Geoscience Reference
In-Depth Information
Figure 5.24 Characteristic photographs of the berlinite crystals (a
d)
[83,90]
.
It is observed that these admixtures play an important role in the process of crystal-
lization of AlPO
4
. In the actual experiments without any admixtures, well-developed
rhombohedral and hexagonal crystals have been obtained, but with the addition of var-
ious admixtures the crystal changes to fibrous, rod-shaped, acicular, massive, equi-
dimensional and irregular shapes (
Figure 5.24c and d
). In the case of Zr and Ti as the
admixtures, fibrous or acicular crystals of berlinite have been obtained; such results
were earlier obtained only in experiments containing Al(OH)
3
as the starting compo-
nent
[83,98]
.
Growth defects in synthetic berlinite samples have been studied by several
workers through X-ray topography
[96,100]
. The berlinite crystals, in general,
show internal structural defects along with a high density of defects on X-ray Lang
topography. It can be seen that crystals which appear transparent from outside
contain many internal defects.
Figure 5.25
shows a typical Lang X-ray topograph
taken in (2110) face
[90]
. Line defects were attributed to the disorder in crystal
structure and more likely to the impurities existing in the boundary of repetitive
overgrowth. However, it is possible to distinguish various types of contrasts that
