The discovery of aluminium was announced in 1825 by Danish physicistHans Christian Ørsted. The first industrial production of aluminium was initiated by French chemistHenri Étienne Sainte-Claire Deville in 1856. Aluminium became much more available to the public with theHall–Héroult process developed independently by French engineerPaul Héroult and American engineerCharles Martin Hall in 1886, and the mass production of aluminium led to its extensive use in industry and everyday life. In theFirst andSecond World Wars, aluminium was a crucialstrategic resource foraviation. In 1954, aluminium became the most producednon-ferrous metal, surpassingcopper. In the 21st century, most aluminium was consumed in transportation, engineering, construction, and packaging in theUnited States, Western Europe, andJapan.
Despite its prevalence in the environment, no living organism is known tometabolize aluminiumsalts, but this 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 are ongoing.
Of aluminium isotopes, only27 Al is stable. This situation is common for elements with an odd atomic number.[b] It is the onlyprimordial aluminium isotope, i.e. the only one that has existed on Earth in its current form since the formation of the planet. It is therefore amononuclidic element and itsstandard atomic weight is virtually the same as that of the isotope. This makes aluminium very useful innuclear magnetic resonance (NMR), as its single stable isotope has a high NMR sensitivity.[16] The standard atomic weight of aluminium is low in comparison with many other metals.[c]
All other isotopes of aluminium areradioactive. The most stable of these is26Al: while it was present along with stable27Al in the interstellar medium from which the Solar System formed, having been produced bystellar nucleosynthesis as well, itshalf-life is only 717,000 years and therefore a detectable amount has not survived since the formation of the planet.[17] However, minute traces of26Al are produced fromargon in theatmosphere byspallation caused bycosmic ray protons. The ratio of26Al to10Be has been used forradiodating of geological processes over 105 to 106 year time scales, in particular transport, deposition,sediment storage, burial times, and erosion.[18] Most meteorite scientists believe that the energy released by the decay of26Al was responsible for the melting anddifferentiation of someasteroids after their formation 4.55 billion years ago.[19]
The remaining isotopes of aluminium, withmass numbers ranging from 21 to 43, all have half-lives well under an hour. Threemetastable states are known, all with half-lives under a minute.[15]
Electron shell
An aluminium atom has 13 electrons, arranged in anelectron configuration of[Ne] 3s2 3p1,[20] with three electrons beyond a stable noble gas configuration. Accordingly, the combined first threeionization energies of aluminium are far lower than the fourth ionization energy alone.[21] Such an electron configuration is shared with the other well-characterized members of its group,boron,gallium,indium, andthallium; it is also expected fornihonium. Aluminium can surrender its three outermost electrons in many chemical reactions (seebelow). Theelectronegativity of aluminium is 1.61 (Pauling scale).[22]
High-resolutionSTEM-HAADF micrograph of Al atoms viewed along the [001] zone axis.
A free aluminium atom has aradius of 143 pm.[23] With the three outermost electrons removed, theradius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom.[23] Atstandard temperature and pressure, aluminium atoms (when not affected by atoms of other elements) form aface-centered cubic crystal system bound bymetallic bonding provided by atoms' outermost electrons; hence aluminium (at these conditions) is a metal.[24] This crystal system is shared by many other metals, such aslead andcopper; the size of a unit cell of aluminium is comparable to that of those other metals.[24] The system, however, is not shared by the other members of its group: boron has ionization energies too high to allow metallization, thallium has ahexagonal close-packed 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 formetallic bonding in aluminium are a probable cause for it being soft with a low melting point and lowelectrical resistivity.[25]
Bulk
Aluminium ingot from furnace
Aluminium metal has an appearance ranging from silvery white to dull gray depending on itssurface roughness.[d] Aluminium mirrors are the most reflective of all metal mirrors for nearultraviolet and farinfrared light. It is also one of the most reflective for light in the visible spectrum, nearly on par with silver in this respect, and the two therefore look similar. Aluminium is also good at reflectingsolar radiation, although prolonged exposure to sunlight in air adds wear to the surface of the metal; this may be prevented if aluminium isanodized, which adds a protective layer of oxide on the surface.[citation needed]
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.[28] 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 ofgroups 1 and2, which apart fromberyllium andmagnesium are too reactive for structural use (and beryllium is very toxic).[29] Aluminium is not as strong or stiff as steel, but the low density makes up for this in theaerospace industry and for many other applications where light weight and relatively high strength are crucial.[30]
Pure aluminium is quite soft and lacking in strength. In most applications variousaluminium alloys are used instead because of their higher strength and hardness.[31] Theyield strength of pure aluminium is 7–11MPa, whilealuminium alloys have yield strengths ranging from 200 MPa to 600 MPa.[32] Aluminium isductile, with a percent elongation of 50–70%,[33] andmalleable allowing it to be easilydrawn andextruded.[34] It is also easilymachined andcast.[34]
