Manganese And Cobalt

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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(Dell 1691P battery).

Historically, manganese is named for various black minerals (such as pyrolusite) from the same region of Magnesia in Greece which gave names to similar-sounding magnesium, Mg, and magnetite, an ore of the element iron, Fe. By the mid-18th century, Swedish chemist Carl Wilhelm Scheele had used pyrolusite to produce chlorine(Dell 310-6321 battery). Scheele and others were aware that pyrolusite (now known to be manganese dioxide) contained a new element, but they were not able to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, by reducing the dioxide with carbon.

Manganese phosphating is used as a treatment for rust and corrosion prevention on steel. Depending on their oxidation state(Dell 312-0068 battery), manganese ions have various colors and are used industrially as pigments. The permanganates of alkali and alkaline earth metals are powerful oxidizers. Manganese dioxide is used as the cathode (electron acceptor) material in standard and alkaline disposable dry cells and batteries.

In biology, manganese(II) ions function as cofactors for a large variety of enzymes with many functions(Dell 312-0078 battery). Manganese enzymes are particularly essential in detoxification of superoxide free radicals in organisms that must deal with elemental oxygen. Manganese also functions in the oxygen-evolving complex of photosynthetic plants. The element is a required trace mineral for all known living organisms. In larger amounts, and apparently with far greater activity by inhalation(Dell 312-0079 battery), manganese can cause a poisoning syndrome in mammals, with neurological damage which is sometimes irreversible.

Characteristics

[edit]Physical properties

Electrolytically refined manganese chips and 1 cm3 cube

Manganese is a silvery-gray metal resembling iron. It is hard and very brittle, difficult to fuse, but easy to oxidize.[1] Manganese metal and its common ions are paramagnetic.[2]

[edit]Isotopes

Main article: Isotopes of manganese

Naturally occurring manganese is composed of one stable isotope, 55Mn. Eighteen radioisotopes have been characterized(Dell 312-0305 battery), with the most stable being 53Mn with a half-life of 3.7 million years, 54Mn with a half-life of 312.3 days, and 52Mn with a half-life of 5.591 days. All of the remaining radioactive isotopes have half-lives that are less than three hours and the majority of these have half-lives that are less than one minute. This element also has three meta states(Dell 312-0326 battery).[3]

Manganese is part of the iron group of elements, which are thought to be synthesized in large stars shortly before the supernova explosion. 53Mn decays to 53Cr with a half-life of 3.7 million years. Because of its relatively short half-life, 53Mn occurs only in tiny amounts due to the action of cosmic rays on iron in rocks.[4] Manganese isotopic contents are typically combined with chromium isotopic contents and have found application in isotope geology and radiometric dating(Dell 312-0518 battery). Mn–Cr isotopic 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 53Mn provides additional evidence for nucleosynthetic processes immediately before coalescence of the solar system(Dell 312-0566 battery).[3]

The isotopes of manganese range in atomic weight from 46 u (46Mn) to 65 u (65Mn). The primary decay mode before the most abundant stable isotope, 55Mn, is electron capture and the primary mode after is beta decay.[3]

[edit]Chemical properties

The most common oxidation states of manganese are +2, +3, +4, +6 and +7, though oxidation states from −3 to +7 are observed. Mn2+ often competes with Mg2+ in biological systems. Manganese compounds where manganese is in oxidation state +7(Dell 312-0585 battery), which are restricted to the unstable oxide Mn2O7 and compounds of the intensely purple permanganate anion MnO4−, are powerful oxidizing agents.[1] Compounds with oxidation states +5 (blue) and +6 (green) are strong oxidizing agents and are vulnerable to disproportionation.

Manganese chloride crystals - the pale pink color of Mn (II) salts is due to a spin-forbidden 3d transition, which is rare(Dell 312-0831 battery).

Aqueous solution of KMnO4 illustrating the deep purple of Mn(VII) as it occurs in permanganate

The most stable oxidation state for manganese is +2, which has a pale pink color, and many manganese(II) compounds are known, such as manganese(II) sulfate (MnSO4) and manganese(II) chloride (MnCl2). This oxidation state is also seen in the mineral rhodochrosite, (manganese(II) carbonate) (Dell BAT30WL battery). The +2 oxidation state is the state used in living organisms for essential functions; other states are toxic for the human body. The +2 oxidation of Mn results from removal of the two 4s electrons, leaving a "high spin" ion in which all five of the 3d orbitals contain a single electron. Absorption of visible light by this ion is accomplished only by a spin-forbidden transition in which one of the d electrons must pair with another(Dell D6400 battery), to give the atom a change in spin of two units. The unlikeliness of such a transition is seen in the uniformly pale and almost colorless nature of Mn(II) compounds relative to other oxidation states of manganese.[5]

The +3 oxidation state is known in compounds like manganese(III) acetate, but these are quite powerful oxidizing agents and also prone to disproportionation in solution to manganese(II) and manganese(IV) (Dell HF674 battery). Solid compounds of manganese(III) are characterized by their preference for distorted octahedral coordination due to the Jahn-Teller effect and its strong purple-red color.

The oxidation state 5+ can be obtained if manganese dioxide is dissolved in molten sodium nitrite.[7] Manganate (VI) salts can also be produced by dissolving Mn compounds, such as manganese dioxide, in molten alkali while exposed to air(Dell N3010 battery).

