石墨烯/碳纳米管复合材料的微波吸收性能研究

石墨烯和碳纳米管都是新型纳米尺寸碳材料,具有极大的比表面积、良好的导电性以及优秀的机械性能等特性。通过微波膨化法在石墨烯(寡层石墨)表面空隙结构内生长了碳纳米管,制备出石墨烯/碳纳米管复合材料,碳纳米管不仅可以发挥连接石墨烯层片结构的作用,还可以与石墨烯共同发挥协同吸波效应;同时生长碳纳米管所添加的催化剂在微波状态下分解为纳米磁性颗粒,提高整体复合材料的吸波性能。通过采用SEM、EDX、XRD等对材料的形貌、化学成分进行表征,并用矢量网络分析仪测试了材料在2~18GHz频带内的复介电常数和复磁导率,利用计算机模拟出不同厚度的微波衰减性能。结果表明,材料的电磁损耗机制由电介质损耗、磁损耗共同构成,微波吸收峰随着材料厚度的增加向低频移动,当厚度为2.5mm时,在14.4GHz时最大损耗值为-28dB,并且在频带12.4~17.7GHz的范围内达到-10dB的吸收。     

热酸氧化及镀镍对碳纳米管吸波性能的影响

利用浓硝酸沸腾状态下氧化性强的特点,采用冷凝回流的方法对碳纳米管进行纯化处理,并采用化学镀的方法在碳纳米管表面镀上了一层均匀的金属镍.测量了镀镍及原始碳纳米管的介电常数、磁导率以及R～f曲线.研究了浓硝酸氧化及镀镍对碳纳米管复合材料吸波性能的影响.结果表明,与原始碳纳米管相比,镀镍后碳纳米管复合材料的吸波峰向低频移动,出现在6.92GHz,峰值为-10.46dB,吸波频带宽度为2.46GHz(R＜-10dB)和5.41GHz(R＜-6dB).碳纳米管表面镀镍后吸收峰值虽然变小,但吸收峰有宽化的趋势,这种趋势有利于制造宽频吸波材料.     

CIPs@Mn0.8Zn0.2Fe2O4-CNTs复合材料低频吸波性能研究

随着5G无线通信与低频雷达侦察技术的飞速发展,低频电磁波辐射已成为当代的严重问题。目前,中高频段吸波材料的研究已趋于成熟,而设计低频段吸波材料仍面临巨大的挑战,亟待研究者们解决。基于四分之一波长相消机制,本研究设计了0.5～3 GHz低频段复合吸波材料。采用简单的一步水热法,诱导铁氧体在羰基铁粉与碳纳米管表面生长,制备出CIPs@Mn_0.8Zn_0.2Fe₂O₄-CNTs三元复合材料,对比研究了碳纳米管含量对材料吸收峰频率的影响。实验结果表明,引入碳纳米管,一方面为材料带来了界面极化、偶极极化等额外的损耗机制,增加了材料的衰减系数;另一方面基于四分之一波长相消机制,高介电与高磁导率的耦合,使材料在低频段获得良好的阻抗匹配。最终,在4 mm厚度下,样品分别在2.11与1.75 GHz处,获得了–40.8与–32.1 dB的反射损耗,–10 dB带宽分别为1.70～2.70 GHz和1.40～2.20 GHz。该复合材料制备工艺简单,低频吸收性能良好,具有很大的应用潜力,为开发更有效的低频吸波材料提供了新...     

螺旋型非晶态碳纳米管/双马来酰亚胺树脂(HACNT/BMI)复合材料的制备及吸波机理

新型电磁波吸收材料是国防科技中的研究热点和重点,碳材料作为一种轻质吸波材料受到研究者们的广泛重视.本研究利用浮动催化化学气相沉积法制备螺旋非晶碳纳米管,以螺旋非晶碳纳米管作为吸波剂,双马来酰亚胺树脂作为基体制备了螺旋非晶碳纳米管/双马来酰亚胺树脂吸波复合材料.采用扫描电子显微镜、透射电子显微镜、X射线衍射仪和拉曼光谱仪等设备对样品进行微观形貌和结构表征,通过矢量网络分析仪测试其电磁参数.实验结果表明,吸波剂含量的增加增强了螺旋非晶碳纳米管/双马来酰亚胺树脂复合材料的吸波性能,其最大吸收峰值可达-18.35 dB,最大吸波频宽(<-10 dB)为2.56 GHz(9.52～12.08 GHz),反射损耗超过97％,且吸收峰向低频方向移动.螺旋非晶碳纳米管因其特殊的螺旋型结构极大地增加了电磁波反射概率和散射波程,增大了入射电磁波能量损耗.     