Aluminium is an excellentthermal andelectrical conductor, having around 60% the conductivity ofcopper, both thermal and electrical, while having only 30% of copper's density.[35] Aluminium is capable ofsuperconductivity, with a superconducting critical temperature of 1.2kelvin and a critical magnetic field of about 100gauss (10milliteslas).[36] It isparamagnetic and thus essentially unaffected by static magnetic fields.[37] The high electrical conductivity, however, means that it is strongly affected by alternating magnetic fields through the induction ofeddy currents.[38]
Aluminium combines characteristics of pre- and post-transition metals. Since it has few available electrons for metallic bonding, like its heaviergroup 13 congeners, it has the characteristic physical properties of a post-transition metal, with longer-than-expected interatomic distances.[25] Furthermore, as Al3+ is a small and highly charged cation, it is strongly polarizing andbonding in aluminium compounds tends towardscovalency;[39] this behavior is similar to that ofberyllium (Be2+), and the two display an example of adiagonal relationship.[40]
The underlying core under aluminium's valence shell is that of the precedingnoble gas, whereas those of its heavier congenersgallium,indium,thallium, andnihonium 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.[39][e] Aluminium also bears minor similarities to the metalloid boron in the same group: AlX3 compounds are valenceisoelectronic to BX3 compounds (they have the same valence electronic structure), and both behave asLewis acids and readily formadducts.[41] Additionally, one of the main motifs of boron chemistry isregular icosahedral structures, and aluminium forms an important part of many icosahedralquasicrystal alloys, including the Al–Zn–Mg class.[42]
Aluminium has a highchemical affinity to oxygen, which renders it suitable for use as areducing agent in thethermite reaction. A fine powder of aluminium reacts explosively on contact withliquid oxygen; under normal conditions, however, aluminium forms a thin oxide layer (~5 nm at room temperature)[43] that protects the metal from further corrosion by oxygen, water, or dilute acid, a process termedpassivation.[39][44] 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 ofsilver-colored paints.[45] Aluminium is not attacked by oxidizing acids because of its passivation. This allows aluminium to be used to store reagents such asnitric acid, concentratedsulfuric acid, and some organic acids.[46]
In hot concentratedhydrochloric acid, aluminium reacts with water with evolution of hydrogen, and in aqueoussodium hydroxide orpotassium hydroxide at room temperature to formaluminates—protective passivation under these conditions is negligible.[47]Aqua regia also dissolves aluminium.[46] Aluminium is corroded by dissolvedchlorides, such as commonsodium chloride, which is why household plumbing is never made from aluminium.[47] The oxide layer on aluminium is also destroyed by contact withmercury due toamalgamation or with salts of some electropositive metals.[39] As such, the strongest aluminium alloys are less corrosion-resistant due togalvanic reactions with alloyedcopper,[32] and aluminium's corrosion resistance is greatly reduced by aqueous salts, particularly in the presence of dissimilar metals.[25]
Aluminium reacts with most nonmetals upon heating, forming compounds such asaluminium nitride (AlN),aluminium sulfide (Al2S3), and the aluminium halides (AlX3). It also forms a wide range ofintermetallic compounds involving metals from every group on the periodic table.[39]
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+. Thecoordination number of such compounds varies, but generally Al3+ is either six- or four-coordinate. Almost all compounds of aluminium(III) are colorless.[39]
Aluminium hydrolysis as a function of pH. Coordinated water molecules are omitted.[48]
In aqueous solution, Al3+ exists as the hexaaqua cation [Al(H2O)6]3+, which has an approximateKa of 10−5.[16] Such solutions are acidic as this cation can act as a proton donor and progressivelyhydrolyze until aprecipitate ofaluminium hydroxide, Al(OH)3, forms. This is useful forclarification of water, as the precipitate nucleates onsuspended particles in the water, hence removing them. Increasing the pH even further leads to the hydroxide dissolving again asaluminate, [Al(H2O)2(OH)4]−, 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.[39] This behavior of Al(OH)3 is termedamphoterism 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 thataluminium salts with weak acids are hydrolyzed in water to the aquated hydroxide and the corresponding nonmetal hydride: for example,aluminium sulfide yieldshydrogen sulfide. However, some salts likealuminium 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, andsulfate. For similar reasons, anhydrous aluminium salts cannot be made by heating their "hydrates": hydrated aluminium chloride is in fact not AlCl3·6H2O but [Al(H2O)6]Cl3, and the Al–O bonds are so strong that heating is not sufficient to break them and form Al–Cl bonds instead:[39]
2[Al(H2O)6]Cl3heat→ Al2O3 + 6 HCl + 9 H2O
All fourtrihalides are well known. Unlike the structures of the three heavier trihalides,aluminium fluoride (AlF3) features six-coordinate aluminium, which explains its involatility and insolubility as well as highheat of formation. Each aluminium atom is surrounded by six fluorine atoms in a distortedoctahedral arrangement, with each fluorine atom being shared between the corners of two octahedra. Such {AlF6} units also exist in complex fluorides such ascryolite, Na3AlF6.[f] AlF3 melts at 1,290 °C (2,354 °F) and is made by reaction ofaluminium oxide withhydrogen fluoride gas at 700 °C (1,300 °F).[49]
