Everything about Gallium totally explained
or steel., making them very brittle. Also, gallium metal easily alloys with many metals, and was used in small quantities in the core of the first atomic bomb to help stabilize the plutonium crystal structure.
The
melting point temperature of 29.76 °C allows the metal to be melted in one's hand. This metal has a strong tendency to
supercool below its
melting point/
freezing point, thus necessitating
seeding in order to solidify. Gallium is one of the metals (with
caesium,
rubidium,
francium and
mercury) which are liquid at or near normal room temperature, and can therefore be used in metal-in-glass high-temperature
thermometers. It is also notable for having one of the largest liquid ranges for a metal, and (unlike mercury) for having a low
vapor pressure at high temperatures. Unlike mercury, liquid gallium metal
wets glass and skin, making it mechanically more difficult to handle (even though it's substantially less toxic and requires far fewer precautions). For this reason as well as the metal contamination problem and freezing-expansion problems noted above, samples of gallium metal are usually supplied in polyethylene packets within other containers.
Gallium doesn't
crystallize in any of the simple
crystal structures. The stable phase under normal conditions is
orthorhombic with 8 atoms in the conventional
unit cell. Each atom has only one nearest neighbor (at a distance of 244
pm) and six other neighbors within additional 39 pm. Many stable and
metastable phases are found as function of temperature and pressure.
The bonding between the nearest neighbors is found to be of
covalent character, hence Ga
2 dimers are seen as the fundamental building blocks of the crystal. The compound with
arsenic,
gallium arsenide is a
semiconductor commonly used in
light-emitting diodes.
High-purity gallium is dissolved slowly by
mineral acids.
Gallium has no known biological role, although it might be involved in metabolism stimulation.
History
Gallium (the
Latin Gallia means "
Gaul," essentially modern
France; and the Latin
gallus means "rooster") was discovered
spectroscopically by
Lecoq de Boisbaudran in
1875 by its characteristic spectrum (two
violet lines) in an examination of a
zinc blende from the
Pyrenees. 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, Boisbaudran 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'd 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 Le coq denied this supposition.
Occurrence
Gallium doesn't exist in free form in nature, nor do any high-gallium minerals exist to serve as a primary source of extraction of the element or its compounds. Gallium is found and extracted as a trace component in
bauxite,
coal,
diaspore,
germanite, and
sphalerite. The
United States Geological Survey (
USGS) estimates gallium reserves based on 50 ppm by weight concentration in known reserves of bauxite and zinc ores. Some
flue dusts from burning coal have been shown to contain small quantities of gallium, typically less than 1 % by weight.
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.
One chemist estimated in 2007 that at the current rate of usage, the world's supply of gallium would be exhausted by about the year 2017.
The cost for 37.5 grams of gallium is 71.99.
Applications
Semiconductor and electronic industry. The semiconductor applications are the main reason for the low-cost commercial availability of the extremely high-purity (99.9999+%) metal:
As a wetting, and alloy improvement agent:
Because gallium wets glass or porcelain, gallium can be used to create brilliant mirrors.
Gallium readily alloys with most metals, and has been used as a component in low-melting alloys. The plutonium used in nuclear weapon pits is machined by alloying with gallium to stabilize the allotropes of plutonium.
Gallium added in quantities up to 2% in common solders can aid wetting and flow characteristics.
As part of an energy storage mechanism:
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. When gallium is alloyed with aluminium, the coat doesn't form, thus the alloy can potentially provide a solid hydrogen source for transportation purposes, which would be more convenient than a pressurized hydrogen tank. Resmelting the resultant aluminium oxide and gallium mixture to metallic aluminium and gallium and reforming these into electrodes would constitute most of the energy input into the system, while electricity produced by a hydrogen fuel cell could constitute an energy output.The thermodynamic efficiency of the aluminium smelting process is said to be approximately 50 percent. Therefore, at most no more than half the energy that goes into smelting aluminium could be recovered by a fuel cell.
For liquid alloys:
It has been suggested that a liquid gallium-tin alloy could be used to cool computer chips in place of water. As it conducts heat approximately 65 times better than water it can make a comparable coolant. (External Link
)
Gallium is used in some high temperature thermometers.
Biomedical applications:
A low temperature liquid eutectic alloy of gallium, indium, and tin, is widely available in medical thermometers (fever thermometers), replacing problematic mercury. This alloy, with the trade name Galinstan (with the "-stan" referring to the tin), has a freezing point of −20°C.
Gallium salts such as gallium citrate and gallium nitrate are used as radiopharmaceutical agents in nuclear medicine imaging. (The form or salt isn't important, since it's the free dissolved gallium ion Ga3+ which is active). For these applications, a radioactive isotope such as 67Ga is used. The body handles Ga3+ in many ways as though it were iron, and thus it's bound (and concentrates) in areas of inflammation, such as infection, and also areas of rapid cell division. This allows such sites to be imaged by nuclear scan techniques. See gallium scan. This use has largely been replaced by fluorodeoxyglucose (FDG) for positron emission tomography, "PET" scan.
Gallium nitrate, both oral and topical, is finding use in treating arthritis.
Gallium maltolate is in clinical and preclinical trials as a potential treatment for cancer, infectious disease, and inflammatory disease.
Much research is being devoted to gallium alloys as substitutes for mercury dental amalgams, but these compounds have yet to see wide acceptance.
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.
Miscellaneous:
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 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. This wasn't explained until better solar neutrino detectors and theories were constructed (see SNO).(External Link)
As a liquid metal ion source for a focused ion beam.
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. Powdered gallium appears grey. 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 grey skin stain.
Further Information
Get more info on 'Gallium'.
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