Gallium
Encyclopedia
Gallium 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.
In semiconductor
s, 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 diode
s (LEDs) and diode lasers. Semiconductor use is now almost the entire (> 95%) world market for gallium, but new uses in alloys and fuel cell
s 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.
.
Very pure gallium metal has a brilliant silvery color and its solid metal fractures conchoid
ally like glass
. Gallium metal expands by 3.1% 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
.
Gallium attacks
most other metals by diffusing
into their metal lattice
. Gallium for example diffuses into the grain boundaries
of Al
/Zn
alloy
s or steel
, making them very brittle. Also, gallium metal easily alloys with many metals, and was used in small quantities as a plutonium-gallium alloy
in the plutonium cores of the first and third
nuclear bombs, to help stabilize the plutonium crystal structure.
The melting point
of 302.9146 K (29.7646 °C, 85.5763 °F) is near room temperature. Gallium's melting point (mp) is one of the formal temperature reference points in the International Temperature Scale of 1990
(ITS-90) established by BIPM. The triple point
of gallium of 302.9166 K (29.7666 °C, 85.5799 °F), is being used by NIST in preference to gallium's melting point.
Gallium is a metal that will melt in one's hand. This metal has a strong tendency to supercool
below its melting point
/freezing point
. Seeding
with a crystal helps to initiate freezing. 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 thermometer
s. 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 is 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 does not crystal
lize in any of the simple crystal structure
s. 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 Ga2 dimers are seen as the fundamental building blocks of the crystal. This explains the drop of the melting point compared to its neighbour elements aluminium and indium. The compound with arsenic
, gallium arsenide is a semiconductor
commonly used in light-emitting diode
s.
High-purity gallium is dissolved slowly by mineral acid
s.
n chemist Dmitri Mendeleev
, who named it "eka-aluminium
" on the basis of its position in his periodic table
. He also predicted several properties of the element, which correspond close to real gallium properties, such as density
, melting point
, oxide character and bonding in chloride.
Gallium was discovered spectroscopically
by Paul Emile Lecoq de Boisbaudran
in 1875 by its characteristic spectrum (two violet
lines) in an examination of a sphalerite
sample. Later that year, Lecoq obtained the free metal by electrolysis
of its hydroxide
in potassium hydroxide
solution. He named the element "gallia", from Latin
Gallia meaning gaul
, after his native land of France
. It was later claimed that, in one of those multilingual pun
s so beloved of men of science in the 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. (Cf. the naming of the J/ψ meson.)
Its abundance in the Earth's crust is approximately 16.9 ppm
. 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 tonne
s, based on 50 ppm by weight concentration in known reserves of bauxite and zinc ores. Some flue
dust
s from burning coal have been shown to contain small quantities of gallium, typically less than 1% by weight.
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.
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.
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 MESFET
s for low-noise microwave preamplifiers in cell phones. About 20% is used in optoelectronics. World wide gallium arsenide makes up 95% of the annual global gallium consumption.
Gallium arsenide is used in optoelectronics in a variety of infrared applications. Aluminium 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 diode
s 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.
Gallium is used as a dopant
for the production of solid-state devices such as transistor
s. However, worldwide the actual quantity used for this purpose is minute, since dopant levels are usually of the order of a few parts per million.
Multijunction photovoltaic cell
s, developed for satellite
power applications, are made by molecular beam epitaxy
or metalorganic vapour phase epitaxy
of thin film
s of gallium arsenide, indium gallium phosphide
or indium gallium arsenide
.The Mars Exploration Rover
s and several satellites use triple junction gallium arsenide on germanium cells. Gallium is the rarest component of new photovoltaic compounds (such as copper indium gallium selenium sulfide or Cu(In,Ga)(Se,S)2) for use in solar panels as a more efficient alternative to crystalline silicon.
, 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). It has been suggested that this family of alloys could also be used to cool computer chips in place of water. Much research is being devoted to gallium alloys as substitutes for mercury dental amalgams, but these compounds have yet to see wide acceptance.
, being oxidized to aluminium oxide
. However, the aluminium oxide forms a protective coat which prevents further reaction. Galinstan has been applied to activate aluminium (removing the oxide coat), so that aluminium can react with water, generating hydrogen and steam in a reaction being considered as a helpful step in a hydrogen economy
. A number of other gallium-aluminium 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 must be reformed back into electrodes with energy input. The thermodynamic efficiency of the aluminium smelting process is estimated as 50%. Therefore, at most only half the energy that goes into smelting the aluminium could be recovered by a hydrogen fuel cell.
s such as gallium citrate
and gallium nitrate
are used as radiopharmaceutical agents in a nuclear medicine
imaging procedure commonly referred to as a gallium scan
. The form or salt of gallium is not important, since it is the free dissolved gallium ion Ga3+ which is the active radiotracer. For these applications, the radioactive isotope
67Ga is used. The body handles Ga3+ in many ways as though it were iron, and thus it is 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. This use has largely been replaced by fluorodeoxyglucose
(FDG) for positron emission tomography
, "PET" scan and indium-111 labelled leukocyte scans. However, the localization of gallium in the body has some properties which make it unique in some circumstances from competing modalities using other radioisotopes.
Gallium-68, a positron emitter with a half life of 68 min., is now used as a diagnostic radionuclide in PET-CT when linked to pharmaceutical preparations such as DOTATOC, a somatostatin
analogue used for neuroendocrine tumors
investigation, and DOTA-TATE
, a newer one, used for neuroendocrine metastasis
and lung neuroendocrine cancer, such as certain types of microcytoma. Galium-68's preparation as a pharmaceutical is chemical and the radionuclide is extracted by elution
from germanium-68, a synthetic radioisotope
of germanium
, in gallium-68 generator
s.
