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SYNTHESIS OF NANOPARTICLES
BY CHEMICAL ROUTES
NITIN GUPTA CH9249
PRAG KOHLI CH9250
PARUL OHRI CH9251
PRIYAL KHURANA CH9255
PUNEY KIRTI CH9256
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CLASSIFICATION OF PREPARATION METHODS
In terms of phase of
medium for preparation-
Gas phaseLiquid phase
Aerosol phase
Solid phase
In terms of method of
"monomer" preparation-
Physical
Chemical Bulk
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Reverse Microemulsions Method.
Sol-gel Technique.
Mechanochemical Synthesis.
Precipitation of Solutions.
Chemical synthesis of preceramic polymers.
CHEMICAL METHODS
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REVERSE MICROEMULSION OR MICELLE METHOD
It is one of the recent promising routes to
nanocrystalline materials. Surfactants dissolved in
organic solvents form spherical aggregates called
reverse micelles.
In the presence of water, the polar head groups of
surfactant molecules organize themselves around small
water pools ,leading to dispersion of aqueous phase in
the continuous oil phase.
Reverse micelles are used to prepare nanoparticles by
using a water solution of reactive precursors that can be
converted to insoluble nanoparticles.
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Nanoparticle synthesis inside the micelles can be
achieved by various methods including hydrolysis of
reactive precursors and precipitation reactions of
metal salts. Solvent removal and subsequent
calcinations leads to final product.
Surfactants like pentadecaoxyethylene nonyl phenyl
ether(TNP-35), poly nonyl phenol ether(NP5) etc are
used
Parameters affecting the particle size distribution are:Concentration of precursor in the micelle.
Mass of aqueous phase in the microemulsion.
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ADVANTAGES OF THIS METHOD ARE-
Preparation of very small particles
Ability to control the particle size.
DISADVANTAGES ARE-
Low production yields.
Need to use large amounts of liquids.
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SOL GEL METHOD
The sol- gel process is a wet-chemical technique (also known as
chemical solution deposition) is widely used in the fields of
material science .
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Such methods are primarily
used for the fabrication
of materials (typically a metal
oxide) starting from achemical solution (sol, short for
solution) which acts as the
precursor for an integrated
network (or gel) of either
discrete particles or
network polymers.
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Formation of a metal oxide involves connecting the metal centerswith oxo (M-O-M) or hydroxo (M-OH-M) bridges, therefore
generating metal-oxo or metal-hydroxo polymers in solution.
Typical precursors are metal alkoxides and metal chlorides, which
undergo hydrolysis and polycondensationreactions to form either
a network "elastic solid or colloidal suspension (or dispersion)asystem composed of discrete
Thus, the sol evolves towards the formation of a gel-like diphasic
system containing both a liquid phase and solid phase whose
morphologies range from discrete particles to continuous polymer
networks.
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This can be accomplished in many ways-
SEDIMENTATION
CENTRIFUGATION
Removal of the remaining liquid (solvent) phase requires a dryingprocess, which is typically accompanied by a significant amount
of shrinkage and densification.
In the case of the colloid, the volume fraction of particles (or
particle density) may be so low that a significant amount of fluid
may need to be removed initially for the gel-like properties to be
recognized.
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The rate at which the solvent can be removed is ultimately
determined by the distribution of porosity in the gel.
Afterwards, a thermal treatment, or firing process, is often
necessary in order to favour further polycondensation and enhance
mechanical properties and structural stability via final sintering,
densification and grain growth.
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1.Densification is often achieved at a much lower temperature.
2. The sol-gel approach is a cheap and low-temperature
technique that allows for the fine control of the products
chemical composition.
One of the distinct advantages of using this methodology as
opposed to the more traditional processing techniques ---
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PRECIPITATION FROM SOLUTION
(WET CHEMICAL SYNTHESIS)
It is one of the conventional methods for preparing nanoparticles
of metal oxide ceramics. The process involves dissolving a salt
precursor usually a chloride, oxychloride or nitrate , eg-AlCl3to
make Al2O3.
The corresponding metal hydroxides usually form and precipitate
in water on addition of a base such as sodium hydroxide or
ammonium hydroxide.
The resulting chloride salts are then washed away and hydroxide
is calcined after filtration and washing to obtain the final oxide
powder.
