Geoscience Reference
In-Depth Information
Figure 9.24 Phase diagram for the
system SrO
a
Al
2
O
3
a
NaOH
a
H
2
Oat
500
C
[108]
.
N (SrO/SiO
2
)
8.81
5.76
3.92
1.96
Sr
3
[Al(OH)
6
]
2
0.98
0.48
0.24
0.16
0.11
H
2
O
Sr
4
Al
4
O
2
(Al
10
O
23
)
0.25 1.25 2.5
5.0
7.5
C (mole/litre)
Figure 9.25 Habit of the
calcium aluminate crystals
[107]
.
001
011
001
011
122
111
021
131
010
110
101
102
302
011
100
100
450
C
[108]
.
Figure 9.25
shows the habit of the calcium
aluminate crystals. Similarly, the strontium aluminates are also formed.
In weakly concentrated solutions, new phases like Sr
4
Al
14
O
25
, platelike crystals
of aluminates belonging to the rhombohedral symmetry with space group Pmma
are obtained.
In the
temperature interval 300
H
2
O bismuth tetra-aluminate,
Bi
2
Al
4
O
9
crystals have been synthesized under hydrothermal conditions
[109]
.
The crystallization occurs at a higher concentration of Al
2
O
3
in the nutrient in
the order of 45
system Na
2
O(K
2
O)
a
Bi
2
O
3
a
Al
2
O
3
a
90 wt%. The pure phase occurs only when the molar ratio of
Bi
2
O
3
:Al
2
O
3
:H
2
O
0.8:0.05:1, and with a rise in concentration of NaOH, the
monophase synthesis reduces. This is connected with the structure becoming
unstable with the rise in the concentration of NaOH. These crystals belong to the
rhombic system with special group Pbam, and the crystals have (110) and (001)
forms. However, the size of the crystals is
,
1.0 mm. Ivakin et al.
[110]
have
synthesized zinc aluminate (gahnite) single crystals and regulated the crystal size
using the hydrothermal technique. The experimental temperature was in the range
220
5
400
C and they doped the gahnite with Eu
3
1
to obtain luminescence in the
crystals.
