Geoscience Reference
In-Depth Information
Figure 6.14 DTG curves of different gels (a) 24 h
of aging at room temperature, (b) 1 day and
(c) 3 days of heating at 115
C
[82]
.
(a)
383
203
106
(b)
+
373
-
112
(c)
377
108
0
200
400
T (°C)
never been unequivocally identified
[77]
. This information has been used to under-
stand the effect of aging of hydrogel in zeolite synthesis.
These studies indicate that the zeolite nuclei, the hydrogel or precursor, and the
liquid solution are in equilibrium during crystallization, and because of the existence
of this equilibrium, the specific precursor or hydrogel can play a very important role
in influencing the form of nuclei and final productions. Also, the encapsulation of
organic templates or inorganic cations in the hydrogel seems to determine the type
of zeolite production. Thus, gel aging controls the crystallinity and size of the zeo-
lites synthesized to a large extent.
6.5.3 Water in Zeolite Synthesis
As mentioned earlier, zeolites could be synthesized only by the hydrothermal
method. The versatility of hydrothermal chemistry owes much to the mineralizing
role of water
[40,85]
. The factors that promote reactivity in aqueous magmas
include the following
[86]
:
1. Stabilization of porous lattices as zeolites by acting as space fillers, referred to above.
2. Through its presence, especially at high pressures, water may be incorporated into
hydrous glasses, melts, and solids. Through chemisorption into siliceous materials,
Si
a
O
a
Si and Al
a
O
a
Si bonds hydrolyze and reform. Chemical reactivity is enhanced
and magma viscosity is lowered.
