Mechanical elasticity of vapour-liquid-solid grown GaN nanowires

Mechanical elasticity of hexagonal wurtzite GaN nanowires with hexagonal cross sections grown through a vapour-liquid-solid (VLS) method was investigated using a three-point bending method with a digital-pulsed force mode (DPFM) atomic force microscope (AFM). In a diameter range of 57-135?nm, bending deflection and effective stiffness, or spring constant, profiles were recorded over the entire length of end-supported GaN nanowires and compared to the classic elastic beam models. Profiles reveal that the bending behaviour of the smallest nanowire (57.0?nm in diameter) is as a fixed beam, while larger nanowires (89.3-135.0?nm in diameter) all show simple-beam boundary conditions. Diameter dependence on the stiffness and elastic modulus are observed for these GaN nanowires. The GaN nanowire of 57.0?nm diameter displays the lowest stiffness (0.98?N?m(-1)) and the highest elastic modulus (400 ± 15?GPa). But with increasing diameter, elastic modulus decreases, while stiffness increases. Elastic moduli for most tested nanowires range from 218 to 317?GPa, which approaches or meets the literature values for bulk single crystal and GaN nanowires with triangular cross sections from other investigators. The present results together with further tests on plastic and fracture processes will provide fundamental information for the development of GaN nanowire devices.     

Growth of carbon nanotubes on nanoporous titania templates

This work reports the synthesis of multiwalled carbon nanotubes (MWCNTs) on nanoporous titanium dioxide (TiO2) templates. TiO2 nanotubular templates for MWCNTs are produced by anodization of titanium followed by pulsed electrodeposition (PED) of cobalt inside the TiO2 nanotubes. Cobalt acts as a catalyst for the growth of MWCNTs using chemical vapor deposition (CVD) technique. The cobalt catalyst initiates the growth of well graphitized MWCNTs inside the titania pores as well as beyond the titania pores. These materials have been characterized by SEM, EDS, GXRD, XPS, TEM, and ED techniques. The MWCNTs were about 10 mu in length and 80-120 nm in diameter.     

Dispersion of multi-walled carbon nanotubes in biodegradable poly(butylene succinate) matrix

This communication describes the preparation, characterization and properties of biodegradable poly(butylene succinate) (PBS)/multi-walled carbon nanotubes (MWCNTs) nanocomposite. Nanocomposite was prepared by melt-blending in a batch mixer and the amount of MWCNTs loading was 3 wt%. State of dispersion-distribution of the MWCNTs in the PBS matrix was examined by scanning and transmission electron microscopic observations that revealed homogeneous distribution of stacked MWCNTs in PBS matrix. The investigation of the thermomechanical behavior was performed by dynamic mechanical thermal analysis. Results demonstrated substantial enhancement in the mechanical properties of PBS, for example, at room temperature, storage flexural modulus increased from 0.64 GPa for pure PBS to 1.2 GPa for the nanocomposite, an increase of about 88% in the value of the elastic modulus. The tensile modulus and thermal stability of PBS were moderately improved after nanocomposite preparation with 3 wt% of MWCNTs, while electrical conductivity of neat PBS dramatically increased after nanocomposite formation. For example, the in plane conductivity increased from 5.8 x 10(-9) S/cm for neat PBS to 4.4 x 10(-3) for nanocomposite, an increase of 10(6) fold in value of the electrical conductivity.     

Comparative in vitro cytotoxicity study of carbon nanotubes and titania nanostructures on human lung epithelial cells

