Carbon Reduction Kinetics of NiO by Microwave Heating of the Separated Electric and Magnetic Fields

A powder mixture consisting of NiO and graphite was heated by microwave (MW) irradiation, and the reduction reaction kinetics was studied. The heating was performed in a single-mode MW applicator operated at 2.45 GHz. The specimen was placed in the waveguide at the maximum positions of either the electric (E-) field or the magnetic (H-) field. The reaction kinetics was investigated mostly at the E-field with variation of the reaction time, temperature, and grain sizes of NiO and graphite. It was shown that the kinetics was enhanced at the higher temperature and using smaller sized powder particles. The difference of the kinetics in the E-field and the H-field was investigated. A tendency was observed that the reduction rate was larger in the H-field than in the E-field at 600 °C. Considering the fact that NiO was heated well in the E-field, while graphite was heated in both fields, graphite particles in the powder mixture might be selectively heated in the H-field. The obtained results were discussed considering the thermodynamics and the gas-solid reaction mechanisms.