Geoscience Reference
In-Depth Information
Besides, the role of pressure together with temperature helps enhanced molecular
arrangements including those of organic molecules as supported by the synthesis of
organic amino acids and other life-forming complexes, and also the natural subma-
rine hydrothermal ecosystems. Thus, the hydrothermal technique exhibits a great
degree of flexibility or adaptability which is being rightly exploited by a large sci-
entific community with diversified interests.
1.10 Hydrothermal Materials Processing
Hydrothermal materials processing is becoming a popular field of research, particu-
larly after the successful development of ceramic processing technology during
1970s. From 1990 onwards, it has become more popular and an efficient technique
for the processing of advanced nanomaterials including carbon polymorphs and
hybrid nanomaterials. Different carbon polymorphs have been obtained under sub-
natural conditions, and these processes involve the use of organic solvents in the
system
[115]
. Also the in situ surface modification under hydrothermal conditions
is more attractive. A wide range of nanomaterials including nanocomposites have
been prepared using the hydrothermal technique. In this respect, hydrothermal tech-
nology has become a boon to nanotechnology for the preparation of high-quality
materials with size, shape, and surface properties. Further, there is a growing inter-
est in enhancing hydrothermal reaction kinetics using microwaves, acousto-wave
simulations, mechanical mixing, electrochemical reactions, and also addition of
biomolecules. These processes have made the hydrothermal technique more unique
in the twenty-first century to ceramists and preparative chemists because of the
enhanced kinetics. The duration of the experiments is reduced by at least four
orders of magnitude, which makes the technique more economic. In fact, this
approach is popular as multienergy processing of advanced materials, and it takes
materials processing to an altogether new avenue called chemistry at the speed of
light and instant hydrothermal systems
[27]
. The microwave hydrothermal tech-
nique is especially handy for the synthesis of lead zirconium titanate (PZT) and
other oxide ceramics. Added to this, the crystal size, morphology, and level of
agglomeration of the different ceramic oxides can be controlled through careful
selection of the ratio of starting materials, pH, time, and temperature. Submicron
size powders of TiO
2
, ZnO, SnO
2
, ZrO
2
,Fe
2
O
3
, KNbO
3
, BaTiO
3
, PbTiO
3
, and
their solid solutions have been prepared in this way. This has made the technique a
more valuable one in the low-temperature production of fine ceramic powders,
clays, and zeolites
[18,116,117]
.
Similarly, ultrasonic energy and sonochemical simulation are used to prepare
novel materials and accelerate the chemical reactions. In this way, hydrothermal
reactions can be carried out at very rapid rates, and several new phases and high-
temperature phases can be obtained in minutes.
Hydrothermal epitaxy began during 1970s in connection with the development
of magneto-optic and magnetic bubble domain devices, especially thin and highly
crystallized magnetic films of yttrium iron garnets and their solid solutions on
