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134-559: A few prototypes were evaluated and flown during the 1950s, but it was decided not to adopt this type. Several examples have survived as museum pieces into the present day. The design of the original Model XA-8 single-seat lightweight helicopter began in 1951 under the sponsorship of the US Army Transportation Corps and the USAF. The Army's specification in 1950 called for a lightweight, one-man unarmed helicopter that

268-491: A precipitate of aluminium hydroxide , 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 , [Al(H 2 O) 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. This behavior of Al(OH) 3

402-423: A "daughter" nuclide or decay product . In many cases, the daughter nuclide itself is radioactive, resulting in a decay chain , eventually ending with the formation of a stable (nonradioactive) daughter nuclide; each step in such a chain is characterized by a distinct half-life. In these cases, usually the half-life of interest in radiometric dating is the longest one in the chain, which is the rate-limiting factor in

536-525: A "less classical sound". This name persisted: although the -um spelling was occasionally used in Britain, the American scientific language used -ium from the start. Most scientists throughout the world used -ium in the 19th century; and it was entrenched in several other European languages, such as French , German , and Dutch . In 1828, an American lexicographer, Noah Webster , entered only

670-452: A Jeep, and even used the same fuel. The XH-26 could be dropped by air and assembled and be ready for flight in 20 minutes. Both the Army and USAF evaluated the five prototype Jet Jeeps. They proved to be rugged and durable vehicles with a top speed of 80 mph (130 km/h) and a ceiling of 7,000 feet (2,100 m). Unfortunately, the pulse jets produced an unacceptable amount of noise and

804-499: 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 refers to the metal whose oxide is the basis of sapphire , i.e. the same metal, as to aluminium .) A January 1811 summary of one of Davy's lectures at the Royal Society mentioned the name aluminium as a possibility. The next year, Davy published

938-510: A better time resolution than that available from long-lived isotopes, short-lived isotopes that are no longer present in the rock can be used. At the beginning of the solar system, there were several relatively short-lived radionuclides like Al, Fe, Mn, and I present within the solar nebula. These radionuclides—possibly produced by the explosion of a supernova—are extinct today, but their decay products can be detected in very old material, such as that which constitutes meteorites . By measuring

1072-471: A certain temperature, the crystal structure has formed sufficiently to prevent diffusion of isotopes. Thus an igneous or metamorphic rock or melt, which is slowly cooling, does not begin to exhibit measurable radioactive decay until it cools below the closure temperature. The age that can be calculated by radiometric dating is thus the time at which the rock or mineral cooled to closure temperature. This temperature varies for every mineral and isotopic system, so

1206-561: A chemistry textbook in which he used the spelling aluminum . Both spellings have coexisted since. Their usage is currently regional: aluminum dominates in the United States and Canada; aluminium is prevalent in the rest of the English-speaking world. In 1812, 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

1340-408: A consequence of background radiation on certain minerals. Over time, ionizing radiation is absorbed by mineral grains in sediments and archaeological materials such as quartz and potassium feldspar . The radiation causes charge to remain within the grains in structurally unstable "electron traps". Exposure to sunlight or heat releases these charges, effectively "bleaching" the sample and resetting

1474-479: A great affinity towards oxygen , forming 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, nonmagnetic , and ductile . It has one stable isotope, Al, which is highly abundant, making aluminium the twelfth-most common element in the universe. The radioactivity of Al leads to it being used in radiometric dating . Chemically, aluminium

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1608-402: A half-life of 1.3 billion years, so this method is applicable to the oldest rocks. Radioactive potassium-40 is common in micas , feldspars , and hornblendes , though the closure temperature is fairly low in these materials, about 350 °C (mica) to 500 °C (hornblende). This is based on the beta decay of rubidium-87 to strontium-87 , with a half-life of 50 billion years. This scheme

1742-525: A high-temperature furnace. This field is known as thermochronology or thermochronometry. The mathematical expression that relates radioactive decay to geologic time is where The equation is most conveniently expressed in terms of the measured quantity N ( t ) rather than the constant initial value N o . To calculate the age, it is assumed that the system is closed (neither parent nor daughter isotopes have been lost from system), D 0 either must be negligible or can be accurately estimated, λ

1876-479: A higher time resolution at the expense of timescale. I beta-decays to Xe with a half-life of 16.14 ± 0.12 million years . The iodine-xenon chronometer is an isochron technique. Samples are exposed to neutrons in a nuclear reactor. This converts the only stable isotope of iodine ( I ) into Xe via neutron capture followed by beta decay (of I ). After irradiation, samples are heated in

