Large fullerenes in mass spectra

Fullerenes have been studied for nearly three decades and enormous advances have been made. Mass spectrometry is commonly used for investigations on the distribution of fullerenes formed from evaporated graphite targets, and soot produced from such targets. We report distributions of fullerenes formed by graphite evaporation by use of a pulsed supersonic cluster source and compare them to certain distributions synthesised by other techniques, such as arc discharge and combustion methods. We highlight the fact that physical processes can occur during the mass spectral analysis of fullerenes under certain conditions that may skew the observed distribution of cage sizes present in a sample. In some cases, an analysis of fullerene-containing soot can greatly exaggerate the relative abundance of large fullerenes compared to C₆₀ and medium-sized fullerenes, depending on the particular experimental setup.     

Structure and magnetic properties of nanoparticles encapsulated in carbon shells

Ni₂Y and Nd–Fe–Nb–B catalysts were used for the processing of nanoparticles by arc discharge between graphite electrodes. The products were collected from the cathode (deposit and collar) and reactor walls (soot). The ferromagnetic nanoparticles have size in the range of 10–50 nm and are encapsulated in carbon shells. The chemical composition, structure and magnetic properties of the nanoparticles have been studied. For the Ni₂Y catalyst we found that the arc discharge results in decomposition of the intermetallic Ni₂Y phase and formation of Ni nanoparticles encapsulated in carbon shells in the collar and soot, whereas yttrium oxide was found in the deposit. For the Nd–Fe–Nb–B catalysts the magnetic properties depend on the collection place and erosion rate. Fe and Fe–Nd–Nb nanoparticles were found in the soot and deposit, respectively.     

Production of fullerenes in an arc discharge in the presence of hydrogen and oxygen

The production of fullerenes in an arc with graphite electrodes in mixtures of helium with oxygen and hydrogen as well as in pure oxygen and hydrogen is investigated. The radiation spectra of the arc and the mass spectra of the soot obtained in the arc are recorded; the content of fullerenes in the soot is determined. It is shown that fullerenes are formed in appreciable quantities (∼1%) even in pure hydrogen. Zh. Tekh. Fiz. 69, 48–51 (December 1999)     

Structure of fullerene-containing soot at different formation stages of arc discharge vaporization of graphite

Electron microscopy is used in a study of nanoclusters of the carbon soot deposited on a probe in different areas of arc discharge during graphite vaporization under conditions favorable for fullerene synthesis. It is found that the spatial network of soot nanoclusters consists of alternating regions of higher density or associates of carbon particles. Two types of nanoclusters have been identified with the correlation radii of the associates equal to 0.6–0.8 and 1.6–2.2 nm, respectively. Type I nanoclusters are dominant in the soot microparticles, and their structure shows practically no variations with increasing separation r of the soot collector from the discharge axis over the range of distances studied, r=1–9 cm. The effective radius R ₀ of the “elementary” particles making up the associates in the soot nanoclusters of Type I calculated with the use of scaling relationships is 0.15–0.17 nm and is close to the gas-kinetic radius of carbon atoms. Type II nanoclusters have been identified in soot collected at r>3 cm. Values of R ₀ calculated in this case are 0.6–0.9 nm and decrease with increasing r, which indicates the presence of fullerene molecules in these nanocluster associates.     

高效循环电弧放电法制备大量单壁纳米碳管的研究

介绍一种利用电弧放电法高效率制备大量单壁纳米碳管的新方法.以钨代替传统的石墨棒作为放电阴极，采取循环式往返放电法.同时利用高分辨透射电子显微镜及拉曼光谱对制备的单壁纳米碳管进行了观察、表征.实验证明：以钨为阴极的循环电弧放电法可以初步实现单壁纳米碳管的高效率、大批量生产. 关键词： 单壁纳米碳管 钨电极 拉曼光谱     

提高C_(60)产率的吸收光谱分析

对石墨电极放电产物的吸收光谱分析及掺入金属元素 (Fe)的放电实验表明 ,氧是影响C60 产率的重要因素之一。电弧区的扩大对C60 产率的提高也有重要作用。在石墨电极内加入适量Fe ,C60 产率可达到40 %。同时还发现放电产物中产生了胆甾醇的衍生物。     

提高C60产率的吸收光谱分析

对石墨电极放电产物的吸收光谱分析及掺入金属元素（Fe)的放电实验表明,氧是影响C60产率的重要因素之一,电弧区的扩大对C60产率的提高也有重要作用,在石墨电极内加入适量Fe,C60产率可达到40％,同时还发现放电产物中产生了胆甾醇的衍生物。     

