Supersaturation and Rate Processes

As supersaturation is increased in a solution containing crystalline material or surfaces upon which crystals can grow, growth is the dominant process. However, if/when supersaturation reaches a critical value, new nuclei are rapidly formed, relieve much of the supersaUiration and, thereafter, becoming new sites for growth. The control of crystal size in industrial 

Crystallization of Organic Compounds An Industrial Perspective. By H.-H. Tung, E. L. Paul, M. Midler, and J. A. McCauley 

The driving force for CrystaUization is the excess activity of the solute compared to that in equilibrium with the crystalline solid. The most common supersaturation ratio, for example, is y,C,/yisC. For most purposes, it is common to assume an activity coefficient (y) of 1 and to discuss supersaturation in terms of concentration difference (C - C ) or ratio (C/C or [C - C ]/C ). 

The kinetic order in expressions for crystal growth is discussed in Section 4.3.1.6, that for heterogeneous nucleation in Section 4.2.3.1, and that for homogeneous nucleation in Section 4.2.1. 

In combination with vessel geometry and mixing as well as the character of the slurry, supersamration governs the rate and nature of the nucleation and crystal growth processes which will occur. As noted above, this chapter provides a brief discussion of these processes. 

---