2010-399: A kiln. Other methods include: Absolute radiometric dating requires a measurable fraction of parent nucleus to remain in the sample rock. For rocks dating back to the beginning of the solar system, this requires extremely long-lived parent isotopes, making measurement of such rocks' exact ages imprecise. To be able to distinguish the relative ages of rocks from such old material, and to get

2144-458: A particular element is called a nuclide . Some nuclides are inherently unstable. That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into a different nuclide. This transformation may be accomplished in a number of different ways, including alpha decay (emission of alpha particles ) and beta decay ( electron emission, positron emission, or electron capture ). Another possibility

2278-467: A polished slice of a material to determine the density of "track" markings left in it by the spontaneous fission of uranium-238 impurities. The uranium content of the sample has to be known, but that can be determined by placing a plastic film over the polished slice of the material, and bombarding it with slow neutrons . This causes induced fission of U, as opposed to the spontaneous fission of U. The fission tracks produced by this process are recorded in

2412-441: A probable cause for it being soft with a low melting point and low electrical resistivity . Aluminium metal has an appearance ranging from silvery white to dull gray depending on its surface roughness . Aluminium mirrors are the most reflective of all metal mirrors for near ultraviolet and far infrared light. It is also one of the most reflective for light in the visible spectrum, nearly on par with silver in this respect, and

2546-683: 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 , concentrated sulfuric acid , and some organic acids. In hot concentrated hydrochloric acid , aluminium reacts with water with evolution of hydrogen, and in aqueous sodium hydroxide or potassium hydroxide at room temperature to form aluminates —protective passivation under these conditions

2680-438: A range of several hundred thousand years. A related method is ionium–thorium dating , which measures the ratio of ionium (thorium-230) to thorium-232 in ocean sediment . Radiocarbon dating is also simply called carbon-14 dating. Carbon-14 is a radioactive isotope of carbon, with a half-life of 5,730 years (which is very short compared with the above isotopes), and decays into nitrogen. In other radiometric dating methods,

2814-525: A refractory material, and in ceramics , as well as being the starting material for the electrolytic production of aluminium. Sapphire and ruby are impure corundum contaminated with trace amounts of other metals. The two main oxide-hydroxides, AlO(OH), are boehmite and diaspore . There are three main trihydroxides: bayerite , gibbsite , and nordstrandite , which differ in their crystalline structure ( polymorphs ). Many other intermediate and related structures are also known. Most are produced from ores by

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2948-406: A series of steps and the xenon isotopic signature of the gas evolved in each step is analysed. When a consistent Xe / Xe ratio is observed across several consecutive temperature steps, it can be interpreted as corresponding to a time at which the sample stopped losing xenon. Samples of a meteorite called Shallowater are usually included in the irradiation to monitor

3082-435: A single sample to accurately measure them. A faster method involves using particle counters to determine alpha, beta or gamma activity, and then dividing that by the number of radioactive nuclides. However, it is challenging and expensive to accurately determine the number of radioactive nuclides. Alternatively, decay constants can be determined by comparing isotope data for rocks of known age. This method requires at least one of

3216-474: 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 , gallium , indium , and thallium ; it is also expected for nihonium . Aluminium can surrender its three outermost electrons in many chemical reactions (see below ). The electronegativity of aluminium

3350-448: A system can be closed for one mineral but open for another. Dating of different minerals and/or isotope systems (with differing closure temperatures) within the same rock can therefore enable the tracking of the thermal history of the rock in question with time, and thus the history of metamorphic events may become known in detail. These temperatures are experimentally determined in the lab by artificially resetting sample minerals using

3484-460: A variable amount of uranium content. Because the fission tracks are healed by temperatures over about 200 °C the technique has limitations as well as benefits. The technique has potential applications for detailing the thermal history of a deposit. Large amounts of otherwise rare Cl (half-life ~300ky) were produced by irradiation of seawater during atmospheric detonations of nuclear weapons between 1952 and 1958. The residence time of Cl in

3618-820: 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 (MgAl 2 O 4 ), Na-β-alumina (NaAl 11 O 17 ), and tricalcium aluminate (Ca 3 Al 2 O 6 , an important mineral phase in Portland cement ). The only stable chalcogenides under normal conditions are aluminium sulfide (Al 2 S 3 ), selenide (Al 2 Se 3 ), and telluride (Al 2 Te 3 ). 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

3752-575: A way of purifying bauxite to yield alumina, now known as the Bayer process , in 1889. Modern production of aluminium is based on the Bayer and Hall–Héroult processes. As large-scale production caused aluminium prices to drop, the metal became widely used in jewelry, eyeglass frames, optical instruments, tableware, and foil , and other everyday items in the 1890s and early 20th century. Aluminium's ability to form hard yet light alloys with other metals provided

