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12 décembre 2011 1 12 /12 /décembre /2011 02:53

Gallium is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in nature, but as the gallium(III) salt in trace amounts in bauxite and zinc ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures.Sony VAIO VPC CW2MFX/PU Battery

As it liquefies slightly above room temperature, it will melt in the hand. Its melting point is used as a temperature reference point, and from its discovery in 1875 to the semiconductor era, its primary uses were in high-temperature thermometric applications and in preparation of metal alloys with unusual properties of stability, or ease of melting; some being liquid at room temperature or below. The alloy Galinstan (68.5% Ga, 21.5% In, 10% Sn) has a melting point of about ?19 °C (?2 °F).Sony VAIO VPC S11V9E/B Battery

In semiconductors, the major-use compound is gallium arsenide used in microwave circuitry and infrared applications. Gallium nitride and indium gallium nitride, minority semiconductor uses, produce blue and violet light-emitting diodes (LEDs) anddiode lasers.Sony VAIO VPCB119GJ/B Battery

Semiconductor use is now almost the entire (> 95%) world market for gallium, but new uses in alloys and fuel cells continue to be discovered.

Gallium is not known to be essential in biology, but because of the biological handling of gallium's primary ionic saltgallium(III) as though it were iron(III),Sony VAIO VPCB11AGJ Battery

the gallium ion localizes to and interacts with many processes in the body in which iron(III) is manipulated. As these processes include inflammation, which is a marker for many disease states, several gallium salts are used, or are in development, as both pharmaceuticals and radiopharmaceuticals in medicine.Sony VAIO VPCB11AVJ Battery

Properties

Elemental gallium is not found in nature, but it is easily obtained by smelting. Very pure gallium metal has a brilliant silvery color and its solid metal fractures conchoidally like glass. Gallium metal expands by 3.1% when it solidifies, and therefore storage in either glass or metal containers is avoided, due to the possibility of container rupture with freezing.Sony VAIO VPCB11V9E Battery

Gallium shares the higher-density liquid state with only a few materials like silicon, germanium, bismuth, antimony andwater.

Gallium attacks most other metals by diffusing into their metal lattice. Gallium for example diffuses into the grain boundariesof Al/Zn alloys[1] or steel,[2] making them very brittle.Sony VAIO VPCB11X9E Battery

Also, gallium metal easily alloys with many metals, and was used in small quantities as a plutonium-gallium alloy in the plutonium cores of the first and third nuclear bombs, to help stabilize the plutonium crystal structure.Sony VAIO VPCCW18FJ/P Battery

The melting point of 302.9146 K (29.7646 °C, 85.5763 °F) is near room temperature. Gallium's melting point (mp) is one of the formal temperature reference points in the International Temperature Scale of 1990 (ITS-90) established by BIPM. The triple point of gallium of 302.9166 K (29.7666 °C, 85.5799 °F), is being used by NIST in preference to gallium's melting point.Sony VAIO VPCCW18FJ/R Battery

Gallium is a metal that will melt in one's hand. This metal has a strong tendency to supercool below its melting point/freezing point. Seeding with a crystal helps to initiate freezing. Gallium is one of the metals (with caesium,rubidium, francium and mercury) which are liquid at or near normal room temperature, and can therefore be used in metal-in-glass high-temperature thermometers.Sony VAIO VPCCW18FJ/W Battery

It is also notable for having one of the largest liquid ranges for a metal, and (unlike mercury) for having a low vapor pressure at high temperatures. Unlike mercury, liquid gallium metal wets glass and skin, making it mechanically more difficult to handle (even though it is substantially less toxic and requires far fewer precautions).Sony VAIO VPCCW19FJ/W Battery

For this reason as well as the metal contamination problem and freezing-expansion problems noted above, samples of gallium metal are usually supplied in polyethylene packets within other containers.

Gallium does not crystallize in any of the simple crystal structures. The stable phase under normal conditions is orthorhombic with 8 atoms in the conventional unit cell.Sony VAIO VPCCW1AFJ Battery

Each atom has only one nearest neighbor (at a distance of 244 pm) and six other neighbors within additional 39 pm. Many stable and metastable phases are found as function of temperature and pressure.

The bonding between the nearest neighbors is found to be of covalent character, hence Ga2dimers are seen as the fundamental building blocks of the crystal.Sony VAIO VPCCW1AHJ Battery

This explains the drop of the melting point compared to its neighbour elements aluminium and indium. The compound with arsenic, gallium arsenide is a semiconductor commonly used in light-emitting diodes.

High-purity gallium is dissolved slowly by mineral acids.Sony VAIO VPCCW1S1E Battery

In 1871, existence of gallium was first predicted by Russian chemist Dmitri Mendeleev, who named it "eka-aluminium" on the basis of its position in his periodic table. He also predicted several properties of the element, which correspond close to real gallium properties, such as density, melting point, oxide character and bonding in chloride.Sony VAIO VPCCW1S1E/B Battery

Gallium was discovered spectroscopically by Paul Emile Lecoq de Boisbaudran in 1875 by its characteristic spectrum (twovioletlines) in an examination of a sphalerite sample. Later that year, Lecoq obtained the free metal by electrolysis of its hydroxidein potassium hydroxide solution. He named the element "gallia", from Latin Gallia meaning gaul, after his native land of France.Sony VAIO VPCCW1S1E/L Battery

It was later claimed that, in one of those multilingual puns so beloved of men of science in the 19th century, he had also named gallium after himself, as his name, "Le coq", is the French for "the rooster", and the Latin for "rooster" is "gallus"; however, in an 1877 article Lecoq denied this supposition.Sony VAIO VPCCW1S1E/P Battery

Occurrence

Gallium does not exist in free form in nature, and the few high-gallium minerals such as gallite (CuGaS2) are too rare to serve as a primary source of the element or its compounds. Its abundance in the Earth's crust is approximately 16.9 ppm.[11]Gallium is found and extracted as a trace component in bauxite and to a small extent from sphalerite.Sony VAIO VPCCW1S1E/R Battery

The amount extracted from coal, diasporeand germanite in which gallium is also present is negligible. The United States Geological Survey (USGS) estimates gallium reserves to exceed 1 million tonnes, based on 50 ppm by weight concentration in known reserves of bauxite and zinc ores.Sony VAIO VPCCW1S1E/W Battery

Some fluedusts from burning coal have been shown to contain small quantities of gallium, typically less than 1% by weight.

