cryogenics
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What is cryogenics?
Cryogenics is a branch of physics that deals with the production and effects of very low temperatures. The cryogenic temperature range is from -150 °C to absolute zero (-273 °C). At cryogenic temperatures, materials' properties like strength and thermal conductivity are altered, holding theoretical and commercial importance.
Cryogenics started in 1877 when oxygen was cooled to a liquid. In 1908, helium was liquefied, leading to the discovery of superconductivity, where supercooled metals lose electrical resistance. Cryogenics is used for storing and transporting liquefied natural gas and preserving food. It also has applications in cryosurgery and space vehicles.
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Why do scientists study very low temperatures in cryogenics?
Cryogenics, the study of low-temperature phenomena, involves studying materials close to absolute zero to observe altered properties like strength and electrical resistance. At cryogenic temperatures (from −150 °C to absolute zero), molecular motion is minimal, creating a highly ordered state.
Notable phenomena, such as superconductivity (loss of electrical resistance) and superfluidity (flow through tiny holes without friction), occur at these temperatures. Research into Bose-Einstein condensates (BECs), where atoms coalesce into a single quantum state, also requires cryogenic conditions to explore new quantum physics and effects.
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How do materials behave differently at extremely low temperatures?
At extremely low temperatures, materials exhibit significantly altered behaviors, as explored by cryogenics. Cryogenics is the study of the production and application of these low-temperature phenomena.
At cryogenic temperatures, a material's properties, such as strength, thermal conductivity, ductility, and electrical resistance, change. Some materials reach a state of superconductivity, where they lose all resistance to the flow of electricity. Another phenomenon, superfluidity, occurs in liquid helium, allowing it to flow through tiny holes impervious to ordinary liquids. These behaviors are due to the minimal molecular motion and the highly ordered state of materials at these temperatures.
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What tools or methods are used to achieve cryogenic temperatures?
Cryogenics, the study of low-temperature phenomena, employs various methods to achieve cryogenic temperatures, which range from −150 °C (−238 °F) to absolute zero (−273 °C or −460 °F).
One method is the Joule-Thomson effect, where gases cool upon expansion without work or heat transfer, often used to liquefy gases. Another technique is adiabatic demagnetization, which involves removing a magnetic field from certain materials to lower their temperature. This is useful for cooling already cold materials to a small fraction of 1 K.
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What are some common uses of cryogenics in medicine or technology?
Cryogenics involves the production and application of low-temperature phenomena. In medicine, cryosurgery uses low temperatures to freeze and remove unhealthy tissue, with less bleeding than traditional surgery. It has been used to remove tonsils, warts, and even treat Parkinson's disease.
Cryogenics is also used in technology for the storage and swift transportation of liquefied natural gas (LNG). Cryogenic freezing is used to rapidly freeze food by using liquid nitrogen, which extracts heat at extremely fast rates. Furthermore, cryopreservation is employed to preserve cells and tissues by freezing, which is valuable for the storage of embryos, sperm, and hematopoietic stem cells. Superconductivity, a special property of materials cooled to extreme temperatures, has its chief application in the construction of superconducting electromagnets for particle accelerators.
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How has cryogenics helped scientists make new discoveries in physics?
Cryogenics, the study of low-temperature phenomena, has significantly aided scientific discovery in physics. At cryogenic temperatures, materials exhibit altered properties such as strength and electrical resistance, offering insights into their fundamental behavior.
One notable application is in superconductivity, where supercooled metals lose all resistance to electricity. This phenomenon is utilized in superconducting electromagnets for particle accelerators, enabling the creation of powerful magnetic fields without melting conventional electromagnets.
Additionally, the study of helium at temperatures below 3 K has led to the discovery of superfluidity, where liquid helium exhibits unusual properties like being able to flow through microscopic holes.
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cryogenics, production and application of low-temperature phenomena.
The cryogenic temperature range has been defined as from −150 °C (−238 °F) to absolute zero (−273 °C or −460 °F), the temperature at which molecular motion comes as close as theoretically possible to ceasing completely. Cryogenic temperatures are usually described in the absolute or Kelvin scale, in which absolute zero is written as 0 K, without a degree sign. Conversion from the Celsius to the Kelvin scale can be done by adding 273 to the Celsius scale.
Cryogenic temperatures are considerably lower than those encountered in ordinary physical processes. At these extreme conditions, such properties of materials as strength, thermal conductivity, ductility, and electrical resistance are altered in ways of both theoretical and commercial importance. Because heat is created by the random motion of molecules, materials at cryogenic temperatures are as close to a static and highly ordered state as is possible.
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Cryogenics had its beginning in 1877, the year that oxygen was first cooled to the point at which it became a liquid (−183 °C, 90 K). Since then the theoretical development of cryogenics has been connected to the growth in capability of refrigeration systems. In 1895, when it had become possible to reach temperatures as low as 40 K, air was liquefied and separated into its major components; in 1908 helium was liquefied (4.2 K). Three years later the propensity of many supercooled metals to lose all resistance to electricity—the phenomenon known as superconductivity—was discovered. By the 1920s and 1930s temperatures close to absolute zero were reached, and by 1960 laboratories could produce temperatures of 0.000001 K, a millionth of a degree Kelvin above absolute zero.
Temperatures below 3 K are primarily used for laboratory work, particularly research into the properties of helium. Helium liquefies at 4.2 K, becoming what is known as helium I. At 2.19 K, however, it abruptly becomes helium II, a liquid with such low viscosity that it can literally crawl up the side of a glass and flow through microscopic holes too small to permit the passage of ordinary liquids, including helium I. (Helium I and helium II are, of course, chemically identical.) This property is known as superfluidity.
The most important commercial application of cryogenic gas liquefaction techniques is the storage and transportation of liquefied natural gas (LNG), a mixture largely composed of methane, ethane, and other combustible gases. Natural gas is liquefied at 110 K, causing it to contract to 1/600th of its volume at room temperature and making it sufficiently compact for swift transport in specially insulated tankers.
Very low temperatures are also used for preserving food simply and inexpensively. Produce is placed in a sealed tank and sprayed with liquid nitrogen. The nitrogen immediately vaporizes, absorbing the heat content of the produce.
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Cryonics is the practice of freezing an individual who has died, with the object of reviving the individual sometime in the future.
In cryosurgery a low-temperature scalpel or probe can be used to freeze unhealthy tissue. The resulting dead cells are then removed through normal bodily processes. The advantage to this method is that freezing the tissue rather than cutting it produces less bleeding. A scalpel cooled by liquid nitrogen is used in cryosurgery; it has proved successful in removing tonsils, hemorrhoids, warts, cataracts, and some tumours. In addition, thousands of patients have been treated for Parkinson disease by freezing the small areas of the brain believed to be responsible for the problem.
The application of cryogenics has also extended to space vehicles. In 1981 the U.S. space shuttle Columbia was launched with the aid of liquid hydrogen/liquid oxygen propellants.
Of the special properties of materials cooled to extreme temperatures, superconductivity is the most important. Its chief application has been in the construction of superconducting electromagnets for particle accelerators. These large research facilities require such powerful magnetic fields that conventional electromagnets could be melted by the currents required to generate the fields. Liquid helium cools to about 4 K the cable through which the currents flow, allowing much stronger currents to flow without generating heat by resistance.