Chromium (pronounced /ˈkroʊmiəm/ KROH-mee-əm) is a chemical element A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon, which has the symbol Cr and atomic number In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element. In an atom of neutral charge, the atomic number is also equal to the number of 24, first element in Group 6. It is a steely-gray, lustrous Lustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. For example, a diamond is said to have an adamantine lustre and pyrite is said to have a metallic lustre. The term is also used to describe other items with a particular sheen (for example, fabric, especially silk and satin, or metals), hard metal A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by that takes a high polish and has a high melting point. It is also odorless, tasteless, and malleable. The name of the element is derived from the Greek word "chrōma" (χρώμα), meaning color Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects, materials,, because many of its compounds are intensely colored. It was discovered by Louis Nicolas Vauquelin Vauquelin was born at Saint-André-d'Hébertot in Normandy, France. His first acquaintance with chemistry was gained as laboratory assistant to an apothecary in Rouen , and after various vicissitudes he obtained an introduction to A.F. Fourcroy, in whose laboratory he was an assistant from 1783 to 1791 in the mineral crocoite Gold is often found associated with this mineral. Crystals far surpassing in beauty any previously known have been found in the Adelaide Mine at Dundas, Tasmania; they are long slender prisms, 3 or 4 in. in length, with a brilliant lustre and color. Crocoite is also the official Tasmanian mineral emblem (lead chromate Lead chromate may also be known as chrome yellow, chromic acid lead(II) salt, canary chrome yellow 40-2250, chrome green, chrome green UC61, chrome green UC74, chrome green UC76, chrome lemon, crocoite, dianichi chrome yellow G, lemon yellow, king's yellow, Leipzig yellow, lemon yellow, Paris yellow, pigment green 15, plumbous chromate, pure lemon) in 1797. Crocoite was used as a pigment, and after the discovery that the mineral chromite also contains chromium this latter mineral was used to produce pigments as well.

Chromium was regarded with great interest because of its high corrosion Corrosion is the disintegration of an engineered material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means electrochemical oxidation of metals in reaction with an oxidant such as oxygen. Formation of an oxide of iron due to oxidation of the iron atoms in solid solution is a resistance and hardness. A major development was the discovery that steel could be made highly resistant to corrosion and discoloration by adding chromium to form stainless steel In metallurgy stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass. Stainless steel does not stain, corrode, or rust as easily as ordinary steel, but it is not stain-proof. It is also called corrosion-resistant steel or CRES when the. This application, along with chrome plating Chrome plating, often referred to simply as chrome, is a technique of electroplating a thin layer of chromium onto a metal object. The chromed layer can be decorative, provide corrosion resistance, ease cleaning procedures, or increase surface hardness (electroplating Electroplating is a plating process that uses electrical current to reduce cations of a desired material from a solution and coat a conductive object with a thin layer of the material, such as a metal. Electroplating is primarily used for depositing a layer of material to bestow a desired property to a surface that otherwise lacks that property with chromium) are currently the highest-volume uses of the metal. Chromium and ferrochromium Ferrochrome is an alloy of chromium and iron containing between 50% and 70% chromium. The ferrochrome is produced by electric arc melting of chromite, an iron magnesium chromium oxide and the most important chromium ore. Most of the world's ferrochrome is produced in South Africa, Kazakhstan and India, which have large domestic chromite resources are produced from the single commercially viable ore, chromite, by silicothermic or aluminothermic reaction Aluminothermic reactions are exothermic chemical reactions using aluminium as the reducing agent at high temperature. The most prominent example is the thermite reaction between aluminium and iron oxides: or by roasting Roasting is a metallurgical process involving gas-solids reactions at elevated temperatures. A common example is the process in which sulfide ores are converted to oxides, prior to smelting. Roasting differs from calcination, which merely involves decomposition at elevated temperatures. A typical sulfide roasting chemical reaction takes the and leaching Leaching is a widely used extractive metallurgy technique which converts metals into soluble salts in aqueous media. Compared to pyrometallurgical operations, leaching is easier to perform and much less harmful, because no gaseous pollution occurs. The only drawback of leaching is its lower efficiency caused by the low temperatures of the processes. Although trivalent chromium (Cr(III)) is required in trace amounts for sugar Sugar is an informal term for a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose characterized by a sweet flavor. In food, sugar almost exclusively refers to sucrose, which primarily comes from sugar cane and sugar beet. Other sugars are used in industrial food preparation, but are usually known by more specific and lipid Lipids are a broad group of naturally occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, phospholipids, and others. The main biological functions of lipids include energy storage, as structural components of cell membranes, and as important signaling molecules metabolism Metabolism is the set of chemical reactions that happen in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories. Catabolism breaks down organic matter, for example to harvest energy in cellular, few cases have been reported where its complete removal from the diet has caused chromium deficiency Chromium deficiency is a disorder that results from an insufficient dietary intake of chromium. Whether or not such a deficiency ever occurs in people eating a normal diet is debated, and clear cases of deficiency have only been observed in hospital patients who were fed defined liquid diets intravenously for long periods of time. Although. It is toxic in larger amounts. Hexavalent chromium Hexavalent chromium refers to chemical compounds that contain the element chromium in the +6 oxidation state. Virtually all chromium ore is processed via conversion to sodium dichromate. Approximately 136,000,000 kilograms of hexavalent chromium were produced in 1985. Other hexavalent chromium compounds are chromium trioxide and various salts of (Cr(VI)) is toxic and carcinogenic A carcinogen is any substance, radionuclide or radiation, that is an agent directly involved in the exacerbation of cancer or in the increase of its propagation. This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive substances are considered carcinogens, but their carcinogenic, so that abandoned chromium production sites need environmental cleanup Generally, remediation means providing a remedy, so environmental remediation deals with the removal of pollution or contaminants from environmental media such as soil, groundwater, sediment, or surface water for the general protection of human health and the environment or from a brownfield site intended for redevelopment. Remediation is.

