Fullerene black: Structure, properties and possible applications

This review concerns the fullerene black, a poorly known nano-sized carbon material, the insoluble residue after extraction of fullerenes from fullerene soot obtained by arc vaporization of carbon material (usually graphite) in a helium atmosphere. This by-product of the production of fullerenes, whose yield reaches 80 wt %, is a finely dispersed material with a particle size of 40–50 nm. It includes amorphous carbon, graphitized particles, and graphite. Test reactions showed the presence in the structure of fullerene black of curved surfaces, and, like fullerenes, of alternating nonconjugated ordinary and double bonds. In addition to the double bonds, its structure includes dangling bonds in the concentration not higher than one per 1200 carbon atoms. Fullerene black absorbs oxygen from the atmosphere and water, and enters into the reactions of nucleophilic addition. The fullerene black cannot be graphitized, and its application is extremely important. The fullerene black was shown to activate hydrogen and thus to undergo a hydrogenolysis in the absence of a catalyst and to catalyze the dehydrogenation and dehydrocyclization of alkanes. This carbon nanomaterial can be used as a sorbent and a catalyst carrier, a tribotechnical additive; it can interact with carbide-forming metals and harden their surface.     

Extraction of fullerene mixture from fullerene soot with organic solvents

Investigation of extraction of fullerene mixture from the fullerene soot obtained by plasma erosion of graphite rod in helium atmosphere with different solvents such as α-chloronaphthalene, o-dichlorobenzene, o-xylene, toluene, benzene, carbon tetrachloride, and n-hexane at 25°C was carried out. Completeness and effectiveness of extraction as well as relative content of light (C₆₀, C₇₀) and heavy (C₇₆, C₇₈, C₈₄) fullerenes in the extract were evaluated.     

Yield of fullerenes generated by contact arc method under He and Ar: dependence on gas pressure

The yields of toluene-soluble material from carbon soot depend on the buffer gas as well as the pressure. Helium was more effective for yielding fullerenes than argon, and the optimum pressure was 20 Torr, under which a maximum yield of about 13 wt% was obtained. C₆₀ showed a maximum abundance at 20 Torr, while C₇₀ and higher fullerenes (C₇₆, C₇₈ and C₈₄) at a slightly higher pressure between 20 and 50 Torr. Raw soot was also studied by electron microscopy. The pressure dependence of the fullerene yield is discussed in terms of the cooling rate and diffusion of carbon vapor around the evaporation source.     

交流放电法合成多种形态的碳纳米管

碳纳米管的发现［１］引起了科学界的广泛重视,人们对于这种新型材料在纳米导线、高强纤维、超导等方面的应用寄予厚望．目前,合成碳纳米管的方法主要是采用不等径石墨棒直流放电,在阴极上得到含有碳纳米管的沉积物［２］．对于碳纳米管的应用,有关的理论研究［３］及...     

Cathode erosion in inert gases: The importance of electrode contamination

Experimental results are presented for electrode erosion on copper electrodes in magnetically rotated arcs in argon and helium. Measurements were also made of the arc voltage and velocity. The effects due to the contamination of the electrode surface by either a native contaminant layer (copper oxide and carbon traces) or the continuous injection of very small amounts of various diatomic gases (nitrogen, oxygen, chlorine, and carbon monoxide) into the inert plasma gases were determined. The erosion rates for pure argon were significantly higher than those for pure helium (13.5 g/C for argon and 1 g/C for helium) and with both gases, very high arc velocities were measured initially (>60 m/s for argon and >160 m/s for helium) when a natural contaminant layer was still present on the cathode. The removal of this layer resulted in lower velocities (2m/s for argon and 20m/s for helium) and higher erosion rates. The removal of the layer was much faster with argon, due possibly to higher electrode surface current densities for argon arcs.     

A Mathematical Model of the Carbon Arc Reactor for Fullerene Synthesis

A mathematical model of the carbon arc process for the synthesis of fullerenes (C ₆₀ , C ₇₀ ) is developed. The two-dimensional model solves for the velocities, temperature, and total concentration of carbon species. The net emission coefficient method is used for the radiation term. The carbon species conservation equations consider the evaporation of carbon from the anode, cathode surface deposition, and carbon condensation. The thermodynamic and transport properties are calculated as a function of temperature and carbon mass fraction, using the method of Chapman–Enskog. Erosion rates used by the model are determined experimentally. Calculated fields of the velocities, temperatures, carbon mass fraction and current intensity are presented. Comparison is made of the behavior of the arc at 1 and 4 mm interelectrode gaps, and between operation in argon and in helium. The results of simulations provide a justification for the higher yields observed in helium compared to the argon case.     

