Geoscience Reference
In-Depth Information
The scope of this topic has been restricted to recent developments under each
one of the applications described above with the exception of the natural hydrother-
mal systems which are not within the purview of the present handbook. Although
we have given the historical aspects of the technique in Chapter 2, the emphasis
has been focused mainly on the crystal growth and materials processing including
nanomaterials through the ages.
This chapter clearly reveals the fact that the hydrothermal technique is drawing
the attention of scientists from different branches of natural science. The future of
this technique lies in this kind of multidisciplinary approach. More and more new
findings and applications in this field are not only contributing to the scientific
knowledge of the hydrothermal technique but are also posing new problems. The
role of organics both as solvents and as surfactants in hydrothermal systems, for
example, has to be studied more seriously, which would definitely twist the geolog-
ical thinking to a greater extent. It is well known that the organics in hydrothermal
systems not only lead to the formation of new phases or new structures, and stabil-
ity of metastable phases but can also bring down the pressure and the temperature
conditions of crystallization. Similarly, they also modify the surface properties and
provide control over the size, shape, and dispersibility in case of nanomaterials. In
nature, we can expect a very wide range of chemical components including hydro-
carbons, which greatly contribute to the crystallization of rocks, minerals, and ore
deposits. The role of these organics in the earth's crust has not been understood
properly by geoscientists in the context of thermodynamics and kinetics of crystal-
lization. It is expected that such studies will definitely propose much lower temper-
ature and lower pressure conditions of crystallization for various rock bodies and
add many more new questions to experimental petrology. Thus,
the future of
Table 1.6 Comparison of Various Powder Synthesis Methods
[21]
Parameter
Solid-State
Reactions
Coprecipitation
Sol
Gel Polymerizable
Complex
Hydrothermal
Cost
Low to
moderate
Moderate
High
High
Moderate
State of
development
Commercial
Demonstration/
commercial
R&D
R&D
R&D/demonstration
Compositional
control
Poor
Good
Excellent
Excellent
Good/Excellent
Morphology
control
Poor
Moderate
Moderate
Moderate
Good
Powder
reactivity
Poor
Good
Good
Good
Good
Purity (%)
,
99.5
.
99.5
.
99.9
.
99.9
.
99.5
Calcination
step
Yes (multiple)
Yes
Yes
Yes
No
Milling step
Yes (multiple)
Yes
Yes
Yes
No
