Frost crystallization on a shrub.

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. Image File history File linksMetadata Download high resolution version (1600x1200, 912 KB) February 26, 2005 saw some unique snow formations in Akureyri, Iceland. ... Image File history File linksMetadata Download high resolution version (1600x1200, 912 KB) February 26, 2005 saw some unique snow formations in Akureyri, Iceland. ... Quartz crystal Synthetic bismuth hopper crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid in which the constituent atoms... Dissolving table salt (NaCl) in water This article is about a chemical solution; for other uses of the term solution, see solution (disambiguation). ... A substance is soluble in a fluid if it dissolves in the fluid. ...

Process

The crystallization process consists of two major events, nucleation and crystal growth. Bubbles in a soft drink each nucleate independently, responding to a decrease in pressure. ... Crystals are entities of atoms, ions or even polymer strings in which the subunits (i. ...

Nucleation is the step where the solute molecules dispersed in the solvent start to gather into clusters, on the nanometer scale (elevating solute concentration in a small region), that becomes stable under the current operating conditions. These stable clusters constitute the nuclei. However when the clusters are not stable, they redissolve. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by the operating conditions (temperature, supersaturation, etc.). It is at the stage of nucleation that the atoms arrange in a defined and periodic manner that defines the crystal structure — note that "crystal structure" is a special term that refers to the internal arrangement of the atoms, not the macroscopic properties of the crystal: size and shape. A substance is soluble in a fluid if it dissolves in the fluid. ... A solvent is a liquid that dissolves a solid, liquid, or gaseous solute, resulting in a solution. ... A nanometre (American spelling: nanometer) is 1. ... This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... The term supersaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances. ... In mathematics, a periodic function is a function that repeats its values, after adding some definite period to the variable. ... Enargite crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ...

The crystal growth is the subsequent growth of the nuclei that succeed in achieving the critical cluster size. Nucleation and growth continue to occur simultaneously while the supersaturation exists. Supersaturation is the driving force of the crystallization, hence the rate of nucleation and growth is driven by the existing supersaturation in the solution. Depending upon the conditions, either nucleation or growth may be predominant over the other, and as a result, crystals with different sizes and shapes are obtained (control of crystal size and shape constitutes one of the main challenges in industrial manufacturing, such as for pharmaceuticals). Once the supersaturation is exhausted, the solid-liquid system reaches equilibrium and the crystallization is complete, unless the operating conditions are modified from equilibrium so as to supersaturate the solution again.

Many compounds have the ability to crystallize with different crystal structures, a phenomenon called polymorphism. Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, shape (angles between facets and facet growth rates), melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products. In general, polymorphism describes multiple possible states for a single property (it is said to be polymorphic). ...

Crystallization in nature

Snow flakes are a very well known example, where subtle differences in crystal growth conditions result in different geometries.

There are many examples of natural process that involve crystallization. Galunggung in 1982, showing a combination of natural events. ... Image File history File links Size of this preview: 469 × 600 pixel Image in higher resolution (1124 × 1437 pixel, file size: 479 KB, MIME type: image/jpeg) http://www. ... Image File history File links Size of this preview: 469 × 600 pixel Image in higher resolution (1124 × 1437 pixel, file size: 479 KB, MIME type: image/jpeg) http://www. ... Animation of snowcover changing with the seasons Trees covered with snow Snow covering a leaf. ... The first four iterations of the Koch snowflake. ...

Geological time scale process examples include: The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ...

• Natural (mineral) crystal formation (see also gemstone);
• Stalactite/stalagmite, rings formation.

Usual time scale process examples include: Quartz crystal Synthetic bismuth hopper crystal Insulin crystals Gallium, a metal that easily forms large single crystals A huge monocrystal of potassium dihydrogen phosphate grown from solution by Saint-Gobain for the megajoule laser of CEA. In chemistry and mineralogy, a crystal is a solid in which the constituent atoms... A selection of gemstone pebbles made by tumbling rough rock with abrasive grit, in a rotating drum. ... Water droplet coming out of the central canal of a stalactite A stalactite (Greek stalaktites, (Σταλακτίτης), from the word for drip and meaning that which drips) is a type of speleothem(secondary mineral) that hangs from the ceiling or wall of limestone caves. ... The Witchs Finger in the Carlsbad Caverns A stalagmite (from the Greek stalagma (Σταλαγμίτης), drop or drip) is a type of speleothem that rises from the floor of a limestone cave due to the dripping of mineralized solutions and the deposition of calcium carbonate. ...

• Snow flakes formation (see also Koch snowflake);
• Honey crystallization (nearly all types of honey crystallize).

Animation of snowcover changing with the seasons Trees covered with snow Snow covering a leaf. ... The first four iterations of the Koch snowflake. ... A jar of honey, shown with a wooden honey server and scones/biscuits. ...

