What is Sublimation (chemistry)?

Separation processes
Processes
Acid-base extraction • Chromatography • Crystallization • Dissolved air flotation • Distillation • Drying • Electrochromatography • Filtration • Flocculation • Froth flotation • Liquid-liquid extraction • Recrystallization • Sedimentation • Sublimation
Devices
API oil-water separator • Centrifuge • Mixer-settler • Protein skimmer • Sublimation apparatus • Still
Multiphase systems
Aqueous two phase system • Azeotrope • Eutectic
Scientists
	others
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Sublimation of an element or compound is a transition from the solid to gas phase with no intermediate liquid stage. Sublimation is a phase transition that occurs at temperatures and pressures below the triple point (see phase diagram).

At normal pressures, most chemical compounds and elements possess three different states at different temperatures. In these cases the transition from the solid to the gaseous state requires an intermediate liquid state. However, for some elements or substances at some pressures the material may transition directly from solid to the gaseous state. Note that the pressure referred to here is the vapor pressure of the substance, not the total pressure of the entire system.

The opposite of sublimation is deposition. The formation of frost is an example of meteorological deposition.

Examples

Some materials (such as zinc and cadmium) will sublimate at low pressures and thus may be a problem encountered in high-vacuum applications.

Carbon dioxide is a common example of a chemical compound that sublimates at atmospheric pressure—a block of solid CO₂ (dry ice) at room temperature and at one atmosphere of pressure will turn into gas without first becoming a liquid. Iodine is another example of a substance that visibly sublimates at room temperature. In contrast to CO₂, though, it is possible to obtain liquid iodine at atmospheric pressure by heating it. Snow and other water ices also sublimate, although more slowly, at below-freezing temperatures. This phenomenon, used in freeze drying, allows wet cloth to be hung outdoors in freezing weather and retrieved later in a dry state. Naphthalene, a common ingredient in mothballs, also sublimes easily. Arsenic can also sublimate at high temperatures. Sublimation requires additional energy and is an endothermic change. The enthalpy of sublimation can be calculated as the enthalpy of fusion plus the enthalpy of vaporization.

Other substances, such as ammonium chloride, appear to sublime because of chemical reactions. When heated, it decomposes into hydrogen chloride and ammonia, which quickly react to reform ammonium chloride.

Sublimation purification

Sublimation is a technique used by chemists to purify compounds. Typically a solid is placed in a vessel which is then heated under vacuum. Under this reduced pressure the solid volatilizes and condenses as a purified compound on a cooled surface, leaving the non-volatile residue impurities behind. This cooled surface often takes the form of a cold finger. Once heating ceases and the vacuum is released, the sublimated compound can be collected from the cooled surface. Usually this is done using a sublimation apparatus‎.

Uses

Frost-free freezers work by having a fan and air circulation inside the freezer. The sub-zero temperature combined with the air circulation that keeps the air arid significantly accelerates the sublimation process. This keeps freezer walls and shelves free of ice, although ice-cubes will continually sublimate.

Dye sublimation is also often used in color printing on a variety of substrates, including paper. A small heater is used to vaporize the solid dye material, which then solidifies upon the paper. As this type of printer allows extremely fine control of the primary color ratios it is possible to obtain a good quality picture even with relatively low printer resolution, as compared to other printer types of similar resolution. Standard black and white laser printers are capable of printing on plain paper using a special "transfer toner" containing sublimation dyes which can then be permanently heat transferred to T-shirts, hats, mugs, metals, puzzles and other surfaces.

In alchemy, sublimation typically refers to the process by which a substance is heated to a vapor, then immediately collects as sediment on the upper portion and neck of the heating medium (typically a retort or alembic). It is one of the 12 core alchemical processes.

In the Fast-Freeze, Deep-Etch technique, samples (for example, tissue samples) are rapidly frozen in liquid nitrogen and transferred to a vacuum device in which surface ice is sublimed. This effectively etches the sample surface, revealing the preserved 3D structure of the hydrated material. A rotary shadowed surface replica can then be obtained via electron microscopy.

Sublimation is also used to create freeze-dried substances, for example tea, soup or drugs in a process called lyophilization, which consists in freezing a solution or suspension and heating it very slowly under medium to high vacuum - specifically, a pressure lower than the vapor pressure of the solvent at its melting point. This can be well under the melting point of water if there are organic solvents or salts in the sample being freeze-dried. The resulting solid is usually much easier to dissolve or resuspend than one that is produced from a liquid system, and the low temperatures involved cause less damage to sensitive or reactive substances.

See also

• Phase diagram
• Phase transition

From	To
	Solid	Liquid	Gas	Plasma
Solid	Solid-Solid Transformation	Melting	Sublimation	-
Liquid	Freezing	N/A	Boiling/Evaporation	-
Gas	Deposition	Condensation	N/A	Ionization
Plasma	-	-	Recombination/Deionization	N/A

In chemistry and chemical engineering, a separation process is used to transform a mixture of substances into two or more compositionally-distinct products.