With heavier halides, the coordination numbers are lower. The other trihalides aredimeric orpolymeric with tetrahedral four-coordinate aluminium centers.[g]Aluminium trichloride (AlCl3) has a layered polymeric structure below its melting point of 192.4 °C (378 °F) but transforms on melting to Al2Cl6 dimers. At higher temperatures those increasingly dissociate into trigonal planar AlCl3 monomers similar to the structure ofBCl3.Aluminium tribromide andaluminium triiodide form Al2X6 dimers in all three phases and hence do not show such significant changes of properties upon phase change.[49] These materials are prepared by treating aluminium with the halogen. The aluminium trihalides form manyaddition compounds or complexes; theirLewis acidic nature makes them useful ascatalysts for theFriedel–Crafts reactions. Aluminium trichloride has major industrial uses involving this reaction, such as in the manufacture ofanthraquinones andstyrene; 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 (atranshalogenation reaction).[49]
Aluminium forms one stable oxide with thechemical formula Al2O3, commonly calledalumina.[50] It can be found in nature in the mineralcorundum, α-alumina;[51] there is also a γ-alumina phase.[16] Its crystalline form, corundum, is very hard (Mohs hardness 9), has a high melting point of 2,045 °C (3,713 °F), 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 inceramics, as well as being the starting material for the electrolytic production of aluminium.Sapphire andruby are impure corundum contaminated with trace amounts of other metals.[16] The two main oxide-hydroxides, AlO(OH), areboehmite anddiaspore. There are three main trihydroxides:bayerite,gibbsite, andnordstrandite, which differ in their crystalline structure (polymorphs). Many other intermediate and related structures are also known.[16] 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 asspinel (MgAl2O4), Na-β-alumina (NaAl11O17), andtricalcium aluminate (Ca3Al2O6, an important mineral phase inPortland cement).[16]
The only stablechalcogenides under normal conditions arealuminium sulfide (Al2S3),selenide (Al2Se3), andtelluride (Al2Te3). All three are prepared by direct reaction of their elements at about 1,000 °C (1,800 °F) and quickly hydrolyze completely in water to yield aluminium hydroxide and the respectivehydrogen chalcogenide. As aluminium is a small atom relative to these chalcogens, these have four-coordinate tetrahedral aluminium with various polymorphs having structures related towurtzite, 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.[52]
Aluminium alloys well with most other metals (with the exception of mostalkali metals and group 13 metals) and over 150intermetallics with other metals are known. Preparation involves heating fixed metals together in certain proportion, followed by gradual cooling andannealing. Bonding in them is predominantlymetallic and the crystal structure primarily depends on efficiency of packing.[53]
There are few compounds with lower oxidation states. A fewaluminium(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.[49] A stable derivative of aluminium monoiodide is the cyclicadduct formed withtriethylamine, Al4I4(NEt3)4. Al2O and Al2S also exist but are very unstable.[54] 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[55] and in stellar absorption spectra.[56] More thoroughly investigated are compounds of the formula R4Al2 which contain an Al–Al bond and where R is a large organicligand.[57]
Structure oftrimethylaluminium, a compound that features five-coordinate carbon.
A variety of compounds of empirical formula AlR3 and AlR1.5Cl1.5 exist.[58] 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.Pri,Bui, Me3CCH2); for example,triisobutylaluminium exists as an equilibrium mixture of the monomer and dimer.[59][60] These dimers, such astrimethylaluminium (Al2Me6), usually feature tetrahedral Al centers formed by dimerization with some alkyl group bridging between both aluminium atoms. They arehard acids and react readily with ligands, forming adducts. In industry, they are mostly used in alkene insertion reactions, as discovered byKarl Ziegler, most importantly in "growth reactions" that form long-chain unbranched primary alkenes and alcohols, and in the low-pressure polymerization ofethene andpropene. There are also someheterocyclic and cluster organoaluminium compounds involving Al–N bonds.[59]
Aluminium's per-particle abundance in theSolar System is 3.15ppm (parts per million).[62][h] 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.[62] 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 becomeType II supernovas: this fusion creates26Mg, which upon capturing free protons and neutrons, becomes aluminium. Some smaller quantities of27Al are created inhydrogen burning shells of evolved stars, where26Mg can capture free protons.[63] Essentially all aluminium now in existence is27Al.26Al was present in the early Solar System with abundance of 0.005% relative to27Al but its half-life of 728,000 years is too short for any original nuclei to survive;26Al is thereforeextinct.[63] Unlike for27Al, hydrogen burning is the primary source of26Al, with the nuclide emerging after a nucleus of25Mg catches a free proton. However, thetrace quantities of26Al that do exist are the most commongamma ray emitter in theinterstellar gas;[63] if the original26Al were still present,gamma ray maps of the Milky Way would be brighter.[63]
Earth
Bauxite, a major aluminium ore. The red-brown color is due to the presence ofiron oxide minerals.
