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The electromagnetic properties of materials are the basis of study for the microwave absorbing properties. The relative complex dielectric constant εr and relative complex magnetic conductance μr, which reflect the ability of absorbing and consuming the electromagnetic energy, are defined as the main physical parameters to indicate the electromagnetic properties of materials. The microwave loss mechanism mainly involves dielectric loss, magnetic loss, insulation shell, column capacitance, etc.The high carbon ferromanganese powders can be decarburized with solid phase in the microwave field. CO2formed calcium carbonate powders by thermal decomposition had a good effect of decarburization. But the phase of powders was changed during the decarburization process, and their electromagnetic properties also had corresponding change. These changes affected the interaction between microwave field and materials. Therefore, it was very important to investigate electromagnetic properties of high carbon ferromanganese powders and the interaction between microwave field and materials.The powders of calcium carbonate and high carbon ferromanganese were Uniformly mixed with the mole ratio (CO2calcium carbonate:C high-carbon ferromanganese=1.80:1.00), and were heated respectively at900℃,1000℃,1100℃,1200 ℃for60minutes in microwave field and a muffle furnace. Vector network analyzer was used to analyze the electromagnetic properties. The results show that the changes of the electromagnetic properties of high carbon ferromanganese powders are apparent before and after the decarburization. Specific research results are as follows:(1)High carbon ferromanganese powders have a certain dispersion effect in the microwave field. The carbon in the high carbon ferromanganese powders is one type of conductivity loss material, and the carbon atom absorbs microwave by conductivity loss. The mainly phase of high carbon ferromanganese powders is ferromanganese carbide, and its relative dielectric constant εr’ was between323.75and9.5in microwave frequency2～18GHz. And εr’ tends to be smaller with the increasing of microwave frequency. The relative dielectric constant εr’ of high carbon ferromanganese powders is252.12in the microwave heating frequency2.45GHz, and it proves that the high carbon ferromanganese powders are conductivity loss materials.(2)With microwave heating temperature900℃,1000℃,1100℃,1200℃and60min heat insulating respectively, the electromagnetic properties of decarburization materials are similar in microwave frequency2-18GHz, in addition to1100℃. And εr’ value is between7.60and8.58, relative permeability μr’ value is in the range of0.91to1.04. Dielectric properties of decarburization materials change greatly with microwave heating at1100℃. And εr’ value is between8.18and10.00, relative permeability μr’ value is in the range of0.88to1.04in microwave frequency2-18GHz. Because the mainly phase of original high carbon ferromanganese powders is (Mn, Fe)7C3, belonging to the rich carbon ferromanganese carbide, that is Mn atoms closely pack to the octahedron, and carbon atoms are interstitial atoms in the octahedron. CO2(decomposed from calcium carbonate) and (Mn,Fe)7C3reaction, and the octagonal structure is out of shape a large extent. carbon atoms separate out and combine with CO2, produce a large amount of cation vacancy, lead to the moment of dipole reset, conductivity loss increases, εr’ increases. With microwave heating temperature1200℃and60min heat insulating, εr’ of decarburization materials reduce, because oxidation of decarburization materials increases (Mn3O4increase), conductivity loss reduces. But with microwave heating temperature900℃,1000℃and60min heat insulating respectively, εr’ of decarburization materials reduce, because (Mn,Fe)5C2increases, conductivity loss reduces.(3)With conventional heating temperature900℃,1000℃,1100℃1200℃and60min heat insulating respectively, the electromagnetic properties of decarburization materials are decrease first then rise in microwave frequency2～18GHz. And εr’ value is between6.51and8.61,μr’ value is in the range of0.91to1.04. With conventional heating temperature1200℃and60min heat insulating, εr’ value is higher from7.80to8.61. Because MnO2increases from decarburization materials with conventional heating, polarization loss enhanced. And εr’ value reduced with conventional heating temperature900℃,1000℃,1100℃and60min heat insulating respectively, because forming more MnO, Mn3O4shell on the surface, conductivity loss reduced.(4) With microwave heating temperature900℃,1000℃,1100℃,1200℃and60min heat insulating respectively, εr’ value are7.58,7.44,8.39,7.51at microwave frequency2.45GHz. Variation trend of εr’ is undulatory property in general, and the same with εr’ at microwave frequency2～18GHz. With microwave heating temperature1100℃and60min heat insulating, the εr’ of decarburization materials’has maximum8.39, because (Mn,Fe)23C6increases, and conductivity loss increases, εr’ increases. With conventional heating temperature900℃,1000℃,1100℃,1200℃and60min heat insulating respectively, εr’ value are7.76,6.72,7.39,8.48at microwave frequency2.45 GHz. Variation trend of εr’ decreases first then rise, and the same with εr’ at microwave frequency2～18GHz. With conventional heating temperature1200℃and60min heat insulating, the εr’ of decarburization materials ’has maximum8.48, because MnO2increases, and polarization loss increases, εr’ increases.
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