| As a conventional magnetic material, magnetite (Fe3O4) is also used frequently as a promoter for the enhancement of microwave absorption due to its cheap, non-toxic, easy preparation and excellent magnetic properties and other characteristics. However, as a wave-absorbing material, it is difficult for the traditional Fe3O4to satisfy the comprehensive requirements of lightweight, thin-layered, broadband and strong-absorbing at the same time. Therefore, manufacturing of some unique aggregates of Fe3O4powders with special morphology or composite with other materials can result in a better impedance matching. Polyaniline (PANI) is a conductive polymer, which has received extensive attention and been considered as promising candidates in the field of microwave absorption because of its high electrical conductivity, low density, easy preparation. Composite of polyaniline with magnetic materials can result in multi-functional composite materials, and through the modification of the electromagnetic properties of the composite, the aim for improvement of material absorbing properties can be realized.In this paper, solvothermal method is adopted to manufacture Fe3O4single-pieces with the diameter of1-6μm, the thickness of100-200nm. The crystalline structure, micromorphology, and electromagnetic properties of Fe3O4-pieces have been studied. Due to the shape anisotropy of the Fe3O4-pieces, the coercivity is larger than that of the Fe3O4nano-particles, and the imaginary part of permeability in Fe3O4-pieces has a wide resonance absorption peak. At room temperature, when the applied magnetic field is3KOe, the current is100μA, the maximum magnetoresistance of Fe3O4-pieces reach1.58%, higher than that obtained at77K under the same external field and current.The Fe3O4piece and polyaniline composites (Fe3O4-piece/PANI) are obtained by in situ polymerization with a core-shell structure. It is found that when the mass ratio of Fe3O4piece/PANI composite with paraffin is7:3, the mixture has good absorption properties. For200wt%Fe3O4-piece/PANI/paraffin composite, when RL<-10dB, the bandwidth is up to15.41GHz, which indicates that the composite is a very good broad-band absorbing marerial. Moreover, when the thickness is d=2.0mm, the reflection loss is less than-10dB during the frequency range from8.8GHz to12.3GHz. In order to further improve the electric, magnetic properties of the composite material, we chose the carbonyl iron powder (CIP) with high saturation magnetization as the magnetic phase, and synthesized a carbonyl iron and polyaniline composite (CIP/PANI) via an one-step in situ polymerization method. And it is found that the doped acid mole ratio has great influence on the properties of the composites. At proper mole ratio of doped acid to aniline, a non-magnetic phase appears due to interaction between the micro-sphere CIP and the PANI polymer, which weakens the magnetic loss and dielectric loss of the composite simultaneously, but improves the impedance matching of the composite and strongly enhances the microwave absorbing properties. Moreover, for CIP/PANI composite with the mole ratio of doped acid of0.005/1, when the RL<-20dB, indicating99.9%of microwave can be absorbed, the matching thickness range is2.5-4.5mm,, and the corresponding frequency range is from1.0to3.6GHz. And when the mole ratio of doped acid is0.2/1, when the thickness of the absorber is less than2.0mm, the value of RL<-20dB is obtained in the frequency range of8.8-16GHz, demonstrating a good broadband absorption. |
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