[iScience]

this is more of a conceptual question:

suppose i have a metal rod. I heat up one end. I'm told that the free electrons (C-band electrons) density in this region will be lower than in regions of lower temperature. So then, if i heat up one end of the metal rod until it is say.. red hot, and then i cut off this portion of the rod, does this mean that i will end up with a net positive charge on this portion that was cut off? since, a fraction of the electrons "diffused" away from this region towards the other end?

[billnotgatez]

When I first saw this I thought you would be discussing Thermocouple

http://en.wikipedia.org/wiki/Thermocouple

[Enthalpy]

Yes, you would obtain a net charge. Not very efficient, though.

For charges q, the equivalent potential is around 26meV for 300K, so if one end is 600K hotter, you get 52mV difference.

Imagine that the hot end is about (20mm)³: its capacity to infinite distance is roughly 8.85pF*10mm*4pi or 1.1pF, so the charge there is 58fC or 36,000 electrons removed, all from the surface. Compare with 7*10²³ atoms in the cut end.

That's not the whole picture. As both parts are near, the capacitance is bigger, so you get more charges. These stay in the separated parts, you bring work by pulling them apart, and the voltage and electric energy increases. You can start this with different materials instead of different temperatures, and it works better. Old standard method to produce static electricity.

C-band: conduction band? They all overlap in metals, so telling a difference between a valence and a conduction band would be hard.