nanopartikel materi
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IV (5)
Synthesis of NanoparticlesMethods and Techniques
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Using no fuels (one reactant serves as fuel)
Combustion SynthesisS elf-Propagating High-Temperature S ynthesis (SHS)
(A) solid solid
(B) solid liquid
(C) solid gas
(D) gas gas
ceramics, composites, elements,
intermetallics, polymers.
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(B) Particle Formation Processes in a Flame
SiCl 4(g)H2O, O 2 SiO 2(g)
AlCl3(g) Al2O 3(g)H2O, O 2
TiCl4(g)H2O, O 2
TiO 2(g)
Condensing species(flame)
Nucleation Initial Particles
Initial Particles(flame)
GrowthProduct Particles
ReactantsChemical reaction
(flame)Condensing Species(particle forming species)
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Classification of Flame (or flame structures)
flame
premixed flame (fuel andoxidizer arepremixed beforefeeding intoburner)
diffusion flame
(fuel andoxidizer are fedseparately intoburner)
parallel flowdiffusion flame
counter flowdiffusion flame
F 1
F 3
F 2
F 7
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Premixed flame characteristics ignition
Rate of Comb. Rxn = f (T, [F], [O], [inert])
For ignition
= ( ,[ ])rxnQ f T radicals
radicals H, OH, CH, CH2,
rxn lossQ Q ignition occurs when
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(a) by increasing temperaturee.g., by using a hot metal stick
(b) by creating radicalse.g., by UV illmination
(c) by both increasing temperature and creating radicalse.g., pilot flame (math, lighter, )
techniques for ignition
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Extinction
by decreasing temperature e.g., water spraying, blowing
by decreasing radical concentration
e.g., increasing contact surface area with solid.
F 4
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Flash Back
combustion velocity Vcom
stationary flame
flash back
blow off
Vgas Vcom
| V com | | V gas |
Vgas
Vcom
F + O
(stay still) V gas =0
bot plateflame
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(D) Rate of fusion of an Agglomerate in a Flame
1/ 3(1 ) 1dRdt
R primary particle radius
number of neighbors
t time
surface tension
viscosity
Frenkel (1945)
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f (Temp, mixing with other oxides)strong
Temp or/and
mixing of SiO 2 and Al 2O 3
dR
dt
F 7F 14.46F 6F 5F 7.2 F 14.50
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II. Combustion Synthesis
Self Propagating High Temperature Synthesis (SHS)
or Combustion Synthesis
A. Introduction Characteristics of SHS
Highly Exothermic Reaction
High Temperature(2000 -4000K), Visible Radiation,
and Self-Propagation.
Rapid, Combustion Velocity 1-10 mm/sec
Maximum Combustion Temperature
1 2 3
4 5
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Why self-propagating
(1) large contact surface area between reactant particles(a) compaction of reactants(b) melting and capillary spreading
(2) high reaction temperature
(3) small heat losses(heat retained due to compaction of reactants)
(4) assisted by liquid and/or gas formation
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(B) Types of SHS Reactions
(A) Metals
(a) ( ) 44 g Na SiCl 4l g Si NaCl
(b) ( ) 55/ 2
g g Mg NbCl
( ) 25/ 2
l g Nb MgCl
Examples for Combustion Synsthesis
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(B) Oxides
2 3 2 20.5 2 3Y O BaO Cu O 2 3 6 xYBa Cu O
(C) Carbides
(a) Ti+C TiC
(b) N b+(1-x)/2 N 2+ xC NbN 1-xCx
(c) Si+C SiC
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Typical Solution Methods
Preparation
of Solution
Precipitation
of SoluteSpecies
Filtration of
Precipitates
Washing Calcination
Precise control of components, e.g., Ce(NO 3)2 :ZrO(NO 3)=0.75:0.25 for Ce 0.75 Zr 0.25 O 2 powder.
Complete solution or complete mixing on molecutar level. (otherwise, e.g., singlephase CeO 2 or ZrO 2 will form instead of Ce 0.75 Zr 0.25 O 2)
*Solution-precipitation method: OK
*Coprecipitation method: OK
*Sol-gel method: OK
*Spoay pyrolysis: OK
*Freeze drying: OK
*Solution combustion: OK
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Precipitation of Solute Species
Simultaneous precipitation (or simultaneous nucleation or Co-precipitation)of all desired species to form uniform composition, e.g., 0.75Ce+0.25Zr for Ce 0.75 Zr 0.25 O 2
Uniform and short growth duration to obtain nanoparticales.
= abrupt (rapid) charge in conditions to bring about precipitation
= short processing duration
*Solution-evaporation: too slow
*Solution-precipitation, coprecipitation: too slow [adjustment of PH by adding
acids or bases (or addition of precipitation agentes) with mixing is slow andnot uniform)
*Sol-gel method: OK
*Spray pyrolysis, freeze drying: OK
*Solution combustion: OK
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Abrupt occeurence of ignition, rapid propagation of combustion, shortcombustion duration
Generation and evolution of large amounts of gases carry away large
grantities of heat, create pores in the product and causes rapid cooling of the product= shorter the time for growth, generating nano size particleswith large specific surface area.
