What Causes Metals to Conduct Heat?

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Discussion Overview

The discussion revolves around the mechanisms that enable metals and materials like diamond to conduct heat effectively. Participants explore the roles of free electrons, lattice vibrations, and phonon propagation in thermal conductivity, as well as the differences between metals and insulators.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that metals conduct heat due to liberated electrons, while others clarify that metals do absorb heat and that the conduction mechanism involves both lattice vibrations and free electrons.
  • One participant notes that the majority of heat absorption in metals occurs through lattice vibrations, with free electrons facilitating efficient heat transfer.
  • Questions are raised about diamond's high thermal conductivity, with some attributing it to its strong covalent bonds and unique crystal structure, while others challenge the sufficiency of this explanation by comparing it to corundum's lower conductivity despite having strong bonds.
  • There is a distinction made between photons and heat, with participants discussing the relationship between phonons and heat transfer, as well as clarifying the difference between heat and temperature.

Areas of Agreement / Disagreement

Participants express differing views on the mechanisms of heat conduction in metals and diamond, with no consensus reached on the sufficiency of explanations provided for diamond's thermal conductivity compared to other materials.

Contextual Notes

Some discussions involve assumptions about the definitions of heat and temperature, as well as the specific mechanisms of heat transfer in different materials, which remain unresolved.

at2341
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Hi,

I understand what make metal a conductor of electricity, but what allows it to conduct heat? Is it that it does not absorb heat because it's electrons are easily liberated?
 
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What do you mean by " it does not absorb heat"? Metals do absorb heat and even faster than those can not conduct heat well. The reason that metals conduct heat well is the liberated electrons.
 
at2341 said:
Hi,

I understand what make metal a conductor of electricity, but what allows it to conduct heat? Is it that it does not absorb heat because it's electrons are easily liberated?

Remember what "heat" is in thermodynamics. It is nothing more than "energy of vibration".

In metals, there are 2 different ways for them to absorb heat: via lattice vibration, and via the free electron gas. Most of the heat is absorbed by the lattice vibration because the free electron gas has a very low specific heat. However, the ability of metal to conduct heat very well and transfer it very efficiently throughout its volume better than an insulator is due to these very mobile conduction electrons. So these electrons can carry the heat energy faster throughout the metal.

So how come an insulator doesn't? Other than the lack of these free conduction electrons, insulator also tends to have an amorphous crystal structure (unlike metals that tend to be crystalline), or highly polycrystalline (not large single-crystals like metals). When you have something amorphous or polycrystalline, the vibrations in one part of the material do not transfer well to other parts. So the heat transfer is very slow in such material.

Zz.
 
About that, why diamond has a very high heat conduction coefficient? I assume it has a very "efficient" way of propagating phonons, and if this is true, why?
 
...why diamond has a very high heat conduction coefficient? I assume it has a very "efficient" way of propagating phonons, and if this is true, why?

The covalent bonds in diamond are strong. The crystal structure consists of two interpenetrating face-centered-cubic lattices (this is called a diamond cubic structure), which means that each carbon atom has tetragonal coordination. The result is a 3-D arrangement of bonds that is strong in all directions (in contrast to graphite, which is characterized by a 2-D molecular arrangement).

Diamond can be thought of as a single giant molecule that is held together tightly. Its strong bonds and particular crystal structure lead to high stiffness, low thermal expansion, high sublimation point, brittle fracture, and finally, high thermal conductivity.
 
Mapes said:
...why diamond has a very high heat conduction coefficient? I assume it has a very "efficient" way of propagating phonons, and if this is true, why?

The covalent bonds in diamond are strong. The crystal structure consists of two interpenetrating face-centered-cubic lattices (this is called a diamond cubic structure), which means that each carbon atom has tetragonal coordination. The result is a 3-D arrangement of bonds that is strong in all directions (in contrast to graphite, which is characterized by a 2-D molecular arrangement).

Diamond can be thought of as a single giant molecule that is held together tightly. Its strong bonds and particular crystal structure lead to high stiffness, low thermal expansion, high sublimation point, brittle fracture, and finally, high thermal conductivity.

Corundum (aluminum oxide), e.g., has very strong bonds too (yes, not so strong, but however very strong) but it's 30 times less conductive than diamond and at least 6 times less conductive than aluminum. Why? Your explanation doesn't seem so good.
 
Last edited:
OK, let's hear your explanation. :smile: To be fair, it should explain diamond's high thermal conductivity, plus an experimental fact of my choosing, to be disclosed after you reply.
 
lightarrow said:
About that, why diamond has a very high heat conduction coefficient? I assume it has a very "efficient" way of propagating phonons, and if this is true, why?

Photons and heat are different concepts.
 
clouded.perception said:
Photons and heat are different concepts.

Phonons and heat are very closely linked.
 
  • #10
clouded.perception said:
Photons and heat are different concepts.

As are heat and temperature. It's a bit inaccurate to say an object possesses "heat," because heat is one way of transferring energy (the other being work). If a metal is "hot," it just has a high average molecular kinetic energy which translates into a high temperature in human tactile terms.
 
  • #11
Mapes said:
OK, let's hear your explanation. :smile: To be fair, it should explain diamond's high thermal conductivity, plus an experimental fact of my choosing, to be disclosed after you reply.
That's perfect!
One little note, anyway: if I had that answer, I wouldn't have asked the question in my post N. 4. :smile:
 

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