Aluminum
Aluminium is the third most abundant element (after oxygen and silicon), and the most abundant metal, in the Earth's crust. It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is so chemically reactive that native specimens are rare and limited to extreme reducing environments. Instead, it is found combined in over 270 different minerals. The chief ore of aluminium is bauxite.
Aluminium is remarkable for the metal's low density and for its ability to resist corrosion due to the phenomenon of passivation. Structural components made from aluminium and its alloys are vital to the aerospace industry and are important in other areas of transportation and structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.
Despite its prevalence in the environment, aluminium salts are not known to be used by any form of life. In keeping with its pervasiveness, aluminium is well tolerated by plants and animals. Owing to their prevalence, potential beneficial (or otherwise) biological roles of aluminium compounds are of continuing interest.
Natural occurrence
Stable aluminium is created when hydrogen fuses with magnesium either in large stars or in supernovae.
In the Earth's crust, aluminium is the most abundant (8.3% by weight) metallic element and the third most abundant of all elements (after oxygen and silicon). Because of its strong affinity to oxygen, it 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. Native aluminium metal 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 and Chen et al. (2011) have proposed a theory of its origin as resulting by reduction from tetrahydroxoaluminate Al(OH)4– to metallic aluminium by bacteria.
It also occurs in the minerals beryl, cryolite, garnet, spinel and turquoise. Impurities in Al2O3, such as chromium or iron yield the gemstones ruby and sapphire, respectively.
Although aluminium is an extremely common and widespread element, the common aluminium minerals are not economic sources of the metal. Almost all metallic aluminium is produced from the ore bauxite (AlOx(OH)3–2x). Bauxite occurs as a weathering product of low iron and silica bedrock in tropical climatic conditions. Large deposits of bauxite occur in Australia, Brazil, Guinea and Jamaica and the primary mining areas for the ore are in Australia, Brazil, China, India, Guinea, Indonesia, Jamaica, Russia and Suriname.
| Symbol | Al | |
| Atomic Number | 13 | |
| Atomic Weight | 26.981539 | |
| Oxidation States | +3 | |
| Electronegativity, Pauling | 1.61 | |
| State at RT | Solid, Metal | |
| Melting Point, K | 933.5 | |
| Boiling Point, K | 2740 |
Interesting Facts about Aluminum
- Aluminum manufacturing takes a lot of energy – 17.4 megawatt hours of electrical energy to produce one metric ton of aluminum; that’s three times more energy than is needed to make a metric ton of steel.
- Aluminum is a great metal to recycle. Recycling uses only 5% of the energy needed to produce aluminum from its ore, bauxite.
- Aluminum does not stick to magnets under normal conditions.
- There is more aluminum in the Earth’s crust than any other metal. At about 8 percent, aluminum is the third most abundant element in our planet’s crust, behind oxygen and silicon.
- Despite its high abundance, in the 1850s aluminum was more valuable than gold. In 1852 aluminum was priced at $1200 per kg and gold was $664 per kg.
- Aluminum prices illustrate the perils of financial speculation: in 1854 Saint-Claire Deville found a way of replacing potassium with much cheaper sodium in the reaction to isolate aluminum. By 1859, aluminum was priced at $37 per kg; its price had dropped 97% in just five years.
- Where the previous item highlights the perils of speculation, this item highlights one of the triumphs of chemistry: the Hall-Heroult electrolytic process was discovered in 1886. By 1895, aluminum’s price had dropped to just $1.20 per kg.
- Ruby gemstones are mainly aluminum oxide in which a small number of the aluminum ions have been replaced by chromium ions.
- Aluminum is made in the nuclear fires of heavy stars when a proton adds to magnesium. (Magnesium is itself made in stars by nuclear fusion of two carbons.)
Appearance and Characteristics
Harmful effects:
No proven issues; ingestion may cause alzheimer’s disease
Characteristics:
- Aluminum is a silvery-white metal. It does not stick to magnets (it is paramagnetic and so its magnetism under normal conditions is very, very weak). It is an excellent electrical conductor. It is of low density and high ductility. It is too reactive to be commonly found as the metal although, very rarely, the native metal can be found.
- Aluminum’s appearance is dulled and its reactivity is passivated by a film of aluminum oxide that naturally forms on the surface of the metal under normal conditions. The oxide film results in a material that resists corrosion. The film can be thickened using electrolysis or oxidizing agents and aluminum in this form will resist attack by dilute acids, dilute alkalis and concentrated nitric acid.
- Aluminum lies sufficiently far on the right side of the periodic table that it shows some hints of nonmetal behavior, reacting with hot alkalis to form aluminate ions [Al(OH)4]- as well as the more typical metal reaction with acids to release hydrogen gas and form the positively charged metal ion, Al3+. i.e. aluminum is amphoteric.
- Pure aluminum is quite soft and lacking in strength. Aluminum used in commercial applications has small amounts of silicon and iron (less than 1%) added, resulting in greatly improved strength and hardness.
Uses of Aluminum
- As a result of its low density, low cost, and corrosion resistance, aluminum is widely used around the world.
- It is used in an extensive range of products from drinks cans to window frames and boats to aircraft. A Boeing 747-400 contains 147,000 pounds (66,150 kg) of high-strength aluminum.
- Unlike some metals, aluminum has no aroma – hence its widespread use in food packaging and cooking pots.
- Although not quite as good as silver or copper, aluminum is an excellent electrical conductor. It is also considerably cheaper and lighter than these metals, so it is used widely in overhead power lines.
- Of all the metals, only iron is used more widely than aluminum.
