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ژرمانیوم سی و دومین عنصر جدول تناوبی است. ژرمانیوم یکی از اعضای مهم خانواده نیمهرساناها میباشد و در صنعت نیمههادی کاربرد فراوان دارد. نام این عنصر لاتین واژه ژرمن (آلمان) است.
ژرمانیم عنصر شیمیایی است که با نشان Ge و عدد اتمی ۳۲ در جدول تناوبی وجود دارد. ژرمانیم شبه فلزی است سخت، درخشان، به رنگ سفیدخاکستری که از نظر شیمیایی شبیه قلع میباشد. این عنصر تعداد بسیار زیادی از ترکیبات آلی – فلزی را تشکیل داده و ماده نیمه هادی مهمی در ترانزیستورها و نورسنجها به حساب میآید.
ژرمانیم عنصری سخت و به رنگ سفید مایل به خاکستری است که دارای درخشش فلزی و ساختار بلوری همانند الماس میباشد. توجه به این نکته ضروری است که ژرمانیم یک نیمه هادی با ویژگیهای الکتریکی بین فلز و عایق میباشد. نوع خالص این شبه فلز، بلورین و شکننده بوده و در دمای اتاق درخشش خود در هوا را حفظ میکند. روشهای تصفیه منطقهای باعث تولید ژرمانیم بلورین برای نیمه هادیها گشته که فقط دارای یک جز در ۱۰۱۰ ناخالصی هستند.
خاصیت اکاسیلیکون ژرمانیوم، جرم اتمی ۷2 (72.59) چگالی 5.35 (g/cm3) نقطه جوش(°C) بالا ۹۴۷ و دارای رنگ خاکستری میباشد.
ژرمانیم (از واژه لاتین Germania به معنی آلمان) یکی از عناصری بود که Dmitri Mendeleev در سال ۱۸۷۱ وجود آن را به عنوان یک آنالوگ گم شده گروه سیلیکون پیشبینی کرده بود (مندلیف آن را "ekasilicon " نامید). وجود این عنصر را Clemens Winkler در سال ۱۸۸۶ اثبات نمود. این کشف تاییدیه مهمی برای نظریه مندلیف در مورد وضعیت تناوبی عناصر بود.
ساخت ترانزیستورهای ژرمانیم مقدمه استفادههای بی شمار از علم الکترونیک solid-state گشت.
از سال ۱۹۵۰ تا اوایل دهه ۸۰ این حوزه بازار روزافزونی برای ژرمانیم بوجود آورد اما بعد از آن سیلیکون خالص کمکم در ترانزیستورها، دیودها و یکسو کنندهها جایگزین ژرمانیم شد. سیلیکون خصوصیات الکتریکی برتری دارد اما نمونههای بسیار خالص تری نیاز دارد- درجه خلوصی که در روزهای اولیه بصورت تجاری قابل دستیابی نبود- درحالیکه نیاز به ژرمانیم در شبکههای ارتباطی فیبر نوری، سیستمهای مادون قرمز دید در شب و کاتالیزورهای پلیمریزاسیون شدیداً افزایش یافت. این کاربردهای نهایی، ۸۵٪ مصرف جهانی ژرمانیم را در سال ۲۰۰۰ تشکیل میدهد.
این فلز در کانیهای آرژیرودیت یا سیم سنگ (سولفید ژرمانیم و نقره)، زغال سنگ، ژرمانیت، روی و کانیهای دیگر یافت میشود. ژرمانیم بصورت تجاری از پردازش سنگ معدن مذاب روی و از سوختن محصولات جانبی زغال سنگهای خاصی بدست میآید؛ بنابراین اندوخته زیادی از این عنصر در منابع زغال سنگ وجود دارند.
این شبه فلز را میتوان بوسیله تقطیر جزئی تتراکلرید فرار آن از فلزات دیگر نیز تهیه نمود. این روش باعث تولید ژرمانیم با خلوص بسیار بالا میشود. قیمت هر گرم ژرمانیم در سال ۱۹۹۷ تقریباً ۳ دلار آمریکا و قیمت هر کیلو آن در پایان سال ۲۰۰۰ معادل ۱۱۵۰ دلار بود.
ژرمانیم برخلاف بیشتر نیمه هادیها دارای band gap (شکاف نوار) کوچکی است که امکان واکنش مؤثر به اشعه مادون قرمز را بوجود میآورد؛ بنابراین ژرمانیم در طیف نماهای مادون قرمز و سایر تجهیزات دیداری که نیازمند یابندههای حساس مادون قرمز است کاربرد دارد. ضریب شکست و ویژگیهای تجزیه اکسید آن، استفاده از ژرمانیم را در عدسیهای زاویه باز دوربین و عدسیهای شیئی میکروسکوپ سودمند میکند. موسیقیدانانی که مایل به بازآفرینی حالت خاص تقویت کنندههای اوایل دوره Rock and roll هستند، هنوز هم در تقویت کنندههای گیتار برقی از ترانزیستورهای ژرمانیم استفاده میکنند. آلیاژ ژرمانید سیلیکون (SiGe) در حال تبدیل سریع به ماده نیمه هادی مهم در ICهای سرعت بالا میباشد. مدارهایی که از پیوندهای Si-SiGe استفاده میکنند میتوانند نسبت به مدارهایی که تنها سیلیکون بکار میبرند سرعت خیلی بیشتری داشته باشند. سایر کاربردها:
Germanium is not thought to be an essential element for any living organism. Some complex organic germanium compounds are being investigated as possible pharmaceuticals, though none have yet proven successful. Similar to silicon and aluminum, natural 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.
