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11/24/10

Carbon nanotubes in brief

Carbon nanotubes can be considered as graphitic sheets rolled into open cylindrical form with diameters in the range of few nanometers and lengths up to several micrometers. Each nanotube is a single molecule made up of a hexagonal network of covalently bonded carbon atoms.

Types
Carbon nanotubes are of both single-walled and multi-walled. A single-walled carbon nanotube (SWNT) has a single grapheme cylinder, while a multi-walled carbon nanotube (MWNT) has several concentric grapheme cylinders.
Properties
Nanotubes have unusual properties due to strong covalent bonding, nanometer size and unique one-dimensional structure. The extraordinary properties include very high tensile strength, high resilience, electronic properties ranging from metallic to semi-conducting, the ability to sustain high current densities and high thermal conductivity. This makes carbon nanotubes a suitable material to be used as fillers in super-strong composite materials, as wires and components in nano-electronic devices, as tips of scanning probe microscopes and in flat panel displays and gas sensors.
Basis of properties
In a single carbon nanotube, every atom is on two surfaces - the inside and the outside, and a single gram of nanotubes has over 2400 m2 of surface area. The nature of the carbon bonding gives the tubes their great tensile strength and electrical and thermal conductivity. The carbon nanotubes stiffness and toughness derives from their molecular perfection. In most materials the actual observed stiffness and toughness are degraded very substantially by the occurrence of defects in their structure. For example, high strength steel typically fails at about 1% of its theoretical breaking strength. Carbon nanotubes, however, achieve values very close to their theoretical limits because of their perfection of structure - there are no structural defects where mechanical failures can begin. It is, however, the tubular geometry of carbon nanotubes that gives them their most exotic properties.
An example of CNT typical properties:
Purity of CNTs90%, Content of SWNTs, 60%, Diameter 2 nm, Length 20 nm, Amorphous carbon 5%, Ash (catalyst residue) 3%, surface area 450 m2/g, Thermal conductivity 4000 W/m•k.
Preparation
MWNTs were earlier prepared by the arc-discharge of graphite electrodes, but now, MWNTs are prepared in large quantities by the chemical vapor deposition process. High yields of SWNTs can be obtained by the following methods.
1.Arc-discharge of Ni-Y catalyzed graphite electrodes,
2.Laser ablation of Ni-Co catalyzed graphite targets and
3.Vapor phase paralysis of CO and Fe(CO)5 (HiPCO process).
Purity
Carbon nanotubes are always get contaminated with impurities like amorphous carbon, residual metal catalyst and graphitic nanoparticles during manufacture and handling and hence purification and chemical processing are vital steps in before any application of Carbon nanotubes.
Applications
• Electronical nanocomponents (diodes, transistors, nano-wires, etc.)
• Field emission
• Multi-functional composites(EMI shielding, thermal conducting, strengthen, conducting, etc.)
• Hydrogen storage
• Rechargeable lithium batteries
• Atomic force microscope (AFM) tips
• Electrode material of supercapacitors
• Biosensors
Cost (approx.)
SWNT
SWNTs prepared by the electric arc method with purity 40-60%, price $50/gram,
Processed AP-SWNTs containing lower carbonaceous and catalyst related impurities with purity 70-90%, price $ 400/gram,
Purified SWNTs with high carboxylic acid content 80-90%, price $ 400/gram,
Water soluble SWNTs functionalized with poly m-aminobenzene sulfonic acid (PABS) price $ 1500/gram
MWNT
Coiled multi-walled carbon nanotubes with purity: > 60%, Outside diameter: 100-200 nm, Length: 1-10 um,SSA: > 50 m2/g, price $70/g
Multi-walled nanotubes Purity: 95+%, Amorphous carbon: <3%,>
Multi-wall nanotubes purity 99+%, outside dia <>
Suppliers
There are a number of manufacturers and suppliers of carbon nanotubes and it is difficult to list them all. In general North American manufacturers focus more on single wall Carbon nanotubes. In Asia and Europe, Japan tops the list and China stands second in the production of multi wall Carbon nanotubes. Showa Denko, Mitsui and Hodogaya Chemical are among the largest suppliers. Many of the nanotubes marketed by the suppliers are incorporated into transparent conductive films for the display and touch panel industries. Nanotubes are sold to select customers as powders and in suspensions in liquids, also called inks.
Cheap production, purification and separation of conducting and semiconducting nanotubes of selective and uniform size with specific diameter, length and electrical properties is yet to be completely achieved in commercial scale.
Safety
Safe-handling and environmentally sound handling of carbon nanotube by academic, governmental and industry organizations is very important. Due to difficulty in safe-handling requirements these materials, manufacturers do not sell nanotubes directly to the public and the consumer products containing nanotubes have minimal risk of exposure because the nanotubes are bound in polymeric solid or film, isolated from the consumer and environment. The chemical industries adopt well-established procedures for protecting workers who are handling nanomaterials. Always waste materials resulting from the manufacture of nanotubes are disposed of in accordance with regulations.

2 Responses to “Carbon nanotubes in brief”

Reinstenanoventures said...
May 17, 2011 at 11:58 PM

Your article is very informatiove and useful abour carbon nanotubes.
Large numbers of nanotechnology companies are offering these prodcuts. we are also selling carbon nanotubes, multiwallled carbon nanotubes, singlewalled carbon nanotubes etc

http://www.reinste.com


preeti said...
December 10, 2012 at 4:20 AM

very good post. carbon nanotubes have lots of usage, it is used in various industries. Nanoshel provide various nano products.


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