The aim of this study is to assess in vitro cytotoxic effects of titania nanostructures and carbon nanotubes (CNTs) by exposing A549 lung epithelial cell line to these materials. Titania nanotubes (TiNTs) were grown by hydrothermal treatment of TiO(2) nanoparticles, followed by annealing them at 400°C. The titania nanostructures obtained on annealing (mixture of nanotubes and nanorods) were hollow and open ended, containing 3-5 layers of titania sheets, with an internal diameter ～3-5 nm and external diameter ～8-10 nm, and a specific surface area of 265 m(2)/g. As-supplied single walled (SWCNTs) and microwave plasma enhanced chemical vapour deposition (MPCVD) grown multi walled carbon nanotubes (MWCNTs) were used in this study. The lengths and diameters of the SWCNTs were 5-10nm and 0.5-3 nm respectively. The lengths and diameters of the MWCNTs were 25-30 μm and 10-30 nm respectively. The cell viability was evaluated using the MTT (3-(4,-dimethylthiazol-2-yl)-2, 5-diphenyl-tetrazolium) assay. No significant cytotoxic effects of titania nanostructures were observed over a period of a week of testing time, while the presence of CNTs in some cases demonstrated significant cytotoxic effects. Finally, possible reason of cytotoxicity is discussed in the light of microstructures of materials.     

CO-Mo/MgO催化剂上甲烷化学气相沉积制备高纯度多壁碳纳米管

以甲烷为碳源,co-Mo/MgO为催化剂,通过气相化学沉积制备了直径均匀的多壁碳纳米管(MWC-NTs).采用溶胶-凝胶法所制双金属催化剂的组成为Co∶Mo∶MgO=5∶20∶75(质量比).热重分析表明多壁碳纳米管产率高达313.67%.催化剂对于多壁碳纳米管生长的选择性是91.17%(其余为无定形碳).透射电子显微镜分析显示:催化剂七生长的MWCNTs平均直径为6.2±0.5nm(平均±标准偏差).通过稀酸的简单纯化处理,纯化样品的催化剂残存率降至0.72%.     

Synthesis of carbon nanotube-TiO(2) nanotubular material for reversible hydrogen storage

A material consisting of multi-walled carbon nanotubes (MWCNTs) and larger titania (TiO(2)) nanotube arrays has been produced and found to be efficient for reversible hydrogen (H(2)) storage. The TiO(2) nanotube arrays (diameter ～60?nm and length ～2-3?μm) are grown on a Ti substrate, and?MWCNTs a few μm in length and ～30-60?nm in diameter are grown inside these TiO(2) nanotubes using chemical vapor deposition with cobalt as a catalyst. The resulting material has been used in H(2) storage experiments based on a volumetric method using the pressure, composition, and temperature relationship of the storage media. This material can store up to 2.5?wt% of H(2) at 77?K under 25?bar with more than 90% reversibility.     

Mechanical properties of nylon-6/SiO2 nanofibers prepared by electrospinning

SiO₂ nanoparticles reinforced nylon-6 nanofibers were prepared by electrospinning of nylon-6/SiO₂ solution in formic acid. The effect of concentration and applied voltage on the diameter of the fibers was investigated. A nanoscale three-point bending test was used to evaluate the mechanical property of a single nylon-6/SiO₂ nanofiber. It was found that the elastic modulus of the nanofibers decreased with the increase in fiber diameter. This elastic modulus was in the range of 3.1-6.9GPa as the diameter ranged from 600 to 100nm.     

一种适于碳纳米管制备的绿色前驱体

根据绿色化学原理尝试探索一种合成多壁碳纳米管的天然可再生前驱体.应用化学气相沉积(CVD)法,采用一种天然可再生前躯体(椰仁油),通过系列步骤合成了MWCNTs.氮气既作为气化前驱体载气(气体流速:100mL/min)又维持合成在惰性氛围中进行.合成的MWCNTs使用SEM、EDX、TEM和Raman表征,最佳条件下得到的碳纳米管直径为80nm～90nm.     

