What is Carbon Nanotubes

8/3/2019 What is Carbon Nanotubes

1/6

1.0 Carbon Nanotubes (CNTs)

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,[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 ofmaterials science and technology. In particular, owing to their extraordinary thermal

conductivity and mechanical and electrical properties, carbon nanotubes may find

applications as additives to various structural materials. There are two main types of

nanotubes: single-walled nanotubes and multi-walled nanotubes.

1.1 Allotropes of Carbon
http://en.wikipedia.org/wiki/Allotropes_of_carbonhttp://c/Users/user/Desktop/carbon%20nanotube/Carbon_nanotube.htm%23cite_note-Longest-0http://c/Users/user/Desktop/carbon%20nanotube/Carbon_nanotube.htm%23cite_note-Longest-0http://c/Users/user/Desktop/carbon%20nanotube/Carbon_nanotube.htm%23cite_note-Longest-0http://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Nanotechnologyhttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Materials_sciencehttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Single-walled_nanotubeshttp://en.wikipedia.org/wiki/MWNThttp://en.wikipedia.org/wiki/MWNThttp://en.wikipedia.org/wiki/Single-walled_nanotubeshttp://en.wikipedia.org/wiki/Electricityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Thermal_conductivityhttp://en.wikipedia.org/wiki/Materials_sciencehttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Electronicshttp://en.wikipedia.org/wiki/Nanotechnologyhttp://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Carbonhttp://c/Users/user/Desktop/carbon%20nanotube/Carbon_nanotube.htm%23cite_note-Longest-0http://en.wikipedia.org/wiki/Allotropes_of_carbon


2/6

1.2 Single-Walled Nanotubes

Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometer, with a tube

length that can be many millions of times longer.

Figure 1.2: Single-walled nanotubes (SWNT)

1.3 Multi-Walled Nanotubes

Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric tubes) of

graphite. There are two models that can be used to describe the structures of multi-walled

nanotubes.

Figure 1.3: Multi-walled nanotubes (MWNT)
http://en.wikipedia.org/wiki/Single-walled_nanotubeshttp://en.wikipedia.org/wiki/Single-walled_nanotubes


3/6

2.0 Techniques:

Techniques have been developed to produce nanotubes:

1. Arc discharge2. Laser ablation3. High pressure carbon monoxide (HiPco)4. Chemical Vapor Deposition (CVD)

2.1 Arc Discharge

The carbon arc discharge method, initially used for producing C60 fullerenes, is the

most common and perhaps easiest way to produce Carbon Nanotubes , as it is rather

simple. However, it is a technique that produces a complex mixture of components,

and requires further purification to separate the Carbon Nanotubes from the soot and

the residual catalytic metals present in the crude product. This method creates Carbon

Nanotubes through arc-vaporization of two carbon rods placed end to end, separated

by approximately 1mm, in an enclosure that is usually filled with inert gas at low

pressure. Recent investigations have shown that it is also possible to create Carbon

Nanotubes with the arc method in liquid nitrogen. A direct current of 50 to 100A,

driven by a potential difference of approximately 20 V, creates a high temperature

discharge between the two electrodes. The discharge vaporizes the surface of one of

the carbon electrodes, and forms a small rod-shaped deposit on the other electrode.

Producing Carbon Nanotubes in high yield depends on the uniformity of the plasma

arc, and the temperature of the deposit forming on the carbon electrode.
http://en.wikipedia.org/wiki/Electric_archttp://en.wikipedia.org/wiki/Laser_ablationhttp://en.wikipedia.org/w/index.php?title=HiPco&action=edit&redlink=1http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://en.wikipedia.org/w/index.php?title=HiPco&action=edit&redlink=1http://en.wikipedia.org/wiki/Laser_ablationhttp://en.wikipedia.org/wiki/Electric_arc


4/6

2.2 Laser Ablation

Laser ablation is the process of removing material from a solid (or occasionally

liquid) surface by irradiating it with a laser beam. At low laser flux, the material is

heated by the absorbed laser energy and evaporates or sublimates. At high laser flux,

the material is typically converted to a plasma. Usually, laser ablation refers to

removing material with a pulsed laser, but it is possible to ablate material with a

continuous wave laser beam if the laser intensity is high enough.