氩气电弧等离子体炬提纯大鳞片石墨研究

石墨材料作为一种工业原料,特别是纯度在99.9%以上的高纯石墨被应用在各大高科技领域,现有物理法和化学法的石墨提纯技术成本高、酸碱对设备和环境破坏严重、工艺流程复杂,因此开发一种优良有效的石墨提纯技术,已成为近年来国内外研究的热点。建立了一种利用非转移电弧等离子体炬提纯大鳞片石墨的方法,利用电弧可快速产生高温的特性,对黑龙江省鸡西市纯度为94.18%的大鳞片石墨样品进行高温处理。研究显示在本文电弧装置下提纯石墨的最佳放电参数范围气流量为25 L/min、电流为400 A、功率为10 kW,此时的电弧表面温度高达3350 ℃,利用扫描电子显微镜等对电弧处理前后石墨样品的微观结构对比发现石墨样品出现粉碎、断裂等特点,根据石墨化学分析方法国家标准GB/T 3521 2008对石墨纯度及其杂质进行研究分析,经电弧处理后石墨纯度提高到99.21%。     

Hall effect in the natural glassy carbon of schungites

The temperature dependences (80–500 K) of the Hall coefficient and the resistivity of samples of schungite of types I and III (schungite I and schungite III), as well as a commercial glassy carbon, with carbon contents equal to 98, 30, and 99.99%, respectively, are measured. The character of the dependences of the resistivity and its numerical values are similar to those observed in polycrystalline graphites with a high degree of disorder and in synthetic glassy carbon. Conversely, the Hall coefficient in the schungite samples, as in high-quality single crystals and n-type intercalated compounds of graphite, is found to be negative, small in magnitude, and weakly dependent on the temperature. At room temperature it is equal to 2.83×10⁻²² and 0.305 cm³/C in schungite I and schungite III, respectively, the Hall mobility of the charge carriers in these materials is 8.0 and 9.2 cm²/V·s, and the Hall carrier concentration is 2.2×10²⁰ and 2.0×10¹⁹ cm⁻³. Fiz. Tverd. Tela (St. Petersburg) 39, 1783–1786 (October 1997)     

THE RAMAN SCATTERING OF CARBON NANOTUBES PRODUCED IN DIFFERENT INERT GASES AND THEIR PRESSURES BY ARC DISCHARGE

First- and second-order Raman spectra of carbon nanotubes produced in helium and argon atmospheres at a pressure ranging from 11 to 92 kPa by arc discharge have been measured and compared with each other. The position and bandwidth of the spectral lines depend on the kind of inert gases and their pressure. The Raman spectra of the nanotubes produced in argon gas atmosphere are much more similar to that of polycrystalline graphite than those of the nanotubes produced in helium gas atmosphere. The position and bandwidth of nanotube Raman peaks change with gas pressure in arc discharge because different diameter distribution of nanotubes is produced at different inert gas pressure. The Raman spectra of nanotubes produced at high pressure is much more like that of graphite than those produced in lower pressure     

Effect of heat-pretreatment of the graphite rod on the quality of SWCNTs by arc discharge

Single-walled carbon nanotubes (SWCNTs) have been synthesized in high yield by the dc arc discharge technique under heat-pretreatment of the graphite rod conditions. Before executing arc discharge, the graphite rods containing the catalysts were heat treated at 600, 700, 800 and 900 °C for 1–3 h, respectively. Effects of heat-pretreatment of the graphite rod on the quality of SWCNTs by arc discharge were investigated. The heat-treatment temperature and time were found to be crucial for a high yield of high-purity SWCNTs. Optimum parameter was found to be at the heat-treatment temperature of 800 °C for 2 h. The SWCNTs synthesized under the optimum condition have better field-emission characteristics. The turn-on field needed to produce a current density of 10 μA/cm² is found to be 1.9 V/μm and the threshold field where current density reaches 10 mA/cm² is 3.9 V/μm.     

Spectroscopy of the regenerative soot

The mechanisms and processes of the formation of the regenerative soot in a graphite hollow cathode discharge that produces and emits carbon clusters are presented. Mass spectrometry with a specially designed E×B velocity filter analyzes the entire range of the charged clusters from C ₁ to ∼C ₄₃₀₀. The state of the carbon vapour within the source is evaluated by using the characteristic line emissions from the carbonaceous discharge whose formative mechanisms depend upon the kinetic and potential sputtering of the sooted cathode. The carbonaceous discharge generates atomic and ionic C and its clusters C _m (m≥ 2), noble gas metastable atoms and ions, energetic electrons and photons in the cavity of the graphite hollow cathode. The parameters of soot formation and its recycling depend critically on the discharge parameters, the geometry of the hollow cathode and 3D profile of the cusp magnetic field contours. Received 2nd July 2001 and Received in final form 10 September 2001     