多尺度功能性填料PVDF基纳米复合材料的制备和性能

先以两种直径(50 nm,100 nm)的羟基化钛酸钡(BT)和两种长度(10~20 nm,20~40 nm)的酸化多壁碳纳米管(MWCNTs)为功能填料,进行液相反应制备四种BT/MWCNTs杂化纳米填料(分别记为BT-A/MWCNTs-B,其中A=5,10;B=1,2),再用熔融共混-压板成型技术分别将其与PVDF复合制备出BT-A/MWCNTs-B/PVDF纳米复合材料。使用X射线衍射(XRD)、红外光谱(FTIR)、差示扫描量热分析(DSC)、扫描电子显微镜(SEM)、拉伸性能测试和介电性能测试系统研究了多尺度功能性填料BT-A/MWCNTs-B对这种纳米复合材料的组织结构和结晶性能、介电性能和力学性能的影响。结果表明,与BT/PVDF和MWCNTs/PVDF体系相比,BT-A/MWCNTs-B/PVDF纳米复合材料具有更高的结晶度和热性能,BT-10的含量(质量分数,下同)为16%、MWCNTs-2的含量为5%的BT-10/MWCNTs-2/PVDF纳米复合材料其熔融温度可达173.8℃,比纯PVDF(159.6℃)提高了14.2℃,其结晶度可达43.1%。三相BT-A/MWCNTs-B/PVDF纳米复合材料比两相纳米复合材料具有更优异的介电性能,BT-10/MWCNTs-2/PVDF纳米复合材料100Hz下的介电常数为119,为纯PVDF的14倍,其介电损耗只有0.051。BT-10/MWCNTs-2/PVDF纳米复合材料的拉伸强度和弹性模量分别达到57.7 MPa和1226 MPa。     

Variation of radial elasticity in multiwalled carbon nanotubes

Correlations between the local diameter and local radial elastic modulus in multiwalled carbon nanotubes (MWNTs) were investigated via ultrasonic force microscopy. Spatial cross-correlation analysis showed that local radial modulus variations were inversely correlated with local diameter gradients ("bamboo" structures) in MWNTs grown via chemical vapor deposition (CVD). In contrast, uniform MWNTs grown via arc discharge exhibited no such correlation, indicating that reductions of elastic modulus previously reported for CVD-grown MWNTs originated from increased defect density associated with local increases in diameter.     

多孔氧化铝模板的纳米力学性能测试与分析

为了掌握多孔氧化铝模板的纳米力学性能,采用二次氧化法制备孔径在30～40nm之间且高度有序的纳米阵列氧化铝模板,并使用扫描电子显微镜(SEM)对其形貌进行表征;在原位纳米力学测试系统上进行微压痕实验,对样品表面力学性能(纳米硬度、模量)进行测试;利用原子力成像功能对实验区域扫描成像,在纳米尺度下观察和分析样品形貌.结果表明,AAO模板在同一深度处对应的硬度、模量值明显高于相应的基体材料铝,膜基体系的抗载能力明显提高;在压入深度为70～240nm时,AAO膜板的硬度和模量值分别为5.8GPa和106GPa,但从深度250nm时开始出现减小趋势;单晶铝与压针的接触为理想刚塑性接触,AAO模板与压针的接触为弹塑性接触.     

Root growth of multi-wall carbon nanotubes by MPCVD

This work examines the relationships among the growth and interlayer reactions of carbon nanotubes (CNTs) to develop an effective process for controlling the nanostructure, orientation and characteristics of CNTs. Vertically oriented CNTs were successfully synthesized by microwave plasma chemical vapor deposition (MPCVD) with CH₄/H₂ as source gases. Additionally, the Ti and SiO₂ barrier layers and the Co catalyst were used in an experiment on the growth of CNTs on the Si wafer. Then, the SiO₂ barrier layer was deposited by low-pressure chemical vapor deposition (LPCVD). The Ti barrier layer and Co catalyst films were deposited on the Si wafer by physical vapor deposition (PVD). The deposited nanostructures were characterized by scanning and transmission electron microscopy, the results of which reveal that the deposited MWCNTs were grown under the influence of a catalyst on Si substrates with or without a barrier layer, by MPCVD. Vertically grown, dense MWCNTs attached to a catalytic film demonstrate that various MWCNTs penetrated the root particles. The diameter of the root particles, of approximately in the order of 100 nm, is larger than those of the tube, 10–15 nm. The well-known model of the growth of CNTs includes base- and tip-root growth. The interaction between the catalytic film and the supporting barrier layer is suggested to determine whether the catalytic particles are driven up or pinned down on the substrate during the growth.     

