Geoscience Reference
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Figure 3.16 The minimized volume between the
autoclave and the noble metal lining [43] .
Fill tube
Toroidal space
filler
Noble metal can
Hemispherical space
filler
are hemispherical and can bottoms are flat. A hemispherical metal “space filler”
can be used to fill this volume. Similarly, a readily deformed region in the liner
(a bellows, a soft metal section, or a thinner-walled separate portion) is used
where deformation will preferentially take place and will be of less importance. If
the deformation is large during cooling, rapid cooling is advantageous as long as
thermal shock does not crack large grown crystals. Such studies are very impor-
tant in the self-energized closures.
All the above-discussed conventional autoclaves are externally heated ones.
Though these autoclaves enjoy a great advantage of simplicity and convenience,
they are limited with reference to temperature and pressure by the high-temperature
strengths of alloys used. In contrast to this, another group or class of equipment in
which the pressure vessel is cooled and the sample is heated internally had been
designed by several workers. We shall discuss one or two such designs. In this cat-
egory, one of the earliest designs was proposed in 1923 by Smyth and Adams [44]
and was modified later in 1931 by Goranson [45] and again in 1950 by Yoder [46] .
This type of vessel is capable of attaining an experimental temperature as high as
1600 C and pressure
10 kbar. Thus, much of the later geochemical research has
been carried out worldwide using such apparatus. Figure 3.17 shows the schematic
diagram of the internally heated high-pressure apparatus. It consists of a heavy-
walled, heat-treated vessel of tool steel (usually 41
.
Mo), which contains
the pressure, and an internal furnace and sample support. This vessel is admirably
suited for the study of reactions by dynamic methods like differential thermal anal-
yses at a series of pressures. In Yoder's modification, it is possible that a tempera-
ture of 2000 C may be attained although no data have been recorded at
temperatures above 1500 C. It cannot be used directly with water as the pressure
transmitting fluid, but by sealing charges containing water in the platinum tube.
Studies of such systems have also been made up to these temperatures [45] .
50 Cr
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