The paper presents experimental results of reduction of cupric oxide (CuO) by low-temperature hydrogen plasma in a microwave-assisted plasma set-up. The experiments were carried out at low microwave powers in the range of 600-750 W and low hydrogen flow rates in the range of 0.833 9 10 -6 to 2.5 9 10 -6 m 3 s -1 . In all the experiments for reduction of CuO with hydrogen plasma, an initial induction period was observed in the kinetic plots. The induction period decreases with increase in pressure or temperature. The induction period leads to the formation of active sites for adsorption of H 2 . After the induction period, fast autocatalytic reduction takes place followed by a sluggish period towards the end. The reduction process proceeds in sequential steps through the formation of sub-oxides. The kinetic data fits the Avrami-Erofeev equation with 'n' value close to 3. The resultant activation energy measured during hydrogen plasma processing is around 75.64 kJ mol -1 . This is lower compared to activation energies measured by other methods of reduction indicating a clear advantage.
This paper describes the effects of various parameters on the reduction of hematite in the presence of microwave assisted non-thermal hydrogen plasma. The parameters include microwave power, hydrogen flowrate, pressure, microwave power density and temperature. It has been shown that hydrogen flowrate, pressure and microwave power are interrelated to effect the microwave power density that controls the plasma temperature. The experimental conditions encounter three temperatures: surrounding the sample, associated with the plasma and at the plasma/substrate interface. It has been deduced that the third one is the most effective in determining the rate of the reaction, and in the present case, activation energy of 20 kJ mol 21 is reported.
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