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Carbon nanotubes cn ts
1.
2.
3. Outline
• Introduction on Nanotechnology
• Introduction to Carbon Nanotubes
• Properties of carbon Nanotubes
• Production of carbon Nanotubes
• Applications of carbon Nanotubes
4. What Does ‘Nano' Mean?
The 'nano' in 'nanotechnology' is often thought of as a
shortened form of 'nanometer‘, which is one billionth
(10-9
) of a meter. The diameter of one human hair is
about 10,000 to 80,000 nanometers.
A picture of nanofibrils shown with a human hair for reference
5. CNTS
• 1991, Ijima- described the new form of carbon
known as Carbon nanotubes
• CNTS are allotropes of carbon with a
nanostructure having a length-to–diameter ratio
greater than 1,000,000.
• CNTs consist of graphite sheets seamlessly
wrapped into a nano size cylindrical tube.
• Carbon nanotubes are lattice of carbon atoms,
in which each carbon is covalently bonded to
three other carbon atoms.
6. Structure (or) types of carbon
nanotubes
• When graphite sheets are rolled into a
cylinder, their edges joined to form carbon
nanotubes ie, carbon nanotubes are
extended tubes of rolled graphite sheets.
• Nanotubes naturally align themselves into
ropes and held together by Vander Waals
forces. But each carbon atoms in the
carbon nanotubes are linked by the
covalent bond.
7. Classification
• Depending upon the way in which graphite
sheets are rolled, two types of CNTs are
formed.
• 1. Single- walled nanotubes (SWNTs)
• 2. Multi- walled nanotubes (MWNTs).
8. 1. Single –walled nanotubes (SWNTs).
• SWNTs consist of one tube of graphite. It is one–
atom thick having a diameter of 2nm and a length of
100nm.
• SWNTs are very important , because they exhibit
important electrical properties. It is an excellent
conductor.
• Three kinds of nanotubes are resulted based on the
orientation of the hexagon lattice.
• 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.
9. Classification(based on orientation of the hexagon)
• The tubes with n = m are called armchair
The lines of hexagons are parallel to the
axis of the nanotube.
• Tubes with either n = 0 or m = 0 are
called zig-zag
The lines of carbon bonds are down the
centre.
• All others have chiral symmetry. It exhibits
twist or spiral around the nanotubes.
10. CNTS
• The (n,m) nanotube
naming scheme can be
thought of as a vector (Ch)
in an infinite graphene
sheet that describes how
to "roll up" the graphene
sheet to make the
nanotube.
• T denotes the tube axis,
and a1 and a2 are the unit
vectors of graphene in
real space
11. CNTS
It has been confirmed that
armchair carbon
nanotubes are metallic
while zig-zag and chiral
nanotubes are
semiconducting
Armchair (n,n)
Chiral (n,m)
Zigzag (n,0)
12. Multi-walled nanotubes (MWNTs
• MWNTs (nested nanotubes) consist of multiple
layers of graphite rolled in on themselves to form
a tube shape. It exhibits both metallic and
semiconducting properties. It is used for fuels
such as hydrogen and methane.
• (i) A1g mode: It involves in and out oscillation.
• (ii) E2g mode: It involves a squashing of the
tube (oscillation between sphere and an
ellipse.)
• The frequencies of two modes of vibrations are
Raman –active. The inner tubes of MWNTs can
slide without any friction within the outer
nanotubes leading to an atomically perfect
rotational bearing.
13. CNTS
Conceptual diagram of single-walled carbon nanotube (SWCNT) (A) and
multiwalled carbon nanotube (MWCNT) (B) delivery systems showing typical
dimensions of length, width, and separation distance between graphene
layers in MWCNTs.
14.
15.
16. Properties
• Mechanical properties
• Carbon nanotubes are very strong and their elastic
flexibility is indicated by young’s modulus.
• Young’s modulus of carbon nanotubes are 10 times
greater than that of steel.
• CNTs withstand extreme strain and tension. Most of the
materials fracture on bending because of the presence
of more defects, but CNTs possess only few defects in
the structure.
• Electrical properties
• The electrical properties of CNTs vary between metallic
to semiconducting materials. It depends on the diameter
and chirality of the nanotubes. The very high electrical
conductivity of CNT is due to the minimum defects in the
structure.
