Bulk Synthesis of Nanotube-Like Carbon Material
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ABSTRACT Nanoporous carbons have been synthesised through a selective etching reaction, performed by halogenisation of metal carbides. The structures obtained can be controlled by choice of starting materials and reaction parameters, and here one example, chlorination of aluminium carbide at 700 'C, is given. The produced material is nanotube-like with agglomerates of short and wide interconnected tubular structures, which are here described as nanobarrels. The synthesis process gives a pure product with high-yield, and may be scaled up to produce bulk amounts.
INTRODUCTION Nanoporous carbons have been used extensively for their strong adsorptive properties and high surface areas in a number of applications ranging from adsorbents and electrodes to inorganic membranes. The current literature contains numerous references on synthesis and properties of "active" or microporous (nanoporous) carbons made from different precursors and different processes. However, little is found on carbons made from halogenisation of metal carbides at high temperatures, although it is known that chlorination will produce nanoporous amorphous carbons, and their possible use as adsorbents was suggested early [1]. In a subsequent publication it was pointed out that the pore volume could be controlled by the choice of metal carbide, for instance silicon carbide or carbides from the group titanium or chromium [2]. The carbon materials from refs. [1] and [2] were produced by chlorination of a metal carbide at elevated temperature. The general reaction was
MC,(s) + 2x- C12 (g)
-> x C(s) + MC14x(g)
and was performed at a temperature at which the formed metal chloride was gaseous and could be transported away from the reaction site. It has also more recently been shown that chlorine gas, even very diluted in argon, actively can transform the surface of silicon carbide to carbon films, which has an application in the forming of tribological films on ceramics [3,4]. The films were examined with a variety of techniques, and the nanoporous carbon films, with surface areas exceeding 1000 m2gl', were characterised by Raman spectroscopy and electron diffraction data as nanocrystalline graphite.
87 Mat. Res. Soc. Symp. Proc. Vol. 593 © 2000 Materials Research Society
The structures of amorphous carbon powders, synthesised by chlorination of metal carbides, have been studied [5], and indications showed that there was a close relationship between the structure of the initial carbide and the formed nanoporous carbon. In carbon materials produced from SiC and TiC, very small amounts of nanotube-like structures were found, and it was assumed that the amount of these structural entities could be increased by modulating the synthesis parameters, and by a choice of starting material having a crystal structure that could initiate tube formation. The result of one of these studies is reported here, which represents a route for producing a nanotube-like carbon consisting of agglomerates of interconnected short and wide multiple wall tubes, here called nanob
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