| In order to solve the long-standing electromagnetic radiation problems in civil and military security fields,an efficient electromagnetic absorbent with thin coating,light weight,wide frequency band and strong absorption is urgently needed.According to the loss mechanism of electromagnetic wave,absorbing materials can be divided into magnetic loss type and dielectric loss type.The combination of magnetic loss and dielectric loss materials can not only inherit their respective advantages,but also overcome individual shortcomings and obtain unexpected functional characteristics.Based on this,the composite system of magnetic metal and carbon material was constructed in this paper,and the effects of chemical composition,geometric morphology and interface structure on the electromagnetic parameters and absorbing performance of the absorbing material were studied.The main contents are as follows:(1)Based on the sponge template strategy,using melamine sponge as the supporting template and ac etylacetones as the magnetic particle precursors,the FeCo alloy particles were successfully grown onto the three-dimensional porous carbon sponge framework(CS),and the FeCo/CS composites were obtained.The effects of the chemical composition of the magnetic particles and the carbonization degree of the sponge skeleton on the electromagnetic absorption properties of the materials were studied.The effective absorption bandwidth of FeCo/CS-800 sample can reach 6 GHz(12-18 GHz)when the absorption layer thickness is 1.5 mm,covering the entire Ku band.When the thickness of absorbing layer is 2.5 mm,the maximum reflection loss can reach-53.7 dB.In order to investigate whether this synthesis strategy is universal,we synthesized other samples loaded with only ferric acetylacetone(Fe/C S-X)or cobalt acetylacetone(Co/CS-X).The effective absorption bandwidth of Fe/CS-700 composite is 4.7 GHz when the thickness of the absorption layer is 2 mm.(2)The imaginary part of magnetic permeability plays an important role in the magnetic loss of the absorbing material,but how to improve the imaginary part of the magnetic permeability of the material in the microwave frequency band is a difficult point of current research.We intend to use Fe@C composite material as a model system to discuss the influencing factors of the imaginary part of permeability.A homogeneous Yolk-Shell FeOx/Fe@C composite was prepared by in-situ transformation of Fe2O3@PDA(polydopamine)precursor.The effects of carbon layer thickness,carbon shell layer number and particle size on the imaginary part of permeability were studied.The results show that the increasing regularity of μ" is closely related to particle size.When the particle size is small(～1 um),μ"mainly presents "right half resonance peak"in 2-18 GHz band,and the overall trend is downward.When the particle size is moderate(～3.1 um),μ" shows "left half resonance peak",and the whole shows an upward trend.When the particle size is large(～5.9 um),μ" presents a "complete resonance peak",with both rising and falling parts.Therefore,by reasonably adjusting the particle size of the Yolk-Shell structure Fe@C composite materials,the effective control of μ" can be achieved,which is of great significance for improving the magnetic loss ability of the sample. |
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