多壁碳纳米管复合材料在8 mm波段的吸波性能

将相同厚度不同碳纳米管含量, 以及不同厚度相同碳纳米管含量的多壁碳纳米管加入玻璃纤维增强复合材料中, 并研究了其在26. 5～40. 0 GHz 频段的吸波性能。结果发现, 多壁碳纳米管具有吸波性能, 而且吸波性能随着多壁碳纳米管含量的增加而提高。多壁碳纳米管/ 玻璃纤维/ 环氧树脂复合材料层板在26. 5～40. 0 GHz频段表现出较好的吸收效果, 其吸波性在于碳纳米管本身具有吸波性能, 此外还与吸波材料的谐振吸波原理有关。通过对该复合材料的电磁参数的测定并计算, 证明实验结果与吸波原理相符合。      

碳纳米管/镍铁氧体涂层的吸波性能及吸波机理

采用柠檬酸络合物形成的溶胶凝胶制备了镍铁氧体,并将所得镍铁氧体与碳纳米管混合均匀,得到不同碳纳米管质量分数的复合材料。采用微波矢量网络分析仪测量了复合材料的电磁参数,根据电磁参数研究了1mm厚涂层在2~18GHz频段的微波反射率。结果表明:复合材料的吸波性能明显优于单纯的镍铁氧体材料,而且复合材料中碳纳米管含量对吸波性能有明显的影响。对于厚度为1mm的薄涂层,当碳纳米管的质量分数为20%时,涂层具有最优的吸波性能,最大吸收峰值达-14.02dB,小于-10dB的有效带宽达3GHz;然后通过电损耗功率密度分析了复合材料的微波吸收机理,并给出了厚度为1mm的薄涂层,当其中的碳纳米管含量为20%时,吸波效果最佳的理论解释。     

化学镀镍碳纳米管的微波吸收性能研究

采用化学镀的方法对碳纳米管进行表面镀镍,TEM观察证实了碳纳米管上已镀覆了镍层,镀层厚度约8～15nm.采用HP8722ES矢量网络分析仪测量了样品在2～18GHz频率范围内的复介电常数(ε=ε′-jε″)和复磁导率(μ=μ′-jμ″).用吸收屏理论公式计算其反射损耗(R.L.)、匹配厚度(dm)及匹配频率(fm).结果表明,随着匹配厚度的增大,化学镀镍碳纳米管的吸收峰没有发生移动,当匹配厚度dm=0.2mm时,样品最低反射损耗达-11.40dB,对应的匹配频率fm=15.6GHz,而且在整个电磁波频率测试范围内,反射损耗值均＜-10.5dB,能够作为一种理想的电、磁损耗型吸波材料.     

填充α-Fe碳纳米管的电磁性能研究

通过热解二茂铁的工艺简便地制备了填充有α-Fe纳米线的碳纳米管(记为FCNT),铁纳米线的长度在30～500 nm之间.碳纳米管的保护作用可以使铁纳米线的抗氧化能力得到提高,测试了所得FCNT产物与石蜡组成的复合材料在2～18 GHz频段的介电谱和磁谱,并计算和测试了其吸波性能.与普通碳纳米管相比,FCNT产物的介电常数实部和虚部均有较大提高;FCNT产物的磁导率实部也比普通碳纳米管高,但虚部值在2～13GHz频段略低;FCNT吸波涂层在频率为3.5和5.0GHz处分别有两个较强的吸收峰,其强度值分别为-3.9和-4.0dB,表明这种新型吸收剂有望在2～4GHz频段实现对电磁波的有效吸收.     

