Ylijäähtymistä

Ylijäähtymistä is a phenomenon where a liquid is cooled below its freezing point without solidifying. This unstable state is known as a metastable phase. For pure substances, the transition from a supercooled liquid to a solid is typically triggered by nucleation, which can occur spontaneously through random molecular fluctuations or be induced by external factors.

Nucleation can be homogeneous, arising from within the liquid itself, or heterogeneous, initiated by impurities or the container surface. Once nucleation begins, the liquid rapidly crystallizes, releasing the latent heat of fusion and warming up to the freezing point. The extent to which a liquid can be supercooled depends on factors such as its purity, the presence of nucleation sites, and the rate of cooling.

Ylijäähtymistä is a common occurrence in everyday life, such as when water is cooled in a freezer without ice crystals forming. Disturbing the supercooled liquid, for instance by tapping the container or introducing an ice crystal, can cause immediate solidification. This phenomenon has applications in various fields, including cryopreservation, meteorology (formation of ice crystals in clouds), and food science. The study of ylijäähtymistä helps in understanding phase transitions and controlling crystallization processes.