Production

The only two economic sources for gallium are as byproduct of aluminium and zinc production, while the sphalerite for zinc production is the minor source.Sony VAIO VPCCW21FX/B Battery

Most gallium is extracted from the crude aluminium hydroxide solution of the Bayer process for producing alumina and aluminium. A mercury cell electrolysis and hydrolysisof the amalgam with sodium hydroxide leads to sodium gallate. Electrolysis then gives gallium metal.Sony VAIO VPCCW21FX/L Battery

For semiconductor use, further purification is carried out usingzone melting, or else single crystal extraction from a melt (Czochralski process). Purities of 99.9999% are routinely achieved and commercially widely available. An exact number for the world wide production is not available, but it is estimated that in 2007 the production of gallium was 184 tonnes with less than 100 tonnes from mining and the rest from scrap recycling.Sony VAIO VPCCW21FX/R Battery

The semiconductor applications are the main reason for the low-cost commercial availability of the extremely high-purity (99.9999+%) metal.

Gallium arsenide (GaAs) and gallium nitride (GaN) used in electronic components represented about 98% of the gallium consumption in the United States in 2007.Sony VAIO VPCCW21FX/W Battery

About 66% of semiconductor gallium is used in the U.S. in integrated circuits (mostly gallium arsenide), such as the manufacture of ultra-high speed logic chips and MESFETs for low-noise microwave preamplifiers in cell phones. About 20% is used in optoelectronics. World wide gallium arsenide makes up 95% of the annual global gallium consumption.Sony VAIO VPCCW26EC Battery

Gallium arsenide is used in optoelectronics in a variety of infrared applications. Aluminium gallium arsenide (AlGaAs) is used in high-powered infrared laser diodes. As a component of the semiconductors indium gallium nitride and gallium nitride, gallium is used to produce blue and violet optoelectronic devices, mostly laser diodes and light-emitting diodes.Sony VAIO VPCCW26FX/B Battery

For example, gallium nitride 405 nm diode lasers are used as a violet light source for higher-density compact disc data storage, in the Blu-ray Discstandard.

Gallium is used as a dopant for the production of solid-state devices such as transistors. However, worldwide the actual quantity used for this purpose is minute, since dopant levels are usually of the order of a few parts per million.Sony VAIO VPCCW28EC Battery

Multijunction photovoltaic cells, developed for satellite power applications, are made by molecular beam epitaxy or metalorganic vapour phase epitaxy of thin filmsof gallium arsenide, indium gallium phosphide or indium gallium arsenide.The Mars Exploration Rovers and several satellites use triple junction gallium arsenide on germanium cells.Sony VAIO VPCCW28FJ/P Battery

Gallium is also a component in photovoltaic compounds (such as copper indium gallium selenium sulfide or Cu(In,Ga)(Se,S)2) for use in solar panels as a cost-efficient alternative to crystalline silicon.Sony VAIO VPCCW28FJ/R Battery

Wetting and alloy improvement

  • Because gallium wets glass or porcelain, gallium can be used to create brilliant mirrors. When the wetting action of gallium-alloys is not desired (as inGalinstan glass thermometers), the glass must be protected with a transparent layer of gallium(III) oxide.Sony VAIO VPCCW28FJ/W Battery
  • Gallium readily alloys with most metals, and has been used as a component in low-melting alloys. The plutonium used in nuclear weapon pits is machined by alloying with gallium to stabilize its ? phase.
  • Gallium added in quantities up to 2% in common solders can aid wetting and flow characteristics.Sony VAIO VPCCW29FJ/W Battery

Galinstan and other liquid alloys

A nearly eutectic alloy of gallium, indium, and tin is a room temperature liquid which is widely available in medical thermometers, replacing problematic mercury. This alloy, with the trade-name Galinstan (with the "-stan" referring to the tin), has a low freezing point of ?19 °C (?2.2°F).Sony VAIO VPCCW2AFJ Battery

It has been suggested that this family of alloys could also be used to cool computer chips in place of water. Much research is being devoted to gallium alloys as substitutes for mercury dental amalgams, but these compounds have yet to see wide acceptance.Sony VAIO VPCCW2AHJ Battery

Energy storage

Aluminium is reactive enough to reduce water to hydrogen, being oxidized to aluminium oxide. However, the aluminium oxide forms a protective coat which prevents further reaction. Galinstan has been applied to activate aluminium (removing the oxide coat),Sony VAIO VPCCW2S1E Battery

so that aluminium can react with water, generating hydrogen and steam in a reaction being considered as a helpful step in a hydrogen economy. A number of other gallium-aluminium alloys are also usable for the purpose of essentially acting as chemical energy store to generate hydrogen from water, on-site.Sony VAIO VPCCW2S1E/B Battery

After reaction with water the resultant aluminium oxide and gallium mixture must be reformed back into electrodes with energy input. The thermodynamic efficiency of the aluminium smelting process is estimated as 50%. Therefore, at most only half the energy that goes into smelting the aluminium could be recovered by a hydrogen fuel cell.Sony VAIO VPCCW2S1E/L Battery

