Apparatus - Hydrothermal Technology - page 98

Figure 3.13 Construction of a welded
closure [31] .

Plug

Retaining ring
Welded and machined joint
1 in. × 12 in. chamber

Liner
Casing cap

Casing

and a new liner is inserted. Thus, for a sequence of experiments, rather extensive
machine shop services are needed. However, welded liners are still relatively inex-
pensive when compared with an entire vessel.

Modified Bridgman Autoclave
A further advancement temperature capabilities, size, and design

among the steel autoclaves is the modified Bridgman high-pressure autoclave. This
is embodied in several commercially available autoclaves. Figure 3.14 shows a cross
section. The initial seal that closes the vessel is made by mechanically tightening the
plunger against the deformable gasket ( Figure 3.15 shows a deformed copper ring)
by the setscrews in the head. The unsupported area closure makes its seal. The force
of the generated pressure acts upon the piston, moving it upward against the deform-
able gasket and creating a perfect sealing. Such vessels can be used quite success-
fully in the temperature of 500 C and pressure of 3.7 kbar. Construction materials
such as stainless steel or Inconel are chosen according to the requirements of the par-
ticular experimental conditions. For general applications, quartz is commonly grown
under hydrothermal conditions directly in steel autoclaves. Autoclave attack is mini-
mal because the common mineralizers react with iron to form sodium iron silicates,
which adhere to the autoclave wall and inhibit further corrosion. The iron content in
the solution is so low that Fe in the grown quartz crystals is typically only a few
parts per million so that crystals of excellent acoustic quality and watch grade qual-
ity can be obtained [15,38] . However, almost all other hydrothermal crystals require

in pressure