Iron

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Iron (International Phonetic Alphabet: ) is a chemical element with the symbol Fe () and atomic number 26. Iron is a Group 8 element and Period 4 element metal. Iron is a lustrous, silvery soft metal. Iron and nickel are notable for being the final elements produced by stellar nucleosynthesis, and thus are the heaviest elements which do not require a supernova or similarly cataclysmic event for formation. Iron and nickel are therefore the most abundant metals in metallic meteorites and in the dense-metal cores of planets such as Earth.

Iron is one of the few ferromagnetic elements.

Characteristics Iron is believed to be the tenth most Abundance of the chemical elements in the universe, and the fourth most abundant in the Earth's crust. The concentration of iron in the various layers in the structure of the Earth ranges from high (probably greater than 80%, perhaps even a nearly pure iron crystal) at the inner core, to only 5% in the outer crust. Iron is second in abundance to aluminum among the metals and fourth in abundance in the crust. Iron is the most abundant element by mass of our entire planet, making up 35% of the mass of the Earth as a whole.

Iron is a metal extracted from iron ore, and is almost never found in the free elemental state. In order to obtain elemental iron, the impurities must be removed by chemical reduction (chemistry). Iron is the main component of steel, and it is used in the production of alloys or solid solutions of various metals, as well as some non-metals, particularly carbon. The many iron-carbon alloys, which have very different properties, are discussed in the article on steel.

Nuclei of iron have some of the highest binding energies per nucleon, surpassed only by the nickel isotope 62Ni. The universally most abundant of the highly stable nuclides is, however, 56Fe. This is formed by nuclear fusion in stars. Although a further tiny energy gain could be extracted by synthesizing 62Ni, conditions in stars are unsuitable for this process to be favoured, and iron abundance on Earth greatly favors iron over nickel, and also presumably in supernova element production. Iron and Nickel Abundances in H~II Regions and Supernova Remnants When a very large star contracts at the end of its life, internal pressure and temperature rise, allowing the star to produce progressively heavier elements, despite these being less stable than the elements around mass number 60, known as the "iron group". This leads to a supernova.

Iron (as Fe2+, ferrous ion) is a necessary trace element used by almost all living organisms, the only exceptions are a few prokaryotic organisms which live in iron-poor conditions (such as the lactobacilli in iron-poor milk) which use manganese for catalysis, instead. Iron-containing enzymes, usually containing heme prosthetic groups, participate in catalysis of oxidation reactions in biology, and in transport of a number of soluble gases. See hemoglobin, cytochrome, and catalase.

Applications Iron is the most used of all the metals, comprising 95% of all the metal tonnage produced worldwide. Its combination of low cost and high strength make it indispensable, especially in applications like automobiles, the hull (ship)s of large ships, and structural components for buildings. Steel is the best known alloy of iron, and some of the forms that iron can take include:

Pig iron has 4% – 5% carbon and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Its only significance is that of an intermediate step on the way from iron ore to cast iron and steel.
Cast iron contains 2% – 4.0% carbon , 1% – 6% silicon , and small amounts of manganese. Contaminants present in pig iron that negatively affect material properties, such as sulfur and phosphorus, have been reduced to an acceptable level. It has a melting point in the range of 1420–1470 K, which is lower than either of its two main components, and makes it the first product to be melted when carbon and iron are heated together. Its mechanical properties vary greatly, dependent upon the form carbon takes in the alloy. 'White' cast irons contain their carbon in the form of cementite, or iron carbide. This hard, brittle compound dominates the mechanical properties of white cast irons, rendering them hard, but unresistant to shock. The broken surface of a white cast iron is full of fine facets of the broken carbide, a very pale, silvery, shiny material, hence the appellation. In grey iron the carbon exists free as fine flakes of graphite, and also renders the material brittle due to the stress-raising nature of the sharp edged flakes of graphite. A newer variant of grey iron, referred to as ductile iron is specially treated with trace amounts of magnesium to alter the shape of graphite to spheroids, or nodules, vastly increasing the toughness and strength of the material.
Carbon steel contains between 0.4% and 1.5% carbon, with small amounts of manganese, sulfur, phosphorus, and silicon.
Wrought iron contains less than 0.2% carbon. It is a tough, malleable product, not as fusible as pig iron. It has a very small amount of carbon, a few tenths of a percent. If honed to an edge, it loses it quickly. Wrought iron is characterised, especially in old samples, by the presence of fine 'stringers' or filaments of slag entrapped in the metal. Wrought iron does not rust particularly quickly when used outdoors. It has largely been replaced by mild steel for "wrought iron" gates and blacksmithing. Mild steel does not have the same corrosion resistance but is cheaper and more widely available.
Alloy steels contain varying amounts of carbon as well as other metals, such as chromium, vanadium, molybdenum, nickel, tungsten, etc. They are used for structural purposes, as their alloy content raises their cost and necessitates justification of their use. Recent developments in ferrous metallurgy have produced a growing range of microalloyed steels, also termed 'HSLA' or high-strength, low alloy steels, containing tiny additions to produce high strengths and often spectacular toughness at minimal cost.
Iron(III) oxides are used in the production of magnetic storage media in computers. They are often mixed with other compounds, and retain their magnetic properties in solution.

The main drawback to iron and steel is that pure iron, and most of its alloys, suffer badly from rust if not protected in some way. Painting, galvanization, plastic coating and Bluing (steel) are some techniques used to protect iron from rust by excluding water and oxygen or by sacrificial protection.

Iron is believed to be the critical missing nutrient in the ocean that limits the growth of plankton. Experimental iron fertilization of areas of the ocean using iron(II) sulfate has proven successful in increasing plankton growth. Larger scaled efforts are being attempted with the hope that iron seeding and ocean plankton growth can remove carbon dioxide from the atmosphere, thereby counteracting the greenhouse effect that is generally agreed by climatologists to cause global warming.

Iron compounds See also :category:Iron compounds.

Iron(III) acetate (Fe(C2H3O2)3 is used in the dyeing of cloth.

Iron(III) ammonium oxalate (Fe(NH4)3(C2O4)4) is used in blueprints.

Iron(III) arsenate (FeAsO4) is used in insecticide.

Iron(III) chloride (FeCl3) is used: in water purification and sewage treatment, in the dyeing of cloth, as a coloring agent in paints, as an additive in animal feed, and as an etching material for engravement, photography and printed circuits.

Iron(III) chromate (Fe2(CrO4)3) is used as a yellow pigment for paints and ceramic.

Iron(III) hydroxide (Fe(OH)3) is used as a brown pigment for rubber and in water purification systems.

Iron(III) phosphate (FePO4) is used in fertilizer and as an additive in human and animal food.

Iron(II) acetate (Fe(C2H3O2)2 is used in the dyeing of fabrics and leather, and as a wood preservative.

Iron(II) gluconate (Fe(C6H11O7)2) is used as a dietary supplement in iron pills.

Iron(II) oxalate (FeC2O4) is used as yellow pigment for paints, plastics, glass and ceramic, and in photography.

Iron(II) sulfate (FeSO4) is used in water purification and sewage treatment systems, as a catalyst in the production of ammonia, as an ingredient in fertilizer and herbicide, as an additive in animal feed, in wood preservative and as an additive to flour to increase iron levels.

Iron-Fluorine complex (FeF6)3- is found in solutions containing both Fe(III) ions and fluoride ions.

Historical aspects to make pig iron from wrought iron, with the right illustration displaying men working a blast furnace, from the Tiangong Kaiwu encyclopedia, published 1637 by Song Yingxing.The first iron used by mankind, far back in prehistory, came from meteors. The smelting of iron in bloomery probably began in Anatolia or the Caucasus in the second millennium BC or the latter part of the preceding one. Cast iron was first produced in China about 550 BC, but not in Europe until the medieval period. 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.

