Single-walled

Table 5 Comparison of wire IQI sensitivities obtained with Selenium and iridium for different pipe diameters and thicknesses (DW=double wall, SW=single wall)[2].

The manipulator consist of two parts, an outer part and an inner part. The pipe is x-rayed through single wall with the x-ray camera placed inside the pipe and the x-ray source placed outside the pipe (see figure 2). In this figure the two welds to be tested can be seen. 

Flafner J FI, Bronikowski M J, Azamian B R, Nikolaev P, Rinzier A G, Colbert A T, Smith K A and Smalley R E 1998 Catalytic growth of single-wall carbon nanotubes from metal particles Chem. Phys. Lett. 296 195... 

The field of fullerene chemistry expanded in an unexpected direction in 1991 when Sumio lijima of the NEC Fundamental Research Laboratories in Japan discovered fibrous carbon clusters in one of his fullerene preparations This led within a short time to substances of the type portrayed in Figure 11 7 called single-walled nanotubes The best way to think about this material IS as a stretched fullerene Take a molecule of Ceo cut it in half and place a cylindrical tube of fused six membered carbon rings between the two halves... 

Single Wall. Single-wall tanks are usually cylindrical and may have either vertical or horizontal orientation. Horizontal tanks are generally supported by two saddle supports and use more space than vertical tanks. Horizontal tanks have an advantage in that leaks can be seen as they occur. 

Fig. 8. A, Structure of a single wall nanotube B, schematic illustration of arm-chair, zigzag and spiral forms of single wall nanotubes the arrows denote the tubule axis.

The diameter distribution of single-wall carbon nanotubes is of great interest for both theoretical and experimental reasons, since theoretical studies indicate that the physical properties of carbon nanotubes are strongly dependent on the nanotube diameter. Early results for the diameter distribution of Fe-catalyzed single-wall nanotubes (Fig. 15) show a diameter range between 0.7 nm and 1.6 nm, with the largest peak in the distribution at 1.05 nm, and with a smaller peak at 0.85 nm [154]. The smallest reported diameter for a single-wall carbon nanotube is 0.7 nm [154], the same as the diameter of the Ceo molecule (0.71 nm) [162]. 

Fig. 15. Histogram of the single-wall nanotube diameter distribution for Fe-catalyzed nanotubes [154], A relatively small range of diameters are found, the smallest diameter corresponding to that for the fullerene Ceo.

Whereas multi-wall carbon nanotubes require no catalyst for their growth, either by the laser vaporization or carbon arc methods, catalyst species are necessary for the growth of the single-wall nanotubes [156], while two different catalyst species seem to be needed to efficiently synthesize arrays of single wall carbon nanotubes by either the laser vaporization or arc methods. The detailed mechanisms responsible for the growth of carbon nanotubes are not yet well understood. Variations in the most probable diameter and the width of the diameter distribution is sensitively controlled by the composition of the catalyst, the growth temperature and other growth conditions. 

Fig. 17. Schematic models for a single-wall carbon nanotubes with the nanotube axis normal to (a) the 6 = 30° direction (an armchair (n, n) nanotube), (b) the 0 = 0°...

Because of the speeial atomie arrangement of the earbon atoms in a carbon nanotube, substitutional impurities are inhibited by the small size of the carbon atoms. Furthermore, the serew axis disloeation, the most eommon defeet found in bulk graphite, is inhibited by the monolayer strueture of the Cfj() nanotube. For these reasons, we expeet relatively few substitutional or struetural impurities in single-wall earbon nanotubes. Multi-wall carbon nanotubes frequently show bamboo-like defects associated with the termination of inner shells, and pentagon-heptagon (5 - 7) defects are also found frequently [7]. 

Structurally, carbon nanotubes of small diameter are examples of a onedimensional periodic structure along the nanotube axis. In single wall carbon nanotubes, confinement of the stnreture in the radial direction is provided by the monolayer thickness of the nanotube in the radial direction. Circumferentially, the periodic boundary condition applies to the enlarged unit cell that is formed in real space. The application of this periodic boundary condition to the graphene electronic states leads to the prediction of a remarkable electronic structure for carbon nanotubes of small diameter. We first present... 

Fig. 19. The energy gap FJ, for a general chiral single-wall carbon nanotube as a function of 100 kidt, where dt is the nanotube diameter in A [179].

Early transport measurements on individual multi-wall nanotubes [187] were carried out on nanotubes with too large an outer diameter to be sensitive to ID quantum effects. Furthermore, contributions from the inner constituent shells which may not make electrical contact with the current source complicate the interpretation of the transport results, and in some cases the measurements were not made at low enough temperatures to be sensitive to 1D effects. Early transport measurements on multiple ropes (arrays) of single-wall armchair carbon nanotubes [188], addressed general issues such as the temperature dependence of the resistivity of nanotube bundles, each containing many single-wall nanotubes with a distribution of diameters d/ and chiral angles 6. Their results confirmed the theoretical prediction that many of the individual nanotubes are metallic. 

Fig. 23. Experimental room temperature Raman spectrum from a sample consisting primarily of bundles or ropes of single-wall nanotubes with diameters near that of the (10,10) nanotube. The excitation laser wavelength is 514.5 nm. The inset shows the lineshape analysis of the vibrational modes near 1580 cm . SWNT refers to singlewall carbon nanotubes [195].

Fig. 24. The armchair index n vs mode frequency for the Raman-active modes of single-wall armchair (n,n) carbon nanotubes [195]. From Eq. (2), the nanotube diameter is given by d = Ttac-cnj-K.

Fig. 25. Room temperature Raman spectra for purified single-wall carbon nanotubes excited at five different laser wavelengths, showing evidence for the resonant enhancement effect. As a consequence of the ID density of states, specific nanotubes (n, m) are resonant at each laser frequency [195].

Many of the carbon nanotube applications presently under consideration relate to multi-wall carbon nanotubes, partly because of their greater availability, and because the applications do not explicitly depend on the ID quantum effects associated with the small diameter single-wall carbon nanotubes. 

Interest has rapidly focused on the single-walled, capped tubes, as shown in Figure 11.7. They can currently be grown up to 100 pm in length, i.e., about 100,000 times their diameter. As the figure shows, there are two ways of folding a graphene sheet in such a way that the resultant tube can be seamlessly closed with a Cfto hemisphere... one way uses a cylinder axis parallel to some of the C—C bonds in... 

Figure 11.7. Two types of single-walled carbon nanotubes.

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