nanopartikel materi

7/27/2019 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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