Sublimation has come to have three distinct general meanings.
- In Chemistry: The transformation of a substance from a solid state to a gaseous state foregoing the liquid state, and vice versa.
- In Psychology: The transformation of a negative impulses into positive outcomes.
- In Printing: The transformation of an image from one surface onto another.
Clearly, the linking theme is transformation. The first definition is the most common use of this word, but how did it come to be known as Sublimation? The word stems from "Sublime" meaning; majestic, inspiring awe, impressive, lofty, supreme, excelled, of great intellectual worth and of divine order ~ and herein lies the clue.
Imagine watching, under the skillful direction of a wise old mage or alchemist, a solid substance subliming1; it would give the illusion of vanishing ~ and again observing a jar of nothing (which is actually the gaseous form of the sublime substance) and watching crystals form apparently out of thin air... would that process of transformation not fit the meaning of sublime?
The psychological and printing definitions of the word are derived from this chemical context of transformation. This entry deals with the original meaning of sublimation found in chemistry.
Change of State
Matter exists in the familiar states of a solid, liquid or gas. With a change in temperature and pressure on a substance, it can transform from one state to another, as in the following example of water.
When heated, Ice (solid) melts into water (liquid) which evaporates into vapour (gas). When cooled, vapour condenses into water which freezes into ice.
However under special circumstances of temperature and pressure vapour can turn directly into ice and ice directly into vapour, foregoing the liquid stage. This is Sublimation.
This definitin of the process worked fine until things started getting a little more complicated, and people needed to distinguish between the directions of change in sublimation. Commonly "condensation" is also used to mean the process of a gas transforming directly into a solid (as it simply gets denser2) as well as the process of a gas transforming into a liquid. To be precise you could use "sublime condensation" or "sublime evaporation", but it's in Physics that the distinction is most clearly made.
Phase Transformation and Deposition
Physicists don't talk about 'state', they talk about 'phase'. Carbon exists as a solid in the form of a black substance called graphite found in pencils, and a glittering crystal called diamond found in engagement rings. They are both examples of solid 'state', but are examples of different 'phase'. This applies to solids, liquids and gases alike, plus the mysterious phase of Plasma!
This all starts getting very complicated with many combinations of phase possible, and fortunately drifts beyond the scope of this entry. What is relevant, though, is that these clever people needed distinctions. So they took the ambiguous transformation of phase from gas to solid and called it "Deposition".
Therefore the six distinct changes of State can clearly and distinctly be defined under Phase Transformation as follows; (with alternative nomenclature in braces)
- Solid to Liquid = Melting (Liquefying)
- Liquid to Gas = Evaporation
- Solid to Gas = Sublimation (Sublime Evaporation)
- Gas to Liquid = Condensation
- Liquid to Solid = Freezing (Setting)
- Gas to Solid = Deposition (Condensation / Sublime Condensation)
Thus Sublimation definitely refers to the process of a solid transforming into a gas, is sometimes the reverse process which can also be called condensation, sublime condensation or deposition.
Deposition and the clarity of Physicists
On last thing ~ in making the elusive Gas to Solid transformation unambiguous, whoever coined the term "Deposition" may have rather compounded confusion as deposition also means:~
- In law, the taking of testimony outside of court.
- In chemistry, molecules settling out of a solution.
- In geology, material (like sediment) being added to a landform.
- In meteorology, when water vapour (specifically) changes directly to ice without becoming a liquid first.
- In politics, the removal a person of authority from power.
- In Christianity, the removal of Christ from the cross after the Crucifixion.
- In Archaeology, the laying down of a horizon containing archaeological information such as that provided by an artefact.
- In Aerosol physics, a process where aerosol particles set down onto surfaces.
- In rapid prototyping, fused deposition modelling is a process by which a part is constructed by depositing material layer by layer.
- In the history of European universities, was an initiation ritual for new students practiced from the Middle Ages to the 18th century.
- And finally, in biology, passing a No2.
Quite the other end of the scale to it's original designation.