Aluminum

Aluminium is a silvery white and ductile member of the poor metal group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water, under normal circumstances. Aluminium is the most abundant metal in the Earth's crust, and the third most abundant element overall, after oxygen and silicon. It makes up about 8% by weight of the Earth's solid surface. Aluminium is too reactive chemically to occur in nature as the free metal. Instead, it is found combined in over 270 different minerals. The chief source of aluminium is bauxite ore. Aluminium is remarkable for its ability to resist corrosion (due to the phenomenon of passivation) and its light weight. Structural components made from aluminium and its alloys are vital to the aerospace industry and very important in other areas of transportation and building.

Aluminium is a soft, lightweight, malleable metal with appearance ranging from silvery to dull gray, depending on the surface roughness. Aluminium is nontoxic, (Aluminium is a neurotoxin), nonmagnetic, and nonsparking. It is also insoluble in alcohol, though it can be soluble in water only in certain forms. The yield strength of pure aluminium is 7-11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has about one-third the density and stiffness of steel. It is ductile, and easily machined, cast, and extruded.

Corrosion resistance is excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation. The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper.

Aluminium atoms are arranged in an FCC structure. Aluminium has a high stacking-fault energy of approximately 200 mJ/m2.

Aluminium is one of the few metals that retain full silvery reflectance in finely powdered form, making it an important component of silver paints. Aluminium mirror finish has the highest reflectance of any metal in the 200-400 nm (UV) and the 3000-10000 nm (far IR) regions, while in the 400-700 nm visible range it is slightly outdone by silver and in the 700-3000 (near IR) by silver, gold, and copper.

Aluminium is a good thermal and electrical conductor, by weight better than copper. Aluminium is capable of being a superconductor, with a superconducting critical temperature of 1.2 kelvins.

Aluminium has nine isotopes, whose mass numbers range from 23 to 30. Only 27Al (stable isotope) and 26Al (radioactive isotope, t1/2 = 7.2 x 105 y) occur naturally, however 27Al has a natural abundance of 99.9+ %. 26Al is produced from argon in the atmosphere by spallation caused by cosmic-ray protons. Aluminium isotopes have found practical application in dating marine sediments, manganese nodules, glacial ice, quartz in rock exposures, and meteorites. The ratio of 26Al to 10Be has been used to study the role of transport, deposition, sediment storage, burial times, and erosion on 105 to 106 year time scales. Cosmogenic 26Al was first applied in studies of the Moon and meteorites. Meteorite fragments, after departure from their parent bodies, are exposed to intense cosmic-ray bombardment during their travel through space, causing substantial 26Al production. After falling to Earth, atmospheric shielding protects the meteorite fragments from further 26Al production, and its decay can then be used to determine the meteorite's terrestrial age. Meteorite research has also shown that 26Al was relatively abundant at the time of formation of our planetary system. Most meteoriticists believe that the energy released by the decay of 26Al was responsible for the melting and differentiation of some asteroids after their formation 4.55 billion years ago.

Aluminium is a soft, lightweight, malleable metal with appearance ranging from silvery to dull gray, depending on the surface roughness. Aluminium is nontoxic, (Aluminium is a neurotoxin), nonmagnetic, and nonsparking. It is also insoluble in alcohol, though it can be soluble in water only in certain forms. The yield strength of pure aluminium is 7-11 MPa, while aluminium alloys have yield strengths ranging from 200 MPa to 600 MPa. Aluminium has about one-third the density and stiffness of steel. It is ductile, and easily machined, cast, and extruded.

Corrosion resistance is excellent due to a thin surface layer of aluminium oxide that forms when the metal is exposed to air, effectively preventing further oxidation. The strongest aluminium alloys are less corrosion resistant due to galvanic reactions with alloyed copper. Aluminium atoms are arranged in an FCC structure. Aluminium has a high stacking-fault energy of approximately 200 mJ/m².

Aluminium is one of the few metals that retain full silvery reflectance in finely powdered form, making it an important component of silver paints. Aluminium mirror finish has the highest reflectance of any metal in the 200–400 nm (UV) and the 3000–10000 nm (far IR) regions, while in the 400–700 nm visible range it is slightly outdone by silver and in the 700–3000 (near IR) by silver, gold, and copper.