Overall, the Earth is about 1.59% aluminium by mass (seventh in abundance by mass).[64] Aluminium occurs in greater proportion in the Earth's crust than in the universe at large. This is because aluminium easily forms the oxide and becomes bound into rocks and stays in theEarth's crust, while less reactive metals sink to the core.[63] In the Earth's crust, aluminium is the most abundant metallic element (8.23% by mass[33]) and the third most abundant of all elements (after oxygen and silicon).[65] A large number of silicates in the Earth's crust contain aluminium.[66] In contrast, the Earth'smantle is only 2.38% aluminium by mass.[67] Aluminium also occurs in seawater at a concentration of 0.41 μg/kg.[68]
Because of its strong affinity for oxygen, aluminium is almost never found in the elemental state; instead it is found in oxides or silicates.Feldspars, the most common group of minerals in the Earth's crust, are aluminosilicates. Aluminium also occurs in the mineralsberyl,cryolite,garnet,spinel, andturquoise.[69] Impurities in Al2O3, such aschromium andiron, yield thegemstonesruby andsapphire, respectively.[70]Native aluminium metal is extremely rare and can only be found as a minor phase in low oxygenfugacity environments, such as the interiors of certain volcanoes.[71] Native aluminium has been reported incold seeps in the northeasterncontinental slope of theSouth China Sea. It is possible that these deposits resulted frombacterialreduction of tetrahydroxoaluminate Al(OH)4−.[72]
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 theorebauxite (AlOx(OH)3–2x). Bauxite occurs as aweathering product of low iron and silica bedrock in tropical climatic conditions.[73] In 2017, most bauxite was mined inAustralia,China,Guinea, andIndia.[74]
Friedrich Wöhler, the chemist who first thoroughly described metallic elemental aluminium
The history of aluminium has been shaped by usage ofalum. The first written record of alum, made byGreek historianHerodotus, dates back to the 5th century BCE.[75] The ancients are known to have used alum as a dyeingmordant and for city defense.[75] After theCrusades, alum, an indispensable good in the European fabric industry,[76] was a subject of international commerce;[77] it was imported to Europe from the eastern Mediterranean until the mid-15th century.[78]
The nature of alum remained unknown. Around 1530, Swiss physicianParacelsus suggested alum was a salt of an earth of alum.[79] In 1595, German doctor and chemistAndreas Libavius experimentally confirmed this.[80] In 1722, German chemistFriedrich Hoffmann announced his belief that the base of alum was a distinct earth.[81] In 1754, German chemistAndreas Sigismund Marggraf synthesized alumina by boiling clay in sulfuric acid and subsequently addingpotash.[81]
Attempts to produce aluminium date back to 1760.[82] The first successful attempt, however, was completed in 1824 by Danish physicist and chemistHans Christian Ørsted. He reacted anhydrousaluminium chloride with potassiumamalgam, yielding a lump of metal looking similar to tin.[83][84][85] He presented his results and demonstrated a sample of the new metal in 1825.[86][87] In 1827, German chemistFriedrich Wöhler repeated Ørsted's experiments but did not identify any aluminium.[88] (The reason for this inconsistency was only discovered in 1921.)[89] He conducted a similar experiment in the same year by mixing anhydrous aluminium chloride with potassium (theWöhler process) and produced a powder of aluminium.[85] In 1845, he was able to produce small pieces of the metal and described some physical properties of this metal.[89] For many years thereafter, Wöhler was credited as the discoverer of aluminium.[90]
The statue ofAnteros inPiccadilly Circus, London, was made in 1893 and is one of the first statues cast in aluminium.
As Wöhler's method could not yield great quantities of aluminium, the metal remained rare; its cost exceeded that of gold.[88] The first industrial production of aluminium was established in 1856 by French chemistHenri Etienne Sainte-Claire Deville and companions.[91] Deville had discovered that aluminium trichloride could be reduced by sodium, which was more convenient and less expensive than potassium, which Wöhler had used.[92] Even then, aluminium was still not of great purity and produced aluminium differed in properties by sample.[93] Because of its electricity-conducting capacity, aluminium was used as the cap of theWashington Monument, completed in 1885, the tallest building in the world at the time. The non-corroding metal cap was intended to serve as alightning rod peak.
