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1、摘 要 第 I 页 碳纳米管碳纳米管/钡铁氧体复合材料的制备、表征与电磁参数初探钡铁氧体复合材料的制备、表征与电磁参数初探 摘摘 要要 在电磁波吸收材料领域，碳纳米管（CNTs）由于具有导电性以及作为一维纳米材料而具有的表面效应，小尺寸效应，量子尺寸效应，宏观量子隧道效应，因此对微波表现出较强的宽带吸收性能，已经成为国内外新型吸波材料的研究热点之一。然而 CNTs 是一种典型的电损耗型吸波剂，其具有相当大的复介电常数，但由于纯 CNTs 没有任何磁性，这就使得其阻抗匹配很差，电磁波在其表面的反射非常强烈，因此较差的阻抗匹配是应用 CNTs 作为吸波剂的瓶颈之一。现在许多研究工作都集中在如何对
2、CNTs 进行改性以改善其阻抗匹配上。 本文的研究目标为实现钡铁氧体（BaFe12O19）对多壁碳纳米管（MWNTs）的包覆而制备出 MWNTs-BaFe12O19纳米复合材料，利用导电性很差的磁性铁氧体去改善MWNTs 的磁学性能与导电性能，从而达到改善其阻抗匹配、增强吸波性能的目的。 本文首先在对 MWNTs 的水热氧化处理做了研究，因为 MWNTs 的氧化效果直接影响到后面 BaFe12O19对其的包覆效果。利用 XPS 对水热氧化 MWNTs 进行含氧量测定，发现其含氧量与反应温度 （T） 、 反应时间 （t） 以及混酸浓度 （c） 成正相关关系。 当 T=200，t=5h，c=70%
3、时，可以得到较为优化的水热氧化处理条件，此时 MWNTs 的含氧量为22.6%，较普通酸化氧化处理（6%左右）大大提高了 MWNTs 的氧化效果。利用 SEM对此条件下的水热氧化 MWNTs 进行形貌观察，发现其具有完整的形貌及结构，管长较长。 然后本文对水热合成纳米级BaFe12O19做了前期准备性研究。 本文在在140、 160、180三个温度下合成出了纳米级 M 型 BaFe12O19。利用 XRD 与 TEM 对其进行了物相与形貌表征，并发现 BaFe12O19纳米颗粒的粒径随着合成温度的升高而增大，180下晶粒发育的较为完善，粒径在 60nm 左右。利用同轴法对 180合成的样品进行
4、了复介电摘 要 第 II 页 常数与复磁导率的测定，发现水热合成的 BaFe12O19为良好的磁损耗型吸波剂，其介电性能与自由空间的性质类似而复磁导率虚部 ”较大（” max=0.5） ，对微波具有较高的磁损耗，可以用作对多壁碳纳米管进行磁学性能改善的改性体。 本文还通过在 BaFe12O19的水热合成反应中引入水热氧化 MWNTs 而成功的合成出了 BaFe12O19包覆 MWNTs 的 MWNTs- BaFe12O19纳米复合材料。利用 XRD 与 TEM 对其进行了物相与形貌表征，并发现 BaFe12O19纳米颗粒对 MWNTs 有着较好的包覆。利用同轴法对 180合成的样品进行了复介电
5、常数与复磁导率的测定，并发现其有着较为均衡的复介电常数与复磁导率，阻抗匹配得到了很大改善。与水热氧化 MWNTs（ max=170，“max=130，max=0.85，” max=0.25）相比，BaFe12O19对 MWNTs 的包覆有效降低了 MWNTs 的介电性质（ max=60-100，“max=45-55）并提高了其复磁导率虚部（” max=0.4） ， 增加了对电磁波的磁损耗。MWNTs 相相对含量的降低有利于降低复合材料的复介电常数数值，增大复磁导率虚部数值。 关键关键词：词：水热法，碳纳米管，碳纳米管改性，钡铁氧体，复介电常数，复磁导率，复合材料 ABSTRACT 第 III
6、页 Synthesis, Characterization and the Study of Electromagnetic Parameters of MWNTs-BaFe12O19 Composite ABSTRACT In the field of microwave absorbing material, carbon nanotubes (CNTs), as a novel microwave absorber, have been extensively studied, which show a strong microwave absorbing capability in a
7、 relatively wide band, due to their electric conductivity and the properties of surface effect, small size effect, quantum size effect and macroscopic quantum tunneling effect as one dimensional nano material. However, the poor impedance match is the bottle-neck of CNTs in the application as microwa
8、ve absorber, for it has a relatively large complex permittivity and pure CNTs has no magnetism, which cause a very strong reflection of microwave on the surface of CNTs absorber. Now a lot of study has focus on how to improve the impedance match of CNTs by modification. This paper is aim to synthesi
9、ze a novel MWNTs-BaFe12O19 composite with MWNTs coated by BaFe12O19 in nanometer scale, in which magnetic BaFe12O19 with a poor electric conductivity is utilized to improve the impedance match and finally strengthen the microwave-absorbing capability of MWNTs, by optimizing its magnetic property and
10、 electric conductivity. Firstly, this paper has studied the hydrothermal oxidizing treatment to MWNTs, for the oxidation of MWNTs directly affects the following coating performance. The content of oxygen element in hydrothermal oxidized MWNTs is measured by XPS, which is found to have a positive cor
11、relation with the reaction temperature (T), reaction time (t) and the concentration of mixed acid (c) in the hydrothermal oxidizing treatment. In a optimized condition of T=200, t=5h and c=70%, the hydrothermal oxidized MWNTs with an oxygen ABSTRACT 第 IV 页 element content of 22.6% can be gained, whi
12、ch is much more higher than the content of oxygen in regular concentrated acid oxidized MWNTs (around 6%). The micrograph of hydrothermal oxidized MWNTs are observed using SEM. It is found that the effect to MWNTs mechanic properties is supposed to be under control, for the tube structure and the tu
13、be length is maintained during the hydrothermal oxidizing process. Secondly, this paper has done a preparative study of synthesizing nanosized BaFe12O19 applying a hydrothermal process. Nanosized M type BaFe12O19 has been synthesized at 140, 160 and 180, respectively. The obtained barium ferrite pow
14、der is characterized using XRD and TEM. It is found that the grain size of BaFe12O19 increases as the synthesis temperature increases and the barium ferrite synthesized at 180 has a more perfect cystalinity with a grain size at 60nm. Complex permittivity and permeability are measured using a vector
15、network analyzer in a scan range of 2-18GHz. It is found that the barium ferrite so synthesized is a good magnetic loss type microwave absorber with a relatively high imaginary part of complex permeability (”max=0.5) and can be used to improve the magnetic properties of MWNTs in the following chapte
16、r. Lastly, this paper has successfully synthesized a kind of MWNTs-BaFe12O19 composite by bringing hydrothermal oxidized MWNTs in the hydrothermal synthesis reaction of BaFe12O19. The composite powder is characterized by XRD and TEM. It is found that the MWNTs are well coated by BaFe12O19. The complex permittivity and permeability of the composite is measured using a vector network analyzer in a scan range of 2-18GHz. It is found that the impedance match of MWNTs has
