Preparation Of Fe-based/C Nanofibers By Electrospinning And Their Electromagnetic Wave Absorption Performance

One-dimensional nanocrystalline/carbon material with large aspect ratio can easily assemble into a three-dimensional network structure,which is conducive to improve the electron transmission ability and accelerate the heat energy dissipation.Electrospinning is a simple,low-cost and efficient method for preparing nanocrystalline/carbon nanofibers.Compared with ferrites,FeCo and Fe₃C have larger saturation magnetization,which is expected to provide higher magnetic permeability.Based on these considerations,we prepared FeCo/C and Fe₃C/C nanofibers by electrospinning,and investigated their electromagnetic wave absorption properties.The main results are as follows:1. FeCo alloy is an excellent magnetic loss material,which shows high saturation magnetization,low coercivity,high Curie temperature and low magnetocrystalline anisotropy.The FeCo/C nanofibers were fabricated by electrospinning technique,which show a density of 1.1 g/cm³.The dielectric carbon nanofibers were uniformly decorated by tiny magnetic FeCo nanocrystals.The FeCo/nanofibers show good impedance matching conditions and high attenuation ability when the mass fraction is 40 wt%,which perform excellent electromagnetic wave absorption performance.The optimal FeCo/C nanofibers have a minimum RL value of-59.9 d B with broad absorption bandwidth of 6.0 GHz at13.2 GHz,when the thickness is only 2.6 mm.Investigations show that the boosting microwave absorption performance of FeCo/C nanofibers is mainly originated synergistic effects caused by nature resonance,exchange resonance,dipole polarization,interface polarization and micro-current.2. The crystallinity and chemical compositions of microwave absorption materials play an important role on the complex permittivity and permeability.We prepared a series of Fe_xCo_1-x/C nanofibers with different element ratios and crystallinity by changing the raw material ratios and annealing temperatures,and investigated their electromagnetic wave absorption performance.The precursor fibers were treated at 600℃,700℃,800℃,and900℃,respectively.The rusults show that the grain size of FeCo increases as the temperature increases,and the carbon component converts into crystalline phase when the temperature rises above 800℃.FeCo/C nanofibers prepared at high temperature reveal excellent electromagnetic wave absorption performance,even when the mass fraction is small.The optimal FeCo/C nanofibers have a minimum RL value of-58.8 d B with broad absorption bandwidth of 4.2 GHz at 1.6 mm,when the the mass fraction of FeCo/C nanofibers is only 20 wt%.Four kinds of nanofibers including Fe_0.3Co_0.7/C,Fe_1/3Co_2/3/C,Fe_0.5Co_0.5/C and Fe_0.7Co_0.3/C,were prepared by changing the raw material ratio of Fe/Co.The ratio of Fe/Co can adjust the electromagnetic parameters,which can achieve effective electromagnetic wave absorption performance at a lower thickness.Among them,the Fe_0.5Co_0.5/C nanofibers have a minimum RL value of-18.9 d B,when the the thickness is1.5 mm.3. The anti-oxidation ability of electromagnetic wave absorption material directly affects their practical application.During the research,we found that the FeCo alloy can be oxidized at 200℃.Herein,we prepared Fe₃C/C nanofibers by electrospinning with iron acetylacetonate as the iron source.The crystal phase did not change at 200℃,revealing a good thermal stability.Electromagnetic wave absorption performance investigations show that the Fe₃C/C nanofibers have a minimum RL value of-54.5 d B with broad absorption bandwidth of 2.7 GHz at 17.8 GHz,when the thickness is only 1.5 mm.Meanwhile,the Fe₃C/C nanofibers have a RL value of-57.9 d B at 5.8 GHz with broad absorption bandwidth ranging from 4.8 to 7.0 GHz,which located in the C band.The Fe₃C/C nanofibers show high thermal stability,good oxidation resistance and remarkable electromagnetic wave absorption performance in the C band,which have broad application prospects in the fields of satellite TV broadcasting,weather radar and civil aviation communication.