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.     

Optical limiting with higher fullerenes

Optical limiting has been investigated for higher fullerenes and compared with C₆₀. The transmission through an aperture placed after solutions of C₇₆, C₇₈, and C₈₄ in tetrahydronaphthalene was measured using Q-switched laser pulses with a wavelength of 532 nm and a pulse width of 8 ns FWHM. Unlike C₆₀, the transmission for these higher fullerene solutions decreased linearly with increasing optical pulse energy. We attribute the linearized optical limiting response to self-defocusing of the optical beam and the absence of excited-state absorption. The ground state absorption spectra for the higher fullerenes suggest their use for optical limiting in the near infrared, and the C₈₄-tetrahydronaphthalene solution was found to be an optical limiter at 1.064 m.     

Autowave synthesis of cast aluminum oxynitrides with a high nitrogen content

Aluminum oxynitrides Al₂₂O₃₀N₂ and Al₂₃O₂₇N₅ and a number of Al-O-N solid solutions with a nitrogen content of 2.3 to 6.5 wt % were prepared from (CrO₃-Al-Al₂O₃-AlN) thermite-type mixtures with a high combustion temperature (2950–3200 K) by using the autowave synthesis method. The synthesis was conducted in a hermetically sealed reactor at an initial nitrogen pressure of 4.0 to 8.0 MPa. The aluminum nitride content was demonstrated to influence the nitrogen content in cast aluminum oxynitrides and on their microstructure and phase composition.     

Evolution of carbon from atomic clusters to fullerenes in an arc discharge

The formation of fullerenes from an arc-produced turbulent jet of carbon vapor is described. Both direct and backward mono-and bimolecular reactions are analyzed. Initial characteristics of the jet are used as the input parameters of the problem. The analytical dependences of the fullerene yield on the initial velocity of the jet and carbon vapor concentration explain experimental relationships between the fullerene yield, current, pressure, and buffer gas sort.     

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)     

Carbon flows from an arc discharge in regimes optimum for production of fullerenes

Radial flows of carbon particles from the interelectrode gap of an arc discharge in modes optimum for production of fullerenes are measured. From the experimental data conclusions are made concerning transformations of the carbon particles in a gas-plasma jet.     

A study of the synthesis products of fullerenes with nickel and cobalt

Qualitative analysis of the products of plasmochemical synthesis of fullerenes with metallic nickel and cobalt has been carried out using electron paramagnetic resonance (EPR) and electron microscopy. These studies show that the synthesis products are mainly fullerenes, metallic nanoparticles coated with an insulating layer, and isolated atomic clusters.     

Composition of higher fullerenes obtained by laser ablation of carboniferous materials

The compositions of higher fullerenes produced by ablation of various carboniferous materials are experimentally studied. The yield of fullerenes versus the type of carboniferous materials and laser radiation parameters is found.     

Molecular interactions in fullerenes and equilibrium of higher fullerites C76 and C84 with their vapors

From simple topological considerations on the molecular shapes, a new method for calculating the coefficients of the Girifalco intermolecular potential for various fullerenes is proposed. This eliminates the necessity for fitting the coefficients to data of measurements for each specific fullerene. We calculate them for C₇₆ and C₈₄ and apply this potential to perform research on the equilibrium of these fullerites with their vapors. The temperature dependence of the lattice parameters, the saturated vapor pressures and the enthalpies of sublimation is studied. Results are in good agreement with available experimental data. Received 13 January 2000 and Received in final form 18 June 2000     

Effect of deuterium on phase transformations in fullerenes at high temperatures and high pressures

The effect deuterium has on phase transformations is studied for amorphous and crystalline fullerenes C₆₀ and C₇₀ at high temperatures of up to 1300°C and high pressures (2–8 GPa). Amorphous fullerene phases are obtained via long grinding in a planetary mill. Structure is studied by means of neutron diffraction. In all cases, amorphous graphite (nanographite) forms in the temperature range of 800–1100°C. This material has different diffraction spectra distinguished by the heights of the halos observed on the graphite diffraction maxima and their relative intensities. These spectra (the structure of nanographite) are affected by preliminary amorphization, the number of carbon atoms in the fullerenes (C60 or C70), and the introduction of deuterium atoms. The different spectra of amorphous (disordered) graphite testify to its varying structure.     

