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Aluminium (aluminum in American and Canadian English) is a
chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that species. Unlike chemical compounds, chemical elements canno ...
with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common
metal
metal
s, at approximately one third that of
steel
steel
. It has a great affinity towards
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
, and forms a protective layer of oxide on the surface when exposed to air. Aluminium visually resembles silver, both in its color and in its great ability to reflect light. It is soft,
non-magnetic
non-magnetic
and
ductile
ductile
. It has one stable isotope, 27Al; this isotope is very common, making aluminium the twelfth most common element in the Universe. The radioactivity of 26Al is used in radiodating. Chemically, aluminium is a post-transition metal in the boron group; as is common for the group, aluminium forms compounds primarily in the +3 oxidation state. The aluminium cation Al3+ is small and highly charged; as such, it is polarizing, and bonds aluminium forms tend towards covalency. The strong affinity towards oxygen leads to aluminium's common association with oxygen in nature in the form of oxides; for this reason, aluminium is found on Earth primarily in rocks in the crust, where it is the third most abundant element after
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
and
silicon
silicon
, rather than in the mantle, and virtually never as the free metal. The discovery of aluminium was announced in 1825 by Danish physicist
Hans Christian Ørsted
Hans Christian Ørsted
. The first industrial production of aluminium was initiated by French chemist Henri Étienne Sainte-Claire Deville in 1856. Aluminium became much more available to the public with the Hall–Héroult process developed independently by French engineer Paul Héroult and American engineer Charles Martin Hall in 1886, and the mass production of aluminium led to its extensive use in industry and everyday life. In World Wars
I
I
and II, aluminium was a crucial strategic resource for
aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes airplane, fixed-wing and helicopter, rotary-wing types, morphable wings, wing-less lifting bodies, as well as aerostat, lighter- ...
. In 1954, aluminium became the most produced non-ferrous metal, surpassing
copper
copper
. In the 21st century, most aluminium was consumed in transportation, engineering, construction, and packaging in the United States, Western Europe, and Japan. Despite its prevalence in the environment, no living organism is known to use aluminium salts metabolically, but aluminium is well tolerated by plants and animals. Because of the abundance of these salts, the potential for a biological role for them is of interest, and studies continue.


Physical characteristics


Isotopes

Of aluminium isotopes, only is stable. This situation is common for elements with an odd atomic number. It is the only primordial aluminium isotope, i.e. the only one that has existed on Earth in its current form since the formation of the planet. Nearly all aluminium on Earth is present as this isotope, which makes it a
mononuclidic element A mononuclidic element or monotopic element is one of the 21 chemical elements that is found naturally on Earth essentially as a single nuclide (which may, or may not, be a stable nuclide). This single nuclide will have a characteristic atomic m ...
and means that its
standard atomic weight The standard atomic weight of a chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance consisting only of that specie ...
is virtually the same as that of the isotope. This makes aluminium very useful in
nuclear magnetic resonance Nuclear magnetic resonance (NMR) is a physical phenomenon in which atomic nucleus, nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near and far field, near field) and respond by producing ...
(NMR), as its single stable isotope has a high NMR sensitivity. The standard atomic weight of aluminium is low in comparison with many other metals. All other isotopes of aluminium are
radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive Decay chain, disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nucl ...

radioactive
. The most stable of these is
26Al
<sup>26</sup>Al
: while it was present along with stable 27Al in the interstellar medium from which the Solar System formed, having been produced by
stellar nucleosynthesis Stellar nucleosynthesis is the creation (nucleosynthesis) of chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substance c ...
as well, its
half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...
is only 717,000 years and therefore a detectable amount has not survived since the formation of the planet. However, minute traces of 26Al are produced from
argon Argon is a chemical element with the Symbol (chemistry), symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 Parts-per notatio ...

argon
in the
atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

atmosphere
by
spallation Spallation is a process in which fragments of material (spall) are ejected from a body due to impact or stress. In the context of impact (mechanics), impact mechanics it describes ejection of material from a target during impact by a projecti ...

spallation
caused by
cosmic ray Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
protons. The ratio of 26Al to
10Be
<sup>10</sup>Be
has been used for radiodating of geological processes over 105 to 106 year time scales, in particular transport, deposition,
sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently sediment transport, transported by the action of wind, water, or ice or by the force of gravity acting on the particles. ...

sediment
storage, burial times, and erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some
asteroids An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic o ...

asteroids
after their formation 4.55 billion years ago. The remaining isotopes of aluminium, with
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 proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive e ...
s ranging from 22 to 43, all have half-lives well under an hour. Three
metastable In chemistry and physics, metastability denotes an intermediate Energy level, energetic state within a dynamical system other than the system's ground state, state of least energy. A ball resting in a hollow on a slope is a simple example of me ...

metastable
states are known, all with half-lives under a minute.


Electron shell

An aluminium atom has 13 electrons, arranged in an
electron configuration In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in Atomic orbital, atomic or molecular orbitals. For example, the electron configuration of ...
of , with three electrons beyond a stable noble gas configuration. Accordingly, the combined first three ionization energies of aluminium are far lower than the fourth ionization energy alone. Such an electron configuration is shared with the other well-characterized members of its group,
boron Boron is a chemical element with the Chemical symbol, symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron g ...

boron
,
gallium Gallium is a chemical element with the Symbol (chemistry), symbol Ga and atomic number 31. Discovered by France, French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in boron group, group 13 of the periodic table and is similar to ...

gallium
,
indium Indium is a chemical element with the Symbol (chemistry), 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 ma ...

indium
, and
thallium Thallium is a chemical element with the Symbol (chemistry), 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 W ...

thallium
; it is also expected for
nihonium Nihonium is a Synthetic element, synthetic chemical element with the Symbol (chemistry), symbol Nh and atomic number 113. It is extremely radioactive; its most stable known isotope, nihonium-286, has a half-life of about 10 seconds. In the peri ...

nihonium
. Aluminium can relatively easily surrender its three outermost electrons in many chemical reactions (see below). The
electronegativity Electronegativity, symbolized as ''Chi (letter), χ'', is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its ato ...

electronegativity
of aluminium is 1.61 (Pauling scale). A free aluminium atom has a
radius In classical geometry, a radius (plural, : radii) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', ...

radius
of 143  pm. With the three outermost electrons removed, the
radius In classical geometry, a radius (plural, : radii) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', ...
shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At
standard temperature and pressure Standard temperature and pressure (STP) are Technical standard, standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the I ...
, aluminium atoms (when not affected by atoms of other elements) form a face-centered cubic crystal system bound by
metallic bonding Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. It may be describ ...

metallic bonding
provided by atoms' outermost electrons; hence aluminium (at these conditions) is a metal. This crystal system is shared by many other metals, such as
lead Lead is a chemical element with the Symbol (chemistry), symbol Pb (from the Latin ) and atomic number 82. It is a heavy metals, heavy metal that is density, denser than most common materials. Lead is Mohs scale of mineral hardness#Intermediate ...

lead
and ; the size of a unit cell of aluminium is comparable to that of those other metals. The system, however, is not shared by the other members of its group; boron has ionization energies too high to allow metallization, thallium has a
hexagonal close-packed In geometry Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field of ...
structure, and gallium and indium have unusual structures that are not close-packed like those of aluminium and thallium. The few electrons that are available for
metallic bonding Metallic bonding is a type of chemical bonding that arises from the electrostatic attractive force between conduction electrons (in the form of an electron cloud of delocalized electrons) and positively charged metal ions. It may be describ ...

metallic bonding
in aluminium metal are a probable cause for it being soft with a low melting point and low
electrical resistivity Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current. A low resistivity indicates a material that readily allows ...
.Greenwood and Earnshaw, pp. 222–4


Bulk

Aluminium metal has an appearance ranging from silvery white to dull gray, depending on the
surface roughness Surface roughness, often shortened to roughness, is a component of surface finish, surface finish (surface texture). It is quantified by the deviations in the direction of the normal (geometry), normal vector of a real surface from its ideal for ...
. Aluminium mirrors are the most reflective of all metal mirrors for the near
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
and far
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
light, and one of the most reflective in the visible spectrum, nearly on par with silver, and the two therefore look similar. Aluminium is also good at reflecting
solar radiation Solar irradiance is the power (physics), power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per ...
, although prolonged exposure to sunlight in air adds wear to the surface of the metal; this may be prevented if aluminium is
anodized Anodizing is an electrolyte, electrolytic Passivation (chemistry), passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. The process is called ''anodizing'' because the part to be treated fo ...
, which adds a protective layer of oxide on the surface. The density of aluminium is 2.70 g/cm3, about 1/3 that of steel, much lower than other commonly encountered metals, making aluminium parts easily identifiable through their lightness. Aluminium's low density compared to most other metals arises from the fact that its nuclei are much lighter, while difference in the unit cell size does not compensate for this difference. The only lighter metals are the metals of groups 1 and 2, which apart from
beryllium Beryllium is a chemical element with the Symbol (chemistry), symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other ...
and
magnesium Magnesium is a chemical element with the Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group ...
are too reactive for structural use (and beryllium is very toxic). Aluminium is not as strong or stiff as steel, but the low density makes up for this in the
aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astrona ...
industry and for many other applications where light weight and relatively high strength are crucial. Pure aluminium is quite soft and lacking in strength. In most applications various
aluminium alloys An aluminium alloy (or aluminum alloy; see American and British English spelling differences, spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, sil ...
are used instead because of their higher strength and hardness. The
yield strength In materials science and engineering, the yield point is the point on a stress-strain curve that indicates the limit of Elasticity (physics), elastic behavior and the beginning of Plasticity (physics), plastic behavior. Below the yield point, ...
of pure aluminium is 7–11 MPa, while
aluminium alloy An aluminium alloy (or aluminum alloy; see American and British English spelling differences, spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, sil ...
s have yield strengths ranging from 200 MPa to 600 MPa. Aluminium is , with a percent elongation of 50-70%, and
malleable Ductility is a List of materials properties, mechanical property commonly described as a material's amenability to Drawing (manufacturing), drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a materia ...
allowing it to be easily drawn and
extruded Extrusion is a process used to create objects of a fixed cross section (geometry), cross-sectional profile by pushing material through a Die (manufacturing), die of the desired cross-section. Its two main advantages over other manufacturing pro ...
. It is also easily
machined Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...
and
cast Cast may refer to: Music * Cast (band), an English alternative rock band * Cast (Mexican band), a progressive Mexican rock band * The Cast, a Scottish musical duo: Mairi Campbell and Dave Francis * ''Cast'', a 2012 album by Trespassers William * ...
. Aluminium is an excellent
thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...
and
electrical conductor In physics and electrical engineering, a conductor is an object or type of material that allows the flow of Electric charge, charge (electric current) in one or more directions. Materials made of metal are common electrical conductors. Electric ...
, having around 60% the conductivity of , both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of
superconductivity Superconductivity is a set of physical properties observed in certain materials where electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its Multiplicative inverse, ...
, with a superconducting critical temperature of 1.2
kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its metric prefix, prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based eng ...
and a critical magnetic field of about 100
gauss Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refer ...
(10
millitesla The tesla (symbol: T) is the unit of Magnetic field#The B-field, magnetic flux density (also called Magnetic field#The B-field, magnetic B-field strength) in the International System of Units (SI). One tesla is equal to one weber (unit), weber p ...
s). It is
paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior ...
and thus essentially unaffected by static magnetic fields. The high electrical conductivity, however, means that it is strongly affected by alternating magnetic fields through the induction of
eddy currents Eddy currents (also called Foucault's currents) are loops of electrical current induced within Conductor (material), conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a ...
.


