Dielectric properties and carbothermic reduction of zinc oxide and zinc ferrite by microwave heating

摘要

This paper aims to study the dielectric properties and carbothermic reduction of zinc oxide (zincite, ZnO) and zinc ferrite (franklinite, ZnFe₂O₄) by microwave heating. To achieve this aim, the dielectric properties were measured with an open-ended coaxial method to understand the behaviour of the samples under microwave irradiation. The effects of microwave power, duration time and sample mass on the heating rate, and the effects of the stoichiometric amount of graphite on the reduction of ZnO and decomposition of ZnFe₂O₄ were investigated. The results show that ZnFe₂O₄ has significantly higher dielectric properties compared to ZnO. Generally, for both samples, the dielectric values at room temperature were quite low, indicating that both ZnO and ZnFe₂O₄ are poor microwave absorbers. It was found that the temperatures have a more significant effect on the imaginary permittivities than on the real permittivities. The heating rate showed that the sample temperature increased with increase in microwave power and sample mass. Using 700?W of microwave power and two times the stoichiometric amount of graphite, almost complete reduction of ZnO was achieved in 12?min, while ZnFe₂O₄ completely decomposed to zincite and wustite in 3?min.