SWNT were synthesized in high yield in the presence of a Ni/Cr alloy catalyst and studied through TEM observations, Raman spectroscopy and thermal gravimetric analysis (TGA). A “sandwich” structure of the anode is used, where a Ni/Cr alloy foil of 0.1 mm in thickness is inserted longitudinally as a catalyst between two rectangular graphite anode rods. HRTEM observations show that SWNT are bound in long bundles of tens μm in length and about 10 nm in diameter. Raman spectra show the diameter of SWNT ranging between 1.2 and 1.5 nm with maximum abundance of 1.24 nm. The initial content of SWNT in the samples is about 20%. Thermal treatment of the as‐produced sample under various temperatures and dosed air supply results in a notable mass loss of the sample and change in its content. So heating up to 600 K results in 40% loss in the mass of a sample, enhancing the SWNT yield up to 35% without any notable destruction. Heating above 600K results in practically full thermal destruction of the SWNT.

We have investigated the reduction of initial C 60 electronic structure under the influence of a growing number of attached fluorines in C 60 F 48, C 60 F 36, C 60 F 24, and C 60 F 18. The reduction of the low-energy π-electron subsystem reveals itself in lowering of the optical absorption in the visible region and in gradual blueshift of the luminescence. The absorption of C 60 F 24 and C 60 F 18 films strongly resembles that of C 60, thus showing the similarity of electronic structures of C 60 and these compounds. This resemblance disappears in the absorption spectra of C 60 F 48 and C 60 F 36. The absorption of these compounds looks like that of C 6 H 6, because the π-bonds are isolated. The luminescence of C 60 F 18 film has an unexpected two-component structure, with the first component close to the C 60 luminescence spectra, and the second one lying pproximately in the same region with C 60 F 36. We attribute this splitting of luminescence spectra to the two different channels for relaxation of the electronic excitation. The first one is correlated with the fluorinated part of the C 60 F 18 molecule, the second one with the part free of fluorine atoms.

We have undertaken to investigate optical absorption spectra of matrix-isolated halogenofullerene molecules C60Cl60, C60Cl24, and C60Br24 in the visible and near-IR regions of the spectrum. The results for C60Cl24 presented here, show that this molecule possesses a rich well-structured spectrum. The analysis of the spectrum allows to suggest a tentative scheme of the electron energy levels of C60Cl24 molecule in the region of its HOMO=LUMO gap. The optimized geometry of C60Cl24 and its charge distribution calculated at the AM1 level are also presented. The Shpol'skii effect in the absorption spectrum of C60Cl24 molecules embedded in crystalline toluene was clearly detected, in agreement with our theoretical investigation of the geometrical structure of C60Cl24 centers in toluene crystals.

The photoluminescence and absorption properties of C60 fluorides have been examined. We have found that the obtained optical spectra are shifted gradually to the higher energy side due to the partial elimination of the π-electron subsystem from the molecule. We derived the relationship between the icosahedral C60 skeleton structure and π-electron subsystem under the influence of F attachment and treated it on the basis of absorption spectra. The excitation with the highest efficiency of luminescent relaxation is probably due to CF bonds.

Synthesis of fullerides of alkali metals (Na, K) was performed under chemical activation in aromatic solvents. High speed of the fulleride formation processes provides the possibility to conduct syntheses at relatively low temperatures (110-130 degreesC), compared to the vapour method, Under those conditions the solvent is able to introduce itself into the lattice of the fulleride considerably changing its properties compared to the one synthesised under high temperature in vacuum.

