Hydrogen Arc Research Articles

Synthesis of carbon nanowires as electrochemical electrode materials

One dimension carbon nanowires were synthesized by direct current hydrogen arc discharge. The nanowires with an average diameter of ~ 15 nm were studied by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman, and X-ray diffraction (XRD). Electrochemical test indicated that the carbon nanowires exhibited a high electrochemical performance. Such nanowires as electrochemical electrical double layer capacitance for potential energy storage applications exhibit a high specific capacitance of ~ 200 F g − 1 at a charge and discharge current density of 1 A/g with excellent cycling ability. These results indicate that this simple synthesis technique for providing carbon nanowire materials has great potential in various applications such as energy storage.

Ultra-thin double-walled carbon nanotubes: A novel nanocontainer for preparing atomic wires

Double-walled carbon nanotubes (DWCNTs) with high graphitization have been synthesized by hydrogen arc discharge. The obtained DWCNTs have a narrow distribution of diameters of both the inner and outer tubes, and more than half of the DWCNTs have inner diameters in the range 0.6-1.0 nm. Field electron emission from a DWCNT cathode to an anode has been measured, and the emission current density of DWCNTs reached 1 A/cm2 at an applied field of about 4.3 V/{\mu}m. After high-temperature treatment of DWCNTs, long linear carbon chains (C-chains) can be grown inside the ultra-thin DWCNTs to form a novel C-chain@DWCNT nanostructure, showing that these ultra-thin DWCNTs are an appropriate nanocontainer for preparing truly one-dimensional nanostructures with one-atom-diameter.

Synthesis and field emission property of carbon nanotubes with sharp tips

Carbon nanotubes (CNTs) with sharp tips were synthesized by a hydrogen arc discharge method. Three unusual morpholo- gies, i.e., a cone-shaped tip, a suddenly-shrinking tip, and a pencil point-like tip were observed. These novel tip structures are considered to be related to the addition of a small amount of silicon powder in the raw material, which may introduce structural defects in the CNTs. The field emission property of the sharp-tip CNTs was investigated, and a low threshold electric field of 3.75 V/m, a high field emission current density of ~1.6×10 5 A/cm 2 , and a good emission stability were demonstrated. The superior field emission performance of the CNTs can be attributed to their good crystallinity and unique tip structures.

Synthesis and field emission property of carbon nanotubes with sharp tips

Carbon nanotubes (CNTs) with sharp tips were synthesized by a hydrogen arc discharge method. Three unusual morphologies, i.e., a cone-shaped tip, a suddenly-shrinking tip, and a pencil point-like tip were observed. These novel tip structures are considered to be related to the addition of a small amount of silicon powder in the raw material, which may introduce structural defects in the CNTs. The field emission property of the sharp-tip CNTs was investigated, and a low threshold electric field of 3.75 V/m, a high field emission current density of ∼1.6×10 5 A/cm 2, and a good emission stability were demonstrated. The superior field emission performance of the CNTs can be attributed to their good crystallinity and unique tip structures.

Effective and efficient purification of single-wall carbon nanotubes based on hydrogen treatment

A simple, effective and efficient purification method for single-wall carbon nanotubes (SWCNTs) prepared by hydrogen arc discharge has been developed. Hydrogen treatment has been used to remove the amorphous carbon and graphene sheets encapsulating Fe catalyst nanoparticles. The exposed Fe nanoparticles can be easily dissolved in concentrated hydrochloric acid. Carbon content higher than 99 wt.% can be achieved. The small SWCNTs with a diameter of 0.9 nm are found to survive during the purification processes. This new purification method enables us to obtain purified SWCNTs with high-crystallinity and without obvious damage.

