Iron ?symbol Fe and atomic number 26

Iron is a chemical element with the symbol Fe (from Latin: ferrum) and atomic number 26. It is a metal in the first transition series. It is the most common element (by mass) forming the planet Earth as a whole, forming much of Earth'souter and inner core. It is the fourth most common element in the Earth's crust.HP Pavilion DV4 Battery

Iron's very common presence in rocky planets like Earth is due to its abundant production as a result of fusion in high-mass stars, where the production ofnickel-56 (which decays to iron) is the last nuclear fusion reaction that is exothermic. This allows radioactive nickel to become the last element to be produced before collapse of a supernova leads to events that scatters this precursorradionuclide of iron into space.HP Pavilion DV4-1000 Battery

Like other Group 8 elements, iron exists in a wide range of oxidation states, ?2 to + 6, 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 iron oxides, also known as rust.HP Pavilion DV4-1000EA Battery

Unlike many other metals which form passivating oxide layers, iron oxides occupy more volume than iron metal, and thus iron oxides flake off and expose fresh surfaces for corrosion.

Iron metal has been used since ancient times, though lower-melting copper alloys were used first in history.HP Pavilion DV4-1000ET Battery

Pure iron is soft (softer than aluminium), but is unobtainable by smelting. The material is significantly hardened and strengthened by impurities from the smelting process, such as carbon. A certain proportion of carbon (between 0.2% and 2.1%) producessteel, which may be up to 1000 times harder than pure iron.HP Pavilion DV4-1001 Battery

Crude iron metal is produced in blast furnaces, where ore is reduced by coke to cast iron, which has a high carbon content. Further refinement with oxygen reduces the carbon content to the correct proportion to make steel. Steels and low carbon iron alloys with other metals (alloy steels) are by far the most common metals in industrial use, due to their great range of desirable properties.HP Pavilion DV4-1001AX Battery

Iron chemical compounds, which include ferrous and ferric compounds, have many uses. Iron oxide mixed with aluminium powder can be ignited to create a thermite reaction, used in welding and purifying ores. It forms binary compounds with thehalogens and the chalcogens.HP Pavilion DV4-1001TU Battery

Among its organometallic compounds, ferrocene was 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 transport proteins in vertebrates.HP Pavilion DV4-1001TX Battery

Iron is also the metal used at the active site of many important redox enzymes dealing with cellular respiration and oxidation and reduction in plants and animals.

Mechanical properties of iron and its alloys are evaluated using a variety of tests, such as the Brinell test, Rockwell test, or tensile strength tests, among others;HP Pavilion DV4-1002 Battery

the results on iron are so consistent that iron is often used to calibrate measurements or to relate the results of one test to another.Those measurements reveal that mechanical properties of iron crucially depend on purity: Purest research-purpose single crystals of iron are softer than aluminium.HP Pavilion DV4-1002AX Battery

Addition of only 10 parts per million of carbon doubles their strength.[1] The hardness increases rapidly with carbon content up to 0.2% and saturates at ~0.6%.[4] The purest industrially produced iron (about 99.99% purity) has a hardness of 20–30 Brinell.HP Pavilion DV4-1002TU Battery

Phase diagram and allotropes

Iron represents an example of allotropy in a metal. There are at least four allotropic forms of iron, known as ?, ?, ?, and ?; at very high pressures, some controversial experimental evidence exists for a phase ? stable at very high pressures and temperatures.HP Pavilion DV4-1002TX Battery

As molten iron cools down it crystallizes at 1538 °C into its ? allotrope, which has abody-centered cubic (bcc) crystal structure. As it cools further its crystal structurechanges to face-centered cubic (fcc) at 1394 °C, when it is known as ?-iron, oraustenite. At 912 °C the crystal structure again becomes bcc as ?-iron, or ferrite, is formed, and at 770 °C (the Curie point, Tc) iron becomes magnetic.HP Pavilion DV4-1003AX Battery

As the iron passes through the Curie temperature there is no change in crystalline structure, but there is a change in "domain structure", where each domain contains iron atoms with a particular electronic spin. In unmagnetized iron, all the electronic spins of the atoms within one domain are in the same direction; the neighboring domains point in various directions and thus cancel out.HP Pavilion DV4-1003TU Battery

In magnetized iron, the electronic spins of all the domains are aligned, so that the magnetic effects of neighboring domains reinforce each other. Although each domain contains billions of atoms, they are very small, about 10 micrometres across.HP Pavilion DV4-1003TX Battery

At pressures above approximately 10 GPa and temperatures of a few hundred kelvin or less, ?-iron changes into a hexagonal close-packed (hcp) structure, which is also known as ?-iron; the higher-temperature ?-phase also changes into ?-iron, but does so at higher pressure.HP Pavilion DV4-1004AX Battery

The ?-phase, if it exists, would appear at pressures of at least 50 GPa and temperatures of at least 1500 K; it has been thought to have an orthorhombic or a double hcp structure.

Iron is of greatest importance when mixed with certain other metals and with carbon to form steels.HP Pavilion DV4-1004TU Battery

There are many types of steels, all with different properties, and an understanding of the properties of the allotropes of iron is key to the manufacture of good quality steels.

?-iron, also known as ferrite, is the most stable form of iron at normal temperatures. It is a fairly soft metal that can dissolve only a small concentration of carbon (no more than 0.021% by mass at 910 °C).HP Pavilion DV4-1004TX Battery

Above 912 °C and up to 1400 °C ?-iron undergoes a phase transition from bcc to the fcc configuration of ?-iron, also called austenite. This 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.HP Pavilion DV4-1005TX Battery

The 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 assumed to consist essentially of an iron-nickel alloy with ? (or ?) structure.

The melting point of iron is experimentally well constrained for pressures up to approximately 50 GPa. HP Pavilion DV4-1006TX Battery

For higher pressures, different studies placed the ?-?-liquid triple point at pressures differing by tens of gigapascals and yielded differences of more than 1000 K for 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.HP Pavilion DV4-1007TX Battery

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 is predicted to undergo double beta decay, but this process had never been observed experimentally for these nuclei, and only the lower limit on the half-life was established: t1/2>3.1×1022 years.HP Pavilion DV4-1008TX Battery

60Fe is an extinct radionuclide of long half-life (2.6 million years).[10] It is not found on Earth, but its ultimate decay product is forms part of the natural abundance of the stable nuclide nickel-60.

Much of the past work on measuring the isotopic composition of Fe has focused on determining 60Fe variations due to processes accompanying nucleosynthesis (i.e.,meteorite studies) and ore formation.HP Pavilion DV4-1009TX Battery

In the last decade however, advances in mass spectrometry technology have allowed the detection and quantification of minute, naturally occurring variations in the ratios of the stable isotopes of iron. Much of this work has been driven by the Earth and planetary science communities, although applications to biological and industrial systems are beginning to emerge.HP Pavilion DV4-1010TX Battery

The most abundant iron isotope 56Fe is of particular interest to nuclear scientists as it represents the most common endpoint of nucleosynthesis. It is often cited, falsely, as the isotope of highest binding energy, a distinction which actually belongs to nickel-62.HP Pavilion DV4-1011TX Battery

Since 56Ni is easily produced from lighter nuclei in thealpha process in nuclear reactions in supernovae (see silicon burning process), nickel-56 (14 alpha particles) is the endpoint of fusion chains inside extremely massive stars, since addition of another alpha particle would result in zinc-60, which requires a great deal more energy.HP Pavilion DV4-1012TX Battery

This nickel-56, which has a half-life of about 6 days, is therefore made 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 cobalt-56, and then stable iron-56.HP Pavilion DV4-1013TX Battery

This last nuclide is therefore common in the universe, relative to other stable metals of approximately the same atomic weight.

