A SEMINAR ONSYNTHESIS OF CNT BY ARC-

DISCHARGE METHOD

K. GANAPATHI RAO(13031D6603)

PresentedBy

Presence ofMr. G. Venkaiah

Outline

Introduction Synthesis OverviewArc Discharge ApplicationsReference

Carbon Nano Tubes

These are allotropes of carbon with

a cylindrical nanostructure.

Nanotubes have been constructed with length-to-

diameter ratio of up to 132,000,000:1

Nanotubes are members of the fullerene structural

family.Naturally align themselves into "ropes" held together by van der Waals forces.The chemical bonding of nanotubes is composed entirely of sp2 bonds.In 1991 Sumio Iijima  (Japanese Scientist) observed Multiwalled carbon Nanotube and in 1993 he discovered Single wall carbon Nanotube.

Types:

CNT types can be described by the chiral vector (n, m), where n and m are integers of the vector equation R = na1 + ma2.

CNT Synthesis Methods Overview

1 Arc discharge synthesis2 Laser ablation synthesis3 Thermal synthesis

3.1 Chemical vapor deposition

3.2 High-pressure carbon monoxide synthesis

3.3 Flame synthesis4 PECVD synthesis

Arc Discharge Method:

Arc evaporation technique involves evaporation of graphite anode rod and condensation of the deposit on the cathode rod under inert atmosphere.A plasma is achieved by making a gas to conduct electricity by providing a potential difference across two electrodesElectrodes are made of conducting materialsIn arc discharge method, two high purity graphite electrodes as anode and cathode are held a short distance apart under a helium atmosphere.

Inert atmosphere/Gas

Inert gas is meant for cooling / condensation of the sample.The chamber must be connected both to a vacuum line with a diffusion pump and to helium supply.

Important parameters of gas

Pressure Material 1000 torr Soot/ Carbon onions 500 torr Carbon nanotubes 100 torr Fullerenes 20 torr Amorphous carbon/soot Therefore pressure & type of inert gas used determines the structure of carbons to be obtained.

Electrodes:

In arc evaporation method, graphite rods are used as electrodes.Graphite rods with 99.99% purity are used.Major impurities in graphite are sulphur atoms as Sulphur changes the morphology of CNTs.The anode is a long rod of 6mm diameter & the cathode is a short rod of 9mm diameter

Cooling of Electrode

Efficient cooling of the electrodes & the chamber are essential to produce good quality nanotubes and also to avoid excessive sintering.Without proper cooling-sintering occurs-with a hard deposit of massWith proper cooling-sintering does not occurs- forms a uniform deposit i.e., Homogeneous deposit with aligned bundles of nanotubes.

Current & Voltage DC power supply is given in the range of 50-100mA

and the discharge voltage is between 20 – 50 V.

DISTANCE BETWEEN ELECTRODES

The position of the anode can be adjustable from outside the chamber.Distance between the electrodes must be constant to obtain a stable current.The two electrodes are maintained at constant distance for obtaining CNTsWhen two electrodes are in contact / not at a particular distance - fullerenes can be formed.

Arc Discharge Method Parameters of SWNTs: In the arc discharge production method sulfur

functions as a SWNTs growth promoter and surfactant when added together with Ni/Fe/Co, Ni/Co, Ni/Y/Fe or Ni/Ce/Fe catalysts into the anode.

The metal-sulfur interactions change surface tension and melting point of small droplets of metals. This can support the creation of SWNTs for metals which in pure form catalyze badly.

The highest yield of web product containing the smallest concentration of metals was obtained for the sample C where the composition of the anode is Fe:Y:S:C at6.6%:1.1%:1.6%:90.7%.

SEM images of the samples which were synthesized (a) in an air atmosphere at 300 Torr and (b) in the helium atmosphere at 500 Torr

SEM images of MWNT’s produced by arc discharge (Kunsan National Univ)

ApplicationsElectrical circuitsElectrical cables and wiresActuatorsPaper batteriesSolar cellsHydrogen storageSuper capacitorRadar absorptionMedicalTextileOptical power detectorsEnvironmental remediation

References:

http://en.wikipedia.org/wiki/Carbon_nanotubehttp://www.nanocyl.com/en/CNT-Expertise-Centre/

Carbon-Nanotubeshttp://www.sciencedaily.com/articles/c/carbon_nan

otube.htmhttps://www.youtube.com/watch?v=B4VTfgaKLAM

&hd=1http://www.azonano.com/article.aspx?ArticleID=15

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