1. Mimic alkoxide method: Well-sinterable nano-crystalline powder
(Motivation)
Aqueous precipitation:
nanocrystalline but hard agglomeration
of ultra-fine particles
- Powder calcined at 600oC
- primary particle: ~ 15nm
- secondary particle: ~50nm
- ~37 primary particle within
the secondary particle
(Suggest Mimic alkoxide method)
a. Ce(NO3)3•6H2O + 1-butanol : 0.1M
b. DEA(diethylamine) (C2H5)2NH + 1-butanol : 1.0M
c. Cerium source solution was dripped into precipitant solution(DEA)
(C2H5)2NH + H2O → (C2H5)2NH2+ + OH-
: OH - ions from the hydrolysis of molecular water of the cerium salt
: involves minimum amount of water (better dispersion)
J. -G. Li, T. Ikegami, J. -H. Lee, T. Mori, Acta mater. 49, 419-426 (2001)
Advanced Electronic Ceramics I (2004)
Example: Mimic Alkoxide method
- maximize the driving force for the sintering
(excess free energy of surface)
- reduce the sintering temperature
- provide fast densification kinetics (Herring’s scaling law: t2 =λn t1)
Decrease T
for full density Aggregate
problem
J. -G. Li, T. Ikegami, J. -H. Lee, T. Mori, Acta mater. 49, 419-426 (2001)
Advanced Electronic Ceramics I (2004)

2. Example: Mimic Alkoxide Method
Ex) CeO2
- at high temperature
4CeO2 → 2Ce2O3 + O2 (g)
: retard the densification
- Low-temperature sintering
is desirable!
- full density at 1000oC
( ~ 0.42 Tm)
J. -G. Li, T. Ikegami, J. -H. Lee, T. Mori, Acta mater. 49, 419-426 (2001)
Advanced Electronic Ceramics I (2004)
Hydrothermal synthesis
(Definition)
The process using hot and pressurized water for precipitation of oxides
(Driving force)
The difference in solubility of the oxide phase from the least soluble
precursor or intermediate
A(OH) (s) + B(OH) (s)dissolution A(OH) (aq.) + B(OH) (aq.)PrecipitationABO3
(Characteristics)
1. Crystalline, anhydrous ceramic powder
2. Temperature : 100~370oC
3. Pressure : 6 ~ 15MPa
4. Do not need calcination and milling
(avoid the contamination during the processing)
5. Employ relatively inexpensive raw materials
From W.J.Dawson, Am.Ceram.Soc.Bull., 67(10), 1673 (1988)
Advanced Electronic Ceramics I (2004)

3. Hydrothermal synthesis for MLCC
(Strong points of Hydrothermal Synthesis in MLCC)
1. The ability to produce solid-solution particles of controlled size
(can attain complex composition)
cf) in poorly prepared co-precipitation
- did not result solid solution
- requires the calcination (and thereby ball milling)
- large particle size ( d<1 µm is difficult by mall milling)
- result higher sintering temperature (energy-consuming process)
- result the coarse grain size (harmful for size reduction)
2. Well sinterable and small particles without any calcination
- offers the energy-saving process to fabricate the integrated MLCC
3. Doping during the powder preparation is possible
From W.J.Dawson, Am.Ceram.Soc.Bull., 67(10), 1673 (1988)
Advanced Electronic Ceramics I (2004)
Hydrothermal synthesis: BaTiO3
1. TiCl4 (aq.) + NH4OH → Ti-hydroxide.
2. Washing till No Cl- ions are detected.
3. Mixed with Ba(OH)2•6H2O
(Ba/Ti = 1.5 in atomic ratio, concentration=0.5M )
4. Treatment in 200oC for 5h in autoclave
K.Abe and S. Matumoto, Ceramic Tracsaction, Vol.22, p.15 (1987)
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4. Hydrothermal conversion from TiO2 into BaTiO3
1. TiCl4 (aq.) + alcohol + HPC (steric stabilizer)
2. Uniform heating using microwave oven formation of spherical gel
3. Adding NH4OH
4. Washing and separation using centrifugal
J. Y. Choi, J. H. Kim and D. K. Kim, J. Am. Ceram. Soc., 81(5), 1353 (1998)
Advanced Electronic Ceramics I (2004)
Hydrothermal conversion from TiO2 into BaTiO3
Lead acetate trihydrate
Barium hydroxide octahydrate
Strontium hydroxide octahydrate
J. Y. Choi, J. H. Kim and D. K. Kim, J. Am. Ceram. Soc., 81(5), 1353 (1998)
Advanced Electronic Ceramics I (2004)

