hydrothermal synthesis
   HOME

TheInfoList



OR:

Hydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solutions at high
vapor pressure Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phas ...
s; also termed "hydrothermal method". The term "
hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...
" is of geologic origin. Geochemists and
mineralogist Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proce ...
s have studied hydrothermal
phase equilibria In thermodynamics, the phase rule is a general principle governing "pVT" systems, whose thermodynamic states are completely described by the variables pressure (), volume () and temperature (), in thermodynamic equilibrium. If is the number of d ...
since the beginning of the twentieth century. George W. Morey at the
Carnegie Institution The Carnegie Institution of Washington (the organization's legal name), known also for public purposes as the Carnegie Institution for Science (CIS), is an organization in the United States established to fund and perform scientific research. T ...
and later,
Percy W. Bridgman Percy Williams Bridgman (April 21, 1882 – August 20, 1961) was an American physicist who received the 1946 Nobel Prize in Physics for his work on the physics of high pressures. He also wrote extensively on the scientific method and on other as ...
at
Harvard University Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of high ...
did much of the work to lay the foundations necessary to containment of reactive media in the temperature and pressure range where most of the hydrothermal work is conducted. Hydrothermal synthesis can be defined as a method of synthesis of
single crystal In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries.RIWD. "Re ...
s that depends on the solubility of minerals in hot water under high pressure. The
crystal growth A crystal is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. Crystal growth is a major stage of a crystallization process, and consists of the ...
is performed in an apparatus consisting of a steel pressure vessel called an
autoclave An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to ambient pressure and/or temperature. Autoclaves are used before surgical procedures to perform sterilizati ...
, in which a nutrient is supplied along with
water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
. A temperature gradient is maintained between the opposite ends of the growth chamber. At the hotter end the nutrient solute dissolves, while at the cooler end it is deposited on a seed crystal, growing the desired crystal. Advantages of the hydrothermal method over other types of crystal growth include the ability to create crystalline phases which are not stable at the melting point. Also, materials which have a high vapour pressure near their melting points can be grown by the hydrothermal method. The method is also particularly suitable for the growth of large good-quality crystals while maintaining control over their composition. Disadvantages of the method include the need of expensive autoclaves, and the impossibility of observing the crystal as it grows if a steel tube is used. There are autoclaves made out of thick walled glass, which can be used up to 300 °C and 10 bar.


History

The first report of the hydrothermal growth of crystals was by German geologist Karl Emil von Schafhäutl (1803–1890) in 1845: he grew microscopic quartz crystals in a pressure cooker. In 1848,
Robert Bunsen Robert Wilhelm Eberhard Bunsen (; 30 March 1811 – 16 August 1899) was a German chemist. He investigated emission spectra of heated elements, and discovered caesium (in 1860) and rubidium (in 1861) with the physicist Gustav Kirchhoff. The Bu ...
reported growing crystals of barium and strontium carbonate at 200 °C and at pressures of 15 atmospheres, using sealed glass tubes and aqueous ammonium chloride (''"Salmiak"'') as a solvent. In 1849 and 1851, French crystallographer Henri Hureau de Sénarmont (1808–1862) produced crystals of various minerals via hydrothermal synthesis. Later (1905) Giorgio Spezia (1842–1911) published reports on the growth of macroscopic crystals. He used solutions of sodium silicate, natural crystals as seeds and supply, and a silver-lined vessel. By heating the supply end of his vessel to 320–350 °C, and the other end to 165–180 °C, he obtained about 15 mm of new growth over a 200-day period. Unlike modern practice, the hotter part of the vessel was at the top. A shortage in the electronics industry of natural quartz crystals from Brazil during World War 2 led to postwar development of a commercial-scale hydrothermal process for culturing quartz crystals, by A. C. Walker and Ernie Buehler in 1950 at Bell Laboratories. Other notable contributions have been made by Nacken (1946), Hale (1948), Brown (1951), and Kohman (1955).


Uses

A large number of compounds belonging to practically all classes have been synthesized under hydrothermal conditions: elements, simple and complex oxides,
tungstate In chemistry, a tungstate is a compound that contains an oxyanion of tungsten or is a mixed oxide containing tungsten. The simplest tungstate ion is , "orthotungstate". Many other tungstates belong to a large group of polyatomic ions that are ...
s,
molybdate In chemistry a molybdate is a compound containing an oxoanion with molybdenum in its highest oxidation state of 6. Molybdenum can form a very large range of such oxoanions which can be discrete structures or polymeric extended structures, althou ...
s, carbonates, silicates, germanates etc. Hydrothermal synthesis is commonly used to grow synthetic
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
,
gems Gems, or gemstones, are polished, cut stones or minerals. Gems or GEMS may also refer to: Arts, entertainment and media * ''Gems'' (Aerosmith album), 1988 * ''Gems'' (Patti LaBelle album), 1994 * ''Gems'' (Michael Bolton album), 2011 * Gems TV, ...
and other single crystals with commercial value. Some of the crystals that have been efficiently grown are emeralds,
rubies A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum ( aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sap ...
, quartz, alexandrite and others. The method has proved to be extremely efficient both in the search for new compounds with specific physical properties and in the systematic physicochemical investigation of intricate multicomponent systems at elevated temperatures and pressures.


