Carbon Arc Plasma Research Articles

In situ diagnostics for nanomaterial synthesis in carbon arc plasma

Developments in the recent application of in situ diagnostics to improve understanding of nanomaterial synthesis processes in carbon arc plasma are summarized. These diagnostics measure the plasma conditions in the arc core and the precursor species to nanoparticle formation and the presence and sizes of nanoparticles in the synthesis region surrounding the hot arc core. They provide information that could not be obtained by the ex situ diagnostics used in previous studies of nanomaterial synthesis in arc plasma. The following diagnostics are covered: optical emission spectroscopy, planar laser induced fluorescence, laser induced incandescence, fast frame imaging, coherent Rayleigh Brillouin scattering, and the nanomaterial extractor probe. The diagnostic measurements are consistent with a recently developed two-dimensional fluid model of nanomaterial synthesis in the arc plasma.

Formation of polyhedral graphite particles by high-density carbon arc discharge with ethanol vapor

Polyhedral graphite (PG) particles that have a structure composed of many polyhedra with 100 nm −1 μm diameters were formed by using a modified arc discharge method (high-density carbon arc discharge method). The high-density carbon arc discharge was maintained by pyrolysis of ethanol during sublimation of a carbon anode. In this study, we investigated the most effective conditions for forming PG particles in high-density carbon arc plasma with ethanol vapor. We found that diameters of PG particles depended on arc current and that PG particles were effectively formed by using the high-density carbon arc discharge method. Furthermore, results of heat treatment at 2000 °C indicated that the obtained PG particles were graphitized well and that surfaces of the particles with diameters over 400 nm tended to peel off. Compared with the conventional laser vaporization method, the newly developed high-density carbon arc discharge method does not require an expensive equipment and high-pressure atmosphere gas, and is easy to scale up for mass production of PG particles.

Carbon arc plasma: characterization and synthesis of nanosized SiC

Silicon carbide SiC is an important ceramic material with many applications. The nanomaterials can posess novel electronic and mechanical properties. Thus, we attempted to produce SiC nanopowder via a fast, one-step direct plasma synthesis. Two experimental systems were tested regarding the efficiency of SiC formation (for comparison): (i) arc plasma and (ii) high-temperature aerosol route. The products were characterized by wet chemical analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Almost total plasma conversion of starting Si-bearing reactants (Si, SiO and SiO2) was achieved with SiC nanopowder (well below 100 nm) as a main product. From the emission spectroscopy measurements the arc plasma temperatures were evaluated to be within 3500-6000 K.

Diagnostics of carbon arc plasma under formation of carbon-encapsulated iron nanoparticles by optical emission and absorption spectroscopy

Absorption and emission spectra pertaining to the electronic transition a 3Πu–d 3Πg (0–0 band) of C2 molecule as present in the carbon arc discharge zone are analysed to determine the temperature and C2 radical content in function of carbon–iron anode composition. One of the objectives was to explore the use of emission and absorption, both approximate, methods for diagnostics of carbon arc plasma used for synthesis of carbon-encapsulated iron nanoparticles. The theory behind both methods was exploited to estimate the errors resulting from both approximate methods. The results obtained showed that the uncertainty in the determination of average temperatures and C2 column densities should not exceed ±3% and 10%, respectively. Contrary to these predictions, the experimental values of temperature and C2 column density determined from the plasma radiation significantly exceeded those resulting from the absorption measurements. It is concluded that some non-equilibrium state is between the ground (a 3Πu) and excited (d 3Πg) electronic states in carbon arc plasma under consideration. The column density distributions of non-excited C2 radical were transformed into radial concentration distributions, and then to carbon vapour pressures assuming thermodynamic equilibrium between carbon species. Both quantities rise with Fe content in the anode. Additionally, clear relationship between the carbon vapour pressure and the yield of carbon encapsulated iron nanoparticles synthesis was found.

