consists literature review, classification,synthesis methods, properties, advantages and limitations, applications,etc

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DEPARTMENT OF MECHANICAL ENGINEERING, AGMRCET, VARUR Page 1
CHAPTER 1
INTRODUCTION
This chapter provides a quick introduction about carbon nanotubes structures, and
production methods of carbon nanotubes and their applications in various fields.
Carbon nanotubes (CNTs) take the form of cylindrical carbon molecules and have
novel properties that make them potentially useful in a wide variety of applications in
nanotechnology, electronics, optics, and other fields of materials science. They exhibit
extraordinary strength and unique electrical properties, and are efficient conductors of
heat. Inorganic nanotubes have also been synthesized.
Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical
nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to
132,000,000:1, significantly larger than for any other material. These cylindrical carbon
molecules have unusual properties, which are valuable for nanotechnology, electronics,
optics and other fields of materials science and technology. In particular, owing to their
extraordinary thermal conductivity and mechanical and electrical properties, carbon
nanotubes find applications as additives to various structural materials. For instance,
nanotubes form a tiny portion of the material(s) in some (primarily carbon fibre) baseball
bats, golf clubs, or car parts.
Techniques have been developed to produce nanotubes, including arc discharge,
laser ablation and chemical vapour deposition (CVD). Most of these processes take place
in vacuum or with process gases. Nanotubes are members of the fullerene structural
family. Their name is derived from their long, hollow structure with the walls formed by
one-atom-thick sheets of carbon, called graphene. These sheets are rolled at specific and
discrete ("chiral") angles and the combination of the rolling angle and radius decides the
nanotube properties; for example, whether the individual nanotube shell is a metal or
semiconductor. Nanotubes are categorized as single-walled nanotubes (SWNTs) and
multi-walled nanotubes (MWNTs). Individual nanotubes naturally align themselves into
"ropes" held together by van der Waals forces, more specifically, pi-stacking.
Applied quantum chemistry, specifically, orbital hybridization best describes
chemical bonding in nanotubes. The chemical bonding of nanotubes is composed entirely
of sp2 bonds, similar to those of graphite. These bonds, which are stronger than the sp3
bonds found in alkanes and diamond, provide nanotubes with their unique strength.

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CHAPTER 2
LITERATURE SURVEY
This chapter includes the literature survey about the carbon nanotubes, and its
structure and synthesis of carbon nanotubes.
In 1985, a confluence of events led to an unexpected and unplanned experiment
with a new kind of microscope resulting in the discovery of a new molecule made purely
of carbon – the very element chemists felt there was nothing more to learn about. Bucky
balls – sixty carbon atoms arranged in a soccer ball shape – had been discovered and the
chemical world, not to mention the physical and material worlds, would never be the
same. 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 known as graphene. Carbon Nanotubes have many structures,
differing in length, thickness, and in the type of helicity and number of layers. Although
they are formed from essentially the same graphite sheet, their electrical characteristics
differ depending on these variations, acting either as metals or as semiconductors.
Elemental carbon in the sp2 hybridization can form a variety of amazing structures Apart
from the well-known graphite; carbon can build closed and open cages with honeycomb
atomic arrangement. The first such structure to be discovered was the C60 molecule by
Kroto et al 1985. Although various carbon cages were studied, it was only in 1991, when
Iijima observed for the first time tubular carbon structures. The Nanotubes consisted of up
to several tens of graphitic shells (so-called multi-walled carbon nanotubes (MWNT))
with adjacent shell separation of 0.34 nm, diameters of 1 nm and high length/diameter
ratio. As a group, Carbon Nanotubes typically have diameters ranging from <1 nm up to
50 nm. Their lengths are typically several microns, but recent advancements have made
the Nanotubes much longer, and measured in centimeters.
S.R. Ahmad, A. M. Keszler, L. Nemes, X. Fang, reported the case study of
multiwalled and single walled samples of CNT characterization by Raman spectroscopy
and microscopy. Raman spectroscopy had proved to be a powerful tool in understanding
of CNT, based on vibration and electronic properties of pure sp2 and sp3 hybridized
Carbon allotropes of graphite and diamond. The multiwall samples were prepared by
metal oxide catalyzed decomposition of acetylene at 1000 K. This yielded thick bundles
of multiwall tubes, which were purified to remove metal oxide and metal particles, but

