Freezing and Supercooling of Water

Abstract The solid form of water is known as ice, which is the physically stable form of water at temperatures below 0°C. The transition of water from the liquid to the solid state is known as freezing, and 0°C is usually referred to as the freezing point or melting point of water. However, small samples of liquid water will usually not freeze until they are cooled far below 0°C. The maintenance of the liquid state below the melting point is referred to as supercooling or undercooling , and the temperature at which spontaneous freezing takes place is referred to as the supercooling point . Freezing is initiated either by the water molecules themselves or by freezing promoting agents or ice nucleators , which may trigger freezing at high subzero temperatures. Increasing concentrations of solutes and increasing hydrostatic pressure depress melting point as well as supercooling point, whereas increasing sample volume causes an elevation of the supercooling point.