nano particulate technology nag

7/31/2019 Nano Particulate Technology Nag

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Nano-Particulate Technology:

Synthesis


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Feynmans Vision in 1959

There is plenty of room at the bottom

Microtechnology is a frontier to be pushed

back, like HP, HV, LT

Ordinary machines could build small

machines, which could build smaller

machines,. to atomic level

22 years later, first journal publication ofarticle on molecular nanotechnology

(Drexler, 1981)


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Excerpts from The Hindu interview with Prof. Pradeep,

Dept of Chemistry, IIT Madras; March 28, 2007

What is nano technology?

The term nano technology refers to a broad range of technologies, all of whichinvolve the utilisation of the properties of nano scale objects. Nano scale refers tothe size regime of nanometers or 10 to the power of -9 meters. The properties of

materials in this size regime are unique. Nano technologies became possible as aresult of our capability to manipulate matter with atomic precision. At the scale ofnanometer, all disciplines converge. Therefore, nano technology is a fusiontechnology.

At this length scale, new properties and new phenomena come about. Materialsstart behaving differently. An example is reactive gold. Till now we knew onlyabout noble metal gold, which does not change with time. Now we have highlyreactive gold. In addition, we know of fluorescent and magnetic gold. Thisexample suggests that numerous other materials with completely differentproperties could be made. This possibility is a result of the capability tomanipulate matter at this length scale the length scale of atoms.


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Excerpts from The Hindu interview with Prof. Pradeep,

Dept of Chemistry, IIT Madras; March 28, 2007

Why is it necessary to know about nanotechnology?

Well, look at nature. Leaves make complex molecules called

carbohydrates starting from a single carbon molecule,carbon-dioxide, present in air. These molecules make lifepossible for all of us. Every molecular assembly in nature isby this atom-by-atom approach. From amoeba to elephant ismade this way. These synthetic routes are the most energy

efficient, green and sustainable. The motion of a musclefibre, or a flagellum is the result of nano technologies.Therefore, ultimately an understanding of these will help usto do things better, with improved efficiency in much moreeco-friendly, sustainable manner. Of course when you lookat properties at this length scale, one may find new things.

That drives the other side of scientific enquiry curiosity.


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Nano-Engineered Products

Semiconductor nano-crystallites for use inmicroelectronics

Ceramics for use in demanding environments

Polymers with enhanced functional properties

Transparent coatings with UV/ IR absorption properties,abrasion resistance

Static dissipative/ conductive films

Enhanced heat-transfer fluids

Catalysis

Topical personal care (e.g., sunscreen) &pharmaceutical applications

Ultrafine polishing of e.g., rigid mememory disks, opticallenses, etc.


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Functional Polymer Fillers

To improve viscoplastic properties

By addition of inorganic fillers Glass fiber, talcum, kaolin

20-60% dosage Disadvantage: incresed density of the composite

materials

Late 80s: Toyota developed nano-clays

(bentonite) for automotive applications Functional polymers are very versatile, even tiny

amounts can have dramatic impact


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Other Applications

Nanowire & Nanotube arrays for EMI Shielding Superior thermal, electrical, mechanical properties

SWNT, MWNT

Metallic or semiconducting

Carbon nanotubes provide special advantage in shielding

Chemical Gas Sensing Low-power sensor arrays with high sensitivity, selectivity

e.g., humidity sensors, solid-state resistive sensors, combustible gassensors, etc.

Ceramic MEMS 2D & 3D microcomponents & microelectromechanical devices for harsh

environments Energy Conversion: Photo-voltaics, radiation detection, electroluminescent devices, etc.

Electronics & Related Fields: Scanning probe, scanning microscopy standards

Storage & memory media

Flat panel displays, etc.


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Other Applications, contd

Marine Anti-Fouling: Nanoparticles held in coating lattice, not leached out by marine

environment

Slowly release ions to provide long-term protection

Assure longevity of antimicrobial activity

Textile Fibers: Nanoparticles in nylon, PP for antimicrobial character in extremeenvironments, after extensive thermal cycling

Nanosized ZnO and CuO in synthetic fibers with minimal effects oncolor & clarity

Permanent Coatings: For long-term antimicrobial protection in many coating formulations

Healthcare, insdustrial, food processing, general paints & coatings

Catalysts: Allows thinner active layers, less usage of precious metals

High, stable solids dispersions

Key application: automotive catalytic converters


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Other Applications, contd

Fuel Cells: Rare-earth metal oxides , nanoceria

As components in electrodes

As low-temperature electrolytes in solid xide fuel cells

(SOFC) Sunscreen:

To protect human screen from harmful UV rays

Nanomaterials are effective sun blockers

Semiconductor Polishing: CMP slurries with fumed silica, collidal silica

Ceria, alumina dispersions in nano-sizes

High planarity, efficient removal, unique surfacechemistry


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Nano-Particles

Fundamental building blocks of nano-

technology

Starting point for bottom-up approaches

for preparing nano-structured materials &

devices

Their synthesis is an important research

component


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Nano-Particle Synthesis Methods

