Iron

This article is about the metallic element. For other uses,see Iron (disambiguation).

Iron is a chemical element with symbol Fe (from Latin:ferrum) and atomic number 26. It is a metal in the rsttransition series.[3] It is by mass the most common ele-ment on Earth, forming much of Earths outer and innercore. It is the fourth most common element in the Earthscrust. Its abundance in rocky planets like Earth is dueto its abundant production by fusion in high-mass stars,where the production of nickel-56 (which decays to themost common isotope of iron) is the last nuclear fusionreaction that is exothermic. Consequently, radioactivenickel is the last element to be produced before the violentcollapse of a supernova scatters precursor radionuclide ofiron into space.Like other group 8 elements, iron exists in a wide rangeof oxidation states, 2 to +6, although +2 and +3 are themost common. Elemental iron occurs in meteoroids andother low oxygen environments, but is reactive to oxygenand water. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron ox-ides, commonly known as rust. Unlike many other metalswhich form passivating oxide layers, iron oxides occupymore volume than the metal and thus ake o, exposingfresh surfaces for corrosion.Iron metal has been used since ancient times, althoughcopper alloys, which have lower melting temperatures,were used even earlier in human history. Pure iron is soft(softer than aluminium), but is unobtainable by smelting.The material is signicantly hardened and strengthenedby impurities, in particular carbon, from the smelting pro-cess. A certain proportion of carbon (between 0.002%and 2.1%) produces steel, which may be up to 1000 timesharder than pure iron. Crude iron metal is produced inblast furnaces, where ore is reduced by coke to pig iron,which has a high carbon content. Further renement withoxygen reduces the carbon content to the correct pro-portion to make steel. Steels and low carbon iron alloysalong with other metals (alloy steels) are by far the mostcommon metals in industrial use, due to their great rangeof desirable properties and the widespread abundance ofiron-bearing rock.Iron chemical compounds have many uses. Iron oxidemixed with aluminium powder can be ignited to cre-ate a thermite reaction, used in welding and purifyingores. Iron forms binary compounds with the halogens andthe chalcogens. Among its organometallic compounds is

ferrocene, the rst sandwich compound discovered.Iron plays an important role in biology, formingcomplexes with molecular oxygen in hemoglobin andmyoglobin; these two compounds are common oxygentransport proteins in vertebrates. Iron is also the metalat the active site of many important redox enzymes deal-ing with cellular respiration and oxidation and reductionin plants and animals.

1 Characteristics

1.1 Mechanical properties

The mechanical properties of iron and its alloys can beevaluated using a variety of tests, including the Brinelltest, Rockwell test and the Vickers hardness test. Thedata on iron is so consistent that it is often used to cali-brate measurements or to compare tests.[5][6] However,the mechanical properties of iron are signicantly af-fected by the samples purity: pure research-purpose sin-gle crystals of iron are actually softer than aluminium,[4]and the purest industrially produced iron (99.99%) hasa hardness of 2030 Brinell.[7] An increase in the car-bon content of the iron will initially cause a signicantcorresponding increase in the irons hardness and tensilestrength. Maximum hardness of 65 R is achieved with a0.6% carbon content, although this produces a metal witha low tensile strength.[8]

Molar volume vs. pressure for iron at room temperature

Because of its signicance for planetary cores, the phys-ical properties of iron at high pressures and temperatureshave also been studied extensively. The form of iron that

1

2 1 CHARACTERISTICS

is stable under standard conditions can be subjected topressures up to ca. 15 GPa before transforming into ahigh-pressure form, as described in the next section.

1.2 Phase diagram and allotropesMain article: Allotropes of iron

Iron represents an example of allotropy in a metal. Thereare at least four allotropic forms of iron, known as , , ,and ; at very high pressures, some controversial exper-imental evidence exists for a phase stable at very highpressures and temperatures.[9]

Low-pressure phase diagram of pure iron

As molten iron cools it crystallizes at 1538 C into its allotrope, which has a body-centered cubic (bcc) crystalstructure. As it cools further to 1394 C, it changes to its-iron allotrope, a face-centered cubic (fcc) crystal struc-ture, or austenite. At 912 C and below, the crystal struc-ture again becomes the bcc -iron allotrope, or ferrite.Finally, at 770 C (the Curie point, T) iron becomesmagnetic. As the iron passes through the Curie tempera-ture there is no change in crystalline structure, but thereis a change in domain structure, where each domaincontains iron atoms with a particular electronic spin. Inunmagnetized iron, all the electronic spins of the atomswithin one domain are in the same direction, however, theneighboring domains point in various other directions andthus over all they cancel each other out. As a result, theiron is unmagnetized. In magnetized iron, the electronicspins of all the domains are aligned, so that the magneticeects of neighboring domains reinforce each other. Al-though each domain contains billions of atoms, they arevery small, about 10 micrometres across.[10] At pressuresabove approximately 10 GPa and temperatures of a fewhundred kelvin or less, -iron changes into a hexagonalclose-packed (hcp) structure, which is also known as -iron; the higher-temperature -phase also changes into -iron, but does so at higher pressure. The -phase, if it

exists, would appear at pressures of at least 50 GPa andtemperatures of at least 1500 K; it has been thought tohave an orthorhombic or a double hcp structure.[9]

Iron is of greatest importance when mixed with certainother metals and with carbon to form steels. There aremany types of steels, all with dierent properties, and anunderstanding of the properties of the allotropes of ironis key to the manufacture of good quality steels.-iron, also known as ferrite, is the most stable form ofiron at normal temperatures. It is a fairly soft metal thatcan dissolve only a small concentration of carbon (nomore than 0.021% by mass at 910 C).[11]

Above 912 C and up to 1400 C -iron undergoes aphase transition from bcc to the fcc conguration of -iron, also called austenite. This is similarly soft andmetallic but can dissolve considerably more carbon (asmuch as 2.04% by mass at 1146 C). This form of iron isused in the type of stainless steel used for making cutlery,and hospital and food-service equipment.[10]

The high-pressure phases of iron are important as end-member models for the solid parts of planetary cores.The inner core of the Earth is generally assumed to consistessentially of an iron-nickel alloy with (or ) structure.The melting point of iron is experimentally well denedfor pressures up to approximately 50 GPa. For higherpressures, dierent studies placed the --liquid triplepoint at pressures diering by tens of gigapascals andyielded dierences of more than 1000 K for the meltingpoint. Generally speaking, molecular dynamics computersimulations of iron melting and shock wave experimentssuggest higher melting points and a much steeper slopeof the melting curve than static experiments carried outin diamond anvil cells.[12]

