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Carbon Nanotubes (CNT)

Notes

From 08/12/2014 through 11/26/2011   

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Notes

1. Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure.  Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material. These cylindrical carbon molecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. In particular, owing to their extraordinary thermal conductivity and mechanical and electrical properties, carbon nanotubes find applications as additives to various structural materials. For instance, in (primarily carbon fiber) "baseball bats, car parts" and even "golf clubs”, where nanotubes form only a tiny portion of the material(s).

Nanotubes are members of the fullerene structural family, which also includes the spherical buckyballs, and the ends of a nanotube may be capped with a hemisphere of the buckyball structure. Their name is derived from their long, hollow structure with the walls formed by one-atom-thick sheets of carbon, called graphene. These sheets are rolled at specific and discrete ("chiral”) angles, and the combination of the rolling angle and radius decides the nanotube properties; for example, whether the individual nanotube shell is a metal or semiconductor.  Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). Individual nanotubes naturally align themselves into "ropes" held together by van der Waals forces, more specifically, pi-stacking.

Applied quantum chemistry, specifically, orbital hybridization best describes chemical bonding in nanotubes. The chemical bonding of nanotubes is composed entirely of sp2 bonds, similar to those of graphite.  These bonds, which are stronger than the sp3 bonds found in alkanes, provide nanotubules with their unique strength.

(Wikipedia, Carbon Nanotubes, 11/26/2011)

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2. Carbon nanotubes have also been shown to have unexpected interactions with electromagnetic radiation. Recently, a surprising feature has been the ignition of nanotubes in the presence of an ordinary camera flash. See Ajayan et al., "Nanotubes in a Flash--Ignition and Reconstruction," Science, 296, p. 705 (2002); Bockrath et al., "Igniting Nanotubes with a Flash," Science, 297, pp. 192-193 (2002). Nanotubes will also ignite when exposed to microwaves in air. See Imholt et al., "Nanotubes in Microwave Fields: Light Emission, Intense Heat, Out-Gassing and Reconstruction," Chem. Mater. 15, pp. 3969-3970 (2003). Methods that would exploit these interactions in an effort to produce engineered materials would be of tremendous benefit.  [Tour et al, US Patent 8,080,199 (12/20/2011)]

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3. “Carbon nanotubes, an allotrope of carbon with a cylindrical nanostructure, have attracted a considerable amount of interest recently due to their unique properties. Their use is highly attractive across many fields of technology, including electronics, optics and other fields of materials science, as well as potential uses in construction methods. Nanotubes are characterised by their extremely large length-to-diameter ratio of many thousand times to 1 and exhibit extraordinary strength and unique electrical properties, as well as high efficiency as thermal conductors.

There are various conventional methods of producing carbon nanotubes: electric arc discharge, catalytic hydrocarbon decomposition, laser ablation, high pressure carbon monoxide (HiPco), thermal chemical deposition, plasma chemical deposition and others.

Nanotubes are formed as graphite sheets (also known as graphene), in which atoms of carbon are arranged hexagonally in a sheet a single atom thick, and wrapped into a seamless cylinder. A cylinder formed from a single graphite sheet is a known as single-walled nanotubes, and typically has a diameter between about one nanometer to a few tens of nanometers (about 30 to 50 nm) and a length that may be many orders of magnitude longer. Multi-walled nanotubes may also be formed from concentric cylinders of graphite sheet, itself comprising several graphite sheets, which may be between two and about 50 walls, typically between about 2 to 10. Such multi-walled nanotubes may have a diameter between about a few (about 2 to 5 nm) nanometers to a few tens of nanometers (about 30 to 50 nm). Single-walled carbon tubes are primarily produced using an arc discharge method utilizing carbon electrodes in an environment containing a metallic catalyst, or where the anode electrode used for producing the arc discharge comprises a metallic catalyst substance. The main limitations of the arc discharge method, however is low nanotube yield, typically no more than about 25% to 30% by weight of total carbon mass, the relatively small size of the nanotubes produced (typically having lengths of up to about 50 to 1000 nanometers, difficulties associated with separating out the nanotubes in a pure form, and difficulties with varying diameter and length dimensions of the nanotubes formed by this process.”

[Predtechensky et al, US Patent 8,137,653 (3/20/2012)]

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Copyright 2012 by Roger D. Corneliussen.
No part of this transmission is to be duplicated in any manner or forwarded by electronic mail without the express written permission of Roger D. Corneliussen
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* Date of latest addition; date of first entry is 5/15/2012.