carbon nanotubes _ ashish singla

8/7/2019 Carbon Nanotubes _ Ashish Singla

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Material TechnologyCarbon Nanotube

CARBON NANOTUBE

Carbon nanotubes are fullerene-related structures which consist of graphene cylinders closed at

either end with caps containing pentagonal rings. Nanotubes come in a variety of flavors: long,

short, single-walled, multi-walled, and open, closed, with different types of spiral structure, etc.

Each type has specific production costs and applications.

Discovery

In 1970, Morinobu Endo prepared the first carbon filament of nanometer dimensions.

In 1985, Richard E. Smalley discovered the buckyball (C60) and other fullerenes.

In 1991, Japanese electron microscopist Sumio Iijima who was studying the material

deposited on the cathode during the arc-evaporation synthesis of fullerenes. He found

that the central core of the cathodic deposit contained a variety of closed graphitic structures

including nanoparticles and nanotubes.

In 1993, Iijima's group and Donald Bethune independently discovered the simplest kind

of carbon nanotubes which is called Single-walled carbon nanotubes.

In 2000, the smallest CNTs was discovered by Lu-Chang Qin, Xinluo Zhao, Kaori Hirahara,

Yoshiyuki Miyamoto, Yoshinori Ando,Sumio Iijima

Introduction Of Carbon Nanotube

Carbon nanotubes (CNTs) also known as buckytubes. CNT are allotropes of carbon with a

cylindrical nanostructure. Nanotubes have been constructed with length to diameter ratio of up to

132,000,000:1, which is significantly larger than any other material. These cylindrical carbon

molecules have novel properties which make them potentially useful in many applications in

nanotechnology, electronics, optics, and other fields ofscience, as well as potential uses in

architectural fields. They exhibit extraordinary strength and unique electrical properties, and are

UNIVERSITY COLLEGE OF ENGINEERING PATIALA1
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efficient conductors. This is a nanoscopic structure made of carbon atoms in the shape of a

hollow cylinder. The cylinders are typically closed at their ends by semi-fullerene-like structures.

Nanotubes are members of the fullerene structural family, which also includes the spherical

buckyballs. The ends of a nanotube may be capped with a hemisphere of the buckyball structure.

Their name is derived from their size, since the diameter of a nanotube is on the order of a few

nanometers (approximately 1/50,000th of the width of a human hair), while they can be up to 18

centimeters in length.Nanotubes are categorized as single-walled nanotubes (SWNTs) and multi-

walled nanotubes (MWNTs).

Molecular And Supramolecular Structure

Nanotubes form different types, which can be described by the chiral vector (n, m), where n and

m are integers of the vector equation R = na1 + ma2.

Fig. 1 Structure

1. The nanotube is unraveled into a Graphene sheet. Draw two lines (the blue lines) along the

tube axis where the separation takes place.

2. Pick an atom (A) on a blue line.

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3. Draw the Armchair line (the thin yellow line), which travels across each hexagon, separating

them into two equal halves.

4. Find a point along the other tube axis that intersects a carbon atom nearest to the Armchair

line (point B). Connect A and B with chiral vector, R (red arrow).

5. The wrapping angle is formed between R and the Armchair line. a1 lines along the zigzag line.

a2 is reflection of a1 about armchair vector.

When added together, they equal the chiral vector R. (R = na1 + ma2)

Cases:

(a) If R lies along the Armchair line (=0), then it is called an "Armchair" nanotube.

(b) If =30, then the tube is of the "zigzag" type.

(c) If 0<


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There are three types of carbon nanotubes:

1. Armchair nanotube

2. Zig-Zag nanotube

3. Chiral (helical) nanotube

Fig. 2 Armchair nanotube



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Fig.3 Zig-Zag nanotube

Fig.4 Chiral nanotube



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Synthesis

Methods

1. Arc discharge

2. Laser ablation

3. Chemical vapor deposition

Arc Discharge

At 100 amps ,Carbon is vaporized between two carbon electrodes

Small diameter, single-wall nanotubes can be synthesized using a Miller XTM 304 dc arc

welder to maintain the optimal settings between two horizontal electrodes in helium or argon

atmospheres.

The voltage is controlled by an automatic feedback loop that senses the voltage differences

between the two electrodes and adjusts them accordingly.

Fig. 5 Arc Discharge

Laser ablation

The flow tube is heated to 1200C by a tube furnace.

Laser pulses enter the tube and strike a target consisting of a mixture of graphite and a metal catalyst

such as Co or Ni.



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SWNTs condense from the laser vaporization plume and are deposited on a collector outside the

furnace zone.