In phases of the meteorites Semarkona and Chervony Kut a correlation between the concentration of 60Ni,HP Pavilion DV4-1014NR Battery

the daughter product of 60Fe, and the abundance of the stable iron isotopes could be found which is evidence for the existence of 60Fe at the time of formation of the solar system. Possibly the energy released by the decay of60Fe contributed, together with the energy released by decay of the radionuclide 26Al,HP Pavilion DV4-1014TX Battery

to the remelting and differentiation of asteroids after their formation 4.6 billion years ago . The abundance of 60Ni present in extraterrestrial material may also provide further insight into the origin of the solar systemand its early history.HP Pavilion DV4-1015TX Battery

Nuclei of iron atoms have some of the highest binding energies per nucleon, surpassed only by the nickel isotope 62Ni. This is formed by nuclear fusion in stars. Although a further tiny energy gain could be extracted by synthesizing 62Ni, conditions in stars are unsuitable for this process to be favored.HP Pavilion DV4-1015TX Battery

Elemental distribution on Earth greatly favors iron over nickel, and also presumably in supernova element production.

Iron-56 is the heaviest stable isotope produced by the alpha process in stellar nucleosynthesis; elements heavier than iron and nickel require a supernova for their formation.HP Pavilion DV4-1016TX Battery

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 planetssuch as Earth.

Nucleosynthesis

Iron is created by extremely large, extremely hot (over 2.5 billion kelvin) stars, through a process called the silicon burning process.HP Pavilion DV4-1017TX Battery

It is the heaviest stable element to be produced in this manner. The process starts with the second largest stable nucleus created by silicon burning: calcium. One stable nucleus of calcium fuses with one helium nucleus, creating unstable titanium. Before the titanium decays, it can fuse with another helium nucleus, creating unstable chromium.HP Pavilion DV4-1018TX Battery

Before the chromium decays, it can fuse with another helium nucleus, creating unstable iron. Before the iron decays, it can fuse with another helium nucleus, creating unstable nickel-56. Any further fusion of nickel-56 consumes energy instead of producing energy, so after the production of nickel-56, the star does not produce the energy necessary to keep the core from collapsing.HP Pavilion DV4-1019TX Battery

Eventually, the nickel-56 decays to unstable cobalt-56 which, in turn decays to stable iron-56 When the core of the star collapses, it creates a Supernova. Supernovas also create additional forms of stable iron via the r-process.

Planetary occurrence

Iron is the sixth most abundant element in the Universe, formed as the final step of nucleosynthesis, by silicon fusing in massive stars.HP Pavilion DV4-1020TX Battery

Metallic 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. HP Pavilion DV4-1020US Battery

Iron is consequently the most abundant element on Earth, but only the fourth most abundant element in the Earth's crust. Most of the iron in the crust is found combined with oxygen as iron oxide minerals such as hematite and magnetite. Large deposits of iron are found in banded iron formations.HP Pavilion DV4-1021TX Battery

These geological formations are a type of rock consisting of repeated thin layers of iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor shale and chert. The banded iron formations are common in the time between 3,700 million years ago and 1,800 million years ago.HP Pavilion DV4-1022TX Battery

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. It was proven by Mössbauer spectroscopy that the red color of the surface of Mars is derived from an iron oxide-rich regolith.HP Pavilion DV4-1023TX Battery

In-use stocks in society

According to the International Resource Panel's Metal Stocks in Society report, the global per capita stock of iron in use in society is 2200kg. Much of this is in more-developed countries (7000–14000kg per capita) rather than less-developed countries (2000kg per capita).HP Pavilion DV4-1024TX Battery

Chemistry and compounds

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, an example being the purple potassium ferrate (K2FeO4) which contains iron in its +6 oxidation state.HP Pavilion DV4-1025TX Battery

Iron(IV) is a common intermediate in many in biochemical oxidation reactions. Numerousorganometallic 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.HP Pavilion DV4-1026TX Battery

There are also many mixed valence compounds that contain both iron(II) and iron(III) centers, such as magnetite and Prussian blue (Fe4(Fe[CN]6)3).[21] The latter is used as the traditional "blue" in blueprints.

The iron compounds produced on the largest scale in industry are iron(II) sulfate (FeSO4·7H2O) andiron(III) chloride (FeCl3).HP Pavilion DV4-1027TX Battery

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.

Unlike many other metals, iron does not form amalgams with mercury. As a result, mercury is traded in standardized 76 pound flasks (34 kg) made of iron.HP Pavilion DV4-1028TX Battery

Binary compounds

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.HP Pavilion DV4-1028US Battery

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, usefulmagnetic 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.HP Pavilion DV4-1029TX Battery

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 binary halogen acid to give the corresponding hydrated salts.HP Pavilion DV4-1030EE Battery

Fe + 2 HX ? FeX2 + H2

Iron reacts with fluorine, chlorine, and bromine to give the corresponding ferric halides, ferric chloride being the most common:

2 Fe + 3 X2 ? 2 FeX3 (X = F, Cl, Br) HP Pavilion DV4-1030EI Battery

Coordination and organometallic compounds

e complexes are known. The most famous example is Prussian blue, (Fe4(Fe[CN]6)3). Potassium ferricyanide andpotassium ferrocyanide are also known; the formation of Prussian blue upon reaction with iron(II) and iron(III) respectively forms the basis of a "wet" chemical test.HP Pavilion DV4-1030EJ Battery

Prussian blue is also used as an antidote for thallium and radioactive caesiumpoisoning. Prussian blue can be used in laundry bluing to correct the yellowish tint left by ferrous salts in water.

Several carbonyl compounds of iron are known. 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.HP Pavilion DV4-1030EN Battery

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.HP Pavilion DV4-1030TX Battery

Ferrocene is an extremely stable complex. The first sandwich compound, it contains an iron(II) center with two cyclopentadienyl ligands bonded through all ten carbon atoms. This arrangement was a shocking novelty when it was first discovered,[29] but the discovery of ferrocene has led to a new branch of organometallic chemistry.HP Pavilion DV4-1031TX Battery

Ferrocene itself can be used as the backbone of a ligand, e.g. dppf. Ferrocene can itself be oxidized to the ferrocenium cation (Fc+); the ferrocene/ferrocenium couple is often used as a reference in electrochemistry.

Wrought iron

Iron objects of great age are much rarer than objects made of gold or silver due to the ease of corrosion of iron.HP Pavilion DV4-1032TX Battery

Beads made of meteoric iron in 3500 B.C. 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 has very little to no nickel content.HP Pavilion DV4-1033TX Battery

Meteoric iron was highly regarded due to its origin in the heavens and was often used to forge weapons and tools or whole specimens placed in churches. Items that were likely made of iron by Egyptians date from 2500 to 3000 BC. Iron had a distinct advantage over bronze in warfare implements.HP Pavilion DV4-1034TX Battery

It was much harder and more durable than bronze, although susceptible to rust. However, this is contested. Hittitologist Trevor Bryce argues that before advanced iron-working techniques were developed in Europe and India, cast-iron weapons used by early Mesopotamian armies had a tendency to shatter in combat, due to their high carbon content.HP Pavilion DV4-1035LA Battery

The first iron production started in the Middle Bronze Age but it took several centuries before iron displaced bronze. Samples ofsmelted iron from Asmar, Mesopotamia and Tall Chagar Bazaar in northern Syria were made sometime between 2700 and 3000 BC.HP Pavilion DV4-1035TX Battery

TheHittites appear to be the first to understand the production of iron from its ores and regard it highly in their society.[27] They 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.HP Pavilion DV4-1036TX Battery

The subsequent period is called the Iron Age. Iron smelting, and thus the Iron Age, reached Europe two hundred years later and arrived in Zimbabwe, Africa by the 8th century.

