Geoscience Reference
In-Depth Information
Figure 10.57 Schematic representation
of mass transport and the film growth
mechanism
[309]
.
A (OH)
2
solution
Ti
electrode
ATiO
3
film
Path
ATiO
3
A (OH)
2
solution
A
2+
, OH
-
,
H
2
O
Ti
growth films. All the films have a similar cross sectional microstructure, regardless of
their treatment processes. The advantage thickness of the thin layer is
m.
Such studies have been carried out by several other workers on different com-
pounds. For example, Cho and Yoshimura
[295]
have studied, in detail, the hydro-
thermal
0.1
0.2
μ
B
electrochemical synthesis of highly crystallized barium tungstate films on
tungsten metal substrates at fairly low temperatures. The hydrothermal method did
not produce a film because only discrete BaWO
4
particles appeared on the tungsten
substrate. The electrolysis experiments were carried out using tungsten substrates as
an anode (i.e., working electrode) and a platinum substrate as a cathode (i.e., counter
electrode). A reference electrode (KCl-saturated Ag/AgCl) was put in a glass tube
with a capillary tip close to the working electrode. Ba(OH)
2
solutions were made
from redistilled water.
Figure 10.59
shows the schematic diagram of the autoclave
assembly used in the hydrothermal
electrochemical method. The authors propose a
model that interprets the mechanism for the formation and growth of the amorphous
tungsten oxide film. The schematic diagram in
Figure 10.60
illustrates the mass
transport and the amorphous film formation during anodic oxidation. Similarly,
Figure 10.61
shows the SEM photograph of sample surface prepared by the hydro-
thermal
electrochemical treatment.
In general, the morphology, grain size, and quality of the film can be controlled
through several parameters, like temperature, pH of the solution at the interface,
electrode current density, impurities (dopants), and duration of the experiment.
Figure 10.62a
d
shows the BaWO
4
film morphology in 0.01 M Ba(OH)
2
formed
during conduction after (a) 1 min, (b) 15 min, (c) 20 min, and (d) 25 min.
The crystallization was characterized by 3D nucleation and growth. Thus,
the