Chemical element
A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...
that has the symbol Ga and atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...
31. Elemental gallium does not occur in nature, but as the gallium(III) salt in trace amounts in bauxite
Bauxite
Bauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO, and diaspore α-AlO, in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2...
and zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
ores. A soft silvery metallic poor metal, elemental gallium is a brittle solid at low temperatures. As it liquefies slightly above room temperature
Room temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...
, 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
Galinstan
Galinstan is a family of eutectic alloys mainly consisting of gallium, indium, and tin, which are liquids at room temperature, typically freezing at . Due to the low toxicity and low reactivity of its component metals, it finds use as a replacement for many applications that previously employed...
(68.5% Ga, 21.5% In, 10% Sn) has a melting point of about -19 °C.
In semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
s, the major-use compound is gallium arsenide used in microwave circuitry and infrared applications. Gallium nitride and indium gallium nitride
Indium gallium nitride
Indium gallium nitride is a semiconductor material made of a mix of gallium nitride and indium nitride . It is a ternary group III/group V direct bandgap semiconductor. Its bandgap can be tuned by varying the amount of indium in the alloy...
, minority semiconductor uses, produce blue and violet light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
s (LEDs) and diode lasers. Semiconductor use is now almost the entire (> 95%) world market for gallium, but new uses in alloys and fuel cell
Fuel cell
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. Hydrogen is the most common fuel, but hydrocarbons such as natural gas and alcohols like methanol are sometimes used...
s 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
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
, which is a marker for many disease states, several gallium salts are used, or are in development, as both pharmaceuticals and radiopharmaceuticals
Radiopharmacology
Radiopharmacology is the study and preparation of radiopharmaceuticals, which are radioactive pharmaceuticals. Radiopharmaceuticals are used in the field of nuclear medicine as tracers in the diagnosis and treatment of many diseases. Many radiopharmaceuticals use technetium-99m which has many...
in medicine.
Properties
Elemental gallium is not found in nature, but it is easily obtained by smeltingSmelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...
.
Very pure gallium metal has a brilliant silvery color and its solid metal fractures conchoid
Conchoidal fracture
Conchoidal fracture describes the way that brittle materials break when they do not follow any natural planes of separation. Materials that break in this way include flint and other fine-grained minerals, as well as most amorphous solids, such as obsidian and other types of glass.Conchoidal...
ally like glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
. Gallium metal expands by 3.1% 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
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
, germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
, bismuth
Bismuth
Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...
, antimony
Antimony
Antimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
and water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
.
Gallium attacks
Liquid metal embrittlement
Liquid metal embrittlement is a phenomenon of practical importance, where certain ductile metals experience drastic loss in tensile ductility or undergo brittle fracture when tested in the presence of specific liquid metals. Generally, a tensile stress, either externally applied or internally...
most other metals by diffusing
Diffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
into their metal lattice
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
. Gallium for example diffuses into the grain boundaries
Grain boundary
A grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are defects in the crystal structure, and tend to decrease the electrical and thermal conductivity of the material...
of Al
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
/Zn
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
alloy
Alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s or steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...
, making them very brittle. Also, gallium metal easily alloys with many metals, and was used in small quantities as a plutonium-gallium alloy
Plutonium-gallium alloy
Plutonium-gallium alloy is an alloy of plutonium and gallium, used in nuclear weapon pits – the component of a nuclear weapon where the fission chain reaction is started....
in the plutonium cores of the first and third
Fat Man
"Fat Man" is the codename for the atomic bomb that was detonated over Nagasaki, Japan, by the United States on August 9, 1945. It was the second of the only two nuclear weapons to be used in warfare to date , and its detonation caused the third man-made nuclear explosion. The name also refers more...
nuclear bombs, to help stabilize the plutonium crystal structure.
The melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
of 302.9146 K (29.7646 °C, 85.5763 °F) is near room temperature. Gallium's melting point (mp) is one of the formal temperature reference points in the International Temperature Scale of 1990
International Temperature Scale of 1990
The International Temperature Scale of 1990 is an equipment calibration standard for making measurements on the Kelvin and Celsius temperature scales. ITS–90 is an approximation of the thermodynamic temperature scale that facilitates the comparability and compatibility of temperature measurements...
(ITS-90) established by BIPM. The triple point
Triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium...
of gallium of 302.9166 K (29.7666 °C, 85.5799 °F), is being used by NIST in preference to gallium's melting point.
Gallium is a metal that will melt in one's hand. This metal has a strong tendency to supercool
Supercooling
Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its freezing point without it becoming a solid....
below its melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
/freezing point
Freezing Point
Freezing Point is a news journal in the People's Republic of China which has been the subject of controversy over its criticism of Communist Party officials and the sympathetic ear it lent to a Chinese historian who had criticized official history textbooks...
. Seeding
Seed crystal
A seed crystal is a small piece of single crystal/polycrystal material from which a large crystal of the same material typically is to be grown...
with a crystal helps to initiate freezing. Gallium is one of the metals (with caesium
Caesium
Caesium or cesium is the chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-gold alkali metal with a melting point of 28 °C , which makes it one of only five elemental metals that are liquid at room temperature...
, rubidium
Rubidium
Rubidium is a chemical element with the symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group. Its atomic mass is 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other elements in group 1, such as very rapid...
