Transcript Nano-Particulate Technology

Nano-Particulate Technology:
Synthesis
Feynman’s 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 of
article on molecular nanotechnology
(Drexler, 1981)
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 which
involve the utilisation of the properties of nano scale objects. Nano scale refers to
the 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 a
result of our capability to manipulate matter with atomic precision. At the scale of
nanometer, all disciplines converge. Therefore, nano technology is a fusion
technology.
At this length scale, new properties and new phenomena come about. Materials
start behaving differently. An example is reactive gold. Till now we knew only
about noble metal gold, which does not change with time. Now we have highly
reactive gold. In addition, we know of fluorescent and magnetic gold. This
example suggests that numerous other materials with completely different
properties could be made. This possibility is a result of the capability to
manipulate matter at this length scale — the length scale of atoms.
Excerpts from “The Hindu” interview with Prof. Pradeep,
Dept of Chemistry, IIT Madras; March 28, 2007
Why is it necessary to know about nano
technology?
Well, look at nature. Leaves make complex molecules called
carbohydrates starting from a single carbon molecule,
carbon-dioxide, present in air. These molecules make life
possible for all of us. Every molecular assembly in nature is
by this atom-by-atom approach. From amoeba to elephant is
made this way. These synthetic routes are the most energy
efficient, green and sustainable. The motion of a muscle
fibre, or a flagellum is the result of nano technologies.
Therefore, ultimately an understanding of these will help us
to do things better, with improved efficiency — in much more
eco-friendly, sustainable manner. Of course when you look
at properties at this length scale, one may find new things.
That drives the other side of scientific enquiry — curiosity.
Nano-Engineered Products
• Semiconductor nano-crystallites for use in
microelectronics
• 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, optical
lenses, etc.
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
Other Applications
• Nanowire & Nanotube arrays for EMI Shielding
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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 gas
sensors, 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.
Other Applications, cont’d
• 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 extreme
environments, after extensive thermal cycling
– Nanosized ZnO and CuO in synthetic fibers with minimal effects on
color & 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
Other Applications, cont’d
• 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 surface
chemistry
Nano-Particles
• Fundamental building blocks of nanotechnology
• Starting point for “bottom-up” approaches
for preparing nano-structured materials &
devices
• Their synthesis is an important research
component
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)
Colloidal Process
• Nanoparticles produced directly to required
specifications, assembled to perform a specific
task
• Involves use of surface-active agents
– e.g., CdS 50 nm particles by mixing two solutions
containing inverted micelles of sodium bis(2-ethyl
hexyl) sulfosuccinate in heptane
– e.g., antiferromagnetic nanoparticles of Fe2O3 by
decomposition of Fe(CO)5 in a mixture of decaline
and oleyl sarcosine
• Coordinating ligands used to produce
nanoclusters
• Surfactants play a major role
Vapor-Phase Synthesis
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Vapor phase mixture rendered thermodynamically unstable relative to formation of
desired solid material
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“supersaturated vapor”
“chemical supersaturation”
particles nucleate homogeneously if
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Once nucleation occurs, remaining supersaturation relieved by
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Weak dependence on particle size
At high temperatures, particles coalesce (sinter) rather than coagulate
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By removing source of supersaturation, or
By slowing the kinetics
Coagulation rate proportional to square of number concentration
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Condensation, or
Reaction of vapor-phase molecules on resulting particles
This initiates particle growth phase
Rapid quenching after nucleation prevents particle growth
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Degree of supersaturation is sufficient
Reaction/ condensation kinetics permit
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
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Loosely agglomerated particles can be re-dispersed with reasonable effort
Hard (partially sintered) agglomerates cannot be fully redispersed
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
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
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High purity
Low sintering temperature
High degree of homogeneity
Particularly suited to production of nano-sized multicomponent ceramic powders
Gas-Phase Synthesis
• Supersaturation achieved by vaporizing material
into a background gas, then cooling the gas
– Methods using solid precursors
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Inert Gas Condensation
Pulsed Laser Ablation
Spark Discharge Generation
Ion Sputtering
– Methods using liquid or vapor precursors
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Chemical Vapor Synthesis
Spray Pyrolysis
Laser Pyrolysis/ Photochemical Synthesis
Thermal Plasma Synthesis
Flame Synthesis
Flame Spray Pyrolysis
Low-Temperature Reactive Synthesis
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 to
prepare compounds (e.g., oxides)
• Cntrolled sintering after particle formation used
to prepare composite nanoparticles (e.g., PbS/
Ag, Si/In, Ge/In, Al/In, Al/Pb)
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, hydrogenatedsilicon nanoparticles
• Strong dependence of particle formation
dynamics on BG gas
Spark Discharge Generation
• Charge electrodes made of metal to be vaporized in
presence of inert BG gas until breakdown voltage is
reached
– 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 make
