Carbon Nano-tubes

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Carbon Nanotubes
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General Fact
Graphite vs. Diamonds
What's the difference between graphite
and diamonds? Both materials are
made of carbon, but both have vastly
different properties. Graphite is soft;
diamonds are hard. Graphite conducts
electricity, but diamonds are insulators
and can't conduct electricity. Graphite is
opaque; diamonds are usually
transparent. Graphite and diamonds
have these properties because of the
way the carbon atoms bond together at
the nanoscale.


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 A carbon nanotube is a Nano-size cylinder of carbon atoms.
 Imagine a sheet of carbon atoms, which would look like a sheet of
hexagons. If you roll that sheet into a tube, you'd have a carbon nanotube.
 Carbon nanotube properties depend on how you roll the sheet.
 In other words, even though all carbon nanotubes are made of carbon,
they can be very different from one another based on how you align the
individual atoms.
 With the right arrangement of atoms, you can create a carbon nanotube
that's hundreds of times stronger than steel, but six times lighter
 Engineers plan to make building material out of carbon nanotubes,
particularly for things like cars and airplanes.
 Lighter vehicles would mean better fuel efficiency, and the added strength
translates to increased passenger safety.
 Carbon nanotubes can also be effective semiconductors with the right
arrangement of atoms.
 Scientists are still working on finding ways to make carbon nanotubes a
realistic option for transistors in microprocessors and other electronics.


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Carbon Nanotube
• Discovered in 1991 by Lijima
• It has Unique material properties
• They are nearly One-dimensional structures
• There are two types Single-walled and Multi-walled


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Introduction:
nanotube structure
Roll a Graphene sheet in a certain direction:
• Armchair structure
• Zigzag structure
• Chiral structure

• Single-walled carbon nanotubes exist in a variety of
structures corresponding to the many ways a sheet of
Graphene can be wrapped into a seamless tube.
• Each structure has a Wrapping Angle say (a).


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Rolling a graphene sheet to get SWNT


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Armchair
• The “armchair” structures, with a = 30°, have metallic
character


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Zigzag
• The “zigzag” tubes, for which a = 0°, can be either
semimetallic or semiconducting, depending on the specific
diameter.


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Chiral

• Nanotubes with chiral angles intermediate between 0 and 30° include both semimetals
and semiconductors. (“Armchair” and “zigzag” refer to the pattern of carbon–carbon
bonds along a tube’s circumference.)


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Special properties
• Difference in chemical reactivity for
end caps and side wall
• High axial mechanical strength
• Special electrical properties:
• Metallic
• Semi conducting


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Properties of nanotubes
• CNTs have High Electrical Conductivity
• CNTs have Very High Tensile Strength
• CNT are Highly Flexible- can be bent considerably without
damage
• CNTs are Very Elastic ~18% elongation to failure
• CNTs have High Thermal Conductivity
• CNTs have a Low Thermal Expansion Coefficient
• CNTs are Good Electron Field Emitters
• CNTs have a High Aspect Ratio (length = ~1000 x diameter


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MWNT


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Synthesis: overview
• Commonly applied techniques:
• Chemical Vapor Deposition (CVD)
• Arc-Discharge
• Laser ablation

• Techniques differ by:
• Type of nanotubes (SWNT / MWNT )
• Catalyst used
• Yield
• Purity

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Synthesis:
CVD

•Gas phase deposition
•Large scale possible
•Relatively cheap


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Arc discharge

• Relatively cheap
• Many side-products


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Synthesis: laser ablation

• Use of very strong laser
• Expensive (energy costs)
• Commonly applied

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Purification
• Contaminants:
• Catalyst particles
• Carbon clusters
• Smaller fullerenes: C60 / C70

• Demerits in purification of Nanotubes:
• Completely retain nanotube structure
• Single-step purification
• Only possible on very small scale:
• Isolation of either semi-conducting SWNTs


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Purification techniques
• Removal of catalyst:
• Acidic treatment (+ sonication)
• Thermal oxidation
• Magnetic separation (Fe)
• Removal of small fullerenes
• Micro filtration
• Extraction with CS2
• Removal of other carbonaceous
impurities
• Thermal oxidation
• Selective functionalisation of nanotubes
• Annealing

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Applications
• Thermal Conductivity of CNTs
• Field Emission of CNTs
• Conductive Plastics with CNTs
• Energy Storage using CNTs
• Conductive Adhesives and Connectors with CNTs
• Molecular Electronics based on CNTs
• Thermal Materials with CNTs
• Structural Composites with CNTs
• Fibers and Fabrics with CNTs
• Catalyst Supports using CNTs
• Biomedical Applications of CNTs
• Air and Water Filtration using CNTs
• Ceramic Applications with CNTs


Carbon Nano-tubes

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