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contained significant amounts of amorphous Carbon. The Raman spectra of CNTs
contained first-order and higher-order features attributed to the vibration excitation of
fundamental and composite excitations (overtone and combination tones respectively).
The Raman spectra of graphite sample taken with 514.5 nm argon ion laser light
was discussed and the slight dispersion of the Raman bands upon laser excitation energy
changes can be increased by using a broader range of excitation wavelengths.
.A. Chowdhury, V. Gupta, K. Sreenivas, R. Kumar, S. Mazumdar, P.K. Patanjali,
prepared MWCNT attached to NH2/ITO substrate which can be utilized as an effective
electrode. Ultrasonication of the sample leads to enhancement of MWCNT loading on the
ITO surface in a uniform manner. The paper reported the electrochemical activity of uric
acid on MWCNT composite. The presence of amino ion on the sample surface was
confirmed from XPS and Fourier transforms infra-red spectroscopy. It was found that the
amino-ion interacts with MWCNT in an electrostatic manner.

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CHAPTER 3
CONCEPT AND CLASSIFICATION OF CARBON
NANOTUBES
This chapter gives the information about concept, and all types of carbon
nanotubes.
3.1 Concept
Carbon comes from Latin word “carbo” which is delivered from a French word
“charbon”, meaning charcoal. It is fourth most abundant chemical element in the universe
by mass, after hydrogen, helium and oxygen.
Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical
nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to
132,000,000:1, significantly larger than for any other material. These cylindrical
nanotubes have unusual properties, which are valuable for nanotechnology, electronics,
optics and other fields of technology. In particular, owing to their extraordinary thermal
conductivity and mechanical and electrical properties, carbon nanotubes find applications
as additives to various structural materials. For instance, nanotubes form a tiny portion of
the material(s) in some (primarily carbon fibre) baseball bats, golf clubs, or car parts.
These carbon nanotubes are now used in the technology of solar panels to increase the
efficiency of the solar panels up to 80%. The discussion mentioned ahead will help in
understanding how these carbon nanotubes can be used in solar panels.
Nanotubes are member of the fullerene structural family. Their name is delivered
from their long, hollow structure with the walls formed by one-atom-thick sheets of
carbon, called graphite.
Applied Quantum chemistry, specifically, orbital hybridization best describes
chemical bonding in nanotubes. The chemical bonding of nanotubes involves entirely sp2-
hybrid carbon atoms. These bonds which are similar to those of graphite and stronger
than those found in alkanes and diamond, provide nanotubes with their unique strength.
3.2 Classificationofcarbon nanotubes
Carbon nanotubes are mainly classified into two types:-
1. Single-walled Nanotubes (SWNTs)
2. Multi-walled Nanotubes (MWNTs)

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3.2.1 Single-WalledNanotubes (SWNTs)
Most Single-Walled Nanotubes (SWNT) have a diameter of close to 1 nanometer,
with a tube length that can be many millions of times longer. The structure of a SWNT
can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene
into a seamless cylinder. The way the graphene sheet is wrapped is represented by a pair
of indices (n, m) called the chiral vector. The integer’s 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”, which is named for the pattern of hexagons as we move
on circumference of the tube. If n = m, the Nanotubes are called "armchair", which
describes one of the two confirmers of cyclohexene a hexagon of carbon atoms.
Otherwise, they are called "chiral", in which the m value lies between zigzag and
armchair structures. The word chiral means handedness and it indicates that the tubes may
twist in either direction. The fig 3.1 shows the single walled carbon nanotube structure.
Single-walled nanotubes are an important variety of carbon nanotube because they
exhibit electrical that are not shared by the multi-walled carbon nanotubes (MWNT)
variant.
Fig 3.1: Single-walled Carbon Nanotubes
3.2.2 Multi-Walled Nanotubes (MWNTs)
There are two models which can be used to describe the structures of multi-walled
nanotubes. In the Russian Doll model, sheets of graphite are arranged in concentric
cylinders, e.g. a single-walled nanotube (SWNT) within a larger single-walled nanotube.
In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a