Gallium(III) salts

  • Gallium nitrate (brand name Ganite) has been used as an intravenous pharmaceutical to treat hypercalcemia associated with tumor metastasis to bones. Gallium is thought to interfere with osteoclast function. It may be effective when other treatments for maligancy-associated hypercalcemia are not.Sony VAIO VPCCW2S1E/P Battery
  • Gallium maltolate, an orally-aborbable form of gallium(III) ion, is in clinical and preclinical trials as a potential treatment for a number of types of cancer, infectious disease, and inflammatory disease.
  • Research is being conducted to determine whether gallium ion can be used to fight bacterial infections in people with cystic fibrosis.Sony VAIO VPCCW2S1E/R Battery
  • Gallium is similar in size to iron, an essential nutrient for respiration. When gallium ions are mistakenly picked up by bacteria such as Pseudomonas, the bacteria's ability to respire is interfered with and the bacteria die. The mechanism behind this is that iron is redox active, which allows for the transfer of electrons during respiration, but gallium is redox inactive.Sony VAIO VPCCW2S1E/W Battery
  • In several studies, a complex amine-phenol Ga(III) compound MR045 was found to be selectively toxic to parasites that have developed resistance to chloroquine, a common drug against malaria. Both the Ga(III) complex and chloroquine act by inhibiting crystallization of hemozoin, a disposal product formed from the digestion of blood by the parasites.Sony VAIO VPCCW2S5C CN1 Battery

Radiogallium salts

Gallium-67 salts such as gallium citrate and gallium nitrate are used as radiopharmaceutical agents in a nuclear medicine imaging procedure commonly referred to as agallium scan. The form or salt of gallium is not important, since it is the free dissolved gallium ion Ga3+ which is the active radiotracer.Sony VAIO VPCF112FX/B Battery

For these applications, the radioactive isotope 67Ga is used. The body handles Ga3+ in many ways as though it were iron, and thus it is bound (and concentrates) in areas of inflammation, such as infection, and also areas of rapid cell division. This allows such sites to be imaged by nuclear scan techniques.Sony VAIO VPCF115FG/B Battery

This use has largely been replaced byfluorodeoxyglucose (FDG) for positron emission tomography, "PET" scan and indium-111 labelled leukocyte scans. However, the localization of gallium in the body has some properties which make it unique in some circumstances from competing modalities using other radioisotopes.Sony VAIO VPCF116FGBI Battery

Gallium-68, a positron emitter with a half life of 68 min., is now used as a diagnostic radionuclide in PET-CT when linked to pharmaceutical preparations such asDOTATOC, a somatostatin analogue used for neuroendocrine tumors investigation, and DOTA-TATE, a newer one, used for neuroendocrine metastasis and lung neuroendocrine cancer, such as certain typesof microcytoma.Sony VAIO VPCF117FJ/W Battery

Galium-68's preparation as a pharmaceutical is chemical and the radionuclide is extracted by elution from germanium-68, a synthetic radioisotope of germanium, in gallium-68 generators.Sony VAIO VPCF117HG/BI Battery

Other uses

  • Magnesium gallate containing impurities (such as Mn2+), is beginning to be used in ultraviolet-activated phosphor powder.
  • Neutrino detection. Possibly the largest amount of pure gallium ever collected in a single spot is the Gallium-Germanium Neutrino Telescope used by the SAGEexperiment at the Baksan Neutrino Observatory in Russia.Sony VAIO VPCF118FJ/W Battery
  • This detector contains 55–57 tonnes of liquid gallium  Another experiment was the GALLEX neutrino detector operated in the early 1990s in an Italian mountain tunnel. The detector contained 12.2 tons of watered gallium-71. Solar neutrinos caused a few atoms of Ga-71 to become radioactive Ge-71, which were detected.Sony VAIO VPCF119FC Battery
  • The solar neutrino flux deduced was found to have a deficit of 40% from theory. This was not explained until better solar neutrino detectors and theories were constructed (see SNO).
  • As alloying element in the magnetic shape memory alloy Ni-Mn-Ga.
  • In a classic prank by scientists, who fashion gallium spoons and serve tea to unsuspecting guests. The spoons melt in the hot tea.Sony VAIO VPCF119FJ/BI Battery
  • As an additive in glide wax for skiis, and other low friction surface materials. US 5069803, Sugimura, Kentaro; Shoji Hasimoto & Takayuki Ono, "Use of a synthetic resin composition containing gallium particles in the glide surfacing material of skis and other applications", issued 1995Sony VAIO VPCF11AFJ Battery

Chemistry

Gallium is found primarily in the +3 oxidation state. The +1 oxidation is also attested in some compounds, although they tend to disproportionate into elemental gallium and gallium(III) compounds. What are sometimes referred to as gallium(II) compounds are actually mixed-oxidation state compounds containing both gallium(I) and gallium(III).Sony VAIO VPCF11AGJ Battery

Chalcogen compounds

At room temperature, gallium metal is unreactive towards air and water due to the formation of a passive, protective oxide layer. At higher temperatures, however, it reacts with oxygen in the air to form gallium(III) oxide, Ga2O3.Sony VAIO VPCF11AHJ Battery

Reducing Ga2O3 with elemental gallium in vacuum at 500 °C to 700 °C yields the dark browngallium(I) oxide, Ga2O.[39]:285 Ga2O is a very strong reducing agent, capable of reducing H2SO4 to H2S.[39]:207 It disproportionates at 800 °C back to gallium andGa2O3.Sony VAIO VPCF11JFX/B Battery

Gallium sulfide, Ga2S3, has 3 possible crystal modifications.[40]:104 It can be made by the reaction of gallium with hydrogen sulfide(H2S) at 950 °C.[39]:162Alternatively, Ga(OH)3 can also be used at 747 °C:[41]

2 Ga(OH)3 + 3 H2S ? Ga2S3 + 6 H2OSony VAIO VPCF11M1E Battery

Reacting a mixture of alkali metal carbonates and Ga2O3 with H2S leads to the formation of thiogallates containing the [Ga2S4]2?anion. Strong acids decompose these salts, releasing H2S in the process. The mercury salt, HgGa2S4, can be used as a phosphor.Sony VAIO VPCF11M1E/H Battery

Gallium also forms sulfides in lower oxidation states, such as gallium(II) sulfide and the green gallium(I) sulfide, the latter of which is produced from the former by heating to 1000 °C under a stream of nitrogen.

