Nucleatsioonikiirus

Nucleatsioonikiirus, often translated as nucleation rate, is a fundamental concept in materials science and physical chemistry that describes how quickly a new phase (such as a solid from a liquid or gas, or a new crystal structure) forms within a parent phase. It quantifies the number of stable nuclei, or tiny clusters of the new phase, that appear per unit volume per unit time.

The nucleation rate is a complex function influenced by several factors. Key among these are the degree of supersaturation or supercooling, which is the difference between the current concentration of the solute or temperature and the equilibrium value. A higher degree of supersaturation or supercooling generally leads to a faster nucleation rate. Surface tension or interfacial energy between the parent and new phases also plays a crucial role; higher interfacial energy hinders nucleation, thus reducing the rate.

Temperature is another critical parameter. While increased supercooling can increase the rate, very low temperatures can significantly reduce the atomic mobility required for atoms to arrange into stable nuclei, thereby decreasing the nucleation rate. The presence of impurities or defects in the parent phase can act as nucleation sites, promoting heterogeneous nucleation and increasing the overall nucleation rate compared to homogeneous nucleation, which occurs spontaneously within the pure phase. Understanding nucleation rates is vital for controlling processes like crystallization, precipitation, and the formation of microstructures in alloys and polymers.