Carbon Nanotubes And Its Applications 1

Carbon Nanotubes and its Applications.

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

Introduction • Carbon nanotubes are unique nanostructures with remarkable electronic and mechanical properties.

 

• Electronic transport properties, Raman

spectra, unusual mechanical properties Carbon nanotubes are potentially used in nanometer-sized electronics and in a variety of other applications.

 

• An ideal nanotube can be considered as a

hexagonal network of carbon atoms that has been rolled up to make a seamless hollow cylinder. Length – 10s of micrometers,

gle-wall nanotubes (SWNT) - a cylindrical shell with only one m in thickness, can be considered as the fundamental struct t.

uctural units form the building blocks of both multi-wall otubes (MWNT) - containing multiple coaxial cylinders of r- increasing diameter about a common axis.

notube ropes - consisting of ordered arrays of SWNTs arrange a triangular lattice.

first reported observation of carbon nanotubes was by Iijima 991 for MWNTs.

fter the discovery of MWNTs, it took 2 years for the discovery SWNTs, by Iijima using High-Resolution Transmission ectron Microscopy (HRTEM).

The observation by TEM of multi-wall coaxial nanotubes with various inner and outer diameters, di and do, and numbers of cylindrical shells N reported by Iijima in 1991: (a) N = 5, do=67Ǻ; (b) N = 2, do=55 Ǻ; and (c) N = 7, di=23 Ǻ, do=65 Ǻ.  

Carbon Materials • Very small diameter (<10 nm) carbon

filaments were prepared through the synthesis of vapor grown carbon fibers.

• In 1992, Russian workers also reported the

discovery of carbon nanotubes and nanotube bundles, but generally having a much smaller length to diameter ratio.

 

• The connection between carbon nanotubes and fullerenes - terminations of the carbon nanotubes were fullerene-like caps or hemispheres.

e smallest reported diameter for a carbon nanotube is the sa the diameter of the C60 molecule, which is the smallest erene to follow the isolated pentagon rule.

s rule requires that no two pentagons be adjacent to one other, thereby lowering the strain energy of the fullerene cag

ecent report shows that a carbon nanotube has a diameter o nm.

bon nanotubes could be either semiconducting or metallic pending on their geometrical characteristics like diameter an orientation of their hexagons with respect to the nanotube a

996, aligned SWNTs were synthesized, with a small diameter ribution - sensitive experiments relevant to 1D quantum phy

ual carbon nanotubes have finite length, contain defects, and ract with other nanotubes or with the substrate and these fa n complicate their behavior.

Relation of Carbon Nanotubes to Other Carbon Materials

   

Graphite Graphite Whiskers Carbon Fibers Liquid Carbon

Graphite The ideal crystal structure - consists of layers in which the carbon atoms are arranged in an open honeycomb network containing two atoms per unit cell in each layer. (Labeled A and B in fig.)   Bernal stacking arrangement – “ABAB”.   An in-plane nearest-neighbor distance aC−C of 1.421 Ǻ.   An in-plane lattice constant a0 of 2.462 Ǻ.   A c-axis lattice constant c of 6.708 Ǻ.

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

consequence of the small value of aC−C in graphite is that urity species are unlikely to enter the covalently bonded in-p ce sites substitutionally (except for boron), but rather occupy e interstitial position between the graphene layer planes whi ded by a weak van der Waals force.

e are also applicable for Carbon nanotubes and substitution ng of individual SWNTs with species other than boron is diffic

ddition, carbon nanotubes can adsorb other species on their rnal and internal surfaces and in interstitial sites between ad otubes.

The crystal structure of hexagonal single crystal graphite, in which the two distinct planes of carbon hexagons called A and B planes are stacked in an ABAB... sequence. The notation for the A and B planes is not to be confused with the two distinct atoms A and B on a single graphene plane.

