Carbon Nanotubes Seminar Report

CARBON NANOTUBES Seminar Report 2012-13

ACKNOWLEDGEMENT

I express my sincere gratitude to Mr. Sojan P Antony, Lecturer in mechanical

Engineering, on this occasion for his suggestion of this topic and presentation of this

Seminar.

I also take this opportunity to express my sincere thanks to Mr. Jayachandran,

Head of Department, Mr. M V Revi and Mr. P.P Devdas for their valuable advice and

guidance in completion this seminar in pristine form.

At this juncture, I gratefully remember the moral support and co-operation

extended by my classmates on this seminar presentation. Their active participation

really brought life to my seminar.

My sincere thanks to one and all

SREESANGH P. GHOSH

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Dept. of Mechanical Engg. S.R.G.P.T.C Triprayar


ABSTRACT

Nanotechnology is a field of applied science and technology covering a broad
range of topics. The main unifying theme is the control of matter on a scale smaller than
1 micrometer, as well as the fabrication of devices on this same length scale. It is a
highly multidisciplinary field, drawing from fields such as colloidal science, device
physics, and supramolecular chemistry. Much speculation exists as to what new science
and technology might result from these lines of research.

Nanotechnology and Nano science got started in the early 1980s with two major
developments; the birth of cluster science and the invention of the scanning tunneling
microscope(STM). This development leads to the discovery of fullerenes in 1985 and
carbon nanotubes a few years later. Carbon nanotubes (CNTs) are a recently discovered
allotrope of carbon. Carbon nanotubes have recently received extensive attention due to
their Nano scale dimensions and outstanding materials properties.

Since their discovery in 1991 by a Japanese scientist Sumio Iijima, Carbon
Nanotubes have been of great interest, both from a fundamental point of view and for
future applications. The most eye- catching features of these structures are their
electronic, mechanical, optical & chemical characteristics, which open a way to future
applications.

The above characteristics have generated strong interest in their possible use in
Nano-electronic and Nano-mechanical devices. They possess unusual properties,
valuable for nanotechnology, electronics, optics, Mechanical Engg. And other fields of
material science & Technology.

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CONTENTS

TOPIC NO. TOPIC NAME PAGE-NO.

1. INTRODUCTION 4

2. HISTORY 5

3. DISCOVERY 6

4. CLASSIFICATION OF CARBON NANOTUBES 7

5. SYNTHESIS OF CARBON NANOTUBES 12

6. MILESTONES IN CNT EVOLUTION 17

7. PROPERTIES OF CNT’S 18

8. ADVANTAGES 20

9. DISADVANTAGES 20

10. APPLICATIONS 21

11. CHALLENGES 22

12. CONCLUSION 23

13. REFRENCES 24

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1. INTRODUCTION

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.

Manufacturing a nanotube is dependent on applied quantum chemistry,
specifically, orbital hybridization. Nanotubes are composed entirely of sp2
bonds, similar to those of graphite. This bonding structure, stronger than the sp3
bonds found in diamond, provides the molecules with their unique strength.
Nanotubes naturally align themselves into "ropes" held together by Van der
Waals forces. Under high pressure, nanotubes can merge together, trading some
sp2 bonds for sp3 bonds, giving great possibility for producing strong,
unlimited-length wires through high-pressure nanotube linking.

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 fiber) baseball bats, golf
clubs, or car parts.

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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2. HISTORY

