Carbon Nanotube Reinforced Composites: Metal and Ceramic ...

Table 1.3 Patent processes for the purification of carbon nanotubes.
Patent
Number
and Year
US 7135158
(2006)
US 7029646
(2006)
US 7115864
(2006)
US 6841003
(2005)
Type of
Nanotubes
Purification
Process Inventor Assignee
SWNTs Multiple-step Goto, H., Furuta, T.,
Fujiwara, Y., Ohashi, T.
1.4 Purification of Carbon Nanotubesj21
Honda Giken Kogyo
Kabushiki Kaisha
(Japan)
Rice University
(USA)
Rice University
(USA)
SWNTs Fluorination Margrave, J.L., Gu, Z.,
Hauge, R.H., Smalley, R.E.
SWNTs Liquid-phase Colbert, D.T., Dai, H.,
oxidation Hafner, J.H., Rinzler, A.G.,
Smalley, R.E., Liu, J.,
Smith, K.A., Guo, T.,
Nikolaev, P., Thess, A.
SWNTs Plasma Kang, S.G., Bae, C. cDream Display
etching
Corporation (USA)
Electron microscopy coupled with EDS gives rise to qualitative information for
purified nanotubes. In general, TEM observation is preferred because it offers
high-resolution images. However, sample preparation for TEM examination is
tediousandtimeconsuming.Moreover,electronmicroscopicobservationsaremainly
focused on localized regions of the samples, thus the analyzed sampling volumes
are relatively small.
Raman spectroscopy is a qualitative tool for determining vibrational frequency of
molecular allotropes of carbon. All carbonaceous moieties such as fullerenes, CNTs,
diamond, and amorphous carbon are Raman active. The position, width and relative
intensity of Raman peaks are modified according to the sp 3 and sp 2 configurations of
carbon [122–124]. Raman spectra of the SWNTs are well characterized by the low
frequency radial breathing mode (RBM) at 150–200 cm 1 , with frequency depending
on the tube diameter and the tangential mode at 1400–1700 cm 1 . From the spectral
analysis, a sharp G peak at 1590 cm 1 is related to the (C C) stretching mode, and a
band at 1350 cm 1 is associated with disorder-induced band (D band). Moreover,
a second order mode at 2450–2650 cm 1 is assigned to the first overtone of D mode
and commonly referred to as G mode. The D-peak is forbidden in perfect graphite
and only becomes active in the presence of disorder [122]. In general, the full-width at
half-maximum (FWHM) intensity of the D-peak for various carbon impurities is
generally much broader than that of the nanotubes. Thus, the purity level of SWNTs
can be simply obtained by examining the linewidth of the D-peak [120, 123].
Alternatively, the D/G intensity ratio can be used as an indicator for the purity levels
of SWNTs. In the presence of defects, a slight increase in the D-band intensity relative
to the intensity of G-band is observed [125].
XRD is a powerful tool for identifying the crystal structure of metal catalysts and
carbonaceous moieties. The lattice constant of these species can be determined