Gallium is a
chemical element
A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...
with the
symbol Ga and
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
31. Discovered by
French chemist
A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties. Chemists carefully describe t ...
Paul-Émile Lecoq de Boisbaudran
Paul-Émile Lecoq de Boisbaudran, also called François Lecoq de Boisbaudran (18 April 1838 – 28 May 1912), was a French chemist known for his discoveries of the chemical elements gallium, samarium and dysprosium.
He developed methods for s ...
in 1875, Gallium is in
group 13
The Group 13 network ( pl, Trzynastka, Yiddish: ''דאָס דרײַצענטל'') was a Jewish Nazi collaborationist organization in the Warsaw Ghetto during the German occupation of Poland in World War II. The rise and fall of the Group ...
of the periodic table and is similar to the other metals of the group (
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
,
indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
, and
thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes an ...
).
Elemental gallium is a soft, silvery
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
in
standard temperature and pressure. In its liquid state, it becomes silvery white. If too much force is applied, the gallium may fracture
conchoidally. Since its discovery in 1875, gallium has widely been used to make
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
s with low melting points. It is also used in
semiconductor
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...
s, as a
dopant
A dopant, also called a doping agent, is a trace of impurity element that is introduced into a chemical material to alter its original electrical or optical properties. The amount of dopant necessary to cause changes is typically very low. When ...
in semiconductor substrates.
The melting point of gallium is used as a temperature reference point. Gallium alloys are used in thermometers as a non-toxic and
environmentally friendly alternative to mercury, and can withstand higher temperatures than mercury. An even lower melting point of , well below the freezing point of water, is claimed for the alloy
galinstan (62–95% gallium, 5–22%
indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
, and 0–16%
tin
Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal.
Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
by weight), but that may be the freezing point with the effect of
supercooling
Supercooling, also known as undercooling, is the process of lowering the temperature of a liquid or a gas below its melting point without it becoming a solid. It achieves this in the absence of a seed crystal or nucleus around which a crystal ...
.
Gallium does not occur as a free element in nature, but as gallium(III) compounds in trace amounts in
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
ores (such as
sphalerite) and in
bauxite
Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO ...
. Elemental gallium is a liquid at temperatures greater than , and will melt in a person's hands at normal human body temperature of .
Gallium is predominantly used in
electronics
The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...
.
Gallium arsenide, the primary
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
of gallium in electronics, is used in
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
circuits, high-speed switching circuits, and
infrared
Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
circuits. Semiconducting
gallium nitride
Gallium nitride () is a binary III/ V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords ...
and
indium gallium nitride
Indium gallium nitride (InGaN, ) is a semiconductor material made of a mix of gallium nitride (GaN) and indium nitride (InN). It is a ternary group III/ group V direct bandgap semiconductor. Its bandgap can be tuned by varying the amount of i ...
produce blue and violet
light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (co ...
s and
diode laser
The laser diode chip removed and placed on the eye of a needle for scale
A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with e ...
s. Gallium is also used in the production of artificial
gadolinium gallium garnet for jewelry. Gallium is considered a
technology-critical element
A technology-critical element (TCE) is a chemical element that is critical to modern and emerging technologies. Technology-critical elements are elements for which a striking acceleration in usage has emerged, relative to past consumption. Many adv ...
by the
United States National Library of Medicine
The United States National Library of Medicine (NLM), operated by the United States federal government, is the world's largest medical library.
Located in Bethesda, Maryland, the NLM is an institute within the National Institutes of Health. Its ...
and
Frontiers Media.
Gallium has no known natural role in biology. Gallium(III) behaves in a similar manner to
ferric
In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+.
The adjective ferric or the prefix ferri- is often used to sp ...
salts in biological systems and has been used in some medical applications, including pharmaceuticals and
radiopharmaceuticals
Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which is ...
.
Physical properties
![Gallium kristallisiert](https://upload.wikimedia.org/wikipedia/commons/b/bb/Gallium_kristallisiert.JPG)
Elemental gallium is not found in nature, but it is easily obtained by
smelting
Smelting is a process of applying heat to ore, to extract a base metal. It is a form of extractive metallurgy. It is used to extract many metals from their ores, including silver, iron, copper, and other base metals. Smelting uses heat and a ...
. Very pure gallium is a silvery blue metal that fractures
conchoidally like
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
. Gallium liquid expands by 3.10% when it solidifies; therefore, it should not be stored in glass or metal containers because the container may rupture when the gallium changes state. Gallium shares the higher-density liquid state with a short list of other materials that includes
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
,
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic ta ...
,
germanium,
bismuth
Bismuth is a chemical element with the symbol Bi and atomic number 83. It is a post-transition metal and one of the pnictogens, with chemical properties resembling its lighter group 15 siblings arsenic and antimony. Elemental bismuth occurs ...
, and
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
.
[Greenwood and Earnshaw, p. 222]
Gallium forms alloys with most metals. It readily diffuses into cracks or
grain boundaries
In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure, and tend to decrease the electrical and thermal ...
of some metals such as aluminium,
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
–
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
s and
steel, causing extreme loss of strength and ductility called
liquid metal embrittlement
Liquid metal embrittlement (LME), also known as liquid metal induced embrittlement, is a phenomenon of practical importance, where certain ductile metals experience drastic loss in tensile ductility or undergo brittle fracture when exposed to speci ...
.
The
melting point
The melting point (or, rarely, liquefaction point) of a substance 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 depen ...
of gallium, at 302.9146 K (29.7646 °C, 85.5763 °F), is just above room temperature, and is approximately the same as the average summer daytime temperatures in Earth's mid-latitudes. This melting point (mp) is one of the formal temperature reference points in the
International Temperature Scale of 1990 (ITS-90) established by the
International Bureau of Weights and Measures
The International Bureau of Weights and Measures (french: Bureau international des poids et mesures, BIPM) is an intergovernmental organisation, through which its 59 member-states act together on measurement standards in four areas: chemistry ...
(BIPM). The
triple point
In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at which the sub ...
of gallium, 302.9166 K (29.7666 °C, 85.5799 °F), is used by the US
National Institute of Standards and Technology
The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical s ...
(NIST) in preference to the melting point.
The melting point of gallium allows it to melt in the human hand, and then solidify if removed. The liquid metal has a strong tendency to
supercool below its
melting point
The melting point (or, rarely, liquefaction point) of a substance 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 depen ...
/
freezing point
The melting point (or, rarely, liquefaction point) of a substance 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 depend ...
: Ga nanoparticles can be kept in the liquid state below 90 K.