Permanganate (+7 oxidation state) compounds are purple, and can give glass a violet color. Potassium permanganate, sodium permanganate and barium permanganate are all potent oxidizers. Potassium permanganate, also called Condy's crystals, is a commonly used laboratory reagent because of its oxidizing properties and finds use as a topical medicine (for example, in the treatment of fish diseases) (Dell Inspiron N4010 battery). Solutions of potassium permanganate were among the first stains and fixatives to be used in the preparation of biological cells and tissues for electron microscopy.[8]

[edit]History

The origin of the name manganese is complex. In ancient times, two black minerals from Magnesia in what is now modern Greece, were both called magnes from their place of origin, but were thought to differ in gender(Dell INSPIRON 1100 battery). The male magnes attracted iron, and was the iron ore we now know as lodestone or magnetite, and which probably gave us the term magnet. The female magnes ore did not attract iron, but was used to decolorize glass. This feminine magnes was later called magnesia, known now in modern times as pyrolusite or manganese dioxide. Neither this mineral nor manganese itself is magnetic(Dell Inspiron 1200 battery). In the 16th century, manganese dioxide was called manganesum (note the two n's instead of one) by glassmakers, possibly as a corruption and concatenation of two words, since alchemists and glassmakers eventually had to differentiate a magnesia negra (the black ore) from magnesia alba (a white ore, also from Magnesia, also useful in glassmaking). Michele Mercati called magnesia negra manganesa(Dell Inspiron 1420 battery), and finally the metal isolated from it became known as manganese (German: Mangan). The name magnesia eventually was then used to refer only to the white magnesia alba (magnesium oxide), which provided the name magnesium for that free element, when it was eventually isolated, much later.[9]

Some of the cave paintings in Lascaux, France, use manganese-based pigments.[10]

Several oxides of manganese(Dell Inspiron 1464 battery), for example manganese dioxide, are abundant in nature, and owing to their color, these oxides have been used as since the Stone Age. The cave paintings in Gargas contain manganese as pigments and these cave paintings are 30,000 to 24,000 years old.[11]

Manganese compounds were used by Egyptian and Roman glassmakers, to either remove color from glass or add color to it.[12] The use as "glassmakers soap" continued through the Middle Ages until modern times and is evident in 14th-century glass from Venice(Dell Inspiron 1564 battery).[13]

Credit for first isolating manganese is usually given to Johan Gottlieb Gahn.

Because of the use in glassmaking, manganese dioxide was available to alchemists, the first chemists, and was used for experiments. Ignatius Gottfried Kaim (1770) and Johann Glauber (17th century) discovered that manganese dioxide could be converted to permanganate, a useful laboratory reagent.[14] By the mid-18th century(Dell Inspiron 1764 battery), the Swedish chemist Carl Wilhelm Scheele used manganese dioxide to produce chlorine. First, hydrochloric acid, or a mixture of dilute sulfuric acid and sodium chloride was made to react with manganese dioxide, later hydrochloric acid from the Leblanc process was used and the manganese dioxide was recycled by the Weldon process. The production of chlorine and hypochlorite containing bleaching agents was a large consumer of manganese ores(Dell Inspiron 1520 battery).

Scheele and other chemists were aware that manganese dioxide contained a new element, but they were not able to isolate it. Johan Gottlieb Gahn was the first to isolate an impure sample of manganese metal in 1774, by reducing the dioxide with carbon.

The manganese content of some iron ores used in Greece led to the speculations that the steel produced from that ore contains inadvertent amounts of manganese, making the Spartan steel exceptionally hard. (Dell Inspiron 1521 battery)Around the beginning of the 19th century, manganese was used in steelmaking and several patents were granted. In 1816, it was noted that adding manganese to iron made it harder, without making it any more brittle. In 1837, British academic James Couper noted an association between heavy exposures to manganese in mines with a form of Parkinson's disease(Dell inspiron 1525 battery).[16] In 1912, manganese phosphating electrochemical conversion coatings for protecting firearms against rust and corrosion were patented in the United States, and have seen widespread use ever since.[17]

The invention of the Leclanché cell in 1866 and the subsequent improvement of the batteries containing manganese dioxide as cathodic depolarizer increased the demand of manganese dioxide. Until the introduction of the nickel-cadmium battery and lithium-containing batteries(Dell inspiron 1526 battery), most batteries contained manganese. The zinc-carbon battery and the alkaline battery normally use industrially produced manganese dioxide, because natural occurring manganese dioxide contains impurities. In the 20th century, manganese dioxide has seen wide commercial use as the chief cathodic material for commercial disposable dry cells and dry batteries of both the standard (zinc-carbon) and alkaline types. (Dell Inspiron 1720 battery)

[edit]Occurrence and production

See also: Category:Manganese minerals

Manganese makes up about 1000 ppm (0.1%) of the Earth's crust, making it the 12th most abundant element there.[19] Soil contains 7–9000 ppm of manganese with an average of 440 ppm.[19] Seawater has only 10 ppm manganese and the atmosphere contains 0.01 µg/m3.[19] Manganese occurs principally as pyrolusite (MnO2), braunite, (Mn2+Mn3+6)(SiO12),[20] psilomelane (Ba,H2O)2Mn5O10, and to a lesser extent as rhodochrosite (MnCO3) (Dell Inspiron 2000 battery).

The most important manganese ore is pyrolusite (MnO2). Other economically important manganese ores usually show a close spatial relation to the iron ores.[1] Land-based resources are large but irregularly distributed. About 80% of the known world manganese resources are found in South Africa; other important manganese deposits are in Ukraine, Australia, India, China, Gabon and Brazil(Dell INSPIRON 2600 battery).[21] In 1978, 500 billion tons of manganese nodules were estimated to exist on the ocean floor.[22] Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s.[23]

Manganese is mined in South Africa, Australia, China, Brazil, Gabon, Ukraine, India and Ghana and Kazakhstan. US Import Sources (1998–2001): Manganese ore: Gabon, 70%; South Africa, 10%; Australia, 9%; Mexico, 5%; and other, 6%(Dell INSPIRON 3800 battery). Ferromanganese: South Africa, 47%; France, 22%; Mexico, 8%; Australia, 8%; and other, 15%. Manganese contained in all manganese imports: South Africa, 31%; Gabon, 21%; Australia, 13%; Mexico, 8%; and other, 27%.[21][24]

For the production of ferromanganese, the manganese ore is mixed with iron ore and carbon, and then reduced either in a blast furnace or in an electric arc furnace.[25] The resulting ferromanganese has a manganese content of 30 to 80%(Dell INSPIRON 4000 battery).[1] Pure manganese used for the production of noniron alloys is produced by leaching manganese ore with sulfuric acid and a subsequent electrowinning process.[26]

[edit]Applications

Manganese has no satisfactory substitute in its major applications, which are related to metallurgical alloy use.[21] In minor applications, (e.g., manganese phosphating), zinc and sometimes vanadium are viable substitutes. In disposable battery manufacture, standard and alkaline cells using manganese will be generally replaced in the future with lithium battery technology(Dell Inspiron 5000 battery).

