电磁防护材料专题

题目：新型吸波碳纤维的研究进展 作者：谢炜、程海峰、楚增勇、陈朝辉 摘要：碳纤维吸波材料是一类多功能复合材料，具有承载和减小雷达反射截面的双重功能，是一种非常有发展前途的吸波材料。分别详细介绍了螺旋碳纤维、改性碳纤维、异形碳纤维和纳米碳纤维等新型碳纤维的制备、吸波机理及吸波性能，并对其最新研究现状进行了评述。     

纳米碳纤维烟幕红外消光性能研究

利用烟幕箱测试分析了纳米碳纤维作为烟幕干扰材料的红外消光性能.在容积为20 m3烟幕箱中喷洒20g不同尺寸分布的纳米碳纤维,通过测量激光透过率和烟幕浓度,得到纳米碳纤维对1.06μm和10.6μm两种波长的激光最大质量消光系数分别为2.1304m2·g-1和1.2362m2·g-1;利用红外热像仪通过对靶标图像的观测记录,表明纳米碳纤维烟幕在8μm～12μm波段也具有显著的红外图像遮蔽能力.     

纳米碳材料场发射特性研究进展

碳纳米结构材料如纳米碳管、纳米金刚石、纳米碳纤维都具有良好的场电子发射性能,它们低的发射阈值和高发射电流密度极具应用潜力。该文对这几种碳纳米结构材料的场发射特性的研究进展进行了评述,着重讨论了影响场发射材料的性能指标,并讨论了研究中存在的问题。     

纳米碳纤维作锂离子电池负极材料的嵌锂性能

用化学气相沉积法(CVD)制备了纳米碳纤维,并通过2800℃高温处理得到石墨化纳米碳纤维。采用XRD、SEM和TEM对所制的材料进行微结构分析,并考察其作为锂离子电池负极材料的嵌锂性能。结果表明:纳米碳纤维初次嵌锂容量可达到533mA·h/g,25次循环后可逆容量保持在274mA·h/g,循环效率超过99%;经过石墨化处理以后,材料初次可逆容量达到311mA·h/g,首次循环效率从55%提高到78%,25次循环后可逆容量的保持率为99%以上。     

纳米聚苯胺-镀镍碳纤维复合材料屏蔽/吸波性能

以T300碳纤维经超声波化学镀镍制成的导电镀镍碳纤维作为电磁屏蔽体,以在丁醇/水溶液体系中采用界面聚合法制备的纳米结构聚苯胺为吸波体,与环氧乙烯基酯树脂复合,制得兼具电磁屏蔽与吸波功能的电磁防护碳纤维复合材料,研究了它的力学性能、电磁屏蔽性能、吸波性能、微观形貌等。结果表明:控制碳纤维化学镀镍的施镀时间、纳米结构聚苯胺的用量,可得到具有良好力学性能、电磁屏蔽性能、吸波性能的电磁防护碳纤维复合材料。当化学镀镍的施镀时间为20 min、纳米结构聚苯胺的用量为3.5wt%时,复合材料的拉伸强度为894.3 MPa,屏蔽效能为43~72 d B(10 k Hz^4 GHz),在10.77~18 GHz范围内,反射率≤-10 d B,峰值-23.2 d B(13.62 GHz)。     

碳纳米材料在导热聚合物复合材料中的应用

介绍了三种具有较高热导率的碳纳米材料:碳纳米管、纳米石墨片及纳米碳纤维的结构与导热性能,概述了三种碳纳米材料在改善聚合物复合材料导热性能方面的应用,重点分析了碳纳米材料的种类、用量、表面改性方法及复合材料的制备方法对聚合物复合材料热导率的影响,并对含碳纳米材料的导热聚合物复合材料未来的发展方向进行了分析与展望。     

纳米半导体器件及其应用

本文介绍了纳米半导体器件及其应用，如纳米二极管、纳米晶体管和纳米集成电路等。     

跨世纪新学科—纳米电子学

本世纪最后十年，一个崭新的学科领域－纳米科学技术诞生了，这一新领域为多科性交叉学科，包括纳米电子学、纳米材料科学、纳米生物学、纳米机械学、纳米显微学和纳米制造等。本文讨论联新颖的纳米电子学的提出、设想、内容、现状和前景。纳米科学技术的最终目标是直接操纵单个原子或分子，制造具有特定功能的产品，从而将惊人地改变着人类的生产和生活模式。     

