16-03-2010, 03:21 PM
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CARBON NANO-TUBES
PRESENTED BY
DEBKUMAR SAHA
M.RAMPRAKASH
CARBON NANO-TUBES
These nanoscopic structures are made of carbon atoms.
The carbon nano-tubes can be thought of as graphene planes 'rolled up' in a cylinder which are typically closed at their ends by semi-fullerene-like structures.
Depending upon the manner the graphene planes are cut before rolling , different types of carbon nano-tubes are obtained.
Based on the geometrical structures , carbon nano-tubes are classified into the following:
Armchair,
Zig-zag and
Chiral (helical) nano-tubes.
Depending upon the size of graphene area folded onto a cylinder , nano-tubes of different radii are obtained.
These tubes are extremely long and possess different symmetry.
STRUCTURE OF CNT
Nanotubes are formed by rolling up a graphene sheet into a cylinder and
capping each end with half of a fullerene molecule
A CNT is characterized by its Chiral Vector: Ch = n â1 + m â2,
Chiral Angle with respect to the zigzag axis.
The diameter of the nano-tubes depends on the values of n and m.
This helps to identify whether the carbon atoms are arranged in zig-zag , armchair or helical shape.
PROPERTIES OF CNT
Excellent field emitter :- higher aspect ratio and a smaller tip radius of curvature wich are ideal for field emission.
Very high current carrying capacity , electrical conductivity six orders higher than copper.
Thermal conductivity ~3000 W/mK in axial direction with small values in the radial direction
High mechanical and thermal stability
Carbon nano-tubes are one of the strongest materials both in terms of tensile strength and elastic modulus. and most flexible molecular material because of C-C covalent bonding and seamless hexagonal network architecture
These tubes have very high tensile strength ,multi-walled tubes have a tensile strength as high as 63GPa.
PROCESSING TECHNIQUES
PROCESSING TECHNIQUES
Laser Ablation Method
A laser is used to vaporize a graphite target in an oven at 12000C.
Then helium or argon gas is filled to keep the pressure in the oven at 500 Torr.
The graphite target gets vaporized to form small carbon molecules and atoms which condense to form single walled nano-tubes held together by Van der Waals forces.
MWNT would be synthesized in the case of a pure graphite.
Uniform SWNT could be synthesized if a graphite of a mixture of Co, Ni, Fe, Y are used instead of a pure graphite.
Laser vaporization are higher in yield than arc-discharge and can synthesize large and aligned high quality SWNTs.
By far the most costly, because expensive lasers required.
PROCESSING TECHNIQUES
Thermal Chemical Vapor Deposition
Fe, Ni, Co, or alloy of the tree catalytic metals is initially deposited on a substrate.
To initiate the growth of nano-tubes, two gases are bled into the reactor: a process gas (such as ammonia, nitrogen, hydrogen, etc.) and a carbon-containing gas (such as acetylene, ethylene, ethanol, etc.).
The substrate is heated to approximately 700°C.
Nano-tubes grow at the sites of the metal catalyst; the carbon-containing gas is broken apart at the surface of the catalyst particle, and the carbon is transported to the edges of the particle, where it forms the nano-tubes.
Nano-structures provide interesting perspectives of applications because of their unique properties.
Carbon Nano-tubes possess many unique and remarkable properties (chemical, physical, and mechanical), which make them desirable for many applications.
Enhancements in miniaturization, speed and power consumption, size reduction of information processing devices, memory storage devices and flat displays for visualization are currently being developed.
The most immediate application for nano-tubes is in making strong, lightweight materials.
Carbon nano-tubes can emit a high electron field emission current from their tip, when submitted to a bias voltage. The emission from the nano-tubes are intense and very coherent, so they can be used in electron microscopes where electron sources are essential.
FUTURE APPLICATIONS
Apart from the above mentioned perspectives the carbon nano-tubes will find heir use in the following areas in near future
CONCLUSION
The phenomenal mechanical properties and the unique electronic properties make the carbon nano-tubes ,both interesting as well as potentially useful in the present and future technologies.
The electronics and mechanical properties of cnt depend on the growth conditions and the type of synthesis.
By controllable growth ,a significant improvement over the current state electronics can be achieved.
The CNTS have paved the way for miniaturizing the present technological systems providing greater strength, flexibility, agility, conductivity [electric & thermal] in a wide range of applications in different fields.
Though in the primary stage of development , the CNTs have great perspective in a very wide range of applications , thus revolutionizing & enhancing the field of science and technology in every possible manner.
REFERENCES
Dai H (2002), Surface Science, 500, 218-241.
Chen R.J, Zhang Y, Wang D, Dai H (2001), Journal of American Chemical Society, 123, 3838-3839.
Functionalization of Single-Walled Carbon Nanotubes, Andreas Hirsch.
Topics in Applied Physics Carbon Nanotubes: Synthesis, Structure, Properties and Applications, M.S. Dresselhaus, G. Dresselhaus, Ph. Avouris.
Carbon Nanotubes: Introduction to Nanotechnology 2003, Mads Brandbyge.
Carbon Nanotubes: Single molecule wires Sarah Burke, Sean Collins, David Montiel, Mikhail Sergeev
Nanopedia.cwru.edu
http://photon.t.u.tokyo.ac.jp/~maruyama/nanotube.html
CARBON NANO-TUBES
PRESENTED BY
DEBKUMAR SAHA
M.RAMPRAKASH
CARBON NANO-TUBES
These nanoscopic structures are made of carbon atoms.