Colloidal processes Bognolo, 2003

Liquid-phase synthesis

Grieve et al., 2000 Gas-phase synthesis

Kruis et al., 1998

Vapor-phase synthesis

Swihart, 2003

Sono-fragmentation Gopi, 2007! (Ph.D. thesis)


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Colloidal Process

Nanoparticles produced directly to requiredspecifications, assembled to perform a specifictask

Involves use of surface-active agents e.g., CdS 50 nm particles by mixing two solutionscontaining inverted micelles of sodium bis(2-ethylhexyl) sulfosuccinate in heptane

e.g., antiferromagnetic nanoparticles of Fe2O3 by

decomposition of Fe(CO)5 in a mixture of decalineand oleyl sarcosine

Coordinating ligands used to producenanoclusters

Surfactants play a major role


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Vapor-Phase Synthesis Vapor phase mixture rendered thermodynamically unstable relative to formation of

desired solid material supersaturated vapor

chemical supersaturation particles nucleate homogeneously if

Degree of supersaturation is sufficient

Reaction/ condensation kinetics permit

Once nucleation occurs, remaining supersaturation relieved by Condensation, or

Reaction of vapor-phase molecules on resulting particles

This initiates particle growth phase

Rapid quenching after nucleation prevents particle growth By removing source of supersaturation, or

By slowing the kinetics

Coagulation rate proportional to square of number concentration Weak dependence on particle size

At high temperatures, particles coalesce (sinter) rather than coagulate Spherical particles produced

At low temperatures, loose agglomerates with open structures formed At intermediate temperatures, partially-sintered, non-spherical particles form

Control of coagulation & coalescence critical

Nanoparticles in gas phase always agglomerate Loosely agglomerated particles can be re-dispersed with reasonable effort

Hard (partially sintered) agglomerates cannot be fully redispersed


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Liquid-Phase Synthesis

Used widely for preparation of quantum

dots (semiconductor nanoparticles)

Sol-Gel method used to synthesize

glass, ceramic, and glasss-ceramic

nanoparticles

Dispersion can be stabilized indefinitely by

capping particles with appropriate ligands


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Sol-Gel Method

Aqueous or alcohol-based

Involves use of molecular precursors, mainly alkoxides Alternatively, metal formates

Mixture stirred until gel forms

Gel is dried @ 100 C for 24 hours over a water bath,then ground to a powder

Powder heated gradually (5 C/min), calcined in air @500 1200 C for 2 hours

Allows mixing of precursors at molecular level

better control High purity

Low sintering temperature

High degree of homogeneity

Particularly suited to production of nano-sized multi-component ceramic powders


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Gas-Phase Synthesis

Supersaturation achieved by vaporizing materialinto a background gas, then cooling the gas Methods using solid precursors

Inert Gas Condensation

Pulsed Laser Ablation Spark Discharge Generation

Ion Sputtering

Methods using liquid or vapor precursors Chemical Vapor Synthesis

Spray Pyrolysis Laser Pyrolysis/ Photochemical Synthesis

Thermal Plasma Synthesis

Flame Synthesis

Flame Spray Pyrolysis

Low-Temperature Reactive Synthesis


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Inert Gas Condensation

Suited for production of metal (e.g., Bi)nanoparticles Reasonable evaporation rates at attainable

temperatures

Procedure: Heat solid to evaporate it into a BG gas

Mix vapor with a cold inert gas to reduce temperature

Include reactive gas (e.g., O2) in cold gas stream toprepare compounds (e.g., oxides)

Cntrolled sintering after particle formation usedto prepare composite nanoparticles (e.g., PbS/

Ag, Si/In, Ge/In, Al/In, Al/Pb)


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Pulsed Laser Ablation

Use pulsed laser to vaporize a plume of material Tightly confined, spatially & temporally

Can generally only produce small amounts of

nanoparticles But can vaporize materials that cannot be easily

evaporated e.g., synthesis of Si, MgO, titania, hydrogenated-

silicon nanoparticles Strong dependence of particle formation

dynamics on BG gas


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Spark Discharge Generation

Charge electrodes made of metal to be vaporized inpresence of inert BG gas until breakdown voltage isreached Arc formed across electrodes vaporizes small amount of metal

e.g., Ni Produces very small amounts of nanoparticles

but in a reproducible manner

Reactive BG gas (e.g., O2) can be used to makecompounds (e.g., oxide)

BG gas can be pulsed between electrodes as arc isinitiated Pulsed arc molecular beam deposition system


