| The electromagnetic wave absorbing materials have become a hotspot in research now due to the extensive applications of absorbers in civil life and military industry.The graphene and its derivatives are highly evaluated by researchers from many different fields because of their remarkable physical and chemical properties.Especially,reduced graphene oxide(r GO)is considered as one of the most promising materials in virtue of its distinct advantages of good conductivity,residual functional group and high surface area.The combination of reduced graphene oxide and magnetic materials can well remain the merits of dielectric and magnetic materials so that it is expected to obtain the high-performance microwave absorption materials.In this thesis,we mainly focus on the facile and feasible fabrications of Fe Ni alloy/reduced graphene oxide composites with different structure via reasonable design of morphology and control of microstructure.We aim to establish the absorbing mechanism of the hierarchical material,by considering the synergistic effect and interface effect of components and the regulation of the electromagnetic parameters.Ultimately,we intend to develop a new design idea for the construction of "thin,light,wide and strong” ideal absorber.The main content of the thesis are summarized as follows:1.The embedded magnetic mesoporous microspheres material is synthesized via a hydrothermal and carbonization process.The morphology is characterized by scanning electron microscopy and transmission electron microscopy.It indicates that the nanosized Fe Ni alloy nanoparticles are encapsulated by carbon matrix and the Fe Ni alloy particles are evenly dispersed in carbon microspheres,which can form the interface polarization.The existence of mesoporous is tested by N2 adsorption-desorption isotherms.The mesopores can not only form more defects and dangling bonded atoms to improve polarization loss,but also prompt the electromagnetic wave to access to the material's interior and restrict the microwave in the materials,then enhance the loss of microwave by multiple scattering and reflection.Given the above,the synergistic effect of polarization loss and multiple scattering and reflection delivers the microwave absorbing performance.In order to improve the absorption performance of material,reduced graphene oxide(r GO)modified embedded magnetic mesoporous microsphere composite is synthesized through the way of introducing graphene.By comparison,its performance is improved dramatically.The minimum reflection loss of-45.2 d B is achieved at a thickness of 1.5 mm,and effective absorption bandwidth reaches 5.0 GHz.An analysis based on the data shows that the introduction of graphene that enhances effectively dielectric loss and matching capability couple with specific structure can obtain the material with excellent property.2.A series of Fe Ni alloy nanoparticles supported on two-dimensional graphene composites are prepared through the facile and feasible one-pot method.The nanosized Fe Ni alloy particles are evenly supported onto graphene sheets without aggregation because of the introduction of glucose and the interaction between the oxygen-containing groups on the surface of graphene oxide and metal ions in the reaction system.The experimental results show that microwave absorption performance can be modulated by adjusting the proportion of dielectric and magnetic components during the course of the experiment.The two-dimensional magnetic composite(Fe Ni/r GO-100)displays the most excellent electromagnetic wave absorbing capability.The minimum reflection loss can be up to-46.2 d B and the effective absorption bandwidth reaches 4.0 GHz with an absorber thickness of 1.5 mm.The research demonstrates that the synergistic effect of magnetic nanoparticles,reduced graphene oxide and amorphous carbon layers can significantly enhance the microwave absorbing capability of the materials. |
PDF Full Text Request