Steel (with a smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity. New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century AD. 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 and other 19th century and later processes have led to wrought iron no longer being produced.

Occurrence Iron is one of the most common elements on Earth, making up about 5% of the Earth's crust. Most of this iron is found in various iron oxides, such as the minerals hematite, magnetite, and taconite. The earth's core is believed to consist largely of a metallic iron-nickel alloy. About 5% of the meteorites similarly consist of iron-nickel alloy. Although rare, these are the major form of natural metallic iron on the earth's surface.

The reason for Mars's red colour is thought to be an iron-oxide-rich soil.

See also :category:Iron minerals.

Production of iron from iron ore pellets will be used in steel production.Industrially, iron is produced starting from iron ores, principally haematite (nominally Fe2O3) and magnetite (Fe3O4) by a carbothermic reaction (reduction with carbon) in a blast furnace at temperatures of about 2000 °C. In a blast furnace, iron ore, carbon in the form of coke (fuel), and a flux such as limestone (which is used to remove impurities in the ore which would otherwise clog the furnace with solid material) are fed into the top of the furnace, while a blast of heated Earth's atmosphere is forced into the furnace at the bottom.

In the furnace,(hot/oven) the coke (fuel) reacts with oxygen in the air blast to produce carbon monoxide:

2 carbon + oxygen → 2 carbon monoxide

The carbon monoxide reduces the iron ore (in the chemical equation below, hematite) to molten iron, becoming carbon dioxide in the process:

3 carbon monoxide + haematite → 2 Fe + 3 carbon dioxide

The flux is present to melt impurities in the ore, principally silicon dioxide sand and other silicates. Common fluxes include limestone (principally calcium carbonate) and dolomite (calcium-magnesium carbonate). Other fluxes may be used depending on the impurities that need to be removed from the ore. In the heat of the furnace the limestone flux decomposes to calcium oxide (quicklime):

calcium carbonate → calcium oxide + carbon dioxide

Then calcium oxide combines with silicon dioxide to form a slag.

calcium oxide + silicon dioxide → wollastonite

The slag melts in the heat of the furnace, which silicon dioxide would not have. In the bottom of the furnace, the molten slag floats on top of the more dense molten iron, and apertures in the side of the furnace are opened to run off the iron and the slag separately. The iron once cooled, is called pig iron, while the slag can be used as a material in road construction or to improve mineral-poor soils for agriculture.

Pig iron is not pure iron, but has 4-5% carbon dissolved in it. This is subsequently reduced to steel or commercially pure iron, known as wrought iron, using other furnaces or converters.

In 2005, approximately 1,544 Mt (million metric tons) of iron ore was produced worldwide. China was the top producer of iron ore with at least one-fourth world share followed by Brazil, Australia and India, reports the British Geological Survey.

Isotopes Naturally occurring iron consists of four isotopes: 5.845% of radioactive 54Fe (half-life: >3.1×1022 years), 91.754% of stable 56Fe, 2.119% of stable 57Fe and 0.282% of stable 58Fe.60Fe is an extinct radionuclide of long half-life (1.5 million years).

Much of the past work on measuring the isotopic composition of Fe has centered on determining 60Fe variations due to processes accompanying nucleosynthesis (i.e., meteorite studies) and ore formation. In the last decade however, advances in mass spectrometry technology have allowed the detection and quantification of minute, naturally-occurring variations in the ratios of the stable isotopes of iron. Much of this work has been driven by the Earth science and planetary science communities, although applications to biological and industrial systems are beginning to emerge.Dauphas, N. & Rouxel, O. 2006. Mass spectrometry and natural variations of iron isotopes. Mass Spectrometry Reviews, 25, 515-550

The isotope 56Fe is of particular interest to nuclear scientists. A common misconception is that this isotope represents the most stable nucleus possible, and that it thus would be impossible to perform fission or fusion on 56Fe and still liberate energy. This is not true, as both 62Ni and 58Fe are more stable, being the most stable nuclei. However, since 56Fe is much more easily produced from lighter nuclei in nuclear reactions, it is the endpoint of fusion chains inside Metallicity#Population III stars and is therefore common in the universe, relative to other Metallicity.

