Shao XiaoPing, Dai Bo, Zhang XiaoWei, Ma YongJun
School of Materials Science and Engineering, Southwest University of Science and Technology, Sichuan 621010, PR China.
J Nanosci Nanotechnol. 2012 Feb;12(2):1122-7. doi: 10.1166/jnn.2012.4275.
Nanoparticles of Fe3O4 with various sizes were synthesized from FeCl3 x 6H2O, FeCl2 x 4H2O and NaOH by coprecipitation process. The crystal structure, morphology, particle size and magnetic property of the products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). It was found that the molar ratio of ferrous to ferric played an important role in the formation of Fe3O4 nanoparticles. The particle mean diameter swelled from approximately 10 to approximately 20 nm with the molar ratio range from 1:2 to 6:1. The saturation magnetization and the coercivity increased correspondingly. The complex permittivity epsilon(r) and permeability mu(r) of the Fe3O4 mixture with paraffin were measured using vector network analysis. Values of epsilon(r), and mu(r) were used to determine the reflection loss at various sample thicknesses, based on a model of microwave absorbing layer backed by a metal plate. The minimal reflection loss or the dip shifts to a lower frequency region with increasing thickness. When the thickness is 5 mm, the minimal reflection loss of Fe3O4 synthesized with the molar ratio of 6:1 and paraffin wax composites reaches -35.1 dB at 5.2 GHz and -30.2 dB at 17.6 GHz, respectively. The minimal reflection loss is attributed to the thickness of the absorber approximates an odd number multiple of a quarter of the propagation wavelength.
通过共沉淀法，以FeCl₃·6H₂O、FeCl₂·4H₂O和NaOH为原料合成了不同尺寸的Fe₃O₄纳米颗粒。采用X射线衍射（XRD）、透射电子显微镜（TEM）和振动样品磁强计（VSM）对产物的晶体结构、形貌、粒径和磁性进行了表征。发现亚铁与铁的摩尔比对Fe₃O₄纳米颗粒的形成起着重要作用。随着摩尔比从1:2增加到6:1，颗粒平均直径从约10 nm增大到约20 nm。饱和磁化强度和矫顽力相应增加。使用矢量网络分析仪测量了Fe₃O₄与石蜡混合物的复介电常数ε(r)和磁导率μ(r)。基于金属板支撑的微波吸收层模型，用ε(r)和μ(r)的值来确定不同样品厚度下的反射损耗。随着厚度增加，最小反射损耗或凹陷向低频区域移动。当厚度为5 mm时，摩尔比为6:1合成的Fe₃O₄与石蜡复合材料的最小反射损耗在5.2 GHz时达到-35.1 dB，在17.6 GHz时达到-30.2 dB。最小反射损耗归因于吸收体的厚度近似为传播波长四分之一的奇数倍。