, francium
Francium
Francium is a chemical element with symbol Fr and atomic number 87. It was formerly known as eka-caesium and actinium K.Actually the least unstable isotope, francium-223 It has the lowest electronegativity of all known elements, and is the second rarest naturally occurring element...
and mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
) which are liquid at or near normal room temperature, and can therefore be used in metal-in-glass high-temperature thermometer
Thermometer
Developed during the 16th and 17th centuries, a thermometer is a device that measures temperature or temperature gradient using a variety of different principles. A thermometer has two important elements: the temperature sensor Developed during the 16th and 17th centuries, a thermometer (from the...
s. It is also notable for having one of the largest liquid ranges for a metal, and (unlike mercury) for having a low vapor pressure
Vapor pressure
Vapor pressure or equilibrium vapor pressure is the pressure of a vapor in thermodynamic equilibrium with its condensed phases in a closed system. All liquids have a tendency to evaporate, and some solids can sublimate into a gaseous form...
at high temperatures. Unlike mercury, liquid gallium metal wets
Wetting
Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting is determined by a force balance between adhesive and cohesive forces.Wetting is important in the bonding or adherence of...
glass and skin, making it mechanically more difficult to handle (even though it is 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.
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
lize in any of the simple crystal structure
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
s. 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
Picometre
A picometre is a unit of length in the metric system, equal to one trillionth, i.e. of a metre, which is the current SI base unit of length...
) 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 Ga2 dimers are seen as the fundamental building blocks of the crystal. This explains the drop of the melting point compared to its neighbour elements aluminium and indium. The compound with arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
, gallium arsenide is a semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
commonly used in light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
s.
High-purity gallium is dissolved slowly by mineral acid
Mineral acid
A mineral acid is an acid derived from one or more inorganic compounds. A mineral acid is not organic and all mineral acids release hydrogen ions when dissolved in water.-Characteristics:...
s.
History
In 1871, existence of gallium was first predicted by RussiaRussia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n chemist Dmitri Mendeleev
Dmitri Mendeleev
Dmitri Ivanovich Mendeleev , was a Russian chemist and inventor. He is credited as being the creator of the first version of the periodic table of elements...
, who named it "eka-aluminium
Mendeleev's predicted elements
Professor Dmitri Mendeleev published the first Periodic Table of the Atomic Elements in 1869 based on properties which appeared with some regularity as he laid out the elements from lightest to heaviest....
" on the basis of its position in his periodic table
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...
. He also predicted several properties of the element, which correspond close to real gallium properties, such as density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
, oxide character and bonding in chloride.
Gallium was discovered spectroscopically
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
by Paul Emile Lecoq de Boisbaudran
Paul Emile Lecoq de Boisbaudran
Paul Émile Lecoq de Boisbaudran was a French chemist known for his discoveries of the chemical elements gallium, samarium and dysprosium.-Biography:...
in 1875 by its characteristic spectrum (two violet
Violet (color)
As the name of a color, violet is synonymous with a bluish purple, when the word "purple" is used in the common English language sense of any color between blue and red, not including either blue or red...
lines) in an examination of a sphalerite
Sphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...
sample. Later that year, Lecoq obtained the free metal by electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
of its hydroxide
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
in potassium hydroxide
Potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula KOH, commonly called caustic potash.Along with sodium hydroxide , this colorless solid is a prototypical strong base. It has many industrial and niche applications. Most applications exploit its reactivity toward acids and its corrosive...
solution. He named the element "gallia", from Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
Gallia meaning gaul
Gaul
Gaul was a region of Western Europe during the Iron Age and Roman era, encompassing present day France, Luxembourg and Belgium, most of Switzerland, the western part of Northern Italy, as well as the parts of the Netherlands and Germany on the left bank of the Rhine. The Gauls were the speakers of...
, after his native land of France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. It was later claimed that, in one of those multilingual pun
Pun
The pun, also called paronomasia, is a form of word play which suggests two or more meanings, by exploiting multiple meanings of words, or of similar-sounding words, for an intended humorous or rhetorical effect. These ambiguities can arise from the intentional use and abuse of homophonic,...
s so beloved of men of science in the 19th century, he had also named gallium after himself, as his name, "Le coq", is the French for "the rooster
Rooster
A rooster, also known as a cockerel, cock or chanticleer, is a male chicken with the female being called a hen. Immature male chickens of less than a year's age are called cockerels...
", and the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for "rooster" is "gallus"; however, in an 1877 article Lecoq denied this supposition. (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
Parts-per notation
In science and engineering, the parts-per notation is a set of pseudo units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they are pure numbers with no associated units of measurement...
. Gallium is found and extracted as a trace component in bauxite
Bauxite
Bauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO, and diaspore α-AlO, in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2...
and to a small extent from sphalerite
Sphalerite
Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...
. The amount extracted from coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
, diaspore
Diaspore
Diaspore is a native aluminium oxide hydroxide, α-AlO, crystallizing in the orthorhombic system and isomorphous with goethite. It occurs sometimes as flattened crystals, but usually as lamellar or scaly masses, the flattened surface being a direction of perfect cleavage on which the lustre is...
and germanite
Germanite
Germanite is a rare copper iron germanium sulfide mineral, Cu26Fe4Ge4S32. It was first discovered in 1922, and named for its germanium content. It is only a minor source of this important semiconductor element, which is mainly derived from the processing of the zinc sulfide mineral sphalerite...
in which gallium is also present is negligible. The United States Geological Survey
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
(USGS
United States Geological Survey
The United States Geological Survey is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The organization has four major science disciplines, concerning biology,...
) estimates gallium reserves to exceed 1 million tonne
Tonne
The tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
s, based on 50 ppm by weight concentration in known reserves of bauxite and zinc ores. Some flue
Flue
A flue is a duct, pipe, or chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors. In the United States, they are also known as vents and for boilers as breeching for water heaters and modern furnaces...
dust
Dust
Dust consists of particles in the atmosphere that arise from various sources such as soil dust lifted up by wind , volcanic eruptions, and pollution...
s from burning coal have been shown to contain small quantities of gallium, typically less than 1% by weight.