Fig.6Laser ablation

Chemical vapor deposition

Gas enters chamber at room temperature (cooler than the reaction temperature)

Place substrate in oven, heat to 600C, and slowly add a carbon-bearing gas such as

methane. As gas decomposes it frees up carbon atoms, which recombine in the form of

NTs.

Gaseous products are then removed from the reaction chamber.



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Fig. 7Chemical vapor deposition

Applications Of Carbon Nanotubes

Structural

Electromagnetic

Chemical Mechanical

Electrical circuits

o (a) Interconnects

o (b) Transistors

Structural

Textiles: CNT can make waterproof and tear-resistant fabrics.

Body armor (Combat Jackets):MIT is working on combat jackets that use CNT fibers to

stop bullets and to monitor the condition of the wearer.

Concrete : CNT in concrete increase its tensile strength and halt crack propagation.

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Polyethylene : Adding CNT to polyethylene can increase the polymer's elastic modulus by

30%.

Sports equipment: Stronger and lightertennis rackets, bicycle parts, golf balls, golf clubs,

and baseball bats.

Synthetic muscles: Due to their high contraction/extension ratio given an electric current,

CNTs are ideal for synthetic muscle.

High tensile strength fibers : Fibers produced withpolyvinyl alcohol required 600 J/g to

break. In comparison, the bullet-resistant fiberKevlarfails at 2733 J/g.

Bridges: CNT may be able to replace steel in suspension and other bridges.

Flywheels : The high strength/weight ratio enables very high rotational speeds.

Fire protection: Thin layers ofbuckypapercan significantly improve fire resistance due to

the efficient reflection of heat by the dense, compact layer of CNT orcarbon fibers.

Electromagnetic

Artificial muscles : CNT's have sufficient contractility to make them candidates to replace

muscle tissue. Buckypaper : Thin nanotube sheets are 250 times stronger than steel and 10 times lighter

and could be used as a heat sinkfor chipboards, a backlight forLCD screens or as a faraday

cage to protect electrical devices/aeroplanes.

Chemical nanowires: CNTs can be used to produce nanowires of other

elements/molecules, such as gold orzinc oxide. These nanowires in turn can be used to cast

nanotubes of other chemicals, such as gallium nitride. These can have very different

properties from CNTs: for example, gallium nitride nanotubes are hydrophilic, while CNTs

are hydrophobic, giving them possible uses in organic chemistry.

Conductive films: Nanotube films show promise for use in displays for computers, cell

phones, Personal digital assistants, and automated teller machines.

Electric motor brushes: Conductive CNTs are used in brushes for commercial electric

motors. They replace traditional carbon black, which is mostly impure spherical carbon

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fullerenes. The nanotubes improve electrical and thermal conductivity because they stretch

through the plastic matrix of the brush. This permits the carbon filler to be reduced from

30% down to 3.6%, so that more matrix is present in the brush. Nanotube composite motor

brushes are better-lubricated, cooler-running (both from better lubrication and superior

thermal conductivity), less brittle (fiber reinforcement), stronger and more accurately

moldable. Since brushes are a critical failure point in electric motors, and also don't need

much material, they became economical before almost any other application.

Displays : CNTs can be used as extremely fine electron guns, which could be used as

miniature cathode ray tubes in thin high-brightness, low-energy, low-weight displays. This

type of display would consist of a group of many tiny CRTs, each providing the electrons

to hit the phosphor of one pixel, instead of having one giant CRT whose electrons are

aimed using electric and magnetic fields. These displays are known as field emission

displays (FEDs).

Transistor : CNT transistors have been developed at Delft, IBM, and NEC.

Electromagnetic antenna : CNTs can act as antennas for radios and otherelectromagnetic

devices.

Chemical

Air pollution filter : CNT membranes can filter carbon dioxide from power plant

emissions.

Biotech container: CNT can be filled with biological molecules, aidingbiotechnology.

Hydrogen storage: CNT have the potential to store between 4.2 and 65% hydrogen by

weight.

Water filter: CNT membranes can aid in filtration. This can purportedly reduce

desalination costs by 75%. The tubes are so thin that small particles (like water molecules)

can pass through them, while blocking larger particles (such as the chloride ions in salt).

Mechanical

Oscillator : Oscillators based on CNT have achieved higher speeds than other

technologies.

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Nanotube membrane: Liquid flows up to five orders of magnitude faster than predicted

by classical fluid dynamics.

Slick surface: Some CNT-based fabrics have shown lower friction than Teflon.

Waterproof: Some CNT-fabrics are waterproof.

Infrared detector : The reflectivity of thebuckypaperproduced with "super-growth"

chemical vapor deposition method is 0.03 or less, potentially enabling performance gains

forpyroelectric infrared detector.

Electrical circuits

A nanotube formed by joining two nanotubes of different diameters end to end can act as a

diode, suggesting the possibility of constructing computer circuits entirely of nanotubes.