The other binary chalcogenides, Ga2Se3 and Ga2Te3, have zincblende structure. They are all semiconductors, but are easily hydrolysed, limiting their usefulness.Sony VAIO VPCF11MFX/B Battery

Aqueous chemistry

Strong acids dissolve gallium, forming gallium(III) salts such as Ga2(SO4)3 and Ga(NO3)3. Aqueous solutions of gallium(III) salts contain the hydrated gallium ion,[Ga(H2O)6]3+.[43]:1033 Gallium(III) hydroxide, Sony VAIO VPCF11S1E Battery

Ga(OH)3, may be precipitated from gallium(III) solutions by adding ammonia. Dehydrating Ga(OH)3 at 100 °C produces gallium oxide hydroxide, GaO(OH).[39]:140–141

Alkaline hydroxide solutions dissolve gallium, forming gallate salts containing the Ga(OH)?Sony VAIO VPCF11S1E/B Battery

4 anion.[38][43]:1033[44] Gallium hydroxide, which is amphoteric, also dissolves in alkali to form gallate salts.[39]:141 Although earlier work suggested Ga(OH)3?

6 as another possible gallate anion,[45] this species was not found in later work.Sony VAIO VPCF11Z1E Battery

Pnictogen compounds

Gallium reacts with ammonia at 1050 °C to form gallium nitride, GaN. Gallium also forms binary compounds with phosphorus, arsenic, and antimony: gallium phosphide(GaP), gallium arsenide (GaAs), and gallium antimonide (GaSb).Sony VAIO VPCF11Z1E/BI Battery

These compounds have the same structure as ZnS, and have important semiconducting properties.[43]:1034GaP, GaAs, and GaSb can be synthesized by the direct reaction of gallium with elemental phosphorus, arsenic, or antimony.[40]:99 They exhibit higher electrical conductivity than GaN.Sony VAIO VPCF11ZHJ Battery

GaP can also be synthesized by the reaction of Ga2O with phosphorus at low temperatures.

Gallium also forms ternary nitrides; for example:[40]:99

Li3Ga + N2 ? Li3GaN2

Similar compounds with phosphorus and antimony also exist: Li3GaP2 and Li3GaAs2. These compounds are easily hydrolyzed by dilute acids and water.[40]:101Sony VAIO VPCF127HGBI Battery

Halides

Gallium(III) oxide reacts with fluorinating agents such as HF or F2 to form gallium(III) fluoride, GaF3. It is an ionic compound strongly insoluble in water. However, it does dissolve in hydrofluoric acid, in which it forms an adduct with water, GaF3·3H2O.Sony VAIO VPCF137HG/BI Battery

Attempting to dehydrate this adduct instead forms GaF2OH·nH2O. The adduct reacts with ammonia to form GaF3·3NH3, which can then be heated to form anhydrous GaF3.[39]:128–129

Gallium trichloride is formed by the reaction of gallium metal with chlorine gas.Sony VAIO VPCS111FM/S Battery

Unlike the trifluoride, gallium(III) chloride exists as dimeric molecules,Ga2Cl6, with a melting point of 78 °C. This is also the case for the bromide and iodide, Ga2Br6and Ga2I6.[39]:133

Like the other group 13 trihalides, gallium(III) halides are Lewis acids, reacting as halide acceptors with alkali metal halides to form salts containing GaX?Sony VAIO VPCS115EC Battery

4anions, where X is a halogen. They also react with alkyl halides to form carbocations and GaX?

4.[39]:136–137

When heated to a high temperature, gallium(III) halides react with elemental gallium to form the respective gallium(I) halides. For example, GaCl3 reacts with Ga to form GaCl:Sony VAIO VPCS115FG Battery

2 Ga + GaCl3 3 GaCl (g)

At lower temperatures, the equilibrium shifts toward the left and GaCl disproportionates back to elemental gallium and GaCl3. GaCl can also be made by the reaction of Ga with HCl at 950 °C; it can then be condensed as red solid.Sony VAIO VPCS117GG Battery

Gallium(I) compounds can be stabilized by forming adducts with Lewis acids. For example:

GaCl + AlCl3 ? Ga+[AlCl4]?

The so-called "gallium(II) halides", GaX2, are actually adducts of gallium(I) halides with the respective gallium(III) halides, having the structure Ga+[GaX4]?. For example:Sony VAIO VPCS117GGB Battery

GaCl + GaCl3 ? Ga+[GaCl4]?

Hydrogen compounds

Like aluminium, gallium also forms a hydride, GaH3, known as gallane, which may be obtained by the reaction of lithium gallanate (LiGaH4) with gallium(III) chlorideat ?30 °C:Sony VAIO VPCS118EC Battery

3 LiGaH4 + GaCl3 ? 3 LiCl + 4 GaH3

In the presence of dimethyl ether as solvent, GaH3 polymerizes to (GaH3)n. If no solvent is used, the dimer Ga2H6 (digallane) is formed as a gas. Its structure is similar to diborane, having two hydrogen atoms bridging the two gallium centers,[43]:1031 unlike ?-AlH3 in which aluminium has a coordination number of 6.Sony VAIO VPCS119FJ/B Battery

Gallane is unstable above ?10 °C, decomposing to elemental gallium and hydrogen.

Precautions

While not considered toxic, the data about gallium are inconclusive. Some sources suggest that it may cause dermatitis from prolonged exposure; other tests have not caused a positive reaction.Sony VAIO VPCS119GC Battery

Like most metals, finely divided gallium loses its luster and powdered gallium appears gray. Thus, when gallium is handled with bare hands, the extremely fine dispersion of liquid gallium droplets, which results from wetting skin with the metal, may appear as a gray skin stain.Sony VAIO VPCS11AFJ Battery

Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon.Sony VAIO VPCS11AGJ Battery

Like silicon, germanium naturally reacts and forms complexes with oxygen in nature. Unlike silicon, it is too reactive to be found naturally on Earth in the free (native) state.

