Geoscience Reference
In-Depth Information
BaO
ð
crystal
Þ
1
TiO
2
ð
crystal
Þ
2
BaTiO
3
ð
crystal
Þ
ð
10
:
2
Þ
Ba
ð
vapor
Þ
1
Ti
ð
vapor
Þ
1
3
=
2O
2
ð
gas
Þ
2
BaTiO
3
ð
crystal
Þ
ð
10
:
3
Þ
Ba
2
1
Ti
4
1
3O
2
2
ð
gas
Þ
2
BaTiO
3
ð
crystal
Þ
ð
10
:
4
Þ
ð
gas
Þ
1
ð
gas
Þ
1
Ba
2
1
2OH
ð
aq
:Þ
2
TiO
2
ð
crystal
Þ
1
BaTiO
3
ð
crystal
Þ
ð
10
:
5
Þ
ð
aq
:Þ
1
Ba
2
1
2H
ð
aq
:Þ
2
Ti
ð
OH
Þ
4
ð
aq
:Þ
2
H
2
O
ð
aq
:Þ
2
BaTiO
3
ð
crystal
Þ
ð
10
:
6
Þ
ð
aq
:Þ
1
Because the raw materials of Ba and Ti must be solid oxides or carbonate ores,
processing using gas/vapor requires a huge energy expenditure of 727
3685 kcal/
mol to make solid BaTiO
3
and this energy must be discarded into the environment.
On the other hand, as the lattice energy of BaO and TiO
2
is almost equal, the
hydration (solvation) energy of Ba
2
1
and Ti
4
1
ions, solution processing consumes
very little energy if the synthesis activation energy (
G
) can be overcome.
Δ
G)
η
, where
G
is inversely proportional to (
Generally,
Δ
Δ
Δ
G and the activation
G
) are sufficiently provided for reaction to yield crystallization com-
pounds with the desired shape/size via several steps, such as diffusion, adsorption,
reaction, nucleation, and growth
[429]
. On the other hand, species in aqueous solu-
tions are hydrated (or chelated by some complexing agents). Thus, they have only
a small driving of force (
energy (
Δ
G) for the reaction and rather high activation energies
are necessary for reaction to occur by defeating the hydration (chelation) energies
of ions. Electro- or electroless-plating for metals is achieved by reducing metal ion
(s) electrochemically or chemically. However, in the case of ceramics, anions must
be oxidized at the same time as the reduction of cations. Because, some particular
activation processes, such as electro-, photo-, sono-, complexo-, organo-, and
mechanoactivation are required to accelerate the kinetics of synthesis of crystal-
lized single/multicomponent ceramic materials from the solution (
Figure 10.89
).
Schematic diagram of a temperature
Δ
pressure map for various kinds of materi-
als processing is shown in Figure 1.10. Solution processing is located in the pres-
sure temperature range characteristic for conditions of life on earth. All other
processing routes are connected with increasing temperature and/or increasing (or
decreasing) pressure; therefore, they are environmentally stressed.
Although environmental problems have been argued from various points of
view, ecologically, biologically, technologically, economically, and even politi-
cally, the most scientific arrangements, thus universally acceptable, are the thermo-
dynamic ones.
Thus, important subjects of technology in the twenty-first century are predicted
to be the balance of environmental and resource and/or energy problems. This has
led to the development of a new concept, related to the processing of advanced
materials in the twenty-first century, namely, industrial ecology—science of sus-
tainability
[430]
. The first textbook on the subject, written by two AT&T authori-
ties, provides the following definition:
