碳纳米管在聚合物基吸波复合材料中的应用

碳纳米管作为一种新型电磁吸波剂,因其独特的物理和化学性能引起了人们极大的关注。本文简述了碳纳米管的吸波机理及吸波性能的表征,重点介绍了碳纳米管在聚合物吸波复合材料中的应用,如碳纳米管/树脂基复合材料、碳纳米管/导电高聚物复合材料、碳纳米管/橡胶基复合材料,最后展望了吸波材料的发展方向。     

静电纺丝纳米纤维在吸波材料中的应用

随着电子设备的迅速普及，电磁干扰和电磁污染问题随之而来，因此，高性能电磁波吸收材料的设计迫在眉睫。静电纺丝纳米纤维复合材料具有质量轻、柔性大、易加工、兼容性强等优势，有望实现吸波材料“薄、轻、宽、强”的技术要求。该文首先介绍了电磁波吸收材料的吸波原理，之后综述了静电纺丝技术在吸波材料中的研究进展，包括静电纺丝纳米纤维与金属及其氧化物、碳纳米材料与导电聚合物、过渡金属碳化物的复合以及在多层吸波材料中的应用，总结了不同种类复合材料的优缺点。最后，展望了静电纺丝纳米纤维在吸波领域的发展趋势以及应该关注的问题。     

Formation of Sn filled CNTs nanocomposite: Study of their magnetic,dielectric properties and enhanced microwave absorption performance at gigahertz frequencies

The Simplistic formation, advantageous configuration, non-colossal magnetoresistance and broadband absorption are important parameters for microwave absorbent materials. In this study, a core-shell nanocomposite comprising of Sn-filled carbon nanotubes (Sn/CNTs) was prepared by arc discharge method. The microstructure, morphology and surface composition of Sn/CNTs-based core-shell nanocomposites were characterized in detail. Sn/CNTs nanocomposite showed a magnetic signal due to the broken bonds and defects at interfaces in Sn/CNTs. The weak ferromagnetism was found to be helpful in improving magnetic permeability in the Sn/CNTs which confirms its role as a magnetic loss material under incident electromagnetic wave. Sn-filled CNTs revealed an appropriate value of dielectric constant, which plays an important role in impedance matching upon incident electromagnetic wave. The composite of Sn-CNTs and paraffin with a 50 wt % loading showed the lowest reflection loss (RL) of ?43.87 dB at 10 GHz, with a wide effective absorption band (RL ≤ ?10 dB) of 3 GHz in thickness of 2.3 mm. This enhanced performance is attributed to the combined effect of the conduction loss in one-dimensional core-shell architecture, the interfacial loss Sn-CNT interface, the magnetic loss due to defects-induced ferromagnetism in Sn shell, and in the carbon-containing atomic layers of CNTs.     

Electromagnetic wave absorbing properties of In–Sn/rGO composites supported by impurity defect

With the fast development of E-communication technology, effective electromagnetic wave absorbing materials are highly needed to address the growing electromagnetic pollution. Herein, Indium doped tin microsphere/reduced graphene oxide (In–Sn/rGO) composites with rich impurity defects were synthesized via the sol-gel and hydrothermal method. The excellent microwave absorption of In–Sn/rGO composites can be attributed to the modifications of electronics status and Fermi energy level after In doping. This can significantly increase the carrier mobility between In–Sn microspheres and rGO sheets to strike a superior interfacial polarization loss. As a result, the maximum absorptivity can reach ?51.16 dB at 8.73 GHz (thickness: 3.5 mm) with a lower filler loading of 10 wt%. Meanwhile, the synthesized In–Sn/rGO composites also exhibit an ultra-wide absorbing frequency range of 13.84 GHz (within the X band, Ku band, and most of the C band). This research provides a new idea for the synthesis of effective microwave absorbing material by introducing impurity defects.     

