Geoscience Reference
In-Depth Information
Solvent H 3 PO 4 (molar)
6.1
% Fill
81
45 presaturation at 25 C
AlPO 4 charge (gm)
Initial temperature ( C)
150
Final temperature ( C)
275
Differential temperature, dT ( C)
1 2
Heating rate ( C)/day
10
Method of heat rate increase
10
Yield (gm)
. 60 mesh a
19.5 gm (70% yield)
, 0 mesh
8.1 gm
Total yield
27.6 gm
Run duration (day)
15
a 60 mesh 5 0.25 mm.
Crystal growth by slow heating method. The method was previously described
in Refs [83,88
92] , and it was mainly used for improving the quality of seeds and
to enhance the size of the crystal with conditions similar to those used to obtain
nucleations. A major drawback of this method is the impossibility of obtaining
crystals of sufficient size in one operation due to the limited quantity of aluminum
phosphate available in the solution.
Synthesis of berlinite crystals under lower temperature and pressure conditions
using slow heating method was
carried out using acid digestion bombs
250 C; P
250 C;
(T
5
100
5
100
300 atm) and smaller Morey autoclaves (T
5
200
P
5
1000 atm). The nutrient was taken in Teflon liners.
The experiments at higher temperature (T
300
500 C and P
.
.
100 bar) yielded
the
-berlinite. With an increase in the pressure, other high-pressure modi-
fications of aluminum orthophosphate belonging to the cristobalite form were
obtained.
Crystal growth by composite gradient method. In order to gain more flexibility
in adjusting the growth rates for Z seeds and to avoid the preliminary work of crys-
tal growth, nutrients of sufficient size (that did not cause crystallites to drop on
crystals) needed to be obtained [93] . A modification of the horizontal gradient
method was originally proposed in Ref. [94] . Berlinite crystals have been obtained
by this method successfully [94] . The autoclave used in the initial experiment is
shown in Figure 5.20 . The following growth conditions were chosen by the authors
[93,94] after experimental trials:
β
Silica glass autoclave: 100 cm, diameter 30 mm
Ratio hot/cold zone: x/1
Solution: H 3 PO 4 ,H 2 O/AlPO 4 (6.5/1.1)
Growth temperature: 170 C
Horizontal temperature difference: 5 C , T , 30 C
Construction diameter: 10 mm
Powdered nutrient
Filling: 80%.
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