Electroless plating of carbon nanotubes and their millimeter-wave absorbing properties

A method of electroless plating was utilized to deposit Cu, Ni, Co, Ag on the surface of carbon nanotubes (CNTs) respectively, in order to prepare millimeter-wave absorbing materials. Field emission scanning electron microscope (FE-SEM) and energy dispersive spectrometer (EDS) were used to observe morphologies and chemical compositions of the samples respectively. Millimeter-wave radiometer imaging detection was employed to measure the absorbing properties of the samples. FE-SEM and EDS results demonstrate the effectiveness of successful metal deposition. The results of millimeter-wave radiometer imaging detection reveal that the millimeter-wave absorbing properties of electroless-silver plating are better than other kinds of samples.     

Microwave absorbing properties of high titanium slag

Microwave absorbing properties of high titanium slag were investigated by using microwave cavity perturbation technique. High titanium slag containing more than 90% TiO₂ was prepared by carbothermal reduction of ilmenite. The temperature rise curve of high titanium slag in microwave heating process was obtained. Crystalline compounds of high titanium slag before and after microwave irradiation were obtained and characterized by X-ray diffractometry (XRD). Effects of particle size of high titanium slag and mixtures of high titanium slag with different mass fractions of V₂O₅ on microwave absorbing properties were investigated systematically. The results show that high titanium slag has good microwave absorption property; untreated high titanium slag mainly consists of crystalline compounds of anatase and iron titanium oxide, while the microwave-irradiation treated one is mainly composed of crystalline compounds of rutile and iron titanium oxide. Synthetic anatase is transformed completely into rutile at about 1 050 °C for 20 min under microwave irradiation. High frequency shift and low amplitude of voltage make high titanium slag an ideal microwave absorbent. 180 μm of particle size and 10% mass fraction of V₂O₅ are found to be the optimum conditions for microwave absorption. Foundation item: Project(2007CB613606) supported by the Major State Basic Research and Development Program of China; Project(50734007) supported by the National Natural Science Foundation of China     

钴填充碳纳米管的微波吸收性能研究

分析了钴填充碳纳米管的磁性能,深入探讨了钴填充碳纳米管的微波吸收机理,对钴纳米粒子填充碳纳米管的微波吸收特性进行了数值模拟,计算了其自然共振频率,理论结果与实验数据相吻合.研究结果表明:钴填充碳纳米管对微波的强烈吸收主要是样品中钴纳米粒子在微波作用下产生了磁共振的结果;随着钴填充碳纳米管薄膜厚度的增加,其共振频率向低频...     

Synthesis of flowerlike nickel particles and their microwave absorbing properties

Two kinds of nickel particles with flower-like struc~＇es assembled with a number of nano-flakes were synthesized and the relationship of their morphology and microwave absorbing properties was studied. The electromagnetic parameters of these flower-like Ni were measured with vector network analyzer at 2-18 GHz frequency and the reflection losses （RL） with different sample thicknesses were calculated. The results indicate that the flower-like nickel-wax composites with the sample thickness less than 2 mm show excellent absorbing ability. This result is expected to play a guiding role in the preparation of the highly efficient absorber.     

含氮复合缺陷改性单壁碳纳米管的电学性能

基于第一性原理的密度泛函理论,利用非平衡格林函数方法本文研究了氮原子与SW（Stone-Wales）缺陷组成的复合缺陷对碳纳米管几何结构及电子透射系数的影响。结果显示SW缺陷和掺杂都对单壁管的几何结构和电子性能有显著的影响。对于半导体性（8,0）碳纳米管,复合缺陷增强了体系的输运性能,但是输运特性明显受到杂质原子的位置的影响。     

Laccase biosensor using magnetic multiwalled carbon nanotubes and chitosan/silica hybrid membrane modified magnetic carbon paste electrode

A simple and rapid strategy to construct laccase biosensor for determination of catechol was investigated. Magnetic multiwalled carbon nanotubes (MMCNT) which possess excellent capability of electron transfer were prepared by chemical coprecipitation method. Scanning electron microscope (SEM) and vibrating sample magnetometer (VSM) were used to identify its surfacetopography and magnetization, respectively. Laccase was immobilized on the MMCNT modified magnetic carbon paste electrode by the aid of chitosan/silica (CS) hybrid membrane. Using current-time detection method, the biosensor shows a linear response related to the concentration of catechol in the range from 10⁻⁷ to 0.165×10⁻³ mol/L. The corresponding detection limit is 3.34×10⁻⁸ mol/L based on signal-to-noise ratios (S/N) ≥3 under the optimized conditions. In addition, its response current retains 90% of the original after being stored for 45 d. The results indicate that this proposed strategy can be expected to develop other enzyme-based biosensors.     

