2. Nucleation

2.1 General

There are five nucleation mechanisms. Primary nucleation occurs when the nuclei originate directly from the mother solution. This primary nucleation may be homogeneous (1), if the nuclei form in the volume of the solution, or heterogeneous (2), if the nuclei form on the walls of the crystallizers, on the stirrer or on foreign solid particles in suspension. As the crystals grow, they may themselves promote secondary nucleation. Surface secondary nucleation (3) is a mechanism by which nuclei are torn from crystal surfaces. Contact secondary nucleation (4) results from the release of microscopic particles following shocks when the suspension is dense. Apparent secondary nucleation (5) concerns seeded crystallizations: the seed may release crystalline debris in suspension,...