Cryogenics

In physics, cryogenics is the production and behaviour of materials at very low temperatures.

The 13th International Institute of Refrigeration’s (IIR) International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cryogenic” by accepting a threshold of 120 K (−153 °C) to distinguish these terms from conventional refrigeration. This is a logical dividing line, since the normal boiling points of the so-called permanent gases (such as helium, hydrogen, neon, nitrogen, oxygen, and normal air) lie below 120 K, while the Freon refrigerants, hydrocarbons, and other common refrigerants have boiling points above 120 K.

Discovery of superconducting materials with critical temperatures significantly above the boiling point of nitrogen has provided new interest in reliable, low-cost methods of producing high-temperature cryogenic refrigeration. The term “high temperature cryogenic” describes temperatures ranging from above the boiling point of liquid nitrogen, −195.79 °C (77.36 K; −320.42 °F), up to −50 °C (223 K; −58 °F). The discovery of superconductive properties is first attributed to Heike Kamerlingh Onnes on July 10, 1908. The discovery came after the ability to reach a temperature of 2 K. These first superconductive properties were observed in mercury at a temperature of 4.2 K.

Cryogenicists use the Kelvin or Rankine temperature scale, both of which measure from absolute zero, rather than more usual scales such as Celsius which measures from the freezing point of water at sea level or Fahrenheit which measures from the freezing point of a particular brine solution at sea level.

Definitions and distinctions

Cryogenics

The branches of engineering that involve the study of very low temperatures (ultra low temperature i.e. below 123 K), how to produce them, and how materials behave at those temperatures.

Cryobiology

The branch of biology involving the study of the effects of low temperatures on organisms (most often for the purpose of achieving cryopreservation). Other applications include Lyophilization (freeze-drying) of pharmaceutical components and medicine.

Cryoconservation of animal genetic resources

The conservation of genetic material with the intention of conserving a breed.

The conservation of genetic material is not limited to non-humans. Many services provide genetic storage or the preservation of stem cells at birth. They may be used to study the generation of cell lines or for stem-cell therapy.

Cryosurgery

The branch of surgery applying cryogenic temperatures to destroy and kill tissue, e.g. cancer cells. Commonly referred to as Cryoablation.

Cryoelectronics

The study of electronic phenomena at cryogenic temperatures. Examples include superconductivity and variable-range hopping.

Cryonics

Cryopreserving humans and animals with the intention of future revival. “Cryogenics” is sometimes erroneously used to mean “Cryonics” in popular culture and the press.