carbon nano tubes

SYNTHESIS OF CARBON NANOTUBES BY USING CVD METHOD

ByJEETENDRA KUMAR

SHRI MATA VAISHNO DEVI UNIVERSITY KATRA (J&K)

ToDr. PRATHAP HARIDOSSASSOCIATE PROFESSOR

IIT MADRAS

Carbon Nano Tubes

Contents:1. Introduction2. Classification of CNTs3. Properties & Applications4. Synthesis methods5. Precursors6. Catalysts7. Catalyst supporters8. Growth mechanism9. References

Introduction

Carbon nano tubes are allotrope of carbon with a cylindrical nanostructure or Carbon nanotubes (CNTs) are rolled up cylinders of graphene sheets.

Classification

Carbon nano tubes

Single walled carbon nano

tube (SWCNT)

Multi walled carbon nano

tube (MWCNT)

Arm chairZigzagChiral

Herringbone

Bamboo

(a) Armchair, (b) Zigzag, (c) ChiralNano tubes

Textures of MWCNTs (a) herringbone texture and (b) bamboo texture

Multi walled carbon nano tube

Properties:-132,000,000:1 Length-To Diameter RatioDiameter of 3 to 9 nmLengths in the millimeter rangeEfficient electrical conductorsHigh thermal conductivity(6000 W/MK for SWCNT & MWCNT is 3000 W/MK) that is grater then diamond (2000 W/MK).Its tensile strength is (45GPa)more then diamond, steel, etc.

Applications:- In automobileAerospace designBio medical sensorsElectronic circuit designMechanical reinforcement Energy storage (hydrogen storage.)

Synthesis of CNT:-There are three methods of synthesis of Carbon Nano Tubes-•Electric arc-discharge method,•Laser ablation method and•Chemical Vapor Deposition (CVD)

Electric arc-discharge method

Laser ablation method

Chemical Vapor Deposition (CVD)

Reactor tube is made up of Quartz.CxHx- Carbon precursor

Substrates- SiO2, Al2O3, MgO, TiO2

List of different precursors with their phase and decomposition temperature:-

S No. Precursors Phase Decomposition Temperature �c

1. Methane Gas 500-8002. Ethane Gas 550-6403. Acetylene Gas 1500-18004. Ethanol Liquid 780-10855. Carbon mono

oxide(with catalyst)

Gas 700

6. Carbon mono oxide(without

catalyst)

Gas 2900

7. Acetylene(with catalyst- Fe) used

for MWCNTs

Gas 700

Different catalysts used in synthesis of carbon nano tubes by using chemical vapor deposition (CVD):-Ni, Fe, Co, Mo, Cu, Au etc.

Catalysts supportersMgO, Al2O3, SiO2, TiO2. these aare also called substrates where catalysts are placed in the tube furnace and heated upto 500 to 1000ºC.

Some important points regarding to catalyst supporters-• Metal supported on MgO shows low catalytic activity towards decomposition of methane and this reason impels the researchers to search the suitable transition metal supported on MgO for effective production of SWCNTs.• Ni/Ti02has an advantage over Ni/Si02 by reason of the catalytic activity of Ni/Ti02 is kept higher during catalyst regeneration cycles. Conversely, catalytic activity of Ni/Si02 for methane decomposition is higher at early cycles and decreases gradually with the regeneration cycles. This phenomenon is mainly due to the changes of these metallic particles size after several regeneration cycles, i.e. nickel particles in Ni/Ti02 approach the optimum size for methane decomposition (60-100nm)-

Some important points regarding to catalyst supporters contd.

-with the regeneration cycles while nickel particles in Ni/Si02 aggregated into size larger than 150nm, which are inactive for methane decomposition, after several regeneration cycles.

• Ti02 helps to reduce the activation energy in methane decomposition, and 60 KJ/mol was achieved over 13wt% Ni/Ti02 in methane decomposition reaction. This activation energy is the lowest activation energy reported in literature for this reaction.

We are working on synthesis of carbon nano tubes by using chemical vapor deposition based on Methane.Methane decomposition temperature for

different catalysts:-S.No. Catalysts Temperature in

1. Ni/SiO2 500-600

2. Fe/SiO2 680-1200

3. Co/MgO 900-1000

4. Co/Al2O3 475-500

5. Ni/SiO2 700

6. Fe–Co-impregnated zeolite support

1200

CNTs growth mechanism:-1. Tip growth model

2. Base growth model

References

1. Fabrication And Characterization Of Carbon Nano tubes thesis by Zhiyang Rong

2. Production of carbon nano tubes by chemical vapor deposition thesis by Umut Baris Ayhan.

3. Synthesis and Electronic Transport in Known Chirality Single Wall Carbon Nanotubes by Bhupesh Chandra.

4. A Review on Growth Mechanism and Mass Production of CNTs by Mukul Kumar and Yoshinori Ando.