Germanium was discovered comparatively late in the history of chemistry, because very few minerals contain it in high concentration.Sony VAIO VPCS11AHJ Battery

Germanium ranks near fiftieth in relative abundance of the elements in the Earth's crust. In 1869, Dmitri Mendeleevpredicted its existence and some of its properties based on its position on his periodic table and called the element eka-silicon.Sony VAIO VPCS11AVJ Battery

Nearly two decades later, in 1886, Clemens Winkler found the new element along with silver and sulfer, in a rare mineral called argyrodite. Although the new element somewhat resembled arsenic and antimony in appearance, its combining ratios in the new element's compounds agreed with Mendeleev's predictions for a predicted relative of silicon.Sony VAIO VPCS11J7E/B Battery

Winkler named the element after his country, Germany. Today, germanium is mined primarily from sphalerite (the primary ore of zinc), though germanium is also recovered commercially from silver, lead, and copper ores.

Germanium "metal" (isolated germanium) is used as semiconductor in transistors and various other electronic devices.Sony VAIO VPCS11M1E/W Battery

Historically the first several decades of semiconductor electronics were entirely based on germanium, although its production for such use today is a small fraction (2%) of that of ultra-high purity silicon, which has largely replaced it. Germanium's major end uses in the present are fiber-optic systems and infrared optics.Sony VAIO VPCS11V9E Battery

It is used in solar cellapplications. Germanium compounds are used for polymerizationcatalysts. Germanium is finding a new use in nanowires. Germanium forms a large number of organometallic compounds, such as tetraethylgermane, which are useful in chemistry.Sony VAIO VPCS11V9E/B Battery

Germanium is not thought to be an essential element for any living organism. Some complexed organic germanium compounds are being investigated as possible pharmaceuticals but none has had success. Similar to silicon and aluminum, natural germanium compounds, which tend to be insoluble in water, have little oral toxicity.Sony VAIO VPCS11X9E/B Battery

However, synthetic soluble germanium salts are nephrotoxic, and synthetic chemically-reactive germanium compounds with halogens and hydrogen, are irritants and toxins.

In his report on The Periodic Law of the Chemical Elements, in 1869, the Russian chemist Dmitri Ivanovich Mendeleev predicted the existence of several unknown chemical elements,Sony VAIO VPCS123FGB Battery

including one that would fill a gap in the carbon family in his Periodic Table of the Elements, located between silicon and tin.Because of its position in his Periodic Table, Mendeleev called it ekasilicon (Es), and he estimated its atomic weight as about 72.0.Sony VAIO VPCS125EC Battery

In mid-1885, at a mine near Freiberg, Saxony, a new mineral was found. It was named argyrodite, because of its high silver(metal) content. The chemist Clemens Winkler analyzed this new mineral, which proved to be a comination of silver, sulfer, and a new elemment.Sony VAIO VPCS128EC Battery

Winker was able to isolate this new element and found it somewhat similar to antimony, in 1886.  Before Winkler published his results on the new element, he decided that he would name his element neptunium, since the recent discovery of planet Neptune in 1846 had been preceded by mathematical predictions of its existence.?Sony VAIO VPCS129GC Battery

However, the name "neptunium" had already been given to another chemical element (though not the element that today bears the name neptunium, which was discovered in 1940), so instead, Winkler named the new element germanium (from the Latinword, Germania, for Germany) in honor of his homeland. Argyrodite proved empirically to be Ag8GeS6.Sony VAIO VPCS12C7E/B Battery

Because this new element showed some similarities with the elements arsenic and antimony, its proper place in the periodic table was under consideration, but its similarities with Dmitri Mendeleev's predicted element "ekasilicon" confirmed that it belonged in this place on the periodic table.Sony VAIO VPCS12L9E/B Battery

With further material from 500 kg of ore from the mines in Saxony, Winkler confirmed the chemical properties of the new element in 1887. He also determined an atomic weight of 72.32 by analyzing pure germanium tetrachloride (GeCl4), while Lecoq de Boisbaudran deduced 72.3 by a comparison of the lines in the spark spectrum of the element.Sony VAIO VPCS12V9E/B Battery

Winkler was able to prepare several new compounds of germanium, including its fluorides, chlorides, sulfides, germanium dioxide, and tetraethylgermane (Ge(C2H5)4), the first organogermane. The physical data from these compounds — which corresponded well with Mendeleev's predictions — made the discovery an important confirmation of Mendeleev's idea of element periodicity.Sony VAIO VPCY115FGS Battery

Until the late 1930s, germanium was thought to be a poorly conducting metal. Germanium did not become economically significant until after 1945, when its properties as a semiconductor were recognized as being very useful in electronics. However, during World War II, small amounts of germanium had begun to be used in some special electronic devices, mostlydiodes.Sony VAIO VPCY115FX/BI Battery

Its first major use was the point-contact Schottky diodes for radar pulse detection during the War. The first silicon-germaniumalloys were obtained in 1955. Before 1945, only a few hundred kilograms of germanium were produced in smelters each year, but by the end of the 1950s, the annual worldwide production had reached 40 metric tons.Sony VAIO VPCY115FXBI Battery

The development of the germanium transistor in 1948 opened the door to countless applications of solid state electronics.[22]From 1950 through the early 1970s, this area provided an increasing market for germanium, but then high-purity silicon began replacing germanium in transistors, diodes, and rectifiers.Sony VAIO VPCY118EC Battery

Silicon has superior electrical properties, but it requires far higher purity, and this purity could not be commercially achieved in the early years ofsemiconductor electronics.