3886-734: Is Al : while it was present along with stable Al in the interstellar medium from which the Solar System formed, having been produced by stellar nucleosynthesis as well, its half-life is only 717,000 years and therefore a detectable amount has not survived since the formation of the planet. However, minute traces of Al are produced from argon in the atmosphere by spallation caused by cosmic ray protons. The ratio of Al to Be has been used for radiodating of geological processes over 10 to 10  year time scales, in particular transport, deposition, sediment storage, burial times, and erosion. Most meteorite scientists believe that

4020-434: Is Al. Al was present in the early Solar System with abundance of 0.005% relative to Al but its half-life of 728,000 years is too short for any original nuclei to survive; Al is therefore extinct . Unlike for Al, hydrogen burning is the primary source of Al, with the nuclide emerging after a nucleus of Mg catches a free proton. However, the trace quantities of Al that do exist are the most common gamma ray emitter in

4154-407: Is paramagnetic 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 . 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

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4288-437: Is spontaneous fission into two or more nuclides. While the moment in time at which a particular nucleus decays is unpredictable, a collection of atoms of a radioactive nuclide decays exponentially at a rate described by a parameter known as the half-life , usually given in units of years when discussing dating techniques. After one half-life has elapsed, one half of the atoms of the nuclide in question will have decayed into

4422-483: Is 1.61 (Pauling scale). A free aluminium atom has a radius of 143  pm . With the three outermost electrons removed, the radius shrinks to 39 pm for a 4-coordinated atom or 53.5 pm for a 6-coordinated atom. At standard temperature and pressure , aluminium atoms (when not affected by atoms of other elements) form a face-centered cubic crystal system bound by metallic bonding provided by atoms' outermost electrons; hence aluminium (at these conditions)

4556-418: 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 Al is small and highly charged ; as such, it has more polarizing power , and bonds formed by aluminium have a more covalent character. The strong affinity of aluminium for oxygen leads to the common occurrence of its oxides in nature. Aluminium

4690-548: Is a metal. This crystal system is shared by many other metals, such as lead and copper ; 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 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 in aluminium are

4824-445: Is a technique which is used to date materials such as rocks or carbon , in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. The use of radiometric dating was first published in 1907 by Bertram Boltwood and

4958-522: 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 minerals beryl , cryolite , garnet , spinel , and turquoise . Impurities in Al 2 O 3 , such as chromium and iron , yield the gemstones ruby and sapphire , respectively. Native aluminium metal

5092-405: Is also easily machined and cast . Aluminium is an excellent thermal and electrical conductor , having around 60% the conductivity of copper , both thermal and electrical, while having only 30% of copper's density. Aluminium is capable of superconductivity , with a superconducting critical temperature of 1.2 kelvin and a critical magnetic field of about 100 gauss (10 milliteslas ). It

5226-553: Is extremely rare and can only be found as a minor phase in low oxygen fugacity environments, such as the interiors of certain volcanoes. Native aluminium has been reported in cold seeps in the northeastern continental slope of the South China Sea . It is possible that these deposits resulted from bacterial reduction of tetrahydroxoaluminate Al(OH) 4 . Although aluminium is a common and widespread element, not all aluminium minerals are economically viable sources of

5360-438: Is found on Earth primarily in rocks in the crust , where it is the third-most abundant element , after oxygen and silicon , rather than in the mantle , and virtually never as the free metal . It is obtained industrially by mining bauxite , a sedimentary rock rich in aluminium minerals. The discovery of aluminium was announced in 1825 by Danish physicist Hans Christian Ørsted . The first industrial production of aluminium

5494-536: 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 (Al 2 S 3 ), and the aluminium halides (AlX 3 ). It also forms a wide range of intermetallic compounds involving metals from every group on the periodic table. The vast majority of compounds, including all aluminium-containing minerals and all commercially significant aluminium compounds, feature aluminium in

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5628-492: Is in fact more basic than that of gallium. Aluminium also bears minor similarities to the metalloid boron in the same group: AlX 3 compounds are valence isoelectronic to BX 3 compounds (they have the same valence electronic structure), and both behave as Lewis acids and readily form adducts . Additionally, one of the main motifs of boron chemistry is regular icosahedral structures, and aluminium forms an important part of many icosahedral quasicrystal alloys, including

5762-432: Is known to high precision, and one has accurate and precise measurements of D* and N ( t ). The above equation makes use of information on the composition of parent and daughter isotopes at the time the material being tested cooled below its closure temperature . This is well established for most isotopic systems. However, construction of an isochron does not require information on the original compositions, using merely

