Aluminium (or aluminum) metal is very rare in native form, and the process to refine it from ores is complex, so for most of human history it was unknown. However, the compound alum has been known since the 5th century BCE and was used extensively by the ancients for dyeing. During the Middle Ages, its use for dyeing made it a commodity of international commerce. Renaissance scientists believed that alum was a salt of a new earth; during the Age of Enlightenment, it was established that this earth, alumina, was an oxide of a new metal. Discovery of this metal was announced in 1825 by Danish physicist Hans Christian Ørsted, whose work was extended by German chemist Friedrich Wöhler.
Aluminium was difficult to refine and thus uncommon in actual use. Soon after its discovery, the price of aluminium exceeded that of gold. It was reduced only after the initiation of the first industrial production 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 Bayer process developed by Austrian chemist Carl Josef Bayer in 1889. These processes have been used for aluminium production up to the present.
The introduction of these methods for the mass production of aluminium led to extensive use of the light, corrosion-resistant metal in industry and everyday life. Aluminium began to be used in engineering and construction. In World Wars I and II, aluminium was a crucial strategic resource for aviation. World production of the metal grew from 6,800 metric tons in 1900 to 2,810,000 metric tons in 1954, when aluminium became the most produced non-ferrous metal, surpassing copper.
In the second half of the 20th century, aluminium gained usage in transportation and packaging. Aluminium production became a source of concern due to its effect on the environment, and aluminium recycling gained ground. The metal became an exchange commodity in the 1970s. Production began to shift from developed countries to developing ones; by 2010, China had accumulated an especially large share in both production and consumption of aluminium. World production continued to rise, reaching 58,500,000 metric tons in 2015. Aluminium production exceeds those of all other non-ferrous metals combined.
Early history
The history of aluminium was shaped by the usage of its compound alum. The first written record of alum was in the 5th century BCE by Greek historian Herodotus. The ancients used it as a dyeing mordant, in medicine, in chemical milling, and as a fire-resistant coating for wood to protect fortresses from enemy arson. Aluminium metal was unknown. Roman writer Petronius mentioned in his novel Satyricon that an unusual glass had been presented to the emperor: after it was thrown on the pavement, it did not break but only deformed. It was returned to its former shape using a hammer. After learning from the inventor that nobody else knew how to produce this material, the emperor had the inventor executed so that it did not diminish the price of gold. Variations of this story were mentioned briefly in Natural History by Roman historian Pliny the Elder (who noted the story had "been current through frequent repetition rather than authentic") and Roman History by Roman historian Cassius Dio. Some sources suggest this glass could be aluminium. It is possible aluminium-containing alloys were produced in China during the reign of the first Jin dynasty (266–420).
After the Crusades, alum was a commodity of international commerce; it was indispensable in the European fabric industry. Small alum mines were worked in Catholic Europe but most alum came from the Middle East. Alum continued to be traded through the Mediterranean Sea until the mid-15th century, when the Ottomans greatly increased export taxes. In a few years, alum was discovered in great abundance in Italy. Pope Pius II forbade all imports from the east, using the profits from the alum trade to start a war with the Ottomans. This newly found alum long played an important role in European pharmacy, but the high prices set by the papal government eventually made other states start their own production; large-scale alum mining came to other regions of Europe in the 16th century.
Establishing the nature of alum
At the start of the Renaissance, the nature of alum remained unknown. Around 1530, Swiss physician Paracelsus recognized alum as separate from vitriole (sulfates) and suggested it was a salt of an earth. In 1595, German doctor and chemist Andreas Libavius demonstrated that alum and green and blue vitriole were formed by the same acid but different earths; for the undiscovered earth that formed alum, he proposed the name "alumina". German chemist Georg Ernst Stahl stated that the unknown base of alum was akin to lime or chalk in 1702; this mistaken view was shared by many scientists for half a century. In 1722, German chemist Friedrich Hoffmann suggested that the base of alum was a distinct earth. In 1728, French chemist Étienne Geoffroy Saint-Hilaire claimed alum was formed by an unknown earth and sulfuric acid; he mistakenly believed burning that earth yielded silica. (Geoffroy's mistake was corrected only in 1785 by German chemist and pharmacist Johann Christian Wiegleb. He determined that earth of alum could not be synthesized from silica and alkalis, contrary to contemporary belief.) French chemist Jean Gello proved the earth in clay and the earth resulting from the reaction of an alkali on alum were identical in 1739. German chemist Johann Heinrich Pott showed the precipitate obtained from pouring an alkali into a solution of alum was different from lime and chalk in 1746.
