Geoscience Reference
In-Depth Information
At 300°C
ZrGeO
4
Na
4
Zr
2
Ge
5
O
16
·H
2
O(Q
2.5
)
Na
3
HZrGe
2
O
8
(Q
2
Na
)
At 400°C
Na
3
ZrGe
2
O
7
(Q
2
)
ZrGeO
4
Na
4
Zr
2
Ge
5
O
16
·H
2
O(Q
2.5
)
Na
3
HZrGe
2
O
8
(Q
2
Na
)
At 500°C
Na
4
Zr
2
Ge
3
O
12
ZrGeO
4
Na
4
Zr
2
Ge
5
O
16
·H
2
O(Q
2.5
)
Na
2
ZrGe
2
O
7
(Q
2
)
Na
2
ZrGeO
5
(Q
1
)
Figure 7.52 Reaction scheme of germanate formation in the hydrothermal
Na
2
O
a
ZrO
2
a
GeO
2
a
H
2
O system
[95]
.
n
5
5, [Ge
5
O
16
] island chains in Na
4
Zr
2
Ge
5
O
16
H
2
O.
n
5
2, [Ge
2
O
7
] diorthogroups in Na
2
ZrGe
2
O
7
.
n
5
1, [HGeO
4
] and [GeO
4
] type tetrahedra in Na
3
HZrGe
2
O
8
.
n
5
1, [GeO
4
] tetrahedra in Na
2
ZrGeO
5
and Na
4
Zr
2
Ge
3
O
12
.
The germanate system has no compounds analogous to silicates with the TO
2
/
ZrO
2
ratio
3. The maximum GeO
2
/ZrO
2
ratio is equal to 2.5. The substitution of
Si by Ge results in the change of the structure type of alkali-free compound to
ZrGeO
4
crystallizing in the scheelite type. The general scheme of the interaction
between the zirconium and germanium oxides and NaOH solutions at high tem-
peratures and pressures may be represented in the form:
5
ZrO
2
(M)
ZrO
2
(T)
ZrGeO
4
Na
4
Zr
2
Ge
5
O
16
· H
2
O
Na
2
ZrGe
2
O
7
[GeO
4
]
[Ge
5
O
16
]
[Ge
2
O
7
]
GeO
2
(H)
GeO
2
(T)
[GeO
6
]
[GeO
4
]
Na
3
HZrGe
2
O
8
Na
4
Zr
2
Ge
3
O
12
Na
2
ZrGeO
5
·
[GeO
4
] [HGeO
4
]
[GeO
4
]
[GeO
4
]
The sequence of the formation of NaZr and Na germanates reflects a general
trend in the decondensation of Ge
O radicals with an increase of the alkali content
in the system. The formation of each subsequent phase in the chain accompanied
by the separation of GeO
2
either participates in the formation of the accessory
phase or remains in the solution:
Na
4
Zr
2
Ge
5
O
16
H
2
O
!
2Na
2
ZrGe
2
O
7
1
GeO
2
1
H
2
O
