Carbon Nanocoils Research Articles

Analytical and Experimental Characterization of Stiffness and Damping in Carbon Nanocoil Reinforced Polymer Composites

This study focuses on understanding the stiffness and damping characteristics of carbon nanocoil (CNC)/polymer composites. To determine the effective elastic and viscoelastic properties of a polymer reinforced with aligned CNCs, the finite element analysis was performed using a three-dimensional unit cell model. The coil morphology of CNCs was examined using a scanning electron microscope. The effects of coil diameter, tube diameter, coil pitch and number of coil turns on the effective properties are discussed. The effective properties of a polymer reinforced with randomly oriented CNCs were also predicted by the results for the unit cell model. The tradeoffs between stiffness and damping characteristics are assessed by changing the volume fraction and geometrical parameters of CNCs. Additionally, experimental measurements of the elastic modulus and the loss factor of the manufactured CNC/polymer composites were carried out by using dynamic mechanical analysis. The predictions were then compared with the experimental results. Furthermore, scanning electron microscopy was performed to observe the fracture surface of CNC/polymer composites.

ヘリカルカーボンナノファイバ，ナノホーン，およびナノバルーンの合成と応用

This paper outlines the preparation methods and feasible applications of new nano-carbon materials; helical carbon nanofiber (HCNF), carbon nanohorn (CNH), and carbon nanoballoon (CNB). The HCNF is fibrilliform carbon materials with spiral and twisted shapes. The HCNF is divided into the groups of carbon nanocoil (CNC) and nanotwist (CNTw). They are synthesized by means of catalytic chemical vapor deposition (catalytic-CVD) with different catalysts. One of their applications is field emitter for next-generation plat panel display. The CNH is a particulate-form material and is produced by the evaporation of graphite with a laser or an arc discharge. The one of possible applications is the catalyst-supported electrode for fuel cell. The CNB is synthesized from an arc soot (or called arc black) and also from a particular-type acetylene black by means of high-temperature treatment under inert gas. Its potential applications are mentioned.

Catalytic effects of various metal carbides and Ti compounds for the growth of carbon nanocoils (CNCs)

The catalytic effect of various metal carbides and Ti compounds on the growth of carbon nanocoils (CNCs) was examined. TiC was the most effective carbides for the preparation of the CNCs. Furthermore, some other Ti compounds were also used as catalysts, and pure CNCs could be effectively produced using a NiTiO 3 catalyst at 660–690 °C. On the other hand, CNCs were poorly obtained using the pure metals catalysts Ti, Ta, Mo, Cr and W. The CNCs obtained were generally twisted-forms with coil diameters of 100–600 nm and coil lengths of 1–3 mm, irrespective of the catalysts used.

Morphology of Carbon Nanostructures in Alcohol Chemical Vapor Deposition

We have investigated the growth of carbon nanocoils (CNCs) using a combination of a Ni catalyst and alcohol chemical vapor deposition (CVD). When using an Fe or Co catalyst, only normal carbon nanotubes (CNTs) are grown at 700 and 900 °C. On the other hand, when using a Ni catalyst, CNCs with various helical structures are grown at 900 °C in addition to CNTs. When a Ni/Fe or Ni/Co alloyed catalyst is used, the yield of the CNCs decreases and the shape of the CNCs becomes elongated as the Fe or Co content increases. These results will contribute to our understanding of the CNC growth mechanism.

Reverse Monte Carlo Modeling of Atomic Configuration for Amorphous Materials

Reverse Monte Carlo (RMC) modeling, based on diffraction data, was applied to various kinds of amorphous materials to visualizing the three-dimensional atomic arrangement and to elucidate topological characteristics. For an as-grown amorphous carbon nanocoil, it could be clarified that graphene sheets are winding and the regular ABAB… stacking is lost and the configuration gradually changes to the hexagonal network with great regularity through heat treatment. Voronoi analysis of the RMC model could characterize the atomic configurations for NiZr2 and CuZr2 metallic glasses. The Zr environments are very similar in the two systems, but there are marked differences between the polyhedra around Ni and Cu atoms. The polyhedra around Ni atoms are dominated by prismatic-like polyhedra. In contrast, icosahedron-like polyhedra are preferred for Cu.

Diameter Control of Carbon Nanocoils by the Catalyst of Organic Metals

Carbon nanocoils with controlled diameters have been synthesized by thermal chemical vapor deposition using carboxylic acid metals as a precursor of the catalyst. It has been found that the line diameter of the nanocoils is determined by the size of the catalyst particles which can be controlled by adjusting the concentration of carboxylic acid metals in the solution. It is confirmed that the coil diameter of the nanocoils is proportional to the size of the catalyst particles. This is consistent with a proposed hodograph of carbon extrusion from a catalyst particle.

