Cryogenics

In physics, cryogenics is the production and behaviour of materials at very low temperatures.
It is not well defined at what point on the temperature scale refrigeration ends and cryogenics begins. A gas may be cryogenic if it can be liquefied at or below . 
The U.S. National Institute of Standards and Technology considers cryogenics as involving temperatures below . The normal boiling points of helium, hydrogen, neon, nitrogen, oxygen, and normal air are below −180 °C. 
The Freon refrigerants, hydrocarbons, and other common refrigerants have boiling points above −180 °C.
Discovery of superconducting materials has raised interest in reliable, low cost methods of producing high temperature cryogenic refrigeration. The term "high temperature cryogenic" means temperatures from above the boiling point of liquid nitrogen, , up to .
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 with its zero at an arbitrary temperature.