The word cryogenics comes from the Greek word cryosmeaning "cold," combined with a shortened form of the English verb "to generate. More specifically, a low-temperature environment is termed a cryogenic environment when the temperature range is below the point at which permanent gases begin to liquefy.
Play media Rapid formation of ice crystals in supercool water home freezer experiment In spite of the second law of thermodynamicscrystallization of pure liquids usually begins at a lower temperature than the melting pointdue to high activation energy of homogeneous nucleation.
The creation of a nucleus implies the formation of an interface at the boundaries of the new phase. Some energy is expended to form this interface, based on the surface energy of each phase. If a hypothetical nucleus is too small, the energy that would be released by forming its volume is not enough to create its surface, and nucleation does not proceed.
Freezing does not start until the temperature is low enough to provide enough energy to form stable nuclei. In presence of irregularities on the surface of the containing vessel, solid or gaseous impurities, pre-formed solid crystals, or other nucleators, heterogeneous nucleation may occur, where some energy is released by the partial destruction of the previous interface, raising the supercooling point to be near or equal to the melting point.
Enthalpy of fusion Freezing is almost always an exothermic process, meaning that as liquid changes into solid, heat and pressure is released. This is often seen as counter-intuitive,  since the temperature of the material does not rise during freezing, except if the liquid were supercooled.
But this can be understood, since heat must be continually removed from the freezing liquid or the freezing process will stop. The energy released upon freezing is a latent heatand is known as the enthalpy of fusion and is exactly the same as the energy required to melt the same amount of the solid.
Low-temperature helium is the only known exception to the general rule. Helium-4 also has a very slightly negative enthalpy of fusion below 0.
This means that, at appropriate constant pressures, heat must be added to these substances in order to freeze them. Glass transition Certain materials, such as glass and glycerolmay harden without crystallizing; these are called amorphous solids.
Amorphous materials as well as some polymers do not have a freezing point, as there is no abrupt phase change at any specific temperature.
Instead, there is a gradual change in their viscoelastic properties over a range of temperatures. Because vitrification is a non-equilibrium process, it does not qualify as freezing, which requires an equilibrium between the crystalline and liquid state.
Some substances, such as water and bismuthexpand when frozen. Freezing of living organisms[ edit ] Main article: Cryobiology Many living organisms are able to tolerate prolonged periods of time at temperatures below the freezing point of water. Most living organisms accumulate cryoprotectants such as anti-nucleating proteinspolyols, and glucose to protect themselves against frost damage by sharp ice crystals.
Animals[ edit ] The nematode Haemonchus contortus can survive 44 weeks frozen at liquid nitrogen temperatures. Many species of reptiles and amphibians survive freezing. See cryobiology for a full discussion. Human gametes and 2- 4- and 8-cell embryos can survive freezing and are viable for up to 10 years, a process known as cryopreservation.
Experimental attempts to freeze human beings for later revival are known as cryonics.
Frozen food Freezing is a common method of food preservation that slows both food decay and the growth of micro-organisms. Besides the effect of lower temperatures on reaction ratesfreezing makes water less available for bacterial growth.Life. Everyday Cheapskate; Dorchester's largest crab processing plants have used cryogenic freezing for several years to extend the viability of their products, including whole crabs.
Cryogenics is defined as the scientific study of materials and their behavior at extremely low tranceformingnlp.com word comes from the Greek cryo, which means "cold", and genic, which means "producing".The term is usually encountered in the context of physics, materials science, and medicine.
Nov 18, · Watch video · Cryogenic freezing is the process of preserving a dead body with liquid nitrogen. Advocates believe that scientists will one day work out how to warm the bodies up and bring them back to life, by which time doctors might be able to cure cancer and other diseases which are untreatable tranceformingnlp.com: Reiss Smith.
The Applications of Cryogenic Freezing in Everyday Life.
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3, words. 5 pages. A Research on Solar Energy. words. Because of its extremely cold temperatures, immersion freezing in liquid nitrogen is the fastest freezing method known for producing Individually Quick Frozen (IQF) foods.
Nitrogen also plays a key role in reducing spoilage, discoloration and off–flavors, giving strength to retail packaging. Cryogenic tempering has numerous advantages for any industry requiring the benefit of longer lasting, more durable metal parts.
It is especially helpful in industries with moving parts that experience a large amount of cycles in daily operations. Below are some of the benefits and potential applications of cryogenically treated pieces: Cryogenic .