Characteristics

Occurrence

Chromium is the 21st most abundant element in Earth's crust Categories: Structure of the Earth | Chemical elements with an average concentration of 100 ppm.^[2] Chromium compounds are found in the environment, due to erosion Erosion is the process of weathering and transport of solids in the natural environment or their source and deposits them elsewhere. It usually occurs due to transport by wind, water, or ice; by down-slope creep of soil and other material under the force of gravity; or by living organisms, such as burrowing animals, in the case of bioerosion of chromium-containing rocks and can be distributed by volcanic eruptions. The concentrations range in soil is between 1 and 3000 mg/kg, in sea water 5 to 800 µg/liter, and in rivers and lakes 26 µg/liter to 5.2 mg/liter.^[3] The relation between Cr(III) and Cr(VI) strongly depends on pH In chemistry, pH is a measure of the acidity or basicity of a solution. It approximates but is not equal to p[H], the negative logarithm of the molar concentration of dissolved hydronium ions (H3O+); a low pH indicates a high concentration of hydronium ions, while a high pH indicates a low concentration. Crudely, this negative of the logarithm and oxidative Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process such as the oxidation of carbon to yield carbon dioxide or the reduction of carbon by hydrogen to yield methane (CH4), or it can be a complex process such as the oxidation of sugar in the human body properties of the location, but in most cases, the Cr(III) is the dominating species,^[3] although in some areas the ground water can contain up to 39 µg of total chromium of which 30 µg is present as Cr(VI).^[4]

Chromium is mined as chromite Chromite is an iron chromium oxide: FeCr2O4. It is an oxide mineral belonging to the spinel group. Magnesium can substitute for iron in variable amounts as it forms a solid solution with magnesiochromite ; substitution of aluminium occurs leading to hercynite (FeCr₂O₄) ore.^[5] About two-fifths of the chromite ores and concentrates in the world are produced in South Africa Coordinates: 29°02′46″S 25°03′47″E / 29.046°S 25.063°E The Republic of South Africa is a country located at the southern tip of Africa, with a 2,798 kilometres coastline on the Atlantic and Indian Oceans. To the north lie Namibia, Botswana and Zimbabwe; to the east are Mozambique and Swaziland; while Lesotho is an independent, while Kazakhstan Kazakhstan , officially the Republic of Kazakhstan, is one of the six independent Turkic states. It is located in Eurasia and ranked as the ninth largest country in the world. It is also ranked the world's largest landlocked country, its territory of 2,727,300 km² is greater than Western Europe. It is neighbored clockwise from the north by Russia,, India India, officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with 1.18 billion people, and the most populous democracy in the world. Mainland India is bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal on the, Russia Russia (pronounced /ˈrʌʃə/ ; Russian: Россия, tr. Rossiya, pronounced [rɐˈsʲijə] ( listen)), also officially known as the Russian Federation (Russian: Российская Федерация, tr. Rossiyskaya Federatsiya, pronounced [rɐˈsʲijskəjə fʲɪdʲɪˈraʦəjə] ( listen)), is a country in northern Eurasia. It is a federal, and Turkey Turkey , known officially as the Republic of Turkey ( Türkiye Cumhuriyeti (help·info)), is a Eurasian country that stretches across the Anatolian peninsula in western Asia and Thrace (Rumelia) in the Balkan region of southeastern Europe. Turkey is one of the six independent Turkic states. Turkey is bordered by eight countries: Bulgaria to the are also substantial producers. Untapped chromite deposits are plentiful, but geographically concentrated in Kazakhstan and southern Africa.^[6]

Though native A native metal is any metal that is found in its metallic form, either pure or as an alloy, in nature. Metals that can be found as native deposits include bismuth, cadmium, chromium, indium, iron, nickel, tellurium, tin, titanium, and zinc, as well as two groups of metals: the gold group, and the platinum group. The gold group consists of gold, chromium deposits are rare, some native chromium metal has been discovered.^[7][8] The Udachnaya Pipe in Russia Russia (pronounced /ˈrʌʃə/ ; Russian: Россия, tr. Rossiya, pronounced [rɐˈsʲijə] ( listen)), also officially known as the Russian Federation (Russian: Российская Федерация, tr. Rossiyskaya Federatsiya, pronounced [rɐˈsʲijskəjə fʲɪdʲɪˈraʦəjə] ( listen)), is a country in northern Eurasia. It is a federal produces samples of the native metal. This mine is a kimberlite Kimberlite is a type of potassic volcanic rock best known for sometimes containing diamonds. It is named after the town of Kimberley in South Africa, where the discovery of an 83.5-carat diamond in 1871 spawned a diamond rush, eventually creating the Big Hole pipe rich in diamonds In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions. Diamond is renowned as a material with superlative, and the reducing environment Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in the helped produce both elemental chromium and diamond.^[9]

Isotopes

Naturally occurring chromium is composed of three stable isotopes Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. In a corresponding manner, isotopes differ in mass number (or number of nucleons) but never in atomic number. The number of protons (the atomic number) is the same because that is what characterizes a chemical element. For example,; ⁵²Cr, ⁵³Cr and ⁵⁴Cr with ⁵²Cr being the most abundant (83.789% natural abundance In chemistry, natural abundance refers to the abundance isotopes of a chemical element as naturally found on a planet. The relative atomic mass (a weighted average) of these isotopes is the atomic weight listed for the element in the periodic table. The abundance of an isotope varies from planet to planet but remains relatively constant in time). Nineteen radioisotopes A radionuclide is an atom with an unstable nucleus, which is a nucleus characterized by excess energy which is available to be imparted either to a newly-created radiation particle within the nucleus, or else to an atomic electron . The radionuclide, in this process, undergoes radioactive decay, and emits a gamma ray(s) and/or subatomic particles have been characterized with the most stable being ⁵⁰Cr with a half-life Half-life is the period of time it takes for a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but may apply to any quantity which follows a set-rate decay of (more than) 1.8 × 10¹⁷ years, and ⁵¹Cr with a half-life of 27.7 days. All of the remaining radioactive Radioactive decay is the process by which an unstable atomic nucleus loses energy by emitting ionizing particles or radiation. The emission is spontaneous in that the nucleus decays without collision with another particle. This decay, or loss of energy, results in an atom of one type, called the parent nuclide, transforming to an atom of a isotopes have half-lives that are less than 24 hours and the majority of these have half-lives that are less than 1 minute. This element also has 2 meta states A nuclear isomer is a metastable state of an atomic nucleus caused by the excitation of one or more of its nucleons. A nuclear isomer occupies a higher energy state than the corresponding non-excited nucleus, called the ground state. Most nuclear excited states decay by gamma ray emission or internal conversion, though, far from stability, other.^[10]