High combustion temperature ( 900 ): (1). dry powders; (2). desiredcrystalline structure; (3). high purity (impurities are decomposed andraporiad) (4). does not need filtration, washing and calcination.
*Microwave-assisted solution combustion synthesis
same ao solution combustion with even better uniform temperaturedistribution and additional control of temperature
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Sol- Gel Auto- Combustion Synthesis Method(Sol gel method + SHS)
Example ISynthesis of nanocrystalline LaFeO 3 (magnetic materials with
potential applications in sensors and monitoring)
Fe(NO 3) 9H 2O
La(NO3) 6H
2O
C6H8O 7 H2Odissol
d.i.H 2OClear solution
NH3soln sol130 C
brown dried gel
ignition
combustionLaFeO 3
Example IISynthesis of NiCuZn Ferrite(Ni0.25Cu0.25Zn0.25Fe2O4, magneticmaterial having potential applications in multilayer chip inductor (MLCI))
metal nitrates
citric acid
disso
d.i.H 2O
NH3soln sol130 C
gelignition
combustion
NiCuZn Ferrite
nanopowder
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SHS Various Materials ceramics
intermetallics
elements
composites
polymers
SHS Commercialization ???
advantages:
fast reaction
low energy consumption
simple processing
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Commercialization of SHS Processes
high values (market prices) of the products
other synthesis methods: difficult or high
production costs low prices of the raw materials for the SHS
Economics
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Properties of AlN
high thermal conductivity
Al:300,, Si:148, AlN:130 260,SiO 2:1.4, Al 2O 3:20(w/m-k)high electrical resistivity
(10 13 cm)low thermal expansion coefficient
Si:4, AlN:4.3, Al 2O 3:7.2, SiO 2 :15(PPM/ )low dieletric constant (8.0 9.0)good mechanical strengthgood corrosion resistancegood thermal-shock resistance
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Applications of AlNsemiconductor substratesIC packagesIC encapsulantheat sinksthermal greasethermally conductive filler high thermally conductive compositesheat radiation platesSi-Al-O-N compoundsMolten metal crucibles and linersCorrosion resistant parts
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D-1 Particle Formation Processes in a Flame
(1) Reactants Chemical reactions
(flame)
Condensing Species
SiCl 4 (g) H2O, O 2
SiO 2 (g)
AlCl3(g) Al2O 3 (g)H2O, O 2
TiCl4(g) H2O, O 2 TiO 2(g)
(2) Condensing speciesNucleation Initial Particles
(3) Initial ParticlesGrowth
Product Particles
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solution of sodium
aluminate (NaAlO 2)+ waste
seedingwith fine
Al(OH)3particles
hydrolyzed coolingTempagitation
aluminum gydroxide
(precipitated)time
filtration washing
Aluminum hydroxide(Al(OH) 3)
calcination1200
cooling
(size, texture, purity)
40~100 m particles
size reduction
1 m or finer
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2 BaTiO 3 ( )
Ba+2C 3H7OH B(OC 3H7)2 +H282
TiCl4+4C
3H
7OH+4NH
3Ti (OC
3H
7)
4+4NH
4Cl
C 6H65
Ti(OC 4H7)4 4C 5H11 OH reflux 24hC4H6
Ti (OC 5H11)4 4C 3H7OH
Ba(OC 3H7)2 Ti(OC 5H11)+3H 2O BatiO 3+ BaTiO 3+2C 3H7OH+4C 5H11OH
(C) Solvent Extraction-Piltration
to reach supersaturation or to esceed the solubility product
(D) Sol-Gel Techniques
(E) solvent combustion
(F) Hydrothermal Precipitation
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. Using fuels Flame Synthesis
(A)Optical fiber
(B)Diamond film(C)Fine particles
carbon particles (carbon black)
oxide ceramic powders(SiO 2, TiO 2, Al 2O3......)
non-oxide ceramic powders
(AlN, Si 3N4.............)
Materials Synthesis by Combustion
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. Using no fuels (one reactant serves as fuel)
Combustion Synthesis
Self-Propagating High-Temperature Synthesis (SHS)
(A)solid solid(B)solid liquid
(C)solid gas
(D)gas gas
ceramics
intermetallics
composites
polymers
elements
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General Scheme for Flame Synthesis of Fine Powders
flame
(Chem. rxn,nucleation,
growth)
reactants
(e.g., SiCl 4 or AlCl 3)
fuel (e.g., H 2 or CH 4)combust gases
particles
particles
collectionproductpowder
combustgases
pollution
control
exhaustgases
Oxidizer (e.g., O 2 or air)
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A. Formation Process of Powder Particles
reactantsChem. Rxn .
Particle Forming Species Nucleation
Nuclei (Initial particles)Growth
Product Particles
Particle Forming Species
(a) Vapor atoms or molecules in gas phase .
(b) Solute atoms, molecules, or ions in liquid solution; pure melt; atoms, molecules, or ions in a melt solution .
(c) Solute atoms, molecules, or ions in a solid solution
(d) Newly formed phase materials.
Phys. Rxn.
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