Chemistry

Aluminium combines characteristics of pre- and post-transition metals. Since it has few available electrons for metallic bonding, like its heavier group 13 congeners, it has the characteristic physical properties of a post-transition metal, with longer-than-expected interatomic distances. Furthermore, as Al3+ is a small and highly charged cation, it is strongly polarizing and bonding in aluminium compounds tends towards covalency; this behavior is similar to that of
beryllium Beryllium is a chemical element with the Symbol (chemistry), symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other ...
(Be2+), and the two display an example of a
diagonal relationship A diagonal relationship is said to exist between certain pairs of diagonally adjacent chemical element, elements in the second and third periods (first 20 elements) of the periodic table. These pairs (lithium (Li) and magnesium (Mg), beryllium (B ...
. The underlying core under aluminium's valence shell is that of the preceding
noble gas The noble gases (historically also the inert gases; sometimes referred to as aerogens) make up a class of chemical elements with similar properties; under Standard conditions for temperature and pressure, standard conditions, they are all odorle ...
, whereas those of its heavier congeners
gallium Gallium is a chemical element with the Symbol (chemistry), symbol Ga and atomic number 31. Discovered by France, French chemist Paul-Émile Lecoq de Boisbaudran in 1875, Gallium is in boron group, group 13 of the periodic table and is similar to ...

gallium
,
indium Indium is a chemical element with the Symbol (chemistry), 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 ma ...

indium
,
thallium Thallium is a chemical element with the Symbol (chemistry), 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 W ...

thallium
, and
nihonium Nihonium is a Synthetic element, synthetic chemical element with the Symbol (chemistry), symbol Nh and atomic number 113. It is extremely radioactive; its most stable known isotope, nihonium-286, has a half-life of about 10 seconds. In the peri ...

nihonium
also include a filled d-subshell and in some cases a filled f-subshell. Hence, the inner electrons of aluminium shield the valence electrons almost completely, unlike those of aluminium's heavier congeners. As such, aluminium is the most electropositive metal in its group, and its hydroxide is in fact more basic than that of gallium. Aluminium also bears minor similarities to the metalloid boron in the same group: AlX3 compounds are valence
isoelectronic Isoelectronicity is a phenomenon observed when two or more molecules have the same chemical structure, structure (positions and connectivities among atoms) and the same electron configuration, electronic configurations, but differ by what specif ...
to BX3 compounds (they have the same valence electronic structure), and both behave as
Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty Non-bonding orbital, orbital which is capable of accepting an electron pair from a Lewis Base (chemistry), base to form a Lewis a ...
s and readily form
adduct An adduct (from the Latin ''adductus'', "drawn toward" alternatively, a contraction of "addition product") is a product of a Addition reaction, direct addition of two or more distinct molecules, resulting in a single reaction product containing a ...
s. Additionally, one of the main motifs of boron chemistry is regular icosahedral structures, and aluminium forms an important part of many icosahedral
quasicrystal A Quasiperiodicity, quasiperiodic crystal, or quasicrystal, is a structure that is Order and disorder (physics), ordered but not Bravais lattice, periodic. A quasicrystalline pattern can continuously fill all available space, but it lacks transl ...
alloys, including the Al–Zn–Mg class. Aluminium has a high
chemical affinity In chemical physics and physical chemistry, chemical affinity is the electronic property by which dissimilar chemical species are capable of forming chemical compounds. Chemical affinity can also refer to the tendency of an atom or compound to comb ...
to oxygen, which renders it suitable for use as a
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 meta ...
in the
thermite Thermite () is a pyrotechnic composition of powder metallurgy, metal powder and metal oxide. When ignited by heat or chemical reaction, thermite undergoes an exothermic redox, reduction-oxidation (redox) reaction. Most varieties are not explos ...
reaction. A fine powder of aluminium metal reacts explosively on contact with
liquid oxygen Liquid oxygen—abbreviated LOx, LOX or Lox in the aerospace Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military appli ...
; under normal conditions, however, aluminium forms a thin oxide layer (~5 nm at room temperature) that protects the metal from further corrosion by oxygen, water, or dilute acid, a process termed passivation. Because of its general resistance to corrosion, aluminium is one of the few metals that retains silvery reflectance in finely powdered form, making it an important component of silver-colored paints. Aluminium is not attacked by oxidizing acids because of its passivation. This allows aluminium to be used to store reagents such as
nitric acid Nitric acid is the inorganic compound with the formula . It is a highly corrosive mineral acid. The compound is colorless, but older samples tend to be yellow cast due to decomposition into oxides of nitrogen. Most commercially available ni ...
, concentrated
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid (English in the Commonwealth of Nations, Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen ...
, and some organic acids. In hot concentrated
hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungency, pungent smell. It is classified as a acid strength, strong acid. It is a component of the gas ...
, aluminium reacts with water with evolution of hydrogen, and in aqueous
sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive, caustic base (c ...
or
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 ...
at room temperature to form
aluminates In chemistry, an aluminate is a compound containing an oxyanion An oxyanion, or oxoanion, is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). Oxyanions are formed by a large majority of the c ...
—protective passivation under these conditions is negligible. Aqua regia also dissolves aluminium. Aluminium is corroded by dissolved
chlorides The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride ...
, such as common
sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salt (chemistry), salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of ...
, which is why household plumbing is never made from aluminium. The oxide layer on aluminium is also destroyed by contact with mercury due to amalgamation or with salts of some electropositive metals. As such, the strongest aluminium alloys are less corrosion-resistant due to galvanic reactions with alloyed , and aluminium's corrosion resistance is greatly reduced by aqueous salts, particularly in the presence of dissimilar metals. Aluminium reacts with most nonmetals upon heating, forming compounds such as aluminium nitride (AlN),
aluminium sulfide Aluminum sulfide or aluminium sulphide is a chemical compound with the formula Aluminium, Al2Sulfur, S3. This colorless species has an interesting structural chemistry, existing in several forms. The material is sensitive to moisture, hydrolyzing ...
(Al2S3), and the aluminium halides (AlX3). It also forms a wide range of
intermetallic compound An intermetallic (also called an intermetallic compound, intermetallic alloy, ordered intermetallic alloy, and a long-range-ordered alloy) is a type of metallic alloy An alloy is a mixture of chemical elements of which at least one is a meta ...
s involving metals from every group on the periodic table.


Inorganic compounds

The vast majority of compounds, including all aluminium-containing minerals and all commercially significant aluminium compounds, feature aluminium in the oxidation state 3+. The
coordination number In chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structu ...
of such compounds varies, but generally Al3+ is either six- or four-coordinate. Almost all compounds of aluminium(III) are colorless. In aqueous solution, Al3+ exists as the hexaaqua cation l(H2O)6sup>3+, which has an approximate Ka of 10−5. Such solutions are acidic as this cation can act as a proton donor and progressively hydrolyze until a
precipitate In an aqueous solution, precipitation is the process of transforming a dissolved chemical substance, substance into an insoluble solid from a Supersaturated solution, super-saturated solution. The solid formed is called the precipitate. In cas ...
of
aluminium hydroxide Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer Polymorphism (materials science), polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is Amphoter ...
, Al(OH)3, forms. This is useful for clarification of water, as the precipitate nucleates on suspended particles in the water, hence removing them. Increasing the pH even further leads to the hydroxide dissolving again as
aluminate In chemistry, an aluminate is a compound containing an oxyanion of aluminium, such as sodium aluminate. In the naming of inorganic compounds, it is a suffix that indicates a polyatomic ion, polyatomic anion with a central aluminum atom. Aluminate ...
, l(H2O)2(OH)4sup>−, is formed. Aluminium hydroxide forms both salts and aluminates and dissolves in acid and alkali, as well as on fusion with acidic and basic oxides. This behavior of Al(OH)3 is termed
amphoterism In chemistry, an amphoteric chemical compound, compound () is a molecule or ion that can react both as an acid and as a base (chemistry), base. What exactly this can mean depends on acid–base reaction, which definitions of acids and bases are b ...
and is characteristic of weakly basic cations that form insoluble hydroxides and whose hydrated species can also donate their protons. One effect of this is that aluminium salts with weak acids are hydrolyzed in water to the aquated hydroxide and the corresponding nonmetal hydride: for example,
aluminium sulfide Aluminum sulfide or aluminium sulphide is a chemical compound with the formula Aluminium, Al2Sulfur, S3. This colorless species has an interesting structural chemistry, existing in several forms. The material is sensitive to moisture, hydrolyzing ...
yields
hydrogen sulfide Hydrogen sulfide is a chemical compound with the chemical formula, formula . It is a colorless Chalcogen hydride, chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic ...
. However, some salts like aluminium carbonate exist in aqueous solution but are unstable as such; and only incomplete hydrolysis takes place for salts with strong acids, such as the halides,
nitrate Nitrate is a polyatomic ion with the chemical formula . salt (chemistry), Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are solubility, soluble in wat ...
, and
sulfate The sulfate or sulphate ion is a polyatomic ion, polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salt (chemistry), ...
. For similar reasons, anhydrous aluminium salts cannot be made by heating their "hydrates": hydrated aluminium chloride is in fact not AlCl3·6H2O but l(H2O)6l3, and the Al–O bonds are so strong that heating is not sufficient to break them and form Al–Cl bonds instead: :2 l(H2O)6l3 Al2O3 + 6 HCl + 9 H2O All four trihalides are well known. Unlike the structures of the three heavier trihalides,
aluminium fluoride Aluminium fluoride refers to inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a s ...
(AlF3) features six-coordinate aluminium, which explains its involatility and insolubility as well as high
heat of formation In chemistry and thermodynamics, the standard enthalpy of formation or standard heat of formation of a Chemical compound, compound is the change of enthalpy during the formation of 1 mole (unit), mole of the substance from its constituent Chemical ...
. Each aluminium atom is surrounded by six fluorine atoms in a distorted
octahedral In geometry Geometry (; ) is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space such as the distance, shape, size, and relative position of figures. A mathematician who works in the field ...
arrangement, with each fluorine atom being shared between the corners of two octahedra. Such units also exist in complex fluorides such as
cryolite Cryolite (Na3AlF6, sodium hexafluoroaluminate) is an uncommon mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific cryst ...
, Na3AlF6. AlF3 melts at and is made by reaction of aluminium oxide with
hydrogen fluoride Hydrogen fluoride (fluorane) is an Inorganic chemistry, inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an imp ...
gas at . With heavier halides, the coordination numbers are lower. The other trihalides are dimeric or
polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules called macromolecules, composed of many Repeat unit, repeating subunits. Due to t ...
ic with tetrahedral four-coordinate aluminium centers.
Aluminium trichloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six Water of hydration, water molecules of hydration. Both are colourless crystals, but sampl ...
(AlCl3) has a layered polymeric structure below its melting point of but transforms on melting to Al2Cl6 dimers. At higher temperatures those increasingly dissociate into trigonal planar AlCl3 monomers similar to the structure of BCl3.
Aluminium tribromide Aluminium bromide is any chemical compound with the empirical formula AlBrx. Aluminium tribromide is the most common form of aluminium bromide. It is a colorless, sublimable hygroscopic solid; hence old samples tend to be hydrated, mostly as al ...
and aluminium triiodide form Al2X6 dimers in all three phases and hence do not show such significant changes of properties upon phase change. These materials are prepared by treating aluminium metal with the halogen. The aluminium trihalides form many addition compounds or complexes; their
Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty Non-bonding orbital, orbital which is capable of accepting an electron pair from a Lewis Base (chemistry), base to form a Lewis a ...
ic nature makes them useful as
catalysts Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...
for the
Friedel–Crafts reaction The Friedel–Crafts reactions are a set of reactions developed by Charles Friedel and James Crafts in 1877 to attach substituents to an aromatic ring. Friedel–Crafts reactions are of two main types: alkylation reactions and acylation rea ...
s. Aluminium trichloride has major industrial uses involving this reaction, such as in the manufacture of
anthraquinone Anthraquinone, also called anthracenedione or dioxoanthracene, is an aromatic hydrocarbon, aromatic organic compound with formula . Isomers include various quinone derivatives. The term anthraquinone however refers to the isomer, 9,10-anthraquinon ...
s and
styrene Styrene () is an organic compound with the chemical formula C6H5CH=CH2. This derivative of benzene is a colorless oily liquid, although aged samples can appear yellowish. The compound evaporates easily and has a sweet smell, although high concen ...
; it is also often used as the precursor for many other aluminium compounds and as a reagent for converting nonmetal fluorides into the corresponding chlorides (a transhalogenation reaction). Aluminium forms one stable oxide with the
chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...
Al2O3, commonly called alumina. It can be found in nature in the mineral
corundum Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock (geology), rock-forming mineral. It is a naturally transparency and translucency, transparent material, but ca ...
, α-alumina; there is also a γ-alumina phase. Its crystalline form,
corundum Corundum is a crystalline form of aluminium oxide () typically containing traces of iron, titanium, vanadium and chromium. It is a rock (geology), rock-forming mineral. It is a naturally transparency and translucency, transparent material, but ca ...
, is very hard (
Mohs hardness The Mohs scale of mineral hardness () is a Qualitative property, qualitative ordinal scale, from 1 to 10, characterizing scratch hardness, scratch resistance of various minerals through the ability of harder material to scratch softer material. ...
9), has a high melting point of , has very low volatility, is chemically inert, and a good electrical insulator, it is often used in abrasives (such as toothpaste), as a refractory material, and in
ceramics A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain, ...
, as well as being the starting material for the electrolytic production of aluminium metal.
Sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphir ...
and
ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum (aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapp ...
are impure corundum contaminated with trace amounts of other metals. The two main oxide-hydroxides, AlO(OH), are
boehmite Boehmite or böhmite is an aluminium oxide hydroxide (γ-AlO(OH)) mineral, a component of the aluminium Aluminium (aluminum in American and Canadian English) is a chemical element A chemical element is a species of atoms that hav ...
and
diaspore Diaspore , also known as diasporite, empholite, kayserite, or tanatarite, is an aluminium oxide hydroxide mineral, α-AlO(OH), crystallizing in the orthorhombic system and Isomorphism (crystallography), isomorphous with goethite. It occurs somet ...
. There are three main trihydroxides:
bayerite Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer Polymorphism (materials science), polymor ...
,
gibbsite Gibbsite, Al(OH)3, is one of the mineral forms of aluminium hydroxide Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer Polymorphism (materials science), polymor ...
, and nordstrandite, which differ in their crystalline structure ( polymorphs). Many other intermediate and related structures are also known. Most are produced from ores by a variety of wet processes using acid and base. Heating the hydroxides leads to formation of corundum. These materials are of central importance to the production of aluminium and are themselves extremely useful. Some mixed oxide phases are also very useful, such as
spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals. Properties Sp ...
(MgAl2O4), Na-β-alumina (NaAl11O17), and
tricalcium aluminate Tricalcium aluminate Ca3Al2O6, often formulated as 3CaO·Al2O3 to highlight the proportions of the oxides from which it is made, is the most basic of the calcium aluminates. It does not occur in nature, but is an important mineral phase in Port ...
(Ca3Al2O6, an important mineral phase in
Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in t ...
). The only stable chalcogenides under normal conditions are
aluminium sulfide Aluminum sulfide or aluminium sulphide is a chemical compound with the formula Aluminium, Al2Sulfur, S3. This colorless species has an interesting structural chemistry, existing in several forms. The material is sensitive to moisture, hydrolyzing ...
(Al2S3),
selenide A selenide is a chemical compound containing a selenium Selenium is a chemical element with the Symbol (chemistry), symbol Se and atomic number 34. It is a nonmetal (more rarely considered a metalloid) with properties that are intermediate betwee ...
(Al2Se3), and telluride (Al2Te3). All three are prepared by direct reaction of their elements at about and quickly hydrolyze completely in water to yield aluminium hydroxide and the respective
hydrogen chalcogenide Hydrogen chalcogenides (also chalcogen hydrides or hydrogen chalcides) are binary compounds of hydrogen with chalcogen atoms (elements of group 16: oxygen, sulfur, selenium, tellurium, and polonium). Water, the first chemical compound in this series ...
. As aluminium is a small atom relative to these chalcogens, these have four-coordinate tetrahedral aluminium with various polymorphs having structures related to
wurtzite Wurtzite is a zinc and iron sulfide mineral with the chemical formula , a less frequently encountered Polymorphism (materials science), structural polymorph form of sphalerite. The iron content is variable up to eight percent.Palache, Charles, Har ...
, with two-thirds of the possible metal sites occupied either in an orderly (α) or random (β) fashion; the sulfide also has a γ form related to γ-alumina, and an unusual high-temperature hexagonal form where half the aluminium atoms have tetrahedral four-coordination and the other half have trigonal bipyramidal five-coordination. Four pnictides – aluminium nitride (AlN),
aluminium phosphide Aluminium phosphide is a highly toxic inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compou ...
(AlP), aluminium arsenide (AlAs), and aluminium antimonide (AlSb) – are known. They are all III-V semiconductors isoelectronic to and
germanium Germanium is a chemical element with the Symbol (chemistry), symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to it ...
, all of which but AlN have the
zinc blende 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 deposits, sedimen ...
structure. All four can be made by high-temperature (and possibly high-pressure) direct reaction of their component elements. Aluminium alloys well with most other metals (with the exception of most
alkali metals The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
and group 13 metals) and over 150
intermetallics An intermetallic (also called an intermetallic compound, intermetallic alloy, ordered intermetallic alloy, and a long-range-ordered alloy) is a type of metallic alloy An alloy is a mixture of chemical elements of which at least one is a meta ...
with other metals are known. Preparation involves heating fixed metals together in certain proportion, followed by gradual cooling and annealing. Bonding in them is predominantly metallic and the crystal structure primarily depends on efficiency of packing. There are few compounds with lower oxidation states. A few aluminium(I) compounds exist: AlF, AlCl, AlBr, and AlI exist in the gaseous phase when the respective trihalide is heated with aluminium, and at cryogenic temperatures. A stable derivative of aluminium monoiodide is the cyclic
adduct An adduct (from the Latin ''adductus'', "drawn toward" alternatively, a contraction of "addition product") is a product of a Addition reaction, direct addition of two or more distinct molecules, resulting in a single reaction product containing a ...
formed with
triethylamine Triethylamine is the chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) containing atoms from more than one chemical element held together by chemical ...
, Al4I4(NEt3)4. Al2O and Al2S also exist but are very unstable. Very simple aluminium(II) compounds are invoked or observed in the reactions of Al metal with oxidants. For example, aluminium monoxide, AlO, has been detected in the gas phase after explosion and in stellar absorption spectra. More thoroughly investigated are compounds of the formula R4Al2 which contain an Al–Al bond and where R is a large organic
ligand In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electro ...
.


