Crystallization - Theoretical aspects

Crystals produced industrially in a wide range of fields (food, specialty chemicals, pharmaceuticals, microelectronics, etc.) have to meet very specific specifications, such as crystalline phase, facies, purity, strength, size and so on. For industry, crystallization is a very important unitary chemical engineering operation, as it is at this stage that crystals acquire the physical quality required for their application. Process developers and operators therefore need a sound theoretical grounding in crystal generation and development processes.

Crystallization is a change of state that leads from a gaseous or liquid phase (solution or melt) to a solid called a crystal, with a regular, organized structure. In what follows, we will deal with solution crystallization, although the mechanisms of vapor-phase and molten-bath crystallization are similar.

In the first part, we'll see that these mechanisms are governed by two basic parameters: concentration and supersaturation. In the second part, we'll look in detail at the various crystal-building mechanisms known as nucleation, specifying which are predominant in a given crystallization process. The third part is devoted to crystal growth. The effects of impurities and additives are described. Finally, the last part is devoted to the subsequent evolution of crystals in suspension, whether by phase transition, agglomeration and breakage or ripening.

This article is an update of the original version by Jean-Paul Klein, Roland Boistelle and Jacques Dugua.

The application of this knowledge to processes is the subject of articles [J 2 711] and [J 2 712] in the present treaty.