Microwave Absorption in the GHz Range of Nanostructure Produced by Disproportionation Reaction of Rare Earth-Iron Compound

在1 ~ 5ghz频率范围内，尖晶石型铁氧体和金属磁性材料均可作为电磁波吸收剂。然而，由于后者材料的饱和磁化强度较大，其Snoek极限在较高的频率，因此其相对复磁导率值在该频率范围内保持较高。因此，可以用金属磁性材料制作更薄的吸收体。电磁波引起的导电磁性材料的磁化强度由于涡流损耗而降低。因此，在用这种材料制作电磁波吸收器时，最好使用比皮肤深度更小的颗粒。本文研究了利用Sm_2Fe_<17>化合物的歧化反应制备具有良好α-Fe结构的粉体的可能性，该粉体可作为工作在GHz频率范围内的电磁波吸收剂。Sm_2Fe_<17>化合物在氢气和空气中歧化后分别形成亚微米级的α-Fe…More / SmH_2和α-Fe / SmO结构。通过这种方法，得到了具有良好α-Fe结构的磁粉。粉末在氢气中歧化，在空气中加热以氧化Sm氢化物，得到α-Fe / SmO两相组织，从而提高粉末的电阻率。用该粉末制备了环形环氧树脂复合材料，并对其微波吸收性能进行了测试。未歧化的样品在这个频率范围内没有电磁波吸收。然而，歧化样品（在氢气中873 K加热1小时，铣削30分钟，在空气中473 K氧化2小时）在频率（f_m） 0.73至1.30 GHz范围内表现出电磁波吸收（R.L.< -20dB），吸收厚度（dm）分别为13.1至7.9 mm。歧化后的样品（473K加热2小时，研磨30分钟）也表现出良好的电磁波吸收性能（f_m=-1.21 ~ 2.50 GHz, d_m= 8.0 ~ 4.2 GHz）。结果表明，歧化反应在氢气和空气中都是制备α-Fe结构精细粉体的有效方法，该粉体可用于工作在几GHz范围内的微波吸收剂。少

For the 1-5 GHz frequency range, both Spinel-type ferrites and metallic magnetic materials can be used as electromagnetic wave absorbers. However, because the latter materials have larger values of saturation magnetization, their Snoek's limit are at a higher frequency and so their values of relative complex permeability remain high in this frequency range. Therefore, it is possible to make thinner absorbers from metallic magnetic materials.The magnetization of electrically conductive magnetic materials, induced by electromagnetic waves, decreases due to eddy current losses. For this reason, it is best to use smaller particles, compared to the skindepth, when making electromagnetic wave absorbers from such materials. In this study, the possibility of using the disproportionation reaction of the Sm_2Fe_<17> compound for the production of powders with a fine α-Fe structure was investigated, for use as electromagnetic wave absorbers that can operate in the GHz frequency range. A fine α-Fe … More / SmH_2 or α-Fe / SmO structure with a sub-micrometer size is formed from the Sm_2Fe_<17> compound after disproportionation in hydrogen or air, respectively. In this way, magnetic powders with a fine structure of α-Fe were obtained. The powders disproportionated in hydrogen, were heated in air in order to oxidize the Sm hydride, to give a α-Fe / SmO two-phase microstructure, and thereby increase the resistivity of the powders. Toroidally shaped epoxy-resin composites were made from this powder, and the microwave absorption properties of these samples were measured. An undisproportionated sample did not show any electromagnetic wave absorption in this frequency range. However, the disproportionated samples (heated in hydrogen at 873 K for 1 hour, milled for 30 minutes and oxidized at 473 K for 2 hours in air) exhibited electromagnetic wave absorption (R.L.< -20dB) in the frequency (f_m) range 0.73 to 1.30 GHz, for absorber thicknesses (dm) ranging from 13.1 to 7.9 mm, respectively. The disproportionated samples in air (heated at 473K for 2 hours and milled for 30 minutes) also showed good electromagnetic wave absorption properties (f_m=-1.21 - 2.50 GHz and d_m= 8.0 - 4.2 GHz). It is concluded that the disproportionation reaction, in either hydrogen or in air, is a useful method for the production of powders with a fine α-Fe structure, which can be used for microwave absorbers that operate in the several GHz range. Less