Samples were prepared by laser vaporization of graphite rods with a 50:50 catalyst

mixture of Cobalt and Nickel at 1200C in flowing argon, followed by heat treatment

in a vacuum at 1000C to remove the C60 and other fullerenes. The initial laser

vaporization pulse was followed by a second pulse, to vaporize the target more

uniformly. The use of two successive laser pulses minimizes the amount of carbon

deposited as soot. The second laser pulse breaks up the larger particles ablated by the

first one, and feeds them into the growing nanotube structure. The material produced

by this method appears as a mat of "ropes", 10-20nm in diameter and up to 100m or

more in length. Each rope is found to consist primarily of a bundle of single walled

nanotubes, aligned along a common axis. By varying the growth temperature, the

catalyst composition, and other process parameters, the average nanotube diameter

and size distribution can be varied.
http://en.wikipedia.org/wiki/Laserhttp://en.wikipedia.org/wiki/Fluxhttp://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Sublimation_%28chemistry%29http://en.wikipedia.org/wiki/Plasma_%28physics%29http://en.wikipedia.org/wiki/Continuous_wavehttp://en.wikipedia.org/wiki/Continuous_wavehttp://en.wikipedia.org/wiki/Plasma_%28physics%29http://en.wikipedia.org/wiki/Sublimation_%28chemistry%29http://en.wikipedia.org/wiki/Evaporationhttp://en.wikipedia.org/wiki/Fluxhttp://en.wikipedia.org/wiki/Laser


5/6

2.3 High Pressure Carbon Monoxide (HiPco)

The process involves rapidly mixing a gaseous catalyst precursor (such as iron

carbonyl) with a flow of carbon monoxide gas in a chamber at high pressure and high

temperature. The catalyst precursor decomposes, and nanometer-sized metal particles

form from the decomposition products. These tiny metal particles serve as a catalyst.

On the catalyst surface, carbon monoxide molecules react to form carbon dioxide and

carbon atoms, which bond together to form carbon nanotubes. This process

selectively produces 100% single walled carbon nanotubes (SWNTs). These carbon

nanotubes can be used in electronics, biomedical applications and fuel cell electrodes.

2.4 Chemical vapor deposition (CVD).

Chemical vapor deposition of hydrocarbons over a metal catalyst is a classical method

that has been used to produce various carbon materials such as carbon fibers and

filaments for over twenty years. Large amounts ofCarbon Nanotubes can be formed

by catalytic CVD of acetylene over Cobalt and iron catalysts supported on silica or

zeolite. Fullerenes and bundles of single walled nanotubes were also found among the

multi walled nanotubes produced on the carbon/zeolite catalyst.

The production of single walled nanotubes, as well as double-walled Nanotubes, on

molybdenum and molybdenum-iron alloy catalysts has also been demonstrated. CVD

of carbon within the pores of a thin alumina template with or without a Nickel catalyst

has been achieved. Ethylene was used with reaction temperatures of 545C for

Nickel-catalyzed CVD, and 900C for an uncatalyzed process. The resultant carbon

nanostructures have open ends, with no caps. Methane has also been used as a carbon
http://en.wikipedia.org/wiki/Chemical_vapor_depositionhttp://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://www.azonano.com/ads/abmc.aspx?b=247http://en.wikipedia.org/wiki/Chemical_vapor_deposition


6/6

source. In particular it has been used to obtain nanotube chips containing isolated

single walled nanotubes at controlled locations. High yields of single walled

nanotubes have been obtained by catalytic decomposition of an H2/CH4 mixture over

well-dispersed metal particles such as Cobalt, Nickel, and Iron on magnesium oxide at

1000C. It has been reported that the synthesis of composite powders containing well-

dispersed CNTs can be achieved by selective reduction in an H2/CH4 atmosphere of

oxide solid solutions between a non-reducible oxide such as Al2O3 or MgAl2O4 and

one or more transition metal oxides. The reduction produces very small transition

metal particles at a temperature of usually >800C. The decomposition of CH4 over

the freshly formed nanoparticles prevents their further growth, and thus results in a

very high proportion of single walled nanotubes and fewer multi walled nanotubes.

3.0 References

1. Nanotechnology: Basic Science and Emerging Technologies, M. Wilson etal, (2002)

2. Carbon Nanotubes, Wikipedia (2011)3. Processing-structure-multi-functional property relationship in carbon

nanotube/epoxy composites, Erik T. Thostenson, Tsu-Wei Chou (2006)

Documents

What is Carbon Nanotubes