In the gaseous state, nitrogen surrounds us constantly – it is the main component of the air on the Earth. But we rarely encounter liquid nitrogen in everyday life. However, it is manufactured industrially and extremely useful for certain applications.
Nitrogen becomes liquid only at extremely cold temperatures, since it boils from -196 ° C. This makes liquid nitrogen a refrigerant that can maintain a temperature well below the freezing point of water – a property that is used for different applications.
Liquid nitrogen is also a source of easily transportable nitrogen gas, itself used for various applications.
Preservation of biological material
Liquid nitrogen is especially a refrigerant suitable for the preservation of biological materials such as cells or blood, for laboratory work at low temperature or for transport. It keeps the equipment refrigerated until all of the nitrogen has evaporated.
Cooling of superconductors at high temperature
Liquid nitrogen also plays a role in creating powerful magnetic fields using superconductors. This works in the following way: in a whole series of electrical conductors, the electrical resistance suddenly disappears below a certain temperature (very low), the electric current can then circulate without encountering any resistance. This property is called superconductivity. The superconducting conductor transition normally occurs at a temperature of -270 ° C. But now it is also known to produce materials that become superconductors to -170 ° C, called high temperature superconductors. Because liquid nitrogen has a temperature of -196 ° C, it is suitable for refrigerating these superconductors. It is also a little less expensive and easier to manufacture than liquid helium which is used for other superconductors. Superconductivity is used today to create powerful magnetic fields with superconducting coils. This is needed, for example, in nuclear magnetic resonance tomography for medical diagnostics or in particle accelerators for basic physics research.
Molecular cooking uses biochemical, physical and chemical processes to prepare dishes in a new and unusual way. Liquid nitrogen is thermally shocked to foods due to its low temperature and is therefore ideally suited for making ice creams and sorbets. For this purpose, the liquid nitrogen is mixed gradually with the other ingredients, stirring constantly. Thanks to the fast frost, the aromas are preserved and the ice cream is particularly creamy. In some cities in Germany, there are already glaciers that make all their ice creams in this way!
How is liquid nitrogen produced?
To obtain liquid nitrogen, the air is first cooled until it liquefies. The liquid nitrogen can then be distilled from the liquid air. Liquid nitrogen can be transported in containers called Dewar vases, which operate on the principle of the insulated bottle. These containers formed of two layers of metal or glass separated by a space almost free of air makes them particularly insulating. The temperature is maintained at -196 ° C and the liquid boils and evaporates only very slowly.
Care must be taken when using liquid nitrogen as a coolant: if the liquid nitrogen comes into contact with a much hotter object, it immediately boils and a layer of nitrogen gas forms around it. This layer insulates from direct contact with liquid nitrogen (Leidenfrost effect). This is why liquid nitrogen is not always indicated as a refrigerant.
It is the Leidenfrost effect that makes it possible to immerse one’s hand for a short time directly in liquid nitrogen without undergoing frostbite. But do not try! If, for example, a ring or other thermal conductor is worn, the insulating layer is broken and frostbite occurs immediately. This is why wearing thick gloves is mandatory for the handling of liquid nitrogen.