Effects of size and surface modification of multi-walled carbon nanotubes on mechanical properties of polyurethane-based nanocomposites

Polyurethanes/multi-walled carbon nanotube (PU/CNT) composites were prepared with a help of ultrasonically dispersing CNT in the traditional procedure of synthesizing polyurethane. In this case, the various loading levels, sizes and surface-modified groups were considered to regulate the mechanical performances of the PU/CNT nanocomposites. Moreover, the structure and mechanical properties of all the PU/CNT nanocomposites were investigated by attenuated total reflection-Fourier transform infrared spectroscopy, dynamic mechanical analysis, scanning electron microscope, transmission electron microscope, and tensile testing. The experimental results showed that a moderate loading-level of 0.1wt% and a diameter of 10-15 nm for CNT could produce the maximum tensile strength and elongation while it was worth noting that the surface carboxylation of CNT could further enhance the tensile strength and elongation of the PU/CNT nanocomposites.     

Effects of hydrothermal temperatures on properties of magnetic titanate nanotubes

NiFe2O4 dopeded with magnetic titanate nanotubes(MTNT)were prepared by a hydrothermal method using magnetic nanoparticles TiO2/SiO2/NiFe2O4 as the precursor.The effects of hydrothermal temperatures on their composition,morphologies and magnetic properties of products were characterized by transmission electron microscopy(TEM),scanning electron microscopy(SEM),X-ray diffraction(XRD),vibration sample magnetometer(VSM)and energy dispersive X-ray spectroscopy(EDS).The results show that the hydrothermal temperature has a significant impact on the morphology of the products.The MTNT is synthesized in the temperature range of 120-160 ℃ and the inner diameter of MTNT is about 3-10 nm,the wall thickness 4-12nm and the length 100-200 nm.The components of MTNT are Na0.8H1.2Ti3O7 and a little of anatase TiO2 and NiFe2O4.The ferrimagnetisms and magnetic hysteresis phenomena are shown in the prepared MTNT.The hydrothermal temperature has no clear effect on the magnetic properties in the range of 120-180 ℃.The visible-light photo-catalytic activity of the products decreases as the temperature increases.The decolorization of methylene blue is 94.6% by the MTNT obtained at 120 ℃ and the recovery rate of MTNT is more than 95 percent.The MTNT has excellent photocatalytic activity and is easy to recovery.     

磁性纳米Fe_3O_4颗粒掺杂多壁碳纳米管修饰的葡萄糖生物传感器

磁性纳米Fe3O4颗粒掺杂多壁纳米碳管混合分散于壳聚糖中,得到壳聚糖胶质液.将其修饰到玻碳电极表面,通过交联剂戊二醛固定葡萄糖氧化酶,制得一种新型的传感器.该传感器在pH=6.8的磷酸盐缓冲溶液中,对葡萄糖的线性响应范围为1.0×10^-5-2.3×10^-2mol/L,响应时间5.3 s.     

Microwave magnetic properties of laminates with thin FeCoBSi films

The microwave permeability of laminated composites based on thin FeCoBSi films was under study.The level of permeability increased with increasing of the ferromagnetic inclusions in the laminates.The intrinsic permeability spectra of ferromagnetic inclusion are parametrically reconstructed.The obtained parameters of magnetic resonance were specially analyzed.To avoid the effect of eddy current and to obtain large-volume fractions of ferromagnetic constituent,laminates consisting of alternating FeCoBSi/SiO2 multi-layers and mylar substrates were also investigated.For the same volume fractions of ferromagnetic constituent (8.7%),laminates based on multi-layered films are found to possess higher values of permeability than those based on one-layered films.     

碳基吸波材料的研究进展

为了研究铁氧体的电磁性能以及铁氧体引入量的质量分数和样块厚度对材料性能的影响,以玻璃和陶瓷造粒料为基料,炭黑为发泡剂,引入铁氧体,经过球磨、烧结、发泡、退火工艺后制备出泡沫吸波材料. 结果表明:900℃处理对铁氧体的电磁性能无明显影响. 铁氧体引入量的质量分数为5%和10%的吸波性能优于铁氧体为15%和20%引入量的吸波性能;研究初步显示,该结果是由于铁氧体的引入影响多孔材料的泡孔结构. 铁氧体引入量的质量分数为10%时,材料的吸波性能随着样块厚度的增加而增大;样块厚度为50mm时,材料的有效吸收带宽(反射率小于-10dB)达18GHz,反射率低至-23.4dB.

     

碳纳米管中氢等离子体的介电特性及微波吸收机理研究

运用双流体理论和唯象模型,导出了碳纳米管中氢等离子体的复介电常数和微波吸收系数,构建了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模型,从理论上证明了铁催化高压歧化生成的碳纳米管氢等离子体中的带电粒子对微波产生的碰撞吸收是其主要微波吸收机理,揭示了铁催化高压歧化生成的碳纳米管对2.45 GHz的微波产生强烈吸收的物理机制.     

