Number and Nature of Nuclei

It is instructive to consider the shape of the isotherms in order to gain some insight into the crystallization process. For this purpose, a shape parameter h may be defined  

Evidently, the existence of these classes reflects variations in size and morphology, which in turn reflect variations in the number and nature of the nuclei. With type 1 crystallization it was shown that the size varied inversely with the concentration of nuclei and it was concluded that the slight increase in n was due to a slight increase in the number of defective crystals, e.g., those having screw dislocations. Such crystals, having greater surface areas for growth, would increase the observed rate of crystallization, as is observed. 

The situation is much more complex in crystallization of type 2. Here it appears that nuclei are effectively destroyed in heating to 7, and that a relatively few new nuclei form sporadically with time. These nuclei tend to be complex in form, and induce secondary crystallization. Such a conclusion is in accord with microscopic observation of complexity and heterogeneity. Once the nuclei initiate crystallization, many growth surfaces are involved, and the rate (and n) increases very rapidly. On the other hand, seeding of a type 2 system during its incubation period results in kinetics 

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