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Chapter II Solution Growth….
2.25 Nucleation Studies of KDP and Related Systems
The reliability of homogenous nucleation studies is difficult to judge.
Melia and Moffit [112], while studying the nucleation of ammonium chloride
and ammonium bromide in aqueous solution have reported that the value of
pre-exponential factor lies in the range 10 3 to 10 5 cm -3 S -1 , which is well
outside the range predicted from Gibbs-Volmer theory 10 25 . Because of the
experimental difficulty of preparing solutions completely free from foreign
bodies, most of the crystallization and nucleation experiments reported in the
literature have been concerned with heterogeneous nucleation.
The nucleation behavior of a solute can be affected considerably by the
presence of impurities. The presence of small amounts of impurities can
suppress nucleation in aqueous solution and certain surface active agents
also exert strong inhibiting effect. The presence of insoluble foreign crystals
reduces the super-saturation required to form crystals from their solutions.
It would be unwise to attempt a general explanation of the
phenomenon of nucleation suppression by added impurities. Some impurities
can suppress the nucleation entirely; some may enhance nucleation while
others may exert a highly selective effort. The effect of soluble impurities on
the nucleation of supersaturated KDP solution has been studied by the
several authors and presented here by briefly.
The classical homogeneous nucleation theory has been successfully
verified for different crystal systems. In 1976, Paul and Joshi [113] studied the
effect of super-saturation on the induction period of KDP crystal. They
calculated the surface energy at the phase boundary separating the growing
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