Organoaluminium compounds and related hydrides

A variety of compounds of empirical formula AlR3 and AlR1.5Cl1.5 exist. The aluminium trialkyls and triaryls are reactive, volatile, and colorless liquids or low-melting solids. They catch fire spontaneously in air and react with water, thus necessitating precautions when handling them. They often form dimers, unlike their boron analogues, but this tendency diminishes for branched-chain alkyls (e.g. Pr''i'', Bu''i'', Me3CCH2); for example,
triisobutylaluminium Triisobutylaluminium (TiBA) is an organoaluminium compound with the formula Al(CH2CH(CH3)2)3. This colorless pyrophoricity, pyrophoric liquid is mainly used to make linear primary alcohol (chemistry), alcohols and α-olefins.Michael J. Krause, Fr ...
exists as an equilibrium mixture of the monomer and dimer. These dimers, such as
trimethylaluminium Trimethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemica ...
(Al2Me6), usually feature tetrahedral Al centers formed by dimerization with some alkyl group bridging between both aluminium atoms. They are hard acids and react readily with ligands, forming adducts. In industry, they are mostly used in alkene insertion reactions, as discovered by
Karl Ziegler Karl Waldemar Ziegler (26 November 1898 – 12 August 1973) was a German people, German chemist who won the Nobel Prize in Chemistry in 1963, with Giulio Natta, for work on polymers. The Nobel Committee recognized his "excellent work on organomet ...
, most importantly in "growth reactions" that form long-chain unbranched primary alkenes and alcohols, and in the low-pressure polymerization of
ethene Ethylene (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and ...
and
propene Propylene, also known as propene, is an unsaturated organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon chemical bond, bonds. Due to carbon's ability to Catena ...
. There are also some
heterocyclic A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis ...
and cluster organoaluminium compounds involving Al–N bonds. The industrially most important aluminium hydride is
lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula lithium, Lialuminium, Alhydride, H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a re ...
(LiAlH4), which is used in as a reducing agent in
organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...
. It can be produced from
lithium hydride Lithium hydride is an inorganic compound with the formula Lithium, LiHydride, H. This alkali metal hydride is a colorless solid, although commercial samples are grey. Characteristic of a Hydride#Ionic hydrides, salt-like (ionic) hydride, it has a ...
and
aluminium trichloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six Water of hydration, water molecules of hydration. Both are colourless crystals, but sampl ...
. The simplest hydride,
aluminium hydride Aluminium hydride (also known as alane and alumane) is an inorganic compound with the Chemical formula, formula Aluminium, AlHydrogen, H3. Alane and its derivatives are common Redox, reducing (hydride addition) reagents in organic synthesis that ...
or alane, is not as important. It is a polymer with the formula (AlH3)''n'', in contrast to the corresponding boron hydride that is a dimer with the formula (BH3)2.


Natural occurrence


Space

Aluminium's per-particle abundance in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
is 3.15 ppm (parts per million). It is the twelfth most abundant of all elements and third most abundant among the elements that have odd atomic numbers, after hydrogen and nitrogen. The only stable isotope of aluminium, 27Al, is the eighteenth most abundant nucleus in the Universe. It is created almost entirely after fusion of carbon in massive stars that will later become
Type II supernova A Type II supernova (plural: ''supernovae'' or ''supernovas'') results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, but no more than 40 to 50 times, the solar mass, mass of the Sun () to ...
s: this fusion creates 26Mg, which, upon capturing free protons and neutrons becomes aluminium. Some smaller quantities of 27Al are created in hydrogen burning shells of evolved stars, where 26Mg can capture free protons. Essentially all aluminium now in existence is 27Al. 26Al was present in the early Solar System with abundance of 0.005% relative to 27Al but its half-life of 728,000 years is too short for any original nuclei to survive; 26Al is therefore
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the Endling, last individual of the species, although the Functional ext ...
. Unlike for 27Al, hydrogen burning is the primary source of 26Al, with the nuclide emerging after a nucleus of 25Mg catches a free proton. However, the trace quantities of 26Al that do exist are the most common
gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nucleus, atomic nuclei. It consists of the shortest wavelength electromagnetic wav ...
emitter in the
interstellar gas In astronomy, the interstellar medium is the matter and radiation that exist in the outer space, space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as cosmic dust, dust and cosmic ray ...
; if the original 26Al were still present, gamma ray maps of the Milky Way would be brighter.


Earth

Overall, the Earth is about 1.59% aluminium by mass (seventh in abundance by mass).William F McDonoug
The composition of the Earth
quake.mit.edu, archived by the Internet Archive Wayback Machine.
Aluminium occurs in greater proportion in the Earth's crust than in the Universe at large, because aluminium easily forms the oxide and becomes bound into rocks and stays in the
Earth's crust Earth's crust is Earth's thin outer shell of Rock (geology), rock, referring to less than 1% of Earth's radius and volume. It is the top component of the lithosphere, a division of Earth's layers that includes the Crust (geology), crust and the ...
, while less reactive metals sink to the core. In the Earth's crust, aluminium is the most abundant metallic element (8.23% by mass) and the third most abundant of all elements (after oxygen and silicon). A large number of silicates in the Earth's crust contain aluminium. In contrast, the Earth's mantle is only 2.38% aluminium by mass. Aluminium also occurs in seawater at a concentration of 2 μg/kg. Because of its strong affinity for oxygen, aluminium is almost never found in the elemental state; instead it is found in oxides or silicates.
Feldspar Feldspars are a group of rock-forming aluminium Aluminium (aluminum in American and Canadian English) is a chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, ...
s, the most common group of minerals in the Earth's crust, are aluminosilicates. Aluminium also occurs in the minerals
beryl Beryl ( ) is a mineral composed of beryllium aluminium Silicate minerals#Cyclosilicates, silicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and Aquamarine (gem), aquamarine. Naturally occurring, Hex ...
,
cryolite Cryolite (Na3AlF6, sodium hexafluoroaluminate) is an uncommon mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific cryst ...
,
garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different spe ...
,
spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , which means ''spine'' in reference to its pointed crystals. Properties Sp ...
, and
turquoise Turquoise is an Opacity (optics), opaque, blue-to-green mineral that is a hydrated phosphate of copper and aluminium, with the chemical formula . It is rare and valuable in finer grades and has been prized as a gemstone and ornamental stone for ...
. Impurities in Al2O3, such as
chromium Chromium is a chemical element with the Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium me ...
and
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundance ...
, yield the
gemstone A gemstone (also called a fine gem, jewel, precious stone, or semiprecious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewellery, jewelry or other adornments. However, certain Rock (geology), rocks (suc ...
s
ruby A ruby is a pinkish red to blood-red colored gemstone, a variety of the mineral corundum (aluminium oxide). Ruby is one of the most popular traditional jewelry gems and is very durable. Other varieties of gem-quality corundum are called sapp ...
and
sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphir ...
, respectively. Native aluminium metal is extremely rare and can only be found as a minor phase in low oxygen
fugacity In chemical thermodynamics, the fugacity of a real gas is an effective partial pressure which replaces the mechanical partial pressure in an accurate computation of the chemical equilibrium constant. It is equal to the pressure of an ideal gas whic ...
environments, such as the interiors of certain volcanoes. Native aluminium has been reported in
cold seep A cold seep (sometimes called a cold vent) is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. ''Cold'' does not mean that the temperature of the seep ...
s in the northeastern
continental slope A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being oceanic basin, deep-ocean basins and mid-ocean ridges. The conti ...
of the
South China Sea The South China Sea is a marginal sea of the Western Pacific Ocean. It is bounded in the north by the shores of South China (hence the name), in the west by the Indochinese Peninsula, in the east by the islands of Taiwan island, Taiwan and nor ...
. It is possible that these deposits resulted from
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometre The micrometre (Amer ...
l reduction of tetrahydroxoaluminate Al(OH)4. Although aluminium is a common and widespread element, not all aluminium minerals are economically viable sources of the metal. Almost all metallic aluminium is produced from the
ore Ore is natural Rock (geology), rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Ret ...
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(OH ...
(AlO''x''(OH)3–2''x''). Bauxite occurs as a
weathering Weathering is the deterioration of Rock (geology), rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little o ...
product of low iron and silica bedrock in tropical climatic conditions. In 2017, most bauxite was mined in Australia, China, Guinea, and India.