1.3 Isotopes

Main article: Isotopes of iron

Naturally occurring iron consists of four stable isotopes:5.845% of 54Fe, 91.754% of 56Fe, 2.119% of 57Fe and0.282% of 58Fe. Of these stable isotopes, only 57Fe hasa nuclear spin (12). The nuclide 54Fe is predicted to un-dergo double beta decay, but this process had never beenobserved experimentally for these nuclei, and only thelower limit on the half-life was established: t/>3.11022years.60Fe is an extinct radionuclide of long half-life (2.6 mil-lion years).[13] It is not found on Earth, but its ultimatedecay product is the stable nuclide nickel-60.Much of the past work on measuring the isotopic com-position of Fe has focused on determining 60Fe vari-ations due to processes accompanying nucleosynthesis(i.e., meteorite studies) and ore formation. In the lastdecade however, advances in mass spectrometry tech-

1.5 Occurrence 3

nology have allowed the detection and quantication ofminute, naturally occurring variations in the ratios of thestable isotopes of iron. Much of this work has been drivenby the Earth and planetary science communities, althoughapplications to biological and industrial systems are be-ginning to emerge.[14]

The most abundant iron isotope 56Fe is of particular in-terest to nuclear scientists as it represents the most com-mon endpoint of nucleosynthesis. It is often cited, falsely,as the isotope of highest binding energy, a distinctionwhich actually belongs to nickel-62.[15] Since 56Ni is eas-ily produced from lighter nuclei in the alpha process innuclear reactions in supernovae (see silicon burning pro-cess), nickel-56 (14 alpha particles) is the endpoint offusion chains inside extremely massive stars, since ad-dition of another alpha particle would result in zinc-60,which requires a great deal more energy. This nickel-56,which has a half-life of about 6 days, is therefore madein quantity in these stars, but soon decays by two succes-sive positron emissions within supernova decay productsin the supernova remnant gas cloud, rst to radioactivecobalt-56, and then stable iron-56. This last nuclide istherefore common in the universe, relative to other stablemetals of approximately the same atomic weight.In phases of the meteorites Semarkona and ChervonyKut a correlation between the concentration of 60Ni, thedaughter product of 60Fe, and the abundance of the stableiron isotopes could be found which is evidence for the ex-istence of 60Fe at the time of formation of the Solar Sys-tem. Possibly the energy released by the decay of 60Fecontributed, together with the energy released by decay ofthe radionuclide 26Al, to the remelting and dierentiationof asteroids after their formation 4.6 billion years ago.The abundance of 60Ni present in extraterrestrial mate-rial may also provide further insight into the origin of theSolar System and its early history.[16]

Nuclei of iron atoms have some of the highest binding en-ergies per nucleon, surpassed only by the nickel isotope62Ni. This is formed by nuclear fusion in stars. Althougha further tiny energy gain could be extracted by synthesiz-ing 62Ni, conditions in stars are unsuitable for this processto be favored. Elemental distribution on Earth greatly fa-vors iron over nickel, and also presumably in supernovaelement production.[17]

Iron-56 is the heaviest stable isotope produced by the al-pha process in stellar nucleosynthesis; elements heavierthan iron and nickel require a supernova for their forma-tion. Iron is the most abundant element in the core of redgiants, and is the most abundant metal in iron meteoritesand in the dense metal cores of planets such as Earth.

1.4 NucleosynthesisIron is created by extremely large, extremely hot (over 2.5billion kelvin) stars through the silicon burning process.It is the heaviest stable element to be produced in this

manner. The process starts with the second largest stablenucleus created by silicon burning, which is calcium. Onestable nucleus of calcium fuses with one helium nucleus,creating unstable titanium. Before the titanium decays, itcan fuse with another helium nucleus, creating unstablechromium. Before the chromium decays, it can fuse withanother helium nucleus, creating unstable iron. Beforethe iron decays, it can fuse with another helium nucleus,creating unstable nickel-56. Any further fusion of nickel-56 consumes energy instead of producing energy, so afterthe production of nickel-56, the star does not produce theenergy necessary to keep the core from collapsing. Even-tually, the nickel-56 decays to unstable cobalt-56, whichin turn decays to stable iron-56. When the core of the starcollapses, it creates a supernova. Supernovas also createadditional forms of stable iron via the r-process.

1.5 Occurrence1.5.1 Planetary occurrence

Iron meteorites, similar in composition to the Earths inner- andouter core

Iron is the sixth most abundant element in the Universe,and the most common refractory element.[18] It is formedas the nal exothermic stage of stellar nucleosynthesis, bysilicon fusion in massive stars.Metallic or native iron is rarely found on the surface ofthe Earth because it tends to oxidize, but its oxides arepervasive and represent the primary ores. While it makesup about 5% of the Earths crust, both the Earths innerand outer core are believed to consist largely of an iron-nickel alloy constituting 35% of the mass of the Earth asa whole. Iron is consequently the most abundant elementon Earth, but only the fourth most abundant element inthe Earths crust.[19][20] Most of the iron in the crust isfound combined with oxygen as iron oxide minerals suchas hematite (Fe2O3) and magnetite (Fe3O4). Large de-posits of iron are found in banded iron formations. Thesegeological formations are a type of rock consisting of re-peated thin layers of iron oxides alternating with bandsof iron-poor shale and chert. The banded iron formations

4 2 CHEMISTRY AND COMPOUNDS

were laid down in the time between 3,700 million yearsago and 1,800 million years ago[21][22]

About 1 in 20 meteorites consist of the unique iron-nickelminerals taenite (3580% iron) and kamacite (9095%iron). Although rare, iron meteorites are the main formof natural metallic iron on the Earths surface.[23]

The red color of the surface of Mars is derived froman iron oxide-rich regolith. This has been proven byMssbauer spectroscopy.[24]

1.5.2 Stocks in use in society

According to the International Resource Panel's MetalStocks in Society report, the global stock of iron in usein society is 2200 kg per capita. Much of this is in more-developed countries (700014000 kg per capita) ratherthan less-developed countries (2000 kg per capita).

