CARBON NANO TUBE

PREPARATION – METHODS

Fathima.P.E

CBPST,KOCHI

INTRODUCTION:

Carbon nanotubes are hexagonally shaped arrangements of carbon atoms that have been rolled into tubes.

These tiny straw-like cylinders of pure carbon have useful electrical propeties. They have already been used to make tiny transistor and one-dimentional copper wire

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

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 .

CNT: ROLLING-UP A GRAPHENE SHEET TO FORM

A TUBE

Schematic

of a CNT

SEMimage

of CNT

TYPES OF CARBON NANO TUBES:

Single walled CNT (SWCNT)

Multi walled CNT (MWCNT)

Can be metallic or semi conducting

SINGLE WALLED

-Most single-walled nanotubes (SWNTs) have a diameter of cloes to 1

nanometer,with a tube length that can be many millions of time longer

-The structure of a SWNTs can be conceptualized by wrapping a one-atom-thick

layer of graphite called graphene in to a seamless cylender

• The way the graphene sheet is wrapped is represented by a pair of indices (n,m) called the chiral vector.

• The integers n and m denote the number of unit vectors along two directions in the honeycomb crystal lattice of graphene

• If m = 0, the nanotubes are called "zigzag". If n = m, the nanotubes are called "armchair". Otherwise, they are called "chiral".

MULTI WALLED

• Multi-walled nanotubes (MWNTs) consist of multiple rolled layer( concentric tubes) of

graphene

In the Russian Doll model, sheets of graphite are arranged in concentric cylinders

• In the Russian Doll model, sheets of graphite are arranged in concentric cylinders, e.g., a (0,8) single-walled nanotube (SWNT) within a larger (0,17) single-walled nanotube.

• In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or a rolled newspaper.

• The interlayer distance in multi-walled nanotubes is close to the distance between graphene layers in graphite, approximately 3.4 Å. The Russian Doll structure is observed more commonly. Its individual shells can be described as SWNTs, which can be metallic or semiconducting.

the Russian Doll model, sheets of graphite are arranged in concentric cylinders

In the Russian Doll model, sheets of graphite are arranged in concentric cylinders

In the Russian Doll model, sheets of graphite are arranged in concentric cylinders

In the Russian Doll model, sheets of graphite are arranged in concentric cylindersIn the Russian Doll model, sheets of graphite are arranged in concentric cylinders

In the Russian Doll model, sheets of graphite

are arranged in concentric cylinders.

In the

SYNTHESIS OF CARBON NANO TUBES

• Commonly applied techniques:

• Chemical Vapor Deposition (CVD)

• Arc-Discharge

• Laser ablation

• Techniques differ by:

• Type of nanotubes (SWNT / MWNT )

• Catalyst used

• Yield

• Purity

ARC DIS CHARGE

• CNT production requires 3 elements ,

I. Carbon feed

II. Metal catalyst

III. Heat

a) Two Graphite electrodes placed in an inert Helium atmosphere .

b) When DC current is passed anode is consumed and material forms

on cathode.

c) For SWNT mixed metal catalyst is inserted into anode

d) Pure iron catalyst + Hydrogen-inert gas mixture gives 20 to 30cm

long tube.

e) The nanotubes were initially discovered using this technique, it has

been the most widely-used method of nanotube synthesis.

ARC DIS CHARGE PROCESS

• The carbon arc discharge method, is the most common and perhaps easiest way to produce CNTs, as it is rather simple.

• However, it is a technique that produces a complex mixture of components, and requires further purification - to separate the CNTs from the soot and the residual catalytic metals present in the crude product.

• This method creates CNTs through arc-vaporization of two carbon rods placed end to end, separated by approximately 1mm, in an enclosure that is usually filled with inert gas at low pressure.

• A direct current of 50 to 100A, driven by a potential difference of approximately 20 V, creates a high temperature discharge between the two electrodes.

• The discharge vaporizes the surface of one of the carbon electrodes, and forms a small rod-shaped deposit on the other electrode.

• Producing CNTs in high yield depends on the uniformity of the plasma arc, and the temperature of the deposit forming on the carbon electrode.

LASER ABLATION PROCESS

Another method to grow SWNTs using laser ablation was demonstrated in 1996 by Smalley's group and has prompted a lot of interest.

The synthesis could be carried out in a horizontal flow tube under a flow of inert gas at controlled pressure.