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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 3.3
Å (330pm). The special place of double-walled carbon nanotubes (DWNT) must be
emphasized here because their morphology and properties are similar to SWNT but their
resistance to chemicals is significantly improved. This is especially important when
Functionalization is required (this means grafting of chemical functions at the surface of
the nanotubes) to add new properties to the CNT. In the case of SWNT, covalent
Functionalization will break some C=C double bonds, leaving "holes" in the structure on
the nanotube and thus modifying both its mechanical and electrical properties. In the case
of DWNT, only the outer wall is modified. DWNT synthesis on the gram scale was first
proposed in 2003 by the CVD technique, from the selective reduction of oxide solutions
in methane and hydrogen. The multi-walled carbon nanotube structure is shown in fig 3.2.
The telescopic motion ability of inner shells and their unique mechanical
properties will permit the use of multi-walled nanotubes as main movable arms in coming
Nano mechanical devices.
Fig 3.2: Multi-Walled Carbon Nanotubes
3.2.3 Nanotorus
A nanotorus is theoretically described as carbon nano tube bent into a torus
(doughnut shape). Nanotori are predicted to have many unique properties, such as
magnetic moments 1000 times larger than previously expected for certain specific radii.
Properties such as magnetic moment, thermal stability etc. varies widely depending on

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radius of the torus and radius of the tube. Nano-torus particles are promising in nano-
photonics applications. The fig 3.3 shows the nanotorus structure of the carbon nano
tubes.
Fig 3.3: Nanotorus structure
3.2.4 Nanobuds
Carbon Nanobuds are a newly created material combining two previously
discovered allotropes of carbon; carbon nanotubes and fullerenes. In this new material
fullerene-like "buds" are covalently bonded to the outer sidewalls of the underlying
carbon nanotube. This hybrid material has useful properties of both fullerenes and carbon
nanotubes. In particular, they have been found to be exceptionally good field emitters. In
composite materials, the attached fullerene molecules may function as molecular anchors
preventing slipping of the nanotubes, thus improving the composite‘s mechanical
properties. The nanobuds structure of carbon nano tubes is shown in the fig 3.4.
Fig 3.4: Nanobuds

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CHAPTER 4
SYNTHESIS OF CARBON NANOTUBES
Techniques have been developed to produce nanotubes, including arc discharge,
laser ablation and chemical vapor deposition (CVD). Most of these processes take place
in vacuum or with process gases. CVD growth of CNTs can take place in vacuum or at
atmospheric pressure. Large quantities of nanotubes can be synthesized by these methods;
advances in catalysis and continuous growth processes are making CNTs more
commercially viable.
SWNTs and MWNTs are usually made by carbon-arc discharge, laser ablation of
carbon, or chemical vapour deposition (typically on catalytic particle). Nanotube
diameters range from 0.4 to 3 nm for SWNTs and from 1.4 to at least 100 nm for
MWNTs. Nanotube properties can thus be tuned by changing the diameter.
Unfortunately, SWNTs are presently produced only on a small scale and are extremely
expensive. All currently known synthesis methods for SWNTs result in major
concentrations of impurities. These impurities are typically removed by acid treatment,
which introduces other impurities, can degrade nanotube length and perfection, and adds
to nanotube cost.
MWNTs produced catalytically by gas-phase pyrolysis, like the Hyperion
nanotubes, have high defect densities compared to those produced by the more expensive
carbon- arc process.
4.1 Plasma based synthesis methods:
The plasma based synthesis methods are explained as follow. This includes arc discharge
method and laser ablation method.
4.1.1 Arc discharge method
The nanotubes were initially discovered using this technique; it has been the most
widely-used method of carbon nanotubes.
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 vaporize, 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

