01 - Fundamentals of Nano Materials

8/3/2019 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

01 - Fundamentals of Nano Materials

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