[edit]Steel

US Marine Corps steel helmet

Manganese is essential to iron and steel production by virtue of its sulfur-fixing, deoxidizing, and alloying properties. Steelmaking,[27] including its ironmaking component, has accounted for most manganese demand, presently in the range of 85% to 90% of the total demand.[26] Among a variety of other uses, manganese is a key component of low-cost stainless steel formulations. (Dell INSPIRON 500M battery)

Small amounts of manganese improve the workability of steel at high temperatures, because it forms a high melting sulfide and therefore prevents the formation of a liquid iron sulfide at the grain boundaries. If the manganese content reaches 4%, the embrittlement of the steel becomes a dominant feature. The embrittlement decreases at higher manganese concentrations and reaches an acceptable level at 8%(Dell INSPIRON 5100 battery). Steel containing 8 to 15% of manganese can have a high tensile strength of up to 863 MPa.[29][30] Steel with 12% manganese was used for British steel helmets. This steel composition was discovered in 1882 by Robert Hadfield and is still known as Hadfield steel.[31]

[edit]Aluminium alloys

Main article: Aluminium alloy

The second large application for manganese is as alloying agent for aluminium. Aluminium with a manganese content of roughly 1.5% has an increased resistance against corrosion due to the formation of grains absorbing impurities which would lead to galvanic corrosion(Dell INSPIRON 510M battery).[32] The corrosion-resistant aluminium alloys 3004 and 3104 with a manganese content of 0.8 to 1.5% are the alloys used for most of the beverage cans.[33] Before year 2000, in excess of 1.6 million tonnes have been used of those alloys; with a content of 1% manganese, this amount would need 16,000 tonnes of manganese.[33]

[edit]Other uses

World-War-II-era nickel (1942-5 identified by mint mark P,D or S above dome) made from a 56% copper-35% silver-9% manganese alloy(Dell INSPIRON 6000 battery)

Methylcyclopentadienyl manganese tricarbonyl is used as an additive in unleaded gasoline to boost octane rating and reduce engine knocking. The manganese in this unusual organometallic compound is in the +1 oxidation state.[34]

Manganese(IV) oxide (manganese dioxide, MnO2) is used as a reagent in organic chemistry for the oxidation of benzylic alcohols (i.e. adjacent to an aromatic ring). Manganese dioxide has been used since antiquity to oxidatively neutralize the greenish tinge in glass caused by trace amounts of iron contamination(Dell INSPIRON 600M battery).[13] MnO2 is also used in the manufacture of oxygen and chlorine, and in drying black paints. In some preparations, it is a brown pigment that can be used to make paint and is a constituent of natural umber.

Manganese(IV) oxide was used in the original type of dry cell battery as an electron acceptor from zinc, and is the blackish material found when opening carbon–zinc type flashlight cells. The manganese dioxide is reduced to the manganese oxide-hydroxide MnO(OH) during discharging, preventing the formation of hydrogen at the anode of the batter(Dell Inspiron 6400 battery)y.[35]

MnO2 + H2O + -

e → MnO(OH) + OH−

The same material also functions in newer alkaline batteries (usually battery cells), which use the same basic reaction, but a different electrolyte mixture. In 2002, more than 230,000 tons of manganese dioxide was used for this purpose.[18][35]

The metal is very occasionally used in coins; until 2000, the only United States coin to use manganese was the "wartime" nickel from 1942–1945. (Dell INSPIRON 7000 battery) An alloy of 75% copper and 25% nickel was traditionally used for the production of nickel coins. However, because of shortage of nickel metal during the war, it was substituted by more available silver and manganese, thus resulting in an alloy of 56% copper, 35% silver and 9% manganese. Since 2000, dollar coins, for example the Sacagawea dollar and the Presidential $1 coins, are made from a brass containing 7% of manganese with a pure copper core(Dell INSPIRON 700M battery).[37] In both cases of nickel and dollar, the use of manganese in the coin was to duplicate the electromagnetic properties of a previous identically sized and valued coin, for vending purposes. In the case of the later U.S. dollar coins, the manganese alloy was an attempt to duplicate properties of the copper/nickel alloy used in the previous Susan B. Anthony dollar.

Manganese compounds have been used as pigments and for the coloring of ceramics and glass(Dell Inspiron 710m battery). The brown color of ceramic is sometimes based on manganese compounds.[38] In the glass industry, manganese compounds are used for two effects. Manganese(III) reacts with iron(II) to induce a strong green color in glass by forming less-colored iron(III) and slightly pink manganese(II), compensating for the residual color of the iron(III).[13] Larger amounts of manganese are used to produce pink colored glass(Dell INSPIRON 8200 battery).

[edit]Biological role

Reactive center of arginase with boronic acid inhibitor - the manganese atoms are shown in yellow.

