Comparison Between Microwave Heating and Conventional Heating of Magnetite During Hydrogen Reduction

The microstructure mechanism and kinetics of magnetite powder reduction in the H2 atmosphere were studied by both microwave heating and conventional heating methods. Cross-sectional morphologies of the reduction products obtained through these two heating methods were compared. In both cases, the reduction occurred layer by layer and with the formation of irregular pores in the iron layer. The difference between the two methods was the occurrence of cracks in the particles during conventional heating. The macroscopic kinetics of magnetite reduction was analyzed by measuring the water content with a hygrometer. In a reducing atmosphere comprising 60 pct H2-Ar at 1173-1373 K, the reduction of magnetite took place in two stages: from Fe3O4 to FeO and from FeO to Fe. Microwave radiation increased the atomic diffusion coefficient, thereby enhancing diffusion and reaction rate. The reduction rate at 1173 K under microwave was nearly equal to that of 1373 K under conventional conditions, despite a temperature difference of 200 K. Compared to conventional heating, microwave heating reduced the reaction activation energy.