Equatorward moving arcs and substorm onset

Key observations of phenomena during the growth phase of a substorm are being reviewed with particular attention to the equatorward motion of the hydrogen and electron arcs. The dynamic role of the electron, the so‐called growth phase arc, is analyzed. It is part of a current system of type II that is instrumental in changing the dominantly equatorward convection from the polar cap into a sunward convection along the auroral oval. A quantitative model of the arc and associated current system allows determining the energy required for the flow change. It is suggested that high‐β plasma outflow from the central current sheet of the tail creates the current generator. Assessment of the energy supplied in this process proves its sufficiency for driving the arc system. The equatorward motion of the arcs is interpreted as a manifestation of the shrinkage of the near‐Earth transition region (NETR) between the dipolar magnetosphere and the highly stretched tail. This shrinkage is caused by returning magnetic flux to the dayside magnetosphere as partial replacement of the flux eroded by frontside reconnection. As the erosion of the NETR is proceeding, more and more magnetic flux is demanded from the central current sheet of the near‐Earth tail until highly accelerated plasma outflow causes the current sheet to collapse. Propagation of the collapse along the tail triggers reconnection and initiates the substorm.

ChemInform Abstract: Hydrogen Storage in Single-Walled Carbon Nanotubes at Room Temperature.

Masses of single-walled carbon nanotubes (SWNTs) with a large mean diameter of about 1.85 nanometers, synthesized by a semicontinuous hydrogen arc discharge method, were employed for hydrogen adsorption experiments in their as-prepared and pretreated states. A hydrogen storage capacity of 4.2 weight percent, or a hydrogen to carbon atom ratio of 0.52, was achieved reproducibly at room temperature under a modestly high pressure (about 10 megapascal) for a SWNT sample of about 500 milligram weight that was soaked in hydrochloric acid and then heat-treated in vacuum. Moreover, 78.3 percent of the adsorbed hydrogen (3.3 weight percent) could be released under ambient pressure at room temperature, while the release of the residual stored hydrogen (0.9 weight percent) required some heating of the sample. Because the SWNTs can be easily produced and show reproducible and modestly high hydrogen uptake at room temperature, they show promise as an effective hydrogen storage material.

Synthesis of Graphene Sheets with High Electrical Conductivity and Good Thermal Stability by Hydrogen Arc Discharge Exfoliation

We developed a hydrogen arc discharge exfoliation method for the synthesis of graphene sheets (GSs) with excellent electrical conductivity and good thermal stability from graphite oxide (GO), in combination with solution-phase dispersion and centrifugation techniques. It was found that efficient exfoliation and considerable deoxygenation of GO, and defect elimination and healing of exfoliated graphite can be simultaneously achieved during the hydrogen arc discharge exfoliation process. The GSs obtained by hydrogen arc discharge exfoliation exhibit a high electrical conductivity of approximately 2 x 10(3) S/cm and high thermal stability with oxidization resistance temperature of 601 degrees C, which are much better than those prepared by argon arc discharge exfoliation (approximately 2 x 10(2) S/cm, 525 degrees C) and by conventional thermal exfoliation (approximately 80 S/cm, 507 degrees C) with the same starting GO. These results demonstrate that this hydrogen arc discharge exfoliation method is a good approach for the preparation of GSs with a good quality.

Ferromagnetic properties of single-walled carbon nanotubes synthesized by Fe catalyst arc discharge

Abstract Single-walled carbon nanotubes (SWCNTs) were directly synthesized by a hydrogen arc discharge method using only Fe catalyst. The synthesized carbon materials indicated high-purity SWCNTs with Fe catalyst encapsulated with several graphite layers. The diameter of Fe catalysts encapsulated with graphene layers is 1.5–2.0 nm. From the ferromagnetic resonance measurements, the as-synthesized SWCNTs show the ferromagnetic properties at room temperature. The ferromagnetic properties of SWCNTs would be attributed to Fe catalysts encapsulated by graphite layers.

