Germanium is not thought to be an essential element for anyliving organism. Similar to silicon and aluminium, naturally occurring germanium compounds tend to be insoluble in water and thus have little oraltoxicity. However, synthetic soluble germanium salts arenephrotoxic, and synthetic chemically reactive germanium compounds withhalogens andhydrogen are irritants and toxins.
Prediction of germanium, "?=70" (periodic table 1869)
In his report onThe Periodic Law of the Chemical Elements in 1869, the Russian chemistDmitri Mendeleev predicted the existence of several unknown chemical elements, including one that would fill a gap in thecarbon family, located betweensilicon andtin.[13] Because of its position in his periodic table, Mendeleev called itekasilicon (Es), and he estimated itsatomic weight to be 70 (later 72).
In mid-1885, at a mine nearFreiberg, Saxony, a newmineral was discovered and namedargyrodite because of its highsilver content.[note 1] The chemistClemens 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 toantimony. He initially considered the new element to be eka-antimony, but was soon convinced that it was instead eka-silicon.[15][16] Before Winkler published his results on the new element, he decided that he would name his elementneptunium, since the recent discovery of planetNeptune in 1846 had similarly been preceded by mathematical predictions of its existence.[note 2] However, the name "neptunium" had already been given to another proposed chemical element (though not the element that today bears the nameneptunium, which was discovered in 1940).[note 3] So instead, Winkler named the new elementgermanium (from theLatin word,Germania, for Germany) in honor of his homeland.[16] Argyrodite proved empirically to be Ag8GeS6.Because this new element showed some similarities with the elementsarsenic and antimony, its proper place in the periodic table was under consideration, but its similarities with Dmitri Mendeleev's predicted element "ekasilicon" confirmed that place on the periodic table.[16][23] With further material from 500 kg of ore from the mines in Saxony, Winkler confirmed the chemical properties of the new element in 1887.[15][16][24] He also determined an atomic weight of 72.32 by analyzing puregermanium tetrachloride (GeCl 4), whileLecoq de Boisbaudran deduced 72.3 by a comparison of the lines in the sparkspectrum of the element.[25]
Winkler was able to prepare several new compounds of germanium, includingfluorides,chlorides,sulfides,dioxide, andtetraethylgermane (Ge(C2H5)4), the first organogermane.[15] The physical data from those compounds—which corresponded well with Mendeleev's predictions—made the discovery an important confirmation of Mendeleev's idea of elementperiodicity. Here is a comparison between the prediction and Winkler's data:[15]
Until the late 1930s, germanium was thought to be a poorly conductingmetal.[26] Germanium did not become economically significant until after 1945 when its properties as anelectronic semiconductor were recognized. DuringWorld War II, small amounts of germanium were used in some specialelectronic devices, mostlydiodes.[27][28] The first major use was the point-contactSchottky diodes forradar pulse detection during the War.[26] The firstsilicon–germanium alloys were obtained in 1955.[29] 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 40metric tons (44short tons).[30]
The development of the germaniumtransistor in 1948[31] opened the door to countless applications ofsolid state electronics.[32] 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, andrectifiers.[33] For example, the company that becameFairchild 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 ofsemiconductor electronics.[34]
Meanwhile, the demand for germanium forfiber optic communication networks, infrarednight vision systems, andpolymerizationcatalysts increased dramatically.[30] These end uses represented 85% of worldwide germanium consumption in 2000.[33] The US government even designated germanium as a strategic and critical material, calling for a 146 ton (132 tonne) supply in the national defense stockpile in 1987.[30]
Germanium differs from silicon in that the supply is limited by the availability of exploitable sources, while the supply of silicon is limited only by production capacity since silicon comes from ordinary sand andquartz. While silicon could be bought in 1998 for less than $10 per kg,[30] the price of germanium was almost $800 per kg.[30]
Germanium is a semiconductor having anindirect bandgap, as is crystalline silicon.Zone refining techniques have led to the production of crystalline germanium for semiconductors that has an impurity of only one part in 1010,[38]making it one of the purest materials ever obtained.[39]The first semi-metallic material discovered (in 2005) to become asuperconductor in the presence of an extremely strongelectromagnetic field was analloy of germanium, uranium, and rhodium.[40]
Pure germanium is known to spontaneously extrude very longscrew dislocations, referred to asgermanium 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 anelectrical short.[41]
Elemental germanium starts to oxidize slowly in air at around 250 °C, formingGeO2 .[42] Germanium is insoluble in diluteacids andalkalis but dissolves slowly in hot concentrated sulfuric and nitric acids and reacts violently with molten alkalis to producegermanates ([GeO 3]2− ). Germanium occurs mostly in theoxidation state +4 although many +2 compounds are known.[43] Other oxidation states are rare: +3 is found in compounds such as Ge2Cl6, and +3 and +1 are found on the surface of oxides,[44] or negative oxidation states ingermanides, such as −4 inMg 2Ge. 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 ofethylenediamine or acryptand.[43][45] The oxidation states of the element in these ions are not integers—similar to theozonides O3−.