Artifacts from smelted iron occur in India from 1800 to 1200 BC, and in the Levant from about 1500 BC (suggesting smelting inAnatolia or the Caucasus).HP Pavilion DV4-1037TX Battery

The Book of Genesis, fourth chapter, verse 22 contains the first mention of iron in the Old Testament of the Bible; "Tubal-cain, an instructor of every artificer in brass and iron." Other verses allude to iron mining (Job 28:2), iron used as a stylus (Job 19:24), furnace (Deuteronomy 4:20),HP Pavilion DV4-1038TX Battery

chariots (Joshua 17:16), nails (I Chron. 22:3), saws and axes (II Sam. 12:31), and cooking utensils (Ezekiel 4:3).[38] The metal is also mentioned in the New Testament, for example in Acts chapter 12 verse 10, "[Peter passed through] the iron gate that leadeth unto the city" of Antioch.[39] The Quran referred to Iron 1400 years ago.HP Pavilion DV4-1039TX Battery

Iron working was introduced to Greece in the late 11th century BC.[40] 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.[32] The annual iron output of the Roman Empire is estimated at 84,750 t, while the similarly populous Han China produced around 5,000 t.HP Pavilion DV4-1040EE Battery

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.HP Pavilion DV4-1040EI Battery

Cast iron

Cast iron was first produced in China about 550 BC, but was hardly in Europe until the medieval period. During the medieval period, means were found in Europe of producing wrought iron from cast iron (in this context known as pig iron) using finery forges. For all these processes, charcoal was required as fuel.HP Pavilion DV4-1040TX Battery

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.[45] Modern blast furnaces have grown much bigger.

In 1709, Abraham Darby I established a coke-fired blast furnace to produce cast iron.HP Pavilion DV4-1041TX Battery

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 wasn't implicated as the reason for the differences in properties of wrought iron, cast iron and steel until the 18th century.HP Pavilion DV4-1042TX Battery

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.

Steel

Steel (with smaller carbon content than pig iron but more than wrought iron) was first produced in antiquity by using a bloomery.HP Pavilion DV4-1043TX Battery

Blacksmiths in Luristan in western Iran were making good steel by 1000 BC. Then improved versions, Wootz steel by India and Damascus steel by China were developed around 300 B.C. and 500 A.D. respectively. These methods were specialized, and so steel did not become a major commodity until the 1850s.HP Pavilion DV4-1044TX Battery

New methods of producing it by carburizing bars of iron in the cementation process were devised in the 17th century AD. In the Industrial Revolution, new methods of producing bar iron without charcoal were devised and these were later applied to produce steel.HP Pavilion DV4-1045TX Battery

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.HP Pavilion DV4-1046TX Battery

Foundations of modern chemistry

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 mass conservation. Anaerobic oxidation of iron at high temperature can be schematically represented by the following reactions:HP Pavilion DV4-1047TX Battery

Fe + H2O ? FeO + H2

2 Fe + 3 H2O ? Fe2O3 + 3 H2

3 Fe + 4 H2O ? Fe3O4 + 4 H2

Recent discoveries

• discovery of Mössbauer effectHP Pavilion DV4-1048TX Battery

• many enzymes use iron in the catalytic center
• Nickel-56 is the natural end product of silicon burning in massive stars. However Nickel-56 decays to cobalt-56 and then to stable iron-56, ultimately making iron the most abundant heavy element produced by that nucleosynthesis.
• superconductivity?HP Pavilion DV4-1049TX Battery
• magnetic effect
• ferrocene

Industrial production

The production of iron or steel is a process containing two main stages, unless the desired product is cast iron. The first stage is to produce pig iron in a blast furnace. Alternatively, it may be directly reduced. The second is to make wrought iron or steel from pig iron by a further process.HP Pavilion DV4-1050 Battery

For a few limited purposes like electromagnet cores, pure iron is produced by electrolysis of a ferrous sulfate solution

Blast furnace

Ninety percent of all mining of metallic ores is for the extraction of iron .HP Pavilion DV4-1050EE Battery

Industrially, iron production involves iron ores, principally hematite (nominally Fe2O3) and magnetite (Fe3O4) in a carbothermic reaction (reduction with carbon) in a blast furnace at temperatures of about 2000 °C. In a blast furnace, iron ore, carbon in the form of coke, and a flux such aslimestoneHP Pavilion DV4-1050EL Battery

(which is used to remove silicon dioxide impurities in the ore which would otherwise clog the furnace with solid material) are fed into the top of the furnace, while a massive blast of heated air, about 4 tons per ton of iron,[45] is forced into the furnace at the bottom.HP Pavilion DV4-1050EP Battery

2 C + O2 ? 2 CO

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

Fe2O3 + 3 CO ? 2 Fe + 3 CO2

Some iron in the high-temperature lower region of the furnace reacts directly with the coke:HP Pavilion DV4-1050ER Battery

2 Fe2O3 + 3 C ? 4 Fe + 3 CO2

The flux is present to melt impurities in the ore, principally silicon dioxide sand and othersilicates. Common fluxes include limestone (principally calcium carbonate) and dolomite (calcium-magnesium carbonate). Other fluxes may be used depending on the impurities that need to be removed from the ore.HP Pavilion DV4-1050TX Battery

In the heat of the furnace the limestone flux decomposes tocalcium oxide (also known as quicklime):

CaCO3 ? CaO + CO2

Then calcium oxide combines with silicon dioxide to form a liquid slag.HP Pavilion DV4-1051 Battery

CaO + SiO2 ? CaSiO3

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.HP Pavilion DV4-1051TX Battery

In 2005, approximately 1,544 million metric tons of iron ore were produced worldwide. According to the British Geological Survey, China was the top producer of iron ore with at least one quarter world share, followed by Brazil, Australia and India.HP Pavilion DV4-1052 Battery

Direct iron reduction

Since coke is becoming more regulated due to environmental concerns, alternative methods of processing iron have been developed. One of them is known as direct iron reduction.HP Pavilion DV4-1052TX Battery

It reduces iron ore to a powder substance called sponge iron, which is suitable for steelmaking. There are two main reactions that go on in the direct reduction process:

Natural gas is partially oxidized (with heat and a catalyst):HP Pavilion DV4-1053 Battery

2 CH4 + O2 ? 2 CO + 4 H2

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

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

Silica is removed by adding a flux, i.e. limestone, later.HP Pavilion DV4-1053TX Battery

Further processes

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.HP Pavilion DV4-1054TX Battery

This form of iron, also known as cast iron, is used to cast articles in foundries such as 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).HP Pavilion DV4-1055TX Battery

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.HP Pavilion DV4-1070 Battery

The hardness of the steel depends upon its carbon content: the higher the percentage of carbon, the greater the hardness and the lesser the malleability. The properties of the steel can also be changed by several methods.

Annealing involves the heating of a piece of steel to 700–800 °C for several hours and then gradual cooling. It makes the steel softer and more workable.HP Pavilion DV4-1070EE Battery

Steel may be hardened by cold working. The metal is bent or hammered into its final shape at a relatively cool temperature. Cold forging is the stamping of a piece of steel into shape by a heavy press. Wrenches are commonly made by cold forging.HP Pavilion DV4-1070EF Battery

Cold rolling, which involves making a thinner but harder sheet, and cold drawing, which makes a thinner but stronger wire, are two other methods of cold working. To harden the steel, it is heated to red-hot and then cooled by quenching it in the water. It becomes harder and more brittle.HP Pavilion DV4-1070ER Battery

If it is too hardened, it is then heated to a required temperature and allowed to cool. The steel thus formed is less brittle.

