Cryogenics is a study that is of great importance to the human race and has been a major project for engineers for the last 100 years.  Cryogenics, which is derived from the Greek word kryos meaning “Icy Cold,” is the study of matter at low temperatures.  However low is not even the right word for the temperatures involved in cryogenics, seeing as the highest temperature dealt with in cryogenics is 100 (C (-148 (F) and the lowest temperature used, is the unattainable temperature -273.15 (C (-459.67 (F).  Also, when speaking of cryogenics, the terms Celsius and Fahrenheit are rarely used.  Instead scientists use a different measurement called the Kelvin (K).  The Kelvin scale for Cryogenics goes from 173 K to a fraction of a Kelvin above absolute zero.  There are also two main sciences used in cryogenics, and they are Superconductivity and Superfluidity.

Cryogenics first came about in 1877, when a Swiss Physicist named Rasul Pictet and a French Engineer named Louis P. Cailletet liquefied oxygen for the first time.  Cailletet created liquid oxygen in his lab using a process known as adiabatic expansion, which is a “thermodynamic process in which the temperature of a gas is expanded without adding or extracting heat from the gas or the surrounding system”(Vance 26).  At the same time Pictet used the “Joule-Thompson Effect,” a thermodynamic process that states that the “temperature of a fluid is reduced in a process involving expansion below a certain temperature and pressure”(McClintock 4).  After Cailletet and Pictet, a third method, known as cascading, was developed by Karol S. Olszewski and Zygmut von Wroblewski in Poland.  At this point in history Oxygen was now able to be liquefied at 90 K, then soon after liquid Nitrogen was obtained at 77 K, and because of these advancements scientist all over the world began competing in a race to lower the temperature of matter to Absolute Zero (0 K) [Vance, 1-10].

Then in 1898, James DeWar mad a major advance when he succeeded in liquifying hydrogen at 20 K.  The reason this advance was so spectacular was that at 20 K hydrogen is also boiling, and this presented a very difficult handling and storage problem.  DeWar solved this problem by inventing a double-walled storage container known as the DeWar flask, which could contain and hold the liquid hydrogen for a few days.  However, at this time scientists realized that if they were going to make any more advances they would have to have better holding containers.  So, scientists came up with insulation techniques that we still use today.  These techniques include expanded foam materials and radiation shielding. [McClintock 43-55]

The last major advance in cryogenics finally came in 1908 when the Dutch physicist Heike Kamerling Onnes liquefied Helium at 4.2 and then 3.2 K.  The rest of the advances in cryogenics have been extremely small since it is a fundamental Thermodynamic law that you can approach but never actually reach absolute zero.  Since 1908 our technology has greatly increased and we can now freeze sodium gas to within 40 millionths of a Kelvin above absolute zero.  However, in the back of every physicists head they want to break the Thermodynamic law and reach a temperature of absolute zero where every proton, electron, and neutron in an atom is absolutely frozen.

Also , their are two subjects that are also closely related to cryogenics called Superconductivity and Superfluidity.  Superconductivity is a low-temperature phenomenon where a metal loses all electrical resistance below a certain temperature, called the Critical Temperature(Tc), and transfers to “…a state of zero resistance,…”(Tilley 11).  This unusual behavior was also discovered by Heike Kamerlingh Onnes.  It was discovered when Onnes and one of his graduate students realized that Mercury loses all of its electrical resistance when it reaches a temperature of 4.15 K.  However, almost all elements and compounds have Tc’s between 1 K and 15 K (or -457.68 (F and -432.67 (F) so they would not be very useful to us on a day to day basis[McClintock 208-226].

Then in 1986, J Gregore Bednorz and K. Alex Muller discovered that an oxide of lanthanum, barium, and copper becomes superconductive at 30 K.  This discovery shocked the world and stimulated scientists to find even more “High-Temperature Superconductors”.  After this discovery, in 1987, scientists at the University of Houston and the University of Alabama discovered YBCO, a compound with a Tc of 95 K.  This discovery made superconductivity possible above the boiling point of liquid Nitrogen, so now the relatively cheap, liquid nitrogen could replace the high priced liquid helium required for cryogenic experiments.  To date the highest reported Tc is 125 K, which belongs to a compund made of Thallium, Barium, Calcium, Copper, and Oxygen.  Now, with the availability of high-temperature superconductors, all the sciences including,  cryogenics have made extraordinary advances.  Some applications are demonstrated by magnetically levitated trains, energy storage, motors, and Zero-Loss Transmission Lines.  Also, superconducting electromagnets are used in Particle Accelerators, Fusion Energy Plants, and Magnetic Resonance Imaging devices (MRI’s) in Hospitals.  Furthermore high-speed cryogenic computer memories and communication devices are in various stages of research.  This field has grown immensely since 1986 as you can see and will probably keep growing.

The second subject related to cryogenics is Superfluidity.  Superfluidity is a strange state of matter that is most common in liquid Helium, when it is below a temperature of 2.17 K.  Superfluidity means that the liquid “…discloses no viscosity when traveling through a capillary or narrow slit…”(Landau 195) and also flows “…through the slit disclosing no friction…”(Landau 195)  That this means is that when Helium reaches this state it can flow, without any friction, through the smallest holes and in between atoms in a compund.  If the top is off the beaker it is also possible for the liquid Helium to flow up the side of the baker and out of the beaker until all the liquid helium is gone.  It was then discovered that when any liquid approaches about .2 K it has almost the exact same properties of  superconducting metals, as far as specific heat, magnetic properties, and thermal conductivity.  Even though, both superconducting and Superfluidic materials have similar properties, the phenomenon of Superfluidity is much more complex, and is not completely understood by today’s physicists.[McClintock 103-107]

Cryogenics also consists of many smaller sciences, including Cryobiology, which is “the study of the effects of low-temperatures on materials of biological origin.”(Vance 528)  Developments in this field have led to modern methods of preserving blood, semen, tissue, and organs below the temperature that was obtained by the use of liquid nitrogen.  Also Cryobiology has led to the development of the cryogenic scalpel which can deaden or destroy tissue with a high degree of accuracy, making it possible to clot cuts as soon as you cut them.  So in theory you could one day have surgery without having to deal with any blood.

Another field is Cryopumping.  Cryopumping is the process “of condensing gas or vapor on a low-temperature surface.”(Vance 339)  This is done by extracting gas from a vacuum vessel by conventional methods then freezing the remaining gas on low temperature coils.  This process has been useful when trying to simulate the properties that the vacuum in outerspace will.

References

Khalatnikov, I. M., An Introduction to the Theory of Superfluidity (New York: W.A. Benjamin Inc., 1965).

McClintock, Michael, Cryogenics (New York: Reinhold Publishing Corp., 1964)

Tilley, David R. and Tilley, John, Superfluidity and Superconductivity (New York: John       Wiley and Sons, 1974)

Vance, Robert W., Cryogenic Technology (London: John Wiley & Sons, Inc., 1963)

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