–400°C.