In the laser ablation process, a pulsed laser vaporizes a graphite target in a high-temperature reactor while an inert gas is bled into the chamber.

Nanotubes develop on the cooler surfaces of the reactor as the vaporized carbon condenses.

A water-cooled surface may be included in the system to collect the nanotubes.

The laser ablation method yields around 70% and produces primarily single-walled carbon nanotubes with a controllable diameter determined by the reaction temperature.

it is more expensive than either arc discharge or chemical vapordeposition.

CHEMICAL VAPOR DEPOSITION (CVD):

During CVD, a substrate is prepared with a layer of metal catalyst articles, most

commonly nickel, cobalt, iron, or a combination.

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

metal particles.

The substrate is heated to approximately 700°c.

To initiate the growth of nanotubes, two gases are bled into the reactor: a process

gas (such as ammonia, nitrogen or hydrogen) and a carbon-containing gas (such

as acetylene, ethylene, ethanol or methane).

Nanotubes 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 nanotubes.

APPLICATIONS:

CVD is used to grow a thin layer of advanced materials on the surface of a substrate.

Applications may be found in the areas of:

integrated circuits, optoelectronic devices and sensors

catalysts

micromachines, and fine metal and ceramic powders protective coatings

PURIFICATION:

The main impurities :graphite (wrapped up) sheets, amorphous carbon, metal catalyst and the smaller fullerenes…

Rules :-separate the SWNTs from the impurities

- give a more homogeneous diameter or size distribution.

The techniques that will be discussed are oxidation, acid treatment, annealing, ultrasonication, micro filtration, ferromagnetic separation, cutting, functionalisation and chromatography techniques.

Arc Discharge Method Chemical Vapor Deposition Laser Ablation (Vaporization)

Connect two graphite rods to a

power supply, place them

millimeters apart, and throw

switch. At 100 amps, carbon

vaporizes in a hot plasma.

Place substrate in oven, heat to

600 C, and slowly add a carbon-

bearing gas such as methane. As

gas decomposes it frees up

carbon atoms, which recombine in

the form of NTS

Blast graphite with intense laser

pulses; use the laser pulses rather

than electricity to generate carbon

gas from which the NTS form; try

various conditions until hit on one

that produces prodigious amounts

of SWNTS

Can produce SWNT and MWNTs

with few structural defects

Easiest to scale to industrial

production; long length

Primarily SWNTS, with a large

diameter range that can be

controlled by varying the reaction

temperature

Tubes tend to be short with

random sizes and directions

NTS are usually MWNTS and

often riddled with defects

By far the most costly, because

requires expensive lasers

ADVANTAGES:

Extremely small and lightweight.

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

Improves conductive, mechanical, and flame barrier properties of plastics and composites.

Enables clean, bulk micromachining and assembly of components.

Improves conductive, mechanical, and flame barrier properties of plastics and composites.

DIS ADVANTAGES:

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:

Micro-electronics / semiconductors

Conducting Composites

Controlled Drug Delivery/release

Artificial muscles

Super capacitors

Batteries

Field emission flat panel displays

Field Effect transistors and Single electron transistors

Molecular Quantum wires

Hydrogen Storage

Noble radioactive gas storage

Solar storage

Waste recycling

Electromagnetic shielding

Dialysis Filters

Thermal protection

Nanotube reinforced composites

Reinforcement of armour and other materials

Reinforcement of polymer

Avionics

Collision-protection materials

Fly wheels

CONCLUSION:

CNTs are nanometer-length shells of carbon.

Possess a combination of unique physical and chemical properties.

Programmable .

Can be applied in a variety of fields.

Exhibits incredible strength, elasticity, thermal electrical conductivity.

Pivotal element in Nano technology.

Exhibits incredible strength, elasticity, thermal and electrical conductivity.

Can be applied to a variety of fields.

Technology is in its infancy and will take several years to develop.

REFERENCE:

1. D.A.Bochvar and E.G.Gal'pern, Dokl.Akad.Nauk.USSR, 209, (610, 1973 )

2.http://www.ou.edu/engineering/nanotube, 2003

3. http://nanotube.msu.edu/

4.http://www.pa.msu.edu/cmp/csc/nanotube.html

5.http://en.wikipedia.org/wiki/Carbon_nanotube

6.http://students.chem.tue.nl/carbonnanotubes/applications.html

Thanks for your listening…