共查询到20条相似文献,搜索用时 328 毫秒
1.
Amit K. Chakraborty Tiia Plyhm Michel Barbezat Adly Necola Giovanni P. Terrasi 《Journal of nanoparticle research》2011,13(12):6493-6506
A systematic investigation of the dispersion of carbon nanotubes (CNTs), 1–6 nm in diameter and a few microns in length, in
a bisphenol F-based epoxy resin has been presented. Several dispersing techniques including high-speed dissolver, ultrasonic
bath/horn, 3-roll mill, etc. have been employed. Optical microscopy has been extensively used to systematically characterise
the state of CNT dispersion in the epoxy resin during the entire processing cycle from mixing CNT with resin to adding and
curing with hardener. Complimentary viscosity measurements were also performed at various stages of nanocomposite processing.
A method to produce a good CNT dispersion in resin was established, but the state of CNT dispersion was found to be extremely
sensitive to its physical and chemical environments. The cured nanocomposites were further tested for their thermo-mechanical
properties by dynamic mechanical thermal analysis (DMTA), and for flexural and compressive mechanical properties. The measured
properties of various nanocomposite plates were then discussed in view of the corresponding CNT dispersion. 相似文献
2.
The relationships among the nominal thickness of Co catalyst, the structure of the catalyst particles, and the structure of carbon nanotubes (CNTs) growing from the catalyst during chemical vapor deposition were investigated. Various morphologies of CNTs such as individuals, random networks parallel to the surface of the substrate (‘grasses’), and vertically aligned forests of single- and multi-walled carbon nanotubes were grown by only varying the nominal thickness of catalyst under the same reaction condition. These different morphologies at the same growth time were due to the different areal density rather than to the length of CNTs. With increasing nominal thickness of catalyst, the catalyst particles changed in diameter while their areal density remained relatively almost constant. The change in diameter possibly affected the number ratio of active catalyst particles to the whole particles, which in turn affected the areal density of CNTs and yielded the various morphologies. Longer growth time increased the CNT length, which caused further change in CNT morphologies from individuals to grasses and grasses to forests. 相似文献
3.
Zhou Yang Qiang Zhang Guohua Luo Jia-Qi Huang Meng-Qiang Zhao Fei Wei 《Applied Physics A: Materials Science & Processing》2010,100(2):533-540
Efficient conversion of waste plastics into advanced materials is of conspicuous environmental, social and economic benefits.
A coupled process of plastic pyrolysis and chemical vapor deposition for vertically aligned carbon nanotube (CNT) array growth
was proposed. Various kinds of plastics, such as polypropylene, polyethylene, and polyvinyl chloride, were used as carbon
sources for the controllable growth of CNT arrays. The relationship between the length of CNT arrays and the growth time was
investigated. It was found that the length of aligned CNTs increased with prolonged growth time. CNT arrays with a length
of 500 μm were obtained for a 40-min growth and the average growth rate was estimated to be 12 μm/min. The diameter of CNTs
in the arrays can be modulated by controlling the growth temperature and the feeding rate of ferrocene. In addition, substrates
with larger specific surface area such as ceramic spheres, quartz fibers, and quartz particles, were adopted to support the
growth of CNT arrays. Those results provide strong evidence for the feasibility of conversion from waste plastics into CNT
arrays via this reported sustainable materials processing. 相似文献
4.
The aim of this paper is to present a theoretical study of the aerosol penetration
through an electret fibrous filter, using a numerical approach. The aerosol sizes
considered in this study were in the submicron range, and in the numerical model,
the conventional mechanical mechanisms (impaction, interception, diffusion and
gravitationally settling) were taken into consideration along with the electrostatic
mechanisms, including the Coulombic and dielectrophoretic effects. The aerosol
penetration through an electret fibrous filter is heavily dependent on the aerosol
penetration of a single fibre. The aerosol penetration through a single electret
fibre under various filtration conditions was calculated. The effects of aerosol
diameter, aerosol and fibre charge state, face velocity, packing density and aerosol
dielectric constant on the aerosol penetration were investigated. 相似文献
5.