The first industrial large-scale production method was independently developed in 1886 by French engineerPaul Héroult and American engineerCharles Martin Hall; it is now known as theHall–Héroult process.[94] The Hall–Héroult process converts alumina into metal. Austrian chemistCarl Joseph Bayer discovered a way of purifying bauxite to yield alumina, now known as theBayer process, in 1889.[95] Modern production of aluminium is based on the Bayer and Hall–Héroult processes.[96]
As large-scale production caused aluminium prices to drop, the metal became widely used in jewelry, eyeglass frames, optical instruments, tableware, andfoil, and other everyday items 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.[97] DuringWorld War I, major governments demanded large shipments of aluminium for light strong airframes;[98] duringWorld War II, demand by major governments for aviation was even higher.[99][100][101]
From the early 20th century to 1980, the aluminium industry was characterized bycartelization, as aluminium firms colluded to keep prices high and stable.[102] The first aluminium cartel, the Aluminium Association, was founded in 1901 by thePittsburgh Reduction Company (renamed Alcoa in 1907) andAluminium Industrie AG.[103] TheBritish Aluminium Company, Produits Chimiques d’Alais et de la Camargue, and Société Electro-Métallurgique de Froges also joined the cartel.[103]
By the mid-20th century, aluminium had become a part of everyday life and an essential component of housewares.[104] In 1954, production of aluminium surpassed that ofcopper,[i] historically second in production only to iron,[107] making it the most producednon-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,[108] and increasingly being used in military engineering, for both airplanes and land armor vehicle engines.[109]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.[96] Thealuminium can was invented in 1956 and employed as a storage for drinks in 1958.[110]
World production of aluminium since 1900
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.[105] In the 1970s, the increased demand for aluminium made it an exchange commodity; it entered theLondon Metal Exchange, the oldest industrial metal exchange in the world, in 1978.[96] The output continued to grow: the annual production of aluminium exceeded 50,000,000 metric tons in 2013.[105]
Thereal price for aluminium declined from $14,000 per metric ton in 1900 to $2,340 in 1948 (in 1998 United States dollars).[105] 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;[111] the real price began to grow in the 1970s with the rise of energy cost.[112] Production moved from the industrialized countries to countries where production was cheaper.[113] 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.[114] TheBRIC countries' combined share in primary production and primary consumption grew substantially in the first decade of the 21st century.[115] China is accumulating an especially large share of the world's production thanks to an abundance of resources, cheap energy, and governmental stimuli;[116] it also increased its consumption share from 2% in 1972 to 40% in 2010.[117] In the United States, Western Europe, and Japan, most aluminium was consumed in transportation, engineering, construction, and packaging.[118] In 2021, prices for industrial metals such as aluminium have soared to near-record levels asenergy shortages in China drive up costs for electricity.[119]
Etymology
The namesaluminium andaluminum are derived from the wordalumine, an obsolete term foralumina,[j] the primary naturally occurringoxide of aluminium.[121]Alumine was borrowed from French, which in turn derived it fromalumen, the classical Latin name foralum, the mineral from which it was collected.[122] The Latin wordalumen stems from theProto-Indo-European root*alu- meaning "bitter" or "beer".[123]
1897 American advertisement featuring thealuminum spelling
Origins
British chemistHumphry Davy, 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 wasalumium, which Davy suggested in an 1808 article on his electrochemical research, published inPhilosophical Transactions of the Royal Society.[124] It appeared that the name was created from the English wordalum and the Latin suffix-ium; but it was customary then to give elements names originating in Latin, so 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.[125] The English namealum does not come directly from Latin, whereasalumine/alumina comes from the Latin wordalumen (upondeclension,alumen changes toalumin-).
One example wasEssai sur la Nomenclature chimique (July 1811), written in French by a Swedish chemist,Jöns Jacob Berzelius, in which the namealuminium is given to the element that would be synthesized from alum.[126][k] (Another article in the same journal issue also refers to the metal whose oxide is the basis ofsapphire, i.e. the same metal, as toaluminium.)[128] A January 1811 summary of one of Davy's lectures at theRoyal Society mentioned the namealuminium as a possibility.[129] The next year, Davy published a chemistry textbook in which he used the spellingaluminum.[130] Both spellings have coexisted since. Their usage is currently regional:aluminum dominates in the United States andCanada;aluminium is prevalent in the rest of the English-speaking world.[131]
Spelling
In 1812, British scientistThomas Young[132] wrote an anonymous review of Davy's book, in which he proposed the namealuminium instead ofaluminum, which he thought had a "less classical sound".[133] This name persisted: although the-um spelling was occasionally used in Britain, the American scientific language used-ium from the start.[134]
Ludwig Wilhelm Gilbert had proposedThonerde-metall, after the German "Thonerde"[l] for alumina, in hisAnnalen der Physik but that name never caught on at all even in Germany.[135]Joseph W. Richards[m] in 1891 found just one occurrence ofargillium in Swedish, from the French "argille"[n] for clay.[135] The French themselves had usedaluminium from the start.[135] However, in England and Germany Davy's spellingaluminum was initially used; until German chemistFriedrich Wöhler published his account of theWöhler process in 1827 in which he used the spellingaluminium[o], which caused that spelling's largely wholesale adoption in England and Germany, with the exception of a small number of what Richards characterized as "patriotic" English chemists that were "averse to foreign innovations" who occasionally still usedaluminum.[135]
Most scientists throughout the world used-ium in the 19th century;[131] and it was entrenched in several other European languages, such asFrench,German, andDutch.[p]
In 1828, an American lexicographer,Noah Webster, entered only thealuminum spelling in hisAmerican Dictionary of the English Language.[136] In the 1830s, the-um spelling gained usage in the United States; by the 1860s, it had become the more common spelling there outside science.[134] In 1892, Hall used the-um spelling in his advertising handbill for his new electrolytic method of producing the metal, despite his constant use of the-ium 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 preferredaluminum since its introduction because it resembledplatinum, the name of a prestigious metal.[137] By 1890, both spellings had been common in the United States, the-ium spelling being slightly more common; by 1895, the situation had reversed; by 1900,aluminum had become twice as common asaluminium; in the next decade, the-um spelling dominated American usage. In 1925, theAmerican Chemical Society adopted this spelling.[131]
World's largest producing countries of aluminium, 2023[141]
Country
Output (thousand tons)
China
45,000
Russia
4,080
India
4,060
Canada
3,270
United Arab Emirates
2,790
Australia
1,730
Bahrain
1,600
Norway
1,460
United States
1,360
Brazil
1,280
Malaysia
1,080
Iceland
880
Other countries
10,000
Total
79,000
The production of aluminium starts with the extraction ofbauxite rock from the ground. The bauxite is processed and transformed using theBayer process intoalumina, which is then processed using theHall–Héroult process, resulting in the final aluminium.
