overfreezing

Overfreezing refers to a phenomenon observed in certain biological and chemical systems where the temperature is lowered below the normal freezing point without solidification occurring. This state, known as supercooling or undercooling, is metastable. The liquid remains in a liquid state despite being below its freezing point because the formation of ice crystals requires a nucleation event. Nucleation can be spontaneous, initiated by impurities in the liquid, or induced by external factors such as agitation or seeding with ice crystals. Once nucleation occurs, the liquid rapidly solidifies, releasing the latent heat of fusion.

In biological contexts, overfreezing is significant for cryopreservation. Cells, tissues, and organs can be overcooled to very low temperatures to minimize ice crystal formation, which can cause cellular damage. However, excessive overcooling can lead to devitrification, where previously vitrified (glass-like amorphous solid) water transitions into ice. This process is detrimental to cell viability. Strategies in cryopreservation aim to balance the extent of cooling to maximize survival rates.

Chemically, overfreezing is a fundamental concept in understanding phase transitions and the kinetics of crystallization. The degree of supercooling influences the rate of nucleation and crystal growth, affecting the final microstructure and properties of the solidified material. This phenomenon is relevant in various industrial processes, including food freezing, metallurgy, and the production of pharmaceuticals.