Evaporation Of Graphite Research Articles

Bone modification with carbon nanoparticles formed by evaporation of graphite under glass: Yb, Er laser radiation

In this work carbon nanostructures preparation opportunity under impact of Glass: Yb, Er laser beam with wavelength 1.54 μm on graphite surface, and its size dependence on laser radiation parameters were investigated. Bone modification with obtained particles was carried out. Microhardness of intact and modified bone was estimated.

Perchloropyracylene and its Fusion with C60 by Chlorine-Assisted Radio-Frequency Furnace Synthesis

Elusive perchloropyracylene has been obtained during conventional fullerene synthesis in a chlorine-containing atmosphere by using the radio-frequency furnace technique. In contrast to its hydrocarbon analogue, the title compound was found to be unexpectedly stable. Although the high stability of perchloropyracylene impedes its direct addition to C(60) fullerene, the corresponding adduct was found in the synthesis products extracted from the raw soot. Both new species were separated and unambiguously characterized by single-crystal X-ray analysis. According to experimental observations and quantum chemical calculations, the addition of perchloropyracylene to the C(60) fullerene can only be realized by involving highly reactive species such as C(14) clusters displaying the pyracylene connectivity. Such a viable mechanism includes capturing of free or partially chlorinated C(14) clusters with pyracylene-type connectivity by the fullerene molecule and subsequent stabilization through chlorine addition. The data obtained provide experimental evidence for the presence of pyracylene-like C(14) clusters in the gas phase, which have evolved during the graphite vaporization process. According to the pentagon road mechanism, such clusters are regarded as crucial intermediates in fullerene formation.

Outer and inner diameters of multi-walled carbon nanotubes grown by laser vaporization

Multi-walled carbon nanotubes (MWCNTs) were grown by continuous-wave laser vaporization of graphite containing B4C in Ar, Ne, and He gases. The use of Ne and He gases resulted in the growth of shorter (up to 12 and 6μm long for Ne and He, respectively) and thinner (3.3–41.7nm thick) MWCNTs, compared to long and thick (up to 30μm long and 6.6–53.2nm thick) MWCNTs grown in Ar, along with their reduced fractions in the deposits (approximately 30 and 1% for Ne and He, respectively). Measurements of the outer and innermost diameters and wall numbers of the more than 150 MWCNTs grown in each gas indicated that the outermost diameters of the grown MWCNTs correlated with wall numbers rather than with innermost diameters. The sizes of the molten boron carbide particles, acting as seeds in a vapor-liquid-solid growth process, and their dynamic deformation in the nucleation stage of cone-shaped caps, which lead to the growth of MWCNTs, are thought to be crucial in determining MWCNT outer and inner diameters.

Synthesis, properties, and examples of the use of carbon nanomaterials

The results of a series of works on the synthesis and investigation of various carbon nanostructures and elaboration of functional materials of their basis are generalized and reviewed. Fullerenes and single-, double-, and multi-walled carbon nanotubes were prepared by the electric arc evaporation of graphite and metal—graphite rods. Diverse types of carbon nanofibers and nanotubes were grown by the catalytic pyrolysis of ethylene and methane. Graphene structures were synthesized by the chemical reduction of graphite oxide. Methods for isolation, purification, and functionalization of carbon nanostructures were elaborated. Chemical transformations in the fullerene—metal phase—hydrogen system were studied. Methods for metal cluster application on carbon nanostuctures and formation of metal hydride—carbon composites were developed. The possibilities were elucidated of using carbon nanostructures for the development of hydrogen accumulating and hydrogen generating composites, for forming carbon—polymer and carbon—ceramic composites, for preparing hardening additives to polymers and glue compositions, and for producing high-performance catalysts for hydrogenation and redox processes in fuel cells.

Synthesis of carbon nanostructures by electron-beam graphite evaporation

The results of graphite evaporation by electron beam are presented. The evaporation rate as a function of the beam power and electron bombardment duration is measured. The dependence that the evaporation rate has on the beam power has a threshold character. The lowest power for evaporation is 600 W in our experiments. The graphite evaporation rate was 0.3–0.4 mg/s. The deposition rate was about 0.5–1.0 μm/min on substrates disposed 40–50 mm from graphite target. The evaporation and deposition rates for the targets containing Ni as the catalyst were the same. The Raman spectra (RS) showed the presence of carbon nanotubes in deposited layers.

