| A variety of electronic communication devices are emerging with the rapid development of science and technology.It was a double-edged sword,which not only brings convenience but also brings harm to human beings.Because of it plays an important role in anti-electromagnetic radiation,electromagnetic compatibility and military radar stealth,etc.Thus it has been become one of the important research objects of advanced functional materials.With the rapid development of microwave technology,people have put forward performance requirements for "thin,light,wide,strong" and other aspects of absorbing materials.In particular,magnetic metal materials show excellent performance in many fields such as electromagnetic wave absorption.In this work,the magnetic material has been investigated by using first principle methods.Predict and design relevant experimental programs according to the calculation results,and then study the preparation and absorbing performance of the magnetic composite material,the detail contents are as follows:(1)The electronic structure,magnetic and dielectric properties of three kinds of magnetic materials(?-Fe,FeSiAl and Fe3Si)have been investigated by using first principle methods based on plane-wave pseudo-potential theory.From the electronic structure level analyzes the change mechanism of magnetic and dielectric properties.The calculated result indicates that three materials exhibit metallic magnetic spin systems and most of the magnetism comes from Fe 3d electrons.Fe3Si had the highest total magnetic moment(19.92 ?B)among the three materials;The calculation of forming heat(?H)and binding energy(?E)show that the structural stability of Fe3Si is between the other two,and its corresponding values were-2.4519 eV and 8.8386 eV,respectively.In addition,compared with ?-Fe and FeSiAl alloy,Fe3Si alloy has the maximum dielectric constant,so the Fe3Si alloy as the kernel of the structure model of the cladding material.(2)The ideal Fe3Si@SiO2 calculation model were obtained through the crystal structure design of the selected Fe3Si alloy core material and SiO2 cladding material.The electronic structure,magnetic and dielectric properties of the Fe3Si@SiO2 structure model were calculated by the same calculation method.The calculation results show that the average bond length of Fe-Fe decreased from 2.825 to 2.209,Fe-Si decreased from 2.447 to 2.400,(Si-O)1 increases from 1.601 to 1.771,(Si-O)2 increases from 1.608 to 1.726.This is mainly due to the strong interaction take place between the SiO2 shell layer and the Fe3Si core atoms during the optimization process.Compared with uncoated Fe3Si,SiO2 coated Fe3Si is still a metallic magnetic spin system;The Fermi energy level shifted to the right and intersected with the state density curve at the lowest point between the two peaks,indicating that the cladding model is structurally stable;The state density of Fe(A,C)atom decreases(1.5?1.3),the state density of Fe(B)atom and Si atom increases(0.5?1,0.4?0.5),but the overall state density increases after SiO2 coating Fe3Si.According to Boltzmann equation,the resistivity increases and further decreased the dielectric constant of the system.Compared with the uncoated Fe3Si,the initial dielectric constant real part and imaginary part of SiO2 coated Fe3Si reduces by about 40 and 20,respectively.the imaginary part of the dielectric constant is smaller than that before coated in the whole energy range,indicating that SiO2 coating Fe3Si is conducive to reducing the dielectric constant of the composite.(3)Fe3Si magnetic particles were successfully prepared by mechanical alloying and vacuum annealing in the experiment,and then they were compounded with SiO2 particles by the sol-gel method.At the same time,by changing the content of TEOS,ammonia and ethanol,respectively,the influence of the change of parameter contents on the microstructure,morphology,electromagnetic properties and wave absorption properties of the Fe3Si@SiO2 composite particles were studied.Experimental results show that when the TEOS content is 6 ml(a-3),Fe3Si@SiO2 composites could reach a minimum RL value of-52.19 dB with thickness of 3 mm at 8.55 GHz and-47.22 dB with thickness of 2 mm at 4.95 GHz(with the EAB value as broad as 6.48 GHz).In addition,when the TEOS content of 8 ml(a-4),Fe3Si@Sio2 composites could also reach a minimum RL value of-51.34 dB with thickness of 4 mm at 4.95 GHz;When the ammonia content of 8 ml(b-3),Fe3Si@Sio2 composites could reach a minimum RL value of-34.33 dB with thickness of 4 mm at 5.13 GHz,it shows that the composite particle has the smallest reflection loss value and the best wave absorption performance when the absorber is 4mm;When the ethanol content is 160 ml(c-3)and the thickness of the absorber d=3 mm,the minimum reflection loss reaches-36.45 dB at 7.65 GHz.To sum up,when TEOS,ammonia and ethanol contents are 6mL,8ml and 160ml,respectively,the composite material has the best microwave absorption performance. |
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