Re: What is a superconductor?

Kelly:

You're right...superconductors conduct electricity with almost no resistance, viz. 10e-24 Ohms, which is minimal. Another important property that superconductors possess is a very strong magnetic field.

Superconductors are materials (and they can be metals, ceramics or compounds) that exhibit curious behavior at temperatures below their critical temperature.

Superconductivity was discovered in 1911 by a "Mad Scientist", whose name I cannot recall at this moment, and since then, a few hundred superconducting materials have been discovered.

When these materials are brought below their critical temperature (which varies between 4 degrees Kelvin and 77K) they lose almost all resistance which is unusual because materials usually have their resistance increase in proportion to their temperature. It's a physical property some materials possess, and that's it.

Superconductors also possess magnetic fields. When you bring a magnet close to a superconducting material, the magnet correspondingly induces an electric field in the superconducting material (eg. YBa2Cu3O7). The superconducting material also produces a magnetic field that is equally strong, and this field opposes the field of the magnet that you are bringing close to it, and completely cancels it out! As you successively bring your magnet closer to this superconducting material, the opposing magnetic field from the superconducting material become greater than the magnetic field of your magnet. That is when your magnet starts levitating above the superconducting material. All this time, you must remember, the superconducting material is kept at a temperature below it's critical temperature.

You've probably heard of MAGLEV trains, that have been built in Japan. These trains magnetically levitate above superconductive materials and they have reached speeds of above 400km/h!!! Yet, the tracks above these trains hover, atop an air cushion, are cooled to 77K, and so it isn't still really feasible to use MAGLEV trains.

Some of the difficulties faced in applying superconducting materials is the low critical temperature needed, the extreme difficulty faced in fabricating these materials, etc.

In the U.S., General Electric has used them in Magnetic Resonance Induction (MRI) Imaging, which is used in the medical industry to view the insides of bodies.

They've also used superconductive materials to generate power and they've achieved twice the efficiency, which is great.

If you wish to read further on the subject, a good text for a Freshperson in college is "Engineering Materials Science" by Milton Ohring. The professor who wrote this text was one of my teachers at Stevens Institute of Technology in Hoboken, New Jersey, and he can be reached in the Dept. of Materials Science and Engineering at (201) 216-5268.

I hope I was able to help you, Kelly.