⁵³Cr is the radiogenic 1) In comparison with the quantity of the radioactive 'parent isotope' in a system, the quantity of the radiogenic 'daughter product' is used as a radiometric dating tool decay product of ⁵³Mn Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature (often in combination with iron), and in many minerals. As a free element, manganese is a metal with important industrial metal alloy uses, particularly in stainless steels. Chromium isotopic Isotopes are different types of atoms of the same chemical element, each having a different number of neutrons. In a corresponding manner, isotopes differ in mass number (or number of nucleons) but never in atomic number. The number of protons (the atomic number) is the same because that is what characterizes a chemical element. For example, contents are typically combined with manganese Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature (often in combination with iron), and in many minerals. As a free element, manganese is a metal with important industrial metal alloy uses, particularly in stainless steels isotopic contents and have found application in isotope geology. Mn-Cr isotope ratios reinforce the evidence from ²⁶Al and ¹⁰⁷Pd for the early history of the solar system. Variations in ⁵³Cr/⁵²Cr and Mn/Cr ratios from several meteorites indicate an initial ⁵³Mn/⁵⁵Mn ratio that suggests Mn-Cr isotopic composition must result from in-situ decay of ⁵³Mn in differentiated planetary bodies. Hence ⁵³Cr provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system.^[11]

The isotopes of chromium range in atomic mass from 43 u (⁴³Cr) to 67 u (⁶⁷Cr). The primary decay mode before the most abundant stable isotope, ⁵²Cr, is electron capture and the primary mode after is beta decay.^{[10] 53}Cr has been posited as a proxy for atmospheric oxygen concentration.^[12]

Chemistry

Chromium is a member of the transition metals, in group 6. Chromium has an electronic configuration of 4s¹3d⁵, due to the lower energy of the high spin configuration. Chromium exhibits a wide range of possible oxidation states. The most common oxidation states of chromium are +2, +3, and +6, with +3 being the most stable. The +1, +4 and +5 states are rare.

The following is the Pourbaix diagram for chromium in pure water, perchloric acid or sodium hydroxide:^[3][14]

Chromium(III)

The oxidation state +3 is the most stable, and a large number of chromium(III) compounds are known. Chromium(III) can be obtained by dissolving elemental chromium in acids like hydrochloric acid or sulfuric acid. The Cr³⁺ ion has a similar radius (63 pm) to the Al³⁺ ion (radius 50 pm), so they can replace each other in some compounds, such as in chrome alum and alum. When a trace amount of Cr³⁺ replaces Al³⁺ in corundum (aluminium oxide, Al₂O₃), the red-colored ruby is formed.

Chromium ions tend to form complexes; chromium ions in water are usually octahedrally coordinated with water molecules to form hydrates. The commercially available chromium(III) chloride hydrate is the dark green complex [CrCl₂(H₂O)₄]Cl, but two other forms are known: pale green [CrCl(H₂O)₅]Cl₂, and the violet [Cr(H₂O)₆]Cl₃. If water-free green chromium(III) chloride is dissolved in water then the green solution turns violet after some time, due to the substitution of water for chloride in the inner coordination sphere. This kind of reaction is also observed in chrome alum solutions and other water-soluble chromium(III) salts. The reverse reaction may be induced by heating the solution.

Chromium(III) hydroxide (Cr(OH)₃) is amphoteric, dissolving in acidic solutions to form [Cr(H₂O)₆]³⁺, and in basic solutions to form [Cr(OH)₆]³⁻. It is dehydrated by heating to form the green chromium(III) oxide (Cr₂O₃), which is the stable oxide with a crystal structure identical to that of corundum.^[15]

Chromium(VI)

Chromium(VI) compounds are powerful oxidants at low or neutral pH, and, except the hexafluoride, contain oxygen as a ligand, such as the chromate anion (CrO2−4) and chromyl chloride (CrO₂Cl₂).^[15]

Chromium(VI) is most commonly encountered in the chromate (CrO2−4) and dichromate (Cr₂O2−7) anions. Chromate is produced industrially by the oxidative roasting of chromite ore with calcium or sodium carbonate. The chromate and dichromate anions are in equilibrium:

2 CrO2−4 + 2 H₃O⁺ → Cr₂O2−7 + 3 H₂O

The dominant species is therefore, by the law of mass action, determined by the pH of the solution. The change in equilibrium is visible by a change from yellow (chromate) to orange (dichromate), such as when an acid is added to a neutral solution of potassium chromate. At yet lower pH values, further condensation to more complex oxyanions of chromium is possible.

Both the chromate and dichromate anions are strong oxidizing reagents at low pH:^[15]

Cr₂O2−7 + 14 H₃O⁺ + 6 e⁻ → 2 Cr³⁺ + 21 H₂O (ε₀ = 1.33 V)

However, they are only moderately oxidizing at high pH:^[15]

CrO2−4 + 4 H₂O + 3 e⁻ → Cr(OH)₃ + 5 OH⁻ (ε₀ = −0.13 V)

Chromium(VI) compounds in solution can be detected by adding an acidic hydrogen peroxide solution. The unstable dark blue chromium(VI) peroxide (CrO₅) is formed, which can be stabilized as an ether adduct CrO₅·OR₂.^[15]

Chromic acid has the hypothetical structure H₂CrO₄. Neither chromic nor dichromic acid can be isolated, but their anions are found in a variety of compounds, the chromates and dichromates. The dark red chromium(VI) oxide CrO₃, the acid anhydride of chromic acid, is sold industrially as "chromic acid".^[15] It can be produced by mixing sulfuric acid with dichromate, and is an extremely strong oxidizing agent.

