| Development of high-performance microwave absorption materials has been attracting great interests due to its wide applications in solving the main interference for electronics utilized currently,it is usually required to possess multiple merits such as lightweight,strong absorption,broad frequency band and high thermal stability,all of which are directly related to the components and microstructures of absorbers.An ideal electromagnetic wave absorbing material should be lightweight and exhibit high absorption efficiency in a broad frequency band at a low filler loading ratio.Among many electromagnetic wave absorbing materials,nanomaterials have a great potential for resolving these requirements,attracted by their unique characteristics of low density,distinct size effect,and nanostructure.The microwave absorption capacity is also related to the electromagnetic matching between the microwave and materials,and intrinsic electromagnetic properties,like complex permeability(?r=?'+i?")and permittivity(?r=?'+i?")which could be enhanced by integrating magnetic and/or dielectric compositions and specific structural units.In this paper,we Preparation of dielectric loss composite nanomaterials and porous graphite and its modification,and their microwave absorption has been investigated.The main research results of this paper are as follows:We synthesized the Mo and Mo@MoS2 nanocomposite by in-situ arcdischarging,a compressed anode of molybdenum and molybdenum disulfide powders in Ar and H2 atmosphere.The Mo@MoS2 nanocomposite are irregular spherical and have a main distribution in the range of 10 nm in diameter and outer layer has 1-3 layer of molybdenum disulfide.The dielectric loss of molybdenum disulfide coated with few layers can be increased obviously.The maximum absorption of the Mo@MoS2 nanocomposites achieves at-51.2 dB with the frequency of 13.9 GHz.In addition,the bandwidth of<-10 dB are centered at 5.618 GHz with the absorbers thicknesses of 2-5 mm.We synthesized the Co@C and Co@CoNx@C(N)nanocomposite by in-situ arcdischarging,a compressed anode of cobalt?graphite and carbamide powders in Ar and H2 atmosphere.It is characterized by the nano-structure of yolk shell with heterogeneous interfaces.Nitrogen of light element is doped into carbon layer in atomic state to form dipole and absorb electromagnetic wave effectively.At the same time,the CoNx layer of heterogeneous interface effectively optimizes its impedance matching to achieve effective electromagnetic microwave absorption.At the 2-18 GHz,compared with Co@C,the dielectric loss full increased.Especially in 6.6 GHz and 17.1 GHz,the dielectric loss reached 36.3 and 37.8 times.Three-dimensional porous graphene was obtained by chemical deposition of the reprocessed NaY molecular sieves.The three dimensional porous graphene modified by light elements and iron nanoparticles was prepared by gas phase doping and liquid phase doping.Firstly,we obtained three-dimensional porous graphene by using furfuryl alcohol and propylene as carbon source and hydrofluoric acid and concentrated hydrochloric acid as detergent.Then,oxygen or/and nitrogen-doped three-dimensional porous graphene was prepared in the atmosphere of oxygen or/and ammonia.Finally,we prepared three dimensional porous graphene modified with iron nanoparticles by impregnation with ferric salt solution and hydrothermal reaction.Compared with the traditional graphene,the threedimensional porous graphene shows excellent electromagnetic microwave absorption characteristics due to its large defect and three-dimensional ordered pore structure.In addition,through further doping of light elements,its defects are further enlarged and electric dipole is formed to further enhance the energy efficiency of electromagnetic microwave absorption.Finally,the three-dimensional porous graphene modified with iron nanoparticles impedance matching is optimized to achieve more favorable microwave absorption by impedance matching is optimized to achieve more favorable microwave absorption. |
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