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Iron ( with the symbol '''Fe''' () and Atomic Number 26. Iron is a Group 8 and Period 4 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. CHARACTERISTICS Iron is believed to be the tenth most Abundant Element 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 Aluminium 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 . Iron is the main component of Steel , and it is used in the production of Alloy s or Solid Solution s 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. 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 Automobile s, the Hull s of large Ship s, and structural components for Building s. Steel is the best known alloy of iron, and some of the forms that iron can take include:
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. Paint ing, Galvanization , plastic coating and Bluing 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 growth123. 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 4. Iron compounds See also .
HISTORICAL ASPECTS See Also: History of ferrous metallurgy 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 Bloomeries 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 Forge s. 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 Oxide s, 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 Meteorite s 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 .'' PRODUCTION OF IRON FROM IRON ORE See Also: Blast furnace pellets will be used in Steel production.]] Industrially, iron is produced starting from Iron Ore s, 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 , 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 Air is forced into the furnace at the bottom. In the furnace, the Coke reacts with Oxygen in the air blast to produce Carbon Monoxide : :2 C + O2 → 2 CO The carbon monoxide reduces the iron ore (in the Chemical Equation below, hematite) to molten iron, becoming Carbon Dioxide in the process: :3 CO + Fe2O3 → 2 Fe + 3 CO2 The flux is present to melt impurities in the ore, principally Silicon Dioxide Sand and other Silicate s. 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): : CaCO3 → CaO + CO2 Then calcium oxide combines with silicon dioxide to form a ''slag''. : CaO + SiO2 → CaSiO3 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 1,544Mt (million 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 See Also: isotopes of iron Naturally occurring iron consists of four Isotope s: 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 Isotope s of iron. Much of this work has been driven by the Earth 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 Extremely Massive Stars and is therefore common in the universe, relative to other Metals . In phases of the meteorites ''Semarkona'' and ''Chervony Kut'' a correlation between the concentration of 60 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 (−1/2). IRON IN ORGANIC SYNTHESIS The usage of iron metal filings in organic synthesis is mainly for the of amine oxidesden Hertog, J.; Overhoff, J. ''Recl. Trav. Chim. Pays-Bas'' 1950, ''69'', 468.. IRON IN BIOLOGY ]] See Also: human iron metabolism Iron is essential to nearly all known Organism s. In Cell s, iron is generally stored in the centre of Metalloprotein s, because "free" iron -- which binds non-specifically to many cellular components -- can catalyse production of toxic Free Radical s. 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 Cluster s of many Enzyme s, 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 Biosynthesis ), Hemerythrin s ( Oxygen transport and fixation in Marine Invertebrate s) and Purple Acid Phosphatase ( Hydrolysis of Phosphate Ester s). Nutrition and dietary sources Good sources of dietary iron include Red Meat , Fish , Poultry , Lentil s, Bean s, Leaf Vegetable s, Tofu , Chickpea s, Black-eyed Peas , potatoes with skin, bread made from completely whole-grain flour, Molasses , Teff and Farina . Iron in meat is more easily absorbed than iron in vegetables.http://www.eatwell.gov.uk/healthissues/irondeficiency/ Regulation of iron uptake Excessive iron can be toxic, because free ferrous iron reacts with Peroxide s to produce Free Radical s, 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. Iron Uptake 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 . 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 Disorder s, 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 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[Medline]. The medical management of iron toxicity is complex, and can include use of a specific Chelating agent called deferoxamine to bind and expel excess iron from the body. BIBLIOGRAPHY
REFERENCES 16. 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. SEE ALSO
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