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Multiwalled Carbon Nanotubes: Synthesis and Applications

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NSF-MRSEC Advanced Carbon Materials Center. Carbon Fiber Diameters ... Surfactant assisted. Tensile strength and modulus. Experimental and Theoretical Moduli ... – PowerPoint PPT presentation

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Title: Multiwalled Carbon Nanotubes: Synthesis and Applications


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_at_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 MERs 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 (gt95 MWNT produced)
  • 60-65 carbon conversion to MWNT
  • aligned mats normal to growth surface

R. Andrews et al., Chem Phys Lets, 303 (1999)
467-474.
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 FeC ratio
  • Diameter distribution widens

18
Distribution of MWNT Diameters
Diameter function of temperature, partial
pressure and time.
19
Outer diameter relates to particle size.
Core diameter is constant (3-10 nm, average of
6nm)
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
  • Growth on substrates and walls
  • metal particle seeds growth
  • extrusion up from surface
  • tip growth following a particle

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 (birds 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, gt 95

26
Pyrograf III
  • Nanofibers
  • Applied Sciences, Inc.
  • entangled
  • some pyrolytic carbon
  • commercially available
  • lower cost, 65/lb

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

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
MWNT in HIPS
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
1 mm die, L/D 20
Composite Filament
Rotating wind-up drum
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)
Sword-in-sheath fracture
MWNTs align normal to the crack direction as
they bridge the crack
a. nanotube fracture in crack wake b. debonding
at nanotube-PS interface c. cavities from
nanotube pullout
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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