Meanwhile, the demand for germanium for use in fiber optics communication networks, infrared night vision systems, andpolymerization catalysts increased dramatically.Sony VAIO VPCY118GX/BI Battery

These end uses represented 85% of worldwide germanium consumption in 2000.[23] The U.S. government even designated germanium as a strategic and critical material, calling for a 146 ton (132 t) supply in the national defense stockpile in 1987.Sony VAIO VPCY119FJ/S Battery

Germanium differs from silicon in that the supply for germanium is limited by the availability of exploitable sources, while the supply of silicon is only limited by production capacity since silicon comes from ordinary sand or quartz. As a result, while silicon could be bought in 1998 for less than $10 per kg,the price of 1 kg of germanium was then almost $800.Sony VAIO VPCY11AFJ Battery

Characteristics

Under standard conditions germanium is a brittle, silvery-white, semi-metallic element. This form constitutes anallotropetechnically known as ?-germanium, which has a metallic luster and a diamond cubic crystal structure, the same asdiamond.Sony VAIO VPCY11AGJ Battery

At pressures above 120 kbar, a different allotrope known as ?-germanium forms, which has the same structure as ?-tin.[26] Along with silicon, gallium, bismuth, antimony, and water, it is one of the few substances that expands as it solidifies (i.e. freezes) from its molten state.Sony VAIO VPCY11AHJ Battery

Germanium is a semiconductor. Zone refining techniques have led to the production of crystalline germanium for semiconductors that has an impurity of only one part in 1010, making it one of the purest materials ever obtained. The first metallic material discovered (in 2005) to become a superconductor in the presence of an extremely strongelectromagnetic field was an alloy of germanium with uranium and rhodium.Sony VAIO VPCY11AVJ Battery

Pure germanium is known to spontaneously extrude very long screw dislocations. They are one of the primary reasons for the failure of older diodes and transistors made from germanium; depending on what they eventually touch, they may lead to an electrical short.Sony VAIO VPCY11M1E/S Battery

Chemistry

Elemental germanium oxidizes slowly to GeO2 at 250 °C.[30] Germanium is insoluble in dilute acids and alkalis but dissolves slowly in concentrated sulfuric acid and reacts violently with molten alkalis to produce germanates ([GeO3]2?).Sony VAIO VPCY11S1E Battery

Germanium occurs mostly in the oxidation state +4 although many compounds are known with the oxidation state of +2. Other oxidation states are rare, such as +3 found in compounds such as Ge2Cl6, and +3 and +1 observed on the surface of oxides,[32] or negative oxidation states in germanes, such as -4 in GeH4.Sony VAIO VPCY11V9E/S Battery

Germanium cluster anions (Zintl ions) such as Ge42?, Ge94?, Ge92?, [(Ge9)2]6? have been prepared by the extraction from alloys containing alkali metals and germanium in liquid ammonia in the presence of ethylenediamine or a cryptand. The oxidation states of the element in these ions are not integers—similar to the ozonidesO3?.Sony VAIO VPCY218EC/BI Battery

Two oxides of germanium are known: germanium dioxide (GeO2, germania) and germanium monoxide, (GeO).[26] The dioxide, GeO2can be obtained by roasting germanium sulfide (GeS2), and is a white powder that is only slightly soluble in water but reacts with alkalis to form germanates.Sony VAIO VPCY218EC/G Battery

The monoxide, germanous oxide, can be obtained by the high temperature reaction of GeO2 with Ge metal.[26] The dioxide (and the related oxides and germanates) exhibits the unusual property of having a high refractive index for visible light, but transparency to infrared light. Bismuth germanate, Bi4Ge3O12, (BGO) is used as a scintillator.Sony VAIO VPCY218EC/L Battery

Binary compounds with other chalcogens are also known, such as the disulfide (GeS2), diselenide (GeSe2), and the monosulfide (GeS), selenide (GeSe), and telluride(GeTe).[31] GeS2 forms as a white precipitate when hydrogen sulfide is passed through strongly acid solutions containing Ge(IV).Sony VAIO VPCY218EC/P Battery

The disulfide is appreciably soluble in water and in solutions of caustic alkalis or alkaline sulfides. Nevertheless, it is not soluble in acidic water, which allowed Winkler to discover the element.[37] By heating the disulfide in a current of hydrogen, the monosulfide (GeS) is formed, which sublimes in thin plates of a dark color and metallic luster, and is soluble in solutions of the caustic alkalis.Sony VAIO VPCY21S1E/L Battery

Upon melting with alkaline carbonates and sulfur, germanium compounds form salts known as thiogermanates.

Four tetrahalides are known. Under normal conditions GeI4 is a solid, GeF4 a gas and the others volatile liquids. For example, germanium tetrachloride, GeCl4, is obtained as a colorless fuming liquid boiling at 83.1 °C by heating the metal with chlorine.Sony VAIO VPCY21S1E/P Battery

All the tetrahalides are readily hydrolyzed to hydrated germanium dioxide.[26] GeCl4 is used in the production of organogermanium compounds.[31] All four dihalides are known and in contrast to the tetrahalides are polymeric solids.Sony VAIO VPCY21S1E/SI Battery

Additionally Ge2Cl6 and some higher compounds of formula GenCl2n+2 are known.[26] The unusual compound Ge6Cl16 has been prepared that contains the Ge5Cl12 unit with a neopentane structure.[39]

Germane (GeH4) is a compound similar in structure to methane.Sony VAIO VPCCW2S5C CN1 Battery

Polygermanes—compounds that are similar to alkanes—with formula GenH2n+2containing up to five germanium atoms are known. The germanes are less volatile and less reactive than their corresponding silicon analogues. GeH4 reacts with alkali metals in liquid ammonia to form white crystalline MGeH3 which contain the GeH3? anion.Sony VAIO VPCEA20 Battery

The germanium hydrohalides with one, two and three halogen atoms are colorless reactive liquids.

