Preparation Of Electrospun Tantalum Carbide/Carbon-Based Composite Fibrous Membranes And Its Application In Electromagnetic Shielding

The rapid development of modern electronic device technology and gradual application of fifth-generation（5G）wireless communication systems has caused increasingly severe electromagnetic interference（EMI）and pollution,which poses a serious threat to environment and health of human beings.Thus,it is urgent to explore EMI shielding materials in the field of aerospace,information security,and wearable electronic devices.Although traditional metallic materials exhibit efficient EMI shielding capacity,the high density and poor chemical stability limit their applications for EMI shielding.Carbon-based materials with advantages such as low density and excellent chemical stability can become potential electromagnetic interference shielding materials.In order to further reduce material weight,while allowing more electromagnetic waves into the internal carbon materials,the preparation of the electrospinning technique of carbon fiber materials caused wide attention because of its lightweight advantages of the low density and high porosity and high electrical conductivity.Electrospinning,as a mature process,can be used to prepare one-dimensional polymer nanofibers.It has the advantages of simple process,adjustable components,controllable morphology and other advantages.Meanwhile,excellent electrical conductivity of carbon-based fibers will generate a large number of free electrons and cause surface plasmon resonance,resulting in impedance mismatch,and a large number of electromagnetic waves are reflected.However,the application of pure carbon fiber in the field of electromagnetic shielding still faces many problems,for example,the electrical conductivity is still insufficient,and the mechanical properties and flexibility need to be improved.Therefore,we introduce conductive nanofillers to enhance the electrical conductivity and mechanical properties of pure carbon fiber.Transition metal carbide nanofillers have become emerging conductive fillers by virtue of their outstanding electrical conductivity and effective enhancement of mechanical properties.A large number of carriers converge at the interface of medium with different electrical conductivity,causing interface polarization effect and converting electromagnetic waves into heat energy and other energy loss.The main loss mechanism is dielectric loss.However,shielding ability is often limited with a single loss mechanism,magnetic loss including magnetic response and hysteresis losses caused by magnetic coupling natural/exchange resonance can effectively improve the electromagnetic shielding ability.The introduction of magnetic metal carbides can effectively solve this problem,the enhanced conductivity at the same time,enrich the electromagnetic loss mechanism,effectively enhances the ability of electromagnetic shielding fiber membrane.To sum up,the key of this study is to first find polymer precursors that can be used to prepare carbon fibers with excellent electromagnetic shielding ability.Polyacrylonitrile（PAN）can be used as a common precursor of carbon fiber after carbonization due to its high carbon yield.Tantalum carbide（TaC）nanoparticles,can be added to the carbon fiber matrix because of its high conductivity,high hardness,high melting point and other advantages.In order to further improve the shielding ability,iron carbide-iron（Fe₃C-Fe）nanoparticles are introduced to enhance the magnetic loss ability.Specific work is mainly carried out from the following aspects:（1）Preparation and optimum carbonization temperature of TaC/C electrospun fiber fabrics.A certain amount of TaCl₅ was introduced into carbon fiber with PAN as precursor,and the target samples were obtained after pre-oxidation and carbonization at different temperatures（800℃～1400℃）.Through XRD and TEM test,the phase evolution process of TaCl₅/PAN nanofibers in 800℃～1400℃temperature range was studied and the crystallinity of different temperature range was calculated.After conductivity test and mechanical property test,1200℃was the best carbonization temperature.（2）Characterization of structure and electromagnetic shielding properties of TaC/C electrospinning fiber fabrics.On the basis of exploring the optimal carbonization temperature1200℃,we prepared a carbon fiber skeleton with excellent electrical conductivity,including TaC nanoparticles,by means of electrostatic spinning and high temperature pyrolysis.The electrospun composite fiber membrane possess outstanding properties such as an excellent tensile strength of 9.5 MPa and excellent flexibility.Furthermore,the TaC nanoparticles with appropriate concentration can interconnect with each other endowing the composite fabrics with high electrical conductivity of 10.4 S·cm^-1.It also has great EMI SE of up to 37.7 dB in X band with only 0.2 mm thickness,and the SSE/t values of 4290.1 dB·cm²·g^-1.Due to its porosity and high electrical conductivity of the fiber membrane,its shielding mainly comes from the reflection of most of the electromagnetic waves on the fiber surface and interface.Finite element simulation and physical demonstration further intuitively confirm its good shielding ability.（3）Preparation and electromagnetic shielding properties of electrospun TaC/Fe₃C-Fe/C composite fiber fabrics.Innovative carbon based materials incorporated with conductive and magnetic fillers have aroused wide concern.Herein,we fabricated TaC/Fe₃C-Fe carbon composite fiber membrane via electrospinning technology and high-temperature pyrolysis,which exhibited low density(0.34 g·cm^-3),excellent electrical conductivity(15.4 S·cm^-1),and good saturation magnetization(13.3 emu·g^-1).By investigating the optimum mass ratio of Ta and Fe,the maximum EMI shielding performance of 46.4 dB could be achieved with a thickness of 0.18mm.The loss mechanism is mainly based on reflection.Most of the electromagnetic wave is reflected on the surface of the fiber membrane,and the rest of the electromagnetic wave is exhausted under the synergistic effect of dielectric loss and magnetic loss.The physical demonstration can also prove its excellent ability to shield electromagnetic wave.