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Ion Sputtering

Sputter solid with beam of inert gas ions

e.g., magnetron sputtering of metal targets

Low pressure (appr 1 mTorr) required

Further processing of nanoparticles in aerosol

form difficult


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Chemical Vapor Synthesis Vapor phase precursors brought into a hot-wall reactor under nucleating

condition Vapor phase nucleation of particles favored over film deposition on surfaces

CVC reactor (Chemical Vapor Condensation) versus CVD

Very flexible, can produce wide range of materials

Can take advantage of huge database of precursor chemistries developedfor CVD processes

Precursors can be S, L or G under ambient conditions

but delivered to reactor as vapor (using bubbler, sublimator, etc) Examples:

Oxide-coated Si nanoparticles for high-density nonvolatile memory devices

W nanoparticles by decomposition of tungsten hexacarbonyl

Cu and CuxOy nanoparticles from copper lacetonate

Allows formation of doped or multi-component nanoparticles by use of

multiple precursors nanocrystalline europium doped yttria from organometallic yttrium & europiumprecursors

erbium in Si nanoparticles

zirconia doped with alumina

one material encapsulated within another (e.g., metal in metal halide) Can prevent agglomeration


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Spray Pyrolysis

Use of a nebulizer to inject very small

droplets of precursor solution

Also known as aerosol decomposition

synthesis, droplet-to-particle conversion

Reaction takes place in solution in the

droplets, followed by solvent evaporation

e.g.: preparation of TiO2 and Cu

nanoparticles


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Laser Pyrolysis/ Photothermal

Synthesis

Precursors heated by absorption of laserenergy

Allows highly localized heating & rapid

cooling Infrared (CO2) laser used

Energy absorbed by precursors, or by inert

photosensitizer (SF6) e.g.: Si from silane, MOS2, SiC

Pulsed laser shortens reaction time, allowspreparation of even smaller particles


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Thermal Plasma Synthesis

Inject precursors into a thermal plasma

Precursors generally decomposed fullyinto atoms

Which then react or condense to formparticles

When cooled by mixing with cool gas, or

expansion through a nozzle Used for production of SiC and TiC for

nanophase hard coatings


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Flame Synthesis

Particle synthesis within a flame

Heat produced in-situ by combustion reactions

Most commercially successful approach Millions of metric tons per year of carbon black and metal oxides

produced Complex process, difficult to control

Primarily useful for making oxides

Recent advances:

g-Fe2O3 nanoparticles Titania, silica sintered agglomerates

Application of DC electric field to flame can influenceparticle size


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Flame Spray Pyrolysis

Directly spray liquid precursor into

flame

Allows use of low-vapor-pressureprecursors

Applied to synthesis of silica particles

from hexamethyldisiloxane


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Low-Temperature Reactive

Synthesis

React vapor phase precursors directly w/oexternal addition of heat

and w/o significant production of heat

e.g.: ZnSe nanoparticles fromdimethylzinc-trimethylamine and hydrogenselenide

by mixing in a counter-flow jet reactor at RT heat of reaction sufficient to allow particlecrystallization


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Advances in Instrumentation for

Nano-Particle SynthesisNeed to analyze processes with short time-scales, in small

regions of a reactor, in complex mixtures

FTIR spectroscopy (in emission & transmission modes)to simultaneously characterize gas temperature,

gas concentrations,

particle temperature, and

particle concentration during synthesis

Localized thermophoretic sampling and in-situ lightscattering measurements of particle concentration, size, and

morphology

Particle mass spectrometry and TEM imaging ofextracted samples


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Advances in Modeling for Nano-

Particle Synthesis

Compute particle nucleation rates based ondetailed chemical reaction kinetics in cases where nucleation does not occur by simple

condensation of a supersaturated vapor

Model multi-dimensional particle sizedistributions where both particle volume and surface area are

explicitly treated

Model simultaneous coagulation and phasesegregation in multi-component particlescontaining mutually immiscible phases


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Sonochemical Nano-Synthesis

Sonochemistry: molecules undergo a chemical reactiondue to application of powerful ultrasound (20 kHz 10MHz) Acoustic cavitation can break chemical bonds

Hot Spot theory: As bubble implodes, very high temperatures (5,000 25,000 K) are realized for a few nanoseconds; this is

followed by very rapid cooling (1011

K/s) High cooling rate hinders product crystallization, henceamorphous nanoparticles are formed

Superior process for: Preparation of amorphous products (cold quenching)

Insertion of nano-materials into mesoporous materials By acoustic streaming

Deposition of nanoparticles on ceramic and polymeric surfaces

Formation of proteinacious micro- and nano-spheres Sonochemical spherization

Very small particles


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Sonochemical Nano-Synthesis:

Examples S-2, Se-2, Te-2

used in non-linear optic detectors, photorefractive devices,photovoltaic solar cells, optical storage media