Meng-Qiang Zhao 《Journal of Physics and Chemistry of Solids》2010,71(4):624-847
Short aligned carbon nanotubes (CNTs) were intercalated grown among vermiculite layers from ethylene using a simple fluidized bed chemical vapor deposition (CVD) process. The length of CNTs ranged from 0.5 to 1.5 μm after a synthesizing duration of 1-5 min at 650 °C. The as-grown CNTs vertically aligned to the vermiculite layers were with the mean outer and inner diameter of 6.7 and 3.7 nm, respectively. A CNT yield of 0.22 g/gcat was obtained for a 5-min growth. Those indicated that the fluidized bed CVD was an effective way for mass production of short CNTs. 相似文献
6.
B. Zhu Y. X. Wang Z. Y. Pan D. Cheng M. Hou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,57(2):219-226
The coalescence of Au13, Au55 and Au147 icosahedral clusters
encapsulated inside single walled carbon nanotubes (CNTs) of different
diameters are investigated using molecular dynamics simulation with
semi-empirical potentials. Three steps needed for the formation of
encapsulated nanowires are followed in detail, namely, the penetration of
clusters in CNTs, the coalescence between two clusters inside CNTs and their
accumulation to form wires. It is suggested that no significant energy
barrier is encountered during the penetration of free clusters into CNTs
provided the CNT radius is large enough, that is, about 0.3 nm larger than
the cluster radius. The relative orientation of clusters imposed by the CNT
favors their spontaneous coalescence. After coalescence of two clusters, the
Au atoms are rearranged to form new structures of cylindrical symmetry that
may be seven fold, six fold, five fold, helical or fcc depending on the CNT
diameter. The thermal stability of these structures is discussed and the
structural properties of nanowires formed by accumulation of many clusters
in CNTs are analyzed in detail. A geometrical method is presented which
allows the prediction of the structure of multi-shell helical wires, when
knowing only the CNT radius.
These modeling results suggest the possibility of synthesizing metallic
nanowires with controlled diameter and structure by embedding clusters into
nanotubes with suitable diameters. 相似文献
7.
This site study was conducted in a chemical laboratory to evaluate nanomaterial emissions from 20–30-nm-diameter bundles of single-walled carbon nanotubes (CNTs) during product development activities. Direct-reading instruments were used to monitor the tasks in real time, and airborne particles were collected using various methods to characterize released nanomaterials using electron microscopy and elemental carbon (EC) analyses. CNT clusters and a few high-aspect-ratio particles were identified as being released from some activities. The EC concentration (0.87 μg/m3) at the source of probe sonication was found to be higher than other activities including weighing, mixing, centrifugation, coating, and cutting. Various sampling methods all indicated different levels of CNTs from the activities; however, the sonication process was found to release the highest amounts of CNTs. It can be cautiously concluded that the task of probe sonication possibly released nanomaterials into the laboratory and posed a risk of surface contamination. Based on these results, the sonication of CNT suspension should be covered or conducted inside a ventilated enclosure with proper filtration or a glovebox to minimize the potential of exposure. 相似文献
8.
Dao Quang Duy Dang Mo Yoon Jung Woong Ha Choong Hun Lee Bach Thanh Cong 《Applied Surface Science》2009,256(4):1065-1068
We report on the fabrication of carbon nanotubes (CNTs) on Ni-coated stainless steel (SUS) substrates by using dc plasma enhanced chemical vapor deposition. The synthesized CNTs have the diameter of about 30 nm and the length of about 1.2 μm. To verify the effects of SUS substrates on the growth of CNTs, CNTs had also been grown on Ni-coated Si substrates. CNTs grown on the SUS substrates were more uniform compared with those grown on the Si substrates. Field emission properties of the CNT films were measured in the diode configuration, and the turn-on electric field of 3.87 V/μm and field enhancement factor β of about 1737 were obtained from the synthesized CNTs at the gap of 500 μm between the SUS substrate and the anode. These results have not only clarified the effects of the substrate on the growth of CNTs, but also shown the potential of CNTs in field emission applications, especially CNT-based cold-cathode X-ray tubes. 相似文献
9.