Carbon arc production of heptagon-containing fullerene[68

A carbon heptagon ring is a key unit responsible for structural defects in sp2-hybrized carbon allotropes including fullerenes, carbon nanotubes and graphenes, with consequential influences on their mechanical, electronic and magnetic properties. Previous evidence concerning the existence of heptagons in fullerenes has been obtained only in off-line halogenation experiments through top-down detachment of a C2 unit from a stable fullerene. Here we report a heptagon-incorporating fullerene C68, tentatively named as heptafullerene[68], which is captured as C68Cl6 from a carbon arc plasma in situ. The occurrence of heptagons in fullerenes is rationalized by heptagon-related strain relief and temperature-dependent stability. 13C-labelled experiments and mass/energy conservation equation simulations show that heptafullerene[68] grows together with other fullerenes in a bottom-up fashion in the arc zone. This work extends fullerene research into numerous topologically possible, heptagon-incorporating isomers and provides clues to an understanding of the heptagon-involved growth mechanism and heptagon-dependent properties of fullerenes.

Removal of Diamond-Like Carbon Film by Oxygen-Dominated Plasma Beam Converted from Filtered Carbon-Cathodic Arc

Diamond-like carbon (DLC) film is sometimes removed using oxygen plasma in order to reuse workpieces such as cutting tools and press molds. In this study, an oxygen-dominated plasma beam was generated by converting the cathodic carbon arc plasma beam formed in T-shaped filtered-arc-deposition (T-FAD) in order to investigate the feasibility of using the plasma beam for the removal of DLC film. When the oxygen (O2) gas flow rate was relatively high (50 ml/min) and the substrate was biased (DC -500 V), the plasma beam in front of the substrate was confirmed to contain a considerable amount of excited oxygen atoms, since an atomic oxygen spectral line (777 nm) emitted from the plasma beam had relatively strong radiation intensity. The plasma beam was irradiated on a tetrahedral amorphous carbon film, a hydrogen-free sp3-rich DLC film, prepared on a hard alloy (WC with 6 wt % Co binder) substrate. It was found that a plasma beam generated with an appropriate O2 gas flow rate and applied substrate bias was able to etch the DLC film proportionally to the treatment time. The surface was not roughened when the treatment time was 1.5 times longer than the intended time to remove a given thickness of DLC film.

Removal of Diamond-Like Carbon Film by Oxygen-Dominated Plasma Beam Converted from Filtered Carbon-Cathodic Arc

Diamond-like carbon (DLC) film is sometimes removed using oxygen plasma in order to reuse workpieces such as cutting tools and press molds. In this study, an oxygen-dominated plasma beam was generated by converting the cathodic carbon arc plasma beam formed in T-shaped filtered-arc-deposition (T-FAD) in order to investigate the feasibility of using the plasma beam for the removal of DLC film. When the oxygen (O2) gas flow rate was relatively high (50 ml/min) and the substrate was biased (DC -500 V), the plasma beam in front of the substrate was confirmed to contain a considerable amount of excited oxygen atoms, since an atomic oxygen spectral line (777 nm) emitted from the plasma beam had relatively strong radiation intensity. The plasma beam was irradiated on a tetrahedral amorphous carbon film, a hydrogen-free sp3-rich DLC film, prepared on a hard alloy (WC with 6 wt % Co binder) substrate. It was found that a plasma beam generated with an appropriate O2 gas flow rate and applied substrate bias was able to etch the DLC film proportionally to the treatment time. The surface was not roughened when the treatment time was 1.5 times longer than the intended time to remove a given thickness of DLC film.

Influence of carbon structure of the anode on the synthesis of single-walled carbon nanotubes in a carbon arc plasma

Arc plasma evaporation of carbon electrodes doped with various catalysts is one of the most effective methods of single-walled carbon nanotube fabrication. It was found that the reaction yield is strongly influenced not only by the appropriate choice of the catalyst(s), but also by the type of carbon material used for electrode fabrication. Several different carbon powders i.e. graphite powders, glassy carbon and coke, have been tested in order to establish which parameters (primary particle size, granulation, density or conductivity of the electrode) affected the outcome of the reaction the most. The highest yield of single-walled nanotubes was found for anodes fabricated from graphite powders, whilst the electrodes made from glassy carbon or coke yielded significantly smaller amounts of nanotubes. The reaction zone where carbon radicals nucleate (close to the arc gap) was probed by optical absorption spectroscopy. The estimated temperature distributions and contents of C 2 radicals did not depend on the anode characteristics.

