Unit - V Nano-Materials Engineering Physics: Origin of Nano Technology
Unit - V Nano-Materials Engineering Physics: Origin of Nano Technology
Unit - V Nano-Materials Engineering Physics: Origin of Nano Technology
Nano-materials
Engineering Physics
Introduction
In recent years nanotechnology has become one of the most important and
exiting forefront fields in physics, chemistry, biology and engineering and technology.
Nano means 10 m. A nanometer (nm) is one thousand millionth of a meter. Atoms
are extremely small and the diameter of a single atom varies from 0.1 to 0.5 nm
depending on the type of the element. For example, one carbon atom is approximately
0.15nm in diameter and a water molecule is almost 0.3nm across. A red blood cell is
approximately 7,000 nm wide and human hair is 80,000 nm wide.
Origin of Nano technology
While the word nano technology is relatively new, the existence of nanostructures
and nanodevices is not new. Such structures existed on the earth as life itself. Though
it is not known when humans began to use nanosized materials, the first known, Roman
glassmakers were fabricated glasses containing nanosized metals.
When the material size of the object is reduced to nanoscale, then it exhibits different
properties than the same material in bulk form.
Nanoscience
Nano science deals with the study of properties of materials at nano scales where
properties differ significantly than those at larger scale.
Nanotechnology
Nanotechnology deals with the design, characterization, production and applications of
nanostructures and nanodevices and nanosystems.
1. Nano materials
All materials are composed of grains. The visibility of grains depends on their
size. Convectional materials have grains varying in size from hundreds of microns to
millimeters. The materials processing grains size ranging from 1 to 100 nm, known as
nano materials. Nano materials can be produced in different dimensionalities. These
are classified as
One dimensional nano materials
Two dimensional nano materials
Three dimensional nano materials
One dimensional nano materials
In this, the grains will be layered in the form of multi layers, such as thin films or
surface coatings.
Two dimensional nano materials
In this, the ultrafine grains will be layered, such as nano wires or nano tubes
Three dimensional nano materials
In this, the grains will be in nano size, such as precipitates and colloids.
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Unit V
Nano-materials
Engineering Physics
Due to increase of surface of surface area, more number of atoms will appear at the
surface of compared to those inside. For example, a nano material of size 10nm has
20% of its atoms on its surface and 3nm has 50% of its atoms. This makes the
nanomaterials more chemically reactive and affects the properties of nano materials.
Quantum confinement effect:
According to band theory, the solid atoms have energy bands and isolated atoms
possess discrete energy levels. Nano materials are the intermediate state to solids and
atoms. When the material size is reduced to nanoscale, the energy levels of electrons
change. This effect is called quantum confinement effect. This affects the optical,
electrical and magnetic properties of nanomaterials.
Unit V
Nano-materials
Engineering Physics
powder from the balls depends on many factors such as rotational speed of the balls,
number of balls, milling time and the milling medium.
Vapour
generator
Particle
Collection
Unit V
Nano-materials
Engineering Physics
This method is used to produce the nano powders of oxides and carbides of metals.
Production of pure metal powders is also possible using this method.
6. Sol-gel method
Sol-gel method is one of the bottom up approach for the fabrication of
nanoparticles by assembling the atoms. The sol-gel process is a wet technique i.e.,
chemical solution deposition technique used for the production of high purity and
homogeneous nanomaterials. In solutions the molecules of nanometer size are
dispersed and move around randomly and hence the solution are clear. In colloids the
molecules of size ranging from 20 to 100 are suspended in a solvent. When
mixed with a liquid is called as sol. A suspension that keeps its shape is called a gel.
Thus the colloids are suspensions of colloids in liquids that keep their shape. The
formation of sol-gels involves four steps:
a) Hydrolysis and alcoholysis
b) Water or alcohol condensation and polymerization of monomers to form particles
c) Growth of particles and
d) Formation of networks.
In general, all the above steps are dependent on several initial conditions such
as pH value of the sol temperature of reaction, reagent concentrations, time of
reaction etc. by controlling these parameters, it is possible to vary the structural,
electrical and optical properties of the sol-gel derived inorganic networks over a wide
range.
Once the gel is formed, there are several ways to convert this gel to the desired
solid form. Depending on the deposition and drying processes or conditions, this gel
can be converted into various forms such as aerogel, xerogel, gelled spheres, nano
powders, thin film coatings, nano structured layers, etc. as shown in the figure.
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Unit V
V
Nano-materials
Engineering Physics
Unit V
Nano-materials
materials
Engineering Physics
9. Properties of nanomaterials
Physical properties
Inter atomic distance:
When the material size is reduced to nanoscale, surface area to volume ratio
increases. Due to increase of surface area, more number of atoms will appear at the
surface of compared to those inside. This changes the surface pressure and results in
change in the Interatomic spacing. The variation of Interatomic spacing in copper with
decrease of particle
icle is shown in figure.
0.26
0.25
0.24
0.23
0.22
0.21
0.2
1.00
2.00
3.00
4.00
5.00
Diameter nm
Melting point
Melting point for nano materials are different from that of bulk materials. The
Debye Temperature and ferroelectric phase transition temperature are lower for nano
materials. The melting point of nano gold decreases from 1200 K to 800K as the size of
particle decreases form 300A0 to 200A0. The variation of melting point in gold with
decrease of particle is shown in figure.
Unit V
Nano-materials
Engineering Physics
Optical properties:
Absorption
Different sized nano particles scatters different of light incident on it and hence
they appear with different colours. For example nano gold does not act as bulk gold.
The nano particles of gold appear as orange, purple, red or greenish in colour
depending on their grain size. The bulk copper is opaque where as nanoparticle copper
is transparent. The optical absorption spectrum of gold as a function of particle size is
shown in figure.
100
90
80
70
60
50
40
30
20
10
0
60 nm
20 nm
400
450
500
550
600
650
700
Wave length nm
Magnetic properties:
The magnetic properties of nano materials are different from that of bulk materials. In
explaining the magnetic behavior of nanomaterials, we use single domains unlike large
number of domains in bulk materials. The coercivity values of single domain are very
large. The variation of remanet magnetization and coercivity as a function of grain size
is shown in figure.
For example, Fe,Co, and Ni are ferromagnetic in bulk but they exhibit super par
magnetism. Na, K, and Rh are paramagnetic in bulk but they exhibit ferro-magnetic.
Cr is anti ferromagnetic in bulk but they exhibit super paramagnetic.
Unit V
Nano-materials
Engineering Physics
Mechanical properties
The mechanical properties such as hardness, toughness, elastic modulus,
youngs modulus etc., of nano materials are different from that of bulk materials. In
metals and alloys, the hardness and toughness are increased by reducing the size of
the nano particles. In ceramics, ductility and super plasticity are increased on reducing
grain size. Hardness increases 4 to 6 times as one goes from bulk Cu to
nanocrystalline and it is 7 to 8 times for Ni.
Thermal properties
Chemical properties
Nanocrystalline materials are strong, hard, erosion and corrosion resistant. They are
chemically active and have the following chemical properties.
1. In electrochemical reactions, the rate of increase in mass transport increases as
the particle size decreases.
2. The equilibrium vapour pressure, chemical potentials and solubilites of
nanoparticles are greater than that for the same bulk material.
3. Most of the metals do not absorb hydrogen. But the hydrogen absorption
increases with the decrease of cluster size in Ni, Pt and Pd metals.
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Unit V
Nano-materials
Engineering Physics
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Unit V
Nano-materials
Engineering Physics
Material technology
Nanocrystalline aerogel are light weight and porous, so they are used for
insulation in offices homes, etc,.
Cutting tools made of nanocrystalline materials are much harder, much more
wear- resistance, and last stranger.
Nanocrystalline material sensors are used for smoke detectors, ice detectors
on air crfr wings, etc,.
Nanocrystalline materials are used for high energy density storage batteries.
Nanosized titanium dioxide and zinc dioxide are used in sunscreens to absorb
and reflect ultraviolet rays.
Nan coating of highly activated titanium dioxide acts as water repellent and
antibacterial.
The hardness of metals can be predominately enhanced by using
nanoparticles.
Nanoparticles in paints change colour in response to change in temperature
or chemical environment, and reduce the infrared absorption and heat loss.
Nanocrystalline ceramics are used in automotive industry as high strength
springs, ball bearings and valve lifters.
Information technology
Nanoscale fabricated magnetic materials are used in data storage
Nano computer chips reduce the size of the computer.
Nanocrystalline starting light emitting phosphors are used for flat panel
displays.
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Unit V
Nano-materials
Engineering Physics
Biomedicals
Biosensitive nanomaterials are used for ragging of DNA and DNA chips.
In the medical field, nanomaterials are used for disease diagnosis, drug
deliveryaand molecular imaging.
Nanocrystalline silicon carbide is used for artificial heart valves due to its low
weight and high strength.
Energy storage
Nanoparticles are used hydrogen storage.
Nano particles are used in magnetic refrigeration.
Metal nanoparticles are useful in fabrication of ionic batteries.
14. Graphene based FET
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