碳纳米管的拉曼散射

本文报道了经电弧放电产生的阴极沉积物外壳与内芯，以及石墨电极的喇曼光谱。     

不同惰性气氛及压强下的碳纳米管的拉曼光谱

本文比较了央弧法中在两种不同气氛和不同压强下制备出的碳纳米管的一级和二级拉曼光谱。我们用直流碳弧法分别在He气氛下和Ar气氛下，压强从11kPa到92kPa制备出碳纳米管，对它们的拉曼光谱进行了分析和比较，发现谱线的峰位置和峰宽度取决于所制备的惰性气氛种类和气体压强。在Ar气氛下制备的碳纳米管的拉曼光谱更接近于石墨的拉曼光谱，而He气氛下制备的碳纳米管，其拉曼光谱与石墨比较，差别较大。并且拉曼位移的峰位置和宽度随着压强的变化而改变，在较高压强下产生的碳纳米管的拉曼光谱更类似于石墨的拉曼光谱。     

Arc discharge with a vaporizable anode: Why is the fullerene formation process affected by the kind of buffer gas?

A model for calculating an arc discharge with the vaporizable graphite anode used in production of fullerenes has been proposed. Calculations with the use of this model give a clue to the dependence of fullerene formation efficiency on the kind of buffer gas used.     

Electric-arc high-capacity reactor for the synthesis of carbon soot with a high content of endohedral metallofullerenes

An electric-arc reactor is designed for synthesizing carbon soot containing endohedral metallofullerenes during the sequential evaporation of five composite graphite electrodes. The preparation conditions of the composite graphite electrodes and the electric-arc evaporation parameters are optimized, which increases the reactor capacity and the content of endohedral metallofullerenes in carbon soot.     

Electric-arc synthesis of soot with high content of higher fullerenes in parallel arc

Soot with a relatively high content of higher fullerenes (C₇₆, C₇₈, C₈₀, C₈₂, C₈₄, C₈₆, etc.) is synthesized in a parallel arc upon evaporation of pure carbon electrodes. The content of higher fullerenes in soot extract amounts to 13.8 wt % when two electrodes are simultaneously burnt in electric-arc reactor. Such a content is comparable with the content obtained upon evaporation of composite graphite electrodes with potassium carbonate impurity.     

Iron nanoparticles grown in a carbon arc discharge

Summary Iron particles, encapsulated by graphite layers, were produced by means of the Kratschmer arc discharge method in an iron pentacarbonyl atmosphere. The M?ssbauer effect is dominated by the vibration of the particles as a whole. Superparamegnetism is dominant for iron oxide particles. No endohedral iron fullerenes were observed, contrary to a previous report. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

Mass transport in a gas discharge

The effect of different parameters on the nature of the axial distribution of atoms evaporated from an electrode in a gas discharge is investigated. Theoretical calculations employing an analytical relation proposed earlier for the atomic concentration have been checked experimentally by changing the transport parameters and the (radial) dimensions of the atomic source. In the first case an arc discharge between graphite electrodes is used, and in the second case a pulsed discharge between metal electrodes, making it possible to localize and vary the dimensions of the source on the surface of the electrode. On the basis of these investigations, the experimentally observed breakdown of proportionality of the atomic concentrations and also the nonlinearity of the calibration graphs used in spectral analysis are explained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 77–80, November, 1973.     

强流脉冲电弧作用下石墨电极蒸发特性

气体开关电弧的热侵蚀作用是电极损耗的主要成因。石墨电极在电弧作用下发生蒸发并在多次放电后有明显的质量损耗,改变了开关内的气体环境和电极间距,导致开关动作可靠性降低。为研究石墨电极在脉冲电弧冲击下的侵蚀特征,基于开关电弧瞬态扩散特征和石墨材料参数,在弧根区域建立了电弧-电极能量耦合模型,得到了等离子体-固体区域的传热特性。考虑石墨电极的相变特征,计算瞬态热作用下石墨电极的加热范围以及临界相变点,研究瞬态电弧热冲击作用下的石墨电极相变机制。研究结果表明,电弧-电极界面热流主要集中在电弧接触面中心,电弧沉积的能量密度最高可达109 W/m2,石墨在电流上升初期基本处于加热状态,在能量积聚作用下,石墨转变为升华状态,传热强度随半径急剧衰减,蒸发区域略小于电弧半径。通过实验记录了5种开关工况下石墨电极烧蚀形貌和质量损失情况,结果表明,电极质量损失与电弧沉积在电极表面的能量线性相关,近似为0.015 mg/J。研究了电弧关键参数对电极质量损失速率的影响,为延缓电极损耗提供数据支撑。