Solubility supersolubility diagram

In considering the state of supersaturation, Ostwald(20) introduced the terms labile and metastable supersaturation to describe conditions under which spontaneous (primary) nucle-ation would or would not occur, and Miers and Isaac(21) have represented the metastable zone by means of a solubility-supersolubility diagram, as shown in Figure 15.8. 

The state of supersaturation is an essential requirement for all crystallization operations. Ostwald (1897) first introduced the terms labile and metastable supersaturation to classify supersaturated solutions in which spontaneous (primary) nucleation (see section 5.1) would or would not occur, respectively. The work of Miers and Isaac (1906, 1907) on the relationship between supersaturation and spontaneous crystallization led to a diagrammatic representation of the metastable zone on a solubility-supersolubility diagram Figure 3.9). The... 

Figure 19.9 Generic solubility-supersolubility diagram. Reprinted with permission from Mullin (1993).

The equilibrium phase diagram or solubility-supersolubility plot (Miers and Isaac, 1907), shown in Figure 3.1, provides a useful starting point for considering why crystallization occurs and what type of process might be most suitable for production of a particular substance. It can be divided into three zones (Ostwald, 1897)... 

The area of conditions called the metastable zone is situated between the solubility and supersolubility curves on the crystallization phase diagram (Fig. 3.1). The supersolubility curve is defined as the line that separates the conditions where spontaneous nucleation (or phase separation or precipitation) occurs, from those where the crystallization solution remains clear if left undisturbed (Ducruix and Giege, 1992 Ducruix and Giege, 1999). 

In spite of the fact that the supersolubility curve is ill-defined, there is no doubt that a region of metastability exists in the supersaturated region above the solubility curve. The diagram is therefore divided into three zones, one well-defined and the other two variable to some degree ... 

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