Nuclepore filter collection with subsequent electron microscopy analysis for nanosized agglomerates (20–500 nm in mobility diameter) was carried out to examine the feasibility of the method to assess the personal engineered nanoparticle exposure. The number distribution of the nanoparticles collected on the filter surface was obtained by visual counting and converted to the distribution in the air using validated capillary tube models. The model was validated by studying the overall penetrations of nanoparticles (Ag and soot) with different agglomeration degrees through 1 μm pore diameter Nuclepore filters at different face velocities (2–15 cm/s). In the model, the effects of the maximum length of agglomerates on interception deposition and the dynamic shape factor on impaction deposition were taken into account. Results showed that the data of the overall penetration were in very good agreement with the properly applied models. A good agreement of filter surface collection between the validated model and the SEM analysis of this study was obtained, indicating a correct particle number distribution in the air can be converted from the Nuclepore filter surface collection and this method can be applied for quantitative engineered nanoparticle exposure assessment. 相似文献
10.
《Current Applied Physics》2009,9(3):629-632
An idea of using pure iron and graphite electrodes was employed for synthesizing carbon nanoparticles by arc discharge in liquid nitrogen. The synthesized products consist of multiwalled carbon nanotubes (MW–CNT), carbon nanohorns (CNH), and carbon nanocapsules (CNC) with core–shell structure. Effect of metallic cathode and discharge current on product structure and yield had been experimentally investigated. Typical evidence of transmission electron microscopic images revealed that under some certain conditions of discharge in liquid nitrogen the synthesized products mainly consisted of CNCs with mean diameter of 50–400 nm. When conventional graphitic electrodes were employed, CNHs with some MW–CNTs were mainly synthesized. Meanwhile, MW–CNTs with diameter of 8–25 nm and length 150–250 nm became less selectively synthesized as cathode deposit under the condition of discharge in liquid nitrogen with higher arc current. The production yield of carbon nanoparticles synthesized by either carbon–carbon or carbon–iron electrodes became also lower with an increase in the arc current. 相似文献
11.
采用丝网印刷工艺制作了碳纳米管(CNTs)薄膜阴极.经适当能量激光烧蚀后,相互粘连的CNTs随表面粘附有机物的蒸发而分散开,管间隙增加、屏蔽效应减小,使得场发射性能大幅度提高,开启场强降低、场倍增因子β增大.Raman光谱分析表明,随激光能量增加,CNTs表面缺陷增多,成为新的场发射点,对其β增大的贡献加强.相对于两电极结构,三电极中平栅极结构场发射性能经激光烧蚀有更显著的改善.这说明激光烧蚀是提高CNTs场发射性能的有效方法.
关键词:
碳纳米管薄膜
场发射
激光烧蚀
Raman光谱 相似文献
12.
Qitu Hu Zibao Gan Xiuwen Zheng Aihua Zhao Xu Zhang 《Journal of nanoparticle research》2011,13(8):3191-3197
High-density attachment and one-dimensional (1D) array of FePt nanoparticles (NPs) along carbon nanotubes (CNTs) surface to
generate FePt/CNT nanocomposites were successfully obtained via a facile CNT-mediated microwave polyol method. The as-prepared
1D FePt/CNTs is about 10–20 nm in diameter and up to μm scale in length. By adjusting the solvents, the ratio of Fe/Pt and
the attached density of FePt NPs on the surface of CNTs could be well controlled. The structures, composition, and magnetic
properties of the FePt/CNTs were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution
transmission electron microscopy (HRTEM), and magnetic measurements. The possible growth mechanism has also been proposed. 相似文献
13.
Using the carbon nanotube (CNT) arrays embedded in anodic aluminum oxide (AAO) template as an electrode, large amounts of Ni nanoparticles have been encapsulated into the CNTs by an alternating current (AC) electrodepostion technique. As deposited Ni nanoparticles with a typical size of 50–60 nm randomly nucleated on the CNT walls, thus inhomogeneously distributed in the CNTs. After annealing at 600 °C, the nanoparticles transformed into quasi-spherical structures with the diameter increasing to 60–80 nm. The quasi-spherical nanoparticles were aligned in orderly rows along the axis of the CNT channels. Magnetic hysteresis measured at 5 K showed that the coercivity was 450 Oe for the as-deposited sample and 385 Oe for annealed sample, with the applied magnetic field parallel with the CNT’s axis. The structures and magnetic properties were discussed for both as-deposited and annealed samples. 相似文献
14.
