A chemical substance that, when added to a liquid such as water, reduces the freezing point of the mixture. Antifreezes are used in a wide variety of applications, the most common being automotive cooling systems. Antifreeze liquids are also used in refrigeration systems (as a secondary coolant), heating and air-conditioning systems, ice skating rinks, and solar energy units, and as deicing agents for runways and aircraft. See also Engine cooling; Refrigeration.
Properties of a desirable antifreeze include the ability to depress the freezing point of the liquid (typically water), good solubility, high boiling point (to provide boil-over protection), chemical compatibility with materials of construction, good heat transfer properties, appropriate viscosity, and low cost.
Chemicals that have been used as antifreezes include glycols, glycerol, brines (such as calcium chloride), and alcohols. Ethylene glycol is the most common antifreeze used in automotive cooling systems because of the outstanding freezing-point depression effect, boil-over protection, heat transfer characteristics, high flash point, and low vapor pressure. Propylene glycol, diethylene glycol, and methanol have also been used to a limited extent. Commercial automotive antifreezes contain corrosion inhibitors to protect the various types of metals in the cooling system. See also Ethylene glycol; Inhibitor (chemistry).
Glycol antifreeze solutions are often used in aircraft deicing. These contain additional components for corrosion protection and wetting. Aircraft anti-icing fluids also contain a polymeric thickening agent to increase the fluid viscosity, which allows the fluid to adhere to the aircraft surface and provide protection against freezing for a limited period of time.