Manganese is an essential trace nutrient in all forms of life.[19] The classes of enzymes that have manganese cofactors are very broad, and include oxidoreductases, transferases, hydrolases, lyases, isomerases, ligases, lectins, and integrins. The reverse transcriptases of many retroviruses (though not lentiviruses such as HIV) contain manganese(Dell INSPIRON 8600 battery). The best-known manganese-containing polypeptides may be arginase, the diphtheria toxin, and Mn-containing superoxide dismutase (Mn-SOD).[39]

Mn-SOD is the type of SOD present in eukaryotic mitochondria, and also in most bacteria (this fact is in keeping with the bacterial-origin theory of mitochondria). The Mn-SOD enzyme is probably one of the most ancient, for nearly all organisms living in the presence of oxygen use it to deal with the toxic effects of superoxide, formed from the 1-electron reduction of dioxygen(Dell INSPIRON 9100 battery). Exceptions include a few kinds of bacteria, such as Lactobacillus plantarum and related lactobacilli, which use a different nonenzymatic mechanism, involving manganese (Mn2+) ions complexed with polyphosphate directly for this task, indicating how this function possibly evolved in aerobic life.

The human body contains about 12 mg of manganese, which is stored mainly in the bones; in the tissue, it is mostly concentrated in the liver and kidneys(Dell INSPIRON 9200 battery).[19] In the human brain, the manganese is bound to manganese metalloproteins, most notably glutamine synthetase in astrocytes.[40]

Manganese is also important in photosynthetic oxygen evolution in chloroplasts in plants. The oxygen-evolving complex (OEC) is a part of photosystem II contained in the thylakoid membranes of chloroplasts; it is responsible for the terminal photooxidation of water during the light reactions of photosynthesis, and has a metalloenzyme core containing four atoms of manganese.[41] For this reason, most broad-spectrum plant fertilizers contain manganese(Dell INSPIRON 9300 battery).

[edit]Precautions

Manganese compounds are less toxic than those of other widespread metals, such as nickel and copper.[42] However, exposure to manganese dusts and fumes should not exceed the ceiling value of 5 mg/m3 even for short periods because of its toxicity level.[43] Manganese poisoning has been linked to impaired motor skills and cognitive disorders(Dell Inspiron 9400 battery).[44]

The permanganate exhibits a higher toxicity than the manganese(II) compounds. The fatal dose is about 10 g, and several fatal intoxications have occurred. The strong oxidative effect leads to necrosis of the mucous membrane. For example, the esophagus is affected if the permanganate is swallowed. Only a limited amount is absorbed by the intestines, but this small amount shows severe effects on the kidneys and on the liver. (Dell Inspiron E1505 battery)

In 2005, a study suggested a possible link between manganese inhalation and central nervous system toxicity in rats.[47]

Manganese exposure in United States is regulated by Occupational Safety and Health Administration.[48]

Generally, exposure to ambient Mn air concentrations in excess of 5 μg Mn/m3 can lead to Mn-induced symptoms. Increased ferroportin protein expression in human embryonic kidney (HEK293) cells is associated with decreased intracellular Mn concentration and attenuated cytotoxicity(Dell Inspiron E1705 battery), characterized by the reversal of Mn-reduced glutamate uptake and diminished lactate dehydrogenase leakage.[49]

[edit]Environmental health concerns

[edit]Manganese in drinking water

Waterborne manganese has a greater bioavailability than dietary manganese. According to results from a 2010 study,[50] higher levels of exposure to manganese in drinking water are associated with increased intellectual impairment and reduced intelligence quotients in school-age children. It is hypothesized that long-term exposure to the naturally occurring manganese in shower water puts up to 8.7 million Americans at risk. (Dell Inspiron Mini 9 battery)

[edit]Manganese in gasoline

Methylcyclopentadienyl manganese tricarbonyl (MMT) is a gasoline additive used to replace lead compounds for unleaded gasolines, to improve the octane number in low octane number petrol distillates. It functions as an antiknock agent by the action of the carbonyl groups. Fuels containing manganese tend to form manganese carbides(Dell Latitude D400 battery), which damage exhaust valves. The need to use lead or manganese compounds is merely historic, as the availability of reformation processes which create high-octane rating fuels increased. The use of such fuels directly or in mixture with non-reformed distillates is universal in developed countries (EU, Japan, etc.) (Dell STUDIO 1450 battery). In USA the imperative to provide the lowest possible price per volume on motor fuels (low fuel taxation rate) and lax legistation of fuel content (before 2000) caused refineries to use MMT. Compared to 1953, levels of manganese in air have dropped.[53] Many racing competitions specifically ban manganese compounds in racing fuel (cart, minibike). MMT contains 24.4-25.2% manganese. There is strong correlation between elevated atmospheric manganese concentrations and automobile traffic density(Dell Vostro 1400 battery).

Role in neurological disorders

Manganism

Manganese overexposure is most frequently associated with manganism, a rare neurological disorder associated with excessive manganese ingestion or inhalation. Historically, persons employed in the production or processing of manganese alloys have been at risk for developing manganism; however, current health and safety regulations protect workers in developed nations. (Dell Vostro 1500 battery) The disorder was first described in 1837 by British academic James Couper, who studied two patients who were manganese grinders.[56]

Manganism is a biphasic disorder. In its early stages, an intoxicated person may experience depression, mood swings, compulsive behaviors, and psychosis. Early neurological symptoms give way to late-stage manganism, which resembles Parkinson's disease(Dell XPS GEN 2 battery). Symptoms include weakness, monotone and slowed speech, an expressionless face, tremor, forward-leaning gait, inability to walk backwards without falling, rigidity, and general problems with dexterity, gait and balance.[56][57] Unlike Parkinson's disease, manganism is not associated with loss of smell and patients are typically unresponsive to treatment with L-DOPA. (Dell XPS M1210 battery) Symptoms of late-stage manganism become more severe over time even if the source of exposure is removed and brain manganese levels return to normal.[57]