Aluminium is a good thermal and electrical conductor, by weight better than copper. Aluminium is capable of being a superconductor, with a superconducting critical temperature of 1.2 kelvins.

Although aluminium is the most abundant metallic element in the Earth's crust (believed to be 7.5 to 8.1 percent), it is rare in its free form, occurring in oxygen-deficient environments such as volcanic mud, and it was once considered a precious metal more valuable than gold. Napoleon III, emperor of the French, is reputed to have given a banquet where the most honoured guests were given aluminium utensils, while the other guests had to make do with gold ones. Aluminium has been produced in commercial quantities for just over 100 years.

Aluminium is a reactive metal that is difficult to extract from ore, aluminium oxide (Al2O3). For example, direct reduction with carbon is not economically viable, since aluminium oxide has a melting point of about 2,000 °C. Therefore, it is extracted by electrolysis; that is, the aluminium oxide is dissolved in molten cryolite and then reduced to the pure metal. By this process, the operational temperature of the reduction cells is around 950 to 980 °C. Cryolite is found as a mineral in Greenland, but in industrial use it has been replaced by a synthetic substance. Cryolite is a mixture of aluminium, sodium, and calcium fluorides: (Na3AlF6). The aluminium oxide (a white powder) is obtained by refining bauxite in the Bayer process of Karl Bayer. (Previously, the Deville process was the predominant refining technology.)

The electrolytic process replaced the Wöhler process, which involved the reduction of anhydrous aluminium chloride with potassium. Both of the electrodes used in the electrolysis of aluminium oxide are carbon. Once the ore is in the molten state, its ions are free to move around. The reaction at the cathode — the negative terminal — is:

Al3++ 3 e- ->Al

Here the aluminium ion is being reduced (electrons are added). The aluminium metal then sinks to the bottom and is tapped off.

At the positive electrode (anode), oxygen is formed:

2 O2- -> O2 + 4 e-

This carbon anode is then oxidized by the oxygen, releasing carbon dioxide. The anodes in a reduction cell must therefore be replaced regularly, since they are consumed in the process:

O2 + C -> CO2

Unlike the anodes, the cathodes are not oxidised because there is no oxygen present at the cathode. The carbon cathode is protected by the liquid aluminium inside the cells. Nevertheless, cathodes do erode, mainly due to electrochemical processes. After five to ten years, depending on the current used in the electrolysis, a cell has to be rebuilt because of cathode wear.

Casting

Casting is a manufacturing process by which a liquid material such as a suspension of minerals as used in ceramics or molten metal or plastic is introduced into a mould, allowed to solidify within the mould, and then ejected or broken out to make a fabricated part. Casting is used for making parts of complex shape that would be difficult or uneconomical to make by other methods, such as cutting from solid material.

Casting may be used to form hot, liquid metals or meltable plastics (called thermoplastics), or various materials that cold set after mixing of components such as certain plastic resins such as epoxy, water setting materials such as concrete or plaster, and materials that become liquid or paste when moist such as clay, which when dry enough to be rigid is removed from the mold, further dried, and fired in a kiln or furnace.

Substitution is always a factor in deciding whether other techniques should be used instead of casting. Alternatives include parts that can be stamped out on a punch press or deep-drawn, forged, items that can be manufactured by extrusion or by cold-bending, and parts that can be made from highly active metals.

The casting process is subdivided into two distinct subgroups: expendable and nonexpendable mold casting.

Cobalt

Cobalt is a hard, lustrous, silver-grey metal, a chemical element with symbol Co. It is found in various ores, and is used in the preparation of magnetic, wear-resistant, and high-strength alloys. Its compounds are used in the production of inks, paints, and varnishes.

Cobalt metal is a silver or gray ferromagnetic. Pure cobalt is not found in nature, but compounds of cobalt occur naturally in many forms. Small amounts of it are found in most rocks, soil, water, plants, and animals. It is an element of atomic number 27. The Curie temperature is of 1388 K with 1.6~1.7 Bohr magnetons per atom. In nature, it is frequently associated with nickel, and both are characteristic ingredients of meteoric iron. Mammals require small amounts of cobalt which is the basis of vitamin B12. Cobalt-60, an artificially produced radioactive isotope of cobalt, is an important radioactive tracer and cancer-treatment agent. Cobalt has a relative permeability two thirds that of iron. Metallic cobalt commonly presents a mixture of two crystallographic structures hcp and fcc with a transition temperature hcp?fcc of 722 K. Cobalt has a hardness of 5.5 on the Mohs scale of mineral hardness.

