5
$\begingroup$

I was having a conversation when the topic of sublimation came up. Prior to the discussion, I had always thought that sublimation was caused by a great pressure/temperature difference, but another person stated that whether or not an element sublimates depends on its composition.

Will any element sublimate under the right conditions? Or are there elements which will always pass through a liquid state?

$\endgroup$
3
$\begingroup$

To a first approximation, any pure substance can sublimate. However, complex substances may decompose or change their structure before any appropriate sublimation conditions are reached.

The only (and very remarkable) exception is helium (in fact, helium is so special that helium-3 and helium-4 have quite different phase diagrams even though they're isotopes!). Note that due to the presence of superfluid phases, there is no direct transition between the solid and gas phases in either isotope.

As an aside, there is nothing prohibiting a substance to exhibit a solid-gas transition curve crossing a region of mild temperature and pressure conditions. Though unusual, an interesting example is iodine heptafluoride. It has a very narrow liquid range at ambient pressures (meaning a small decrease in pressure is enough to go below the triple point pressure), and the liquid range happens to fall near very reasonable temperatures.

$\endgroup$
1
$\begingroup$

Depending on the field of study sublimation is either always possible, or dependent upon the substance.

In Organic chemistry, sublimation only occurs if the phase diagram (wikipedia, phase diagram) would allow it. If a phase change from solid towards gas is possible in the phase diagram, sublimation is possible when changing temperature and pressure in the right way. When no transition can be made between the two, sublimation is not possible. It all depends upon thermodynamics.

In the field of inorganic chemistry however, sublimation-like techniques are almost alway possible. If I'm not mistaken, with low pressure and high temperature, sputtering (wikipedia, sputtering) can be used to deposit single elements in a film.

I am an organic chemist myself, so the details of the sputtering I don't particularly know, sorry.

Hopefully this does answer your question.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.