Ri. Ristic et al., THE INFLUENCE OF TENSILE STRAIN ON THE GROWTH OF CRYSTALS OF POTASH ALUM AND SODIUM-NITRATE, Journal of crystal growth, 179(1-2), 1997, pp. 194-204
Using a specially designed growth cell in which the crystal could be s
ubjected to tensile stain during growth, studies have been made of the
influence of strain on the growth rates of the habit faces of potash
alum and sodium nitrate. These materials are, respectively, typical of
brittle and ductile materials. In both cases, the application of stra
in led to a reduction in growth rate, In the case of brittle potash al
um the reduction in growth fate of the {1 0 0} faces was directly prop
ortional to the applied stress. On removal of the constraint, the grow
th rate returned to its initial value. The growth rate of the {1 1 1}
faces was influenced by strain, but to a much lesser extent. In contra
st, sodium nitrate showed a time dependent decrease in growth rate con
sistent with the gradual partial release of strain by plastic deformat
ion. On release of the strain, the growth rate of the unconstrained cr
ystal was higher than that observed initially. X-ray topographic analy
sis of the crystals showed that potash alum had undergone only limited
plastic deformation during straining to produce few dislocations the
orientation of which could not influence growth of the {1 0 0} and {1
1 0} faces. In contrast, sodium nitrate had undergone massive plastic
deformation to form large numbers of dislocations many of which inters
ected the growing interface. Where this had occurred some of these dis
locations converted to growth dislocations in the subsequent growth, t
hus contributing to the noted increase in growth rate, The results are
extended to consider the equivalent behaviour of micro crystals and a
re discussed in the context of growth rate dispersion in industrial cr
ystallisation.