The first organogermanium compound was synthesized by Winkler in 1887; the reaction of germanium tetrachloride withdiethylzincyielded tetraethylgermane (Ge(C2H5)4).Sony VAIO VPCEB10 Battery

Organogermanes of the type R4Ge (where R is an alkyl) such astetramethylgermane(Ge(CH3)4) and tetraethylgermane are accessed through the cheapest available germanium precursorgermanium tetrachloride and alkyl nucleophiles. Organic germanium hydrides such as isobutylgermane ((CH3)2CHCH2GeH3) were found to be less hazardous and may be used as a liquid substitute for toxic germane gas in semiconductor applications.Sony VAIO VPCEB11FM Battery

Many germanium reactive intermediates are known: germyl free radicals, germylenes (similar to carbenes), and germynes (similar to carbynes). The organogermanium compound 2-carboxyethylgermasesquioxane was first reported in the 1970s, and for a while was used as a dietary supplement and thought to possibly have anti-tumor qualities.Sony VAIO VPCEB11FM/BI Battery

Germanium has five naturally occurring isotopes, 70Ge, 72Ge, 73Ge, 74Ge, 76Ge. Of these, 76Ge is very slightly radioactive,decaying by double beta decay with a half-life of 1.78×1021 yr. 74Ge is the most common isotope, having a natural abundance of approximately 36%. 76Ge is the least common with a natural abundance of approximately 7%.Sony VAIO VPCEB11FM/T Battery

When bombarded with alpha particles, the isotope 72Ge will generate stable 77Se, releasing high energy electrons in the process.[44] Because of this, it is used in combination with radon for nuclear batteries.

At least 27 radioisotopes have also been synthesized ranging in atomic mass from 58 to 89.Sony VAIO VPCEB11FM/WI Battery

The most stable of these is 68Ge, decaying by electron capture with a half-life of 270.95 days. The least stable is 60Ge with a half-life of 30 ms. While most of germanium's radioisotopes decay by beta decay, 61Ge and 64Ge decay by ?+delayed proton emission.84Ge through 87Ge also have minor ??delayed neutron emission decay paths.Sony VAIO VPCEB11FX Battery

Natural abundance

Germanium is created through stellar nucleosynthesis, mostly by the s-process in asymptotic giant branch stars. The s-process is a slow neutron capture of lighter elements inside pulsating red giant stars. Germanium has been detected in the atmosphere of Jupiter and in some of the most distant stars.Sony VAIO VPCEB11FX/BI Battery

Its abundancein the Earth's crust is approximately 1.6 ppm. There are only a few minerals like argyrodite, briartite, germanite, and renierite that contain appreciable amounts of germanium, but no minable deposits exist for any of them. Some zinc-copper-lead ore bodies contain enough germanium that it can be extracted from the final ore concentrate.Sony VAIO VPCEB11FX/T Battery

An unusual enrichment process causes a high content of germanium in some coal seams, which was discovered by Victor Moritz Goldschmidtduring a broad survey for germanium deposits. The highest concentration ever found was in the Hartley coal ash with up to 1.6% of germanium.Sony VAIO VPCEB11FX/WI Battery

The coal deposits near Xilinhaote, Inner Mongolia, contain an estimated 1600 tonnes of germanium.

Production

Worldwide production in 2006 was roughly 100 tonnes of germanium.Sony VAIO VPCEB11GX Battery

Currently, it is recovered as a by-product from sphaleritezinc ores where it is concentrated in amounts of up to 0.3%, especially from sediment-hosted, massive Zn–Pb–Cu(–Ba) deposits and carbonate-hosted Zn–Pb deposits. Figures for worldwide Ge reserves are not available, but in the US it is estimated to be around 500 tonnes.Sony VAIO VPCEB11GX/BI Battery

In 2007 35% of the demand was met by recycled germanium.

While it is produced mainly from sphalerite, it is also found in silver, lead, and copper

 ores. Another source of germanium isfly ash of coal power plants which use coal from certain coal deposits with a large concentration of germanium. Russia and China used this as a source for germanium.Sony VAIO VPCEB11GX/T Battery

Russia's deposits are located in the far east of the country on Sakhalin Island. The coal mines northeast of Vladivostok have also been used as a germanium source.The deposits in China are mainly located in thelignite mines near Lincang, Yunnan; coal mines near Xilinhaote, Inner Mongolia are also used.Sony VAIO VPCEB11GX/WI Battery

The ore concentrates are mostly sulfidic; they are converted to the oxides by heating under air, in a process known as roasting:

GeS2 + 3 O2 ? GeO2 + 2 SO2

Part of the germanium ends up in the dust produced during this process, while the rest is converted to germanates which are leached together with the zinc from the cinder by sulfuric acid.Sony VAIO VPCEB12FX Battery

After neutralization only the zinc stays in solution and the precipitate contains the germanium and other metals. After reducing the amount of zinc in the precipitate by the Waelz process, the residing Waelz oxide is leached a second time. Thedioxide is obtained as precipitate and converted with chlorine gas or hydrochloric acid to germanium tetrachloride,Sony VAIO VPCEB12FX/BI Battery

which has a low boiling point and can be distilled off :

GeO2 + 4 HCl ? GeCl4 + 2 H2O

GeO2 + 2 Cl2 ? GeCl4 + O2

Germanium tetrachloride is either hydrolyzed to the oxide (GeO2) or purified by fractional distillation and then hydrolyzed.Sony VAIO VPCEB12FX/BIC Battery

The highly pure GeO2 is now suitable for the production of germanium glass. The pure germanium oxide is reduced by the reaction with hydrogen to obtain germanium suitable for the infrared optics or semiconductor industry:

GeO2 + 2 H2 ? Ge + 2 H2O

The germanium for steel production and other industrial processes is normally reduced using carbon:Sony VAIO VPCEB12FX/T Battery

GeO2 + C ? Ge + CO2

Applications

The major end uses for germanium in 2007, worldwide, were estimated to be: 35% for fiber-optic systems, 30% infrared optics, 15% for polymerization catalysts, and 15% for electronics and solar electric applications.[23] The remaining 5% went into other uses such as phosphors, metallurgy, and chemotherapy.Sony VAIO VPCEB14FX Battery

Optics

The most notable physical characteristics of germania (GeO2) are its high index of refraction and its low optical dispersion. These make it especially useful for wide-angle camera lenses, microscopy, and for the core part of optical fibers.Sony VAIO VPCEB14FX/BI Battery

It also replaced titania as the silica dopant for silica fiber, eliminating the need for subsequent heat treatment, which made the fibers brittle. At the end of 2002 the fiber optics industry accounted for 60% of the annual germanium use in the United States, but this use accounts for less than 10% of world wide consumption.Sony VAIO VPCEB14FX/T Battery

GeSbTe is a phase change alloy used for its optic properties, such as in rewritable DVDs.