compounds (e.g., oxide)
• BG gas can be pulsed between electrodes as arc is
initiated
– Pulsed arc molecular beam deposition system
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
Chemical Vapor Synthesis
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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
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Very flexible, can produce wide range of materials
Can take advantage of huge database of precursor chemistries developed
for CVD processes
Precursors can be S, L or G under ambient conditions
– but delivered to reactor as vapor (using bubbler, sublimator, etc)
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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 & europium
precursors
– erbium in Si nanoparticles
– zirconia doped with alumina
– one material encapsulated within another (e.g., metal in metal halide)
• Can prevent agglomeration
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
Laser Pyrolysis/ Photothermal
Synthesis
• Precursors heated by absorption of laser
energy
• 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, allows
preparation of even smaller particles
Thermal Plasma Synthesis
• Inject precursors into a thermal plasma
• Precursors generally decomposed fully
into atoms…
• Which then react or condense to form
particles
– When cooled by mixing with cool gas, or
expansion through a nozzle
• Used for production of SiC and TiC for
nanophase hard coatings
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 influence
particle size
Flame Spray Pyrolysis
• Directly spray liquid precursor into
flame
• Allows use of low-vapor-pressure
precursors
• Applied to synthesis of silica particles
from hexamethyldisiloxane
Low-Temperature Reactive
Synthesis
• React vapor phase precursors directly w/o
external addition of heat
– and w/o significant production of heat
• e.g.: ZnSe nanoparticles from
dimethylzinc-trimethylamine and hydrogen
selenide
– by mixing in a counter-flow jet reactor at RT
– heat of reaction sufficient to allow particle
crystallization
Advances in Instrumentation for
Nano-Particle Synthesis
Need 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
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gas temperature,
gas concentrations,
particle temperature, and
particle concentration during synthesis
• Localized thermophoretic sampling and in-situ light
scattering measurements of
– particle concentration,
– size, and
– morphology
• Particle mass spectrometry and TEM imaging of
extracted samples
Advances in Modeling for NanoParticle Synthesis
• Compute particle nucleation rates based on
detailed chemical reaction kinetics
– in cases where nucleation does not occur by simple
condensation of a supersaturated vapor
• Model multi-dimensional particle size
distributions
– where both particle volume and surface area are
explicitly treated
• Model simultaneous coagulation and phase
segregation in multi-component particles
containing mutually immiscible phases
Sonochemical Nano-Synthesis
• Sonochemistry: molecules undergo a chemical reaction
due to application of powerful ultrasound (20 kHz – 10
MHz)
– 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, hence
amorphous 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
Sonochemical Nano-Synthesis:
Examples
• S-2, Se-2, Te-2
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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
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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
Sono-Processing of Nanocomposites
• Power ultrasound can assist in synthesis,
blending, dispersion & erosion-testing of nanocomposites
– 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
Sono- Fragmentation
(Size Reduction)
Bubble
Particles
Sono- Fragmentation
(Size Reduction)
Bubble
Bubble Collapse
due to Implosion
Particle Fragments
due to
Particles
a) Violent Bubble
collapse
b) Inter-particle
attrition
Sono- Fragmentation
(Size Reduction)
Bubble
Bubble Collapse
due to Implosion
Particle Fragments
due to
Particles
a) Violent Bubble
collapse
b) Inter-particle
attrition
Fragmented Particle
Feed Sample
Distilled
Water
Micron sized
feed particles
Sonication
20 kHz, 1000 W,
Probe type
Sonication/
58 kHz, 500 W, Tank
Distilled
Water
Micron sized
feed particles
Sono-Processed Sample
20 kHz, 1000 W,
Probe type
Sonication/
58 kHz, 500 W, Tank
Distilled
Water
Micron sized
feed particles
Micron sized
particles
Sub-Micron
/Nano Sized
Particles
Sono-Processed Sample
(stratified Mix)
Submicron/
nano
Particles
Micron
Sized
Particles
Sono-Blending
(Particle Size De-stratification)
High
Frequency
Sonication
Submicron/
nano
Particles
Micron
Sized
Particles
Sono-Blended Particles For
Composite Formulation
Drying
out at 105
Deg C
High
Frequency
Sonication
Submicron/
nano
Particles
Micron
Sized
Particles
Good Blend of
Sub-micron
/Micron-sized
particle
Blended sample
Ready for
composite
Formulation
Polymer Precursor Preparation
Solvent
e.g CHCl3
Blended sample
Ready for
composite
Formulation
Polymer Precursor Preparation
Solvent
e.g CHCl3
Sonication
For 2 mts
Blended sample
Ready for
composite
Formulation
Polymer
Precursor
( Particles
Dispersed in
solvent)
Polymer Matrix
Particle Reinforced Polymer Matrix
Particle
Polymer Matrix
Caviation Erosion On the ceramic
Particle Reinforced Polymer Matrix
Particle
Cavitation
Bubble
Polymer Matrix
Superior Cavitation Erosion Resistance on
Nano-Composites
Erosion Resistance Ehancement
Mass loss (grams)
0.001
with filler material
0.0005
without filler material
0
0
2
4
6
8
10
Sonication time (minutes)
Erosion Resistance Enhancement, PMMA
1.2
Turbidity N.T.U
- Mass loss and turbidity
data show same relative
trends
0.9
Withfiller material
0.6
with out filler material
0.3
0
0
2
4
6
8
10
Sonication T ime
(minutes)
-Sono-Cavitation test results shown to correlate with classical impacterosion test results.
Thicknes
s (m)
Unfilled PMMA
Filled PMMA
Den
sity
mu
LAM
BDA
E
nu
G
VL
VS
0.541
1.232
0.675
1.1
0.501
0.669
1.288
0.286
0.501
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 = Possion’s 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.moduli
and shear moduli
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
– pro’s & con’s must be weighed for specific application
• PSP Lab in ChE Dept @ IITM has cutting-edge
research program in various aspects of nanotechnology