Study On Preparation And Property Of Multilayer Nano Magnetic Absorbing Materials

To improve the infrared absorbing performance of ferrite magnetic material which has good electromagnetic wave absorbing performance, the core/shell structured multilayer coating is introduced to achieve multiple wavelength range absorbing. A series of materials, Fe₃O₄/SiO₂/Al₂O₃, Fe₃O₄/SiO₂/TiO₂, Fe₃O₄/SnO₂/Al₂O₃ and Fe₃O₄/SnO₂/TiO₂ have been prepared by heterogeneous nucleation and sol-gel methods. The microstructure, coating state, magnetic and infrared absorbing properties of as-prepared materials have been studied by various experimental equipments such as TEM, XRD, FT-IR,VSM and dual wavelength range emissivity apparatus.First, the preparation processes of heterogeneous nucleation and sol-gel methods were investigated, from which some key process parameters were achieved and then used to prepare the multilayer coated nanoparticles studied in this thesis.It is shown that the average diameters of Fe₃O₄, Fe₃O₄/SiO₂, Fe₃O₄/SnO₂, Fe₃O₄/SiO₂/Al₂O₃, Fe₃O₄/SiO₂/TiO₂, Fe₃O₄/SnO₂/Al₂O₃ and Fe₃O₄/SnO₂/TiO₂ are all in nano-scale and that multilayer coated structures exit in Fe₃O₄/SiO₂/Al₂O₃, Fe₃O₄/SiO₂/TiO₂, Fe₃O₄/SnO₂/Al₂O₃ and Fe₃O₄/SnO₂/TiO₂.The specific saturation magnetization (σs) and the coercivity (Hc) of Fe₃O₄ are 72emu/g and 48Oe, respectively. Further coating of SiO₂, SnO₂, Al₂O₃ and TiO₂ affects magnetic performances little.By using the dual wavelength range apparatus, it is shown that the infrared absorbing performance of Fe₃O₄ is very bad. There is no obvious improvement of the infrared absorbing ability of Fe₃O₄ in coating of SiO₂ or SnO₂. While further coating of Al₂O₃ or TiO₂, the infrared emissivity of the multilayer coated nanoparticles has been reduced to 0.82⁰.83 from 0.97 of Fe₃O₄. These results show that core/shell structured multilayer coated nano composites have the potential for multiple wavelength range absorbing, and they are expected to become a series of absorbing materials in the future.