用于热传感的形状记忆合金

加拿大因特格兰公司在加拿大政府支持下正在进行一项用纳米硬涂层提高歼击机上复杂设备使用寿命的计划。因特格兰公司曾开发过一种Nanovate—NV，这是一种热膨胀系数小，用于保护碳纤维增强塑料（CFRP）复杂设备的硬纳米金属表面涂层。它提高了设备的耐用性、降低了维修和更换成本。新的涂层的硬度是Invar合金的5倍，它高于工具钢的硬度，而且具有相当高的韧性（公司对涂层成分尚未公布）。     

不同条件下乙炔裂解产物的电镜分析

实验发现乙炔在氢气与氨气气氛中催化裂解产物完全不同，反应温度973K，氦气气氛下，乙炔在LaFeO3纳米催化剂上裂解为碳纳米管，平均管径为30nm；在氢气气氛中乙炔主要在热电偶上裂解为碳纤维，直径平均为600nm左右。实验在没有催化剂存在时，对乙炔直接热裂解进行了研究．结果表明在没有氢气条件下，乙炔很少积碳；随氢气量的增加乙炔在热电偶上的积碳量逐渐增加，沉积的碳均成纤维状结构，平均直径随氢气量的增加逐渐增大。在1073K氢气气氛下，乙炔裂解产物中发现了大量螺旋状结构的碳纤维，其直径为80～200nm，长度一般在几um～十几um。     

通过控制原子实现纳米图形制作研究

基于激光冷却和捕获原子的原理,初步探讨了利用原子进行纳米量级图形制作的基本原理和实验研究。研究结果表明,此可实现分辨率高达几个纳米大小的超微细图形制作,制作效率极高。     

退火温度对碳注入外延硅蓝光发射特性的影响

获得了不同退火温度注碳外延硅的蓝光发射谱,分析了退火温度对其蓝光发射特性的影响,发现退火温度为 1 000℃样品具有最强的发射强度。认为经碳注入所引入的杂质C = O 复合体是发光的重要因素;经碳注入氮气氛中退火及电化学腐蚀处理形成纳米硅镶嵌结构,因量子限制效应–表面复合效应而发光。     

正交排布碳纤维材料的电磁防护性能研究

分别研究微量改性碳纤维/环氧树脂复合微波电磁防护材料不同排布的电磁防护性能。简要讨论了电磁防护机理以及影响电磁防护效果的因素。实验结果表明:改性碳纤维复合材料电磁防护性能与改性碳纤维的排布方式以及纤维含量密切相关;正交排布试样的电磁防护效果总体上优于原纤维布排布试样;原纤维含量为3000根/束,间距1cm时的正交排布方式获得-30dB以下的反射衰减。     

高温热解法制备碳螺线管的扫描电子显微镜研究

采用高温热解法,以乙炔为碳源,在金属催化剂和促进剂的作用下,大量制备碳螺线管.利用扫描电子显微镜对二重螺旋状碳纤维的形成和碳粒子纳米结构进行了观察研究,探讨螺旋生长机制.螺旋状生长的推动力是催化剂中间体的晶面的各向异性。本文还利用扫描电子显微镜表征其拉弹性。     

镀镍中间相沥青基碳纤维的吸波性能

为了改善中间相沥青基碳纤维的磁性能和吸波性能,通过化学镀工艺在中间相沥青基碳纤维表面均匀包覆了金属镍,研究了镀镍中间相沥青基碳纤维的磁性能和微波吸收性能。以镀镍中间相沥青基碳纤维作为吸收剂,环氧树脂为基体制备了单层吸波涂层,涂层的厚度为1.02 mm时,吸波涂层在15.4~18 GHz反射率R小于-10 dB,最大吸收峰在18 GHz,反射率R为-20.74 dB。探讨了镀镍中间相沥青基碳纤维的吸收机理,在含镀镍中间相沥青基碳纤维的吸波涂层中,镀镍中间相沥青基碳纤维作为偶极子在电磁场的作用下,会产生耗散电流,在周围基体作用下,耗散电流被衰减,从而电磁波能量转换为其它形式的能量,主要为热能,这是镀镍中间相沥青基碳纤维偶极子吸波涂层的主要吸波机理。     