Because germanium is transparent in the infrared it is a very important infrared optical material, that can be readily cut and polished into lenses and windows.Sony VAIO VPCEB14FX/WI Battery

It is especially used as the front optic in thermal imaging cameras working in the 8 to 14 micron wavelengthrange for passive thermal imaging and for hot-spot detection in military, night vision system in cars, and fire fighting applications. It is therefore used in infrared spectroscopes and other optical equipment which require extremely sensitive infrared detectors.Sony VAIO VPCEB15FM Battery

The material has a very high refractive index (4.0) and so needs to be anti-reflection coated. Particularly, a very hard special antireflection coating of diamond-like carbon (DLC), refractive index 2.0, is a good match and produces a diamond-hard surface that can withstand much environmental rough treatment.Sony VAIO VPCEB15FM/BI Battery

Electronics

Silicon-germanium alloys are rapidly becoming an important semiconductor material, for use in high speed integrated circuits. Circuits utilizing the properties of Si-SiGe junctions can be much faster than those using silicon alone.Sony VAIO VPCEB15FM/T Battery

Silicon-germanium is beginning to replace gallium arsenide (GaAs) in wireless communications devices. The SiGe chips, with high-speed properties, can be made with low-cost, well-established production techniques of the silicon chip industry.

The recent rise in energy cost has improved the economics of solar panels, a potential major new use of germanium.Sony VAIO VPCEB15FM/WI Battery

Germanium is the substrate of the wafers for high-efficiency multijunction photovoltaic cells for space applications.

Gallium arsenide germanium solar cell

Because germanium and gallium arsenide have very similar lattice constants, germanium substrates can be used to make gallium arsenide solar cells.Sony VAIO VPCEB15FX Battery

The Mars Exploration Rovers and several satellites use triple junction gallium arsenide on germanium cells.

Germanium-on-insulator substrates are seen as a potential replacement for silicon on miniaturized chips. Other uses in electronics include phosphors influorescent lamps, and germanium-base solid-state light-emitting diodes (LEDs).Sony VAIO VPCEB15FX/BI Battery

Germanium transistors are still used in some effects pedals by musicians who wish to reproduce the distinctive tonal character of the "fuzz"-tone from the early rock and roll era, most notably the Dallas Arbiter Fuzz Face.

Other uses

Germanium dioxide is also used in catalysts for polymerization in the production of polyethylene terephthalate (PET).Sony VAIO VPCEB15FX/T Battery

The high brilliance of the produced polyester is especially used for PET bottles marketed in Japan. However, in the United States, no germanium is used for polymerization catalysts. Due to the similarity between silica (SiO2) and germanium dioxide (GeO2), the silica stationary phase in some gas chromatography columns can be replaced by GeO2.Sony VAIO VPCEB15FX/WI Battery

In recent years germanium has seen increasing use in precious metal alloys. In sterling silver alloys, for instance, it has been found to reduce firescale, increase tarnish resistance, and increase the alloy's response to precipitation hardening. A tarnish-proof sterling silver alloy, trademarked Argentium, requires 1.2% germanium.Sony VAIO VPCEB16FX Battery

High purity germanium single crystal detectors can precisely identify radiation sources—for example in airport security.[68]Germanium is useful for monochromators for beamlines used in single crystal neutron scattering and synchrotron X-ray diffraction.Sony VAIO VPCEB16FX/B Battery

The reflectivity has advantages over silicon in neutron and high energy X-ray applications. Crystals of high purity germanium are used in detectors for gamma spectroscopy and the search for dark matter.

Dietary supplements, pharmaceutical development, and health hazard

Germanium is not thought to be essential to the health of plants or animals.Sony VAIO VPCEB16FX/G Battery

Germanium in the environment has little or no health impact because it usually occurs only as a trace element in ores and carbonaceous materials, and is used in very small quantities that are not likely to be ingested, in its various industrial and electronic applications.Sony VAIO VPCEB16FX/L Battery

For similar reasons, germanium in end-uses has little impact on the environment as a biohazard. Some reactive intermediate compounds of germanium are poisonous (see precautions, below).

As early as 1922, doctors in the United States used the inorganic form of germanium (usually the sesquioxide) to treat patients with anemia.Sony VAIO VPCEB16FX/P Battery

It was used in other forms of treatments, such as a purported immune system booster, but its efficiency has been dubious. Its role in cancer treatments has been debated, with the The American Cancer Society contending that no anticancer effects have been demonstrated.Sony VAIO VPCEB16FX/W Battery

U.S. Food and Drug Administration research has concluded that germanium, when used as a nutritional supplement, "presents potential human health hazard".

Certain germanium compounds are available in low dose in the U.S. as nonprescription dietary "supplements" in oral capsules or tablets.Sony VAIO VPCEB17FX Battery

Other germanium compounds have been administered by alternative medical practitioners as non-FDA-allowed injectable solutions. Soluble inorganic forms of germanium used at first, notably the citrate-lactate salt, led to a number of cases of renal dysfunction, hepatic steatosis and peripheral neuropathy in individuals using them on a chronic basis. Sony VAIO VPCEB17FX/B Battery

Plasma and urine germanium concentrations in these individuals, several of whom died, were several orders of magnitude greater than endogenous levels. A more recent organic form, beta-carboxyethylgermanium sesquioxide (propagermanium), has not exhibited the same spectrum of toxic effects.Sony VAIO VPCEB17FX/G Battery

Certain compounds of germanium have low toxicity to mammals, but have toxic effects against certain bacteria. However, no germanium compound has yet demonstrated a pharmaceutical use, as either an antibacterial or cancer chemotherapeutic agent.Sony VAIO VPCEB17FX/L Battery


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