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 hydroxideAluminium hydroxide
Aluminium hydroxide, Al3, ATH, sometimes erroneously called Hydrate of alumina, is found in nature as the mineral gibbsite and its three, much more rare forms, polymorphs: bayerite, doyleite and nordstrandite. Closely related are aluminium oxide hydroxide, AlO, and aluminium oxide, Al2O3,...
solution of the Bayer process
Bayer process
The Bayer process is the principal industrial means of refining bauxite to produce alumina .Bauxite, the most important ore of aluminium, contains only 30–54% alumina, Al2O3, the rest being a mixture of silica, various iron oxides, and titanium dioxide. The alumina must be purified before it can...
for producing alumina and aluminium. A mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
cell electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
and hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of the amalgam
Amalgam (chemistry)
An amalgam is a substance formed by the reaction of mercury with another metal. Almost all metals can form amalgams with mercury, notable exceptions being iron and platinum. Silver-mercury amalgams are important in dentistry, and gold-mercury amalgam is used in the extraction of gold from ore.The...
with sodium hydroxide leads to sodium gallate. Electrolysis then gives gallium metal. For semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
use, further purification is carried out using zone melting
Zone melting
Zone melting is a group of similar methods of purifying crystals, in which a narrow region of a crystal is molten, and this molten zone is moved along the crystal...
, or else single crystal extraction from a melt (Czochralski process
Czochralski process
The Czochralski process is a method of crystal growth used to obtain single crystals of semiconductors , metals , salts, and synthetic gemstones...
). Purities of 99.9999% are routinely achieved and commercially widely available.
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.
Semiconductors
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 MESFET
MESFET
MESFET stands for metal semiconductor field effect transistor. It is quite similar to a JFET in construction and terminology. The difference is that instead of using a p-n junction for a gate, a Schottky junction is used...
s for low-noise microwave preamplifiers in cell phones. About 20% is used in optoelectronics. World wide gallium arsenide makes up 95% of the annual global gallium consumption.
Gallium arsenide is used in optoelectronics in a variety of infrared applications. Aluminium gallium arsenide
Aluminium gallium arsenide
Aluminium gallium arsenide is a semiconductor material with very nearly the same lattice constant as GaAs, but a larger bandgap. The x in the formula above is a number between 0 and 1 - this indicates an arbitrary alloy between GaAs and AlAs.The bandgap varies between 1.42 eV and 2.16 eV...
(AlGaAs) is used in high-powered infrared laser diodes. As a component of the semiconductors indium gallium nitride
Indium gallium nitride
Indium gallium nitride is a semiconductor material made of a mix of gallium nitride and indium nitride . It is a ternary group III/group V direct bandgap semiconductor. Its bandgap can be tuned by varying the amount of indium in the alloy...
and gallium nitride, gallium is used to produce blue and violet optoelectronic devices, mostly laser diode
Laser diode
The laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common type of laser diode is formed from a p-n junction and powered by injected electric current...
s and light-emitting diodes
LEd
LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....
. 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
Blu-ray Disc
Blu-ray Disc is an optical disc storage medium designed to supersede the DVD format. The plastic disc is 120 mm in diameter and 1.2 mm thick, the same size as DVDs and CDs. Blu-ray Discs contain 25 GB per layer, with dual layer discs being the norm for feature-length video discs...
standard.
Gallium is used as a dopant
Dopant
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...
for the production of solid-state devices such as transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
s. However, worldwide the actual quantity used for this purpose is minute, since dopant levels are usually of the order of a few parts per million.
Multijunction photovoltaic cell
Multijunction photovoltaic cell
Multi-junction solar cells or tandem cells are solar cells containing several p-n junctions. Each junction is tuned to a different wavelength of light, reducing one of the largest inherent sources of losses, and thereby increasing efficiency...
s, developed for satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
power applications, are made by molecular beam epitaxy
Molecular beam epitaxy
Molecular beam epitaxy is one of several methods of depositing single crystals. It was invented in the late 1960s at Bell Telephone Laboratories by J. R. Arthur and Alfred Y. Cho.-Method:...
or metalorganic vapour phase epitaxy
Metalorganic vapour phase epitaxy
Metalorganic vapour phase epitaxy , also known as organometallic vapour phase epitaxy or metalorganic chemical vapour deposition , is a chemical vapour deposition method of epitaxial growth of materials, especially compound semiconductors, from the surface reaction of organic compounds or...
of thin film
Thin film
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....
s of gallium arsenide, indium gallium phosphide
Indium gallium phosphide
Indium gallium phosphide , also called gallium indium phosphide , is a semiconductor composed of indium, gallium and phosphorus...
or indium gallium arsenide
Indium gallium arsenide
Indium gallium arsenide is a semiconductor composed of indium, gallium and arsenic. It is used in high-power and high-frequency electronics because of its superior electron velocity with respect to the more common semiconductors silicon and gallium arsenide. InGaAs bandgap also makes it the...
.The Mars Exploration Rover
Mars Exploration Rover
NASA's Mars Exploration Rover Mission is an ongoing robotic space mission involving two rovers, Spirit and Opportunity, exploring the planet Mars...
s and several satellites use triple junction gallium arsenide on germanium cells. Gallium is the rarest component of new photovoltaic compounds (such as copper indium gallium selenium sulfide or Cu(In,Ga)(Se,S)2) for use in solar panels as a more efficient alternative to crystalline silicon.
