Iron is a chemical element with symbol Fe (from Latin: ferrum) and atomic number 26. It is a metal in the first transition series. It is by mass the most common element on Earth, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust. Its abundance in rocky planets like Earth is due to its abundant production by fusion in high-mass stars, where it is the last element to be produced with release of energy before the violent collapse of a supernova, which scatters the iron into space.
Like the other group 8 elements, ruthenium and osmium, iron exists in a wide range of oxidation states, −2 to +7, although +2 and +3 are the most common. Elemental iron occurs in meteoroids and other low oxygen environments, but is reactive to oxygen and water. Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust. Unlike the metals that form passivating oxide layers, iron oxides occupy more volume than the metal and thus flake off, exposing fresh surfaces for corrosion.
Iron metal has been used since ancient times, although copper alloys, which have lower melting temperatures, were used even earlier in human history. Pure iron is relatively soft, but is unobtainable by smelting because it is significantly hardened and strengthened by impurities, in particular carbon, from the smelting process. A certain proportion of carbon (between 0.002% and 2.1%) produces steel, which may be up to 1000 times harder than pure iron. Crude iron metal is produced in blast furnaces, where ore is reduced by coke to pig iron, which has a high carbon content. Further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and iron alloys formed with other metals (alloy steels) are by far the most common industrial metals because they have a great range of desirable properties and iron-bearing rock is abundant.
Iron chemical compounds have many uses. Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. Iron forms binary compounds with the halogens and the chalcogens. Among its organometallic compounds is ferrocene, the first sandwich compound discovered.
Iron plays an important role in biology, forming complexes with molecular oxygen in hemoglobin and myoglobin; these two compounds are common oxygen-handling proteins in vertebrates (hemoglobin for oxygen transport, and myoglobin for oxygen storage). Iron is also the metal at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals. Iron is distributed throughout the human body, and is especially abundant in hemoglobin. Total iron content of the adult human body is approximately 3.8 grams in males and 2.3 grams in females. Iron is a critical element in the metabolism of hundreds of proteins and enzymes involved in diverse body functions, such as oxygen transport, DNA synthesis, and cell growth.
|Appearance||lustrous metallic with a grayish tinge|
|Standard atomic weight Ar, std(Fe)||55.845(2)|
|Iron in the periodic table|
|Atomic number (Z)||26|
|Element category||transition metal|
|Electron configuration||[Ar] 3d6 4s2|
Electrons per shell
|2, 8, 14, 2|
|Phase at STP||solid|
|Melting point||1811 K (1538 °C, 2800 °F)|
|Boiling point||3134 K (2862 °C, 5182 °F)|
|Density (near r.t.)||7.874 g/cm3|
|when liquid (at m.p.)||6.98 g/cm3|
|Heat of fusion||13.81 kJ/mol|
|Heat of vaporization||340 kJ/mol|
|Molar heat capacity||25.10 J/(mol·K)|
|Oxidation states||−4, −2, −1, +1, +2, +3, +4, +5, +6, +7 (an amphoteric oxide)|
|Electronegativity||Pauling scale: 1.83|
|Atomic radius||empirical: 126 pm|
|Covalent radius||Low spin: 132±3 pm|
High spin: 152±6 pm
Spectral lines of iron
|Crystal structure|| body-centered cubic (bcc)|
|Crystal structure|| face-centered cubic (fcc)|
between 1185–1667 K
|Speed of sound thin rod||5120 m/s (at r.t.) (electrolytic)|
|Thermal expansion||11.8 µm/(m·K) (at 25 °C)|
|Thermal conductivity||80.4 W/(m·K)|
|Electrical resistivity||96.1 nΩ·m (at 20 °C)|
|Curie point||1043 K|
|Young's modulus||211 GPa|
|Shear modulus||82 GPa|
|Bulk modulus||170 GPa|
|Vickers hardness||608 MPa|
|Brinell hardness||200–1180 MPa|
|Discovery||before 5000 BC|
|Main isotopes of iron|
|Pure, single-crystal iron||10||3|
The mechanical properties of iron and its alloys can be evaluated using a variety of tests, including the Brinell test, Rockwell test and the Vickers hardness test. The data on iron is so consistent that it is often used to calibrate measurements or to compare tests. However, the mechanical properties of iron are significantly affected by the sample's purity: pure, single crystals of iron are actually softer than aluminium, and the purest industrially produced iron (99.99%) has a hardness of 20–30 Brinell. An increase in the carbon content will cause a significant increase in the hardness and tensile strength of iron. Maximum hardness of 65 Rc is achieved with a 0.6% carbon content, although the alloy has low tensile strength. Because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium.
Because of its significance for planetary cores, the physical properties of iron at high pressures and temperatures have also been studied extensively. The form of iron that is stable under standard conditions can be subjected to pressures up to ca. 15 GPa before transforming into a high-pressure form, as described in the next section.
Iron represents an example of allotropy in a metal. At least four allotropic forms of iron are known as α, γ, δ, and ε; at very high pressures and temperatures, some controversial experimental evidence exists for a stable β phase.
As molten iron cools past its freezing point of 1538 °C, it crystallizes into its δ allotrope, which has a body-centered cubic (bcc) crystal structure. As it cools further to 1394 °C, it changes to its γ-iron allotrope, a face-centered cubic (fcc) crystal structure, or austenite. At 912 °C and below, the crystal structure again becomes the bcc α-iron allotrope. Finally, at 770 °C (the Curie point, Tc) iron's magnetic ordering changes from paramagnetic to ferromagnetic. As it passes through the Curie temperature, iron does not change its structure, but "magnetic domains" appear, where each domain contains iron atoms with a particular electronic spin. In unmagnetized iron, all the electronic spins of the atoms within one domain have the same axis orientation; however, the electrons of neighboring domains have other orientations with the result of mutual cancellation and no magnetic field. In magnetized iron, the electronic spins of the domains are aligned and the magnetic effects are reinforced. Although each domain contains billions of atoms, they are very small, about 10 micrometres across. This happens because the two unpaired electrons on each iron atom are in the dz2 and dx2 − y2 orbitals, which do not point directly at the nearest neighbors in the body-centered cubic lattice and therefore do not participate in metallic bonding; thus, they can interact magnetically with each other so that their spins align.
At pressures above approximately 10 GPa and temperatures of a few hundred kelvin or less, α-iron changes into a hexagonal close-packed (hcp) structure, which is also known as ε-iron; the higher-temperature γ-phase also changes into ε-iron, but does so at higher pressure. The β-phase, if it exists, would appear at pressures of at least 50 GPa and temperatures of at least 1500 K and have an orthorhombic or a double hcp structure. These high-pressure phases of iron are important as endmember models for the solid parts of planetary cores. The inner core of the Earth is generally presumed to be an iron-nickel alloy with ε (or β) structure. Somewhat confusingly, the term "β-iron" is sometimes also used to refer to α-iron above its Curie point, when it changes from being ferromagnetic to paramagnetic, even though its crystal structure has not changed.
The melting point of iron is experimentally well defined for pressures less than 50 GPa. For greater pressures, studies put the γ-ε-liquid triple point at pressures that differ by tens of gigapascals and 1000 K in the melting point. Generally speaking, molecular dynamics computer simulations of iron melting and shock wave experiments suggest higher melting points and a much steeper slope of the melting curve than static experiments carried out in diamond anvil cells. The melting and boiling points of iron, along with its enthalpy of atomization, are lower than those of the earlier 3d elements from scandium to chromium, showing the lessened contribution of the 3d electrons to metallic bonding as they are attracted more and more into the inert core by the nucleus; however, they are higher than the values for the previous element manganese because that element has a half-filled 3d subshell and consequently its d-electrons are not easily delocalized. This same trend appears for ruthenium but not osmium.
Naturally occurring iron consists of four stable isotopes: 5.845% of 54Fe, 91.754% of 56Fe, 2.119% of 57Fe and 0.282% of 58Fe. Of these stable isotopes, only 57Fe has a nuclear spin (−1⁄2). The nuclide 54Fe theoretically can undergo double electron capture to 54Cr, but the process has never been observed and only a lower limit on the half-life of 3.1×1022 years has been established.
60Fe is an extinct radionuclide of long half-life (2.6 million years). It is not found on Earth, but its ultimate decay product is its granddaughter, the stable nuclide 60Ni. Much of the past work on isotopic composition of iron has focused on the nucleosynthesis of 60Fe through studies of meteorites and ore formation. In the last decade, advances in mass spectrometry have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work is driven by the Earth and planetary science communities, although applications to biological and industrial systems are emerging.
In phases of the meteorites Semarkona and Chervony Kut, a correlation between the concentration of 60Ni, the granddaughter of 60Fe, and the abundance of the stable iron isotopes provided evidence for the existence of 60Fe at the time of formation of the Solar System. Possibly the energy released by the decay of 60Fe, along with that released by 26Al, contributed to the remelting and differentiation of asteroids after their formation 4.6 billion years ago. The abundance of 60Ni present in extraterrestrial material may bring further insight into the origin and early history of the Solar System.
The most abundant iron isotope 56Fe is of particular interest to nuclear scientists because it represents the most common endpoint of nucleosynthesis. Since 56Ni (14 alpha particles) is easily produced from lighter nuclei in the alpha process in nuclear reactions in supernovae (see silicon burning process), it is the endpoint of fusion chains inside extremely massive stars, since addition of another alpha particle, resulting in 60Zn, requires a great deal more energy. This 56Ni, which has a half-life of about 6 days, is created in quantity in these stars, but soon decays by two successive positron emissions within supernova decay products in the supernova remnant gas cloud, first to radioactive 56Co, and then to stable 56Fe. As such, iron is the most abundant element in the core of red giants, and is the most abundant metal in iron meteorites and in the dense metal cores of planets such as Earth. It is also very common in the universe, relative to other stable metals of approximately the same atomic weight. Iron is the sixth most abundant element in the Universe, and the most common refractory element.
Although a further tiny energy gain could be extracted by synthesizing 62Ni, which has a marginally higher binding energy than 56Fe, conditions in stars are unsuitable for this process. Element production in supernovas and distribution on Earth greatly favor iron over nickel, and in any case, 56Fe still has a lower mass per nucleon than 62Ni due to its higher fraction of lighter protons. Hence, elements heavier than iron require a supernova for their formation, involving rapid neutron capture by starting 56Fe nuclei.
In the far future of the universe, assuming that proton decay does not occur, cold fusion occurring via quantum tunnelling would cause the light nuclei in ordinary matter to fuse into 56Fe nuclei. Fission and alpha-particle emission would then make heavy nuclei decay into iron, converting all stellar-mass objects to cold spheres of pure iron.
Metallic or native iron is rarely found on the surface of the Earth because it tends to oxidize, but its oxides are pervasive and represent the primary ores. While it makes up about 5% of the Earth's crust, both the Earth's inner and outer core are believed to consist largely of an iron-nickel alloy constituting 35% of the mass of the Earth as a whole. Iron is consequently the most abundant element on Earth, but only the fourth most abundant element in the Earth's crust, after oxygen, silicon, and aluminium. Most of the iron in the crust is found combined with oxygen as iron oxide minerals such as hematite (Fe2O3), magnetite (Fe3O4), and siderite (FeCO3). Many igneous rocks also contain the sulfide minerals pyrrhotite and pentlandite.
