Carbon Nanotubes and Its Applications 1

8/14/2019 Carbon Nanotubes and Its Applications 1

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Carbon Nanotubes andits Applications.

By

Abisheka M (CB105PE002)Gayathri M (CB105PE013)Karthikeyan G (CB105PE023)Sneha R (CB105PE036)


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Introduction

Carbon nanotubes are unique nanostructureswith remarkable electronic and mechanicalproperties.

Electronic transport properties, Ramanspectra, unusual mechanical properties -Carbon nanotubes are potentially used innanometer-sized electronics and in a variety of

other applications. An ideal nanotube can be considered as a

hexagonal network of carbon atoms that hasbeen rolled up to make a seamless hollow

cylinder. Length 10s of micrometers,-


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le-wall nanotubes (SWNT) - a cylindrical shell with only onein thickness, can be considered as the fundamental struc

.

ctural units form the building blocks of both multi-wallotubes (MWNT) - containing multiple coaxial cylinders of

- increasing diameter about a common axis.

otube ropes - consisting of ordered arrays of SWNTs arrangtriangular lattice.

first reported observation of carbon nanotubes was by Iijim991 for MWNTs.


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ter the discovery of MWNTs, it took 2 years for the discoverSWNTs, by Iijima using High-Resolution Transmission

ctron Microscopy (HRTEM).


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The observation by TEMof multi-wall coaxialnanotubes with variousinner and outerdiameters, di and do,

and numbers ofcylindrical shells Nreported by Iijima in1991: (a) N = 5, d

o=67;

(b) N = 2, do=55 ; and(c) N = 7, di=23 ,do=65 .


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Carbon Materials Very small diameter (


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smallest reported diameter for a carbon nanotube is the she diameter of the C60 molecule, which is the smallest

rene to follow the isolated pentagon rule.

rule requires that no two pentagons be adjacent to onether, thereby lowering the strain energy of the fullerene ca

cent report shows that a carbon nanotube has a diameterm.

bon nanotubes could be either semiconducting or metallic

ending on their geometrical characteristics like diameter aorientation of their hexagons with respect to the nanotube


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96, aligned SWNTs were synthesized, with a small diameteibution - sensitive experiments relevant to 1D quantum ph

al carbon nanotubes have finite length, contain defects, anact with other nanotubes or with the substrate and these fcomplicate their behavior.


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Relation of Carbon Nanotubes toOther Carbon Materials

Graphite

Graphite Whiskers Carbon Fibers Liquid Carbon


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Graphite

The ideal crystal structure - consists of layers inwhich the carbonatoms are arranged in an open honeycombnetwork containing twoatoms per unit cell in each layer. (Labeled A and B

in fig.)Bernal stacking arrangement ABAB.

An in-plane nearest-neighbor distance aCC of 1.421.An in-plane lattice constant a0 of 2.462 .

A c-axis lattice constant c of 6.708 .


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crystal structure is consistent with the space group and hasn atoms per unit cell.

consequence of the small value ofaCC in graphite is thatrity species are unlikely to enter the covalently bonded in-e sites substitutionally (except for boron), but rather occup

interstitial position between the graphene layer planes whed by a weak van der Waals force.

e are also applicable for Carbon nanotubes and substitutiong of individual SWNTs with species other than boron is diffi

dition, carbon nanotubes can adsorb other species on theirnal and internal surfaces and in interstitial sites between atubes.


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The crystal structure of

hexagonal single crystalgraphite, in which thetwo distinct planes ofcarbon hexagons called

A and B planes arestacked in an ABAB...sequence. The notationfor the A and B planesis not to be confusedwith the two distinctatoms A and B on asingle graphene plane.


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An STM image showingthe trigonal network ofhighly oriented pyrolyticgraphite (HOPG) in whichonly one site of the

carbon hexagonalnetwork appears, as forexample, the B site,denoted by black balls.