Gold, Co, Fe, Pg, Ni, Au/Pd, Fe/Co

Nanophased oxides (titania, silica, ZnO, ZrO2, MnOx More uniform dispersion, higher surface area, better thermal

stability, phase purity of nanocrystalline titania reported

MgO coating on LiMn2O4 Magnetic Fe2O3 particles embedded in MgB2 bulk

Nanotubes of C, hydrocarbon, TiO2, MeTe2 Nanorods of Bi2S3, Sb2S3, Eu2O3, WS2, WO2, CdS, ZnS,

PbS, Fe3O4 Nanowires of Se


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Sono-Processing of Nanocomposites

Power ultrasound can assist in synthesis,blending, dispersion & erosion-testing of nano-composites dispersed phase having at least one dimensin < 100

nm High-intensity ultrasound used with melt

processing for polymer-clay nano-composites e.g., PP/PS-clay & PMMA/clay nano-composites

prepared by ultrasonic-assisted melt mixing

clay aggregates more finely dispersed Superior overall homogeneity of composite, improved

performance


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Sono- Fragmentation

(Size Reduction)

Particles

Bubble


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Sono- Fragmentation

(Size Reduction)

Particles

Bubble

Bubble Collapse

due to Implosion

Particle Fragments

due to

a) Violent Bubble

collapse

b) Inter-particle

attrition


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Sono- Fragmentation

(Size Reduction)

Particles

Bubble

Bubble Collapse

due to Implosion

Particle Fragments

due to

a) Violent Bubble

collapse

b) Inter-particle

attrition

Fragmented Particle


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Feed Sample

Micron sized

feed particles

Distilled

Water


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Sonication

20 kHz, 1000 W,

Probe type

Sonication/

58 kHz, 500 W, Tank

Micron sized

feed particles

Distilled

Water


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Sono-Processed Sample

20 kHz, 1000 W,

Probe type

Sonication/

58 kHz, 500 W, Tank

Micron sized

feed particles

Distilled

Water

Sub-Micron

/Nano Sized

ParticlesMicron sized

particles


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Sono-Processed Sample

(stratified Mix)

Sub-

micron/

nano

ParticlesMicron

Sized

Particles


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Sono-Blending

(Particle Size De-stratification)

Sub-

micron/

nano

ParticlesMicron

Sized

Particles

High

Frequency

Sonication


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Sono-Blended Particles For

Composite Formulation

Sub-

micron/

nano

ParticlesMicron

Sized

Particles

High

Frequency

Sonication

Good Blend ofSub-micron

/Micron-sized

particle

Drying

out at 105

Deg C

Blended sample

Ready for

composite

Formulation


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Polymer Precursor Preparation

Blended sampleReady for

composite

Formulation

Solvent

e.g CHCl3


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Polymer Precursor Preparation

Blended sampleReady for

composite

Formulation

Solvent

e.g CHCl3

Sonication

For 2 mts

Polymer

Precursor

( Particles

Dispersed in

solvent)


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Polymer Matrix


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Particle Reinforced Polymer Matrix

Particle

Polymer Matrix

C i i E i O h i


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Caviation Erosion On the ceramic

Particle Reinforced Polymer Matrix

Particle

Polymer Matrix

CavitationBubble

Superior Cavitation Erosion Resistance on


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Superior Cavitation Erosion Resistance on

Nano-Composites

Erosion Resistance Enhancement, PMMA

0

0.3

0.6

0.9

1.2

0 2 4 6 8 10

Sonication T ime

(minutes)

Turbidity

N.T.U

Withfiller materialwith out filler material

Erosion Resistance Ehancement

0

0.0005

0.001

0 2 4 6 8 10

Sonication time (minutes)

Massloss(grams)

with filler material

without filler material

- Mass loss and turbiditydata show same relativetrends

-Sono-Cavitation test results shown to correlate with classical impact-erosion test results.


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Thicknes

s ( m) VL VS

Den

sity mu

LAM

BDA E nu G

Unfilled PMMA 0.541 1.232 0.675 1.1 0.501 0.669 1.288 0.286 0.501

Filled PMMA 0.8712 1.421 0.846 1.16 0.83 0.683 2.034 0.226 0.83

E = Youngs Modulus in GPa.

G = Shear Modulus in GPa.Nu = Possions ratio.

VL= longitudinal velocity mm/micro sec.

VS= Shear velocity mm/micro sec.

Lamda and mu are Lamis constant

WFA Filled PMMA

has Higher E.moduliand shear moduli

C l i


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Conclusion

Nano-particulate technology is gaining

prominence as nano-science becomes old

news (& pico-science, femto-science begin to

emerge!)

Opportunities abound in scale-up &commercialization of nano-particle synthesis

Bottom-up & Top-down methods are both

used

pros & cons must be weighed for specific application

PSP Lab in ChE Dept @ IITM has cutting-edge

research program in various aspects of nano-

nano particulate technology nag

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