Because of their good thermal transmission properties, CNT can potentially dissipate heat

from computer chips. The longest electricity conducting circuit is a fraction of an inch long.

Standard IC fabrication processes use chemical vapor deposition to add layers to a wafer. CNT

can so far not be mass produced using such techniques.

Researchers can manipulate nanotubes one-by-one with the tip of an atomic force microscope

in a time-consuming process. Using standard fabrication techniques would still require

designers to position one end of the nanotube. During the deposition process, an electric field

can potentially direct the growth of the nanotubes, which tend to grow along the field lines

from negative to positive polarity. Another technique for self-assembly uses chemical or

biological techniques to move CNT in solution to determinate places on a substrate.

InterconnectsMetallic carbon nanotubes as very-large-scale integration (VLSI) interconnects because of

their high thermal stability, high thermal conductivity and large current carrying capacity. An

isolated CNT can carry current densities in excess of 1000 MA/sq-cm without damage even at

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an elevated temperature of 250 C (482 F), eliminating electromigration reliability concerns

that plague Cu interconnects..

(b)Transistors

Nanotubes are usually grown on nanoparticles of magnetic metal (Fe, Co) that facilitates

production of electronic (spintronic) devices. In particular control of current through a field-

effect transistor by magnetic field has been demonstrated in such a single-tube nanostructure.

Medicine

Identifying location of cancer cells.

Nanoshells that concentrate the heat from infrared light to destroy cancer

cells with minimal damage to surrounding healthy cells.

Nanotubes used in broken bones to provide a structure for new bone

material to grow.

Nanoparticles that can attach to cells infected with various diseases and

allow a lab to identify, in a blood sample, the particular disease.

Properties

Hardness

Under conditions of high temperature and high pressure, graphite transforms into diamond.The

hardness of material was measured with a nanoindenteras 62152 GPa. Thebulk modulus of

compressed SWNTs was 462546 GPa, surpassing the value of 420 GPa for diamond.

Strength

Carbon nanotubes are the strongest and stiffest .This strength results from the covalent sp 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). Since carbon nanotubes have a low

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density for a solid of 1.3 to 1.4 gcm3, its specific strength of up to 48,000 kNmkg1 is the best

of known materials, compared to high-carbon steel's 154 kNmkg1.

Kinetic

Multi-walled nanotubes are multiple concentric nanotubes precisely nested within one another.

These 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.

Electrical

The symmetry and unique electronic structure of graphene, the structure of a nanotube strongly

affects its electrical properties. For a given (n,m) nanotube, ifn = 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. this rule has exceptions, because curvature

effects in small diameter carbon nanotubes can influence strongly electrical properties. Metallic

nanotubes can carry an electric current density of 4 109 A/cm2 which is more than 1,000 times

greater than metals such as copper.

Multiwalled carbon nanotubes with interconnected inner shells show superconductivity with arelatively high transition temperature Tc = 12 K. In contrast, the Tc value is an order of

magnitude lower for ropes of single-walled carbon nanotubes .

Thermal

All nanotubes are expected to be very good thermal conductors along the tube, exhibiting a

property known as "ballistic conduction", but good insulators laterally to the tube axis. SWNT

has a room-temperature thermal conductivity along its axis of about 3500 Wm1

K1

;comparethis to copper, a metal well-known for its good thermal conductivity, which transmits 385

Wm1K1. A SWNT has a room-temperature thermal conductivity across its axis (in the radial

direction) of about 1.52 Wm1K1, which is about as thermally conductive as soil. The

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temperature stability of carbon nanotubes is estimated to be up to 2800 C in vacuum and about

750 C in air.

Advantages Of Nanomaterials

Nanomaterials provides:

High surface area (capacity)

Well defined structure

High reactivity

Easy dispersability

Reference

1. University of Wisconsin Materials Research Science and Engineering Center on

Nanostructured Materials and Interfaces and the James Lovell Museum of Science,

Economics & Technology in Milwaukee, Wisconsin; Carbon Nanotubes Activity Guide,

(2002)

2. Physics Department, Faculty of Science, Mahidol University by Mr. Anurak Udomvech

3. Introduction to Nanoscale Science and Technology by Massimiliano Di Ventra

4. T. Guo, P. Nikolaev, A. Thess et al., Chem. Phys. Lett. 243, 49 (1995).

5. A. Thess, R. Lee, P. Nikolaev et al., Science 273, 483 (1996).

6. C. Journet, W. K. Maser, P. Bernier et al.,Nature 388, 756 (1997).

7. S. Amelinckx, A. Lucas, and P. Lambin, Reports on Progress in Physics 62, 1471 (1999).

http://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Vacuum

carbon nanotubes _ ashish singla

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