15 Examples of Crystallization - encyclopedia

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Examples of crystallization
Other techniques for separating mixtures

The crystallization is the chemical process of transformation of a gas, liquid or one dissolution, in a network of molecular bonds that result in a set of solid crystals.

These crystals are pure in nature, so this method can be used to separate elements from some homogeneous mixture. The crystallization can be carried out through various methods, including selective alteration of the temperature or pressure, as well as mixing with other chemicals and substances.

The shape, size and quality of the crystals obtained will depend on the conditions and the time during which their formation is allowed.

Crystals are solid formations that show a well-defined diffraction pattern. They are common in nature and are classified according to their constitution as: solid, luminous, ionic, covalent, molecular and metallic.

Examples of crystallization

Frost formation. On particularly cold days, ambient water vapor can crystallize on cold surfaces such as glass or certain metals, much like snow forms. This is known as frost, but they are water crystals with a very regular and well-formed constitution.
Freezing water. Although ice as such is not a crystal, during the first stages of freezing of water it is possible to see the formation of dendrites and other submerged structures in the container that are very similar in appearance to crystals.
Salt water evaporation. This procedure is very common both in obtaining salt crystals and in desalinating water. When boiling, liquid becomes gaseous and the salts dissolved in it remain, rejoining their molecules in the form of saline crystals at the bottom.
Manufacture of aspirin. Acetylsalicylic acid, the active compound of the popular remedy, is actually an ester that crystallizes in the presence of ethanoic anhydride and acid sulfuric, in addition to the injection of heat.
Winterization of oils. This process is useful to obtain oils of greater clarity and lower density, from the rapid and sustained cooling of the oil to cause the crystallization of stearins, saturated glycerides, waxes and other unwanted substances. Once these have formed solid crystals, it is filtered and centrifuge oil before they can regain their liquidity and are extracted from the mixture.
Sugar crystallization. Sucrose and other sweeteners whose commercial presentation is in crystals to be dissolved in drinks, have undergone a crystallization process from the sweet syrup from which they are obtained. Then the mixture is centrifuged to separate the honey crystals. The "blond" or "brown" sugar, not white, is precisely sugar in its first stage of crystallization (unrefined).
Covalent crystals of carbon. Under enormous underground pressure and slow metamorphosis processes, carbon can become any of its three allotropes: carbon, graphite or diamond. This last case is, precisely, an example of glass, whose atoms are so closely united that they present a hardness and very low melting point recognized.
Backward sublimation. Some solid that when exposed to heat pass to a gaseous state (sublimation) can later regain their physical form as crystals, when exposed to a decrease in temperature, in what is called reverse sublimation. In the process, impurities from the solid will have been lost and there will be pure crystals in their place. This process is useful for purifying iodine or sulfur, for example.
Silicon Purification. Although silicon does not sublimate, it is possible to purify it by melting it and then selectively cooling it, to cleave the soluble impurities from the high-purity silicon single crystals that are then used in the superconductor industry.
Benzoic acid crystallization. This crystallization process occurs from a solution of benzoic acid in acetone, with the simple addition of water. The interaction between the two solvents creates a new mixture and the benzoic acid crystallizes at the bottom of the container.
The marine calcareous formations. Like those of mollusks, corals and bivalves, which through the action of certain protein they can not only precipitate, but mold the creation of calcite or quartz crystals on the rock in which their colony will form.
Molecular crystal formation. In substances such as sulfur dioxide (SO₂), Van der Waals forces and hydrogen bonds lead to the formation of molecular crystals, which are usually brittle and meltable below 100 ° C.
Silver crystals for films. Obtaining silver crystals is useful for certain implements of the filmic or early photographic industry (not digital), since they are sensitive to light and allowed the rearrangement of the substance according to the light impression through the lens. They are obtained from chemical compounds as silver bromide, chloride or iodide.
Calcium oxalate crystals. These crystals are formed by the deposition of you go out and calcium in the kidneys, where they oxidize and form small dark stones that then have to be painfully expelled along with the urine. It is a common kidney ailment known as kidney stones, or also "stone" or "grit" in the kidneys.
Uric acid crystallization. This is the phenomenon of the disease known as gout, in which uric acid crystals form in the joints, causing pain and decreased movement. It can be a consequence of the ingestion of purines in excess, or of renal failure of diverse magnitude.