Other oxidation states

The oxidation state +5 is only realized in few compounds. The only binary compound is the highly volatile chromium(V) fluoride (CrF₅). This red solid has a melting point of 30 °C and a boiling point of 117 °C, and can be synthesized by reacting fluorine with chromium at 400 °C and 200 bar pressure. The peroxochromate(V) is another example of the +5 oxidation state. Potassium peroxochromate (K₃[Cr(O₂)₄]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures. This red brown compound is stable at room temperature but decomposes spontaneously at 150–170 °C.^[16]

Chromium(IV) compounds (in the +4 oxidation state) are slightly more stable than the chromium(V) compounds. The tetrahalides, CrF₄, CrCl₄, and CrBr₄, can be produced by reacting the trihalides (CrX₃) with excess amounts of the corresponding halogen at elevated temperatures. Most of the compounds are susceptible to disproportionation reactions and are not stable in water.

An example of a stable chromium(II) compound is the water-stable chromium(II) chloride, CrCl₂, which can be made by reduction of chromium(III) chloride with zinc. The resulting bright blue solution is only stable at neutral pH when the solution is very pure.^[15]

Passivation

Chromium metal left standing in air is passivated by oxygen, forming a thin protective oxide surface layer. This layer is a spinel structure only a few atoms thick. It is very dense, and prevents the diffusion of oxygen into the underlying material. This is in contrast to iron or plain carbon steels, where the oxygen migrates into the underlying material and causes rusting.^[17] The passivation can be increased by short contact with oxidizing acids like nitric acid. Passivated chromium is stable against acids. The opposite effect can be achieved by treatment with a strong reducing reactant that destroys the protective oxide layer on the metal. Chromium metal treated in this way readily dissolves in weak acids.^[15]

Chromium, unlike metals such as iron and nickel, does not suffer from hydrogen embrittlement. However, it does suffer from nitrogen embrittlement, reacting with nitrogen from air and forming brittle nitrides at the high temperatures necessary to work the metal parts.^[18]

Quintuple bond

Chromium is notable for its ability to form quintuple covalent bonds. The product of a reaction between chromium(I) and a hydrocarbon radical was shown via X-ray diffraction to contain a quintuple bond of length 183.51(4) pm joining the two central chromium atoms.^[19] Extremely bulky monodentate ligands stabilize this compound by shielding the quintuple bond from further reactions.

Physical properties

Chromium is remarkable for its magnetic properties: it is the only elemental solid which shows antiferromagnetic ordering at room temperature (and below). Above 38 °C, it transforms into a paramagnetic state.^[1]

History

Weapons found in burial pits dating from the late 3rd century BC Qin Dynasty of the Terracotta Army near Xi'an, China have been analyzed by archaeologists. Although buried more than 2,000 years ago, the ancient bronze tips of crossbow bolts and swords found at the site showed no sign of corrosion, because the bronze was coated with chromium.^[20]

Chromium came to the attention of westerners in the 18th century. On 26 July 1761, Johann Gottlob Lehmann found an orange-red mineral in the Beryozovskoye mines in the Ural Mountains which he named Siberian red lead. Though misidentified as a lead compound with selenium and iron components, the mineral was Crocoite (lead chromate) with a formula of PbCrO₄.^[21]

In 1770, Peter Simon Pallas visited the same site as Lehmann and found a red lead mineral that had useful properties as a pigment in paints. The use of Siberian red lead as a paint pigment developed rapidly. A bright yellow pigment made from crocoite also became fashionable.^[21]

In 1797, Louis Nicolas Vauquelin received samples of crocoite ore. He produced chromium oxide (CrO₃) by mixing crocoite with hydrochloric acid. In 1798, Vauquelin discovered that he could isolate metallic chromium by heating the oxide in a charcoal oven.^[22] He was also able to detect traces of chromium in precious gemstones, such as ruby or emerald.^[21][23]

During the 1800s, chromium was primarily used as a component of paints and in tanning salts. At first, crocoite from Russia was the main source, but in 1827, a larger chromite deposit was discovered near Baltimore, United States. This made the United states the largest producer of chromium products till 1848 when large deposits of chromite where found near Bursa, Turkey.^[5]

Chromium is also known for its luster when polished. It is used as a protective and decorative coating on car parts, plumbing fixtures, furniture parts and many other items, usually applied by electroplating. Chromium was used for electroplating as early as 1848, but this use only became widespread with the development of an improved process in 1924.^[24]

Metal alloys now account for 85% of the use of chromium. The remainder is used in the chemical industry and refractory and foundry industries.

Production

Approximately 4.4 million metric tons of marketable chromite ore were produced in 2000, and converted into ~3.3 million tons of ferro-chrome with an approximate market value of 2.5 billion United States dollars.^[25] The largest producers of chromium ore have been South Africa (44%) India (18%), Kazakhstan (16%) Zimbabwe (5%), Finland (4%) Iran (4%) and Brazil (2%) with several other countries producing the rest of less than 10% of the world production.^[25]

The two main products of chromium ore refining are ferrochromium and metallic chromium. For those products the ore smelter process differs considerably. For the production of ferrochromium, the chromite ore (FeCr₂O₄) is reduced in large scale in electric arc furnace or in smaller smelters with either aluminium or silicon in an aluminothermic reaction.^[26]

For the production of pure chromium, the iron has to be separated from the chromium in a two step roasting and leaching process. The chromite ore is heated with a mixture of calcium carbonate and sodium carbonate in the presence of air. The chromium is oxidized to the hexavalent form, while the iron forms the stable Fe₂O₃. The subsequent leaching at higher elevated temperatures dissolves the chromates and leaves the insoluble iron oxide. The chromate is converted by sulfuric acid into the dichromate.^[26]

4 FeCr₂O₄ + 8 Na₂CO₃ + 7 O₂ → 8 Na₂CrO₄ + 2 Fe₂O₃ + 8 CO₂

2 Na₂CrO₄ + H₂SO₄ → Na₂Cr₂O₇ + Na₂SO₄ + H₂O

The dichromate is converted to the chromium(III) oxide by reduction with carbon and then reduced in an aluminothermic reaction to chromium.^[26]

