Unterkühlte

Unterkühlte refers to a state where a liquid is cooled below its normal freezing point without solidifying. This phenomenon occurs because the liquid molecules are not provided with sufficient nucleation sites, which are points where crystallization can begin. In the absence of these sites, the molecules remain in a liquid state despite the reduced temperature.

For water, the normal freezing point is 0 degrees Celsius. However, pure water can be supercooled to temperatures well below this. When a nucleation site is introduced, such as a disturbance or the addition of an impurity, the supercooled liquid rapidly solidifies. This can be observed in experiments where supercooled water freezes instantly upon being shaken or when a seed crystal is added.

The degree of supercooling possible depends on factors such as the purity of the liquid, the presence of impurities, and the rate of cooling. Different liquids exhibit varying degrees of supercooling. This concept has applications in various fields, including meteorology (formation of ice crystals in clouds), cryopreservation (preserving biological materials at low temperatures), and industrial processes.