Cryogenic (technology)
Cryogenic ( Greek κρυος kryos “frost, ice”; Latin generare “create, create”) is a term for substances, processes and properties in connection with extremely low temperatures.
Cryogens
Liquid cryogens are helium (boiling point (bp) 4.222 K = -268.928 ° C), hydrogen (bp 20.268 K = -252.882 ° C), nitrogen (bp 77.35 K = -195.80 ° C), argon (Bp 87.15 K = −185.8 ° C), oxygen (bp 90.18 K = −182.97 ° C). A solid cryogen is dry ice (frozen carbon dioxide , sublimation point 194.5 K = −78.5 ° C).
The cryogens hydrogen and oxygen are not allowed to be used in laboratories and pilot plants because they are dangerous, and instead of argon, cheaper nitrogen is usually used as a cryogen.
Uses
Cryogens are used, among other things, to freeze and preserve sperm cells or to cool superconductors . Liquid hydrogen ( LH2 ) and oxygen ( LOX ) are used as fuel or oxidizer for rocket engines, e.g. B. in the main engines of the Ariane 5 rocket or the space shuttle .
Another use is the stripping of surfaces. First, the layer to be removed (e.g. paint ) is frozen. As a result, it loses its elasticity and becomes brittle. The layer can then be blasted. Deep freezing and sandblasting can also be done in one step with dry ice. Both processes are more environmentally friendly than the use of organic solvents.
As cryoliquids cold liquids are called, which are used to (for example, in technical applications magnetic resonance imaging ) to make or scientific experiments necessary low temperatures. In cryostats , they are used to provide a cold environment from which the desired, possibly even lower temperatures can be reached using suitable methods. The cryofluids are generated by central facilities or commercial providers by liquefying the corresponding gases (for air / nitrogen, e.g. using the Linde process ) and brought to the respective application using special transport containers. Mostly liquid nitrogen and / or liquid helium are used .
Use in science fiction
In many films and works of science fiction - literature , the cryogenic technique is used to freeze people to reduce drastically to their vital functions. For example, long space flights can be bridged without normal aging becoming noticeable.
literature
- Frank Pobell: Matter and Methods at Low Temperatures. Springer, 1996 ISBN 3-540-58572-9 .