In 1952 L. V. Radushkevich and V. M. Lukyanovich published clear
images of 50 nanometer diameter tubes made of carbon in the Soviet Journal of
Physical Chemistry. This discovery was largely unnoticed, as the article was
published in the Russian language, and Western scientists' access to Soviet press
was limited during the Cold War. It is likely that carbon nanotubes were
produced before this date, but the invention of the transmission electron
microscope (TEM) allowed direct visualization of these structures.
Carbon nanotubes have been produced and observed under a variety of
conditions prior to 1991. A paper by Oberlin, Endo, and Koyama published in
1976 clearly showed hollow carbon fibers with nanometer-scale diameters using
a vapor-growth technique. Additionally, the authors show a TEM image of a
nanotube consisting of a single wall of graphene. Later, Endo has referred to this
image as a single-walled nanotube.
In 1979, John Abrahamson presented evidence of carbon nanotubes at
the 14th Biennial Conference of Carbon at Pennsylvania State University. The
conference paper described carbon nanotubes as carbon fibers that were
produced on carbon anodes during arc discharge. A characterization of these
fibers was given as well as hypotheses for their growth in a nitrogen atmosphere
at low pressures.
In 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. Using TEM images
and XRD patterns, the authors suggested that their “carbon multi-layer tubular
crystals” were formed by rolling graphene layers into cylinders. They speculated
that by rolling graphene layers into a cylinder, many different arrangements of
graphene hexagonal nets are possible. They suggested two possibilities of such
arrangements: circular arrangement (armchair nanotube) and a spiral, helical
arrangement (chiral tube).
In 1987, Howard G. Tennett of Hyperion Catalysis was issued a U.S.
patent for the production of "cylindrical discrete carbon fibrils with a "constant
diameter between about 3.5 and about 70 nanometers..., length 102 times the
diameter, and an outer region of multiple essentially continuous layers of
ordered carbon atoms and a distinct inner core.

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3. DISCOVERY

They were discovered In 1991 by the Japanese electron microscopist
SUMIO IIJIMA NEC Laboratory in Tsukuba-- used high-resolution transmission
electron microscopy to observe carbon nanotubes, And into the awareness of the
scientific community. Iijima's discovery of multi-walled carbon nanotubes in the
insoluble material of arc-burned graphite rods in 1991 and Mintmire, Dunlap, and
White's independent prediction that if single-walled carbon nanotubes could be
made, then they would exhibit remarkable conducting properties helped create the
initial buzz that is now associated with carbon nanotubes. Nanotube research
accelerated greatly following
the independent discoveries by
Bethune at IBM and Iijima at
NEC of single-walled carbon
nanotubes and methods to
specifically produce them by
adding transition-metal catalysts
to the carbon in an arc
discharge. The arc discharge
technique was well-known to
produce the famed Buckminster
fullerene on a preparative scale,
and these results appeared to
extend the run of accidental
discoveries relating to
fullerenes. The original
observation of fullerenes in
mass spectrometry was not
anticipated, and the first mass-
production technique by
Krätschmer and Huffman was
used for several years before
realizing that it produced
fullerenes.

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4. CLASSIFICATION OF CARBON NANOTUBES

Carbon nanotubes are mainly classified into two :-

 Single-walled Nanotubes (SWNTS);

 Multi-walled Nanotubes (MWNTS).

4.1 SINGLE-WALLED NANOTUBES (SWNTS)

• A single-walled carbon nanotube (SWNT) may be thought of as a single atomic
layer thick sheet of graphite (called graphene) rolled into a seamless cylinder.

• Most single-walled nanotubes (SWNT) have a diameter of close to 1 nanometre,
with a tube length that can be many millions of times longer.

• Single-walled nanotubes are an important variety of carbon nanotube because
they exhibit electric properties that are not shared by the multi-walled carbon
nanotube (MWNT) variants.

Single walled CNTS
(Graphical Representation)

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4.1.1 ROLLING OF GRAPHENE SHEET INTO CNT’S

 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 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".

Rolling angle of Graphene Sheet

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4.2 MULTI-WALLED NANOTUBES (MWNT)

 Multi-walled nanotubes (MWNT) consist of multiple rolled layers (concentric
tubes) of graphite.
 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.
 In the Parchment model, a single sheet of graphite is rolled in around itself,
resembling a scroll of parchment or a rolled newspaper.(The Russian Doll
structure is observed more commonly).
 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.

MULTI-WALLED CNTS

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4.3 OTHER CARBON NANOTUBE STRUCTURES

 Torus :-

carbon nanotube 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. vary widely depending on radius of the torus and
radius of the tube.

 Nanobud :-

Carbon Nanobud 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. They 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.

NORMAL NANOBUDS 

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 GRAPHENATED CARBON NANOTUBES (G-CNTS) :-

Graphenated CNTs are a relatively new hybrid that combines graphitic foliates grown
along the sidewalls of multi walled or bamboo style CNTs use in super capacitor
applications.

 PEAPOD :-

A Carbon peapod] is a novel hybrid carbon material which traps fullerene inside a
carbon nanotube.