The aim of the present work was the study of dissociation kinetics of molecular fluorine on the hot surface of a nickel catalyst. The concentration of fluorine atoms was measured by EPR spectroscopy using molecular oxygen as a reference. The fluorine atom concentration was measured with an random error of about 3%. Molecular fluorine dissociation on the walls of a heated nickel tubes was measured. For process simulation and analysis of the experimental curves a one-dimensional kinetic model of the reactor which did not take into account axial and radial diffusion of the gas in the reactor and radial gas speed distribution was used, but account was taken of the pressure drop in the reactor and tubes between the reactor and ESR spectrometer.In the experiments we measured the fluorine atom concentration dependencies on the gas flow velocity and fluorine pressure (10-30 Torr). The dissociation constant on the surface of nickel foil is k(d) = (2.4 +/- 0.7) x 10(4) exp[-(19 000 +/- 500)/RT] cm/s (at 700-900 K), the probability of heterogeneous recombination on the nickel surface gamma = (2.2 +/- 0.5) x 10(-4), rate constant of the three-body gas phase recombination on molecular fluorine as 'third' body at room temperature k(rec) = (4.7 +/- 1.2) x 10(-34) cm(6)/s. This last value coincides with literature value. Our measurements confirmed the value of the equilibrium constant of the fluorine dissociation process: K = 1.11 x 10(25) exp(-37 840/RT)cm(-3) (K is expressed in cal/mole). (C) 1999 Elsevier Science S.A. All rights reserved.

Experimental data on the concentration dependence of nonlinear third-order optical susceptibility of fullerene C(60) in benzene solution are analyzed. The deviation of the dependence from a linear behavior is attributed to the fullerene aggregation phenomenon in solution investigated previously. The aggregation shifts the four-photon resonance frequency. It is inferred from a comparison of the size distribution function of fullerene clusters in solution calculated previously based on the drop model of clusters with the experimental chi((3))(C) dependence that fullerene molecules incorporated in clusters do not virtually experience resonant four-photon interaction, so that the nonlinear optical response depends only on isolated molecules C, in the solution studied. The possibility of utilizing the nonlinear optical characteristics of fullerenes in solutions in studies of their aggregation is discussed.

The droplet model of fullerene clusters in solutions is used for analysis of experimental data on the concentration dependence of the third order nonlinear optical susceptibility of fullerene C-60 benzene solution and also for determination of heat of solution of fullerenes versus concentration and temperature. The absorption frequency of fullerene molecules involved into clusters is removed out the four-wave mixing resonance which causes the decrease in a number of fullerene molecules interacting with radiation. Therefore the third order nonlinear optical susceptibility is defined only by separate C-60 molecules which are not involved into clusters. The use of cluster size distribution function of aggregated fullerenes in solutions found earlier provides quite good coincigence between the measured dependencies chi((3))(C) and concentration dependence of separate fullerene molecules. The same function is used for determination of the concentration and temperature dependencies of the heat of solution of aggregated fullerenes. The calculated results shed a light on the reason of apparent contradiction between measured data of various authors.

The results of optical investigations of C-60 fluorine derivatives using synchrotron, laser and traditional light sources are presented and discussed. Optical absorption and luminescence spectra were studied. Luminescence and luminescence excitation spectra enable us to assume that the luminescent state is derived from the excitation of the pi double bonds of the C-60 skeleton and that the excitation of the C-F bonds of the C60F2x molecule relaxes through the luminescent state with high probability.

Phenomenon of aggregation of fullerenes in solutions determines the main features of their behavior. The general theoretical approach to the description of this phenomenon is developed. The approach is based on the droplet model of clusters consisting of a number of fullerenes molecules. The model taking into account the volumetric and surface energy characteristics of cluster showed itself quite well in the explanation of the extraordinary temperature dependence of fullerene solubility observed earlier. Results of the numerical evaluation of the cluster size distribution function in dependence on temperature and concentration are presented. These data are used for determination of the diffusion and thermal diffusion coefficient of fullerenes in solutions. It is shown that the concentration dependence of the fullerene diffusion coefficient can be used as the basis of a new approach to the problem of fullerene enrichment. The higher fullerenes are usually presented as a low admixture to C-60 and do not form clusters. For this reason they have the higher diffusion coefficient than C-60 and can be partially separated from C-60 through diffusion. The different specific separation schemes are considered.

