Carbon nanotube

Dr. Jivraj Mehta Institute Of Technology, Mogar, Anand

GrapheneIn graphite, each carbon atom is linked to three other carbon atoms through covalent bonds forming hexagonal rings connected to each other to form plane sheets known as Graphene.

The Structure of Carbon Nanotubes (CNT) can be imagined as a cylinder formed by rolling a graphene sheet and then closing it on both sides by fullerene hemispheres.


Types of CNTThe CNT’s are of Two types:-

1. Single Walled Nanotubes (SWNT)

These can be imagined as a single atom thick graphite sheet, i.e. graphene, rolled into a cylinder and capped by fullerene hemisphere.

2. Multiwalled Nanotubes (MWNT)

These can be considered as Nanotubes within Nanotubes.


StructureThe graphene sheet can be rolled in different ways to get the three type of SWNTS:

1. Zigzag

2. Armchair

3. Chiral

These three types are classified on the Chiral vector.

1. Zigzag

In these the graphene sheet is rolled up along a vector greater then the chiral angle.

2. Armchair

In these the graphene sheet is rolled up along the vector smaller than the chiral angle.

3. Chiral

In these it is rolled up on the chiral vector.


Fabrication

• CNT’s can be fabricated by 3 method

Electric Arc Method

Laser Deposition

Chemical Vapor Deposition


Electric Arc MethodMost common method of CNT fabrication.

1. A current is run through an anode, or a positively charged piece of carbon.

2. This current jumps through a plasma material to a cathode, or a negatively charged piece of carbon, where there is an evaporation and deposition of carbon particles in through the plasma.

3. Finally an outer hard-shell region made of decomposed graphite is formed and an inner core region with loosely packed columns which consist of straight, stiff multishell carbon nanotubes and closed polyhedral particles Dr. Jivraj Mehta Institute Of Technology,

Mogar, Anand

Pulsed Laser Deposition• Uses an intense laser pulse to

vaporize a carbon target, which also contains small amount of metals such as nickel and cobalt and is placed in a tube furnace at 1200oC, And pressure of 500 torr.

• Inert gas is passed through the chamber carrying the grown nanotubes on a cold finger for collection.

• This method mainly produces SWCNT in the form of ropes.

• It produces nanotubes of 10-20 nm in diameter about 100 micro m in length.

• About 80% of graphite material is converted into nanotubes in this method. Dr. Jivraj Mehta Institute Of Technology,

Mogar, Anand

Chemical Vapor Deposition• A mixture of hydrocarbon, metal

catalyst along with inert gas is introduced into the reaction chamber.

• During the reaction, nanotubes form on the substrate by the decomposition of hydrocarbon at temperatures 700–900oC and atmospheric pressure.

• The diameters of nanotubes that are to be grown are related to the size of the metal particles

• This technique offers more control over the length and structure of the produced nanotubes compared to arc and laser methods.


Carbon Nanotubes

Advantages

• Extremely small and lightweight, making them excellent replacements for metallic wires

• Resources required to produce them are plentiful, and many can be made with only a small amount of material

• Are resistant to temperature changes, meaning they function almost just as well in extreme cold as they do in extreme heat

Disadvantages• Despite all the research, scientists

still don't understand exactly how they work

• Extremely small, so are difficult to work with.

• Currently, the process is relatively expensive to produce the nanotubes

• Would be expensive to implement this new technology in and replace the older technology in all the places that we could

• At the rate our technology has been becoming obsolete, it may be a gamble to bet on this technology


Applications• Carbon nanotubes can store lithium due to which they can be used in

batteries. CNT’s can also store hydrogen and hence find potential applications in fuel cells.

• They are used in the tips for atomic force microscope probes.

• They are being used to develop flat panel displays for television and computer monitors.

• They are being used to develop light weight shield for electromagnetic radiation.

• Field effect transistors are being developed using semi conducting CNT’s which can be used to build faster processors for computers. It is estimated that these processors will ne 104 times faster than the present processors.

• CNT’s are being used to produce light weight materials with higher strength than steel. These can be used in Auto mobile, Aircraft and rocket parts.

• They are used in chemical sensors to detect gases.


Properties

1. Mechanical:

The carbon nanotubes are highly elastic. The Young’s Modulus is a measure of the elasticity. The Young’ Modulus for carbon nanotubes is about 1800 Gpa whereas it is about 210 Gpa for steel.

Carbon Nanotubes exhibit large strength in tension. They are about twenty times stronger than steel. The yield stress is a measure of the strength.

Carbon Nanotubes can withstand larger strains than steel. They can be bent without breaking.


Properties2. Electrical:

The electrical properties of carbon nanotubes depends upon their diameter and chirality. They show electrical properties ranging from semiconductors to those of good conductors. The energy gap decreases as the diameter of the CNT is increased.Due to very low resistivity, the heat dissipation in the CNT is very small and hence they can carry much larger currents than the metals.The conductivity of a CNT is maximum along its axis and very low in a perpendicular direction. Hence they are equivalent to one dimensional conductors.At low temperatures, the resistance decreases with increasing magnetic field applied across the CNT. This effect is known as magneto resistance.


Properties

3. Thermal:Carbon nanotubes are very good conductors of heat. Their thermal conductivity is more than twice that of diamond. The thermal conductivity also varies with direction. The conductivity is very good along the axis of the tube and very low in a perpendicular direction.

4. Physical:CNT’s have very high strength to weight ratio. They have low density.

5. Chemical:CNT’s are chemically more inert compared to other forms of carbon.



Science

Carbon nanotube