what materials combine high electrical conductivity with very low thermal conductivity?

Question

Need to start search on which materials (metallic alloys, but not necessarily restricted to metallic alloys) combine the property of good electrical but low thermal conductivity. For example, Stainless steel is better than Copper in this respect.

Fluids - liquids or gases - dont qualify because they can allow convection - heat is transferred efficiently even if standard conduction is impeded...

Answer 1

Because both electrical and heat conduction in metals is largely accomplished by free electrons, good electrical conductors are also good thermal conductors. To the extent that one can neglect thermal transport in metals by lattice vibrations (aka phonons), which is the dominant thermal transport mechanism in insulators, the ratio of the thermal conductivity to the electrical conductivity is a linear function of temperature, and the constant of proportionality is the same for all metals. This relationship is known as the Wiedemann-Franz Law:

K/s = L*T

where K is the thermal conductivity,
s is the electrical conductivity
T is the absolute temperature
L is a constant of proportionality known as the "Lorenz number" = 2.45*10^-8 W*ohm/K^2 (calculated assuming the electrons in the metal can be modeled as a free-electron gas).

Most metals, therefore, are going to have quite similar thermal/electrical conductivity ratios.

To get a material with a really high Lorenz number, you'll have to start looking at more exotic materials, such as composities, or even carbon nanotubes (which can have Lorenz numbers about 1000 times higher than those for typical metals.)

Answer 2

Not many. Usually better electrical conductors make better thermal conductors, and vice versa. For example, copper has both higher thermal conductivity and higher electrical conductivity than steel (stainless or otherwise). The only exception I can think of is superconductors -- exotic substances, usually compounds of rare-earth elements, that act as superconductors of electricity at low temperatures (usually hundreds of degrees below zero), but since they're compounds rather than pure metals, they don't conduct heat particularly well.
The other way around -- poor electrical conductivity and good thermal conductivity -- is easier. Diamond is one example. Alumina is another. These substances have strong crystalline structures. The electrons aren't free to move around, so they don't conduct electricity well, but the crystalline structure puts the atoms close together so that they conduct heat (atomic vibration) fairly well.

Answer 3

Uhhh...none.

The mechanism that transports electrical conductivity is also a great conductor of heat.

Try silicone or germanium. These are semi-conductors which may allow for limited electrical conductivity while still insulating.

Carbon might work also. Try lay-up material used for carbon composite fabrication.

What in the world are you trying to do, anyway? There's probably a better way to skin that cat...

Answer 4

Does Salt Water qualify?

Answer 5

h20