The diffusion of fullerenes in solution is studied taking into account the recently established formation of clusters containing numbers of aggregated fullerence molecules. Based on a droplet model of a cluster, the distribution function of fullerence clusters by size is obtained for various concentrations of solution. It is shown that dissolved fullerene is present mainly in the form of clusters at saturation conditions, but the contribution of clusters diminishes as the concentration decreases. Since the diffusion mobility of clusters is much less than that of molecules, it leads to the dependence of an effective diffusion coefficient on concentration, which is computed for the case of fullerence C60. The feasibility of the use of this dependence as a basis for a diffusion method of the separation and enrichment of the fullerene extract with a small addition of higher fullerenes is analyzed. Possible schemes for enrichment are discussed.

A new source of elemental fluorine is described, based on the electrochemical decomposition of a solid F− conducting electrolyte. The use of a chemically and thermally stable solid electrolyte provides the possibility of pure fluorine production over a wide temperature range and also under high vacuum conditions. Fluorine evolution was investigated by volumetric and mass-spectrometric methods.

The phenomenon of the thermal diffusion of fullerenes in solutions concerned with the fact aggregation of fullerence molecules in clusters in organic solvents discovered recently is studied. The mechanism of this phenomenon based on the temperature dependence of the cluster size distribution function is proposed. The temperature and concentration dependencies of the cluster size distribution function calculated previously are used to calculate the thermal diffusion coefficient of C60 fullerene in toluene solution as a function of temperature and concentration. It is shown that the mechanism spoken of dominates in thermal diffusion at the temperature above the phase transition temperature in solid C60. A contribution of the conventional mechanism of thermal diffusion caused by a considerable difference in fullerene and solvent molecule dimensions is estimated.

Alkali metal fullerene compounds XC(60) and XC(70) (X = Li, Na, K) in toluene solution at room temperature with the fullerene monoanion as the reaction product were synthesized. The ratio of the rate constants for the reaction of joining of the sodium atom to the molecule C-70 and that for C-60 is as large as 2.5, which shows that the C-70 molecule is more reactive than C-60. The reaction product (metal/fullerene approximate to 1/1) was filtered and dried. As products of its slow hydrolysis the pristine fullerene and a water soluble compound have been obtained. This compound is dark-brown colored and has the solubility in water of order 150 g/l. VIS and IR absorption spectra show the presence of the intense bands 3500 cm(-1) belonging to OH group. As it follows from XPS data this compound contains the carbon, sodium and oxygen atoms in the approximate ratio 10/1/3. The presence of fullerenes in this compound is questionable, because the quantity of free fullerenes obtained in the hydrolysis reaction is close to the initial one. The possibility for usage the difference in the reaction rates for fullerenes of different kinds for development of a new procedure for chemical enrichment in solutions is discussed.

The kinetics of the reaction of C60 and C70 with metallic sodium in toluene solution at room temperature has been studied. The initial stage of reaction gives the fullerene monoanion, and the ratio of the reaction rate constants k(C70)/k(C60) = 2.5 ± 0.1. This ration does not depend on the relative fullerene concentrations and absolute reaction rates, the latter being sensitive to the condition of the metal surface and so varies in an irregular manner. The possibility of using the difference in the reaction rate constants for the development of a fullerene separation and purification technology is discussed.

The application of high pressure considerably extends the potential for synthesis of different carbon compounds /!/. The transformation of fullerene, accompanied by a large volume decrease, is enhanced under high pressure conditions. Under non-hydrostatic pressure at room temperature, Cöo forms the metastable phase 111 with a high content of sp hybridized carbon atoms similar to diamond. It is known that a fiillerene, Ceo, under high pressure (30 40 GPa) is transformed into a diamond-like modification of carbon at room temperature 131. The aim of this work is the determination of P-T conditions of Ceo stability and transformations of the mixture C60-C250 at high pressure and temperature in agreement with our supposition that transformation occurs more easily at elevated temperatures or for higher fullerenes.