Superconductors

[templar165]

What is the material that has been used attain superconductivity at a temperature closest to 273K(from below)?

 

[Agashka]

isn't it liquid nitrogen?

 

[bobsmith1492]

Originally posted by: Agashka
isn't it liquid nitrogen?

OP - do you mean the coolant material or the material in the superconductor?

Most superconductors are forms of ceramic. Wikipedia says the highest temperature at which superconductivity has been attained is 138K, or possibly up to 164K under pressure; that material is:

mercury thallium barium calcium copper oxide (Hg12Tl3Ba30Ca30Cu45O125)

Liquid nitrogen coolant boils at 77K. Before finding "high-temp" superconductors, liquid helium was required which boils at 4.22K.

 

[templar165]

I meant the material in the superconductor.

Yes, even I've heard that ceramic were the most prominently used materials for this purpose, but wasn't able find the one at highest temperature.

 

[Mark R]

Originally posted by: bobsmith1492
Most high temperature superconductors are forms of ceramic. Wikipedia says the highest temperature at which superconductivity has been attained is 138K, or possibly up to 164K under pressure; that material is:

fixed.

The HTS materials tend to be ceramics. Because of this, they have few practical uses - wires are very easy to work with, and most electrical design is based on wires, not cast ceramics. There are a few HTS ribbons commercially available, which consist of a metal foil to which a ceramic coating is applied - but they are fiendishly expensive, and absurdly fragile - to the extent that they can't really be handled like wires.

In terms of practical superconductors, virtually all are metals (usually a niobium-titanium alloy), but the problem with these low temp superconductors is that they need liquid helium temperatures.

The other catch is the presence of magnetic fields (e.g. due to large electrical currents). HTS materials have hopeless magnetic properties, and their superconductivity collapses in the presence of even moderate fields. If you want to make something which uses magnetic fields - e.g. motor/transformer/generator/magnet, then it's LTS or nothing.

 

[f95toli]

Originally posted by: Mark R


The HTS materials tend to be ceramics. Because of this, they have few practical uses - wires are very easy to work with, and most electrical design is based on wires, not cast ceramics. There are a few HTS ribbons commercially available, which consist of a metal foil to which a ceramic coating is applied - but they are fiendishly expensive, and absurdly fragile - to the extent that they can't really be handled like wires.

There are plenty of HTS cables around, and they are not really more fragile than ordinary power cables. The main problem tends to be with the cooling system (the tube where the nitrogen flows etc) which can break if you bend the cable too much. But that is a problem with the cable, it has nothing to do with the superconductor as such. The ribbons themselves are really flexible since the superconductor is multi-granular and very thin (and the ribbon itself is made from metal); the word "ceramic" might give people the wrong idea here.

The other catch is the presence of magnetic fields (e.g. due to large electrical currents). HTS materials have hopeless magnetic properties, and their superconductivity collapses in the presence of even moderate fields. If you want to make something which uses magnetic fields - e.g. motor/transformer/generator/magnet, then it's LTS or nothing.

HTS superconductors have MUCH higher critical fields (AND much higher critical currents) than conventional superconductors, to the point where we don't even know how to measure Bc because we can't generate fields that strong (many tens of tesla). It is true that Nb or NBTi is usually still a better choice for magnets but HTS magnets are being used and are acutually being considered for some of the magnets for ITER (and DEMO).
HTS Transformers and generators have been around for quite a while, and while they are still a bit too expensive (and possibly unreliable) to be used in commerciall installations, they DO definitly work.
See e.g the website of American Superconductor.
http://www.amsc.com/

Note that I am not saying that HTS materials are perfect, but they are not quite as useless as many people think.

 

[templar165]

That's pretty interesting indeed!

What other practical uses can be expected out of a superconductor (LTS/HTS) ?

 

[Comdrpopnfresh]

Originally posted by: templar165
That's pretty interesting indeed!

What other practical uses can be expected out of a superconductor (LTS/HTS) ?

~100% efficient storage and transmission of electricity, anything you can think of dealing with levitation, very exact manipulation of magnetic fields (for use with fusion, plasmas), emps, faster computers, smaller motors, medical imaging

 

[Carlis]

There are in fact some exotic substances that are superconducting at very high temperatures. The pressure in neutron stars make protons (there are some protons there as well) form cooper pairs and super-conduct.

How would you use a super conductor to store energy?

 

[Comdrpopnfresh]

Originally posted by: Carlis

How would you use a super conductor to store energy?

Because superconductors have ~0 resistance, if you apply a current to a circuit of superconductor, and then tie it off into a loop, you can come back when you please, and the same electrical flow will still be going around and around. So, say utilities generate too much electricity; rather than pumping water up towers or hills, the additional electricity can enter one of these loops, and be released at will- especially because superconducting circuits are super responsive to load characteristics, such as with fault limiters. For SC materials able to withstand magnetic fields, 1000s of watts can be stored in magnetic energy storage units.

 

[bobsmith1492]

Originally posted by: Comdrpopnfresh

Originally posted by: Carlis

How would you use a super conductor to store energy?

Because superconductors have ~0 resistance, if you apply a current to a circuit of superconductor, and then tie it off into a loop, you can come back when you please, and the same electrical flow will still be going around and around. So, say utilities generate too much electricity; rather than pumping water up towers or hills, the additional electricity can enter one of these loops, and be released at will- especially because superconducting circuits are super responsive to load characteristics, such as with fault limiters. For SC materials able to withstand magnetic fields, 1000s of watts can be stored in magnetic energy storage units.

Watts aren't a unit of energy... [/nitpick]

 

[Comdrpopnfresh]

Correction: potential work