Heat treatment is another way to harden steel. The steel is heated red-hot, then cooled quickly. The iron carbide molecules are decomposed by the heat, but do not have time to reform.HP Pavilion DV4-1070ES Battery

Since the free carbon atoms are stuck, it makes the steel much harder and stronger than before.

Sometimes both toughness and hardness are desired. A process called case hardening may be used. Steel is heated to about 900 °C then plunged into Oil or Water. Carbon from the oil can diffuse into the steel, making the surface very hard.HP Pavilion DV4-1080EI Battery

The surface cools quickly, but the inside cools slowly, making an extremely hard surface and a durable, resistant inner layer.

Iron may be passivated by dipping it into a concentrated nitric acid solution. This forms a protective layer of oxide on the metal, protecting it from further corrosion.HP Pavilion DV4-1080EO Battery

Applications

Iron is the most widely used of all the metals, accounting for 95% 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.HP Pavilion DV4-1080ES Battery

Since pure iron is quite soft, it is most commonly used in the form of steel.

Commercially available iron is classified based on purity and the abundance of additives. Pig iron has 3.5–4.5% carbon[49] and contains varying amounts of contaminants such as sulfur, silicon and phosphorus.HP Pavilion DV4-1090EO Battery

Pig iron is not a saleable product, but rather an intermediate step in the production of cast iron and steel from iron ore. Cast iron contains 2–4% carbon, 1–6% silicon, and small amounts of manganese. Contaminants present in pig iron that negatively affect material properties, such as sulfur and phosphorus, have been reduced to an acceptable level.HP Pavilion DV4-1090ES Battery

It has a melting point in the range of 1420–1470 K, which is lower than either of its two main components, and makes it the first product to be melted when carbon and iron are heated together. Its mechanical properties vary greatly, dependent upon the form carbon takes in the alloy.HP Pavilion DV4-1100 Battery

"White" cast irons contain their carbon in the form of cementite, or iron carbide. This hard, brittle compound dominates the mechanical properties of white cast irons, rendering them hard, but unresistant to shock. The broken surface of a white cast iron is full of fine facets of the broken carbide, a very pale, silvery, shiny material, hence the appellation.HP Pavilion DV4-1100EA Battery

In gray iron the carbon exists free as fine flakes of graphite, and also renders the material brittle due to the stress-raising nature of the sharp edged flakes of graphite. A newer variant of 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, vastly increasing the toughness and strength of the material.HP Pavilion DV4-1101 Battery

Wrought iron contains less than 0.25% carbon. 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 in the metal. Wrought iron is more corrosion resistant than steel.HP Pavilion DV4-1101TU Battery

It has been almost completely replaced by mild steel for traditional "wrought iron" products and blacksmithing.

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 ofmanganese, sulfur, phosphorus, and silicon.HP Pavilion DV4-1101TX Battery

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.HP Pavilion DV4-1102 Battery

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.HP Pavilion DV4-1102TU Battery

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.HP Pavilion DV4-1102TX Battery

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. Painting, galvanization,passivation, plastic coating and bluing are all used to protect iron from rust by excluding water and oxygen or by cathodic protection.HP Pavilion DV4-1103TU Battery

Of compounds

Although its metallurgical role is dominant in terms of amounts, iron compounds are pervasive in industry as well being used in many niche uses. 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.HP Pavilion DV4-1103TX Battery

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.HP Pavilion DV4-1104TU Battery

It can also be dissolved in alcohol to form tincture of iron.[27] The other halides tend to be limited to laboratory uses.

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.HP Pavilion DV4-1104TX Battery

These are its main uses. 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.HP Pavilion DV4-1105EF Battery

Biological role

Iron is abundant in biology. Iron-proteins are found in all living organisms, ranging from the evolutionarily primitive archaea to humans. The color of blood is due to the hemoglobin, an iron-containing protein. As illustrated by hemoglobin, iron often is bound to cofactors, e.g. in hemes.HP Pavilion DV4-1105EM Battery

The iron-sulfur clusters are pervasive and include nitrogenase, the enzymes responsible for biological nitrogen fixation. Influential theories of evolution have invoked a role for iron sulfides, iron-sulfur world theory.

Iron is a necessary trace element found in nearly all living organisms.HP Pavilion DV4-1105TU Battery

Iron-containing enzymes and proteins, often containingheme prosthetic groups, participate in many biological oxidations and in transport. Examples of proteins found in higher organisms include hemoglobin, cytochrome (see high-valent iron), and catalase.HP Pavilion DV4-1105TX Battery

Bioinorganic compounds

The most famous bioinorganic compounds of iron are heme proteins: hemoglobin, myoglobin, and cytochrome P450. These compounds can transport gases, build enzymes, and be used in transferring electrons. Metalloproteins are a group of proteins with metal ioncofactors.HP Pavilion DV4-1106EE Battery

Some examples of iron metalloproteins are ferritin and rubredoxin. Many enzymes vital to life contain iron, such ascatalase, lipoxygenases, and IRE-BP.

Health and diet

Iron is pervasive, but particularly rich sources of dietary iron include red meat, lentils, beans, poultry, fish, leaf vegetables, tofu, chickpeas, black-eyed peas, blackstrap molasses, fortified bread, and fortified breakfast cerealsHP Pavilion DV4-1106EM Battery

Iron in low amounts is found in molasses, teff and farina. Iron in meat (heme iron) is more easily absorbed than iron in vegetables. Although some studies suggest that heme/hemoglobin from red meat has effects which may increase the likelihood of colorectal cancer, there is still some controversy,and even a few studies suggesting that there is not enough evidence to support such claims.HP Pavilion DV4-1106TX Battery

Iron provided by dietary supplements is often found as iron(II) fumarate, although iron 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.HP Pavilion DV4-1107TX Battery

Iron is most available to the body when chelated to amino acids and is also available for use as a common iron supplement. Often the amino acid chosen for this purpose is the cheapest and most common amino acid, glycine, leading to "iron glycinate" supplements.HP Pavilion DV4-1108TX Battery

The Recommended Dietary Allowance(RDA) for iron varies considerably based on age, gender, and source of dietary iron (heme-based iron has higher bioavailability). Infants may require iron supplements if they are bottle-fed cow's milk. Blood donors and pregnant women are at special risk of low iron levels and are often advised to supplement their iron intake.HP Pavilion DV4-1109TX Battery

Uptake and storage

In cells, iron storage is carefully regulated; "free" iron ions do not exist as such. 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.HP Pavilion DV4-1110EO Battery

In animals, plants, and fungi, iron is often the metal ion incorporated into the heme complex. Heme is an essential component of cytochrome proteins, which mediate redox reactions, and of oxygen carrier proteins such as hemoglobin, myoglobin, andleghemoglobin.HP Pavilion DV4-1110TX Battery

Inorganic iron also contributes to redox reactions in the iron-sulfur clusters of many enzymes, such as nitrogenase (involved in the synthesis ofammonia from nitrogen and hydrogen) and hydrogenase. Non-heme iron proteins include the enzymes methane monooxygenase (oxidizes methane to methanol), ribonucleotide reductase (reduces ribose to deoxyribose;HP Pavilion DV4-1111TX Battery

DNA biosynthesis), hemerythrins (oxygen transport and fixation in Marine invertebrates) and purple acid phosphatase(hydrolysis of phosphate esters).