Twooxides of germanium are known:germanium dioxide (GeO 2, germania) andgermanium monoxide, (GeO).[37] The dioxide, GeO2, can be obtained by roastinggermanium disulfide (GeS 2), and is a white powder that is only slightly soluble in water but reacts with alkalis to formgermanates.[37] The monoxide, germanous oxide, can be obtained by the high temperature reaction of GeO2 with elemental Ge.[37] The dioxide (and the related oxides and germanates) exhibits the unusual property of having a high refractive index for visible light, but transparency toinfrared light.[46][47]Bismuth germanate, Bi4Ge3O12 (BGO), is used as ascintillator.[48]
Binary compounds with otherchalcogens are also known, such as thedisulfide (GeS 2) anddiselenide (GeSe 2), and themonosulfide (GeS),monoselenide (GeSe), andmonotelluride (GeTe).[43] GeS2 forms as a white precipitate when hydrogen sulfide is passed through strongly acid solutions containing Ge(IV).[43] 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.[49] By heating the disulfide in a current ofhydrogen, 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.[37] Upon melting withalkaline carbonates andsulfur, germanium compounds form salts known as thiogermanates.[50]
Four tetrahalides are known. Under normal conditionsgermanium tetraiodide (GeI4) is a solid,germanium tetrafluoride (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.[37] All the tetrahalides are readily hydrolyzed to hydrated germanium dioxide.[37] GeCl4 is used in the production of organogermanium compounds.[43] All four dihalides are known and in contrast to the tetrahalides are polymeric solids.[43] Additionally Ge2Cl6 and some higher compounds of formula GenCl2n+2 are known.[37] The unusual compound Ge6Cl16 has been prepared that contains the Ge5Cl12 unit with aneopentane structure.[51]
Germane (GeH4) is a compound similar in structure tomethane. Polygermanes—compounds that are similar toalkanes—with formula GenH2n+2 containing up to five germanium atoms are known.[43] The germanes are less volatile and less reactive than their corresponding silicon analogues.[43] GeH4 reacts with alkali metals in liquid ammonia to form white crystalline MGeH3 which contain theGeH3−anion.[43] The germanium hydrohalides with one, two and three halogen atoms are colorless reactive liquids.[43]
Nucleophilic addition with an organogermanium compound
Using a ligand called Eind (1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl) germanium is able to form a double bond with oxygen (germanone). Germanium hydride and germanium tetrahydride are very flammable and even explosive when mixed with air.[55]
Germanium occurs in five naturalisotopes:70 Ge,72 Ge,73 Ge,74 Ge, and76 Ge. Of these,76 Ge is very slightly radioactive, undergoingdouble beta decay with ahalf-life of2.02×1021 years.[12]74 Ge is the most common isotope, having anatural abundance of 36.52% and76 Ge is the least common with a natural abundance of 7.75%.[56]
Apart from76 Ge, at least 27 otherradioisotopes have been synthesized, ranging in atomic mass from 58 to 89. The most stable of these is68 Ge, decaying byelectron capture with a half-life of270.95 d. This is followed by71 Ge, also decaying by electron capture with half-life11.468 d,[11] and the rest are all less than two days, most under two hours.[56]
Germanium's abundancein the Earth's crust is approximately 1.6 ppm.[60] Only a few minerals likeargyrodite,briartite,germanite,renierite andsphalerite contain appreciable amounts of germanium.[33][61] Only few of them (especially germanite) are, very rarely, found in mineable amounts.[62][63][64] Some zinc–copper–lead ore bodies contain enough germanium to justify extraction from the final ore concentrate.[60] An unusual natural enrichment process causes a high content of germanium in some coal seams, discovered byVictor Moritz Goldschmidt during a broad survey for germanium deposits.[65][66] The highest concentration ever found was inHartley coal ash with as much as 1.6% germanium.[65][66] The coal deposits nearXilinhaote,Inner Mongolia, contain an estimated 1600 tonnes of germanium.[60]
