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= Germanium =
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Introduction
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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 in the carbon group that is
chemically similar to its group neighbors silicon and tin. 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 his country of
birth, Germany. 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
considered a technology-critical element.
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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In mid-1885, at a mine near Freiberg, Saxony, a new mineral was
discovered and named 'argyrodite' because of its high silver
content.{{NoteTag|From Greek, 'argyrodite' means
'silver-containing'.}} 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.
Argyrodite proved empirically to be Ag8GeS6.
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 place on the periodic table. 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. The physical
data from those compounds—which corresponded well with Mendeleev's
predictions—made the discovery an important confirmation of
Mendeleev's idea of element periodicity. Here is a comparison between
the prediction and Winkler's data:
Property !! Ekasilicon !! Germanium
atomic mass 72.64 72.63
density (g/cm3) 5.5 5.35
melting point (°C) high 947
color gray gray
oxide type refractory dioxide refractory dioxide
oxide density (g/cm3) 4.7 4.7
oxide activity feebly basic feebly basic
chloride boiling point (°C) under 100 86 (GeCl4)
chloride density (g/cm3) 1.9 1.9
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 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. The first silicon-germanium alloys 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 MT.
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
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Under standard conditions, germanium is a brittle, silvery-white,
semi-metallic element. This form constitutes an allotrope known as
'α-germanium', which has a metallic luster and a diamond cubic crystal
structure, the same as diamond. While in crystal form, germanium has a
displacement threshold energy of . At pressures above 120 kbar,
germanium becomes the allotrope 'β-germanium' with the same structure
as β-tin. Like silicon, gallium, bismuth, antimony, and water,
germanium is one of the few substances that expands as it solidifies
(i.e. freezes) from the molten state.
Germanium is a semiconductor having an indirect 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,
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 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 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. The
monoxide, germanous oxide, can be obtained by the high temperature
reaction of GeO2 with elemental Ge. 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.
Binary compounds with other chalcogens are also known, such as the
disulfide () and diselenide (), and the monosulfide (GeS),
monoselenide (GeSe), and monotelluride (GeTe). GeS2 forms as a white
precipitate when hydrogen sulfide is passed through strongly acid
solutions containing Ge(IV). 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. 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. 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. All the tetrahalides
are readily hydrolyzed to hydrated germanium dioxide. GeCl4 is used in
the production of organogermanium compounds. All four dihalides are
known and in contrast to the tetrahalides are polymeric solids.
Additionally Ge2Cl6 and some higher compounds of formula Ge'n'Cl2'n'+2
are known. The unusual compound Ge6Cl16 has been prepared that
contains the Ge5Cl12 unit with a neopentane structure.
Germane (GeH4) is a compound similar in structure to methane.
Polygermanes—compounds that are similar to alkanes—with formula
Ge'n'H2'n'+2 containing 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. 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 with diethylzinc yielded
tetraethylgermane (). Organogermanes of the type R4Ge (where R is an
alkyl) such as tetramethylgermane () and tetraethylgermane are
accessed through the cheapest available germanium precursor germanium
tetrachloride and alkyl nucleophiles. Organic germanium hydrides such
as isobutylgermane () were found to be less hazardous and may be used
as a liquid substitute for toxic germane gas in semiconductor
applications. 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.
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.
Isotopes
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Germanium occurs in five natural isotopes: , , , , and . Of these, is
very slightly radioactive, decaying by double beta decay with a
half-life of . is the most common isotope, having a natural abundance
of approximately 36%. is the least common with a natural abundance of
approximately 7%. When bombarded with alpha particles, the isotope
will generate stable , releasing high energy electrons in the process.
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. The most stable of these is , decaying by
electron capture with a half-life of ays. The least stable is , with a
half-life of . While most of germanium's radioisotopes decay by beta
decay, and decay by Positron emission delayed proton emission.
through isotopes also exhibit minor Beta decay delayed neutron
emission decay paths.
Occurrence
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Germanium is created by 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 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. An unusual natural
enrichment process causes a high content of germanium in some coal
seams, discovered by Victor Moritz Goldschmidt during a broad survey
for germanium deposits. 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
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About 118 tonnes of germanium were produced in 2011 worldwide, mostly
in China (80 t), Russia (5 t) and United States (3 t). Germanium is
recovered as a by-product from sphalerite zinc ores where it is
concentrated in amounts as great as 0.3%, 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.