5896-500: Is negligible. Aqua regia also dissolves aluminium. Aluminium is corroded by dissolved chlorides , such as common sodium chloride , 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 copper , and aluminium's corrosion resistance

6030-521: Is not as important. It is a polymer with the formula (AlH 3 ) n , in contrast to the corresponding boron hydride that is a dimer with the formula (BH 3 ) 2 . Aluminium's per-particle abundance in the Solar System 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, Al,

6164-409: Is now the principal source of information about the absolute age of rocks and other geological features , including the age of fossilized life forms or the age of Earth itself, and can also be used to date a wide range of natural and man-made materials . Together with stratigraphic principles , radiometric dating methods are used in geochronology to establish the geologic time scale . Among

6298-533: Is often performed on the mineral zircon (ZrSiO 4 ), though it can be used on other materials, such as baddeleyite and monazite (see: monazite geochronology ). Zircon and baddeleyite incorporate uranium atoms into their crystalline structure as substitutes for zirconium , but strongly reject lead. Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert. Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of

6432-416: Is quite soft and lacking in strength. In most applications various aluminium alloys are used instead because of their higher strength and hardness. The yield strength of pure aluminium is 7–11 MPa , while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium is ductile , with a percent elongation of 50-70%, and malleable allowing it to be easily drawn and extruded . It

6566-419: Is released, the intensity of which varies depending on the amount of radiation absorbed during burial and specific properties of the mineral. These methods can be used to date the age of a sediment layer, as layers deposited on top would prevent the grains from being "bleached" and reset by sunlight. Pottery shards can be dated to the last time they experienced significant heat, generally when they were fired in

6700-422: Is surrounded by six fluorine atoms in a distorted octahedral arrangement, with each fluorine atom being shared between the corners of two octahedra. Such {AlF 6 } units also exist in complex fluorides such as cryolite , Na 3 AlF 6 . AlF 3 melts at 1,290 °C (2,354 °F) and is made by reaction of aluminium oxide with hydrogen fluoride gas at 700 °C (1,300 °F). With heavier halides,

6834-547: Is termed amphoterism 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 yields hydrogen sulfide . 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

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6968-416: Is that of the preceding noble gas , whereas those of its heavier congeners gallium , indium , thallium , and 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

7102-438: Is the Al – Mg chronometer, which can be used to estimate the relative ages of chondrules . Al decays to Mg with a half-life of 720 000 years. The dating is simply a question of finding the deviation from the natural abundance of Mg (the product of Al decay) in comparison with the ratio of

7236-433: 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 supernovas : this fusion creates Mg, which upon capturing free protons and neutrons, becomes aluminium. Some smaller quantities of Al are created in hydrogen burning shells of evolved stars, where Mg can capture free protons. Essentially all aluminium now in existence

7370-535: Is the solid foundation of the common measurement of radioactivity. The accuracy and precision of the determination of an age (and a nuclide's half-life) depends on the accuracy and precision of the decay constant measurement. The in-growth method is one way of measuring the decay constant of a system, which involves accumulating daughter nuclides. Unfortunately for nuclides with high decay constants (which are useful for dating very old samples), long periods of time (decades) are required to accumulate enough decay products in

7504-418: Is used to date old igneous and metamorphic rocks , and has also been used to date lunar samples . Closure temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium–lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample. Application of in situ analysis (Laser-Ablation ICP-MS) within single mineral grains in faults have shown that

7638-411: 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, only Al 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

7772-497: The -ium spelling as primary, and they list both where it is appropriate. The production of aluminium starts with the extraction of bauxite 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. Radiometric dating Radiometric dating , radioactive dating or radioisotope dating

7906-455: The Friedel–Crafts reactions . Aluminium trichloride has major industrial uses involving this reaction, such as in the manufacture of anthraquinones and styrene ; 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

8040-475: The London Metal Exchange , 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

8174-475: The aluminum spelling in his American Dictionary of the English Language . 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. 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

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8308-441: The biosphere as a consequence of industrialization have also depressed the proportion of carbon-14 by a few percent; in contrast, the amount of carbon-14 was increased by above-ground nuclear bomb tests that were conducted into the early 1960s. Also, an increase in the solar wind or the Earth's magnetic field above the current value would depress the amount of carbon-14 created in the atmosphere. This involves inspection of

8442-423: The chemical formula Al 2 O 3 , commonly called alumina . It can be found in nature in the mineral corundum , α-alumina; there is also a γ-alumina phase. 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

