Synthesis,Characterization And Microwave Absorption Performances Research Of Inorganic Micro/Nano Composites Materials

With the rapid development of modern radar and electronic communication technology,the electromagnetic wave interference contamination is becoming a growing problem.To meet the need of highly efficiently absorption,micro/nano materials have become a focus for the research and development for new types of microwave absorption materials.The paper mainly studied synthesis,characterization and microwave absorption properties of micro/nano materials called zinc oxide and ordered mesoporous carbon.And the paper put emphasis on that we can improve the microwave absorption abilities by adjust the particle size,morphology and structure of semiconductor micro/nano ZnO,and optimize the content or species of doping magnetic components for the micro/nano OMC,thus achieving a balance between dielectric loss and magnetic loss.Specific contents are as follows:(1)By solvothermal or hydrothermal method,using glucose(C6H12O6)as the carbon source,zinc nitrate hexahydrate(Zn(NO3)2·6H2O)as zinc source,urea(CO(NH2)2)as precipitant reagents,one-step synthesis for zinc oxide solid spheres(C@ZnO)are successfully made.After removal of the carbon calcined at 500 oC in air,the porous hollow and urchin-like zinc oxide spheres(ZnO)are synthesized by changing the solvent;The Fe-doped CMK-3/SBA-15 composites with different Fe contents were prepared by using a catalytic carbonization procedure followed by high-temperature calcination in N2,making SBA-15 as a fabric-guiding matrix,sucrose and soluble hexahydrated ferric chloride solution(Fe Cl3·6H2O)as carbon source and iron source,respectively.(2)In order to analyze the morphology,composition,structure and optical properties of the as-synthetic materials,many characterization methods are used,such as XRD,SEM,TEM,XPS,Raman and PL testing.The results discovered: synthetic ZnO calcined at 500 oC has porous hollow and urchin-like structures,which contain many pores in the surface of ZnO speres,and an assembly of nanosheets that grow radically from the center outward.Furthermore,SEM and TEM images clearly display a large scale uniformly dispersed porous hollow and urchin-like ZnO spheres with diameter 4-15 ?m and 5-6 ?m;For CMK-3/SBA-15-x Fe-y,the CMK-3 carbon particles are dispersed homogeneously into the SBA-15 silica matrix.Fe-based nanoparticles are dispersed on the surface of amorphous carbon-silica frameworks and estimated to be ~18 nm in diameter.The SBA-15 silica matrix is hexagonal arrangement of cylindrical mesoporous tubes with ~9 nm in diameter.The diameter of the carbon nanowires is estimated to be ~3.6 nm.(3)By using coaxial transmission line method and the equipment: Hewlett-Packard(HP)8753D Vector Network Analyzer made in US,the microwave absorbing properties of the samples determined by the electromagnetic parameters are studied in the range of 2-18 GHz.The results show that: the dielectric loss factors(tan??)of porous hollow and urchin-like ZnO spheres decrease from 0.7 to 0.05 and from 4.1 to 0.5.The average value of the dielectric loss factors(tan??)of them are ~0.38 and ~2.30.Obviously,tan?? for urchin-like ZnO is higher than that for porous hollow ZnO;Especially,when the matching thickness is only 3.0 mm,the minimum reflection loss value(RL)for urchin-like ZnO reaches-20 d B at 14.3 GHz,but the minimum RL value for porous hollow ZnO is-5.62 d B at 16.24 GHz with the thickness of 2.5 mm,indicating an enhanced absorbing properties for urchin-like ZnO materials compared to porous hollow ZnO.The reason with enhanced absorbing properties for urchin-like ZnO materials can attribute to the increased dielectric relaxation polarization and dielectric loss induced by oxygen and zinc vacancies of ZnO nanosheets for urchin-like ZnO.In the electromagnetic field,the interface of needle-like ZnO nanosheets prevent the movement of free electrons resulted from various vacancies and thus induces space charge accumulation at the interfaces,resulting in enhanced interfacial polarization.Furthermore,needle-like ZnO structure can act as permanent dipolar polarization centres,making electromagnetic energy attenuate by scattering and reflection.For CMK-3/SBA-15-3Fe-700 paraffin composites,the minimum RL value reaches-19 d B at 17.2 GHz with a thinner thickness of 2.00 mm.Moreover,the microwave absorption bandwidth less than 10 d B is found to exceed 5.76 GHz as the layer thickness is 2.37 mm.The permittivity dispersion behaviors have been explained based on the Cole–Cole model and the conductivity contribution model.A new simple empirical model was also supposed to find the fitted curves of the multi-resonance imaginary permeability spectra of the composites.The EM wave can hardly be reflected on the absorber surface because of a better match between dielectric loss and magnetic loss,which originates from the combination of dielectric carbon–silica and magnetic Fe species.