Liquid nitrogen

Liquid nitrogen (English liquid nitrogen LN or LN2) is nitrogen in the liquid state, boiling at atmospheric pressure at 77 K (-196 ° C). The clear, colorless liquid having a density of 0.807 g / ml at the boiling point.

Liquid nitrogen is produced industrially in large quantities together with liquid oxygen by fractional distillation of liquid air.

Sufficiently insulated from ambient heat can be stored and transported in liquid nitrogen containers, for example, in jugs. The temperature is maintained by slow boiling of the nitrogen at a constant K 77, wherein nitrogen gas to escape. Depending on the size and structure of the flasks can be between a few hours to a few weeks, the maximum storage period.

Liquid nitrogen can be readily converted into the solid state by being placed in a vacuum chamber with a rotary vane pump. Nitrogen- freeze at a temperature of 63 K ( -210 ° C). A cooling means is nitrogen only limited effectiveness since liquid nitrogen boils at warmer objects immediately contact, whereby the object is isolated by a layer of nitrogen gas to the liquid 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 which has a significantly higher temperature than the boiling point of this liquid. Faster and better cooling can be achieved by an article is placed in a mixture of solid and liquid nitrogen rather than liquid nitrogen alone.

Applications

Liquid nitrogen is a compact and easy to be transported source of nitrogen gas. In addition, it is useful in a wide range of applications because it is capable of maintaining a temperature well below the freezing point of water as a refrigerant. uses:

• For storage of cells and other biological materials at low temperature for laboratory work
• In cryogenics
• As a source of very dry nitrogen gas
• For freezing foods for transport by immersion in liquid nitrogen
• For the cryopreservation of blood, reproductive cells (eggs and sperm ), and other biological samples and materials
• As coolant when overclocking of CPUs ( central processing units ), GPUs ( graphics processing units ), or other types of computer hardware
• If you want to work on a section of water pipes, which can not be separated by valves from the network, you can freeze the afferent and efferent water pipes by means of liquid nitrogen.
• In the cryotherapy to remove unsightly and potentially malignant lesions such as actinic keratosis, and warts
• In the process of Promession, a sort of undertaker
• Cooling of high-temperature superconductors on a sufficiently low temperature to enable superconducting
• To the case of the cryonic preservation of humans and domestic animals, in the hope they revive sometime
• As a refrigerant gas traps in vacuum pumps and in the controlled evaporation of the chemical
• As a cooling means to increase the sensitivity of the infrared sensors
• As a cooling means " to shrink " temporary mechanical components during assembly of the machine (see cold stretching ) to allow a press-fit connection
• As construction methods in civil engineering, in which the bottom is solidified by artificial freezing of the soil water ( soil freezing )

Security

Since the expansion ratio from the liquid to the gaseous state nitrogen is 1:694, the boiling of liquid nitrogen, a large force can be produced. In an accident at the Texas A & M University, the pressure-relief devices were sealed with brass plugs. As a consequence, the tank failed and exploded. The force of the explosion was sufficient to propel the tank through the ceiling directly above the tank.

Because of its low temperature can cause frostbite on living tissue in liquid nitrogen careless use in no time. However, if you wear any good heat conductors such as metallic rings, you can dive about a hand for a short time without freezing directly in liquid nitrogen. This is possible because the nitrogen evaporates immediately and an insulating layer is formed to the hand (see Leidenfrost effect). But you wear a ring or other good conductor of heat, so break this isolation layer, which immediately turn leads to frostbite. For safe loading and refilling often come quick couplings used.

If liquid nitrogen evaporates, it reduces the concentration of oxygen in the air and can thus cause a lack of oxygen, especially in confined areas. Nitrogen is odorless, colorless and tasteless and can shortness of breath without prior ( sensual ) cause notice.

Containers containing liquid nitrogen to the oxygen in the air to condense (see liquid oxygen). The liquid in such a reservoir is increasingly enriched with oxygen as long as nitrogen evaporates ( as the boiling point of oxygen is at 90 K to 13 K higher than that of nitrogen). The liquid oxygen can cause severe oxidation of organic materials.

Costs

The price of liquid nitrogen is dependent upon the distance to the corresponding places of production and the price of energy; Usually, the price between a few cents and five euros per liter, depending on quantity and location.