 CUP-STACKED CARBON NANOTUBES :-

CSCNTs exhibit semiconducting behaviors due to the stacking microstructure of
graphene layers.

 NITROGEN DOPED CARBON NANOTUBES :-

N-doping provides defects in the walls of CNT's allowing for Li ions to diffuse into
inter-wall space. It also increases capacity by providing more favorable bind of N-doped
sites. N-CNT's are also much more reactive to metal oxide nanoparticle deposition
which can further enhance storage capacity, especially in anode materials for Li-ion
batteries. However Boron doped nanotubes have been shown to make batteries with
triple capacity.

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5. SYNTHESIS OF CARBON NANOTUBES :-

Techniques have been developed to produce nanotubes in sizeable quantities, including
arc discharge, laser ablation, high pressure carbon monoxide (HiPco), 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 vapor 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.

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5.1 ARC DISCHARGE METHOD :-

CNT production requires 3 elements,

 Carbon feed
 Metal catalyst
 Heat

The nanotubes were initially discovered using this technique; it has been the most
widely-used method of nanotube synthesis.

1. Two Graphite electrodes placed in an inert Helium atmosphere.
2. When DC current is passed anode is consumed and material forms on cathode.
3. For SWNT mixed metal catalyst is inserted into anode
4. Pure iron catalyst + Hydrogen-inert gas mixture gives 20 to 30cm long tube.

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5.2 LASER ABLATION :-

 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 vapor deposition.

Page 14


5.3 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.

Page 15


COMPARISON OF DIFFERENT SYNTHESIS METHODS OF
CNT’S

ARC DISCHARGE CHEMICAL VAPOR LASER ABLATION
METHOD DEPOSITION (VAPORIZATION)

Connect two graphite
rods to a power supply,
Place substrate in oven, Blast graphite with intense

place them millimeters
heat to 600 C, and slowly laser pulses; use the laser

apart, and throw switch.
add a carbon-bearing gas pulses rather than

At 100 amps, carbon
such as methane. As gas electricity to generate

vaporizes in a hot plasma.
decomposes it frees up carbon gas from which the
carbon atoms, which NTS form; try various
recombine in the form of conditions until hit on one
NTS that produces prodigious
amounts of SWNTS

Can produce SWNT and
MWNTs with few
Easiest to scale to industrial Primarily SWNTS, with a

structural defects
production; long length large diameter range that
can be controlled by
varying the reaction

Tubes tend to be short
temperature

with random sizes and
NTS are usually MWNTS By far the most costly,

directions
and often riddled with because requires expensive
defects lasers

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6. MILESTONES IN CNT EVOLUTION

The observation of the longest carbon nanotubes (18.5 cm long) was reported in
2009. These nanotubes were grown on Si substrates using an improved chemical vapor
deposition (CVD) method and represent electrically uniform arrays of single-walled
carbon nanotubes.

The shortest carbon nanotube is the organic compound cycloparaphenylene,
which was synthesized in early 2009.

The thinnest carbon nanotube is armchair (2,2) CNT with a diameter of 3 Å.
This nanotube was grown inside a multi-walled carbon nanotube. Assigning of carbon
nanotube type was done by combination of high-resolution transmission electron
microscopy (HRTEM), Raman spectroscopy and density functional theory (DFT)
calculations.

The thinnest freestanding single-walled carbon nanotube is about 4.3 Å in
diameter. Researchers suggested that it can be either (5,1) or (4,2) SWCNT, but exact
type of carbon nanotube remains questionable. (3,3), (4,3) and (5,1) carbon nanotubes
(all about 4 Å in diameter) were unambiguously identified using more precise
aberration-corrected high-resolution transmission electron microscopy. However, they
were found inside of double-walled carbon nanotubes.

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7. PROPERTIES OF CARBON NANOTUBES

 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.

 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).

 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.

 Electrical Properties:-

 Because of the symmetry and unique electronic structure of graphene,
the structure of a nanotube strongly affects its electrical properties.-
Very high current carrying capacity.

 Thermal Conductivity :-

 All nanotubes are expected to be very good thermal conductors along
the tube.( Measurements show that a SWNT has a room-temperature
thermal conductivity more than copper.)

Page 18


 Optical properties:-

 EM 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 MWNTs with metals, such as Fe, Ni, Co, etc., to increase the
absorption effectiveness of MWNTs in the microwave regime).