An STM image showing the trigonal network of highly oriented pyrolytic graphite (HOPG) in which only one site of the carbon hexagonal network appears, as for example, the B site, denoted by black balls.

aphite Whiskers

raphite whisker is a graphitic material formed by rolling a phene sheet up into a scroll (~3 cm long and 1–5 µm in diam

phite whiskers are formed in a dc discharge between carbon ctrodes using 75–80V and 70–76A.

ibits great crystalline perfection, high electrical conductivity h elastic modulus.

ilar to the growth of Carbon nanotubes.

phite whiskers were grown at a higher gas pressure, but not otube growth.

WNTs are found to be concentric cylinders of much smaller o ameter, but scroll-like structures have outer diameters less t 0nm.

arbon fibers

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

aving different cross- sectional morphologies.

aphene planes prefer orientation parallel to the fiber axis – h echanical strength to carbon fibers.

por-grown fibers have “onion skin” or “tree ring” morpholog

ating around 2500°C shows a close resemblance to carbon notubes.

ther heating about 3000°C, the outer regions of the vapor-g bon fibers form facets. Graphite like - strong interplanar relations.

e commercially available fibers are exploited for their extrem h bulk modulus and high thermal conductivity.

N (polyacrylonitrile) fibers are widely used for their high tens ength.

pical diameters for individual commercial carbon fibers are 7 µm, and they can be very long.

se fibers are woven into bundles called tows and are then w as a continuous yarn on a spool.

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

der Compression - Carbon nanotubes are flexible (SWNTs), go chanical properties (MWNTs) but Caron fibers fracture easily

nofibers - Vapor-grown carbon fibers (10-100 nm) – intermed perties between VGCFs and MWNTs.

The morphology of VGCF: • as-deposited at 1100◦C, (b) after heat treatment to 3000◦C The morphologies for commercial mesophase-pitch fibers are shown in (c) for a “PAC-man” cross section with a radial arrangement of the straight graphene ribbons and a missing wedge and (d) for a PAN-AM cross-sectional arrangement of graphene planes. (e) a PAN fiber is shown, with a circumferential arrangement of ribbons in the sheath region and a random structure in the core.

Carbon nanotube exposed on the breakage edge of a vapor- grown carbon fiber as grown • and heat-treated at 3000◦C (b). The sample is fractured by pulverization and the core diameter is ~ 5nm. These photos suggest a structural discontinuity between the nanotube core of the fiber and the outer carbon layers deposited by chemical vapor deposition techniques. The photos show the strong mechanical properties of the nanotube core, which maintain its form after breakag of the periphery.

The sword in-sheath failure mode of heat -treated vapor grown carbon fibers. Such failure modes are also observed in multiwall carbon nanotubes.

The breaking strength of various types of carbon fibers plotted as a function of Young’s modulus. Lines of constant strain can be used to estimate the breaking strains.

story of Carbon Fibers in Relation to Carbon notubes first carbon fiber - Thomas A. Edison - electric light bulb.

anese Kyoto bamboo filaments - coiled carbon resistor.

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

stalline filamentous carbons - Carbon fibers by a Catalytic emical Vapor Deposition (CVD).

y small diameter filaments less than 10 nm also observed (in

High-resolution TEM micrograph showing carbon a vapor grown carbon nanofiber (VGCF) with a diameter less than 10 nm and a nanotube.  

quid Carbon

quid carbon - liquid phase of carbon - melting of pure carbon solid phase.

quid carbon is stable at atmospheric pressure only at very hi mperatures.

ucible – made of carbon- to avoid contamination – sufficient pplied - because of highest melting point.

idely manufactured - laser melting of graphite.

amond, graphite gives same liquid carbon. Melting of carbon anotubes also forms liquid carbon.

e vapor pressure over liquid carbon is high.

rmed in carbon clusters rather than independent atoms – gh vapor pressure and the large carbon–carbon-bonding ener ving masses equal to fullerenes.

The electrical resistivity vs. temperature for vapor grown carbon fibers with various heat treatment temperatures (THT = 1700, 2100, 2300, 2800°C). The sharp decrease in ρ (T) above ~ 4000K is identified with the melting of the carbon fibers. The measured electrical resistivity for liquid carbon is shown.