Single-step synthesis of MWCNT/ZnO nanocomposite using co-chemical vapor deposition method

Single-step synthesis of MWCNT and ZnO nanocomposite was conducted by co-chemical vapor deposition method. Electron microscopic analysis revealed that the fabricated nanostructures consisted of MWCNTs with a diameter of 60-70 nm which were coated with ZnO nanoparticles with an average size of 20-30 nm. The growth of ZnO nanoparticles took place after the formation of MWCNTs. EDS and XRD analyses could confirm the high crystallinity of ZnO deposited on the MWCNT surface. In comparison with pristine MWCNTs and ZnO nanoparticles, the UV absorption of MWCNT/ZnO nanocomposite was changed through modification with ZnO nanoparticles.     

Aligning carbon nanotubes using bulk acoustic waves to reinforce polymer composites

Bulk acoustic waves (BAWs) are used to align multi-walled carbon nanotubes (MWCNTs) in polymer composite materials. MWCNTs are first dispersed in the liquid state of a thermoset resin and aligned using standing BAWs. Cross-linking of the resin fixates the aligned MWCNTs in the polymer matrix material. We have quantified the alignment obtained with this method on the macro, micro, and nanoscale, and it is found to be similar to other alignment techniques such as stretching, slicing, and wet spinning. The elastic modulus and ultimate tensile strength of composite material specimens with aligned MWCNTs, fabricated using this technique, are evaluated and compared with specimens consisting of randomly oriented MWCNTs and resin material without MWCNTs. Different MWCNT loading rates are considered. The elastic modulus of composite material specimens with only 0.15 weight percent aligned MWCNTs is observed to be 44% higher than specimens with randomly oriented MWCNTs, and 51% higher than specimens without MWCNTs. However, further increasing the MWCNT loading rate does not significantly increase the elastic modulus and ultimate tensile strength, likely because of insufficient dispersion of MWCNTs in the thermoset matrix material.     

Basalt fiber–epoxy laminates with functionalized multi-walled carbon nanotubes

Cross-ply laminates reinforced with basalt fibers and functionalized multi-walled carbon nanotubes (MWCNTs) were fabricated from unidirectional epoxy prepregs. MWCNTs with varied surface conditions were prepared by oxidization or esterification, and then dispersed into a DGEBA epoxy system. The dispersion of the MWCNTs in the epoxy was improved by surface modification, resulting in improved composite mechanical properties as well. Significant increases in elastic modulus and strength were observed for epoxies with functionalized MWCNTs, especially for esterified species. When MWCNT – filled epoxies were used as matrices for basalt fiber/epoxy laminates, however, the reinforcement effects of MWCNTs on the composite elastic modulus exceeded micromechanics based semi-empirical predictions and were independent of surface functionalization. SEM morphological observations and the results of the micromechanical model revealed that nanotube re-distribution and orientation during processing was responsible for the enhancement of fiber-dominated mechanical properties. This work demonstrated the feasibility of in situ alignment and dispersion of functionalized nanotubes in multi-scale composite laminates.     

On the Role of Stearic Acid on the Surface Properties of Carbon Nanotubes

In this article, modification of multiwalled carbon nanotubes (MWCNTs) with stearic acid (SA) was done using the wet chemical method. For this aim, MWCNTs were treated with high-concentrated nitric acid to create a functional group as a linkage between MWCNTs and SA. The modified MWCNTs with SA were examined by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), differential scanning calorimeter (DSC), and thermogravimetery analysis (TGA) instruments. The results of TGA and DSC indicate the deposition of about 4.3 wt% of SA on the surface of MWCNTs. This proves that the deposition of stearate with a medium diameter size of 20 nm on the surface of MWCNTs can be divided into physical and chemical adsorption. As well, the esterification occurs on the surface of functionalized MWCNTs and there is no SA unreacted on the surface of MWCNTs.     