2 Chemistry and compoundsIron forms compounds mainly in the +2 and +3 oxidationstates. Traditionally, iron(II) compounds are calledferrous, and iron(III) compounds ferric. Iron also oc-curs in higher oxidation states, an example being the pur-ple potassium ferrate (K2FeO4) which contains iron inits +6 oxidation state. Iron(IV) is a common intermedi-ate in many biochemical oxidation reactions.[25][26] Nu-merous organometallic compounds contain formal oxi-dation states of +1, 0, 1, or even 2. The oxidationstates and other bonding properties are often assessed us-ing the technique of Mssbauer spectroscopy.[27] Thereare also many mixed valence compounds that containboth iron(II) and iron(III) centers, such as magnetite andPrussian blue (Fe4(Fe[CN]6)3).[26] The latter is used asthe traditional blue in blueprints.[28]

Hydrated iron(III) chloride, also known as ferric chloride

The iron compounds produced on the largest scale in in-

dustry are iron(II) sulfate (FeSO47H2O) and iron(III)chloride (FeCl3). The former is one of the most read-ily available sources of iron(II), but is less stable to aerialoxidation than Mohrs salt ((NH4)2Fe(SO4)26H2O).Iron(II) compounds tend to be oxidized to iron(III) com-pounds in the air.[26]

Unlike many other metals, iron does not form amalgamswith mercury. As a result, mercury is traded in standard-ized 76 pound asks (34 kg) made of iron.[29]

2.1 Binary compoundsIron reacts with oxygen in the air to form variousoxide and hydroxide compounds; the most common areiron(II,III) oxide (Fe3O4), and iron(III) oxide (Fe2O3).Iron(II) oxide also exists, though it is unstable at roomtemperature. These oxides are the principal ores forthe production of iron (see bloomery and blast furnace).They are also used in the production of ferrites, usefulmagnetic storage media in computers, and pigments. Thebest known sulde is iron pyrite (FeS2), also known asfools gold owing to its golden luster.[26]

The binary ferrous and ferric halides are well known,with the exception of ferric iodide. The ferrous halidestypically arise from treating iron metal with the corre-sponding binary halogen acid to give the correspondinghydrated salts.[26]

Fe + 2 HX FeX2 + H2

Iron reacts with uorine, chlorine, and bromine to givethe corresponding ferric halides, ferric chloride being themost common:

2 Fe + 3 X2 2 FeX3 (X = F, Cl, Br)

2.2 Coordination and organometallic com-pounds

See also: Organoiron chemistrySeveral cyanide complexes are known. The most famous

Prussian blue

example is Prussian blue, (Fe4(Fe[CN]6)3). Potassiumferricyanide and potassium ferrocyanide are also known;the formation of Prussian blue upon reaction with iron(II)and iron(III) respectively forms the basis of a wet chem-ical test.[26] Prussian blue is also used as an antidote forthallium and radioactive caesium poisoning.[30][31] Prus-sian blue can be used in laundry bluing to correct the yel-lowish tint left by ferrous salts in water.

3.1 Wrought iron 5

Ferrocene

Several carbonyl compounds of iron are known. The pre-mier iron(0) compound is iron pentacarbonyl, Fe(CO)5,which is used to produce carbonyl iron powder, a highlyreactive form of metallic iron. Thermolysis of iron pen-tacarbonyl gives the trinuclear cluster, triiron dodecacar-bonyl. Collmans reagent, disodium tetracarbonylfer-rate, is a useful reagent for organic chemistry; it con-tains iron in the 2 oxidation state. Cyclopentadienylirondicarbonyl dimer contains iron in the rare +1 oxidationstate.[32]

Ferrocene is an extremely stable complex. The rstsandwich compound, it contains an iron(II) center withtwo cyclopentadienyl ligands bonded through all ten car-bon atoms. This arrangement was a shocking noveltywhen it was rst discovered,[33] but the discovery of fer-rocene has led to a new branch of organometallic chem-istry. Ferrocene itself can be used as the backbone ofa ligand, e.g. dppf. Ferrocene can itself be oxidized tothe ferrocenium cation (Fc+); the ferrocene/ferroceniumcouple is often used as a reference in electrochemistry.[34]

3 History

Main article: History of ferrous metallurgy

3.1 Wrought ironFurther information: Ancient iron productionIron objects of great age are much rarer than ob-

The symbol for Mars has been used since antiquity to representiron.

The Delhi iron pillar is an example of the iron extraction andprocessing methodologies of early India. The iron pillar at Delhihas withstood corrosion for the last 1600 years.

jects made of gold or silver due to the ease of corro-sion of iron.[35] Beads made from meteoric iron in 3500BCE or earlier were found in Gerzah, Egypt by G. A.

6 3 HISTORY

Wainwright.[36] The beads contain 7.5% nickel, whichis a signature of meteoric origin since iron found in theEarths crust has very little to no nickel content. Me-teoric iron was highly regarded due to its origin in theheavens and was often used to forge weapons and toolsor whole specimens placed in churches.[36] Items thatwere likely made of iron by Egyptians date from 2500 to3000 BCE.[35] Iron had a distinct advantage over bronzein warfare implements. It was much harder and moredurable than bronze, although susceptible to rust. How-ever, this is contested. Hittitologist Trevor Bryce arguesthat before advanced iron-working techniques were de-veloped in India, meteoritic iron weapons used by earlyMesopotamian armies had a tendency to shatter in com-bat, due to their high carbon content.[37]

The rst iron production started in the Middle BronzeAge but it took several centuries before iron dis-placed bronze. Samples of smelted iron from Asmar,Mesopotamia and Tall Chagar Bazaar in northern Syriawere made sometime between 2700 and 3000 BCE.[38]The Hittites appear to be the rst to understand the pro-duction of iron from its ores and regard it highly in theirsociety. They began to smelt iron between 1500 and 1200BCE and the practice spread to the rest of the Near Eastafter their empire fell in 1180 BCE.[38] The subsequentperiod is called the Iron Age. Iron smelting, and thusthe Iron Age, reached Europe two hundred years laterand arrived in Zimbabwe, Africa by the 8th century.[38]In China, iron only appears circa 700500 BCE.[39] Ironsmelting may have been introduced into China throughCentral Asia.[40] The earliest evidence of the use of ablast furnace in China dates to the 1st century AD,[41]and cupola furnaces were used as early as the WarringStates period (403221 BCE).[42] Usage of the blast andcupola furnace remained widespread during the Song andTang Dynasties.[43]

Artifacts of smelted iron are found in India datingfrom 1800 to 1200 BCE,[44] and in the Levant fromabout 1500 BCE (suggesting smelting in Anatolia or theCaucasus).[45][46]

The Book of Genesis, fourth chapter, verse 22 containsthe rst mention of iron in theOld Testament of the Bible;Tubal-cain, an instructor of every articer in brass andiron.[35] Other verses allude to iron mining (Job 28:2),iron used as a stylus (Job 19:24), furnace (Deuteronomy4:20), chariots (Joshua 17:16), nails (I Chron. 22:3), sawsand axes (II Sam. 12:31), and cooking utensils (Ezekiel4:3).[47] The metal is also mentioned in the New Testa-ment, for example in Acts chapter 12 verse 10, "[Peterpassed through] the iron gate that leadeth unto the cityof Antioch.[48]

Iron working was introduced to Greece in the late 11thcentury BCE.[49] The spread of ironworking in Centraland Western Europe is associated with Celtic expansion.According to Pliny the Elder, iron use was common inthe Roman era.[36] The annual iron output of the Roman

Empire is estimated at 84,750 t,[50] while the similarlypopulous Han China produced around 5,000 t.[51]

During the Industrial Revolution in Britain, Henry Cortbegan rening iron from pig iron to wrought iron (or bariron) using innovative production systems. In 1783 hepatented the puddling process for rening iron ore. It waslater improved by others, including Joseph Hall.

