Electro Spun One-dimensional Carbon-based Nanocomposites For Electromagnetic Wave Absorption Performance

With the rapid development of communication technology,electronic devices have become popular in all aspects of human society,while causing electromagnetic pollution,which not only affects the normal use of electronic devices,but also threaten the health of human beings.Wave-absorbing materials can absorb and lose electromagnetic waves energy,which has attracted more and more people’s attention to relieve the electromagnetic pollution.At present,due to its high aspect ratio,specific surface area and anisotropy,large diameter fiber structure is conducive to multiple scattering and conductive loss of electromagnetic waves.Specifically,because of their light weight,stable physicochemical performance and outstanding electrical conductivity,carbon fibers have been widely applied in electromagnetic wave absorption filed.However,the lossy mechanism of pure carbon is simple and the impedance matching of that is poor.Thus,it is usually integrated with semiconductor materials and magnetic particles to prepare nanocomposite fibers with excellent electromagnetic wave absorption performance.Because of its advantages of low spinning cost,controllable process,wide variety of spinnable types,and mature technology,electrostatic spinning has recently become one of the main process methods for preparing nanofibers.In this thesis,ZnO@C core-shell fibers,ZnO/Fe3O4@C hollow core-shell fibers,and CeO2/Co/C nanocomposite fibers are prepared based on electrospinning,combined with calcination,pyrrole coating and carbonization processes.The electromagnetic wave absorption mechanisms are investigated.The main results are as follows.(1)ZnO@C nanocomposite fibers with core-shell structure are prepared by electrospinning method,air calcination,and pyrrole coating process.The effects of different carbon contents in the composite fibers on the electromagnetic wave absorption performance are studied.The introduction of carbon significantly improvs the loss capability and verifies the synergistic effect of semiconductor and carbon materials in improving the electromagnetic wave absorption capability.The absorption performance is calculated after measuring the electromagnetic parameters using a vector network analyzer,and ZC-0.25 reaches a minimum RL(Reflection loss)value of-71.1 dB at a thickness of 2.7 mm and a frequency of 11.8 GHz.The maximum effective absorption bandwidth reaches 4.9 GHz at a matching thickness of 2.2 mm.The results indicates that the increase of carbon content is not only beneficial to increase the loss capacity,but also to reduce the matching thickness.However,it needs to be controlled within a certain range to obtain optimal impedance matching characteristics.(2)Hollow core-shell ZnO/Fe3O4@C nanocomposite fibers are prepared by electrospinning,calcination,and pyrrole carbonization processes.By varying the carbon content,the effect of that on their electromagnetic wave absorption performance is investigated.ZFC-0.25 exhibits excellent wave absorption performance with a minimum RL value of-74.2 dB at a matching thickness of 2.2 mm and an effective absorption bandwidth(EAB)value of 5.5 GHz(12.2-17.7 GHz).Based on the previous chapter,the hollow structure formed by the introduction of magnetic particles,which reduces the density of the absorbing material and satisfies the lightweight design requirements.Also,the introduction of air further facilitates optimization of impedance matching.The core-shell structure brings a large number of heterogeneous interfaces,which also greatly contributes to the interface polarization effect.And the heterogeneous interface polarization effect is verified by HFSS simulations of the material under the excitation of electromagnetic waves.(3)CeO2/Co/C nanocomposite fibers are prepared by electrospinning,preoxidation,and carbonization processes.To investigate the effect of the introduction of rare earth oxides on electromagnetic wave absorption,CeO2 is introduced on the basis of carbon nanofibers(CNFs).As a result,the electromagnetic wave absorption performance is significantly enhanced.Compared with the common metal oxide semiconductors ZnO and MnO,the EAB of CeO2/C nanofibers could reach 7.6 GHz with broadband absorption capability.However,the thickness at the maximum loss and the matching thickness are thicker.The metallic Co is further introduced into CeO2/C nanocomposite fibers,which further optimizes the impedance matching,increases the magnetic loss and reduces the matching thickness.The minimum RL value at 16.8 GHz,2.2 mm can reach-61.4 dB,and the maximum EAB can reach 7.2 GHz,showing excellent electromagnetic wave absorption performance.