8576-551: The interstellar gas ; if the original Al were still present, gamma ray maps of the Milky Way would be brighter. Overall, the Earth is about 1.59% aluminium by mass (seventh in abundance by mass). 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 the Earth's crust , while less reactive metals sink to

8710-526: The 5th century BCE. The ancients are known to have used alum as a dyeing mordant and for city defense. After the Crusades , 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 suggested alum

8844-472: The Al–Zn–Mg class. Aluminium has a high chemical affinity to oxygen, which renders it suitable for use as a reducing agent in the thermite reaction. A fine powder of aluminium reacts explosively on contact with liquid oxygen ; 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,

8978-572: The Jet Jeep was powered by two 6.75-inch (17.1 cm) XPJ49 pulse jet engines mounted on the end of each rotor blade tip as tip jets . Also designed by American Helicopter, each pulse jet weighed 16 pounds (7.3 kg) and produced 35 pounds-force (160 N) of thrust, and were started with an internal compressed air system. Since the engines did not have to be warmed up, the XH-26 could take off in 30 seconds. The pulse jets produced no torque, and

9112-600: The Rb-Sr method can be used to decipher episodes of fault movement. A relatively short-range dating technique is based on the decay of uranium-234 into thorium-230, a substance with a half-life of about 80,000 years. It is accompanied by a sister process, in which uranium-235 decays into protactinium-231, which has a half-life of 32,760 years. While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sediments , from which their ratios are measured. The scheme has

9246-418: The United States dollar, and alumina prices. The BRIC 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

9380-514: 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. The names aluminium and aluminum are derived from the word alumine , an obsolete term for alumina , the primary naturally occurring oxide of aluminium . Alumine

9514-520: The age of the sample even if some of the lead has been lost. This can be seen in the concordia diagram, where the samples plot along an errorchron (straight line) which intersects the concordia curve at the age of the sample. This involves the alpha decay of Sm to Nd with a half-life of 1.06 x 10 years. Accuracy levels of within twenty million years in ages of two-and-a-half billion years are achievable. This involves electron capture or positron decay of potassium-40 to argon-40. Potassium-40 has

9648-444: The ages of the same materials are consistent from one method to another. It is not affected by external factors such as temperature , pressure , chemical environment, or presence of a magnetic or electric field . The only exceptions are nuclides that decay by the process of electron capture, such as beryllium-7 , strontium-85 , and zirconium-89 , whose decay rate may be affected by local electron density. For all other nuclides,

9782-578: The aluminium atoms have tetrahedral four-coordination and the other half have trigonal bipyramidal five-coordination. Four pnictides – aluminium nitride (AlN), aluminium phosphide (AlP), aluminium arsenide (AlAs), and aluminium antimonide (AlSb) – are known. They are all III-V semiconductors isoelectronic to silicon and germanium , all of which but AlN have the zinc blende 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

9916-422: The atmosphere is about 1 week. Thus, as an event marker of 1950s water in soil and ground water, Cl is also useful for dating waters less than 50 years before the present. Cl has seen use in other areas of the geological sciences, including dating ice and sediments. Luminescence dating methods are not radiometric dating methods in that they do not rely on abundances of isotopes to calculate age. Instead, they are

10050-430: The best-known techniques are radiocarbon dating , potassium–argon dating and uranium–lead dating . By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts. Different methods of radiometric dating vary in

10184-436: The characteristic physical properties of a post-transition metal, with longer-than-expected interatomic distances. Furthermore, as Al 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 (Be ), and the two display an example of a diagonal relationship . The underlying core under aluminium's valence shell

10318-416: The clock to zero. The trapped charge accumulates over time at a rate determined by the amount of background radiation at the location where the sample was buried. Stimulating these mineral grains using either light ( optically stimulated luminescence or infrared stimulated luminescence dating) or heat ( thermoluminescence dating ) causes a luminescence signal to be emitted as the stored unstable electron energy

10452-453: The conversion efficiency from I to Xe . The difference between the measured Xe / Xe ratios of the sample and Shallowater then corresponds to the different ratios of I / I when they each stopped losing xenon. This in turn corresponds to a difference in age of closure in the early solar system. Another example of short-lived extinct radionuclide dating

10586-419: The coordination numbers are lower. The other trihalides are dimeric or polymeric with tetrahedral four-coordinate aluminium centers. Aluminium trichloride (AlCl 3 ) has a layered polymeric structure below its melting point of 192.4 °C (378 °F) but transforms on melting to Al 2 Cl 6 dimers. At higher temperatures those increasingly dissociate into trigonal planar AlCl 3 monomers similar to