High electromagnetic wave absorbing performance of activated hollow carbon fibers decorated with CNTs and Ni nanoparticles

Activated hollow carbon fibers (ACHFs) decorated with carbon nanotubes (CNTs) and nickel nanoparticles (CNTs–Ni–ACHFs) were prepared by thermal reduction and chemical vapor deposition technique. Microwave reflection loss, permittivity and permeability of CNTs–Ni–ACHFs composites as novel electromagnetic wave absorbents were studied in the frequency range of 2–18 GHz. It was demonstrated that CNTs–Ni–ACHFs absorbents possessed the best microwave absorbing performances whose minimum reflection loss was −43.457 dB at 13.10 GHz with a thickness of 2.0 mm, which is much better than those of Ni–ACHFs and ACHFs samples. The dielectric polarizations and magnetic loss derived from the effect of the porous structures, Ni nanoparticles, and defects in the CNTs–Ni–ACHFs composites are playing an important role for the excellent microwave absorbing performances.     

Electromagnetic and microwave absorption properties of FeSiAl and flaky graphite filled Al2O3 composites with different FeSiAl particle size

The increasing electromagnetic interference problems have drawn much attention to microwave absorbing materials. To satisfy the needs of practical application, FeSiAl and flaky graphite filled Al₂O₃ composites were sintered by hot-pressing for microwave absorption application. The effect of FeSiAl particle size on the electromagnetic and microwave absorption properties was investigated in the X-band (8.2–12.4 GHz). The results show that the dielectric properties enhance significantly with increasing FeSiAl particle size, which is attributed to the increased interfacial polarization and conductance loss. As a result of the favorable impedance matching and appropriate electromagnetic attenuation, the reflection loss (RL) of the composites filled with 25–48 μm flaky FeSiAl achieves -15.2 dB at 10.6 GHz and the effective absorption bandwidth (RL < -10 dB) is 1.2 GHz in 10.0–11.2 GHz with a matching thickness of 1.0 mm. It indicates that FeSiAl and flaky graphite filled Al₂O₃ composites are potential candidates for thin-thickness microwave absorbing materials, and the microwave absorption properties can be enhanced by adjusting absorbent particle size.     

A low-cost lightweight microwave absorber: Silicon carbide synthesized from tissue

Recently, microwave absorbing materials have been widely used with the development of electromagnetic wave technology such as 5G communication. It is urgent to develop low-cost electromagnetic wave absorbing materials to meet the increasing civil market demand. Herein, we report a novel and simple strategy to synthesize lightweight silicon carbide microwave absorber by calcining tissue and glass microspheres at high temperature. The results show that higher synthesis temperature can improve the crystallinity of SiC, generate more whiskers and reduce the impurity content. This in turn increases the dielectric loss of the material. The products synthesized at 1600 °C have excellent microwave absorption properties. At the thickness of 1.3 mm, it achieves a reflection loss of ?32.5 dB and an effective absorption bandwidth of 4.1 GHz. This study broadens the way for the potential reuse of waste paper and glass, and provides a useful reference for the preparation of low-cost microwave absorbing materials.     

碳纳米管材料低频电磁参数及吸波产热特性

微波的热利用技术促进了吸波材料的应用研究。碳纳米管（CNTs）是近年来新兴的强吸波材料，具有密度小、比表面积大、量子尺寸效应的特点。对碳纳米管吸波材料的复介电常数和复磁导率随碳纳米管含量的变化进行探究。在此基础上，以石蜡油为蓄热介质探究了碳纳米管材料在微波辐照下吸波产热特性。同轴传输法适用于小型样品的测量，具有误差小的优点，故采用此种方法作为测量电磁参数手段。对碳纳米管电磁参数测量实验结果表明，碳纳米管吸波材料在低频下对于微波能的损耗兼具电损耗和磁损耗。对碳纳米管吸波产热特性实验结果表明，碳纳米管是一种强吸波材料。     

