Dictionary:

cobalt

  (kō'bôlt')

A hard, brittle metallic element, found associated with nickel, silver, lead, copper, and iron ores and resembling nickel and iron in appearance. It is used chiefly for magnetic alloys, high-temperature alloys, and in the form of its salts for blue glass and ceramic pigments. Atomic number 27; atomic weight 58.9332; melting point 1,495°C; boiling point 2,900°C; specific gravity 8.9; valence 2, 3.

[German Kobalt, from Middle High German kobolt, variant of kobold, goblin (from silver miners' belief that cobalt had been placed by goblins who had stolen the silver).]

A lustrous, silvery-blue metallic chemical element, Co, with an atomic number of 27 and an atomic weight of 58.93. Metallic cobalt was isolated in 1735 by the Swedish scientist G. Brandt, who called the impure metal cobalt rex, after the ore from which it was extracted. The metal was shown to be a previously unknown element by T. O. Bergman in 1780.See also Periodic table.

Cobalt is a transition element in the same group as rhodium and iridium. In the periodic table it occupies a position between iron and nickel in the third period. Cobalt resembles iron and nickel in both its free and combined states, possessing similar tensile strength, machinability, thermal properties, and electrochemical behavior. Constituting 0.0029% of the Earth's crust, cobalt is widely distributed in nature, occurring in meteorites, stars, lunar rocks, seawater, fresh water, soils, plants, and animals. See also Periodic table; Transition elements.

Cobalt and its alloys resist wear and corrosion even at high temperatures. The most important commercial uses are in making alloys for heavy-wear, high-temperature, and magnetic applications. Small amounts of the element are required by plants and animals. The artificially produced radioactive isotope of cobalt, ⁶⁰Co, has many medical and industrial applications.

Cobalt, with a melting point of 1495°C (2723°F) and a boiling point of 3100°C (5612°F), has a density (20°C; 68°F) of 8.90 g·cm⁻³, an electrical resistivity (20°C) of 6.24 microhm·cm, and a hardness (diamond pyramid, Vickers; 20°C) of 225. It is harder than iron and, although brittle, it can be machined. The latent heat of fusion is 259.4 joules/g, and the latent heat of vaporization is 6276 J/g; the specific heat (15–100°C; 59–212°F) is 0.442 J/g · °C. Cobalt is ferromagnetic, with the very high Curie temperature of 1121°C (2050°F). The electronic configuration is 1s²2s²2p⁶3s²3p⁶3d⁷4s². At normal temperatures the stable crystal form of cobalt is hexagonal close-packed, but above 417°C (783°F) face-centered cubic is the stable structure. Although the finely divided metal is pyrophoric in air, cobalt is relatively unreactive and stable to oxygen in the air, unless heated. It is attacked by sulfuric, hydrochloric, and nitric acids, and more slowly by hydrofluoric and phosphoric acids, ammonium hydroxide, and sodium hydroxide. Cobalt reacts when heated with the halogens and other nonmetals such as boron, carbon, phosphorus, arsenic, antimony, and sulfur. Dinitrogen, superoxo, peroxo, and mixed hydride complexes also exist. In its compounds, cobalt exhibits all the oxidation states from −I to IV, the most common being II and III. The highest oxidation state is found in cesium hexafluorocobaltate(IV), Cs₂CoF₆, and a few other compounds.

There are over 200 ores known to contain cobalt; traces of the metal are found in many ores of iron, nickel, copper, silver, manganese, and zinc. However, the commercially important cobalt minerals are the arsenides, oxides, and sulfides. Zaire is the chief producer, followed by Zambia. Russia, Canada, Cuba, Australia, and New Caledonia produce most of the rest. Zaire and Zambia together account for just over 50% of the world's cobalt reserves. Nickel-containing laterites (hydrated iron oxides) found in the soils of the Celebes, Cuba, New Caledonia, and many other tropical areas are being developed as sources of cobalt. The manganese nodules found on the ocean floor are another large potential reserve of cobalt. They are estimated to contain at least 400 times as much cobalt as land-based deposits.

