Geoscience Reference
In-Depth Information
dependence of the various AlPO
4
phases upon the reaction temperature for different
molar ratios.
The change in temperature results in the appearance of various other phases like
AlPO-11, AlPO-H3, in addition to VPI-5.
Figure 6.29
clearly indicates a very nar-
row temperature range for the crystallization of VPI-5, which depends essentially
upon the molar ratio of DPA
Al
2
O
3
:P
2
O
5
:H
2
O. It has been shown that the use of
bigger autoclaves can reduce the formation of other phases which might be con-
nected with slower heating rate and temperature gradients/thermal currents within
the liners.
Similarly, Schmidt et al.
[133]
have studied the effect of reaction time on the
crystallization of AlPO
4
phases.
Figure 6.30
shows the dependence of the various
AlPO
4
5
124
C for
phases
upon
reaction
time
at
the molar
ratio
1DPA:1Al
2
O
3
:1 P
2
O
5
5
40 H
2
O. Thus, the hydrothermal crystallization of
aluminophosphate zeolites from the reaction gel mixture is usually controlled
kinetically and the first nucleus that reaches the critical size will determine the
final production.
Figure 6.31
shows a schematic representation of the triple helix of water mole-
cules within the 18-ring channel.
Figure 6.30 Dependence of the various
AlPO
4
phases upon reaction time at 124
C
for the molar ratio—1 DPA:1
Al
2
O
3
:1 P
2
O
5
5
40 H
2
O
[133]
.
2.5
2
1.5
1
0.5
0
36
2
Reaction time (r)
9
8 1 0
Figure 6.31 Schematic
representation of the triple helix of
water molecules within the 18-ring
channel
[133]
.