10720-428: 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

10854-535: The cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams. Uranium–lead radiometric dating involves using uranium-235 or uranium-238 to date a substance's absolute age. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years. An error margin of 2–5% has been achieved on younger Mesozoic rocks. Uranium–lead dating

10988-472: The decay products of extinct radionuclides with a mass spectrometer and using isochronplots, it is possible to determine relative ages of different events in the early history of the solar system. Dating methods based on extinct radionuclides can also be calibrated with the U–Pb method to give absolute ages. Thus both the approximate age and a high time resolution can be obtained. Generally a shorter half-life leads to

11122-479: The drag of the engines in the event of power loss would prevent safe landings by autorotation . For these two reasons the Army found the pulse jet helicopters unsuitable as it had those with ramjets. Finally, cost considerations forced the cancellation of the program. The replacement of the XH-26's pulse jets with ramjets was suggested but never undertaken; however, the Hiller YH-32 Hornet helicopter

11256-497: The energy released by the decay of Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago. The remaining isotopes of aluminium, with mass numbers ranging from 21 to 43, all have half-lives well under an hour. Three metastable states are known, all with half-lives under a minute. An aluminium atom has 13 electrons, arranged in an electron configuration of [ Ne ] 3s 3p , with three electrons beyond

11390-422: The event. In situ micro-beam analysis can be achieved via laser ICP-MS or SIMS techniques. One of its great advantages is that any sample provides two clocks, one based on uranium-235's decay to lead-207 with a half-life of about 700 million years, and one based on uranium-238's decay to lead-206 with a half-life of about 4.5 billion years, providing a built-in crosscheck that allows accurate determination of

11524-478: The exception of most alkali metals and group 13 metals) and over 150 intermetallics 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

11658-750: The existing isotope decays with a characteristic half-life (5730 years). The proportion of carbon-14 left when the remains of the organism are examined provides an indication of the time elapsed since its death. This makes carbon-14 an ideal dating method to date the age of bones or the remains of an organism. The carbon-14 dating limit lies around 58,000 to 62,000 years. The rate of creation of carbon-14 appears to be roughly constant, as cross-checks of carbon-14 dating with other dating methods show it gives consistent results. However, local eruptions of volcanoes or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon-14 and give inaccurate dates. The releases of carbon dioxide into

11792-520: 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 and magnesium 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 industry and for many other applications where light weight and relatively high strength are crucial. Pure aluminium

11926-442: The formation of the planet. It is therefore a mononuclidic element and its standard atomic weight is virtually the same as that of the isotope. This makes aluminium very useful in nuclear magnetic resonance (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 . The most stable of these

12060-730: The gas phase after explosion and in stellar absorption spectra. More thoroughly investigated are compounds of the formula R 4 Al 2 which contain an Al–Al bond and where R is a large organic ligand . A variety of compounds of empirical formula AlR 3 and AlR 1.5 Cl 1.5 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 , Bu , Me 3 CCH 2 ); for example, triisobutylaluminium exists as an equilibrium mixture of

12194-453: 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 formed with triethylamine , Al 4 I 4 (NEt 3 ) 4 . Al 2 O and Al 2 S 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

12328-423: The half-life of the parent is accurately known, and enough of the daughter product is produced to be accurately measured and distinguished from the initial amount of the daughter present in the material. The procedures used to isolate and analyze the parent and daughter nuclides must be precise and accurate. This normally involves isotope-ratio mass spectrometry . The precision of a dating method depends in part on

12462-455: The half-life of the radioactive isotope involved. For instance, carbon-14 has a half-life of 5,730 years. After an organism has been dead for 60,000 years, so little carbon-14 is left that accurate dating cannot be established. On the other hand, the concentration of carbon-14 falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades. The closure temperature or blocking temperature represents

12596-646: The halides, nitrate , and sulfate . For similar reasons, anhydrous aluminium salts cannot be made by heating their "hydrates": hydrated aluminium chloride is in fact not AlCl 3 ·6H 2 O but [Al(H 2 O) 6 ]Cl 3 , and the Al–O bonds are so strong that heating is not sufficient to break them and form Al–Cl bonds instead: All four trihalides are well known. Unlike the structures of the three heavier trihalides, aluminium fluoride (AlF 3 ) features six-coordinate aluminium, which explains its involatility and insolubility as well as high heat of formation . Each aluminium atom

12730-676: The heavy parent isotopes were produced by nucleosynthesis in supernovas, meaning that any parent isotope with a short half-life should be extinct by now. Carbon-14, though, is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere and thus remains at a near-constant level on Earth. The carbon-14 ends up as a trace component in atmospheric carbon dioxide (CO 2 ). A carbon-based life form acquires carbon during its lifetime. Plants acquire it through photosynthesis , and animals acquire it from consumption of plants and other animals. When an organism dies, it ceases to take in new carbon-14, and