Na₂Cr₂O₇ + 2 C → Cr₂O₃ + Na₂CO₃ + CO

Cr₂O₃ + 2 Al → Al₂O₃ + 2 Cr

Applications

Metallurgy

The strengthening effect of forming stable metal carbides at the grain boundaries and the strong increase in corrosion resistance made chromium an important alloying material for steel. The high speed tool steels contain between 3 and 5% chromium. Stainless steel, the main corrosion-proof metal alloy, is formed when chromium is added to iron in sufficient, usually more than 11% concentration. For its formation, ferrochromium is added to the molten iron. Also nickel-based alloys increase in strength due to the formation of discrete, stable metal carbide particles at the grain boundaries. For example, Inconel 718 contains 18.6% chromium. Because of the excellent high temperature properties of these nickel superalloys, they are used in jet engines and gas turbines in lieu of common structural materials.^[27]

The relative high hardness and corrosion resistance of unalloyed chromium makes it a good surface coating, being still the most "popular" metal coating with unbeatable combined durability. A thin layer of chromium is deposited on pretreated metallic surfaces by electroplating techniques. There are two deposition methods: Thin, below 1 µm thickness, layers are deposited by chrome plating, and are used for decorative surfaces. If wear-resistant surfaces are needed then thicker chromium layers of up to mm thickness are deposited. Both methods normally use acidic chromate or dichromate solutions. To prevent the energy consuming change in oxidation state, the use of Chromium(III) sulfate is under development, but for most applications, the established process is used.^[24]

In the chromate conversion coating process, the strong oxidative properties of chromates are used to deposit a protective oxide layer on metals like aluminium, zinc and cadmium. This passivation and the self healing properties by the chromate stored in the chromate conversion coating, which is able to migrate to local defects, are the benefits of this coating method.^[28] Because of environmental and health regulations on chromates, alternative coating method are under development.^[29]

Anodizing of aluminium is another electrochemical process, which does not lead to the deposition of chromium, but uses chromic acid as electrolyte in the solution. During anodization, an oxide layer is formed on the aluminium. The use of chromic acid, instead of the normally used sulfuric acid, leads to a slight difference of these oxide layers.^[30] The high toxicity of Cr(VI) compounds, used in the established chromium electroplating process, and the strengthening of safety and environmental regulations demand a search for substitutes for chromium or at least a change to less toxic chromium(III) compounds.^[24]

Dye and pigment

The mineral crocoite (lead chromate PbCrO₄) was used as a yellow pigment shortly after its discovery. After a synthesis method became available starting from the more abundant chromite, Chrome yellow was, together with cadmium yellow, one of the most used yellow pigments. The pigment does not degrade in the light and has a strong color. The signaling effect of yellow was used for school buses in the United States and for Postal Service (for example Deutsche Post) in Europe. The use of chrome yellow declined due to environmental and safety concerns and was substituted by organic pigments or other lead-free alternatives.^[32] Other pigments based on chromium are, for example, the bright red pigment Chrome red, which is a basic lead chromate (PbCrO₄•Pb(OH)₂).^[32] Chrome green is a mixture of Prussian blue and chrome yellow, while the Chrome oxide green is Chromium(III) oxide.^[32]

Glass is colored green by the addition of chromium(III) oxide. This is similar to emerald, which is also colored by chromium.^[33] A red color is achieved by doping chromium(III) into the crystals of corundum, which are then called ruby. Therefore, chromium is used in producing synthetic rubies.^[34]

The toxicity of chromium(VI) salts is used in the preservation of wood. For example, chromated copper arsenate (CCA) is used in timber treatment to prevent wood from decay fungi, wood attacking insects, including termites, and marine borers.^[35] The formulations contain chromium based on the oxide CrO₃ between 35.3% and 65.5%. In the United States, 65,300 metric tons of CCA solution have been used in 1996.^[35]

Tanning

Chromium(III) salts, especially chrome alum and chromium(III) sulfate, are used in the tanning of leather. The chromium(III) stabilizes the leather by cross linking the collagen fibers within the leather.^[36] Chromium tanned leather can contain between 4 and 5% of chromium, which is tightly bound to the proteins.^[5] Better management of chromium in tanning industry such as recovery and reuse, direct/indirect recycling,^[37] use of less chrome or chrome less tanning are practised to better manage chromium in tanning.

Refractory material

The high heat resistivity and high melting point makes chromite and chromium(III) oxide a material for high temperature refractory applications, like blast furnaces, cement kilns, molds for the firing of bricks and as foundry sands for the casting of metals. In these applications, the refractory materials are made from mixtures of chromite and magnesite. The use is declining because of the environmental regulations due to the possibility of the formation of chromium(VI).^[26]

Other use

Several chromium compounds are used as catalyst. For example the Phillips catalysts for the production polyethylene are mixtures of chromium and silicon dioxide or mixtures of chromium and titanium and aluminium oxide.^[38] Chromium(IV) oxide (CrO₂) is a magnetic compound. Its ideal shape anisotropy, which imparted high coercivity and remanent magnetization, made it a compound superior to the γ-Fe₂O₃. Chromium(IV) oxide is used to manufacture magnetic tape used in high performance audio tape and standard audio cassette.^[39] Chromates can prevent corrosion of steel under wet conditions, and therefore chromates are added to the drilling muds.^[40] The long known influence of chromium uptake on diabetes conditions suggested the positive influence of dietary supplement containing chromium(III) also on healthy persons. For this reason, dietary supplement or slimming aid usually contain chromium(III) chloride, chromium(III) picolinate, chromium(III) polynicotinate or amino acid chelate, such as chromium(III) D-phenylalanine. The benefit of those supplements is still under investigation and is questioned by some studies.^[41][42]

• Chromium hexacarbonyl Cr(CO)₆ is used as a gasoline additive.^[43]
• Chromium(III) oxide is a metal polish known as green rouge.
• Chromic acid is a powerful oxidizing agent and is a useful compound for cleaning laboratory glassware of any trace of organic compounds. It is prepared in situ by dissolving potassium dichromate in concentrated sulfuric acid, which is then used to wash the apparatus. Sodium dichromate is sometimes used because of its higher solubility (5 g/100 ml vs. 20 g/100 ml respectively). Potassium dichromate is a chemical reagent, used in cleaning laboratory glassware and as a titrating agent. It is also used as a mordant (i.e., a fixing agent) for dyes in fabric.