Since cobalt production is usually subsidiary to that of copper, nickel, or lead, extraction procedures vary according to which of these metals is associated with the cobalt. In general, the ore is roasted to remove stony gangue material as a slag, leaving a speiss of mixed metal and oxides, which is then reduced electrolytically, reduced thermally with aluminum, or leached with sulfuric acid to dissolve iron, cobalt, and nickel, leaving metallic copper behind. Lime is used to precipitate iron, and sodium hypochlorite is used to precipitate cobalt as the hydroxide. The cobalt hydroxide can be heated to give the oxide, which in turn is reduced to the metal by heating with charcoal.

Cobalt ores have long been used to produce a blue color in pottery, glass, enamels, and glazes. Cobalt is contained in Egyptian pottery dated as early as 2600 B.C. and in the blue and white porcelain ware of the Ming Dynasty in China (1368–1644).

An important modern industrial use involves the addition of small quantities of cobalt oxide during manufacture of ceramic materials to achieve a white color. The cobalt oxide counteracts yellow tints resulting from iron impurities. Cobalt oxide is also used in enamel coatings on steel to improve the adherence of the enamel to the metal. Cobalt arsenates, phosphates, and aluminates are used in artists' pigments, and various cobalt compounds are used in inks for full-color jet printing and in reactive dyes for cotton. Cobalt blue (Thenard's blue), one of the most durable of all blue pigments, is essentially cobalt aluminate. Cobalt linoleates, naphthenates, oleates, and ethylhexoates are used to speed up the drying of paints, lacquers, varnishes, and inks by promoting oxidation. In all, about a third of the world's cobalt production is used to make chemicals for the ceramic and paint industries.See also Dye.

Cobalt catalysts are used throughout the chemical industry for various processes. These include hydrogenations and dehydrogenations, halogenations, aminations, polymerizations (for example, butadiene), oxidation of xylenes to toluic acid, production of hydrogen sulfide and carbon disulfide, carbonylation of methanol to acetic acid, olefin synthesis, denitrogenation and desulfurization of coal tars, reductions with borohydrides, and nitrile syntheses, and such important reactions as the Fisher-Tropsch method for synthesizing liquid fuels and the hydroformylation process. Cobalt catalysts have also been used in the oxidation of poisonous hydrogen cyanide in gas masks and in the oxidation of carbon monoxide in automobile exhausts.

Although cobalt was not used in its metallic state until the twentieth century, the principal use of cobalt is as a metal in the production of alloys, chiefly high-temperature and magnetic types. Superalloys needed to stand high stress at high temperatures, as in jet engines and gas turbines, typically contain 20–65% cobalt along with nickel, chromium, molybdenum, tungsten, and other elements.

In parts of the world where soil and plants are deficient in cobalt, trace amounts of cobalt salts [for example, the chloride and nitrate of Co(II)] are added to livestock feeds and fertilizers to prevent serious wasting diseases of cattle and sheep, such as pining, a debilitating disease especially common in sheep. Symptoms of cobalt deprivation in animals include retarded growth, anemia, loss of appetite, and decreased lactation.

The principal biological role of cobalt involves corrin compounds (porphyrin-like macrocycles). The active forms contain an alkyl group (5′-deoxyadenosine or methyl) attached to the cobalt as well as four nitrogens from the corrin and a nitrogen from a heterocycle, usually 5,6-dimethylbenzimidazole. These active forms act in concert with enzymes to catalyze essential reactions in humans. However, the corrin compounds are not synthesized in the body; they must be ingested in very small quantities. Vitamin B₁₂, with cyanide in place of the alkyl, prevents pernicious anemia but is itself inactive. The body metabolizes the vitamin into the active forms. Although the cobalt in corrins is usually Co(III), both Co(II) and Co(I) are involved in enzymic processes. Roughly one-third of all enzymes are metalloenzymes. Cobalt(II) substitutes for zinc in many of these to yield active forms. Such substitution of zinc may account, in part, for the toxicity of cobalt. See also Enzyme.