3.2 Cast iron

Cast iron was rst produced in China during 5th cen-tury BCE,[52] but was hardly in Europe until the me-dieval period.[53][54] The earliest cast iron artifacts werediscovered by archaeologists in what is nowmodern LuheCounty, Jiangsu in China. Cast iron was used in ancientChina for warfare, agriculture, and architecture.[55] Dur-ing the medieval period, means were found in Europe ofproducing wrought iron from cast iron (in this contextknown as pig iron) using nery forges. For all these pro-cesses, charcoal was required as fuel.

Coalbrookdale by Night, 1801. Blast furnaces light the ironmaking town of Coalbrookdale.

Medieval blast furnaces were about 10 feet (3.0 m) talland made of reproof brick; forced air was usually pro-vided by hand-operated bellows.[54] Modern blast fur-naces have grown much bigger.In 1709, Abraham Darby I established a coke-red blastfurnace to produce cast iron. The ensuing availability ofinexpensive iron was one of the factors leading to the In-dustrial Revolution. Toward the end of the 18th cen-tury, cast iron began to replace wrought iron for cer-tain purposes, because it was cheaper. Carbon contentin iron wasn't implicated as the reason for the dierencesin properties of wrought iron, cast iron, and steel until the18th century.[38]

Since iron was becoming cheaper and more plentiful, italso became a major structural material following thebuilding of the innovative rst iron bridge in 1778.

4.1 Industrial routes 7

3.3 Steel

See also: Steelmaking

Steel (with smaller carbon content than pig iron but morethan wrought iron) was rst produced in antiquity by us-ing a bloomery. Blacksmiths in Luristan in western Iranwere making good steel by 1000 BCE.[38] Then improvedversions, Wootz steel by India and Damascus steel weredeveloped around 300 BCE and 500 CE respectively.These methods were specialized, and so steel did not be-come a major commodity until the 1850s.[56]

New methods of producing it by carburizing bars of ironin the cementation process were devised in the 17th cen-tury AD. In the Industrial Revolution, new methods ofproducing bar iron without charcoal were devised andthese were later applied to produce steel. In the late1850s, Henry Bessemer invented a new steelmaking pro-cess, involving blowing air through molten pig iron, toproduce mild steel. This made steel much more eco-nomical, thereby leading to wrought iron no longer beingproduced.[57]

3.4 Foundations of modern chemistry

Antoine Lavoisier used the reaction of water steam withmetallic iron inside an incandescent iron tube to producehydrogen in his experiments leading to the demonstrationof the mass conservation. Anaerobic oxidation of iron athigh temperature can be schematically represented by thefollowing reactions:

Fe + H2O FeO + H2

2 Fe + 3 H2O Fe2O3 + 3 H2

3 Fe + 4 H2O Fe3O4 + 4 H2

4 Production of metallic iron

4.1 Industrial routes

See also: Iron ore

The production of iron or steel is a process consisting oftwomain stages, unless the desired product is cast iron. Inthe rst stage pig iron is produced in a blast furnace. Al-ternatively, it may be directly reduced. The second stage,pig iron is converted to wrought iron or steel.For a few limited purposes like electromagnet cores, pureiron is produced by electrolysis of a ferrous sulfate solu-tion

The ning process of smelting iron ore to make wrought iron frompig iron, with the right illustration displaying men working a blastfurnace, from the Tiangong Kaiwu encyclopedia, published in1637 by Song Yingxing.

How iron was extracted in the 19th century

4.1.1 Blast furnace processing

Main article: Blast furnace

Industrial iron production starts with iron ores, princi-pally hematite, which has a nominal formula Fe2O3, andmagnetite, with the formula Fe3O4. These ores are re-duced to the metal in a carbothermic reaction, i.e. bytreatment with carbon. The conversion is typically con-ducted in in a blast furnace at temperatures of about 2000C. Carbon is provided in the form of coke. The processalso contains a ux such as limestone, which is used toremove silicaceous minerals in the ore, which would oth-erwise clog the furnace. The coke and limestone are fedinto the top of the furnace, while a massive blast of heatedair, about 4 tons per ton of iron,[54] is forced into the fur-nace at the bottom.In the furnace, the coke reacts with oxygen in the air blastto produce carbon monoxide:

2 C + O2 2 CO

8 4 PRODUCTION OF METALLIC IRON

The carbon monoxide reduces the iron ore (in thechemical equation below, hematite) to molten iron, be-coming carbon dioxide in the process:

Fe2O3 + 3 CO 2 Fe + 3 CO2

Some iron in the high-temperature lower region of thefurnace reacts directly with the coke:

2 Fe2O3 + 3 C 4 Fe + 3 CO2

The ux present to melt impurities in the ore is principallylimestone (calcium carbonate) and dolomite (calcium-magnesium carbonate). Other specialized uxes are useddepending on the details of the ore. In the heat of thefurnace the limestone ux decomposes to calcium oxide(also known as quicklime):

CaCO3 CaO + CO2

Then calcium oxide combines with silicon dioxide toform a liquid slag.

CaO + SiO2 CaSiO3

The slag melts in the heat of the furnace. In the bottomof the furnace, the molten slag oats on top of the densermolten iron, and apertures in the side of the furnace areopened to run o the iron and the slag separately. Theiron, once cooled, is called pig iron, while the slag canbe used as a material in road construction or to improvemineral-poor soils for agriculture[54]

This heap of iron ore pellets will be used in steel production.

4.1.2 Direct iron reduction

Owing to environmental concerns, alternative methods ofprocessing iron have been developed. Direct iron reduc-tion reduces iron ore to a powder called sponge iron ordirect iron that is suitable for steelmaking.[54] Twomainreactions comprise the direct reduction process:Natural gas is partially oxidized (with heat and a catalyst):

2 CH4 + O2 2 CO + 4 H2

These gases are then treated with iron ore in a furnace,producing solid sponge iron:

Fe2O3 + CO + 2 H2 2 Fe + CO2 + 2 H2O

Silica is removed by adding a limestone ux as describedabove.

4.1.3 Further processes

Main articles: Steelmaking and IronworksPig iron is not pure iron, but has 45% carbon dissolved

Iron-carbon phase diagram, various stable solid solution forms

in it with small amounts of other impurities like sulfur,magnesium, phosphorus and manganese. As the carbonis the major impurity, the iron (pig iron) becomes brittleand hard. This form of iron, also known as cast iron, isused to cast articles in foundries such as stoves, pipes,radiators, lamp-posts and rails.Alternatively pig iron may be made into steel (with upto about 2% carbon) or wrought iron (commercially pureiron). Various processes have been used for this, includ-ing nery forges, puddling furnaces, Bessemer convert-ers, open hearth furnaces, basic oxygen furnaces, andelectric arc furnaces. In all cases, the objective is to oxi-dize some or all of the carbon, together with other impu-rities. On the other hand, other metals may be added tomake alloy steels.Annealing involves the heating of a piece of steel to 700800 C for several hours and then gradual cooling. Itmakes the steel softer and more workable.

