Topics: Superconductivity, Electric current, Electron Pages: 9 (2872 words) Published: July 10, 2002


Superconductivity is a phenomenon displayed by certain conductors that show no resistance to the flow of electric current. Conductors are materials in which the electron current goes through. There are 4 different kinds of conductors. Insulators, like glass or wood, have a very high resistance to electron current while semi-conductors, such as silicon, have a medium resistance. Conductors, like copper and other metals, have very low resistance, and superconductors, comprised of certain metals such as mercury and ceramics such as lanthanum-barium-copper-oxide, have no resistance. Resistance is an obstacle in the flow of electricity. Superconductors also have strong diamagnetism. In other words, they are repelled by magnetic fields. Due to these special characteristics of superconductors, no electrical energy is lost while flowing and since magnetic levitation above a superconductor is possible. This principle is employed in high-speed trains that travel at 483 km/h (300 mph) while levitating on a cushion of air.


When superconductivity was first discovered, it was established that the compounds needed to be cooled to within several degrees Kelvin to absolute zero (zero Kelvin). The large amount of cooling was done by putting the compound in liquid helium. Helium, which is usually a gas, liquefies when its temperature drops to 4 K. Once the material had cooled to that temperature, it became a superconductor. However, using liquid helium to cool down material has been a problem. Liquid helium is very expensive, and the cooling equipment is very large. In the past, there was no economic incentive to replace ordinary conductors with superconductors because the cooling costs for superconductors were so high. Scientists have found two ways to overcome the cooling problems. The first is to find a way to cool the material using something less expensive and less bulky than liquid helium. The second way is to raise the temperatures that are necessary to cause superconductivity in the metals, or the critical temperatures. By combining materials into superconducting alloys, the temperature was raised slightly. By 1933, the critical temperature was at 10 K, and it wasn't until 1969 when the critical temperature was raised to 23 K and scientists tried, unsuccessfully, to raise it again. Then, in 1986, 2 IBM researchers in Zurich found a complex ceramic material that was superconducting at 30 K. After being increased to 39 K in late 1986, a critical temperature of 98 K was reported by Ching-WuChu and his research team at the University of Houston in 1987. A new coolant was then used. Liquid nitrogen liquefies at 77 K, is fairly inexpensive, and can even be carried around in a thermos (Mayo 1988, p 7). Liquid nitrogen costs about 50 cents a liter, while liquid helium costs several dollars a liter. Thanks to this new discovery, efficient and cost-effective superconductors could be created.


In 1911, the Dutch physicist Heike Kamerlingh Onnes discovered superconductivity while doing research on the effects of extremely cold temperatures on the properties of metals. While conducting his experiments, he discovered that mercury lost all resistance to the flow of electricity when it was cooled to about 4 K. He then went on to discover superconductivity in other metals. In each case, the material had to be cooled to within several degrees Kelvin to absolute zero. To further his experiments, Onnes once put a current in a superconductor that was formed in the shape of a ring, and cooled it in liquid helium. One year after removing the source of electricity, the current was still flowing at its original strength in the superconductor. The only downside to the new finding was that scientists were unable to explain how it worked.


Since the discovery of superconductivity in 1911, scientists have...

Cited: Seeber, Bernd Handbook of Applied Superconductivity University of Geneva
Switzerland, 1998
Kresin, Vladimir. and Wolf, Stuart Fundamentals of Superconductivity New York and
London Plunum Press., 1990
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