电磁屏蔽论文：电磁屏蔽 铁氮化合物 膨胀石墨 碳纳米管 单分散微球.doc

【关键词】电磁屏蔽 铁氮化合物 膨胀石墨 碳纳米管 单分散微球【英文关键词】Electromagnetic shielding Iron nitride Expanded graphite Bamboo-likecarbon nanotube Monodisperse microspheres电磁屏蔽论文：新型碳基纳米电磁屏蔽基材的制备【中文摘要】电子、电气产业的迅猛发展使得电磁环境日趋复杂,这会造成辐射干扰、电磁泄密、生命体受电磁辐射损伤等危害。电磁屏蔽材料可以减弱辐射有效地预防上述危害,常用的屏蔽材料是导电性好的金属、铁磁材料、铁电材料,但这些材料常常密度大、硬度强、抗腐蚀性能不理想。膨胀石墨(EG)具有较高的电导率,电磁屏蔽性能优异,但由于没有磁性,低频段的吸收损耗低、屏蔽性能较差。本课题组前期将Fe、 Co、 Ni等磁性金属颗粒植入到EG孔道中,所得复合材料低频电磁屏蔽性能得到显著提高,但磁性金属颗粒的抗氧化性不十分理想,长时间使用性能可能存在退化现象；碳纳米(CNT)管密度小、导电性和化学稳定性好,是较好的的电磁屏蔽材料,但制备效率较低、价格昂贵,同时也存在无磁性低频屏蔽效果不理想等不足。超材料(metamaterials)可以具有负的介电常数,且有密度低、参数可调等特点,在电磁屏蔽领域也有应用的前景,但制备困难,其电磁屏蔽应用还停留在理论阶段。针对上述屏蔽材料的不足,本文制备并表征了三种新型电磁屏蔽材料,分别是(1)将Fe/EG在高温下与氨气反应,制备了抗氧化的磁性FexN/EG复合材料；(2)采用廉价的三聚氰胺为原料,用固相热解法制备了抗氧化含磁性金属的竹节状碳纳米管；(3)采用化学镀的方法,制备了可用于构建特殊结构特殊等效电磁参数(如负介电常数)屏蔽材料的单分散镀金属微球。主要结果如下：(1)利用气相【英文摘要】Nowadays, electromagnetic radiations emanating from a wide variety of sources can interfere with electronic devices and affect the health of people. The electromagnetic shielding materials with high effectiveness are increasingly required to meet the high demand for the reliability of electronics and the health of people. EG has been found to be a highly effective electromagnetic shielding material in the range of1-2GHz because of its excellent electrical conductivity. But the shielding effectiveness of EG decreases sharply with the decrease of frequency. Our previous work have been proved that the metals with high magnetic permeability may play the role of absorbing electromagnetic radiations, especially at low frequencies. Thus the composite materials of EG and magnetic metals have exhibited both absorption and reflection losses and increase the shielding effectiveness ultimately in a wide range of frequencies. Unfortunately, it is usually difficult to prevent the metallic nano-particles from environmental oxidation, and such effects usually cause the materials to loss their excellent characters and limit the applications. The nitride metal or the encapsulation of metals inside carbon nanotube can immunize or bate the metallic species against environmental degradation and retain their intrinsic properties. Such composites are highly demanded not only for understanding their fundamental features, but also for applications such as electromagnetic interference shielding materials, bio-materials, high-density magnetic storage media, magnetic fluids, catalysts and more.In this work, we prepared and characterized the composites of magnetic iron nitrides on EG, the magnetic nanopartical in carbon nanotube and the monodisperse melamine formaldehyde resin (MF) microspheres coated with metallic Ag and Ni. Their properties of electromagnetic shielding effectiveness were further determined. The main results are summarized below.(1) The composites with nano-particles of magnetic iron nitrides dispersed on the nano-layers of expanded graphite (EG) were prepared by the impregnation of EG with ethanol solutions of metal acetates, followed by drying and reduction in H2. The iron nanopartical are treated in the NH3flow to obtain iron nitride, and the temperature must be at573-873K. With an increase of reaction temperature, iron first undergoes initial nitriding to Fe4N, and then a further nitridation occurs to form Fe2-3N and Fe2N. The spherical or square nano-particles of nitrided iron were found to be well spread on the layers of EG with particle sizes of mainly100-600nm. The addition of magnetic nano-particles of nitrided iron slightly improved the shielding effectiveness at low frequencies. The composite with30%FexN in EG reached the shielding effectiveness of68-110dB during the frequencies from300kHz to1.5GHz.(2) The composites with bamboo-like carbon nanotube encapsulated magnetic Fe, Co and Ni nano-particles were prepared by pyrolysis of melamine and metal chloride, followed by grinding, carbonization in N2and treament in6M HCl over night. The with nano-particles carbide with the size of20-200nm were found to be well coated by bamboo-like carbon nanotube with200-800nm、200-500nm and100-200nm in diameter. It was found that the bamboo-like carbon nanotube were easily dispersed in water for its hydrophilic and thus the sample for electromagnetic shielding was prepared by filtering. The composite exhibited5-35dB of shielding effectiveness at the frequencies from300kHz to1.5GHz with the areal-density of0.01g/cm2.(3) The monodisperse melamine formaldehyde resin (MF) microspheres (13m) was prepared by dispersion polymerization in water firstly. After pre-treatment of sensitization and activation, the microspheres coated with metallic nickel and silver were prapared with chemical liquid deposition method. The results showed that nickel plated under alkaline condition was of high quality than that of acidic. The DTA and TG results showed that the peak of pyrolysis of MF microspheres was about420, while the peak of pyrolysis of Ni coated and Ag coated MF microspheres were400and382respectively, which imply the enhanced catalytic process by coated metals. In order to simplified the process of chemical deposition, a new method was tested to utilize the active surface group. The MF microspheres were preadsorbed by Fe3+, Pd2+ Ag+and then reducted. The results show that the nanoparticles of metallic Pd and Ag was formed on the surface of MF microsphere, which indicated that possibility of chemical deposition of metals without sensitization and activation.【目录】新型碳基纳米电磁屏蔽基材的制备摘要3-5Abstract5-7目录8-10第一章 绪论10-221.1 电磁辐射的危害10-111.2 电磁场屏蔽机理11-171.2.1 关于远场平面波正入射屏蔽板的电磁屏蔽原理11-151.