Optimization and characterization of a Pilot-psi cascaded arc with non-LTE numerical simulation of Ar, H2 gases

A numerical simulation code, PLASIMO, is used to model non-LTE plasmas in the cascaded arc for hydrogen and argon. The purpose of these simulations is to optimize the cascaded arc plasma source, which is used to produce a high density plasma column in Pilot-psi, a linear device to study plasma surface interaction processes. Results are compared with the experimental findings to validate the model. The effect of a change in the arc channel geometry on the ionization degree is studied. It is found that for the hydrogen arc an increase in length beyond 30 mm will not increase the ionization degree, in contrast to widening the arc. With an increase in radius from 2 mm to 5 mm for a 30 mm long arc the degree of ionization of hydrogen increases from 5.4 to 38. For the argon arc an increase both in the length and in the width increases the ionization degree. With an increase in length from 30 mm to 40 mm for a 2 mm wide arc the degree of ionization of argon increases from 14.5 to 17.1, whereas with an increase in radius from 2 mm to 5 mm for 30 mm long arc the same increases from 14.5 to 37.5. To simulate the influence of the wall material, the effect of hydrogen wall association on the degree of ionization and dissociation is studied. Wall association in the nozzle section, where heating is absent, significantly reduces the degree of dissociation, in agreement with the experimental data. In Pilot-psi, the arc is operated in a high magnetic field, so the effect of a magnetic field on the yield of Ar+ and H+ ions leaving the arc is also studied. It is found that with a 3 T magnetic field the Ar+ yield increases from 1.6 × 1020 to 2.1 × 1020 (25% increase) while the H+ yield increases from 1.4 × 1020 to 2.9 × 1020 (100% increase).

Electronic Structure and Field Emission Properties of Double-Walled Carbon Nanotubes Synthesized by Hydrogen Arc Discharge

We have synthesized high-purity double-walled carbon nanotubes (DWCNTs) by an arc-discharge method in hydrogen ambient. The DWCNTs were synthesized using a mixture of Fe catalyst and FeS promoter. Without FeS promoter, we only obtained single-walled carbon nanotubes (SWCNTs). The synthesized DWCNTs had outer diameters in the range of 3.0−3.4 nm and an average interlayer distance of 0.38 nm between graphene layers. The FeS promoter played a key role for the DWCNT growth. The DWCNTs indicated high electronic density of states in the binding energy region between 3.88 and 13.23 eV below Fermi energy, indicating that the DWCNTs had alot of delocalized graphite σ and σ/π electrons. For field emission properties, the typical turn-on field of DWCNTs was about 3.0 V/μm at the emission current density of 0.1 μA/cm2, and the emission current density of DWCNTs was about 10 mA/cm2 at the applied field of 6.5 V/μm. It is considered that the higher current densities of DWCNTs were mainly attributed to the emitted deloc...

Synthesis and High Thermal Stability of Double-Walled Carbon Nanotubes Using Nickel Formate Dihydrate as Catalyst Precursor

Nickel formate dihydrate is demonstrated to be an effective catalyst precursor for selectively synthesizing double-walled carbon nanotubes (DWNTs) with high thermal stability by using a hydrogen arc discharge technique. High-resolution transmission electron microscopy (HRTEM) observations show that the assynthesized DWNTs are of high quality with good structural integrity and narrow diameter distribution (1.983.47 nm and 1.32-2.81 nm, respectively, for the outer and inner diameter). Thermogravimetric analysis (TGA) in air indicates that the DWNTs have excellent oxidation resistance up to 800 °C, approaching to that of graphitized multiwalled carbon nanotubes and higher than that of DWNTs prepared by other routes or methods. Moreover, Raman analysis and HRTEM observations reveal that these DWNTs can keep good structural stability and other carbon species are removed after oxidation at 650 °C in air flow. The formation of DWNTs with high thermal stability is attributed to the cleaning effect of active radicals such as hydrogen and oxygen originated from the decomposition of nickel formate dihydrate and the in situ defect-healing effect induced by high arc current in the arc growth process. This approach opens various application possibilities for DWNTs with high thermal stability to be used in high-temperature composites, nanoelectronic devices, and electron filed emitters operating at high currents, etc.

