The Application Of Carbon Nano Composite In Electromagnetic Shielding

Aborption and reflection are two electromagnetic shielding mechanism for most electromagnetic shielding materials.The electromagnetic absorbing materials mainly include resistance type,dielectric and magnetic media three categories in accordance with their loss type.The materials studied in this paper are carbon nanomaterials and their composites with ferrite materials.The carbon materials belong to the resistive absorbers of electromagnetic wave.The ferrite materials belong to the magnetic medium absorbent.The composite of above two new electromagnetic wave absorber with wider frequency bandwidth,lower density,and higher absorption performance.Carbon nanomaterials,including carbon nanotubes and graphene,have the excellent properties of bandwidth,light weight of traditional carbon materials,and also combine the large surface area of nano-materials,good conductivity and other advantages.However,their absorption capability is weak,which limit their applications.Compared with carbon nanotubes and graphene materials,the absorption ability of Fe₃O₄ is stronger,but the frequency band is narrower.Their composites can have all the electromagnetic shield features of two kinds of materials,and it is of great significance to develop these kind of materials.In this paper,we prepared carbon nanotubes,graphene,Fe₃O₄ and their composites,and optimized parameters.The morphology,structure and composition of the composites were analyzed by TEM,SEM,XRD,Raman and TGA.The electromagnetic properties and absorbing properties of the materials were tested by VSM and VAN.The main contents are as follows:1)Graphene Oxide?GO?with high specific surface area was prepared by the"Hummer" method using expanded graphite as raw material,and other reactants including concentrated sulfuric acid,potassium permanganate and sodium nitrate oxidant.We improved the washing process and shortened the whole experiment process by using freeze drying system to prepare GO powder.Carbon nanotubes?CNT?were prepared by the floating catalyst chemical vapor deposition?FCCVD?process.The effects of different carbon sources,catalysts,gas flow and the feeding rate on the quality of CNT were investigated.The optimized growth parameters for large scale CNT production were determined.High quality CNT can be produced by using xylene as the carbon source.However,xylene has a certain toxicity,and carbon nanotubes are easy to stick together forming fibrous products,and hard to form film.High-quality CNT can also be prepared using alcohol as the carbon source,and film product can be easily deposited.The weight ratio of ferrocene and thiophene in the catalyst was determined to be 3.5/1?2.5/1.The Ar flow rate was 5L/min,H2 2L/min,and their feeding rate was 0.08ml/min.2)Uniform solid Fe₃O₄ nanospheres were prepared by the hydrothermal method using polyethylene glycol?PEG?as the dispersant and ethylene glycol as the reducing agent in the alkaline environment provided by sodium acetate.The Fe₃O₄ nanospheres/GO composites were prepared by adding GO into the reaction solution.The Fe₃O₄ nanospheres are uniformly supported on the surface of GO films.GO has no effect on the growth and size of Fe₃O₄ nanospheres,and only provide the nucleation sites.The magnetic property test showed that the magnetic saturation intensity of Fe₃O₄ nanosphere/GO complex was 28.7emu/g,and the hysteresis loop was narrower,which indicates that it is a soft magnetic material.The absorption characteristics of Fe₃O₄ nanospheres/GO complex at 2?18GHz were characterized.The results showed that the composite with the content of paraffin 20%had the highest reflection loss of-13dB at 13.5GHz,and-19 dB loss at 8.5 GHz with 30%paraffin content.The Fe₃O₄/GO is dispersed in the epoxy resin,and the four-element materials of Fe₃O₄/GO @ CNT @ carbon fiber cloth were prepared.The electromagnetic properties of the composites were measured in the frequency range of 10MHz?2GHz,showing the peak electromagnetic loss of-45dB at 280MHz.The carbon fiber fabric has the loss of-37dB and-32dB,indicating Fe₃O₄/GO complex can improve the electromagnetic absorption.However,compared with the pure carbon material,the frequency of loss peak is shifted.3)Uniform Fe₃O₄ nanowires of diameter of 100nm were prepared by hydrothermal method using PEG400 as the template and sodium thiosulfate as the oxidant in the alkaline environment provided by sodium hydroxide.Without PEG 400 added and just using aqueous solution as the reactant,octahedral Fe₃O₄ nanoparticles with a grain size of 200 nm were only obtained.Fe₃O₄ nanowires can be also obtained by the addition of a certain amount of GO instead of PEG400 in the aqueous solvent.It was proved that GO is the growth template for nanowires like the effect of PEG400,and Fe₃O₄ nanowire GO composite was obtained.The effect of GO on the synthesis of Fe₃O₄ nanowires is as follows:The lamellar structure of GO is uniformly dispersed in aqueous solution,which decreases the binding speed of ions.Functional groups such as-OH on GO surface may have effects on the growth of different crystalline faces of Fe₃O₄ nanowires.The magnetic saturation intensity of Fe₃O₄ nanowires/GO composite is 37emu/g,and the hysteresis loop is wider than that of Fe₃O₄ nanospheres/GO composites,and it also belongs to soft magnetic material.The electromagnetic absorption properties of Fe₃O₄ nanospheres/GO complexes at 2-18GHz were characterized.The results showed that the reflection loss of the composites is-9dB and-7dB when the paraffin content of the composites is 20%and 30%,respectively.The reflection loss of composite with the paraffin content of 40%is up to-17dB at 6.8GHz.