Structure and mechanical properties of Carbon nanotubes

Structure and mechanical
properties of Carbon nanotubes
J. Gil Sevillano
TECNUN
2003
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Many people considers C nanotubes
(discovered in 1991) as the fiber and cable
material of the future:
Very high stiffness
Very high strength
High aspect ratio
Low density
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Recent press quotation
Not (only) Science Fiction: An Elevator to Space!
With advances toward ultrastrong fibers, the concept of building an
elevator 60,000 miles high to carry cargo into space is moving from the
realm of science fiction to the fringes of reality (?)
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Not science-fiction at all!
"Technically it's feasible," said Robert Cassanova, director
of the NASA Institute for Advanced Concepts. "There's
nothing wrong with the physics."
The key to the concept's feasibility lies in the material that
will be used to construct the ribbon between the Earth and
outer space: NANOTUBES
Nanotubes are essentially sheets of graphite -- a lattice of carbon --
seamlessly rolled into long tubes that are mere
nanometers in diameter. These are 100 times
but much lighter.
as strong as steel,
NIAC has given more than $500,000 to Seattle-based
HighLift Systems to develop the concept under the leadership
of the company's chief technology officer, Bradley Edwards.
Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
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Carbon nanotubes
Elastic modulus and strength of C multi-walled C
nanotubes (MWCNT) measured by direct tension in a
TEM (Demczyk et al., 2002):
E (TPa)
σ f (GPa)
F f (µN)
Tube diameter (nm)
0.91 ( ± 0.18)
150 ( ± 45)
18
12.5
Other experimental values in the literature range from 0.1 to
1.8 TPa and 10 to 150 GPa for, respectively the CNT Young
modulus and strength.
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Theoretical estimations for graphene sheets Young modulus and
fracture strength are, respectively, 1.03 TPa and 140 to 177 GPa
(Demczyk et al., 2002). A thickness of 0.34 nm of the sheet has been
assumed for calculating the stress.
First-principles calculations for SWCNT (single-walled C nanotubes,
Zhou et al., 2001) yield E = 0.76 TPa and = 6.25 GPa.
Molecular dynamics have yielded 3.62 TPa and 9.6 GPa for the same
properties (Yao et al., 2001).
More recent results of MD yield 1.24 to 1.35 TPa for the Young
modulus (Jin and Yuan, 2003) for SWCNT or 1.05 TPa (Li and Chou,
2003) for MWCNT.
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Bundles of CNT
Oriented CNT bundles can be considered Van der Waals solids,
with very weak transverse properties, highly anisotropic.
Up to now, most realizations of CNT “cables” yield very
modest results: Vigolo et al. (2000) have measured 9 to
15 GPa for the apparent Young modulus and about 150
MPa for the apparent tensile strength of bundles of
oriented 1.4 nm diameter SWCNT (fibres up to 100 µm
diameter, 1.3 to 1.5 g/cm3 density).
However, Baughman (2000) has quoted a tensile stregth
of 36 GPa with a 6% elongation for small diameter CNT
bundles.
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
What are CNT?
Tubules of closed graphene sheets
[A very good recent review: Ruoff et al., C. R. Physique, in press, 2003]
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Graphene sheets of
graphite
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
3-D surfaces based on graphene sheets
may be imagined and some of them,
CNT among others, are possible
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Graphene is in-plane anisotropic
The orientation on the sheet plane
is defined by the chiral vector
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Chiral vector
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
SWCNT of different chiral vector
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
MWCNT
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Nanotube
ends
Atomic resolution
STM image of
nanotubes
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
CTN are fabricated by different
methods
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Direct-current electric arc discharge method
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Laser ablation method
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
NT towers or carpets grown by cathalisis
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Mechanical testing of SWCNT: direct tensile testing
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Elastic modulus measured by vibration
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
TENSILE TESTS
WARNING: stress calculated assuming an
equivalent thickness of 0.34 nm for each layer of
loaded CNT!
SWCNT (Yu et al., 2000a)
E (mean): 1002 GPa
MWCNT (Yu et al., 2000b)
E: 270 to 950 MPa
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
An example of calculation of elastic constants of CNT
[with an engineer-mind method]
(Li and Chou, 2003)
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
SWCNT as a frame structure
Covalent bonds are
treated as connecting
beam elements between C
atoms, resisting stretching,
bending and torsion.
Bean dimensions and force
constants are fitted to the
molecular force field
constants (linear behaviour
assumed)
Analysis of tensile deformation
Id. of shear
Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
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Interlayer forces in MWCNT
Non-directional Van der Waals
forces are simulated with a
Lennard-Jones potential
transmitted by rods connected
by rotatable end joints (only
tensile or compressive forces
are transmited)
(Strongly non-linear response)
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
3
1
1
2
2
2
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
3
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Another calculation:
2
3
SWCNT (Natsuki et al. 2003)
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
As mentioned at the beginning, not only rigidity
but CNT strength is exceptional as well!
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
An optimistic view?
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
The strength depends on orientation
Sometimes
the results
reported are
rather poor
Mechanical behaviour is a function of
chiral vector of SWCNT
Stone-Wales defect formation leads to
(soft) plastic behaviour or to brittle
fracture depending on chirality
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Other questions to be considered for the
design of and with CNT
E.g.: flattening, buckling
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Flattening from Van der waals forces
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
TEM
FEM calculation
Buckling on bending, Pantano et al., 2004
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
Torsional buckling
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN
“The importance, due to the high expected strength,
the known high stiffnessin tensile load, and the load
density, of CNT materials means that their
mechanical properties deserve and will surely
receive scrutiny for decades to come”
(R. S. Ruoff, D. Quiang and W. K. Liu, 2003)
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Carbon Nanotubes – Mechanical Properties – J. Gil Sevillano - TECNUN