Germanium

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). 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, dioxide, and tetraethylgermane (Ge(C2H5)4), 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. These end uses represented 85% of worldwide germanium consumption in 2000. 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. 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 and quartz. While silicon could be bought in 1998 for less than $10 per kg, the price of germanium was almost $800 per kg. == Characteristics ==

Under standard conditions, germanium is a brittle, silvery-white, 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 GeO2 . 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 Ge2Cl6, 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 O3−. Two oxides of germanium are known: germanium dioxide (, germania) and germanium monoxide, (). The dioxide, GeO2, 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, Bi4Ge3O12 (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. .|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 (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. Germane (GeH4) is a compound similar in structure to methane. Polygermanes—compounds that are similar to alkanes—with formula GenH2n+2 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. 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. The coal deposits near Xilinhaote, Inner Mongolia, contain an estimated 1600 tonnes of germanium. == Production ==

About 118 tonnes of germanium were produced in 2011 worldwide, mostly in China (80 t), Russia (5 t) and United States (3 t). 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. 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. : GeO2 + C → Ge + CO2 Production by country World refinery production of germanium (germanium content). == Applications ==

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. Optics of the core silica (Item 1). The notable properties 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 the core part of optical fibers. It has replaced titania as the dopant for silica fiber, eliminating the subsequent heat treatment that made the fibers brittle. At the end of 2002, the fiber optics industry consumed 60% of the annual germanium use in the United States, but this is less than 10% of worldwide consumption. Because germanium is transparent in the infrared wavelengths, it is an important infrared optical material that can be readily cut and polished into lenses and windows. It is especially used as the front optic in thermal imaging cameras working in the 8 to 14 micron range for passive thermal imaging and for hot-spot detection in military, mobile night vision, and fire fighting applications. Electronics Germanium can be alloyed with silicon, and silicon–germanium alloys are rapidly becoming an important semiconductor material for high-speed integrated circuits. Circuits using the properties of Si-SiGe heterojunctions can be much faster than those using silicon alone. The SiGe chips, with high-speed properties, can be made with low-cost, well-established production techniques of the silicon chip industry. Germanium is the substrate of the wafers for high-efficiency multijunction photovoltaic cells for space applications, such as the Mars Exploration Rovers, which use triple-junction gallium arsenide on germanium cells. High-brightness LEDs, used for automobile headlights and to backlight LCD screens, are also an important application. Other uses in electronics include phosphors in fluorescent lamps Germanium has been studied as a potential material for implantable bioelectronic sensors that are resorbed in the body without generating harmful hydrogen gas, replacing zinc oxide- and indium gallium zinc oxide-based implementations. 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. 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 smoother transconductance curves, leading to less harsh clipping. Other uses bottle|alt=Photo of a standard transparent plastic bottle. Germanium dioxide is also used in catalysts for polymerization in the production of polyethylene terephthalate (PET). The high brilliance of this polyester is especially favored for PET bottles marketed in Japan. In recent years germanium has seen increasing use in precious metal alloys. In sterling silver alloys, for instance, it reduces firescale, increases tarnish resistance, and improves precipitation hardening. A tarnish-proof silver alloy trademarked Argentium contains 1.2% germanium. Germanium is useful for monochromators for beamlines used in single crystal neutron scattering and synchrotron X-ray diffraction. 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. Germanium crystals are also used in X-ray spectrometers for the determination of phosphorus, chlorine and sulfur. Germanium is emerging as an important material for spintronics and spin-based quantum computing applications. In 2010, researchers demonstrated room temperature spin transport and more recently donor electron spins in germanium has been shown to have very long coherence times. == Germanium and health ==

Germanium is not considered essential to the health of plants or animals. Germanium supplements, made from both organic and inorganic germanium, have been marketed as an alternative medicine capable of treating leukemia and lung cancer. U.S. Food and Drug Administration (FDA) research has concluded that inorganic germanium, when used as a nutritional supplement, "presents potential human health hazard". 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 of renal dysfunction, hepatic steatosis, and peripheral neuropathy 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 than endogenous levels. A more recent organic form, beta-carboxyethylgermanium sesquioxide (propagermanium), has not exhibited the same spectrum of toxic effects. Certain compounds of germanium have low toxicity to mammals, but have toxic effects against certain bacteria. 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 and germane (GeH4) are a liquid and gas, respectively, that can be very irritating to the eyes, skin, lungs, and throat. == See also ==