Common oxidation states of cobalt include +2 and +3, although compounds with oxidation state +1 are also well developed.

Naturally occurring cobalt is "monoisotopic", i.e. only one isotope is stable: 59Co. 22 radioisotopes have been characterized with the most stable being 60Co with a half-life of 5.2714 years, 57Co with a half-life of 271.79 days, 56Co with a half-life of 77.27 days, and 58Co with a half-life of 70.86 days. All of the remaining radioactive isotopes have half-lives that are less than 18 hours and the majority of these have half-lives that are less than 1 second. This element also has 4 meta states, all of which have half-lives less than 15 minutes.

The isotopes of cobalt range in atomic weight from 50 u (50Co) to 73 u (73Co). The primary decay mode for isotopes with atomic mass unit values less than that of the most abundant stable isotope, 59Co, is electron capture and the primary mode of decay for those of greater than 59 atomic mass units is beta decay. The primary decay products before 59Co are element 26 (iron) isotopes and the primary products after are element 28 (nickel) isotopes.

Cobalt-60 (Co-60 or 60Co) is a radioactive metal that is used in radiotherapy. It produces two gamma rays with energies of 1.17 MeV and 1.33 MeV. The 60Co source is about 2 cm in diameter and as a result produces a geometric penumbra, making the edge of the radiation field fuzzy. The metal has the unfortunate habit of producing a fine dust, causing problems with radiation protection. The 60Co source is useful for about 5 years but even after this point is still very radioactive, and so cobalt machines have fallen from favor in the Western world where linacs are common.

Cobalt-57 (Co-57 or 57Co) is a radioactive metal that is used in medical tests; it is used as a radiolabel for vitamin B12 uptake. It is useful for the Schilling's test.

Cobalt-60 (Co-60 or 60Co) is useful as a gamma ray source because it can be produced—in predictable quantity, and high activity—by simply exposing natural cobalt to neutrons in a reactor for a given time. It is used for:



Alloys, such as:
Magnets and magnetic recording media:
  • Catalysts for the petroleum and chemical industries, e.g. for hydroformylation and oxidation.
  • Electroplating because of its appearance, hardness, and resistance to oxidation.
  • Drying agents for paints, varnishes, and inks.
  • Ground coats for porcelain enamels.
  • Pigments (cobalt blue and cobalt green).
    Cobalt is not found as a native metal but generally found in the form of ores. Cobalt is usually not mined alone, and tends to be produced as a by-product of nickel and copper mining activities. The main ores of cobalt are cobaltite, erythrite, glaucodot, and skutterudite.

    There is a wide variety of cobalt compounds. The +2 and +3 oxidation states are most prevalent, however cobalt(I) complexes are also fairly common. Cobalt(II) salts form the red-pink [Co(OH2)6]2+ complex in aqueous solution. Adding excess chloride will also change the colour from pink to blue, due to the formation of [CoCl4]2-. Cobalt oxides are antiferromagnetic at low temperature: CoO (Neel temperature 291 K) and Co3O4 (Neel temperature: 40 K), which is analogous to magnetite (Fe3O4), with a mixture of +2 and +3 oxidation states. The oxide Co2O3 is probably unstable; it has never been synthesized. Other than Co3O4 and the brown fluoride CoF3 (which is instantly hydrolyzed in water), all compounds containing cobalt in the +3 oxidation state are stabilized by complex ion formation.

    Iron

    Iron is a chemical element with the symbol Fe (Latin: ferrum) and atomic number 26. Iron is a group 8 and period 4 element. Iron is a lustrous, silvery soft metal. Iron and nickel are notable for being the final elements produced by stellar nucleosynthesis, and thus are the heaviest elements which do not require a red giant or supernova for formation. Iron and nickel are therefore the most abundant metals in metallic meteorites and in the dense-metal cores of planets such as Earth. It is one of the few ferromagnetic elements.

