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Chapter II Solution Growth….
system. This phenomenon is referred to secondary nucleation. This
classification can be represented as follows:
Nucleation can often be induced by external influences like agitation,
mechanical shock, friction, extreme pressures, electric and magnetic fields,
spark discharge ultraviolet, X-rays, - rays irradation, sonic and ultrasonic
shaking etc. Stirred water can be super-cooled by about 0.5 0 C, whereas,
undisturbed distilled water can be super-cooled to as much as -4 0 C. Similarly,
water in a capillary tube can be super-cooled to lower temperatures than in
larger vessels.
2.18 Nucleation Thermodynamics
In the first order phase transition there is a discontinuous change in
some order parameters between the two phases. Such a change is driven by
the change in the free energy as the new phase is formed. The condition for
stable equilibrium between two large phases is the equality of their chemical
potentials. By chance if the chemical potential of one of them is higher than
that of the other, a mass transport occurs until the chemical potentials
become equal again throughout the system. The driving force of this transport
is the difference between the chemical potentials (∆ μ) of the two phases is
called super-saturation and the product of this quantity and the number of
transported molecules will contribute for the bulk energy change of the new
phase.
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