# Is there a metal for which its gas is necessarily a plasma?

Related to this question: Gaseous metals?

The top answer clarifies that even with metals, the gaseous state is distinct from a plasma.

However, my question is, is this actually true in all cases? Or is there an element and a pressure for which heating it to a gas will necessarily also be hot enough for it to immediately become a plasma? Or is there a situation in which heating can bring about the transition from solid or liquid straight to plasma while skipping gas?

• Well, usually plasma is considered different state of matter then gas, just a nitpick ;) That being said elements with high boiling points under high pressure could go directly from liquid to plasma, I think. There are also more "arcane" ways to make plasma, even very cold one. – Mithoron Nov 17 '18 at 1:51

In principle, all that is required is for a substance to evaporate from a liquid into a plasma directly is for its ionisation energy to be significantly smaller than the average kinetic energy of its particles at its "boiling point". Or in other words, as a very rough estimate this is true when $$\mathrm{k_BT_{boiling}≳EI}$$.
Going further down in the periodic table, elements tend to have higher boiling points and lower ionisation energies. After reaching the superheavy element region (Z>100) things get much more complicated due to strong relativistic effects, but the elements from Rf to Hs (Z=104 to 108) are expected to have the highest boiling points at ambient pressure of any known chemical substance, possibly well past $$\mathrm{6000\ K}$$. However, their calculated ionisation energies of $$\mathrm{6-8\ eV}$$ suggest they would only ionise considerably at temperatures 10 times higher still ($$\mathrm{1\ eV/k_B= 11605\ K}$$), meaning there is still a long way to go.
As others have mentioned, increasing the pressure is a reliable way to push boiling/sublimation points higher, up to where they can match and surpass the energy regime required for ionisation. However, this would require absurdly high pressures; for example, the boiling point of tungsten at $$\mathrm{1000\ bar}$$ is still a mere $$\mathrm{9000-10000\ K}$$ (ref). Thus, a very crude extrapolation would suggest the direct conversion of liquid (or more likely solid) tungsten to a plasma would happen around $$\mathrm{90000\ K}$$ under a pressure of $$\mathrm{20\ Mbar}$$ (20 million atmospheres!).