Seeding
The term seeding and related terms such as seeded are used in several different contexts:
*Sowing, planting seeds in a place or on an object
*Cloud seeding, manipulating cloud formations
*Seeding (computing), a concept in computing and peer-to-pee ...
with a crystal helps to initiate freezing. Gallium is one of the four non-radioactive metals (with
caesium,
rubidium, and
mercury) that are known to be liquid at, or near, normal room temperature. Of the four, gallium is the only one that is neither highly reactive (as are rubidium and caesium) nor highly toxic (as is mercury) and can, therefore, be used in metal-in-glass high-temperature
thermometer
A thermometer is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer ...
s. It is also notable for having one of the largest liquid ranges for a metal, and for having (unlike mercury) a low
vapor pressure
Vapor pressure (or vapour pressure in English-speaking countries other than the US; see spelling differences) or equilibrium vapor pressure is defined as the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phas ...
at high temperatures. Gallium's boiling point, 2673 K, is nearly nine times higher than its melting point on the
absolute scale
There is no single definition of an absolute scale. In statistics and measurement theory, it is simply a ratio scale in which the unit of measurement is fixed, and values are obtained by counting. According to another definition it is a system of ...
, the greatest ratio between melting point and boiling point of any element.
[Greenwood and Earnshaw, p. 224] Unlike mercury, liquid gallium metal
wets
During the 1980s, members of the moderate wing of the British Conservative Party who opposed some of the more hard-line policies of Prime Minister Margaret Thatcher were often referred to by their opponents as "wets". Thatcher coined the usage in ...
glass and skin, along with most other materials (with the exceptions of quartz, graphite,
gallium(III) oxide
Gallium(III) oxide is an inorganic compound and ultra-wide bandgap semiconductor with the formula Ga2 O3. It is actively studied for applications in power electronics, phosphors, and gas sensing. The compound has several polymorphs, of which t ...
and
PTFE),
[Greenwood and Earnshaw, p. 221] making it mechanically more difficult to handle even though it is substantially less toxic and requires far fewer precautions than mercury. Gallium painted onto glass is a brilliant mirror.
For this reason as well as the metal contamination and freezing-expansion problems, samples of gallium metal are usually supplied in polyethylene packets within other containers.
Gallium does not
crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
lize in any of the simple
crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns ...
s. The stable phase under normal conditions is
orthorhombic with 8 atoms in the conventional
unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...
. Within a unit cell, each atom has only one nearest neighbor (at a distance of 244
pm). The remaining six unit cell neighbors are spaced 27, 30 and 39 pm farther away, and they are grouped in pairs with the same distance. Many stable and
metastable
In chemistry and physics, metastability denotes an intermediate energetic state within a dynamical system other than the system's state of least energy.
A ball resting in a hollow on a slope is a simple example of metastability. If the ball i ...
phases are found as function of temperature and pressure.
The bonding between the two nearest neighbors is
covalent
A covalent bond is a chemical bond that involves the sharing of electrons to form electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs. The stable balance of attractive and repulsive forces between atoms ...
; hence Ga
2 dimers are seen as the fundamental building blocks of the crystal. This explains the low melting point relative to the neighbor elements, aluminium and indium. This structure is strikingly similar to that of
iodine and may form because of interactions between the single 4p electrons of gallium atoms, further away from the nucleus than the 4s electrons and the
rd
10 core. This phenomenon recurs with
mercury with its "pseudo-noble-gas"
ef
145d
106s
2 electron configuration, which is liquid at room temperature.
[Greenwood and Earnshaw, p. 223] The 3d
10 electrons do not shield the outer electrons very well from the nucleus and hence the first ionisation energy of gallium is greater than that of aluminium.
Ga
2 dimers do not persist in the liquid state and liquid gallium exhibits a complex low-coordinated structure in which each gallium atom is surrounded by 10 others, rather than 11–12 neighbors typical of most liquid metals.
The physical properties of gallium are highly
anisotropic, i.e. have different values along the three major crystallographic axes ''a'', ''b'', and ''c'' (see table), producing a significant difference between the linear (α) and volume
thermal expansion
Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.
Temperature is a monotonic function of the average molecular kinetic ...
coefficients. The properties of gallium are strongly temperature-dependent, particularly near the melting point. For example, the coefficient of thermal expansion increases by several hundred percent upon melting.
Isotopes
Gallium has 31 known isotopes, ranging in
mass number
The mass number (symbol ''A'', from the German word ''Atomgewicht'' tomic weight, also called atomic mass number or nucleon number, is the total number of protons and neutrons (together known as nucleons) in an atomic nucleus. It is approxima ...
from 56 to 86. Only two isotopes are stable and occur naturally, gallium-69 and gallium-71. Gallium-69 is more abundant: it makes up about 60.1% of natural gallium, while gallium-71 makes up the remaining 39.9%. All the other isotopes are radioactive, with gallium-67 being the longest-lived (half-life 3.261 days). Isotopes lighter than gallium-69 usually decay through
beta plus decay
Positron emission, beta plus decay, or β+ decay is a subtype of radioactive decay called beta decay, in which a proton inside a radionuclide nucleus is converted into a neutron while releasing a positron and an electron neutrino (). Positron ...
(positron emission) or
electron capture
Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. Thi ...
to isotopes of
zinc
Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...
, although the lightest few (mass numbers 56–59) decay through prompt
proton emission
Proton emission (also known as proton radioactivity) is a rare type of radioactive decay in which a proton is ejected from a nucleus. Proton emission can occur from high-lying excited states in a nucleus following a beta decay, in which case t ...
. Isotopes heavier than gallium-71 decay through
beta minus decay
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For exam ...
(electron emission), possibly with delayed
neutron emission
Neutron emission is a mode of radioactive decay in which one or more neutrons are ejected from a nucleus. It occurs in the most neutron-rich/proton-deficient nuclides, and also from excited states of other nuclides as in photoneutron emission and ...
, to isotopes of
germanium, while gallium-70 can decay through both beta minus decay and electron capture. Gallium-67 is unique among the light isotopes in having only electron capture as a decay mode, as its decay energy is not sufficient to allow positron emission.
Gallium-67 and
gallium-68
Natural gallium (31Ga) consists of a mixture of two stable isotopes: gallium-69 and gallium-71. The most commercially important radioisotopes are gallium-67 and gallium-68.
Gallium-67 (half-life 3.3 days) is a gamma-emitting isotope (the gamma r ...
(half-life 67.7 min) are both used in nuclear medicine.
Chemical properties
Gallium is found primarily in the +3
oxidation state
In chemistry, the oxidation state, or oxidation number, is the hypothetical charge of an atom if all of its bonds to different atoms were fully ionic. It describes the degree of oxidation (loss of electrons) of an atom in a chemical compound. C ...
. The +1 oxidation state is also found in some compounds, although it is less common than it is for gallium's heavier congeners
indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
and
thallium
Thallium is a chemical element with the symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Chemists William Crookes an ...
. For example, the very stable GaCl
2 contains both gallium(I) and gallium(III) and can be formulated as Ga
IGa
IIICl
4; in contrast, the monochloride is unstable above 0 °C,
disproportionating into elemental gallium and gallium(III) chloride. Compounds containing Ga–Ga bonds are true gallium(II) compounds, such as
GaS
Gas is one of the four fundamental states of matter (the others being solid, liquid, and plasma).
