Geoscience Reference
In-Depth Information
human life but also with other living forms or species. Also, processing methods
such as fabrication, manipulation, treatment, reuse, and recycling of waste materi-
als should be environmentally friendly. In this respect, the hydrothermal technique
occupies a unique place in modern science and technology. The rapid develop-
ment in the field of hydrothermal research during 2000s. or so, motivated the
present authors to bring out this handbook covering almost all aspects of hydro-
thermal research. Although there is a growing interest among scientists from vari-
ous branches of science, at the moment there are no topics or monographs
available in the field of hydrothermal technology. Most of the major works, even
by the pioneers in this field, have been confined to reviews and edited topics.
Table 1.1
lists important reviews and edited topics in the field of hydrothermal
research.
1.2 Definition
In spite of the fact that the hydrothermal technique has made tremendous progress,
there is no unanimity about its definition. The term hydrothermal usually refers to
any heterogeneous reaction in the presence of aqueous solvents or mineralizers
under high-pressure
high-temperature (HPHT) conditions to dissolve and recrys-
tallize (recover) materials that are relatively insoluble under ordinary conditions.
Morey and Niggli
[14]
defined hydrothermal synthesis as “
in the hydrothermal
method the components are subjected to the action of water, at temperatures gener-
ally near
...
though often considerably above the critical
temperature of water
370
C) in closed bombs, and therefore, under the corresponding high pressures
developed by such solutions.” According to Laudise
[15]
, hydrothermal growth
means growth from aqueous solution at ambient or near-ambient conditions.
Rabenau
[16]
defined hydrothermal synthesis as the heterogeneous reactions in
aqueous media above 100
C and 1 bar. Lobachev
[17]
defined it as a group of
methods in which crystallization is carried out from superheated aqueous solutions
at high pressures. Roy
[18]
declares that hydrothermal synthesis involves water as
a catalyst and occasionally as a component of solid phases in the synthesis at ele-
vated temperature (
(
B
100
C) and pressure (greater than a few atmospheres).
Byrappa
[19]
defines hydrothermal synthesis as any heterogeneous reaction in an
aqueous media carried out above room temperature and at pressure greater than
1 atm. Yoshimura
[20]
proposed the following definition: reactions occurring under
the conditions of high temperature and high pressure (
.
100
C,
.
.
1 atm) in aqueous
solutions in a closed system.
The above definitions hold good for materials synthesis, metal leaching, and
treatment of waste materials. However, there is no definite lower limit for the pres-
sure and temperature conditions. The majority of the authors fix the hydrothermal
synthesis, for example, at above 100
C temperature and above 1 atm. But, with the
vast number of publications under mild hydrothermal conditions in recent years,
we propose to define hydrothermal reaction as “any heterogeneous chemical