吸波材料研究进展

由于电磁波在军事、工业及民用产品中的应用迅速增加,电磁干扰已经成为一种新的社会污染,电磁辐射也对人体健康和各种电子设备造成巨大危害。因此具有吸收电磁波功能的材料已成为近年研究和应用的热点。随着隐身与反隐身技术的发展、电真空器件对大功率的需求以及电子通讯的广泛普及,电磁波吸收材料当前功能材料领域的研究热点之一。本文简述了吸波材料吸波物理机理,吸波特性,吸波材料分类以及吸波材料的应用领域。并最终结合实际指出多晶金属纤维、SiC基陶瓷和C/C复合材料是目前性能最佳、应用前景最好的电磁波吸收材料。     

Recent advances in the development OF Fe3O4-BASED microwave absorbing materials

Electromagnetic pollution has become a serious concern with the immense utilization of wireless information technologies and this has aroused huge interest in the area of microwave absorption. To solve this issue, fabrication of advanced, novel and superior microwave absorbing materials (MAM) with high electromagnetic wave absorption, wide absorption bandwidth, lightweight and cost-efficient are highly required. To date, magnetite (Fe₃O₄) is being thoroughly investigated as MAM, due to its exceptional dual electromagnetic properties (permittivity and permeability), proper saturation magnetization and high Curie temperature. However, large density and impedance mismatch are some of the limiting factors that hinder its microwave absorption performance (MAP). To circumvent these challenges, reduction of size to the nanoscale, fabrication of hierarchical nanostructures and/or conjugation with other lossy materials have been extensively explored as viable solutions to optimize the MAP of Fe₃O₄. In this review, the progressive research in the fabrication of Fe₃O₄ based nanocomposites as MAM is discussed. The factors influencing the MAP of these absorptive materials are likewise discussed in detail. Conclusively, some challenges, limitations, and future prospects in the development of Fe₃O₄ based MAM are put forth.     

Flexible SiC-CNTs hybrid fiber mats for tunable and broadband microwave absorption

Flexible microwave absorbers with high stability are in increasing demand for the applications under harsh conditions. SiC as a functional ceramic material has the feature of high environmental tolerance and adjustable electromagnetic (EM) absorbing properties, making them suitable to be applied for harsh environments. However, the electrical property of SiC requires to be further enhanced to obtain qualified EM absorbing performance. In this work, multiwall carbon nanotubes (CNTs) were introduced to SiC to enhance the electrical properties. Flexible two-dimensional (2D) CNTs loaded SiC fiber mats were prepared as EM absorbers via electrospinning and polymer-derived-ceramic (PDC) methods. The CNTs inside the fibers can form conductive networks and act as reinforcement to ensure high flexibility and enhance the microwave absorption properties of SiC mats. Thus, a reflection loss of ?61 dB and an effective absorption band (EAB) of 2.9 GHz were obtained. More importantly, the EM absorption can be adjusted by tuning the content of CNTs and the EAB can cover the entire X-band by adjusting the material thickness. The work provided a facile strategy to fabricated flexible 2D ceramic mats with high environmental stability and tunable electrical properties, which may shed light on the production of reliable EM absorber for broadband EM absorption applications.     

新型肿瘤热疗用温敏凝胶的制备与表征

采用化学共沉淀结合水热处理的方法,控制一定的反应条件,制备了碳纳米管/四氧化三铁(CNTs/Fe3O4)热种子材料,然后以壳聚糖温敏凝胶为载体,将CNTs/Fe3O4复合材料分散到凝胶中,制备出微波靶向热疗用碳纳米管-四氧化三铁-壳聚糖温敏凝胶。碳纳米管复合热种子材料在凝胶体系中分布均匀,与载体不发生化学反应,25 W下辐照10 min,当CNTs/Fe3O4复合材料的质量浓度为20 mg/mL时,体系温度在初始温度基础上升高了38.7℃,在微波场中具有良好的产热能力,可以满足微波热疗的要求。     