Equipment for hydrothermal crystal growth

The crystallization vessels used are
autoclave An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to ambient pressure and/or temperature. Autoclaves are used before surgical procedures to perform sterilizati ...
s. These are usually thick-walled steel cylinders with a hermetic seal which must withstand high temperatures and pressures for prolonged periods of time. Furthermore, the autoclave material must be inert with respect to the
solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
. The closure is the most important element of the autoclave. Many designs have been developed for seals, the most famous being the Bridgman seal. In most cases, steel-corroding solutions are used in hydrothermal experiments. To prevent
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
of the internal cavity of the autoclave, protective inserts are generally used. These may have the same shape as the autoclave and fit in the internal cavity (contact-type insert), or be "floating" type inserts which occupy only part of the autoclave interior. Inserts may be made of carbon-free
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
,
copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...
,
silver Silver is a chemical element with the symbol Ag (from the Latin ', derived from the Proto-Indo-European ''h₂erǵ'': "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical ...
,
gold Gold is a chemical element with the symbol Au (from la, aurum) and atomic number 79. This makes it one of the higher atomic number elements that occur naturally. It is a bright, slightly orange-yellow, dense, soft, malleable, and ductile me ...
,
platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...
,
titanium Titanium is a chemical element with the Symbol (chemistry), symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resista ...
,
glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
(or
quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
), or
Teflon Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. It is one of the best-known and widely applied PFAS. The commonly known brand name of PTFE-based composition is Teflon by Chemo ...
, depending on the temperature and solution used.


Methods


Temperature-difference method

This is the most extensively used method in hydrothermal synthesis and crystal growing. Supersaturation is achieved by reducing the temperature in the crystal growth zone. The nutrient is placed in the lower part of the autoclave filled with a specific amount of solvent. The autoclave is heated in order to create a temperature gradient. The nutrient dissolves in the hotter zone and the saturated aqueous solution in the lower part is transported to the upper part by convective motion of the solution. The cooler and denser solution in the upper part of the autoclave descends while the counterflow of solution ascends. The solution becomes supersaturated in the upper part as the result of the reduction in temperature and crystallization sets in.


Temperature-reduction technique

In this technique, crystallization takes place without a temperature gradient between the growth and
dissolution Dissolution may refer to: Arts and entertainment Books * ''Dissolution'' (''Forgotten Realms'' novel), a 2002 fantasy novel by Richard Lee Byers * ''Dissolution'' (Sansom novel), a 2003 historical novel by C. J. Sansom Music * Dissolution, in mu ...
zones. The supersaturation is achieved by a gradual reduction in temperature of the solution in the autoclave. The disadvantage of this technique is the difficulty in controlling the growth process and introducing seed crystals. For these reasons, this technique is very seldom used.


Metastable-phase technique

This technique is based on the difference in
solubility In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solub ...
between the phase to be grown and that serving as the starting material. The nutrient consists of compounds that are thermodynamically unstable under the growth conditions. The solubility of the
metastable phase In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy. A ball resting in a hollow on a slope is a simple example of metastability. If the ball ...
exceeds that of the stable phase, and the latter crystallize due to the dissolution of the metastable phase. This technique is usually combined with one of the other two techniques above.


See also

* Chemical vapor deposition *
Czochralski method The Czochralski method, also Czochralski technique or Czochralski process, is a method of crystal growth used to obtain single crystals of semiconductors (e.g. silicon, germanium and gallium arsenide), metals (e.g. palladium, platinum, silver, ...
*
Flux method The flux method of crystal growth is a method where the components of the desired substance are dissolved in a solvent (flux). The method is particularly suitable for crystals needing to be free from thermal strain. It takes place in a crucible ma ...
*
Verneuil method The Verneuil method (or Verneuil process or Verneuil technique), also called flame fusion, was the first commercially successful method of manufacturing synthetic gemstones, developed in the late 1883 by the French chemist Auguste Verneuil. It i ...


References


External links


Hydrothermal crystal growth equipment producer
{{DEFAULTSORT:Hydrothermal Synthesis Chemical synthesis Methods of crystal growth