The carbon nano-tubes can be thought of as graphene planes 'rolled up' in a cylinder which are typically closed at their ends by semi-fullerene-like structures.
Depending upon the manner the graphene planes are cut before rolling , different types of carbon nano-tubes are obtained.
Based on the geometrical structures , carbon nano-tubes are classified into the following:
Armchair,
Zig-zag and
Chiral (helical) nano-tubes.
Depending upon the size of graphene area folded onto a cylinder , nano-tubes of different radii are obtained.
These tubes are extremely long and possess different symmetry.
STRUCTURE OF CNT
Nanotubes are formed by rolling up a graphene sheet into a cylinder and
capping each end with half of a fullerene molecule
A CNT is characterized by its Chiral Vector: Ch = n â1 + m â2,
Chiral Angle with respect to the zigzag axis.
The diameter of the nano-tubes depends on the values of n and m.
This helps to identify whether the carbon atoms are arranged in zig-zag , armchair or helical shape.
PROPERTIES OF CNT
Excellent field emitter :- higher aspect ratio and a smaller tip radius of curvature wich are ideal for field emission.
Very high current carrying capacity , electrical conductivity six orders higher than copper.
Thermal conductivity ~3000 W/mK in axial direction with small values in the radial direction
High mechanical and thermal stability
Carbon nano-tubes are one of the strongest materials both in terms of tensile strength and elastic modulus. and most flexible molecular material because of C-C covalent bonding and seamless hexagonal network architecture
These tubes have very high tensile strength ,multi-walled tubes have a tensile strength as high as 63GPa.
PROCESSING TECHNIQUES
PROCESSING TECHNIQUES
Laser Ablation Method
A laser is used to vaporize a graphite target in an oven at 12000C.
Then helium or argon gas is filled to keep the pressure in the oven at 500 Torr.
The graphite target gets vaporized to form small carbon molecules and atoms which condense to form single walled nano-tubes held together by Van der Waals forces.
MWNT would be synthesized in the case of a pure graphite.
Uniform SWNT could be synthesized if a graphite of a mixture of Co, Ni, Fe, Y are used instead of a pure graphite.
Laser vaporization are higher in yield than arc-discharge and can synthesize large and aligned high quality SWNTs.
By far the most costly, because expensive lasers required.
PROCESSING TECHNIQUES
Thermal Chemical Vapor Deposition
Fe, Ni, Co, or alloy of the tree catalytic metals is initially deposited on a substrate.
To initiate the growth of nano-tubes, two gases are bled into the reactor: a process gas (such as ammonia, nitrogen, hydrogen, etc.) and a carbon-containing gas (such as acetylene, ethylene, ethanol, etc.).
The substrate is heated to approximately 700°C.
Nano-tubes grow at the sites of the metal catalyst; the carbon-containing gas is broken apart at the surface of the catalyst particle, and the carbon is transported to the edges of the particle, where it forms the nano-tubes.
Nano-structures provide interesting perspectives of applications because of their unique properties.
Carbon Nano-tubes possess many unique and remarkable properties (chemical, physical, and mechanical), which make them desirable for many applications.
Enhancements in miniaturization, speed and power consumption, size reduction of information processing devices, memory storage devices and flat displays for visualization are currently being developed.
The most immediate application for nano-tubes is in making strong, lightweight materials.
Carbon nano-tubes can emit a high electron field emission current from their tip, when submitted to a bias voltage. The emission from the nano-tubes are intense and very coherent, so they can be used in electron microscopes where electron sources are essential.
FUTURE APPLICATIONS
Apart from the above mentioned perspectives the carbon nano-tubes will find heir use in the following areas in near future
CONCLUSION
The phenomenal mechanical properties and the unique electronic properties make the carbon nano-tubes ,both interesting as well as potentially useful in the present and future technologies.
The electronics and mechanical properties of cnt depend on the growth conditions and the type of synthesis.
By controllable growth ,a significant improvement over the current state electronics can be achieved.
The CNTS have paved the way for miniaturizing the present technological systems providing greater strength, flexibility, agility, conductivity [electric & thermal] in a wide range of applications in different fields.
Though in the primary stage of development , the CNTs have great perspective in a very wide range of applications , thus revolutionizing & enhancing the field of science and technology in every possible manner.
REFERENCES
Dai H (2002), Surface Science, 500, 218-241.
Chen R.J, Zhang Y, Wang D, Dai H (2001), Journal of American Chemical Society, 123, 3838-3839.
Functionalization of Single-Walled Carbon Nanotubes, Andreas Hirsch.
Topics in Applied Physics Carbon Nanotubes: Synthesis, Structure, Properties and Applications, M.S. Dresselhaus, G. Dresselhaus, Ph. Avouris.
Carbon Nanotubes: Introduction to Nanotechnology 2003, Mads Brandbyge.
Carbon Nanotubes: Single molecule wires Sarah Burke, Sean Collins, David Montiel, Mikhail Sergeev
Nanopedia.cwru.edu
http://photon.t.u.tokyo.ac.jp/~maruyama/nanotube.html