Ferropericlase (Mg,Fe)O, a solid solution of periclase (MgO) and wüstite (FeO), makes up about 20% of the volume of the lower mantle of the Earth, which makes it the second most abundant mineral phase in that region after silicate perovskite (Mg,Fe)SiO3; it also is the major host for iron in the lower mantle. At the bottom of the transition zone of the mantle, the reaction γ-(Mg,Fe)2[SiO4] ↔ (Mg,Fe)[SiO3] + (Mg,Fe)O transforms γ-olivine into a mixture of silicate perovskite and ferropericlase and vice versa. In the literature, this mineral phase of the lower mantle is also often called magnesiowüstite. Silicate perovskite may form up to 93% of the lower mantle, and the magnesium iron form, (Mg,Fe)SiO3, is considered to be the most abundant mineral in the Earth, making up 38% of its volume.
Large deposits of iron are found in banded iron formations. These geological formations are a type of rock consisting of repeated thin layers of iron oxides alternating with bands of iron-poor shale and chert. The banded iron formations were laid down in the time between and .
The mentioned iron compounds have been used as pigments (compare ochre) since historical time and contribute as well to the color of various geological formations, e.g. the Buntsandstein (British Bunter, colored sandstein). In the case of the Eisensandstein (a jurassic 'iron sandstone', e.g. from Donzdorf) in Germany and Bath stone in the UK, iron pigments contribute to the yellowish color of large amounts of historical buildings and sculptures. The proverbial red color of the surface of Mars is derived from an iron oxide-rich regolith.
Significant amounts of iron occur in the iron sulfide mineral pyrite (FeS2), but it is difficult to extract iron from it and it is therefore not used. In fact, iron is so common that production generally focuses only on ores with very high quantities of it. During weathering, iron tends to leach from sulfide deposits as the sulfate and from silicate deposits as the bicarbonate. Both of these are oxidized in aqueous solution and precipitate in even mildly elevated pH as iron(III) oxide.
About 1 in 20 meteorites consist of the unique iron-nickel minerals taenite (35–80% iron) and kamacite (90–95% iron). Although rare, iron meteorites are the main form of natural metallic iron on the Earth's surface. According to the International Resource Panel's Metal Stocks in Society report, the global stock of iron in use in society is 2200 kg per capita. More-developed countries differ in this respect from less-developed countries (7000–14000 vs 2000 kg per capita).
|−2 (d10)||Disodium tetracarbonylferrate (Collman's reagent)|
|0 (d8)||Iron pentacarbonyl|
|1 (d7)||Cyclopentadienyliron dicarbonyl dimer ("Fp2")|
|2 (d6)||Ferrous sulfate, ferrocene|
|3 (d5)||Ferric chloride, ferrocenium tetrafluoroborate|
|6 (d2)||Potassium ferrate|
|7 (d1)||[FeO4]– (matrix isolation, 4K)|
Iron shows the characteristic chemical properties of the transition metals, namely the ability to form variable oxidation states differing by steps of one and a very large coordination and organometallic chemistry: indeed, it was the discovery of an iron compound, ferrocene, that revolutionalized the latter field in the 1950s. Iron is sometimes considered as a prototype for the entire block of transition metals, due to its abundance and the immense role it has played in the technological progress of humanity. Its 26 electrons are arranged in the configuration [Ar]3d64s2, of which the 3d and 4s electrons are relatively close in energy, and thus it can lose a variable number of electrons and there is no clear point where further ionization becomes unprofitable.
Iron forms compounds mainly in the +2 and +3 oxidation states. Traditionally, iron(II) compounds are called ferrous, and iron(III) compounds ferric. Iron also occurs in higher oxidation states, e.g. the purple potassium ferrate (K2FeO4), which contains iron in its +6 oxidation state. Although iron(VIII) oxide (FeO4) has been claimed, the report could not be reproduced and such a species (at least with iron in its +8 oxidation state) has been found to be improbable computationally. However, one form of anionic [FeO4]– with iron in its +7 oxidation state, along with an iron(V)-peroxo isomer, has been detected by infrared spectroscopy at 4 K after cocondensation of laser-ablated Fe atoms with a mixture of O2/Ar. Iron(IV) is a common intermediate in many biochemical oxidation reactions. Numerous organoiron compounds contain formal oxidation states of +1, 0, −1, or even −2. The oxidation states and other bonding properties are often assessed using the technique of Mössbauer spectroscopy. Many mixed valence compounds contain both iron(II) and iron(III) centers, such as magnetite and Prussian blue (Fe4(Fe[CN]6)3). The latter is used as the traditional "blue" in blueprints.
Iron is the first of the transition metals that cannot reach its group oxidation state of +8, although its heavier congeners ruthenium and osmium can, with ruthenium having more difficulty than osmium. Ruthenium exhibits an aqueous cationic chemistry in its low oxidation states similar to that of iron, but osmium does not, favoring high oxidation states in which it forms anionic complexes. In the second half of the 3d transition series, vertical similarities down the groups compete with the horizontal similarities of iron with its neighbors cobalt and nickel in the periodic table, which are also ferromagnetic at room temperature and share similar chemistry. As such, iron, cobalt, and nickel are sometimes grouped together as the iron triad.
The iron compounds produced on the largest scale in industry are iron(II) sulfate (FeSO4·7H2O) and iron(III) chloride (FeCl3). The former is one of the most readily available sources of iron(II), but is less stable to aerial oxidation than Mohr's salt ((NH4)2Fe(SO4)2·6H2O). Iron(II) compounds tend to be oxidized to iron(III) compounds in the air.
Iron is by far the most reactive element in its group; it is pyrophoric when finely divided and dissolves easily in dilute acids, giving Fe2+. However, it does not react with concentrated nitric acid and other oxidizing acids due to the formation of an impervious oxide layer, which can nevertheless react with hydrochloric acid.
Iron reacts with oxygen in the air to form various oxide and hydroxide compounds; the most common are iron(II,III) oxide (Fe3O4), and iron(III) oxide (Fe2O3). Iron(II) oxide also exists, though it is unstable at room temperature. Despite their names, they are actually all non-stoichiometric compounds whose compositions may vary. These oxides are the principal ores for the production of iron (see bloomery and blast furnace). They are also used in the production of ferrites, useful magnetic storage media in computers, and pigments. The best known sulfide is iron pyrite (FeS2), also known as fool's gold owing to its golden luster. It is not an iron(IV) compound, but is actually an iron(II) polysulfide containing Fe2+ and S2−
2 ions in a distorted sodium chloride structure.
The binary ferrous and ferric halides are well-known, with the exception of ferric iodide. The ferrous halides typically arise from treating iron metal with the corresponding hydrohalic acid to give the corresponding hydrated salts.
Ferric iodide is an exception, being thermodynamically unstable due to the oxidizing power of Fe3+ and the high reducing power of I−:
Nevertheless, milligram amounts of ferric iodide, a black solid, may still be prepared through the reaction of iron pentacarbonyl with iodine and carbon monoxide in the presence of hexane and light at the temperature of −20 °C, making sure that the system is well sealed off from air and water.
|Fe2+ + 2 e−||⇌ Fe||E0 = −0.447 V|
|Fe3+ + 3 e−||⇌ Fe||E0 = −0.037 V|
4 + 8 H+ + 3 e−
|⇌ Fe3+ + 4 H2O||E0 = +2.20 V|
The Fe3+ ion has a large simple cationic chemistry, although the pale-violet hexaquo ion [Fe(H2O)6]3+ is very readily hydrolyzed when pH increases above 0 as follows:
|[Fe(H2O)6]3+||⇌ [Fe(H2O)5(OH)]2+ + H+||K = 10−3.05 mol dm−3|
|[Fe(H2O)5(OH)]2+||⇌ [Fe(H2O)4(OH)2]+ + H+||K = 10−3.26 mol dm−3|
|2 [Fe(H2O)6]3+||⇌ [Fe(H
2 + 2 H+ + 2 H2O
|K = 10−2.91 mol dm−3|
As pH rises above 0 the above yellow hydrolyzed species form and as it rises above 2–3, reddish-brown hydrous iron(III) oxide precipitates out of solution. Although Fe3+ has an d5 configuration, its absorption spectrum is not like that of Mn2+ with its weak, spin-forbidden d–d bands, because Fe3+ has higher positive charge and is more polarizing, lowering the energy of its ligand-to-metal charge transfer absorptions. Thus, all the above complexes are rather strongly colored, with the single exception of the hexaquo ion – and even that has a spectrum dominated by charge transfer in the near ultraviolet region. On the other hand, the pale green iron(II) hexaquo ion [Fe(H2O)6]2+ does not undergo appreciable hydrolysis. Carbon dioxide is not evolved when carbonate anions are added, which instead results in white iron(II) carbonate being precipitated out. In excess carbon dioxide this forms the slightly soluble bicarbonate, which occurs commonly in groundwater, but it oxidises quickly in air to form iron(III) oxide that accounts for the brown deposits present in a sizeable number of streams.
Many coordination compounds of iron are known. A typical six-coordinate anion is hexachloroferrate(III), [FeCl6]3−, found in the mixed salt tetrakis(methylammonium) hexachloroferrate(III) chloride. Complexes with multiple bidentate ligands have geometric isomers. For example, the trans-chlorohydridobis(bis-1,2-(diphenylphosphino)ethane)iron(II) complex is used as a starting material for compounds with the Fe(dppe)2 moiety. The ferrioxalate ion with three oxalate ligands (shown at right) displays helical chirality with its two non-superposable geometries labelled Λ (lambda) for the left-handed screw axis and Δ (delta) for the right-handed screw axis, in line with IUPAC conventions. Potassium ferrioxalate is used in chemical actinometry and along with its sodium salt undergoes photoreduction applied in old-style photographic processes. The dihydrate of iron(II) oxalate has a polymeric structure with co-planar oxalate ions bridging between iron centres with the water of crystallisation located forming the caps of each octahedron, as illustrated below.
Prussian blue, Fe4[Fe(CN)6]3, is the most famous of the cyanide complexes of iron. Its formation can be used as a simple wet chemistry test to distinguish between aqueous solutions of Fe2+ and Fe3+ as they react (respectively) with potassium ferricyanide and potassium ferrocyanide to form Prussian blue.
Iron(III) complexes are quite similar to those of chromium(III) with the exception of iron(III)'s preference for O-donor instead of N-donor ligands. The latter tend to be rather more unstable than iron(II) complexes and often dissociate in water. Many Fe–O complexes show intense colors and are used as tests for phenols or enols. For example, in the ferric chloride test, used to determine the presence of phenols, iron(III) chloride reacts with a phenol to form a deep violet complex:
Among the halide and pseudohalide complexes, fluoro complexes of iron(III) are the most stable, with the colorless [FeF5(H2O)]2− being the most stable in aqueous solution. Chloro complexes are less stable and favor tetrahedral coordination as in [FeCl4]−; [FeBr4]− and [FeI4]− are reduced easily to iron(II). Thiocyanate is a common test for the presence of iron(III) as it forms the blood-red [Fe(SCN)(H2O)5]2+. Like manganese(II), most iron(III) complexes are high-spin, the exceptions being those with ligands that are high in the spectrochemical series such as cyanide. An example of a low-spin iron(III) complex is [Fe(CN)6]3−. The cyanide ligands may easily be detached in [Fe(CN)6]3−, and hence this complex is poisonous, unlike the iron(II) complex [Fe(CN)6]4− found in Prussian blue, which does not release hydrogen cyanide except when dilute acids are added. Iron shows a great variety of electronic spin states, including every possible spin quantum number value for a d-block element from 0 (diamagnetic) to 5⁄2 (5 unpaired electrons). This value is always half the number of unpaired electrons. Complexes with zero to two unpaired electrons are considered low-spin and those with four or five are considered high-spin.
Iron(II) complexes are less stable than iron(III) complexes but the preference for O-donor ligands is less marked, so that for example [Fe(NH3)6]2+ is known while [Fe(NH3)6]3+ is not. They have a tendency to be oxidized to iron(III) but this can be moderated by low pH and the specific ligands used.
Cyanide complexes are technically organometallic but more important are carbonyl complexes and sandwich and half-sandwich compounds. The premier iron(0) compound is iron pentacarbonyl, Fe(CO)5, which is used to produce carbonyl iron powder, a highly reactive form of metallic iron. Thermolysis of iron pentacarbonyl gives the trinuclear cluster, triiron dodecacarbonyl. Collman's reagent, disodium tetracarbonylferrate, is a useful reagent for organic chemistry; it contains iron in the −2 oxidation state. Cyclopentadienyliron dicarbonyl dimer contains iron in the rare +1 oxidation state.
Ferrocene was an extremely important compound in the early history of the branch of organometallic chemistry, and to this day iron is still one of the most important metals in this field. It was first synthesised in 1951 during an attempt to prepare the fulvalene (C10H8) by oxidative dimerization of cyclopentadiene; the resultant product was found to have molecular formula C10H10Fe and reported to exhibit "remarkable stability". The discovery sparked substantial interest in the field of organometallic chemistry, in part because the structure proposed by Pauson and Kealy (shown at right) was inconsistent with then-existing bonding models and did not explain its unexpected stability. Consequently, the initial challenge was to definitively determine the structure of ferrocene in the hope that its bonding and properties would then be understood. The shockingly novel sandwich structure, [Fe(η5-C5H5)2], was deduced and reported independently by three groups in 1952: Robert Burns Woodward and Geoffrey Wilkinson investigated the reactivity in order to determine the structure and demonstrated that ferrocene undergoes similar reactions to a typical aromatic molecule (such as benzene), Ernst Otto Fischer deduced the sandwich structure and also began synthesising other metallocenes including cobaltocene; Eiland and Pepinsky provided X-ray crystallographic confirmation of the sandwich structure.
Applying valence bond theory to ferrocene by considering an Fe2+ centre and two cyclopentadienide anions (C5H5−), which are known to be aromatic according to Hückel's rule and hence highly stable, allowed correct prediction of the geometry of the molecule. Once molecular orbital theory was successfully applied and the Dewar-Chatt-Duncanson model proposed, the reasons for ferrocene's remarkable stability became clear. Ferrocene was not the first organometallic compound known – Zeise's salt, K[PtCl3(C2H4)]·H2O was reported in 1831 and Mond's discovery of Ni(CO)4 occurred in 1888, but it was ferrocene's discovery that began organometallic chemistry as a separate area of chemistry. It was so important that Wilkinson and Fischer shared the 1973 Nobel Prize for Chemistry "for their pioneering work, performed independently, on the chemistry of the organometallic, so called sandwich compounds". Ferrocene itself can be used as the backbone of a ligand, e.g. 1,1'-bis(diphenylphosphino)ferrocene (dppf). Ferrocene can itself be oxidized to the ferrocenium cation (Fc+); the ferrocene/ferrocenium couple is often used as a reference in electrochemistry.
Metallocenes like ferrocene can be prepared by reaction of freshly-cracked cyclopentadiene with iron(II) chloride and base. It is an aromatic substance and undergoes substitution reactions rather than addition reactions on the cyclopentadienyl ligands. For example, Friedel-Crafts acylation of ferrocene with acetic anhydride yields acetylferrocene just as acylation of benzene yields acetophenone under similar conditions.
As iron has been in use for such a long time, it has many different names in different languages. The source of its chemical symbol Fe is the Latin word ferrum, and its descendants are the names of the element in the Romance languages (for example, French fer, Spanish hierro, and Italian and Portuguese ferro). The word ferrum itself possibly comes from the Semitic languages, via Etruscan, from a root that also gave rise to Old English bræs "brass". The English word iron derives ultimately from Proto-Germanic *isarnan, which is also the source of the German name Eisen. It was most likely borrowed from Celtic *isarnon, which ultimately comes from Proto-Indo-European *is-(e)ro- "powerful, holy" and finally *eis "strong", referencing iron's strength as a metal. Kluge relates *isarnon to Illyric and Latin ira, 'wrath'). The Balto-Slavic names for iron (e.g. Russian железо [zhelezo], Polish żelazo, Lithuanian geležis) are the only ones to come directly from the Proto-Indo-European *ghelgh- "iron". In many of these languages, the word for iron may also be used to denote other objects made of iron or steel, or figuratively because of the hardness and strength of the metal. The Chinese tiě (traditional 鐵; simplified 铁) derives from Proto-Sino-Tibetan *hliek, and was borrowed into Japanese as 鉄 tetsu, which also has the native reading kurogane "black metal" (similar to how iron is referenced in the English word blacksmith).
Iron is one of the elements undoubtedly known to the ancient world. It has been worked, or wrought, for millennia. However, iron objects of great age are much rarer than objects made of gold or silver due to the ease with which iron corrodes.
Beads made from meteoric iron in 3500 BC or earlier were found in Gerzah, Egypt by G.A. Wainwright. The beads contain 7.5% nickel, which is a signature of meteoric origin since iron found in the Earth's crust generally has only minuscule nickel impurities. Meteoric iron was highly regarded due to its origin in the heavens and was often used to forge weapons and tools. For example, a dagger made of meteoric iron was found in the tomb of Tutankhamun, containing similar proportions of iron, cobalt, and nickel to a meteorite discovered in the area, deposited by an ancient meteor shower. Items that were likely made of iron by Egyptians date from 3000 to 2500 BC. Meteoritic iron is comparably soft and ductile and easily forged by cold working but may get brittle when heated because of the nickel content.
The first iron production started in the Middle Bronze Age but it took several centuries before iron displaced bronze. Samples of smelted iron from Asmar, Mesopotamia and Tall Chagar Bazaar in northern Syria were made sometime between 3000 and 2700 BC. The Hittites established an empire in north-central Anatolia around 1600 BC. They appear to be the first to understand the production of iron from its ores and regard it highly in their society. The Hittites began to smelt iron between 1500 and 1200 BC and the practice spread to the rest of the Near East after their empire fell in 1180 BC. The subsequent period is called the Iron Age.
Artifacts of smelted iron are found in India dating from 1800 to 1200 BC, and in the Levant from about 1500 BC (suggesting smelting in Anatolia or the Caucasus). Alleged references (compare history of metallurgy in South Asia) to iron in the Indian Vedas have been used for claims of a very early usage of iron in India respectively to date the texts as such. The rigveda term ayas (metal) probably refers to copper and bronze, while iron or śyāma ayas, literally "black metal", first is mentioned in the post-rigvedic Atharvaveda.
Some archaeological evidence suggests iron was smelted in Zimbabwe and southeast Africa as early as the eighth century BC. Iron working was introduced to Greece in the late 11th century BC, from which it spread quickly throughout Europe.
The spread of ironworking in Central and Western Europe is associated with Celtic expansion. According to Pliny the Elder, iron use was common in the Roman era. The annual iron output of the Roman Empire is estimated at 84750 t, while the similarly populous and contemporary Han China produced around 5000 t. In China, iron only appears circa 700–500 BC. Iron smelting may have been introduced into China through Central Asia. The earliest evidence of the use of a blast furnace in China dates to the 1st century AD, and cupola furnaces were used as early as the Warring States period (403–221 BC). Usage of the blast and cupola furnace remained widespread during the Song and Tang Dynasties.
During the Industrial Revolution in Britain, Henry Cort began refining iron from pig iron to wrought iron (or bar iron) using innovative production systems. In 1783 he patented the puddling process for refining iron ore. It was later improved by others, including Joseph Hall.
Cast iron was first produced in China during 5th century BC, but was hardly in Europe until the medieval period. The earliest cast iron artifacts were discovered by archaeologists in what is now modern Luhe County, Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, and architecture. 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.
Medieval blast furnaces were about 10 feet (3.0 m) tall and made of fireproof brick; forced air was usually provided by hand-operated bellows. Modern blast furnaces have grown much bigger, with hearths fourteen meters in diameter that allow them to produce thousands of tons of iron each day, but essentially operate in much the same way as they did during medieval times.
In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron, replacing charcoal, although continuing to use blast furnaces. The ensuing availability of inexpensive iron was one of the factors leading to the Industrial Revolution. Toward the end of the 18th century, cast iron began to replace wrought iron for certain purposes, because it was cheaper. Carbon content in iron was not implicated as the reason for the differences in properties of wrought iron, cast iron, and steel until the 18th century.
Since iron was becoming cheaper and more plentiful, it also became a major structural material following the building of the innovative first iron bridge in 1778. This bridge still stands today as a monument to the role iron played in the Industrial Revolution. Following this, iron was used in rails, boats, ships, aqueducts, and buildings, as well as in iron cylinders in steam engines. Railways have been central to the formation of modernity and ideas of progress and various languages (e.g. French, Spanish, Italian and German) refer to railways as iron road.
Steel (with smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity by using a bloomery. Blacksmiths in Luristan in western Persia were making good steel by 1000 BC. Then improved versions, Wootz steel by India and Damascus steel were developed around 300 BC and AD 500 respectively. These methods were specialized, and so steel did not become a major commodity until the 1850s.
New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel. In the late 1850s, Henry Bessemer invented a new steelmaking process, involving blowing air through molten pig iron, to produce mild steel. This made steel much more economical, thereby leading to wrought iron no longer being produced in large quantities.
In 1774, Antoine Lavoisier used the reaction of water steam with metallic iron inside an incandescent iron tube to produce hydrogen in his experiments leading to the demonstration of the conservation of mass, which was instrumental in changing chemistry from a qualitative science to a quantitative one.
Iron plays a certain role in mythology and has found various usage as a metaphor and in folklore. The Greek poet Hesiod's Works and Days (lines 109–201) lists different ages of man named after metals like gold, silver, bronze and iron to account for successive ages of humanity. The Iron Age was closely related with Rome, and in Ovid's Metamorphoses
The Virtues, in despair, quit the earth; and the depravity of man becomes universal and complete. Hard steel succeeded then.— Ovid, Metamorphoses, Book I, Iron age, line 160 ff
An example of the importance of iron's symbolic role may be found in the German Campaign of 1813. Frederick William III commissioned then the first Iron Cross as military decoration. Berlin iron jewellery reached its peak production between 1813 and 1815, when the Prussian royal family urged citizens to donate gold and silver jewellery for military funding. The inscription Gold gab ich für Eisen (I gave gold for iron) was used as well in later war efforts.
The production of iron or steel is a process consisting of two main stages. In the first stage pig iron is produced in a blast furnace. Alternatively, it may be directly reduced. In the second stage, pig iron is converted to wrought iron, steel, or cast iron.
For a few limited purposes when it is needed, pure iron is produced in the laboratory in small quantities by reducing the pure oxide or hydroxide with hydrogen, or forming iron pentacarbonyl and heating it to 250 °C so that it decomposes to form pure iron powder. Another method is electrolysis of ferrous chloride onto an iron cathode.
Industrial iron production starts with iron ores, principally hematite, which has a nominal formula Fe2O3, and magnetite, with the formula Fe3O4. These ores are reduced to the metal in a carbothermic reaction, i.e. by treatment with carbon. The conversion is typically conducted in a blast furnace at temperatures of about 2000 °C. Carbon is provided in the form of coke. The process also contains a flux such as limestone, which is used to remove silicaceous minerals in the ore, which would otherwise clog the furnace. The coke and limestone are fed into the top of the furnace, while a massive blast of air heated to 900 °C, about 4 tons per ton of iron, is forced into the furnace at the bottom.
Some iron in the high-temperature lower region of the furnace reacts directly with the coke:
The flux present to melt impurities in the ore is principally limestone (calcium carbonate) and dolomite (calcium-magnesium carbonate). Other specialized fluxes are used depending on the details of the ore. In the heat of the furnace the limestone flux decomposes to calcium oxide (also known as quicklime):
The slag melts in the heat of the furnace. In the bottom of the furnace, the molten slag floats on top of the denser 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.
Owing to environmental concerns, alternative methods of processing iron have been developed. "Direct iron reduction" reduces iron ore to a ferrous lump called "sponge" iron or "direct" iron that is suitable for steelmaking. Two main reactions comprise the direct reduction process:
Natural gas is partially oxidized (with heat and a catalyst):
Iron ore is then treated with these gases in a furnace, producing solid sponge iron:
Iron is a byproduct of burning a mixture of aluminium powder and rust powder.
Pig iron is not pure iron, but has 4–5% carbon dissolved in it with small amounts of other impurities like sulfur, magnesium, phosphorus, and manganese. As the carbon is the major impurity, the iron (pig iron) becomes brittle and hard. Removing the other impurities results in cast iron, which is used to cast articles in foundries; for example stoves, pipes, radiators, lamp-posts, and rails.
Alternatively pig iron may be made into steel (with up to about 2% carbon) or wrought iron (commercially pure iron). Various processes have been used for this, including finery forges, puddling furnaces, Bessemer converters, open hearth furnaces, basic oxygen furnaces, and electric arc furnaces. In all cases, the objective is to oxidize some or all of the carbon, together with other impurities. On the other hand, other metals may be added to make alloy steels.
Iron is the most widely used of all the metals, accounting for over 90% of worldwide metal production. Its low cost and high strength make it indispensable in engineering applications such as the construction of machinery and machine tools, automobiles, the hulls of large ships, and structural components for buildings. Since pure iron is quite soft, it is most commonly combined with alloying elements to make steel.
α-Iron is a fairly soft metal that can dissolve only a small concentration of carbon (no more than 0.021% by mass at 910 °C). Austenite (γ-iron) is similarly soft and metallic but can dissolve considerably more carbon (as much as 2.04% by mass at 1146 °C). This form of iron is used in the type of stainless steel used for making cutlery, and hospital and food-service equipment.
Commercially available iron is classified based on purity and the abundance of additives. Pig iron has 3.5–4.5% carbon and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Pig iron is not a saleable product, but rather an intermediate step in the production of cast iron and steel. The reduction of contaminants in pig iron that negatively affect material properties, such as sulfur and phosphorus, yields cast iron containing 2–4% carbon, 1–6% silicon, and small amounts of manganese. Pig iron 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 and depend on the form the carbon takes in the alloy.
"White" cast irons contain their carbon in the form of cementite, or iron carbide (Fe3C). 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 iron carbide, a very pale, silvery, shiny material, hence the appellation. Cooling a mixture of iron with 0.8% carbon slowly below 723 °C to room temperature results in separate, alternating layers of cementite and α-iron, which is soft and malleable and is called pearlite for its appearance. Rapid cooling, on the other hand, does not allow time for this separation and creates hard and brittle martensite. The steel can then be tempered by reheating to a temperature in between, changing the proportions of pearlite and martensite. The end product below 0.8% carbon content is a pearlite-αFe mixture, and that above 0.8% carbon content is a pearlite-cementite mixture.
In gray iron the carbon exists as separate, fine flakes of graphite, and also renders the material brittle due to the sharp edged flakes of graphite that produce stress concentration sites within the material. A newer variant of gray iron, referred to as ductile iron, is specially treated with trace amounts of magnesium to alter the shape of graphite to spheroids, or nodules, reducing the stress concentrations and vastly increasing the toughness and strength of the material.
Wrought iron contains less than 0.25% carbon but large amounts of slag that give it a fibrous characteristic. It is a tough, malleable product, but not as fusible as pig iron. If honed to an edge, it loses it quickly. Wrought iron is characterized by the presence of fine fibers of slag entrapped within the metal. Wrought iron is more corrosion resistant than steel. It has been almost completely replaced by mild steel for traditional "wrought iron" products and blacksmithing.
|Country||Iron ore||Pig iron||Direct iron||Steel|
Mild steel corrodes more readily than wrought iron, but is cheaper and more widely available. Carbon steel contains 2.0% carbon or less, with small amounts of manganese, sulfur, phosphorus, and silicon. Alloy steels contain varying amounts of carbon as well as other metals, such as chromium, vanadium, molybdenum, nickel, tungsten, etc. Their alloy content raises their cost, and so they are usually only employed for specialist uses. One common alloy steel, though, is stainless steel. 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.
Apart from traditional applications, iron is also used for protection from ionizing radiation. Although it is lighter than another traditional protection material, lead, it is much stronger mechanically. The attenuation of radiation 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, suffer badly from rust if not protected in some way, a cost amounting to over 1% of the world's economy. Painting, galvanization, passivation, plastic coating and bluing are all used to protect iron from rust by excluding water and oxygen or by cathodic protection. The mechanism of the rusting of iron is as follows:
Although the dominant use of iron is in metallurgy, iron compounds are also pervasive in industry. Iron catalysts are traditionally used in the Haber-Bosch process for the production of ammonia and the Fischer-Tropsch process for conversion of carbon monoxide to hydrocarbons for fuels and lubricants. Powdered iron in an acidic solvent was used in the Bechamp reduction the reduction of nitrobenzene to aniline.
Iron(III) chloride finds use 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 etchant for copper in the manufacture of printed circuit boards. It can also be dissolved in alcohol to form tincture of iron, which is used as a medicine to stop bleeding in canaries.
Iron(II) sulfate is used as a precursor to other iron compounds. It is also used to reduce chromate in cement. It is used to fortify foods and treat iron deficiency anemia. Iron(III) sulfate is used in settling minute sewage particles in tank water. Iron(II) chloride is used as a reducing flocculating agent, in the formation of iron complexes and magnetic iron oxides, and as a reducing agent in organic synthesis.
Iron is required for life. The iron–sulfur clusters are pervasive and include nitrogenase, the enzymes responsible for biological nitrogen fixation. Iron-containing proteins participate in transport, storage and used of oxygen. Iron proteins are involved in electron transfer.
Examples of iron-containing proteins in higher organisms include hemoglobin, cytochrome (see high-valent iron), and catalase. The average adult human contains about 0.005% body weight of iron, or about four grams, of which three quarters is in hemoglobin – a level that remains constant despite only about one milligram of iron being absorbed each day, because the human body recycles its hemoglobin for the iron content.
Iron acquisition poses a problem for aerobic organisms because ferric iron is poorly soluble near neutral pH. Thus, these organisms have developed means to absorb iron as complexes, sometimes taking up ferrous iron before oxidising it back to ferric iron. In particular, bacteria have evolved very high-affinity sequestering agents called siderophores.
After uptake in human cells, iron storage is precisely regulated. A major component of this regulation is the protein transferrin, which binds iron ions absorbed from the duodenum and carries it in the blood to cells. Transferrin contains Fe3+ in the middle of a distorted octahedron, bonded to one nitrogen, three oxygens and a chelating carbonate anion that traps the Fe3+ ion: it has such a high stability constant that it is very effective at taking up Fe3+ ions even from the most stable complexes. At the bone marrow, transferrin is reduced from Fe3+ and Fe2+ and stored as ferritin to be incorporated into hemoglobin.
The most commonly known and studied bioinorganic iron compounds (biological iron molecules) are the heme proteins: examples are hemoglobin, myoglobin, and cytochrome P450. These compounds participate in transporting gases, building enzymes, and transferring electrons. Metalloproteins are a group of proteins with metal ion cofactors. Some examples of iron metalloproteins are ferritin and rubredoxin. Many enzymes vital to life contain iron, such as catalase, lipoxygenases, and IRE-BP.
Hemoglobin is an oxygen carrier that occurs in red blood cells and contributes their color, transporting oxygen in the arteries from the lungs to the muscles where it is transferred to myoglobin, which stores it until it is needed for the metabolic oxidation of glucose, generating energy. Here the hemoglobin binds to carbon dioxide, produced when glucose is oxidized, which is transported through the veins by hemoglobin (predominantly as bicarbonate anions) back to the lungs where it is exhaled. In hemoglobin, the iron is in one of four heme groups and has six possible coordination sites; four are occupied by nitrogen atoms in a porphyrin ring, the fifth by an imidazole nitrogen in a histidine residue of one of the protein chains attached to the heme group, and the sixth is reserved for the oxygen molecule it can reversibly bind to. When hemoglobin is not attached to oxygen (and is then called deoxyhemoglobin), the Fe2+ ion at the center of the heme group (in the hydrophobic protein interior) is in a high-spin configuration. It is thus too large to fit inside the porphyrin ring, which bends instead into a dome with the Fe2+ ion about 55 picometers above it. In this configuration, the sixth coordination site reserved for the oxygen is blocked by another histidine residue.
When deoxyhemoglobin picks up an oxygen molecule, this histidine residue moves away and returns once the oxygen is securely attached to form a hydrogen bond with it. This results in the Fe2+ ion switching to a low-spin configuration, resulting in a 20% decrease in ionic radius so that now it can fit into the porphyrin ring, which becomes planar. (Additionally, this hydrogen bonding results in the tilting of the oxygen molecule, resulting in a Fe–O–O bond angle of around 120° that avoids the formation of Fe–O–Fe or Fe–O2–Fe bridges that would lead to electron transfer, the oxidation of Fe2+ to Fe3+, and the destruction of hemoglobin.) This results in a movement of all the protein chains that leads to the other subunits of hemoglobin changing shape to a form with larger oxygen affinity. Thus, when deoxyhemoglobin takes up oxygen, its affinity for more oxygen increases, and vice versa. Myoglobin, on the other hand, contains only one heme group and hence this cooperative effect cannot occur. Thus, while hemoglobin is almost saturated with oxygen in the high partial pressures of oxygen found in the lungs, its affinity for oxygen is much lower than that of myoglobin, which oxygenates even at low partial pressures of oxygen found in muscle tissue. As described by the Bohr effect (named after Christian Bohr, the father of Niels Bohr), the oxygen affinity of hemoglobin diminishes in the presence of carbon dioxide.
Carbon monoxide and phosphorus trifluoride are poisonous to humans because they bind to hemoglobin similarly to oxygen, but with much more strength, so that oxygen can no longer be transported throughout the body. Hemoglobin bound to carbon monoxide is known as carboxyhemoglobin. This effect also plays a minor role in the toxicity of cyanide, but there the major effect is by far its interference with the proper functioning of the electron transport protein cytochrome a. The cytochrome proteins also involve heme groups and are involved in the metabolic oxidation of glucose by oxygen. The sixth coordination site is then occupied by either another imidazole nitrogen or a methionine sulfur, so that these proteins are largely inert to oxygen – with the exception of cytochrome a, which bonds directly to oxygen and thus is very easily poisoned by cyanide. Here, the electron transfer takes place as the iron remains in low spin but changes between the +2 and +3 oxidation states. Since the reduction potential of each step is slightly greater than the previous one, the energy is released step-by-step and can thus be stored in adenosine triphosphate. Cytochrome a is slightly distinct, as it occurs at the mitochondrial membrane, binds directly to oxygen, and transports protons as well as electrons, as follows:
Although the heme proteins are the most important class of iron-containing proteins, the iron-sulfur proteins are also very important, being involved in electron transfer, which is possible since iron can exist stably in either the +2 or +3 oxidation states. These have one, two, four, or eight iron atoms that are each approximately tetrahedrally coordinated to four sulfur atoms; because of this tetrahedral coordination, they always have high-spin iron. The simplest of such compounds is rubredoxin, which has only one iron atom coordinated to four sulfur atoms from cysteine residues in the surrounding peptide chains. Another important class of iron-sulfur proteins is the ferredoxins, which have multiple iron atoms. Transferrin does not belong to either of these classes.
The ability of sea mussels to maintain their grip on rocks in the ocean is facilitated by their use of organometallic iron-based bonds in their protein-rich cuticles. Based on synthetic replicas, the presence of iron in these structures increased elastic modulus 770 times, tensile strength 58 times, and toughness 92 times. The amount of stress required to permanently damage them increased 76 times.
Iron is pervasive, but particularly rich sources of dietary iron include red meat, oysters, lentils, beans, poultry, fish, leaf vegetables, watercress, tofu, chickpeas, black-eyed peas, and blackstrap molasses. Bread and breakfast cereals are sometimes specifically fortified with iron.
Iron provided by dietary supplements is often found as iron(II) fumarate, although iron(II) sulfate is cheaper and is absorbed equally well. Elemental iron, or reduced iron, despite being absorbed at only one-third to two-thirds the efficiency (relative to iron sulfate), is often added to foods such as breakfast cereals or enriched wheat flour. Iron is most available to the body when chelated to amino acids and is also available for use as a common iron supplement. Glycine, the least expensive amino acid, is most often used to produce iron glycinate supplements.
The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for iron in 2001. The current EAR for iron for women ages 14–18 is 7.9 mg/day, 8.1 for ages 19–50 and 5.0 thereafter (post menopause). For men the EAR is 6.0 mg/day for ages 19 and up. The RDA is 15.0 mg/day for women ages 15–18, 18.0 for 19–50 and 8.0 thereafter. For men, 8.0 mg/day for ages 19 and up. RDAs are higher than EARs so as to identify amounts that will cover people with higher than average requirements. RDA for pregnancy is 27 mg/day and, for lactation, 9 mg/day. For children ages 1–3 years 7 mg/day, 10 for ages 4–8 and 8 for ages 9–13. As for safety, the IOM also sets Tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. In the case of iron the UL is set at 45 mg/day. Collectively the EARs, RDAs and ULs are referred to as Dietary Reference Intakes.
The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR. AI and UL defined the same as in United States. For women the PRI is 13 mg/day ages 15–17 years, 16 mg/day for women ages 18 and up who are premenopausal and 11 mg/day postmenopausal. For pregnancy and lactation, 16 mg/day. For men the PRI is 11 mg/day ages 15 and older. For children ages 1 to 14 the PRI increases from 7 to 11 mg/day. The PRIs are higher than the U.S. RDAs, with the exception of pregnancy. The EFSA reviewed the same safety question did not establish a UL.
For U.S. food and dietary supplement labeling purposes the amount in a serving is expressed as a percent of Daily Value (%DV). For iron labeling purposes 100% of the Daily Value was 18 mg, and as of May 27, 2016 remained unchanged at 18 mg. A table of all of the old and new adult Daily Values is provided at Reference Daily Intake. The original deadline to be in compliance was July 28, 2018, but on September 29, 2017 the U.S. Food and Drug Administration released a proposed rule that extended the deadline to January 1, 2020 for large companies and January 1, 2021 for small companies.
Iron deficiency is the most common nutritional deficiency in the world. When loss of iron is not adequately compensated by adequate dietary iron intake, a state of latent iron deficiency occurs, which over time leads to iron-deficiency anemia if left untreated, which is characterised by an insufficient number of red blood cells and an insufficient amount of hemoglobin. Children, pre-menopausal women (women of child-bearing age), and people with poor diet are most susceptible to the disease. Most cases of iron-deficiency anemia are mild, but if not treated can cause problems like fast or irregular heartbeat, complications during pregnancy, and delayed growth in infants and children.
Iron uptake is tightly regulated by the human body, which has no regulated physiological means of excreting iron. Only small amounts of iron are lost daily due to mucosal and skin epithelial cell sloughing, so control of iron levels is primarily accomplished by regulating uptake. 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 and leads to abnormally low levels of hepcidin, a key regulator of the entry of iron into the circulatory system in mammals. In these people, excessive iron intake can result in iron overload disorders, known medically as hemochromatosis. Many people have an undiagnosed genetic susceptibility to iron overload, and are not aware of 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. Hemochromatosis is estimated to be the cause of 0.3 to 0.8% of all metabolic diseases of Caucasians.
Overdoses of ingested iron can cause excessive levels of free iron in the blood. High blood levels of free ferrous iron react with peroxides to produce highly reactive free radicals that can damage DNA, proteins, lipids, and other cellular components. Iron toxicity occurs when the cell contains free iron, which generally occurs when iron levels exceed the availability of transferrin to bind the iron. Damage to the cells of the gastrointestinal tract can also prevent them from regulating iron absorption, leading to further increases in blood levels. Iron typically damages cells in the heart, liver and elsewhere, causing adverse effects that include coma, metabolic acidosis, shock, liver failure, coagulopathy, adult respiratory distress syndrome, long-term organ damage, and even death. Humans experience iron toxicity when the iron exceeds 20 milligrams for every kilogram of body mass; 60 milligrams per kilogram is considered a lethal dose. Overconsumption of iron, often the result of children eating large quantities of ferrous sulfate tablets intended for adult consumption, is one of the most common toxicological causes of death in children under six. The Dietary Reference Intake (DRI) sets the Tolerable Upper Intake Level (UL) for adults at 45 mg/day. For children under fourteen years old the UL is 40 mg/day.
The role of iron in cancer defense can be described as a "double-edged sword" because of its pervasive presence in non-pathological processes. People having chemotherapy may develop iron deficiency and anemia, for which intravenous iron therapy is used to restore iron levels. Iron overload, which may occur from high consumption of red meat, may initiate tumor growth and increase susceptibility to cancer onset, particularly for colorectal cancer.
the blade's composition of iron, nickel and cobalt was an approximate match for a meteorite that landed in northern Egypt. The result "strongly suggests an extraterrestrial origin"
earliest blast furnace discovered in China from about the first century AD
Anemia is a decrease in the total amount of red blood cells (RBCs) or hemoglobin in the blood, or a lowered ability of the blood to carry oxygen. When anemia comes on slowly, the symptoms are often vague and may include feeling tired, weakness, shortness of breath or a poor ability to exercise. Anemia that comes on quickly often has greater symptoms, which may include confusion, feeling like one is going to pass out, loss of consciousness, or increased thirst. Anemia must be significant before a person becomes noticeably pale. Additional symptoms may occur depending on the underlying cause.The three main types of anemia are due to blood loss, decreased red blood cell production, and increased red blood cell breakdown. Causes of blood loss include trauma and gastrointestinal bleeding, among others. Causes of decreased production include iron deficiency, a lack of vitamin B12, thalassemia, and a number of neoplasms of the bone marrow. Causes of increased breakdown include a number of genetic conditions such as sickle cell anemia, infections like malaria, and certain autoimmune diseases. It can also be classified based on the size of red blood cells and amount of hemoglobin in each cell. If the cells are small, it is microcytic anemia. If they are large, it is macrocytic anemia while if they are normal sized, it is normocytic anemia. Diagnosis in men is based on a hemoglobin of less than 130 to 140 g/L (13 to 14 g/dL), while in women, it must be less than 120 to 130 g/L (12 to 13 g/dL). Further testing is then required to determine the cause.Certain groups of individuals, such as pregnant women, benefit from the use of iron pills for prevention. Dietary supplementation, without determining the specific cause, is not recommended. The use of blood transfusions is typically based on a person's signs and symptoms. In those without symptoms, they are not recommended unless hemoglobin levels are less than 60 to 80 g/L (6 to 8 g/dL). These recommendations may also apply to some people with acute bleeding. Erythropoiesis-stimulating medications are only recommended in those with severe anemia.Anemia is the most common blood disorder, affecting about a third of the global population. Iron-deficiency anemia affects nearly 1 billion people. In 2013, anemia due to iron deficiency resulted in about 183,000 deaths – down from 213,000 deaths in 1990. It is more common in women than men, during pregnancy, and in children and the elderly. Anemia increases costs of medical care and lowers a person's productivity through a decreased ability to work. The name is derived from Ancient Greek: ἀναιμία anaimia, meaning "lack of blood", from ἀν- an-, "not" and αἷμα haima, "blood".Cast iron
Cast iron is a group of iron-carbon alloys with a carbon content greater than 2%. Its usefulness derives from its relatively low melting temperature. The alloy constituents affect its colour when fractured: white cast iron has carbide impurities which allow cracks to pass straight through, grey cast iron has graphite flakes which deflect a passing crack and initiate countless new cracks as the material breaks, and ductile cast iron has spherical graphite "nodules" which stop the crack from further progressing.
Carbon (C) ranging from 1.8 to 4 wt%, and silicon (Si) 1–3 wt% are the main alloying elements of cast iron. Iron alloys with lower carbon content (~0.8%) are known as steel. While this technically makes the Fe–C–Si system ternary, the principle of cast iron solidification can be understood from the simpler binary iron–carbon phase diagram. Since the compositions of most cast irons are around the eutectic point (lowest liquid point) of the iron–carbon system, the melting temperatures usually range from 1,150 to 1,200 °C (2,100 to 2,190 °F), which is about 300 °C (540 °F) lower than the melting point of pure iron of 1,535 °C (2,795 °F).
Cast iron tends to be brittle, except for malleable cast irons. With its relatively low melting point, good fluidity, castability, excellent machinability, resistance to deformation and wear resistance, cast irons have become an engineering material with a wide range of applications and are used in pipes, machines and automotive industry parts, such as cylinder heads (declining usage), cylinder blocks and gearbox cases (also declining usage). It is resistant to destruction and weakening by oxidation.
The earliest cast-iron artifacts date to the 5th century BC, and were discovered by archaeologists in what is now Jiangsu in China. Cast iron was used in ancient China for warfare, agriculture, and architecture. During the 15th century, cast iron became utilized for cannon in Burgundy, France, and in England during the Reformation. The amounts of cast iron used for cannon required large scale production. The first cast-iron bridge was built during the 1770s by Abraham Darby III, and is known as The Iron Bridge. Cast iron was also used in the construction of buildings.Industrial Revolution
The Industrial Revolution was the transition to new manufacturing processes in Europe and the US, in the period from about 1760 to sometime between 1820 and 1840. This transition included going from hand production methods to machines, new chemical manufacturing and iron production processes, the increasing use of steam power and water power, the development of machine tools and the rise of the mechanized factory system. The Industrial Revolution also led to an unprecedented rise in the rate of population growth.
Textiles were the dominant industry of the Industrial Revolution in terms of employment, value of output and capital invested. The textile industry was also the first to use modern production methods.The Industrial Revolution began in Great Britain, and many of the technological innovations were of British origin. By the mid-18th century Britain was the world's leading commercial nation, controlling a global trading empire with colonies in North America and the Caribbean, and with some political influence on the Indian subcontinent, through the activities of the East India Company. The development of trade and the rise of business were major causes of the Industrial Revolution.The Industrial Revolution marks a major turning point in history; almost every aspect of daily life was influenced in some way. In particular, average income and population began to exhibit unprecedented sustained growth. Some economists say that the major impact of the Industrial Revolution was that the standard of living for the general population began to increase consistently for the first time in history, although others have said that it did not begin to meaningfully improve until the late 19th and 20th centuries.GDP per capita was broadly stable before the Industrial Revolution and the emergence of the modern capitalist economy, while the Industrial Revolution began an era of per-capita economic growth in capitalist economies. Economic historians are in agreement that the onset of the Industrial Revolution is the most important event in the history of humanity since the domestication of animals and plants.Although the structural change from agriculture to industry is widely associated with the Industrial Revolution, in the United Kingdom it was already almost complete by 1760.The precise start and end of the Industrial Revolution is still debated among historians, as is the pace of economic and social changes. Eric Hobsbawm held that the Industrial Revolution began in Britain in the 1780s and was not fully felt until the 1830s or 1840s, while T.S. Ashton held that it occurred roughly between 1760 and 1830. Rapid industrialization first began in Britain, starting with mechanized spinning in the 1780s, with high rates of growth in steam power and iron production occurring after 1800. Mechanized textile production spread from Great Britain to continental Europe and the United States in the early 19th century, with important centres of textiles, iron and coal emerging in Belgium and the United States and later textiles in France.An economic recession occurred from the late 1830s to the early 1840s when the adoption of the original innovations of the Industrial Revolution, such as mechanized spinning and weaving, slowed and their markets matured. Innovations developed late in the period, such as the increasing adoption of locomotives, steamboats and steamships, hot blast iron smelting and new technologies, such as the electrical telegraph, widely introduced in the 1840s and 1850s, were not powerful enough to drive high rates of growth. Rapid economic growth began to occur after 1870, springing from a new group of innovations in what has been called the Second Industrial Revolution. These new innovations included new steel making processes, mass-production, assembly lines, electrical grid systems, the large-scale manufacture of machine tools and the use of increasingly advanced machinery in steam-powered factories.Iron Age
The Iron Age is the final epoch of the three-age system, preceded by the Stone Age (Neolithic) and the Bronze Age. It is an archaeological era in the prehistory and protohistory of Europe and the Ancient Near East, and by analogy also used of other parts of the Old World.
The three-age system was introduced in the first half of the 19th century for the archaeology of Europe in particular, and by the later 19th century expanded to the archaeology of the Ancient Near East. Its name harks back to the mythological "Ages of Man" of Hesiod. As an archaeological era it was first introduced for Scandinavia by Christian Jürgensen Thomsen in the 1830s. By the 1860s, it was embraced as a useful division of the "earliest history of mankind" in general and began to be applied in Assyriology. The development of the now-conventional periodization in the archaeology of the Ancient Near East was developed in the 1920s to 1930s.
As its name suggests, Iron Age technology is characterized by the production of tools and weaponry by ferrous metallurgy (ironworking), more specifically from carbon steel.
The duration of the Iron Age varies depending on the region under consideration. It is defined by archaeological convention, and the mere presence of some cast or wrought iron is not sufficient to represent an Iron Age culture; rather, the "Iron Age" begins locally when the production of iron or steel has been brought to the point where iron tools and weapons superior to their bronze equivalents become widespread. For example, Tutankhamun's meteoric iron dagger comes from the Bronze Age. In the Ancient Near East, this transition takes place in the wake of the so-called Bronze Age collapse, in the 12th century BC. The technology soon spreads throughout the Mediterranean region and to South Asia.
Its further spread to Central Asia, Eastern and Central Europe is somewhat delayed, and Northern Europe is reached still later, by about 500 BC.
The Iron Age is taken to end, also by convention, with the beginning of the historiographical record.
This usually does not represent a clear break in the archaeological record; for the Ancient Near East the establishment of the Achaemenid Empire c. 550 BC (considered historical by virtue of the record by Herodotus) is usually taken as a cut-off date, and in Central and Western Europe the Roman conquests of the 1st century BC serve as marking for the end of the Iron Age. The Germanic Iron Age of Scandinavia is taken to end c. AD 800, with the beginning of the Viking Age.
In South Asia, the Iron Age is taken to begin with the ironworking Painted Gray Ware culture and to end with the reign of Ashoka (3rd century BC). The use of the term "Iron Age" in the archaeology of South, East and Southeast Asia is more recent, and less common, than for western Eurasia; at least in China prehistory had ended before iron-working arrived, so the term is infrequently used. The Sahel (Sudan region) and Sub-Saharan Africa are outside of the three-age system, there being no Bronze Age, but the term "Iron Age" is sometimes used in reference to early cultures practicing ironworking such as the Nok culture of Nigeria.Iron Cross
The Iron Cross (German: Eisernes Kreuz , abbreviated EK) is a former military decoration in the Kingdom of Prussia, and later in the German Empire (1871–1918) and Nazi Germany (1933–1945). It was established by King Frederick William III of Prussia in March 1813 backdated to the birthday of his late wife Queen Louise on 10 March 1813 during the Napoleonic Wars (EK 1813). Louise was the first person to receive this decoration (posthumously). The recommissioned Iron Cross was also awarded during the Franco-Prussian War (EK 1870), World War I (EK 1914), and World War II (EK 1939, re-introduced with a swastika added in the center).
The Iron Cross was normally a military decoration only, though there were instances of it being awarded to civilians for performing military functions. Two examples of this were civilian test pilots Hanna Reitsch who was awarded the Iron Cross 2nd Class and 1st Class and Melitta Schenk Gräfin von Stauffenberg, who was awarded the Iron Cross 2nd Class, for their actions as pilots during World War II.
The design of the cross symbol was black with a white or silver outline, was ultimately derived from the cross pattée of the Teutonic Order, used by knights on occasions from the 13th century.The Prussian Army black cross pattée was also used as the symbol of the succeeding German Army from 1871 to March/April 1918, when it was replaced by the Balkenkreuz. In 1956, it was re-introduced as the symbol of the Bundeswehr, the modern German armed forces.Iron Curtain
The Iron Curtain was the name for the non physical boundary dividing Europe into two separate areas from the end of World War II in 1945 until the end of the Cold War in 1991. The term symbolizes the efforts by the Soviet Union to block itself and its satellite states from open contact with the West and its allied states. On the east side of the Iron Curtain were the countries that were connected to or influenced by the Soviet Union, while on the west side were the countries that were allied to the United States or nominally neutral. Separate international economic and military alliances were developed on each side of the Iron Curtain:
Member countries of the Council for Mutual Economic Assistance and the Warsaw Pact, with the Soviet Union as the leading state
Member countries of the North Atlantic Treaty Organization (NATO) and with the United States as the pre-eminent powerPhysically, the Iron Curtain took the form of border defences between the countries of Europe in the middle of the continent. The most notable border was marked by the Berlin Wall and its Checkpoint Charlie, which served as a symbol of the Curtain as a whole.The events that demolished the Iron Curtain started in discontent in Poland, and continued in Hungary, the German Democratic Republic (East Germany), Bulgaria, Czechoslovakia, and Romania. Romania became the only communist state in Europe to overthrow its government with violence.The use of the term iron curtain as a metaphor for strict separation goes back at least as far as the early 19th century. It originally referred to fireproof curtains in theaters. Although its popularity as a Cold War symbol is attributed to its use in a speech Winston Churchill gave on the 5 March 1946 in Fulton, Missouri, Nazi German Minister of Propaganda Joseph Goebbels had already used the term in reference to the Soviet Union.Iron Maiden
Iron Maiden are an English heavy metal band formed in Leyton, East London, in 1975 by bassist and primary songwriter Steve Harris. The band's discography has grown to thirty-eight albums, including sixteen studio albums, twelve live albums, four EPs, and seven compilations.
Pioneers of the new wave of British heavy metal, Iron Maiden achieved initial success during the early 1980s. After several line-up changes, the band went on to release a series of UK and US platinum and gold albums, including 1982's The Number of the Beast, 1983's Piece of Mind, 1984's Powerslave, 1985's live release Live After Death, 1986's Somewhere in Time and 1988's Seventh Son of a Seventh Son. Since the return of lead vocalist Bruce Dickinson and guitarist Adrian Smith in 1999, the band have undergone a resurgence in popularity, with their 2010 studio offering, The Final Frontier, peaking at No. 1 in 28 countries and receiving widespread critical acclaim. Their sixteenth studio album, The Book of Souls, was released on 4 September 2015 to similar success.
Despite little radio or television support, Iron Maiden are considered one of the most successful heavy metal bands in history, with The Sunday Times reporting in 2017 that the band have sold over 100 million copies of their albums worldwide. The band won the Ivor Novello Award for international achievement in 2002. As of October 2013, the band have played over 2000 live shows throughout their career. For over 35 years the band have been supported by their famous mascot, "Eddie", who has appeared on almost all of their album and single covers, as well as in their live shows.Iron Man
Iron Man (Anthony Edward "Tony" Stark) is a fictional superhero appearing in American comic books published by Marvel Comics. The character was co-created by writer and editor Stan Lee, developed by scripter Larry Lieber, and designed by artists Don Heck and Jack Kirby. The character made his first appearance in Tales of Suspense #39 (cover dated March 1963), and received his own title in Iron Man #1 (May 1968).
A wealthy American business magnate, playboy, and ingenious scientist, Anthony Edward "Tony" Stark suffers a severe chest injury during a kidnapping. When his captors attempt to force him to build a weapon of mass destruction, he instead creates a powered suit of armor to save his life and escape captivity. Later, Stark develops his suit, adding weapons and other technological devices he designed through his company, Stark Industries. He uses the suit and successive versions to protect the world as Iron Man. Although at first concealing his true identity, Stark eventually declared that he was, in fact, Iron Man in a public announcement.
Initially, Iron Man was a vehicle for Stan Lee to explore Cold War themes, particularly the role of American technology and industry in the fight against communism. Subsequent re-imaginings of Iron Man have transitioned from Cold War motifs to contemporary matters of the time.Throughout most of the character's publication history, Iron Man has been a founding member of the superhero team the Avengers and has been featured in several incarnations of his own various comic book series. Iron Man has been adapted for several animated TV shows and films. The Marvel Cinematic Universe character is portrayed by Robert Downey Jr. in the live action film Iron Man (2008), which was a critical and box office success. Downey, who received much acclaim for his performance, reprised the role in a cameo in The Incredible Hulk (2008), two Iron Man sequels Iron Man 2 (2010) and Iron Man 3 (2013), The Avengers (2012), Avengers: Age of Ultron (2015), Captain America: Civil War (2016), Spider-Man: Homecoming (2017), Avengers: Infinity War (2018) and will do so again in Avengers: Endgame (2019) in the Marvel Cinematic Universe.
Iron Man was ranked 12th on IGN's "Top 100 Comic Book Heroes" in 2011, and third in their list of "The Top 50 Avengers" in 2012.Iron Man (2008 film)
Iron Man is a 2008 American superhero film based on the Marvel Comics character of the same name, produced by Marvel Studios and distributed by Paramount Pictures. The first installment of the Marvel Cinematic Universe (MCU) and the Infinity Saga, it was directed by Jon Favreau from a screenplay by Mark Fergus, Hawk Ostby, Art Marcum, and Matt Holloway. The film follows Tony Stark (Robert Downey Jr.), an industrialist and master engineer who builds a powered exoskeleton after a life-threatening incident, and becomes the technologically advanced superhero Iron Man.
The film had been in development since 1990 at Universal Pictures, 20th Century Fox, and New Line Cinema at various times, before Marvel Studios reacquired the rights in 2006. Marvel put the project in production as its first self-financed film, with Paramount Pictures as distributor. Favreau signed on as director, aiming for a naturalistic feel, and chose to shoot the film primarily in California, rejecting the East Coast setting of the comics to differentiate the film from numerous superhero films set in New York City-esque environments. Filming began in March 2007 and concluded in June. During filming, the actors were free to create their own dialogue because pre-production was focused on the story and action. Rubber and metal versions of the armors, created by Stan Winston's company, were mixed with computer-generated imagery to create the title character.
Iron Man premiered in Sydney on April 14, 2008, and was released in the United States on May 2, 2008. The film grossed over $585 million on its $140 million budget, becoming the eighth-highest grossing film of 2008. It received praise from critics for its acting (particularly Downey's), screenplay, visual effects, and action sequences, and was selected by the American Film Institute as one of the ten best films of 2008. It received two nominations at the 81st Academy Awards for Best Sound Editing and Best Visual Effects, and was followed by the sequels Iron Man 2 and Iron Man 3 in 2010 and 2013, respectively.Iron Man 2
Iron Man 2 is a 2010 American superhero film based on the Marvel Comics character Iron Man, produced by Marvel Studios and distributed by Paramount Pictures. It is the sequel to 2008's Iron Man, and is the third film in the Marvel Cinematic Universe (MCU). Directed by Jon Favreau and written by Justin Theroux, the film stars Robert Downey Jr. as Tony Stark / Iron Man, alongside Gwyneth Paltrow, Don Cheadle, Scarlett Johansson, Sam Rockwell, Mickey Rourke, and Samuel L. Jackson. Six months after the events of Iron Man, Tony Stark is resisting calls by the United States government to hand over the Iron Man technology while also combating his declining health from the arc reactor in his chest. Meanwhile, rogue Russian scientist Ivan Vanko has developed the same technology and built weapons of his own in order to pursue a vendetta against the Stark family, in the process joining forces with Stark's business rival, Justin Hammer.
Following the successful release of Iron Man in May 2008, Marvel Studios announced and immediately set to work on producing a sequel. In July of that same year Theroux was hired to write the script, and Favreau was signed to return and direct. Downey, Paltrow and Jackson were set to reprise their roles from Iron Man, while Cheadle was brought in to replace Terrence Howard in the role of James Rhodes. In the early months of 2009, Rourke, Rockwell and Johansson filled out the supporting cast, and filming took place from April to July of that year. Like its predecessor the film was shot mostly in California, except for a key sequence in Monaco.
Iron Man 2 premiered at the El Capitan Theatre on April 26, 2010, and was released in the United States on May 7, 2010. The film received generally positive reviews and was commercially successful, grossing over $623.9 million at the worldwide box office, making it the seventh highest-grossing film of 2010, and receiving an Academy Award nomination for Best Visual Effects. The third installment of the Iron Man series, Iron Man 3, was released on May 3, 2013.Iron Man 3
Iron Man 3 (stylized onscreen as Iron Man Three) is a 2013 American superhero film based on the Marvel Comics character Iron Man, produced by Marvel Studios and distributed by Walt Disney Studios Motion Pictures.1 It is the sequel to 2008's Iron Man and 2010's Iron Man 2, and the seventh film in the Marvel Cinematic Universe (MCU). The film was directed by Shane Black from a screenplay he co-wrote with Drew Pearce, and stars Robert Downey Jr. as Tony Stark / Iron Man, alongside Gwyneth Paltrow, Don Cheadle, Guy Pearce, Rebecca Hall, Stéphanie Szostak, James Badge Dale, Jon Favreau, and Ben Kingsley. In Iron Man 3, Tony Stark wrestles with the ramifications of the events of The Avengers, during a national terrorism campaign on the United States led by the mysterious Mandarin.
After the release of Iron Man 2 in May 2010, Favreau, who served as director, decided not to return, and in February 2011 Black was hired to write and direct the film. Black and Pearce opted to make the script more character-centric and focused on thriller elements, which also uses concepts from the "Extremis" story arc by Warren Ellis. Throughout April and May 2012, the film's supporting cast was filled out, with Kingsley, Pearce, and Hall brought in to portray key roles. Filming began on May 23, and lasted through December 17, 2012, primarily at EUE/Screen Gems Studios in Wilmington, North Carolina. Additional shooting took place at various locations around North Carolina, as well as Florida, China, and Los Angeles. The visual effects were handled by 17 companies, including Scanline VFX, Digital Domain, and Weta Digital. The film was converted to 3D in post-production.
Iron Man 3 premiered at the Grand Rex in Paris on April 14, 2013, and released in the United States on May 3. The film received praise for its performances, visual effects, action sequences, humor, story, and Brian Tyler's musical score, while reception to its plot twist was mixed. It was a huge box office success, grossing over $1.2 billion worldwide, making it the second-highest-grossing film of 2013 overall, and the second-highest-grossing film released in 2013 in the United States and Canada. It became the sixteenth film to gross over $1 billion and the fifth-highest-grossing film of all time, with its opening weekend ranking as the sixth-highest-grossing opening of all time. The film received a nomination for the Academy Award in the category of Best Visual Effects, and received another nomination for the BAFTA Award in the same category.Iron ore
Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in colour from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the form of magnetite (Fe3O4, 72.4% Fe), hematite (Fe2O3, 69.9% Fe), goethite (FeO(OH), 62.9% Fe), limonite (FeO(OH)·n(H2O), 55% Fe) or siderite (FeCO3, 48.2% Fe).
Ores containing very high quantities of hematite or magnetite (greater than about 60% iron) are known as "natural ore" or "direct shipping ore", meaning they can be fed directly into iron-making blast furnaces. Iron ore is the raw material used to make pig iron, which is one of the main raw materials to make steel—98% of the mined iron ore is used to make steel. Indeed, it has been argued that iron ore is "more integral to the global economy than any other commodity, except perhaps oil".Knight's Cross of the Iron Cross
The Knight's Cross of the Iron Cross (German: Ritterkreuz des Eisernen Kreuzes), or simply the Knight's Cross (Ritterkreuz), and its variants were the highest awards in the military and paramilitary forces of Nazi Germany during World War II.
The Knight's Cross was awarded for a wide range of reasons and across all ranks, from a senior commander for skilled leadership of his troops in battle to a low-ranking soldier for a single act of military valour. Presentations were made to members of the three military branches of the Wehrmacht (the Heer (army), the Kriegsmarine (navy) and the Luftwaffe, as well as the Waffen-SS, the Reichsarbeitsdienst (RAD—Reich Labour Service) and the Volkssturm (German national militia), along with personnel from other Axis powers.
The award was instituted on 1 September 1939, at the onset of the German invasion of Poland. A higher grade, the Oak Leaves to the Knight's Cross, was instituted in 1940. In 1941, two higher grades of the Knight's Cross with Oak Leaves were instituted: the Knight's Cross with Oak Leaves and Swords and the Knight's Cross with Oak Leaves, Swords and Diamonds. At the end of 1944 the final grade, the Knight's Cross with Golden Oak Leaves, Swords and Diamonds, was created. Over 7,000 awards were made during the course of the war.List of Marvel Cinematic Universe films
The Marvel Cinematic Universe (MCU) films are an American series of superhero films based on characters that appear in publications by Marvel Comics. The MCU is the shared universe in which all of the films are set. The films have been in production since 2007, and in that time Marvel Studios has produced and released 21 films, with 10 more in various stages of production. It is the highest-grossing film franchise of all time, having grossed over $18.4 billion at the global box office.
Kevin Feige has produced every film in the series, alongside Avi Arad for the first two releases, Gale Anne Hurd for The Incredible Hulk, Amy Pascal for the Spider-Man films, and Stephen Broussard for Ant-Man and the Wasp. The films are written and directed by a variety of individuals and feature large, often ensemble, casts. Many of the actors, including Robert Downey Jr., Chris Evans, Chris Hemsworth, Samuel L. Jackson, and Scarlett Johansson signed contracts to star in numerous films.
The first film in the series was Iron Man (2008), which was distributed by Paramount Pictures. Paramount also distributed Iron Man 2 (2010), Thor (2011) and Captain America: The First Avenger (2011), while Universal Pictures distributed The Incredible Hulk (2008). Walt Disney Studios Motion Pictures began distributing the films with the 2012 crossover film The Avengers, which concluded Phase One of the franchise. Phase Two includes Iron Man 3 (2013), Thor: The Dark World (2013), Captain America: The Winter Soldier (2014), Guardians of the Galaxy (2014), Avengers: Age of Ultron (2015), and Ant-Man (2015).