5. Hydrothermal
BaTiO3 SrTiO3
conversion from
TiO2 into BaTiO3
Spherical morphology
TiO2
(from precursor TiO2
or ZrO2)
PbZrO3
PbTiO3
ZrO2
Crystallinity and phase
BZT
(from hydrothermal
treatment)
PZT
ZrTiO4
J. Y. Choi, J. H. Kim and D. K. Kim, J. Am. Ceram. Soc., 81(5), 1353 (1998)
Advanced Electronic Ceramics I (2004)
Hydrothermal synthesis
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6. Spray Pyrolysis
What is Ultrasonic Spray Pyrolysis?
A powder preparation process through the thermal decomposition
of the droplet generated by ultrasonic transducion.
The Advantage of Spray Pyrolysis Process.
1. spherical morphology.
2. narrow particle size distribution.
3. easy preparation of the powder with the complex composition.
4. relatively homogeneous composition.
: compositional heterogeneity is restricted within a spherical secondary powder.
5. Easy manipulation of particle size
6. No calcination
7. Successive processing
The Shortcoming of Spray Pyrolysis Process.
1. Energy-consuming process.
2. makes hollow structures frequently.
[Jong-Heun Lee, Ph.D. Thesis, Seoul National University, 1993]
Advanced Electronic Ceramics I (2004)
Spray Pyrolysis: Schematic
8πγ 1/3
Ddroplet = 0.34
ρf2
Ddroplet : droplet size
γ : surface tension of solution
ρ: density of solution
f: resonance frequency for the
ultrasonic transducer (1.67 MHz)
- typical droplet size for aqueous
solution ranges ~ 3µm
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7. Spray Pyrolysis: Concentration Effect
TiO2/SnO2
from
TiCl4(aq.)
+SnCl4(aq.)
at 800oC
Size manipulation
comes from
the mechanism,
“one particle
from
one droplet”
[Jong-Heun Lee, Ph.D. Thesis, Seoul National University, 1993]
Advanced Electronic Ceramics I (2004)
Spray Pyrolysis: Microstructure 1
TiO2 prepared from 0.19M TiCl4 aqueous solution
at 600oC.
[J.-H.Lee, H.-J.Cho, and S.-J.Park,
Ceramic Transaction Vol.22, pp39-44(1991)]
SnO2 prepared from 0.2M SnCl4 aqueous
solution at 800oC.
[J.-H.Lee and S.-J.Park, J.Am.Ceram.Soc.,
76(3), 777-780, (1993)]
TiO2-SnO2 prepared from 0.2M TiCl4-SnCl4
aqueous solution at 800oC.
[J.-H.Lee and S.-J.Park, J.Mater.Sci.:Materials in
Electronics, 4, 254-258 (1993)]
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8. Spray Pyrolysis: Microstructure 2
Pb(Zr,Ti)O3 prepared from aqueous acetate-base
solution at 700oC.
[H.-B.Kim, J.-H.Lee, and S.-J.Park, J. Mater. Sci.
:Materials in Electronics, 6, 84-89 (1995)]
Zr0.8Sn0.2TiO4 prepared from ZrO(CH3COO)2-
TiCl4 -SnCl4 aqueous solution at 800oC.
[S.-Y.Cho, J.-H.Lee, S.-J.Park, J.Mater.Sci., 30,
3274-3278 (1995)]
Advanced Electronic Ceramics I (2004)
Observation of the inner part of sphere
epoxy
particle
Dimpling and
ion-thinning
Fig. Inner structure of SnO2
spheres prepared at 800oC from
0.2M SnCl4 solution.
Ring patterns of (C) and (D)
were obtained in the area of
inner and crust(see arrow) layer
of the secondary sphere,
respectively.
J.-H.Lee and S.-J.Park, J.Am.Ceram.Soc., 76(3), 777-780, (1993)
Advanced Electronic Ceramics I (2004)

9. Composition analysis in one sphere
1234
J.-H.Lee and S.-J.Park, J.Mater.Sci.:Materials in Electronics, 4, 254-258 (1993)
Advanced Electronic Ceramics I (2004)
Spray Pyrolysis: Application
Easy manipulation of particle size
: manipulation of pore and/or grain size
(ceramic humidity sensor, ZnO varistor, and the control of
the electric properties related to the grain boundary)
: Sintering study
Narrow size distribution, spherical and good flowability
: Screen printing of luminescent materials in display applications
: Controlled compaction
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10. Hydrolysis: metal alkoxide
Preparation of metal alkoxide
HgCl2
Al(OC3H7)3 + 3/2H2↑
Al + 3C3H7OH ∆
HgI
Mg(OC2H5)2 + 2H2↑
Mg + 2C2H5OH ∆ 2
SiCl4 + 4C2H5OH Si(OC2H5)4 + 4HCl↑
TiCl4 + 4ROH Ti(OR)4 + 4NH4Cl
Hydrolysis of metal alkoxide
Ti(OCnH2n+1)4 + 2H2O → TiO2 + 4(CnH2n+1)OH
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Hydrolysis of metal alkoxide: example
Single oxide
1. 0.1-0.2M Ti(iOC3H7)4 : titanium tetraisopropoxide in isopropanol,
+ the mixture between water and isopropanol (0.3-1.5M water)
2. 0.1-0.2M Ti(OC2H5)4 : titanium tetraethoxide in ethanol,
+ the mixture between water and ethanol (0.3-1.5M water)
- the molar ratio (water/alcohol > 0.3)
- yields mono-disperse, spherical titanium hydroxide
From isopropoxide From ethoxide
0.07 - 0.3 µm 0.3 - 0.6 µm
Avg. particle size range
Shape equiaxed spherical
Substructures multinuclear particles mostly singlet
E.A.Barringer and H.K.Bowen, J.Am.Ceram.Soc., Dec., C199, (1982)
Advanced Electronic Ceramics I (2004)