    Iron is believed to be the sixth most abundant element in the universe, formed as the final act of nucleosynthesis by carbon burning in massive stars. Iron is the most abundant element on Earth. While it makes up only about 5% of the Earth's crust, the earth's core is believed to consist largely of a metallic iron-nickel alloy comprising 35% of the mass of the Earth as a whole. Iron is the fourth most abundant element in the Earth's crust[4] and the second most abundant metal after aluminium. Most of the iron in the crust is found combined with oxygen as iron oxide minerals such as hematite, magnetite, and taconite. About 5% of the meteorites similarly consist of iron-nickel alloy. Although rare, these are the major form of natural metallic iron on the earth's surface.

    The reason for Mars' red colour is thought to be an iron-oxide-rich soil.

    Iron is a metal extracted mainly from the iron ore hematite. It oxidises readily in air and water and is rarely found as a free element. In order to obtain elemental iron, oxygen and other impurities must be removed by chemical reduction. Iron is the main constituent of steel, and it is used in the production of alloys or solid solutions of various metals, as well as some non-metals, particularly carbon. The many iron alloys, which have very different properties, are discussed in the article on steel.

    Nuclei of iron have some of the highest binding energies per nucleon, surpassed only by the nickel isotope 62Ni. The universally most abundant of the highly stable nuclides is, however, 56Fe. This is formed by nuclear fusion in stars. Although a further tiny energy gain could be extracted by synthesizing 62Ni, conditions in stars are unsuitable for this process to be favoured, and iron abundance on Earth greatly favors iron over nickel, and also presumably in supernova element production. When a very large star contracts at the end of its life, internal pressure and temperature rise, allowing the star to produce progressively heavier elements, despite these being less stable than the elements around mass number 60, known as the "iron group". This leads to a supernova. Iron (as Fe2+, ferrous ion) is a necessary trace element used by almost all living organisms, the only exceptions are a few prokaryotic organisms which live in iron-poor conditions (such as the lactobacilli in iron-poor milk) which use manganese for catalysis instead as well as organisms which use hemocyanin instead of hemoglobin. Iron-containing enzymes, usually containing heme prosthetic groups, participate in catalysis of oxidation reactions in biology, and in transport of a number of soluble gases. See hemoglobin, cytochrome, and catalase. Iron has 30 neutrons, 26 protons, and 26 electrons.

    Iron represents perhaps the best-known example for allotropy in a metal. There are four allotropic forms of iron, known as alpha, beta, gamma, and delta.

    As molten iron cools down it crystallises at 1535°C into its delta allotrope, which has a body-centred cubic (BCC) crystal structure. As it cools further its crystal structure changes to face centred cubic (FCC) at 1401°C, when it is known as gamma-iron, or austenite. At 912°C the crystal structure again becomes BCC as beta-iron4 is formed, and at 770°C (the Curie point, Tc ) the iron becomes magnetic as alpha-iron, also known as ferrite, which is also BCC, is formed. Thus 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 unmagnetised iron, all the electronic spins of the atoms within one domain are in the same direction. However, in neighbouring domains they point in various directions and thus cancel out. In magnetised iron, the electronic spins of all the domains are all aligned, so that the magnetic effects of neighbouring domains reinforce each other. Although each domain contains billions of atoms, they are very small, about one thousandth of a centimetre across.

    Iron, of course, is of most importance when mixed with certain other metals and with carbon to form steels. 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.

    Alpha 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).

    Above 912°C and up to 1401°C alpha iron undergoes a phase transition from body-centred cubic to the face-centred cubic configuration of gamma 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.

  • Pig iron has 3.5 - 4.5% carbon and contains varying amounts of contaminants such as sulfur, silicon and phosphorus. Its only significance is that of an intermediate step on the way from iron ore to cast iron and steel.
  • Cast iron contains 2% – 4.0% 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. 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. '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. In grey 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 grey 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.
  • Carbon steel contains 2.0% carbon or less, with small amounts of manganese, sulfur, phosphorus, and silicon.
  • 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.[citation needed] Wrought iron is characterised by the presence of fine fibers of slag entrapped in 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. Mild steel does not have the same corrosion resistance but is cheaper and more widely available.
  • Alloy steels contain varying amounts of carbon as well as other metals, such as chromium, vanadium, molybdenum, nickel, tungsten, etc. They are used for structural purposes, as their alloy content raises their cost and necessitates justification of their use. 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.
  • Iron(III) oxides are used in the production of magnetic storage media in computers. They are often mixed with other compounds, and retain their magnetic properties in solution.
    The main drawback to iron and steel is that pure iron, and most of its alloys, suffer badly from rust if not protected in some way. Painting, galvanization, plastic coating and bluing are some techniques used to protect iron from rust by excluding water and oxygen or by sacrificial protection.

