Download Chemical and physical processes for nano particles synthesis

Chemical and physical processes for nano particles synthesis
Process : Aerosol process - flame hydrolysis
Aerosil process Degussa 1942 - synthesis of silica
chemical reactions :
H2
+
O2
2 H2O
SiCl4 +
2 H2O
SiO2
+
4 HCl
SiCl4 +
2 H2 + O2
SiO2
+
4 HCl
silicon tetra chloride
„ fumed silica“
principle :
SiCl4
separation :
air cyclone
electrostatic filters
fabric filters
H2
O2
production in flame reactor
particle size range :
primary particle size 7 – 40 nm, spherical, amorphous particle
powder as agglomerated particles of high porosity
specific surface area 50 – 400 m2 / g
product : titanium dioxide , aluminium oxide, zirconium oxide, zinc oxide
Aerosol processes
Images (transmission electron microscopy) of different
oxides, produced by direct oxidation in an arc
Particle formation in aerosol processes
supersaturated vapour :
reaction
A(g)
nucleation
B(g)
growth
coagulation
separation
°°°°
Gas to particle conversion GPC
solution of precursor :
droplet
generation
solvent
evaporation
intraparticle
reaction
Particle to particle conversion PPC
separation
Particle morphology during flame hydrolysis
particle concentration
aggregation
particle growth
temperature
Chemical and physical processes for nano particle synthesis
process :
aerosol process - flame hydrolysis
synthesis of titanium dioxide - chlorine process
chemical reaction :
1000 – 1300 °C
TiCl4 +
2 H2O
TiO2
titanium tetra chloride
1000 – 1300 °C
4 HCl +
+
4 HCl
titanium dioxide
O2
2 H2O
+
2 Cl2
O2
TiO2
+
2 Cl2
hydrogen chloride
TiCl4 +
titanium dioxide
principle :
apparatus for titanium dioxide powder
particle size :
100 - 400 nm, amorphous particles, product of anatase / rutile,
part of rutile increases with temperature
advantage
products :
:
minimum aggregation and high dispersity of powder
titanium dioxide, zirconium dioxide
Chemical and physical processes for nano particle synthesis
process :
aerosol process – powder synthesis using laser light
synthesis of silicon carbide and silicon nitride
chemical reaction :
SiH4 +
CH4
SiC
4 H2
silicon carbide
silicon hydride
3 SiH4 +
+
4 NH3
Si3N4
silicon hydride
+ 12 H2
silicon nitride
principle :
vacuum pump, filter
reactive zone
KCl - window
KCl - window
laser
argon
reactive gas
Reaction chamber for powder synthesis using a laser
advantage :
particle of high purity , monodisperse particle size distribution, exact stoichiometry
disadvantage :
precursor has to absorpt laser light
only on a laboratory scale, mass produced 1 – 100 g
Methods for powder generation with spray processes
methods
starting material
process steps
spray drying
suspension
solvent evaporation
spray drying
solution
solvent evaporation, crystallization
spray calcination
suspension
solvent evaporation, calcination
spray decomposition
solution of inorganic salts
solvent evaporation, calcination
spray hydrolysis
non aqueous solution or
hydrolysis by water vapour, for solutions
liquid metal compound
solvent evaporation
solution or melt of metal
thermal decomposition, for solutions
organic salts
solvent evaporation
solution
solvent evaporation and nucleation /
spray pyrolysis
plasma evaporation of
solutions
crystallization in a gaseous phase
Spray hydrolysis
chemical reaction : hydrolysis
Ti(OC2H5)4 +
TiCl4
particle :
2 H2O
TiO2
+
4 C2H5OH
2 H2O
TiO2
+
4 HCl
+
mostly non agglomerated, spherical particle with high purity
hollow and porous particle can be formed easily
controlling of powder porosity by concentrations in droplets
and by temperature gradients
droplets
formation of nonporous particle
crust formation
dry particle
nonporous particle
dry particle
densification
nonporous densified particle
porous and hollow particle
Formation of nonporous and porous particle by spray hydrolysis