Page 34 - Carbon Nanotubes

Catalytic production and purification of nanotubules 25

Fig. 12. Carbon nanotubules after separation from the substrate by ultra-sound treatment. Note the SiO,
grains attached to the tubules.

carbon filaments. The deposited carbon in these dependent on the reaction time; very long tubules,
filaments has a graphitic structure, i.e. the as-made even up to 60 pm, can be produced.
tubules can be assumed to be analogous to the The catalytic method provides the basis for synthe-
tubules obtained by the arc-discharge fullerene pro- sis of carbon tubules of a large variety of forms.
duction. By the use of catalysts with very finely Straight tubules, as well as bent and helically wound
dispersed metal or metal oxide particles on the sur- tubules, were observed. The latter regular helices of
face, it was possible to produce nanotubules having fullerene diameter can be of special interest from both
diameters of the same range as nanotubules obtained theoretical and practical points of view.
by the arc-discharge method. We can thus suppose
that the former tubules will possess all the properties Acknowledgements-This text presents research results of
the Belgian Programme on Inter University Poles of
predicted for the fullerene tubules. Attraction initiated by the Belgian State Prime Minister’s
The catalytic method, as was shown in this study, Office of Science Policy Programming. The scientific
has some advantages over arc-discharge tubule pro- responsibility is assumed by the authors. A. Fonseca
duction. First, the yield of nanotubules in the catalytic and D. Bernaerts acknowledge, respectively, the Rbgion
production is higher than in the arc-discharge. It is Wallonne and the National Found for Scientific Research,
for financial support. Thanks are due to Prof. G. Van
possible to optimize the method for the deposition Tendeloo and Prof. J. Van Landuyt for useful discussions
of almost all of the carbon in the form of tubular and for their continued interest in this research.
filaments. In the arc-discharge production the amount
of tubules in the soot is usually no more than 25%. REFERENCES
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