Investigation of condensed products of graphite evaporation in an electric arc in argon and helium atmosphere

The composition of products formed in the discharge chamber at the synthesis of nanostructures by arc discharge was investigated. The fullerene soot obtained in an argon atmosphere was shown to contain at least three structural phases: amorphous carbon, fullerenes, and graphitized particles. In the process of thermal desorption, the water and oxygen adsorbed from the atmosphere, as well as carbon oxides generated at the oxidation evolve from the argon soot. By the reactivity, the fullerene black obtained in different buffer gases form a series: special helium, argon, usual helium. The cathode deposit of the arc discharge in argon, as in helium, contains multiwall nanotubes in its soft parts.

Efficient growth of multi-walled carbon nanotubes by continuous-wave laser vaporization of graphite containing B 4C

Multi-walled carbon nanotubes (MWCNTs), 7–70 nm thick and up to 30 μm long, were efficiently grown by room-temperature continuous-wave laser vaporization of a graphite target containing B 4C in an ambient Ar gas. Adjusting the boron content in the target and Ar gas pressure resulted in a maximum fraction of ∼60% of MWCNTs in the deposits. The straightness of the MWCNTs and graphene layers with an interlayer spacing of ∼0.35 nm indicated that the degree of graphitization was fairly high in the grown MWCNTs. However, the features of D, G, and 2D bands in the Raman spectrum of a deposit suggested boron doping in the MWCNTs. An apparent Young’s modulus of a grown MWCNT was measured to be 0.68 TPa and comparable to those of heat-treated vapor grown carbon nanofibers. MWCNTs are thought to grow on molten boron carbide particles acting as seeds at high temperatures of up to ∼2400 °C.

ChemInform Abstract: Fullerenes C60 and C70 in Flames

THE fullerenes C60 and C70 were first identified1 in carbon vapour produced by laser irradiation of graphite, and have recently been produced in macroscopic quantities2–5 by vaporization of graphite with resistive heating. It has also been suggested6–9 that fullerenes might be formed in sooting flames, and indeed all-carbon ions with mass/charge ratios suggestive of fullerenes have been detected in flames10–12. These species were assumed to have the cage structures of fullerenes, but the mass spectroscopic evidence could not establish this conclusively. We have now collected samples of condensible compounds and soot from hydrocarbon combustion under a range of conditions, and analysed these using conventional techniques in an effort to detect fullerenes. Spectroscopic studies reveal the presence of C60 and C70 in yields and ratios that depend on temperature, pressure, carbon/oxygen ratio and residence time in the flame. Control of these conditions allows optimal yields of 3 g of fullerenes per kilogram of fuel carbon burned, and variation of the C70/C60 ratio over the range 0.26–5.7.

ChemInform Abstract: Formation and Extraction of Very Large All-Carbon Fullerenes.

A series of very large all-carbon fullerenes has been successfully extracted with quinoline from fullerene-rich carbon soot produced by vaporization of graphite with contact arc. The present extracts (black powder) are not soluble in benzene or toluene, which are normally used as extraction solvents from C{sub 60} and C{sub 70}. The fast atom bombardment (FAB) mass spectra of the so-obtained extracts reveal that the extracts are found to contain very large fullerenes as large as C{sub 300}. A series of large even-numbered fullerenes C{sub 70+2n} (90 {ge} n {ge} 1) is detected in the FAB mass spectra. The results indicate that these fullerenes are not fragments of very large fullerenes but are actually present in the graphite soot. It is suggested that giant fullerenes (> C{sub 300}) may also be present in the present quinoline extract.

Near-critical phase explosion promoting breakdown plasma ignition during laser ablation of graphite

