| With the rapid development of modern society, various electronic equipment was used, the amount of electromagnetic waves be filled with our living environment, therefore, it has brought space electromagnetic pollution. As a new social public hazard, electromagnetic radiation caused by electromagnetic interference not only affect the normal operation of all kinds of electronic devices, but also has great harm to human body. So, it is extremely important significance to reduce the space electromagnetic improve the living environment of human beings by researched and utilized absorbing material to absorpt electromagnetic wave.The characteristics of ideal absorbing materials should have the thickness of thin, light weight, strong absorption and wide frequency band. But, so far, we haven’t found a class of absorbing material can meet these requirements. So, the new absorbing materials has become a material one of the hot spot of academic field. Core-shell type nano-absorbing powder is a kind of novel structure, by the interacter between several kinds of nano-meter materials through chemical bonds or coated orderly formation of nanoscale assembly, is a higher level of nanocomposites. Due to nanocomposites collection the nano size change and effect brought by the core-shell structure, such as more dangling bond, large surface area, strong interfacial polarization, and it is expected to be absorbing agent of high performance.Due to nanoscale size of ferrite is far smaller than the wavelength of the electromagnetic wave, so electromagnetic wave through rate is better compared with conventional materials. The present study more ferrite is mainly spinel ferrite and magnetoplumbite ferrite. Spinel ferrite material with cubic crystal system has the advantages of low saturation magnetization, superparamagnetism and high magnetic susceptibility, is a good soft magnetic materials. Hexagonal system stone type ferrite has higher magnetocrystalline anisotropy epuivalent field, so it has natural resonance frequency, and the natural resonance is the main mechanism of ferrite absorbing electromagnetic waves; Secondly, the ferrite has plate structure that the best shape of absorber, so the absorbing performance of magnetoplumbite ferrite is best compared with other kinds of ferrite.The core-shell structure composite powers with soft and hard magnetic phase not only use its electromagnetic properties of complementary, but also can effectively take advantage of this special core-shell structure and interface polarization and interface coupling interaction of soft-hard magnetic phase, further improve the material to absorb electromagnetic waves. Therefore, obtained a absorbing material with more ideal performance.In this paper, spinel ferrite ZnFe2O4, NixZn1-xFe2O4, magnetoplumbite ferrite SrFe12O19nano-powers and SrFe12O19/ZnFe2O4, SrFe12O19/Ni0.6Zn0.4Fe2O4with core-shell structure nano composite absorbing powders were prepared by the improved method on the basis of traditional sol-gel preparation process. The XRD, TEM, VSM and vector network analyzer(VNA) were used to analyze the chemical component, structure, morphology, magnetic property and absorbing property of the nano-powder. Detailed study the physical property change before and after coating of two different crystal structure of hard and soft magnetic phase monomers.Analysis and detection results show that:1. In the process of tradition sol-gel preparation, adding suitable amount of glucose and crylamide, obtained spinel structure ZnFe2O4with high purity, small particle size, good soft magnetic properties and wave absorbing propeity.2. The nano-powder microwave absorber SrFe12O19were prepared by the impoved sol-gel preparation technology, and change the molar ratio of iron strontium,and calcined temperature. Research show that:when the molar ratio of iron strontium is11.5, two-step calcining of precursor, the nano power with high purity, uniform particle size have been greatly improved.3. Coated a layer spinel structure ZnFe2O4at the surface of the magnetoplumbite SrFe12O19with the impoved sol-gel preparation technology, obtained the core-shell structure SrFe12O19/ZnFe2O4composite nanoparticle. Research show that:when the molar ratio of and SrFe12O19to ZnFe2O4is1:2and calcined temperature is850℃, the composite powder has obvious core-shell structure and the particles are scattered homogeneously in ellipsoidal shapes or bar shapes, good hard magnetic properties, and strong absorbing property, the maximum reflection loss reaches to-35.3dB at17.5GHz when matching thickness of2mm, with excellent absorbing performance.4. NixZn1-xFe2O4series sample were prepared by doped with different proportion of Ni2+ions on the basis of spinel structure ZnFe2O4. Research show that:the diffraction peak position of sample move to high diffraction angle with the increase of the content Ni2+ions, the lattice constant was decrease, and saturated magnetization increase gradually, the maximum at x=0.6, and then decrease.5. SrFe12O19as nuclear, Coated a layer spinel structure Ni0.6Zn0.4Fe2O4at the surface of the magnetoplumbite SrFe12O19. Under different calcined temperature, obtained composite SrFe12O19/Ni0.6Zn0.4Fe2O4nano power. Analysis results show that when calcined temperature is900℃, composite powers have high purity, good crystallization and excellent magnetic property. |
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