Nucleering

Nucleering is the process by which a new phase or structure begins to form within a material or system, typically through the creation and stabilization of small, discrete sites called nuclei. The term is closely related to nucleation, and in some contexts nucleering is encountered as an alternative spelling or cognate in non-English literature. In materials science, nucleering marks the onset of phase transitions such as crystallization from a melt, precipitation from a solution, or solidification from a supersaturated vapor.

Two main pathways are recognized: homogeneous nucleering, which occurs within the bulk of the parent phase without preferential surfaces, and heterogeneous nucleering, which occurs at interfaces, defects, or on foreign surfaces. Heterogeneous nucleering generally requires lower driving force and proceeds more readily because surfaces or defects reduce the energetic barrier for nucleus formation. Classical nucleation theory describes the competition between bulk free-energy gain from forming a new phase and the surface free-energy cost of creating an interface, yielding a critical nucleus size: nuclei smaller than this size are unstable and dissolve, while larger nuclei tend to grow.

Factors influencing nucleering include temperature, supersaturation, pressure, impurities, and interfacial energies. Measurement and analysis employ calorimetry, microscopic or spectroscopic imaging, light scattering, and nucleation-rate calculations, often denoted by the symbol J.

Applications span pharmaceuticals (control of crystallization and polymorph formation), metallurgy and materials processing (grain structure and defect control), polymer science (crystallization behavior), and nanomaterial synthesis. Nucleering also underpins natural phenomena such as cloud formation and mineral deposition.