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Gas Phase Reactions
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Gas Phase Reactions
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SiCl4 + H2O  OSiCl2 + 2 HCl
OSiCl2 + H2O  SiClOOH + HCl
SiClOOH  SiO2 + HCl
Gas Phase Reactions
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Gas Phase Reactions
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Y2O3 Particles by Flame Aerosol Process
oxygen
hydrogen
Y(NO3)3
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Particle Size Control
Particle size control by precursor concentration
Higher concentration = larger size
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Calcium phosphate nanoparticles Ca/P molar ratios 1.43 to 1.67
synthesized by simultaneous combustion of
Ca(OAc)2 + OP(OnBu)3 in a flame spray reactor
Fluoro-apatite and zinc or magnesium doped calcium phosphates
adding trifluoroacetic acid or metal carboxylates into the fuel.
Nanoparticle morphology
At a molar ratio of Ca/P < 1.5 promoted the formation of dicalcium pyrophosphate
(Ca2P2O7).
Phase pure tricalcium phosphate TCP - Ca3(PO4)2
obtained with a precursor Ca/P ratio of 1.52 after subsequent calcination at 900 °C
micropores and the facile substitution of both anions and cations
possible application as a biomaterial.
Gas Phase Reactions
Spray Pyrolysis
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(1) mass flow controller – O2 1 L/min
(2) ultrasonic nebulizer – aqueous solution
2 Co(OAc)2 : 1 Ni(OAc)2
(3) 3-zone heater - 400 C
(4) temperature controller
(5) electrostatic precipitator
SEM micrographs of NiCo2O4 particles
obtained from different concentrations of
Co(OAc)2 and Ni(OAc)2 precursor solutions –
Lower concentration reduces particle size
400 C
tubular furnace reactor
Morphology Control
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(a) HAADF-STEM of a rutile@anatase
core@shell microsphere; (b) titanium
L2,3 core-loss EELS spectra acquired
from the indicated areas compared to
reference TiO2 polymorphs [rutile
(green) and anatase (red)] (d−f) EELS
maps: (d) rutile (green), (e) anatase
(red), and (f) rutile and anatase overlaid
color map. (c) 3D tomographic
reconstruction of another typical
rutile@anatase core−shell microsphere,
together with the corresponding
HAADF-STEM image (inset).
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Gas Phase Reactions
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T1T2
traces of a transporting agent B
(e.g. I2)
A
AB
Vapor Phase Transport Syntheses
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Whether T1 < T2 or T1 > T2 depends on the thermochemical balance of the reaction !
Transport can proceed from higher to lower or from lower to higher temperature
Vapor Phase Transport Syntheses
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Vapor Phase Transport Syntheses
van’t Hoff equation
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Estimation of the thermochemical balance (H) of a transport reaction:
e.g.:
ZnS(s) + I2(gas)  ZnI2(gas) + S(g) H = ??
Zn(s) + I2(g)  ZnI2(gas) H = - 88 kJ mol-1
ZnS(s)  Zn(s) + S(g) H = +201 kJ mol-1
----------------------------------------------------------------
 ZnS(s) + I2(gas)  ZnI2(gas) + S(g) H = +113 kJ mol-1
endothermic reaction, transport from hot to cold!
Vapor Phase Transport Syntheses
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Ti + 2I2 TiI4 H = -376 kJ mol-1
exothermic: transport from cold to hot
W-filament (ca. 1500 K)
Ti-powder (ca. 800 K)
I2
Ti-crystals
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Laser-induced homogeneous pyrolysis, LIHP
C2H4 + h  C2H4
*
Excitation energy transferred to
vibrational-translational modes
 T increases
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Sensitizer
SF6
948 cm-1
Isopropanol
958 cm-1
laser wavelength
10.60 ± 0.05 m
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Reaction Zone
Overlap between
the vertical reactant gas stream
and the horizontal laser beam
away from the chamber walls
nucleation of nanoparticles
less contamination
narrow size distribution
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Iron-oxide Nanoparticles by Laser-induced
Pyrolysis
2 Fe(CO)5 + 3 N2O  Fe2O3 + 10 CO + 3 N2