Crystallization is the chemical process of transforming a gas , liquid or solution in a network of molecular bonds that yield results in a set of solid crystals.
These crystals are pure in their nature, so this method can be used to separate elements from some homogeneous mixture . The crystallization can be carried out through various methods, including the selective alteration of the temperature or pressure, as well as mixed with other chemicals and substances .
The shape, size and quality of the crystals obtained will depend on the conditions and time during which their formation is allowed.
The crystals are solid formations that have a well-defined diffraction pattern. They are common in nature and are classified according to their constitution in: solid, luminous, ionic, covalent, molecular and metallic.
- The formation of frost . On particularly cold days, ambient water vapor can crystallize on cold surfaces such as glass or certain metals, similar to the way snow is formed. This is known as frost, but they are very regular and well formed water crystals.
- The freezing of water . While ice as such is not a crystal, during the first phases of freezing water it is possible to see in the package the formation of dendrites and other submerged structures that are very similar in appearance to crystals.
- Evaporation of salt water . This procedure is very common both in the production of salt crystals and in the desalination of water. When boiling, the liquid becomes gaseous and the salts dissolved in it remain, returning to join their molecules in the form of saline crystals in the bottom.
- Manufacture of aspirins . Acetylsalicylic acid, active compound of the popular remedy, is actually an ester that crystallizes in the presence of ethanoic anhydride and sulfuric acid, in addition to the heat injection.
- 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, the oil is filtered and centrifuged before they can recover their liquidity and are extracted from the mixture .
- Crystallization of sugar . Sucrose and other sweeteners whose commercial presentation is in crystals to be dissolved in beverages, have gone through a process of crystallization from the sweet syrup from which they are obtained. Then the mixture is centrifuged to separate the crystals from the honey. The “blond” or “brown” sugar, not white, is just sugar in its first stage of crystallization (unrefined).
- Covalent crystals of carbon . Subjected to enormous pressures underground and slow processes of metamorphosis, carbon can become any of its three allotropes: carbon, graphite or diamond. The latter case is, precisely, an example of crystal, whose atoms are so closely linked that they have a hardness and very low recognized melting point .
- Regressive sublimation . Certain solids that, when exposed to heat, become gaseous ( sublimation ) can then recover their physical form as crystals, when exposed to a temperature decrease, in what is called inverse sublimation. In the process the impurities of the solid will have been lost and there will be pure crystals in 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 fusing it and then selectively cooling it, to cleave the soluble impurities of the high purity silicon whiskers that are then used in the superconducting industry .
- Crystallization of benzoic acid . This crystallization process is given 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 molluscs, corals and bivalves, which through the action of certain proteins can not only precipitate, but mold the creation of calcite or quartz crystals on the rock in which their colony will form.
- Formation of molecular crystals . In substances such as sulfur dioxide (SO 2 ), 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 . The obtaining of silver crystals is useful for certain implements of the early filmic or 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 such as silver bromide, chloride or iodide.
- Calcium oxalate crystals . These crystals are formed by the deposition of salts and calcium in the kidneys, where they are oxidized and form small dark stones that then have to be expelled painfully along with the urine. It is a common kidney disease known as kidney stones, or also “stone” or “grit” in the kidneys.
- Crystallization of uric acid . 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 excess intake of purines, or kidney failure of varying magnitude.