Gallium (pronounced /ˈɡæliəm/, GAL-ee-əm) is a chemical element that has the symbol Ga and atomic number 31. Elemental gallium does not occur in
nature, but as the gallium(III) salt in trace amounts in bauxite
and zinc
ores. A soft silvery metallic poor metal,
elemental gallium is a brittle solid at low temperatures. As it liquefies
slightly above room temperature, it will melt in the hand. Its melting point
is used as a temperature reference point, and from its discovery in 1875 to the
semiconductor era, its primary uses were in high-temperature thermometric
applications and in preparation of metal alloys with unusual properties of
stability, or ease of melting; some being liquid at room temperature or below.
The alloy Galinstan (68.5% Ga, 21.5% In, 10% Sn) has a melting point
of about −19 °C (−2.2 °F).
Detailed description
In semiconductors, the major-use compound is gallium arsenide used in microwave circuitry and
infrared applications. Gallium nitride and indium
gallium nitride,
minority semiconductor uses, produce blue and violet light-emitting
diodes (LEDs) and diode lasers. Semiconductor use is now almost the
entire (> 95%) world market for gallium, but new uses in alloys and fuel cells continue to be discovered.
Gallium is not
known to be essential in biology, but because of the biological handling of
gallium's primary ionic
salt gallium(III) as
though it were iron(III), the gallium ion localizes to and
interacts with many processes in the body in which iron(III) is manipulated. As
these processes include inflammation, which is a marker for many disease
states, several gallium salts are used, or are in development, as both pharmaceuticals and radiopharmaceuticals in medicine.
Notable characteristics
Elemental gallium
is not found in nature, but it is easily obtained by smelting. Very pure gallium metal has a
brilliant silvery color and its solid metal fractures conchoidally like glass. Gallium metal expands by 3.1 percent when it
solidifies, and therefore storage in either glass or metal containers is
avoided, due to the possibility of container rupture with freezing. Gallium
shares the higher-density liquid state with only a few materials like silicon, germanium, bismuth, antimony and water.
History
Gallium (the Latin Gallia means "Gaul", essentially modern France) was discovered spectroscopically by Paul Emile Lecoq de Boisbaudran in 1875 by its characteristic
spectrum (two violet lines) in an examination of a zinc blende from the Pyrenees.[9] Before its discovery, most of its
properties had been predicted and described by Dmitri Mendeleev (who had called the hypothetical
element "eka-aluminium" on the basis of its position in his periodic table). Later, in 1875, Lecoq obtained the
free metal by electrolysis of its hydroxide in potassium
hydroxide solution. He
named the element "gallia" after his native land of France. It was later claimed that, in one of those
multilingual puns so beloved of men of science in the early
19th century, he had also named gallium after himself, as his name, "Le
coq", is the French for "the rooster", and the Latin for "rooster" is "gallus";
however, in an 1877 article Lecoq denied this supposition.[10] (The supposition was also noted in Building
Blocks of the Universe, a book on the elements by Isaac Asimov; cf. the naming of the J/ψ meson.)
Occurrence
Gallium does not
exist in free form in nature, and the few high-gallium minerals such as gallite
(CuGaS2) are too rare to serve as a primary source of the element or
its compounds. Its abundance in the Earth's crust is approximately 16.9 ppm.[11] Gallium is found and extracted as a
trace component in bauxite and to a small extent from sphalerite. The amount extracted from coal, diaspore and germanite in which gallium is also present is
negligible. The United States Geological Survey (USGS) estimates gallium reserves to exceed 1
million tonnes, based on 50 ppm by weight
concentration in known reserves of bauxite and zinc ores.[12][13] Some flue dusts from burning coal have been shown to contain
small quantities of gallium, typically less than 1% by weight.[14][15][16][17]
Production
The only two
economic sources for gallium are as byproduct of aluminium and zinc production,
while the sphalerite for zinc production is the minor source. Most gallium is
extracted from the crude aluminium
hydroxide solution of the Bayer process for producing alumina and aluminium.
A mercury cell electrolysis and hydrolysis of the amalgam with sodium hydroxide leads to sodium gallate. Electrolysis
then gives gallium metal. For semiconductor use, further purification is carried
out using zone
melting, or else single
crystal extraction from a melt (Czochralski
process).
Purities of 99.9999% are routinely achieved and commercially widely available.[18] An exact number for the world wide
production is not available, but it is estimated that in 2007 the production of
gallium was 184 tonnes with less than 100 tonnes from mining and the rest from
scrap recycling.[12]
Applications
Semiconductors
The semiconductor
applications are the main reason for the low-cost commercial availability of
the extremely high-purity (99.9999+%) metal.