Synthesis and High Thermal Stability of Double-Walled Carbon Nanotubes Using Nickel Formate Dihydrate as Catalyst Precursor

Nickel formate dihydrate is demonstrated to be an effective catalyst precursor for selectively synthesizing double-walled carbon nanotubes (DWNTs) with high thermal stability by using a hydrogen arc discharge technique. High-resolution transmission electron microscopy (HRTEM) observations show that the as-synthesized DWNTs are of high quality with good structural integrity and narrow diameter distribution (1.98−3.47 nm and 1.32−2.81 nm, respectively, for the outer and inner diameter). Thermogravimetric analysis (TGA) in air indicates that the DWNTs have excellent oxidation resistance up to ∼800 °C, approaching to that of graphitized multiwalled carbon nanotubes and higher than that of DWNTs prepared by other routes or methods. Moreover, Raman analysis and HRTEM observations reveal that these DWNTs can keep good structural stability and other carbon species are removed after oxidation at 650 °C in air flow. The formation of DWNTs with high thermal stability is attributed to the cleaning effect of active radicals such as hydrogen and oxygen originated from the decomposition of nickel formate dihydrate and the in situ defect-healing effect induced by high arc current in the arc growth process. This approach opens various application possibilities for DWNTs with high thermal stability to be used in high-temperature composites, nanoelectronic devices, and electron filed emitters operating at high currents, etc.

EELS plasmon studies of silver/carbon core/shell nanocables prepared by simple arc discharge

A method for the fabrication of large quantities of high quality silver nanocables encapsulated in carbon nanotubes (Ag@C) using a hydrogen arc is presented. A growth mechanism based on the generation of poly-aromatic hydrocarbons by the hydrogen arc is proposed. The size-dependent electronic structures of the resultant materials are investigated using electron energy loss spectroscopy (EELS). The surface plasmon and bulk-excitation character observed by EELS are discussed. As the diameter of Ag@C nanocable decreases, the surface and bulk plasmons of the silver core shift to lower energy and the peaks broaden. Measurements of electrical conductivity exhibits a liner current–voltage character with a conductivity of 0.5×104 S/cm for the nanocable structure.

Investigation of Field Emission and Photoemission Properties of High-Purity Single-Walled Carbon Nanotubes Synthesized by Hydrogen Arc Discharge

Single-walled carbon nanotubes (SWCNTs) were directly synthesized by a hydrogen arc-discharge method by using only Fe catalyst. The synthesized carbon materials indicated high-purity SWCNTs without amorphous carbon materials from SEM observation. The SWCNTs had diameters of 1.5-2.0 nm from TEM and Raman observation. After a simple purification, TGA indicated that SWCNTs had a purity of ca. 90.1 wt %. Field emission from the SWCNT emitters which were fabricated by using a spray method was measured by a diode structure. The vertically aligned SWCNT emitters showed the low turn-on voltage of 0.86 V/microm and a high emission-current density of 3 mA/cm2 at an applied field of about 3 V/microm. From a Fowler-Nordheim plot, the vertically aligned SWCNT revealed a high field enhancement factor of 2.35 x 10(4). The photoemission measurements, excited by a photon energy of 360 eV, showed significantly delocalized graphite-pi states at the purified SWCNTs. Here, we investigated that the field-emission properties of SWCNTs would be attributed to the high electronic density of states near Fermi energy, including the delocalized graphite-pi states.

Nanotube-based nanoelectromechanical systems

with chiral potential energy surface of interwall interaction, which can be called bolt‐nut pair. We determine conditions for different modes of operation and discuss both their feasibility in various NEMS devices and methods of application of driving forces for various types of motion. We develop a model for computing the interwall interaction energy in nanotubes with atomic structural defects. Our computations of the interwall interaction energy show that periodic distribution of atomic defects in a double-walled nanotube can create conditions required for synthesizing nanotubes that can be used as bolt‐nut pairs with desired thread characteristics. We discuss the feasibility of fabrication of nanotubes of this type by self-organization. We propose novel schemes of carbon-nanotube‐based NEMS devices containing such a bolt‐nut pair: a nanodrill that can be used to modify surfaces (see also [22‐24]) and a nanomotor in which the force directed along the nanotube axis is converted into relative rotation of its walls. We also note that the double-walled nanotubes analyzed theoretically in this paper can be synthesized by the standard arc discharge method [28], by the hydrogen arc discharge method [29], by catalytic decomposition of hydrocarbons [30, 31], and by heating [32] or electron beam lithography [33] applied to single-walled nanotubes containing chains of fullerene molecules.

