Liquid nitrogen

Liquid Nitrogen

Liquid nitrogen is a diatomic liquid, which means that the diatomic character of the covalent N bonding in N2 gas is retained after liquefaction. It is a colorless clear liquid with a density of 0.807 g/ml at its boiling point (−195.79 °C (77 K; −320 °F)) and a dielectric constant of 1.4.

Production

Liquid nitrogen is produced industrially by fractional distillation of liquid air. This process is known as Cryogenic distillation. It involves cooling air until it liquefies, then separating the component gases by boiling them off and capturing them separately. Nitrogen gas produced in this way is then cooled further using a Joule-Thomson cooler, providing liquid nitrogen.

Uses

Liquid nitrogen has a wide range of uses, primarily as a coolant. Its ability to maintain temperatures far below the freezing point of water makes it extremely valuable in a variety of sectors. It is used in Cryogenics, the science of producing and studying low-temperature conditions. The rapid freezing caused by liquid nitrogen also makes it useful in food preparation, such as for making ice cream.

In the medical field, liquid nitrogen is used to freeze and destroy abnormal skin cells or skin lesions, a process known as Cryosurgery. It is also used in Cryopreservation, the process of preserving biological samples at extremely low temperatures.

Safety

While generally safe to handle, liquid nitrogen must be stored and used properly to avoid hazards. It can cause rapid freezing on contact with living tissue, which can lead to frostbite. When vaporized, it can displace oxygen in the air and can act as an asphyxiant, especially in confined spaces.

See also

• Cryogenics
• Cryosurgery
• Cryopreservation
• Joule-Thomson effect