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Processes for the production of nanoparticles

Production processes

in a li uid hase in a aseous hase

Precipitation process in homogeneous solution in surfactant based systems

Sol - gel process

Hydrothermal process

Aerosol process

Flame hydrolysis Spray pyrolysis

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Educts

Agglomerate

Primary particle

Nucleus

Nanoparticles

Nucleus formation

Growth

Agglomeration

Deagglomeration

Critical supersaturation

Mixing of educts, temperature, etc.

Transport mechanism

diffusion or convection-controlled

Particle interaction

van-der-Waals attraction

electrostatical / sterical repulsion

Agglomerate structure

Euklidical geometry, fractals

Integration or diffusion-limitedparticle growth

Stabilisation of the nanoparticles against agglomeration !

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gmax= 3

1

gsurf

Gibbs energy g

radius o nucleicritical radius of nuclei r*

gsurf = 4r2

g = (S- l) 3M 4 r3

Gibbs energy of nu-

cleus formation gConcentration of critical nuclei:

=

22

23*

)ln(3

16exp

SRTkT

MNN

O

Critical radius of nucleus:

MSlnRT

r* 2=

1 . r < r* nuclei dissolve

2. r > r*

nuclei are able to reduce

Gibbs energy by growing

Thermodynamics of nanoparticle formation

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Model of LaMer and Dinegar (1950)

saturation concentration CSCS

supersaturationgrowth

nucleation critical u ersaturation C 0

rocess time

C0

nucleation

growth

+

++

++

++

fast homogeneous nucleation

growth process by diffusion

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monomer, ions etc.

nucleation

growth

primary particles

Ostwald ripening

agglomeration andredispersion

agglomerates

Different approaches to synthesise nanoparticles in liquids

organic monomers inorganic salts inorganic monomers metal organic compounds

hydrolysis hydrolysis hydrolysis

polymerisation as

emulsion suspension

oligomerisation

polycondensation polycondensation polycondensation

particles in suspension particles in suspension particles in suspension particles in suspension

latex sol sol sol

examples:

PS 0.1 - 1000 m Al2O3 SiO2 Al2O3PMMA 0.3 - 1000 m TiO2 TiO2

MF 1.0 - 1000 m ZrO2 ZrO2Fe2O3

microparticles GmbH

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Ag+ + Br - AgBr

Silver bromide

Chemical and physical processes for nano particle synthesis

Process: precipitation in homogeneous solution

synthesis of silver bromide

Chemical reaction:

Principle:precipitation (Controlled double jet precipitation CDJP - technique)

(gelatine)

KBrAgNO3ions

embryos

nuclei

primary particle

growth, coagulation, ...

growth

cluster formation

complex and cluster formation

colloids

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Precipitation reactions in homogeneous solution

AgBr nanoparticle, produced by CDJ - technique at pBr 2,0 (a), 2,8(b), 4,0 (c)

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Precipitation reactions in homogeneous solution

Images (transmission electron microscopy left - scanning electron microscopy right) of

CdS nanoparticles, produced in homogeneous solution at 26C by CDJ - technique

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Precipitation reactions in homogenous solutions

Scanning electron microscopy image of aluminium(III)-oxide, 100C, left

Transmission electron microscopy image of chromium(III)-oxide, 75C, right,

produced by precipitation reaction in homogeneous solution

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Generation of nanoscaled barium sulphate

Process: Precipitation in homogeneous solution Nucleation - Growth

Goal: Nanoscaled particle size distribution (as monodisperse as possible, stabilised)

Theoretical basics and experimental approach:

Chemical reaction: 42

4

2 BaSOSOBa + Concentration of reactants: 0.01 mol/L 0.5 mol/L

Concentration based initial supersaturation SC: 500 25,000Molar ratio of reactants R: 1 10 (excess of Ba

2+ions)

Stabilisation: electrostatic (excess of Ba2+

ions)

sterical (0.03 g dispersing agent / g BaSO4)

Dispersing agent: Melpers 0030:- 30 % w/w PolyethercarboxylateProcess parameter: concentration based initial supersaturation SC

molar ratio of reactants R

feed rate and mixing

concentration of dispersing agent

L

SOBa

cK

ccS

24

2 =

+=24

2

SO

Ba

c

cR

Discontinuous stirred tank reactor

Stirrer rotational speed 800 min-1

Tank reactor volume 1000 ml

Characterisation of particle sizes

Dynamic light scattering

Scanning electron microscopy

Chair for Process Systems Engineering, Institute of ProcessEngineering, Otto-von-Guericke University Magdeburg