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hydrocarbon, over a catalyst. The catalyst consists of nano-sized particles of metal,
usually Fe, Co or Ni. These particles catalyze the breakdown of the gaseous molecules
into carbon, and a tube then begins to grow with a metal particle at the tip. In 1991, Iijima
reported the preparation of a new type of finite carbon structures consisting of needle-like
tubes. The tubes were produced using an arc discharge evaporation method similar to that
used for the fullerene synthesis. The carbon needles, ranging from 4 to 30 nm in diameter
and up to 1 mm in length, were grown on the negative end of the carbon electrode used
for the direct current (dc) arc-discharge evaporation of carbon in an argon-filled vessel
(100 Torr). The perfection of carbon nanotubes produced in this way has generally been
poorer than those made by arc-evaporation, but great improvements in the technique have
been made in recent years. The big advantage of catalytic synthesis over arc-evaporation
is that it can be scaled up for volume production. The third important method for making
carbon nanotubes involves using a powerful laser to vaporize a metal-graphite target. This
can be used to produce single-walled tubes with high yield. Ebbesen and Ajayan in1992
reported large-scale synthesis of MWNT by a variant of the standard arc discharge
technique. It was shown in 1996 that single-walled nanotubes can also be produced
catalytically. The schematic representation of arc discharge method is shown in fig 4.1.
Fig 4.1: Arc discharge method

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4.1.2 Laser ablation method
First large-scale (gram quantities) production of SWNTs was achieved in 1996 by
the Smalley‘s group at Rice University. A pulsed or continuous laser is used to vaporize a
1.2 % of cobalt/nickel with 98.8 % of graphite composite target that is placed in a 1200°C
quartz tube furnace with an inert atmosphere of ~500 Torr of Ar or He. Nanometer-size
metal catalyst particles are formed in the plume of vaporized graphite. The metal particles
catalyze the growth of SWNTs in the plasma plume, but many by-products are formed at
the same time. As the vaporized species cool, small carbon molecules and atoms quickly
condense to form larger clusters, possibly including fullerenes. The catalysts also begin to
condense, but more slowly at first, and attach to carbon clusters and prevent their closing
into cage structures. Catalysts may even open cage structures when they attach to them.
From these initial clusters, tubular molecules grow into single-wall carbon nanotubes
until the catalyst particles become too large, or until conditions have cooled sufficiently
that carbon no longer can diffuse through or over the surface of the catalyst particles. It is
also possible that the particles become that much coated with a carbon layer that they
cannot absorb more and the nanotube stops growing. The fig 4.2 shows the diagrammatic
view of laser ablation method of carbon nanotubes.
Fig 4.2: Laser ablation method
The SWNTs formed in this case are bundled together by van der waals forces. The
nanotubes and by-products are collected via condensation on a cold finger downstream
from the target. In principle, arc discharge and laser ablation are similar methods, as both
use a metal-impregnated graphite target (anode) to produce SWNTs, and both produce
MWNT and fullerenes when pure graphite is used instead. However, the length of
MWNT produced through laser ablation is much shorter than that produced by arc

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discharge method. Therefore, this method does not seem adequate for the synthesis of
MWNT. The diameter distribution of SWNTs made by this method is roughly between
1.0 and 1.6 nm. Because of the good quality of nanotubes produced by this method,
scientists are trying to scale up laser ablation. However, the results are not yet as good as
for the arc-discharge method, but they are still promising. Two new developments in this
field are ultra fast Pulses from a free electron laser method the continuous wave laser-
powder method.
4.2 Thermal synthesis methods:
Arc discharge and laser ablation methods are fundamentally plasma based
synthesis. However, in thermal synthesis, only thermal energy is relied and the hot zone
of reaction never goes beyond 12000C, including the case of plasma enhanced CVD. In
almost all cases, in presence of active catalytic species such as Fe, Ni, and Co, carbon
feedstock produces CNTs. Depending on the carbon feedstock; Mo and Ru are sometimes
added as promoters to render the feedstock more active for the formation of CNTs. In
fact, thermal synthesis is a more generic term to represent various chemical vapor
deposition methods. It includes Chemical Vapor Deposition processes, Carbon monoxide
synthesis processes and flame synthesis.
4.2.1 ChemicalVapourDeposition(CVD) Method:
While the arc discharge method is capable of producing large quantities of
unpurified nanotubes, significant effort is being directed towards production processes
that offer more controllable routes to the nanotube synthesis. A class of processes that
seems to offer the best chance to obtain a controllable process for the selective production
of nanotubes with predefined properties is chemical vapour deposition (CVD). In
principle, chemical vapour deposition is the catalytic decomposition of hydrocarbon or
carbon monoxide feedstock with the aid of supported transition metal catalysts. it is
carried out in two step process:-
● Catalyst is deposited on substrate and then nucleation of catalyst is carried via
chemical etching or thermal annealing. Ammonia is used as an etchant. Metal
catalysts used are Ni, Fe or Co.
● Carbon source is then placed in gas phase in reaction chamber. Then carbon
molecule is converted to atomic level by using energy source like plasma or
heated coil. This carbon will get diffused towards substrate, which is coated with
catalyst and Nanotubes grow over this metal catalyst. Carbon source used is

