Cryogenics is the branch of physics that deals with the production of extremely low temperatures – usually lower than -238 degrees Fahrenheit – and it specifically looks into how materials behave when they are exposed to such temperatures. The experiments performed by Sir Humphry Davy and Michael Faraday paved the way for this new field of physics. Popular literature, however, often mixes up cryogenics with cryonics or the use of cryogenics to preserve biological matter.

Cryogenics, literally "cold production," is also a commonly used term when referring to a state of low temperature. There is still some debate about the exact starting point for the cryogenic range of temperatures. The National Institute of Standards and Technology set the starting point of the cryogenic range at temperatures below -292 F. The reasoning for this lies in the fact that supposedly normal gases – hydrogen (H), Helium (He) and Neon (Ne) among others – have boiling points under -292 F. So far, temperatures as low as 0.00001K or -459 F have already been achieved.

Achieving Cryogenics Temperatures

If a gas which is originally at a moderate temperature is expanded through a valve, there is an increase in temperature. If, however, the original temperature is lower than the gas' inversion temperature, the temperature goes down. The inversion temperature is the temperature where a gas' Joule Thomson coefficient will change its sign; this is extremely low for gases like oxygen and hydrogen. To achieve cryogenic temperatures, therefore, gases have to be cooled beforehand. This usually brings about a phase change in cascades (the Cascade Principle).Cryogenics

Sir Davy's and Faraday's experiments started by first generating a gas by heating a mixture at one end of an inverted V-shaped tube and cooling the other in a mixture of salt and ice. The gas liquefied because of the lower temperature and increased pressure, quickly cooling to its normal boiling point once the tube was opened. They reached their cryogenics-founding temperature – 163 K or -166 F – by evaporating a mixture of solid carbon dioxide and ether at a low pressure. Lower temperatures are further achieved by evaporating other gases like Helium.

The lowest temperatures are achieved through a process known as adiabatic demagnetization. In this process, a magnetic field is created around a paramagnetic substance – one that is unable to bond with another electron to form a lone pair – while the substance is cooled. This aligns the ions. When the field is removed, the ions resume their initial position and this reduces the temperature.

Applications of Cryogenics

Cryogenic processes have been used since World War II to improve the durability of metals. CryoTech, one of the oldest companies in the field, has been extending the life of materials up to 4 times their normal life expectancy. There are also many chemical uses for cryogenics as certain reactions can only be achieved in cryogenic temperatures. Some substances also require extremely low temperatures to remain stable. Cryogenics has also found a market in aeronautics ever since NASA started using cryogenic fuels, mostly hydrogen and oxygen.