nucleationilähtöistä

Nucleation is the initial process that occurs in the formation of a new thermodynamic phase. It is a prerequisite for precipitation, crystal growth, and other phase transitions. In simple terms, nucleation is the birth of a new phase within a parent phase. This new phase can be a solid forming from a liquid melt, a liquid droplet forming from a gas, or a solid crystal forming from a solution.

There are two main types of nucleation: homogeneous and heterogeneous. Homogeneous nucleation occurs spontaneously within a pure substance when it reaches a state of supersaturation or supercooling. This requires a significant degree of supersaturation or supercooling, as it involves the formation of a stable nucleus from the random fluctuations of the parent phase. Heterogeneous nucleation, on the other hand, occurs at the surface of an impurity or a foreign body within the parent phase. This is much more common in practice because these surfaces provide sites where nucleation can occur with a lower energy barrier, meaning less supersaturation or supercooling is required.

The size of a stable nucleus is critical. Below a certain critical size, a nucleus is unstable and will tend to dissolve back into the parent phase. Above this critical size, the nucleus is stable and can grow. This critical size is determined by the balance between the decrease in bulk free energy and the increase in surface free energy associated with forming the new phase. Understanding nucleation is crucial in various scientific and engineering fields, including materials science, meteorology, and geology, as it influences the properties and formation of many materials and phenomena.