History

The history of aluminium has been shaped by usage of
alum An alum () is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula , where is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, ...
. The first written record of alum, made by
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
historian
Herodotus Herodotus ( ; grc, , }; BC) was an ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided in ...
, dates back to the 5th century BCE. The ancients are known to have used alum as a dyeing
mordant A mordant or dye fixative is a substance used to set (i.e. bind) dyes on fabrics by forming a coordination complex with the dye, which then attaches to the fabric (or tissue). It may be used for dyeing fabrics or for intensifying stains ...
and for city defense. After the
Crusades The Crusades were a series of religious wars initiated, supported, and sometimes directed by the Latin Church in the medieval period. The best known of these Crusades are those to the Holy Land in the period between 1095 and 1291 that were in ...
, alum, an indispensable good in the European fabric industry, was a subject of international commerce; it was imported to Europe from the eastern Mediterranean until the mid-15th century. The nature of alum remained unknown. Around 1530, Swiss physician
Paracelsus Paracelsus (; ; 1493 – 24 September 1541), born Theophrastus von Hohenheim (full name Philippus Aureolus Theophrastus Bombastus von Hohenheim), was a Swiss physician, alchemist, lay theologian, and philosopher of the German Renaissance. He w ...
suggested alum was a salt of an earth of alum. In 1595, German doctor and chemist
Andreas Libavius Andreas Libavius or Andrew Libavius was born in Halle (Saale), Halle, Germany c. 1550 and died in July 1616. Libavius was a renaissance man who spent time as a professor at the University of Jena teaching history and poetry. After which he became ...
experimentally confirmed this. In 1722, German chemist
Friedrich Hoffmann Friedrich Hoffmann or Hofmann (19 February 1660 – 12 November 1742) was a German physician and chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a scientist trained in the st ...
announced his belief that the base of alum was a distinct earth. In 1754, German chemist
Andreas Sigismund Marggraf Andreas Sigismund Marggraf (; 3 March 1709 – 7 August 1782) was a German chemist from Berlin, then capital of the Margraviate of Brandenburg, and a pioneer of analytical chemistry. He isolated zinc in 1746 by heating Calamine (mineral), calamine ...
synthesized alumina by boiling clay in sulfuric acid and subsequently adding
potash Potash () includes various mined and manufactured salt (chemistry), salts that contain potassium in water-solute, soluble form.Hans Christian Ørsted
Hans Christian Ørsted
. He reacted anhydrous
aluminium chloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often conta ...
with potassium amalgam, yielding a lump of metal looking similar to tin. He presented his results and demonstrated a sample of the new metal in 1825. In 1827, German chemist Friedrich Wöhler repeated Ørsted's experiments but did not identify any aluminium. (The reason for this inconsistency was only discovered in 1921.) He conducted a similar experiment in the same year by mixing anhydrous aluminium chloride with potassium and produced a powder of aluminium. In 1845, he was able to produce small pieces of the metal and described some physical properties of this metal. For many years thereafter, Wöhler was credited as the discoverer of aluminium. As Wöhler's method could not yield great quantities of aluminium, the metal remained rare; its cost exceeded that of gold. The first industrial production of aluminium was established in 1856 by French chemist
Henri Etienne Sainte-Claire Deville Henri is an Estonian, Finnish, French, German and Luxembourgish form of the masculine given name Henry. People with this given name ; French noblemen :'' See the ' List of rulers named Henry' for Kings of France named Henri.'' * Henri I de Mo ...
and companions. Deville had discovered that aluminium trichloride could be reduced by sodium, which was more convenient and less expensive than potassium, which Wöhler had used. Even then, aluminium was still not of great purity and produced aluminium differed in properties by sample. Because of its electricity-conducting capacity, aluminium was used as the cap of the
Washington Monument The Washington Monument is an obelisk shaped building within the National Mall in Washington, D.C., built to commemorate George Washington, once commander-in-chief of the Continental Army (1775–1784) in the American Revolutionary War and the ...
, completed in 1885. The tallest building in the world at the time, the non-corroding metal cap was intended to serve as a
lightning rod A lightning rod or lightning conductor (British English, British English) is a metal rod mounted on a structure and intended to protect the structure from a lightning strike. If lightning hits the structure, it will preferentially strike the ro ...
peak. The first industrial large-scale production method was independently developed in 1886 by French engineer Paul Héroult and American engineer Charles Martin Hall; it is now known as the Hall–Héroult process. The Hall–Héroult process converts alumina into metal. Austrian chemist Carl Joseph Bayer discovered a way of purifying bauxite to yield alumina, now known as the Bayer process, in 1889. Modern production of the aluminium metal is based on the Bayer and Hall–Héroult processes. Prices of aluminium dropped and aluminium became widely used in jewelry, everyday items, eyeglass frames, optical instruments, tableware, and
foil Foil may refer to: Materials * Foil (metal), a quite thin sheet of metal, usually manufactured with a rolling mill machine * Metal leaf, a very thin sheet of decorative metal * Aluminium foil, a type of wrapping for food * Tin foil, metal foil ma ...
in the 1890s and early 20th century. Aluminium's ability to form hard yet light alloys with other metals provided the metal with many uses at the time. During
World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was List of wars and anthropogenic disasters by death toll, one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, ...
, major governments demanded large shipments of aluminium for light strong airframes; during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
, demand by major governments for aviation was even higher. By the mid-20th century, aluminium had become a part of everyday life and an essential component of housewares. In 1954, production of aluminium surpassed that of , historically second in production only to iron, making it the most produced non-ferrous metal. During the mid-20th century, aluminium emerged as a civil engineering material, with building applications in both basic construction and interior finish work, and increasingly being used in military engineering, for both airplanes and land armor vehicle engines. Earth's first artificial satellite, launched in 1957, consisted of two separate aluminium semi-spheres joined and all subsequent space vehicles have used aluminium to some extent. The aluminium can was invented in 1956 and employed as a storage for drinks in 1958. Throughout the 20th century, the production of aluminium rose rapidly: while the world production of aluminium in 1900 was 6,800 metric tons, the annual production first exceeded 100,000 metric tons in 1916; 1,000,000 tons in 1941; 10,000,000 tons in 1971. In the 1970s, the increased demand for aluminium made it an exchange commodity; it entered the
London Metal Exchange The London Metal Exchange (LME) is a futures and forwards exchange with the world's largest market in standarised forward contracts, futures contracts and options on base metals. The exchange also offers contracts on ferrous metals and precious ...
, the oldest industrial metal exchange in the world, in 1978. The output continued to grow: the annual production of aluminium exceeded 50,000,000 metric tons in 2013. The real price for aluminium declined from $14,000 per metric ton in 1900 to $2,340 in 1948 (in 1998 United States dollars). Extraction and processing costs were lowered over technological progress and the scale of the economies. However, the need to exploit lower-grade poorer quality deposits and the use of fast increasing input costs (above all, energy) increased the net cost of aluminium; the real price began to grow in the 1970s with the rise of energy cost. Production moved from the industrialized countries to countries where production was cheaper. Production costs in the late 20th century changed because of advances in technology, lower energy prices, exchange rates of the United States dollar, and alumina prices. The
BRIC BRIC is a grouping acronym An acronym is a word or name formed from the initial components of a longer name or phrase. Acronyms are usually formed from the initial letters of words, as in ''NATO'' (''North Atlantic Treaty Organization'') ...
countries' combined share in primary production and primary consumption grew substantially in the first decade of the 21st century. China is accumulating an especially large share of the world's production thanks to an abundance of resources, cheap energy, and governmental stimuli; it also increased its consumption share from 2% in 1972 to 40% in 2010. In the United States, Western Europe, and Japan, most aluminium was consumed in transportation, engineering, construction, and packaging. In 2021, prices for industrial metals such as aluminium have soared to near-record levels as energy shortages in China drive up costs for electricity.


Etymology

The names ''aluminium'' and ''aluminum'' are derived from the word ''alumine'', an obsolete term for ''alumina'', a naturally occurring oxide of aluminium. ''Alumine'' was borrowed from French, which in turn derived it from ''alumen'', the classical Latin name for
alum An alum () is a type of chemical compound, usually a hydrated double sulfate salt of aluminium with the general formula , where is a monovalent cation such as potassium or ammonium. By itself, "alum" often refers to potassium alum, ...
, the mineral from which it was collected. The Latin word ''alumen'' stems from the
Proto-Indo-European Proto-Indo-European (PIE) is the reconstructed common ancestor of the Indo-European language family. Its proposed features have been derived by linguistic reconstruction from documented Indo-European languages. No direct record of Proto-Indo-E ...
root ''*alu-'' meaning "bitter" or "beer".


Origins

British chemist
Humphry Davy Sir Humphry Davy, 1st Baronet, (17 December 177829 May 1829) was a British people, British chemist and inventor who invented the Davy lamp and a very early form of arc lamp. He is also remembered for isolating, by using electricity, several C ...
, who performed a number of experiments aimed to isolate the metal, is credited as the person who named the element. The first name proposed for the metal to be isolated from alum was ''alumium'', which Davy suggested in an 1808 article on his electrochemical research, published in
Philosophical Transactions of the Royal Society ''Philosophical Transactions of the Royal Society'' is a scientific journal published by the Royal Society. In its earliest days, it was a private venture of the Royal Society's secretary. It was established in 1665, making it the first journa ...
. It appeared that the name was created from the English word ''alum'' and the Latin suffix ''-ium''; but it was customary then to give elements names originating in Latin, so that this name was not adopted universally. This name was criticized by contemporary chemists from France, Germany, and Sweden, who insisted the metal should be named for the oxide, alumina, from which it would be isolated. The English name ''alum'' does not come directly from Latin, whereas ''alumine''/''alumina'' obviously comes from the Latin word ''alumen'' (upon
declension In linguistics, declension (verb: ''to decline'') is the changing of the form of a word, generally to express its syntactic function in the sentence, by way of some inflection. Declensions may apply to nouns, pronouns, adjectives, adverbs, and ar ...
, ''alumen'' changes to ''alumin-''). One example was ''Essai sur la Nomenclature chimique'' (July 1811), written in French by a Swedish chemist, Jöns Jacob Berzelius, in which the name ''aluminium'' is given to the element that would be synthesized from alum.. (Another article in the same journal issue also gives the name ''aluminium'' to the metal whose oxide is the basis of
sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sapphir ...
.) A January 1811 summary of one of Davy's lectures at the
Royal Society The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, ...
mentioned the name ''aluminium'' as a possibility. The next year, Davy published a chemistry textbook in which he used the spelling ''aluminum''. Both spellings have coexisted since. Their usage is regional: ''aluminum'' dominates in the United States and Canada; ''aluminium'', in the rest of the English-speaking world.


Spelling

In 1812, a British scientist, Thomas Young, wrote an anonymous review of Davy's book, in which he proposed the name ''aluminium'' instead of ''aluminum'', which he thought had a "less classical sound". This name did catch on: although the ' spelling was occasionally used in Britain, the American scientific language used ' from the start. Most scientists throughout the world used ' in the 19th century; and it was entrenched in many other European languages, such as French, German, and Dutch. In 1828, an American lexicographer,
Noah Webster Noah ''Nukh''; am, ኖህ, ''Noḥ''; ar, نُوح '; grc, Νῶε ''Nôe'' () is the tenth and last of the Antediluvian, pre-Flood Patriarchs (Bible), patriarchs in the traditions of Abrahamic religions. His story appears in the Hebrew Bibl ...
, entered only the ''aluminum'' spelling in his ''
American Dictionary of the English Language ''Webster's Dictionary'' is any of the English language dictionaries edited in the early 19th century by American lexicographer Noah Webster (1758–1843), as well as numerous related or unrelated dictionaries that have adopted the Webster's n ...
''. In the 1830s, the ' spelling gained usage in the United States; by the 1860s, it had become the more common spelling there outside science. In 1892, Hall used the ' spelling in his advertising handbill for his new electrolytic method of producing the metal, despite his constant use of the ' spelling in all the patents he filed between 1886 and 1903: it is unknown whether this spelling was introduced by mistake or intentionally; but Hall preferred ''aluminum'' since its introduction because it resembled ''
platinum Platinum is a chemical element with the Symbol (chemistry), symbol Pt and atomic number 78. It is a density, dense, malleable, ductility, ductile, highly unreactive, precious metal, precious, silverish-white transition metal. Its name origina ...
'', the name of a prestigious metal. By 1890, both spellings had been common in the United States, the ' spelling being slightly more common; by 1895, the situation had reversed; by 1900, ''aluminum'' had become twice as common as ''aluminium''; in the next decade, the ' spelling dominated American usage. In 1925, the
American Chemical Society The American Chemical Society (ACS) is a scientific society based in the United States that supports scientific inquiry in the field of chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a na ...
adopted this spelling. The
International Union of Pure and Applied Chemistry The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
(IUPAC) adopted ''aluminium'' as the standard international name for the element in 1990. In 1993, they recognized ''aluminum'' as an acceptable variant; the most recent 2005 edition of the IUPAC nomenclature of inorganic chemistry also acknowledges this spelling. IUPAC official publications use the ' spelling as primary, and they list both where it is appropriate.