A pure gas may be made up of individual atoms (e.g. a noble gas like neon), elemental molecules made from one type of atom (e.g. oxygen), or ...
(which can be formulated as Ga
24+(S
2−)
2) and the
dioxan
1,4-Dioxane () is a Heterocyclic compound, heterocyclic organic compound, classified as an ether. It is a colorless liquid with a faint sweet odor similar to that of diethyl ether. The compound is often called simply dioxane because the other ...
complex Ga
2Cl
4(C
4H
8O
2)
2.
[Greenwood and Earnshaw, p. 240]
Aqueous chemistry
Strong acids dissolve gallium, forming gallium(III) salts such as
(gallium nitrate).
Aqueous
An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...
solutions of gallium(III) salts contain the hydrated gallium ion, .
Gallium(III) hydroxide
Gallium hydroxide, Ga(OH)3 is formed as a gel following the addition of ammonia to Ga3+ salts.Anthony John Downs, (1993), ''Chemistry of Aluminium, Gallium, Indium, and Thallium'', Springer, It is also found in nature as the rare mineral söhngei ...
, , may be precipitated from gallium(III) solutions by adding
ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous wa ...
. Dehydrating at 100 °C produces gallium oxide hydroxide, GaO(OH).
Alkaline
hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...
solutions dissolve gallium, forming ''gallate'' salts (not to be confused with identically named
gallic acid
Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula C6 H2( OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. I ...
salts) containing the anion.
Gallium hydroxide, which is
amphoteric
In chemistry, an amphoteric compound () is a molecule or ion that can react both as an acid and as a base. What exactly this can mean depends on which definitions of acids and bases are being used.
One type of amphoteric species are amphipro ...
, also dissolves in alkali to form gallate salts.
Although earlier work suggested as another possible gallate anion, it was not found in later work.
Oxides and chalcogenides
Gallium reacts with the
chalcogen
The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the radioac ...
s only at relatively high temperatures. At room temperature, gallium metal is not reactive with air and water because it forms a
passive
Passive may refer to:
* Passive voice, a grammatical voice common in many languages, see also Pseudopassive
* Passive language, a language from which an interpreter works
* Passivity (behavior), the condition of submitting to the influence of o ...
, protective
oxide layer. At higher temperatures, however, it reacts with atmospheric
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
to form
gallium(III) oxide
Gallium(III) oxide is an inorganic compound and ultra-wide bandgap semiconductor with the formula Ga2 O3. It is actively studied for applications in power electronics, phosphors, and gas sensing. The compound has several polymorphs, of which t ...
, .
Reducing with elemental gallium in vacuum at 500 °C to 700 °C yields the dark brown
gallium(I) oxide
Gallium(I) oxide, digallium monoxide or gallium suboxide is an inorganic compound with the formula Ga2 O.
Production
Gallium(I) oxide can be produced by reacting gallium(III) oxide with heated gallium in vacuum:
:\mathrm
It can also be obtained ...
, .
is a very strong
reducing agent
In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ).
Examples of substances that are commonly reducing agents include the Earth me ...
, capable of reducing
to
.
It disproportionates at 800 °C back to gallium and .
Gallium(III) sulfide, , has 3 possible crystal modifications.
It can be made by the reaction of gallium with
hydrogen sulfide () at 950 °C.
Alternatively, can 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
phosphor.
Gallium also forms sulfides in lower oxidation states, such as
gallium(II) sulfide 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 the
zincblende
Sphalerite (sometimes spelled sphaelerite) is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in sedimentary exhalative, Mississippi-Va ...
structure. They are all semiconductors but are easily
hydrolysed
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysis ...
and have limited utility.
Nitrides and pnictides
Gallium reacts with ammonia at 1050 °C to form
gallium nitride
Gallium nitride () is a binary III/ V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords ...
, GaN. Gallium also forms binary compounds with
phosphorus
Phosphorus is a chemical element with the symbol P and atomic number 15. Elemental phosphorus exists in two major forms, white phosphorus and red phosphorus, but because it is highly reactive, phosphorus is never found as a free element on Ear ...
,
arsenic
Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...
, and
antimony
Antimony is a chemical element with the symbol Sb (from la, stibium) and atomic number 51. A lustrous gray metalloid, it is found in nature mainly as the sulfide mineral stibnite (Sb2S3). Antimony compounds have been known since ancient t ...
:
gallium phosphide
Gallium phosphide (GaP), a phosphide of gallium, is a compound semiconductor material with an indirect band gap of 2.24 eV at room temperature. Impure polycrystalline material has the appearance of pale orange or grayish pieces. Undoped single ...
(GaP),
gallium arsenide (GaAs), and
gallium antimonide
Gallium antimonide (GaSb) is a semiconducting compound of gallium and antimony of the III-V family. It has a lattice constant of about 0.61 nm. It has a band gap of 0.67 eV.
History
The intermetallic compound GaSb was first prepared in 1926 by V ...
(GaSb). These compounds have the same structure as
ZnS ZNS or ZnS may refer to:
* Zinc sulfide or zinc sulphide (ZnS), a chemical compound
* ZNS-TV, a national radio and TV broadcaster operated by the state-owned Broadcasting Corporation of The Bahamas
** ZNS-1
ZNS-1 (branded as ''Radio Bahamas'') i ...
, and have important
semiconducting
A semiconductor is a material which has an electrical resistivity and conductivity, electrical conductivity value falling between that of a electrical conductor, conductor, such as copper, and an insulator (electricity), insulator, such as glas ...
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 reacting with phosphorus at low temperatures.
Gallium forms ternary
nitride
In chemistry, a nitride is an inorganic compound of nitrogen. The "nitride" anion, N3- ion, is very elusive but compounds of nitride are numerous, although rarely naturally occuring. Some nitrides have a find applications, such as wear-resistant ...
s; for example:
: + →
Similar compounds with phosphorus and arsenic are possible: and . These compounds are easily hydrolyzed by dilute
acids and water.
Halides
Gallium(III) oxide reacts with
fluorinating agents such as
HF or
to form
gallium(III) fluoride, . It is an ionic compound strongly insoluble in water. However, it dissolves in
hydrofluoric acid, in which it forms an
adduct
An adduct (from the Latin ''adductus'', "drawn toward" alternatively, a contraction of "addition product") is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all co ...
with water, . Attempting to dehydrate this adduct forms . The adduct reacts with ammonia to form , which can then be heated to form anhydrous .
Gallium trichloride
Gallium 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, even alkanes, which is truly unusual for a metal h ...
is formed by the reaction of gallium metal with
chlorine
Chlorine is a chemical element with the symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between them. Chlorine i ...
gas.
Unlike the trifluoride, gallium(III) chloride exists as dimeric molecules, , with a melting point of 78 °C. Eqivalent compounds are formed with bromine and iodine,
and
.
Like the other group 13 trihalides, gallium(III) halides are
Lewis acids, reacting as halide acceptors with alkali metal halides to form salts containing anions, where X is a halogen. They also react with
alkyl halides
The haloalkanes (also known as halogenoalkanes or alkyl halides) are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely us ...
to form
carbocations 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 produced by reacting Ga with HCl at 950 °C; the product can be condensed as a 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 + →
Hydrides
Like
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
, gallium also forms a
hydride
In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride ...
, , known as ''
gallane
Gallane, also systematically named trihydridogallium, is an inorganic compound of gallium with the chemical formula (also written as ). It is a photosensitive, colourless gas that cannot be concentrated in pure form. Gallane is both the simplest ...
'', which may be produced by reacting lithium gallanate () with
gallium(III) chloride
Gallium 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, even alkanes, which is truly unusual for a metal h ...
at −30 °C:
:3 + → 3 LiCl + 4
In the presence of
dimethyl ether
Dimethyl ether (DME; also known as methoxymethane) is the organic compound with the formula CH3OCH3,
(sometimes ambiguously simplified to C2H6O as it is an isomer of ethanol). The simplest ether, it is a colorless gas that is a useful precursor ...
as solvent, polymerizes to . If no solvent is used, the dimer (''
digallane
Digallane (systematically named digallane(6)) is an inorganic compound with the chemical formula (also written or ). It is the dimer of the monomeric compound gallane. The eventual preparation of the pure compound, reported in 1989,
was haile ...
'') is formed as a gas. Its structure is similar to
diborane
Diborane(6), generally known as diborane, is the chemical compound with the formula B2H6. It is a toxic, colorless, and pyrophoric gas with a repulsively sweet odor. Diborane is a key boron compound with a variety of applications. It has attracte ...
, having two hydrogen atoms bridging the two gallium centers,
unlike α-
in which aluminium has a coordination number of 6.
Gallane is unstable above −10 °C, decomposing to elemental gallium and
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
.
Organogallium compounds
Organogallium compounds are of similar reactivity to
organoindium compounds, less reactive than
organoaluminium compounds, but more reactive than
organothallium compounds.
[Greenwoood and Earnshaw, pp. 262–5] Alkylgalliums are monomeric.
Lewis acidity decreases in the order Al > Ga > In and as a result organogallium compounds do not form bridged dimers as organoaluminium compounds do. Organogallium compounds are also less reactive than organoaluminium compounds. They do form stable peroxides. These alkylgalliums are liquids at room temperature, having low melting points, and are quite mobile and flammable. Triphenylgallium is monomeric in solution, but its crystals form chain structures due to weak intermolecluar Ga···C interactions.
Gallium trichloride is a common starting reagent for the formation of organogallium compounds, such as in
carbogallation reactions. Gallium trichloride reacts with
lithium
Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...
cyclopentadienide in
diethyl ether
Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable li ...
to form the trigonal planar gallium cyclopentadienyl complex GaCp
3. Gallium(I) forms complexes with
arene
Aromatic compounds, also known as "mono- and polycyclic aromatic hydrocarbons", are organic compounds containing one or more aromatic rings. The parent member of aromatic compounds is benzene. The word "aromatic" originates from the past groupin ...
ligands such as
hexamethylbenzene
Hexamethylbenzene, also known as mellitene, is a hydrocarbon with the molecular formula C12H18 and the condensed structural formula C6(CH3)6. It is an aromatic compound and a derivative of benzene, where benzene's six hydrogen atoms have each ...
. Because this ligand is quite bulky, the structure of the
6-C6Me6)">a(η6-C6Me6)sup>+ is that of a
half-sandwich. Less bulky ligands such as
mesitylene
Mesitylene or 1,3,5-trimethylbenzene is a derivative of benzene with three methyl substituents positioned symmetrically around the ring. The other two isomeric trimethylbenzenes are 1,2,4-trimethylbenzene (pseudocumene) and 1,2,3-trimethylbenze ...
allow two ligands to be attached to the central gallium atom in a bent sandwich structure.
Benzene
Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms ...
is even less bulky and allows the formation of dimers: an example is
6-C6H6)2">a(η6-C6H6)2 4">aCl43C
6H
6.
History
In 1871, the existence of gallium was first predicted by Russian chemist
Dmitri Mendeleev, who named it "
eka-aluminium" from its position in his
periodic table. He also predicted several properties of eka-aluminium that correspond closely to the real properties of gallium, such as its
density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematical ...
,
melting point
The melting point (or, rarely, liquefaction point) of a substance 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 depen ...
, oxide character, and bonding in chloride.
:
Mendeleev further predicted that eka-aluminium would be discovered by means of the
spectroscope
An optical spectrometer (spectrophotometer, spectrograph or spectroscope) is an instrument used to measure properties of light over a specific portion of the electromagnetic spectrum, typically used in spectroscopic analysis to identify mate ...
, and that metallic eka-aluminium would dissolve slowly in both acids and alkalis and would not react with air. He also predicted that M
2O
3 would dissolve in acids to give MX
3 salts, that eka-aluminium salts would form basic salts, that eka-aluminium sulfate should form
alums, and that anhydrous MCl
3 should have a greater volatility than ZnCl
2: all of these predictions turned out to be true.
Gallium was discovered using
spectroscopy by French chemist
Paul Emile Lecoq de Boisbaudran in 1875 from its characteristic spectrum (two
violet
Violet may refer to:
Common meanings
* Violet (color), a spectral color with wavelengths shorter than blue
* One of a list of plants known as violet, particularly:
** ''Viola'' (plant), a genus of flowering plants
Places United States
* Viol ...
lines) in a sample of
sphalerite.
Later that year, Lecoq obtained the free metal by
electrolysis of the
hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...
in
potassium hydroxide
Potassium hydroxide is an inorganic compound with the formula K OH, and is commonly called caustic potash.
Along with sodium hydroxide (NaOH), KOH is a prototypical strong base. It has many industrial and niche applications, most of which exp ...
solution.
He named the element "gallia", from
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''Gallia'' meaning
Gaul
Gaul ( la, Gallia) was a region of Western Europe first described by the Romans. It was inhabited by Celtic and Aquitani tribes, encompassing present-day France, Belgium, Luxembourg, most of Switzerland, parts of Northern Italy (only during ...
, after his native land of France. It was later claimed that, in a multilingual
pun
A pun, also known as paronomasia, is a form of word play that exploits multiple meanings of a term, or of similar-sounding words, for an intended humorous or rhetorical effect. These ambiguities can arise from the intentional use of homophoni ...
of a kind favoured by men of science in the 19th century, he had also named gallium after himself: "Le coq" is French for "the
rooster
The chicken (''Gallus gallus domesticus'') is a domesticated junglefowl species, with attributes of wild species such as the grey and the Ceylon junglefowl that are originally from Southeastern Asia. Rooster or cock is a term for an adult m ...
