Fabrication Of Magnetic Materials And Analysis Of Their Electromagnetic Wave Absorption Properties

The electromagnetic wave absorption materials play an improtant role in the worldwide military high technologies as well as increased civil use such as electronics, information dissemination and microwave protection. However, the studies on electromagnetic wave absorption materials with low thickness, low density, and high bandwidth sill need further. The magnetic material is one of the most widely researched and applied wave-absorbing materials. The concentration三of our investigation are the design of novel micro/nano-architectures of magnetic materials (Ni, Co metallic materials and Fe3O4ferrite) and analysis of their electromagnetic wave absorption properties. The electromagnetic wave absorption properties of magnetic materials with micro/nano-scale hierarchical architectures can be enhanced due to their special morphologies and increased anisotropic field. Based on this, the thesis reveals the synthesis of three kinds of absorbing materials and the investigation of their electromagnetic wave absorption properties.1. Monodispersed Ni flower-like architectures with size of1-2μm were synthesized through a facile solvent-thermal process in1,2-propanediol solution in the presence of polyethylene glycol (PEG), and sodium alkali (NaOH). The morphologies of the products were characterized by the scanning electron microscope (SEM) and the transmission electron microscopy (TEM). The results indicate that the Ni architectures are composed of nanoflakes, which assemble to form three dimensional flower-like structure, and the thickness of nanoflakes is about10-40nm. A possible formation mechanism for the Ni flower-like architectures was proposed and it was confirmed by the control experiments. The influence of the NaOH, PEG, NaCl and the solvent on the final morphology of the products were investigated by comparing experiments. The flower-like Ni architectures exhibited a large coercivity (Hcj) of332.3Oe through the magnetism measurement. The epoxy resin composites with50wt%Ni products provided good electromagnetic wave absorption performance (reflection loss (RL)<-20dB) in the range of5.2-11.7GHz over absorber thickness of2.2-4.3mm. The good electromagnetic wave absorption property is due to the special morphology and higher anisotropic field.2. A template-free approach was reported to prepare sponge-like cobalt nanoporous particles. The nanoporous cobalt particles were synthetized by employing CO3O4as precursors. The products in every step were characterized and analysed by the X-ray diffraction (XRD), SEM, high-resolution transmission electron microscopy (HR-TEM), thermogravimetric (TG) analysis and N2adsorption/desorption analysis, and a three-step formation mechanism for the Co nanoporous structures was proposed on the base of the results. The epoxy resin composites with65wt%rhomb-like or prism-like samples showed efficient EM wave absorption characteristics (RL<-20dB) in ranges of12.8-18GHz and11.2-18GHz over absorber thicknesses of1.0-1.5mm and1.0-1.6mm, respectively. Compared with Co with other structures, the nanoporous cobalt structures demonstrate potential application as more efficient electromagnetic wave absorbers.3. Large-scale octahedral Fe3O4nanocrystallines with crystalline size of100-500nm were synthesized by a facile solvent-thermal method in1,2-propanediol solution in the presence of PEG, and NaOH. The Fe3O4nanocrystallines showed higher saturation magnetization value and large coercivity value than that of magnetite polycrystallines because of their well crystallization and dispersion. The epoxy resin composites with40vol%Fe3O4powders provided good electromagnetic wave absorption performance (RL<-20dB) in the range of2.0-4.3GHz over the absorber thicknesses of3.5-6.8mm. A minimum RL value of-47dB was observed at3.1GHz with a thickness of4.8mm.