Room Temperature Superconductivity

[Larry717]

Some progress has been made in increasing the temperature at which superconductivity occurs. One material called Magnesium Boride has shown good results.

But, actually, wouldn't room temperature superconductivity violate certain physical laws, i.e., the laws of thermodynamics?

Larry

 

[physicsuser]

wouldn't any temperature in a room be room temperature

 

[Chronos]

I am not aware of any thermodynamic or other laws that specifically limit superconductivity. Room temperature is probably beyond reach, however, certain rare Earth oxides are superconductive at temperatures up to 123K. This is pretty toasty compared to the ~20K ceiling back in the old days. A popular, and simple to make metallic oxide of yttrium, barium, and copper is superconducting at about 92 K. This is a practical working temperature because you can use liquid nitrogen, which is cheap and easy to handle, as the refrigerant [BP~77K].

 

[Ivan Seeking]

One of my old professors was doing work with HTSCs [ceramics]. By chance I just saw her recently and asked about her work. She said that intrinsic current limiting issues with these superconductors has seriously thrwarted progress - her funding dried up.

 

[Larry717]

Defining Room Temperature

wouldn't any temperature in a room be room temperature

Isn't room temperature defined to be something like 21-23 deg. C?
I don't know what the actual temperature is (or the range of temperatures).

Can someone help out here?

Larry

 

[Larry717]

Critical Current / Critical Field

One of my old professors was doing work with HTSCs [ceramics]. By chance I just saw her recently and asked about her work. She said that intrinsic current limiting issues with these superconductors has seriously thrwarted progress - her funding dried up.

Can ceramics end up with such a large current that the magnetic field is quenched? Is that the correct terminology: critical current leads to a field value above which the superconductivity is destroyed?

Larry

 

[Larry717]

Superconductivity is Counter Intuitive

ZapperZ, in the classical physics forum, thread suprising physics, 9/3/04, provided an interesting account of how a balloon will respond inside a moving train. His point was that physics can be counter intuitive. When we look at Special Relativity and Quantum Mechanics this is certainly true!

In superconductivity, if you use Ohm's law, you'd expect an infinite current. But we know that this is not so. Whether in classical physics or in nonclassical physics, our intuition is not necessarily our best guide.

Larry

 

[Larry717]

Latest on High Temp Superconductors

The superconducting cuprates (copper-oxides) have achieved astonishingly high Tc's when you consider that by 1985 known Tc's had only reached 23 K. To date, the highest Tc attained at ambient pressure has been 138 K. One theory predicts an upper limit of about 200 K for the layered cuprates (Vladimir Kresin, Phys. Reports 288, 347 - 1997). Others assert there is no limit. Either way, it is almost certain that other, more-synergistic compounds still await discovery among the high-temperature superconductors.

http://superconductors.org/type2.htm

Sounds like the future is promising for room temperature superconductivity. But it won't happen right away. Achieving 200K would be a real breakthrough!

Larry

 

[Ivan Seeking]

Can ceramics end up with such a large current that the magnetic field is quenched? Is that the correct terminology: critical current leads to a field value above which the superconductivity is destroyed?

Larry

IIRC, the problem was [in some cases at least] that magnetic dipoles would arrange themselves on the material such that the maxumum current was limited. I remember a tape that actually showed the dipoles forming and arranging themselves [at a microscopic level]. They looked like little whirlpools running around the material's surface. These would resist the flow of charge. I don't know how the tape was made.

 

[Larry717]

Maybe??

Electronics / October 9, 1980 p41

(my highly condensed version)

Fred Vahldiek, a materials research engineer at Wright-Patterson
Air Force Base, was working with borides of Titanium. Boron is an
insulator. But, "how do you explain a conductivity five, six, seven
times better than the host metal's," he asked.

Vahldiek explained that he was looking for ductility in TiB2
crystals. A compostion change was found by accident through
deformation at room temperature under hydrostatic conditions.

He decided to measure the resistance. Of the three directions he
measured, the third, to his surprise, had no resistance. Vahldiek
patented his methods.

A scientist with IBM's Thomas Watson Research Center said
that if conduction is carried out through exciton or electron-hole
pairs, superconductivity could occur even above room
temperature.
--------------------------------------------------------------------------
Vahldiek's home phone number was in the Dayton, Ohio directory. I
contacted him. He said that the writer of the article sometimes wrote
Titanium Bromide when Titanium Boride was meant.

Larry

 

[Larry717]

More about Vahldiek

Some may wonder how the room temperature superconductor could be an "accident" and yet Vahldiek patented his process. Apparently, he knew what the initial and final conditions were.

The writer of the article asked, "A fluke that never could be repeated?" To which Vahldiek replied, "No, I've got 15 or 16 crystals by now." Each time, Vahldiek's instruments showed a complete lack of resistance.

It is important to note that Google lists only one entry for Vahldiek. That is my previous post. This means that at least as far as Google is concerned, there has been no update since 1980. Perhaps, in other databases, such as Inspec or IEEE there may be more information. But without further confirmation, Vahldiek's "discovery" is doubtful.

Larry

 

[Brane Dead]

There is a probable upper limit in temperature to the usefullness of a superconductor.
All the known high Tc's are type II, that is in the presence of a magnetic field, external or produced by the passage of a current, the field is quantized into vortex lines. These lines feel the Lorentz force of a current and move, crossing the current and creating a voltage, hence dissipation. All known applications of superconductivity need zero electrical resisitance, which requires these vortices to remain stationary. At room temperature there is a good chance in a superconductor the vortices will be liquid and hence no zero resistance.

 

[Larry717]

I Guess We'll Never Know

There is a probable upper limit in temperature to the usefullness of a superconductor.
All the known high Tc's are type II, that is in the presence of a magnetic field, external or produced by the passage of a current, the field is quantized into vortex lines. These lines feel the Lorentz force of a current and move, crossing the current and creating a voltage, hence dissipation. All known applications of superconductivity need zero electrical resisitance, which requires these vortices to remain stationary. At room temperature there is a good chance in a superconductor the vortices will be liquid and hence no zero resistance.

Since Vahldiek works for the Air Force, and his work is not public, I guess we'll
never know.

Larry