Geoscience Reference
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the course of crystallization reactions.
Figure 8.20
shows the TN-diagram of
crystallization of alkali titanates. The experiments were carried out using Tuttle
cold-cone sealed autoclaves provided with platinum liners. The starting materials,
such as TiO
2
and NaOH, were taken in desired molar proportions and placed inside
the platinum liner. The suitable mineralizer solution with a definite molarity was
added into the platinum liner which was sealed later. The platinum liner was later
placed inside an autoclave which was kept at T
500
C and P
1 kbar for a
period of 3 days. Long needle-like crystals of Na
2
Ti
3
O
7
were obtained. The crystals
were about 5
5
5
8 mm long, colorless, and transparent. Such good quality crystals of
Na
2
Ti
3
O
7
have not been obtained by the solid-state reactions method; the resultant
product was mostly a crystalline powder.
The ideal experimental conditions in the growth of Na
2
Ti
3
O
7
crystals are given
below:
NaOH
5.0 gm
TiO
2
2.5 gm
HCOOH
6 ml (3 M)
600
C
Temperature
Pressure
1 kb
Duration
4 days
In experiments with high molarity of HCOOH, the crystal quality was poor, and
beyond 10 M HCOOH, the Na
2
Ti
3
O
7
did not crystallize. In the present work, the
other mineralizers like HCl, HNO
3
,H
2
SO
4
, and H
2
O were tried, but these experi-
ments did not yield good results and instead produced either mixed or other phases.
The crystallization of Na
2
Ti
3
O
7
probably takes place through the following reactions:
Figure 8.20 TN-diagram of
crystallization of alkali titanatses
[75]
.
T
(
°
C)
350
Na
2
Ti
3
O
7
300
260
Na
2
Ti
2
O
5
225
Na
2
Ti
6
O
13
150
1
2
3
4 5 10
NaOH (wt%)
20
30 40