    Iron is believed to be the critical missing nutrient in the ocean that limits the growth of plankton. Experimental iron fertilization of areas of the ocean using iron(II) sulfate has proven successful in increasing plankton growth. Larger scaled efforts are being attempted with the hope that iron seeding and ocean plankton growth can remove carbon dioxide from the atmosphere, thereby counteracting the greenhouse effect that is generally agreed by climatologists to cause global warming.

  • Iron(III) acetate (Fe(C2H3O2)3 is used in the dyeing of cloth.
  • Iron(III) ammonium oxalate (Fe(NH4)3(C2O4)4) is used in blueprints.
  • Iron(III) arsenate (FeAsO4) is used in insecticide.
  • Iron(III) chloride (FeCl3) is used: 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 etching material for engravement, photography and printed circuits.
  • Iron(III) chromate (Fe2(CrO4)3) is used as a yellow pigment for paints and ceramic.
  • Iron(III) hydroxide (Fe(OH)3) is used as a brown pigment for rubber and in water purification systems.
  • Iron(III) phosphate (FePO4) is used in fertilizer and as an additive in human and animal food.
  • Iron(II) acetate (Fe(C2H3O2)2 is used in the dyeing of fabrics and leather, and as a wood preservative.
  • Iron(II) gluconate (Fe(C6H11O7)2) is used as a dietary supplement in iron pills.
  • Iron(II) oxalate (FeC2O4) is used as yellow pigment for paints, plastics, glass and ceramic, and in photography.
  • Iron(II) sulfate (FeSO4) is used in water purification and sewage treatment systems, as a catalyst in the production of ammonia, as an ingredient in fertilizer and herbicide, as an additive in animal feed, in wood preservative and as an additive to flour to increase iron levels.
  • Iron-Fluorine complex (FeF6)3- is found in solutions containing both Fe(III) ions and fluoride ions.
    The production of iron or steel is a process unless the desired final prodcut is cast iron. The first stage is to produce pig iron in a blast furnace. The second is to make wrought iron or steel from pig iron by a further process.

    Ninety percent of all mining of metallic ores is for the extraction of iron. Industrially, iron is produced starting from iron ores, principally haematite (nominally Fe2O3) and magnetite (Fe3O4) by a carbothermic reaction (reduction with carbon) in a blast furnace at temperatures of about 2000 °C. In a blast furnace, iron ore, carbon in the form of coke, and a flux such as limestone (which is used to remove impurities in the ore which would otherwise clog the furnace with solid material) are fed into the top of the furnace, while a blast of heated air is forced into the furnace at the bottom.

    In the furnace,(hot/oven) the coke reacts with oxygen in the air blast to produce carbon monoxide:

    2 C + O2 -> 2 CO

    The carbon monoxide reduces the iron ore (in the chemical equation below, hematite) to molten iron, becoming carbon dioxide in the process: 3 CO + Fe2O3 -> 2 Fe + 3 CO2

    The flux is present to melt impurities in the ore, principally silicon dioxide sand and other silicates. Common fluxes include limestone (principally calcium carbonate) and dolomite (calcium-magnesium carbonate). Other fluxes may be used depending on the impurities that need to be removed from the ore. In the heat of the furnace the limestone flux decomposes to calcium oxide (quicklime):

    CaCO3 -> CaO + CO2

    Then calcium oxide combines with silicon dioxide to form a slag.

    CaO + SiO2 -> CaSiO3

    The slag melts in the heat of the furnace, which silicon dioxide would not have. In the bottom of the furnace, the molten slag floats on top of the more dense molten iron, and apertures in the side of the furnace are opened to run off the iron and the slag separately. The iron once cooled, is called pig iron, while the slag can be used as a material in road construction or to improve mineral-poor soils for agriculture.

    Naturally occurring iron consists of four isotopes: 5.845% of radioactive 54Fe (half-life: >3.1×1022 years), 91.754% of stable 56Fe, 2.119% of stable 57Fe and 0.282% of stable 58Fe. 60Fe is an extinct radionuclide of long half-life (1.5 million years).

