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Iron is a 26. Iron is a Group 8 and Period 4 Metal . Iron is notable for being the final element produced by Stellar Nucleosynthesis , and thus the heaviest element which does not require a Supernova or similarly cataclysmic event for its formation. It is therefore the most abundant Heavy Metal in the universe. NOTABLE CHARACTERISTICS Iron is the most abundant metal on Earth , and is believed to be the tenth most abundant Element in the Universe . Iron is also the second most abundant element using mass, making 34.% of the mass of the Earth; the concentration of iron in the various layers of the Earth ranges from high at the inner core to about 5% in the outer crust; it is possible the Earth's inner core consists of a single iron Crystal although it is more likely to be a mixture of iron and Nickel ; the large amount of iron in the Earth is thought to contribute to its Magnetic Field . 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 used in the production of Steel , an Alloy or Solid Solution of different metals, and some non-metals, particularly Carbon . 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 nucleides is, however, 56Fe. This is formed by nuclear fusion in the stars. Although a further tiny energy gain could be extracted by synthesizing 62Ni, conditions in stars are not right for this process to be favoured. 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 . Some cosmological models with an open universe predict that there will be a phase where as a result of slow fusion and fission reactions, everything will become iron. APPLICATIONS Iron is the most used of all the metals, comprising 95 percent 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 takes include:
HISTORY The first signs of use of iron come from the , Illyrian , Venetic and Messapic forms). By 3500 BC to 2000 BC, increasing numbers of smelted iron objects (distinguishable from meteoric iron by the lack of nickel in the product) appear in Mesopotamia , Anatolia , and Egypt . However, their use appears to be ceremonial, and iron was an expensive metal, more expensive than Gold . In the Iliad , weaponry is mostly Bronze , but iron ingots are used for trade. Some resources (see the reference ''What Caused the Iron Age?'' below) suggest that iron was being created then as a by-product of Copper refining, as Sponge Iron , and was not reproducible by the metallurgy of the time. By 1600 BC to 1200 BC, iron was used increasingly in the Middle East, but did not supplant the dominant use of Bronze . of iron from Swedish Iron Age , found at Gotland , Sweden .]] In the period from the 12th to 10th century BC, there was a rapid transition in the Middle East from bronze to iron tools and weapons. The critical factor in this transition does not appear to be the sudden onset of a superior iron working technology, but instead the disruption of the supply of Tin . This period of transition, which occurred at different times in different parts of the world, is the ushering in of an age of civilization called the Iron Age . The common Alchemical Symbol for iron, the metal of weapons, was that of Mars , the god of war. Concurrent with the transition from bronze to iron was the discovery of ''carburization'', which was the process of adding carbon to the irons of the time. Iron was recovered as sponge iron, a mix of iron and slag with some carbon and/or carbide, which was then repeatedly hammered and folded over to free the mass of slag and oxidise out carbon content, so creating the product wrought iron. Wrought iron was very low in carbon content and was not easily hardened by quenching. The people of the Middle East found that a much harder product could be created by the long term heating of a wrought iron object in a bed of Charcoal , which was then quenched in water or oil. The resulting product, which had a surface of Steel , was harder and less brittle than the bronze it began to replace. In China the first irons used were also meteoric iron, with archaeological evidence for items made of wrought iron appearing in the northwest, near Xinjiang, in the 8th century BC. These items were made of wrought iron, created by the same processes used in the Middle East and Europe, and were thought to be imported by non-Chinese people. In the later years of the Zhou Dynasty (ca 550 BC), a new iron manufacturing capability began because of a highly developed Kiln technology. Producing Blast Furnace s capable of temperatures exceeding 1300 K, the Chinese developed the manufacture of Cast , or Pig Iron . Iron was used in India as early as 250 BCE. The famous iron pillar in the Qutb Complex in Delhi is made of very pure iron (98%) and has not rusted or eroded till this day. consumed up to 11,000 tons of ore and 16,000 Cords of wood annually from 1827 to 1891.]] If iron ores are heated with carbon to 1420–1470 K, a molten liquid is formed, an Alloy of about 96.5% iron and 3.5% carbon. This product is strong, can be cast into intricate shapes, but is too brittle to be worked, unless the product is ''decarburized'' to remove most of the carbon. The vast majority of Chinese iron manufacture, from the Zhou dynasty onward, was of cast iron. Iron, however, remained a pedestrian product, used by farmers for hundreds of years, and did not really affect the nobility of China until the Qin Dynasty (ca 221 BC). Cast iron development lagged in Europe, as the smelters could only achieve temperatures of about 1000 C; or perhaps they did not want hotter temperatures, as they were seeking to produce Bloom s as a precursor of Wrought Iron , not Cast Iron . Through a good portion of the Middle Ages, in Western Europe, iron was thus still being made by the working of iron Bloom s into wrought iron. Some of the earliest casting of iron in Europe occurred in Sweden , in two sites, Lapphyttan and Vinarhyttan, between 1150 and 1350 AD. Cast Iron was then made into Wrought Iron by the Osmond Process . Some scholars have speculated the practice followed the Mongol s across Russia to these sites, but there is no clear proof of this hypothesis. In any event, by the late fourteenth century, a market for cast iron goods began to form, as a demand developed for cast iron cannonballs. Early iron Smelting (as the process is called) used Charcoal as both the heat source and the reducing agent. In 18th century England, wood supplies became inadequate to enable the industry to expand and Coke , a fossil fuel, began to be used an alternative. This innovation is associated with Abraham Darby at Coalbrookdale in 1709 , but it was only later in the century that economically viable means of converting Pig Iron to Bar Iron were devised. The most successful such process was Henry Cort 's Puddling Process , patented in 1784 . Those processes permitted the great expansion in the production of iron that constitutes the Industrial Revolution for that industry. 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. Iron is also one of the least Reactive metals, and therefore, it is sometimes found pure in Nature . ''See also .'' EXTRACTION FROM ORE Industrially, iron is extracted from its Ores , principally Hematite (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 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 : :6 C + 3 O2 → 6 CO The carbon monoxide reduces the iron ore (in the Chemical Equation below, hematite) to molten iron, becoming Carbon Dioxide in the process: :6 CO + 2 Fe2O3 → 4 Fe + 6 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 ( 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 liquid iron, and spouts in the side of the furnace may be opened to drain off either the iron or the slag. 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 . Approximately 1100Mt (million tons) of iron ore was produced in the world in 2000, with a gross market value of approximately 25 billion US dollars. While ore production occurs in 48 countries, the five largest producers were China, Brazil, Australia, Russia and India, accounting for 70% of world iron ore production. The 1100Mt of iron ore was used to produce approximately 572Mt of pig iron. COMPOUNDS pellets will be used in Steel production.]] Common Oxidation State s of iron include:
Note that despite the chemical formula, the iron in the common Pyrite is not in the +4 oxidation state; the sulfur is in the -1 oxidation state.