La2O3:Eu3+纳米晶充填碳纳米管吸波性能的研究

通过湿化学技术法制备了La2O3:Eu3 纳米晶充填碳纳米管复合材料.高分辨透射电镜观测到充填碳纳米管的La2O3:Eu3 纳米晶在碳纳米管内呈准连续状态分布.HP8722ES矢量网络分析仪测量了样品在2～18GHz频率范围内的复介电常数和复磁导率.材料反射率损耗(R.L.)、匹配频段(fm)及匹配厚度(dm)采用吸收屏理论公式计算.结果表明,样品反射率随吸收层匹配厚度的增大,吸收峰向低频方向迁移并有窄化的趋势.吸收层在X波段具有较好的吸波效果.当吸收层匹配厚度为dm=9.0mm时,在10.6～12.8GHz频段内,反射衰减最大达-25.64dB,反射衰减＜-5dB的频宽达2.21GHz.     

多壁碳纳米管/环氧有机硅树脂吸波涂层的介电和吸波性能研究

研究了不同直径和含量多壁碳纳米管填充环氧有机硅树脂吸波涂层在2~18GHz频率范围内的介电和吸波性能.可以得到吸波涂层的介电常数随着碳纳米管含量的增加而增大.当碳纳米管含量相同时,吸波涂层介电常数随着碳纳米管直径的增加而增大.当碳纳米管含量大于5wt%时,吸波涂层的介电常数在低频急剧增加,且随频率增大而减少,出现频散效应.反射率测试结果表明:当涂层中多壁碳纳米管含量为10wt%、厚度为2mm时,吸波涂层的最大吸收峰随碳纳米管直径的增大向低频移动.多壁碳纳米管填充环氧有机硅树脂吸波涂层的吸波性能在7~14GHz范围内可达到-10dB,具有较好的吸波效果.     

X-Band microwave characterization of carbon-based nanocomposite material,absorption capability comparison and RAS design simulation

This paper presents a microwave characterization of several carbon-based composite materials interesting the future aircraft/aerospace systems. They consist in epoxy resin reinforced with five different carbon species: micro-sized granular graphite, fullerenes, carbon nanofibers, single- and multi-walled carbon nanotubes. Main goal of this work is to show how carbon inclusions size and geometry are able to significantly modify the electromagnetic properties at microwave frequencies. Microwave characterization is performed in terms of microwave permittivity and intrinsic wave impedance evaluation; all the computations are based on microwave scattering parameters measured in the X-band (8.2/12.4 GHz) by waveguide method. A theoretical analysis of the microwave absorbing capability is then performed assuming that a multilayer of nanocomposite material was backed on a conductor plate (such a structure is typically called Radar Absorbing Material). The results obtained for the reflection coefficient indicate that nanoparticles give better absorption properties to the matrix than micro-sized ones: nanocomposite materials could thus be used successfully as microwave absorbers, not only for their absorption performances but also for their light weight.     

A review on carbon/magnetic metal composites for microwave absorption

At present,developing high-efficiency microwave absorption materials with properties including light-weight,thin thickness,strong absorbing intensity and broad bandwidth is an urgent demand to solve the electromagnetic pollution issues.An ideal microwave absorber should have excellent dielectric and magnetic loss capabilities,thereby inducing attenuation and absorption of incident electromagnetic radiation.Recently,various carbon/magnetic metal composites have been developed and expected to become promising candidates for high-performance microwave absorbers.In this review,we introduce the mechanisms of microwave absorption and summarize the recent advances in carbon/magnetic metal composites.Preparation methods and microwave absorption properties of carbon/magnetic metal com-posites with different components,morphologies and microstructures are discussed in detail.Finally,the challenges and future prospects of carbon/magnetic metal absorbing materials are also proposed,which will be useful to develop high-performance microwave absorption materials.     