Gallium
arsenide (GaAs) and gallium
nitride (GaN) used in
electronic components represented about 98% of the gallium consumption in the
United States in 2007. About 66% of semiconductor gallium is used in the U.S.
in integrated circuits (mostly gallium arsenide), such as the manufacture of
ultra-high speed logic chips and MESFETs for low-noise microwave preamplifiers in cell
phones. About 20% is used in optoelectronics.[12] World wide gallium arsenide makes up
95% of the annual global gallium consumption.[18]
Gallium arsenide
is used in optoelectronics in a variety of infrared applications. Aluminum
gallium arsenide
(AlGaAs) is used in high-powered infrared laser diodes. As a component of the
semiconductors indium
gallium nitride
and gallium nitride, gallium is used to produce blue and violet optoelectronic
devices, mostly laser
diodes and light-emitting diodes. For example, gallium nitride 405 nm
diode lasers are used as a violet light source for higher-density compact disc
data storage, in the Blu-ray
Disc standard.[19]
Galinstan and other liquid alloys
A nearly eutectic alloy of gallium, indium, and tin is a room temperature liquid which is widely
available in medical thermometers, replacing problematic mercury. This alloy,
with the trade-name Galinstan (with the "-stan" referring
to the tin), has a low freezing point of −19 °C (−2.2°F).[24] It has been suggested that this
family of alloys could also be used to cool computer chips in place of water.[25] Much research is being devoted to
gallium alloys as substitutes for mercury dental amalgams, but these compounds have yet to see
wide acceptance.
Energy storage
Aluminium is
reactive enough to reduce water to hydrogen, being oxidized to aluminium oxide. However, the aluminium oxide forms a
protective coat which prevents further reaction. Galinstan has been applied to
activate aluminum (removing the oxide coat), so that aluminum can react with
water, generating hydrogen and steam in a reaction being considered as a
helpful step in a hydrogen
economy.[26] A number of other gallium-alluminum
alloys are also usable for the purpose of essentially acting as chemical energy
store to generate hydrogen from water, on-site.
After reaction
with water the resultant aluminium oxide and gallium mixture might be reformed
back into electrodes with energy input.[26][27] The thermodynamic efficiency of the
aluminium smelting process is estimated as 50%.[28] Therefore, at most half the energy
that goes into smelting the aluminium could be recovered by a hydrogen fuel
cell.
Biomedical applications
As gallium(III) salts
- Gallium
nitrate
(brand name Ganite) has been used as an intravenous pharmaceutical to
treat hypercalcemia associated
with tumor metastasis to bones.
Gallium is thought to interfere with osteoclast function.
It may be effective when other treatments for maligancy-associated
hypercalcemia are not.[29]
- Gallium
maltolate
is in clinical and preclinical trials as a potential treatment for cancer,
infectious disease, and inflammatory disease.[30]
- Research is
being conducted to determine whether gallium can be used to fight
bacterial infections in people with cystic
fibrosis.
Gallium is similar in size to iron, an essential nutrient for respiration.
When gallium is mistakenly picked up by bacteria such as Pseudomonas, the
bacteria's ability to respire is interfered with and the bacteria die. The
mechanism behind this is that iron is redox active, which allows for the
transfer of electrons during respiration, but gallium is redox inactive.[31][32]
Other uses
- Magnesium gallate containing
impurities (such as Mn2+), is beginning to be used in ultraviolet-activated phosphor powder.
- Neutrino detection.
Possibly the largest amount of pure gallium ever collected in a single
spot is the Gallium-Germanium Neutrino Telescope used by the SAGE experiment
at the Baksan Neutrino Observatory in Russia. This detector contains 55-57
tonnes of liquid gallium.[33] Another
experiment was the GALLEX neutrino
detector operated in the early 1990s in an Italian mountain tunnel. The
detector contained 12.2 tons of watered gallium-71. Solar neutrinos caused
a few atoms of Ga-71 to become radioactive Ge-71, which
were detected. The solar neutrino flux deduced was found to have a deficit
of 40% from theory.
Chemistry
Gallium is found
primarily in the +3 oxidation state. The +1 oxidation is also attested in
some compounds, although they tend to disproportionate into elemental gallium and
gallium(III) compounds. What are sometimes referred to as gallium(II) compounds
are actually mixed-oxidation state compounds containing both gallium(I) and
gallium(III).[35]
Precautions
While not
considered toxic, the data about gallium are inconclusive. Some sources suggest
that it may cause dermatitis from prolonged exposure; other tests
have not caused a positive reaction. Like most metals, finely divided gallium
loses its luster and powdered gallium appears gray. Thus, when gallium is
handled with bare hands, the extremely fine dispersion of liquid gallium
droplets, which results from wetting skin with the metal, may appear as a gray
skin stain.
PRICE
$145/KG OR $65.90/IB
For more information:
mobile: +2348039721941
contact person: emeaba uche
e-mail: emeabau@yahoo.com
Comments
Post a Comment