Artificial methods

For crystallization to occur the solution must be supersaturated. This means that the solution has to contain more solute entities (molecules or ions) dissolved than it would contain under the equilibrium (saturated solution). This can be achieved by various methods, with 1) solution cooling, 2) addition of a second solvent to reduce the solubility of the solute (technique known as anti-solvent or drown-out), 3) chemical reaction and 4) change in pH being the most common methods used in industrial practice. Other methods, such as solvent evaporation, can also be used. In physics, the term supersaturation or oversaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under existing circumstances. ... A substance is soluble in a fluid if it dissolves in the fluid. ... An electrostatic potential map of the nitrate ion (NO3−). Areas coloured red are lower in energy than areas colored yellow An ion is an atom or group of atoms which have lost or gained one or more electrons, making them negatively or positively charged. ...

Applications:

There are two major groups of applications for the artificial crystallization process: crystal production and purification. Categories: Move to Wiktionary | Stub | Chemistry ...

Crystal production

From a material industry perspective: Materials science includes those parts of chemistry and physics that deal with the properties of materials. ...

• Macroscopic crystal production, for supply the demand of natural-like crystals with methods that "accelerate time-scale" for massive production and/or perfection:
  • ionic crystal production;
  • covalent crystal production.
• Tiny size crystals:
  • Powder, sand and smaller sizes: using methods for powder and controlled (nanotechnology fruits) forms.
    • Mass-production: on chemical industry, like salt-powder production.
    • Sample production: small production of tiny crystals for material characterization. Controlled recrystallization is an important method to supply unusual crystals, that are needed to reveal the molecular structure and nuclear forces inside a typical molecule of a crystal. Many techniques, like X-ray crystallography and NMR spectroscopy, are widely used in chemistry and biochemistry to determine the structures of an immense variety of molecules, including inorganic compounds and bio-macromolecules.
  • Thin film production.

Massive production examples: Crystalline materials (mainly metals and alloys, but also stoichiometric salts and other materials) are made up of solid regions of ordered matter (atoms placed in one of a number of ordered formations called Bravais lattices). ... Electron configurations of lithium and fluorine. ... Covalent bonding is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms, or sometimes between atoms and other covalent bonds. ... Powder is a substance that has been crushed into very fine grains. ... Patterns in the sand Sand is a granular material made up of fine rock particles. ... Powder is a substance that has been crushed into very fine grains. ... Buckminsterfullerene C60, also known as the buckyball, is the simplest of the carbon structures known as fullerenes. ... Chemical tanks in Lillebonne, France Chemical industry includes those industries involved in the production of petrochemicals, agrochemicals, pharmaceuticals, polymers, paints, oleochemicals etc. ... Characterization, when used in materials science, refers to the use of external techniques to probe into the internal structure and properties of a material. ... Insulin crystals Recrystallization is an essentially physical process that has meanings in chemistry, metallurgy and geology. ... X-ray crystallography, also known as single-crystal X-ray diffraction, is the oldest and most common crystallographic method for determining the structure of molecules. ... It has been suggested that NMR Data Processing be merged into this article or section. ... A macromolecule is a large molecule with a large molecular mass bonded covalently, but generally the use of the term is restricted to polymers and molecules which structurally include polymers. ... Thin-film deposition is any technique for depositing a thin film of material onto a substrate or onto previously deposited layers. ...

• "Powder salt for food" industry;
• Silicon crystal wafer production.
• Production of sucrose from sugar beet, where the sucrose is crystallized out from an aqueous solution.

Naturally formed salt crystals with a U.S. penny for size reference (19. ... An etched silicon wafer In microelectronics, a wafer is a thin slice of semiconducting material, such as a silicon crystal, upon which microcircuits are constructed by doping (for example, diffusion or ion implantation), etching, and deposition of various materials. ... Binomial name Carolus Linnaeus Beta vulgaris, commonly known as beet is a flowering plant species in the family Chenopodiaceae. ...

Purification

See also: Recrystallization

Well formed crystals are expected to be pure because each molecule or ion must fit perfectly into the lattice as it leaves the solution. Impurities would normally not fit as well in the lattice, and thus remain in solution preferentially. Hence, molecular recognition is the principle of purification in crystallization. However, there are instances when impurities incorporate into the lattice, hence, decreasing the level of purity of the final crystal product. Also, in some cases, the solvent may incorporate into the lattice forming a solvate. In addition, the solvent may be 'trapped' (in liquid state) within the crystal formed, and this phenomenon is known as inclusion. Insulin crystals Recrystallization is an essentially physical process that has meanings in chemistry, metallurgy and geology. ...

Thermodynamic view

The nature of a crystallization process is governed by both thermodynamic and kinetic factors, which can make it highly variable and difficult to control. Factors such as impurity level, mixing regime, vessel design, and cooling profile can have a major impact on the size, number, and shape of crystals produced.