4.2 Laboratory methodsMetallic iron is generally produced in the laboratory bytwo methods. One route is electrolysis of ferrous chlo-

5.1 Metallurgical 9

ride onto an iron cathode. The second method involvesreduction of iron oxides with hydrogen gas at about 500C.[58]

5 Applications

Iron powder

5.1 MetallurgicalIron is the most widely used of all the metals, account-ing for 95% of worldwide metal production. Its low costand high strength make it indispensable in engineeringapplications such as the construction of machinery andmachine tools, automobiles, the hulls of large ships, andstructural components for buildings. Since pure iron isquite soft, it is most commonly combined with alloyingelements to make steel.Commercially available iron is classied based on purityand the abundance of additives. Pig iron has 3.54.5%carbon[60] and contains varying amounts of contaminantssuch as sulfur, silicon and phosphorus. Pig iron is not asaleable product, but rather an intermediate step in theproduction of cast iron and steel. The reduction of con-taminants in pig iron that negatively aect material prop-erties, such as sulfur and phosphorus, yields cast iron con-taining 24% carbon, 16% silicon, and small amountsof manganese. It has a melting point in the range of14201470 K, which is lower than either of its two maincomponents, and makes it the rst product to be meltedwhen carbon and iron are heated together. Its mechan-ical properties vary greatly and depend on the form thecarbon takes in the alloy.White cast irons contain their carbon in the form ofcementite, or iron-carbide. This hard, brittle compounddominates the mechanical properties of white cast irons,rendering them hard, but unresistant to shock. The bro-ken surface of a white cast iron is full of ne facets of thebroken iron-carbide, a very pale, silvery, shiny material,hence the appellation.

In gray iron the carbon exists as separate, ne akes ofgraphite, and also renders the material brittle due to thesharp edged akes of graphite that produce stress concen-tration sites within the material. A newer variant of grayiron, referred to as ductile iron is specially treated withtrace amounts ofmagnesium to alter the shape of graphiteto spheroids, or nodules, reducing the stress concentra-tions and vastly increasing the toughness and strength ofthe material.Wrought iron contains less than 0.25% carbon but largeamounts of slag that give it a brous characteristic.[60] Itis a tough, malleable product, but not as fusible as pigiron. If honed to an edge, it loses it quickly. Wroughtiron is characterized by the presence of ne bers of slagentrapped within the metal. Wrought iron is more cor-rosion resistant than steel. It has been almost completelyreplaced bymild steel for traditional wrought iron prod-ucts and blacksmithing.Mild steel corrodes more readily than wrought iron, butis cheaper and more widely available. Carbon steel con-tains 2.0% carbon or less,[61] with small amounts ofmanganese, sulfur, phosphorus, and silicon. Alloy steelscontain varying amounts of carbon as well as other met-als, such as chromium, vanadium, molybdenum, nickel,tungsten, etc. Their alloy content raises their cost, and sothey are usually only employed for specialist uses. Onecommon alloy steel, though, is stainless steel. Recent de-velopments in ferrous metallurgy have produced a grow-ing range of microalloyed steels, also termed 'HSLA' orhigh-strength, low alloy steels, containing tiny additionsto produce high strengths and often spectacular toughnessat minimal cost.

Photon mass attenuation coecient for iron.

Apart from traditional applications, iron is also used forprotection from ionizing radiation. Although it is lighterthan another traditional protection material, lead, it ismuch stronger mechanically. The attenuation of radia-tion as a function of energy is shown in the graph.The main disadvantage of iron and steel is that pure iron,and most of its alloys, suer badly from rust if not pro-tected in some way. Painting, galvanization, passivation,plastic coating and bluing are all used to protect iron from

10 6 BIOLOGICAL ROLE

rust by excluding water and oxygen or by cathodic protec-tion.

5.2 Iron compoundsAlthough its metallurgical role is dominant in terms ofamounts, iron compounds are pervasive in industry aswell being used in many niche uses. Iron catalysts aretraditionally used in the Haber-Bosch Process for the pro-duction of ammonia and the Fischer-Tropsch process forconversion of carbon monoxide to hydrocarbons for fu-els and lubricants.[62] Powdered iron in an acidic sol-vent was used in the Bechamp reduction the reductionof nitrobenzene to aniline.[63]

Iron(III) chloride nds use in water purication andsewage treatment, in the dyeing of cloth, as a coloringagent in paints, as an additive in animal feed, and as anetchant for copper in the manufacture of printed circuitboards.[64] It can also be dissolved in alcohol to form tinc-ture of iron. The other halides tend to be limited to labo-ratory uses.Iron(II) sulfate is used as a precursor to other iron com-pounds. It is also used to reduce chromate in cement. Itis used to fortify foods and treat iron deciency anemia.These are its main uses. Iron(III) sulfate is used in settlingminute sewage particles in tank water. Iron(II) chlorideis used as a reducing occulating agent, in the formationof iron complexes and magnetic iron oxides, and as a re-ducing agent in organic synthesis.

6 Biological roleIron is abundant in biology.[65] Iron-proteins are foundin all living organisms, ranging from the evolutionarilyprimitive archaea to humans. The color of blood is dueto the hemoglobin, an iron-containing protein. As illus-trated by hemoglobin, iron is often bound to cofactors,e.g. in hemes. The iron-sulfur clusters are pervasive andinclude nitrogenase, the enzymes responsible for biolog-ical nitrogen xation. Inuential theories of evolutionhave invoked a role for iron suldes in the iron-sulfurworld theory.Iron is a necessary trace element found in nearly all liv-ing organisms. Iron-containing enzymes and proteins,often containing heme prosthetic groups, participate inmany biological oxidations and in transport. Examples ofproteins found in higher organisms include hemoglobin,cytochrome (see high-valent iron), and catalase.[66]

6.1 Bioinorganic compoundsThe most commonly known and studied "bioinorganic"compounds of iron (i.e., iron compounds used in biol-ogy) are the heme proteins: examples are hemoglobin,

Structure of Heme b, in the protein additional ligand(s) would beattached to Fe.

myoglobin, and cytochrome P450. These compounds cantransport gases, build enzymes, and be used in transfer-ring electrons. Metalloproteins are a group of proteinswith metal ion cofactors. Some examples of iron met-alloproteins are ferritin and rubredoxin. Many enzymesvital to life contain iron, such as catalase, lipoxygenases,and IRE-BP.