A mineral whose main function is in vitamin B₁₂, although there are some cobalt-dependent enzymes. There is no evidence of cobalt deficiency in human beings, and no evidence on which to base estimates of requirements for inorganic cobalt. ‘Pining disease’ in cattle and sheep is due to cobalt deficiency (their intestinal micro-organisms synthesize vitamin B₁₂) and it is a growth factor for some animals. Cobalt salts are toxic in excess, causing degeneration of the heart muscle, and habitual intakes in excess of 300 mg/day are considered undesirable.

An essential trace mineral. Cobalt is found in all cells but occurs in large quantities in bone marrow where it is required for the production of red blood cells. Until recently it was thought that cobalt in humans was found only as a constituent of vitamin B₁₂ (cobalamin), but it is now known to have a role in some enzymes. Sources of cobalt include liver, lean meat, poultry, fish and milk. Recommended intakes have not been established, but excessive intakes (29.5 mg per day), which were used to treat certain anaemias, have proved toxic. High doses of cobalt salts may also contribute to heart disease. This was a problem in the 1950s when cobalt salts were added to beer in Belgium and Canada to retain the head.

For more information on cobalt, visit Britannica.com.

An essential trace element; it is a component of vitamin B₁₂, essential for the production of red blood cells. It is required in very small amounts. Average daily intakes are about 0.3 mg. Very high doses (above 29 mg per day) have proved toxic. Sources include liver, lean meat, poultry, fish, and milk.

A chemical element, atomic number 27, atomic weight 58.933, symbol Co. A component of vitamin B₁₂.

• c.-57 — a radioisotope of cobalt having a half-life of 270 days; used as a label for cyanocobalamin. Symbol ⁵⁷Co.
• c.-60 — a radioisotope of cobalt having a half-life of 5.27 years and a principal gamma ray energy of 1.33 MeV; used as a radiation therapy source. Symbol ⁶⁰Co.
• c. nutritional deficiency — causes anorexia and poor weight gain. Identification of the disease is based on chemical analysis of pasture and soil and biochemical analysis of animal tissues and fluids. Called also enzootic marasmus, Grand Traverse disease and other regional names.
• c. poisoning — accidental overdosing with cobalt causes listlessness, weight loss and incoordination.

27 iron ← cobalt → nickel - ↑ Co ↓ Rh Periodic table - Extended periodic table
General
Name, symbol, number	cobalt, Co, 27
Chemical series	transition metals
Group, period, block	9, 4, d
Appearance	metallic with gray tinge
Standard atomic weight	58.933195(5) g·mol−1
Electron configuration	[Ar] 3d7 4s2
Electrons per shell	2, 8, 15, 2
Density (near r.t.)	8.90 g·cm−3
Liquid density at m.p.	7.75 g·cm−3
Melting point	1768 K (1495 °C, 2723 °F)
Boiling point	3200 K (2927 °C, 5301 °F)
Heat of fusion	16.06 kJ·mol−1
Heat of vaporization	377 kJ·mol−1
Heat capacity	(25 °C) 24.81 J·mol−1·K−1
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 1790 1960 2165 2423 2755 3198
Atomic properties
Crystal structure	hexagonal
Oxidation states	2, 3 (amphoteric oxide)
Electronegativity	1.88 (Pauling scale)
Ionization energies (more)	1st: 760.4 kJ·mol−1
	2nd: 1648 kJ·mol−1
	3rd: 3232 kJ·mol−1
Atomic radius	135 pm
Atomic radius (calc.)	152 pm
Covalent radius	126 pm
Miscellaneous
Magnetic ordering	ferromagnetic
Electrical resistivity	(20 °C) 62.4 nΩ·m
Thermal conductivity	(300 K) 100 W·m−1·K−1
Thermal expansion	(25 °C) 13.0 µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 4720 m/s
Young's modulus	209 GPa
Shear modulus	75 GPa
Bulk modulus	180 GPa
Poisson ratio	0.31
Mohs hardness	5.0
Vickers hardness	1043 MPa
Brinell hardness	700 MPa
CAS registry number	7440-48-4
Selected isotopes
Main article: Isotopes of cobalt iso NA half-life DM DE (MeV) DP 56Co syn 77.27 d ε 4.566 56Fe 57Co syn 271.79 d ε 0.836 57Fe 58Co syn 70.86 d ε 2.307 58Fe 59Co 100% Co is stable with 32 neutrons 60Co syn 5.2714 years β- 2.824 60Ni
References