Wetting and alloy improvement
- Because gallium wetsWettingWetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. The degree of wetting is determined by a force balance between adhesive and cohesive forces.Wetting is important in the bonding or adherence of...
glass or porcelainPorcelainPorcelain is a ceramic material made by heating raw materials, generally including clay in the form of kaolin, in a kiln to temperatures between and...
, gallium can be used to create brilliant mirrorMirrorA mirror is an object that reflects light or sound in a way that preserves much of its original quality prior to its contact with the mirror. Some mirrors also filter out some wavelengths, while preserving other wavelengths in the reflection...
s. When the wetting action of gallium-alloys is not desired (as in GalinstanGalinstanGalinstan is a family of eutectic alloys mainly consisting of gallium, indium, and tin, which are liquids at room temperature, typically freezing at . Due to the low toxicity and low reactivity of its component metals, it finds use as a replacement for many applications that previously employed...
glass thermometers), the glass must be protected with a transparent layer of gallium(III) oxideGallium(III) oxideGallium oxide is a chemical compound used in vacuum deposition and as part of the manufacturing of semiconductor devices.-Preparation:...
. - Gallium readily alloyAlloyAn alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s with most metals, and has been used as a component in low-melting alloys. The plutoniumPlutoniumPlutonium is a transuranic radioactive chemical element with the chemical symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forming a dull coating when oxidized. The element normally exhibits six allotropes and four oxidation...
used in nuclear weapon pits is machined by alloying with galliumPlutonium-gallium alloyPlutonium-gallium alloy is an alloy of plutonium and gallium, used in nuclear weapon pits – the component of a nuclear weapon where the fission chain reaction is started....
to stabilize its δ phaseAllotropes of plutoniumEven at ambient pressure, plutonium occurs in a variety of allotropes. These allotropes differ widely in crystal structure and density; the α and δ allotropes differ in density by more than 25% at constant pressure....
. - Gallium added in quantities up to 2% in common solderSolderSolder is a fusible metal alloy used to join together metal workpieces and having a melting point below that of the workpiece.Soft solder is what is most often thought of when solder or soldering are mentioned and it typically has a melting range of . It is commonly used in electronics and...
s can aid wetting and flow characteristics.
Galinstan and other liquid alloys
A nearly eutectic alloy of gallium, indiumIndium
Indium is a chemical element with the symbol In and atomic number 49. This rare, very soft, malleable and easily fusible post-transition metal is chemically similar to gallium and thallium, and shows the intermediate properties between these two...
, and tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
is a room temperature liquid which is widely available in medical thermometers, replacing problematic mercury. This alloy, with the trade-name Galinstan
Galinstan
Galinstan is a family of eutectic alloys mainly consisting of gallium, indium, and tin, which are liquids at room temperature, typically freezing at . Due to the low toxicity and low reactivity of its component metals, it finds use as a replacement for many applications that previously employed...
(with the "-stan" referring to the tin), has a low freezing point of −19 °C (−2.2°F). It has been suggested that this family of alloys could also be used to cool computer chips in place of water. 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 hydrogenHydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
, being oxidized to aluminium oxide
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
. However, the aluminium oxide forms a protective coat which prevents further reaction. Galinstan has been applied to activate aluminium (removing the oxide coat), so that aluminium can react with water, generating hydrogen and steam in a reaction being considered as a helpful step in a hydrogen economy
Hydrogen economy
The hydrogen economy is a proposed system of delivering energy using hydrogen. The term hydrogen economy was coined by John Bockris during a talk he gave in 1970 at General Motors Technical Center....
. A number of other gallium-aluminium 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 must be reformed back into electrodes with energy input. The thermodynamic efficiency of the aluminium smelting process is estimated as 50%. Therefore, at most only half the energy that goes into smelting the aluminium could be recovered by a hydrogen fuel cell.
Gallium(III) salts
- Gallium nitrateGallium nitrateGallium nitrate is the gallium salt of nitric acid with the chemical formula Ga3. It is a drug used to treat symptomatic hypercalcemia secondary to cancer. It works by preventing the breakdown of bone through the inhibition of osteoclast activity, thus lowering the amount of free calcium in the...
(brand name Ganite) has been used as an intravenous pharmaceutical to treat hypercalcemia associated with tumor metastasisMetastasisMetastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
to bones. Gallium is thought to interfere with osteoclastOsteoclastAn osteoclast is a type of bone cell that removes bone tissue by removing its mineralized matrix and breaking up the organic bone . This process is known as bone resorption. Osteoclasts were discovered by Kolliker in 1873...
function. It may be effective when other treatments for maligancy-associated hypercalcemia are not. - Gallium maltolateGallium maltolateGallium maltolate is a coordination complex consisting of a trivalent gallium cation coordinated to three maltolate ligands. The compound is undergoing clinical and preclinical testing as a potential therapeutic agent for cancer, infectious disease, and inflammatory disease...
, an orally-aborbable form of gallium(III) ion, is in clinical and preclinical trials as a potential treatment for a number of types of cancer, infectious disease, and inflammatory disease. - Research is being conducted to determine whether gallium ion can be used to fight bacterial infections in people with cystic fibrosisCystic fibrosisCystic fibrosis is a recessive genetic disease affecting most critically the lungs, and also the pancreas, liver, and intestine...
. Gallium is similar in size to iron, an essential nutrient for respiration. When gallium ions are mistakenly picked up by bacteria such as PseudomonasPseudomonasPseudomonas is a genus of gammaproteobacteria, belonging to the family Pseudomonadaceae containing 191 validly described species.Recently, 16S rRNA sequence analysis has redefined the taxonomy of many bacterial species. As a result, the genus Pseudomonas includes strains formerly classified in the...
, 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.