German chemist Andreas Sigismund Marggraf synthesized the earth of alum by boiling clay in sulfuric acid and adding potash in 1754. He realized that adding soda, potash, or an alkali to a solution of the new earth in sulfuric acid yielded alum. He described the earth as alkaline, as he had discovered it dissolved in acids when dried. Marggraf also described salts of this earth: chloride, nitrate and acetate. In 1758, French chemist Pierre Macquer wrote that alumina resembled a metallic earth. In 1760, French chemist Théodore Baron d'Hénouville expressed his confidence that alumina was a metallic earth.
In 1767, Swedish chemist Torbern Bergman synthesized alum by boiling alunite in sulfuric acid and adding potash to the solution. He also synthesized alum as a reaction product between sulfates of potassium and earth of alum, demonstrating that alum was a double salt. Swedish German pharmaceutical chemist Carl Wilhelm Scheele demonstrated that both alum and silica originated from clay and alum did not contain silicon in 1776. Writing in 1782, French chemist Antoine Lavoisier considered alumina an oxide of a metal with an affinity for oxygen so strong that no known reducing agents could overcome it.
Swedish chemist Jöns Jacob Berzelius suggested the formula AlO3 for alumina in 1815. The correct formula, Al2O3, was established by German chemist Eilhard Mitscherlich in 1821; this helped Berzelius determine the correct atomic weight of the metal, 27.
Isolation of metal
In 1760, Baron de Hénouville unsuccessfully attempted to reduce alumina to its metal. He claimed he had tried every method of reduction known at the time, though his methods were unpublished. It is probable he mixed alum with carbon or some organic substance, with salt or soda for flux, and heated it in a charcoal fire. Austrian chemists Anton Leopold Ruprecht and Matteo Tondi repeated Baron's experiments in 1790, significantly increasing the temperatures. They found small metallic particles they believed were the sought-after metal; but later experiments by other chemists showed these were iron phosphide from impurities in the charcoal and bone ash. German chemist Martin Heinrich Klaproth commented in an aftermath, "if there exists an earth which has been put in conditions where its metallic nature should be disclosed, if it had such, an earth exposed to experiments suitable for reducing it, tested in the hottest fires by all sorts of methods, on a large as well as on a small scale, that earth is certainly alumina, yet no one has yet perceived its metallization." Lavoisier in 1794 and French chemist Louis-Bernard Guyton de Morveau in 1795 melted alumina to a white enamel in a charcoal fire fed by pure oxygen but found no metal. American chemist Robert Hare melted alumina with an oxyhydrogen blowpipe in 1802, also obtaining the enamel, but still found no metal.
In 1807, British chemist Humphry Davy successfully electrolyzed alumina with alkaline batteries, but the resulting alloy contained potassium and sodium, and Davy had no means to separate the desired metal from these. He then heated alumina with potassium, forming potassium oxide but was unable to produce the sought-after metal. In 1808, Davy set up a different experiment on electrolysis of alumina, establishing that alumina decomposed in the electric arc but formed metal alloyed with iron; he was unable to separate the two. Finally, he tried yet another electrolysis experiment, seeking to collect the metal on iron, but was again unable to separate the coveted metal from it. Davy suggested the metal be named alumium in 1808 and aluminum in 1812, thus producing the modern name. Other scientists used the spelling aluminium; the former spelling regained usage in the United States in the following decades.
American chemist Benjamin Silliman repeated Hare's experiment in 1813 and obtained small granules of the sought-after metal, which almost immediately burned.
In 1824, Danish physicist Hans Christian Ørsted attempted to produce the metal. He reacted anhydrous aluminium chloride with potassium amalgam, yielding a lump of metal that looked similar to tin. He presented his results and demonstrated a sample of the new metal in 1825. In 1826, he wrote, "aluminium has a metallic luster and somewhat grayish color and breaks down water very slowly"; this suggests he had obtained an aluminium–potassium alloy, rather than pure aluminium. Ørsted placed little importance on his discovery. He did not notify either Davy or Berzelius, both of whom he knew, and published his work in a Danish magazine unknown to the European public. As a result, he is often not credited as the discoverer of the element; some earlier sources claimed Ørsted had not isolated aluminium.
Berzelius tried isolating the metal in 1825 by carefully washing the potassium analog of the base salt in cryolite in a crucible. Prior to the experiment, he had correctly identified the formula of this salt as K3AlF6. He found no metal, but his experiment came very close to succeeding and was successfully reproduced many times later. Berzelius's mistake was in using an excess of potassium, which made the solution too alkaline and dissolved all the newly formed aluminium.