17. • Thermal Conductivity
The thermal conductivity of CNTs is very high ,
this is due to the vibration of covalent bonds. Its
thermal conductivity is 10 times greater than the
metal. The high thermal conductivity is also due
to minimum defects in the structure.
Thermal conductivity ~3000 W/m in the axial in
direction with small values in the radial direction
• Vibrational properties
As in normal molecules, the atoms in a CNT are
continuously vibrating back and forth.
18. • CNT in catalysis
Carbon nanotubes serve as efficient
catalysts for some chemical reaction.
Example
• Hydrogenation reaction
• Nested carbon nanotubes with ruthenium
(Ru) metal bonded to the outside have
been proved to have a strong catalytic
effect in the hydrogenation reaction of
cinnamaldehyde (C6H5 CH=CHCHO) when
compared with the effect of the same
metal Ru attached to other carbon
substrates.
19. • Some chemical reactions are also been carried out
inside the nanotubes.
• (i) Reduction of nickel oxide (NiO) to the base metal Ni
• NiO Ni
• (ii) Reduction of AlCl3 Al
• (iii) A stream of H2 gas at 4750
C partially reduces MoO3 to
MoO2 with the formation of steam (H2O) inside the
multiwalled nanotubes.
• (H2) 470C
• MoO3 → MoO2+ H2O (steam)
• (iv) Cadmium sulfide (CdS) crystals have been formed
inside the carbon nanotubes by reacting cadmium oxide
(CdO) crystals with hydrogen sulfide gas (H2S) at 400C.
• CdO+ H2S 400C →CdS+H2O
• carbon nanotube
27. APPLICATIONS OF CARBON
NANOTUBES
• CNTs in storage devices
Carbon nanotubes play an important role in the battery
technology, because some charge carries can be
successfully stored inside the nanotubes.
• (i) CNT in Fuel cells
• Hydrogen can be stored in the CNT, which may be
used for the development of fuel cells.
• (ii) CNT in Lithium battery
• Lithium atoms, as a very good charge carrier, can be
stored- inside the carbon nanotubes. It has been
estimated that one lithium atom can be stored for every
six carbon atoms of the CNT and hence can be used in
lithium batteries.
28.
29. • CNT as protective shields
CNT s are poor transmitters of electromagnetic
radiation and hence can be used as light weight
shielding materials for protecting electronic
equipment against electromagnetic radiation.
• Sensors of gases
• The gases like NO2 and NH3 can be detected on
the basis of increase in electrical conductivity of
CNTs, electrical conductivity is found to
increase. This is attributed to increase in hole
concentration in CNTs due to charge transfer
from CNTs to NO2 as the gas molecules bind to
the CNTs.
• Drug delivery vessels
• CNTs can be effectively used inside the body
for drug delivery by placing the drugs within the
tubes.
30. • CNT in microscope
• CNTs, attached to the tips of scanning
probe, microscope have been used to image
biological and industrial specimens.
• Reinforcing elements in composites
• The composites of aluminium power, mixed
with CNTs (5%), possesses a greater tensile
strength compared to pure aluminium.
• Components in integrated memory circuits
• The integrated memory circuits , made of
nanotube composites with conducting polymers,
have been found to be effective devices.
• Quantum wires
• The quantum wires, made of metallic carbon
nanotubes, are found to have electrical
conductivity.
31.
32.
33. SYNTHESIS OF CARBON
NANOTUBES
• Pyrolysis
• Carbon nanotube are synthesized by the pyrolysis of
hydrocarbons such as acetylene at about 700 C in the
presence of Fe- silica or Fe- graphite catalyst inert
conditions.
• Laser evaporation
• It involves vapourization of graphite target,
containing small amount of cobalt and nickel, by
exposing it to an intense pulsed laser beam at higher
temperature (1200 C) in a quartz tube reactor. An inert
gas such as argon is simultaneously allowed to pass into
the reactor to sweep the evaporated carbon atoms from
the furnace to the colder copper collector, on which they
condense as carbon nanotubes.
• .
34. • Carbon arc method
• It is carried out by applying direct
current (60-100A and 20-25 V) between
graphite electrodes of 10-20um diameter.
• Chemical vapour deposition
• It involves decomposition of vapour of
hydrocarbons such as methane,
acetylene, etc, at high temperatures
(1100C) in presence of metal nanoparticle
catalysts like nickel, cobalt, iron supported
on MgO or Al2O3. Carbon atoms produced
by the decomposition are condensed on a
cooler surface of the catalyst