" and the
Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
word for "rooster" is "''gallus''". In an 1877 article, Lecoq denied this conjecture.
Originally, de Boisbaudran determined the density of gallium as 4.7 g/cm
3, the only property that failed to match Mendeleev's predictions; Mendeleev then wrote to him and suggested that he should remeasure the density, and de Boisbaudran then obtained the correct value of 5.9 g/cm
3, that Mendeleev had predicted exactly.
From its discovery in 1875 until the era of semiconductors, the primary uses of gallium were high-temperature thermometrics and metal alloys with unusual properties of stability or ease of melting (some such being liquid at room temperature).
The development of
gallium arsenide as a
direct bandgap semiconductor in the 1960s ushered in the most important stage in the applications of gallium.
In 1978, the electronics industry used gallium to fabricate light emitting diodes,
photovoltaics
Photovoltaics (PV) is the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect, a phenomenon studied in physics, photochemistry, and electrochemistry. The photovoltaic effect is commercially ...
and semiconductors, while the metals business used it
to reduce the melting point of
alloys
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility ...
.
Occurrence
Gallium does not exist as a free element in the Earth's crust, and the few high-content minerals, such as gallite (CuGaS
2), are too rare to serve as a primary source.
The abundance
in the Earth's crust is approximately 16.9
ppm.
This is comparable to the crustal abundances of
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
,
cobalt
Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...
, and
niobium. Yet unlike these elements, gallium does not form its own ore deposits with concentrations of > 0.1 wt.% in ore. Rather it occurs at trace concentrations similar to the crustal value in zinc ores,
and at somewhat higher values (~ 50 ppm) in aluminium ores, from both of which it is extracted as a by-product. This lack of independent deposits is due to gallium's geochemical behaviour, showing no strong enrichment in the processes relevant to the formation of most ore deposits.
The
United States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the 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, ...
(USGS) estimates that more than 1 million tons of gallium is contained in known reserves of bauxite and zinc ores.
Some coal
flue
A flue is a duct, pipe, or opening in a chimney for conveying exhaust gases from a fireplace, furnace, water heater, boiler, or generator to the outdoors. Historically the term flue meant the chimney itself. In the United States, they are ...
dust
Dust is made of fine particles of solid matter. On Earth, it generally consists of particles in the atmosphere that come from various sources such as soil lifted by wind (an aeolian process), volcanic eruptions, and pollution. Dust in ho ...
s contain small quantities of gallium, typically less than 1% by weight. However, these amounts are not extractable without mining of the host materials (see below). Thus, the availability of gallium is fundamentally determined by the rate at which bauxite, zinc ores (and coal) are extracted.
Production and availability
![6N Gallium sealed in vacuum ampoule](https://upload.wikimedia.org/wikipedia/commons/c/c0/6N_Gallium_sealed_in_vacuum_ampoule.jpg)
Gallium is produced exclusively as a
by-product during the processing of the ores of other metals. Its main source material is
bauxite
Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO ...
, the chief ore of
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
, but minor amounts are also extracted from sulfidic zinc ores (
sphalerite being the main host mineral).
In the past, certain coals were an important source.
During the processing of
bauxite
Bauxite is a sedimentary rock with a relatively high aluminium content. It is the world's main source of aluminium and gallium. Bauxite consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (γ-AlO(OH)) and diaspore (α-AlO ...
to
alumina in the
Bayer process, gallium accumulates in the
sodium hydroxide liquor. From this it can be extracted by a variety of methods. The most recent is the use of
ion-exchange resin
An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange. It is an insoluble matrix (or support structure) normally in the form of small (0.25–1.43 mm radius) microbeads, usually white or ye ...
.
Achievable extraction efficiencies critically depend on the original concentration in the feed bauxite. At a typical feed concentration of 50 ppm, about 15% of the contained gallium is extractable.
The remainder reports to the
red mud
Red is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet. It has a dominant wavelength of approximately 625–740 nanometres. It is a primary color in the RGB color model and a secondary ...
and
aluminium hydroxide
Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is amphoteric, i.e., it has both basic an ...
streams. Gallium is removed from the ion-exchange resin in solution. Electrolysis then gives gallium metal. For
semiconductor
A semiconductor is a material which has an electrical conductivity value falling between that of a conductor, such as copper, and an insulator, such as glass. Its resistivity falls as its temperature rises; metals behave in the opposite way. ...
use, it is further purified with
zone melting
Zone melting (or zone refining, or floating-zone method, or floating-zone technique) is a group of similar methods of purifying crystals, in which a narrow region of a crystal is melted, and this molten zone is moved along the crystal. The molte ...
or single-crystal extraction from a melt (
Czochralski process). Purities of 99.9999% are routinely achieved and commercially available.
![Bauxite Jamaica 1984](https://upload.wikimedia.org/wikipedia/commons/f/f7/Bauxite_Jamaica_1984.jpg)
Its by-product status means that gallium production is constrained by the amount of bauxite, sulfidic zinc ores (and coal) extracted per year. Therefore, its availability needs to be discussed in terms of supply potential. The supply potential of a by-product is defined as that amount which is economically extractable from its host materials ''per year'' under current market conditions (i.e. technology and price). Reserves and resources are not relevant for by-products, since they ''cannot'' be extracted independently from the main-products. Recent estimates put the supply potential of gallium at a minimum of 2,100 t/yr from bauxite, 85 t/yr from sulfidic zinc ores, and potentially 590 t/yr from coal.
These figures are significantly greater than current production (375 t in 2016). Thus, major future increases in the by-product production of gallium will be possible without significant increases in production costs or price. The average price for low-grade gallium was $120 per kilogram in 2016 and $135–140 per kilogram in 2017.
In 2017, the world's production of low-grade gallium was ca. 315 tons — an increase of 15% from 2016. China, Japan, South Korea, Russia, and Ukraine were the leading producers, while Germany ceased primary production of gallium in 2016. The yield of high-purity gallium was ca. 180 tons, mostly originating from China, Japan, Slovakia, UK and U.S. The 2017 world annual production capacity was estimated at 730 tons for low-grade and 320 tons for refined gallium.
[Galium](_blank)
USGS (2018)
China produced ca. 250 tons of low-grade gallium in 2016 and ca. 300 tons in 2017. It also accounted for more than half of global LED production.
Applications
Semiconductor applications dominate the commercial demand for gallium, accounting for 98% of the total. The next major application is for
gadolinium gallium garnets.
[Greber, J. F. (2012) "Gallium and Gallium Compounds" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, .]
Semiconductors
![Blue LED and Reflection](https://upload.wikimedia.org/wikipedia/commons/3/31/Blue_LED_and_Reflection.jpg)
Extremely high-purity (>99.9999%) gallium is commercially available to serve the semiconductor industry.
Gallium arsenide (GaAs) and
gallium nitride
Gallium nitride () is a binary III/ V direct bandgap semiconductor commonly used in blue light-emitting diodes since the 1990s. The compound is a very hard material that has a Wurtzite crystal structure. Its wide band gap of 3.4 eV affords ...