Effect of Particle Density on the Aligned Growth of Carbon Nanotubes

Aligned carbon nanotubes (CNTs) wre prepared on Ni-coated Ni substrate by microwave plasma chemical vapor deposition (MWPCV D) with a mixture of methane and hydrogen gases at temperature of 550℃ . The experimentul results show a direct correlation between the alignment of CNTs and the density of the catalyst particles at low, temperature, When the particle density is high enough, among CNTs there are strong interactions that can inhibit CNTs from growing randomly. The crowding effect among dense CNTs results in the aligned growth of CNTs at low temperature.     

碳纳米管的合成与制备

金属纳米颗粒和碳纳米管是两种重要的纳米材料,要实现碳纳米管的大批量制备,必须首先解决催化剂连续投放问题和催化剂与产物及时导出的问题.通过特殊的反应装置和工艺可以实现碳纳米管的连续制备,从而达到低成本大批量制备碳纳米管的目的.本文采用一个简单的方法合成了铁钴（Fe/Co）纳米颗粒,并采用化学气相沉积法实现了碳纳米管的批量合成,纳米颗粒的尺寸分布均匀,碳纳米管管径均匀、高纯度、结构完美.合成的碳纳米管机械强度高,同时还有独特的金属或半导体导电性.     

腔体压力对纳米碳管结构的影响

在镍催化剂的催化作用下，利用微波等离子体化学气相沉积法合成了纳米碳管，分析了不同腔体压：匀对所合成的碳材料结构的影响．研究表明，当腔体压力增大时，基片温度上升，有利于纳米碳管管状结构的形成，提高纳米碳管的石墨化程度．     

单壁碳纳米管力学性质的分子动力学模拟

用分子动力学方法研究了在"拉伸"和"悬臂梁"两种模型下单壁碳纳米管的力学性质。通过对扶手椅形式的单壁碳纳米管进行分子动力学计算,得出半径在0.35nm~0.69nm之间的碳纳米管的杨氏模量在1.32623Tpa~1.03947TPa范围内波动。从模拟结果可以看出,在"拉伸"和"悬臂梁"两种模型下得到的单壁碳纳米管的杨氏模量不但在数值上有所差异,而且随其半径的变化趋势相反。     

高纯度纳米碳管的低温合成

以甲醇为碳源，在负载于CaO上的Co催化剂的催化作用下，利用微波等离子体化学气相沉积法低温合成了较高纯度的纳米碳管。经分析认为，等离子体中因甲醇裂解产生的氧离子及含氧基团对无定形碳具有很强的选择性刻蚀能力，为低温合成纳米碳管时提高其纯度创造了条件。     

Effects of carbon nanotubes on mechanical and 2D-3D microstructure properties of cement mortar

To study the influence of multi-wall carbon nanotubes （MWCNTs） on the mechanical and microstructural properties of cementitious composites, 0.00, 0.02, 0.08, 0.10, and 0.20 wt% of multi-wall carbon nanotubes were added into cement mortar, in which the cement-sand ratio was 1：1.5. The flexural and compressive strengths of cement mortar at the age of 3, 7, 28 and 90 d and the fracture performance at the age of 28 d were determined, its 2D micrograph was tested by means of SEM, and the 3D defects distribution was firstly determined with or without CNTs by means of XCT （X-ray computerized tomography）. The results showed that 0.08 wt% of CNTs improved the compressive strength and flexural strength by 18% and 19~A, respectively, and a significant improvement of its fracture property was observed. Moreover lower addition of carbon nanotubes to cement mortars can improve its microstructure and decrease the defects significantly compared to the cement mortar without CNTs. With the increase of the content of CNTs, the mechanical properties of cement mortars presented to be declined largely due to the agglomeration of CNTs.     

含铁粒子修饰碳纳米管的初步研究

采用溶液浸渍法在氧化的碳纳米管上搭载铁离子，并研究了在高温下氮气和乙炔气氛中它的化学性质.在氮气氛中600 °C退火后，铁离子转化成Fe3O4纳米颗粒，并负载于碳纳米管上；当它与乙炔在同样温度下作用时，形成被石墨层包裹的Fe3C纳米晶，石墨层的包裹可以避免空气氧化.高分辨透射电镜观察证实，用铁离子修饰的碳纳米管是一种优异的前躯体，它能够通过简单的工艺处理，合成Fe3O4和Fe3C两种磁性纳米颗粒，且它们均是单晶体.     

Effect of Surface Modification on Microwave Absorbing Properties of Magnetic Metal Fibers

In order to avoid forming an electrical conductive network due to surface connections, the magnetic metal fibers were coated with SiO2, for surface modification by the sol-gel process. The microstructure, composition and electromagnetic characteristics of SiO2-coated and uncoated metal fibers were studied using SEM, EDAX, and a voter network analyzer. The reflectivity was simulated using the RAMCAD software. The electromagnetic parameters and absorption properties of SiO2-coated metal fibers were improved greatly due to optimal impendence matching and the electric conductivity decreased, compared to those of uncoated materials.