About 118 tonnes of germanium were produced in 2011 worldwide, mostly in China (80 t), Russia (5 t) and United States (3 t).[33] Germanium is recovered as a by-product fromsphalerite zinc ores where it is concentrated in amounts as great as 0.3%,[67] especially from low-temperature sediment-hosted, massiveZn–Pb–Cu(–Ba) deposits and carbonate-hosted Zn–Pb deposits.[68] A recent study found that at least 10,000 t of extractable germanium is contained in known zinc reserves, particularly those hosted byMississippi-Valley type deposits, while at least 112,000 t will be found in coal reserves.[69] In 2007 35% of the demand was met by recycled germanium.[60]
While it is produced mainly fromsphalerite, it is also found insilver,lead, andcopper ores. Another source of germanium isfly ash of power plants fueled from coal deposits that contain germanium. Russia and China used this as a source for germanium.[71] Russia's deposits are located in the far east ofSakhalin Island, and northeast ofVladivostok. The deposits in China are located mainly in thelignite mines nearLincang,Yunnan; coal is also mined nearXilinhaote,Inner Mongolia.[60]
The ore concentrates are mostlysulfidic; they are converted to theoxides by heating under air in a process known asroasting:
GeS2 + 3 O2 → GeO2 + 2 SO2
Some of the germanium is left in the dust produced, while the rest is converted to germanates, which are then leached (together with zinc) from the cinder by sulfuric acid. After neutralization, only the zinc stays in solution while germanium and other metals precipitate. After removing some of the zinc in the precipitate by theWaelz process, the residing Waelz oxide is leached a second time. Thedioxide is obtained as precipitate and converted withchlorine gas or hydrochloric acid togermanium tetrachloride, which has a low boiling point and can be isolated by distillation:[71]
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.[71] The highly pure GeO2 is now suitable for the production of germanium glass. It is reduced to the element by reacting it with hydrogen, producing germanium suitable for infrared optics and semiconductor production:
GeO2 + 2 H2 → Ge + 2 H2O
The germanium for steel production and other industrial processes is normally reduced using carbon:[72]
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"
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"
Worldwide, primary germanium was recovered from copper or zinc residues or from coal in Canada (concentrates shipped from the United States), China (multiple sources), Finland (concentrates from Congo Kinshasa), and Russia (lignite coal from Sakhalin)
The major global end uses for germanium were electronics and solar applications, fiber-optic systems, infrared optics, and polymerization catalysts. Other uses included chemotherapy, metallurgy, and phosphors.[91]
Because germanium is transparent in the infrared wavelengths, it is an importantinfrared optical material that can be readily cut and polished into lenses and windows. It is especially used as the front optic inthermal imaging cameras working in the 8 to 14 micron range for passive thermal imaging and for hot-spot detection in military, mobilenight vision, and fire fighting applications.[72] It is used in infraredspectroscopes and other optical equipment that require extremely sensitiveinfrared detectors.[93] It has a very highrefractive index (4.0) and must be coated with anti-reflection agents. Particularly, a very hard special antireflection coating ofdiamond-like carbon (DLC), refractive index 2.0, is a good match and produces a diamond-hard surface that can withstand much environmental abuse.[96][97]
Germanium can be alloyed withsilicon, andsilicon–germanium alloys are rapidly becoming an important semiconductor material for high-speed integrated circuits. Circuits using the properties of Si-SiGeheterojunctions can be much faster than those using silicon alone.[98] The SiGe chips, with high-speed properties, can be made with low-cost, well-established production techniques of thesilicon chip industry.[33]
High efficiencysolar panels are a major use of germanium. Because germanium andgallium arsenide have nearly identicallattice constant, germanium substrates can be used to make gallium-arsenidesolar cells.[99] Germanium is the substrate of the wafers for high-efficiencymultijunction photovoltaic cells for space applications, such as theMars Exploration Rovers, which use triple-junction gallium arsenide on germanium cells.[100] High-brightness LEDs, used for automobile headlights and to backlight LCD screens, are also an important application.[33]
