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It is shown that acid activation of ultralong carbon nanotubes synthesis products increases their reactivity during subsequent thermochemical treatment in air at 480 °C. Such an integrated approach of CNTs processing provides high purity and maximum yield of the target product. For example, the non-CNT fraction decreases by 3.2 times, while the residual iron content decreases by 17–24 times in comparison with thermochemical treatment without acid. Raman spectroscopy and low-temperature nitrogen adsorption showed that acid activation does not lead to extra surface defects, which could initiate further oxidation of carbon matrix in air. It is suggested that the increased reactivity of CNT synthesis products after acid activation during thermo-oxidative degradation may be due to the formation of an "adduct" of carboxyl groups on the surface of nanotube carbon matrix with hydrogen chloride. It was shown by thermogravimetric studies coupled with mass-spectra investigation of gas evolved, that under the constant heating, at the temperatures of the beginning of intensive oxidation (500–600 °C), the decomposition of the "adduct" occurs, bypassing the stage of formation of more temperature-resistant phenolic groups, which can inhibit further oxidation. Water released during the decomposition of the "adduct" can also accelerate the process of thermal oxidation. [ABSTRACT FROM AUTHOR]

Microwave absorption properties are studied for flexible materials based on periodic gratings made of carbon nanotube (CNT) threads. Resonant absorption is observed by free space measurements in the frequency range from 26.5 to 40 GHz. Materials comprised of CNT thread gratings with different periods, a metal backplate, and an intermediate dielectric layer exhibit significant reflection losses (less than −45 dB). The shifts of peaks on the absorption spectra caused by changes in the thickness and rotations of the samples indicate the high sensitivity of the obtained results. [ABSTRACT FROM AUTHOR]

Carbon nanotubes filled with iron oxides can be a promising material for medicine. In this paper, carbon nanotubes containing iron oxides were synthesized by chemical vapor deposition method. Cubic and tetragonal modifications of maghemite Fe2O3 were found inside the nanotubes along with α- and γ-phases of iron and iron carbides by electron microscopy studies. Twins were identified in the tetragonal maghemite with the {103} twinning plane. [ABSTRACT FROM AUTHOR]

Onion-like carbon (OLC) particles were produced as a byproduct of thermal partial oxidation of methane under different O2/Natural Gas (NG) ratio. It was established that the particles have quasi-spherical morphology and concentric shell structure. The particles have an outer diameter of 20–60 nm while the inner cage is rather typical for onions and has a diameter below 1 nm. The concentric graphitic structure and spherical symmetry along with the absence of amorphous carbon were confirmed by transmission electron microscopy, electron diffraction, EDX spectroscopy and Raman investigation. Variation of O2/NG ratio was proved a powerful tool for controlling OLC particles yield and structure. The formation of single-core or multicore OLC can be controlled by thermal partial oxidation process. [ABSTRACT FROM AUTHOR]

The present study addresses the problems of catalytic synthesis of C60-based 3D polymers in the presence of carbon disulfide CS2. It is shown that CS2 lowers the pressure of fullerite 3D polymerization at room temperature. In particular, the pressure at which the 3D ultrahard fullerite C60 phase is formed decreases from 18 GPa to 7 GPa. The catalyst plays no significant role at room temperature and low pressures up to 6 GPa. When the C60 + CS2 is heated to 1200 K, the pressure of the 3D C60 polymerization is further reduced to 2-4 GPa. Based on the TEM data, we propose a 3D polymer structure based on C60 obtained by the catalytic synthesis. [ABSTRACT FROM AUTHOR]

X-ray photoelectron spectroscopy was used for characterization of MWNT-C60composites with assistance of scanning and transmission electron microscopy. The composites were received by immerison of nanotubes into fullerene solution in CS2with consequent processing with green laser irradiation at aproximately 10 W/cm2. It was shown that C1s spectra of composites are different from simple addition of MWNT and C60features. It found that preliminary nanotube purification by oxidative treatment influences strongly the nature of fullerene-nanotube bonding. Hydrophilic surface of oxidized nanotube material has lower affinity to C60molecules and provides for concentration of C60molecules into clusters, which show differential charging effect in XPS spectra. The differential charging effect disappears after laser processing, which induces photopolymerization of fullerene clusters. The as-synthesized nanotubes form composites with more evenly distributed fullerene. [ABSTRACT FROM AUTHOR]