Iron distribution is heavily regulated in mammals, partly because iron ions have a high potential for biological toxicity.HP Pavilion DV4-1112TX Battery

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

Regulation of uptake

Iron uptake is tightly regulated by the human body, which has no regulated physiological means of excreting iron.HP Pavilion DV4-1113TX Battery

Only small amounts of iron are lost daily due to mucosal and skin epithelial cell sloughing, so control of iron levels is mostly 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.HP Pavilion DV4-1114NR Battery

In these people, excessive iron intake can result in iron overload disorders, such ashemochromatosis. Many people have a genetic susceptibility to iron overload without realizing it or being aware of a family history of the problem. For this reason, it is advised that people do not take iron supplements unless they suffer from iron deficiency and have consulted a doctor.HP Pavilion DV4-1114TX Battery

Hemochromatosis is estimated to cause disease in between 0.3 and 0.8% of Caucasians.

MRI finds that iron accumulates in the hippocampus of the brains of those with Alzheimer's disease and in the substantia nigra of those with Parkinson disease.HP Pavilion DV4-1115EF Battery

Permeable reactive barriers

Zero-valent iron is the main reactive material for permeable reactive barriers.

Precautions

Large amounts of ingested iron can cause excessive levels of iron in the blood. High blood levels of free ferrous iron react with peroxides to producefree radicals,HP Pavilion DV4-1115TX Battery

which are highly reactive and can damage DNA, proteins, lipids, and other cellular components. Thus, iron toxicity occurs when there is free iron in the cell, which generally occurs when iron levels exceed the capacity of transferrin to bind the iron.HP Pavilion DV4-1116TX Battery

Damage to the cells of thegastrointestinal 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, which can cause significant adverse effects, including coma, metabolic acidosis, shock, liver failure, coagulopathy,adult respiratory distress syndrome, long-term organ damage, and even death.HP Pavilion DV4-1117CA Battery

Humans experience iron toxicity above 20 milligrams of iron for every kilogram of mass, and 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.HP Pavilion DV4-1117TX Battery

The Dietary Reference Intake (DRI) lists the Tolerable Upper Intake Level (UL) for adults as 45 mg/day. For children under fourteen years old the UL is 40 mg/day.

The medical management of iron toxicity is complicated, and can include use of a specific chelating agent called deferoxamine to bind and expel excess iron from the body.HP Pavilion DV4-1118CA Battery

Iron fertilization is the intentional introduction of iron to the upper ocean to stimulate a phytoplankton bloom. This is intended to enhance biological productivity, which can benefit the marine food chain and remove carbon dioxide from the atmosphere. Iron is a trace element necessary for photosynthesis in all plants.HP Pavilion DV4-1118TX Battery

It is highly insoluble in sea water and is often the limiting nutrient for phytoplankton growth. Large phytoplankton blooms can be created by supplying iron to iron-deficient ocean waters. A number of ocean labs, scientists and businesses are exploring fertilization as a means to sequester atmosphericcarbon dioxide in the deep ocean,HP Pavilion DV4-1119TX Battery

and to increase marine biological productivity which is likely in decline as a result ofclimate change. Since 1993, thirteen international research teams have completed ocean trials demonstrating that phytoplankton blooms can be stimulated by iron addition.HP Pavilion DV4-1120BR Battery

However, controversy remains over the effectiveness of atmospheric CO2 sequestration and ecological effects.[2] The most recent open ocean trial of ocean iron fertilization, dubbed LOHAFEX, was conducted from January to March 2009 in the South Atlantic.HP Pavilion DV4-1120TX Battery

Fertilization also occurs naturally when upwellings bring nutrient-rich water to the surface, as occurs when ocean currents meet an ocean bank or a sea mount. This form of fertilization produces the world's largest marine habitats. Fertilization can also occur when weather carries wind blown dust long distances over the ocean, or iron-rich minerals are carried into the ocean byglaciers, rivers and icebergs.HP Pavilion DV4-1120US Battery

Consideration of iron's importance to phytoplankton growth and photosynthesis dates back to the 1930s when English biologist Joseph Hart speculated that the ocean's great "desolate zones" (areas apparently rich in nutrients, but lacking in plankton activity or other sea life) might simply be iron deficient.HP Pavilion DV4-1120US Battery

Little further scientific discussion of this issue was recorded until the 1980s, when oceanographer John Martin renewed controversy on the topic with his marine water nutrient analyses. His studies indicated it was indeed a scarcity of iron micronutrients that was limiting phytoplankton growth and overall productivity in these "desolate" regions, which came to be called "High Nutrient, Low Chlorophyll" (HNLC) zones.HP Pavilion DV4-1121BR Battery

In an article in the scientific journal Nature (February 1988; 331 (6157): 570ff.), John Gribbin was the first scientist to publicly suggest that the upcoming greenhouse effect might be reduced by adding large amounts of soluble iron compounds to the oceans of the world as a fertilizer for the aquatic plants.HP Pavilion DV4-1121CA Battery

Martin's famous 1991 quip three years later at Woods Hole Oceanographic Institution, "Give me a half a tanker of iron and I will give you another ice age",[5][6]drove a decade of research whose findings suggested that iron deficiency was not merely impacting ocean ecosystems, it also offered a key to mitigating climate change as well.HP Pavilion DV4-1121TX Battery

Perhaps the most dramatic support for Martin's hypothesis was seen in the aftermath of the 1991 eruption of Mount Pinatubo in the Philippines.[citation needed]Environmental scientist Andrew Watson analyzed global data from that eruption and calculated that it deposited approximately 40,000 tons of iron dust into the oceans worldwide.HP Pavilion DV4-1122TX Battery

This single fertilization event generated an easily observed global decline in atmospheric CO2 and a parallel pulsed increase in oxygen levels.

Experiments

Martin hypothesized that increasing phytoplankton photosynthesis could slow or even reverse global warming by sequestering enormous volumes of CO2 in the sea. He died shortly thereafter during preparations for Ironex I,HP Pavilion DV4-1123LA Battery

a proof of concept research voyage, which was successfully carried out near the Galapagos Islands in 1993 by his colleagues at Moss Landing Marine Laboratories.

Despite widespread opposition to LOHAFEX, on 26 January 2009 the German Federal Ministry of Education and Research (BMBF) gave clearance for this fertilization experiment to commence.HP Pavilion DV4-1123TX Battery

The experiment was carried out in waters low in silicic acid which is likely to affect the efficacy of carbon sequestration. A 900 square kilometers (350 sq mi) portion of the southwest Atlantic Ocean was fertilized with iron sulfate. A large phytoplankton bloom was triggered, however this bloom did not contain diatoms because the fertilized location was already depleted in silicic acid, an essential nutrient for diatom growth.HP Pavilion DV4-1123US Battery

In the absence of diatoms, a relatively small amount of carbon was sequestered, because other phytoplankton are vulnerable to predation by zooplankton and do not sink rapidly upon death. These poor sequestration results have caused some to suggest that ocean iron fertilization is not an effective carbon mitigation strategy in general.HP Pavilion DV4-1124LA Battery

However, prior ocean fertilization experiments in high silica locations have observed much higher carbon sequestration rates because of diatom growth. LOHAFEX has just confirmed that the carbon sequestration potential depends strongly upon careful choice of location.HP Pavilion DV4-1124NR Battery

The maximum possible result from iron fertilization, assuming the most favourable conditions and disregarding practical considerations, is 0.29W/m2 of globally averaged negative forcing, which is almost sufficient to reverse the warming effect of about 1/6 of current levels of anthropogenic CO2 emissions.HP Pavilion DV4-1124TX Battery

