Biomedical Engineering Reference
In-Depth Information
(a)
(b)
(c)
FIGURE 4.8
Models of SWNTs at molecular level with different chiralities. (a) Armchair chirality; (b) chiral
conformation; and (c) zigzag arrangement.
4.3.1 Preparation of Carbon Nanotubes
Fullerenes were discovered in 1970 by Richard E. Smalley at Rice University
in Houston, Texas. With this discovery, he was granted the 1996 Nobel prize
in chemistry. After fullerenes, nanocages (also termed graphitic onions)
were presented in 1980, followed by MWNTs in 1991, and lastly, SWNTs were
discovered.
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At present, there are several methods to produce MWNTs and SWNTs.
The first described was the arc-discharge method. This method is based on
the self-assembly (growing) of CNTs in an inert gas atmosphere between
carbon, or catalyst-containing carbon, electrodes.
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Highly crystalline
MWNTs with diameters ranging from 2 to 30 nm, and a length up to 30 μm
can be grown on the cathode, at a pressure of 500 torr.
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SWNTs can be
synthesized by arcing graphite electrodes containing a metal catalyst in a
methane-argon or helium atmosphere.
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As metal catalysts, Fe, Co-Ni, Gd,
Co-Ru, Co, Ni-Y, Rh-Pt, and Co-Ni-Fe-Ce are optional choices.
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Later, other CNT manufacturing procedures were discovered, such as
laser vaporization, chemical vapor deposition (CVD), and pyrolytic methods.
