Geoscience Reference
In-Depth Information
μ
SiO
2
Na
2
ZnSi
3
O
8
Na
2
ZnSi
2
O
6
Na
2
ZnSiO
4
Zn
2
SiO
4
μ
Na
2
O
Figure 7.35 Field of crystallization of Na
2
ZnSi
3
O
8
[182]
.
1:1.
If the concentration of ZnO increases to 7:1, this phase becomes unstable and trans-
forms to Na
2
Zn
3
[SiO
4
]
2
. The crystals are thin plates—like at ZnO/SiO
2
5
Na
2
Zn
2
Si
2
O
7
: This crystallizes in 10
25% NaOH solutions at ZnO/SiO
2
.
2:1 to
1:1. With an increase in the ZnO in the nutrient, the crystals become thicker. The
commonly seen faces are (100), (010), (210), (110), (101), and (111). Crystals are
colorless, transparent, with glassy surfaces. The crystallization of Na
2
Zn
2
Si
2
O
7
takes place
450
C,
6
C,
in 15
18 wt% NaOH solution at T
Δ
T
4
5
5
P
0.5 mm/day along the direction [101]
[183]
. The growth rate of the (001) face increases and becomes equal to the growth
rate along other faces. These crystals show luminescence and strong piezoelectric
effect. Heating above 1090
C, Na
2
Zn
2
Si
2
O
7
starts decomposing to ZnO and melt,
and at 1325
C, it completely melts (
Figure 7.36
)
[182]
.
Na
2
Zn[SiO
4
]: Single crystals of sodium orthozincosilicate have been obtained in
highly concentrated NaOH solution (30% NaOH) and it does not depend upon the
ratio of the starting components. Na
2
Zn[SiO
4
] dissolves congruently. The sche-
matic diagram of the crystal morphology is shown in
Figure 7.37
. The commonly
observed forms are (100), (001), (110), and (011). Twinning is common. Crystals
are colorless, Mn
2
1
-rich crystals are green, Cu
2
1
-rich crystals are blue. The Mn
2
1
doped Na
2
Zn[SiO
4
] crystals show luminescence and also significant piezoelectric
effect. At T
5
1060
6
10
C, NaZn[SiO
4
] undergoes phase transition.
Synthetic sodium zincosilicates are a new group of crystallophosphor materials.
Sodium zincosilicates doped with Mn
2
1
exhibit stronger luminescence. Also,
Na
2
Zn
2
[Si
2
O
7
], Na
2
Zn[Si
3
O
8
], and Na
2
Zn[SiO
4
] show stronger piezoelectric effect
than quartz. However, the basic problem is the growth of large-size single crystals.
400
600 atm. The growth rate is 0.3
5
