Selectivity of microwave energy consumption in the reduction of Fe3O4 with carbon black in mixed powder

In the present work, mixtures of magnetite and carbon black powers were irradiated by a constant microwave power supply of 2.8kW at 2.45GHz. The temperature was measured as a function of the irradiation time from 220 degrees C. The progress of the reduction was examined by XRD analyses of reaction products at various temperatures in the range 400-1 200 degrees C. Under the present experimental conditions magnetite selectively absorbs microwave energy below approximately 650 degrees C; meanwhile carbon black absorbs it in the whole temperature range. The reduction of magnetite to wustite was observed to occur from at least a measured temperature of 400 degrees C but did not occur homogenously inside the mixture. At 800 degrees C, the reduction of wustite to iron started and occurred almost homogeneously inside the reacting mixture mass. A general conclusion of this work is that microwaves are absorbed and used in their path within the irradiated mass by the material of highest absorbing microwave power.