Germanium-on-insulator (GeOI) substrates are seen as a potential replacement for silicon on miniaturized chips.[33] CMOS circuit based on GeOI substrates has been reported recently.[101] Other uses in electronics includephosphors influorescent lamps[38] and solid-state light-emitting diodes (LEDs).[33] Germanium transistors are still used in someeffects pedals by musicians who wish to reproduce the distinctive tonal character of the"fuzz"-tone from the earlyrock and roll era, most notably theDallas Arbiter Fuzz Face.[102]
Germanium has been studied as a potential material for implantable bioelectronic sensors that areresorbed in the body without generating harmful hydrogen gas, replacingzinc oxide- andindium gallium zinc oxide-based implementations.[103]
Germanium was also used to create many of the circuits found in some of the very first pieces of electronic musical gear, initially 1950s, primarily in early transistor-based circuits. The first guitar effects pedals in the 1960s – Fuzz pedals like the Maestro FZ-1 (1962), Dallas-Arbiter Fuzz Face (1966), and Tone Bender (1965) - used germanium transistors.[104] Silicon diodes are more frequently used in more modern equipment, but germanium diodes are still used in some applications as they have lower barrier potential and smoothertransconductance curves, leading to less harshclipping.[105]
Germanium dioxide is also used incatalysts forpolymerization in the production ofpolyethylene terephthalate (PET).[106] The high brilliance of this polyester is especially favored for PET bottles marketed in Japan.[106] In the United States, germanium is not used for polymerization catalysts.[33]
Due to the similarity between silica (SiO2) and germanium dioxide (GeO2), the silica stationary phase in somegas chromatography columns can be replaced by GeO2.[107]
In recent years germanium has seen increasing use in precious metal alloys. Insterling silver alloys, for instance, it reducesfirescale, increases tarnish resistance, and improves precipitation hardening. A tarnish-proof silver alloy trademarkedArgentium contains 1.2% germanium.[33]
Germanium is emerging as an important material forspintronics and spin-basedquantum computing applications. In 2010, researchers demonstrated room temperature spin transport[112] and more recently donor electron spins in germanium has been shown to have very longcoherence times.[113]
Germanium is not considered essential to the health of plants or animals.[114] Germanium in the environment has little or no health impact. This is primarily because it usually occurs only as a trace element in ores andcarbonaceous materials, and the various industrial and electronic applications involve very small quantities that are not likely to be ingested.[33] For similar reasons, end-use germanium has little impact on the environment as a biohazard. Some reactive intermediate compounds of germanium are poisonous (see precautions, below).[115]
Some 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, resulted in some cases ofrenal dysfunction,hepatic steatosis, and peripheralneuropathy in individuals using them over a long term. Plasma and urine germanium concentrations in these individuals, several of whom died, were several orders of magnitude greater thanendogenous levels. A more recent organic form, beta-carboxyethylgermanium sesquioxide (propagermanium), has not exhibited the same spectrum of toxic effects.[116]
Certain compounds of germanium have low toxicity tomammals, but have toxic effects against certainbacteria.[35]
Precautions for chemically reactive germanium compounds
While use of germanium itself does not require precautions, some of germanium's artificially produced compounds are quite reactive and present an immediate hazard to human health on exposure. For example,Germanium tetrachloride andgermane (GeH4) are a liquid and gas, respectively, that can be very irritating to the eyes, skin, lungs, and throat.[117]
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