What are carbon nanotubes

Discovery of carbon nanotubes

Classification of CNTs

Properties of CNTs

Synthesis of nanotubes

Advantages and Disadvantages

A Carbon Nanotube is a tube-shaped material, made of carbon, having a diameter measuring on the nanometer scale.

The graphite layer appears somewhat like a rolled-up chicken wire with a continuous unbroken hexagonal mesh and carbon molecules at the apexes of the hexagons.

Their name is derived from their long, hollow structure with the walls formed by one atom thick sheets of carbon, called graphene.

1952- Radushkevich and Lukyanovich publish a paper in the Soviet Journal of Physical Chemistry showing hollow graphitic carbon fibers that are 50 nanometers in diameter.

1979 - John Abrahamson presented evidence of carbon nanotubes at the 14th Biennial Conference of Carbon at Pennsylvania State University.

1981 - A group of Soviet scientists published the results of chemical and structural characterization of carbon nanoparticles produced by a thermocatalytical disproportionation of carbon monoxide.

1991 - Nanotubes discovered in the soot of arc discharge at NEC, by Japanese researcher Sumio Iijima.

CARBON NANOTUBES

SINGLE-WALLED(SWNT)

MULTI-WALLED(MWNT)

Single-wall nanotubes (SWNT) are tubes of graphite

that are normally capped at the ends. They have a

single cylindrical wall. The structure of a SWNT can

be visualized as a layer of graphite, a single atom

thick, called graphene, which is rolled into a seamless

cylinder.

Most SWNT typically have a diameter of close to 1

nm. The tube length, however, can be many

thousands of times longer.

Russian doll model

(concentric cylindrical arrangement

of various graphite sheets)

Parchment Model

(single sheet of graphite is rolled

in around itself)

Multi-wall nanotubes can appear

either in the form of a coaxial

assembly of SWNT similar to a

coaxial cable, or as a single sheet

of graphite rolled into the shape of

a scroll.

The diameters of MWNT are

typically in the range of 5 nm to

50 nm. The interlayer distance in

MWNT is close to the distance

between graphene layers in

graphite.

They are chemically inert

compared to single walled tubes.

Strength

Electrical

Thermal

Defects

Carbon nanotubes have the strongest tensile strength of

any material known.

It also has the highest modulus of elasticity.

MaterialYoung's Modulus (TPa)

Tensile Strength (GPa)

Elongation at Break (%)

SWNT~1 (from 1 to

5)13-53E 16

Armchair SWNT

0.94T 126.2T 23.1

Zigzag SWNT 0.94T 94.5T 15.6-17.5

MWNT 0.8-0.9E 150

Stainless Steel

~0.2 ~0.65-1 15-50

Kevlar ~0.15 ~3.5 ~2

If the nanotube structure is armchair

then the electrical properties are

metallic

If the nanotube structure is chiral then

the electrical properties can be either

semiconducting with a very small

band gap, otherwise the nanotube is a

moderate semiconductor

In theory, metallic nanotubes can

carry an electrical current density of

4×109 A/cm2 which is more than

1,000 times greater than metals such

as copper

• All nanotubes are expected to be very good thermal

conductors along the tube, but good insulators

laterally to the tube axis.

• It is predicted that carbon nanotubes will be able to

transmit up to 6000 watts per meter per Kelvin at

room temperature; compare this to copper, a metal

well-known for its good thermal conductivity, which

transmits 385 watts per meter per K.

• The temperature stability of carbon nanotubes is

estimated to be up to 2800oC in vacuum and about

750oC in air.

Defects can occur in the form of atomic vacancies. High levels of such defects can lower the tensile strength by up to 85%.

Because of the very small structure of CNTs, the tensile strength of the tube is dependent on its weakest segment in a similar manner to a chain, where the strength of the weakest link becomes the maximum strength of the chain.

Arc Discharge

Laser Ablation

Chemical Vapor

Deposition (CVD)

Ball Milling

A direct current creates a high temperature discharge between two electrodes

Atmosphere is composed of inert gas at a low pressure

Originally used to make C60 fullerenes

Cobalt is a popular catalyst

Typical yield is 30-90%

Advantages

Simple procedure

High quality product

Inexpensive

Disadvantages

Requires further purification

Tubes tend to be short with

random sizes

Discovered in 1995 at Rice

University

Vaporizes graphite at 1200 ⁰C

Helium or argon gas

A hot vapor plume forms and

expands and cools rapidly

Carbon molecules condense

to form large clusters

Similar to arc discharge

Yield of up to 70%

Pulsed

◦ Much higher light

intensity (100 kW/cm2)

Continuous

◦ Much lower light

intensity (12 kW/cm2)

Advantages

Good diameter

control

Few defects

Pure product

Disadvantages

Expensive because

of lasers and high

powered

equipment

Carbon is in the gas phase

Energy source transfers

energy to carbon molecule

Common Carbon Gases

◦ Methane

◦ Carbon monoxide

◦ Acetylene

One of the most common methods of carbon nanotubesynthesis

Temperature between 650 – 900 ⁰C

After energy transfer, the carbon molecule binds to the substrate

Yield is usually about 30%

Advantages

Easy to increase scale to

industrial production

Large length

Simple to perform

Pure products

Disadvantages

Defects are common

Powder graphite is

placed in a stainless

steel container

Argon gas is used

Process occurs at room

temperature

Powder is then annealed

Nanotubes hold the promise of creating novel devices,

such as carbon-based single-electron transistors, that

significantly smaller than conventional transistors.

Scientists have developed the ‘blackest black’ colour using carbon nanotubes

The carbon nanotubes are arranged like blades of grass in a lawn- they absorb nearly all light

Use of carbon nanotubes in solar cells could vastly improve their efficiency.

Badminton racquet manufacturer

Yonex incorporates carbon nanotubes

into their cup stack carbon nanotubes

racquets.

American baseball bat manufacturer

Easton Sports has formed an alliance

with a nanotechnology company

Zyvex to develop baseball bats

incorporating carbon nanotubes

Tennis racquets also incorporate

carbon nanotubes.

Branching and switching of

signals at electronic junctions

is similar to what happens in

nerves

A carbon nanotube ‘neural

tree’ can be trained to

perform complex switching

and computing functions

Could be used to

detect/respond to electronic,

acoustic, chemical or thermal

signals.

Nanotubes and other Fullerenes can be filled

with molecules that have either an electronic

or structural property which can be used to

represent the quantum bit (Qubit) of

information, and which can be associated with

other adjacent Qubits.

• According to scientists at the National Institute of

Standards and Technology, carbon nanotubes shorter

than about 200 nanometers readily enter into human

lung cells similar to the way asbestos does, and may

pose an increased risk to health.

• Carbon nanotubes along with the majority of

nanotechnology, are an unexplored matter, and many of

the possible health hazards are still unknown.

Nano science is the most rapidly developing field that has been fascinating scientists for years and the last decade has been the most productive in terms of research on it.

But for this to be productive in every aspect its impacts both positive and negative are to be studied extensively and thereupon reach a point where negative aspects can be worked around.

It is however a field having quite a potential for future applications.