Geoscience Reference
In-Depth Information
Figure 3.6 The schematic diagram
of a high-pressure autoclave with a
variable-volume silver liner
[18]
.
High-pressure
autoclave
and liner
Silver tube
o.d. 2.2 wall .03
3.0
0.32
0.32
Silver
disc .03
20.5
45° bevel
5.4
2.5
Closure detail
shown in
Figure 3.6
. Here, silver bellows segments are formed from dead-soft cup
stock by hydraulic pressure applied internally. As the tube expands outward into a
die, it is folded longitudinally. The intrinsic advantage of these liner lies in the fact
that the percent fill in the liner may be adjusted without opening the liner. Thus, in
practice the liner is charged with nutrient, a seed, and crystal-growing medium.
Such silver liners have been used by Ashby et al., successfully, hundreds of times up
to 400
C for the hydrothermal growth of crystals. There are several such modifica-
tions in the liner assembly to suit specific crystal growth systems. A silver liner lad-
der assembly consisting of fixed and floating liners has been used in the
hydrothermal crystal growth of oxides for optical applications
[19]
. The authors also
propose that a wide variety of metals including platinum and gold (liners) can be
formed into bellows. Hence, internal assembly of the liner and the lining material
are very important in crystal growth and materials processing.
3.4 Temperature and Pressure Measurements
Several modern electronic controllers are commercially available today to regulate
temperature and pressure in hydrothermal experiments. Pressure vessels heated
externally can be placed in a suitable isothermal zone or multiple heating zone fur-
naces controlled by thyristor-based controllers. Highly sophisticated temperature
programmers
controllers
are
commercially available
for programming the
