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Chapter II Solution Growth….
super-saturation, the growth process is not limited by nucleation but below
this critical super-saturation, the probability of nucleation would diminish to the
negligible value.
The effect of presence of impurities on the nucleation rate has been
reported by many researchers. Turnbull [25] proposed that the free energy of
formation of a critical nucleus can be catalyzed by a suitable surface in
contact with the nucleus.The Nucleation catalysts or nucleates may be solid
particles suspended in liquid, the surface of the container or a solid surface.
This process of nucleation is known as heterogeneous nucleation. In
heterogeneous nucleation, the reaction may be the direct exchange of
monomers between the parent phase and embryo, that is, a cluster of
molecules, or through the surface, which is normally known as substrate. The
theories of heterogeneous nucleation are developed well by many authors
and edited by Zettlemoyer [26]. Moreover, in highly polar molecules, the
dipole-dipole interaction is expected to play a prominent role in modifying the
surface free energy of micro-cluster at the critical stage. In order to determine
the effect of dipole-dipole interaction on the surface free energy, a model was
proposed by Abraham [27] and discussed for various shapes of nucleation. A
nucleation study is discussed in detail in the later sections of this chapter.
One of the major drawbacks of early nucleation theories is that once
the kinked ledge receives sufficient ad-atoms to move it to the edge of the
crystal, it can no longer work as a low energy nucleation site. Now, the
generation of a new ledge requires an adsorption on a flat surface, for which
the estimated super-saturation is of the order of 50 %. But in 1931 Volmer and
Schultze [28] found astonishing results, while studying the growth rate of
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