Chemistry Reference
In-Depth Information
heptagon pair by reorganization of the bonds. Having small structure in
carbon nanotubes lead to dependency of their tensile strength to the weak-
est segment.
Also, electrical properties of CNTs can be affected by crystallographic
defects. A common result is dropped conductivity through the defective
section of the tube. A defect in conductive nanotubes can cause the adja-
cent section to become semiconducting, and particular monatomic vacan-
cies induce magnetic properties.
Crystallographic defects intensively affect the tube's thermal proper-
ties. Such defects cause to phonon scattering, which in turn enhance the
relaxation rate of the phonons. This decreases the mean free path and de-
clines the thermal conductivity of nanotube structures. Phonon transport
simulations show that alternative defects such as nitrogen or boron will
mainly cause to scattering of high frequency optical phonons. However,
larger scale defects such as Stone Wales defects lead to phonon scattering
over a wide range of frequencies, causing to a greater diminution in ther-
mal conductivity.
9.3.3 METHODS OF CNT PRODUCTION
9.3.3.1
ARC DISCHARGE METHOD
Nanotubes were perceived in 1991 in the carbon soot of graphite elec-
trodes during an arc discharge, by using a current of 100amps that was
intended to create fullerenes. However, for the first time, macroscopic
production of carbon nanotubes was done in 1992 by the similar method
of 1991. During this process, the carbon included the negative electrode
sublimates due to the high discharge temperatures. As the nanotubes were
initially discovered using this technique, it has been the most widely used
method for synthesis of CNTs. The revenue for this method is up to 30%
by weight and it produces both single and multi walled nanotubes with
lengths of up to 50 micrometers with few structural defects.
9.3.3.2
LASER ABLATION METHOD
Laser ablation method was developed by Dr. Richard Smalley and co-
workers at Rice University. In that time, they were blasting metals with a
