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Multiwalled Carbon Nanotubes: Synthesis and Applications

Carbon Fiber Diameters. Nanotube Applications. Nano-electronicsMetallic and semi-conducting varietiesMolecular circuitsElectromagnetic interference shielding

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Multiwalled Carbon Nanotubes: Synthesis and Applications

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    1. Multiwalled Carbon Nanotubes: Synthesis and Applications Rodney Andrews University of Kentucky Center for Applied Energy Research NSF-MRSEC Advanced Carbon Materials Center

    2. Carbon Fiber Diameters

    3. Nanotube Applications Nano-electronics Metallic and semi-conducting varieties Molecular circuits Electromagnetic interference shielding ‘Stealth’ composites and coatings

    4. Nanotube Applications Energy Storage Hydrogen storage Super-capacitors and batteries Field emission devices Flat panel displays

    5. High Strength to Weight Materials

    6. Enabling Technology Need for viable synthesis technology Large scale Low cost High purity Controlled properties Lack of entanglement Easily separable Currently this does not exist

    7. Commercial Processes SWNT MER Corp. – 250 g/day (US) Carbolex – 50 g/day (US) Tubes@Rice (US) Nanoledge (France) MWNT MER Corp. – 2 kg/day (US) Hyperion Catalysis – 80 kg/day (US)

    8. Commercial Processes CVD MWNT Showa Denko – 40,000 kg/yr (Japan) Nikkiso (Japan) Fullerene International Technologies MER-Mitsubishi joint venture Based on MER’s arc technology

    9. CVD Synthesis of MWNT “You meant to coke the catalyst?”

    10. MWNT Process Developed at CAER Vapor Growth (CVD) Process quartz tube furnace quartz plate substrates Ar/H2 atmosphere liquid feed xylene as hydrocarbon source ferrocene catalyst controlled injection rate Product high purity (>95% MWNT produced) 60-65% carbon conversion to MWNT aligned mats normal to growth surface

    11. SEM of High Purity MWNT Arrays

    12. HRTEM of a Single MWNT

    13. Reactor System

    14. Parameters Studied

    15. Temperature of Reaction Zone

    16. Carbon Partial Pressure

    17. Catalyst Loading Production rate increases with Fe:C ratio Diameter distribution widens

    18. Distribution of MWNT Diameters

    19. Outer diameter relates to particle size.

    20. Growth Mechanism Form of carbon depends on metal particle size graphite graphite whiskers (VGCF) nanofibers MWNT SWNT As metal becomes smaller curvature is eventually favored (MWNT) ultimately, SWNT is only stable form

    21. ‘Lawn’ Growth Mechanism

    22. Nanotube Composites “You want how many grams of nanotubes?”

    23. Difficulties in Use of Nanotubes “Purity is an issue working in this field” B. McEnaney, 18 Oct, 2000 Supply problem Nanotube form effects dispersability Entanglement (bird’s nest) Physical linkages

    24. Literature Review Recent search yielded ~100 articles on nanotube composite materials Topics covered include: Nanotube-polymer composites Metal-matrix nanotube composites Nanotube-glass composites Nanotube-carbon composites

    25. MWNT Materials CVD synthesis xylene / ferrocene low temperature, 725 oC high purity, > 95%

    26. Pyrograf III Nanofibers Applied Sciences, Inc. entangled some pyrolytic carbon

    27. Solution Processing

    28. Dispersion to single MWNT level Ultrasonic mixing Individual dispersion Surfactant assisted

    29. Tensile strength and modulus

    30. Experimental and Theoretical Moduli

    31. Alignment in shear field

    32. Melt Processing: Shear Mixing

    33. Haake Polylab Shear Mixer 50 gram charges 0 - 25 wt% fiber Matrices: HIPS PP ABS Pitch Mixing Energy Shear Mixing of MWNT into Polymers

    34. Dispersion of MWNT in PP Determination Optical microscopy SEM and TEM 0 - 10 rating

    35. Mixing Energy Increases with Loading

    36. Mixing Energy for Dispersion

    37. Melt Processing Thin Films

    38. Surface resistivity

    39. Conductive Plastics Current technology carbon blacks 10-15% loadings loss of mechanical properties MWNT Composites 0.1 - 1 wt% loadings low percolation threshold tunable

    40. Melt Processing Polymer and Pitch Fibers

    41. Fiber Formation

    42. Polymer Fibers with Aligned MWNT

    43. MWNT/PP Fibers

    44. Carbon Fiber with 1wt% MWNT

    45. Carbon fiber with 2wt% MWNT

    46. MWNT-Pitch Fibers Western KY Coal Extract Pitch Strength: 373 MPa Modulus: 28.7 GPa WKy + 1 wt% MWNT Strength: 506 MPa Modulus: 34 GPa Aromaticity of pitch seems to aid dispersion

    47. Failure of NT-Composite Materials

    48. NT-Composite Failure (Dickey)

    49. Failure modes of MWNT Composites Bridging during crack formation Good adhesion ‘telescopic’ failure Poor adhesion MWNT pull-out

    50. ‘Telescopic’ failure ‘sword-in-sheath’ Good MWNT-matrix adhesion Outer shells fail at some defect Inner shells slide out intact

    51. MWNT Reinforcement Tensile properties Large enhancement in modulus Little effect on tensile strength Similar to what has been seen in VGCF composites (ref. Tibbetts) Compressive properties Similar to tensile Tensile/compressive ? 1 with increasing structural perfection (ref. Wagner)

    52. Benzyne Functionalization of MWNT (Meier, Andrews) Benzyne addition on sidewall of MWNT Composite polystyrene films Improved dispersion Improved matrix-nanotube adhesion Results Good dispersion Reduction in film brittleness Improved flexibility over blank films and unfunctionalized MWNT composites Increased flexural strength!!

    53. Acknowledgements

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