Process for producing single-wall carbon nanotubes uniform...

Details Process for producing single-wall carbon nanotubes uniform... Process for producing single-wall carbon nanotubes uniform...

2000-05-03

2001-12-18

Elve, M. Alexandra (Department: 1725)

Electric heating

Metal heating

By arc

C219S121760, C219S121860, C204S157410, C204S157470, C423S44500R, C423S447300

Reexamination Certificate

active

06331690

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a carbon nanotube and, more particularly, to a process for producing a carbon nanotube and a laser ablation apparatus used therein.
DESCRIPTION OF THE RELATED ART
A typical example of the process for producing carbon nanotubes is disclosed by Andreas Thess et al in “Crystalline Ropes of Metallic Carbon Nanotubes”, Science, vol. 273, pages 483 to 487, Jul. 26, 1996. Metal catalyst particle such as nickel-cobalt alloy is mixed with graphite powder at a predetermined percentage, and the mixture is pressed so as to obtain a pellet. A laser beam is radiated to the pellet. The laser beam evaporates the carbon and the nickel-cobalt alloy, and the carbon vapor is condensed in the presence of the metal catalyst. Single-wall carbon nanotubes are found in the condensation. A problem is encountered in the prior art process in that the single-wall carbon nanotubes are not constant in diameter.
SUMMARY OF THE INVENTION
It is therefore an important object of the present invention to provide a process for producing single-wall carbon nanotubes, which is uniform in diameter.
The present inventors contemplated the problem inherent in the prior art process, and noticed that the ratio between the carbon vapor and the metal catalyst vapor was varied with time due to absorption of the laser light. The graphite powder was black, and took up the laser light rather than the metal catalyst. The laser light thus absorbed raised the temperature rapidly rather than the metal catalyst, and the metal catalyst was left in the surface portion. The metal catalyst layer reflected the laser light, and the graphite powder was less sublimated. This resulted in that the purity of carbon was not uniform. For this reason, the carbon nanotubes did not become constant in diameter.
To accomplish the object, the present invention proposes to independently evaporate carbon and metal catalyst.
In accordance with one aspect of the present invention, there is provided a process for producing carbon nanotubes comprising the steps of preparing a source of carbon vapor and a source of catalyst vapor physically separated from each other, radiating laser beams to the source of carbon vapor and the source of catalyst vapor so as to generate a carbon vapor/cluster and a catalyst vapor/cluster, and allowing the carbon vapor/cluster to be mixed with the catalyst vapor/cluster so as to form the carbon vapor/cluster into carbon nanotubes.
In accordance with another aspect of the present invention, there is provided a laser ablation system for producing carbon nanotubes comprising a reactor having an air-tight chamber where a source of carbon vapor and a source of catalyst vapor are separately provided, a laser beam generator provided for the reactor and radiating laser beams to the source of carbon vapor and the source of catalyst vapor for producing a carbon vapor/cluster and a catalyst vapor/cluster from the source of carbon vapor and the source of catalyst vapor, respectively, an evacuating sub-system connected to the reactor for evacuating a gaseous mixture from the air-tight chamber, a carrier gas supply sub-system connected to the reactor supplying carrier gas to the air-tight chamber for forming a carrier gas flow in the air-tight chamber, and a collector provided in the carrier gas flow and capturing carbon nanotubes formed from the carbon vapor/cluster in the presence of the catalyst vapor/cluster and carried on the carrier gas flow.


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