| In recent years,the development of electronic communication technology brought great convenience to our life,but it also produced a large number of electromagnetic wave,causing electromagnetic pollution,which brought harm to personal health and the normal operation of precise instruments.Electromagnetic wave absorption materials have the ability to convert electromagnetic energy into heat energy,so they have great potential to eliminate the increasingly serious problems of electromagnetic interference and electromagnetic radiation.In a variety of materials,carbon materials own good conductivity,light weight,low price,good chemical stability and thermal stability.And in recent years,studies found that one dimensional material has obvious anisotropy and the larger specific surface area,which are beneficial to absorb more electromagnetic wave,therefore one dimension carbon materials are potential electromagnetic wave absorption materials.Carbon materials were widely explored as one of the most competitive candidates based on high electrical conductivity,which means strong attenuation ability,but the impedance matching usually is poor,therefore this study combined carbon materials and other materials to adjust the impedance matching of composites.In addition,other attenuation processes produced in the composites,made up for the inadequacy of single material.Finally the composites meet practical requirements.The main research contents of this study are as follows:(1)Carbon nanotubes(CNTs)were activated in high temperature and alkaline environment to obtain abundant hydrophilic functional groups.Then CNTs-based composites(CeO2/CNTs)were synthesized by hydrothermal method,and CeO2 was uniformly dispersed on the surface of CNTs.During the experiment,the proportion of cerium oxides in the composites was adjusted by altering the amount of Ce(NO3)3·6H2O.By comparison,it was found that the composites had the three-dimensional network structure when the addition amount of Ce(NO3)3·6H2O is 0.4 mmol.When the addition amount of.Ce(NO3)3·6H2O increased,the CeO2 aggregated,and when the content reached a certain level,a mass of CeO2 would completely wrap the CNTs.By calculating the measured electromagnetic parameters,it was found that the composites had the best electromagnetic absorption performance when the addition amount of Ce(NO3)3·6H2O was 0.4 mmol.When the coating layer thickness(d)was 2.57 mm,the optimal reflection loss(RL)could reach-41.57 dB.When the matching thickness was 2.20 mm,the effective absorption bandwidth(RL<-10 dB)of the sample could reach 2.9 GHz(8.32-11.22 GHz),all of above analyses indicated that the CeO2/CNTs composites could meet the requirements of absorbing electromagnetic waves in some frequency ranges(2)In order to further enrich the loss types of the materials,reduce the thickness of the material and expand the effective absorption bandwidth,so in the synthesis process we added Co(NO3)2·6H2O to synthesize an ternary composites,the process could enhance the interface polarization and induce other electromagnetic loss mechanisms.We obtained ternary Co3O4/CeO2/CNTs composites by pretreatment an d hydrothermal method.XRD,XPS,SEM and TEM analysis indicated that the CNTs formed three-dimensional network structure,and the metal oxide particles were tightly bound to the tube walls.The metal oxides were made up of CeO2 and Co3O4.The calculation results of electromagnetic parameters confirmed that the maximum reflection loss of the composites could reach-59.82 dB(d=1.73 mm),and the effective absorption bandwidth could reach 5.20 GHz(12.76-17.96 GHz)when the thickness was 1.43 mm.The above results also indicated that the Co3O4/CeO2/CNTs composites with strong absorption and wide effective absorption band were qualified electromagnetic wave absorption materials.(3)Carbon nanotubes have poor dispersion and small binding area with metal particles.In order to give full play to the advantages of one-dimensional carbon based materials,we used electrospinning method to prepare carbon based composites.Electrospinning is a method for the preparation of one-dimensional fibrous composites,and has the advantages of simpleness,high efficiency,high safety and easy adjustment of fibers diameter and composition.In this experiment,CNFs/CeO2 composites were synthesized by combining electrospinning and carbonization.CNFs/CeO2 composites showed uniform network structure which was composed of evenly dispersed nano fiber,we adjusted content of metal oxides in the product by changing the amount of metal salt.The study found that when the content of CeO2 passes threshold,the surface of the nanofibers became rough which improved its specific surface area and induced multiple scattering,so when content of the CeO2 reached a certain proportion,it had the best electromagnetic absorption performance.The maximum reflection loss of CNFs/CeO2 composites reached-71.70 dB(d=2.54 mm),and the effective absorption bandwidth reached 6.44 GHz(d=2.40 mm).So Electrospinning is a feasible method which could produce carbon based composites,and the CNFs/CeO2 composites are the outstanding electromagnetic wave absorption materials. |
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