尖锥八面体Fe₃O₄及六角片状Ba（Me）_xCo_2-2xFe₁₆O₂₇微波吸收性能凝聚态物理

【作者】 卢玉娥；

【导师】 周克省； 尹荔松；

【作者基本信息】 中南大学 ， 凝聚态物理， 2011， 硕士

【摘要】 铁氧体是一类传统的吸波材料,但存在密度大、微波吸收频带窄的问题,因此,铁氧体吸波材料的改性仍然是目前的一个研究热点。对铁氧体改性除掺杂和复合等途径外,颗粒形貌特殊化对其微波吸收特性的改善也有重要作用。本文研究了尖锥八面体形貌Fe304和六角片状W型掺杂铁氧体的微波吸收特性。用水热法制备了Fe304晶粉,用X射线衍射仪(XRD)和扫描电子显微镜(SEM)、红外光谱仪(FT-IR)、能谱仪(EDS)对产物结构、形貌及成分进行了表征,分析了颗粒形貌形成机制。用微波矢量网络分析仪测试了样品在2-18GHz微波频率范围内的复介电常数和复磁导率,计算了微波反射率,探讨了材料的微波损耗机制。结果表明：在两种不同水热反应条件下,分别得到颗粒形貌呈尖锥八面体和球状的尖晶石型结构的Fe304粉晶；颗粒形状各向异性有利于材料的微波吸收,尖锥微八面体Fe304是一种低反射率宽带微波吸收材料,其吸收特性优于球形。对反应12小时的尖锥形Fe304样品,厚度2.8mm,7.1GHz频率位置吸收峰值为35dB,大于10dB吸收带宽为7.9GHz；该样品在低频段(2～13GHz)微波吸收主要源于磁损耗兼具介电损耗,在高频段(13-18GHz)微波吸收主要源于介电损耗且磁损耗弱。用溶胶-凝胶法制备了Ba(Me)xCo2-2xFe16O27 (Me=MnCu、CuZn,x=0.0,0.1,0.2,0.3,0.4,0.5)粉体。用差示扫描量热-热重(DSC-TGA)、XRD、SEM、FT-IR对样品结构、形貌及形成过程进行了表征。用微波矢量网络分析仪测试了该样品在2-18 GHz微波频率范围的电磁参数,根据测量数据计算了电磁损耗角正切及微波反射率与频率的关系,探讨了该材料的微波吸收性能与电磁损耗机理。研究结果表明：Ba(Me)xCo2-2XFe16O27样品形成分为凝胶吸附水蒸发和熔融、热分解、晶型形成等阶段；在1235℃以上的温度下煅烧4个小时的Ba(Me)xCo2-2xFe16O27能形成较单一的W型钡铁氧体结构,粉晶均呈微米级六角片状形貌；当Ba(MnCu)xCo2-2xFe16O27样品厚度为2.3mm、x=0.3时,10GHz频率位置吸收峰为24dB,10 dB以上频带宽度达8.8GHz；当Ba(CuZn)xCo2-2xFe16O27样品厚度为2.3mm、x=0.3时,10GHz频率位置吸收峰为17dB,10 dB以上频带宽度达7.6GHz；Ba(Me)xCo2-2xFe16O27的微波吸收主要来自畴壁共振、磁化驰豫和自然共振引起的磁损耗,介电损耗较弱。更多还原

【Abstract】 Ferrite is a kind of traditional material with shortcomings of high density and narrow band for absorbing electromagnetic wave, so that the study of modified ferrite is still an active topic. In addition to modification methods such as doping and compounding, special particle morphology has an important effect on the improvement of ferrite’s microwave absorption properties. In this thesis, the microwave absorption properties of spinel ferrite Fe3O4 with sharp octahedral morphology and doped W-type ferrite with hexagonal flake morphology were researched.Fe3O4 powder samples were synthesized by hydrothermal method. The crystal structure, morphology and composition of these samples were characterized by X-ray diffraction(XRD), fourier transform infrared spectrometer(FT-IR), scanning electron microscopy(SEM) and energy dispersive spectrometer(EDS), and the formation mechanism of particle morphology in the samples was discussed. Their complex permittivity and complex permeability were measured by microwave vector network analyzer in the frequency range from 2 to 18 GHz, the reflection coefficient and loss tangent were calculated according to measurements, and the microwave absorbing mechanism was discussed. The results showed that, two crystalline powders of Fe3O4 with sharp octahedral and spherical morphology were got in two different hydrothermal reaction conditions respectively, and particle shape anisotropy of the material was so helpful to its microwave absorption that sharp octahedral Fe3O4 was a broadband microwave absorbing material with low reflectivity, which is better than spherical. The microwave absorption peak of sharp octahedral Fe3O4 was 35dB at 7.1 GHz frequency and its absorption bandwidth above 10dB was 7.9GHz for the sample with 2.8 mm thickness and hydrothermal growth of 12 hours. The microwave absorption was resulted in magnetic loss mainly as well as dielectric loss secondly in the low-frequency range of 2-13 GHz, and dielectric loss mainly but magnetic loss weakly in the high-frequency range of 13-18 GHz.The crystalline powder samples of Ba(Me)xCo2-2xFe16O27 (Me =MnCu or CuZn, x=0.0,0.1,0.2,0.3,0.4,0.5) were prepared by sol-gel method. The crystal structure, particle morphology and formation of these samples were characterized by XRD, SEM, differential scanning calorimetry-thermal gravity analysis(DSC-TGA) and FT-IR. Their electromagnetic parameters were measured by microwave vector network analyzer in the frequency range from 2 to 18 GHz. The relationships between microwave reflectivity and frequency, between loss tangent and frequency were calculated according to the measurements. The microwave absorbing properties and electromagnetic loss mechanism of the material were studied. The results showed that the formation of Ba(Me)xCo2-2xFe16O27 samples went through several stages such as gel water evaporation and melting, thermal decomposition and crystalline growth, the samples calcined above 1235℃for 4 hours were single W phase ferrite and the particle morphology was micro-hexagonal flake shape. MnCu and CuZn doping were so helpful to improving microwave absorption of W type barium ferrite that the absorption peak of Ba(MnCu)xCo2-2xFe16O27 (x=0.3) with 2.3mm thickness was 24dB at 10GHz and its bandwidth above lOdB was 8.8 GHz, and the peak of Ba(CuZn)xCo2-2xFe16O27 (x=0.3) with 2.3mm was 17dB at 10GHz and its bandwidth was 7.6GHz. The microwave absorption of Ba(Me)xCo2-2xFe16O27 was resulted in magnetic loss mainly but dielectric loss weakly and the magnetic loss was caused by domain wall resonance, magnetization relaxation and natural resonance.更多还原