(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
A MESFET (metal–semiconductor field-effect transistor) is a field-effect transistor semiconductor device similar to a JFET with a Schottky (metal–semiconductor) junction instead of a p–n junction for a gate.
Construction
MESFETs are constr ...
s for low-noise microwave preamplifiers in cell phones. About 20% of this gallium is used in
optoelectronic
Optoelectronics (or optronics) is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, ''light'' often includes invisible forms of radiat ...
s.
Worldwide, gallium arsenide makes up 95% of the annual global gallium consumption.
It amounted to $7.5 billion in 2016, with 53% originating from cell phones, 27% from wireless communications, and the rest from automotive, consumer, fiber-optic, and military applications. The recent increase in GaAs consumption is mostly related to the emergence of
3G and
4G smartphone
A smartphone is a portable computer device that combines mobile telephone and computing functions into one unit. They are distinguished from feature phones by their stronger hardware capabilities and extensive mobile operating systems, whic ...
s, which use 10 times more GaAs than older models.
Gallium arsenide and gallium nitride can also be found in a variety of optoelectronic devices which had a market share of $15.3 billion in 2015 and $18.5 billion in 2016.
Aluminium gallium arsenide
Aluminium gallium arsenide (also gallium aluminium arsenide) ( Alx Ga1−x As) 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 ...
(AlGaAs) is used in high-power infrared laser diodes. The semiconductors gallium nitride and
indium gallium nitride
Indium gallium nitride (InGaN, ) is a semiconductor material made of a mix of gallium nitride (GaN) and indium nitride (InN). It is a ternary group III/ group V direct bandgap semiconductor. Its bandgap can be tuned by varying the amount of i ...
are used in blue and violet optoelectronic devices, mostly
laser diode
The laser diode chip removed and placed on the eye of a needle for scale
A laser diode (LD, also injection laser diode or ILD, or diode laser) is a semiconductor device similar to a light-emitting diode in which a diode pumped directly with e ...
s and
light-emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (co ...
s. For example, gallium nitride 405 nm diode lasers are used as a violet light source for higher-density
Blu-ray Disc compact data disc drives.
Other major application of gallium nitride are cable television transmission, commercial wireless infrastructure, power electronics, and satellites. The GaN radio frequency device market alone was estimated at $370 million in 2016 and $420 million in 2016.
Multijunction photovoltaic cell Multi-junction (MJ) solar cells are solar cells with multiple p–n junctions made of different semiconductor materials. Each material's p-n junction will produce electric current in response to different wavelengths of light. The use of multiple ...
s, developed for
satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioi ...
power applications, are made by
molecular-beam epitaxy
Molecular-beam epitaxy (MBE) is an epitaxy method for thin-film deposition of single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors, and it is considered one of the fundamental tools for the develo ...
or
metalorganic vapour-phase epitaxy
Metalorganic vapour-phase epitaxy (MOVPE), also known as organometallic vapour-phase epitaxy (OMVPE) or metalorganic chemical vapour deposition (MOCVD), is a chemical vapour deposition method used to produce single- or polycrystalline thin films. ...
of
thin film
A thin film is a layer of material ranging from fractions of a nanometer ( monolayer) to several micrometers in thickness. The controlled synthesis of materials as thin films (a process referred to as deposition) is a fundamental step in many ...
s of gallium arsenide,
indium gallium phosphide
Indium gallium phosphide (InGaP), also called gallium indium phosphide (GaInP), is a semiconductor composed of indium, gallium and phosphorus. It is used in high-power and high-frequency electronics because of its superior electron velocity with ...
, or
indium gallium arsenide
Indium gallium arsenide (InGaAs) (alternatively gallium indium arsenide, GaInAs) is a ternary alloy (chemical compound) of indium arsenide (InAs) and gallium arsenide (GaAs). Indium and gallium are ( group III) elements of the periodic table wh ...
. The
Mars Exploration Rover
NASA's Mars Exploration Rover (MER) mission was a robotic space mission involving two Mars rovers, '' Spirit'' and '' Opportunity'', exploring the planet Mars. It began in 2003 with the launch of the two rovers to explore the Martian surface ...
s and several satellites use triple-junction gallium arsenide on germanium cells. Gallium is also a component in
photovoltaic compounds (such as copper indium gallium selenium sulfide ) used in solar panels as a cost-efficient alternative to
crystalline silicon
Crystalline silicon or (c-Si) Is the crystalline forms of silicon, either polycrystalline silicon (poly-Si, consisting of small crystals), or monocrystalline silicon (mono-Si, a continuous crystal). Crystalline silicon is the dominant semiconduc ...
.
Galinstan and other alloys
![Gallium alloy 3D prints (26519727708)](https://upload.wikimedia.org/wikipedia/commons/d/db/Gallium_alloy_3D_prints_%2826519727708%29.jpg)
Gallium readily
alloy
An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductilit ...
s with most metals, and is used as an ingredient in
low-melting alloy A fusible alloy is a metal alloy capable of being easily fused, i.e. easily meltable, at relatively low temperatures. Fusible alloys are commonly, but not necessarily, eutectic alloys.
Sometimes the term "fusible alloy" is used to describe alloys ...
s. The nearly
eutectic alloy of gallium,
indium
Indium is a chemical element with the symbol In and atomic number 49. Indium is the softest metal that is not an alkali metal. It is a silvery-white metal that resembles tin in appearance. It is a post-transition metal that makes up 0.21 parts ...
, and
tin
Tin is a chemical element with the symbol Sn (from la, stannum) and atomic number 50. Tin is a silvery-coloured metal.
Tin is soft enough to be cut with little force and a bar of tin can be bent by hand with little effort. When bent, t ...
is a room temperature liquid used in medical thermometers. This alloy, with the trade-name ''
Galinstan'' (with the "-stan" referring to the tin, ''stannum'' in Latin), has a low melting 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, and is often used as a replacement for
thermal paste
Thermal paste (also called thermal compound, thermal grease, thermal interface material (TIM), thermal gel, heat paste, heat sink compound, heat sink paste or CPU grease) is a thermally conductive (but usually electrically insulating) chemi ...
in high-performance computing. Gallium alloys have been evaluated as substitutes for mercury
dental amalgam
Dental amalgam is a liquid mercury and metal alloy mixture used in dentistry to fill cavities caused by tooth decay. Low-copper amalgam commonly consists of mercury (50%), silver (~22–32%), tin (~14%), zinc (~8%) and other trace metals.
...
s, but these materials have yet to see wide acceptance. Liquid alloys containing mostly gallium and indium have been found to precipitate gaseous CO
2 into solid carbon and are being researched as potential methodologies for
carbon capture Carbon capture may refer to:
* Carbon capture and utilization, where the captured carbon dioxide is used
* Carbon sequestration, where the captured carbon dioxide is stored
** Carbon capture and storage, referring to carbon sequestration from point ...
and possibly
carbon removal
Carbon dioxide removal (CDR), also known as negative emissions, is a process in which carbon dioxide gas () is removed from the atmosphere and sequestered for long periods of time. Similarly, greenhouse gas removal (GGR) or negative greenho ...
