synthesis of nanoparticles by chemical routes

8/13/2019 Synthesis of Nanoparticles by Chemical Routes

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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.
http://en.wikipedia.org/wiki/Chemosynthesishttp://en.wikipedia.org/wiki/Chemosynthesis


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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.
http://en.wikipedia.org/wiki/Moleculehttp://en.wikipedia.org/wiki/Molecule


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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
http://en.wikipedia.org/wiki/Oscillationhttp://en.wikipedia.org/wiki/Oscillation


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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)

synthesis of nanoparticles by chemical routes

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