Iron
Element:
Iron is a chemical element; it has symbol Fe (from Latin ferrum 'iron') and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, just ahead of oxygen (32.1% and 30.1%, respectively), forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust, being mainly deposited by meteorites in its metallic state, with its ores also being found there.
Extracting usable metal from iron ores requires kilns or furnaces capable of reaching 1,500 °C (2,730 °F) or higher, about 500 °C (932 °F) higher than that required to smelt copper. Humans started to master that process in Eurasia during the 2nd millennium BCE and the use of iron tools and weapons began to displace copper alloys—in some regions, only around 1200 BCE. That event is considered the transition from the Bronze Age to the Iron Age. In the modern world, iron alloys, such as steel, stainless steel, cast iron and special steels, are by far the most common industrial metals, due to their mechanical properties and low cost. The iron and steel industry is thus very important economically, and iron is the cheapest metal, with a price of a few dollars per kilogram or pound.
Pristine and smooth pure iron surfaces are a mirror-like silvery-gray. Iron reacts readily with oxygen and water to produce brown-to-black hydrated iron oxides, commonly known as rust. Unlike the oxides of some other metals that form passivating layers, rust occupies more volume than the metal and thus flakes off, exposing more fresh surfaces for corrosion. High-purity irons (e.g. electrolytic iron) are more resistant to corrosion.
The body of an adult human contains about 4 grams (0.005% body weight) of iron, mostly in hemoglobin and myoglobin. These two proteins play essential roles in vertebrate metabolism, respectively oxygen transport by blood and oxygen storage in muscles. To maintain the necessary levels, human iron metabolism requires a minimum of iron in the diet. Iron is also the metal at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals.[6]
Chemically, the most common oxidation states of iron are iron(II) and iron(III). Iron shares many properties of other transition metals, including the other group 8 elements, ruthenium and osmium. Iron forms compounds in a wide range of oxidation states, −4 to +7. Iron also forms many coordination compounds; some of them, such as ferrocene, ferrioxalate, and Prussian blue have substantial industrial, medical, or research applications.
Most notably, Iron is the highest atomic number element that could be created in exothermic nucleosynthesis....
History
Main article: History of ferrous metallurgy
Development of iron metallurgy
Iron is one of the elements undoubtedly known to the ancient world.[80] It has been worked, or wrought, for millennia. However, iron artefacts of great age are much rarer than objects made of gold or silver due to the ease with which iron corrodes.[81] The technology developed slowly, and even after the discovery of smelting it took many centuries for iron to replace bronze as the metal of choice for tools and weapons.
Meteoritic iron
Iron harpoon head from Greenland. The iron edge covers a narwhal tusk harpoon using meteorite iron from the Cape York meteorite, one of the largest iron meteorites known.
Beads made from meteoric iron in 3500 BC or earlier were found in Gerzeh, Egypt by G.A. Wainwright.[82] The beads contain 7.5% nickel, which is a signature of meteoric origin since iron found in the Earth's crust generally has only minuscule nickel impurities.
Meteoric iron was highly regarded due to its origin in the heavens and was often used to forge weapons and tools.[82] For example, a dagger made of meteoric iron was found in the tomb of Tutankhamun, containing similar proportions of iron, cobalt, and nickel to a meteorite discovered in the area, deposited by an ancient meteor shower.[83][84][85] Items that were likely made of iron by Egyptians date from 3000 to 2500 BC.[81]
Meteoritic iron is comparably soft and ductile and easily cold forged but may get brittle when heated because of the nickel content.[86]
Wrought iron
Main article: Wrought iron
Further information: Ancient iron production
The symbol for Mars has been used since antiquity to represent iron.
The iron pillar of Delhi is an example of the iron extraction and processing methodologies of early India.
The first iron production started in the Middle Bronze Age, but it took several centuries before iron displaced bronze. Samples of smelted iron from Asmar, Mesopotamia and Tall Chagar Bazaar in northern Syria were made sometime between 3000 and 2700 BC.[87] The Hittites established an empire in north-central Anatolia around 1600 BC. They appear to be the first to understand the production of iron from its ores and regard it highly in their society.[88] The Hittites began to smelt iron between 1500 and 1200 BC and the practice spread to the rest of the Near East after their empire fell in 1180 BC.[87] The subsequent period is called the Iron Age.
