Geoscience Reference
In-Depth Information
rate is about 0.25 M for NaOH. Concentrations of about 4.0 M for NaOH and
2.0 M for KOH form sodium or potassium silicates along with
-quartz. Laudise
and Ballman (1961)
[44]
have measured the solubility of quartz in 0.5 M NaOH as
a function of the percentage fill and temperature. The quartz solubility dependence
on the percentage fill is shown in
Figure 5.9
.
An important result of solubility determinations is the delineation of the pressure,
temperature, and composition regions where the temperature coefficient (TC) of sol-
ubility is negative. These regions are to be avoided in the growth of quartz, since
they require a different setup; otherwise, they result in the loss of seed crystals.
In recent years, mixed solvents are being used even in the growth of quartz.
High-quality large quartz crystals have been obtained in NaCl and KCl solutions,
NaOH and Na
2
CO
3
solutions, (10%)
[45,46]
. Most of the literature data available
on the solubility of
α
-quartz deals with the data in various solutions at elevated
temperatures and pressures. It was recently observed that, in the growth of quartz
crystals under hydrothermal conditions, the evaluation of pressure generation
and its effect on the dissolution in different aqueous solutions are the important
steps. Hence the authors have studied the solubility of
α
α
-quartz in NaOH
(1 M)
Na
2
CO
3
(1 M) using high-pressure conditions from 200 to 350 MPa at
temperatures of 400
C
[46]
. The impetus for this work was provided by the fact
that high-frequency applications of
1
-quartz require sheets with small thickness of
the same order of size as the defects (such as inclusions, etch pits, and disloca-
tions). Thus, the pressure can make new solvents viable for hydrothermal growth,
especially by reducing their concentrations.
Figures 5.10 and 5.11
show the solubil-
ity limit comparison between NaOH (1 M) and Na
2
CO
3
(1 M) versus pressure at
α
Figure 5.9 Quartz solubility
dependence on % fill
[44]
.
0.54
0.52
380
°
C
0.50
0.48
0.46
360
°
C
320
°
C
0.44
0.42
0.40
0.38
68
72
76
80 84
Percent fill
88
92
96