    Much of the past work on measuring the isotopic composition of Fe has centered on determining 60Fe variations due to processes accompanying nucleosynthesis (i.e., meteorite studies) and ore formation. In the last decade however, advances in mass spectrometry technology have allowed the detection and quantification of minute, naturally-occurring variations in the ratios of the stable 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.

    The isotope 56Fe is of particular interest to nuclear scientists. A common misconception is that this isotope represents the most stable nucleus possible, and that it thus would be impossible to perform fission or fusion on 56Fe and still liberate energy. This is not true, as both 62Ni and 58Fe are more stable, being the most stable nuclei. However, since 56Fe is much more easily produced from lighter nuclei in nuclear reactions, it is the endpoint of fusion chains inside extremely massive stars and is therefore common in the universe, relative to other metals.

    In phases of the meteorites Semarkona and Chervony Kut a correlation between the concentration of 60Ni, 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 of 60Fe contributed, together with the energy released by decay of the radionuclide 26Al, 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 system and its early history. Of the stable isotopes, only 57Fe has a nuclear spin (-1/2).

    Nickel

    Nickel is a metallic chemical element with the symbol Ni and atomic number 28.

    Nickel is a silvery white metal that takes on a high polish. It belongs to the transition metals, and is hard and ductile. It occurs most usually in combination with sulfur and iron in pentlandite, with sulfur in millerite, with arsenic in the mineral nickeline, and with arsenic and sulfur in nickel glance.

    It is clear that in common with massive forms of chromium, aluminium and titanium metal that nickel is very slow to react with air, but it is a very reactive element.

    Because of its permanence in air and its inertness to oxidation, it is used in coins, for plating iron, brass, etc., for chemical apparatus, and in certain alloys, such as German silver. It is magnetic, and is very frequently accompanied by cobalt, both being found in meteoric iron. It is chiefly valuable for the alloys it forms, especially many superalloys, and particularly stainless steel.

    Nickel is one of the five ferromagnetic elements. However, the U.S. "nickel" coin is not magnetic, because it actually is mostly (75%) copper. The Canadian nickel minted at various periods between 1922-81 was 99.9% nickel, and these are magnetic. Nickel is also a naturally magnetostrictive material, meaning that in the presence of a magnetic field, the material undergoes a small change in length. In the case of Nickel, this change in length is negative (contraction of the material), which is known as negative magnetostriction.

    The most common oxidation state of nickel is +2, though 0, +1, +3 and +4 Ni complexes are observed. It is also thought that a +6 oxidation state may exist, however, results are inconclusive.

    The unit cell of nickel is a face centred cube with a lattice parameter of 0.356 nm giving a radius of the atom of 0.126 nm.

    Nickel-62 is the most stable nuclide of all the existing elements; it is more stable even than Iron-56.

    The bulk of the nickel mined comes from two types of ore deposits. The first are laterites where the principal ore minerals are nickeliferous limonite: (Fe, Ni)O(OH) and garnierite (a hydrous nickel silicate): (Ni, Mg)3Si2O5(OH). The second are magmatic sulfide deposits where the principal ore mineral is pentlandite: (Ni, Fe)9S8.

    In terms of supply, the Sudbury region of Ontario, Canada, produces about 30 percent of the world's supply of nickel. The Sudbury Basin deposit is theorized to have been created by a massive meteorite impact event early in the geologic history of Earth. Russia contains about 40% of the world's known resources at the massive Norilsk deposit in Siberia. The Russian mining company MMC Norilsk Nickel mines this for the world market, as well as the associated palladium. Other major deposits of nickel are found in New Caledonia, Australia, Cuba, and Indonesia. The deposits in tropical areas are typically laterites which are produced by the intense weathering of ultramafic igneous rocks and the resulting secondary concentration of nickel bearing oxide and silicate minerals. A recent development has been the exploitation of a deposit in western Turkey, especially convenient for European smelters, steelmakers and factories. The one locality in the United States where nickel is commercially mined is Riddle, Oregon, where several square miles of nickel-bearing garnierite surface deposits are located.

    Based on geophysical evidence, most of the nickel on Earth is postulated to be concentrated in the Earth's core.

    Nickel is used in many industrial and consumer products, including stainless steel, magnets, coinage, and special alloys. It is also used for plating and as a green tint in glass. Nickel is pre-eminently an alloy metal, and its chief use is in the nickel steels and nickel cast irons, of which there are innumerable varieties. It is also widely used for many other alloys, such as nickel brasses and bronzes, and alloys with copper, chromium, aluminum, lead, cobalt, silver, and gold.

