G. N. Churilov

Electron microscopy studies of FCC carbon particles

Abstract A modified form of carbon was found among the products of a plasmachemical synthesis. This form has a face central cubic (fcc) crystal structure with a lattice constant a = 3.57 A. The fcc carbon takes the form of particles of various shapes (round, ellipsoidal, faceted). The faceted particles have six, eight or ten faces. Within some particles various structures with higher density were observed. Some particles have a more dense core or envelope. The fcc carbon is interpreted as a metastable form of pure carbon.

On the mechanism of fullerene formation in a carbon plasma

A conception about the mechanism of fullerene formation in carbon plasma is developed based on the influence of electron concentration on the stability of carbon clusters. Thermodynamic estimates for the efficiency of formation of spheroidal, flat clusters and linear carbon chains depending on the charge of the reacting particles are described. Strong influence of cluster charge upon the geometry and stability of flat clusters is shown. The charge variation of flat clusters can promote both their folding to curved structures and their dissociation. It is concluded that the fluctuations of electron concentration in a carbon plasma can result in the accumulation of fullerene clusters and the dissociation of flat clusters.

Influence of electron concentration and temperature on fullerene formation in a carbon plasma

The influence of electron concentration in ionized carbon vapor on C60 fullerene formation was theoretically investigated. By considering C60 molecule assembly at one or two intermediate stages of cluster collision we determined the plasma parameters (temperature and electron concentration) optimal for the fullerene synthesis. The estimations made showed that waves of electron concentration in plasma changed the rate of C60 fullerene assembling.

Fullerenes and other structures of carbon synthesized in a carbon plasma jet under helium flow

The plasma chemical reactor based on a carbon plasma jet was created for the production of fullerenes. This reactor has the changing temperature zone and provides deposition of soot under different conditions. X-ray powder diffraction investigation is carried out for identification of substances obtained in different parts of the installation. The fullerene crystals and an amorphous phase were found in the chamber. The amorphous fraction is probably composed mainly of the atomic aggregations similar in size and coordination to the fullerene molecules. The residual graphite and its polytype modifications were also found. This residual graphite is better crystallized than the initial one, therefore, it can be considered as a product of carbon crystallization from plasma but not as the particles of the initial graphite seized from the central electrode. The fullerene and amorphous fractions were not found on the external electrode which was cooled by water and where very fast condensation of carbon from plasma takes place. The sample taken from this electrode is composed mainly from a new x-graphite phase which can be considered a result of this fast condensation. This last conclusion is also supported by the fact that this x-graphite was also found on the walls of the chamber where the fast condensation also must take place, but it was not found in the flying soot fraction.

Crystal structures of chloroform solvates of fullerenes

The chloroform solvates of C60 and C70 fullerenes and of the C60/C70 mixture were synthesized and investigated by X-ray powder diffraction.

Impedance spectroscopy of high-molecular poly(ethylene) with carbon nanotubes

The impedance spectra of composite materials based on the high-molecular poly(ethylene) modified by carbon nanotubes have been investigated. A numerical method has been proposed for reconstructing the relaxation time distribution function of the active (R) and reactive (C) elements of a sample directly from the experimentally obtained frequency dependence of the real and imaginary components of the impedance. It has been shown that, with an increase in the concentration of carbon nanotubes, the electrical conductivity of the samples under study increases and their impedance characteristics are described by a nonmonotonic relaxation time distribution function.

A Technique and Device for Studying Alternating-Current Discharge Dynamics. Stratification of a Discharge in an Argon Flow at Atmospheric Pressure

The technique for studying discharge emission dynamics by high-speed photoregistration methods is based on self-tuning of the frequency (44 kHz) and phase of the discharge-supplying generator current to the rotational frequency of the mirror of a high-speed camera, the ratio of these frequencies being equal to 40 : 1. This technique has revealed that the discharge in a system with a hollow copper electrode and an inductor electrode in an argon flow at atmospheric pressure is stratified. Both standing and traveling ionization waves were observed, and their length and speed were determined. A device for supplying powder-like samples to the discharge plasma allowed for measurements of the temperature and electron density distributions along the discharge length. It is shown that the electron density values determined from the width of the Hβhydrogen line and by the method of relative intensities of spectral lines differ by an order of magnitude; therefore, the plasma cannot be considered in thermodynamical equilibrium.

The Influence of Ir and Pt Addition on the Synthesis of Fullerenes at Atmospheric Pressure

Abstract The addition of metallic Ir and Pt to a fullerene‐forming, atmospheric‐pressure plasma reactor was found to influence the generation of carbonaceous products. It was observed that the added metals were efficiently dispersed into the plasma and that their presence increased the yield of fullerenes. The addition of Ir led to a noticeable shift in the fullerene distribution towards C60, whereas the addition of Pt increased the proportion of C60 oxides and decreased the proportion of higher fullerenes. Addition of Ir also caused a reduction of the soot particle size and the formation of a considerable quantity of carbon nanotubes.

A method and apparatus for high-throughput controlled synthesis of fullerenes and endohedral metal fullerenes

A method for synthesis of carbon nanostructures in a high-frequency arc discharge in the flow of helium (3–4 L/min) is presented. It is shown that the plasma-chemical synthesis of fullerenes and endohedral metal fullerenes (EMFs) can be controlled by changing helium pressure in the chamber. Temperature and electron concentration along the line normal to the discharge axis decrease upon moving away from the axis to the periphery; the larger the pressure, the sharper is the decrease in these parameters. The optimal helium pressure of 98 kPa was found in obtaining the Gd@C82 EMF which corresponds to the maximal EMF yield of 5 wt %.

Effect of electrode material on impedance spectra of metal-polyethylene structures with carbon nanotubes

The effect of an electrode material on electrical properties of a composite material based on super-high-molecular polyethylene (SHMPE) filled with carbon nanotubes has been studied using impedance spectroscopy. Using the method of replacing the sample by an equivalent electric circuit, it has been found that, depending on the electrode material, a blocking barrier with high active resistance and a space charge region adjacent to it arise in the interface region. It has been shown that the barrier height is controlled by surface electronic states of SHMPE and weakly depends on the electron work function of metal electrodes (Bardeen barrier). The characteristic times of electrical relaxation characterizing bulk and interface regions of the composite under study have been determined.