 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·m−1·K−1;] compare this to copper, a metal well known for its good thermal
conductivity, which transmits 385 W·m−1·K−1.).

COMPARISON OF MECHANICAL PROPERTIES

Material Young's Tensile Elongation
Modulus Strength At Break
(Tpa) (Gpa) (%)

SWNT ~1 (from 13–53 16
1 to 5)

Chiral 0.92 ----------- ---------------
SWNT

MWNT 0.27-0.8- 11-63- ---------------
-0.95 150

Stainless 0.186- 0.38- 15-50
steel 0.214 1.55

Kevlar– 0.06- 3.6-3.8 ~2
29&149 0.18

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 DEFECTS :-

 Toxicity:-

 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 fibrotic reactions.

 Crystallographic defect:-

 As with any material, the existence of a crystallographic defect affects the
material properties. Defects can occur in the form of atomic vacancies.

8. 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.

9. DISADVANTAGES

 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.

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10. 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
 Nano electronics
 Doping
 Nano balance
 Nano tweezers
 Data storage
 Magnetic nanotube
 Nano gear
 Space Elevator
 Nanotube actuator
 Molecular Quantum wires
 Hydrogen Storage
 Noble radioactive gas storage
 Solar storage
 Waste recycling
 Electromagnetic shielding
 Dialysis Filters
 Thermal protection
 Nanotube reinforced composites
 Reinforcement of armor and other materials
 Reinforcement of polymer
 Avionics
 Collision-protection materials
 Fly wheels

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11. CHALLENGES

The greatness of a single-walled nanotube is that it is a macro-molecule
and a crystal at the same time. The dimensions correspond to extensions of
fullerene molecules and the structure can be reduced to a unit-cell picture, as in
the case of perfect crystals. A new predictable (in terms of atomic structure–
property relations) carbon fiber was born. The last decade of research has shown
that indeed the physical properties of nanotubes are remarkable, as elaborated in
the various chapters of this book. A carbon nanotube is an extremely versatile
material: it is one of the strongest materials, yet highly elastic, highly
conducting, small in size, but stable, and quite robust in most chemically harsh
environments. It is hard to think of another material that can compete with
nanotubes in versatility.

There are also general challenges that face the development of nanotubes
into functional devices and structures. First of all, the growth mechanism of
nanotubes, similar to that of fullerenes, has remained a mystery .With this
handicap; it is not really possible yet to grow these structures in a controlled
way. Especially for electronic applications, which rely on the electronic
structure of nanotubes, this inability to select the size and helicity of nanotubes
during growth remains a drawback. More so, many predictions of device
applicability are based on joining Nano-tubes via the incorporation of
topological defects in their lattices. There is no controllable way, as of yet, of
making connections between nanotubes. Some recent reports, however, suggest
the possibility of constructing these interconnected Structures by electron
irradiation and by template mediated growth and manipulation.

For bulk applications, such as fillers in composites, where the atomic
structure (helicity) has a much smaller impact on the resulting properties, the
quantities of nanotubes that can be manufactured still falls far short of what
industry would need. There are no available techniques that can produce
nanotubes of reasonable purity and quality in kilogram quantities. The industry
would need tonnage quantities of nanotubes for such applications.

Another challenge is in the manipulation of nanotubes. Nano-technology is
in its infancy and the revolution that is unfolding in this .eld relies strongly on the
ability to manipulate structures at the atomic scale. This will remain a major
challenge in this field, among several others.

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12.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.

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.

Page 23


REFERENCE

 http://www.pa.msu.edu/cmp/csc/ntproperties

 http://en.wikipedia.org/wiki/Nanotubes

 http://www.rdg.ac.uk/%7Escsharip/tubes.htm

 www.sciencedaily.com

 www.academicpress.com/inscight/cnt

 How Stuff Works – www.howstuffworks.com

 www.edufive.com

 www.fadooengineers.com

 www.edufive.com/seminartopics.html

 www.pcmag.com/encyclopedia

 http://images.google.co.in/images

 http://www.termpapersmonthly.com

 http://www.megaessays.com/essay_search/ CNT

 http://www.scribd.com/doc/7393272/ CNT

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Carbon Nanotubes Seminar Report

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