Multiwalled production methods

Abstract. It has been revealed that carbonic nanomaterials (fullerene, single- and multiwall nanotubes, nanofibers) display high activity at low temperatures (77K) in reactions of chain halogenation (F2, Cl2) with kinetic chain length up to 104 -105. The ESR spectra of active free- radical intermediates were recorded. The presence of vibration bands of C-Cl bonds in products has been indicated by IR method. 

Abstract. Nanocarbon materials and method of their production, developed by TMSpetsmash Ltd. (Kyiv, Ukraine), are reviewed. Multiwall carbon nanotubes with surface area 200-500 m2/g are produced in industrial scale with use of CVD method. Ethylene is used as a source of carbon and Fe-Mo-Al- mixed oxides as catalysts. Fumed silica is used as a pseudo-liquid diluent in order to decrease aggregation of nanotubes and bulk density of the products. Porous carbon nanofibers with surface area near 300-500 m2/g are produced from acetylene with use of (Fe, Co, Sn)/C/Al203-Si02 catalysts prepared mechanochemically. High surface area microporous nanocarbon materials were prepared by activation of carbon nanofibers. Effective surface area of these nanomaterials reaches 4000-6000 m2/g (by argon desorption method). Such materials are prospective for electrochemical applications. Methods of catalysts synthesis for CVD of nanocarbon materials and mechanisms of catalytic CVD are discussed. 

For large scale production of carbon nanotubes and nanofibers chemical vapor deposition (CVD) method is most effective. Acetylene, ethylene, propylene, methane, natural gas (consisting predominantly of propane), carbon monoxide were used as a source of carbon [ 1 -8] (in view of large number of publications on CNT synthesis these references are selected arbitrary). Ethylene and possibly propylene are most convenient carbon sources for mass synthesis of high quality multiwall CNT (MWNT). 

There are several reports on the preparation of SiC nanowires in the literature but fewer on the preparation of SisKi nanowires.38-39 The methods employed for the synthesis of SiC nanowires have been varied. Since both SiC and Si3N, are products of the carbothermal reduction of SI02, it should be possible to establish conditions wherein one set of specific conditions favor one over the other. We have been able to prepare SijN nanowires,40 by reacting multiwalled carbon nanotubes produced by ferrocene pyrolysis with ammonia and silica gel at 1360... 

The most common method for the production of carbon nanotubes is hydrocarbon-based chemical vapor deposition (CVD) [97] and adaptations of the CVD process [98, 99], where the nanotubes are formed by the dissolution of elemental carbon into metal nanoclusters followed by precipitation into nanotubes [100]. The CVD method is used to produce multiwalled carbon nanotubes (MWCNTs) [101] and double-walled carbon nanotubes (DWCNTs) [102] as well as SWCNTs [103], The biomedical applications of CNTs have been made possible through surface functionalization of CNTs, which has led to drug and vaccine delivery applications [104,105],... 

Figure 21 Carbon nanotube production, (a) carbon arc method for multi-walled carbon nanotubes (b) the carbon arc method with metal impregnated rods for single wall nanotube production (c) laser irradiation of metal impregnated graphite for single wall nanotube production (d) hydrocarbon decomposition in presence of a catalyst for multiwall nanotube production (e) fullerene oven to produce graphitic nanoparticles, including short tubes, by heating fullerene soot to high temperatures in vacuum.

The method developed by Kratschmer and co-workers for the preparation of macroscopic amounts of fuUerenes can also be adapted to produce nanotubes. It has first been employed to make multiwalled nanotubes (Section 3.3.2.1), but by now SWNT production with this method succeeded as weU. In doing so one must see to it that the growth phase of carbon structures is sufficiently long to prevent the cage closure of fuUerenes and have cylindrical species growing instead. 

The reaction with azomethine yUdes is a typical [3+2]-cycloaddition. It leads to the products shown in Figure 3.74b. The reaction is particularly suitable to couple biologically active moieties to carbon nanotubes, which is of great relevance, for example, for the preparation of nanotube-peptide composites. The reaction is normally performed on a nano tube suspension in DMF that is treated with an N-substituted glycine and paraformaldehyde or with an aldehyde carrying a further residue to be coupled. The azomethine ylide is then formed in situ it constitutes the actual reagent. The method is appUcable to single- and multiwalled nanotubes. 

Carbon nanotubes are one of the most important classes of new carbon materials. Distinctions are made between single- and multiwalled as well as between zig-zag, armchair, and chiral nanotubes. The structure is characterized by the descriptors n and m. These structural parameters allow for a prediction of the electric conductivity. Only armchair nano tubes n,n) and such species with m-n = iq are electric conductors. Any other nanotube is semiconducting. These statements have been established from symmetry considerations and from determining the band structure by way of the zone-folding method. There are different approaches to the production of single- and multiwalled nanotubes. Important methods of preparation are ... 

For IF-M0S2 and nanotubes the steps are similar, and a schematic representation of the experimental setup for the synthesis and growth mechanism has been proposed [62]. The nanotubes produced are multiwalled Figure 1 provides a transmission electron micrograph that shows the structural features of these products. Related methods have been used to prepare several layered metal dichalco-... 

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