Question

In a vacuum, will a heated solid sublime?

Answer 1

Not necessarily; it depends on the solid. In the case of `CO_2`, that is true; specifically, if you were at, say, `103 K` at `0.001 atm` of pressure, and you raised the temperature to `173 K` (`-100^oC`) without changing the temperature, then yeah, `CO_2` would act sorta like dry ice and sublime.

In a phase diagram like this, if you start at `103 K` (`-170^oC`) and `0.001 atm` and you move right towards `-100^oC`, 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.

Answer 2

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.