# In a vacuum, will a heated solid sublime?

May 9, 2015

Not necessarily; it depends on the solid. In the case of $C {O}_{2}$, that is true; specifically, if you were at, say, $103 K$ at $0.001 a t m$ of pressure, and you raised the temperature to $173 K$ ($- {100}^{o} C$) without changing the temperature, then yeah, $C {O}_{2}$ would act sorta like dry ice and sublime.

In a phase diagram like this, if you start at $103 K$ ($- {170}^{o} C$) and $0.001 a t m$ and you move right towards $- {100}^{o} C$, you would be doing what I described above.

If the liquid-solid coexistence curve starts at a triple point that exists at really low pressures (a vacuum), and if the solid-gas-liquid-gas coexistence curve is really flat, then even in a vacuum, at a high enough temperature, maybe a solid can still exist as a solid and then heat up until it becomes a liquid rather than a gas.

But you have to look at the phase diagram before assuming that a solid turns into a gas upon heating if in a vacuum.

Aug 11, 2018

If you are very lucky...

#### Explanation:

Given a tube furnace, and a turbomolecular pump, MANY inorganic compounds will sublime. And sometimes this includes simple halide salts...that you would normally not think are volatile. The sublimate is usually very pure; however, you must have special apparatus to store the sublimed (or twice-sublimed salt, I kid you not!) salt, and typically this is an inert atmosphere dry box.