Typically materials which are good conductor of electricity are also good conductor of heat, and vice versa. Are there notable exceptions?
$\begingroup$
$\endgroup$
1
-
$\begingroup$ the free electrons that can travel between atoms also serve to spread thermal energy. ... doitpoms.ac.uk/tlplib/thermal_electrical/images/… ........ tibtech.com/images/conductivite_materiaux.JPG ........... google.fr/…: $\endgroup$– bandybabboonCommented May 14, 2017 at 21:39
Add a comment
|
3 Answers
$\begingroup$
$\endgroup$
Beryllium oxide is a very good electrical insulator but at the same time the best non-metal (except diamond) thermal conductor.
So to summarize. In general, good thermal conductivity is correlated with good electrical conductivity, but it is not a strict relationship.
For example, there is the empirical Wiedemann-Franz law for metals which states that the ratio of thermal conductivity $k$ and electrical conductivity $\sigma$ is proportional to temperature $T$.
$$ \frac{k}{\sigma} =c_0T $$
The proportionality constant is $c_0$. But as the wiki article points out there are exceptions to this empirical relationship.
$\begingroup$
$\endgroup$
1
For metals, good electrical conductivity does indeed imply good thermal conductivity. This is known from the Wiedemann–Franz law, which gives the ratio between electronic contribution of thermal conductivity ($\lambda$) and electrical conductivity ($\sigma$) and is proportional to the temperature ($T$).
$$\frac{\lambda}{\sigma} = LT $$
This gives the empirical constant $L$ known as the Lorenz number.
$$ L = \frac{\lambda}{\sigma T} = \frac{\pi^2}{3}(\frac{\lambda_B}{e})^2 = 2.44 \times 10^{-8} W\Omega K^{-2} $$
As stated, this law applies to metals. Diamond, for example, is an excellent thermal conductor because of its structure, but at the same time it has a very high resistance to electrical current.
-
1$\begingroup$ And, naturally, it gets a little more interesting when playing with semimetals :-) . By which I just mean complicated. Electrons are pretty good at carrying energy. $\endgroup$ Commented May 14, 2017 at 11:29
$\begingroup$
$\endgroup$
As alluded to in the other answers, a most notable exception is diamond. Diamond is an excellent thermal conductor. The thermal conductivity of natural diamond is around 22 W/(cm·K), which makes diamond five times better than copper at conducting heat. At the same time, the electrical resistivity of most diamonds is on the order of 10E11 to 10E18 Ω·m.