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methane, carbon monoxide or acetylene. Temperature used for synthesis of
nanotube is 650 – 9000 C range. The typical yield is 30%.
Using CVD method, several structural forms of carbon are formed such as amorphous
carbon layers on the surface of the catalyst, filaments of amorphous carbon, graphite
layers covering metal particles, SWNTs and MWNTs made from well-crystallized
graphite layers. The general nanotube growth mechanism in the CVD process involves
the dissociation of hydrocarbon molecules catalyzed by the transition metal, and the
saturation of carbon atoms in the metal nanoparticle. The precipitation of carbon from the
metal particle leads to the formation of tubular carbon solids in a sp2 structure.
Fig 4.3: Chemical vapour deposition method
The characteristics of the carbon nanotubes produced by CVD method depend on
the working conditions such as the temperature and the operation pressure, the kind,
volume and concentration of hydrocarbon, the nature, size and the pre-treatment of
metallic catalyst, the nature of the support and the reaction time. The fig shows the
schematic representation of chemical vapour deposition method.
4.3 The hydrothermal methods:
Sonochemical/hydrothermal technique is another synthesis method which is
successful for the preparation of different carbonaceous nanoarchitectures such as nano-
onions, nanorods, nanowires, nanobelts, MWNTs. This process has many advantages in
comparison with other methods
i ) the starting materials are easy to obtain and are stable in ambient temperature
ii) It is low temperature process (about 150–180 °C);
iii) There is no hydrocarbon or carrier gas necessary for the operation.
MWNTs were produced by hydrothermal processing where a mixture of polyethylene
and water with a Ni catalyst is heated from 700 to 800 °C under 60–100 MPa pressure.
Both closed and open end multiwall carbon nanotubes with the wall thickness from

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several to more than 100 carbon layers were produced. An important feature of
hydrothermal nanotubes is the small wall thickness and large inner core diameter, 20–800
nm. Graphitic carbon nanotubes were synthesized by the same research group using
ethylene glycol (C2H4O2) solution in the presence of Ni catalyst at 730–800 °C under 60–
100 MPa pressure. TEM analysis shows that these carbon nanotubes have long and wide
internal channels and Ni inclusions in the tips. Typically, hydrothermal nanotubes have
wall thickness 7–25 nm and outer diameter of 50–150 nm. Thin-wall carbon tubes with
internal diameters from 10–1000 nm have been also produced. During growth of a tube,
the synthesis fluid, which is a supercritical mixture of CO, CO2, H2O, H2, and CH4 enters
the tube. Manafietal have prepared large quantity of carbon nanotubes using
sonochemical/hydrothermal method. 5 mol/l NaOH aqueous solutions of
dichloromethane, CCl2 and metallic Li was used as starting materials. The hydrothermal
synthesis was conducted at 150–160 °C for 24 h. The nanotubes produced in this way
were about 60 nm in diameter and 2–5 μm long. Uniformly distributed catalyst
nanoparticles were observed by SEM analysis as a result of the ultrasonic pre-treatment
of the starting solution. Multiwall carbon nanocells and multiwall carbon nanotubes have
been artificially grown in hydrothermal fluids from amorphous carbon, at temperatures
below 800 °C, in the absence of metal catalysts. Carbon nanocells were formed by
interconnecting multiwalls of graphitic carbon at 600 °C. The bulk made of connected
hollow spherical cells appears macroscopically as disordered carbon. The nanocells have
diameters smaller than 100 nm, with outer diameters ranging from 15 to 100 nm, and
internal cavities with diameters from 10 to 80 nm. The nanotubes observed in the sample
have diameters in the range of tens and length in the range of hundreds of nanometers.

