Geoscience Reference
In-Depth Information
large-scale hydrothermal research before the end of the World War II were virtually
nonexistent, except the Carnegie Institute of Washington, where Bowen began his
hydrothermal research and later moved to the University of Chicago, Bridgman's
high-pressure laboratory at Harvard University during 1940s and 1950s, Kennedy's
at the University of Chicago, and Tuttle's at Penn State University. This situation
dramatically changed with the development of the test tube
type pressure vessel
by Tuttle in which high pressures up to 5 kbar could be maintained at temperatures
of 750
C for a long period of time. However, before going into the contributions of
these great personalities, we shall discuss the early contributions during the turn
of the nineteenth century and the beginning of twentieth century. As mentioned
earlier, the entire activity on hydrothermal research was concentrated in Europe
and there was no activity in North America or Asia, including Japan, China, India,
and Taiwan, which are included today in the top 10 countries actively engaged in
hydrothermal research. Perhaps, the first North American published work on hydro-
thermal research was by Barus
[31]
, who essentially worked on the impregnation
of glass with water to such an extent that it melted below 200
C. He used steel
bombs for these experiments. Subsequently, Allen
[32]
obtained very fine quartz
crystals by heating a solution of MgCl
2
6NH
4
Cl and Na
2
SiO
3
for 3 days at
450
C. Also, large crystals of 2 mm long, often barrel shaped with short
rhombohedral terminal faces, were obtained. Allen used steel bombs closed by a
Cu disk held in place by a screw on steel cap, used either MgCl
2
400
2
6NH
4
Cl solutions
or a mixture of MgCl
2
solution with NaHCO
3
, and either amorphous SiO
2
or
Na
2
SiO
3
, heated for 3
475
C to obtain magnetite, quartz, fosterite,
and so on. However, the early American hydrothermal research was carried out
using the autoclaves of European designs. Around the turn of the century, it was
again the German workers who were active in the field of new designs, especially
Tammann [
33a
] and Boeke [
33b
] from Tottingen who carried out extensive studies
with reference to many carbonate and silicate reactions in the newly designed
bombs at higher pressure and higher temperature conditions with CO
2
pressure.
Perhaps, this is the beginning of the solvothermal research, although the term sol-
vothermal was introduced by French chemists in 1971
[34]
. The autoclaves used by
Tammann and Boeke were all heavy steel vessels, 10 in. diameter, 18 in. long, with
soft metal gaskets which formed the seal when compressed by a set of radially
deployed screws and nuts. The heating was internal with a resistance furnace.
Today, the use of CO
2
as a solvent is one of the most popular routes in hydrother-
mal technology, which is also popularly called green technology, owing to the
near-ambient conditions of materials processing using CO
2
as a solvent. A great
range of pharmaceutical products in the nanosize range are being processed using
continuous flow reactors in the presence of CO
2
solvents
[35]
.
With the establishment of the Geophysical Laboratory at the Carnegie Institute
of Washington, USA, Bowen
[36]
established a fine hydrothermal research
laboratory. Obviously, all the major contributions to the field of hydrothermal
research from the United States of America in the early twentieth century are
solely from this laboratory and have received worldwide recognition. Bowen took
up a systematic study of the phase equilibria in high temperature silicate systems
6 days at 375
2