Production and refinement

The production of aluminium starts with the extraction 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(OH ...
rock from the ground. The bauxite is processed and transformed using the Bayer process into alumina, which is then processed using the Hall–Héroult process, resulting in the final aluminium metal. Aluminium production is highly energy-consuming, and so the producers tend to locate smelters in places where electric power is both plentiful and inexpensive. As of 2019, the world's largest
smelters 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 mining#Ore processing, silver, iron-making, iron, copper extracti ...
of aluminium are located in China, India, Russia, Canada, and the United Arab Emirates, while China is by far the top producer of aluminium with a world share of fifty-five percent. According to the International Resource Panel's Metal Stocks in Society report, the global
per capita ''Per capita'' is a Latin phrase literally meaning "by heads" or "for each head", and idiomatically used to mean "per person". The term is used in a wide variety of social sciences and statistical research contexts, including government statistic ...
stock of aluminium in use in society (i.e. in cars, buildings, electronics, etc.) is . Much of this is in more-developed countries ( per capita) rather than less-developed countries ( per capita).


Bayer process

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(OH ...
is converted to alumina by the Bayer process. Bauxite is blended for uniform composition and then is ground. The resulting
slurry A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids or separating minerals, the liquid being a carrier that is pumped on a device such as a centrifugal pu ...
is mixed with a hot solution of
sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive, caustic base (c ...
; the mixture is then treated in a digester vessel at a pressure well above atmospheric, dissolving the aluminium hydroxide in bauxite while converting impurities into relatively insoluble compounds: After this reaction, the slurry is at a temperature above its atmospheric boiling point. It is cooled by removing steam as pressure is reduced. The bauxite residue is separated from the solution and discarded. The solution, free of solids, is seeded with small crystals of aluminium hydroxide; this causes decomposition of the l(OH)4sup>− ions to aluminium hydroxide. After about half of aluminium has precipitated, the mixture is sent to classifiers. Small crystals of aluminium hydroxide are collected to serve as seeding agents; coarse particles are converted to alumina by heating; the excess solution is removed by evaporation, (if needed) purified, and recycled.


Hall–Héroult process

The conversion of alumina to aluminium metal is achieved by the Hall–Héroult process. In this energy-intensive process, a solution of alumina in a molten () mixture of
cryolite Cryolite (Na3AlF6, sodium hexafluoroaluminate) is an uncommon mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific cryst ...
(Na3AlF6) with
calcium fluoride Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the chemical formula, formula CaF2. It is a white insoluble solid. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing ...
is electrolyzed to produce metallic aluminium. The liquid aluminium metal sinks to the bottom of the solution and is tapped off, and usually cast into large blocks called aluminium billets for further processing. Anodes of the electrolysis cell are made of carbon—the most resistant material against fluoride corrosion—and either bake at the process or are prebaked. The former, also called Söderberg anodes, are less power-efficient and fumes released during baking are costly to collect, which is why they are being replaced by prebaked anodes even though they save the power, energy, and labor to prebake the cathodes. Carbon for anodes should be preferably pure so that neither aluminium nor the electrolyte is contaminated with ash. Despite carbon's resistivity against corrosion, it is still consumed at a rate of 0.4–0.5 kg per each kilogram of produced aluminium. Cathodes are made of
anthracite Anthracite, also known as hard coal, and black coal, is a hard, compact variety of coal that has a lustre (mineralogy)#Submetallic lustre, submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy densit ...
; high purity for them is not required because impurities leach only very slowly. The cathode is consumed at a rate of 0.02–0.04 kg per each kilogram of produced aluminium. A cell is usually terminated after 2–6 years following a failure of the cathode. The Hall–Heroult process produces aluminium with a purity of above 99%. Further purification can be done by the Hoopes process. This process involves the electrolysis of molten aluminium with a sodium, barium, and aluminium fluoride electrolyte. The resulting aluminium has a purity of 99.99%. Electric power represents about 20 to 40% of the cost of producing aluminium, depending on the location of the smelter. Aluminium production consumes roughly 5% of electricity generated in the United States. Because of this, alternatives to the Hall–Héroult process have been researched, but none has turned out to be economically feasible.


Recycling

Recovery of the metal through
recycling Recycling is the process of converting waste materials into new materials and objects. The Energy recycling, recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability t ...
has become an important task of the aluminium industry. Recycling was a low-profile activity until the late 1960s, when the growing use of aluminium
beverage can A drink can (or beverage can) is a metal container designed to hold a fixed portion of liquid such as carbonated soft drinks, alcoholic drinks, fruit juices, teas, herbal teas, energy drinks, etc. Drink cans are made of aluminum (75% of wor ...
s brought it to public awareness. Recycling involves melting the scrap, a process that requires only 5% of the energy used to produce aluminium from ore, though a significant part (up to 15% of the input material) is lost as
dross Dross is a mass of solid impurity, impurities floating on a molten metal or dispersed in the metal, such as in wrought iron. It forms on the surface of low-melting-point metals such as tin, lead, zinc or aluminium or alloys by oxidation of the me ...
(ash-like oxide). An aluminium stack melter produces significantly less dross, with values reported below 1%. White dross from primary aluminium production and from secondary recycling operations still contains useful quantities of aluminium that can be extracted industrially. The process produces aluminium billets, together with a highly complex waste material. This waste is difficult to manage. It reacts with water, releasing a mixture of gases (including, among others,
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the chemical ...
,
acetylene Acetylene (Chemical nomenclature, systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is ...
, and
ammonia Ammonia is an inorganic chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a dis ...
), which spontaneously ignites on contact with air; contact with damp air results in the release of copious quantities of ammonia gas. Despite these difficulties, the waste is used as a filler in
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscosity, viscous liquid or semi-solid form of petroleum. It may be found in natural deposits or may be a refined product, and is classed as a Pitch (resin), pitch. Before the ...
and
concrete Concrete is a composite material composed of fine and coarse construction aggregate, aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after wa ...
.


Applications


Metal

The global production of aluminium in 2016 was 58.8 million metric tons. It exceeded that of any other metal except
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundance ...
(1,231 million metric tons). Aluminium is almost always alloyed, which markedly improves its mechanical properties, especially when tempered. For example, the common
aluminium foil Aluminium foil (or aluminum foil in North American English North American English (NAmE, NAE) is the most generalized variety of the English language English is a West Germanic languages, West Germanic language of the Indo-Europea ...
s and beverage cans are alloys of 92% to 99% aluminium. The main alloying agents are ,
zinc Zinc is a chemical element with the Symbol (chemistry), 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 eleme ...
,
magnesium Magnesium is a chemical element with the Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group ...
,
manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...
, and (e.g.,
duralumin Duralumin (also called duraluminum, duraluminium, duralum, dural(l)ium, or dural) is a trade name for one of the earliest types of age hardening, age-hardenable aluminium alloys. The term is a combination of ''Dürener'' and ''aluminium''. Its ...
) with the levels of other metals in a few percent by weight. Aluminium, both wrought and cast, has been alloyed with:
manganese Manganese is a chemical element with the Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of ...
, ,
magnesium Magnesium is a chemical element with the Symbol (chemistry), symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group ...
, and
zinc Zinc is a chemical element with the Symbol (chemistry), 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 eleme ...
among others. For example, the
Kynal Kynal was a brand name for a series of aluminium alloys developed and originally produced by the British chemical manufacturer Imperial Chemical Industries (ICI). The name was derived from Kynoch, an existing ICI trademark for ammunition, and alu ...
family of alloys was developed by the British chemical manufacturer
Imperial Chemical Industries Imperial Chemical Industries (ICI) was a British Chemical industry, chemical company. It was, for much of its history, the largest manufacturer in Britain. It was formed by the merger of four leading British chemical companies in 1926. Its head ...
. The major uses for aluminium metal are in: * Transportation (
automobile A car or automobile is a motor vehicle with Wheel, wheels. Most definitions of ''cars'' say that they run primarily on roads, Car seat, seat one to eight people, have four wheels, and mainly transport private transport#Personal transport, pe ...
s, aircraft,
truck A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...
s,
railway car A railroad car, railcar ( American and Canadian English Canadian English (CanE, CE, en-CA) encompasses the Variety (linguistics), varieties of English language, English native to Canada. According to the 2016 Canadian Census, 2016 censu ...
s, marine vessels,
bicycle A bicycle, also called a pedal cycle, bike or cycle, is a human-powered or motor-powered assisted, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A is called a cyclist, or bicyclist. ...
s, spacecraft, ''etc.''). Aluminium is used because of its low density; * Packaging ( cans, foil, frame, ''etc.''). Aluminium is used because it is non-toxic (see below), non- adsorptive, and
splinter A splinter (also known as a sliver) is a fragment of a larger object, or a foreign body that penetrates or is purposely injected into a body. The foreign body must be lodged inside Tissue (biology), tissue to be considered a splinter. Splinters ...
-proof; * Building and construction (
window A window is an Hole, opening in a wall, door, roof, or vehicle that allows the exchange of light and may also allow the passage of sound and sometimes air. Modern windows are usually glazing (window), glazed or covered in some other transparenc ...
s,
door A door is a hinged or otherwise movable barrier that allows ingress (entry) into and egress (exit) from an enclosure. The created opening in the wall is a ''doorway'' or ''portal''. A door's essential and primary purpose is to provide security by ...
s, siding, building wire, sheathing, roofing, ''etc.''). Since steel is cheaper, aluminium is used when lightness, corrosion resistance, or engineering features are important; * Electricity-related uses (conductor alloys, motors, and generators, transformers, capacitors, ''etc.''). Aluminium is used because it is relatively cheap, highly conductive, has adequate mechanical strength and low density, and resists corrosion; * A wide range of
household A household consists of two or more persons who live in the same dwelling. It may be of a single family or another type of person group. The household is the basic unit of analysis in many social, microeconomic and government models, and is impo ...
items, from cooking utensils to
furniture Furniture refers to movable objects intended to support various human activities such as seating (e.g., stools, chairs, and sofas), eating ( tables), storing items, eating and/or working with an item, and sleeping (e.g., beds and hammocks) ...
. Low density, good appearance, ease of fabrication, and durability are the key factors of aluminium usage; * Machinery and equipment (processing equipment, pipes, tools). Aluminium is used because of its corrosion resistance, non-
pyrophoricity A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolit ...
, and mechanical strength. * Portable computer cases. Currently rarely used without alloying, but aluminium can be recycled and clean aluminium has residual market value: for example, the used beverage can (UBC) material was used to encase the electronic components of
MacBook Air The MacBook Air is a line of ultrabook computers developed and manufactured by Apple Inc. It consists of a full-size Computer keyboard, keyboard, a machining, machined aluminum case, and, in the more modern versions, a thin light structure. The ...
laptop, Pixel 5 smartphone or Summit Lite smartwatch.