12864-456: The isotope systems to be very precisely calibrated, such as the Pb–Pb system . The basic equation of radiometric dating requires that neither the parent nuclide nor the daughter product can enter or leave the material after its formation. The possible confounding effects of contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since

12998-433: The low-pressure polymerization of ethene and propene . There are also some heterocyclic and cluster organoaluminium compounds involving Al–N bonds. The industrially most important aluminium hydride is lithium aluminium hydride (LiAlH 4 ), which is used as a reducing agent in organic chemistry . It can be produced from lithium hydride and aluminium trichloride . The simplest hydride, aluminium hydride or alane,

13132-529: 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 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

13266-655: 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 . 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 this name was not adopted universally. This name

13400-465: The metal with many uses at the time. During World War I , major governments demanded large shipments of aluminium for light strong airframes; during World War II , 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 copper , historically second in production only to iron, making it

13534-491: The metal. Almost all metallic aluminium is produced from the ore bauxite (AlO x (OH) 3–2 x ). Bauxite occurs as a weathering product of low iron and silica bedrock in tropical climatic conditions. In 2017, most bauxite was mined in Australia, China, Guinea, and India. The history of aluminium has been shaped by usage of alum . The first written record of alum, made by Greek historian Herodotus , dates back to

13668-485: The monomer and dimer. These dimers, such as trimethylaluminium (Al 2 Me 6 ), 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 , most importantly in "growth reactions" that form long-chain unbranched primary alkenes and alcohols, and in

13802-506: 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

13936-614: The next decade, the -um spelling dominated American usage. In 1925, the American Chemical Society adopted this spelling. The International Union of Pure and Applied Chemistry (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

14070-407: The oxidation state 3+. The coordination number of such compounds varies, but generally Al is either six- or four-coordinate. Almost all compounds of aluminium(III) are colorless. In aqueous solution, Al exists as the hexaaqua cation [Al(H 2 O) 6 ] , which has an approximate K a of 10 . Such solutions are acidic as this cation can act as a proton donor and progressively hydrolyze until

14204-460: 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 , the name of a prestigious metal. 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 as aluminium ; in

14338-425: The plastic film. The uranium content of the material can then be calculated from the number of tracks and the neutron flux . This scheme has application over a wide range of geologic dates. For dates up to a few million years micas , tektites (glass fragments from volcanic eruptions), and meteorites are best used. Older materials can be dated using zircon , apatite , titanite , epidote and garnet which have

14472-399: The present ratios of the parent and daughter isotopes to a standard isotope. An isochron plot is used to solve the age equation graphically and calculate the age of the sample and the original composition. Radiometric dating has been carried out since 1905 when it was invented by Ernest Rutherford as a method by which one might determine the age of the Earth . In the century since then

14606-411: The proportion of the original nuclide to its decay products changes in a predictable way as the original nuclide decays over time. This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time from the incorporation of the original nuclides into a material to the present. The radioactive decay constant, the probability that an atom will decay per year,

14740-453: The reservoir when they formed, they should form an isochron . This can reduce the problem of contamination . In uranium–lead dating , the concordia diagram is used which also decreases the problem of nuclide loss. Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample. For example, the age of the Amitsoq gneisses from western Greenland

14874-423: The respective hydrogen chalcogenide . As aluminium is a small atom relative to these chalcogens, these have four-coordinate tetrahedral aluminium with various polymorphs having structures related to wurtzite , 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

15008-436: The sample was created. It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration . Precision is enhanced if measurements are taken on multiple samples from different locations of the rock body. Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with

15142-485: 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

15276-505: The stable isotopes Al / Mg . The excess of Mg (often designated Mg *) is found by comparing the Mg / Mg ratio to that of other Solar System materials. The Al – Mg chronometer gives an estimate of the time period for formation of primitive meteorites of only a few million years (1.4 million years for Chondrule formation). In

15410-408: The structure of BCl 3 . Aluminium tribromide and aluminium triiodide form Al 2 X 6 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 with the halogen. The aluminium trihalides form many addition compounds or complexes; their Lewis acidic nature makes them useful as catalysts for

15544-520: The techniques have been greatly improved and expanded. Dating can now be performed on samples as small as a nanogram using a mass spectrometer . The mass spectrometer was invented in the 1940s and began to be used in radiometric dating in the 1950s. It operates by generating a beam of ionized atoms from the sample under test. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ," depending on their mass and level of ionization. On impact in

