Editing Sublimation (phase transition) (section)

==Purification by sublimation==
[[File:Ferrocen.jpg|thumb|right|Crystals of [[ferrocene]] after purification by vacuum sublimation]]

Sublimation is a technique used by [[chemist]]s to purify [[chemical compound|compounds]]. A solid is typically placed in a [[sublimation apparatus]] and heated under [[vacuum]]. Under this reduced [[pressure]], the solid [[volatility (chemistry)|volatilizes]] and condenses as a purified compound on a cooled surface ([[cold finger]]), leaving a non-volatile residue of [[impurities]] behind. Once heating ceases and the vacuum is removed, the purified compound may be collected from the cooling surface.<ref>R. B. King ''Organometallic Syntheses''. Volume 1 Transition-Metal Compounds; Academic Press: New York, 1965. {{ISBN|0-444-42607-8}}.</ref><ref name=HarwoodMoodyEOCPAP>{{cite book
|last1= Harwood
|first1= Laurence M.
|last2= Moody
|first2= Christopher J.
|year= 1989
|title= Experimental organic chemistry: Principles and Practice
|edition= Illustrated
|publisher= WileyBlackwell
|isbn= 978-0-632-02017-1
|pages= [https://archive.org/details/experimentalorga00harw/page/154 154–155]
|url= https://archive.org/details/experimentalorga00harw/page/154
}}</ref>
For even higher purification efficiencies, a [[temperature gradient]] is applied, which also allows for the separation of different fractions. Typical setups use an evacuated glass tube that is heated gradually in a controlled manner. The material flow is from the hot end, where the initial material is placed, to the cold end that is connected to a pump stand. By controlling temperatures along the length of the tube, the operator can control the zones of re-condensation, with very volatile compounds being pumped out of the system completely (or caught by a separate [[cold trap]]), moderately volatile compounds re-condensing along the tube according to their different volatilities, and non-volatile compounds remaining in the hot end.
Vacuum sublimation of this type is also the method of choice for purification of organic compounds for use in the [[organic electronics|organic electronics industry]], where very high purities (often > 99.99%) are needed to satisfy the standards for consumer electronics and other applications.{{citation needed|date=October 2021}}