Geoscience Reference
In-Depth Information
2
History of Hydrothermal Technology
2.1 Introduction
In the ancient times, Romans used to celebrate the year-end and year-beginning
with great festivities in honor of the God Janus, in whose honor the month January
is named. The God Janus is a deity with two heads: one looking to the past and the
other looking to the future (
Figure 2.1
)
[1]
. Here, we have made a sincere attempt
to explore and review the early history of the hydrothermal technology that has an
extremely promising future in view of its high efficiency in the processing of
nanomaterials.
As mentioned earlier, Sir Roderick Murchison, a British geologist, was the first
to use the term hydrothermal in the mid-nineteenth century
[2]
. The first publica-
tion on hydrothermal research appeared in 1845 (
Figure 2.2
). This reports success-
ful synthesis of tiny quartz crystals upon the transformation of freshly precipitated
silicic acid in Papin's digestor by Schafthaul
[3]
. Following this, mineralogists,
especially from France, Germany, and Italy, started synthesizing various other
minerals. Although the size of the crystals or minerals they obtained did not exceed
thousandths or hundredths of a millimeter, their main objective was to create or
simulate, in the laboratory, the natural conditions existing in the earth's crust. If, in
nature, minerals and mineral assemblages were formed at elevated temperature and
pressure conditions in the presence of volatiles—mainly water, it will be quite
impossible to simulate the natural conditions or processes responsible for the for-
mation of rocks and minerals except under the hydrothermal conditions. Thus, the
early interest in hydrothermal research was merely in the synthesis of a particular
mineral or in obtaining compounds similar to natural minerals rather than in carry-
ing out any systematic investigation pertaining to phase relations or geochemistry
of the earth's interior. Even the conditions under which they worked were, in gen-
eral, simple and sometimes lacking precision. The minerals obtained by the earlier
workers are chiefly those which are stable or at any rate, phanerostable, over a
wide range of conditions, for example, quartz and feldspar. As the resultant
products obtained were very tiny, accurate chemical analysis or identification of
the phase by optical microscopic methods was quite doubtful and many a times led
to speculations. Besides, the experiments were carried out in glass tubes in which it
was difficult to attain higher pressure
temperature conditions; also water was used
in most cases as a solvent. Therefore, the crystals obtained were very small, and
the purity of the crystals could not be studied satisfactorily.
The majority of the early hydrothermal experiments carried out during the
1840s to early 1900s mainly dealt with the nanocrystalline products, which were
