Aluminum

Aluminium is the most abundant metal in the Earth's crust and the most widely used metal after iron and steel. It is light, strong, rust-resistant and endlessly recyclable. Chances are there is aluminium in your kitchen, your phone, your school bag and your bicycle.

• Atomic Number1313 protons, 13 electrons
• Atomic Mass26.981538 uAbout 27× heavier than hydrogen
• State at Room TempSolidlight, strong solid
• Density2.70 g/cm³One third the density of iron
• Melting / Boiling660.3°C / 2518.8°CMelts at 660°C
• DiscoveredAncientHans Christian Ørsted, 1825

What is aluminium?

Aluminium is a post-transition metal in Group 13 of the periodic table. It has 13 protons and three electrons in its outer shell. Although aluminium is highly reactive chemically, it instantly forms a thin, tough layer of aluminium oxide on its surface when exposed to air. That oxide skin protects the metal beneath from further corrosion, which is why aluminium objects do not visibly rust the way iron does.

Aluminium gets its name from alum, a crystalline salt (potassium aluminium sulfate) used since antiquity for dyeing cloth and treating wounds. The name alum comes from the Latin alumen. The British chemist Humphry Davy originally proposed the name alumium, then aluminium. Americans later shortened it to aluminum. Both spellings are in use today, this article uses the British spelling.

Where you find aluminium

In space

Aluminium is the most abundant metal in the Earth's crust. The Moon's highland regions are rich in aluminium silicate minerals, lunar rock samples brought back by Apollo astronauts contain significant amounts. Rocks from Mars also contain aluminium compounds.

On Earth

Aluminium makes up approx. 8% of the Earth's crust by mass, third overall after oxygen and silicon. But because it bonds so readily with other elements, it is never found as a free metal, it must always be extracted from its minerals.

• Bauxite. Bauxite is the ore from which aluminium is extracted. It is a mixture of aluminium hydroxides formed by intense tropical weathering of rocks. Australia, Guinea and Brazil are among the world's largest producers.
• Feldspar and clay. These widespread minerals contain aluminium silicates, but the aluminium is too difficult to extract economically from them.
• Corundum. Pure aluminium oxide forms the mineral corundum. With traces of chromium it becomes a ruby; with iron and titanium, a blue sapphire.

How we use aluminium

• Drink cans and packaging. Aluminium is used for billions of drinks cans and food trays every year. It is light, does not corrode and can be recycled repeatedly without losing quality.
• Aircraft and vehicles. Aluminium alloys are the main structural material in aircraft. A modern passenger jet is approx. 80% aluminium by weight. Cars, trains and buses also use aluminium to save weight.
• Construction. Window frames, cladding panels, roofing and structural supports are made from aluminium because it does not rust and lasts for decades.
• Electrical cables. Aluminium conducts electricity well and weighs far less than copper. High-voltage power lines strung between pylons are almost always aluminium.

How it was discovered

Aluminium was first isolated in 1825 by the Danish physicist Hans Christian Ørsted, who reduced aluminium chloride with potassium amalgam to produce small amounts of impure metal. Friedrich Wöhler produced purer samples in 1827. For decades, producing aluminium was so difficult and expensive that it truly was more valuable than gold.

Everything changed in 1886 when Charles Martin Hall in the USA and Paul Héroult in France independently invented the same electrolytic process to smelt aluminium cheaply from bauxite, on the same day, without knowing about each other. Their process: the Hall-Héroult process, is still used to produce all aluminium today.

Aluminium is the metal of the modern world, light, strong, recyclable and everywhere. Moving along the periodic table to 14 protons brings us to silicon, the element inside every computer chip.