Iron carbide Fe3C is known as Cementite . ''See also .'' ISOTOPES Naturally occurring iron consists of four Isotope s: 5.845% of radioactive 54Fe (half-life: >3.1E22 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. 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. In phases of the meteorites ''Semarkona'' and ''Chervony Kut'' a correlation between the concentration of 60 Ni , 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 time formation of solar system. Possibly the energy released by the decay of 60Fe contributed, together with the energy released by decay of the radionuclide 26 Al , to the remelting and Differentiation of Asteroid s after their formation 4.6 billion years ago. The abundance of 60 Ni present in 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 (−1/2). For this reason, 57Fe has application as a spin isotope in chemistry and biochemistry. BIOLOGICAL ROLE Iron is essential to all Organism s, except for a few Bacteria . It is mostly stably incorporated in the inside of Metalloprotein s, because in exposed or in free form it causes production of Free Radical s that are generally toxic to cells. To say that iron is free doesn't mean that it is free floating in the bodily fluids. Iron binds avidly to virtually all biomolecules so it will adhere nonspecifically to Cell Membranes , Nucleic Acids , Proteins etc. Many animals incorporate iron into the Heme complex, an essential component of Cytochrome s, which are proteins involved in Redox reactions (including but not limited to Cellular Respiration ), and of oxygen carrying proteins Hemoglobin and Myoglobin . Inorganic iron involved in redox reactions is also found 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 . A class of Non-heme Iron Proteins is responsible for a wide range of functions within several life forms, such as 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). When the body is fighting a bacterial Infection , the body sequesters iron inside of cells (mostly stored in the storage molecule Ferritin ) so that it cannot be used by bacteria. Iron distribution is heavily regulated in . Dietary sources Good sources of dietary iron include Meat , Fish , Poultry , Lentil s, Bean s, Leaf Vegetable s, Tofu , Chickpea s, Black-eyed Pea , Strawberries and Farina . Iron provided by . Metallic iron filings are added to some Breakfast Cereals and listed in the ingredients as "reduced iron" ("reduced" referring to Redox chemistry). If the cereal is crushed, the iron filings can be separated with a magnet. PRECAUTIONS Excessive iron is toxic to humans, because excess ferrous iron reacts with Peroxide s in the body, producing Free Radical s. Iron becomes toxic when it exceeds the amount of Transferrin needed to bind free iron. In excess, uncontrollable quantities of free radicals are produced. Iron Uptake Is Tightly Regulated by the human body, which has no physiologic means of excreting iron and regulates iron solely by regulating uptake. However, too much ingested iron can damage the cells of the Gastrointestinal Tract directly, and may enter the bloodstream by damaging the cells that would otherwise regulate its entry. Once there, it causes damage to cells in the Heart , Liver and elsewhere. This can cause serious problems, including the potential of death from overdose, and long-term organ damage in survivors. Humans experience iron toxicity above 20 milligrams of iron for every kilogram of weight, and 60 milligrams per kilogram is a lethal dose. {Link without Title} Over-consumption of iron, often the result of children eating large quantitities of Ferrous Sulfate tablets intended for adult consumption, is the most common toxicological cause of death in children under six. The DRI lists the Tolerable Upper Intake Level (UL) for adults as 45 Mg /day. For children under fourteen years old the UL is 40 mg/day. If iron intake is excessive Iron Overload Disorder s can sometimes result, such as Hemochromatosis . Iron overload disorders require a genetic inability to regulate iron uptake; however, many people have a genetic susceptibility to iron overload without realizing it and without knowing a family history of the problem. For this reason, people should not take iron supplements unless they suffer from Iron Deficiency and have consulted a doctor. Blood Donors are at special risk of low iron levels and are often recommended to supplement their iron intake. The medical management of iron toxicity is complex. One element of the medical approach is a specific Chelating agent called deferoxamine, used to bind and expel excess iron from the body in case of iron toxicity. REFERENCES
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