Cobalt

For other uses, see Cobalt (disambiguation).

Cobalt, ₂₇Co

Cobalt
Pronunciation	/ˈkoʊbɒlt/
Appearance	Hard lustrous bluish gray metal
Standard atomic weight Ar°(Co)
	58.933194±0.000003 58.933±0.001 (abridged)
Cobalt in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson – ↑ Co ↓ Rh iron ← cobalt → nickel
Atomic number (Z)	27
Group	group 9
Period	period 4
Block	d-block
Electron configuration	[Ar] 3d7 4s2
Electrons per shell	2, 8, 15, 2
Physical properties
Phase at STP	solid
Melting point	1768 K ​(1495 °C, ​2723 °F)
Boiling point	3200 K ​(2927 °C, ​5301 °F)
Density (at 20° C)	8.834 g/cm3
when liquid (at m.p.)	7.75 g/cm3
Heat of fusion	16.06 kJ/mol
Heat of vaporization	377 kJ/mol
Molar heat capacity	24.81 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1790 1960 2165 2423 2755 3198
Atomic properties
Oxidation states	common: +2, +3 −3, −1, 0, +1, +4, +5
Electronegativity	Pauling scale: 1.88
Ionization energies	1st: 760.4 kJ/mol 2nd: 1648 kJ/mol 3rd: 3232 kJ/mol (more)
Atomic radius	empirical: 125 pm
Covalent radius	Low spin: 126±3 pm High spin: 150±7 pm
Spectral lines of cobalt
Other properties
Natural occurrence	primordial
Crystal structure	​hexagonal close-packed (hcp) (hP2)
Lattice constants	a = 250.71 pm c = 407.00 pm (at 20 °C)
Thermal expansion	12.9×10−6/K (at 20 °C)
Thermal conductivity	100 W/(m⋅K)
Electrical resistivity	62.4 nΩ⋅m (at 20 °C)
Magnetic ordering	Ferromagnetic
Young's modulus	209 GPa
Shear modulus	75 GPa
Bulk modulus	180 GPa
Speed of sound thin rod	4720 m/s (at 20 °C)
Poisson ratio	0.31
Mohs hardness	5.0
Vickers hardness	1043 MPa
Brinell hardness	470–3000 MPa
CAS Number	7440-48-4
History
Discovery and first isolation	Georg Brandt (1735)
Isotopes of cobalt
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 56Co synth 77.236 d β+ 56Fe 57Co synth 271.811 d ε 57Fe 58Co synth 70.844 d β+ 58Fe 59Co 100% stable 60Co trace 5.2714 y β−100% 60Ni

Cobalt (Template:PronEng) is a hard, lustrous, grey dick, a chemical element with symbol Co. It is found in various metallic-lustred ores such as cobaltite (CoAsS), safflorite (CoAs₂) and skutterudite (CoAs₃), and their oxidation products such as pink erythrite ('cobalt glance': Co₃(AsO₄)₂.8H₂O) and sphaerocobaltite (CoCO₃). Cobalt is used in the preparation of magnetic, wear-resistant, and high-strength alloys. Cobalt blue (cobalt(II) aluminate, CoAl₂O₄) gives a distinctive deep blue color to glass, ceramics, inks, paints, and varnishes.

Notable characteristics

Cobalt is a silver or gray ferromagnetic metal. Pure cobalt is not found in nature, but compounds of cobalt occur naturally in many forms. Small ayou suck dick7. The Curie temperature is 1388 K, and the magnetic moment is 1.6-1.7 Bohr magnetons per atom. In nature, it is frequently associated with nickel, and both are characteristic minor components 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 occurs as two crystallographic structures hcp and fcc. The ideal transition temperature between hcp and fcc structures is 722 K, but in practice, the energy difference is so small that random intergrowth of the two is common. Cobalt has a hardness of 5.5 on the Mohs scale of mineral hardness.

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

Isotopes

Main article: Isotopes of cobalt

⁵⁹Co is the only stable cobalt isotope. 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 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. Cobalt-60 has a radioactive half-life of 5.27 years. This decrease in activity requires periodic replacement of the sources used in radiotherapy. This is one more reason why cobalt machines have been largely replaced by linear accelerators (linacs) in modern radiation therapy.

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 test.

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-57 is used as a source in Mössbauer spectroscopy.

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.

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). Cobalt glass ingots have been recovered from the Uluburun shipwreck, dating to the late 14th century BC.

Swedish chemist George Brandt (1694–1768) is credited with isolating cobalt circa 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. Also,because the primary ores of cobalt always contain arsenic, smelting the ore oxidized into the highly toxic and volatile oxide As₄O₆, which was inhaled by workers.

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.

Compounds

There is a wide variety of cobalt compounds. The +2 and +3 oxidation states are most prevalent, however cobalt(I) complexes are also known. Cobalt(II) salts form the red-pink [Co(OH₂)₆]²⁺ complex in aqueous solution. Adding excess chloride will changes the color 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

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.

Isotopes

⁶⁰Co is a high-energy gamma ray emitter. Acute high-dose exposures to the gamma emissions can cause severe burns and death. Extended exposures increase the risk of morbidity or mortality from cancer.

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.

Precautions

Although cobalt is an essential element for life in minute amounts, at higher levels of exposure it shows mutagenic and carcinogenic effects similar to nickel (see Cobalt Poisoning ).

Powdered cobalt in metal form is a fire hazard.

References & notes

• Los Alamos National Laboratory: Cobalt

External links

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