螺旋形碳纤维结构吸波材料的制备及性能研究

用基板法以乙炔为碳源,镍板为催化剂,PCI,为助催化剂,通过化学气相沉积制备了螺旋形碳纤维手性吸收剂,并研究了其在2～18GHz的微波电磁特性：具有较高的介电损耗,电磁参数随频率的增大有减小的趋势,有利于实现宽频吸波。以螺旋形碳纤维作为吸收剂制备了Nomex蜂窝夹芯结构吸波材料,复合材料的厚度为9．5mm时,在3．76～18GHz反射率R小于-10dB,反射率小于-10dB的频宽为14．24GHz;最大吸收峰在10．4GHz,反射率R为-21．62dB。探讨了螺旋形碳纤维的吸波机理,螺旋形碳纤维是一种非常有发展前景的手性吸收剂和吸波材料。     

Properties of Carbon Nanotube Fibers Spun from DNA‐Stabilized Dispersions

The fabrication of single‐walled carbon nanotube (CNT) fibers containing (salmon) DNA has been demonstrated. The DNA material has been found to be adequate for dispersing relatively large concentrations (up to 1 % by weight) of carbon nanotubes. These dispersions are better suited for fiber spinning than previously studied dispersions based on conventional surfactants, such as sodium dodecyl sulfate (SDS). The DNA‐containing fibers were less conductive than the fibers based on SDS, but they were significantly stronger. Considerably increased conductivity was obtained by thermally annealing the CNT/DNA fibers, a process accompanied by a loss in mechanical strength. Smaller improvements in conductivity could be introduced by annealing the carbon nanotubes before fiber production, with no alteration of the fiber mechanical properties. Those CNT/DNA fibers that were mechanically strong and conductive also exhibited good electrochemical behavior and useful capacitance values (up to 7.2 F g^–1).     

Electromagnetic shielding of nylon-66 composites applied to laser modules

Electromagnetic shielding of nylon-66 composites applied to laser modules was studied experimentally and theoretically. The effects of conductive carbon fiber length and weight percentage upon the shielding effectiveness (SE) of nylon composites were investigated. The SE of long carbon fiber filled nylon-66 composites was found to be higher than short carbon fiber composites under the same weight percentage of carbon fibers. In addition, higher electromagnetic shielding was obtained for the composite with higher carbon fibers contents at the same length. The SE of conductive carbon fiber filled nylon-66 composites was measured to be 42 dB at a low frequency of 30 MHz and 50 dB at a high frequency of 1 GHz. The SE predicted by theoretical models and measured by experiments were in good agreement for filled nylon-66 composites with different length fiber.     

High‐Ampacity Power Cables of Tightly‐Packed and Aligned Carbon Nanotubes

The current‐carrying capacity (CCC), or ampacity, of highly‐conductive, light, and strong carbon nanotube (CNT) fibers is characterized by measuring their failure current density (FCD) and continuous current rating (CCR) values. It is shown, both experimentally and theoretically, that the CCC of these fibers is determined by the balance between current‐induced Joule heating and heat exchange with the surroundings. The measured FCD values of the fibers range from 10⁷ to 10⁹ A m^?2 and are generally higher than the previously reported values for aligned buckypapers, carbon fibers, and CNT fibers. To the authors’ knowledge, this is the first time the CCR for a CNT fiber has been reported. The specific CCC value (i.e., normalized by the linear mass density) of these CNT fibers are demonstrated to be higher than those of copper.     

Electrical Properties of Carbon Nanotube Based Fibers and Their Future Use in Electrical Wiring

The production of continuous fibers made purely of carbon nanotubes has paved the way for new macro‐scale applications which utilize the superior properties of individual carbon nanotubes. These wire‐like macroscopic assemblies of carbon nanotubes were recognized to have a potential to be used in electrical wiring. Carbon nanotube wiring may be extremely light and mechanically stronger and more efficient in transferring high frequency signals than any conventional conducting material, being cost‐effective simultaneously. However, transfer of the unique properties of individual CNTs to the macro‐scale proves to be quite challenging. This Feature Article gives an overview of the potential of using carbon nanotube fibers as next generation wiring, state of the art developments in this field, and goals to be achieved before carbon nanotubes may be transformed into competitive products.