    Nickel consumption can be summarized as: nickel steels (60%), nickel-copper alloys and nickel silver (14%), malleable nickel, nickel clad, Inconel and other Superalloys (9%), plating (6%), nickel cast irons (3%), heat and electric resistance alloys, such as Nichrome (3%), nickel brasses and bronzes (2%), others (3%).

    In the laboratory, nickel is frequently used as a catalyst for hydrogenation, most often using Raney nickel, a finely divided form of the metal.

    Nickel can be recovered using extractive metallurgy. Most sulfide ores have traditionally been processed using pyrometallurgical techniques to produce a matte for further refining. Recent advances in hydrometallurgy have resulted in recent nickel processing operations being developed using these processes. Most sulphide deposits have traditionally been processed by concentration through a froth flotation process followed by pyrometallurgical extraction. Recent advances in hydrometallurgical processing of sulphides has led to some recent projects being built around this technology.

    Nickel is extracted from its ores by conventional roasting and reduction processes which yield a metal of >75% purity. Final purification in the Mond process to >99.99% purity This process was patented by L. Mond and was used in South Wales in the 20th century. Nickel is reacted with carbon monoxide at around 50 degrees Celsius to form volatile nickel carbonyl. Any impurities remain solid. The nickel carbonyl gas is passed into a large chamber at high temperatures in which tens of thousands of nickel spheres are maintained in constant motion. The nickel carbonyl decomposes depositing pure nickel onto the nickel spheres (known as pellets). Alternatively, the nickel carbonyl may be decomposed in a smaller chamber at 230 degrees Celsius to create fine powders. The resultant carbon monoxide is re-circulated through the process. The highly pure nickel produced by this process is known as carbonyl nickel. A second common form of refining involves the leaching of the metal matte followed by the electro-winning of the nickel from solution by plating it onto a cathode. In many stainless steel applications, the nickel can be taken directly in the 75% purity form, depending on the presence of any impurities.

    In 2005, Russia was the largest producer of nickel with about one-fifth world share closely followed by Canada, Australia and Indonesia, as reported by the British Geological Survey.

    Sintering

    Sintering is a method for making objects from powder, by heating the material (below its melting point) until its particles adhere to each other. Sintering is traditionally used for manufacturing ceramic objects, and has also found uses in such fields as powder metallurgy. A special form of sintering, not limited the solid state but still considered part of powder metallurgy is liquid state sintering in which at least one but not all elements are existing in a liquid state. Liquid state sintering is required for making cemented carbides or tungsten carbide.

    The word "sinter" comes from the Middle High German Sinter, a cognate of English "cinder".

    Sintered bronze in particular is frequently used as a material for bearings, since its porosity allows lubricants to flow through it or remain captured within it. In the case of materials with high melting points such as Teflon and tungsten, sintering is used when there is no alternative manufacturing technique. In these cases very low porosity is desirable and can often be achieved.

    Sintered bronze and stainless steel are used as filter materials in applications requiring high temperature resistance while retaining the ability to regenerate the filter element. For example, sintered stainless steel elements are used for filtering steam in food and pharmaceutical applications.

    In most cases the density of a collection of grains increases as material flows into voids, causing a decrease in overall volume. Mass movements that occur during sintering consist of the reduction of total porosity by repacking, followed by material transport due to evaporation and condensation from diffusion. In the final stages, metal atoms move along crystal boundaries to the walls of internal pores, redistributing mass from the internal bulk of the object and smoothing pore walls. Surface tension is the driving force for this movement.

    Metallurgists can sinter most, if not all, metals. This applies especially to pure metals produced in vacuum which suffer no surface contamination. Many nonmetallic substances also sinter, such as glass, alumina, zirconia, silica, magnesia, lime, ice, beryllium oxide, ferric oxide, and various organic polymers. Sintering, with subsequent reworking, can produce a great range of material properties. Changes in density, alloying, or heat treatments can alter the physical characteristics of various products. For instance, the tensile strength En of sintered iron powders remains insensitive to sintering time, alloying, or particle size in the original powder, but depends upon the density (D) of the final product according to En/E = (D/d)3.4, where E is Young's modulus and d is the maximum density of iron.

    Particular advantages of this powder technology include: