Transcript THERMOPLASTICS & THERMOSETTING PLASTICS

Course: B.E & B.Tech
Subject: APPLIED CHEMISTRY
Unit: V
NANOTECHNOLOGY
Dr. K. SIVAKUMAR
Dept. of Chemistry, SCSVMV University
Syllabus: Introduction - Synthesis of nanomaterials by ball milling,
vapour deposition and sol-gel methods.
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Introduction:
A nanometre is one billionth of a metre.
For comparison, Size (thickness) of
• a human hair is ~ 80,000nm
• a red blood cell is ~ 7,000nm
• a water molecule is ~ 0.3nm
•Scientists are interested in nanoscale materials with 1nm to 100nm
Properties:
Properties of materials at nanoscale are different from larger scale
Thermodynamics properties are drastically different from nanoparticles
Examples:
•Melting point of gold decreases from 1200K to 800K when the particle size
decreases from 300ºA to 20 ºA.
•In metals if the size is reduced from the bulk the electronic bands become
narrower and the value of ionization potential is raised.
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Properties…..
•In nanophase metals absorbs hydrogen. This property can be used for
hydrogen storage in metals.
•Fe, Co & Ni are in ferromagnetic in bulk state. But they are changed into
supermagnetic in nanophase.
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(Types of ) Synthesis of Nanomaterials:
1. Top down process:
•Bulk materials are broken into nano sized particle (for processing solidstate materials) Example: Ball milling method.
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(Types of ) Synthesis of Nanomaterials:
2. Bottom-up process:
•Nano materials are produced by building of atom by a atom.
Example: Chemical Vapour Deposition Method
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Synthesis of Nanomaterials:
Top down process: [No control over the
size and Morphology of particles]
Example:
1. Ball Milling
2. Plasma Arcing
3. Laser sputtering
4. Vapour Deposition methods
Bottom up process: [Size and
Morphology can be controlled]
Example:
1. Sol-Gel method
2. Colloidal method
3. Electro deposition
4. Solution phase reductions
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Ball Milling
Principle: Small hard balls are allowed to rotate inside a container and
then it is made to fall on a solid with high force to crush the solid into nano
crystal.
Construction and Working: Hardened steel or tungsten carbide balls are
put in a container along with powder of particles (50m) of a desired
material. The container is closed with tight lids.
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Ball Milling….
When the container is rotating around the central axis, the material is
forced to press against the walls. The milling balls impart energy on
collision and produce smaller grain size of nano particle.
Ball milling is also known as Mechanical alloying or crushing
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Advantages of Ball Milling
•Few mg to several kgs of nanoparticle can be synthesized in a short
time.
•This technique can be operated at large scale.
Applications
•Ball milling method is useful in preparation of elemental and metal oxide
nano crystals like Co, Cr, Al-Fe, Ag-Fe and Fe.
•Variety of intermetallic compounds of Ni and Al can be formed.
•Ball milling method is useful in producing new type building materials,
fire – proof materials, glass ceramics, etc.
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Vapour Deposition Methods: for fabricating thin films & nano
tubes
•Physical Vapour Deposition – involves direct deposition of materials
on surface
•Chemical Vapour Deposition – involves a chemical reaction followed
by the deposition
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Chemical Vapour Deposition (CVD):
Principle: The reactant particles are mixed with carrier gas and allowed to pass on through
the hot solid substrate surface. When the reactant particles and substrate comes in contact,
the heat energy initiate the chemical reactions and form nano film on the substrate surface.
The byproducts of the reactions on the solid surface can be removed by washing.
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CVD…..
Description and Working:
•CVD involves the flow of gas with diffused reactants (substances to
be deposited in vapour) over a hot substrate surface.
•The gas that carries the reactants is called the carrier gas.
•While the gas flows over the hot solid surface, the heat energy
increases chemical reactions of the reactants that form film during
and after the reactions.
•The byproduct of reactions are removed to get the thin film of
desired composition
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Advantages & applications of CVD
•To produce defect free nanoparticles
•Scaling up of the CVD system for manufacturing purpose is achieved
without any major difficulties
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Sol-gel Method:
This method involves two types of materials ‘Sol’ and ‘Gel’
Principle:
•Sol-Gel method involves formation of ‘sols’ in a liquid and then
connecting the sol particles to form a network.
•By drying the liquid, it is possible to obtain powders, thin films etc.,
Methods for sol-gel formation:
Sol can be obtained by,
•Hydrolysis
•Condensation and Polymerization of monomers to form particles
•Agglomeration of particles
After the formation of sol, formation of network (gelation) which extends
throughout the liquid medium is obtained to form a gel.
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Sol-gel Method…
•Synthesis of sol-gel involves hydrolysis of precursors, condensation
followed by polycondensation to form particles, gelation and drying
process by various routes (Figure).
•Precursors (starting chemicals) are to be chosen such that they have a
tendency to form gels.
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Sol-gel Method…
•Rate of hydrolysis and condensation reactions are governed by
various factors such as
•pH
•Temperature
•Molar ratio
•Nature
•Concentration of catalyst
•Process of drying
Finally, at proper conditions spherical nanoparticles are produced.
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Sol-gel Method…
Applications:
•Useful in oxide ceramics synthesis
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Nanopolymers:
•Polymer nanocomposites / Nanopolymer is a polymer having
dispersed in its nanoparticles.
•Nanopolymers
may be of different shape (e.g., platelets, fibers,
spheroids), but at least one dimension must be in the range of 1 to
50 nm.
•These PNC's belong to the category of multi-phase systems (MPS,
viz. blends, composites, and foams) that consume nearly 95% of
plastics production.
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Properties of Nanopolymers:
•The nanofilms show considerable reinforcement when subjected
to small deformations.
•Carbon nanotubes can conduct heat and electricity far better than
copper, and are already being used in polymers to control or
enhance conductivity.
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Preparation of Nanopolymers:
Vapor condensation process:
•Involves
evaporation
of
solid
metal
followed
by
rapid
condensation to form nano-sized clusters.
•Various approaches to vaporize the metal can be used and
variation of the medium in which the vapor is released affects the
size of the particles.
•Inert gases are used to avoid oxygen while creating nanopolymers,
where as the reactive oxygen is used to produce metal oxide
ceramic products.
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Good Luck!
Dr. K. SIVAKUMAR
Department of Chemistry
SCSVMV University
[email protected]
+91 98423 61378
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