Barring a few exceptions, almost every element or compound is found naturally in an impure state such as a mixture of
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Acid-base extraction is a procedure using sequential liquid-liquid extractions to purify acids and bases from mixtures based on their chemical properties. Acid-base extraction is routinely performed during the work-up after chemical syntheses and for the isolation of compounds and
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Chromatography (from Greek χρώμα:chroma, colour and γραφειν:"grafein" to write) is the collective term for a family of laboratory techniques for the separation of mixtures.
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Crystallization is the (natural or artificial) process of formation of solid crystals from a uniform solution. Crystallization is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.
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Dissolved air flotation (DAF) is a water treatment process that clarifies wastewaters (or other waters) by the removal of suspended matter such as oil or solids. The removal is achieved by dissolving air in the water or wastewater under pressure and then releasing the air at
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Distillation is a method of separating chemical substances based on differences in their volatilities in a boiling liquid mixture. Distillation usually forms part of a larger chemical process, and is thus referred to as a unit operation.
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For the food conservation method, see drying (food).

Drying is a mass transfer process resulting in the removal of water moisture or moisture from another solvent, by evaporation from a solid, semi-solid or liquid (hereafter product) to end in a solid
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Electrochromatography is a chemical separation technique in analytical chemistry, biochemistry and molecular biology used to resolve and separate mostly large biomolecules such as proteins.
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Filtration is the processe of using a filter to mechanically separate mixtures. Depending on the application, either one or both of the components may be isolated. Examples of filtration include A) a coffee filter to keep the coffee separate from the grounds and B) the use of HEPA
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Flocculation is a process where a solute comes out of solution in the form of floc or "flakes." The term is also used to refer to the process by which fine particulates are caused to clump together into floc.
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Froth Flotation is a selective process for separating minerals from gangue by using surfactants and wetting agents. The selective separation of the minerals makes processing complex (that is, mixed) ores economically feasible.
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Separation processes

Processes
Acid-base extraction • Chromatography • Crystallization • Dissolved air flotation • Distillation • Drying • Electrochromatography • Filtration • Flocculation • Froth flotation
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Recrystallization (see also crystallization) is an essentially physical process that has meanings in chemistry, metallurgy and geology.

Chemistry

In chemistry, recrystallization is a procedure for purifying compounds.
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Sedimentation describes the motion of molecules in solutions or particles in suspensions in response to an external force such as gravity, centrifugal force or electric force.
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An API oil-water separator is a device designed to separate gross amounts of oil and suspended solids from the wastewater effluents of oil refineries, petrochemical plants, chemical plants, natural gas processing plants and other industrial sources.
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centrifuge is a piece of equipment, generally driven by a motor, that puts an object in rotation around a fixed axis, applying force perpendicular to the axis. The centrifuge works using the sedimentation principle, where the centripetal acceleration is used to separate substances
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Mixer settlers are a class of mineral process equipment used in the solvent extraction process. A mixer settler consists of a first stage that mixes the phases together followed by a quiescent settling stage that allows the phases to separate by gravity.
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A protein skimmer or foam fractionator is a device used mostly in saltwater aquaria to remove organic compounds from the water before they break down into nitrogenous waste.
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1 Cooling water in 2 Cooling water out 3 Vacuum/gas line 4 Sublimation chamber 5 Sublimed compound 6 Crude material 7 External heating]] Sublimation apparatus
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A still is an apparatus used to distill miscible or immiscible (eg. steam distillation) liquid mixtures by heating to selectively boil and then cooling to condense the vapor.
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Aqueous biphasic systems (ABS) or aqueous two phase systems are clean alternatives for traditional organic-water solvent extraction systems.

ABS are formed when 2 polymers, one polymer and one kosmotropic salt, or two salts (one chaotropic salt and the other a
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An azeotrope is a mixture of two or more pure compounds (chemicals) in such a ratio that its composition cannot be changed by simple distillation.^[1] This is because when an azeotrope is boiled, the resulting vapor has the same ratio of constituents as the
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eutectic or eutectic mixture is a mixture at such proportions that the melting point is as low as possible, and that furthermore all the constituents crystallize simultaneously at this temperature from molten liquid solution.
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A solid object is in the states of matter characterized by resistance to deformation and changes of volume. At the microscopic scale, a solid has these properties :

• The atoms or molecules that comprise the solid are packed closely together.

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Gas is one of the four major states of matter, consisting of freely moving atoms or molecules without a definite shape. Compared to the solid and liquid states of matter a gas has lower density and a lower viscosity.
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phase transition or phase change is the transformation of a thermodynamic system from one phase to another. The distinguishing characteristic of a phase transition is an abrupt change in one or more physical properties, in particular the heat capacity, with a small change in
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In physics and chemistry, the triple point of a substance is the temperature and pressure at which three phases (gas, liquid, and solid) of that substance may coexist in thermodynamic equilibrium.

For example, the triple point temperature of mercury is at −38.
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In chemistry and other sciences, STP or standard temperature and pressure is a standard set of conditions for experimental measurements, to enable comparisons to be made between sets of data.
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chemical element, or element, is a type of atom that is defined by its atomic number; that is, by the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons.
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