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During a phase change we can go from solid to gas via the process of sublimation. The diagram given below indicates that there is no analogous process for the transition from solid (or liquid) to plasma. Is this correct and if so what is the physical reason for this (and if not why not)?

Diagram of phase transitions

(source wikipedia, PD)

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    $\begingroup$ You can go form a solid to a plasma in one step, if you like, it's just a matter of rapid heating and there is no stable phase boundary between the two. In some ways metals are similar to a plasma, already, because they have electrons that are freely moving around. We even talk about plasma frequency and plasmons in metals. $\endgroup$ – CuriousOne Jan 5 '16 at 19:05
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As a sort of counter example, the curiosity rover on Mars uses a laser to ionise rocks to study their composition. From a practical standpoint, this looks very much like going directly from solid to plasma.

On the other hand, if you looked very closely, you'd see that the energy from the laser goes both into breaking the intermolecular and molecular bonds in the rock as well as ionising the atoms. This is in a way a necessity for generating the state generally understood by "plasma" since that implies free ions, so atoms must be both taken away from their molecules and ionised, and taking them out of molecules creates a gas, so at a low enough heating rate you go through the typical phase transitions.

CuriousOne points out, however, that the basic characteristic of a plasma - a sea of free electrons containing positive ions - is also well approximated by metals, as the valence electrons in metal crystals are not bound to individual nuclei, and some of the phenomena studied in plasmas appear in metals as well.

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