Germanium
Symbol |
Name |
Atomic Number |
Atomic Weight |
Group Number |
Ge |
Germanium |
32 |
72.61 |
14 |
Standard Sate: solid at 298 K
Color: greyish white
The element is a gray-white metalloid, and in its pure state is crystalline and brittle, retaining its lustre in air at room temperature. It is a very important semiconductor material.
(Ge), a chemical element between silicon and tin in Group IVa of the
periodic table, a silvery-gray metalloid, intermediate in properties
between the metals and the nonmetals. Although germanium was
not discovered until 1886 by Clemens Winkler, a German chemist, its
existence, properties, and position in the periodic system had been
predicted in 1871 by the Russian chemist Dmitry Ivanovich
Mendeleyev, who called the hypothetical element ekasilicon.
Germanium did not become economically significant until after 1945,
when its properties as a semiconductor were recognized as being of
value in electronics. Many other substances now also are used as
semiconductors, but germanium remains of primary importance in
the manufacture of transistors and of components for devices such as
rectifiers and photocells.
A rare element never found free in nature, germanium occurs
mainly as a constituent of such uncommon minerals as argyrodite
(from which it was first isolated), germanite, and renierite. The
occurrence of germanium in the Earth's crust is low--about 1.5 parts
per million. In refining germanium, the low-grade residues obtained
from its ores are treated with strong hydrochloric acid, and the
resulting germanium tetrachloride is distilled, purified by repeated
redistillation, and hydrolyzed to form germanium dioxide, which is
then reduced by hydrogen to a powdery form of the metal that is
melted at a temperature of about 1,100 C (2,000 F [in an inert
atmosphere]) and cast into ingots or billets.
The element is brittle rather than ductile; the atoms in its crystals are
arranged as are the carbon atoms in diamond. It is not attacked by air
at room temperature but is oxidized at 600-700 C (1,100-1,300 F)
and reacts quickly with the halogens to form tetrahalides. Among the
acids, only concentrated nitric or sulfuric acid or aqua regia (a mixture
of nitric and hydrochloric acids) attack germanium appreciably.
Although aqueous caustic solutions produce little effect on it,
germanium dissolves rapidly in molten sodium hydroxide or
potassium hydroxide, thereby forming the respective germanates.
Germanium forms stable oxidation states of +2 and +4, the
compounds of the latter being more stable and numerous. The two
most important compounds of germanium are the dioxide (GeO2)
and the tetrachloride (GeCl4). Germanates, formed by heating the
dioxide with basic oxides, include zinc germanate (Zn2GeO4), used as
a phosphor (a substance that emits light when energized by radiation).
The tetrachloride, already mentioned as an intermediate in obtaining
germanium from its natural sources, is a volatile, colourless liquid
that freezes at about -50 C (-58 F) and boils at 84 C (183.2 F).
For use in electronic devices, germanium ingots or billets require
further purification, which usually is effected by the technique of zone
refining. The highly pure germanium is then melted and "doped" to
produce desired electronic characteristics by adding minute amounts
of arsenic, gallium, or other elements. Finally, single crystals are
generated from the melt at carefully controlled temperatures, using a
seed crystal as a nucleus.
In addition to its applications in electronic devices, germanium is
used as a component of alloys and in phosphors for fluorescent lamps.
Because germanium is transparent to infrared radiation, it is useful in
equipment used for detecting and measuring such radiation, such as
windows and lenses. The high index of refraction of germanium
dioxide renders it valuable as a component of glasses used in optical
devices, such as wide-angle lenses for cameras and microscope
objectives.
The five stable isotopes of germanium occur in the following relative
amounts: germanium-70, 20.5 percent; germanium-72, 27.4
percent; germanium-73, 7.8 percent; germanium-74, 36.5 percent;
and germanium-76, 7.8 percent. Nine radioactive isotopes have been
reported. atomic number 32 atomic weight 72.59 melting point 937.4
C (1,719.3 F) boiling point 2,830 C (5,130 F) density 5.323 g/ml
oxidation states +2, +4 electron config. 2-8-18-4 or 1s22s22p63s23p6
3d104s24p2
"germanium" Encyclop�dia Britannica Online.
Copyright � 1999 Chem-i-Page. Please do not reproduce any material found on this page or its attached sub-pages. If you have any questions please contact the webmaster at mailto:[email protected] Ram