Carbon Materials with Unusual Morphologies and Their Formation Mechanism

Carbon nanocoils and nanofibers with novel morphologies and potential new properties were prepared from controlled delivery of acetylene. Branched carbon nanocoils were produced from continuous acetylene flow. Pulsed delivery of acetylene produced branched carbon nanofibers with even-length subunits. Interrupted acetylene flow resulted in half coil and half fiber hybrid structures. The substrate was found to play an important role in controlling the morphology of carbon materials. On both silicon substrate and phosphorus-doped alumina ceramic substrates, carbon nanocoils and carbon nanofibers could be selectively prepared; however, on graphite or pure alumina substrate, only straight carbon nanofibers were produced. The ability to control the morphology of the carbon materials provided better insight into the mechanism of the formation of these materials.

Proximity electron lithography using permeable electron windows

This letter reports on an electron source consisting of thin electron-permeable windows and a carbon nanocoil emitter. Electron windows with diameters of 250nm were fabricated using silicon micromachining technology. Carbon nanocoils that are selectively grown from silicon were used as emitters. Field-emitted electrons from the emitters are transmitted through the thin silicon electron windows with thicknesses in the range of 15–50nm. The electron transmittance of the electron windows was evaluated and it was demonstrated that transmittances higher than 60% are achievable for the case of electron energies higher than 5keV. Proximity electron lithography is demonstrated using 1.5×1.5μm2 electron windows with a thickness of 50nm.

Preparation of single-helix carbon microcoils by catalytic CVD process

Three-dimensional (3D) single-helix spring-like carbon microcoils (SH-CMCs) were obtained by the catalytic pyrolysis of acetylene at 800–820 °C over the Fe–Ni alloy catalysts; their growth morphologies and microstructure were examined. The diameter of carbon fiber, from which the carbon nanocoils was formed, was about 0.5 μm, the coil diameter was about 1–2 μm, and the coil pitch was about the same with the coil diameter. The SH-CMCs were generally grown by a double-directional growth mode.

Saccharide-based graphitic carbon nanocoils as supports for PtRu nanoparticles for methanol electrooxidation

Highly graphitic carbon nanocoils were synthesised from the catalytic graphitization of carbon spherules obtained by the hydrothemal treatment of different saccharides (sucrose, glucose and starch). This nanostructured carbon was characterized by X-ray power diffraction, N 2 adsorption and microscopy techniques (SEM and TEM). The carbon nanocoils were used as a support for PtRu nanoparticles, which were well-dispersed over the carbon surface. This catalytic system was investigated for use as an electrocatalyst for methanol electrooxidation in an acid medium. The experiments were carried out at two working temperatures (25 °C and 60 °C). It was found that the carbon nanocoils supporting PtRu nanoparticles exhibit a high catalytic activity, which is even higher than that of conventional carbon supports (Vulcan XC-72R). We believe that the high electrocatalytic activity of the carbon nanocoils presented here is due to the combination of a good electrical conductivity, derived from their graphitic structure, and a wide porosity that allows the diffusional resistances of reactants/products to be minimized.

Synthesis and field emission characteristics of carbon nanocoils with a high aspect ratiosupported by copper micro-tips

Carbon nanocoils (CNCs) were synthesized via thermal chemical vapour deposition (CVD) withC2H2 andNH3 gasesat 600 °C. A Ni catalyst was placed upon the copper micro-tip structures that were fabricated on asilicon substrate. Our CNCs had a long rope shape with a length not exceeding100 µm and a nanoscale diameter. The copper micro-tips were formed through high current pulseelectroplating, which played a significant role in characterizing our CNCs. The CNCs grownon the copper micro-tips showed outstanding field emission performance andlong-term stability. Their turn-on field, defined as that at a current density of10 µA cm−2, was1.30 V µm−1 and the maximumcurrent density reached 11.17 mA cm−2 at an electric field of 2.39 V µm−1.

Determination of Carbon Nanocoil Orientation by Dielectrophoresis

The alignment of carbon nanocoils (CNCs) has been demonstrated by electrophoresis and dielectrophoresis. In the case of DC electric field, while most of all CNCs moved toward a cathode and formed a chain structure in a suspension, no CNC alignment was observed after the evaporation of the suspension. In contrast, in the case of AC electric field with a frequency higher than 1 kHz, the CNCs were aligned along the electric field and connected to each other even after the evaporation of the suspension. This difference is discussed in terms of the fluidic perturbation of the suspension.

カーボンナノコイルの低温合成

Synthesis of carbon nanocoils was carried out by the simple apparatus based on hot-filament CVD at catalyst temperatures below 450ºC. Copper was vacuum evaporated onto the nickel particles formed by scratching the poly-crystal nickel plate with sandpaper. These particles were used for the catalysts for synthesis of nanocoils. Heating was not performed at all for forming these particles. Ethanol as a carbon source was introduced into the chamber with argon gas. Synthesis was performed at atmospheric pressure. Carbon nanocoils could be synthesized at temperatures above 400ºC. The yield of nanocoils in total carbon fibers is about 80% at 400ºC. The diameter of these products decreases with the decrease of diameter of catalyst particles.