碳纳米管磁化氢等离子体薄膜的微波吸收特性

为从理论上掌握有外加静磁场存在时铁催化高压歧化生成的碳纳米管中氢等离子体的微波吸收特性,根据磁离子理论和Appleton-Hartee方程,采用W.K.B近似方法,导出了碳纳米管磁化氢等离子体薄膜的微波衰减系数公式,数值计算了不同条件下碳纳米管磁化氢等离子体薄膜在0.3～30 GHz频段的微波衰减系数。研究结果表明:随着外加磁场强度的增加,Att30.00 dB/cm的频宽明显增大,吸收峰向高频方向移动.适当控制碳纳米管中等离子体的自由电子密度、电子碰撞的有效频率和外加磁场强度,能够实现碳纳米管中磁化氢等离子体薄膜对对特定微波段的强吸收.在外磁场等于0时,运用所构建的微波吸收模型得到的数值计算结果与已有的实验数据相吻合.     

Heterostructure design of Fe3N alloy/porous carbon nanosheet composites for efficient microwave attenuation

The self-dissipation and attenuation capacity of materials play an important role in realizing efficient electromagnetic absorption,in this case,the roles of macroscopic composition and micro-structure should be emphasized simultaneously in the reasonable design of microwave absorbent.Given that,Fe₃N alloy embedded in two-dimensional porous carbon composites were fabricated via facile sol-gel and sacrificial template methods.Satisfactorily,the magnetic/dielectric materials combination and porous structure introduction are conductive to the optimization of impedance matching property,as result of the enhancement of microwave absorption capacity.In addition,sufficient magnetic loss capacity,strong conductivity as well as polarization attenuation bring about the outstanding microwave absorbing performance with an effective absorption bandwidth of 6.76 GHz and a minimum reflection loss value of-65.6 d B.It is believed that this work not only lay a foundation to achieve microwave response materials in a wide frequency range,but also emphasize the significant role of the component selection and structural design.     

Synthesis and electromagnetic wave absorption properties of multi-walled carbon nanotubes decorated by BaTiO3 nanoparticles

A hybrid composite material, consisting of BaTiO3 and multi-walled carbon nanotubes, was synthesized by an efficient solvent-thermal route. Transmission electron microscopy images clearly indicate that the surfaces of the multi-walled carbon nanotubes were uniformly decorated by well-crystallized BaTiO3 particles, with diameters of 15-30 nm. Electromagnetic wave absorption properties analysis, determined by the electromagnetic parameters measured by a vector network analyzer, shows that the reflection loss in the BaTiO3/multi-walled carbon nanotube composite was higher than that occurring in pure multi-walled carbon nanotubes or BaTiO3 and that was resulted from a better matched characteristic impedance and an enhanced complex permeability in the high frequency, which was improved by the decrease of eddy currents owing to the finite increase in resistivity. The maximum reflection loss of -37.5 dB in the BaTiO3/multi-walled carbon nanotube composite was obtained at a frequency of 10.4 GHz and the absorption range under -10 dB was from 9.6-13.1 GHz range as the absorber thickness was 2 mm.     

含碳纳米管微波吸收材料的制备及其微波吸收性能研究

用竖式炉流动法,以二茂铁为催化剂,噻吩为助催化剂,苯为碳源通过催化裂解反应制备了碳纳米管,碳纳米管的外径为20-50nm,内径10-30nm,长度50-1000μm.分别以碳纳米管、羰基铁粉、碳纳米管与羰基铁粉的混合物为吸收剂制备了微波吸收材料,研究了上述三种微波吸收材料在2-18GHz的吸波性能,与纯碳纳米管和纯羰基铁粉微波吸收材料相比, 碳纳米管与羰基铁粉复合微波吸收材料在2-18GHz的吸收峰明显向低频移动.在含碳纳米管的微波吸收材料中,碳纳米管作为偶极子在交变电场的作用下,产生极化电流,电磁波的能量转换为其他形式的能量,瑞利散射效应和界面极化也是含碳纳米管微波吸收材料的主要吸波机理.     