Isamu Ogura Hiromu Sakurai Kohei Mizuno Masashi Gamo 《Journal of nanoparticle research》2011,13(3):1265-1280
We investigated the release potential of single-wall carbon nanotubes (CNTs) produced by the super-growth method during their
manufacturing and handling processes at a research facility. We generally sampled air at points both outside and inside of
protective enclosures such as a glove box and fume hood. Sampling the air outside of the enclosures was intended to evaluate
the actual exposure of workers to CNTs, while sampling the air inside the enclosures was performed to quantify the release
of CNTs to the air in order to estimate the potential exposure of workers without protection. The results revealed that airborne
CNTs were generated when (1) CNTs were separated from the substrates using a spatula and placed in a container in a glove
box; (2) an air gun was used to clean the air filters (containing dust that included CNTs) of a vacuum cleaner; (3) a vacuum
cleaner was used to collect CNTs (emission with exhaust air from the cleaner); (4) the container of CNTs was opened; and (5)
CNTs in the bin of the cleaner were transferred to a container. In these processes, airborne CNTs were only found inside the
enclosures, except for a small amount of CNTs released from the glove box when it was opened. Electron microscopic observations
of aerosol particles found CNT clusters, which were fragments of CNT forests, with sizes ranging from submicrometers to tens
of micrometers. 相似文献
15.
Seong Chan Kim Matthew S. Harrington David Y. H. Pui 《Journal of nanoparticle research》2007,9(1):117-125
In this study, nanoparticle penetration was measured with a wide range of filter media using silver nanoparticles from 3 nm
to 20 nm at three different face velocities in order to define nanoparticle filtration characteristics of commercial fibrous
filter media. The silver particles were generated by heating a pure silver powder source via an electric furnace with a temperature
of 870°C, which was found to be the optimal temperature for generating an adequate amount of silver nanoparticles for the
size range specified above. After size classification using a nano-DMA, the particle counts were measured by an Ultrafine
Condensation Particle Counter (UCPC) both upstream and downstream of the test filter to determine the nanoparticle penetration
for each specific particle size. Particle sampling time continued long enough to detect more than 105 counts at the upstream and 10 counts at the downstream sampling point so that 99.99% efficiency can be detected with the
high efficiency filter. The results show a very high uniformity with small error bars for all filter media tested in this
study. The particle penetration decreases continuously down to 3 nm as expected from the classical filtration theory, and
together with a companion modeling paper by␣Wang et al. in this same issue, we found no significant evidence of nanoparticle
thermal rebound down to 3 nm. 相似文献
16.
C.G. Hu W.L. Wang K.J. Liao G.B. Liu Y.T. Wang 《Journal of Physics and Chemistry of Solids》2004,65(10):1731-1736
The functionalization of carbon nanotubes (CNTs) was carried out by using different chemical treatment methods. These functionalized CNTs were characterized by TEM image and FT-IR spectra. The CNT electrodes are measured by thermal resistivity and cyclic voltammetry experiments. The results showed that two important factors controlled the electrochemical properties of the CNT film electrode: one is the active functional group; another is activation energy of the CNT film. From our experiments, we have found the electrode of 10 min nitric acid treated CNTs have the optimal peaks in relation to carboxylic acids, the highest redox peak currents, the biggest value of k0 and well-defined quasi-reversible voltammograms for redox of iron couples, in which the two factors best match. 相似文献
17.
Sergei M. Pimenov Vadim D. Frolov Evgeny V. Zavedeev Nikolay P. Abanshin He-Yun Du Wei-Chao Chen Li-Chyong Chen Jih-Jen Wu Kuei-Hsien Chen 《Applied Physics A: Materials Science & Processing》2011,105(1):11-16
In this paper, we have studied field emission properties of highly dense arrays of multi-walled carbon nanotubes (CNTs) used
as cathodes in diode-type field emission devices with a phosphor screen. For the high-density CNT emitters it is demonstrated
that the emission sites are located on the CNT-cathode edges, which is direct experimental evidence of the ‘edge effect’.
