Synthesis of CNT by Arc discharge method

A complete description of CNT and Arc Discharge method.

1. A SEMINAR ON SYNTHESIS OF CNT BY ARC-DISCHARGE METHOD K. GANAPATHI RAO (13031D6603) Presented By Presence of Mr. G. Venkaiah

2. Outline Introduction Synthesis Overview Arc Discharge Applications Reference

3. Carbon Nano Tubes

4. 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  sp 2  bonds. In 1991 Sumio Iijima  (Japanese Scientist) observed Multiwalled carbon Nanotube and in 1993 he discovered Single wall carbon Nanotube .

5. Types:

6. CNT types can be described by the chiral vector (n, m), where n and m are integers of the vector equation R = na 1  + ma 2 .

7. CNT Synthesis M ethods O verview 1 Arc discharge synthesis 2 Laser ablation synthesis 3 Thermal synthesis 3.1 Chemical vapor deposition 3.2 High-pressure carbon monoxide synthesis 3.3 Flame synthesis 4 PECVD synthesis

8. Arc Discharge Method:

9. 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 electrodes Electrodes are made of conducting materials In arc discharge method, two high purity graphite electrodes as anode and cathode are held a short distance apart under a helium atmosphere.

10. 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.

11. 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.

12. 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

13. 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 mass With proper cooling-sintering does not occurs- forms a uniform deposit i.e., Homogeneous deposit with aligned bundles of nanotubes.

14. 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 CNTs When two electrodes are in contact / not at a particular distance - fullerenes can be formed.

15. 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%.

16. 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

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

18. Applications Electrical circuits Electrical cables and wires Actuators Paper batteries Solar cells Hydrogen storage Super capacitor Radar absorption Medical Textile Optical power detectors Environmental remediation

19. References: http://en.wikipedia.org/wiki/Carbon_nanotube http://www.nanocyl.com/en/CNT-Expertise-Centre/Carbon-Nanotubes http://www.sciencedaily.com/articles/c/carbon_nanotube.htm https://www.youtube.com/watch?v=B4VTfgaKLAM&hd=1 http://www.azonano.com/article.aspx?ArticleID=1561