Germanium

From Free net encyclopedia

Germanium is a chemical element in the periodic table that has the symbol Ge and atomic number 32. This is a lustrous, hard, silver-white metalloid that is chemically similar to tin. Germanium forms a large number of organometallic compounds and is an important semiconductor material used in transistors.

1 Notable characteristics
2 History
3 Applications
4 Occurrence
5 Compounds
6 References
7 External links

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Notable characteristics

Germanium is a hard, grayish-white element that has a metallic luster and the same crystal structure as diamond. In addition, it is important to note that germanium is a semiconductor, with electrical properties between those of a metal and an insulator. In its pure state, this metalloid is crystalline, brittle and retains its luster in air at room temperature. Zone refining techniques have led to the production of crystalline germanium for semiconductors that have an impurity of only one part in 10¹⁰.

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History

Image:GermaniumUSGOV.jpg In 1871 germanium (Latin Germania for Germany) was one of the elements that Dmitri Mendeleev predicted to exist as a missing analogue of the silicon group (Mendeleev called it "ekasilicon"). The existence of this element was proven by Clemens Winkler in 1886. This discovery was an important confirmation of Mendeleev's idea of element periodicity.

Property	Ekasilicon	Germanium
atomic mass	72	72.59
density (g/cm³)	5.5	5.35
melting point (°C)	high	947
color	gray	gray

The development of the germanium transistor 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. Silicon has superior electrical properties, but requires much higher purity samples—a purity which could not be commercially achieved in the early days. Meanwhile, demand for germanium in fiber optics communication networks, infrared night vision systems, and polymerization catalysts increased dramatically. These end uses represented 85% of worldwide germanium consumption for 2000.

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Applications

Unlike most semiconductors, germanium has a small band gap, allowing it to efficiently respond to infrared light. It is therefore used in infrared spectroscopes and other optical equipment which require extremely sensitive infrared detectors. Its oxide's index of refraction and dispersion properties make germanium useful in wide-angle camera lenses and in microscope objective lenses.

Germanium transistors are still used in some stompboxes by musicians who wish to reproduce the distinctive tonal character of the "fuzz"-tone from the early rock and roll era. Vintage stompboxes known to contain germanium transistors have shown marked increases in collector value for this reason alone.

The alloy Silicon germanide (commonly referred to as "silicon-germanium", or SiGe) is rapidly becoming an important semiconductor material, for use in high speed integrated circuits. Circuits utilising the properties of Si-SiGe junctions can be much faster than those using silicon alone.

Other uses:

Alloying agent;
Phosphor in fluorescent lamps; and as a
catalyst
High purity germanium single crystal detectors can precisely identify radiation sources (e.g. for airport security)

Certain compounds of germanium have low toxicity to mammals, but have toxic effects against certain bacteria. This property makes these compounds useful as chemotherapeutic agents.

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Occurrence

This metal is found in argyrodite (sulfide of germanium and silver); coal; germanite; zinc ores; and other minerals. See also Category:Germanium minerals

Germanium is obtained commercially from zinc ore processing smelter dust and from the combustion by-products of certain coals. A large reserve of this element is therefore in coal sources.

This metalloid can be extracted from other metals by fractional distillation of its volatile tetrachloride. This technique permits the production of ultra-high purity germanium.

In 1997 the cost of germanium was about US$3 per gram. The yearend price for germanium in 2000 was $1,150 per kilogram (or $1.15 per gram).

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