Controllable synthesis of carbon microcoils/nanocoils by catalysts supported on ceramics using catalyzed chemical vapor deposition process

Carbon microcoils (CMCs) and carbon nanocoils (CNCs) were prepared by the catalytic pyrolysis of acetylene using Ni-based or Fe-based catalysts supported on molecular sieves by the catalyzed chemical vapor deposition (CCVD) process. The growth pattern, morphology and structure of the CMCs and CNCs (to be called by a joint name ‘carbon coils’) were examined in detail. By using a ceramic supporter, the anisotropy of the catalysts could be utilized and carbon coils could be more effectively obtained compared to non-supported alloy catalysts. Furthermore, the morphologies of the carbon coils could be controlled. The Raman spectra indicated that the structures of all these carbon coils were nanocrystalline phases in amorphous networks in spite of the different catalysts and preparation conditions.

Morphology and growth mechanism of single-helix spring-like carbon nanocoils with laces prepared using Ni/molecular sieve (Fe) catalyst

Single-helix spring-like carbon coils with laces grew over the Ni metal catalyst supported on molecular sieve containing a trace amount of an Fe impurity that originated from a kaolin clay raw material. The morphology, microstructure, and growth mechanism of the single-helix carbon nanocoils and laces were investigated. We found that a trace amount of Fe impurity contained in the molecular sieve was a key factor in the lace growth. It is considered that the Fe impurity may poison, restraint the formation of three crystal faces, resulting in the growth of single helix coils. It is also considered that a very strong inner stress is periodically formed between the boundary of two fibers, and the thin carbon film is swelled to form laces.

Probing Adhesive Interactions along the Sidewalls of Carbon Nanotubes and Nanocoils

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Synthesis of carbon nanocoils on surface morphology changed silicon substrates

By the controlled corrosion of HF, silicon substrates appeared to be in a state of concavo-convex morphology. Carbon nanocoils were synthesized on these silicon substrates by the pyrolysis of acetylene with catalytic thermal chemical vapor deposition (CVD). Scanning electron microscopy and transmission electron microscopy were carried out to observe the regular morphology of carbon nanocoils, while Raman spectra was used to characterize the graphitization degree. The growing process of the nanocoils was regarded as the anisotropic activity of catalyst particles resulting from the different thicknesses of FeO layer.

Various Conformations of Carbon Nanocoils Prepared by Supported Ni–Fe/Molecular Sieve Catalyst

The carbon nanocoils with various kinds of conformations were prepared by the catalytic pyrolysis of acetylene using the Ni metal catalyst supported on molecular Sieves which was prepared using Fe-containing kaolin as the raw material. There are four kinds of carbon nanocoils conformations produced by this catalyst. The influences of reaction temperature and gas conditions on the conformations of the nanocoils were investigated and the reasons of forming nano-size coils were discussed by comparison with pure Ni metal catalyst.

Low-Temperature Synthesis of Amorphous Carbon Nanocoils via Acetylene Coupling on Copper Nanocrystal Surfaces at 468 K: A Reaction Mechanism Analysis

A new type of amorphous helical carbon nanofibers has been synthesized using copper nanocatalysts and an acetylene gas source at atmospheric pressure. The nanofibers are grown at 468 K, which is the lowest temperature by ordinary metal-catalyzed thermal chemical vapor deposition of hydrocarbon, and exhibit a symmetric growth mode in the form of twin helices. IR, XRD, Raman, and C/H molar ratio analyses reveal a polymer-like structure with a weak trans-polyacetylene feature. The nanofibers are a mixture of solid polymers and a small amount of carbon. A reaction mechanism has been proposed on the basis of the previous studies of acetylene adsorption, desorption properties, and surface reactions on copper (111), (110), and (001) planes under ultrahigh-vacuum (UHV) conditions as well as the results obtained in our study. The reaction mechanism of acetylene on copper single-crystal surfaces under UHV conditions indeed reflects the reaction mechanism under practical catalytic conditions at atmospheric pressure. The nanofibers grow mainly via acetylene coupling to solid polymers on copper nanocrystal surfaces. Acetylene also couples to yield small amounts of liquid oligomers and gaseous products, and undergoes slight carbon deposition during the fiber growth.

Synthesis of Carbon Tubule Nanocoils Using Fe−In−Sn−O Fine Particles as Catalysts

We have developed Fe-In-Sn-O fine particle or powder catalysts for synthesizing carbon nanocoils by catalytic thermal chemical vapor deposition. The coprecipitation technique was used to produce the powder catalysts. By optimizing the composition ratios of Fe, In (between 10 and 33% of Fe), and Sn (less than 3.3% of Fe), carbon nanocoils could be grown in high yield. From the study of optimizing the compositions of In and Sn and the study of crystal structures of the catalysts using X-ray diffraction measurements, it was also found that Sn in the catalysts was required to grow carbon nanocoils and that In plays roles in increasing the yield of carbon nanocoils and controlling the coil diameters. This study will lead to the mass production of carbon nanocoils and therefore widen their applications.