Biological role

Trivalent chromium (Cr(III) or Cr³⁺) in trace amounts influences sugar and lipid metabolism in humans, and its deficiency is suspected to cause a disease called chromium deficiency.^[44] However, chromium deficiency is thought to be extremely rare in the general population and has only ever been confirmed in three people on parenteral nutrition, which is when a patient is fed a liquid diet through intravenous drips.^[45] In contrast, hexavalent chromium (Cr(VI) or Cr⁶⁺) is very toxic and mutagenic when inhaled. Cr(VI) has not been established as a carcinogen when in solution, though it may cause allergic contact dermatitis (ACD).^[46]

The use of chromium-containing dietary supplements is controversial due to the complex effects of the used supplements.^[47] The popular dietary supplement chromium picolinate complex generates chromosome damage in hamster cells.^[48] In the United States the dietary guidelines for daily chromium uptake were lowered from 50-200 µg for an adult to 35 µg (adult male) and to 25 µg (adult female).^[49]

Precautions

Water insoluble chromium(III) compounds and chromium metal are not considered a health hazard, while the toxicity and carcinogenic properties of chromium(VI) have been known for a long time.^[50]

Because of the specific transport mechanisms, only limited amounts of chromium(III) enter the cells. Several in vitro studies indicated that high concentrations of chromium(III) in the cell can lead to DNA damage.^[51] Acute oral toxicity ranges between 1500 and 3300 µg/kg.^[52] The proposed beneficial effects of chromium(III) and the use as dietary supplements yielded some controversial results, but recent reviews suggest that moderate uptake of chromium(III) through dietary supplements poses no risk.^[51]

The acute oral toxicity for chromium(VI) ranges between 50 and 150 µg/kg.^[52] In the body, chromium(VI) is reduced by several mechanisms to chromium(III) already in the blood before it enters the cells. The chromium(III) is excreted from the body, whereas the chromate ion is transferred into the cell by a transport mechanism, by which also sulfate and phosphate ions enter the cell. The acute toxicity of chromium(VI) is due to its strong oxidational properties. After it reaches the blood stream, it damages the kidneys, the liver and blood cells through oxidation reactions. Hemolysis, renal and liver failure are the results of these damages. Aggressive dialysis can improve the situation.^[53]

The carcinogenity of chromate dust is known for a long time, and in 1890 the first publication described the elevated cancer risk of workers in a chromate dye company.^[54][55]Three mechanisms have been proposed to describe the genotoxicity of chromium(VI). The first mechanism includes highly reactive hydroxyl radicals and other reactive radicals which are by products of the reduction of chromium(VI) to chromium(III). The second process includes the direct binding of chromium(V), produced by reduction in the cell, and chromium(IV) compounds to the DNA. The last mechanism attributed the genotoxicity to the binding to the DNA of the end product of the chromium(III) reduction.^[56]

Chromium salts (chromates) are also the cause of allergic reactions in some people. Chromates are often used to manufacture, amongst other things, leather products, paints, cement, mortar and anti-corrosives. Contact with products containing chromates can lead to allergic contact dermatitis and irritant dermatitis, resulting in ulceration of the skin, sometimes referred to as "chrome ulcers". This condition is often found in workers that have been exposed to strong chromate solutions in electroplating, tanning and chrome-producing manufacturers.^[57][58]

Environmental issues

As chromium compounds were used in dyes and paints and the tanning of leather, these compounds are often found in soil and groundwater at abandoned industrial sites, now needing environmental cleanup and remediation per the treatment of brownfield land. Primer paint containing hexavalent chromium is still widely used for aerospace and automobile refinishing applications.^[59]

See also

• Chromium compounds
• Chromium minerals

Notes

1. ^ Common oxidation states are in bold.