[edit]Childhood developmental disorders

Several recent studies attempt to examine the effects of chronic low-dose manganese overexposure on development in children. The earliest study of this kind was conducted in the Chinese province of Shanxi. Drinking water there had been contaminated through improper sewage irrigation and contained 240-350 µg Mn/L(Dell XPS M1330 battery). Although WMn concentrations at or below 300 µg Mn/L are considered safe by the US EPA and 500 µg Mn/L are considered safe by the WHO, the 92 children sampled (between 11 and 13 years of age) from this province displayed lower performance on tests of manual dexterity and rapidity, short-term memory, and visual identification when compared to children from an uncontaminated area(Dell XPS 1340 battery). More recently, a study of 10-year-old children in Bangladesh showed a relationship between WMn concentration in well water and diminished IQ scores. A third study conducted in Quebec examined school children between the ages of 6 and 15 living in homes that received water from a well containing 610 µg Mn/L; controls lived in homes that received water from a 160 µg Mn/L well(Dell XPS M1530 battery). Children in the experimental group showed increased hyperactive and oppositional behaviours.[50]

[edit]Neurodegenerative diseases

Chronic low-dose manganese intoxication is strongly implicated in a number of neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. It may also play a role in the development of multiple sclerosis, restless leg syndrome, and Huntington's disease(Dell XPS M170 battery). A protein called DMT1 is the major transporter involved in manganese absorption from the intestine, and may be the major transporter of manganese across the blood-brain barrier. DMT1 also transports inhaled manganese across the nasal epithelium. The putative mechanism of action is that manganese overexposure and/or dysregulation leads to oxidative stress, mitochondrial dysfunction, glutamate-mediated excitoxicity, and aggregates of protein(Dell XPS M1710 battery).

Cobalt ( /ˈkoʊbɒlt/ koh-bolt or /ˈkoʊbɔːlt/ koh-bawlt)[3] is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal.

Cobalt-based blue pigments have been used since ancient times for jewelry and paints, and to impart a distinctive blue tint to glass, but the color was later thought by alchemists to be due to the known metal bismuth(Dell XPS M1730 battery). Miners had long used the name kobold ore (German for goblin ore) for some of the blue-pigment producing minerals; they were named because they were poor in known metals and gave poisonous arsenic-containing fumes upon smelting. In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), and this was ultimately named for the kobold(Dell XPS M2010 battery).

Today, some cobalt is produced specifically from various metallic-lustered ores, for example cobaltite (CoAsS), but the main source of the element is as a by-product of copper and nickel mining. The copper belt in the Democratic Republic of the Congo and Zambia yields most of the cobalt metal mined worldwide(Dell Latitude E5400 battery).

Cobalt is used in the preparation of magnetic, wear-resistant and high-strength alloys. Cobalt silicate and cobalt(II) aluminate (CoAl2O4, cobalt blue) give a distinctive deep blue color to glass, smalt, ceramics, inks, paints and varnishes. Cobalt occurs naturally as only one stable isotope, cobalt-59. Cobalt-60 is a commercially important radioisotope, used as a radioactive tracer and in the production of gamma rays(Dell Latitude E5500 battery).

Cobalt is the active center of coenzymes called cobalamins, the most common example of which is vitamin B12. As such it is an essential trace dietary mineral for all animals. Cobalt in inorganic form is also an active nutrient for bacteria, algae and fungi.

Characteristics

A block of electrolytically refined cobalt (99.9% purity) cut from a large plate

Cobalt is a ferromagnetic metal with a specific gravity of 8.9. Pure cobalt is not found in nature, but compounds of cobalt are common(Dell Latitude E6400 battery). Small amounts of it are found in most rocks, soil, plants and animals. The Curie temperature is 1115 °C[4] and the magnetic moment is 1.6–1.7 Bohr magnetons per atom.[5] In nature, it is frequently associated with nickel, and both are characteristic minor components of meteoric iron. Cobalt has a relative permeability two thirds that of iron.[6] Metallic cobalt occurs as two crystallographic structures(Dell Latitude E6500 battery): hcp and fcc. The ideal transition temperature between the hcp and fcc structures is 450 °C, but in practice, the energy difference is so small that random intergrowth of the two is common.[7][8][9]

Cobalt is a weakly reducing metal that is protected from oxidation by a passivating oxide film. It is attacked by halogens and sulfur. Heating in oxygen produces Co3O4 which loses oxygen at 900 °C to give the monoxide CoO. (Dell Inspiron Mini 12 battery)

[edit]Compounds

See also Category: Cobalt compounds

Common oxidation states of cobalt include +2 and +3, although compounds with oxidation states ranging from −3 to +4 are also known. A common oxidation state for simple compounds is +2. Cobalt(II) salts form the red-pink [Co(H2O)6]2+ complex in aqueous solution. Addition of chloride gives the intensely blue [CoCl4]2−.(Dell XPS M140 battery)

[edit]Oxygen and chalcogen compounds

Several oxides of cobalt are known. Green cobalt(II) oxide (CoO) has rocksalt structure. It is readily oxidized with water and oxygen to brown cobalt(III) hydroxide (Co(OH)3). At temperatures of 600–700 °C, CoO oxidizes to the blue cobalt(II,III) oxide (Co3O4), which has a spinel structure.[2] Black cobalt(III) oxide (Co2O3) is also known.[11] Cobalt oxides are antiferromagnetic at low temperature(Dell XPS 13 battery): 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.[12]

The principal chalcogenides of cobalt include the black cobalt(II) sulfides, CoS2, which adopts a pyrite-like structure, and Co2S3. Pentlandite (Co9S8) is metal-rich.[2]

[edit]Halides

Cobalt(II) chloride hexahydrate

Four dihalides of cobalt(II) are known: cobalt(II) fluoride (CoF2, pink), cobalt(II) chloride (CoCl2, blue), cobalt(II) bromide (CoBr2, green), cobalt(II) iodide (CoI2, blue-black). These halides exist in anhydrous and hydrated forms(Dell XPS 16 battery). Whereas the anhydrous dichloride is blue, the hydrate is red.[13]