Petrova, A., Hintz, W., Tomas, J.: Investigation of the precipitation of barium sulphate nanoparticles, Chem. Eng. Technol. 31 (2008) 604-608

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Particle size distributions during the precipitation process of BaSO4

Influence of the feed rate of potassium sulphate solution on theparticle size distribution Q0(d) of the precipitated BaSO4 particles

100 200 300 400 5000

20

40

60

80

100

ParticlesizedistributionQ0(d)in%

Particle diameter in nm

Feed rate of K2SO4

5 mL/min

10 mL/min

20 mL/min40 mL/min

80 mL/ min

Method:Dynamic light scatteringInstrument: Horiba LB 500

Educts: 0.2 mol/L, Sc=10,000, T= 25C0.03 g dispersing agent / g BaSO4

Mean agglomerate diameterd50,0

Feed rate of K2SO4

5 mL/min d50,0 = 227.8 nm

10mL/min d50,0 = 208.2 nm

20mL/min d50,0 = 178.9 nm

40 mL/min d50,0 = 121.5 nm

80 mL/min d50,0 =105.3 nm

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Method:Dynamic light scatteringInstrument: Horiba LB 500

Educts: 0.05 mol/L - 0.5 mol/L, R=1

Sc = 2,500 25,000, 25C

0.03 g dispersing agent / g

Mean agglomerate diameter:

Sc =2,500 d50,0 = 208.9 nm

Sc = 5,000 d50,0 = 151.4 nmSc = 10,000 d50,0 = 123.9 nm

Sc = 15,000 d50,0 = 109.0 nm

Sc =20,000 d50,0 = 101.4 nm

Sc = 25,000 d 50,0 = 82.5 nm

Particle size distributions during the precipitation process of BaSO4

50 100 150 200 250 300 350 400

0

20

40

60

80

100

Particlesiz

edistribution

Q0(d)in%

Particle diameter d in nm

Initial supersaturation Sc

Sc = 2,500 Sc = 5,000 Sc = 10,000 Sc = 15,000 Sc = 20,000 Sc = 25,000

Influence of the initial supersaturation Sc on the particle

size distribution Q0(d) of the precipitated BaSO4

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10 100 1000 10000

0

20

40

60

80

100

Particlesizedis

tributionQ0(d)in%

Particle diameter d in nm

Molar ratio R

R = 1

R = 2

R = 4

R = 6

R = 8

R = 10

Method:Dynamic light scatteringInstrument : Horiba LB 500

Educts: 0.2 mol/L barium chloride0.05 mol/L-0.5 mol/L sulphate

Sc = 2,500 Sc = 8,000, 25C

without dispersing agent

Mean agglomerate diameter:

R = 1 d50,0 = 3,781.3 nm

R = 2 d50,0 = 506.0 nm

R = 4 d50,0 = 155.8 nm

R = 6 d50,0 = 121.9 nm

R = 8 d50,0 = 100.9 nm

R = 10 d 50,0 = 92.9 nm

Particle size distribution during the precipitation process of BaSO4

Influence of the molar ratio R on the particle size distributionQ0(d) of the precipitated BaSO4 particles

+=24

2

SO

Ba

c

cR

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Structure of precipitated barium sulphate agglomerates

Scanning electron microscopy image of barium sulphate agglomerates (without dispersing agent)

Method: Scanning electron microscopy (SEM), concentration of reactants: 0.5 mol/L, R= 1, Sc = 25,000,

T = 25 C, addition of barium chloride to potassium sulphate, 80 mL/min, without dispersing agent

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10 100 1000 10000

0

20

40

60

80

100

ParticlesizedistributionQ

0(d)in%

Particle diameter d in nm

with 0.02 g dispersing agent /g BaSO4 (DLS)no dispersing agent (DLS): agglomerates

no dispersing agent (SEM): primary particles

Particle size distributions Q0(d) of precipitated BaSO4, with and

without dispersing agent, sizes were determined with dynamic light

scattering (DLS) and scanning electron microscopy (SEM)

Particle size distributions during the precipitation process of BaSO4

Method:Dynamic light scattering

Scanning electron microscopy

Educts: 0.5 mol/L, R=1, Sc =25,000

25 C, 80 mL/min

with/without dispersing agent (0.02 g/g)

Mean agglomerate diameter:

with dispersing agent:

d50,0 = 82.0 nm

without dispersing agent:

d50,0 = 1,498.2 nm (DLS)

d50,0 = 79.0 nm (SEM)