Geoscience Reference
In-Depth Information
3Na
4
Zr
2
Ge
5
O
16
H
2
O
!
4Na
3
HZrGe
2
O
8
1
2ZrO
2
1
5GeO
2
1
H
2
O
3Na
2
ZrGe
2
O
7
!
2Na
3
HZrGe
2
O
8
1
ZrO
2
ð
m
GeO2
5
const
Þ
2Na
2
ZrGe
2
O
7
!
Na
4
Zr
2
Ge
3
O
12
1
GeO
2
Na
4
Zr
2
Ge
3
O
12
!
2Na
2
ZrGeO
5
1
GeO
2
As the NaOH content increases in the solution we get:
2ZrO
2
5GeO
2
4NaOH
Na
4
Zr
2
Ge
5
O
16
· H
2
OH
2
O;
+
+
+
2Na
4
Zr
2
Ge
5
O
16
· H
2
O
+
5Na
2
ZrGe
2
O
7
+
GeO
2
+
+
2NaOH
ZrO
2
2H
2
O;
+
Na
2
ZrGe
2
O
7
NaOH
Na
3
HZrGe
2
O
8
Na
4
Zr
2
Ge
3
O
12
+
GeO
2
+
2NaOH
Na
2
GeO
3
· H
2
O.
The above reactions permit one to draw a conclusion that the stable crystallization
of different phases in the above sequence which was observed with an increase in
the NaOH content will also proceed with a decrease in the GeO
2
content at suffi-
ciently high Na
2
O content in the system.
The
systematic
study
of
hydrothermal
crystallization
in
the
systems
Na
2
O
Ti, Zr, and Hf) revealed the main regularities of
germanate formation and growth. In these systems, compounds having both
network and no-network structure can be obtained. For the compound having net-
work, the value q
a
MO
2
a
GeO
2
a
H
2
O(M
5
Ge/M can be equal to 1, 1.5, 2, 2.5; the value p
Na/M being
5
5
equal to 2. In germanates without network structure q
1 and 1.25, p
1, 1.5, 2,
5
5
and 3.
In the network NaZr-germanates,
the degree of Ge-tetrahedra condensation
increases from n
5. For the network NaZr-silicates which have no ger-
manate analogs, the new crystallization branch takes place (the formation of the
phases with q
1 till n
5
5
). Such change in n-value is connected with
the change of secondary structural units. The analysis of the crystal structure of
the synthesized phases leads to the conclusion that the structural unit common to
all sodium
3; 3; 6, n
3and
N
5
5
zirconium germanates is a centrosymmetric closed dimer grouping of
two Zr-octahedra and two Ge-tetrahedra, M
2
T
2
, which occupy the regular point
system in the centrosymmetric groups. During structural rearrangement, such
groups link in another way. For silicates,
the cyclic dimer M
2
T
4
is typical
[95,44]
.
