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Carbon nanotubes

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Carbon nanotubes

  1. 1. Carbon Nanotubes GC Solan
  2. 2. What is a Carbon Nanotube? Discovery:This new class of materials was first observed by Endo (1975) and later by Iijima (1991) . CNT is a tubular form of carbon with diameter as small as 1nm. Length: few nm to microns. CNT is configurationally equivalent to a two dimensional graphene sheet rolled into a tube. GC Solan Graphene Sheet Carbon Nanotube
  3. 3. SWCNT GC Solan
  4. 4. Multiwall CNTs: Multiwall CNTs consist of rolling sheets of carbon atoms into concentric multiple layers. GC Solan MWCNT
  5. 5. Chemical Bonding of Carbon Nanotubes
  6. 6. 2 Types of Bonding related to Nanotubes • Covalent Bonding – Strong bond between individual neighbouring carbon atoms in a single tube •Bonding found along the 2-D plane in a hexagonally close packed sheet of graphite • Van der Waal Forces – Weak bond between the individual nanotubes themselves • Bonding between separate layers of graphite • (Reason why graphite is an excellent lubricant, and why talcum powder feel so smooth!)
  7. 7. • Nanotubes are composed entirely of sp2 bonds, similar to graphite. Stronger than the sp3 bonds found in diamond. This bonding structure provides them with their unique strength. • Nanotubes naturally align themselves into "ropes" held together by Van Der Waal Force. • Under high pressure, nanotubes can merge together, trading some sp2 bonds for sp3 bonds, giving great possibility for producing strong, unlimited-length wires through high-pressure nanotube linking.
  8. 8. Typical Values of a Single Walled Carbon Nanotube • Equilibrium Structure • Average Diameter of SWNT's 1.2-1.4 nm • Distance from opposite Carbon Atoms 2.83 Å • Analogous Carbon Atom Separation 2.456 Å • Parallel Carbon Bond Separation 2.45 Å • Carbon Bond Length 1.42 Å • C - C Tight Bonding Overlap Energy ~ 2.5 eV • Lattice Constant 17 Å
  9. 9. Conclusions • Covalent bonding is a very strong bond (can often be stronger than Ionic bonding) • Weak VdW forces allow rolling up of indivitual graphite sheets into tubes. • Electrons are shared between Carbon atoms so as to fill outer electron shells. • Covalent bonds are highly directional (unlike Ionic) therefore only a few characteristic shapes are found. • Carbon Nanotubes exhibit quite different properties related to size and width of tube but the bonding type remains the same.
  10. 10. Electronic Structure Of Single Wall CNT • Zigzag: A single wall CNT with one of the indices as zero (0,m or m,0) and zero chiral angle is called as zigzag CNT. It has zigzag type ending at the CNT edge. • Armchair: A single wall CNT with equal indices (n=m) and 300 chiral angle is called as single armchair CNT. It has arms of chair type ending of CNT edges. • Chiral: A single wall CNT with unequal indices (n,m) and chiral angle between 00-300 is called as chiral CNT. GC Solan
  11. 11. GC Solan
  12. 12. GC Solan
  13. 13. GC Solan Nanotube’s chirality can be mathematically defined in terms of a chiral vector Ch , which can determine the tube diameter d. Where (m,n) are indices and a is lattice constant
  14. 14. How CNTs are made • Arc discharge • CNTs Can be found in the carbon soot of graphite electrodes during an arc discharge involving high current. This process yields CNTs with lengths up to 50 microns. • Laser Ablation • In the laser ablation process, a pulsed laser vaporizes a graphite target in a high-temperature reactor while an inert gas is inserted into the reactor. Nanotubes develop on the cooler surfaces of the reactor as the vaporized carbon condenses. • Other methods where CNTs are created: - Chemical Vapor Decomposition - Natural, incidental, and controlled flame environments GC Solan
  15. 15. Strength Properties • Carbon nanotubes have the strongest tensile strength of any material known. • It also has the highest modulus of elasticity. GC Solan Material Young's Modulus (TPa) Tensile Strength (GPa) Elongation at Break (%) SWNT ~1 (from 1 to 5) 13-53E 16 Armchair SWNT 0.94T 126.2T 23.1 Zigzag SWNT 0.94T 94.5T 15.6-17.5 Chiral SWNT 0.92 MWNT 0.8-0.9E 150 Stainless Steel ~0.2 ~0.65-1 15-50 Kevlar ~0.15 ~3.5 ~2 KevlarT 0.25 29.6
  16. 16. Electrical Properties • If the nanotube structure is armchair then the electrical properties are metallic • If the nanotube structure is chiral then the electrical properties can be either semiconducting with a very small band gap, otherwise the nanotube is a moderate semiconductor • In theory, metallic nanotubes can carry an electrical current density of 4×109 A/cm2 which is more than 1,000 times greater than metals such as copper GC Solan
  17. 17. Thermal Properties • All nanotubes are expected to be very good thermal conductors along the tube, but good insulators laterally to the tube axis. • It is predicted that carbon nanotubes will be able to transmit up to 6000 watts per meter per Kelvin at room temperature; compare this to copper, a metal well-known for its good thermal conductivity, which transmits 385 watts per meter per K. • The temperature stability of carbon nanotubes is estimated to be up to 2800oC in vacuum and about 750oC in air.