6.2 Health and diet

Main articles: Iron deciency and Human ironmetabolism

Iron is pervasive, but particularly rich sources of di-etary iron include red meat, lentils, beans, poultry, sh,leaf vegetables, watercress, tofu, chickpeas, black-eyedpeas, blackstrap molasses, fortied bread, and forti-ed breakfast cereals. Iron in low amounts is foundin molasses, te, and farina. Iron in meat (hemeiron) is more easily absorbed than iron in vegetables.[67]Although some studies suggest that heme/hemoglobinfrom red meat has eects which may increase the like-lihood of colorectal cancer,[68][69] there is still somecontroversy,[70] and even a few studies suggesting thatthere is not enough evidence to support such claims.[71]

Iron provided by dietary supplements is often found asiron(II) fumarate, although iron sulfate is cheaper andis absorbed equally well. Elemental iron, or reducediron, despite being absorbed at only one third to twothirds the eciency (relative to iron sulfate),[72] is oftenadded to foods such as breakfast cereals or enrichedwheatour. Iron is most available to the body when chelated toamino acids[73] and is also available for use as a common

6.5 Bioremediation 11

iron supplement. Often the amino acid chosen for thispurpose is the cheapest and most common amino acid,glycine, leading to iron glycinate supplements.[74] TheRecommended Dietary Allowance (RDA) for iron variesconsiderably based on age, gender, and source of dietaryiron (heme-based iron has higher bioavailability).[75] In-fants may require iron supplements if they are bottle-fedcows milk.[76] Blood donors and pregnant women are atspecial risk of low iron levels and are often advised tosupplement their iron intake.[77]

6.3 Uptake and storage

Iron acquisition poses a problem for aerobic organisms,because ferric iron is poorly soluble near neutral pH.Thus, bacteria have evolved high-anity sequesteringagents called siderophores.[78][79][80]

After uptake, in cells, iron storage is carefully regulated;free iron ions do not exist as such. A major componentof this regulation is the protein transferrin, which bindsiron ions absorbed from the duodenum and carries it inthe blood to cells.[81] In animals, plants, and fungi, ironis often the metal ion incorporated into the heme com-plex. Heme is an essential component of cytochromeproteins, which mediate redox reactions, and of oxy-gen carrier proteins such as hemoglobin, myoglobin, andleghemoglobin.Inorganic iron contributes to redox reactions in the iron-sulfur clusters of many enzymes, such as nitrogenase (in-volved in the synthesis of ammonia from nitrogen andhydrogen) and hydrogenase. Non-heme iron proteins in-clude the enzymes methane monooxygenase (oxidizesmethane to methanol), ribonucleotide reductase (reducesribose to deoxyribose; DNA biosynthesis), hemerythrins(oxygen transport and xation in marine invertebrates)and purple acid phosphatase (hydrolysis of phosphateesters).Iron distribution is heavily regulated in mammals, partlybecause iron ions have a high potential for biologicaltoxicity.[82]

6.4 Regulation of uptake

Main article: Hepcidin

Iron uptake is tightly regulated by the human body, whichhas no regulated physiological means of excreting iron.Only small amounts of iron are lost daily due to mucosaland skin epithelial cell sloughing, so control of iron lev-els is mostly by regulating uptake.[83] Regulation of ironuptake is impaired in some people as a result of a geneticdefect that maps to the HLA-H gene region on chromo-some 6. In these people, excessive iron intake can re-sult 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 ofthe problem. For this reason, it is advised that people donot take iron supplements unless they suer from iron de-ciency and have consulted a doctor. Hemochromatosisis estimated to cause disease in between 0.3 and 0.8% ofCaucasians.[84]

MRI nds that iron accumulates in the hippocampus ofthe brains of those with Alzheimers disease and in thesubstantia nigra of those with Parkinson disease.[85]

6.5 Bioremediation

Iron-eating bacteria live in the hulls of sunken shipssuch as the Titanic.[86] The acidophile bacteriaAcidithiobacillus ferrooxidans, Leptospirillum fer-rooxidans, Sulfolobus spp., Acidianus brierleyi andSulfobacillus thermosuldooxidans can oxidize ferrousiron enzymically.[87] A sample of the fungus Aspergillusniger was found growing from gold mining solution, andwas found to contain cyano metal complexes such asgold, silver, copper iron and zinc. The fungus also playsa role in the solubilization of heavy metal suldes.[88]

6.6 Permeable reactive barriers

Zerovalent iron is the main reactive material forpermeable reactive barriers.[89]

7 ToxicityMain article: Iron poisoning

Large amounts of ingested iron can cause excessive lev-els of iron in the blood. High blood levels of free fer-rous iron react with peroxides to produce free radicals,which are highly reactive and can damage DNA, proteins,lipids, and other cellular components. Thus, iron tox-icity occurs when there is free iron in the cell, whichgenerally occurs when iron levels exceed the capacity oftransferrin to bind the iron. Damage to the cells of thegastrointestinal tract can also prevent them from regulat-ing iron absorption leading to further increases in bloodlevels. Iron typically damages cells in the heart, liver andelsewhere, which can cause signicant adverse eects,including coma, metabolic acidosis, shock, liver failure,coagulopathy, adult respiratory distress syndrome, long-term organ damage, and even death.[90] Humans experi-ence iron toxicity above 20 milligrams of iron for everykilogram of mass, and 60 milligrams per kilogram is con-sidered a lethal dose.[91] Overconsumption of iron, oftenthe result of children eating large quantities of ferrous sul-fate tablets intended for adult consumption, is one of themost common toxicological causes of death in childrenunder six.[91] The Dietary Reference Intake (DRI) lists

12 9 REFERENCES

the Tolerable Upper Intake Level (UL) for adults as 45mg/day. For children under fourteen years old the UL is40 mg/day.The medical management of iron toxicity is complicated,and can include use of a specic chelating agent calleddeferoxamine to bind and expel excess iron from thebody.[90][92]

8 See also El Mutn in Bolivia, where 10% of the worlds ac-cessible iron ore is located.

Iron fertilization proposed fertilization of oceansto stimulate phytoplankton growth

Iron (metaphor) Iron in folklore List of countries by iron production Pelletising process of creation of iron ore pellets Rustproof iron Steel

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[89] Roehl, K.E.; Meggyes, T; Simon, F.G.; Stewart, D.I. (27April 2005). Long-Term Performance of Permeable Re-active Barriers. p. 5. ISBN 9780080535616.

[90] Cheney, K.; Gumbiner, C.; Benson, B.; Tenen-bein, M. (1995). Survival after a severe iron poi-soning treated with intermittent infusions of defer-oxamine. J Toxicol Clin Toxicol 33 (1): 616.doi:10.3109/15563659509020217. PMID 7837315.

[91] Toxicity, Iron. Medscape. Retrieved 23 May 2010.

[92] Tenenbein, M (1996). Benets of parenteral deferox-amine for acute iron poisoning. J Toxicol Clin Toxicol 34(5): 485489. doi:10.3109/15563659609028005. PMID8800185.

10 Bibliography

Weeks, Mary Elvira; Leichester, Henry M. (1968).Elements Known to the Ancients. Discovery ofthe Elements. Easton, PA: Journal of Chemical Ed-ucation. pp. 2940. ISBN 0-7661-3872-0. LCCN68-15217.

11 Further reading H. R. Schubert, History of the British Iron and SteelIndustry... to 1775 AD (Routledge, London, 1957)

R. F. Tylecote, History of Metallurgy (Institute ofMaterials, London 1992).

R. F. Tylecote, Iron in the Industrial Revolution inJ. Day and R. F. Tylecote, The Industrial Revolutionin Metals (Institute of Materials 1991), 20060.

12 External links Its Elemental Iron The Most Tightly Bound Nuclei Chemistry in its element podcast (MP3) from theRoyal Society of Chemistry's Chemistry World:Iron

Iron at The Periodic Table of Videos (University ofNottingham)

Metallurgy for the non-Metallurgist

16 13 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

13 Text and image sources, contributors, and licenses13.1 Text

Iron Source: http://en.wikipedia.org/wiki/Iron?oldid=648539396 Contributors: AxelBoldt, The Epopt, Derek Ross, Sodium, CYD, VickiRosenzweig, Mav, Bryan Derksen, The Anome, Tarquin, Jeronimo, Wayne Hardman, Andre Engels, Ted Longstae, PierreAbbat, WilliamAvery, Roadrunner, Ktsquare, Robert Foley, AdamRetchless, Heron, Frank Warmerdam, Lightning, Olivier, Dwmyers, Lir, RTC, D,JohnOwens, Michael Hardy, Wshun, Alan Peakall, Menchi, Ixfd64, Tango, Skysmith, Minesweeper, Shimmin, Egil, Mkweise, Ellywa,Ahoerstemeier, Mgimpel, Suisui, Den fjttrade ankan, JWSchmidt, Mark Foskey, Nikai, Andres, Cimon Avaro, Jedidan747, Lancevor-tex, Mxn, Raven in Orbit, Vargenau, Epo, Schneelocke, Jengod, Emperorbma, Malbi, Molinari, Stone, David Latapie, Paul Stansifer,Wikid, Markhurd, Peregrine981, Freechild, Grendelkhan, Fibonacci, Shizhao, Bcorr, Pakaran, Jerzy, Pollinator, Donarreiskoer, Rob-bot, Vespristiano, Altenmann, Romanm, Naddy, Arkuat, Academic Challenger, Kn1kda, Rursus, Caknuck, Bkell, Moink, Hadal, Profoss,Anthony, Komet, Lupo, Dina, Alan Liefting, Giftlite, DocWatson42, Marnanel, Gene Ward Smith, BenFrantzDale, Bork, Tom harrison,Peruvianllama, Everyking, Dratman, Alison, Bensaccount, Frencheigh, Jfdwol, Unconcerned, Duncharris, Ptk, Mboverload, Eequor, Re-dux, Darrien, Chameleon, Booradley74, Bobblewik, Tagishsimon, Delta G, Mmm, Chowbok, SoWhy, Pgan002, Toytoy, Geni, Knutux,Zeimusu, SlowkingMan, Akkolon, Quadell, DCrazy, Antandrus, HorsePunchKid, Cjewell, TheMoUsY spell-checker, Oneiros, Rogerzilla,Icairns, Karl-Henner, Arcturus, B.d.mills, Wyllium, LiSrt, Adashiel, Trevor MacInnis, Mike Rosoft, Frankchn, PZFUN, Archer3, CALR,Ultratomio, EugeneZelenko, Noisy, Discospinster, Solitude, Rich Farmbrough, Guanabot, Brutannica, Cacycle, Vsmith, Spundun, Flo-rian Blaschke, LeeHunter, Dbachmann, Paul August, Bender235, Rubicon, ESkog, Kbh3rd, Kjoonlee, FrankCostanza, Neko-chan, EricForste, Brian0918, RJHall, CanisRufus, MBisanz, El C, Lankiveil, Joanjoc, Kwamikagami, Edward Z. Yang, Shanes, Joaopais, Roy-Boy, ~K, Femto, Jpgordon, Bobo192, O18, Jsw09, Smalljim, Shenme, Vortexrealm, AllyUnion, SpeedyGonsales, Chirag, La goutte depluie, Rajah, Colonel Cow, Sam Korn, Haham hanuka, Pearle, Jumbuck, Siim, Alansohn, PaulHanson, Nik42, Arthena, Keenan Pepper,Plumbago, Sl, Riana, AzaToth, Lectonar, Splat, Walkerma, Bart133, Snowolf, Ross Burgess, Wtmitchell, Dabbler, Paul1337, 03williss,Naif, NickMartin, Gpvos, RainbowOfLight, Dirac1933, Sciurin, Bsadowski1, BlastOButter42, Freyr, Icco, Gene Nygaard, Dan100,Kenyon, Oleg Alexandrov, Tariqabjotu, Ron Ritzman, Gatewaycat, Lkinkade, Thryduulf, Philthecow, Velho, Pekinensis, Firsfron, LOL,Uncle G, Oliphaunt, Benbest, JeremyA, Stevedegrace, Fred J, Eleassar777, Firien, Bbatsell, Damicatz, Optichan, Steinbach, Sengkang,Zzyzx11, Xiong Chiamiov, Prashanthns, Karam.Anthony.K, Jimtheralley, Dysepsion, MrSomeone, Ashmoo, JEB90, Graham87, Raivein,V8rik, Kbdank71, FreplySpang, JIP, Zzedar, DePiep, Jclemens, Bikeable, Grammarbot, 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Stan J Klimas, Gman124, Ignatzmice, Janus Shadowsong, Kaimiikekamaila, Ahsaniqbal 93,Coppertwig, (jarbarf), Warut, LittleHow, Rominandreu, Trilobitealive, DadaNeem, SJP, NukoMAN, Bobianite, KCinDC, Babedacus,Juliancolton, Cometstyles, Bintang123, WJBscribe, Glyns, Jamesontai, Tibetologist, CuddlySteve, Ja 62, JavierMC, Takiasuu, Useight,Jazzmansam, Halmstad, Xiahou, Squids and Chips, CardinalDan, Richard New Forest, Idioma-bot, Rossnorman, 28bytes, VolkovBot,ABF, Armetrek, Je G., Jennavecia, AlnoktaBOT, Soliloquial, Bartosik, Philip Trueman, Joecunningham2, BSMet94, TXiKiBoT, Issac-newton saif, Jackthebumblebee, Rockstar915, Rei-bot, SK41, Logan242, Donkeyscantalk, Qxz, Backinblack92, Lradrama, Rscott282,Corvus cornix, Martin451, Don4of4, Slysplace, Hienz44, Andylu, Keithm 007, Psyche825, Mumu816, Seb az86556, UnitedStatesian,Martyn1987, Jvbishop, Evil dude69, CO, Plazak, Llajwa, Lerdthenerd, Dirkbb, ChallengeSpacePedia, Carinemily, Synthebot, Veganfa-natic, Geprodis, Enviroboy, 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13.2 Images 17