Influence of Discharge Atmosphere on the Ageing Behaviour of Plasma-Treated Polylactic Acid

The effect of a plasma treatment on polymers is not permanent, since the treated surfaces tend to recover to the untreated state (ageing process). This paper investigates the influence of discharge atmosphere on the ageing behaviour of plasma-treated PLA foils: these foils are plasma-treated with a DBD in 4 different atmospheres (air, nitrogen, argon and helium) and are subsequently stored in air. Results of contact angle and XPS measurements show that the discharge gas has a significant influence on the ageing behaviour of the PLA foils. This influence can be explained by the different cross-linking degree of the plasma-treated surfaces: helium and argon plasma-treated PLA films have a high cross-linking degree, which limits polymer chain mobility and as a result reduces the ageing process. In contrast, the ageing behaviour of air and nitrogen plasma-treated films is more pronounced due to their low cross-linking degree.     

Novel iron-decorated carbon nanorods from fullerene soot

A novel form of nano-sized carbon rods decorated with monodispersed iron particles in a size range of 30-50 nm on their surface is successfully synthesized by arcing discharge of composite electrodes made from iron particles and fullerene soot; this will be of potential as catalyst for hydrogenation reactions.     

Near-edge X-ray absorption fine structure spectroscopy-assisted purification of single-walled carbon nanotubes

Single-walled carbon nanotubes were produced by the conventional arc discharge method, and purified with a two-step treatment. First, the raw soot containing single-walled carbon nanotubes was burned up at ca. 350 °C in air to remove amorphous carbon, and then it was treated by strong acidic solvents to remove metal catalysts. Near-edge X-ray absorption fine structure spectroscopy was applied to analyze the defects on single-walled carbon nanotubes in whole purification process, so the experimental conditions can be optimized, and finally high-purity single-walled carbon nanotubes were obtained as revealed by various spectroscopic characterizations such as scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and Raman spectroscopy.     

An Optical Emission Study on Expanding Low-Temperature Cascade Arc Plasmas

The optical emission spectra from expanding low-temperature cascade arc plasmas were studied. The objective of this study was to examine the distinctive features of low-temperature cascade arc plasmas in comparison with a radio frequency (RF) plasma source. The principal results obtained in this study were: (1) in an expanding cascade arc plasma jet, active heavy particles (mainly excited argon or helium neutral species under our operating conditions), rather than electrons, are responsible for the excitation of reactive species when a reactive gas is injected into the plasma jet, (2) the excitation of reactive species was found to be controlled by the electronic energy levels of these excited argon or helium neutrals, (3) changing the operating parameters affected only the emission intensities of excited species, and no effect on the emission nature of plasmas was observed.     

Three-phase double-arc plasma for spectrochemical analysis of environmental samples

A new instrument, which uses a three-phase current to support a double-arc argon plasma torch for evaporation, atomization and excitation of solid or powder samples, is described. The sampling arc is ignited between the first and second electrode while the excitation arc is ignited between the second and third electrode. Aerosol generated from the sample (first electrode) is swept by argon gas, through a hole in the second electrode (carbon tubing electrode), into the excitation plasma. A tangential stream of argon gas is introduced through an inlet orifice as a coolant gas for the second electrode. This gas stream forces the excitation arc discharge to rotate reproducibly around the electrode surface. Discharge rotation increases the stability of the excitation plasma. Spectroscopic measurements are made directly in the current-carrying region of the excitation arc. An evaluation of each parameter influencing the device performance was performed. Analytical calibration curves were obtained for Fe, Al, K, and Pb. Finally, the present technique was applied for the analysis of environmental samples. The present method appears to have significant, low cost analytical utility for environmental measurements. Received: 7 July 2000 / Revised: 6 September 2000 / Accepted: 10 September 2000     

Emission characteristics of mixed gas plasmas in low-pressure glow discharges

Glow discharge optical emission spectrometry (GD-OES) with mixed plasma gases is reviewed. The major topic is the effect of type and content of gases added to an argon plasma on the emission characteristics as well as the excitation processes. Emphasis is placed on argon–helium, argon–oxygen, and argon–nitrogen mixed gas plasmas. Results for non-argon-matrix plasmas, such as neon–helium and nitrogen–helium mixtures, are also presented. Apart from the GD-OES, glow discharge mass spectrometry and furnace atomization plasma emission spectrometry with mixed plasma gases are also discussed.     

