Liquid nitrogen
Liquid nitrogen ( English liquid nitrogen , LN or LN 2 ) is nitrogen in the liquid aggregate state , the under normal pressure at 77 K (-196 ° C) boiling . The clear, colorless liquid has a density of 0.807 g / ml at the boiling point and a viscosity of about 1.5 millipoise .
Liquid nitrogen is industrially produced in large quantities together with liquid oxygen by fractional distillation of liquid air . Sufficiently isolated from ambient heat, liquid nitrogen can be stored and transported in so-called Dewar vessels. The temperature is kept constant at 77 K by slowly boiling the nitrogen, with nitrogen gas escaping. Depending on the size and structure of the insulating vessels, the maximum storage time can be between a few hours and a few weeks.
Liquid nitrogen can easily be converted to the solid state by placing it in a vacuum chamber with a rotary vane pump . Nitrogen freezes at a temperature of 63 K (−210 ° C). As a coolant, nitrogen is only of limited efficiency, as liquid nitrogen immediately boils on contact with warmer objects, which isolates the object from the liquid nitrogen by a layer of gaseous nitrogen. This effect is known as the Leidenfrost effect and occurs in all situations in which a liquid is brought into contact with an object that is at a much higher temperature than the boiling point of that liquid. Faster and better cooling can be achieved by placing an object in a mixture of solid and liquid nitrogen rather than in liquid nitrogen alone.
Applications
Liquid nitrogen is a compact and easily transportable source of nitrogen gas. It is also useful in a wide range of applications because, as a refrigerant, it can maintain a temperature well below the freezing point of water. Uses:
- In cryogenics
- For cryopreservation and storage of blood , egg cells , sperm and other cells, biological samples and materials
- As a source of very dry nitrogen gas
- For freezing food for transportation
- As a coolant for CPUs (main processors), GPUs (graphics processors) and other electronic components
- In the cryotherapy to unsightly or pathological lesions such as warts and actinic keratosis remove
- For cooling high-temperature superconductors to a low temperature that enables superconductivity
- As a coolant for gas traps in vacuum pumps and in controlled evaporation in chemistry
- As a coolant to the sensitivity of infrared sensors to increase
- As a coolant to shrink mechanical parts in mechanical engineering (see cold stretching ) to enable a press connection
- To connect shafts and impellers by cross pressing
- As a construction method in civil engineering, in which the soil is solidified by artificially freezing the soil water ( soil freezing )
- For pipe frosting to create a temporary closure of a pipe
- For the production of ice cream
- For inerting tanks to prevent explosions
- In the cryonic preservation of humans and pets in the hope of being able to revive them at some point
- In the so-called promession , a form of funeral burial
safety
Because of its low temperature, liquid nitrogen can cause frostbite in a very short time if used carelessly . You can dip your hand briefly in liquid nitrogen, provided you are not wearing good heat conductors such as metal rings, because the nitrogen that evaporates on the skin forms an insulating gas layer ( Leidenfrost effect ). However, if you come into contact with metal or other heat conductors, the insulation is immediately interrupted, which leads to severe frostbite and death of the tissue. Quick couplings are therefore often used for safe filling and transferring.
Like all substances, nitrogen expands greatly when it boils. Its volume increases by a factor of 694 during the transition from liquid to gaseous state at room temperature. This can trigger explosive forces. In an accident at Texas A&M University , a clogged tank failed, exploded, and was thrown through the ceiling above the tank.
Liquid nitrogen can be transported and stored in so-called dewar vessels with an evacuated double wall made of glass or steel. It must always be possible to equalize the pressure with the surrounding atmosphere. Liquid nitrogen should only be handled by trained personnel. In the past, there have been serious injuries and even fatalities due to improper handling of liquid nitrogen, for example when liquid nitrogen, which was obtained for molecular cuisine, was transported in a tightly closed thermos.
When liquid nitrogen evaporates and mixes with air, the oxygen concentration in the air drops . This can lead to a lack of oxygen , especially in closed rooms . Because nitrogen is odorless, colorless and tasteless, hypoxia can develop unnoticed . In elevators, cars and trucks, nitrogen may only be transported in containers approved for this purpose.
Liquid nitrogen has a lower boiling point (−196 ° C, 77 K) than oxygen (−183 ° C, 90 K), so oxygen from the air can condense on liquid nitrogen lines and react spontaneously with organic material. Even in open containers that contain liquid nitrogen, oxygen from the air can condense and drip into the container. The liquid nitrogen in the container is then increasingly contaminated with liquid oxygen . In the event of later use, this mixture can lead to severe oxidation and even explosion, especially if it comes into contact with organic materials. Liquid oxygen has a pale bluish color in a thick layer, so that a bluish color of liquid nitrogen in a Dewar vessel can already indicate condensed oxygen. In its pure form, liquid nitrogen is colorless and transparent.
costs
The price of liquid nitrogen depends on the energy price and the distance to the corresponding production sites. In industrialized areas it is in the order of 10–50 cents per liter. Small quantities and delivery to remote locations can be significantly more expensive.
See also
Web links
- LP - experiments with liquid nitrogen: freezing of materials - text, sketch, videos
- Behind the scenes video ("Behind the scenes video") - How liquid nitrogen is used in restaurants for cooking and for cocktails
Individual evidence
- ↑ Cryogenic Fluids European Advanced Cryogenics School Part 16 Retrieved January 7, 2017
- ^ W. Umrath: Cooling bath for rapid freezing in electron microscopy . In: Journal of Microscopy . tape 101 , no. 1 , 1974, p. 103-105 .
- ↑ Scott Wainner, Robert Richmond: The Book of Overclocking: Tweak Your PC to Unleash Its Power . No Starch Press, 2003, ISBN 188641176X , p. 44.
- ^ Brochure from Lüderbach. Accessed on January 9, 2017
- ↑ Ice cream from the laboratory ( Memento of the original from April 15, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. by Patricia Schäfer on ZDF heute - in Europe on August 10, 2015, accessed on April 15, 2016
- ↑ Brochure from Messer Griesheim ( Memento of the original from January 9, 2017 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved January 9, 2017
- ↑ Information Specific to Liquid Nitrogen . University of Florida. Retrieved August 29, 2013.
- ↑ Brent S. Mattox: Investigative Report on Chemistry 301A Cylinder Explosion (reprint; PDF; 9.7 MB) Texas A&M University. Archived from the original on April 30, 2014. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved December 29, 2010.
- ^ British Compressed Gases Association (2000) BCGA Code of Practice CP30. The Safe Use of Liquid nitrogen dewars up to 50 liters. ISSN 0260-4809 . [1]
- ^ Price of Liquid Nitrogen . In: The Physics Factbook . 2007. Retrieved August 29, 2008.
