2015-01-02 Metals IX (iron/steel)

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stålIron, with symbol Fe and chemical number 26, is the fourth most abundant element in the earth’s crust, and by mass the most common element on Earth; melting temperature 1538°C and boiling temperature 2862°C. Iron exists in at least four different crystal structures, changing with temperature. At 770°C (the so-called Curie point) it becomes magnetic.
The reddish colour of planet Mars derives from minerals rich in iron oxide, and meteorites found on Earth can contain up to 95% iron – often mixed with nickel. Iron beads found in Egypt have been dated back to at least 3500 BCE; as the material also contains nickel, it bears witness of meteoric origin. Iron production from metallic ore only began some hundred years later. In biology, iron compounds are key components in oxygen transporting (hemoglobin), cellular respiration, oxidation and reduction.
Pure iron is soft, but can be hardened by a smelting process including carbon. The resulting alloy is called steel. Rust is the common name for iron oxide.
Iron oxides (“earth pigments”) are also among the oldest known pigments, in use since prehistoric times. There exist a range of different colours, from yellow (ochres) and red (siennas, Venetian red, caput mortuum) to brown (umbers) and black. A synthetic compound with carbon and nitrogen, known as Prussian blue, yields an intense metallic blue colour.

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