The reduction potential for the reaction

Co3+ + -

e → Co2+

is +1.92 V, beyond that for chlorine to chloride, +1.36 V. As a consequence cobalt(III) and chloride would result in the cobalt(III) being reduced to cobalt(II). Because the reduction potential for fluorine to fluoride is so high, +2.87 V, cobalt(III) fluoride is one of the few simple stable cobalt(III) compounds. Cobalt(III) fluoride, which is used in some fluorination reactions, reacts vigorously with water. (Dell XPS 1640 battery)

[edit]Coordination compounds

As for all metals, molecular compounds of cobalt are classified as coordination complexes, that is molecules or ions that contain cobalt linked to several ligands. The principles of electronegativity and hardness–softness of a series of ligands can be used to explain the usual oxidation state of the cobalt. For example Co+3 complexes tend to have ammine ligands(Dell XPS 1645 battery). As phosphorus is softer than nitrogen, phosphine ligands tend to feature the softer Co2+ and Co+, an example being tris(triphenylphosphine)cobalt(I) chloride ((P(C6H5)3)3CoCl). The more electronegative (and harder) oxide and fluoride can stabilize Co4+ derivatives, e.g. caesium hexafluorocobaltate (Cs2CoF6) and potassium percobaltate (K3CoO4). (Dell XPS 1647 battery)

Alfred Werner, a Nobel-prize winning pioneer in coordination chemistry, worked with compounds of empirical formula CoCl3(NH3)6. One of the isomers determined was cobalt(III) hexammine chloride. This coordination complex, a "typical" Werner-type complex, consists of a central cobalt atom coordinated by six ammine ligands orthogonal to each other and three chloride counteranions(Dell Latitude 131L battery). Using chelating ethylenediamine ligands in place of ammonia gives tris(ethylenediamine)cobalt(III) chloride ([Co(en)3]Cl3), which was one of the first coordination complexes that was resolved into optical isomers. The complex exists as both either right- or left-handed forms of a "three-bladed propeller". This complex was first isolated by Werner as yellow-gold needle-like crystals. (Dell Latitude C400 battery)

[edit]Organometallic compounds

Main article: Organocobalt chemistry

Cobaltocene is a structural analog to ferrocene, where cobalt substitutes for iron. Cobaltocene is sensitive to oxidation, much more than ferrocene.[16] Cobalt carbonyl (Co2(CO)8) is a catalyst in carbonylation reactions.[17] Vitamin B12 (see below) is an organometallic compound found in nature and is the only vitamin to contain a metal atom. (Dell Latitude C500 battery)

[edit]Isotopes

Main article: Isotopes of cobalt

59Co is the only stable cobalt isotope and the only isotope to exist in nature. 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 shorter than 18 hours, and the majority of these are shorter than 1 second(Dell Latitude C510 battery). This element also has 4 meta states, all of which have half-lives shorter than 15 minutes.[19]

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. (Dell Latitude C540 battery)

[edit]History

Early Chinese blue and white porcelain, manufactured circa 1335

Cobalt compounds have been used for centuries to impart a rich blue color to glass, glazes and ceramics. Cobalt has been detected in Egyptian sculpture and Persian jewelry from the third millennium BC, in the ruins of Pompeii (destroyed in 79 AD), and in China dating from the Tang dynasty (618–907 AD) and the Ming dynasty (1368–1644 AD). (Dell Latitude C600 battery)

Cobalt has been used to color glass since the Bronze Age. The excavation of the Uluburun shipwreck yielded an ingot of blue glass, which was cast during the 14th century BC.[21][22] Blue glass items from Egypt are colored with copper, iron, or cobalt. The oldest cobalt-colored glass was from the time of the Eighteenth dynasty in Egypt (1550–1292 BC). The location where the cobalt compounds were obtained is unknown. (Dell Latitude C610 battery)

The word cobalt is derived from the German kobalt, from kobold meaning "goblin", a superstitious term used for the ore of cobalt by miners. The first attempts at smelting these ores to produce metals such as copper or nickel failed, yielding simply powder (cobalt(II) oxide) instead. Also, because the primary ores of cobalt always contain arsenic(Dell Latitude C640 battery), smelting the ore oxidized the arsenic content into the highly toxic and volatile arsenic oxide, which also decreased the reputation of the ore for the miners.[25]

Swedish chemist Georg Brandt (1694–1768) is credited with discovering cobalt circa 1735, showing it to be a new previously unknown element different from bismuth and other traditional metals, and calling it a new "semi-metal."[26][27] He was able to show that compounds of cobalt metal were the source of the blue color in glass(Dell Latitude C800 battery), which previously had been attributed to the bismuth found with cobalt. Cobalt became the first metal to be discovered since the pre-historical period, during which all the known metals (iron, copper, silver, gold, zinc, mercury, tin, lead and bismuth) had no recorded discoverers.[28]

During the 19th century, a significant part of the world's production of cobalt blue (a dye made with cobalt compounds and alumina) and smalt (cobalt glass powdered for use for pigment purposes in ceramics and painting) was carried out at the Norwegian Blaafarveværket. (Dell Latitude C810 battery) The first mines for the production of smalt in the 16th to 18th century were located in Norway, Sweden, Saxony and Hungary. With the discovery of cobalt ore in New Caledonia in 1864 the mining of cobalt in Europe declined. With the discovery of ore deposits in Ontario, Canada in 1904 and the discovery of even larger deposits in the Katanga Province in the Congo in 1914 the mining operations shifted again(Dell Latitude C840 battery).[25] With the Shaba conflict starting in the 1978 the main source for cobalt the copper mines of Katanga Province nearly stopped their production.[31][32] The impact on the world cobalt economy from this conflict was smaller than expected, because industry established effective ways for recycling cobalt materials and in some cases was able to change to cobalt-free alternatives. (Dell Latitude CPI battery)

In 1938, John Livingood and Glenn T. Seaborg discovered cobalt-60.[33] This isotope was famously used at Columbia University in the 1950s to establish parity violation in radioactive beta decay.[34][35]

After World War Two, the US wanted to be sure it was never short of the ore needed for cobalt like the German's were and went exploring for a supply with the US border. A good supply of the ore needed was found in Idaho near Blackbird canyon in the side of a mountain(Dell Latitude D410 battery). The firm Calera Mining Company got production started at the site. [36]

[edit]Occurrence

The stable form of cobalt is created in supernovas via the r-process.[37] It comprises 0.0029% of the Earth's crust and is one of the first transition metal series.

Cobalt occurs in copper and nickel minerals and in combination with sulfur and arsenic in the sulfidic cobaltite (CoAsS), safflorite (CoAs2) and skutterudite (CoAs3) minerals.[10] The mineral cattierite is similar to pyrite and occurs together with vaesite in the copper deposits of the Katanga Province. (Dell Latitude D420 battery)Upon contact with the atmosphere, weathering occurs and the sulfide minerals oxidize to form pink erythrite ("cobalt glance": Co3(AsO4)2·8H2O) and sphaerocobaltite (CoCO3).[39][40]

Cobalt is not found as a native metal but is mainly obtained as a by-product of nickel and copper mining activities. The main ores of cobalt are cobaltite, erythrite, glaucodot and skutterudite(Dell Latitude D430 battery).

[edit]Production

Cobalt ore

Cobalt output in 2005

World production trend

See also: Cobalt extraction techniques

In 2005, the copper deposits in the Katanga Province (former Shaba province) of the Democratic Republic of the Congo were the top producer of cobalt with almost 40% world share, reports the British Geological Survey.[43] The political situation in the Congo influences the price of cobalt significantly. (Dell Latitude D500 battery)

The Mukondo Mountain project, operated by the Central African Mining and Exploration Company in Katanga, may be the richest cobalt reserve in the world. It is estimated to be able to produce about one third of total global production of cobalt in 2008.[45] In July 2009 CAMEC announced a long term agreement under which CAMEC would deliver its entire annual production of cobalt in concentrate from Mukondo Mountain to Zhejiang Galico Cobalt & Nickel Materials of China. (Dell Latitude D505 battery)

Several methods exist for the separation of cobalt from copper and nickel. They depend on the concentration of cobalt and the exact composition of the used ore. One separation step involves froth flotation, in which surfactants bind to different ore components, leading to an enrichment of cobalt ores. Subsequent roasting converts the ores to the cobalt sulfate(Dell Latitude D510 battery), whereas the copper and the iron are oxidized to the oxide. The leaching with water extracts the sulfate together with the arsenates. The residues are further leached with sulfuric acid yielding a solution of copper sulfate. Cobalt can also be leached from the slag of the copper smelter.[47]

The products of the above-mentioned processes are transformed into the cobalt oxide (Co3O4). This oxide is reduced to the metal by the aluminothermic reaction or reduction with carbon in a blast furnace(Dell Latitude D520 battery).[10]

[edit]Applications

The main application of cobalt is as the metal in alloys.[41][42]

[edit]Alloys

Cobalt-based superalloys consume most of the produced cobalt.[41][42] The temperature stability of these alloys makes them suitable for use in turbine blades for gas turbines and jet aircraft engines, though nickel-based single crystal alloys surpass them in this regard.[48] Cobalt-based alloys are also corrosion and wear-resistant(Dell Latitude D600 battery). This makes them useful in the medical field, where cobalt is often used (along with titanium) for orthopedic implants that do not wear down over time. The development of the wear-resistant cobalt alloys started in the first decade of the 19th century with the stellite alloys, which are cobalt-chromium alloys with varying tungsten and carbon content. The formation of chromium and tungsten carbides makes them very hard and wear resistant(Dell Latitude D610 battery).[49] Special cobalt-chromium-molybdenum alloys like Vitallium are used for prosthetic parts such as hip and knee replacements.[50] Cobalt alloys are also used for dental prosthetics, where they are useful to avoid allergies to nickel.[51] Some high speed steels also use cobalt to increase heat and wear-resistance. The special alloys of aluminium, nickel, cobalt and iron, known as Alnico(Dell Latitude D620 battery), and of samarium and cobalt (samarium-cobalt magnet) are used in permanent magnets.[52] It is also alloyed with 95% platinum for jewelry purposes, yielding an alloy that is suitable for fine detailed casting and is also slightly magnetic.[53]

[edit]Batteries

Lithium cobalt oxide (LiCoO2) is widely used in lithium ion battery cathodes. The material is composed of cobalt oxide layers in which the lithium is intercalated. During discharging the lithium intercalated between the layers is set free as lithium ion(Dell Latitude D630 battery).[54] Nickel-cadmium [55] (NiCd) and nickel metal hydride[56] (NiMH) batteries also contain significant amounts of cobalt; the cobalt improves the oxidation capabilities of nickel in the battery.[55]

[edit]Catalysis

Several cobalt compounds are used in chemical reactions as oxidation catalysts. Cobalt acetate is used for the conversion of xylene to terephthalic acid, the precursor to the bulk polymer polyethylene terephthalate(Dell Latitude D800 battery). Typical catalysts are the cobalt carboxylates (known as cobalt soaps). They are also used in paints, varnishes, and inks as "drying agents" through the oxidation of drying oils.[54] The same carboxylates are used to improve the adhesion of the steel to rubber in steel-belted radial tires.

Cobalt-based catalysts are also important in reactions involving carbon monoxide. Steam reforming, useful in hydrogen production, uses cobalt oxide-base catalysts. Cobalt is also a catalyst in the Fischer–Tropsch process(Dell Latitude D810 battery), used in the hydrogenation of carbon monoxide into liquid fuels.[57] The hydroformylation of alkenes often rely on cobalt octacarbonyl as the catalyst,[58] although such processes have been partially displaced by more efficient iridium- and rhodium-based catalysts, e.g. the Cativa process.