.
Because gallium
wets
During the 1980s, members of the moderate wing of the British Conservative Party who opposed some of the more hard-line policies of Prime Minister Margaret Thatcher were often referred to by their opponents as "wets". Thatcher coined the usage in ...
glass or
porcelain
Porcelain () is a ceramic material made by heating substances, generally including materials such as kaolinite, in a kiln to temperatures between . The strength and translucence of porcelain, relative to other types of pottery, arises main ...
, gallium can be used to create brilliant
mirror
A mirror or looking glass is an object that reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the im ...
s. When the wetting action of gallium-alloys is not desired (as in
Galinstan glass thermometers), the glass must be protected with a transparent layer of
gallium(III) oxide
Gallium(III) oxide is an inorganic compound and ultra-wide bandgap semiconductor with the formula Ga2 O3. It is actively studied for applications in power electronics, phosphors, and gas sensing. The compound has several polymorphs, of which t ...
.
The
plutonium
Plutonium is a radioactive chemical element with the symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, and forms a dull coating when oxidized. The element normally exhibi ...
used in
nuclear weapon pits is stabilized in the
δ phase and made machinable by
alloying with gallium.
Biomedical applications
Although gallium has no natural function in biology, gallium ions interact with processes in the body in a manner similar to
iron(III)
In chemistry, iron(III) refers to the element iron in its +3 oxidation state. In ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+.
The adjective ferric or the prefix ferri- is often used to sp ...
. Because these processes include
inflammation
Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...
, a marker for many disease states, several gallium salts are used (or are in development) as
pharmaceuticals and
radiopharmaceuticals
Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which is ...
in medicine. Interest in the anticancer properties of gallium emerged when it was discovered that
67Ga(III) citrate injected in tumor-bearing animals localized to sites of tumor. Clinical trials have shown gallium nitrate to have antineoplastic activity against non-Hodgkin's lymphoma and urothelial cancers. A new generation of gallium-ligand complexes such as tris(8-quinolinolato)gallium(III) (KP46) and gallium maltolate has emerged.
Gallium nitrate
Gallium nitrate (brand name Ganite) is the gallium Salt (chemistry), salt of nitric acid with the chemical formula Ga(NO3)3. It is a drug used to treat symptomatic hypercalcemia secondary to cancer. It works by preventing the breakdown of bone thr ...
(brand name Ganite) has been used as an intravenous pharmaceutical to treat
hypercalcemia associated with tumor
metastasis
Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then ...
to bones. Gallium is thought to interfere with
osteoclast
An osteoclast () is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodeling of bones of the vertebral skeleton. The osteoclast disassembles and digests the composite of hydrated pro ...
function, and the therapy may be effective when other treatments have failed.
Gallium maltolate
Gallium maltolate is a coordination complex consisting of a trivalent gallium cation coordinated to three maltolate ligands. The compound is a potential therapeutic agent for cancer, infectious disease, and inflammatory disease. A cosmetic skin ...
, an oral, highly absorbable form of gallium(III) ion, is an anti-proliferative to pathologically proliferating cells, particularly cancer cells and some bacteria that accept it in place of ferric iron (Fe
3+). Researchers are conducting clinical and preclinical trials on this compound as a potential treatment for a number of cancers, infectious diseases, and inflammatory diseases.
When gallium ions are mistakenly taken up in place of iron(III) by bacteria such as ''
Pseudomonas
''Pseudomonas'' is a genus of Gram-negative, Gammaproteobacteria, belonging to the family Pseudomonadaceae and containing 191 described species. The members of the genus demonstrate a great deal of metabolic diversity and consequently are able t ...
'', the ions interfere with respiration, and the bacteria die. This happens because iron is redox-active, allowing the transfer of electrons during respiration, while gallium is redox-inactive.
A complex
amine
In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen
Hydrogen is the chemical element wi ...
-
phenol
Phenol (also called carbolic acid) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile. The molecule consists of a phenyl group () bonded to a hydroxy group (). Mildly acidic, it ...
Ga(III) compound MR045 is selectively toxic to parasites resistant to
chloroquine
Chloroquine is a medication primarily used to prevent and treat malaria in areas where malaria remains sensitive to its effects. Certain types of malaria, resistant strains, and complicated cases typically require different or additional medi ...
, a common drug against
malaria
Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. S ...
. Both the Ga(III) complex and chloroquine act by inhibiting crystallization of
hemozoin
Haemozoin is a disposal product formed from the digestion of blood by some blood-feeding parasites. These hematophagous organisms such as malaria parasites (''Plasmodium spp.''), ''Rhodnius'' and ''Schistosoma'' digest haemoglobin and release high ...
, a disposal product formed from the digestion of blood by the parasites.
Radiogallium salts
Gallium-67
Natural gallium (31Ga) consists of a mixture of two stable isotopes: gallium-69 and gallium-71. The most commercially important radioisotopes are gallium-67 and gallium-68.
Gallium-67 (half-life 3.3 days) is a gamma-emitting isotope (the gamma ...
salts
In chemistry, a salt is a chemical compound consisting of an ionic assembly of positively charged cations and negatively charged anions, which results in a compound with no net electric charge. A common example is table salt, with positively c ...
such as gallium
citrate
Citric acid is an organic compound with the chemical formula HOC(CO2H)(CH2CO2H)2. It is a colorless weak organic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the ...
and gallium
nitrate are used as
radiopharmaceutical
Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which ...
agents in the
nuclear medicine
Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is " radiology done inside out" because it records radiation emi ...
imaging known as
gallium scan
A gallium scan is a type of nuclear medicine test that uses either a gallium-67 (67Ga) or gallium-68 (68Ga) radiopharmaceutical to obtain images of a specific type of tissue, or disease state of tissue. Gallium salts like gallium citrate and gal ...
. The
radioactive isotope
A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess nuclear energy, making it unstable. This excess energy can be used in one of three ways: emitted from the nucleus as gamma radiation; transferr ...
67Ga is used, and the compound or salt of gallium is unimportant. The body handles Ga
3+ in many ways as though it were Fe
3+, and the ion is bound (and concentrates) in areas of inflammation, such as infection, and in areas of rapid cell division. This allows such sites to be imaged by nuclear scan techniques.
Gallium-68
Natural gallium (31Ga) consists of a mixture of two stable isotopes: gallium-69 and gallium-71. The most commercially important radioisotopes are gallium-67 and gallium-68.
Gallium-67 (half-life 3.3 days) is a gamma-emitting isotope (the gamma r ...
