Geoscience Reference
In-Depth Information
Figure 2.1 The God Janus.
discarded as failures due to the lack of sophisticated electron microscopic techni-
ques available during that time to observe such small-size products. Thus, the
whole focus was on the processing of bulk crystals or bulk materials. Many times
when bulk crystals or single crystals were not obtained as products of several milli-
meters in size, the experiments were considered failures and the materials were
washed away. Prior to X-ray techniques, chemical techniques were mainly
employed in identifying the products. It was only after the application of X-rays
for crystal studies that the researchers slowly began to study the powder diffraction
patterns of the resultant products, and by the 1920s a systematic understanding of
the products began. Before that the experiments were considered as failures. The
experiments were concluded by stating that the solubility was not suitable for grow-
ing crystals
[4]
. Until the works of Giorgio Spezia in 1900
[5]
, hydrothermal technol-
ogy did not gain much importance in the growth of bulk crystals, as the products in
the majority of the cases were very fine grained without any X-ray data. Most of the
experiments during the nineteenth century under hydrothermal conditions, with some
exceptions, were related to silicate synthesis. Therefore, the contribution from the
glass tubes to the resultant product could not be precisely understood. After the intro-
duction of steel autoclaves and suitable metal linings, attempts were initiated to reach
higher pressure
temperature conditions to obtain other compounds and purer phases.
However, no attention was paid to the chemistry of the solvent, the frequent appear-
ance of metastable phases, solubility relations, kinetics, phase equilibria, and related
phenomena. Thus, the frequent appearance of metastable phases also complicated the
earlier studies.
Most of the work on hydrothermal research during the nineteenth century was
confined only to Europe, especially to the Mineralogy, Petrology, and Geochemistry
laboratories in Germany, France, Switzerland, and Italy. Bunsen
[6]
carried out
hydrothermal experiments for the first time using thick-walled glass tubes to contain
high-temperature and high-pressure liquids and prepared strontium and barium car-
bonates. Wohler
[7]
recrystallized apophyllite by heating apophyllite in water solu-
tions at 180
190
C under 10
12 atm pressure. In fact, all the early hydrothermal
experiments, until 1881, were carried out in simple glass tubes with sealed ends, of
course, with an exception of one or two attempts with steel tubes. Even the term
2
2