The hydrodesulfurization of petroleum uses a catalyst derived from cobalt and molybdenum. This process helps to rid petroleum of sulfur impurities that interfere with the refining of liquid fuels. (Dell Latitude D820 battery)

[edit]Pigments and coloring

Cobalt blue glass

Cobalt-colored glass

Before the 19th century, the predominant use of cobalt was as pigment. Since the Middle Ages, it has been involved in the production of smalt, a blue colored glass. Smalt is produced by melting a mixture of the roasted mineral smaltite, quartz and potassium carbonate, yielding a dark blue silicate glass which is ground after the production(Dell Latitude D830 battery).[59] Smalt was widely used for the coloration of glass and as pigment for paintings.[60] In 1780, Sven Rinman discovered cobalt green and in 1802 Louis Jacques Thénard discovered cobalt blue.[61] The two varieties of cobalt blue, cobalt aluminate and cobalt green (a mixture of cobalt(II) oxide and zinc oxide), were used as pigments for paintings because of their superior stability. (Dell Latitude 2100 battery)

[edit]Radioisotopes

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 bombarding cobalt with neutrons. It produces two gamma rays with energies of 1.17 and 1.33 MeV.[19][64]

Its uses include external beam radiotherapy, sterilization of medical supplies and medical waste, radiation treatment of foods for sterilization (cold pasteurization),[65] industrial radiography (e.g. weld integrity radiographs) (Dell Latitude 2110 battery), density measurements (e.g. concrete density measurements), and tank fill height switches. The metal has the unfortunate habit of producing a fine dust, causing problems with radiation protection. Cobalt from radiotherapy machines has been a serious hazard when not disposed of properly, and one of the worst radiation contamination accidents in North America occurred in 1984(Dell Latitude E4300 battery), after a discarded radiotherapy unit containing cobalt-60 was mistakenly disassembled in a junkyard in Juarez, Mexico.[66][67]

Cobalt-60 has a radioactive half-life of 5.27 years. This decrease in activity requires periodic replacement of the sources used in radiotherapy and is one reason why cobalt machines have been largely replaced by linear accelerators in modern radiation therapy.[68]

Cobalt-57 (Co-57 or 57Co) is a cobalt radioisotope most often used in medical tests, as a radiolabel for vitamin B12 uptake(Dell Vostro 1310 battery), and for the Schilling test. Cobalt-57 is used as a source in Mössbauer spectroscopy and is one of several possible sources in X-ray fluorescence devices.[69][70]

Nuclear weapon designs could intentionally incorporate 59Co, some of which would be activated in a nuclear explosion to produce 60Co. The 60Co, dispersed as nuclear fallout, creates what is sometimes called a cobalt bomb. (Dell Vostro 1320 battery)

[edit]Other uses

Other uses of cobalt are in electroplating, owing to its attractive appearance, hardness and resistance to oxidation,[72] and as ground coats for porcelain enamels.[73]

[edit]Biological role

Cobalt is essential to all animals, including humans. It is a key constituent of cobalamin, also known as vitamin B12, which is the primary biological reservoir of cobalt as an "ultratrace" element. Bacteria in the guts of ruminant animals convert cobalt salts into vitamin B12(Dell Vostro 1510 battery), a compound which can only be produced by bacteria. The minimum presence of cobal

t in soils therefore markedly improves the health of grazing animals, and an uptake of 0.20 mg/kg a day is recommended for them, as they can obtain vitamin B12 in no other way.[74] In the early 20th century during the development for farming of the North Island Volcanic Plateau of New Zealand(Dell Vostro 1520 battery), cattle suffered from what was termed "bush sickness". It was discovered that the volcanic soils lacked cobalt salts, which was necessary for cattle.[75] The ailment was cured by adding small amounts of cobalt to fertilisers.

Non-ruminant herbivores produce vitamin B12 from bacteria in their colons which again make the vitamin from simple cobalt salts. However the vitamin cannot be absorbed from the colon(Dell Vostro 2510 battery), and thus non-ruminants must ingest feces to obtain the nutrient. Animals that do not follow these methods of getting vitamin B12 from their own gastrointestinal bacteria or that of other animals, must obtain the vitamin pre-made in other animal products in their diet, and they cannot benefit from ingesting simple cobalt salts.

The cobalamin-based proteins use corrin to hold the cobalt(Dell Vostro 1014 battery). Coenzyme B12 features a reactive C-Co bond, which participates in its reactions.[76] In humans, B12 exists with two types of alkyl ligand: methyl and adenosyl. MeB12 promotes methyl (-CH3) group transfers. The adenosyl version of B12 catalyzes rearrangements in which a hydrogen atom is directly transferred between two adjacent atoms with concomitant exchange of the second substituent, X, which may be a carbon atom with substituents(Dell Inspiron 1410 battery), an oxygen atom of an alcohol, or an amine. Methylmalonyl coenzyme A mutase (MUT) converts MMl-CoA to Su-CoA, an important step in the extraction of energy from proteins and fats.[77]

Although far less common than other metalloproteins (e.g. those of zinc and iron), cobaltoproteins are known aside from B12. These proteins include methionine aminopeptidase 2 an enzyme that occurs in humans and other mammals which does not use the corrin ring of B12(Dell Vostro 1014N battery), but binds cobalt directly. Another non-corrin cobalt enzyme is nitrile hydratase, an enzyme in bacteria that are able to metabolize nitriles.[78]

[edit]Precautions

Main article: Cobalt poisoning

Cobalt is an essential element for life in minute amounts. The LD50 value for soluble cobalt salts has been estimated to be between 150 and 500 mg/kg. Thus, for a 100 kg person the LD50 would be about 20 grams(Dell Vostro 1015 battery).[79]

After nickel and chromium, cobalt is a major cause of contact dermatitis.[80] In 1966, the addition of cobalt compounds to stabilize beer foam in Canada led to cardiomyopathy, which came to be known as beer drinker's cardiomyopathy. (Dell Vostro A840 battery)

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