Geoscience Reference
In-Depth Information
electrodes into a hydrothermal bomb and studied the influence of an electric field on
the synthesis of kaolinite. They showed a very substantial effect (
100
C) of low-
ering the crystallization temperature of kaolinite. Yoshimura popularized this
concept by extending it to the synthesis of electroceramics, particularly perovskite-
type oxides
[88
.
90]
. Basca et al.
[91]
reported its advantages and disadvantages
compared with a pure hydrothermal method, and Bendale et al.
[92]
investigated the
thin film formation at
100
C). Yoshimura's group has
worked extensively on this and successfully prepared perovskite-type titanates such
as SrTiO
3
, CaTiO
3
, and BaTiO
3
thin films up to several micrometers in thickness,
almost linearly, at fairly lower temperatures (
lower temperature (29
90
C). They have also studied the
growing interface, the transport mechanism of the atoms across the growing film
without concentration gradients.
Figure 3.32
shows the schematic diagram of the autoclave designed in
Yoshimura's laboratory at the Tokyo Institute of Technology, Japan, for hydrother-
mal
,
electrochemical reactions, using the three-electrode technique of Bard and
Faulkner
[93]
. This has a provision to measure the potentials of electrodes in aque-
ous solutions at high temperatures and high pressures on a thermodynamically
meaningful scale, regardless of the electrolysis conditions
[93
95]
. The prepro-
cessed Ti substrate and the platinum plate were suspended as the working electrode
(anode) and the counter electrode (cathode), respectively, by 0.5 mm diameter
wires of the same metal keeping an interval of 30 mm between them in the electro-
lytic cell containing 500 ml of the solution. The Ti electrode is kept at a desired
potential until a prescribed quantity of electricity passes through it. The Ti
Figure 3.32 Schematic diagram of the
autoclave designed by Yoshimura's
laboratory
[88]
.
DC power supply
Galvanostat
Ammeter
A
Potentiometer
V
Electrolytic
autoclave
Teflon beaker
B
Ba
2+
Redistilled
water
Sol.
CD
Stainless
spacer
A