Captain America: Civil War (2016) is the first film in the franchise's Phase Three, and is followed by Doctor Strange (2016), Guardians of the Galaxy Vol. 2 (2017), Spider-Man: Homecoming (2017), Thor: Ragnarok (2017), Black Panther (2018), Avengers: Infinity War (2018), Ant-Man and the Wasp (2018), and Captain Marvel (2019), with Avengers: Endgame (2019) still scheduled for the phase. The first three phases have collectively been called The Infinity Saga. Spider-Man: Far From Home has also been scheduled for 2019, beginning Phase Four. Two untitled films are scheduled for 2020, three for 2021, and three for 2022. Sony Pictures distributes the Spider-Man films, which they continue to own, finance, and have final creative control over.Marvel Cinematic Universe
The Marvel Cinematic Universe (MCU) is an American media franchise and shared universe that is centered on a series of superhero films, independently produced by Marvel Studios and based on characters that appear in American comic books published by Marvel Comics. The franchise has expanded to include comic books, short films, television series, and digital series. The shared universe, much like the original Marvel Universe in comic books, was established by crossing over common plot elements, settings, cast, and characters. Phil Coulson, portrayed by Clark Gregg, is an original character to the MCU and the only character to appear across all its different media.
The first film released in the MCU was Iron Man (2008), which began the first phase of films culminating in the crossover film Marvel's The Avengers (2012). Phase Two began with Iron Man 3 (2013), and concluded with Ant-Man (2015). The MCU is currently in Phase Three, which began with the release of Captain America: Civil War (2016) and is set to conclude with Avengers: Endgame (2019). The first three phases are collectively known as The Infinity Saga. Phase Four will begin with the release of Spider-Man: Far From Home (2019). Marvel Television expanded the universe further, first to network television with Marvel's Agents of S.H.I.E.L.D. on ABC in the 2013–14 television season, followed by online streaming with Marvel's Daredevil on Netflix in 2015 and Marvel's Runaways on Hulu in 2017, and then to cable television with Marvel's Cloak & Dagger on Freeform in 2018. Marvel Television has also produced the digital series Marvel's Agents of S.H.I.E.L.D.: Slingshot, which is a supplement to Agents of S.H.I.E.L.D. Soundtrack albums have been released for all of the films, along with many of the television series, as well as the release of compilation albums containing existing music heard in the films. The MCU also includes tie-in comics published by Marvel Comics, while Marvel Studios has also produced a series of direct-to-video short films and a viral marketing campaign for its films and the universe with the faux news program WHIH Newsfront.
The franchise has been commercially successful as a multimedia shared universe, though some critics have found that some of its films and television series have suffered in service of the wider universe. It has inspired other film and television studios with comic book character adaptation rights to attempt to create similar shared universes. The MCU has also been the focus of other media, outside of the shared universe, including attractions at various Walt Disney Parks and Resorts, an attraction at Discovery Times Square, a Queensland Gallery of Modern Art exhibit, two television specials, guidebooks for each film, multiple tie-in video games, and commercials.Northern Ireland
Northern Ireland (Irish: Tuaisceart Éireann [ˈt̪ˠuəʃcəɾˠt̪ˠ ˈeːɾʲən̪ˠ] (listen); Ulster-Scots: Norlin Airlann) is a part of the United Kingdom in the north-east of the island of Ireland, variously described as a country, province or region. Northern Ireland shares a border to the south and west with the Republic of Ireland. In 2011, its population was 1,810,863, constituting about 30% of the island's total population and about 3% of the UK's population. Established by the Northern Ireland Act 1998 as part of the Good Friday Agreement, the Northern Ireland Assembly holds responsibility for a range of devolved policy matters, while other areas are reserved for the British government. Northern Ireland co-operates with the Republic of Ireland in some areas, and the Agreement granted the Republic the ability to "put forward views and proposals" with "determined efforts to resolve disagreements between the two governments".Northern Ireland was created in 1921, when Ireland was partitioned between Northern Ireland and Southern Ireland by the Government of Ireland Act 1920. Unlike Southern Ireland, which would become the Irish Free State in 1922, the majority of Northern Ireland's population were unionists, who wanted to remain within the United Kingdom. Most of these were the Protestant descendants of colonists from Great Britain. However, a significant minority, mostly Catholics, were nationalists who wanted a united Ireland independent of British rule. Today, the former generally see themselves as British and the latter generally see themselves as Irish, while a distinct Northern Irish or Ulster identity is claimed both by a large minority of Catholics and Protestants and by many of those who are non-aligned.For most of the 20th century, when it came into existence, Northern Ireland was marked by discrimination and hostility between these two sides in what First Minister of Northern Ireland, David Trimble, called a "cold house" for Catholics. In the late 1960s, conflict between state forces and chiefly Protestant unionists on the one hand, and chiefly Catholic nationalists on the other, erupted into three decades of violence known as the Troubles, which claimed over 3,500 lives and caused over 50,000 casualties. The 1998 Good Friday Agreement was a major step in the peace process, including the decommissioning of weapons, although sectarianism and religious segregation still remain major social problems, and sporadic violence has continued.Northern Ireland has historically been the most industrialised region of Ireland. After declining as a result of the political and social turmoil of the Troubles, its economy has grown significantly since the late 1990s. The initial growth came from the "peace dividend" and the links which increased trade with the Republic of Ireland, continuing with a significant increase in tourism, investment and business from around the world. Unemployment in Northern Ireland peaked at 17.2% in 1986, dropping to 6.1% for June–August 2014 and down by 1.2 percentage points over the year, similar to the UK figure of 6.2%. 58.2% of those unemployed had been unemployed for over a year.
Prominent artists and sportspeople from Northern Ireland include Van Morrison, Rory McIlroy, Joey Dunlop, Wayne McCullough and George Best. Some people from Northern Ireland prefer to identify as Irish (e.g., poet Seamus Heaney and actor Liam Neeson) while others prefer to identify as British (e.g. actor Sir Kenneth Branagh). Cultural links between Northern Ireland, the rest of Ireland, and the rest of the UK are complex, with Northern Ireland sharing both the culture of Ireland and the culture of the United Kingdom. In many sports, the island of Ireland fields a single team, a notable exception being association football. Northern Ireland competes separately at the Commonwealth Games, and people from Northern Ireland may compete for either Great Britain or Ireland at the Olympic Games.Robert Downey Jr.
Robert John Downey Jr. (born April 4, 1965) is an American actor and singer. His career has included critical and popular success in his youth, followed by a period of substance abuse and legal difficulties, and a resurgence of commercial success in middle age. For three consecutive years from 2012 to 2015, Downey topped the Forbes list of Hollywood's highest-paid actors, making an estimated $80 million in earnings between June 2014 and June 2015.Making his acting debut at the age of five, appearing in his father's film Pound (1970), Downey appeared in roles associated with the Brat Pack, such as the teen sci-fi comedy Weird Science (1985) and the drama Less Than Zero (1987). He starred as the title character in the 1992 film Chaplin, for which he earned a nomination for the Academy Award for Best Actor and he won the BAFTA Award for Best Actor in a Leading Role. After being released in 2000 from the California Substance Abuse Treatment Facility and State Prison where he was incarcerated on drug charges, Downey joined the cast of the TV series Ally McBeal playing Calista Flockhart's love interest. For that he earned a Golden Globe Award. His character was terminated when Downey was fired after two drug arrests in late 2000 and early 2001. After his last stay in a court-ordered drug treatment program, Downey achieved sobriety.
Downey's career prospects improved when he featured in the black comedy crime Kiss Kiss Bang Bang (2005), the mystery thriller Zodiac (2007), and the satirical action comedy Tropic Thunder (2008); for the latter he was nominated for an Academy Award for Best Supporting Actor. Beginning in 2008, Downey began portraying the role of Marvel Comics superhero Iron Man in the Marvel Cinematic Universe, appearing in several films as either the lead role, member of an ensemble cast, or in a cameo. Each of these films, with the exception of The Incredible Hulk, has grossed over $500 million at the box office worldwide; four of these—The Avengers, Avengers: Age of Ultron, Iron Man 3 and Captain America: Civil War—earned over $1 billion, while Avengers: Infinity War earned over $2 billion.
Downey has also played the title character in Guy Ritchie's Sherlock Holmes (2009), which earned him his second Golden Globe win, and its sequel (2011), both of which have earned over $500 million at the box office worldwide.
As of 2018, the U.S. domestic box-office grosses of Downey's films total over US $4.9 billion, with worldwide grosses surpassing $11.6 billion, making Downey the third highest-grossing U.S. domestic box-office star of all time.Steel
Steel is an alloy of iron and carbon, and sometimes other elements. Because of its high tensile strength and low cost, it is a major component used in buildings, infrastructure, tools, ships, automobiles, machines, appliances, and weapons.
Iron is the base metal of steel. Iron is able to take on two crystalline forms (allotropic forms), body centered cubic and face centered cubic, depending on its temperature. In the body-centered cubic arrangement, there is an iron atom in the center and eight atoms at the vertices of each cubic unit cell; in the face-centered cubic, there is one atom at the center of each of the six faces of the cubic unit cell and eight atoms at its vertices. It is the interaction of the allotropes of iron with the alloying elements, primarily carbon, that gives steel and cast iron their range of unique properties.
In pure iron, the crystal structure has relatively little resistance to the iron atoms slipping past one another, and so pure iron is quite ductile, or soft and easily formed. In steel, small amounts of carbon, other elements, and inclusions within the iron act as hardening agents that prevent the movement of dislocations that are common in the crystal lattices of iron atoms.
The carbon in typical steel alloys may contribute up to 2.14% of its weight. Varying the amount of carbon and many other alloying elements, as well as controlling their chemical and physical makeup in the final steel (either as solute elements, or as precipitated phases), slows the movement of those dislocations that make pure iron ductile, and thus controls and enhances its qualities. These qualities include such things as the hardness, quenching behavior, need for annealing, tempering behavior, yield strength, and tensile strength of the resulting steel. The increase in steel's strength compared to pure iron is possible only by reducing iron's ductility.
Steel was produced in bloomery furnaces for thousands of years, but its large-scale, industrial use began only after more efficient production methods were devised in the 17th century, with the production of blister steel and then crucible steel. With the invention of the Bessemer process in the mid-19th century, a new era of mass-produced steel began. This was followed by the Siemens–Martin process and then the Gilchrist–Thomas process that refined the quality of steel. With their introductions, mild steel replaced wrought iron.
Further refinements in the process, such as basic oxygen steelmaking (BOS), largely replaced earlier methods by further lowering the cost of production and increasing the quality of the final product. Today, steel is one of the most common manmade materials in the world, with more than 1.6 billion tons produced annually. Modern steel is generally identified by various grades defined by assorted standards organizations.War Machine
War Machine (James Rupert "Rhodey" Rhodes) is a fictional superhero appearing in American comic books published by Marvel Comics. Jim Rhodes first appeared in Iron Man #118 (January 1979) by David Michelinie and John Byrne. The War Machine armor, which became his signature armored battlesuit, was created by Len Kaminski and Kevin Hopgood.In 2012, War Machine was ranked 31st in IGN's list of "The Top 50 Avengers". The character has been featured in the Iron Man animated series, the Iron Man: Armored Adventures series, and the animated film The Invincible Iron Man. USAF Lt.Colonel James Rhodes was portrayed by Terrence Howard in Iron Man, which takes place before Rhodes took on the War Machine mantle, and by Don Cheadle as a USAF Colonel in Iron Man 2, Iron Man 3, Avengers: Age of Ultron, Captain America: Civil War, Avengers: Infinity War, Captain Marvel, and is expected to do so in the fourth Avengers film Avengers: Endgame in the Marvel Cinematic Universe.