In phases of the meteorites Semarkona and Chervony Kut a correlation between the concentration of 60Nickel, the daughter product of 60Fe, and the abundance of the stable iron isotopes could be found which is evidence for the existence of 60Fe at the time of formation of the solar system. Possibly the energy released by the decay of 60Fe contributed, together with the energy released by decay of the radionuclide 26Aluminium, to the remelting and planetary differentiation of asteroids after their formation 4.6 billion years ago. The abundance of 60nickel present in wikt:extraterrestrial material may also provide further insight into the origin of the solar system and its early history.Of the stable isotopes, only 57Fe has a nuclear spin (physics) (−1/2).

Iron in organic synthesis The usage of iron metal filings in organic synthesis is mainly for the reduction of nitro compounds of nitro compounds.Fox, B. A.; Threlfall, T. L. Organic Syntheses, Coll. Vol. 5, p.346 (1973); Vol. 44, p.34 (1964). ( Article) Additionally, iron has been used for desulfurizations,Blomquist, A. T.; Dinguid, L. I. J. Org. Chem. 1947, 12, 718 & 723. redox of aldehydes,Clarke, H. T.; Dreger, E. E. Org. Syn., Coll. Vol. 1, p.304 (1941); Vol. 6, p.52 (1926). ( Article). and the deoxygenation of amine oxides.den Hertog, J.; Overhoff, J. Recl. Trav. Chim. Pays-Bas 1950, 69, 468.

Iron in biology

Iron is essential to nearly all known organisms. In cell (biology)s, iron is generally stored in the centre of metalloproteins, because "free" iron -- which binds non-specifically to many cellular components -- can catalyse production of toxic free radicals.

In animals, plants, and fungi, iron is often incorporated into the heme complex. Heme is an essential component of cytochrome proteins, which mediate redox reactions, and of oxygen carrier proteins such as hemoglobin, myoglobin, and leghemoglobin. Inorganic iron also contributes to redox reactions in the iron-sulfur clusters of many enzymes, such as nitrogenase (involved in the synthesis of ammonia from nitrogen and hydrogen) and hydrogenase. Non-heme iron proteins include the enzymes methane monooxygenase (oxidizes methane to methanol), ribonucleotide reductase (reduces ribose to deoxyribose; DNA replication), hemerythrins (oxygen transport and fixation in marine biology#other sea lifes) and purple acid phosphatase (hydrolysis of phosphate esters).

Iron distribution is heavily regulated in mammals, partly because iron has a high potential for biological toxicity. Iron distribution is also regulated because many bacteria require iron, so restricting its availability to bacteria (generally by wiktionary:sequestering it inside cells) can help to prevent or limit infections. This is probably the reason for the relatively low amounts of iron in mammalian milk. A major component of this regulation is the protein transferrin, which binds iron absorbed from the duodenum and carries it in the bloodstream to cells.{{cite web|url=http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0000079 |title=How Mammals Acquire and Distribute Iron Needed for Oxygen-Based Metabolism |author=Tracey A. Rouault |accessdate=2006-06-19 -->

Nutrition and dietary sources Good sources of dietary iron include red meat, fish, poultry, lentils, beans, leaf vegetables, tofu, chickpeas, black-eyed peas, potatoes with skin, bread made from completely whole-grain flour, molasses, teff and farina (food). Iron in meat is more easily absorbed than iron in vegetables.http://www.eatwell.gov.uk/healthissues/irondeficiency/