!Year !! Cost ($/kg)
|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
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.
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
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 the Waelz process, the
residing Waelz oxide is leached a second time. The dioxide is obtained
as precipitate and converted with chlorine gas or hydrochloric acid to
germanium tetrachloride, which has a low boiling point and can be
isolated by distillation:
: 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. 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:
: GeO2 + C → Ge + CO2
Applications
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The major end uses for germanium in 2007, worldwide, were estimated to
be: 35% for fiber-optics, 30% infrared optics, 15% polymerization
catalysts, and 15% electronics and solar electric applications. The
remaining 5% went into such uses as phosphors, metallurgy, and
chemotherapy.
Optics
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|Core 8 µm
|Cladding 125 µm
|Buffer 250 µm
|Jacket 400 µm
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. GeSbTe is a phase change material used
for its optic properties, such as that used in rewritable DVDs.
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. It is used in
infrared spectroscopes and other optical equipment that require
extremely sensitive infrared detectors. It has a very high refractive
index (4.0) and must be coated with anti-reflection agents.
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
abuse.
Electronics
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Germanium can be alloyed with silicon, and silicon-germanium alloys
are rapidly becoming an important semiconductor material for
high-speed integrated circuits. Circuits utilizing 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.
High efficiency solar panels are a major use of germanium. Because
germanium and gallium arsenide have nearly identical lattice constant,
germanium substrates can be used to make gallium-arsenide solar cells.
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.
Germanium-on-insulator (GeOI) substrates are seen as a potential
replacement for silicon on miniaturized chips. CMOS circuit based on
GeOI substrates has been reported recently. Other uses in electronics
include phosphors in fluorescent lamps and solid-state light-emitting
diodes (LEDs). 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.
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.
Other uses
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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 the United States, germanium is not 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.
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.
Semiconductor detectors made of single crystal high-purity germanium
can precisely identify radiation sources—for example in airport
security. 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.
Strategic importance
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Due to its use in advanced electronics and optics, Germanium is
considered a technology-critical element (by e.g. the European Union),
essential to fulfill the green and digital transition. As China
controls 60% of global Germanium production it holds a dominant
position over the world's supply chains.
On 3 July 2023 China suddenly imposed restrictions on the exports of
germanium (and gallium), ratcheting up trade tensions with Western
allies. Invoking "national security interests," the Chinese Ministry
of Commerce informed that companies that intend to sell products
containing germanium would need an export licence. The
products/compounds targeted are: germanium dioxide, germanium
epitaxial growth substrate, germanium ingot, germanium metal,
germanium tetrachloride and zinc germanium phosphide. It sees such
products as "dual-use" items that may have military purposes and
therefore warrant an extra layer of oversight.
The new dispute opened a new chapter in the increasingly fierce
technology race that has pitted the United States, and to a lesser
extent Europe, against China. The US wants its allies to heavily curb,
or downright prohibit, advanced electronic components bound to the
Chinese market in order to prevent Beijing from securing global
technology supremacy. China denied any tit-for-tat intention behind
the Germanium export restrictions.
Following China's export restrictions, Russian state-owned company
Rostec announced an increase in germanium production to meet domestic
demand.
Germanium and health
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Germanium is not considered essential to the health of plants or
animals. Germanium in the environment has little or no health impact.
This is primarily because it usually occurs only as a trace element in
ores and carbonaceous materials, and the various industrial and
electronic applications involve very small quantities that are not
likely to be ingested. 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).
Germanium supplements, made from both organic and inorganic germanium,
have been marketed as an alternative medicine capable of treating
leukemia and lung cancer. There is, however, no medical evidence of
benefit; some evidence suggests that such supplements are actively
harmful. 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
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* Germanene
* Vitrain
* History of the transistor
External links
======================================================================
* [
http://www.periodicvideos.com/videos/032.htm Germanium] at 'The
Periodic Table of Videos' (University of Nottingham)
License
=========
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Original Article:
http://en.wikipedia.org/wiki/Germanium
