For the non-science geeks out there, supercooling basically refers to the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid. When you cool liquids, like beer and water for example, to this point, you can achieve some really cool results when you take it out of the freezer. Continue reading to see more.
A liquid below its standard freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form creating a solid. However, lacking any such nucleus, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs. Homogeneous nucleation can occur above the glass transition temperature, but if homogenous nucleation has not occurred above that temperature an amorphous (non-crystalline) solid will form.
Droplets of supercooled water often exist in stratiform and cumulus clouds. Aircraft flying through these clouds seed an abrupt crystallization of these droplets, which can result in the formation of ice on the aircraft's wings or blockage of its instruments and probes, unless the aircraft are equipped with an appropriate de-icing system. Freezing rain is also caused by supercooled droplets.
The process opposite to supercooling, the melting of a solid above the freezing point, is much more difficult, and a solid will almost always melt at the same temperature for a given pressure. For this reason, it is the melting point which is usually identified, using melting point apparatus; even when the subject of a paper is "freezing-point determination", the actual methodology is "the principle of observing the disappearance rather than the formation of ice". It is, however, possible, at a given pressure to superheat a liquid above its boiling point without it becoming gaseous.
Supercooling is often confused with freezing-point depression. Supercooling is the cooling of a liquid below its freezing point without it becoming solid. Freezing point depression is when a solution can be cooled below the freezing point of the corresponding pure liquid due to the presence of the solute; an example of this is the freezing point depression that occurs when sodium chloride is added to pure water.
1. Ice Formations
One commercial application of supercooling is in refrigeration. For example, there are freezers that cool drinks to a supercooled level so that when they are opened, they form a slush. Another example is a product that can supercool the beverage in a conventional freezer. The Coca-Cola Company also briefly marketed special vending machines containing Sprite in the UK, and Coke in Singapore, which stored the bottles in a supercooled state so that their content would turn to slush upon opening.