Iron provided by dietary supplements is often found as ferrous fumarate, although iron sulfate is cheaper and is absorbed equally well. Elemental iron, despite being absorbed to a much smaller extent (stomach acid is sufficient to convert some of it to ferrous iron), is often added to foods such as breakfast cereals or "enriched" wheat flour (where it is listed as "reduced iron" in the list of ingredients). Iron is most available to the body when chelated to amino acids - iron in this form is ten to fifteen times more bioavailable than any other, and is also available for use as a common iron supplements. Often the amino acid chosen for this purpose is the cheapest and most common amino acid, glycine, leading to "iron glycinate" supplements.{{cite book|last = Ashmead |first = H. DeWayne |authorlink = |coauthors = |year = 1989 |title = ''Conversations on Chelation and Mineral Nutrition'' |publisher = Keats Publishing |location = |id = ISBN 0-87983-501-X --> The Recommended Dietary Allowance for iron varies considerably based on age, gender, and source of dietary iron (heme-based iron has higher bioavailability).{{cite web|url=http://www.iom.edu/Object.File/Master/7/294/0.pdf |title=Dietary Reference Intakes: Elements |format=PDF --> Infants will require iron supplements if they are not breast-fed. Blood donation are at special risk of low iron levels and are often advised to supplement their iron intake.

Regulation of iron uptake Excessive iron can be toxic, because free ferrous iron reacts with peroxides to produce free radicals, which are highly reactive and can damage DNA, proteins, lipids, and other cellular components. Thus, iron toxicity occurs when there is free iron in the cell, which generally occurs when iron levels exceed the capacity of transferrin to bind the iron.

human iron metabolism is tightly regulated by the human body, which has no physiological means of excreting iron, so controls iron levels solely by regulating uptake. Although uptake is regulated, large amounts of ingested iron can cause excessive levels of iron in the blood, because high iron levels can cause damage to the cells of the gastrointestinal tract that prevents them from regulating iron absorption. High blood concentrations of iron damage cells in the heart, liver and elsewhere, which can cause serious problems, including long-term organ damage and even death.

Humans experience iron toxicity above 20 milligrams of iron for every kilogram of mass, and 60 milligrams per kilogram is a lethal dose.{{cite web] tablets intended for adult consumption, is one of the most common toxicological cause of death in children under six. The Dietary Reference Intake lists the Tolerable Upper Intake Level (UL) for adults as 45 milligram/day. For children under fourteen years old the UL is 40 mg/day.

Regulation of iron uptake is impaired in some people as a result of a genetic defect that maps to the HLA-H gene region on chromosome 6. In these people, excessive iron intake can result in iron overload disorders, such as hemochromatosis. Many people have a genetic susceptibility to iron overload without realizing it or being aware of a family history of the problem. For this reason, it is advised that people should not take iron supplements unless they suffer from iron deficiency (medicine) and have consulted a doctor. Hemochromatosis is estimated to cause disease in between 0.3 and 0.8% of Caucasians. Durupt S, Durieu I, Nove-Josserand R, et al: hemochromatosis. Rev Med Interne 2000 Nov; 21(11): 961-71.

The medical management of iron toxicity is complex, and can include use of a specific chelation agent called deferoxamine to bind and expel excess iron from the body.

Bibliography

Los Alamos National Laboratory — Iron
H. R. Schubert, History of the British Iron and Steel Industry ... to 1775 AD (Routledge, London, 1957)
R. F. Tylecote, History of Metallurgy (Institute of Materials, London 1992).
R. F. Tylecote, 'Iron in the Industrial Revolution' in J. Day and R. F. Tylecote, The Industrial Revolution in Metals (Institute of Materials 1991), 200-60.
Crystal structure of iron

References

Doulias PT, Christoforidis S, Brunk UT, Galaris D. Endosomal and lysosomal effects of desferrioxamine: protection of HeLa cells from hydrogen peroxide-induced DNA damage and induction of cell-cycle arrest. Free Radic Biol Med. 2003;35:719-28.