Thermodynamic and transport properties of argon/carbon and helium/carbon mixtures in fullerene synthesis

The equilibrium composition and thermodynamic and transport properties of argon; carbon and helium/carbon mixtures are calculated in the temperature range 300–20,000 K. The curves for the composition of mixtures of 50%, carbon in argon or helium are shown fir a pressure of 1.33 × 10⁴ Pa. The calculations for the heat capacity at constant pressure (C_p) and transport coefficients are validated with other studies, for the cases or pure argon and pure helium at a pressure of 10⁵ Pa. The properties of mixtures with various proportions of carbon in argon and helium are calculated. Results are presented at pressures of 105 and 1.33 × 10⁴ Pa, typical of reactors for the synthesis of fullerenes and nanotubes. It is observed that the properties of carbon and mixtures of carbon with a buffer gas (argon or helium) are very different from those of the buffer gas, thus the need to consider this effect in simulations. In general, the mixtures follow trends intermediate to those of the pure gases from which they are composed except for the thermal conductivity which shows a deviation from this tendency in the region between 11,500 and 19,000 K for argon/carbon mixtures and between 8,000 and 12,000 K for helium/carbon mixtures. Also, the electrical conductivity of mixtures of low carbon concentration is very close to that ofpure carbon. A datafile containing the transport properties of mixtures for pressures between 10⁴ and 10⁵ Pa is available free of charge from the authors.     

The effect of thermal annealing on the microstructure and mechanical properties of magnetron sputtered hydrogenated amorphous carbon films

Hydrogenated amorphous carbon films were deposited by magnetron sputtering of a carbon target in a methane/argon atmosphere. A postdeposition annealing at 300 °C was performed and the microstructure, bonding structure and mechanical properties of the as‐deposited and annealed films were analyzed and compared directly by high‐resolution transmission electron microscopy, micro‐Raman spectroscopy, XPS, and nanoindentation. The results showed that the carbon films are quite stable upon annealing, since there are only minor changes in microstructure and chemical bonding in the amorphous matrix. The hardness of the films remained unaffected, but the elastic properties were somewhat deteriorated. In comparison to the outcomes of our previous work on the growth of fullerene‐like hydrogenated carbon films, we can state that the formation of fullerene‐like carbon structures requires different sputtering process conditions, such as a higher ion energy and/or different sputtering target. Copyright © 2011 John Wiley & Sons, Ltd.     

Three-phase double-arc plasma for spectrochemical analysis of environmental samples

A new instrument, which uses a three-phase current to support a double-arc argon plasma torch for evaporation, atomization and excitation of solid or powder samples, is described. The sampling arc is ignited between the first and second electrode while the excitation arc is ignited between the second and third electrode. Aerosol generated from the sample (first electrode) is swept by argon gas, through a hole in the second electrode (carbon tubing electrode), into the excitation plasma. A tangential stream of argon gas is introduced through an inlet orifice as a coolant gas for the second electrode. This gas stream forces the excitation arc discharge to rotate reproducibly around the electrode surface. Discharge rotation increases the stability of the excitation plasma. Spectroscopic measurements are made directly in the current-carrying region of the excitation arc. An evaluation of each parameter influencing the device performance was performed. Analytical calibration curves were obtained for Fe, Al, K, and Pb. Finally, the present technique was applied for the analysis of environmental samples. The present method appears to have significant, low cost analytical utility for environmental measurements.     