Argon-dominated plasma beam generated by filtered vacuum arc and its substrate etching

A new technique to etch a substrate as a pre-treatment prior to functional film deposition was developed using a filtered vacuum arc plasma. An Ar-dominated plasma beam was generated from filtered carbon arc plasma by introducing appropriate flow rate of Ar gas in a T-shape filtered arc deposition (T-FAD) system. The radiation spectra emitted from the filtered plasma beam in front of a substrate table were measured. The substrate was etched by the Ar-dominated plasma beam. The principal results are summarized as follows. At a high flow rate of Ar gas (50 ml/min), when the bias was applied to the substrate, the plasma was attracted toward the substrate table and the substrate was well etched without film formation on the substrate. Super hard alloy (WC), bearing steel (SUJ2), and Si wafer were etched by the Ar-dominated plasma beam. The etching rate was dependent on the kind of substrate. The roughness of the substrate increased, when the etching rate was high. A pulse bias etched the substrate without roughening the substrate surface excessively.

Mössbauer spectroscopy studies of carbon-encapsulated magnetic nanoparticles obtained by different routes

Carbon-encapsulated magnetic nanoparticles (CEMNPs) are nanomaterials with a core-shell structure. Their intrinsic properties result both from the unique nature of the encapsulated magnetic phases and the high chemical stability of the external carbon shells. CEMNPs may find many prospective applications, e.g., in magnetic data storage, catalysis, xerography, magnetic resonance imaging, and in biomedical applications. Herein, we present detailed structural studies of such nanostructures by Mössbauer spectroscopy, x-ray diffraction (XRD), scanning electron microscopy, and transmission electron microscopy. CEMNPs have been obtained by three different techniques: carbon arc, combustion synthesis, and radio frequency thermal plasma. The evaluation of the phase composition of the products was strongly limited due to the broadening and overlapping of the lines in XRD diffraction patterns. The presence of the semicrystalline phases, which could not been identified by XRD, was established by Mössbauer spectroscopy. Furthermore, the magnetic core phase composition was evaluated quantitatively. The products were purified before structural analyses to remove the nonencapsulated particles. The purification caused significant changes in the mass and the saturation magnetization. The Mössbauer spectra of the purified products were compared with the literature data concerning the as-produced CEMNPs.

Hydrodynamic description of the mechanism of formation of carbon nanotubes

The electric-arc process of synthesis of carbon nanotubes has been investigated with the aim of searching for the mechanical trajectories of the ionic component of a carbon arc plasma and evaluating their influence on the formation of carbon nanotubes on the cathode. The conclusion on the predominantly ionic composition of the plasma has been drawn on the basis of experimental study of the degree of ionization. It has been proposed that a magnetohydrodynamic model be used for description of the motion of the charged component. The calculated region of the predominant accumulation of carbon ions has been compared to the actual distribution of carbon nanotubes.

Comparative Process Analysis of Fullerene Production by the Arc and the Radio-Frequency Discharge Methods

In this work, comparative analysis of processes in carbon arc and radio frequency (RF) plasma during fullerene synthesis has been presented. The kinetic model of fullerene formation developed earlier has been verified in both types of plasma reactors. The fullerene yield depended on carbon concentration, velocity of plasma flame and rotational temperature of C2 radicals predominantly. When mean rotational temperature of C2 radicals was 3000 K, the fullerene yield was the highest regardless of the type of used reactor. The zone of fullerene formation is larger significantly in RF plasma reactor compared to arc reactor.

Influence of carbon structure on carbon nanotube formation and carbon arc plasma

Carbon electrodes with different grain size (1–26 nm) and doped with Fe (ca. 1 at.%) catalyst were tested in the process of production of single-walled carbon nanotubes (SWCNTs) in Ar-H 2 arc plasma. We have found that the use of the carbon material with smaller microcrystals comparing to the well-graphitized electrodes drastically increased the yield of SWCNTs, while plasma parameters (temperature, C 2 radical content and carbon vapor pressure) remained on similar levels. We have also shown that carbon black can be used for production of SWCNTs with high quality and yield by Ar-H 2 arc discharge.

Optical Emission Measurements of Rotational Temperature of C2 Radicals in Fullerene Processing

In this work, the results of optical emission study of C2 radicals generated in carbon arc plasma are presented. It was found that a rotational temperature of carbon vapor depends significantly on carbon concentration and inert gas pressure. Experimentally obtained rotational temperature of C2 emission spectra has been fitted with calculated spectra.