- In several studies, a complex amineAmineAmines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
-phenolPhenolPhenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
Ga(III) compound MR045 was found to be selectively toxic to parasites that have developed resistance to chloroquineChloroquineChloroquine is a 4-aminoquinoline drug used in the treatment or prevention of malaria.-History:Chloroquine , N'--N,N-diethyl-pentane-1,4-diamine, was discovered in 1934 by Hans Andersag and co-workers at the Bayer laboratories who named it "Resochin". It was ignored for a decade because it was...
, a common drug against malariaMalariaMalaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...
. Both the Ga(III) complex and chloroquine act by inhibiting crystallization of hemozoinHemozoinHemozoin is a disposal product formed from the digestion of blood by some blood-feeding parasites. These hematophagous organisms such as Malaria parasites , Rhodnius and Schistosoma digest hemoglobin and release high quantities of free heme, which is the non-protein component of hemoglobin...
, a disposal product formed from the digestion of blood by the parasites.
Radiogallium salts
Gallium-67 saltSalt
In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...
s such as gallium citrate
Citrate
A citrate can refer either to the conjugate base of citric acid, , or to the esters of citric acid. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate.-Other citric acid ions:...
and gallium nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
are used as radiopharmaceutical agents in a nuclear medicine
Nuclear medicine
In nuclear medicine procedures, elemental radionuclides are combined with other elements to form chemical compounds, or else combined with existing pharmaceutical compounds, to form radiopharmaceuticals. These radiopharmaceuticals, once administered to the patient, can localize to specific organs...
imaging procedure commonly referred to as a gallium scan
Gallium scan
A gallium scan or gallium 67 scan is a type of nuclear medicine study that uses a radioactive tracer to obtain images of a specific type of tissue, or disease state of tissue. Gallium salts like gallium citrate and gallium nitrate are used. The form of salt is not important, since it is the freely...
. The form or salt of gallium is not important, since it is the free dissolved gallium ion Ga3+ which is the active radiotracer. For these applications, the radioactive isotope
Radionuclide
A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy available to be imparted either to a newly created radiation particle within the nucleus or to an atomic electron. The radionuclide, in this process, undergoes radioactive decay, and emits gamma...
67Ga is used. The body handles Ga3+ in many ways as though it were iron, and thus it is 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. This use has largely been replaced by fluorodeoxyglucose
Fluorodeoxyglucose
Fludeoxyglucose or fluorodeoxyglucose , commonly abbreviated 18F-FDG or FDG, is a radiopharmaceutical used in the medical imaging modality positron emission tomography...
(FDG) for positron emission tomography
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
, "PET" scan and indium-111 labelled leukocyte scans. However, the localization of gallium in the body has some properties which make it unique in some circumstances from competing modalities using other radioisotopes.
Gallium-68, a positron emitter with a half life of 68 min., is now used as a diagnostic radionuclide in PET-CT when linked to pharmaceutical preparations such as DOTATOC, a somatostatin
Somatostatin
Somatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones.Somatostatin...
analogue used for neuroendocrine tumors
Neuroendocrine tumors
Neuroendocrine tumors are neoplasms that arise from cells of the endocrine and nervous systems. Many are benign, while some are cancers...
investigation, and DOTA-TATE
DOTA-TATE
DOTA-TATE, DOTATATE or DOTA-octreotate is a substance which, when bound to various radionuclides, has been tested for the treatment and diagnosis of certain types of cancer, mainly neuroendocrine tumours.-Chemistry and mechanism of action:...
, a newer one, used for neuroendocrine metastasis
Metastasis
Metastasis, or metastatic disease , is the spread of a disease from one organ or part to another non-adjacent organ or part. It was previously thought that only malignant tumor cells and infections have the capacity to metastasize; however, this is being reconsidered due to new research...
and lung neuroendocrine cancer, such as certain types of microcytoma. Galium-68's preparation as a pharmaceutical is chemical and the radionuclide is extracted by elution
Elution
Elution is a term used in analytical and organic chemistry to describe the process of extracting one material from another by washing with a solvent ....
from germanium-68, a synthetic radioisotope
Synthetic radioisotope
A synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. Examples include technetium-95 and promethium-146. Many of these are found in, and harvested...
of germanium
Germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
, in gallium-68 generator
Gallium-68 generator
A gallium-68 generator is a device used to extract the positron-emitting isotope 68Ga of gallium from a source of decaying germanium-68. The parent isotope 68Ge has a half-life of 271 days and can be easily sent to hospitals within the generator, where it is storable for almost a year...
s.
Other uses
- MagnesiumMagnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
gallate containing impurities (such as Mn2+), is beginning to be used in ultravioletUltravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
-activated phosphorPhosphorA phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
powder. - NeutrinoNeutrinoA neutrino is an electrically neutral, weakly interacting elementary subatomic particle with a half-integer spin, chirality and a disputed but small non-zero mass. It is able to pass through ordinary matter almost unaffected...
detection. Possibly the largest amount of pure gallium ever collected in a single spot is the Gallium-Germanium Neutrino Telescope used by the SAGESAGE (Soviet-American Gallium Experiment)SAGE is a collaborative experiment devised by several prominent physicists to measure the solar neutrino flux.-The Experiment:...
experiment at the Baksan Neutrino Observatory in Russia. This detector contains 55–57 tonnes of liquid gallium. Another experiment was the GALLEXGALLEXGALLEX or Gallium Experiment was a radiochemical neutrino detection experiment that ran between 1991 and 1997 at the Laboratori Nazionali del Gran Sasso...
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 GeGermaniumGermanium is a chemical element with the symbol Ge and atomic number 32. It is a lustrous, hard, grayish-white metalloid in the carbon group, chemically similar to its group neighbors tin and silicon. The isolated element is a semiconductor, with an appearance most similar to elemental silicon....
