Post-transition metal
Aluminium (the Commonwealth and preferred IUPAC name) or aluminum (North American English) is a chemical element; it has symbol Al and atomic number 13. It has a density lower than other common metals, about one-third that of steel. Aluminium has a great affinity toward oxygen, forming a protective layer of oxide on the surface when exposed to air. It 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, 27Al, which is highly abundant, making aluminium the 12th-most abundant element in the universe. The radioactivity of 26Al leads to it being used in radiometric dating.
Chemically, aluminium is a post-transition metal in the boron group; as is common for the group, aluminium forms compounds primarily in the +3 oxidation state. The aluminium cation Al3+ is small and highly charged; as such, it 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 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 history of aluminium has been shaped by usage of alum. The first written record of alum, made by Greek historian Herodotus, dates back to the 5th century BCE. The ancients are known to have used alum as a dyeing mordant and for city defense as a fire-resistant coating for wood. 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 until Swiss physician Paracelsus suggested alum was a salt of an earth of alum around 1530. German doctor and chemist Andreas Libavius experimentally confirmed this in 1595. German chemist Friedrich Hoffmann announced his belief that the base of alum was a distinct earth in 1722. German chemist Andreas Sigismund Marggraf synthesized alumina in 1754 by boiling clay in sulfuric acid and subsequently adding potash.
Attempts to produce aluminium date back to 1760. The first successful attempt, however, 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. …
Aluminium metal has an appearance ranging from silvery white to dull gray depending on its surface roughness. Aluminium mirrors provides high reflectivity for light in the ultraviolet, visible (on par with silver), and far infrared regions. Aluminium is also good at reflecting solar radiation, although prolonged exposure to sunlight in air can deteriorate the reflectivity 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/cm3, about one-third that of steel, much lower than other commonly encountered metals, making aluminium parts easily identifiable through their lightness. Aluminium's low density compared to most other metals arises from the fact that its unit cell size is relatively large in proportion to the number of nucleons. 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 is quite soft and lacking in strength. In most applications, various aluminium alloys are used instead because of their higher strength and hardness. …
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, 27Al, is the eighteenth most abundant nucleus in the universe. It is created almost entirely after fusion of carbon in massive stars that will later become Type II supernovas: this fusion creates 26Mg, which upon capturing free protons and neutrons, becomes aluminium. Some smaller quantities of 27Al are created in hydrogen burning shells of evolved stars, where 26Mg can capture free protons.
Essentially all aluminium now in existence is 27Al. 26Al was present in the early Solar System with abundance of 0.005% relative to 27Al but its half-life of 728,000 years is too short for any original nuclei to survive; 26Al is therefore extinct. Unlike for 27Al, hydrogen burning is the primary source of 26Al, with the nuclide emerging after a nucleus of 25Mg catches a free proton. However, the trace quantities of 26Al that do exist are the most common gamma ray emitter in the interstellar gas; if the original 26Al 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. …
The global production of aluminium in 2016 was 58.8 million metric tons. It exceeded that of any other metal except iron (1,231 million metric tons).
Aluminium is almost always alloyed, which markedly improves its mechanical properties, especially when tempered. For example, the common aluminium foils and beverage cans are alloys of 92% to 99% aluminium. The main alloying agents for both wrought and cast aluminium are copper, zinc, magnesium, manganese, and silicon (e.g., duralumin) with the levels of other metals in a few percent by weight.
The major uses for aluminium are in:
Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles, spacecraft, etc.). Aluminium is used because of its low density, durability, and corrosion resistance;
Packaging (cans, foil, frame, etc.). Aluminium is used because it is non-toxic (see below), non-adsorptive, and splinter-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 of household items, from cooking utensils to furniture. …
Aluminium has one stable isotope, 27Al, which comprises virtually all of the naturally-occurring element. This is common for elements with an odd atomic number. It is therefore a mononuclidic element for standard atomic weight, which is determined completely by that isotope. Aluminium is useful in nuclear magnetic resonance (NMR), as its single stable isotope (though quadrupolar) has a high NMR sensitivity.
All other isotopes of aluminium are radioactive. The most stable of these is 26Al, with a half-life of 717,000 years. While it was present along with stable 27Al in the interstellar medium from which the Solar System formed (believed to have been produced by stellar nucleosynthesis also), no detectable amount could have survived the time since the formation of the planet. However, minute traces of 26Al are still produced from decay of argon in the atmosphere induced by ionizing radiation of cosmic rays. The ratio of 26Al to 10Be has been used for the radiodating of geological processes over 105 to 106 year time scales, in particular transport, deposition, sediment storage, burial times, and erosion. Most meteorite scientists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.
The other known isotopes of aluminium, with mass numbers ranging from 20 to 43, all have half-lives less than 7 minutes, as do the four detected metastable states.
Aluminium is classified as a non-carcinogen by the United States Department of Health and Human Services. A review published in 1988 said that there was little evidence that normal exposure to aluminium presents a risk to healthy adult, and a 2014 multi-element toxicology review was unable to find deleterious effects of aluminium consumed in amounts not greater than 40 mg/day per kg of body mass. Most ingested aluminium is eliminated in feces, and much of what enters the bloodstream is excreted in urine; however, not all absorbed or parenterally administered aluminium is cleared through urinary excretion.