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CHAPTER 5
PROPERTIES OF CARBON NANOTUBES
The followings are the several physical and chemical properties of the carbon
nanotubes as obtained from the literature review.
5.1 Strength:
● Carbon nanotubes are the strongest, flexible and stiffest materials yet discovered
in terms of tensile strength and elastic modulus respectively.
● This strength results from the covalent sp2 bonds formed between the individual
carbon atoms (which is stronger than the sp3 bonds found in Diamond &
Alkenes).
● CNTs are not nearly as strong under compression. Because of their hollow
structure and high aspect ratio, they tend to undergo buckling when placed under
compressive, torsional or bending stress.
5.2 Hardness:
● The hardness (152 GPa) and bulk modulus (462–546) of carbon nanotubes are
greater than diamond, which is considered the hardest material. (: that of diamond
is 150GPa & 420GPa).
5.3 Kinetic property:
● Multi-walled nanotubes, multiple concentric nanotubes precisely nested within
one another; exhibit a striking telescoping property whereby an inner nanotube
core may slide, almost without friction, within its outer nanotube shell thus
creating an atomically perfect linear or rotational bearing, the precise positioning
of atoms to create useful machines.
5.4 Electrical properties:
● Because of the symmetry and unique electronic structure of graphene, the
structure of a nanotube strongly affects its electrical properties. It is having very
high current carrying capacity.
5.5 Electromagnetic wave absorption:
● Current military push for radar absorbing materials (RAM) to better the stealth
characteristics of aircraft and other military vehicles. (There has been some
research on filling MWCNTs with metals, such as Fe, Ni, Co, etc., to increase the
absorption effectiveness of MWNTs in the microwave regime).

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5.6 Thermal properties:
● All nanotubes are expected to be very good thermal conductors along the tube, but
good insulators laterally to the tube axis. (Measurements show that a SWNT has a
room-temperature thermal conductivity along its axis of about 3500 W/mK
compares this to copper, a metal well known for its good thermal conductivity,
which transmits 385 W/mK.).

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CHAPTER 6
ADVANTAGES AND DISADVANTAGES OF
CARBON NANOTUBES
6.1 Advantages:
1. Extremely small and lightweight.
2. Resources required to produce them are plentiful, and many can be made with only a
small amount of material.
3. Are resistant to temperature changes, meaning they function almost just as well in
extreme cold as they do in extreme heat.
4. Improves conductive, mechanical, and flame barrier properties of plastics and
composites.
5. Enables clean, bulk micromachining and assembly of components.
6. Improves conductive, mechanical, and flame barrier properties of plastics and
composites.
6.2 Disadvantages:
1. Despite all the research, scientists still don't understand exactly how they work.
2. Extremely small, so are difficult to work with.
3. Currently, the process is relatively expensive to produce the nanotubes.
4. Would be expensive to implement this new technology in and replace the older
technology in all the places that we could.

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CHAPTER 7
APPLICATIONS OF CARBON NANO TUBES
7.1 Structural:
● CNT can produce water proof and tear resistant fabrics.
● CNT fibres are used as combat jackets to provide protection from bullets.
● Golf balls, golf club, stronger and lighter tennis rackets, bicycle parts and base
ball parts make use of CNT in manufacturing.
● The high strength to weight ratio of CNT enables very high rotational speeds.
● Many engineering problems, such as making long span bridges and light weight
vehicles could potentially be solved by the use of these CNTs.
7.2 Electrical applications:
● Wires for carrying electrical current may be fabricated from pure nanotubes and
nanotube-polymer composites. It has already been demonstrated that carbon
nanotube wires can successfully be used for power or data transmission.
● Recently small wires have been fabricated with specific conductivity exceeding
copper and aluminium; these cables are the highest conductivity carbon nanotube
and also highest conductivity non-metal cables.
● CNTs are used as heat sink for chipboards and backlight for LCD screens.
● CNTs can be used as alternative to tungsten filaments in incandescent bulbs.
7.3 Filters:
● CNTs are one of the best materials for the air filtration and can aid in water
filtration too. They detect the pollutants in air by changing their conductivity and
in water filtration, only water molecules are allowed to pass and hence reducing
the cost of distillation by 75%.
7.4 Sensors and actuators:
● CNT based sensors can detect temperature, air pressure, chemical gases,
molecular pressure, strain by operating based on the generation of current and
voltage.
● Oscillators based on CNTs have achieved higher speeds than any other
technologies (<50GHz) operating on the basis of low friction and low wear
bearing of multi walled CNT.

