铁基纳米复合物的电磁波吸收性能的研究

IMR OpenIR

	铁基纳米复合物的电磁波吸收性能的研究
	韩拯
学位类型	硕士
导师	张志东 ; 李达
	2010
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料物理与化学
关键词	纳米复合物电磁波吸收混合理论
摘要	"本文研究了具有铁磁内核/介电外壳微观结构的铁基纳米复合物在2~18 GHz频段的电磁波吸收性能。基于金属板衬底模型，主要采用表面自然氧化法、介电碳壳层包裹法、稀土元素掺杂法以及逾渗效应系统地研究纳米颗粒/胶囊的微结构和磁电耦合对其电磁波吸收性能的影响。对决定纳米材料微波吸收吸收性能的d，e′，e″，m′，m″以及体积分数六个因素进行了初步研究。本文从Maxwell方程求解同轴椭球颗粒混合物的有效介电常数入手，分析并说明了电磁波在多相混合物中衰减吸收的决定因素，通过实验手段为寻找更优良的纳米复合物微波吸收剂做了试探性的研究。并对混合理论的有效即介电常数和磁导率的计算做了简要的文献综述，初步研究了铁基纳米复合物在微波吸收方面的应用。对掺杂少量Mn的FeMn合金靶材进行电弧蒸发，利用铁锰不同凝固点得到了壳层中含锰较多的纳米颗粒，再经过表面氧化得到了Fe(Mn)/ferrite纳米胶囊。其中，由Fe99Mn1靶材制得的Fe(Mn)/ferrite纳米胶囊在9~18 GHz之间有小于-10 dB的吸收，其热稳定性良好，230℃以下结构稳定，是性能良好的微波吸收剂。采用乙醇气氛下电弧裂解制备得到碳包覆铁钴纳米晶的纳米胶囊，其微波吸收性能非常优秀，在2~18 GHz范围内，可以通过选择任意厚度来实现任意波段的反射损失小于-20 dB的微波吸收。我们还研究了掺杂稀土的铁纳米颗粒的微波吸收。在铁中掺杂少量铽之后，体系的磁导率和介电常数发生变化。掺杂铽之后的铁纳米颗粒在最佳吸收区域有一定的红移现象。此外，我们对铁钴纳米颗粒填充的碳纳米管与不同质量分数的石蜡进行混合，测量了它们的电磁参数。计算发现在逾渗阈值(34 wt %)附近，体系有最大吸收。每一厚度对应的吸收峰均得到不同程度的增强，并且峰位有所偏移。在11 GHz，8 mm处最强吸收达到-37 dB。也为寻找更好的微波吸收剂提供了一个新的途径。"
其他摘要	"This paper starts with the solution of the Maxwell equation of the confocal ellipsoids dispersed in dielectic matrix, and then gives the main reseaons which determine the attenuation of the incident electromagnetic waves of an absorbant. We have performed experiments to tentatively study the way of finding better nano-absorbants. Also we have introduced briefly the mixture theory and literatures on calculating the effective permittivity and permaeability of muli-phase mixtures, by which we performed fundamental study of the Fe-based nanocomposites and their microwave absorption applications. By arc-discharging FeMn alloy, which contains very little Mn (1-10 a.t.%), Fe(Mn)/ferrite nanocapsules with a natural oxidize ferrite shell and Fe(Mn) core have been synthesized. The Fe(Mn)/ferrite nanocapsules made from Fe99Mn1 master alloy show reflection loss exceeding -10 dB in the 9-18 GHz range. It has a good thermal stability under 230℃, which makes it good candidates of microwave absorbent. Carbon coated FeCo-nanocrystalline nanocapsules have been synthesized by arc-discharging FeCo master alloy in the ethanol atmosphere. The Fe55Co45 nanocapsules are found to exhibit excellent absorption properties, which show reflection loss exceeding -20 dB in the whole 2-18 GHz by choosing an appropriate layer thickness between 2-10 mm. Tb-doped and undoped Fe nanoparticles have been investigated in the microwave absorption properties in the 2-18 GHz range. The particle size of Fe nanoparticle is found to be refined with Tb-doping. After doping with Tb, there is a red-shift in the absorption frequency and the best absorption area shifts to thinner thickness. Microwave absorption was also investigated in the FeCo/CNTs-paraffin samples with different mass ratios. Percolation threshold of the FeCo/CNTs fillers in paraffin is determined to be 34 wt % by AC conductivity measurements. Reflection losses of the FeCo/CNTs-paraffin composites were found to be strongly enhanced when the mass ratio of the FeCo/CNTs fillers approaches to the percolation threshold. RL values exceeding -10 dB are obtained in the 30 wt % sample in a frequency range from 8 to 18 GHz, for a layer thickness from 5 to 10 mm. Ulitzing the percolation effect can be an effective way of finding better nano-absorbants in microwave frequency range."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64209
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	韩拯. 铁基纳米复合物的电磁波吸收性能的研究[D]. 北京. 中国科学院金属研究所,2010.