Compounds

The great majority (about 90%) of aluminium oxide is converted to metallic aluminium. Being a very hard material (
Mohs hardness The Mohs scale of mineral hardness () is a Qualitative property, qualitative ordinal scale, from 1 to 10, characterizing scratch hardness, scratch resistance of various minerals through the ability of harder material to scratch softer material. ...
9), alumina is widely used as an abrasive; being extraordinarily chemically inert, it is useful in highly reactive environments such as
high pressure sodium A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nanometre, nm. Two varieties of such lamps exist: low pressure and high pressure. Low-pressure sodium ...
lamps. Aluminium oxide is commonly used as a catalyst for industrial processes; e.g. the Claus process to convert
hydrogen sulfide Hydrogen sulfide is a chemical compound with the chemical formula, formula . It is a colorless Chalcogen hydride, chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic ...
to sulfur in
refineries A refinery is a production facility composed of a group of chemical engineering unit processes and unit operations refining certain materials or converting raw material into products of value. Types of refineries Different types of refineries ar ...
and to
alkylate An alkylation unit (alky) is one of the conversion processes used in Oil industry, petroleum refineries. It is used to convert isobutane and low-molecular-weight alkenes (primarily a mixture of propene and butene) into alkylate, a high octane gaso ...
amine In chemistry, amines (, ) are chemical compound, compounds and functional groups that contain a base (chemistry), basic nitrogen atom with a lone pair. Amines are formally derivative (chemistry), derivatives of ammonia (), wherein one or mo ...
s. Many industrial
catalysts Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...
are supported by alumina, meaning that the expensive
catalyst Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...
material is dispersed over a surface of the inert alumina. Another principal use is as a drying agent or absorbent. Several sulfates of aluminium have industrial and commercial application.
Aluminium sulfate Aluminium sulfate is a salt with the formula Al2 (SO4)3. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water and wastewater treatment pla ...
(in its hydrate form) is produced on the annual scale of several millions of metric tons. About two-thirds is consumed in
water treatment Water treatment is any process that improves the quality of water Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main ...
. The next major application is in the manufacture of paper. It is also used as a mordant in dyeing, in pickling seeds, deodorizing of mineral oils, in
leather tanning Tanning is the process of treating Skinning, skins and Hide (skin), hides of animals to produce leather. A tannery is the place where the skins are processed. Tanning hide into leather involves a process which permanently alters the protein str ...
, and in production of other aluminium compounds. Two kinds of alum,
ammonium alum Ammonium aluminium sulfate, also known as ammonium alum or just alum (though there are many different substances also called "alum"), is a white crystalline double sulfate usually encountered as the dodecahydrate, Chemical formula, formula (NH4)Al( ...
and
potassium alum Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the double sulfate of potassium and aluminium, with chemical formula KAl(SO4)2. It is commonly encountered as the hydrate, dodecahydrate, KAl(SO4)2·12H2O. It c ...
, were formerly used as mordants and in leather tanning, but their use has significantly declined following availability of high-purity aluminium sulfate. Anhydrous
aluminium chloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often conta ...
is used as a catalyst in chemical and petrochemical industries, the dyeing industry, and in synthesis of various inorganic and organic compounds. Aluminium hydroxychlorides are used in purifying water, in the paper industry, and as antiperspirants.
Sodium aluminate Sodium aluminate is an inorganic In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemi ...
is used in treating water and as an accelerator of solidification of cement. Many aluminium compounds have niche applications, for example: *
Aluminium acetate Aluminium acetate or aluminium ethanoate (also "aluminum ~"), sometimes abbreviated AlAc in geochemistry, can refer to a number of different salts of aluminum with acetic acid. In the solid state, three salts exist under this name: basic aluminium m ...
in solution is used as an
astringent An astringent (sometimes called adstringent) is a chemical that shrinks or constricts body tissues. The word derives from the Latin ''adstringere'', which means "to bind fast". Calamine lotion, Witch hazel (astringent), witch hazel, and Anemops ...
. *
Aluminium phosphate Aluminium phosphate is a chemical compound. In nature it occurs as the mineral berlinite. Many synthetic forms of aluminium phosphate are known. They have framework structures similar to zeolites and some are used as catalysts, ion-exchangers or ...
is used in the manufacture of glass, ceramic, pulp and paper products,
cosmetics Cosmetics are constituted mixtures of chemical compounds derived from either Natural product, natural sources, or synthetically created ones. Cosmetics have various purposes. Those designed for personal care and skin care can be used to Clea ...
, paints,
varnish Varnish is a clear Transparency (optics), transparent hard protective coating or film. It is not a wood stain, stain. It usually has a yellowish shade from the manufacturing process and materials used, but it may also be pigmented as desired, ...
es, and in dental
cement A cement is a binder (material), binder, a chemical substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel ...
. *
Aluminium hydroxide Aluminium hydroxide, Al(OH)3, is found in nature as the mineral gibbsite (also known as hydrargillite) and its three much rarer Polymorphism (materials science), polymorphs: bayerite, doyleite, and nordstrandite. Aluminium hydroxide is Amphoter ...
is used as an
antacid An antacid is a substance which neutralization (chemistry), neutralizes gastric acid, stomach acidity and is used to relieve heartburn, indigestion or an upset stomach. Some antacids have been used in the treatment of constipation and diarrhea. ...
, and mordant; it is used also in
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 ...
purification, the manufacture of glass and ceramics, and in the
waterproofing Waterproofing is the process of making an object or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environme ...
of
fabrics Textile is an Hyponymy and hypernymy, umbrella term that includes various Fiber, fiber-based materials, including fibers, yarns, Staple (textiles)#Filament fiber, filaments, Thread (yarn), threads, different #Fabric, fabric types, etc. At f ...
. *
Lithium aluminium hydride Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula lithium, Lialuminium, Alhydride, H4. It is a white solid, discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a re ...
is a powerful reducing agent used in
organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clay ...
. * Organoaluminiums are used as
Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty Non-bonding orbital, orbital which is capable of accepting an electron pair from a Lewis Base (chemistry), base to form a Lewis a ...
s and co-catalysts. * Methylaluminoxane is a co-catalyst for Ziegler–Natta
olefin In organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms th ...
polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer, monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are ...
to produce
vinyl polymer In polymer chemistry Polymer chemistry is a sub-discipline of chemistry that focuses on the structures of chemicals, chemical synthesis, and Chemical property, chemical and physical properties of polymers and macromolecules. The principles and ...
s such as
polyethene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bott ...
. * Aqueous aluminium ions (such as aqueous aluminium sulfate) are used to treat against fish parasites such as '' Gyrodactylus salaris''. * In many
vaccine A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifie ...
s, certain aluminium salts serve as an immune
adjuvant In pharmacology, an adjuvant is a drug or other substance, or a combination of substances, that is used to increase the efficacy#Pharmacology, efficacy or Potency (pharmacology), potency of certain drugs. Specifically, the term can refer to: * Adju ...
(immune response booster) to allow the
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metabo ...
in the vaccine to achieve sufficient potency as an immune stimulant.


Aluminized substrates

Aluminizing is the process of coating a structure or material with a thin layer of aluminium. It is done to impart specific traits that the underlying substrate lacks, such as a certain chemical or physical property. Aluminized materials include: *
Aluminized steel Aluminized steel is steel that has been plated with aluminium or aluminium-silicon alloy, in a process analogous to hot-dip galvanizing. The steel workpiece is immersed in molten aluminum to produce a tight metallic bond between the steel and co ...
, for corrosion resistance and other properties * Aluminized screen, for display devices * Aluminized cloth, to reflect heat * Aluminized mylar, to reflect heat


Biology

Despite its widespread occurrence in the Earth's crust, aluminium has no known function in biology. At pH 6–9 (relevant for most natural waters), aluminium precipitates out of water as the hydroxide and is hence not available; most elements behaving this way have no biological role or are toxic.
Aluminium sulfate Aluminium sulfate is a salt with the formula Al2 (SO4)3. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water and wastewater treatment pla ...
has an LD50 of 6207 mg/kg (oral, mouse), which corresponds to 435 grams for an person.


Toxicity

Aluminium is classified as a non-carcinogen by the
United States Department of Health and Human Services The United States Department of Health and Human Services (HHS) is a cabinet-level executive branch The Executive, also referred as the Executive branch or Executive power, is the term commonly used to describe that part of government whi ...
. A review published in 1988 said that there was little evidence that normal exposure to aluminium presents a risk to healthy adult, and a 2014 multi-element toxicology review was unable to find deleterious effects of aluminium consumed in amounts not greater than 40 mg/day per kg of
body mass Human body weight is a person's Mass versus weight, mass or weight. Strictly speaking, body weight is the measurement of weight without items located on the person. Practically though, body weight may be measured with clothes on, but without shoe ...
. Most aluminium consumed will leave the body in feces; most of the small part of it that enters the bloodstream, will be excreted via urine; nevertheless some aluminium does pass the blood-brain barrier and is lodged preferentially in the brains of Alzheimer's patients. Evidence published in 1989 indicates that, for Alzheimer's patients, aluminium may act by electrostatically
crosslink In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
ing proteins, thus down-regulating genes in the
superior temporal gyrus The superior temporal gyrus (STG) is one of three (sometimes two) gyrus, gyri in the temporal lobe of the human brain, which is located laterally to the head, situated somewhat above the external ear. The superior temporal gyrus is bounded by: * ...
.


