Study On The Prepareation Of New Carbon/Magnetic Matericals Composite Absorbents And Electromagnetic Properties Of Their Paraffin Composites

Carbon/magnetic matericals composite absorbent is a new kind of nanocomposites, which can not only improve the thermal stability of the magnetic particles, but also modulate the microwave electromagnetic properties of the magnetic particles. In the current study, a variety of synthesis techniques were applied to prepare a series of carbon/magnetic matericals composite absorbers. Moreover, their formation mechanism and the influencing factors, as well as magnetic properties and microwave electromagnetic and absorbing characteristics were systematically investigated. The main results of this paper are as follows:Using steel slag and charcoal as raw materials, the steel slag/charcoal nano-/micro-composites with magnetic-resistance mixed loss mode were fabricated by a high-performance milling process, and then the composition, phase structure, morphology, and electromagnetic (EM) characteristics of the products were characterized by XRD, EDS, SEM, and vector network analyzer, respectively. The results showed that EM characteristics of the products were strongly dependent on the content of the charcoal (Wcharcoal).The real and imaginary parts of the permittivity of the steel slag/charcoal nano-/micro-composites significantly increased with the increasing Wcharcoal.Among them, the steel slag/charcoal composites with WCharcoal=50wt%exhibited the best EM-wave absorption performance, with a maximum reflectivity value of-33.4dB, the effective bandwidth15.2GHz(=-10dB) and8.6GHz (=-20dB), respectively, which is a consequence of enhanced dielectric loss and a proper EM matching.Using expanded graphite and FeSO4as precursor, Fe/expanded graphite (Fe/EG) intercalation compounds were prepared by a facile one-step reduction approach. The influences of Fe nanoparticles content wFe on the morphology, structure, and microwave electromagnetic and absorbing properties of the corresponding intercalation compounds were studied by SEM, XRD, and network vector analyzer, respectively. The results showed that the change of wFe could effectively tune the microwave electromagnetic and absorbing characteristics. As the wFe was increased from27.5to71.5wt%, Fe/EG intercalation compounds show a maximal permittivity at wFe=27.5wt%, the permeability with a multiresonant behavior, and the gradually increasing microwave absorbing properties. The excellent microwave-absorption properties of Fe/EG intercalation compounds are as a consequence of a proper electromagnetic matching and enhanced magnetic resonant loss.Flower-like Co superstructures composed of leaf-like flakes were synthesized via a facile hydrothermal approach independent of surfactants or complex precursors. The evolution of the morphology and crystal phase was closely related to the variation of the electrode potentials, in which NaOH and hydrazine hydrate played crucial roles. The microwave electromagnetic and absorbing properties of the flower-like Co/wax composites varied strongly with the mass ratios (λ) of Co powder to wax. At the low λ of Co powder to wax, flower-like Co superstructures functioned as the random distributed patches in wax matrix and, therefore composites exhibited frequency selective surface (FSS) behaviors. Owing to high conductance and eddy current losses, however, composites with high λ showed excellent microwave absorption performances, with a minimum reflection loss(RL) of-40.25dB observed at6.08GHz, corresponding to a matching thickness of2.5mm. In particular, the absorption bandwidth (RL=-20dB) was13.28GHz. The current work provides insights into the absorption mechanism of flower-like complex absorption materials. Using glucose as carbon source and the above-mentioned cobalt particles as the core, a hydrothermal method was developed to synthesize Co/C core-shell composite particles with different structure and composition. Change in the glucose content enables effectively controlling the shell thickness of the Co/C core-shell composite particles. Coated carbon film can not only improve the chemical stability of the Co samples but also tailor their electromagnetic characteristics. Among them, flower Co/C/paraffin composites corresponding to a thickness of8.0mm coating show the maximum reflection loss of-55.35dB at11.52GHz. When the coating thickness varies at the range of1～10mm, the paraffin composites containing50wt%flower-like Co/C samples, the absorption bandwidth (RL<-10dB) is9.92GHz.