Recent advances and prospect of cobalt based microwave absorbing materials

With the advances and extensive application of electromagnetic (EM) waves in electronic and communication devices. EM pollution has been identified as a threat to human health whereby EM interference also affects the proper functioning of electronic devices. Therefore, the fabrication of novel microwave absorbing materials (MAMs) has become important to mitigate EM pollution and protect humans as well as other nearby electronic devices. The use of sole cobalt as MAM has gained significant attention due to its EM properties and suitable saturation magnetization. However, large density, eddy current loss, and poor corrosion resistance are some of the factors that hinder its practical application as an ideal MAMs. In this paper, recent advances towards overcoming these challenges have been reviewed. In particular, ways of regulating the morphology and optimizing the EM properties of cobalt-based MAM. Furthermore, fabrication of high-performance lightweight absorbers with hierarchical structures and formation of cobalt-based hybrid MAM with other lossy materials are discussed. Several factors affecting the microwave absorption performance of cobalt-based MAM are further discussed. Finally, the present limitations as well as prospects are put forward to give a new insight into the design of improved cobalt-based MAM.     

Microwave absorption performance of nitrile butadiene rubber/ethylene propylene diene monomer rubber filled with multiwalled carbon nanotubes

In recent times, there is an increasing need for effective control of electromagnetic pollution, which can avoid excessive radiation effects on the human body. Microwave absorption materials are attracting wide research interests to reduce electromagnetic pollution due to the rapid development of electronic equipment. In this study, Nitrile butadiene rubber (NBR)/ethylene propylene diene monomer rubber (EPDM) were mixed with multiwalled carbon nanotubes (MWCNT) to prepare microwave absorbing materials. The distribution of fillers, AC conductivity, complex permittivity, and microwave absorption performance of the composites were systematically investigated. It found that the AC conductivity, both real and imaginary parts of the permittivity were significantly improved in the composite with the increasing ratio of MWCNT contents. The NBR/EPDM/MWCNT composites with eight parts per hundred concerning with rubber (phr) MWCNT had a minimum reflection loss (RLmin) of −48.1 dB at the optimum thickness of 2.07 mm. Importantly, the adding sequence of MWCNT and plasticizer dioctyl phthalate (DOP) to the rubber matrix is found to play an important role in determining the distribution of fillers and the structure of polymer blends. The composite with plasticizer added before MWCNT exhibited a better impedance matching and as a result, achieved a good microwave absorption performance.     

A review on electrospinning nanofibers in the field of microwave absorption

As important functional materials for absorbing and attenuating incident electromagnetic waves, microwave absorption (MA) materials have found a wide range of applications in civil and military fields. In addition to the study of the compositions, the structural design of the MA materials is also a research hotspot in the field. Among the various structures, the one-dimensional (1D) structure has drawn wide attention because of the unique shape anisotropy and spatial confinement effect. Electrospinning technology has become one of the main ways to prepare continuous 1D micro-nano fibers due to the advantages of many types of spinnable materials, low spinning cost, and high controllability of process parameters. This review involves an introduction and a classification of the research progresses achieved in electrospinning technology concerning MA nanofibers from the perspective of compositions, as well as the list of their minimum reflection loss (RL_min) and effective absorption bandwidth (EAB).     

Recent progress in synthesis,growth mechanisms,and electromagnetic wave absorption properties of silicon carbide nanowires

With the research and development of nanomaterials, one-dimensional (1D) nanowire structures have received a lot of attention due to their unique physical and chemical properties. Among them, silicon carbide nanowires (SiC NWs) have low density, excellent oxidation resistance, dielectric properties, and electromagnetic (EM) wave absorption properties, which can well meet the development needs of civilian equipment and military weaponry. SiC NWs have outstanding research and application potential in the field of EM wave absorption. However, comprehensive summaries of SiC NWs have not been available so far. Based on this, this paper reviews the research progress of SiC NWs microwave absorbing materials, various micro-morphologies of SiC NWs are introduced in detail, as well as diverse preparation strategies and multiple growth mechanisms are also stated. Ultimately, recent advances in research progress of SiC NWs and their composites in EM wave absorption are elaborated, along with the future research directions of SiC NWs in the field of EM wave absorption.     

