Transcript Slide 1

Outline:
Introduction
Gas phase synthesis methods
- gas condensation processing
- chemical vapor condensation
- expansion cooling
Difference in products
Advantages
Introduction:
Synthesis methods of nanostructure
materials is divided into two different
groups:
- top-down methods
- bottom-up methods:
gas phase synthesis
Gas phase synthesis
methods:
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Inert gas condensation:
- gas condensation processing (GPC)
- chemical vapor condensation (CVC)
Expansion cooling
Gas condensation
processing:
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Inert gas pressure:
1 - 50 mbar
Glass evacuated
Crucible
temperature:
500-1000 c
Growth of nanoparticles:
Collisions with inert gas atoms
Metal vapor becomes cold
Homogeneous nucleation
Losing energy
supersaturation
coalescence
Changes in size of
nanoparticles:
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higher source temperature
higher evaporation rate
higher inert gas pressure
heavier inert gas atoms
Longer residence time in growth regime
larger particles
Chemical vapor
condensation method:
GPC evaporative source
is replaced by a hot-wall
tubular reactor.
 CVC instead of GPC for:
- high melting points material

- low vapor pressure
Schematic diagrams of:
CVC apparatus
reactor
CVC process:
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A low concentration of precursors in
the carrier gas
Rapid expansion of the gas stream
through the uniformly heated tubular
reactor
Rapid quenching of the gas phase
clusters in a low pressure chamber
Expansion-cooling:
Expansion of a
condensable gas
through a nozzle
leads to cooling of
the gas and a
subsequent
homogeneous
nucleation and
condensation.
Changes through nozzle:
change in velocity
change in pressure
& temperature
Size distribution:
change in pressure
change in the
length of nozzle
Difference in products:
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Expansion
cooling is used
more for metals.
CVC is used to
produce a variety
of ceramics more
than GPC.
Advantages :
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high purity
ability to create
complex chemical
structures
Products are loosely
agglomerated.
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continuous process
controllable process
and products