Preparation And Electromagnetic Wave Absorption Performance Of One-dimensional Nanocomposites Based On Electrospinning

The progress of electronic communication technology and the utilization of various electronic products have greatly enriched and facilitated people's lives,in the meantime,have caused an increasingly serious problem of electromagnetic(EM)wave pollution.EM radiation influences the operation of precise equipments,which is also hazardous to human health.Therefore,the research of EM wave absorption materials has an extensive and important role for military and civil EM protection The researches indicate that one-dimensional nanofibers with high aspect ratio and large specific surface area can be used to fabricate absorbing materials.A multi-layered geometric effect can be achieved by modifying the fiber's surface,and the construction of complex microstructure can affect the EM wave absorption performance.What's more,nanofibers can combine magnetic metals with semiconductor materials and carbon materials,to avoid the problems of poor impedance matching and single loss mechanism.The impedance matching level can be optimized by adjusting the proportion of each component,and the synergistic effect of different loss mechanisms is beneficial to develop materials with excellent EM wave absorption performance.Besides,electrospinning technology has the advantages of low cost,simple operation and strong controllability,which lays a technical foundation for the design of nanocomposites with one-dimensional structure.In this paper,based on the electrospinning method,through the design of microstructure and the composition of different components,three nanocomposites with excellent absorbing properties were prepared,and the intrinsic properties of the materials were characterized,the EM wave absorption performance and the corresponding absorbing mechanism were studied.The main research results are summarized as follows:(1)The flakes-assembled ZnO/Ni hybrid microtubes was prepared by combining electrospinning and hydrothermal reaction,coupled with following calcination and reduction process.We studied the effects of the construction of microstructure and the introduction of magnetic particles Ni on the EM wave absorption performance.The testing results showed that the composite was a self-assembled hollow microtube structure with a diameter of 1.5 ?m and a wall thickness of about 400 nm.The magnetic properties and the conductivity of the composite were improved.A vector network analyzer(VNA)was used to characterize the electromagnetic performance.The results show that the ZnO/Ni hybrid microtubes exhibit excellent absorption performance.The minimum reflection loss(RL)is-71.2 dB at the matching thickness of 3.4 mm and the frequency of 15.3 GHz,the maximum effective absorption bandwidth(EAB ?-10 dB)is 9.4 GHz(8.6-1 8.0 GHz),when the matching thickness is 4.2 mm.The improved EM wave absorption performance is due to the optimized impedance matching level of the hollow microtubes assembled by the nanosheets,and the synergistic effects of magnetic and dielectric losses achieved by the introduction of Ni nanoparticles.(2)ZnO/Ni/C nanofibers were successfully synthesized by electrospinning and carbonization reduction at high temperature.The magnetic metals were composited with semiconductor and carbon fibers.The effects of magnetic metals on morphology,magnetic performance and EM wave absorption properties in ternary-composite system were studied.The results show that the fiber's diameter is about 250 nm,in which ZnO and Ni nanoparticles are embedded.With the introduction of Ni,the coercivity of the nanocomposite is enhanced and the magnetic properties are improved.The conductivity is promoted with the increase of Ni content,which causes the enhanced conductivity loss.Besides,the adjusted dielectric constant reduces the impedance matching thickness.The minimum RL value reaches-66.5 dB at 10.2 GHz with the thickness of 3.9 mm,and the maximum EAB is 5.9 GHz(12.1 GHz-18.0 GHz)at the matching thickness of 2.8 mm.(3)In addition to the composite of magnetic materials and dielectric materials,the preparation of bi-component dielectric absorbing materials by combining high dielectric metal oxides with carbon fibers is also one of the feasible strategies.Among the rare earth metal oxides,gadolinium oxide(Gd2O3)has great physical and chemical stability,but it is seldom application in the field of EM wave absorption.The Gd2O3/C nanofibers were prepared by electrospinning and then high-temperature carbonization.We have investigated the influence on the microstructure and EM wave absorption properties by the introduction of Gd2O3.The fibers with slippy surface have about 300 nm in diameter.The Gd2O3/C nanofibers exhibit the characteristics of light weight,wide bandwidth and strong absorption intensity.When the thickness is 3.1 mm,the minimum absorption reaches-67.5 dB at 11.6 GHz,and the EAB reaches 7.2 GHz(10.8-18 GHz)at the thickness of 2.8 mm.Gd2O3 can maintain the fibers'morphology greatly,and improve the dielectric constant effectively,which enhances the conductivity loss capability.The matching thickness is reduced on account of the optimization of impedance matching level of carbon-based materials.