Co含量对轻质微波吸收剂C/Co纳米纤维吸波性能的影响

采用静电纺丝法结合热处理制备了一种可应用于2~18 GHz频段的高性能轻质微波吸收剂C/Co纳米纤维, 详细研究了金属Co含量对纳米纤维的电磁特性及微波吸收性能的影响。相对于纯碳纳米纤维, C/Co纳米纤维的微波吸收性能得到显著加强, 其主要吸波机制仍是介电损耗。随着Co含量的增加, C/Co纳米纤维的电磁衰减能力逐渐下降, 而微波吸收却先增强后减弱, 含37.8wt% Co的C/Co-5纳米纤维因金属Co粒子和纳米碳纤维的良好结合与协同效应, 以及纤维中特殊的Co粒子@石墨核壳结构所带来的良好阻抗匹配与足够高的电磁衰减能力而表现出最好的吸波性能。模拟计算结果表明, 涂层厚度在1.1~5.0 mm间变化时, 填充5wt% C/Co-5纳米纤维的硅胶吸波涂层的反射损耗(RL)值超过-20 dB的频率范围在3.2~18 GHz, 最小RL值达到-78.8 dB, 其中当涂层厚度仅为1.5 mm时, RL值低于-20 dB的吸收带宽可达6.0 GHz (12~18 GHz)。C/Co纳米纤维优异的微波吸收性能表明, 这些磁性碳杂化纳米纤维有望成为一种极具应用前景的新型吸波材料。     

Electromagnetic absorption properties of Sn-filled multi-walled carbon nanotubes synthesized by pyrolyzing

Multi-walled carbon nanotubes (MWCNTs) filled with Sn nanocrystals were synthesized by metal-organic chemical vapour deposition at relatively lower pyrolysis temperature. Their electromagnetic parameters and microwave absorbing properties were investigated in the frequency range of 2-18 GHz. An obvious increase in the complex permittivity and electric loss tangent of the Sn-filled MWCNTs has been observed. The dielectric and magnetic properties were significantly improved. The Sn nanocrystals encapsulated in MWCNTs modify the electromagnetic parameters of the MWCNTs. The variation of the normalized input impedance induces the enhancement of absorbing properties. The modified MWCNTs exhibit much broader absorbing bandwidth and larger reflectivity than those of unfilled MWCNTs. The calculated results indicate that the Sn-filled MWCNTs have excellent absorbing properties and potential applications in thin thickness and light weight microwave absorbers.     

Dielectric, magnetic, and microwave absorbing properties of multi-walled carbon nanotubes filled with Sm2O3 nanoparticles

This study investigates the dielectric, magnetic, and microwave absorbing properties of Sm₂O₃-filled multi-walled carbon nanotubes (MWCNTs) synthesized by wet chemical method. The complex permittivity and permeability were measured at a microwave frequency range of 2-18 GHz. Sm₂O₃ nanoparticles encapsulated in the cavities enhance the magnetic loss of MWCNTs. The calculated results indicate that the bandwith of absorbing peak of the modified MWCNTs is much broader than that of unfilled MWCNTs. The maximum reflectivity (R) is about − 12.22 dB at 13.40 GHz and corresponding bandwidth below − 5 dB is more than 5.11 GHz. With the increase of thickness, the peak of R shifts to lower frequency, and multiple absorbing peaks appear, which helps to broaden microwave absorbing bandwidth.     

镀镍碳纳米管的微波吸收性能研究

用竖式炉流动法制备了碳纳米管,碳纳米管的外径40nm～70nm,内径7nm～10nm,长度50μm～1000μm,呈直线型,用化学镀法在碳纳米管表面镀上了一层均匀的金属镍。碳纳米管吸波涂层在厚度为0.97mm时,在8GHz～18GHz,最大吸收峰在11.4GHz(R=-22.89dB),R<-10dB的频宽为3.0Hz,R<-5dB的频宽为4.7GHz。镀镍碳纳米管吸波涂层在相同厚度下,最大吸收峰在14GHz(R=-11.85dB),R<-10dB的频宽为2.23Hz,R<-5dB的频宽为4.6GHz。碳纳米管表面镀镍后虽然吸收峰值变小,但吸收峰有宽化的趋势,这种趋势对提高材料的吸波性能是有利的。碳纳米管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,从而雷达波能量被转换为其它形式的能量。