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

Notable characteristics

Cobalt metal is a silver or grey ferromagnetic element of atomic number 27. The Curie temperature is of 1388 K with 1.6~1.7 Bohr magnetons per atom. In nature, it is frequently associated with nickel, and both are characteristic ingredients of meteoric iron. Mammals require small amounts of cobalt which is the basis of vitamin B₁₂. Cobalt-60, an artificially produced radioactive isotope of cobalt, is an important radioactive tracer and cancer-treatment agent. Cobalt has a relative permeability two thirds that of iron. Metallic cobalt commonly presents a mixture of two crystallographic structures hcp and fcc with a transition temperature hcp→fcc of 722 K.

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

Applications

• Alloys, such as
  • Superalloys, for parts in gas turbine aircraft engines.
  • Corrosion- and wear-resistant alloys.
  • High speed steels.
  • Cemented carbides (also called hard metals) and diamond tools.
• Magnets and magnetic recording media.
  • Alnico magnets.
  • Samarium-cobalt magnets.
• Catalysts for the petroleum and chemical industries, e.g. for hydroformylation and oxidation.
• Electroplating because of its appearance, hardness, and resistance to oxidation.
• Drying agents for paints, varnishes, and inks.
• Ground coats for porcelain enamels.
• Pigments (cobalt blue and cobalt green).

Cobalt blue glass

• Lithium ion battery electrodes.
• Steel-belted radial tires.
• Purification of histidine-tagged fusion proteins in biotechnology applications.

Radioisotopes of Cobalt

Main article: Isotopes of cobalt

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

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

Cobalt Isotopes^[1]

Isotope	Decay mechanism	Half life
Co-50	positron emission	44 millisecond
Co-51	positron emission	unmeasured
Co-52	positron emission	0.12 second
Co-53	positron emission	0.24 second
Co-54	positron emission	193.2 millisecond
Co-55	positron emission	17.53 h
Co-56	electron capture, positron emission	77.3 d
Co-57	positron emission	271.8 d
Co-58	electron capture	70.88 d
Co-59	stable	∞
Co-60	beta decay	5.271 yr
Co-61	beta decay	1.65 hr
Co-62	beta decay	1.5 min
Co-63	beta decay	27.5 second
Co-64	beta decay	0.30 second
Co-65	beta decay	1.17 second
Co-66	beta decay	0.190 second
Co-67	beta decay	0.43 second
Co-68	beta decay	0.20 second
Co-69	beta decay	0.22 second
Co-70	beta decay	0.13 second
Co-71	beta decay	0.21 second
Co-72	beta decay	90 millisecond

Cobalt radioisotopes in medicine

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

Cobalt-57 (Co-57 or ⁵⁷Co) is a radioactive metal that is used in medical tests; it is used as a radiolabel for vitamin B₁₂ uptake. It is useful for the Schilling's test.^[2]

Industrial uses for radioactive isotopes

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

• sterilization of medical supplies, and medical waste;
• radiation treatment of foods for sterilization (cold pasteurization);
• industrial radiography (e.g., weld integrity radiographs);
• density measurements (e.g., concrete density measurements); and
• tank fill height switches.

Cobalt-59 is used as a source in Mössbauer spectroscopy.

History

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 AD 79), and in China dating from the Tang dynasty (AD 618–907) and the Ming dynasty (AD 1368–1644)^[3]. Cobalt glass ingots have been recovered from shipwrecks dating to the time of the Minoans ^{[citation needed]} (BC 2700-1450).

Swedish chemist George Brandt (1694–1768) is credited with isolating cobalt in 1735. He was able to show that cobalt was the source of the blue color in glass, which previously had been attributed to the bismuth found with cobalt.

During the 19th century, cobalt blue was produced at the Norwegian Blaafarveværket (70-80% of world production), led by the Prussian industrialist Benjamin Wegner.

In 1938, John Livingood and Glenn Seaborg discovered cobalt-60.

