Carbon Nanotubes

General Fact

Graphite vs. DiamondsWhat'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.

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.

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

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).

Rolling a graphene sheet to get SWNT

Armchair

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

Zigzag

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

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.)

Special properties

• Difference in chemical reactivity for end caps and side wall

• High axial mechanical strength• Special electrical properties:

• Metallic• Semi conducting

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

MWNT

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

Synthesis: CVD

•Gas phase deposition•Large scale possible•Relatively cheap

Arc discharge

• Relatively cheap• Many side-products

Synthesis: laser ablation

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

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

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

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 • Other Applications