References

1. ^ ^{a b} Fawcett, Eric (1988). "Spin-density-wave antiferromagnetism in chromium". Reviews of Modern Physics 60: 209. doi:10.1103/RevModPhys.60.209.
2. ^ Emsley, John (2001). "Chromium". Nature's Building Blocks: An A-Z Guide to the Elements. Oxford, England, UK: Oxford University Press. pp. 495–498. ISBN 0198503407.
3. ^ ^{a b c} Kotaś, J.; Stasicka, Z (2000). "Chromium occurrence in the environment and methods of its speciation". Environmental Pollution 107 (3): 263–283. doi:10.1016/S0269-7491(99)00168-2. PMID 15092973.
4. ^ Gonzalez, A. R.; Ndung'u, K; Flegal, AR (2005). "Natural Occurrence of Hexavalent Chromium in the Aromas Red Sands Aquifer, California". Environmental Science and Technology 39 (15): 5505–5511. doi:10.1021/es048835n. PMID 16124280.
5. ^ ^{a b c} National Research Council (U.S.). Committee on Biologic Effects of Atmospheric Pollutants (1974). Chromium. National Academy of Sciences. pp. 155. ISBN 9780309022170. http://books.google.com/?id=ZZsrAAAAYAAJ.
6. ^ Papp, John F. "Commodity Summary 2009: Chromium". United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/chromium/mcs-2009-chrom.pdf. Retrieved 2009-03-17.
7. ^ Fleischer, Michael (l982). "New Mineral Names". American Mineralogist 67: 854–860. http://www.minsocam.org/ammin/AM67/AM67_854.pdf.
8. ^ http://www.mindat.org/min-1037.html Mindat with location data
9. ^ http://www.mindat.org/locentry-27628.html Mindat
10. ^ ^{a b} Georges, Audi (2003). "The NUBASE Evaluation of Nuclear and Decay Properties". Nuclear Physics A (Atomic Mass Data Center) 729: 3–128. doi:10.1016/j.nuclphysa.2003.11.001.
11. ^ Birck, J. L.; Rotaru, M; Allegre, C (1999). "⁵³Mn-⁵³Cr evolution of the early solar system". Geochimica et Cosmochimica Acta 63 (23–24): 4111–4117. doi:10.1016/S0016-7037(99)00312-9.
12. ^ Frei, R.; Gaucher; Poulton; Canfield, D. (2009). "Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes". Nature 461 (7261): 250. doi:10.1038/nature08266. PMID 19741707. Lay summary.
13. ^ Schmidt, Max (1968). "VI. Nebengruppe" (in German). Anorganische Chemie II.. Wissenschaftsverlag. pp. 119–127.
14. ^ Ignasi Puigdomenech, Hydra/Medusa Chemical Equilibrium Database and Plotting Software (2004) KTH Royal Institute of Technology, freely downloadable software at [1]
15. ^ ^{a b c d e f g h} Holleman, Arnold F.; Wiberg, Egon; Wiberg, Nils; (1985). "Chromium" (in German). Lehrbuch der Anorganischen Chemie (91–100 ed.). Walter de Gruyter. pp. 1081–1095. ISBN 3110075113.
16. ^ Haxhillazi, Gentiana. "Preparation, Structure and Vibrational Spectroscopy of Tetraperoxo Complexes of Cr^V+, V^V+, Nb^V+ and Ta^V+ (PhD thesis, University of Siegen, 2003)". http://deposit.ddb.de/cgi-bin/dokserv?idn=969592612&dok_var=d1&dok_ext=pdf&fi....
17. ^ Wallwork, G. R. (1976). "The oxidation of alloys". Reports on the Progress Physics 39: 401–485. doi:10.1088/0034-4885/39/5/001. http://www.iop.org/EJ/article/0034-4885/39/5/001/rpv39i5p401.pdf.
18. ^ National Research Council (U.S.). Committee on Coatings (1970). High-temperature oxidation-resistant coatings: coatings for protection from oxidation of superalloys, refractory metals, and graphite. National Academy of Sciences. ISBN 0309017696. http://books.google.com/?id=CGMrAAAAYAAJ.
19. ^ T. Nguyen, A. D. Sutton, M. Brynda, J. C. Fettinger, G. J. Long and P. P. Power (2005). "Synthesis of a Stable Compound with Fivefold Bonding Between Two Chromium(I) Centers". Science 310 (5749): 844–847. doi:10.1126/science.1116789. PMID 16179432.
20. ^ Cotterell, Maurice. (2004). The Terracotta Warriors: The Secret Codes of the Emperor's Army. Rochester: Bear and Company. ISBN 159143033X. Page 102.
21. ^ ^{a b c} Jacques Guertin, James Alan Jacobs, Cynthia P. Avakian, (2005). Chromium (VI) Handbook. CRC Press. pp. 7–11. ISBN 9781566706087.
22. ^ Vauquelin, Louis Nicolas (1798). "Memoir on a New Metallic Acid which exists in the Red Lead of Sibiria". Journal of Natural Philosophy, Chemistry, and the Art 3: 146. http://books.google.com/?id=6dgPAAAAQAAJ.
23. ^ van der Krogt, Peter. "Chromium". http://elements.vanderkrogt.net/elem/cr.html. Retrieved 2008-08-24.
24. ^ ^{a b c} Dennis, J. K.; Such, T. E. (1993). "History of Chromium Plating". Nickel and Chromium Plating. Woodhead Publishing. pp. 9–12. ISBN 9781855730816.
25. ^ ^{a b c} Papp, John F. "Mineral Yearbook 2002: Chromium". United States Geological Survey. http://minerals.usgs.gov/minerals/pubs/commodity/chromium/chrommyb02.pdf. Retrieved 2009-02-16.
26. ^ ^{a b c d} Papp, John F; Lipin Bruce R. (2006). "Chromite". Industrial Minerals & Rocks: Commodities, Markets, and Uses (7th ed.). SME. ISBN 9780873352338. http://books.google.com/?id=zNicdkuulE4C&pg=PA309.
27. ^ Bhadeshia, H. K. D. H.. "Nickel-Based Superalloys". University of Cambridge. http://www.msm.cam.ac.uk/phase-trans/2003/Superalloys/superalloys.html. Retrieved 2009-02-17.
28. ^ Edwards, Joseph (1997). Coating and Surface Treatment Systems for Metals. Finishing Publications Ltd. and ASMy International. pp. 66–71. ISBN 0-904477-16-9.
29. ^ Zhao, J. (2001). "Effects of chromate and chromate conversion coatings on corrosion of aluminum alloy 2024-T3" (). Surface and Coatings Technology 140 (1): 51–57. doi:10.1016/S0257-8972(01)01003-9. http://www.chemistry.ohio-state.edu/~rmccreer/group/mccreery157.pdf.
30. ^ Sprague, J. A.; Smidt, F. A. (1994). ASM Handbook: Surface Engineering. ASM International. ISBN 9780871703842. http://books.google.com/?id=RGtsPjqUwy0C&pg=PA484. Retrieved 2009-02-17.
31. ^ Worobec, Mary Devine; Hogue, Cheryl (1992). Toxic Substances Controls Guide: Federal Regulation of Chemicals in the Environment. Washington, D.C.: BNA Books. p. 13. ISBN 9780871797520. http://books.google.com/?id=CjWQ6_7AnI4C&pg=PA13.
32. ^ ^{a b c} Gettens, Rutherford John (1966). "Chrome yellow". Painting Materials: A Short Encyclopaedia. Courier Dover Publications. pp. 105–106. ISBN 9780486215976. http://books.google.com/?id=bdQVgKWl3f4C&pg=PA106.
33. ^ Carstens, Harald (1973). "The red-green change in chromium-bearing garnets". Contributions to Mineralogy and Petrology 41 (3): 273–276. doi:10.1007/BF00371036.