The results of computer simulations (using ‘ANSYS Electromagnetic’ software) are presented to confirm the experimental data
and to analyze the effect of patterning on the electric field distribution for high-density CNT arrays. It is shown that selective-area
removal of nanotubes in the arrays leads to the formation of additional edges characterized by the high field enhancement
factor and enhanced emission from the CNT cathodes. In addition, scanning probe microscopy techniques are employed to examine
surface properties of the high-density CNT arrays. For CNT arrays of ‘short’ nanotubes, the work function distribution over
the sample surface is detected using a scanning Kelvin microscopy method. 相似文献
18.
B. R’mili C. Dutouquet J. B. Sirven O. Aguerre-Chariol E. Frejafon 《Journal of nanoparticle research》2011,13(2):563-577
Carbon Nanotubes (CNTs) are deemed as revolutionary materials very likely to be utilized in numerous fields such as electronics,
energy, and medicine, to name but a few. The emergence of this new fiber-shaped material with remarkable properties and dimensions
of a few micrometers in length and a few tens of nanometers in diameter raises concerns about potential exposure of workers
involved in the whole production cycle. These risks emphasize the need to develop tools allowing identifying such objects,
either as isolated fibers or entangled in bundles, in situ and if possible in real time. In this context, experiments aiming
at detecting potential particle release while manipulating raw CNT powders were performed at ARKEMA research center in a high
safety cell dedicated to scientific experiments. Two techniques were employed. First, particle collection on TEM grids was
achieved using two samplers, the first based on aspiration and the second on diffusion assisted with thermophoretic repulsion.
These allowed differed analysis of single particle morphology, size and chemical composition. Second, real time multi-elemental
composition of particle emission was monitored using LIBS. Eventually, though not quantitative, the coupling of TEM grid analysis
with LIBS data demonstrated the possibility of real time detection of CNTs entangled in bundles. 相似文献
19.
J.H. Kim 《Applied Surface Science》2010,256(8):2636-2642
We successfully fabricated field emitter arrays of carbon nanotube (CNT) dots of 10 μm diameter with excellent field emission properties by using photosensitive CNT paste. The CNT paste was investigated in terms of morphologies, current-voltage properties, and luminous uniformities by varying the mixing ratios of micro and nanoparticle inorganic fillers and the amount of CNTs added into the paste. The 3:1 mixing of micro and nanoparticle fillers and the addition of 5% CNTs in the paste brought about the best field emission characteristics of dot-patterned CNT field emitter arrays. 相似文献
20.
Carbon nanotubes (CNTs) were controllably coated with the uninterrupted CuO and CeO2 composite nanoparticles by a facile pyridine-thermal method and the high catalytic performance for CO oxidation was also found. The obtained nanocomposites were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction as well as X-ray photoelectron spectroscopy. It is found that the CuO/CeO2 composite nanoparticles are distributed uniformly on the surface of CNTs and the shell of CeO2/CuO/CNT nanocomposites is made of nanoparticles with a diameter of 30-60 nm. The possible formation mechanism is suggest as follows: the surface of CNTs is modified by the pyridine due to the π-π conjugate role so that the alkaline of pyridine attached on the CNT surface is more enhanced as compared to the one in the bulk solvent, and thus, these pyridines accept the proton from the water molecular preferentially, which result in the formation of the OH− ions around the surface of CNTs. Subsequently, the metal ions such as Ce3+ and Cu2+ in situ react with the OH− ions and the resultant nanoparticles deposit on the surface of CNTs, and finally the CeO2/CuO/CNT nanocomposites are obtained. The T50 depicting the catalytic activity for CO oxidation over CeO2/CuO/CNT nanocomposites can reach ∼113 °C, which is much lower than that of CeO2/CNT or CuO/CNT nanocomposites or CNTs. 相似文献