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AFAIK Glass is insulator, it doesn't have free electron. It's said metal is a good conductor of heat because it has free electron, glass doesn't have free electron, why it is a good conductor of heat?

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Glass is about 100 times more thermally insulating than metal, so this question really hinges purely on what you define as a "good" conductor of heat. –  Colin K Apr 18 '12 at 3:21
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up vote 4 down vote accepted

There are at least two mechanism of thermal conductivity - free electrons and thermal phonons. The first mechanism can be prevalent in metals, the second one is important in dielectrics. I did not look up thermal conductivity of glass, but such excellent dielectric as diamond has higher thermal conductivity than any metal, as far as I know.

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IIRC it has to do with the lattice structure. A Strong frame can be easily vibrated. Glass and diamond are both tetrahedral networks(?), so their mechanism would be the same. I guess. –  Manishearth Apr 18 '12 at 3:55
glass by definition does not have a lattice structure Manis –  BebopButUnsteady Apr 18 '12 at 4:16
@Manishearth: phonons are typically just lattice excitations, so we don't contradict each other. However, unlike diamond, glass typically does not have a regular lattice, so it is difficult to compare glass and diamond. –  akhmeteli Apr 18 '12 at 4:19
@akh Oh, whoops. I read "photons". –  Manishearth Apr 18 '12 at 4:22
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