2. The properties
of
nanomaterials
depend upon :
• Size
For example: copper nanoparticles smaller
than 50nm are super hard
Materials and do not exhibit the
properties of mallaebility or ductility of
bulk copper
3. The different
types of
properties
shown by
nanomaterials
are:
Physical properties
Chemical properties
Electrical properties
Optical properties
Magnetic properties
Mechanical properties
4. Physical
properties of
nanomaterials
By reducing the size of the particle the
surface to volume ratio increases.
This changes the surface pressure
,resulting in decrease in the interatomic
spacing .
The change in inter atomic spacing and
large surface to volume ratio have a
combined effect on material properties
such as,
5. Melting point:
• The melting point decreases with
size and at very small sizes the
decrease is faster
6. Chemical
properties
The large surface to volume ratio ,the
variations in geometry have a strong effect
on catalytic properties.
One such property is the absorption of
hydrogen in metals ,most of the metals do
not absorb hydrogen ,only few met also
absorb on their surfaces with a hydrogen-to-
metal atom ratio of 1.This limit is
significantly increased in small sizes.
7. Chemical
properties
• In small positively charged clusters of
Ni, Pd and Pt can absorb up to eight
hydrogen atoms per metal atom
• The number of absorbed atoms
increases with decrease in cluster size
• This shows that small particles are very
useful in hydrogen storage devices in
metals
8. Quantum well, wire,dot
Quantum well-If only one of the three dimensional nano
structure is of a nano dimension then it is called a quantum well
Quantum wire: if two dimensions of a nanomaterial are in
nanoscale then it is called a quantum wire
Quantum dot: if all three dimensions are in nanoscale then it is
called as quantum dot.
9. Electrical
properties
In case of metals with L=1cm separation
between consecutive energy levels can be
shown to be in a order of 10^-14eV.This we can
consider to be continuous or quari- continuous
But in nano scale range separation between
energy levels works out to be 10^-4eV.thus we
find that in nanoscale range ,energy levels are
discrete.
The density of states of conduction electrons is
strongly affected by the dimensionality of the
material
10. Electrical properties
• In the figure we see that due
quantum confinement the energy
levels narrow down and become
discrete when we move from bulk
to dot
• Tn nanomaterials the electrical
conductivity increases with
reduction in particle size
11. Optical properties
• Depending on the particle size ,different
colors are seen for example gold nano
spheres of 100nm appear orange in colour
while 50 nm nanospheres appear green in
colour
• Particles can be made to emit or absorb a
specific wavelength by controlling their size
This Photo by Unknown author is licensed under CC BY-SA.
12. Magnetic properties
• Nano materials show high coercivity and
magnetization values
• These values increase with decrease in the grain
size and an increase in the specific surface area
of the grains
• The magnetic moment of Co particles of approx
2nm exhibited 20% higher value than that of
bulk
• Nano particles of even non- magnetic solids are
found to be magnetic
13. Mechanical
properties
• If the grains are nanoscale in size ,the
interface within the material greatly
increases, which enhances the strength
• For example: nanocrystalline nickel is as
strong hardened steel
• Decreasing hardness with decreasing
grain size in the nanoscale grain regime
• Superplastic behaviour of ceramic
14. Superplasticity
Is the capability of some
polycrystalline materials to exhibit
very large texture deformations
without necking or fracture
Superplasticity is observed in nano
materials at lower temperatures
and high strain rates.