Effects

Aluminium, although rarely, can cause vitamin D-resistant
osteomalacia Osteomalacia is a disease characterized by the softening of the bone A bone is a rigid organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instrum ...
,
erythropoietin Erythropoietin (; EPO), also known as erythropoetin, haematopoietin, or haemopoietin, is a glycoprotein cytokine secreted mainly by the kidneys in response to cellular Hypoxia (medical), hypoxia; it stimulates red blood cell production (erythrop ...
-resistant
microcytic anemia Microcytic anaemia is any of several types of anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in th ...
, and central nervous system alterations. People with kidney insufficiency are especially at a risk. Chronic ingestion of hydrated aluminium silicates (for excess gastric acidity control) may result in aluminium binding to intestinal contents and increased elimination of other metals, such as
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundance ...
or
zinc Zinc is a chemical element with the Symbol (chemistry), 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 eleme ...
; sufficiently high doses (>50 g/day) can cause anemia. During the 1988 Camelford water pollution incident people in
Camelford Camelford ( kw, Reskammel) is a town and civil parishes in England, civil parish in north Cornwall, England, United Kingdom, situated in the River Camel valley northwest of Bodmin Moor. The town is approximately ten miles (16 km) north of ...
had their drinking water contaminated with
aluminium sulfate Aluminium sulfate is a salt with the formula Al2 (SO4)3. It is soluble in water and is mainly used as a coagulating agent (promoting particle collision by neutralizing charge) in the purification of drinking water and wastewater treatment pla ...
for several weeks. A final report into the incident in 2013 concluded it was unlikely that this had caused long-term health problems. Aluminium has been suspected of being a possible cause of
Alzheimer's disease Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...
, but research into this for over 40 years has found, , no good evidence of causal effect. Aluminium increases
estrogen Estrogen or oestrogen is a category of sex steroid, sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogeny (biology), endogenous estrogens th ...
-related
gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. T ...
in human
breast cancer Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a Breast lump, lump in the breast, a change in breast shape, dimpling of the skin, Milk-rejection sign, milk rejection, fluid coming from the nipple, ...
cells cultured in the laboratory. In very high doses, aluminium is associated with altered function of the blood–brain barrier. A small percentage of people have contact
allergies Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and ...
to aluminium and experience itchy red rashes, headache, muscle pain, joint pain, poor memory, insomnia, depression, asthma, irritable bowel syndrome, or other symptoms upon contact with products containing aluminium. Exposure to powdered aluminium or aluminium welding fumes can cause
pulmonary fibrosis Pulmonary fibrosis is a condition in which the lungs become scarred over time. Symptoms include shortness of breath, a dry cough, feeling tired, weight loss, and nail clubbing. Complications may include pulmonary hypertension, respiratory failur ...
. Fine aluminium powder can ignite or explode, posing another workplace hazard.


Exposure routes

Food is the main source of aluminium. Drinking water contains more aluminium than solid food; however, aluminium in food may be absorbed more than aluminium from water. Major sources of human oral exposure to aluminium include food (due to its use in food additives, food and beverage packaging, and cooking utensils), drinking water (due to its use in municipal water treatment), and aluminium-containing medications (particularly antacid/antiulcer and buffered aspirin formulations). Dietary exposure in Europeans averages to 0.2–1.5 mg/kg/week but can be as high as 2.3 mg/kg/week. Higher exposure levels of aluminium are mostly limited to miners, aluminium production workers, and
dialysis Dialysis may refer to: * Dialysis (chemistry), a process of separating molecules in solution **Electrodialysis Electrodialysis (ED) is used to transport salt ions from one Solution (chemistry), solution through ion-exchange membranes to another ...
patients. Consumption of
antacid An antacid is a substance which neutralization (chemistry), neutralizes gastric acid, stomach acidity and is used to relieve heartburn, indigestion or an upset stomach. Some antacids have been used in the treatment of constipation and diarrhea. ...
s, antiperspirants,
vaccine A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifie ...
s, and cosmetics provide possible routes of exposure. Consumption of acidic foods or liquids with aluminium enhances aluminium absorption, and
maltol Maltol is a naturally occurring organic compound that is used primarily as a flavor enhancer. It is found in the bark of larch tree, in pine needles, and in roasted malt (from which it gets its name). It is a white crystalline powder that is so ...
has been shown to increase the accumulation of aluminium in nerve and bone tissues.


Treatment

In case of suspected sudden intake of a large amount of aluminium, the only treatment is deferoxamine mesylate which may be given to help eliminate aluminium from the body by
chelation Chelation is a type of bonding of ions and molecules to metal ions. It involves the formation or presence of two or more separate coordinate bonds between a Denticity, polydentate (multiple bonded) ligand and a single central metal atom. These l ...
. However, this should be applied with caution as this reduces not only aluminium body levels, but also those of other metals such as copper or iron.


Environmental effects

High levels of aluminium occur near mining sites; small amounts of aluminium are released to the environment at the coal-fired power plants or
incinerators Incineration is a waste treatment process that involves the combustion Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that ...
. Aluminium in the air is washed out by the rain or normally settles down but small particles of aluminium remain in the air for a long time. Acidic
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, Rain and snow mixed, sleet, snow, ice pellets, ...
is the main natural factor to mobilize aluminium from natural sources and the main reason for the environmental effects of aluminium; however, the main factor of presence of aluminium in salt and freshwater are the industrial processes that also release aluminium into air. In water, aluminium acts as a toxiс agent on
gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...
-breathing animals such as
fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...
when the water is acidic, in which aluminium may precipitate on gills, which causes loss of
plasma Plasma or plasm may refer to: Science * Plasma (physics) Plasma () 1, where \nu_ is the electron gyrofrequency and \nu_ is the electron collision rate. It is often the case that the electrons are magnetized while the ions are not. Magnetized ...
- and
hemolymph Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body, remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in whic ...
ions leading to osmoregulatory failure. Organic complexes of aluminium may be easily absorbed and interfere with metabolism in mammals and birds, even though this rarely happens in practice. Aluminium is primary among the factors that reduce plant growth on acidic soils. Although it is generally harmless to plant growth in pH-neutral soils, in acid soils the concentration of toxic Al3+ cations increases and disturbs root growth and function.
Wheat Wheat is a Poaceae, grass widely Agriculture, cultivated for its seed, a cereal grain that is a worldwide staple food. The Taxonomy of wheat, many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat ...
has developed a tolerance to aluminium, releasing
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon chemical bond, bonds. Due to carbon's ability to Catenation, catenate (form chains with other carbon atoms), millions of organic c ...
s that bind to harmful aluminium
cations An ion () is an atom or molecule with a net electric charge, electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be po ...
.
Sorghum ''Sorghum'' () is a genus of about 25 species of flowering plants in the grass family (Poaceae). Some of these species are grown as cereals for human consumption and some in pastures for animals. One species is grown for grain, while many other ...
is believed to have the same tolerance mechanism. Aluminium production possesses its own challenges to the environment on each step of the production process. The major challenge is the
greenhouse gas emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, petroleum, oil, and natural gas. The top contributors to greenhouse gas emi ...
. These gases result from electrical consumption of the smelters and the byproducts of processing. The most potent of these gases are
perfluorocarbons Fluorocarbons are chemical compounds with carbon-fluorine bonds. Compounds that contain many C-F bonds often has distinctive properties, e.g., enhanced stability, volatility, and hydrophobicity. Fluorocarbons and their derivatives are commercia ...
from the smelting process. Released
sulfur dioxide Sulfur dioxide ( IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcani ...
is one of the primary precursors of
acid rain Acid rain is rain or any other form of Precipitation (meteorology), precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). Most water, including drinking water, has a neutral pH that exists b ...
. Biodegradation of metallic aluminium is extremely rare; most aluminium-corroding organisms do not directly attack or consume the aluminium, but instead produce corrosive wastes. The fungus '' Geotrichum candidum'' can consume the aluminium in
compact disc The compact disc (CD) is a Digital media, digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then rele ...
s. The bacterium ''
Pseudomonas aeruginosa ''Pseudomonas aeruginosa'' is a common Bacterial capsule, encapsulated, Gram-negative bacteria, gram-negative, Aerobic organism, aerobic–facultative anaerobe, facultatively anaerobic, Bacillus (shape), rod-shaped bacteria, bacterium that can ca ...
'' and the fungus ''
Cladosporium ''Cladosporium'' is a genus of fungus, fungi including some of the most common indoor and outdoor Mold (fungus), molds. Species produce olive-green to brown or black colonies, and have dark-pigmented conidia that are formed in simple or branching ...
resinae'' are commonly detected in aircraft fuel tanks that use
kerosene Kerosene, paraffin, or lamp oil is a combustibility, combustible hydrocarbon liquid which is derived from petroleum. It is widely used as a fuel in Aviation fuel, aviation as well as households. Its name derives from el, κηρός (''keros' ...
-based fuels (not
avgas Avgas (aviation gasoline, also known as aviation spirit in the United Kingdom, UK) is an aviation fuel used in aircraft with spark-ignited internal combustion engines. ''Avgas'' is distinguished from conventional gasoline (petrol) used in moto ...
), and laboratory cultures can degrade aluminium.


See also

* Aluminium granules * Aluminium joining * Aluminium–air battery *
Panel edge staining Panel edge staining is a naturally occurring problem that occurs to anodized aluminium and stainless steel panelling and façades. It is semi-permanent staining that dulls the panel or façade's surface (in particular the edges of the panelling ...
* Quantum clock


Notes


References


Bibliography

* * * * * * * * *


Further reading

* Mimi Sheller, ''Aluminum Dream: The Making of Light Modernity''. Cambridge, Mass.: Massachusetts Institute of Technology Press, 2014.


External links


Aluminium
at ''
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) *
Toxic Substances Portal – Aluminum
' – from the
Agency for Toxic Substances and Disease Registry The Agency for Toxic Substances and Disease Registry (ATSDR) is a federal public health List of United States federal agencies, agency within the United States Department of Health and Human Services. The agency focuses on minimizing human healt ...
, United States Department of Health and Human Services
CDC – NIOSH Pocket Guide to Chemical Hazards – Aluminum



Price history of aluminum, according to the IMF

History of Aluminium
– from the website of the International Aluminium Institute

* {{Authority control Chemical elements Post-transition metals
Aluminium Aluminium (aluminum in American and Canadian English) is a chemical element A chemical element is a species of atoms that have a given number of protons in their atomic nucleus, nuclei, including the pure Chemical substance, substan ...
Electrical conductors Pyrotechnic fuels Airship technology Reducing agents E-number additives Native element minerals Chemical elements with face-centered cubic structure