Removal rate, air shock, and ablative recoil pressure parameters were measured as a function of laser intensity I(peak) during nanosecond laser ablation of graphite. Surface vaporization of molten graphite at low intensities I(peak)<0.15 GW/cm(2) was observed to transform into its near-critical phase explosion (intense homogeneous boiling) at the threshold intensity I(PE)≈0.15 GW/cm(2) in the form of a drastic, correlated rise of removal rate, air shock, and ablative recoil pressure magnitudes. Just above this threshold (I(peak)≥0.25 GW/cm(2)), the explosive mass removal ended up with saturation of the removal rate, much slower increase of the air and recoil pressure magnitudes, and appearance of a visible surface plasma spark. In this regime, the measured far-field air shock pressure amplitude exhibits a sublinear dependence on laser intensity (∝I(peak)(4/9)), while the source plasma shock pressure demonstrates a sublinear trend (∝I(peak)(3/4)), both indicating the subcritical character of the plasma. Against expectations, in this regime the plasma recoil pressure increases versus I(peak) superlinearly (∝I(peak)(1.1)), rather than sublinearly (∝I(peak)(3/4)), with the mentioned difference related to the intensity-dependent initial spatial plasma dimensions within the laser waist on the graphite surface and to the plasma formation time during the heating laser pulse (overall, the pressure source effect). The strict coincidence of the phase explosion, providing high (kbar) hydrodynamic pressures of ablation products, and the ignition of ablative laser plasma in the carbon plume may indicate the ablative pressure-dependent character of the underlying optical breakdown at the high plume pressures, initiating the plasma formation. The experimental data evidence that the spatiotemporal extension of the plasma in the laser plume and ambient air during the heating laser pulse is supported by fast lateral electron and radiative heat conduction (laser-supported combustion wave regime), rather than by propagation of a strong shock wave (laser-supported detonation wave regime).

Direct synthesis of β-silicon carbide nanowires from graphite only without a catalyst

One-dimensional (1D) β-SiC nanowires were successfully fabricated on bare Si (1 0 0) substrate using simple carbo-thermal evaporation of graphite at 1200 °C. The obtained β-SiC nanowires were aligned with diameters ranged between 40 and 500 nm. The majority of crystal planes were β-SiC (1 1 1) with other less intensity of (2 0 0), (2 2 0) and (3 1 1). The silicon substrate location inside the furnace found to be critical in the formation of the β-SiC nanowires. Also, introducing oxygen gas as an ambient gas instead of argon reduces the growth at locations close to the graphite source.

Shapes of laser radiation pulses modified by nonlinear scattering in aqueous suspension of carbon nanotubes

An improved scheme of z-scanning was used to study the parameters of nanosecond 1064-nm laser radiation pulses scattered at right angle under the conditions of optical limiting in an aqueous suspension of purified carbon nanotubes (CNTs). CNTs were synthesized by the electric-arc evaporation of graphite. It is established that the amplitude, shape, duration, and temporal position of the peak of scattered light pulses significantly depend on the laser radiation power density. The results agree with the mechanism of thermoinduced nonlinear scattering that is operative during the optical limiting of laser pulses in CNT suspensions.

Fabrication of completely filled carbon nanotubes with copper nanowires in a confined space

Carbon nanotubes (CNTs) filled completely with polycrystalline Cu nanowires were synthesized by laser vaporization of Cu and graphite under high-pressure Ar gas atmosphere. Depending on the Ar gas pressure (0.1–0.9 MPa) and the Cu content (1–40 at.%) in graphite targets for laser vaporization, various products with different morphologies were observed by scanning and transmission electron microscopy. The ratios of the Cu-filled CNTs and carbon nanocapsules particularly increased as Ar gas pressure was increased. The maximum ∼60% fraction of Cu-filled CNTs with outer diameter of 10–50 nm and length of 0.3–3 μm was achieved at 0.9 MPa from graphite containing 20 at.% Cu. Most of the encapsulated Cu-nanowires were surrounded by single, double, or triple graphitic layers. Although the yield of the Cu-filled CNTs was also dependent on the Cu content in the graphite targets, no unfilled CNTs were produced even for low Cu content. The growth of Cu-filled CNTs is explained by the formation of molten Cu–C composite particles with an unusually C-rich composition in a space confined by high-pressure Ar gas, followed by precipitating Cu and C from the particles and subjecting them to phase separation.

Adsorption of lanthanides(III) from aqueous solutions by fullerene black modified with di(2-ethylhexyl)phosphoric acid

AbstractFullerene black (FB) - a product of electric arc graphite vaporization after extraction of fullerenes - was modified with the di(2-ethylhexyl)phosphoric acid (D2EHPA). The distribution of D2EHPA between FB and aqueous HNO3 solutions has been studied. The effect of HNO3 concentration in the aqueous phase and that of D2EHPA concentration in the sorbent phase on the adsorption of microquantities of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y nitrates from HNO3 solutions by D2EHPA-modified FB are considered. The stoichiometry of the sorbed complexes has been determined by the slope analysis method. The efficiency of lanthanides’ adsorption increases with an increase in the element atomic number. A considerable synergistic effect has been observed upon the addition of the neutral bidentate tetraphenylmethylenediphosphine dioxide ligand to D2EHPA in the sorbent phase.

