Download Carbon nanotubes are molecular-scale tubes of graphitic carbon

Applied materials
Victoria Riabicheva
Olexandra Tupalo
English supervisor- Ekaterina Kuznetsova
Science supervisor- Oleg Uzlov
THE DISCOVERY, STRUCTURE, PROPERTIES AND APPLICATION OF
CARBON NANOTUBES
ВІДКРИТТЯ, СТРУКТУРА, ВЛАСТИВОСТІ ТА ЗАСТОСУВАННЯ ВУГЛЕЦЕВИХ
НАНОТРУБОК
У даній роботі розглядаються визначення, структура, синтез та застосування
вуглецевих нанотрубок, як важливої частини сучасного ринку виготовлення
матеріалів.
In the following work the definition, structure, synthesis and application of carbon
nanotubes, being an important part of the modern material producing market, are considered.
Keywords: carbon
nanotubes,
fullerene, graphene, multi-walled,
superhard
phasenanotubes.
Carbon nanotubes are molecular-scale tubes of graphitic carbon with outstanding
properties. They are among the stiffest and strongest fibres known, and have remarkable
electronic properties and many other unique characteristics. For these reasons they have
attracted huge academic and industrial interest.
History
The discovery that carbon could form stable, ordered structures other than graphite
and diamond stimulated researchers worldwide to search for other new forms of carbon. It
was shown in 1990 that C60 could be produced in a simple arc-evaporation apparatus readily
available in all laboratories. It was using such an evaporator that the Japanese scientist Sumio
Iijima discovered fullerene-related carbon nanotubes in 1991.
Structure
The bonding in carbon nanotubes is sp², with each atom joined to three neighbours, as
in graphite. The tubes can therefore be considered as rolled-up graphene sheets (graphene is
an individual graphite layer). There are three distinct ways in which a graphene sheet can be
rolled into a tube.
The first two of these, known as “armchair” and “zig-zag” have a high degree of
symmetry. The terms "armchair" and "zig-zag" refer to the arrangement of hexagons around
the circumference. The third class of tube is known as chiral, meaning that it can exist in two
mirror-related forms.[1]
Synthesis
The arc-evaporation method, which produces the best quality nanotubes, involves
passing a current of about 50 amps between two graphite electrodes in an atmosphere of
helium. This causes the graphite to vaporise, some of it condensing on the walls of the
reaction vessel and some of it on the cathode. It is the deposit on the cathode which contains
the carbon nanotubes. Single-walled nanotubes are produced when Co and Ni or some other
metal is added to the anode. It has been known since the 1950s, if not earlier, that carbon
nanotubes can also be made by passing a carbon-containing gas, such as a hydrocarbon, over
a catalyst. The catalyst consists of nano-sized particles of metal, usually Fe, Co or Ni. These
particles catalyse the breakdown of the gaseous molecules into carbon, and a tube then begins
to grow with a metal particle at the tip. The big advantage of catalytic synthesis over arcevaporation is that it can be scaled up for volume production. The third important method for
making carbon nanotubes involves using a powerful laser to vaporise a metal-graphite target.
This can be used to produce single-walled tubes with high yield.
Properties
The strength of the material results from the covalent sp² bonds formed between the
individual carbon atoms. In 2000, a multi-walled carbon nanotube was tested to have a tensile
strength of 63 gigapascals (GPa)
Standard single walled carbon nanotubes can withstand a pressure up to 24GPa
without deformation. Maximum pressures measured using current experimental techniques
are around 55GPa.
Because of the symmetry and unique electronic structure of graphene, the structure of
a nanotube strongly affects its electrical properties. For a given (n,m) nanotube, if n = m, the
nanotube is metallic; if n − m is a multiple of 3, then the nanotube is semiconducting with a
very small band gap, otherwise the nanotube is a moderate semiconductor. [3]
Potential uses include:

Textiles - can make waterproof and/or tear-resistant fabrics

Concrete - CNTs in concrete increase its tensile strength, and halt crack
propagation.

Polyethylene - Adding CNT to polyethylene can increase the polymer's elastic
modulus by 30%.

Sports equipment - Stronger and lighter tennis rackets, bicycle parts, etc.

Space elevator - CNTs are under investigation as possible components of
the tether up which a space elevator can climb.

Synthetic muscles - CNTs are ideal for synthetic muscle.

Bridges - CNTs may be able to replace steel in suspension and other bridges.

Fire protection - Thin layers of buckypaper can significantly improve fire
resistance due to the efficient reflection of heat by the dense, compact layer of CNT
or carbon fibers.

Air pollution filter - CNT membranes can filter carbon dioxide from power
plant emissions.

Water filter - CNT can purportedly reduce desalination costs by 75%. [2]
Defects
As with any material, the existence of a crystallographic defect affects the material
properties. Defects can occur in the form of atomic vacancies. High levels of such defects can
lower the tensile strength by up to 85%. Another form of carbon nanotube defect is the Stone
Wales defect, which creates a pentagon and heptagon pair by rearrangement of the bonds.
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.
Determining the toxicity of carbon nanotubes has been one of the most pressing
questions in nanotechnology. Available data clearly show that, under some conditions,
nanotubes can cross membrane barriers, which suggests that if raw materials reach the organs
they can induce harmful effects such as inflammatory and fibro tic reactions.
REFERENCES:
1.
ЗОЛОТУХИН И.В. «УГЛЕРОДНЫЕ НАНОТРУБКИ».
ФИЗИКА. 1999
2.
HTTP://NANOTRUBKI.NAROD.RU
3.
HTTP://EN.WIKIPEDIA.ORG