Controlled synthesis of carbon nanoparticles by arc in water method with forced convective jet

Forced convective jet applied onto carbon arc plasma has significant effects on the formation of carbon nanoparticles (CNPs) containing multiwalled carbon nanotubes mixed with multishelled nanoparticles produced by the “arc in water” method. There is an optimized flow rate of the convective jet that leads to the highest production yield, largest hydrodynamic diameter of the products, and the reduced crystalline defects. With the convective flow rate of 1.36 dm3/min, the highest yield and production rate of CNPs could be obtained at 48.5% and 9.32 g/h, respectively. These effects of the forced convective jet originate from the enhanced quenching of carbon clusters vaporized from graphite anode. Analysis of convective flow field subjected to the arc plasma zone is conducted to indicate that synthesis of CNPs by the arc in water method can be elaborately controlled.

Carbon arc plasma as a source of nanotubes: emission spectroscopy and formation mechanism.

Diagnostics of carbon arc plasma by optical emission spectroscopy during the synthesis of carbon nanotubes is reviewed. Spatial distributions of temperature and C2 radicals in different plasmas are presented. The influence of gas pressure, anode composition, and reaction environment is discussed. Mechanisms of carbon nanotube formation are reviewed, with an emphasis on surface diffusion processes and catalytic effects.

Influence of Gadolinium on Carbon Arc Plasma and Formation of Fullerenes and Nanotubes

Gadolinium-doped (0.8 at.%) graphite anodes were dc arced to produce different nanocarbons. Emission spectroscopy was performed to determine the temperature and column density distributions of C 2 (a 3 Π u v=0) in the arc plasma under 13.3 and 60 kPa pressures in helium atmosphere. The solid products were analyzed by UV-VIS, TOF MS, HR SEM, and TEM techniques. The influence of metal catalyst on the formation of C 6 0 , and endohedral fullerenes, and carbon nanotubes is discussed.

Carbon arc plasma transport through different off-plane double bend filters

An off-plane double bend (OPDB) magnetic filter is used to remove macroparticles from the plasma beam of cathodic vacuum arcs, making it suitable for the preparation of high quality thin films. A filter with high plasma transmission efficiency is desirable and essential for high deposition rate, which is the key to the commercialization of the technology. Hence, an investigation has been carried out to study the carbon arc plasma transport under varying arc current and magnetic field conditions. The plasma efficiency tests were carried out on different sizes of off-plane double bend (OPDB) filters by measuring the ion saturation output current and ion density using a copper plate and Langmuir probes, respectively. It was found that in our FCVA systems, there exists an optimum arc current operation for obtaining the maximum plasma efficiency. This seems to be as an important factor for future filter design.

Influence of nitrogen on carbon arc plasma and formation of fullerenes

The influence of nitrogen on the process of fullerene formation in the carbon arc discharge in a helium/nitrogen atmosphere has been studied. Applying optical emission spectroscopy and using the self-absorption effect, the spatial distribution of the temperatures and chemical species, i.e. C 2( a 3Π u , v″=0) and CN( X 2Σ +, v″=0) radicals produced by the d.c. arc discharge between pure graphite electrodes, were determined across the arc gap. The soot product was analyzed spectrophotometrically to determine C 60 content. C 60 was detected even when pure nitrogen was used (at about 0.5 wt%). The relative content of higher fullerenes was measured by mass spectrometry and their formation was found to be significantly enhanced in the presence of nitrogen.

Influence of Fe and Co/Ni on Carbon Arc Plasma and Formation of Fullerenes and Nanotubes

Carbon nanostructures (fullerenes and nanotubes) were obtained using the carbon arc technique employing homogeneous carbon−iron and carbon−cobalt−nickel anodes. The influence of these catalysts on the arc plasma was studied by optical emission spectroscopy to determine temperatures and C2 radical content in the arc zone. The solid products were analyzed by spectrophotometry and mass spectrometry to determine the C60 yield and relative mass distributions of the higher fullerenes, respectively. SEM and TEM techniques were used to affirm the presence of carbon nanotubes in the resulting soot product.