Geoscience Reference
In-Depth Information
450
C
[350]
.They
hydrothermal conditions within the temperature range 250
obtained the crystals through the following chemical reactions:
3LiOH
5H
3
BO
3
!
Li
3
B
5
O
8
ð
OH
Þ
2
1
8H
2
O
ð
7
:
26
Þ
1
This has two polymorphic modifications: (i) Li
3
B
5
O
8
(OH)
2
and (ii) Li
3
B
5
O
8
(OH).
They have obtained a series of lithium borates: LiBO
2
,Li
2
B
4
O
7
,Li
3
B
5
O
8
(OH)
2
,and
mixed Zn borates: LiZnBO
3
,2Li
2
O
3B
2
O
3
.Among
these, Li
3
B
5
O
8
(OH)
2
crystallizes within a narrow region (as shown in
Figure 7.82
)
when MnO was added into the nutrient in a very small quantity. Contrary to these ear-
lier works, Byrappa et al.
[364]
obtained Li
3
B
5
O
8
(OH)
2
crystals in the system
Li
2
O
3ZnO
2B
2
O
3
,4Li
2
O
4ZnO
240
C, P
a
B
2
O
3
a
H
2
O under lower PT conditions (T
100 atm) in the
5
5
absence of any other components like MnO or CuO.
The experiments were carried out using a Morey-type autoclave provided with
Teflon liners. The starting materials such as LiOH and H
3
BO
3
were taken in
Teflon liners. The % fill was varied from 50% to 60%. Several mineralizers were
tried and the HCOOH was found to be a better mineralizer with its molarity vary-
ing from 1.5 to 5 M. In most of the earlier works, LiOH has been taken as a miner-
alizer. A change in the concentration of LiOH in the system changes the resultant
lithium compound. Byrappa et al.
[364]
observed that LiOH exists in the system,
the presence of additional mineralizer namely HCOOH enhances the solubility of
this compound and the solvation processes.
Figure 7.88
shows the solubility of
Li
3
B
5
O
8
(OH)
2
in HCOOH
[365]
. The formation of Li
3
B
5
O
8
(OH)
2
takes place
according to the following reactions:
LiOH
H
3
BO
3
!
LiBO
2
1
2H
2
O
ð
7
:
27
Þ
1
Figure 7.88 Solubility of
Li
3
B
5
O
8
(OH)
2
in HCOOH
[365]
.
80
T
= 250º
P
= 100
bar
60
40
20
0.5
1.0
1.5
2.0
2.5
HCOOH (M)
