alijäähtyneisyyden

Alijäähtyneisyys, also known as supercooling, is a phenomenon where a substance is cooled below its freezing point without becoming solid. This is achieved by preventing the formation of nucleation sites, which are points where crystallization can begin. In pure liquids, this can be difficult, but impurities or rough surfaces can act as nucleation sites, initiating the freezing process.

When a supercooled liquid is disturbed, either by agitation or the introduction of a seed crystal, it can rapidly freeze. This is because the disturbance provides the necessary nucleation sites for the molecules to arrange themselves into a crystalline structure. The transition from liquid to solid is often accompanied by a release of heat, known as latent heat of fusion.

Supercooling is observed in various natural phenomena, such as the formation of ice crystals in clouds. In meteorology, it's crucial for understanding precipitation processes. In laboratory settings, supercooling can be used to study the kinetics of crystallization and the properties of metastable states. It has practical applications, including in flash freezing of food, where rapid cooling preserves texture and quality. However, uncontrolled supercooling can also lead to hazards, such as the sudden freezing of liquids in pipes. The temperature at which a substance supercools before freezing is dependent on its purity and the presence of nucleation sites.