Now put yourself in the place of a molecule within a pure and perfect crystal, being heated by an external source. At some sharply defined temperature, a bell rings, you must leave your neighbours, and the complicated architecture of the crystal collapses to that of a liquid. Textbook thermodynamics says that melting occurs because the entropy, S, gain in your system by spatial randomization of the molecules has overcome the enthalpy, H, loss due to breaking the crystal packing forces: This article includes a list of works cited or a list of external links, but its sources remain unclear because it lacks in-text citations. ... Ice melting - classic example of entropy increasing[1] described in 1862 by Rudolf Clausius as an increase in the disgregation of the molecules of the body of ice. ... t In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H or ΔH, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the useful work obtainable from a closed thermodynamic system under constant pressure. ...

This rule suffers no exceptions when the temperature is rising. By the same token, on cooling the melt, at the very same temperature the bell should ring again, and molecules should click back into the very same crystalline form. The entropy decrease due to the ordering of molecules within the system is overcompensated by the thermal randomization of the surroundings, due to the release of the heat of fusion; the entropy of the universe increases.

But liquids that behave in this way on cooling are the exception rather than the rule; in spite of the second principle of thermodynamics, crystallization usually occurs at lower temperatures (supercooling). This can only mean that a crystal is more easily destroyed than it is formed. Similarly, it is usually much easier to dissolve a perfect crystal in a solvent than to grow again a good crystal from the resulting solution. The nucleation and growth of a crystal are under kinetic, rather than thermodynamic, control.

Equipment for Crystallization

1. Tank crystallizers. Tank crystallization is an old method still used in some specialized cases. Saturated solutions, in tank crystallization, are allowed to cool in open tanks. After a period of time the mother liquid is drained and the crystals removed. Nucleation and size of crystals are difficult to control. Typically, labor costs are very high.

2. Scraped surface crystallizers. One type of scraped surface crystallizer is the Swenson-Walker crystallizer, which consists of an open trough 0.6m wide with a semicircular bottom having a cooling jacket outside. A slow-speed spiral agitator rotates and suspends the growing crystals on turning. The blades pass close to the wall and break off any deposits of crystals on the cooled wall. The product generally has a somewhat wide crystal-size distribution. Categories: Move to Wiktionary | Stub ... An agitator at a political demonstration in France. ...

3. Double-pipe scraped surface crystallizer. Also called a votator, this type of crystallizer is used in crystallizing ice cream and plasticizing margarine. Cooling water passes in the annular space. An internal agitator is fitted with spring-loaded scrapers that wipe the wall and provide good hear-transfer coefficients. Missing image Ice cream is often served on a stick Boxes of ice cream are often found in stores in a display freezer. ... Margarine in a tub Margarine (pronunciation: ), as a generic term, can indicate any of a wide range of butter-substitutes. ... Annular, annulate, &c. ... An agitator at a political demonstration in France. ...

4. Circulating-liquid evaporator-crystallizer. Also called Oslo crystallizer. Here supersaturation is reached by evaporation. The circulating liquid is drawn by the screw pump down inside the tube side of the condensing stream heater. The heated liquid then flows into the vapor space, where flash evaporation occurs, giving some supersaturation.The vapor leaving is condensed. The supersaturated liquid flows down the downflow tube and then up through the bed of fluidized and agitated crystals, which are growing in size. The leaving saturated liquid then goes back as a recycle stream to the heater, where it is joined by the entering fluid. The larger crystals settle out and slurry of crystals and mother liquid is withdrawn as a product. The term supersaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances. ... The term supersaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances. ... Software being used to design HVAC systems HVAC (pronounced either H-V-A-C or, occasionally, H-VAK) is an initialism/acronym that stands for heating, ventilation and air-conditioning. This is sometimes referred to as climate control. ... A slurry is in general a thick suspension of solids in a liquid and may be: Look up slurry in Wiktionary, the free dictionary. ...

5. Circulating-magma vacuum crystallizer. The magma or suspension of crystals is circulated out of the main body through a circulating pipe by a screw pump. The magma flows though a heater, where its temperature is raised 2-6 K. The heated liquor then mixes with body slurry and boiling occurs at the liquid surface. This causes supersaturation in the swirling liquid near the surface, which deposits in the swirling suspended crystals until they leave again via the circulating pipe. The vapors leave through the top. A steam-jet ejector provides vacuum. Boiling, a type of phase transition, is the rapid vaporization of a liquid, which typically occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding atmospheric pressure. ... The term supersaturation refers to a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances. ... An injector is a pump-like device without rotating parts or a pump piston, which charges or discharges containers under pressure with suitable arrangements. ... Look up Vacuum in Wiktionary, the free dictionary. ...

References

• Glynn P.D. and Reardon E.J. (1990) "Solid-solution aqueous-solution equilibria: thermodynamic theory and representation". Amer. J. Sci. 290, 164-201.

• • Geankoplis, C.J. (2003) "Transport Processes and Separation Process Principles". 4th Ed. Prentice-Hall Inc.

External links

• Industrial Crystallization

See also