15678-413: The temperature below which the mineral is a closed system for the studied isotopes. If a material that selectively rejects the daughter nuclide is heated above this temperature, any daughter nuclides that have been accumulated over time will be lost through diffusion , resetting the isotopic "clock" to zero. As the mineral cools, the crystal structure begins to form and diffusion of isotopes is less easy. At

15812-428: The timescale over which they are accurate and the materials to which they can be applied. All ordinary matter is made up of combinations of chemical elements , each with its own atomic number , indicating the number of protons in the atomic nucleus . Additionally, elements may exist in different isotopes , with each isotope of an element differing in the number of neutrons in the nucleus. A particular isotope of

15946-407: The tiny, belt-driven tail rotor was used only to improve directional control. The only mechanical item that had to be replaced after so many hours of flight was the intake air vanes, which were small and inexpensive and could be replaced with a small tool in minutes. American Helicopter chose the name "Jet Jeep", because the XH-26 could be used like a Jeep , but in the air. It could be transported by

16080-536: The two therefore look similar. Aluminium is also good at reflecting solar radiation , although prolonged exposure to sunlight in air adds wear to the surface of the metal; this may be prevented if aluminium is anodized , which adds a protective layer of oxide on the surface. The density of aluminium is 2.70 g/cm , 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

16214-500: The ultimate transformation of the radioactive nuclide into its stable daughter. Isotopic systems that have been exploited for radiometric dating have half-lives ranging from only about 10 years (e.g., tritium ) to over 100 billion years (e.g., samarium-147 ). For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially constant. This is known because decay constants measured by different techniques give consistent values within analytical errors and

16348-421: Was a crucial strategic resource for aviation . In 1954, aluminium became the most produced non-ferrous metal , surpassing 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 metabolize aluminium salts , but this aluminium

16482-461: Was a salt of an earth of alum. In 1595, German doctor and chemist Andreas Libavius experimentally confirmed this. In 1722, German chemist Friedrich Hoffmann announced his belief that the base of alum was a distinct earth. In 1754, German chemist Andreas Sigismund Marggraf synthesized alumina by boiling clay in sulfuric acid and subsequently adding potash . Attempts to produce aluminium date back to 1760. The first successful attempt, however,

16616-494: Was borrowed from French, which in turn derived it from alumen , the classical Latin name for alum , the mineral from which it was collected. The Latin word alumen stems from the Proto-Indo-European root *alu- meaning "bitter" or "beer". British chemist Humphry 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

16750-560: Was built using blade tip ramjets. Data from The Illustrated Encyclopedia of Helicopters General characteristics Performance Aircraft of comparable role, configuration, and era Related lists Aluminium Aluminium (or aluminum in North American English ) is a chemical element ; it has symbol   Al and atomic number  13. Aluminium has a density lower than that of other common metals , about one-third that of steel . It has

16884-543: Was collapsible, capable of aerial delivery to troops in rugged terrain, and assembled quickly with simple tools. The helicopter was to be used for both light observation and as an air-droppable rescue vehicle for downed aircrews. After a review of all proposals American Helicopter was awarded the development contract in June 1951, based on its XA-8 design proposal. The first of five prototype XH-26s flew in January 1952. The XH-26

17018-422: Was completed in 1824 by Danish physicist and chemist Hans Christian Ørsted . He reacted anhydrous aluminium chloride 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

17152-497: Was constructed of aluminium , except for the aft fuselage, which was laminated fiberglass, and possessed a well-glazed, pyramidal-shaped cockpit. When collapsed, its 5 by 5 by 14 feet (1.5 by 1.5 by 4.3 m) container fit on a trailer that could be towed by a military Jeep. If stripped for air drop, the Jet Jeep weighed less than 300 pounds (140 kg). It could be assembled by two men in 20 minutes. The XH-26 did not use any gears, or an internal engine like other helicopters. Rather,

17286-496: 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 , alumen changes to alumin- ). One example was Essai sur la Nomenclature chimique (July 1811), written in French by

17420-443: Was determined to be 3.60 ± 0.05 Ga (billion years ago) using uranium–lead dating and 3.56 ± 0.10 Ga (billion years ago) using lead–lead dating, results that are consistent with each other. Accurate radiometric dating generally requires that the parent has a long enough half-life that it will be present in significant amounts at the time of measurement (except as described below under "Dating with short-lived extinct radionuclides"),

17554-517: 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 the First and Second World Wars, aluminium

17688-418: 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

17822-433: 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,

17956-580: Was used as the cap of the Washington Monument , 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 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

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