Double-walled carbon nanotubes synthesized using carbon black as the dot carbonsource

Double-walled carbon nanotubes (DWNTs) were synthesized used carbon black as the dotcarbon source by a semi-continuous hydrogen arc discharge process. High-resolutiontransmission electron microscopy (HRTEM) observations revealed that most of thetubes were DWNTs with outer and inner diameters in the range of 2.67–4 nm and1.96–3.21 nm, respectively. Most of the DWNTs were in a bundle form of about10–30 nm in diameter with high purity (about 70%) from thermal gravimetric analysis(TGA), resonant laser Raman spectroscopy, scanning electron microscopy (SEM)and TEM characterizations. It was found that carbon black as the dot carbonsource could be easy controlled to synthesize one type of nanotube. A simpleprocess combining oxidation and acid treatment to purify the DWNT bundles wasused without damaging the bundles. The structure of carbon black, as the keyelement for influencing purity, bundle formation and purification of DWNTs, isdiscussed.

Development of a 100eV, high-flux ion beam acceleration system

A new system of electrodes has been developed for a high-flux, steady-state ion source with a large irradiation area to study plasma-wall interaction in fusion reactors at energies in the 100eV range. These electrodes are multiaperture triode electrodes—the sizes of which are smaller as compared with those used in similar applications for previous systems. In particular, these electrodes have a thickness of 0.5mm and an aperture size of 0.9mm in diameter with 0.5mm gaps between them. The influence of the plasma sheath on the beam energy has to be estimated since the plasma sheath potential is comparable to the acceleration voltage in such a low energy region. Source plasma is produced by a hydrogen arc discharge, following which hydrogen ions are extracted by using the new electrode system. Ion fluxes of 1.5×1020–5.3×1020H∕m2s with energies ranging from 28to102eV∕H were obtained. These values are comparable to those of conventional high-flux ion sources with higher energies. This low energy ion beam can be used to investigate the plasma-wall interaction in fusion reactors.

Plasma-Prepared Ni/Al2O3: Preparation, Characterization and Toluene Hydrogenation

Nano-nickel particles were prepared using hydrogen arc plasma method and new nano-nickel hydrogenation catalysts were prepared through calcinating mixtures of the plasma-prepared nano-nickel particles and a ?-alumina support. The catalysts were characterized by using SEM, XRD, and TPR. The activities of the catalysts were evaluated through the hydrogenation of toluene in a fixed be microreactor. Catalysts prepared by conventional comulling and impregnation methods were also examined for comparative purposes. The characterization results showed that the nano-nickel catalysts had an egg-shell structure in terms of nickel-alumina distribution, with most of the nickel located at the outer surface of the catalyst particles. The hydrogenation experiments showed that the nano-nickel catalyst provided much higher activities than those co-precipitated and impregnated nickel catalysts with similar nickel contents. However, both types of catalysts followed first-order reaction kinetics and similar activation energies were observed.

Anisotropies in Carbon Nanotube Synthesis by the Hydrogen Arc Plasma Jet Method

Single‐wall carbon nanotubes were prepared under hydrogen gas atmosphere with a DC arc discharge maintained between the tip of a sharpened graphite cathode and an anode formed by a catalytic mixture of graphite, FeS, Ni, Fe and Co compressed powders. The cathode is placed with an inclination with respect to the anode, so that the plasma jet of the discharge is deviated towards the empty space of the growth chamber. Samples were classified and analyzed according to their type and growth positions relative to the direction of the plasma jet flow. Characterization of the samples was performed with mass spectrometry, Raman spectroscopy and transmission electron microscopy. A subtle variation is found in the properties of the nanotubes obtained in different locations due to the directionality of the plasma jet flow. Observed differences in sample properties may be qualitatively understood in terms of accepted mechanisms of SWNT growth.