34. ^ Moss, S. C. (1964). "The chromium position in ruby". Zeitschrift fur Kristallographie 120: 359–363. http://rruff.geo.arizona.edu/doclib/zk/vol120/ZK120_359.pdf.
35. ^ ^{a b} "Leaching of chromated copper arsenate wood preservatives: a review". Environmental Pollution 111 (1): 53–66. 2001. doi:10.1016/S0269-7491(00)00030-0. PMID 11202715.
36. ^ Brown, E. M. (1997). "A Conformational Study of Collagen as Affected by Tanning Procedures". Journal of the American Leather Chemists Association 92: 225–233.
37. ^ K. J. Sreeram; T. Ramasami (2002). "Sustaining tanning process through conservation, recovery and better utilization of chromium". Resources, Conservation and Recycling 38 (3): 185-212. doi:10.1016/S0921-3449(02)00151-9.
38. ^ Weckhuysen, Bert M. (1999). "Olefin polymerization over supported chromium oxide catalysts". Catalysis Today 51 (2): 215–221. doi:10.1016/S0920-5861(99)00046-2.
39. ^ Mallinson, John C. (1993). "Chromium Dioxide". The foundations of magnetic recording. Academic Press. ISBN 9780124666269. http://books.google.com/?id=rNifWsBxnWkC&pg=PA32.
40. ^ Garverick, Linda (1994). Corrosion in the Petrochemical Industry. ASM International. ISBN 9780871705051. http://books.google.com/?id=qTfNZZRO758C&pg=PA278.
41. ^ Heimbach, J.T. (2005). "Chromium: Recent Studies Regarding Nutritional Roles and Safety". Nutrition Today 40 (4): 189–-195. doi:10.1097/00017285-200507000-00013. http://journals.lww.com/nutritiontodayonline/Abstract/2005/07000/Chromium__Recent_Studies_Regarding_Nutritional.13.aspx.
42. ^ Vincent,, John B . (2003). "The Potential Value and Toxicity of Chromium Picolinate as a Nutritional Supplement, Weight Loss Agent and Muscle Development Agent". Sports Medicine:Volume 33 (3): 213–230. doi:10.2165/00007256-200333030-00004.
43. ^ Patnaik, Pradyot (2003). "Chromium hexacarbonyl". Handbook of Inorganic Chemicals. McGraw-Hill Professional. pp. 222–223. ISBN 9780070494398. http://books.google.com/?id=Xqj-TTzkvTEC&pg=PA222.
44. ^ Mertz, Walter (1 April 1993). "Chromium in Human Nutrition: A Review". Journal of Nutrition 123 (4): 626–636. PMID 8463863. http://jn.nutrition.org/cgi/content/abstract/123/4/626.
45. ^ {Moukarzel A (November 2009). "Chromium in parenteral nutrition: too little or too much?". Gastroenterology 137 (5 Suppl): S18–28. doi:10.1053/j.gastro.2009.08.048. PMID 19874946.
46. ^ "ToxFAQs: Chromium". Agency for Toxic Substances & Disease Registry, Centers for Disease Control and Prevention. February 2001. http://www.atsdr.cdc.gov/tfacts7.html. Retrieved 2007-10-02.
47. ^ Cronin, Joseph R. (2004). "The Chromium Controversy". Alternative and Complementary Therapies 10 (1): 39–42. doi:10.1089/107628004772830393.
48. ^ Stearns, D. M.; W; P; W (1 December 1995). "Chromium(III) picolinate produces chromosome damage in Chinese hamster ovary cells". Federation of American Societies for Experimental Biology 9 (15): 1643–1648. PMID 8529845. http://www.fasebj.org/cgi/content/abstract/9/15/1643.
49. ^ Vincent, J. B. (2007). "Recent advances in the nutritional biochemistry of trivalent chromium". Proceedings of the Nutrition Society 63 (01): 41–47. doi:10.1079/PNS2003315. PMID 15070438.
50. ^ Barceloux, Donald G.; Barceloux, Donald (1999). "Chromium". Clinical Toxicology 37 (2): 173–194. doi:10.1081/CLT-100102418. PMID 10382554.
51. ^ ^{a b} Eastmond, David A.; MacGregor, JT; Slesinski, RS (2008). "Trivalent Chromium: Assessing the Genotoxic Risk of an Essential Trace Element and Widely Used Human and Animal Nutritional Supplement". Critical Reviews in Toxicology 38 (3): 173–190. doi:10.1080/10408440701845401. PMID 18324515.
52. ^ ^{a b} Katz, Sidney A.; Salem, H (1992). "The toxicology of chromium with respect to its chemical speciation: A review". Journal of Applied Toxicology 13 (3): 217–224. doi:10.1002/jat.2550130314. PMID 8326093.
53. ^ Dayan, A. D.; Paine, A. J. (2001). "Mechanisms of chromium toxicity, carcinogenicity and allergenicity: Review of the literature from 1985 to 2000". Human & Experimental Toxicology 20 (9): 439–451. doi:10.1191/096032701682693062.
54. ^ Newman, D. (1890). "A case of adeno-carcinoma of the left inferior turbinated body, and perforation of thenasal septum, in the person of a worker in chrome pigments". Glasgow Medical Journal 33: 469–470.
55. ^ Langard, Sverre (1990). "One Hundred Years of Chromium and Cancer: A Review of Epidemiological Evidence and Selected Case Reports". American Journal of Industrial Medicine 17 (2): 189–215. doi:10.1002/ajim.4700170205. PMID 2405656.
56. ^ M. D., Cohen; Kargacin, B.; Klein, C. B.; Costa, M. (1993). "Mechanisms of chromium carcinogenicity and toxicity". Critical reviews in toxicology 23 (3): 255–81. doi:10.3109/10408449309105012. PMID 8260068.
57. ^ "Chrome Contact Allergy". DermNet NZ. http://dermnetnz.org/dermatitis/chrome-allergy.html.
58. ^ Basketter, David; Horev, L.; Slodovnik, D.; Merimes, S.; Trattner, A.; Ingber, A. (2000). "Investigation of the threshold for allergic reactivity to chromium". Contact Dermatitis 44 (2): 70–74. doi:10.1034/j.1600-0536.2001.440202.x. PMID 11205406.
59. ^ Baselt, Randall C. (2008 pages = 305–307). Disposition of Toxic Drugs and Chemicals in Man (8th ed.). Foster City: Biomedical Publications. ISBN 9780962652370.

External links

• ATSDR Case Studies in Environmental Medicine: Chromium Toxicity U.S. Department of Health and Human Services
• Los Alamos National Laboratory - Chromium
• WebElements.com – Chromium
• IARC Monograph "Chromium and Chromium compounds"
• International Chromium Development Association
• It's Elemental – The Element Chromium
• National Pollutant Inventory - Chromium (III) compounds fact sheet
• The Merck Manual – Mineral Deficiency and Toxicity
• National Institute for Occupational Safety and Health - Chromium Page

Categories: Chemical elements | Transition metals | Chromium | Dietary minerals | Occupational safety and health | Biology and pharmacology of chemical elements

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