-71, which were detected. The solar neutrino flux deduced was found to have a deficit of 40% from theory. This was not explained until better solar neutrino detectors and theories were constructed (see SNOSnö"Snö" is a song by Iranian-Swedish singer-songwriter Laleh recorded with the London Symphony Orchestra for the film Arn - The Knight Templar. It was released on December 19, 2007 as her ninth single and was later placed on her third studio album, Me and Simon...
). - As a liquid metal ion sourceLiquid metal ion sourceIn a Liquid metal ion source , a metal is heated to the liquid state and provided at the end of a capillary or a needle. Then a Taylor cone is formed under the application of a strong electric field. As the cone's tip get sharper, the electric field becomes stronger, until ions are produced by...
for a focused ion beamFocused ion beamFocused ion beam, also known as FIB, is a technique used particularly in the semiconductor industry, materials science and increasingly in the biological field for site-specific analysis, deposition, and ablation of materials. An FIB setup is a scientific instrument that resembles a scanning...
. - As alloying element in the magnetic shape memory alloyShape memory alloyA shape-memory alloy is an alloy that "remembers" its original, cold-forged shape: returning the pre-deformed shape by heating. This material is a lightweight, solid-state alternative to conventional actuators such as hydraulic, pneumatic, and motor-based systems...
Ni-Mn-Ga. - In a classic prank by scientists, who fashion gallium spoons and serve tea to unsuspecting guests. The spoons melt in the hot tea.
- As an additive in glide wax for skiis, and other low friction surface materials.
Chemistry
Gallium is found primarily in the +3 oxidation stateOxidation stateIn chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
. The +1 oxidation is also attested in some compounds, although they tend to disproportionateDisproportionationDisproportionation, also known as dismutation is used to describe a specific type of redox reaction in which a species is simultaneously reduced and oxidized so as to form two different products....
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).
Chalcogen compounds
At room temperature, gallium metal is unreactive towards air and water due to the formation of a passive, protective oxide layer. At higher temperatures, however, it reacts with oxygen in the air to form gallium(III) oxideGallium(III) oxideGallium oxide is a chemical compound used in vacuum deposition and as part of the manufacturing of semiconductor devices.-Preparation:...
, . Reducing with elemental gallium in vacuum at 500 °C to 700 °C yields the dark brown gallium(I) oxide, . is a very strong reducing agentReducing agentA reducing agent is the element or compound in a reduction-oxidation reaction that donates an electron to another species; however, since the reducer loses an electron we say it is "oxidized"...
, capable of reducingSulfuric acidSulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
toHydrogen sulfideHydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
. It disproportionates at 800 °C back to gallium and .
Gallium sulfide, , has 3 possible crystal modifications. It can be made by the reaction of gallium with hydrogen sulfideHydrogen sulfideHydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
at 950 °C. Alternatively, can also be used at 747 °C:
- 2 + 3 → + 6
Reacting a mixture of alkali metal carbonates and with leads to the formation of thiogallates containing the anion. Strong acids decompose these salts, releasing in the process. The mercury salt, , can be used as a phosphorPhosphorA phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
.
Gallium also forms sulfides in lower oxidation states, such as gallium(II) sulfideGallium(II) sulfideGallium sulfide, GaS, is a chemical compound of gallium and sulfur. The normal form of gallium sulfide as made from the elements has a hexagonal layer structure containing Ga24+ units which have a Ga-Ga distance of 248pm. This layer structure is similar to GaTe, GaSe and InSe...
and the green gallium(I) sulfide, the latter of which is produced from the former by heating to 1000 °C under a stream of nitrogen.
The other binary chalcogenides, and , have zincblende structure. They are all semiconductors, but are easily hydrolysedHydrolysisHydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
, limiting their usefulness.
Aqueous chemistry
Strong acids dissolve gallium, forming gallium(III) salts such as and . Aqueous solutions of gallium(III) salts contain the hydrated gallium ion, . Gallium(III) hydroxideGallium(III) hydroxideGallium hydroxide, Ga3, is the normal mineral form of gallium in the Earth's crust.Gallium hydroxide is very rarely found as a discrete mineral called söhngeite. More commonly, gallium replaces aluminium in ores such as bauxite. Rich sources may contain almost 1% Ga replacing Al, but a more typical...
, , may be precipitated from gallium(III) solutions by adding ammoniaAmmoniaAmmonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
. Dehydrating at 100 °C produces gallium oxide hydroxide, GaO(OH).
Alkaline hydroxideHydroxideHydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
solutions dissolve gallium, forming gallate salts containing the anion. Gallium hydroxide, which is amphoteric, also dissolves in alkali to form gallate salts. Although earlier work suggested as another possible gallate anion, this species was not found in later work.
Pnictogen compounds
Gallium reacts with ammonia at 1050 °C to form gallium nitride, GaN. Gallium also forms binary compounds with phosphorusPhosphorusPhosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...
, arsenicArsenicArsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
, and antimonyAntimonyAntimony is a toxic chemical element with the symbol Sb and an atomic number of 51. A lustrous grey metalloid, it is found in nature mainly as the sulfide mineral stibnite...
: gallium phosphide (GaP), gallium arsenide (GaAs), and gallium antimonide (GaSb). These compounds have the same structure as ZnSZinc sulfideZinc sulfide is a inorganic compound with the formula ZnS. ZnS is the main form of zinc in nature, where it mainly occurs as the mineral sphalerite...
, and have important semiconductingSemiconductorA semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
properties. GaP, GaAs, and GaSb can be synthesized by the direct reaction of gallium with elemental phosphorus, arsenic, or antimony. They exhibit higher electrical conductivity than GaN. GaP can also be synthesized by the reaction of with phosphorus at low temperatures.
