Iron Fe

Discovery

The earliest iron objects were made from meteorites. Beads hammered from meteoritic iron were found in Egyptian graves dating to before 3000 BCE, and the blade of a dagger from Tutankhamun's tomb is also of meteoritic origin.

Smelting iron from ore is harder than smelting copper, because it needs higher temperatures and careful control of charcoal and air. The technique developed gradually in Anatolia and the Near East, and by around 1200 BCE iron working was spreading widely, marking the beginning of the Iron Age in many regions. In China, cast iron was being produced by about the fifth century BCE, far earlier than in Europe.

In 1709 Abraham Darby in England began smelting iron with coke instead of charcoal, helping fuel the Industrial Revolution. In 1856 Henry Bessemer patented a process for turning molten pig iron into steel cheaply by blowing air through it, and steel soon became the backbone of modern industry.

Origin of the name

The English word iron comes from Old English and related Germanic words. The symbol Fe comes from the Latin ferrum, which also gives us words such as ferrous and ferric. Iron was one of the seven metals known in antiquity, and alchemists linked it with Mars, the war god, a fitting partner for the metal of weapons.

Main uses

• Steel: iron alloyed with a little carbon, and often chromium, nickel or manganese, accounts for about 95 percent of all metal produced by mass. World crude steel output is around two billion tonnes a year.
• Construction and transport: structural beams, reinforcing bars, rails, ships, cars and pipelines.
• Cast iron: engine blocks, pipes and cookware.
• Magnets and electrical equipment: soft iron and electrical steels form the cores of transformers and motors.
• Chemistry: iron catalysts are used in the Haber–Bosch ammonia process, and iron oxides are common red, yellow and black pigments.

Isotopes

Iron has four stable isotopes: iron-54, iron-56 (about 92 percent), iron-57 and iron-58. Iron-56 has one of the most tightly bound nuclei of any isotope, which is why fusion in massive stars stops around iron. Iron-57 is used in Mössbauer spectroscopy to study iron-containing minerals, including on Mars. The radioactive iron-60, with a half-life of about 2.6 million years, has been found in deep-sea crusts and Antarctic snow, evidence of nearby supernovae in the geologically recent past. Iron-59 (about 45 days) traces iron metabolism in medicine.

In everyday life

An adult body contains about 3 to 4 grams of iron, most of it in haemoglobin, which carries oxygen in red blood cells. Iron deficiency is one of the most common nutritional problems worldwide and causes anaemia and fatigue. Meat, beans, lentils and leafy greens are good sources.

Iron supplements can be dangerous if children swallow them by accident, so they should be stored safely. Rust, the reddish oxide that forms in moist air, costs economies enormous sums every year.