Advances in the mass spectrometric study of the laser vaporization of graphite

Reliable experimental data on graphite vaporization and especially on carbon vapor composition exist only up to 2500–3000 K. Data measured at higher temperatures are questionable due to several experimental limitations, such as the difficult temperature determination and the not straightforward correlation of measured temperatures and intensities of signals in mass spectra. That is why a new method of high-temperature mass spectrometry with laser vaporization was developed, in order to extend the accessible temperature range while overcoming these limitations and to shed more light on the still poorly known behavior of carbon at high temperatures. Thus, carbon sublimation relative partial pressures of the species C1, C2, C3, C4, and C5 were measured up to 4100 K. Moreover, the values of the relative vaporization coefficients of C1, C2, C3, C4, and C5, estimated by comparison of the experimentally obtained partial pressures with the predicted equilibrium ones, are proposed.

Fullerenes from aromatic precursors by surface-catalysed cyclodehydrogenation

Graphite vaporization provides an uncontrolled yet efficient means of producing fullerene molecules. However, some fullerene derivatives or unusual fullerene species might only be accessible through rational and controlled synthesis methods. Recently, such an approach has been used to produce isolable amounts of the fullerene C(60) from commercially available starting materials. But the overall process required 11 steps to generate a suitable polycyclic aromatic precursor molecule, which was then dehydrogenated in the gas phase with a yield of only about one per cent. Here we report the formation of C(60) and the triazafullerene C(57)N(3) from aromatic precursors using a highly efficient surface-catalysed cyclodehydrogenation process. We find that after deposition onto a platinum (111) surface and heating to 750 K, the precursors are transformed into the corresponding fullerene and triazafullerene molecules with about 100 per cent yield. We expect that this approach will allow the production of a range of other fullerenes and heterofullerenes, once suitable precursors are available. Also, if the process is carried out in an atmosphere containing guest species, it might even allow the encapsulation of atoms or small molecules to form endohedral fullerenes.

Spectroscopic studies of the interaction of a high-power plasma stream with a solid on the GOL-3 facility

Experiments involving irradiation of carbon targets with a hot electron plasma stream performed on the GOL-3 facility were aimed at the simulation of the effect of hot plasma of a thermonuclear reactor on plasma collectors in regimes close to those expected in the ITER. In these experiments, the emphasis was on the study of the surface-erosion processes exposed to the plasma stream. The graphite evaporation and chemical-erosion processes were studied with absolutely calibrated spectroscopic systems of the visible region. Spectroscopic experiments yielded data on the flow of carbon atoms from the surface of a plasma collector and on the contribution of chemical erosion to the surface-damage process. The obtained values are compared with the results of direct measurements of the erosion depth and the results of numerical calculations.

Raman spectroscopy of carbon dust samples from NSTX

The Raman spectrum of dust particles exposed to the NSTX plasma is different from the spectrum of unexposed particles scraped from an unused graphite tile. For the unexposed particles, the high energy G-mode peak (Raman shift ∼ 1580 cm −1) is much stronger than the defect-induced D-mode peak (Raman shift ∼ 1350 cm −1), a pattern that is consistent with Raman spectrum for commercial graphite materials. For dust particles exposed to the plasma, the ratio of G-mode to D-mode peaks is lower and becomes even less than 1. The Raman measurements indicate that the production of carbon dust particles in NSTX involves modifications of the physical and chemical structure of the original graphite material. These modifications are shown to be similar to those measured for carbon deposits from atmospheric pressure helium arc discharge with an ablating anode electrode made from a graphite tile material. We also demonstrate experimentally that heating to 2000–2700 K alone cannot explain the observed structural modifications indicating that they must be due to higher temperatures needed for graphite vaporization, which is followed either by condensation or some plasma-induced processes leading to the formation of more disordered forms of carbon material than the original graphite.

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.

An Effective Method of Producing Small Neutral Carbon Clusters

An effective method of producing small neutral carbon clusters Cn(n = 1–6) is described. The small carbon clusters (positive ornegative charge or neutral) are formed by plasma which are produced bya high power 532 nm pulse laser ablating the surface of the metal Mn rodto react with small hydrocarbons supplied by a pulse valve, then theneutral carbon clusters are extracted and photo-ionized by anotherlaser (266 nm or 355 nm) in the ionization region of a lineartime-of-flight mass spectrometer. The distributions of the initialneutral carbon clusters are analysed with the ionic species appeared inmass spectra. It is observed that the yield of small carbon clusterswith the present method is about 10 times than that of the traditionalwidely used technology of laser vaporization of graphite.