Structural,mechanical, and electrical properties of carbon nanoparticles synthesized from diesel

We studied the elemental analysis, structural morphology, mechanical, and electrical properties of carbon nanoparticles synthesized from diesel. The spherical carbon particle size in the range of about 10 to 80 nm in diameter was observed in scanning electron microscope (SEM) studies that were identified by Atomic force microscopy (AFM) study as an aggregation of carbon particles of average size 2.5 nm. The surface rms of carbon nanoparticle thin film (CNTF) was measured directly by AFM and found 0.22 nm. The Derjaguin–Muller–Toporov (DMT) elastic modulus of carbon nanoparticles (CNPs) was measured by PeakForce QNM mode of AFM. The minimum and maximum elastic modulus was measured of 0.40 GPa and 43.89 GPa, respectively. The resistivity, conductivity, magneto resistance, mobility, and average Hall co-efficient were measured by “Ecopia Hall-effect measurement system” by four-point Van der Pauw approach at ambient condition. We demonstrated I–V characteristic at the Indium/CNTF thin film interface, which is accompanied by rectifying behavior.     

不同温度环境中沥青混凝土动态抗压性能试验研究

为研究沥青混凝土在不同温度环境中的动态力学特性,该研究在-20~30℃和10-5~10-2 s-1条件下对其进行了动态抗压试验研究。试验结果表明:温度和应变速率对沥青混凝土的力学性能有显著影响,降低温度或增加应变速率导致抗压强度和弹性模量增加,峰值应变减小;当温度大于20℃或小于-10℃时,应变速率由10-5 s-1增加到10-2 s-1,温度对抗压强度和弹性模量的影响逐渐减小,该研究提出的温度影响因子经验公式较好地反映了抗压强度和弹性模量随温度变化的规律。在-20~0℃温度区间,抗压强度和弹性模量的动态增强因子随应变速率呈线性增长;在0~30℃温度区间,抗压强度和弹性模量的动态增强因子随应变速率呈非线性增长。在此基础之上,基于时温等效原理,建立了沥青混凝土抗压强度和弹性模量的计算模型。该模型考虑了温度和应变速率对沥青混凝土的共同作用,与试验结果吻合较好。     

Fabrication and characterization of nano-particles-enhanced epoxy

Epoxy has been widely used as adhesives in retrofitting structures with carbon fiber reinforced polymer (CFRP). In this study, different weight fractions of multi-walled carbon nanotubes (MWCNTs) and Silicon Carbide nanopowder (SiC) will be dispersed into epoxy to produce toughened adhesives that can effectively improve the CFRP/structure bonding performance. The preliminary experimental results indicate that adding 2 wt.% MWCNTs into Araldite-420 will increase its ultimate strength by 17% and its elastic modulus by 14%. On the other hand, Araldite-420’s elastic modulus will increase by nearly 50% when 1.0 wt.% of SiC powder is added. Ultrasonic mixing may increase the elastic modulus of Sikadur-30 but reduce its strength and ductility regardless of the amount of nanoparticles dispersed. No significant effect of nano-particle infusion on the glass transition temperature of the epoxies was found. The mechanism of nanoparticles infusion effects on the mechanical properties of the epoxies is also examined using SEM.     

Synthesis of individual ultra-long carbon nanotubes and transfer to other substrates

In this article, we report the synthesis of ultra-long carbon nanotubes (CNTs) by thermal chemical vapour deposition method. Ultra-long, individual and aligned CNTs were directly grown on a flat silicon substrate. The orientation of the nanotubes was found parallel to the gas flow direction. The ultra-long CNTs were grown with different transition metallic salts, such as nickel chloride, iron (III) chloride, cobalt acetate and ruthenium acetate, as the catalysts. The influence of the growth conditions, such as growth temperature, reactive gas flow on the length and alignment of the CNTs was studied in detail. By using different catalysts, ultra-long single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) were successfully grown. These ultra-long CNTs were transferred to other substrates by two methods. (1) The first method is to use polydimethylsiloxane as a stamp. (2) The second method is to use KOH as an etching agent. The diameter and length of the CNTs were characterised by transmission electron microscope, scanning electron microscope, atomic force microscope and Raman spectroscopy. The results indicate that the length of the CNTs can reach up to 4?mm. The diameter of the SWCNTs is in the range of 0.7–2.1?nm and the diameter of the MWCNTs is approximately 150?nm.