20 EXAMPLES OF CHEMICAL SUBLIMATION AND CHARACTERISTICS - CHEMISTRY - 2025

Some examples of chemical sublimation are the processes that water, carbon dioxide, iodine, arsenic, or sulfur undergo. In them the direct phase change from a solid to a gas is observed without the previous transition to the liquid phase.

The classic examples of sublimation are established by dry ice (bottom image), which consists of frozen carbon dioxide; and iodine, with its purple crystals. To know if a compound can sublimate or not, you have to go to its phase diagram as a function of pressure and temperature (PV).

A piece of dry ice reacts and neutralizes a sodium hydroxide solution colored by phenolphthalein. Source: Alessandro e Damiano

In these phase diagrams a point is observed where the three lines that separate the solid, liquid and gas phases join (and coexist at the same time): the triple point. Below this point there are two zones in equilibrium: one for the solid and one for the gas. Thus, by manipulating the pressure, the direct solid-gas transition is achieved.

That is why many other solid compounds are able to sublimate if heated by lowering pressure or applying vacuum.

Examples of sublimation

Dry ice

Dry ice or solid CO ₂ is the most representative example of a sublimation. It is called dry because it does not leave a trace of moisture, it is cold, and it gives off the white smoke that has been used so much in plays.

As soon as it is manufactured (at -78.5 ºC) it begins to sublimate at any temperature; just expose it to the sun for it to sublime immediately. It can be seen in the following image:

Iodine

Both dry ice and iodine are molecular solids. Iodine is made up of I ₂ molecules that are coupled to form purple crystals. Because their intermolecular forces are weak, a significant portion of these crystals sublimate rather than melt when heated. The above explains why purple vapors emanate from iodine.

Ice and snow

On the heights of snowy peaks, snow can sublimate due to the lower pressure experienced by its crystals. However, such sublimation is extremely slow compared to dry ice and iodine; the vapor pressure of ice and snow is much lower and therefore does not sublimate as quickly.

If the wind factor is added to this slow sublimation, which drags the molecules from the surface of ice and snow, eroding its surface, then the frozen masses end up being ablated; that is, they are reduced in size while spreading or spreading hills (moraines) of snow. The following image shows the sublimation of the ice:

Menthol

Although iodine has a certain characteristic odor, from menthol we can bring out a quality shared by all solids capable of sublimating under specific conditions of pressure or temperature: they are fragrant compounds.

The fact that a solid is odorous means that its vapor pressure is high enough so that we can perceive its molecules with our sense of smell. Thus, menthol crystals can sublimate if they are heated in a vacuum. If the vapors come into contact with a cold surface, they will settle into a collection of bright, purified crystals.

Therefore, sublimation is a technique that allows the purification of volatile solids; solid examples of which there are still examples to mention.

Zinc

Zinc has a considerably low boiling point (419.5ºC) compared to other metals. If it is also heated by applying vacuum, your crystals will end up sublimating.

Arsenic

The case of arsenic is more distinguished than that of zinc: it does not even need the pressure to decrease to sublimate at 615ºC; temperature at which excessively toxic arsenic vapors are formed. To melt or melt, it must be heated to high pressures.

Organometallic compounds

Although it cannot be generalized that all organometallic compounds can sublimate, a wide repertoire of them, made up of metallocenes, M (C ₅ H ₅) ₂, and metal carbonyls, with coordinated M-CO bonds, do sublimate because of their weak intermolecular interactions.

For example, metallocenes, including nickelocene (green) and vanadocene (purple), sublimate and then deposit their crystals in attractive and bright geometries. Less strikingly, the same is true for metallic carbonyls.

Fullerenes

Balloons C ₆₀ and C ₇₀ interact with each other by means of London dispersion forces, differing only by their molecular masses. The relative "weakness" of such interactions gives fullerenes a vapor pressure capable of equaling atmospheric pressure at 1796 ºC; and in the process, they sublimate their black crystals.

Caffeine

The caffeine extracted from tea or coffee beans can be purified if it is heated to 160 ºC, because instead of melting it sublimates at once. This method is used to purify caffeine samples, although some of its content is lost if the vapors escape.

Theobromine

Like caffeine, theobromine, but coming from chocolates or cocoa beans, is purified by sublimation at 290ºC once extracted. The process is facilitated by applying vacuum.

Saccharin

Saccharin crystals sublimate and are purified by vacuum action.

Morphine

The synthesized morphine to be used as an analgesic is purified, again, by sublimation at 110ºC and applying vacuum. Both morphine and caffeine consist of large molecules, but with relatively weak intermolecular forces relative to their masses.

Camphor

Like menthol, camphor is a fragrant solid, which sublimates white vapors if properly heated.

1,4-dichlorobenzene

1,4-Dichlorobenzene is a very fragrant solid, with an odor similar to naphthalene, which also melts at 53ºC. Because of this it is to be supposed, rightly, that it can sublimate; even to an appreciable degree without even warming up and for a month.

Benzoin

Like camphor, benzoin, with a camphor-like odor, is purified by sublimation.

Purina

Purine and other nitrogenous bases can sublimate at temperatures above 150ºC and applying vacuum from bacterial cells.

Arsenic

At the temperature of 615 ° C, arsenic sublimates. This represents a danger given the toxicity of the element.

Sulfur

This element sublimates between 25 and 50 ° C causing toxic and suffocating gases.

Aluminum

This metal is sublimated at temperatures above 1000 ° C for certain industrial processes.

Metallurgy

Certain alloys are purified by sublimation methods. In this way, the compounds that make up the alloy are separated, obtaining purified products.

Sublimation printing

Sublimation is also used to print images on polyester or polyethylene objects or surfaces. An image made with sublimable solid pigments is heated on the object to permanently imprint it on it. The applied heat also helps the pores of the material to open so that the colored gases pass through them.

Comet trails

Comet contrails are the result of sublimation of their content from ice and other frozen gases. As the pressure in the Cosmos is practically non-existent, when these rocks surround a star, their heat heats its surface and causes them to give off a halo of gaseous particles that reflect the light radiated on them.

Artistic sublimation

Although it leaves the chemical or physical realms, the word 'sublime' also applies to that which goes beyond the conventional; an inconceivable beauty, tenderness and depth. From the simple or plain (solid), an artistic work or any other element can rise (gas) to transform into something sublime.

Printing inks

Dry sublimation printers use the sublimation process to print photo quality images. The process begins when there are special films that contain solid pigments that, when heated, sublimate and are later recaptured.

Images can be printed on polyester sleeves, pots, or aluminum or chrome foil.

Flavorings

Solid air fresheners also sublimate. These compounds are generally esters, including those that hang in the toilet. This is the way chemicals get directly into the air and make the smell fresh.

Cadmium

Another element that sublimates at low pressure. This is especially problematic in situations where you are working in high vacuum.

Graphite

This material is sublimated by passing a high amperage electrical current in a high vacuum. This procedure is used in transmission electron microscopy to make the samples conductive and have higher resolution.

Gold

Gold sublimation is used to make inexpensive medals and "gold plated" jewelry. It is also used for the treatment of scanning electron microscopy samples.

Anthracene

It is a white solid that sublimates easily. This method is generally used for purification.

Salicylic acid

It is used as an ointment to relieve fever since it sublimates easily. This method is also used for its purification.

References

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