Aluminium production is highly energy-consuming, and so the producers tend to locate smelters in places where electric power is both plentiful and inexpensive.[142] Production of one kilogram of aluminium requires 7 kilograms of oil energy equivalent, as compared to 1.5 kilograms for steel and 2 kilograms for plastic.[143] As of 2023, the world's largest producers of aluminium were China,Russia, India, Canada, and theUnited Arab Emirates,[141] while China is by far the top producer of aluminium with a world share of over 55%.
According to theInternational Resource Panel'sMetal Stocks in Society report, the globalper capita stock of aluminium in use in society (i.e. in cars, buildings, electronics, etc.) is 80 kg (180 lb). Much of this is in more-developed countries (350–500 kg (770–1,100 lb) per capita) rather than less-developed countries (35 kg (77 lb) per capita).[144]
Bauxite is converted to alumina by the Bayer process. Bauxite is blended for uniform composition and then is grounded. The resultingslurry is mixed with a hot solution ofsodium hydroxide; 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:[145]
Al(OH)3 + Na+ + OH− → Na+ + [Al(OH)4]−
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 [Al(OH)4]− 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.[145]
The conversion ofalumina to aluminium is achieved by theHall–Héroult process. In this energy-intensive process, a solution of alumina in a molten (940 and 970 °C (1,720 and 1,780 °F)) mixture ofcryolite (Na3AlF6) withcalcium fluoride iselectrolyzed to produce metallic aluminium. The liquid aluminium sinks to the bottom of the solution and is tapped off, and usually cast into large blocks calledaluminium billets for further processing.[46]
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 ofanthracite; high purity for them is not required because impuritiesleach 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.[46]
The Hall–Heroult process produces aluminium with a purity of above 99%. Further purification can be done by theHoopes 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%.[46][146]
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.[138] Because of this, alternatives to the Hall–Héroult process have been researched, but none has turned out to be economically feasible.[46]
Recycling
Common bins for recyclable waste along with a bin for unrecyclable waste. The bin with a yellow top is labeled "aluminum". Rhodes, Greece.
Recovery of the metal throughrecycling has become an important task of the aluminium industry. Recycling was a low-profile activity until the late 1960s, when the growing use of aluminiumbeverage cans brought it to public awareness.[147] 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 asdross (ash-like oxide).[148] An aluminium stack melter produces significantly less dross, with values reported below 1%.[149]
White dross from primary aluminium production and from secondary recycling operations still contains useful quantities of aluminium that can beextracted 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,acetylene,[150]hydrogen sulfide and significant amounts ofammonia.[151] Despite these difficulties, the waste is used as a filler inasphalt andconcrete.[152] Its potential for hydrogen production has also been considered and researched.[153][154]
The global production of aluminium in 2016 was 58.8 million metric tons. It exceeded that of any other metal exceptiron (1,231 million metric tons).[155][156]
Packaging (cans, foil, frame, etc.). Aluminium is used because it is non-toxic (seebelow), non-adsorptive, andsplinter-proof;
Building and construction (windows,doors,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 ofhousehold items, fromcooking utensils tofurniture. 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, and mechanical strength.
Several sulfates of aluminium have industrial and commercial application.Aluminium sulfate (in its hydrate form) is produced on the annual scale of several millions of metric tons.[168] About two-thirds is consumed inwater treatment.[168] The next major application is in the manufacture of paper.[168] It is also used as a mordant in dyeing, in pickling seeds, deodorizing of mineral oils, inleather tanning, and in production of other aluminium compounds.[168] Two kinds of alum,ammonium alum andpotassium alum, were formerly used as mordants and in leather tanning, but their use has significantly declined following availability of high-purity aluminium sulfate.[168] Anhydrousaluminium chloride is used as a catalyst in chemical and petrochemical industries, the dyeing industry, and in synthesis of various inorganic and organic compounds.[168] Aluminium hydroxychlorides are used in purifying water, in the paper industry, and asantiperspirants.[168]Sodium aluminate is used in treating water and as an accelerator of solidification of cement.[168]
Many aluminium compounds have niche applications, for example:
Aqueous aluminium ions (such as aqueous aluminium sulfate) are used to treat against fish parasites such asGyrodactylus salaris.[177]
In manyvaccines, certain aluminium salts serve as an immuneadjuvant (immune response booster) to allow theprotein in the vaccine to achieve sufficient potency as an immune stimulant.[178] Until 2004, most of the adjuvants used in vaccines were aluminium-adjuvanted.[179]
Biology
Schematic of aluminium absorption by human skin.[180]
Despite its widespread occurrence in the Earth's crust, aluminium has no known function in biology.[46] 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.[181]Aluminium sulfate has anLD50 of 6207 mg/kg (oral, mouse), which corresponds to 435 grams (about one pound) for a 70 kg (150 lb) mouse.
