Geoscience Reference
In-Depth Information
(a)
B-eucryptite
B-spodumen
a-eucryptite
A-zeolithe
200
300
400
500
600
700
800
Temperature (°C)
(b)
101
101
110
110
110
110
010
101
101
(i)
85
μ
(ii)
100
μ
Figure 6.20 (a) Schematic diagrams of zeolite crystals obtained under hydrothermal
conditions. Development of mineral phase depending on the temperature. (b) Crystal of
A-zeolite at (i) 150
C and (ii) 250
C
[117]
.
pressure and at an experimental duration of 6 weeks maximum, the zeolite phases,
thomsonite and edingtonite, were formed in the whole temperature range between
80
C and 230
C, and at 1 kbar pressure and at an experiment duration of 8 weeks
maximum, the zeolite phase-natrolite was formed in a temperature range between
80
C and 150
C.
Among all the zeolite groups of materials, only sodalite has been obtained as
bulk single crystals, owing to its attractive optical properties as nanocomposites in
quantum electronics and nonlinear optics. Sodalites may be represented by the general
formula M
8
[AlSO
4
]
6
.
The sodalite framework consists of alternating SiO
4
and AlO
4
corner sharing tetrahe-
dra forming 4 and 6 rings, which make up the basic
X
2
, where M
Na, Li, Ag,
,andX
Cl, Br, ClO
4
,
5
...
5
...
-case unit common to several
zeolites. A semicondensed structure is formed through the linkage of the
β
-cases via
six rings, with M
4
X clusters located at the center of each cage as shown in
Figure 6.24 [124]
. The replacement of the framework Al and Si by the larger Ga and
Ge affects the structure, the introduction of larger framework atoms may also allow
the enclathration of larger anions which cannot be normally incorporated into alumi-
nosilicate sodalites. The most promising method for the production of sodalite single
crystals is the hydrothermal method, as any attempt to grow sodalite from the melt
simply produces glass of an analogous composition while growing from solution
in the melt yields small crystals of
β
2mm
[123]
. Thus, sodalite is normally synthe-
sized from strong basic media under mild hydrothermal conditions; however, by
using ethylene glycol as a solvent, Bibby and Dale
[125]
prepared a purely siliceous
,