It is notable, however, that the addition of silicic acid or choosing the proper location could, at least mathematically, eliminate and exceed all man made CO2. Further tests and experiments are required to test this theory and observe potential negative impact.HP Pavilion DV4-1125BR Battery

The role of iron

About 70% of the world's surface is covered in oceans, and the upper part of these (where light can penetrate) is inhabited by algae. In some oceans, the growth and reproduction of these algae is limited by the amount of iron in the seawater.HP Pavilion DV4-1125LA Battery

Iron is a vital micronutrient for phytoplankton growth and photosynthesis that has historically been delivered to the pelagic sea by dust storms from arid lands. This Aeolian dust contains 3–5% iron and its deposition has fallen nearly 25% in recent decades.HP Pavilion DV4-1125NR Battery

The Redfield ratio describes the relative atomic concentrations of critical nutrients in plankton biomass and is conventionally written "106 C: 16 N: 1 P." This expresses the fact that one atom of phosphorus and 16 of nitrogen are required to "fix" 106 carbon atoms (or 106 molecules of CO2).HP Pavilion DV4-1125TX Battery

Recent research has expanded this constant to "106 C: 16 N: 1 P: .001 Fe" signifying that in iron deficient conditions each atom of iron can fix 106,000 atoms of carbon,or on a mass basis, each kilogram of iron can fix 83,000 kg of carbon dioxide. The 2004 EIFEX experiment reported a carbon dioxide to iron export ratio of nearly 3000 to 1.HP Pavilion DV4-1126LA Battery

The atomic ratio would be approximately: "3000 C: 58,000 N: 3,600 P: 1 Fe".

Therefore small amounts of iron (measured by mass parts per trillion) in "desolate" HNLC zones can trigger large phytoplankton blooms. Recent marine trials suggest that one kilogram of fine iron particles may generate well over 100,000 kilograms of plankton biomass.HP Pavilion DV4-1126TX Battery

The size of the iron particles is critical, however, and particles of 0.5–1 micrometer or less seem to be ideal both in terms of sink rate and bioavailability. Particles this small are not only easier for cyanobacteriaand other phytoplankton to incorporate, the churning of surface waters keeps them in the euphotic or sunlit biologically active depths without sinking for long periods of time.HP Pavilion DV4-1127LA Battery

Carbon sequestration

Previous instances of biological carbon sequestration have triggered major climatic changes, such as theAzolla event. Plankton that generate calcium or silicon carbonate skeletons, such as diatoms,coccolithophores and foraminifera, account for most direct carbon sequestration.HP Pavilion DV4-1127TX Battery

When these organisms die their carbonate skeletons sink relatively quickly and form a major component of the carbon-rich deep sea precipitation known as marine snow. Marine snow also includes fish fecal pellets and other organic detritus, and can be seen steadily falling thousands of meters below active plankton blooms.HP Pavilion DV4-1128TX Battery

Of the carbon-rich biomass generated by plankton blooms, half (or more) is generally consumed by grazing organisms (zooplankton, krill, small fish, etc.) but 20 to 30% sinks below 200 meters (660 ft) into the colder water strata below the thermocline.HP Pavilion DV4-1129LA Battery

Much of this fixed carbon continues falling into the abyss, but a substantial percentage is redissolved and remineralized. At this depth, however, this carbon is now suspended in deep currents and effectively isolated from the atmosphere for centuries. (The surface to benthic cycling time for the ocean is approximately 4,000 years.)HP Pavilion DV4-1129TX Battery

Analysis and quantification

Evaluation of the biological effects and verification of the amount of carbon actually sequestered by any particular bloom requires a variety of measurements, including a combination of ship-borne and remote sampling, submarine filtration traps, tracking buoy spectroscopy and satellite telemetry.HP Pavilion DV4-1130BR Battery

Unpredictable ocean currents have been known to remove experimental iron patches from the pelagic zone, invalidating the experiment.

The potential of iron fertilization as a geoengineering technique to tackle global warming is illustrated by the following figures.HP Pavilion DV4-1130TX Battery

If phytoplankton converted all the nitrate and phosphate present in the surface mixed layer across the entire Antarctic circumpolar current into organic carbon, the resulting carbon dioxide deficit could be compensated by uptake from the atmosphere amounting to about 0.8 to 1.4 gigatonnes of carbon per year.HP Pavilion DV4-1131BR Battery

This quantity is comparable in magnitude to annual anthropogenic fossil fuels combustion of approximately 6 gigatonnes. It should be noted that the Antarctic circumpolar current region is only one of several in which iron fertilization could be conducted—the Galapagos islands area being another potentially suitable location.HP Pavilion DV4-1131TX Battery

Dimethyl sulfide and clouds

Some species of plankton produce dimethyl sulfide (DMS), a portion of which enters the atmosphere where it is oxidized by hydroxyl radicals (OH), atomic chlorine(Cl) and bromine monoxide (BrO) to form sulfate particles and ultimately clouds.HP Pavilion DV4-1132TX Battery

This may increase the albedo of the planet and so cause cooling. This is the basic tenet of the Gaia hypothesis and was presented in James Lovelock's first paper published on this topic.

During the Southern Ocean Iron Enrichment Experiments (SOFeX), DMS concentrations increased by a factor of four inside the fertilized patch.HP Pavilion DV4-1133TX Battery

Widescale iron fertilization of the Southern Ocean could lead to significant sulfur-triggered cooling in addition to that due to the increased CO2 uptake and that due to the ocean's albedo increase, however the amount of cooling by this particular effect is very uncertain.HP Pavilion DV4-1134TX Battery

Financial opportunities

Since the advent of the Kyoto Protocol, several countries and the European Union have established carbon offset markets which trade certified emission reduction credits (CERs) and other types of carbon credit instruments internationally.HP Pavilion DV4-1135BR Battery

In 2007 CERs sell for approximately €15–20/ton CO2e and European analysts project these prices will nearly double by 2012. Iron fertilization is relatively inexpensive compared to scrubbing, direct injection and other industrial approaches, and can theoretically sequester for less than €5/ton CO2, creating a substantial return.HP Pavilion DV4-1135EE Battery

In August, 2010, Russia established a minimum price of €10/ton for offsets to reduce uncertainty for offset providers. Scientists have reported a minimum 6–12% decline in global plankton production since 1980,A full-scale international plankton restoration program could regenerate approximately 3–5 billion tons of sequestration capacity worth €50-100 billion in carbon offset value.HP Pavilion DV4-1135EI Battery

Given this potential return on investment, carbon traders and offset customers are watching the progress of this technology with interest.

Multilateral reaction

The parties to the London Dumping Convention (Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972) adopted a non-binding resolution in 2008 on fertilization (labeled LC-LP.1(2008)).HP Pavilion DV4-1135TX Battery

The resolution states that ocean fertilization activities, other than legitimate scientific research, "should be considered as contrary to the aims of the Convention and Protocol and do not currently qualify for any exemption from the definition of dumping".

An Assessment Framework for Scientific Research Involving Ocean Fertilization, regulating the dumping of wastes at sea (labeled LC-LP.2(2010)) was adopted by the Contracting Parties to the Convention in October 2010 (LC 32/LP 5).HP Pavilion DV4-1136BR Battery

Sequestration definitions

Carbon is not considered "sequestered" unless it settles to the ocean floor where it remains for eons. Most of the carbon that sinks beneath plankton blooms is dissolved and remineralized well above the seafloor and will eventually (days to centuries) return to the atmosphere, negating the original effect.HP Pavilion DV4-1136TX Battery

Advocates argue that modern climate scientists and Kyoto Protocol policy makers define sequestration in much shorter time frames. For example, they recognize trees and grasslands as important carbon sinks. Forest biomass only sequesters carbon for decades, but carbon that sinks below the marine thermocline (100–200 meters)HP Pavilion DV4-1137TX Battery

is effectively removed from the atmosphere for hundreds of years, whether it is remineralized or not. Since deep ocean currents take so long to resurface, their carbon content is effectively sequestered by the criterion in use today.

