01 - fundamentals of nano materials
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Nanomaterials:
Introduction & Properties
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How Small is NANO?
A nanometer is a billionth of a meter (Nano: 10-9)
About 1/80,000 of the diameter of a human hair
10 times the diameter of a hydrogen atom.
Ant
(1 mm)
Red blood cell (2-5
micrometer)Hydrogen
Atom
(10 nm)
1 m 1 mm (10-3 m) 1 m (10-6 m) 1 nm (10-9 m)
Human being
(1.7 m)
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Moors Law
The amount of the space required to
install a transistor on a chip shrinksby roughly half every 18 months
There is plenty of room at the bottom (Feynman 1959)
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Packing Efficiency: FCC Nanoparticle
The dark atom is surrounded by 12 nearest atoms (neighbors)
These 13 atoms constitute a smallest theoretical nanoparticlefor an FCC lattice
C.P. Poole Jr. and F.J. Owens, Introduction to Nanotechnology, Wiley-Interscience, New Jersey, 2003
In nanomaterials, the
size range is very small.
They tend to be closepacked.
Closely packed
structures are FCC and
HCP.
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Number of Atoms in FCC Nanoparticles
Shell Number Number of Atoms in FCC Nanoparticles
Total On Surface % Surface
1 1 1 100
2 13 12 92.3
3 55 42 76.4
4 147 92 62.6
5 309 162 52.4
6 561 252 44.9
7 923 362 39.2
8 1415 492 34.8
9 2057 642 31.2
10 2869 812 28.3
11 3871 1002 25.9
12 5083 1212 23.8
25 4.90 x 104 5.76 x 103 11.7
50 4.04 x 105 2.40 x 104 5.9
75 1.38 x 106 5.48 x 104 4.0
100 3.28 x 106 9.80 x 104 3.0
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0 2 4 6 8 10 12
0
1000
2000
3000
4000
5000 Total
On Surface
No
ofAtoms
No of Shells
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Melting Point of Nano Gold Particles
Melting Point of Au is 1337 K (1064 C)
Clusters of Au have same M.P. as bulk Au when they contain
1000 atoms or more.
C.P. Poole Jr. and F.J. Owens, Introduction to Nanotechnology, Wiley-Interscience, New Jersey, 2003
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Strength and Hardness
In conventional materials, strength and hardness are give by Hall
Petch relation.
As grain size decreases, hardness and strength increases.
Strengthening occurs due to movement of dislocations whichassemble at grain boundary resulting in strengthening.
If this concept is extrapolated for very small grains, exceedingly
high
(yield stress), almost theoretical limit for shearing atomicplanes should be obtained.
However, it is not true and a decrease in strength is observed forgrain size
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Inverse Hall Petch Behavior
The fall in strength for grain sizebelow 10-25nm is called InverseHall Petch behavior
As grain size become very small(10-25 nm), grains cannot supportdislocations.
New dislocations cannot be
created at grain size 10nmbecause needed to activateFrank Read dislocation source are 1/distance.
This results in Inverse Hall PetchRelation.
S. Takeuchi, The Mechanism of the Inverse Hall-Petch Relation of Nanocrystals, Scripta Materialia, 44, 2001,
14831487
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DuctilityMaterials with smaller grain size
Posses higher dislocation density
Causing quick strain hardening and thus lower ductility.
Elongation to failure is lower with a decrease in grain size
Bimodal Distribution and Fracture Toughness
The smaller grains impart high yield
strength according to Hall-Petch
relationship.
The larger grains provide strain hardening
effect attributed to their comparatively low
grain boundary area.
Bimodal distribution over a range will have a beneficial
influence on the fracture toughness by improving tensile
ductility while maintaining high yield strength.
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Mechanical Properties
Strength as grain size
Hardness as grain size Ductility as grain size
Toughness as grain size
Elastic Modulus does not change as grain size
C. Suryanarayana and C.C. Koch, Non-Equilibrium Processing of Materials, ed. C. Suryanarayana, Elsevier Science
Ltd, Oxford, UK, pp 313-344, 1999
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Superparamagnetism is a form of magnetism
Appears in ferromagnetic or ferrimagnetic nanoparticles
An external magnetic field is able to magnetize the
nanoparticles, similarly to a paramagnet.
Data storage application
Superparamagnetism