Geoscience Reference
In-Depth Information
Table 7.14 Early Hydrothermal Synthesis of Various Dense
Anhydrous Aluminosilicates [128]
Temperature ( C)
Silicate
Starting Material
Pressure
1 20,000 kg/cm 4
Jadeite
Sodium sulfate, kaolin 1 silica
900
20,000 kg/cm 2
NaCr(SiO 3 ) 2
Sodium dichromate 1 silica
900
20,000 30,000
kg/cm2
600 900
Andalusite
Kaolin 1 sodium salts
Kyanite
Alumina
silica
20,000
40,000
kg/cm 2
600
900
1
Sillimanite
Kaolin 1 fluorides
20,000 30,000
kg/cm 2
600 900
Topaz
Kaolin 1 fluorides, but
higher fluoride contents
or kaoline 1 NH 4 HF 2
20,000 kg/cm 2
Epidote and zoisite
hydrated calcium and
iron nitrates, hydrated
alumina and silica
800
Garnet
Grossularite
15,000 kg/cm 2
600 800
20,000 kg/cm 2
Andradite
600 800
20,000 kg/cm 2
Almandine
600 900
30,000 kg/cm 2
Pyrope
900
30,000 kg/cm 2
Mg 3 Fe 2 (SiO 4 ) 3
900
20,000 kg/cm 2
Mn 3 Fe 2 (SiO 4 )3
800
20,000 kg/cm 2
Fe 3 Fe 2 (SiO 4 )3
800
20,000 kg/cm 2
Mg 3 Cr 2 (SiO 4 )3
800
7.9.1 Bismuth Silicate
Bismuth silicate, Bi 12 SiO 20 (BSO), is of considerable interest for optical signal pro-
cessing. It is popular as a photorefracting crystal. The photorefractive effect can be
described as a combination of the photoconductive and the electro-optic effects
used in a variety of applications like nonlinear mixing including active spatial filter-
ing phase conjugation by way of degenerating four-wave mixing optical processing
devices such as optical oscillators, and as a technique useful for nondestructive mate-
rials analysis. Litvin [129] has studied the system Na 2 O
a
Bi 2 O 3 a
SiO 2 a
H 2 Ounder
450 C, P 5
hydrothermal conditions: T 5
350
400
500 atm in NaOH solution up
to 40 wt%.
Figure 7.26 shows the fields of crystallization of BSOs in the system
Na 2 O
-Bi 2 O 3
(bismite), Bi 2 SiO 20 (sillenite), and Bi 4 Si 3 O 12 (eulytite). Bi 2 SiO 20 crystallizes under
hydrothermal conditions in NaOH (1
a
Bi 2 O 3 a
SiO 2 a
H 2 O. The following phases have been obtained:
α
40 wt%) solutions
and 350 atm pressure [130] . Whereas eulytite crystallizes with NaOH (21 wt%),
and it does not depend on the ratio of the starting components (Bi 2 O 3 1
60 wt%) and KOH (1
SiO 2 ). It
Search WWH ::




Custom Search