Microwave synthesis of worm-like SiC nanowires for thin electromagnetic wave absorbing materials

Thin thickness is always the pursuit of excellent electromagnetic wave absorbing materials. Herein, SiC nanowires with worm-like morphology were synthesized by microwave heating the mixture of expanded graphite and silica. The worm-like SiC nanowires exhibit an excellent microwave absorption ability at a thin thickness. With the filling ratio of SiC nanowires increases in the matrix, the dielectric loss and microwave absorbing ability are significantly enhanced; meanwhile the number of absorption peaks is gradually increased, and the absorption peaks also move toward a thinner thickness. When the nanowires filling ratio was 40?wt%, the minimum reflection loss reached down to ?35.2?dB and the effective absorption (RL?<??10?dB) bandwidth was 1.8?GHz?at a thickness of 1.3?mm. The possible growth mechanism of the worm-like SiC nanowires is that the intermediate reaction gas phases, SiO and CO, were confined in the relatively independent tiny pores of expanded graphite. This resulting in an excessive local gas phase pressure, which causes the nanowire growth direction changes randomly.     

Development of Low Density,Heat Resistant and Broadband Microwave Absorbing Materials (MAMs) for Stealth Applications

The development of low density and broadband microwave absorbers are the need of the hour to cater for the needs of all military platforms for stealth technology. The low density and broadband properties can be inculcated in microwave absorbers using dielectric lossy materials (e.g. carbon fibres, carbon nanotubes, carbon black, fullerene, graphite, graphene and silicon carbide fibre). Therefore, we designed low density and heat resistant microwave absorbing materials (MAMs) using a novel approach of ceramic fibre board manufacturing technology. The microwave absorbing composites were prepared with varying percentage of milled carbon fibres, discontinuous aluminosilicate fibres and silicone resin as the matrix. The physico-mechanical properties of microwave absorbing composites were determined. Reflection loss of microwave absorbing composites was measured in the frequency range 2–18 GHz by unique single horn interferometry technique. The electromagnetic properties were measured in X-band using free space measurement system. Based on these properties the effect of thickness on the microwave absorbing properties in X-band was simulated The effect of weight % variation of milled carbon fibres on the microwave absorbing properties of composites have been studied in the frequency range 2–18 GHz.     

A review on the processing–morphology–property relationship in biodegradable polymer composites containing carbon nanotubes and nanofibers

Carbon nanofillers containing biodegradable polymer composites have become an emerging frontier in materials science and engineering because of their potential as environmentally friendly materials in multiple applications, from load-bearing to advanced packaging to biomedical applications. Herein, we present the effect of processing parameters on the final morphology and the resulting properties of the biodegradable polymer composites containing carbon nanotubes (CNTs) or carbon nanofibers (CNFs). Various strategies can be employed to develop such composites; however, the type of morphology, which results during processing, significantly affects the final properties of the obtained composites. Therefore, various processing strategies such as melt-blending, additive manufacturing, and electrospinning are critically reviewed, together with the potential applications in load-bearing, tissue engineering, electromagnetic shielding, gas sensing, and packaging. Finally, we discuss the existing challenges and future directions in designing CNTs/CNFs containing biodegradable polymer composites with desired properties.     

活化碳纳米管的孔结构及微波吸收性能的研究

以KOH为活化剂对碳纳米管进行活化处理，将碳纳米管的比表面积从24．5m^2/g提高到360．1m^2／g，孔容从0．051cc／g提高到0．572cc/g。对碳纳米管的微波吸收性能进行测试，研究结果发现，未活化碳纳米管在9．91～14．16GHz范围内对电磁波的反射率低于-5dB，最大衰减峰值为8．57dB；活化碳纳米管在5．37～18GHz范围内对电磁波的反射率低于一5dB，在6．48～10．88GHz范围内对电磁波的反射率低于一10dB，最大的衰减峰值达到22．58dB。通过比较得出，活化能够有效地提高碳纳米管的微波吸收性能。产生的原因是由于活化碳纳米管具有大的比表面积和丰富的孔结构，电磁波在这些孔结构中不断的被反射、漫射而逐渐衰减。