Germanium is a chemical element; it has symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid (sometimes considered a nonmetal) in the carbon group that is chemically similar to silicon. Like silicon, germanium naturally reacts and forms complexes with oxygen in nature.
Because it seldom appears in high concentration, germanium was found comparatively late in the discovery of the elements. Germanium ranks 50th in abundance of the elements in the Earth's crust. In 1869, Dmitri Mendeleev predicted its existence and some of its properties from its position on his periodic table, and called the element ekasilicon. On February 6, 1886, Clemens Winkler at Freiberg University found the new element, along with silver and sulfur, in the mineral argyrodite. Winkler named the element after Germany, his country of birth. Germanium is mined primarily from sphalerite (the primary ore of zinc), though germanium is also recovered commercially from silver, lead, and copper ores.
Elemental germanium is used as a semiconductor in transistors and various other electronic devices. Historically, the first decade of semiconductor electronics was based entirely on germanium. Presently, the major end uses are fibre-optic systems, infrared optics, solar cell applications, and light-emitting diodes (LEDs). Germanium compounds are also used for polymerization catalysts and have most recently found use in the production of nanowires. This element forms a large number of organogermanium compounds, such as tetraethylgermanium, useful in organometallic chemistry.
Germanium is not thought to be an essential element for any living organism. Similar to silicon and aluminium, naturally occurring germanium compounds tend to be insoluble in water and thus have little oral toxicity. However, synthetic soluble germanium salts are nephrotoxic, and synthetic chemically reactive germanium compounds with halogens and hydrogen are irritants and toxins.
History
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thumb|[[Clemens Winkler|alt=Photo of a bust of a middle-aged man in a suit with a white short beard and gray moustache.]] THESE PHOTOS are hard to arrange due to the infobox; they are not essential for Germanium-->
upright|left|thumb |Prediction of germanium, "?=70" (periodic table 1869)
In his report on The Periodic Law of the Chemical Elements in 1869, the Russian chemist Dmitri Mendeleev predicted the existence of several unknown chemical elements, including one that would fill a gap in the carbon family, located between silicon and tin. Because of its position in his periodic table, Mendeleev called it ekasilicon (Es), and he estimated its atomic weight to be 70 (later 72).<!-- Mendeleev studied several minerals in an unsuccessful search for this new element. -->
<!-- thumb|left|Samples of germanium compounds prepared by Freiberg University's [[Clemens Winkler, discoverer of the element]] -->In mid-1885, at a mine near Freiberg, Saxony, a new mineral was discovered and named argyrodite because of its high silver content. The chemist Clemens Winkler analyzed this new mineral, which proved to be a combination of silver, sulfur, and a new element. Winkler was able to isolate the new element in 1886 and found it similar to antimony. He initially considered the new element to be eka-antimony, but was soon convinced that it was instead eka-silicon. 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 similarly been preceded by mathematical predictions of its existence. However, the name "neptunium" had already been given to another proposed 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 Latin word, Germania, for Germany) in honor of his homeland. 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 (), while Lecoq de Boisbaudran deduced 72.3 by a comparison of the lines in the spark spectrum of the element.
Winkler was able to prepare several new compounds of germanium, including fluorides, chlorides, sulfides<!--intentional link to DAB page-->, dioxide, and tetraethylgermane (Ge(C<sub>2</sub>H<sub>5</sub>)<sub>4</sub>), the first organogermane. Germanium did not become economically significant until after 1945 when its properties as an electronic semiconductor were recognized. During World War II, small amounts of germanium were used in some special electronic devices, mostly diodes. The first major use was the point-contact Schottky diodes for radar pulse detection during the War. 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 .
The development of the germanium transistor in 1948 opened the door to countless applications of solid state electronics. 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. For example, the company that became Fairchild Semiconductor was founded in 1957 with the express purpose of producing silicon transistors. Silicon has superior electrical properties, but it requires much greater purity that could not be commercially achieved in the early years of semiconductor electronics.
Meanwhile, the demand for germanium for fiber optic communication networks, infrared night vision systems, and polymerization catalysts increased dramatically. At pressures above 120 kbar, germanium becomes the metallic allotrope β-germanium with the same structure as β-tin.
making it one of the purest materials ever obtained.
The first semi-metallic material discovered (in 2005) to become a superconductor in the presence of an extremely strong electromagnetic field was an alloy of germanium, uranium, and rhodium.
Pure germanium is known to spontaneously extrude very long screw dislocations, referred to as germanium whiskers. The growth of these whiskers is one of the primary reasons for the failure of older diodes and transistors made from germanium, as, depending on what they eventually touch, they may lead to an electrical short.
Chemistry
Elemental germanium starts to oxidize slowly in air at around 250 °C, forming GeO<sub>2</sub> . Germanium is insoluble in dilute acids and alkalis but dissolves slowly in hot concentrated sulfuric and nitric acids and reacts violently with molten alkalis to produce germanates (). Germanium occurs mostly in the oxidation state +4 although many +2 compounds are known. Other oxidation states are rare: +3 is found in compounds such as Ge<sub>2</sub>Cl<sub>6</sub>, and +3 and +1 are found on the surface of oxides, or negative oxidation states in germanides, such as −4 in . Germanium cluster anions (Zintl ions) such as , , , 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 ozonides O<sub>3</sub><sup>−</sup>.
Two oxides of germanium are known: germanium dioxide (, germania) and germanium monoxide, (). The dioxide, GeO<sub>2</sub>, can be obtained by roasting germanium disulfide (), and is a white powder that is only slightly soluble in water but reacts with alkalis to form germanates. Bismuth germanate, Bi<sub>4</sub>Ge<sub>3</sub>O<sub>12</sub> (BGO), is used as a scintillator.
