Good conductor of electricty => Good conductor of heat?

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Discussion Overview

The discussion explores the relationship between electrical conductivity and thermal conductivity in materials, particularly focusing on metals and exceptions like graphite and diamond. Participants examine theories and laws that may explain these phenomena, as well as specific examples of materials that do not conform to expected behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants note that most good electrical conductors are also good thermal conductors, with exceptions like graphite.
  • One participant references the Wiedemann-Franz law, which suggests a constant ratio of thermal to electrical conductivity in metals.
  • Another participant expresses confusion about how electrical conduction relates to thermal conduction, proposing that the presence of free electrons in good conductors may lead to higher thermal energy and thus better heat conduction.
  • A participant explains that in metals, the overlapping of the valence band and conductance band allows electrons to transport internal energy, contributing to heat conduction.
  • It is mentioned that while metals typically show a correlation between electrical and thermal conductivity, materials like diamond and sapphire can be excellent thermal conductors while being electrical insulators.
  • Another participant points out that graphite can conduct both electricity and heat, challenging the initial assumption about its conductivity.

Areas of Agreement / Disagreement

Participants express a mix of agreement and disagreement regarding the relationship between electrical and thermal conductivity, with some supporting the correlation while others highlight exceptions and nuances in specific materials.

Contextual Notes

Participants discuss the role of free electrons and energy bands in conductivity without resolving the complexities of these interactions or the implications of the Wiedemann-Franz law in all materials.

Who May Find This Useful

This discussion may be of interest to those studying materials science, physics, or engineering, particularly in the context of conductivity and thermal properties of materials.

jobsism
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I've noticed that almost every good conductor of electricity, is also a good conductor of heat, except for certain exceptions like Graphite. Why is this so? I can't seem to associate electron flow with heat conduction.
 
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Check the Wiedemann-Franz law that explains how the ratio of thermal to electrical conductivity in metals is almost a constant
 


Gordianus said:
Check the Wiedemann-Franz law that explains how the ratio of thermal to electrical conductivity in metals is almost a constant

Ah, thank you for your reply! I understand the law, but I'm still confused on how electrical conduction contributes to thermal conduction. I'm thinking, that in good electricity conductors, there are more number of free electrons, the motion of which causes them to acquire higher thermal energy. But is this what allows higher heat conduction?
 


jobsism said:
Ah, thank you for your reply! I understand the law, but I'm still confused on how electrical conduction contributes to thermal conduction. I'm thinking, that in good electricity conductors, there are more number of free electrons, the motion of which causes them to acquire higher thermal energy. But is this what allows higher heat conduction?

I confirm it's about the electrons.
In metals the valence band and the conductance band are overlapping.

In any material the internal energy (the heat) redistributes over the available degrees of freedom. In a metal heat redistributes to the electron population too. The nature of a metal is that the electrons can have any energy within a certain extended band. In an insulator only a big jump in energy will free an electron to move away from its current atom. At normal temperatures the available energy is not enough for that jump, so there is high electric resistance.

Coming back to metals: part of the total internal energy is in the electron population, and the electrons can move freely through the metal, transporting the internal energy to other parts.


For more information look up things like 'valence band' and 'conductance band'.
 
Thank you, Cleonis! I think I understand now.
 
Not always one-to-one the other way though. The best thermal conductor is diamond and it's a great insulator. Sapphire is similar.

Actually graphite is an ok conductor of both current and heat.
 

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