Modification of polyurethane–carbon fibre (CF) interface by grafting carbon nanotubes onto a surface of the fibre is reported. The grafting technique allows avoiding the fibre mechanical properties deterioration. The technique includes desizing of CFs, introduction of a protective aluminium oxide coating, deposition of Fe catalyst and then chemical vapour deposition for nanotube growth. Re-enforced composites were fabricated with polyurethane as a matrix. Polymer–fiber interface properties were estimated through the measurement of interfacial shear strength (IFSS). It was shown that IFSS increased more than twice due to nanotube grafting. The enhancement of both thermal conductivity and mechanical properties of composites with modified interface was observed. Significant improvement of delamination resistance was proven for composites with modified polymer–fibre interface. [ABSTRACT FROM AUTHOR]

One of the most important problems in the synthesis of carbon nanotubes is the problem of controlling their morphology, namely, length, aspect ratio, alignment and so forth. Catalytic synthesis of carbon nanotubes in a suspended bed reactor allowed for the study of the possibilities of controlling the growth of nanotubes by introducing a certain amount of water vapor and carbon-containing materials in the reaction zone. The synthesized long carbon nanotubes were studied by Raman spectroscopy, transmission and scanning electron microscopy. We found that water concentration influences both yield and structure of nanotubes. It is shown that the yield of centimeter-long nanotubes can be maximized at an optimum H2O/C ratio, while deviations dramatically change morphology and thickness of the nanotubes. [ABSTRACT FROM AUTHOR]

Carbon nanotubes can become a cheaper alternative to carbon fibers based on traditional technology. The conditions for successful longer carbon nanotube catalytic growth are formulated. Optimization is needed in order to break through three general limitations, which prevent nanotubes from reaching great length: slow growth; growth quenching, which is manifested by stopping growth due to catalyst capsulation or poisoning or due to other reasons; and competition between the nanotube elongation and the nanotube thickening. The experimental results on CNT growth show the possibility of producing centimeter-long nanotubes suitable as precursors for manufacturing super-strength carbon threads and also new kinds of functional nanocomposites. [ABSTRACT FROM AUTHOR]

The paper presents the results of competitive catalysis investigation of the carbon nanotube growth in situ of the partial oxidation process of methane. The competition between Ni and Fe results in suppression of Ni catalytic activity and the growth of Fe‐capped carbon nanotubes. The discrimination is so strong that iron is segregated from Ni–Fe based stainless steel alloy leaving characteristic Ni‐enriched corrosion caverns. The process strongly depends on temperature. Depending on particular catalyst bed composition, the nanotubes of various morphology may occur. In particular, the use of perovskite‐type catalyst leads to formation of “olive‐branch”‐like peculiar carbon nanostructures. [ABSTRACT FROM AUTHOR]

Laser vaporization of graphite proved to be an unbelievably flexible instrument allowing selective fabrication of various novel forms of carbon (diamond or fullerenes or different types of carbon nanotubes). In this work, the extension of the laser vaporization method to composite fullerene-containing carbon targets is presented. It is shown that, depending on the pressure in an experimental chamber, different products come out of the ablation plume and get deposited on the substrate. The experimental results of this work allow to suggest a mechanism of formation of different carbon forms from laser-produced carbon plasma at different experimental conditions. [ABSTRACT FROM AUTHOR]

Two different processes, which lead to formation of multishell fullerenes, are reported and discussed. The first process is 3000°C high temperature treatment of C 60 -containing carbon blacks. The second process is laser vaporization of composite carbon targets, containing C 60 and vapor-grown carbon fibers (VGCF). It has been shown that the laser vaporization technique allows increasing the yield up to 40%. Possible mechanisms of formation of the outer shells are discussed. [ABSTRACT FROM PUBLISHER]

Two different processes, which lead to formation of multishell fullerenes, are reported and discussed. The first process is 3000°C high temperature treatment of C 60 -containing carbon blacks. The second process is laser vaporization of composite carbon targets, containing C 60 and vapor-grown carbon fibers (VGCF). It has been shown that the laser vaporization technique allows increasing the yield up to 40%. Possible mechanisms of formation of the outer shells are discussed. [ABSTRACT FROM AUTHOR]

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The present study addresses the problems of catalytic synthesis of C60-based 3D polymers in the presence of carbon disulfide CS2. It is shown that CS2 lowers the pressure of fullerite 3D polymerization at room temperature. In particular, the pressure at which the 3D ultrahard fullerite C60 phase is formed decreases from 18 GPa to 7 GPa. The catalyst plays no significant role at room temperature and low pressures up to 6 GPa. When the C60 + CS2 is heated to 1200 K, the pressure of the 3D C60 polymerization is further reduced to 2-4 GPa. Based on the TEM data, we propose a 3D polymer structure based on C60 obtained by the catalytic synthesis. [ABSTRACT FROM AUTHOR]