Geoscience Reference
In-Depth Information
x. CO
2(g)
5
CO
2(aq.)
xi. CO
2
ð
aq
:Þ
1
H
2
O
5
H
1
1
HCO
3
xii. HCO
3
5
H
1
1
CO
2
3
xiii. BaCO
3
ð
s
Þ
5
Ba
2
1
1
CO
2
3
xiv. BaCO
3
ð
aq
:Þ
5
Ba
2
1
1
CO
2
3
xv. BaHCO
3
5
Ba
2
1
1
HCO
3
TiOH
3
1
1
H
1
xvii. TiOH
3
1
1
H
2
O
5
Ti
ð
OH
Þ
xvi. Ti
4
1
H
2
O
5
2
1
H
1
2
2
3
1
1
H
1
xix. Ti(OH)
3
1
1
H
2
O
5
Ti(OH)
4(aq.)
1
H
1
xx. Ti(OH)
4(aq.)
5
TiO
2(s)
1
2H
2
O
xxi. PbO
ð
s
Þ
H
2
O
5
Pb
2
1
1
2OH
2
xxii. PbO
ð
aq
:Þ
H
2
O
5
PbOH
1
1
OH
2
xxiii. PbOH
1
5
Pb
2
1
1
OH
2
xxiv. Pb(OH)
2(s)
5
Pb
2
1
1
2OH
2
xxv. Pb
2
1
1
2OH
2
5
H
1
1
HPbO
2
xxvi. Pb
2
OH
3
1
1
H
1
5
2Pb
2
1
1
H
2
O
xxvii. Pb
3
(OH)
4
2
1
5
3Pb
2
1
1
4OH
2
xxviii. Pb
4
(OH)
4
4
1
5
4Pb
2
1
1
4OH
2
xxix. Pb
6
ð
OH
Þ
xviii. Ti
ð
OH
Þ
1
H
2
O
5
Ti
ð
OH
Þ
4
8
5
6Pb
2
1
1
8OH
2
xxx. PbTiO
3(s)
1
H
2
O
5
Pb
2
1
1
2OH
2
1
TiO
2(s)
About 30 independent reactions consisting of 31 species are shown above. The
thermodynamic modeling also helps in estimating the morphology of the products
to some extent, and the work needs some more validation for a large number of
variables.
Figure 10.37
shows the representative images of PZT and other com-
pounds with a control over their morphology as obtained by Riman and coworkers.
Yin and Alivisatos
[172]
have made similar attempt for kinetic size control of
nanomaterials in a colloidal system with organic
inorganic interface. The critical
size depends on the monomer concentration, with low monomer concentration
favoring a larger critical size.
Aksay et al.
[173]
have prepared nanometer-sized BaTiO
3
particles under hydro-
thermal conditions by dispersing TiO
2
powders in a concentrated aqueous solution
of Ba(OH)
2
.The TiO
2
particles dissolve in the aqueous Ba(OH)
2
solution and lead
to the nucleation of nanometer-sized cubic phase BaTiO
3
particles. In concentrated
solutions, the BaTiO
3
particles grow through multiple clustering. These authors
have used a similar approach to obtain BaTiO
3
films from organometallic precur-
sors at 80
C and below. It was found that the grain size of the film depends on the
nucleation rate of the BaTiO
3
particles.
For the preparation of fine particles of this perovskite-type mixed oxide, knowl-
edge of stability diagrams under hydrothermal conditions is very important. The
stability diagram shows the regions of reagent concentrations and pH at which vari-
ous species predominate in the system (
Figure 10.38
). Thus, the stability diagrams
indicate the optimum synthesis conditions for which desirable products are thermo-
dynamically stable. However, the stability diagrams were considered for a limited
number of hydrothermal systems on the assumption that the aqueous solutions were
ideal
[174,175]
. They are especially inaccurate when concentrated electrolyte
