nukleációs

Nukleation is the initial stage of a phase transition, where a small, stable cluster of the new phase forms within the parent phase. This cluster, known as a nucleus, must overcome an energy barrier to grow into a macroscopic phase. The process is fundamental to many physical phenomena, including crystallization, precipitation, and condensation.

There are two primary types of nucleation: homogeneous and heterogeneous. Homogeneous nucleation occurs spontaneously within a pure substance, requiring a significant degree of supersaturation or supercooling. This process is less common in practice as it necessitates a high energy barrier. Heterogeneous nucleation, on the other hand, is facilitated by the presence of impurities, surfaces, or defects in the parent phase. These act as nucleation sites, lowering the energy barrier and promoting the formation of the new phase at lower supersaturation or supercooling levels.

The rate of nucleation depends on factors such as temperature, pressure, and the degree of supersaturation or supercooling. It is a critical step in determining the microstructure and properties of materials formed through phase transitions. Understanding nucleation is essential for controlling processes in fields ranging from materials science and metallurgy to atmospheric science and medicine. For example, in cloud formation, heterogeneous nucleation on dust particles is crucial for raindrop formation.