Toxicity
Aluminium is classified as a non-carcinogen by theUnited States Department of Health and Human Services.[182][r] A review published in 1988 said that there was little evidence that normal exposure to aluminium presents a risk to healthy adult,[185] 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 ofbody mass.[182] 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;[186] nevertheless some aluminium does pass the blood-brain barrier and is lodged preferentially in the brains of Alzheimer's patients.[187][188] Evidence published in 1989 indicates that, for Alzheimer's patients, aluminium may act byelectrostaticallycrosslinking proteins, thus down-regulating genes in thesuperior temporal gyrus.[189]
Effects
Aluminium, although rarely, can cause vitamin D-resistantosteomalacia,erythropoietin-resistantmicrocytic anemia, and central nervous system alterations. People with kidney insufficiency are especially at a risk.[182] 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 asiron orzinc; sufficiently high doses (>50 g/day) can cause anemia.[182]
There are five major aluminium forms absorbed by human body: the free solvated trivalent cation (Al3+(aq)); low-molecular-weight, neutral, soluble complexes (LMW-Al0(aq)); high-molecular-weight, neutral, soluble complexes (HMW-Al0(aq)); low-molecular-weight, charged, soluble complexes (LMW-Al(L)n+/−(aq)); nano and micro-particulates (Al(L)n(s)). They are transported across cell membranes or cell epi-/endothelia through five major routes: (1)paracellular; (2)transcellular; (3)active transport; (4) channels; (5) adsorptive or receptor-mediatedendocytosis.[180]
During the 1988Camelford water pollution incident people inCamelford had their drinking water contaminated withaluminium sulfate for several weeks. A final report into the incident in 2013 concluded it was unlikely that this had caused long-term health problems.[190]
Aluminium has been suspected of being a possible cause ofAlzheimer's disease,[191] but research into this for over 40 years has found, as of 2018[update], no good evidence of causal effect.[192][193]
Aluminium increasesestrogen-relatedgene expression in humanbreast cancer cells cultured in the laboratory.[194] In very high doses, aluminium is associated with altered function of the blood–brain barrier.[195] A small percentage of people[196] have contactallergies 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.[197]
Exposure to powdered aluminium or aluminium welding fumes can causepulmonary fibrosis.[198] Fine aluminium powder can ignite or explode, posing another workplace hazard.[199][200]
Exposure routes
Food is the main source of aluminium. Drinking water contains more aluminium than solid food;[182] however, aluminium in food may be absorbed more than aluminium from water.[201] 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).[202] Dietary exposure in Europeans averages to 0.2–1.5 mg/kg/week but can be as high as 2.3 mg/kg/week.[182] Higher exposure levels of aluminium are mostly limited to miners, aluminium production workers, anddialysis patients.[citation needed]
Consumption ofantacids, antiperspirants,vaccines, and cosmetics provide possible routes of exposure.[203] Consumption of acidic foods or liquids with aluminium enhances aluminium absorption,[204] andmaltol has been shown to increase the accumulation of aluminium in nerve and bone tissues.[205]
Treatment
In case of suspected sudden intake of a large amount of aluminium, the only treatment isdeferoxamine mesylate which may be given to help eliminate aluminium from the body bychelation therapy.[206][207] 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.[206]
Environmental effects
"Bauxite tailings" storage facility inStade, Germany. The aluminium industry generates about 70 million tons of this waste annually.
High levels of aluminium occur near mining sites; small amounts of aluminium are released to the environment at coal-fired power plants orincinerators.[186] 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.[186]
Acidicprecipitation is the main natural factor to mobilize aluminium from natural sources[182] and the main reason for the environmental effects of aluminium;[208] however, the main factor of presence of aluminium in salt and freshwater are the industrial processes that also release aluminium into air.[182]
In water, aluminium acts as a toxiс agent ongill-breathing animals such asfish when the water is acidic, in which aluminium may precipitate on gills,[209] which causes loss ofplasma- andhemolymph ions leading toosmoregulatory failure.[208] Organic complexes of aluminium may be easily absorbed and interfere with metabolism in mammals and birds, even though this rarely happens in practice.[208]
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.[210][211][212][213]Wheat hasdeveloped a tolerance to aluminium, releasingorganic compounds that bind to harmful aluminiumcations.Sorghum is believed to have the same tolerance mechanism.[214]
Aluminium production possesses its own challenges to the environment on each step of the production process. The major challenge is theemission of greenhouse gases. These gases result from electrical consumption of the smelters and the byproducts of processing.[215] The most potent of these gases areperfluorocarbons, namely CF4 and C2F6, from the smelting process.[216]
Biodegradation of metallic aluminium is extremely rare; most aluminium-corroding organisms do not directly attack or consume the aluminium, but instead produce corrosive wastes.[217][218] The fungusGeotrichum candidum can consume the aluminium incompact discs.[219][220][221] The bacteriumPseudomonas aeruginosa and the fungusCladosporium resinae are commonly detected in aircraft fuel tanks that usekerosene-based fuels (notavgas), and laboratory cultures can degrade aluminium.[222]
^Davy's 1812 written usage of the wordaluminum was predated by other authors' usage ofaluminium. However, Davy is often mentioned as the person who named the element; he was the first to coin a name for aluminium: he usedalumium in 1808. Other authors did not accept that name, choosingaluminium instead. Seebelow for more details.