Samples of germanium compounds prepared by Clemens Winkler, discoverer of the element
In his report on The Periodic Law of the Chemical Elements in 1869, the Russian chemist Dmitri Ivanovich Mendeleev predicted the existence of several unknown chemical elements, including one that would fill a gap in the carbon family in his Periodic Table of the Elements, 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 about 72.0.
In mid-1885, at a mine near Freiberg, Saxony, a new mineral was discovered and named argyrodite because of the high silver content.[n 1] 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.[n 2] 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).[n 3] 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 (GeCl 4), 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:
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 metric tons.
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 polymerizationcatalysts 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 t) 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.
Pure germanium suffers from the forming of whiskers by spontaneous screw dislocations. If a whisker grows long enough to touch another part of the assembly or a metallic packaging, it can effectively shunt out a p-n junction. This is one of the primary reasons for the failure of old germanium diodes and transistors.
Elemental germanium oxidizes slowly to GeO2 at 250 °C. 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 ([GeO 3]2− ). 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 germanes, such as −4 in GeH 4. 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 (GeO 2, germania) and germanium monoxide, (GeO). The dioxide, GeO2 can be obtained by roasting germanium disulfide (GeS 2), 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 Ge metal. 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 (GeS 2), diselenide (GeSe 2), and the monosulfide (GeS), selenide (GeSe), and telluride (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 GenCl2n+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 GenH2n+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.
Germanium occurs in 5 natural isotopes: 70 Ge , 72 Ge , 73 Ge , 74 Ge , and 76 Ge . Of these, 76 Ge is very slightly radioactive, decaying by double beta decay with a half-life of 7028561725280000000♠1.78×1021 years. 74 Ge is the most common isotope, having a natural abundance of approximately 36%. 76 Ge is the least common with a natural abundance of approximately 7%. When bombarded with alpha particles, the isotope 72 Ge will generate stable 77 Se , 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 68 Ge , decaying by electron capture with a half-life of 7007234100800000000♠270.95 days. The least stable is 60 Ge , with a half-life of 6998300000000000000♠30 ms. While most of germanium's radioisotopes decay by beta decay, 61 Ge and 64 Ge decay by β+ delayed proton emission.84 Ge through 87 Ge isotopes also exhibit minor β− delayed neutron emission decay paths.
About 118 tonnes of germanium was 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 sphaleritezinc 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.
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
A typical single-mode optical fiber. Germanium oxide is a dopant of the core silica (Item 1). 1. Core 8 µm 2. Cladding 125 µm 3. Buffer 250 µm 4. Jacket 400 µm
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.
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.
Silicon-germanium alloys are rapidly becoming an important semiconductor material for high-speed integrated circuits. Circuits utilizing the properties of Si-SiGe junctions can be much faster than those using silicon alone. Silicon-germanium is beginning to replace gallium arsenide (GaAs) in wireless communications devices. The SiGe chips, with high-speed properties, can be made with low-cost, well-established production techniques of the silicon chip industry.
Solar panels are a major use of germanium. Germanium is the substrate of the wafers for high-efficiency multijunction photovoltaic cells for space applications. High-brightness LEDs, used for automobile headlights and to backlight LCD screens, are an important application.
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.
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 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).
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
Some of germanium's artificially-produced compounds are quite reactive and present an immediate hazard to human health on exposure. For example, germanium chloride and germane (GeH4) are a liquid and gas, respectively, that can be very irritating to the eyes, skin, lungs, and throat.
As of the year 2000, about 15% of United States consumption of germanium was used for infrared optics technology and 50% for fiber-optics. Over the past 20 years, infrared use has consistently decreased; fiber optic demand, however, is slowly increasing. In America, 30–50% of current fiber optic lines are unused dark fiber, sparking discussion of over-production and a future reduction in demand. Worldwide, demand is increasing dramatically as countries such as China are installing fiber optic telecommunication lines throughout the country.
^From Greek, argyrodite means silver-containing.
^Just as the existence of the new element had been predicted, the existence of the planet Neptune had been predicted in about 1843 by the two mathematicians John Couch Adams and Urbain Le Verrier, using the calculation methods of celestial mechanics. They did this in attempts to explain the fact that the planet Uranus, upon very close observation, appeared to be being pulled slightly out of position in the sky.James Challis started searching for it in July 1846, and he sighted this planet on September 23, 1846.
^R. Hermann published claims in 1877 of his discovery of a new element beneath tantalum in the periodic table, which he named neptunium, after the Greek god of the oceans and seas. However this metal was later recognized to be an alloy of the elements niobium and tantalum. The name "neptunium" was much later given to the synthetic element one step past uranium in the Periodic Table, which was discovered by nuclear physics researchers in 1940.
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