Debate

While many advocates of ocean iron fertilization see it as modern society's last best hope to slow global warming, some academics, deep greens and proponents of competing technologies cite a variety of concerns.HP Pavilion DV4-1138TX Battery

Precautionary principle

The precautionary principle (PP) states that if an action or policy has a suspected risk of causing harm, in the absence of scientific consensus, the burden of proofthat it is not harmful falls on those who would take the action. The side effects of large-scale iron fertilization are not yet known.HP Pavilion DV4-1139TX Battery

Creating phytoplankton blooms in naturally iron-poor areas of the ocean is like watering the desert: in effect it changes one type of ecosystem into another. Such large and rapid conversions have no precedent.

The argument can be applied in reverse, by considering emissions to be the action and remediation an attempt to partially offset the damage.HP Pavilion DV4-1140EK Battery

20th century phytoplankton decline

While advocates argue that iron addition would help to reverse a supposed decline in phytoplankton, this decline may not be real. One study reported a decline in ocean productivity comparing the 1979–1986 and 1997–2000 periods,[35] but two others found increases in phytoplankton.HP Pavilion DV4-1140GO Battery

Comparison to prior phytoplankton cycles

Fertilization advocates respond that similar algal blooms have occurred naturally for millions of years with no observed ill effects. The Azolla event occurred around 49 million years ago and accomplished what fertilization is intended to achieve (but on a larger scale).HP Pavilion DV4-1140TX Battery

Sequestration efficiency

Fertilization may sequester too little carbon per bloom, supporting the food chain rather than raining on the ocean floor, and thus require too many seeding voyages to be practical. A 2009 Indo-German team of scientists examined the potential of the south-western Atlantic to sequester significant amounts of carbon dioxide, but found few positive results.HP Pavilion DV4-1141TX Battery

The counter-argument to this is that the low sequestration estimates that emerged from some ocean trials are largely due to these factors:

1. Data: none of the ocean trials had enough boat time to monitor their blooms for more than 27 days, confining their measurements to that period. Blooms generally last 60–90 days with the heaviest "precipitation" occurring during the last two months.HP Pavilion DV4-1142TX Battery
2. Scale: most trials used less than 1,000 kilograms (2,200 lb) of iron and thus created small blooms that were quickly devoured by opportunistic zooplankton, krill, and fish that swarmed into the seeded region.HP Pavilion DV4-1143GO Battery

Some ocean trials reported positive results. IronEx II reported conversion of 1,000 kilograms (2,200 lb) to carbonaceous biomass equivalent to one hundred full-grownredwoods within two weeks. Eifex recorded fixation ratios of nearly 300,000 to 1.HP Pavilion DV4-1143TX Battery

Current estimates of the amount of iron required to restore all the lost plankton and sequester 3 gigatons/year of CO2 range widely, from approximately 2 hundred thousand tons/year to over 4 million tons/year. The latter scenario involves 16 supertanker loads of iron and a projected cost of approximately €20 billion ($27 billion).HP Pavilion DV4-1144TX Battery

Ecological issues

Critics are concerned that fertilization will create harmful algal blooms (HAB). The species that respond most strongly to fertilization vary by location and other factors and could possibly include species that cause red tides and other toxic phenomena.HP Pavilion DV4-1144US Battery

These factors affect only near-shore waters, although they show that increased phytoplankton populations are not universally benign.

Most species of phytoplankton are harmless or beneficial, given that they constitute the base of the marine food chain.HP Pavilion DV4-1145BR Battery

Fertilization increases phytoplankton only in the deep oceans (far from shore) where iron deficiency is the problem. Most coastal waters are replete with iron and adding more has no useful effect.

A 2010 study of iron fertilization in an oceanic high-nitrate, low-chlorophyll environment, however, found that fertilizedPseudo-nitzschia diatom spp.,HP Pavilion DV4-1145GO Battery

which are generally nontoxic in the open ocean, began producing toxic levels of domoic acid. Even short-lived blooms containing such toxins could have detrimental effects on marine food webs.

Deep water oxygen levels

When organic bloom detritus sinks into the abyss, a significant fraction will be devoured by bacteria, other microorganisms and deep sea animals which also consume oxygen.HP Pavilion DV4-1145TX Battery

A large enough bloom could render certain regions of the sea deep beneath it anoxic and threaten other benthic species.

The largest plankton replenishment projects under consideration are less than 10% the size of most natural wind-fed blooms.HP Pavilion DV4-1146TX Battery

In the wake of major dust storms, natural blooms have been studied since the beginning of the 20th century and no such deep water dieoffs have been reported.

Ecosystem effects

Depending upon the composition and timing of delivery, iron infusions could preferentially favor certain species and alter surface ecosystems to unknown effect.HP Pavilion DV4-1147CL Battery

Population explosions of jellyfish, disturbance of the food chain impacting whale populations or fisheries are potential risks.

A 2010 study shows that iron enrichment stimulates toxic diatom production in high-nitrate, low-chlorophyll areas , which, the authors argue, raises "serious concerns over the net benefit and sustainability of large-scale iron fertilizations".HP Pavilion DV4-1147TX Battery

However, CO2-induced surface water heating and rising carbonic acidity are already shifting population distributions for phytoplankton, zooplankton and many other creatures. Optimal fertilization could potentially help restore lost/threatened ecosystem services.HP Pavilion DV4-1148TX Battery

Conclusion and further research

Critics and advocates generally agree that most questions on the impact, safety and efficacy of ocean iron fertilization can only be answered by much larger studies.HP Pavilion DV4-1149TX Battery

A statement published in Science in 2008 maintained that it would be premature to sell carbon offsets from the first generation of commercial-scale OIF experiments unless there is better demonstration that OIF effectively removes CO2, retains that carbon in the ocean for a quantifiable amount of time, and has acceptable and predictable environmental impacts.HP Pavilion DV4-1150BR Battery

One pilot project planned by Planktos, a U.S. company, was cancelled in 2008 for lack of funding. The company blamed environmental organizations for the failure.

Iron has a long and varied tradition in the mythology and folklore of the world.HP Pavilion DV4-1150EO Battery

As human blood smells of the iron which its cells contain, and blood in many traditions is equated with the life-force, so iron and minerals have been considered to be the blood or life-force of the Earth. This relationship is charted further in literature on geomancy, ley lines and songlines.HP Pavilion DV4-1150EP Battery

Fred Hoyle's observation of stellar formation champions iron as the core of celestial bodies.

In Plutarch's mystical writings, iron and lodestone is referred to as the 'bone' or 'core' of the gods. Symbolically, iron is the bone, the foundation or the mineral core of both blood and red ochre.HP Pavilion DV4-1150ER Battery

Cold iron is a poetic and archaic term for iron, referring to the fact that it feels cold to the touch. In modern usage the term has been most associated with folkloric beliefs that iron could ward off ghosts, fairies, witches, and/or other malevolent supernatural creatures.HP Pavilion DV4-1150ES Battery

Francis Grose's 1811 Dictionary of the Vulgar Tongue defines cold iron as "A sword, or any other weapon for cutting or stabbing." This usage often appears as "cold steel" in modern parlance.