  18. 18. Nanotube Vibrations GC Solan
  19. 19. Various Modes Of Vibrations GC Solan Radial Breathing Mode High Energy Mode
  20. 20. Nanotube Vibrations GC Solan
  21. 21. Applications Of CNTs • Nanotubes hold the promise of creating novel devices, such as carbon-based single-electron transistors, that significantly smaller than conventional transistors.
  22. 22. World’s Smallest Transistor GC Solan In 2016 Berkeley Lab-led research breaked major barrier in transistor size by creating gate only 1 nanometer long!
  23. 23. Various properties of CNTs that allow it to be used in FETs and switching components of electronic circuits: • CNTs act as a channel for flow of electrons from source to drain. • Switching time of CNT based FET is very fast • It can be joined with metal-semiconductor to form metal- semiconductor junction that allows the current to flow in only one direction, thus acting as a rectifier. GC Solan
  24. 24. Nanotubes’ excellent strength to weight ratio creates the potential to build an elevator to space.
  25. 25. Field Emission and Shielding • The emission of electrons by a substance under the influence of high applied electric field is called as field emission. • CNTs have a low value of threshold electric field for emission of high current density. • The high aspect ratios of CNTs makes them ideal field-emission materials. • CNTs have several advantages over traditionally used field emission materials like Si or W. 1. They are physically inert to sputtering 2. Chemically inert 3. Can carry a huge current density of 109 A/cm2 4. Longer life 5. More efficient GC Solan
  26. 26. Emission property of CNT can be used in flat panel display, television, computer monitors, microwave amplifiers, and in electron guns in electron microscopes. • Since CNTs are good electrical conductors it means they are very poor transmitter of electromagnetic energy. Thus CNT reinforced plastic plastic composite could be a light weight shielding material for electromagnetic shielding. Thus this shielding property of CNT can be used in military , computer controlled weapons and in communications. GC Solan
  27. 27. Fuel Cells • Graphite and carbon fiber electrodes are commonly used in fuel cells, batteries and other electrochemical applications. Advantages of considering CNTs for energy storage are their:- I. Small dimensions II. Smooth surface topology III. Perfect surface specificity Because of their cylindrical and hollow geometry and nanometer scale diameters, it has been predicted that CNTs can store a liquid or a gas in the inner cores through capillary effect. Therefore CNTs can be used to a gas like hydrogen for making hydrogen fuel cell. This could revolutionize battery technology. GC Solan
  28. 28. Catalysis Catalyst: Any agent, material or chemical compound which is used to enhance the rate of reaction is called a catalyst. CNTs have properties such as:  Large specific surface areas  Excellent electron conductivity  Good chemical inertness  Relatively high oxidation stability which makes it a promising support material for heterogeneous catalysis. GC Solan
  29. 29. Physical and Chemical Sensors Physical Sensors-are used o examine environmental conditions whereas the Chemical sensors are used to detect the kind and concentration of the substances in the environment. CNTs suit this task very well especially because all their atoms are found on the surface of the structure. There is strong dependence of the properties of CNTs:  Surface modification  Mechanical deformation  Doping  Coating These properties make CNT a very useful material for chemical, biological and physical sensors. Small changes in the environment of the CNTs can cause drastic change in current voltage relationship. The change in the magnitude and direction of current depends upon the kind of molecule attached to the surface of nanotubes. Physical sensors are sensitive to external parameters such as temperature, pressure, mechanical strain etc. In the sensing process, the sensor generates a signal that can be measured and assigned to a certain value. GC Solan
  30. 30. Reinforcement • The carbon nanotubes(CNT) reinforced functionally graded composite materials(FGCM) is expected to be the new generation material having a wide range of unexplored potential applications in various technological areas such as aerospace, defence, energy, automobile, medicine, structural and chemical industry. GC Solan
  31. 31. Quantum Computing • Nanotubes and other Fullerenes can be filled with molecules that have either an electronic or structural property which can be used to represent the quantum bit (Qubit) of information, and which can be associated with other adjacent Qubits.
  32. 32. Health Hazards • According to scientists at the National Institute of Standards and Technology, carbon nanotubes shorter than about 200 nanometers readily enter into human lung cells similar to the way asbestos does, and may pose an increased risk to health. • Carbon nanotubes along with the majority of nanotechnology, are an unexplored matter, and many of the possible health hazards are still unknown.
  33. 33. Thank You! GC Solan

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