Study Of Nickel Ferrite And Titanium Dioxide Composite Mesoporous Materials

All kinds of electronic appliances are increasing with the development of science andtechnology. Influence of electromagnetic wave radiation on the environment is increasing dayby day, people has surrounded by the ubiquity of electromagnetic waves. Meanwhile, radar iswidely used as a kind of mature military detection means, stealth technology pointing at radarhas become a focus in the research institutions at home and abroad. No matter stealth of themilitary implementation or governance of electromagnetic pollution in daily life environmentis closely related with the absorbing materials. So far, however Searching absorbing materialsfor researchers to resist and weaken the electromagnetic wave radiation have become a majortopic in materials science. It is well known that ideal absorbing materials have thecharacteristics of strong absorption, broad-band, thin thickness, and light quality. So far,however, it is not found that the materials can completely meet these requirements. The ferritehas excellent microwave properties and acts as the main material in the microwave absorptiontechnique. But the ferrite absorbing materials have also many problems of high density, lowfrequency microwave absorption difference, and narrow absorption band. So, it is required toact appropriate modification and design of existing absorbing materials make compositeferrite absorbers with better matched electromagnetic parameters. The main research workand results are summarized as follows.In the design of the ferrite absorbing material structure and component, we designedabsorbing material into the mesoporous morphology. Preparing hollow multiple coatmesoporous materials by compositing the magnetic phase ferrite and non-magnetic phasesilica, titania composite multilayer, and absorbing material with different microwave lossfrequency distribute in different layers of partical.The nickel ferrite nanocrystals were synthesized by hydrothermal method using PEG andSDBS as surface active agent. The size of the nickel ferrite nanocrystals distribute on20-40nm. With the improvement of heat treatment temperature, the nickel ferrite crystallinetend to perfect, the lattice distortion decreasing obviously, saturation magnetization increasedfrom38.26emu/g to59.23emu/g, closing to saturation magnetization of the nickel ferrite bulk.Taken nanoparticles NiFe2O4as magnetic carrier, the PS-SiO2/NiFe2O4magneticmicrospheres were prepared from styrene，tetraethoxysilane，by emulsion polymerizationusing KH-570as a cross-linking agent. The VSM results indicated that the magnetism ofSiO2/NiFe2O4and PS-SiO2/NiFe2O4declined sharply, its’ specific saturation magnetization,Coercivity and remanence less than NiFe2O4. TiO2/PS/SiO2/NiFe2O4magnetic microspheres material were prepared by sol-gel process with tetrabutyl titanat as raw materials，PS-SiO2/NiFe2O4particle as the core, SDBS and PVP as templating agent. TiO2/SiO2/NiFe2O4magnetic mesoporous microspheres material was prepared by eliminating PS ofTiO2/PS/SiO2/NiFe2O4. The crystal structure and surface morphology of TiO2/SiO2/NiFe2O4magnetic mesoporous microspheres material was characterized by X-ray diffraction(XRD),S-4800high-resolution field emission scanning electron microscope(SEM), Nitrogenadsorption and desorption and so on. The results indicated that the TiO2/SiO2/NiFe2O4isspherical particle, the particle size of60-70nm, pore size of3-4nm.Ce and Co codoping modification of TiO2on the surface of the TiO2/SiO2/NiFe2O4canincrease crystal defects and the number of all kinds of dipole of TiO2/SiO2/NiFe2O4. Researchshows that the introduction of Ce, Co can not obviously influence crystal structure andchannel structure of TiO2/SiO2/NiFe2O4, but can increase specific surface area and porevolume, make particle size and pore size become smaller and more uniform. The introductionof Ce, Co causes the red-shift of the absorption spectrum of TiO2/SiO2/NiFe2O4. New wideabsorption band has emergence in wavelength of550nm, improve utilization efficiency ofsunlight. Ce, Co dispersed evenly in the TiO2/SiO2/NiFe2O4mesoporous materials, and smallangle XRD diffraction peak has a very small offset in the direction of low Angle, thediffraction intensity is reduced.The complex permittivity and permeability of composites made from SiO2/NiFe2O4,TiO2/NiFe2O4,TiO2/SiO2/NiFe2O4,(Co,Ce)-TiO2/SiO2/NiFe2O4multilayer magneticmesoporous microspheres material embedded in paraffin matrix separately are measured byvoter network analyzer and the reflectivity is calculated within1-18GH. Analyse the effect ofsilica, titanium dioxide, mesoporous material properties and metal ions on the electromagneticparameters of materials. Test results show that the real and imaginary of complex permittivityof the particles coated by SiO2is decline. The influence of the magnetic permeability ofmagnetic particles is smaller. Composite magnetic particles SiO2/NiFe2O4coated by TiO2mesoporous, complex permittivity and permeability of TiO2/SiO2/NiFe2O4increasesignificantly. With the increase of TiO2, complex permittivity and permeability ofTiO2/SiO2/NiFe2O4increase, the imaginary peak of the complex permeability move to the lowfrequency. The amplitude attenuation coefficient e-2dαof composite mesoporous materialstrends to decline, intrinsic impedance first increase then decrease.Analysis shows that magnetization curve of (Co,Ce)-TiO2/SiO2/NiFe2O4multilayermesoporous materials has obvious hysteresis phenomenon, the saturation magnetization equal31.68emu/g, coercive force equal236oe. The peak position of complex permittivity andpermeability of (Co,Ce)-TiO2/SiO2/NiFe2O4have no change in compared with TiO2/SiO2/NiFe2O4,, peak value increases, real permittivity increased about2, imaginary ofcomplex permittivity and permeability, the real and imaginary of complex permeability increasedabout0.5. Calculating the single layer eflectivity of (Co,Ce)-TiO2/SiO2/NiFe2O4r by theelectromagnetic parameters of the simulation. The absorption mechanisms of magneticmesoporous material are studied based on the electromagnetic wave propagation laws in lossymedium. The absorption peak of the Co-Ce codoped TiO2/SiO2/NiFe2O4magnetic mesoporousmaterials shifts to the low frequency. When the TiO2content (Co,Ce)-TiO2/SiO2/NiFe2O4is30%, the maximum microwave loss efficiency reaches31dB，and the continuous frequency rangewith the loss above20dB reaches2GHz.