| Nowadays,electronic devices and radio communications play an increasingly important role in the fields of commerce,industry,medical treatment and military affairs.However,electromagnetic pollution caused by electromagnetic radiation and electromagnetic interference has seriously affected people's life as well as national security.Therefore,research on new type of electromagnetic wave absorbing materials(absorbing materials for short)has become a new hot spot in the field of materials research,which not only increases the absorbing materials,but also broadened the application field of absorbing materials.What's more,it has a high theoretical value.The electromagnetic wave absorbing material can effectively attenuate the energy generated by the electromagnetic wave radiation,thereby reducing or even avoiding the pollution problem caused by the electromagnetic wave radiation.The ideal high-efficiency absorbing material should have strong absorption performance,absorption frequency bandwidth,light weight and thin thickness.High resistivity,low cost,good thermal stability and chemical stability.Iron-cobalt alloy(FeCo)is a kind of soft magnetic material with cubic spinel structure.It has the advantages of simple preparation process,high magnetic loss and high Curie temperature,so it is widely used in the field of microwave absorption.Graphene has a unique two-dimensional structure of carbon material,which forms a hexagonal honeycomb crystal plane film through carbon atom sp2 hybrid orbital.It has large specific surface area,excellent electrical conductivity and thermal conductivity,excellent mechanical properties,strong chemical stability and low density.Therefore,by introducing functional materials such as dielectric materials and magnetic particles,a new type of ternary composite material is constructed,which has both magnetic loss and dielectric loss,so as to improve the impedance matching of the material and thus improve its wave absorbing performance.In this paper,the variety of ternary composites absorbents have been prepared and their microwave absorption has been investigated on the basis of the magnetic particles of FeCo alloy,reduced graphene oxide,conductive polymer(C4H5N,C6H7N)and dielectric materials(SiO2,C)as raw materials.The main research results of this paper are as follows:Firstly,The FeCo alloy,which was synthesized using liquid-phase reduction with some modification,Secondly,FeCo@SiO2and FeCo@C binary composites were prepared from FeCo alloy,glucose and ethyl orthosilicate(TEOS)and by sol-gel and high-temperature calcination methods.On this basis,the variety of ternary composites have been prepared by combining with graphene,conductive polymer and dielectric materials.The FeCo@SiO2 composites have been prepared by gel-sol method.On this basis,the preparation of FeCo@SiO2@C ternary composites were performed by combining hydrothermal reaction and high-temperature calcination with FeCo@SiO2and glucose as raw materials.With the introduction of carbon materials,the absorbing properties of ternary composites were greatly enhanced.The maximum RL of FeCo@SiO2@C ternary composites reaches-47.4 d B at 8.64 GHz with a thickness of 4.5 mm.The effective absorption bandwidth of reflection loss(below-10 d B)reaches 4.16 GHz when the thickness is 5.5 mm.The ternary composite material showed excellent performance of electromagnetic wave absorption.The ternary composites of FeCo@SiO2@RGO were prepared by hydrothermal reaction using FeCo@SiO2 and GO as raw materials.the FeCo@SiO2 composites are of core-shell structure with a diameter of about 150-200 nm.Compared with FeCo@SiO2 and FeCo@RGO composites,the as-prepared FeCo@SiO2@RGO composites exhibit excellent electromagnetic wave absorption properties.the maximum RLreaches-52.9 d B at 9.12 GHz with a thickness of 3.0 mm,and the absorption bandwidth with the reflection loss below-10 d B was up to 5.36 GHz with a thickness of 2.5 mm.It is believed that the FeCo@SiO2@RGO composites can serve as an excellent microwave absorbent and can be widely used in the microwave absorbing area.The FeCo@SiO2/HRGO composite was successfully prepared by combining liquid-phase reduction reaction in argon atmosphere with high-temperature calcination using FeCo@SiO2 and GO as raw materials.FeCo@SiO2 with irregular size particles was distributed on the surface of the HRGO sheets.The nanoparticles are evenly dispersed in the sheets of rpgo or embedded in the holes of HRGO.Multiple interfaces are generated between them and multilevel reflections are generated to enhance the wave absorption performance of the composites.The maximum reflection loss of FeCo@SiO2/HRGO composite reaches-46.28 d B at 16.16 GHz with the thickness of1.5 mm and the absorption bandwidth with the reflection loss below-10 d B was up to3.92 GHz with the thickness of 1.5 mm.The maximum RL of the absorbers shift toward the lower frequency as the absorber thickness increases.The FeCo@SiO2@PANI composite has been synthesized by a sample two-step method.The results shown that the composites have an excellent microwave absorption at a relatively thin absorber thickness.The maximum RL value reaches-48.6 d B at 9.84GHz and 1.6 mm.A ternary composite material FeCo@SiO2@PPy with high-performance electromagnetic absorption have been successfully synthesized and characterized.The maximum RL of FeCo@SiO2@PPy composites reaches-65.17 d B with the thickness of 2.1 mm at 16.48 GHz and the absorption frequency bandwidth RL-10 d B was up to6.8 GHz with the layer of 2.5 mm.The introduction of PPy have a vital effect on microwave absorption ability of composite.The FeCo@C/HRGO composite was synthesized using liquid-phase reduction,followed by hydrothermal processes and high-temperature calcination.The maximum RL for FeCo@C/HRGO reaches-76.6 d B at 16.64 GHz with a thickness of 1.7 mm.The absorption frequency bandwidth RL-10 d B was up to 4.4 GHz with the layer of1.7mm.This confirms that microwave absorption of FeCo@C can be substantially improved upon decoration with HRGO nanosheets. |
PDF Full Text Request