Binary compounds with other chalcogens are also known, such as the disulfide () and diselenide (), and the monosulfide (GeS), monoselenide (GeSe), and monotelluride (GeTe). 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.
class=skin-invert-image|upright|left|thumb|Germane is similar to [[methane.|alt=Skeletal chemical structure of a tetrahedral molecule with germanium atom in its center bonded to four hydrogen atoms. The Ge–H distance is 152.51 picometers.]]
Four tetrahalides are known. Under normal conditions germanium tetraiodide (GeI<sub>4</sub>) is a solid, germanium tetrafluoride (GeF<sub>4</sub>) a gas and the others volatile liquids. For example, germanium tetrachloride, GeCl<sub>4</sub>, is obtained as a colorless fuming liquid boiling at 83.1 °C by heating the metal with chlorine.
Germane (GeH<sub>4</sub>) is a compound similar in structure to methane. Polygermanes—compounds that are similar to alkanes—with formula Ge<sub>n</sub>H<sub>2n+2</sub> containing up to five germanium atoms are known. 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.
Isotopes
Germanium occurs in five natural isotopes: , , , , and . Of these, is very slightly radioactive, undergoing double beta decay with a half-life of .
Apart from , at least 27 other radioisotopes have been synthesized, ranging in atomic mass from 58 to 89. The most stable of these is , decaying by electron capture with a half-life of . This is followed by , also decaying by electron capture with half-life , Germanium has been detected in some of the most distant stars and in the atmosphere of Jupiter.
Germanium's abundance in the Earth's crust is approximately 1.6 ppm. Only a few minerals like argyrodite, briartite, germanite, renierite and sphalerite contain appreciable amounts of germanium. Only few of them (especially germanite) are, very rarely, found in mineable amounts.<!--Ore found in the Pend Orielle Mine near Detroit has exceptionally high amounts of germanium.--> Some zinc–copper–lead ore bodies contain enough germanium to justify extraction from the final ore concentrate. The highest concentration ever found was in Hartley coal ash with as much as 1.6% germanium. especially from low-temperature sediment-hosted, massive Zn–Pb–Cu(–Ba) deposits and carbonate-hosted Zn–Pb deposits. A recent study found that at least 10,000 t of extractable germanium is contained in known zinc reserves, particularly those hosted by Mississippi-Valley type deposits, while at least 112,000 t will be found in coal reserves. In 2007 35% of the demand was met by recycled germanium.
|-
|1999 || 1,400
|-
|2000 || 1,250
|-
|2001 || 890
|-
|2002 || 620
|-
|2003 || 380
|-
|2004 || 600
|-
|2005 || 660
|-
|2006 || 880
|-
|2007 || 1,240
|-
|2008 || 1,490
|-
|2009 || 950
|-
|2010 || 940
|-
|2011 || 1,625
|-
|2012 || 1,680
|-
|2013 || 1,875
|-
|2014 || 1,900
|-
|2015 || 1,760
|-
|2016 || 950
|-
|2017 || 1,358
|-
|2018 || 1,300
|-
|2019 || 1,240
|-
|2020 || 1,000
|}
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While it is produced mainly from sphalerite, it is also found in silver, lead, and copper ores. Another source of germanium is fly ash of power plants fueled from coal deposits that contain germanium. Russia and China used this as a source for germanium. Russia's deposits are located in the far east of Sakhalin Island, and northeast of Vladivostok. The deposits in China are located mainly in the lignite mines near Lincang, Yunnan; coal is also mined near Xilinhaote, Inner Mongolia.
: GeO<sub>2</sub> + C → Ge + CO<sub>2</sub>
Production by country
World refinery production of germanium (germanium content).
{| class="wikitable"
|+ World refinery production / total supply (USGS), with country groups where available
! Year !! China (t) !! Canada (t) !! Russia (t) !! Other (t) !! U.S. refinery (t) !! World total (t) !! Comment !! Source
|-
| 1970 || || || || || ~15 || ~85 || ||
|-
| 1980 || || || 14 || || 27 || ~115 || USSR 14 (est.), Japan 13 t, France 10, Austria 5. Significant recovery also believed in Belgium, China, FRG, Italy. ||
|-
| 1999 || || || || || 20 || 91 || World total market supply (58 t primary refinery + 25 t recycling + 8 t stock releases) ||
|-
| 2000 || || || || || 23 || 105 || World total market supply (slightly >70 t primary refinery + 25 t recycling + 9 t stock releases) ||
|-
| 2001 || || || || || 20 || 110 || World total market supply (~<70 t primary refinery + 30 t recycling + 12 t stock releases) ||
|-
| 2002 || || || || || 12 || 80 || World total market supply (50 t primary refinery + 30 t recycling) ||
|-
| 2003 || || || || || 12 || 80 || World total market supply (50 t primary refinery + 30 t recycling) - "Starting in 2001, there had been a growing surplus of germanium owing to a major downturn in the fiber optics market. By yearend 2003, supply and demand were in close balance" ||
|-
| 2004 || || || || || 4.4 || 87 || World total market supply (50 t primary refinery + 30 t recycling + 7 t stock releases) ||
|-
| 2006 || || || || || 4.6 || 100 || World total market supply (including 35 t recycling). "In 2006, production decreased, while consumption strongly rose, resulting in a deficit. Prices of germanium metal and germanium dioxide in 2007 had increased to record levels" ||
|-
| 2007 || || || || || 4.6 || 145 || Including 6,902 kg released from the NDS. The recycling supplied about 30% of the world's total ||
|-
| 2008 || ~100 || ~27 || ~5 || ~2 || 4.6 || ~140 || Worldwide, the vast majority of germanium production was concentrated in Canada and China ||
|}