Gallium also forms ternary nitrides; for example:
- + →
Similar compounds with phosphorus and antimony also exist: and . These compounds are easily hydrolyzed by dilute acids and water.
Halides
Gallium(III) oxide reacts with fluorinating agents such as HFHydrogen fluorideHydrogen fluoride is a chemical compound with the formula HF. This colorless gas is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the...
orFluorineFluorine is the chemical element with atomic number 9, represented by the symbol F. It is the lightest element of the halogen column of the periodic table and has a single stable isotope, fluorine-19. At standard pressure and temperature, fluorine is a pale yellow gas composed of diatomic...
to form gallium(III) fluorideGallium(III) fluorideGallium fluoride is a chemical compound. A white solid it melts above 1000°C but sublimes around 950°C. It has the FeF3 structure where the gallium atoms are 6 coordinate. GaF3 can be prepared by reacting F2 or HF with Ga2O3 or by thermal decomposition of 3GaF6.GaF3 is virtually insoluble in...
, . It is an ionic compound strongly insoluble in water. However, it does dissolve in hydrofluoric acidHydrofluoric acidHydrofluoric acid is a solution of hydrogen fluoride in water. It is a valued source of fluorine and is the precursor to numerous pharmaceuticals such as fluoxetine and diverse materials such as PTFE ....
, in which it forms an adduct with water, . Attempting to dehydrate this adduct instead forms . The adduct reacts with ammonia to form , which can then be heated to form anhydrous .
Gallium trichlorideGallium trichlorideGallium trichloride is the chemical compound with the formula GaCl3. Solid gallium trichloride exists as a dimer with the formula Ga2Cl6. It is colourless and soluble in virtually all solvents, which is unusual for a metal halide. It is the main precursor to most derivatives of gallium and a...
is formed by the reaction of gallium metal with chlorineChlorineChlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
gas. Unlike the trifluoride, gallium(III) chloride exists as dimeric molecules, , with a melting point of 78 °C. This is also the case for the bromide and iodide,Gallium(III) bromideGallium bromide is a chemical compound.It may be formed by the reaction of gallium metal or gallium oxide with hydrobromic acid.Another approach is the reaction of gallium with elemental bromine....
andGallium(III) iodideGallium iodide is the chemical compound with the formula Ga2I6. It is the most common iodide of gallium. In the chemical vapor transport method of growing crystals of gallium arsenide uses iodine as the transport agent...
.
Like the other group 13 trihalides, gallium(III) halides are Lewis acidLewis acid]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
s, reacting as halide acceptors with alkali metal halides to form salts containing anions, where X is a halogen. They also react with alkyl halideHaloalkaneThe haloalkanes are a group of chemical compounds derived from alkanes containing one or more halogens. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially and, consequently, are known under many chemical and...
s to form carbocationCarbocationA carbocation is an ion with a positively-charged carbon atom. The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer valence shell instead of the eight valence electrons that ensures maximum stability . Therefore carbocations are often reactive,...
s and .
When heated to a high temperature, gallium(III) halides react with elemental gallium to form the respective gallium(I) halides. For example, reacts with Ga to form :
- 2 Ga + 3 GaCl (g)
At lower temperatures, the equilibrium shifts toward the left and GaCl disproportionates back to elemental gallium and . GaCl can also be made by the reaction of Ga with HCl at 950 °C; it can then be condensed as red solid.
Gallium(I) compounds can be stabilized by forming adducts with Lewis acids. For example:
- GaCl + →
The so-called "gallium(II) halides", , are actually adducts of gallium(I) halides with the respective gallium(III) halides, having the structure . For example:
- GaCl + →
Hydrogen compounds
Like aluminiumAluminiumAluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
, gallium also forms a hydride, , known as gallane, which may be obtained by the reaction of lithium gallanate with gallium(III) chloride at −30 °C:
- 3 + → 3 LiCl + 4
In the presence of dimethyl etherDimethyl etherDimethyl ether , also known as methoxymethane, is the organic compound with the formula . The simplest ether, it is a colourless gas that is a useful precursor to other organic compounds and an aerosol propellant. When combusted, DME produces minimal soot and CO, though HC and NOx formation is...
as solvent, polymerizes to . If no solvent is used, the dimer (digallane) is formed as a gas. Its structure is similar to diboraneDiboraneDiborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
, having two hydrogen atoms bridging the two gallium centers, unlike α-Aluminium hydrideAluminium hydride is an inorganic compound with the formula AlH3. It is a colourless solid that is pyrophoric. Although rarely encountered outside of research laboratory, alane and its derivatives are used as reducing agents in organic synthesis.-Structure:...
in which aluminium has a coordination number of 6.
Gallane is unstable above −10 °C, decomposing to elemental gallium and hydrogen.
Precautions
While not considered toxic, the data about gallium are inconclusive. Some sources suggest that it may cause dermatitisDermatitis-Etymology:Dermatitis derives from Greek derma "skin" + -itis "inflammation" and genetic disorder.-Terminology:There are several different types of dermatitis. The different kinds usually have in common an allergic reaction to specific allergens. The term may describe eczema, which is also called...
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.
See also
External links
- Material safety data sheetMaterial safety data sheetA Material Safety Data Sheet is a form with data regarding the properties of a particular substance....
at acialloys.com - High-resolution photographs of molten gallium, gallium crystals and gallium ingots under Creative Commons licence
- www.lenntech.com – textbook information regarding gallium
- Environmental effects of gallium
- Price development of gallium 1959–1998
- Technology produces hydrogen by adding water to an alloy of aluminum and gallium