How: Thermally conductive yet electrically resistive.

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Alumina exhibits both thermal conductivity and electrical resistivity due to its crystalline structure. Thermal conduction occurs through the vibration of stiff bonds in the crystal lattice, making alumina a good thermal conductor. In contrast, electrical conduction relies on the presence of free electrons; alumina has tightly held electrons, which contributes to its electrical resistivity. This duality is common in materials, where strong bonds enhance thermal conduction while limiting electrical conductivity. Diamond serves as an example of a material with an optimal balance of high thermal conductivity and low electrical conductivity, illustrating this principle. Additionally, in metals, free valence electrons facilitate both thermal and electrical conduction, explaining why good electrical conductors often also exhibit good thermal properties.
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Today I had a materials lab where we looked through various properties of materials. One of the materials we had was alumina, and we had to describe how it was both thermally conductive and electrically resistive. I couldn't figure out the answer on my own. Could anyone describe the reasoning behind this?

Note: This isn't for homework or a class I'm just curious. Thanks!
 
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Thermal conduction is by bonds vibrating - so most crystals with stiff bonds are good conductors.
Electrical conduction is by free electrons, so good resistors are those with strongly held electrons - again crystals are good.

Diamond is the best ratio of thermal conduction to electrical resistance.
 
I don’t know if it’s still relevant, but some of the thermal conduction is also made by the free valence electrons in conducting metals, that’s why a good electrical conductor is in general also a good thermal conductor =)
 

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