Triggered discharges with high arc voltages in a vacuum interrupter

Studies of nonsustained disruptive discharges (NSDDs), isolated cases of which can occur in vacuum interrupters, indicate lateral discharges between the cathode and shield, which can initiate a brief discharge between the contacts. To facilitate the study of such discharges, the sample discharges were triggered by a surface discharge induced by a spark gap, built into the side of the cathode, and observed with a high-speed film camera and image-converter camera. The tests showed a cathode spot after igniting. The emitted electrons first charge the shield negatively and then are directed toward the anode. The discharge burns at a high voltage, with current ranging from 10 to 100 A. After a period of up to 400 μs, the current demand increases abruptly; an arc discharge occurs between the contacts and discharges the capacitances near the switch. The contact gap undergoes a rapid dielectric recovery, and the restored voltage is maintained. These types of discharge were also observed with NSDDs; thus it can be assumed that the triggered discharges studied correspond to the NSDD type     

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.     

Direct synthesis and characterization of highly ordered functional mesoporous silica thin films with high amino-groups content

A series of continuous, crack-free, highly ordered amino-functionalized mesoporous silica thin films have been directly synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of cationic CH₃(CH₂)₁₅N⁺(CH₃)₃Br⁻ (CTAB), nonionic C₁₆H₃₃(OCH₂CH₂)₁₀OH (Brij-56) or triblock copolymer H(OCH₂CH₂)₂₀(OCH(CH₃)CH₂)₇₀(OCH₂CH₂)₂₀)OH (P123) surfactant species under acidic conditions by sol-gel dip-coating. The molar ration of APTES/(TEOS + APTES) in the starting sol attains a value of 0.4. The effect of the sol aging on the mesostructure of thin films is systematically studied, and the optimal sol aging time is obtained for different surfactant systems. The amino-functionalized mesoporous silica thin films exhibit long-range ordering of 2D hexagonal (p6mm) and 3D cubic (Fm3m) pore arrays of size range from 2.2 to 8.3 nm following surfactants extraction as demonstrated by XRD, TEM and physical adsorption techniques. Based on BET surface area and weight loss, the surface coverage of amino-groups for thin films prepared using different surfactants is calculated to be 3.2 and above amino-groups per nm², which is very useful and promising for incorporating inorganic ions and biomolecules into these mesoporous silica materials.     

Properties of high pressure arc plasma

High pressure argon arc discharges are investigated in the pressure range up to 1000 atm. Experimental values of radiative properties such as the frequency-dependent emission coefficient and the total radiation source strength are compared with theoretical predictions. Solutions of the energy balance of wall stabilized high pressure arcs are presented, the agreement with measurements is good. A comparison of measured electrical conductivities of non-ideal argon plasmas with order measurements and with computations following different theoretical approaches, confirms the poor agreement between theory and experiment found by other authors for this regime. Auszug aus einer Habilitationsschrift am Fachbereich für Elektrotechnik der TU München.     

Electronic absorption spectra determination of C60 content in soot produced in hydrocarbon flames

We analyze the possibilities of eliminating hydrocarbon compounds from soot produced in hydrocarbon flames for the purpose of using the method of electronic absorption spectra to measure the content of fullerenes. The sensitivity limit of the spectral-absorption method has been determined. The solubility of C₆₀ in ether has been measured. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 4, pp. 253–256, March–April, 2000.     

多路Marx并联高压脉冲电源研究

脉冲功率技术在工业和生物医学领域有着广泛的应用,很多应用场合要求输出数百安培的高压脉冲。固态Marx发生器虽已研究多年,但是被广泛采用直插封装的IGBT和MOSFET功率半导体开关管的额定电流通常都低于100 A,无法满足低阻抗负载的应用需求。为提高输出脉冲电流幅值,提出两种多路Marx发生器并联的脉冲电源的拓扑结构,第一种方案采用多路Marx发生器直接并联,第二种是共用一组充电开关管的多路Marx发生器并联。由FPGA提供充放电控制信号,采用串芯磁环隔离驱动方案实现带负压偏置的同步驱动,主电路选用开通速度快、通流能力强的IGBT为主开关的半桥式固态方波Marx电路。实验结果表明,6路16级Marx直接并联的脉冲发生器能输出重频100 Hz高压方波脉冲幅值可达10 kV,在30 Ω负载侧输出峰值电流可达300 A,上升时间230 ns。共用充电开关管的6路4级Marx并联发生器在5 Ω电阻负载上的输出电流峰值可达300 A,最大输出电流可达460 A,上升时间272 ns。表明多路Marx发生器并联可以有效地减小系统内阻,提高系统带载能力;改进后的并联方案实现大电流脉冲输出的同时,所采用的开关管数量减小近一半,提高了系统的抗干扰能力的同时,降低了脉冲电源的成本;且增加级间并联导线可进一步改善均流效果。