11. Hydrolysis of metal alkoxide: example
Multi oxide
1. The mixing between
Ti(OC2H5)4 in EtOH
Ta(OC2H5)5 in EtOH
Nb(OC2H5)5 in EtOH
2. Adding the mixture
between water and ethanol
3. Hydrolysis reaction in N2
4. Washing with de-ionized water
5. Re-dispersion in a dilute aqueous solution of SrCl2
6. Adding aqueous solution of (NH4)2CO3 to precipitate the Sr
on the surface of TiO2 surface
(B. Fegley, Jr., E.A.Barringer and H.K.Bowen, J.Am.Ceram.Soc., June, C113 (1984)
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Hydrolysis
Stirring
Thermocouple Cooling
water
Source solution
Heating mantle
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12. Hydrolysis: example (ZrO2)
pH decrease
ZrOCl2 + (n+1) H2O → ZrO2•nH2O + 2H+ + 2Cl-
K.Matsui and M.Ohagai, J.Ceram.Soc.Jpn., 106(9), 883-887 (1998)
Advanced Electronic Ceramics I (2004)
Hydrolysis: example (ZrO2)
Control parameter
1. Starting and ending pH
- adding NH4OH or HCl
* the measurement of
highly acidic oH
- measure the pH of the
diluted solution and
calculate the pH
2. The [ZrO2+] in the clear
solution as a function of
reaction time
3. The temperature of
solution
4. Boiling time
K.Matsui and M.Ohagai, J.Am.Ceram.Soc., 80(8),1949-56 (1997)
Advanced Electronic Ceramics I (2004)

13. Freeze Drying
a. Solution droplets are sprayed
into a bath of immiscible liquid
(hexane) or directly into liquid
N2
b. The frozen product is skimmed
from the top of the refrigerant
(the diameter of the frozen
beads: 0.01 ~ 0.5 mm)
c. Frozen sample is introduced
into a vacuum chamber
(P:~1torr)
⇒ sublimation of solvent
4. Calcination
J. S. Reed, “Principles of Ceramic
Processings,”
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Powders from Vapor-Phase Reactions
1. Sub-micron size (good)
2. Well-dispersed particles (good)
3. Narrow particle-size distribution (good)
4. Formation of non-oxide powder due to easy control of atmosphere
5. Requires large volume of gases for reaction (disadvantage)
6. Energy-consuming process(heat) (disadvantage)
7. Requires relatively expensive equipment for reaction (disadvantage)
8. Restriction in the choice of reactor materials
(to avoid corrosion by reactant gases)
(ex.)
1. TiCl4(g) + 2H2O(g) → TiO2(s) + 4HCl(g)
2. SiCl4(g) + 4NH3(g) → Si3N4(s) + 12HCl(g)
3. Thermal decomposition of (CH3)2SiCl2 and CH3SiH5
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14. Powders from Vapor-Phase Reactions
Temperature(K)
Japanese Ceramics Society, Ceramic Processing, Powder Preparation and Forming, (1984)
Advanced Electronic Ceramics I (2004)
Powders from Vapor-Phase Reactions
44000x4.2/(2.303X8.3144X773)
Log Kp = - ∆Go /(2.303RT)
Japanese Ceramics Society, Ceramic Processing, Powder Preparation and Forming, (1984)
Advanced Electronic Ceramics I (2004)

15. Powders from Vapor-Phase Reactions
Log Kp = - ∆Go /(2.303RT)
Powder
Powder formation at Log Kp> 3
formation
(homogeneous nucleation)
The formation of thin film, powder,
Thin film, Powder,
and fiber on substrate at 2>Log Kp> 0
and fiber on substrate
(heterogeneous nucleation)
Powder Thin film
fiber
Japanese Ceramics Society, Ceramic Processing, Powder Preparation and Forming, (1984)
Advanced Electronic Ceramics I (2004)