alijäähtymisen

Alijäähtymisen, known in English as supercooling or undercooling, refers to the phenomenon where a liquid is cooled below its freezing point without solidifying. This state is metastable, meaning the liquid is not in its most stable phase. For a liquid to exist below its freezing point without becoming a solid, nucleation sites must be absent. Nucleation is the initial process where tiny clusters of molecules arrange themselves into a solid structure. If there are no impurities, rough surfaces, or vibrations to initiate this process, the liquid can remain in its liquid state even at temperatures where it would typically freeze.

When nucleation finally does occur in a supercooled liquid, the solidification process can be very rapid, often releasing a significant amount of latent heat. This release of heat can cause the temperature of the substance to rise back to its freezing point. Common examples of alijäähtymisen include water left undisturbed in a clean container and cooled carefully in a freezer. Upon disturbance, such as tapping the container or adding an ice crystal, rapid freezing can be observed. This phenomenon has practical applications in fields like weather forecasting, where understanding cloud formation and precipitation relies on the behavior of supercooled water droplets. It also has implications in materials science and cryogenics.