Excitation of singly ionized argon species in helium-matrix glow discharge plasma—role of the energy transfer from helium metastables

When a small amount of argon is added to the helium plasma in a Grimm-type glow discharge radiation source, the interaction between helium and argon species is investigated from analyzing the intensities of emission lines of of argon ion (ArII). The excitation energy as well as the term multiplicity concerning the optical transitions to which the ArII emission lines are identified are significant factors for determining their emission intensities in the helium-matrix plasma. In the case where the excitation energy of ArII lines is higher than the internal energy of the helium metastable states, the emission intensity in the helium-matrix plasma is observed to be much weaker than that obtained only with argon gas. On the other hand, the intensity is enhanced when the excitation energy is slightly lower. In the excited levels of argon ion having quartet multiplicity, closer interactions with the triplet rather than the singlet metastable level of helium atom are recognized, with the singlet helium metastable in the argon excited levels having doublet multiplicity.     

Relationships of the synthesis of silicon dioxide nanoparticles in low-temperature plasma created in helium and argon at atmospheric pressure

Low-temperature plasma-chemical synthesis of silicon dioxide nanoparticles from tetraethoxysilane, performed at atmospheric pressure in a reactor with flat perforated electrodes coated with an insulating layer, was studied. The use of such electrodes allows reaching stable sustaining of RF discharge (α-mode) with helium and argon used as plasma-forming gases. The relationships of the synthesis of silicon dioxide nanoparticles from tetraethoxysilane in helium and argon plasma differ insignificantly. Most probably, nanoparticles with the size in the interval 100–150 nm are formed in the zone of the discharge sustaining, but, as the particles are transported with the gas flow beyond the plasma zone, they undergo agglomeration. An increase in the nanoparticle size to 100–150 nm, observed when using perforated electrodes with an insulating coating, is most probably due to an increase in the residence time of the reaction gas medium in the zone of the discharge sustaining.     

Spectroscopic characterization of a neon surface-wave sustained (2.45 GHz) discharge at atmospheric pressure

In this paper a spectroscopic study of a microwave (2.45 GHz) neon surface-wave sustained discharge (SWD) at atmospheric pressure in a quartz tube has been carried out in order to determine the plasma characteristic parameters (e.g. electron temperature and density, gas temperature, absorbed power per electron) and also to identify possible deviations from the thermodynamic equilibrium for this kind of microwave discharge. The results have been compared to experiments in the literature for other noble gas (helium and argon) SWDs generated under similar experimental conditions. Intermediate values between those of argon and helium plasmas were obtained for characteristic neon plasma parameters (temperatures and electron density). An important departure from the Saha equilibrium was exhibited by neon SWDs.     

Structure,chemical bonding and electrochemical behavior of heteroatom-substituted carbons prepared by arc discharge and chemical vapor deposition

The structural characteristics, chemical bonding and electrochemical properties of the heteroatom-substituted carbons synthesized by arc discharge and chemical vapor deposition have been investigated. C_xN was prepared only as a soot by arc discharge in nitrogen atmosphere; BC_x and B_xC_yN_z were obtained both as soot and cathode deposits by arc discharge of graphite rods having B₄C and boron nitride (BN) in argon and nitrogen atmospheres, respectively. Transmission electron microscopic study showed that C_xN, BC_x and B_xC_yN_z soots were composed of nanoparticles with diameters of 20–100 nm, while cathode deposits contained nanotubes with diameters of ca. 20 nm or less and nanoparticles with diameters less than 100 nm. It was found from XPS study that C_xN contained a large amount of pyridine type nitrogen atoms at the edge of graphene layer; the BBC₂ structure was dominant in BC_x; and B₃N, B₂NC and BNC₂ structures might exist in B_xC_yN_z. Carbon- and C_xN-coated graphite were prepared by deposition of carbon and C_xN onto natural graphite powder, respectively. The concentrations of coated C_xN layers were between C₂₁N and C₆₂N. Charge–discharge profiles of C_xN, BC_x and B_xC_yN_z soots prepared by arc discharge were similar to each other, giving linearly increasing potential with lithium ion deintercalation. C_xN soot heat-treated at 3000°C showed a similar profile for charge–discharge curves to that of graphite with a charge capacity of 334 mAh g⁻¹. On the other hand, C_xN-coated graphite exhibited as high as 397 mAh g⁻¹ larger than ∼365 mAh g⁻¹ for carbon-coated graphite and that of heat-treated C_xN soot.