, 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
Edotreotide (USAN, also known as (DOTA0- Phe1- Tyr3) octreotide, DOTA-TOC, DOTATOC) is a substance which, when bound to various radionuclides, is used in the treatment and diagnosis of certain types of cancer. When used therapeutically it is an ...
, a
somatostatin analogue used for
neuroendocrine tumors
Neuroendocrine tumors (NETs) are neoplasms that arise from cells of the endocrine (hormonal) and nervous systems. They most commonly occur in the intestine, where they are often called carcinoid tumors, but they are also found in the pancreas, lun ...
investigation, and
DOTA-TATE
DOTA-TATE (DOTATATE, DOTA-octreotate, oxodotreotide, DOTA-(Tyr3)-octreotate, and DOTA-0-Tyr3-Octreotate) is an eight amino acid long peptide, with a covalently bonded DOTA bifunctional chelator.
DOTA-TATE can be reacted with the radionuclides ...
, a newer one, used for neuroendocrine
metastasis
Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then ...
and lung neuroendocrine cancer, such as certain types of ''
microcytoma''. Gallium-68's preparation as a pharmaceutical is chemical, and the radionuclide is extracted by
elution
In analytical and organic chemistry, elution is the process of extracting one material from another by washing with a solvent; as in washing of loaded ion-exchange resins to remove captured ions.
In a liquid chromatography experiment, for exam ...
from germanium-68, a
synthetic radioisotope of
germanium, in
gallium-68 generator
A germanium-68/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 utilized for in-hospital ...
s.
Other uses
Neutrino detection: Gallium is used for
neutrino
A neutrino ( ; denoted by the Greek letter ) is a fermion (an elementary particle with spin of ) that interacts only via the weak interaction and gravity. The neutrino is so named because it is electrically neutral and because its rest mass ...
detection. Possibly the largest amount of pure gallium ever collected in a single location is the Gallium-Germanium Neutrino Telescope used by the
SAGE experiment at the Baksan Neutrino Observatory in Russia. This detector contains 55–57 tonnes (~9 cubic metres) of liquid gallium. Another experiment was the
GALLEX
GALLEX or Gallium Experiment was a radiochemical neutrino detection experiment that ran between 1991 and 1997 at the Laboratori Nazionali del Gran Sasso (LNGS). This project was performed by an international collaboration of French, German, Itali ...
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
71Ga to become radioactive
71 Ge, which were detected. This experiment showed that the solar neutrino flux is 40% less than theory predicted. This deficit was not explained until better solar neutrino detectors and theories were constructed (see
SNO
Tin(II) oxide (stannous oxide) is a compound with the formula SnO. It is composed of tin and oxygen where tin has the oxidation state of +2. There are two forms, a stable blue-black form and a metastable red form.
Preparation and reactions
Blue ...
).
Ion source: Gallium is also used as a
liquid metal ion source A liquid metal ion source (LMIS) is an ion source which uses metal that is heated to the liquid state and used to form an electrospray to form ions. An electrospray Taylor cone is formed by the application of a strong electric field and ions are ...
for a
focused ion beam
Focused 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. A FIB setup is a s ...
. For example, a focused gallium-ion beam was used to create the world's smallest book, ''
Teeny Ted from Turnip Town
''Teeny Ted from Turnip Town'' (2007), published by Robert Chaplin, is certified by ''Guinness World Records'' as the world's smallest reproduction of a printed book. The book was produced in the Nano Imaging Laboratory at Simon Fraser University ...
''.
["Nano lab produces world's smallest book"](_blank)
. Simon Fraser University. 11 April 2007. Retrieved 31 January 2013.
Lubricants: Gallium serves as an additive in glide wax for skis and other low-friction surface materials.
Flexible electronics: Materials scientists speculate that the properties of gallium could make it suitable for the development of flexible and wearable devices.
Hydrogen generation: Gallium disrupts the
protective oxide layer on aluminium, allowing water to react with the aluminium in
AlGa
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
to produce hydrogen gas.
Humor: A well-known
practical joke among chemists is to fashion gallium spoons and use them to serve tea to unsuspecting guests, since gallium has a similar appearance to its lighter homolog aluminium. The spoons then melt in the hot tea.
Gallium in the ocean
Advances in trace element testing have allowed scientists to discover traces of dissolved gallium in the Atlantic and Pacific Oceans
In recent years, dissolved gallium concentrations have presented in the Beaufort Sea.
These reports reflect the possible profiles of the Pacific and Atlantic Ocean waters.
For the Pacific Oceans, typical dissolved gallium concentrations are between 4–6 pmol/kg at depths <~150 m. In comparison, for Atlantic waters 25–28 pmol/kg at depths >~350 m.
Gallium has entered oceans mainly through aeolian input, but having gallium in our oceans can be used to resolve aluminium distribution in the oceans.
The reason for this is that gallium is geochemically similar to aluminium, just less reactive. Gallium also has a slightly larger surface water residence time than aluminium.
Gallium has a similar dissolved profile similar to that of aluminium, due to this gallium can be used as a tracer for aluminium.
Gallium can also be used as a tracer of aeolian inputs of iron.
Gallium is used as a tracer for iron in the northwest Pacific, south and central Atlantic Oceans.
For example, in the northwest Pacific, low gallium surface waters, in the subpolar region suggest that there is low dust input, which can subsequently explain the following
high-nutrient, low-chlorophyll environmental behavior.
Precautions
Metallic gallium is not toxic. However, exposure to gallium halide complexes can result in acute toxicity.
The Ga
3+ ion of soluble gallium salts tends to form the insoluble hydroxide when injected in large doses; precipitation of this hydroxide resulted in
nephrotoxicity Nephrotoxicity is toxicity in the kidneys. It is a poisonous effect of some substances, both toxic chemicals and medications, on kidney function. There are various forms, and some drugs may affect kidney function in more than one way. Nephrotoxins ...
in animals. In lower doses, soluble gallium is tolerated well and does not accumulate as a poison, instead being excreted mostly through urine. Excretion of gallium occurs in two phases: the first phase has a
biological half-life
Biological half-life (also known as elimination half-life, pharmacologic half-life) is the time taken for concentration of a biological substance (such as a medication) to decrease from its maximum concentration ( Cmax) to half of Cmax in the bl ...
of 1 hour, while the second has a biological half-life of 25 hours.
References
Bibliography
*
External links
Galliumat ''
The Periodic Table of Videos
''Periodic Videos'' (also known as ''The Periodic Table of Videos'') is a video project and YouTube channel on chemistry. It consists of a series of videos about chemical elements and the periodic table, with additional videos on other topics i ...
'' (University of Nottingham)
*
Safety data sheet a
acialloys.comHigh-resolution photographs of molten gallium, gallium crystals and gallium ingots under Creative Commons licencePrice development of gallium 1959–1998Gallium: A Smart MetalUnited States Geological Survey
The United States Geological Survey (USGS), formerly simply known as the 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, ...
Thermal conductivityPhysical and thermodynamical properties of liquid gallium(doc pdf)
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