^No elements with odd atomic numbers have more than two stable isotopes; even-numbered elements have multiple stable isotopes, with tin (element 50) having the highest number of stable isotopes of all elements, ten. The single exception isberyllium which is even-numbered but has only one stable isotope.[15] SeeEven and odd atomic nuclei for more details.
^Most other metals have greater standard atomic weights: for instance, that of iron is55.845; copper63.546; lead207.2.[3] which has consequences for the element's properties (seebelow)
^The two sides of aluminium foil differ in their luster: one is shiny and the other is dull. The difference is due to the small mechanical damage on the surface of dull side arising from the technological process of aluminium foil manufacturing.[26] Both sides reflect similar amounts of visible light, but the shiny side reflects a far greater share of visible lightspecularly whereas the dull side almost exclusivelydiffuses light. Both sides of aluminium foil serve as goodreflectors (approximately 86%) ofvisible light and an excellent reflector (as much as 97%) of medium and farinfrared radiation.[27]
^In fact, aluminium's electropositive behavior, high affinity for oxygen, and highly negativestandard electrode potential are all better aligned with those ofscandium,yttrium,lanthanum, andactinium, which like aluminium have three valence electrons outside a noble gas core; this series shows continuous trends whereas those of group 13 is broken by the first added d-subshell in gallium and the resultingd-block contraction and the first added f-subshell in thallium and the resultinglanthanide contraction.[39]
^These should not be considered as [AlF6]3− complex anions as the Al–F bonds are not significantly different in type from the other M–F bonds.[49]
^Such differences in coordination between the fluorides and heavier halides are not unusual, occurring in SnIV and BiIII, for example; even bigger differences occur betweenCO2 andSiO2.[49]
^Abundances in the source are listed relative to silicon rather than in per-particle notation. The sum of all elements per 106 parts of silicon is 2.6682×1010 parts; aluminium comprises 8.410×104 parts.
^Compare annual statistics of aluminium[105] and copper[106] production by USGS.
^The spellingalumine comes from French, whereas the spellingalumina comes from Latin.[120]
^Davy discovered several other elements, including those he namedsodium andpotassium, after the English wordssoda andpotash. Berzelius referred to them as tonatrium andkalium. Berzelius's suggestion was expanded in 1814[127] with his proposed system of one or two-letterchemical symbols, which are used up to the present day; sodium and potassium have the symbolsNa andK, respectively, after their Latin names.
^Wöhler had previously usedaluminium in 1824, when translating a paper byJöns Jacob Berzelius from Swedish.[135]
^Some European languages, likeSpanish orItalian, use a different suffix from the Latin-um/-ium to form a name of a metal, some, likePolish orCzech, have a different base for the name of the element, and some, likeRussian orGreek, do not use theLatin script altogether.
^For instance, see the November–December 2013 issue ofChemistry International: in a table of (some) elements, the element is listed as "aluminium (aluminum)".[140]
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The French chemists have given a new name to this pure earth; alumine in French, and alumina in Latin. I confess I do not like this alumina.
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Origin: Formed within English, by derivation.Etymons:aluminen.,-iumsuffix,aluminumn.
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Etymology: < Frenchalumine (L. B. Guyton de Morveau 1782,Observ. sur la Physique19 378) < classical Latinalūmin-,alūmenalumn.1, after French-ine-ine suffix4.
^"Philosophical Transactions of the Royal Society of London. For the Year 1810. — Part I".The Critical Review: Or, Annals of Literature. The Third.XXII: 9. January 1811.hdl:2027/chi.36013662.
Potassium, acting upon alumine and glucine, produces pyrophoric substances of a dark grey colour, which burnt, throwing off brilliant sparks, and leaving behind alkali and earth, and which, when thrown into water, decomposed it with great violence. The result of this experiment is not wholly decisive as to the existence of what might be calledaluminium andglucinium
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^Romero, Elvira; Ferreira, Patricia; Martínez, Ángel T.; Jesús Martínez, María (April 2009). "New oxidase fromBjerkandera arthroconidial anamorph that oxidizes both phenolic and nonphenolic benzyl alcohols".Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics. Proteins and Proteomics 1794 (4):689–697.doi:10.1016/j.bbapap.2008.11.013.PMID19110079.AGeotrichum-type arthroconidial fungus was isolated by the authors from a deteriorated compact disc found in Belize (Central America)....In the present paper, we report the purification and characterization of an H2O2-generating extracellular oxidase produced by this fungus, which shares catalytic properties with bothP. eryngii AAO andP. simplicissimum VAO. See also the abstract ofRomero et al. 2007.
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