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The method is useful in preparing ceramic composites of differentoxides by co-precipitation of corresponding hydroxides in same
solution.
Disadvantage of this method is the difficulty in controlling the
particle size distribution.
Fast and uncontrolled precipitation often takes place, resulting in
large particles.
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CHEMICAL SYNTHESIS OF PRECERAMIC
POLYMERS
This method involves the use of molecular precursors that facilitate
the synthesis of nanomaterials containing phase of desired
composition.
Using chemical reactions to prepare the preceramic polymer
overcomes the limitation of low production yields of physicalmethods.
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This method is useful in preparing non-oxide ceramics such as
silicon carbide and silicon nitride.
Metal carbides and metal nitrides are obtained by pyrolysis of
polymers containing appropriate metal like silver or aluminium
and carbon or nitrogen(preceramic polymers).
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5. MECHANO-CHEMICAL METHODS
In conventional chemical synthesis or chemosynthesis, reactive molecules
encounter one another through random thermal motion in a liquid or vapor.
The particle morphology of Al2O3-20
wt.%ZrO2 sprayable feedstocks after
first calcination.
(a) Morphology of feedstock and (b)
high resolution of feedstock.
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In a hypothesized process of mechanosynthesis, reactive moleculeswould be
attached to molecular mechanical systems, and their encounters would result from
mechanical motions bringing them together in planned sequences, positions, and
orientations.
Nano sized particles of less than 100 nm in diameter have significant potential for a number
of applications including super plastically formed high-strength structural ceramics, optical
materials and ion conductors.Most of the unique properties of nanoparticles require not
only nano-sized particles,but also particles dispersed without agglomeration.
A relatively new solid state process named mechanochemical treatment has been applied for
the synthesis of nanopowders ie powders with particles in nano metersize range.Ingeneral,mechanochemical treatment has been recognised as a powerful technique for the
synthesis of a wide range of materials,which may be otherwise difficult to prepare by a
conventional high temprature treatment.Mechanochemical treatment is a non-equilibrium
solid-state process in which the final product retainsb a v finetypically nanocrystalline or
amorphous structure. Therefore such powders may be used as a precursor for later solid-
state reactions.It has been realized that that the use of,for instance,hydrated oxides orhydroxides relieves mechanochemical reactions.such a novel approach,mild
mechanochemical synthesis based on reactions of solid acids,bases,hydrated
compounds,basic and acidic salts is known as soft mechanochemistry.
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It is envisioned that mechanosynthesis would avoid unwanted reactions by keeping
potential reactants apart, and would strongly favor desired reactions by holding
reactants together in optimal orientations for many molecular vibrationcycles.
Mechanochemicalsynthesis of
alumina nanoparticles:
Formation mechanism and
phase transformation
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XRD patterns of (a) the
stoichiometric AlCl3/CaO initial
powder mixture, (b) after 5
hour milling, (c) after 50 hour
milling, (d) the as-milledsample calcined at 250, (e) the
as-milled sample calcined at
300 C and (f) HR-TEM image of
the 5 hour milled initial powder
mixture (inset: FFT images of
the amorphous AlCl3 andcrystalline CaO phases).
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Mechanochemical synthesis involves mechanical activation of solid state displacement
reactions. The process is used to make nanoparticles of ceramics like Al2O3and ZrO2.
Zirconium Oxide (ZrO2)
Nanopowder / Nanoparticles
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It involves the milling of precursor powders to form a nanoscale composite structure that
react during milling and subsequent heating.
Nanosized alumina powders
were synthesized bymechanochemical treatment of
stoichiometric mixture of
anhydrous AlCl3 and CaO.
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E.g.- nanoparticles of Al2O3are prepared by milling AlCl3with CaO powder. A
nanocomposite of CaO particles embedded within AlCl3matrix is obtained. Subsequent
heating at 573K led to nanoparticles of -Al2O3within a CaCl2matrix . The by-product
CaCl2can be removed by washing.
AlCl3 CaO powder
nanocomposite of CaO particles embedded
within AlCl3matrix
by-product CaCl2
can be removed by
washing.
nanoparticles of -
Al2O3within a
CaCl2matrix
On
milling
Heat(573K)