The word cobalt is derived from the German kobalt, from kobold meaning "goblin", a term used for the ore of cobalt by miners. The first attempts at smelting the cobalt ores to produce cobalt metal failed, yielding cobalt(II) oxide instead; not only that, but because of cobalt's curious affinity for arsenic, the primary ores of cobalt always contain arsenic, and upon smelting the arsenic oxidized into the highly toxic As₄O₆, which was breathed in by workers.

Biological role

Cobalt in small amounts is essential to many living organisms, including humans. Having 0.13 to 0.30 mg/kg of cobalt in soils markedly improves the health of grazing animals. Cobalt is a central component of the vitamin cobalamin, or vitamin B₁₂.

Occurrence

Cobalt ore

Cobalt output in 2005

World production trend

Cobalt is not found as a native metal but generally found in the form of ores. Cobalt is usually not mined alone, and tends to be produced as a by-product of nickel and copper mining activities. The main ores of cobalt are cobaltite, erythrite, glaucodot, and skutterudite.

In 2005, the Democratic Republic of the Congo was the top producer of cobalt with almost 40% world share followed by Canada, Zambia, Russia, Brazil and Cuba, reports the British Geological Survey.

see also Category:Cobalt minerals

Compounds

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

see also Category:Cobalt compounds

Precautions

Powdered cobalt in metal form is a fire hazard.

Cobalt compounds should be handled with care due to cobalt's slight toxicity.

⁶⁰Co is a high-energy gamma ray emitter. Acute high-dose exposures to the gamma emissions, such as can occur when irradiation equipment is inadvertently diverted into scrap, can cause severe burns and death. Extended exposures increase the risk of morbidity or mortality from cancer.^[4]

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 dirty bomb or cobalt bomb, once predicted by physicist Leó Szilárd as being capable of wiping out all life on earth.

References & notes

• Los Alamos National Laboratory: Cobalt

1. ^ Nuclides and Isotopes: Chart of the Nuclides, 16th Edition, by Edward Baum, Harold Knox, and Thomas Miller; Knolls Atomic Power Laboratory; 2002
2. ^ JPNM Physics Isotopes
3. ^ Encyclopedia Britannica Online.
4. ^ The Juarez accident

External links

Wikimedia Commons has media related to:

Cobalt

• National Pollutant Inventory - Cobalt fact sheet
• WebElements.com – Cobalt
• London celebrates 50 years of Cobalt-60 Radiotherapy

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - kobolt

idioms:

• cobalt blue    koboltblå

Nederlands (Dutch)
Kobalt

Français (French)
n. - cobalt

idioms:

• cobalt blue    bleu-cobalt

Deutsch (German)
n. - (chem.) Kobalt

idioms:

• cobalt blue    kobaltblau

Ελληνική (Greek)
n. - κοβάλτιο
adj. - του κοβαλτίου

idioms:

• cobalt blue    ανοιχτογάλαζο(ς)

Italiano (Italian)
idioms:

• cobalt blue    blu cobalto, cobalto

Português (Portuguese)
n. - cobalto (m) (Quím.)
adj. - de cobalto

idioms:

• cobalt blue    azul (m) de cobalto

Русский (Russian)
кобальт

idioms:

• cobalt blue    кобальтовая синь

Español (Spanish)
n. - cobalto

idioms:

• cobalt blue    azul de cobalto

Svenska (Swedish)
n. - kobolt
adj. - kobolt-

中文（简体） (Chinese (Simplified))
钴, 由钴制的深蓝色, 钴类颜料

idioms:

• cobalt blue    钴蓝色, 艳蓝色

中文（繁體） (Chinese (Traditional))
n. - 鈷, 由鈷制的深藍色, 鈷類顏料

idioms:

• cobalt blue    鈷藍色, 豔藍色

한국어 (Korean)
n. - 원소기호 코발트, 코발트 색

日本語 (Japanese)
n. - コバルト

idioms:

• cobalt blue    コバルトブルー

العربيه (Arabic)
‏(الاسم) مادة الكوبالت (صفه) كوبالتي, بلون الكوبالت‏

עברית (Hebrew)
n. - ‮קובלט‬

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