Geoscience Reference
In-Depth Information
Figure 5.21 Schematic diagram showing the
position of seeds, nutrient, and the baffle in the
growth of berlinite crystals
[85]
.
Plunger shank
Set screw
Lock nut
Thust washer
Main nut
Body
Seal ring
Plunger
Nutrient
Seeds
The relative growth rates are in general agreement with the morphology of the
equilibrium form, as judged from
ob
serving spontaneously nucleated crystals,
which are bounded by small prism
ð
Þ
faces and terminated by minor and major
rhombohedral faces. Thus, it would b
e
expected that the rates on prism, major and
minor faces, are smaller than for
1010
and (0001) faces, since the latter two do
not exist as bounding equilibrium surfaces. In general, the morphology of the
spontaneously nucleated crystals depends upon various parameters like pressure,
temperature, volume, and composition of the nutrient and mineralizer
[96
ð
1120
Þ
98]
. For
example, impurities in the powder come into the corresponding nutrient and cause
twinning. The starting material like sodium aluminate or aluminum hydroxide gives
needle-like crystals, whereas pure AlPO
4
gives rhombohedral and pyramidal crys-
tals
[83]
.
Yaroslavskii and Popolitov (1990)
[99]
have studied the growth of berlinite on
seeds in detail using fine crystalline charge and also aluminophosphate glass charge
as nutrients. They found that dissolution rate of the aluminophosphate glass charge
is three times greater than that of the crystalline charge. The solubility growth rate
and crystal quality have been studied in great detail using different solvents like
H
3
PO
4
, HCl, HNO
3
, and H
2
SO
4
. If the acid concentrations are increased above
2.5 M, the spontaneous crystals form, and the mother liquor is captured by the
edges of the growing crystal. The growth rates differ greatly between the fine
