Structure Regulation And Microwave Absorption Mechanism Of Graphene Loaded Magnetic Nanoparticles

The novel microwave absorbing materials have the features of light-weight, high absorption efficiency, wide-band, corrosion resistance and good thermal stability, which made these new materials being the hot research topic in preventing electromagnetic radiation pollution and improving the survivability of the military targets. The direction of these new absorbing materials is to be compound, broadband and light-weight, because the single absorbing mechanism cannot meet the current microwave absorbing requirements. To obtain strong absorption and broadband absorbing materials, we can regulate the structure to get the better impedance matching and the multiple losses synergistic effect.Metal magnetic materials have the advantages of high saturation magnetization and magnetic permeability. The attenuation of electromagnetic depends on magnetic loss. The disadvantages of metal magnetic materials are high densities, low temperature stability and weak corrosion resistance. Decreasing the particle size, regulating and controlling the complex structure, as well as compounding with other materials are the efficient methods to reduce the eddy current loss, increase the impedance matching, and get the better absorption properties. Graphene is a promising prospects of dielectric loss-absorbing material with the advantages of large surface area and quality of light, thermal and chemical stability. In this paper, the Co (Ni, CoxNiy)/rGO materials were produced and investigated. The absorbing properties of these materials were studied by composition control, structure and absorbing mechanism adjusting in the frequency of 1-18 GHz. The preparative technique of the microwave absorbing material in the "structure function integration" was explored. In this way, the composites of zero dimensional (one dimensional and two dimensional and three dimensional)/two dimensional materials were also fabricated. The microwave absorption properties of these composites were enhanced. The minimum reflection loss is -53.51 dB, the bandwidth of effective absorbing is 5.24 GHz.In this study, graphite oxide was prepared by Hummers method, then, it was reduced by hydrazine hydrate. The prepared graphene has plentiful defects, which could be regarded as the center of polarization and the oxygen atomic in the residues functional groups, which could promote electronic movement and lead to electric moment. The above factors could induce polarization relaxation and promote electromagnetic waves attenuation in the alternating electromagnetic field. The graphene's complex permeability is closer to the complex dielectric constant and has a better impedance match relative to other carbon materials (graphite, oxidation graphite). The best absorption of graphene is-17.39 dB at 14.26 GHz. and the width of effectively absorbing is 5.9GHz (12.1-18.0GHz).The Ni, Co and CoxNiy magnetic nanoparticles were synthesized by hydrothermal reduction method on the surface of graphene oxide. The Co (Ni, CoxNiy)/rGO composites were synthesized using in situ method, which ensures the generation of two phases with uniform adhesions synchronously.The variations and related mechanisms were investigated on absorbing properties through designing of component loading level and particle size. When the Co:Ni:rGO is 9:3:2 (mass ratio), the Co3Ni1/rGO composites show the outstanding microwave absorption properties. The best absorbing properties could reach -42.64 dB in the absorbing thickness of 3.0 mm at the 9.54 GHz and the effectively absorbing width is 8.28-13.14 GHz. The absorption mechanism is shown as follows:(1) the metal particles dispersed on the surface of graphene produced large interface, which ccould result in interfacial polarization in the electric magnetic field; (2) the metal particles gathered in the surface of graphene could form a conductive channel and cause conductivity loss; (3) the Co3Ni1/rGO composite has a large number of defects containing oxygen functional groups, which could produce a variety of polarized center and promote the absorption of electromagnetic waves in the presence of an external electric field; (4) the synergistic effect of electric loss and magnetic loss could promote the attenuation of electromagnetic waves.The one-dimensional chain, two-dimensional coins and three-dimensional flower Co3Ni1 materials were preparated by adding the surface agent, changing reaction time and adjusting other recipes of synthesis conditions, which were induced on graphene surface, respectively. In this way, the growth process and absorbing mechanism of morphologies were analyzed, the influence of microstructure on the wave absorbing performance was explored. The two-dimensional coin-shaped Co3Ni1/rGO has the best microwave absorption properties at 9.36 GHz, in the absorbing thickness of 3.6 mm, and the minimum loss absorbing value is-53.51 dB. The effectively absorbing width is 7.75-11.88GHz. The two-dimensional coin shaped composites led to the multiple reflection and scattering of electromagnetic waves, and caused the dissipation of electromagnetic wave energy in a finite space. Then, the eddy current loss between the magnetic sheet could lead to the dissipation of electromagnetic wave. The increases of anisotropy of the particle shape made the increasing of natural resonance frequency of the system gradually. Thus, the magnetic alloy Snoek limit is improved.Summarily, the microstructure, the mechanism of electromagnetic waves, interface size effect and interface polarization behavior of the fabricated composites were investigated. In this way, the electromagnetic waves loss and impedance matching were analyzed. The absorbing mechanism model was built, and the analysis of magnetic field and electric field was achieved. The interfacial polarization behaviors of magnetic metal/graphene composites were imitated in the specific microstructure under the electromagnetic wave, and the absorbing mechanism of magnetic effect, interface effect, electric conductivity and dielectric effect were revealed.A method of "integration of structure-function" composites in structure regulation and simple controllable preparation was introduced in this paper. The theory of collaborative absorbing wave mechanism of magnetic loss and electric loss, and the effective way was provided, which can help us to reach the target of producing absorbing materials with "wide, strong, light, thin" features. The above mentioned method and technique have certain strategic significances in military and civil electronic applications.