Geoscience Reference
In-Depth Information
Table 10.9 XRD Analysis of BaTiO
3
, SrTiO
3
, and Ba
0.5
Sr
0.5
TiO
3
Produced by the
Microwave-Hydrothermal Technique
[391]
T
(
C) Duration (h) Reaction Products in
Order of Abundance
as Determined by
XRD
Concentration (M)
Ba(NO
3
)
2
Sr(NO
3
)
2
TiCl
4
KOH
BaTiO
3
0.35
0
0.33
10
109
2
BaTiO
3
0.35
0
0.33
10
194
0.5
BaTiO
3
, trace BaCO
3
0.35
0
0.33
10
194
2
BaTiO
3
SrTiO
3
0
0.1334
0.13
10
164
2
SrTiO
3
0
0.1334
0.13
10
194
2
SrTiO
3
Ba
0.5
Sr
0.5
TiO
3
0
0.1334
0.26
10
194
2
Ba
0.5
Sr
0.5
TiO
3
BaZrO
3
,SrZrO
3
,andPbTiO
3
powders produced by microwave-hydrothermal and
conventional-hydrothermal techniques. Komarneni et al.
[38]
had carried out earlier,
similar studies on ceramic powders synthesis (titania, zirconia, iron oxide, chromia,
etc.), using both conventional- and microwave-hydrothermal conditions and had
obtained similar results. Thus, the crystal size, morphology, and level of agglomera-
tion of the different ceramic oxides can be controlled by parameters such as concen-
tration of the chemical species, pH, time, and temperature. Submicron powders of
TiO
2
,ZrO
2
,Fe
2
O
3
,KNO
3
, and BaTiO
3
have been obtained by this means.
Cheng et al.
[396]
have studied in detail the microwave processing of tungsten
carbide-cobalt composites and ferroic titanates. This helps the sintering of tool bits
and related parts with better properties in about one-tenth the cycle time required by
conventional means, and most significantly, it can help in retaining very fine micro-
structures when starting with very fine powders.
Komarneni et al.
[397]
have studied the microwave-hydrothermal processing of
metal clusters supported in and/or on montmorillonite. The authors could obtain
novel Ag
1
,Pt
1
- and Pd
1
-metal intercalated clays, which may be useful in catalysis.
These are prepared by using the combination of microwave-hydrothermal and polyol
reduction processes. Fang et al.
[398,399]
have carried out extensive studies on HAp
ceramics using microwave-hydrothermal conditions. This not only enhances the
reaction kinetics but also gives better densification and mechanical properties
[273]
.
The application of microwave-hydrothermal techniques to process modern mate-
rials is becoming highly popular and is a rapidly expanding area of research and
development. A reader can get more useful information in the reviews of Komarneni
[383,384]
and Ehsani et al.
[273a]
.
The mechanochemical
hydrothermal synthesis utilizes aqueous solution as a reac-
tion medium. Mechanochemical activation of slurries can generate local zones of high