"Cold iron" is sometimes asserted to repel, contain, or harm ghosts, fairies, witches, and/or other malevolent supernatural creatures. This belief continued into later superstitions in a number of forms:HP Pavilion DV4-1150TX Battery

• Nailing an iron horseshoe to a door was said to repel evil spirits or later, to bring good luck.
• Surrounding a cemetery with an iron fence was thought to contain the souls of the dead.
• Burying an iron knife under the entrance to one's home was alleged to keep witches from entering.HP Pavilion DV4-1151TX Battery

In his story, Redgauntlet, the Scottish author Sir Walter Scott wrote, "Your wife's a witch, man; you should nail a horse-shoe on your chamber-door."

Rudyard Kipling's poem "Cold Iron", found in his 1910 collection of stories Rewards and Fairies, used the term poetically to mean 'weapon'.HP Pavilion DV4-1152TX Battery

Faeries and iron

Iron, particularly "Cold iron", was employed as a protective substance or charm against faeries. In various folklores, supernatural creatures are held to hold an aversion to iron or even be harmed by the touch of iron. Conversely, amongst Asian traditions, there are tales of ironworking fairies.HP Pavilion DV4-1153TX Battery

For luck

Horseshoes are considered a good luck charm in many cultures, including those of England, Denmark and Estonia, and its shape, fabrication, placement and manner of sourcing are all important. A common tradition is that if a horseshoe is hung on a door with the two ends pointing up (as shown here) then good luck will occur.HP Pavilion DV4-1154TX Battery

However, if the two ends point downwards then bad luck will occur. Traditions do differ on this point, though. In some cultures, the horseshoe is hung points down (so the luck pours onto you); in others, it is hung points up (so the luck doesn't fall out); still in others it doesn't matter so long as the horseshoe has been used (not new), was found (not purchased), and can be touched.HP Pavilion DV4-1155SE Battery

In all traditions, luck is contained in the shoe and canpour out through the ends.

In some traditions, any good or bad luck achieved will only occur to the owner of the horseshoe, not the person who hangs it up. Therefore, if the horseshoe was stolen, borrowed or even just found then the owner, not the person who found or stole the horseshoe will get any good or bad luck.HP Pavilion DV4-1155TX Battery

Other traditions require that the horseshoe be found to be effective.

One reputed origin of the tradition of lucky horseshoes is the story of Saint Dunstan and the Devil. Dunstan, who would become the Archbishop of Canterbury in AD 959, was a blacksmith by trade.HP Pavilion DV4-1156TX Battery

The story relates that he once nailed a horseshoe to the Devil's hoof when he was asked to reshoe the Devil's horse. This caused the Devil great pain, and Dunstan only agreed to remove the shoe and release the Devil after the Devil promised never to enter a place where a horseshoe is hung over the door.HP Pavilion DV4-1157TX Battery

Another theory concerning the placing of horseshoes above doorways is to ward off Faeries; the theory being that supernatural beings are repelled by iron and as horseshoes were an easily available source of iron, they could be nailed above a door to prevent any unwanted, otherworldly guests.HP Pavilion DV4-1158TX Battery

Meteoric Iron in Tibet

Thogcha means 'sky-iron' in Tibetan. Meteoric iron was highly prized throughout the Himalayas where it was included in sophisticated polymetallic alloys for ritual implements such as the singing bowl (Jansen, 1992) and phurba (Müller-Ebeling, et al., 2002).HP Pavilion DV4-1159TX Battery

Beer (1999: p. 234) holds that:

"Meteoric iron or 'sky-iron' (Tib. gnam lcags) is the supreme substance for forging the physical representation of the vajra or other iron weapons, since it has already been tempered by the celestial gods in its passage across the heavens.HP Pavilion DV4-1160ES Battery

The indivisibility of form and emptiness is a perfect metaphor for the image of a meteorite or 'stone fallen from the sky', manifesting out of the voidness of space as a shooting star or fireball, and depositing a chunk of fused 'sky iron' on the earth below.HP Pavilion DV4-1160TX Battery

Many vajras held by deities as weapons are described as being forged from meteorite iron, and Tibet, with its high altitude, thin atmosphere and desolate landscape, received an abundance of meteorite fragments. Tibetan vajras were often cast from meteorite iron, and as an act of sympathetic magic a piece of the meteoric iron was often returned to its original site."HP Pavilion DV4-1161TX Battery

Blood and ochre

In many indigenous Australian Aboriginal peoples' traditions ochre and blood, both high in iron content and considered Maban, are applied to the bodies of dancers for ritual. As Lawlor (1991: p. 102-103) states:HP Pavilion DV4-1162TX Battery

In many Aboriginal rituals and ceremonies, red ochre is rubbed all over the naked bodies of the dancers. In secret, sacred male ceremonies, blood extracted from the veins of the participant's arms is exchanged and rubbed on their bodies. Red ochre is used in similar ways in less secret ceremonies.HP Pavilion DV4-1163TX Battery

Blood is also used to fasten the feathers of birds onto people's bodies. Bird feathers contain a protein that is highly magnetically sensitive.

Lawlor comments that blood employed in this fashion is held by these peoples to attune the dancers to the invisible energetic realm of the Dreamtime. HP Pavilion DV4-1164TX Battery

Lawlor then draws information from different disciplines charting a relationship between these invisible energetic realms and magnetic fields. Iron and magnetism having a marked relationship.HP Pavilion DV4-1165TX Battery

Songlines, magnetic fields and wayfinding

Lawlor (1991: p. 105) quotes the biophysicists F. A. Brown and F. H. Barnwell who have conducted research on the biological effects of the Earth's magnetic field (and particularly how it relates with directionality and wayfinding):HP Pavilion DV4-1166CA Battery

There remains no reasonable doubt that living systems are extraordinarily sensitive to magnetic fields. By extremely simple experiments it is shown that highly diverse plants and animals may have their orientation modified by artificial fields of the order of strength of the geo-magnetic field...HP Pavilion DV4-1166TX Battery

The nature of the response properties suggest that the organism is normally integrated with its geo-magnetic environment to a striking degree.

Lawlor then builds on this with citing research conducted on homing pigeons which has pinpointed a tiny crystal in their brain.HP Pavilion DV4-1167TX Battery

This crystal which is supersensitive to the Earth's magnetic fields or geomagnetic currents, works in tandem with the birds other wayfinding propensities. As Mathrani (2002) states:

Many animals have the ability to sense the geomagnetic field and utilize it as a source of directional (compass) information.HP Pavilion DV4-1168TX Battery

Studies have shown that salamanders and frogs use magnetic fields for orientation when they have to find a way to escape from danger, such as from predators. Other animals that have been known to migrate via the detection of the Earth's magnetic field include sparrows, pigeons, bobolinks, yellow fin tuna fish, honeybees, and bacteria.HP Pavilion DV4-1169TX Battery

Magnetite has been found in the tissues of all these organisms.

Crystals of magnetite have been found in some bacteria (e.g., Magnetospirillum magnetotacticum) and in the brains of bees, of termites, of some birds (e.g., thepigeon), and of humans.HP Pavilion DV4-1180BR Battery

These crystals are thought to be involved in magnetoreception, the ability to sense the polarity or the inclination of the Earth's magnetic field, and to be involved in navigation. Also, chitons have teeth made of magnetite on their radula making them unique among animals. This means they have an exceptionally abrasive tongue with which to scrape food from rocks.HP Pavilion DV4-1190BR Battery

The study of biomagnetism began with the discoveries of Caltech paleoecologist Heinz Lowenstam in the 1960s.HP Pavilion DV4-1190EA Battery,HP Pavilion DV4-1190EJ Battery,HP Pavilion DV4-1190EL Battery,HP Pavilion DV4-1198ER Battery,HP Pavilion DV4-1199EA Battery