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7.5 Solar cells:
● One of the promising applications of single-walled carbon nanotubes (SWNTs) is
their use in solar panels, due to their strong UV absorption characteristics.
Research has shown that they can provide a sizable increase in efficiency, even at
their current un-optimized state.
7.6 Medical field:
● CNTs due to their unique cylindrical structure and properties are used as carrier
for genes (gene therapy) and drugs to treat cancer and genetic disorder. It is also
used in DNA analysis.
● CNTs filled with calcium and arranged in the structure of bone can act as a bone
substitute.
● Nano size robots and motors with CNTs can be used in studying cells and
biological systems which also reduces the labour cost and maintenance cost as
well.
7.7 Hydrogen storage:
● In addition to being able to store electrical energy, there has been some research in
using carbon nanotubes to store hydrogen to be used as a fuel source. By taking
advantage of the capillary effects of the small carbon nanotubes, it is possible to
condense gases in high density inside single-walled nanotubes. This allows for
gases, most notably hydrogen (H2), to be stored at high densities without being
condensed into a liquid. Potentially, this storage method could be used on vehicles
in place of gas fuel tanks for a hydrogen-powered car.

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CONCLUSION
Nanotubes appear destined to open up a host of new practical applications and
help improve our understanding of basic physics at the nonmetric scale. Nanotechnology
is predicted to spark a series of industrial revolutions in the next two decades that will
transform our lives to a far greater extent than silicon microelectronics did in the 20th
century.
Carbon nanotubes could play a pivotal role in this upcoming revolution if their
remarkable structural, electrical and mechanical properties can be exploited. The
remarkable properties of carbon nanotubes may allow them to play a crucial role in the
relentless drive towards miniaturization scale. Lack of commercially feasible synthesis
and purification methods is the main reason that carbon nanotubes are still not widely
used nowadays. At the moment, nanotubes are too expensive and cannot be produced
selectively. Some of the already known and upcoming techniques look promising for
economically feasible production of purified carbon nanotubes.
The properties and characteristics of Carbon Nanotubes are still being researched
heavily and scientists have barely begun to tap the potential of these structures. Among
the various methods of nanotube production the Chemical Vapour Deposition method
clearly emerges as the best one for large scale production of Multi Wall Nanotubes.
However, the production of Single Wall Nanotubes is still in the gram scale and the
helical carbon nanotubes are only obtained together with linear Carbon nanotubes.
Some future applications of carbon nanotubes look very promising. All we need
are better production technique for large amounts of purified nanotubes that have to be
found in the near future. Nanotube promises to open up a way to new applications that
might be cheaper, lower in weight and have a better efficiency.

20. Carbon Nanotubes
DEPARTMENT OF MECHANICAL ENGINEERING, AGMRCET, VARUR Page 20
REFERENCES
1. Carbon Nanotubes: A Review on Synthesis, Properties and Applications by
Kalpna Varshney, International Journal of Engineering Research and General
Science Volume 2, Issue 4, June-July, 2014.
2. Chemical Vapor Deposition of Carbon Nanotubes: A Review on Growth
Mechanism and Mass Production by Mukul Kumar and Yoshinori Ando,
Journal of Nanoscience and Nanotechnology Vol. 10, 3739–3758, 2010.
3. Production of Carbon Nanotubes by Different Routes-A Review by
Muhammad Musaddique Ali Rafique, Javed Iqbal, Journal of Encapsulation and
Adsorption Sciences, 2011, 1, 29-34.
4. Nano: The Essentials a Text book by T. Pradeep, Tata McGraw Hill Education.
5. Carbon Nanotubes Manufacturing and Applications – A WTEC
International Study by Pulickel M. Ajayan.
6. Images:google.co.in/images.