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GALLIUM ORES

Gallium (pronounced ɡæliəm/, GAL-ee-əm) 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. 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 (−2.2 °F).
Detailed description
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) and diode lasers. 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 salt gallium(III) as though it were iron(III), 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.
Notable characteristics
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 percent when it solidifies, and therefore storage in either glass or metal containers is avoided, due to the possibility of container rupture with freezing. Gallium shares the higher-density liquid state with only a few materials like silicon, germanium, bismuth, antimony and water.
History
Gallium (the Latin Gallia means "Gaul", essentially modern France) was discovered spectroscopically by Paul Emile Lecoq de Boisbaudran in 1875 by its characteristic spectrum (two violet lines) in an examination of a zinc blende from the Pyrenees.[9] Before its discovery, most of its properties had been predicted and described by Dmitri Mendeleev (who had called the hypothetical element "eka-aluminium" on the basis of its position in his periodic table). Later, in 1875, Lecoq obtained the free metal by electrolysis of its hydroxide in potassium hydroxide solution. He named the element "gallia" after his native land of France. It was later claimed that, in one of those multilingual puns so beloved of men of science in the early 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.[10] (The supposition was also noted in Building Blocks of the Universe, a book on the elements by Isaac Asimov; cf. the naming of the J/ψ meson.)
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. The amount extracted from coal, diaspore and 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.[12][13] Some flue dusts from burning coal have been shown to contain small quantities of gallium, typically less than 1% by weight.[14][15][16][17]
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. Most gallium is extracted from the crude aluminium hydroxide solution of the Bayer process for producing alumina and aluminium. A mercury cell electrolysis and hydrolysis of the amalgam with sodium hydroxide leads to sodium gallate. Electrolysis then gives gallium metal. For semiconductor use, further purification is carried out using zone melting, or else single crystal extraction from a melt (Czochralski process). Purities of 99.9999% are routinely achieved and commercially widely available.[18] 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.[12]
Applications
Semiconductors
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. 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.[12] World wide gallium arsenide makes up 95% of the annual global gallium consumption.[18]
Gallium arsenide is used in optoelectronics in a variety of infrared applications. Aluminum 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. 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 Disc standard.[19]
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).[24] It has been suggested that this family of alloys could also be used to cool computer chips in place of water.[25] Much research is being devoted to gallium alloys as substitutes for mercury dental amalgams, but these compounds have yet to see wide acceptance.
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 aluminum (removing the oxide coat), so that aluminum can react with water, generating hydrogen and steam in a reaction being considered as a helpful step in a hydrogen economy.[26] A number of other gallium-alluminum alloys are also usable for the purpose of essentially acting as chemical energy store to generate hydrogen from water, on-site.
After reaction with water the resultant aluminium oxide and gallium mixture might be reformed back into electrodes with energy input.[26][27] The thermodynamic efficiency of the aluminium smelting process is estimated as 50%.[28] Therefore, at most half the energy that goes into smelting the aluminium could be recovered by a hydrogen fuel cell.
Biomedical applications
As 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.[29]
  • Gallium maltolate is in clinical and preclinical trials as a potential treatment for cancer, infectious disease, and inflammatory disease.[30]
  • Research is being conducted to determine whether gallium can be used to fight bacterial infections in people with cystic fibrosis. Gallium is similar in size to iron, an essential nutrient for respiration. When gallium is 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.[31][32]
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 SAGE experiment at the Baksan Neutrino Observatory in Russia. This detector contains 55-57 tonnes of liquid gallium.[33] 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. The solar neutrino flux deduced was found to have a deficit of 40% from theory. 
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).[35]
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. 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.


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