Artifacts of smelted iron are found in India dating from 1800 to 1200 BC,[89] and in the Levant from about 1500 BC (suggesting smelting in Anatolia or the Caucasus).[90][91] Alleged references (compare history of metallurgy in South Asia) to iron in the Indian Vedas have been used for claims of a very early usage of iron in India respectively to date the texts as such. The rigveda term ayas (metal) refers to copper, while iron which is called as śyāma ayas, literally "black copper", first is mentioned in the post-rigvedic Atharvaveda.[92]
Some archaeological evidence suggests iron was smelted in Zimbabwe and southeast Africa as early as the eighth century BC.[93] Iron working was introduced to Greece in the late 11th century BC, from which it spread quickly throughout Europe.[94]
Iron sickle from Ancient Greece.
The spread of ironworking in Central and Western Europe is associated with Celtic expansion. According to Pliny the Elder, iron use was common in the Roman era.[82] In the lands of what is now considered China, iron appears approximately 700–500 BC.[95] Iron smelting may have been introduced into China through Central Asia.[96] The earliest evidence of the use of a blast furnace in China dates to the 1st century AD,[97] and cupola furnaces were used as early as the Warring States period (403–221 BC).[98] Usage of the blast and cupola furnace remained widespread during the Tang and Song dynasties.[99]
During the Industrial Revolution in Britain, Henry Cort began refining iron from pig iron to wrought iron (or bar iron) using innovative production systems. In 1783 he patented the puddling process for refining iron ore. It was later improved by others, including Joseph Hall.[100]
Cast iron
Main article: Cast iron
Cast iron was first produced in China during 5th century BC,[101] but was hardly in Europe until the medieval period.[102][103] The earliest cast iron artifacts were discovered by archaeologists in what is now modern Luhe County, Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, and architecture.[104] During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel.[105]
Coalbrookdale by Night*, 1801. Blast furnaces light the iron making town of Coalbrookdale.
Medieval blast furnaces were about 10 feet (3.0 m) tall and made of fireproof brick; forced air was usually provided by hand-operated bellows.[103] Modern blast furnaces have grown much bigger, with hearths fourteen meters in diameter that allow them to produce thousands of tons of iron each day, but essentially operate in much the same way as they did during medieval times.[105]
In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron, replacing charcoal, although continuing to use blast furnaces. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper. Carbon content in iron was not implicated as the reason for the differences in properties of wrought iron, cast iron, and steel until the 18th century.[87]
Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the innovative first iron bridge in 1778. This bridge still stands today as a monument to the role iron played in the Industrial Revolution. Following this, iron was used in rails, boats, ships, aqueducts, and buildings, as well as in iron cylinders in steam engines.[105] Railways have been central to the formation of modernity and ideas of progress[106] and various languages refer to railways as iron road (e.g. French chemin de fer, German Eisenbahn, Turkish demiryolu, Russian железная дорога, Chinese, Japanese, and Korean 鐵道, Vietnamese đường sắt).
Steel
Main article: Steel
See also: Steelmaking
Steel (with smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity by using a bloomery. Blacksmiths in Luristan in western Persia were making good steel by 1000 BC.[87] Then improved versions, Wootz steel by India and Damascus steel were developed around 300 BC and AD 500 respectively. These methods were specialized, and so steel did not become a major commodity until the 1850s.[107]
New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel. In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron, to produce mild steel. This made steel much more economical, thereby leading to wrought iron no longer being produced in large quantities.[108]
Foundations of modern chemistry
In 1774, Antoine Lavoisier used the reaction of water steam with metallic iron inside an incandescent iron tube to produce hydrogen in his experiments leading to the demonstration of the conservation of mass, which was instrumental in changing chemistry from a qualitative science to a quantitative one.[109]
Symbolic role
"Ich gab Gold für Eisen" – "I gave gold for iron". German-American brooch from WWI.
Iron plays a certain role in mythology and has found various usage as a metaphor and in folklore. The Greek poet Hesiod's Works and Days (lines 109–201) lists different ages of man named after metals like gold, silver, bronze and iron to account for successive ages of humanity.[110] The Iron Age was closely related with Rome, and in Ovid's Metamorphoses
The Virtues, in despair, quit the earth; and the depravity of man becomes universal and complete. Hard steel succeeded then.
— Ovid, Metamorphoses, Book I, Iron age, line 160 ff
An example of the importance of iron's symbolic role may be found in the German Campaign of 1813. Frederick William III commissioned then the first Iron Cross as military decoration. Berlin iron jewellery reached its peak production between 1813 and 1815, when the Prussian royal family urged citizens to donate gold and silver jewellery for military funding. The inscription Ich gab Gold für Eisen (I gave gold for iron) was used as well in later war efforts.[111]
Production of metallic iron...
Metal:
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