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phite Whiskers

aphite whisker is a graphitic material formed by rolling ahene sheet up into a scroll (~3 cm long and 15m in dia

hite whiskers are formed in a dc discharge between carbotrodes using 7580V and 7076A.

bits great crystalline perfection, high electrical conductivityelastic modulus.

lar to the growth of Carbon nanotubes.

hite whiskers were grown at a higher gas pressure, but notube growth.


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NTs are found to be concentric cylinders of much smallermeter, but scroll-like structures have outer diameters less0nm.

rbon fibers

rbon fibers - graphite-related materials - close connection trbon nanotubes (structure and properties).

ving different cross- sectional morphologies.

phene planes prefer orientation parallel to the fiber axis chanical strength to carbon fibers.

por-grown fibers have onion skin or tree ring morpholo


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ting around 2500C shows a close resemblance to carbonotubes.

her heating about 3000C, the outer regions of the vapor-bon fibers form facets. Graphite like - strong interplanarrelations.

commercially available fibers are exploited for their extrebulk modulus and high thermal conductivity.

(polyacrylonitrile) fibers are widely used for their high ten

ngth.

ical diameters for individual commercial carbon fibers arem, and they can be very long.


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se fibers are woven into bundles called tows and are thens a continuous yarn on a spool.

se superior mechanical properties (modulus and tensile strcompared equal to the steel.

er Compression - Carbon nanotubes are flexible (SWNTs), g

hanical properties (MWNTs) but Caron fibers fracture easily

ofibers - Vapor-grown carbon fibers (10-100 nm) intermeerties between VGCFs and MWNTs.


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The morphology of VGCF: as-deposited at 1100C, (b)after heat treatment to 3000

The morphologies forcommercial mesophase-pitchfibers are shown in (c) for aPAC-man cross section witha radial arrangement of thestraight graphene ribbons anda missing wedge and (d) for aPAN-AM cross-sectionalarrangement of graphene

planes. (e) a PAN fiber isshown, with a circumferentialarrangement of ribbons in thesheath region and a random

structure in the core.


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Carbon nanotube exposed on thebreakage edge of a vapor- growncarbon fiber as grown and heat-treated at 3000C(b). The sample is fractured bypulverization and the corediameter is ~ 5nm. These

photos suggest a structuraldiscontinuity between the nanotubecore of the fiber and the outercarbon layers deposited by chemical

vapor deposition techniques. Thephotos show the strong mechanicalproperties of the nanotube core,which maintain its form after breakaof the periphery.


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The sword in-sheathfailure mode of heat-treated vaporgrown carbon fibers.Such failure modesare also observedin multiwall carbonnanotubes.


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The breakingstrength of varioustypes of carbonfibers plotted as

a function ofYoungs modulus.Lines of constantstrain can be used

to estimate thebreaking strains.


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tory of Carbon Fibers in Relation to Carbonnotubes

first carbon fiber - Thomas A. Edison - electric light bulb.

nese Kyoto bamboo filaments - coiled carbon resistor.

ce and aircraft industry strong, lightweight fibers - superihanical properties - Rayon, Polyacrylonitrile (PAN).

talline filamentous carbons - Carbon fibers by a Catalyticmical Vapor Deposition (CVD).

small diameter filaments less than 10 nm also observed (i


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High-resolution TEMmicrograph showing carbona vapor grown carbon

nanofiber (VGCF) with adiameter less than 10 nmand a nanotube.


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quid Carbon

uid carbon - liquid phase of carbon - melting of pure carboolid phase.

uid carbon is stable at atmospheric pressure only at very h

peratures.ucible made of carbon- to avoid contamination sufficienplied - because of highest melting point.

dely manufactured - laser melting of graphite.

mond, graphite gives same liquid carbon. Melting of carbonotubes also forms liquid carbon.


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The electrical resistivityvs. temperature for

vapor grown carbonfibers with various heattreatment temperature(THT = 1700, 2100,

2300, 2800C). Thesharp decrease in (T) above ~ 4000Kis identified with themelting of the carbon

fibers. The measuredelectrical resistivityfor liquid carbon isshown.

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Carbon Nanotubes and Its Applications 1