[...]... temperature and with the percentage of acetylene in the reaction mixture Even in optimal conditions not less than 50% of the carbon was deposited in the form of amorphous carbon in accordance with[ 131 As it was established by Geus et aL[l8, 191 the decrease of the rate of carbon deposition is a positive factor for the growth of fibres on metal catalysts SiO, is an inhibitor of carbon condensation as was shown... rate of acetylene was varied from 0.15 to 0.59 mol C,H, g-' h-' The amount of condensed carbon at 973 K changed as a function of hydrocarbon rate from 20 to 50 wt% relatively The optimal C,H, rate was found to be 0.34 mol g-' h-' At this rate, 40-50 wt% of carbon precipitates on the catalyst surface after 30 minutes of reaction The increase of acetylene rate leads to an increase of the -amount of amorphous... graphitization of carbon into the tubular structures on metal-supported catalysts is generally accompanied by the formation of amorphous carbon Both processes are temperature dependent The filaments grown at low temperature (773 K) are relatively free of amorphous carbon The amount of amorphous carbon increases with increasing temperature and represents about 10% of all carbon condensed on the external surface of. .. after cooling and reheating the carbon deposited sample Metal particles even found near the tips of the tubules were always covered by graphite layers It supports the model of an “extrusion” of the carbon tubules from the surface of active particles [24] 3.2.4 Injuence of hydrogen The influence of the presence of hydrogen in the reaction mixture on the formation of nanofibres has been shown in various... nanofibers during the decomposition of hydrocarbons in the presence of either supported or unsupported metals, has been widely studied over the last years[ 1-61 The main goal of these studies was to avoid the formation of "filamentous" carbon, which strongly poisons the catalyst More recently, carbon tubules of nanodiameter were found to be a byproduct of arc-discharge production of fullerenes [7] Their calculated... like that of the annual growth of trees The structure of VGCFs, especially those with hollow cores, are very similar to the structure of arc-formed carbon nanotubes (ACNTs) Both types of nanotubes, the ACNTs and the present PCNTs, appear to be essentially Russian Doll-like sets of elongated giant ful,lerenes[ll,12] Possible growth processes have 2 VAPOR-GROWN CARBON FIBERS AND PYROLYTIC CARBON NANOTUBES... STRUCTURES OF PCNTS In Fig 1l a is shown an HRTEM image of part of the end of a PCNTs The initial material consisted of a single-walled nanotube upon which bi-conical spindle-like growth can be seen at the tip Originally, this tip showed no apparent structure in the HRTEM image at the as-grown state, suggesting that it might consist largely of some form of “amorphous” carbon After a second stage of heat... separation of tubules from the substrate, their purification and opening were also investigated Key Words-Nanotubules, fullerenes, catalysis production The synthesis of the nanotubules of various diameters, length and structure as dependent on the parameters of the method is studied in detail The elimination of amorphous carbon is also investigated 1 INTRODUCTION The catalytic growth of graphitic carbon nanofibers... and interlayer distance of successive layers in multilayer carbon nanotubes are discussed in the paper by Setton Study of the structure of carbon nanotubes and their common defects is well summarized in the review by Sattler, who was able to obtain scanning tunneling microscopy (STM) images of carbon nanotube surfaces with atomic resolution A discussion of common defects found in carbon nanotubes, including... preparation Unfortunately, carbon filaments usually obtained in catalytic processes are rather thick, the thickness being related to the size of the active metal particles The graphite layers of as-made fibres contain many defects These filaments are strongly covered with amorphous carbon, which is a product of the thermal decomposition of hydrocarbons [ 131 The catalytic formation of thin nanotubes was . class="bi x0 y0 w0 h0" alt="" CARBON NANOTUBES Elsevier Journals of Related Interest Applied Superconductivity Carbon Journal of Physics and Chemistry of Solids Nanostructured Materials. research on carbon nanotubes and related materials. 'The birth of the field of carbon nanotubes is marked by the publication by Iijima of the observation of multi-walled nanotubes with. on carbon nanotubes. Carbon nanotubes have the same range of diameters as fullerenes, and are expected to show various kinds of size effects in their structures and properties. Carbon nanotubes