The Fabrication Of Zinc Oxide-Barium Ferrite Composites And Its Microwave Absorbing Properties

Recently, the lighting, broadening and high-efficiency of microwave absorbing material have been research highlights. Hence, the thesis attempts to synthesize microwave absorber-zinc oxide via solution assisted with high temperature oxidation reaction method; and M-type barium ferrites are fabricated with sol-gel self-propagating high-temperature synthesis and further solid state method; a novel microwave absorbing composite material of ZnO-BaAlxFe12-xO19has been obtained through compounding of ZnO and M-type barium ferrites, and its microwave absorbing properties are studied.The ZnO dandelions and multilevel spheres were fabricated through solution assisted with high temperature oxidation reaction method with ball-like zinc powder as templates. Both of the dandelions and spheres are composed of one-demensional zinc oxide with diameter of tens to hundreds nano meters. The diameter of dandelions and multilevel spheres were2-5μm and10-20μm respectively. The phases and micro structures of ZnO were characterized with XRD, SEM, FESEM and TEM, and furthermore the formation mechanisms of ZnO with different microwave structures were discussed.The pure phase M-type barium ferrites were fabricated with sol-gel self-propagating high-temperature synthesis and further solid state method. The final calcinations schedule was determined by DSC-TGA and XRD analysis. The results indicate that M-type barium ferrite formation temperature is800℃and the pure phase M-type barium ferrite with100-400nm in diameter is obtained after calcinations at1000℃in6hours. The Al3+being doped BaAlxFe12-xO19(x=0.25-2.00) was also fabricated with the same method. The phase, crystal structure, and micro structure were characterized by XRD, Raman, SEM, and FESEM respectively. As the increasing of doped Al3+, crystal package parameter of BaAlxFe12-xO19and the particle size of products were decreased; and the doped Al3+mainly replaced the Fe3+in FeO6octahedron.The zinc oxide-barium ferrites composite material was fabricated with ZnO from solution method and M-type barium ferrites. The electromagnetic parameters of ZnO, BaAlxFe12-xO19and ZnO-BaAlxFe12-xO19were analyzed via microwave vector network analyzer. The reflection loss (RL) was calculated by transmission lines theory. The test results indicate that the RL minimum value of zinc oxide sample is-11.50dB at9.8GHz; the RL minimum value of M-type barium ferrite sample is-9.26dB at12.5GHz. Experimental results show that dielectric properties of M-type barium ferrites have much to do with the content of Fe2+. The doped Al3+could weaken the dielectric properties and microwave absorbing property of M-type barium ferrites to make the matching frequency shift to high frequency with the increasing addition of Al3+. Comparing with the microwave absorbing properties of single phase ZnO or M-type barium ferrite, the microwave absorbing properties of zinc oxide-barium ferrite composite material were enhanced and the RL minimum value of zinc oxide-barium ferrite composite material was as low as-15.50dB at12.20GHz; the interval of RL below-6dB (Reflectivity15.8%) could reach as high as7.6GHz (8.7-16.3GHz), the properties of broadband microwave absorbing materials mainly ascribed to the composition process of two different mechianism materials, furthermore, the absorbing band at12.20GHz due to interfacial coupling effect from generated ZnO during treatment with high temperature.