Lazarus1907, Pinkadelica, Nergaal, Jons63, Escape Orbit, Explicit, TheCatalyst31, SpectrumAnalyser, Spirosv, ClueBot, Avenged Eight-fold, PipepBot, The Thing That Should Not Be, Limebite, IceUnshattered, Arakunem, Saddhiyama, Drmies, Shinpah1, CounterVandalism-Bot, LizardJr8, Shjacks45, Neverquick, Mayqueen2, Puchiko, Jacques47, Metalxzxz, DragonBot, Begaluki, Excirial, Andy pyro, Muhan-des, SpikeToronto, Shinkolobwe, Lajimmy, LarryMorseDCOhio, Dekisugi, Grisunge, Thingg, Aitias, Plasmic Physics, Macpros561, HisManliness, Coin167, Vanished User 1004, Chhe, DumZiBoT, RMFan1, Finalnight, Crazy Boris with a red beard, XLinkBot, Drinkcoco,Yojimbo501, Humblekabc, Ekke44, Gnowor, Gundog48, Takashi 29, Dark Mage, Rror, AMRDeuce, Bradv, Asder smit, Wikiislove997,Little Mountain 5, Demonic cube, SilvonenBot, PL290, Noctibus, Bit Lordy, ElMeBot, Bob23456, Ketchup krew, Playinpoker4alivin,Applepie231, PengiunMan, Basilicofresco, Denali134, Tbarkley12, Willking1979, Some jerk on the Internet, DOI bot, Friginator, Orci,Holt, Nikhilvijay raut, TutterMouse, Franky1985, Fieldday-sunday, CanadianLinuxUser, Leszek Jaczuk, Chaza super man, Lon of Oak-dale, CarsracBot, RTG, Mjr162006, Ld100, Debresser, Lines Away, Lucian Sunday, HappyXD, LinkFA-Bot, West.andrew.g, Da pope224,Smartguy71, Pominthehouse, Numbo3-bot, Krepusculoko, Pomlikespee, Saltanon, Tide rolls, Lightbot, Avono, Luckas Blade, Gail, Jarble,Greyhood, Arbitrarily0, Jkaresh, Brucem101, Sammoth55, Ben Ben, Siduk, Luckas-bot, Yobot, 2D, Fraggle81, Xu Davella, II MusLiMHyBRiD II, Hulek, Kilom691, DB.Gerry, THENWHOWAS PHONE?, KamikazeBot, Plasticbot, South Bay, , Synchronism,AnomieBOT, Tigax, Hrneo, Jim1138, Mistaya, JackieBot, Piano non troppo, Apau98, Theseeker4, Ulric1313, Materialscientist, RafeekMalotra, Citation bot, Prabhat278205, E2eamon, Didsrocks, Neurolysis, ArthurBot, LilHelpa, Aksel89, MauritsBot, Xqbot, S h i v a(Visnu), Sionus, Gopal81, Cureden, Klozglowski, PangYikHei, Srich32977, Almabot, Apollo1195, Hax fax, Mwcmatthew, George94, Ri-botBOT, SassoBot, Chris.urs-o, Chedder14, Gbruin, Ulm, Basharh, Brutaldeluxe, Doulos Christos, IcedNut, Dmitriduggan, DeNoel, Reb-bing, GT5162, Maddydonnelly, FrescoBot, Foo1942, Tobby72, Eldin raigmore, Peterapple, Deadskull56, Citation bot 1, Pinethicket, Ab-ductive, Fuzbaby, 10metreh, Jonesey95, Tom.Reding, RedBot, MastiBot, GentleMiant, Xeworlebi, Pristino, KnowledgeRequire, FoxBot,Double sharp, TobeBot, Ticklewickleukulele, Dinamik-bot, Vrenator, Pepper543210, Begoon, Reaper Eternal, Lghoel, Diannaa, Kcsk1998,MacCambridge, DARTH SIDIOUS 2, Whisky drinker, The Utahraptor, Bondith, Regancy42, Slon02, EmausBot, John of Reading, Wik-itanvirBot, GoingBatty, 1Martin33, NotAnonymous0, Tommy2010, Wikipelli, P. S. F. Freitas, Sheeana, ZroBot, F, Neonightshade,StringTheory11, Denver & Rio Grande, Chemicalinterest, Bustermythmonger, KarthikSoun, SporkBot, AManWithNoPlan, Wayne Slam,Trippinshrumes, Metallica23, IGeMiNix, Brandmeister, L Kensington, Jj98, MonoAV, Anonimski, Edward001, Holbenilord, Ego WhiteTray, Mentibot, ChuispastonBot, Magneticlifeform, Hej1337, DASHBotAV, Whoop whoop pull up, Mjbmrbot, Special Cases, ClueBotNG, Malanoqa, Abrahamschulte, XD0248, Lanthanum-138, Monsoon Waves, S.kamber, Morgan Riley, Rurik the Varangian, T-piston,Nao1958, Jk2q3jrklse, Kemal Koza, Helpful Pixie Bot, Art and Muscle, JohnSRoberts99, Gob Lofa, Bibcode Bot, Doorknob747, Todan,Grimmeh, TomeHale, Zedshort, Duxwing, Lieutenant of Melkor, 4Jays1034, He to Hecuba, JYBot, 3bobby123, Harsh 2580, Dexbot, We-bclient101, GaryMHoover, Numbermaniac, TheArowPro, Jnargus, Reatlas, CensoredScribe, AioftheStorm, Schwobator, Ramendoctor,Kind Tennis Fan, Medmyco, Connymenzel, Benjamaster1, Monkbot, Ca2james, Heytrevorthisisscott, Wynstol and Anonymous: 1363

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18 13 TEXT AND IMAGE SOURCES, CONTRIBUTORS, AND LICENSES

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CharacteristicsMechanical propertiesPhase diagram and allotropesIsotopesNucleosynthesisOccurrencePlanetary occurrenceStocks in use in society

Chemistry and compoundsBinary compoundsCoordination and organometallic compounds

HistoryWrought ironCast ironSteelFoundations of modern chemistry

Production of metallic ironIndustrial routesBlast furnace processingDirect iron reductionFurther processes

Laboratory methods

ApplicationsMetallurgicalIron compounds

Biological roleBioinorganic compoundsHealth and dietUptake and storageRegulation of uptakeBioremediationPermeable reactive barriers

ToxicitySee alsoReferencesBibliographyFurther readingExternal linksText and image sources, contributors, and licensesTextImagesContent license