Nick Maclaren wrote:

In article ,
Rusty Hinge 2 wrote:

For an even stronger effect, take several miles of niobium wire and wind
on a hollow core so as to produce an axial field.

Seal windings in a case, and introduce liquid nitrogen.

When the temperature of the windings has equalised with the liquid
nitrogen, their electrical resistance disappears, and a current can be
maintained by only overcoming the back-e.m.f. of the system.

Oh, really? I think that you have the wrong gas :-)

Niobium tends to be immersed in liquid helium to be superconducting,
perhaps surrounded by a radiation sheild and a jacket of LN2.

High-temperature superconductivity hasn't yet reached the liquid
nitrogen stage - it will make a BIG difference if and when it does,
as the cost differential between liquid helium and liquid nitrogen
is large. Liquid hydrogen is intermediate, but a slight fire and
explosion risk ....

Most of the high Tc cermic superconductors are superconducting in LN2
but the problem is they are brittle ceramics and hard to make into
coils, and even worse when you try to make them carry large currents the
resulting magnetic fields take it out of the superconducting state.

http://www.answers.com/topic/high-te...uperconductors

It is feasible for a school chemistry lab with a pottery kiln in the art
department to make their own high Tc superconductor. You can then see it
float over a strong magnet by cooling it with LN2.

http://www.futurescience.com/scpart1.html

Toxicity of barium dust is the main worry in the preparation.
US schools info includes "do not eat" warnings.

Regards,
Martin Brown