Reduction of Cobalt Oxide (Co3O4) by Low Temperature Hydrogen Plasma

The paper reports on reduction of cobalt oxide (Co3O4) to cobalt metal by low temperature hydrogen plasma. Hydrogen flow rate was varied between 1.167 x 10(-6) to 2.5 x 10(-6) m(3) s(-1) at a fixed microwave power of 750 W which gave rise to increase in pressure from 1.866 x 10(3) to 2.933 x 10(3) Pa and increase in temperature of the plasma-cobalt oxide interface from 823 to 1,039 K. Reduction of cobalt oxide to cobalt occurred in steps: Co3O4 -> CoO -> Co. The chemical reaction leading to reduction of cobalt oxide to cobalt is found to be first order with respect to hydrogen flow rate. The activation energy for the first stage of reduction i.e. Co3O4 to CoO is found to be 26.2 kJ/mol and that for the second stage reduction of CoO to Co metal is 13.3 kJ/mol.