Difference between revisions of "Cobalt" - New World Encyclopedia

From New World Encyclopedia
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Cobalt is not found as a free [[metal]] but is generally found in the form of [[ore]]s. It is usually produced as a byproduct of [[nickel]] and [[copper]] mining activities. The main ores of cobalt are:
 
Cobalt is not found as a free [[metal]] but is generally found in the form of [[ore]]s. It is usually produced as a byproduct of [[nickel]] and [[copper]] mining activities. The main ores of cobalt are:
−
* [[cobaltite]]* - [[cobalt]], [[iron]], [[arsenic]] [[sulfide]], or (Co,Fe)AsS
+
* [[cobaltite]]* - [[cobalt]] [[arsenic]] [[sulfide]]* (CoAsS)
−
* [[glaucodot]]* - [[cobalt]], [[iron]] [[arsenic]] [[sulfide]], or (Co,Fe)AsS, in which the cobalt:iron(II) ratio is typically 3:1
+
* [[erythrite]]* - hydrated cobalt arsenate (Co<sub>3</sub>(AsO<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O)
−
* [[erythrite]]* - hydrated cobalt arsenate, or Co<sub>3</sub>(AsO<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O
+
* [[glaucodot]]* - [[cobalt]], [[iron]] [[arsenic]] [[sulfide]]* ((Co,Fe)AsS), in which the cobalt:iron(II) ratio is typically 3:1
−
* [[skutterudite]]* - a [[cobalt]] [[arsenide]] mineral in which variable amounts of [[nickel]] and [[iron]] substitute for cobalt; (Co,Ni,Fe)As<sub>3</sub>
+
* [[skutterudite]]* - a [[cobalt]] [[arsenide]] mineral in which variable amounts of [[nickel]] and [[iron]] substitute for cobalt ((Co,Ni,Fe)As<sub>3</sub>)
 +
 
 
The world's major producers of cobalt are the [[Democratic Republic of the Congo]], [[China]], [[Zambia]], [[Russia]], and [[Australia]]. It is also found in [[Finland]], [[Azerbaijan]], and [[Kazakhstan]]. In the town of [[Cobalt, Ontario]]*, it is a byproduct of [[silver]] mining.
 
The world's major producers of cobalt are the [[Democratic Republic of the Congo]], [[China]], [[Zambia]], [[Russia]], and [[Australia]]. It is also found in [[Finland]], [[Azerbaijan]], and [[Kazakhstan]]. In the town of [[Cobalt, Ontario]]*, it is a byproduct of [[silver]] mining.
  
−
== History ==
+
== History and etymology ==
  
−
Cobalt compounds have been used for centuries to impart a rich blue color to [[glass]], [[glaze]]s, and [[Ceramics (art)|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)<ref>Encyclopedia Britannica Online.</ref>.
+
Cobalt compounds have been used for centuries to impart a rich blue color to [[glass]], [[glaze]]*s, and [[Ceramics (art)|ceramics]]*. Cobalt has been detected in Egyptian sculpture and Persian jewelry from the third millennium BCE, in the ruins of [[Pompeii]]* (destroyed CE 79), and in China dating from the [[Tang dynasty]]* (CE 618–907) and [[Ming dynasty]]* (CE 1368–1644)<ref>Encyclopedia Britannica Online.</ref>.
  
−
Swedish chemist [[Georg Brandt]] (1694–1768) is credited with isolating cobalt sometime between 1730 and 1737. 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.
+
Swedish chemist [[Georg Brandt]]* (1694–1768) is credited with isolating cobalt sometime between 1730 and 1737. He showed that cobalt was the source of the blue color in glass, which previously had been attributed to [[bismuth]] found with cobalt. During the nineteenth century, cobalt blue was produced at the Norwegian [[Blaafarveværket]]* (70-80 % of world production), led by the [[Prussia]]*n industrialist [[Benjamin Wegner]]*. In 1938, [[John Livingood]]* and [[Glenn Seaborg]] discovered the radioisotope [[Cobalt-60 (isotope)|cobalt-60]]*.
  
−
During the 19th century, cobalt blue was produced at the Norwegian [[Blaafarveværket]] (70-80 % of world production), led by the [[Prussia]]n industrialist [[Benjamin Wegner]].
+
The word ''cobalt'' is derived from the German ''kobalt'', from ''[[kobold]]*'' meaning "goblin." Miners used this term for the ore of cobalt, because they thought it worthless and found that it was poisonous and degraded other mined elements. The poisonous nature was mainly because of the presence of [[arsenic]] and [[sulfur]] in the ore<ref>Oxford English Dictionary, Second Edition. 1989.</ref>.
 +
 
 +
== Notable characteristics ==
  
−
In 1938, [[John Livingood]] and [[Glenn Seaborg]] discovered [[Cobalt-60 (isotope)|cobalt-60]].
+
In chemistry, cobalt is a member of a group of [[transition metal]]s. It is located in period 4 of the [[periodic table]], situated between [[iron]] and [[nickel]]. In addition, it lies at the top of group 9 (former group 8B). In combining with other elements, its common [[oxidation states]]* are  +2 and +3, but +1 is also seen.
  
−
The word ''cobalt'' is derived from the German ''kobalt'', from ''[[kobold]]'' meaning "goblin", a term used for the ore of cobalt by miners, who thought it worthless and who found that it was poisonous and that it polluted and degraded other mined elements<!--Former example of "nickel" needs sourcing, OED has "silver ores"—>, mainly due to the [[arsenic]] and [[sulfur]] also found in the ore<ref>Oxford English Dictionary, Second Edition. 1989.</ref>.
+
Cobalt is [[Magnetism|ferromagnetic]]. The [[Curie temperature]]* is 1388 K, with 1.6~1.7 [[Bohr magneton]]*s per [[atom]]. It is frequently associated with [[nickel]], and both are characteristic ingredients of meteoric [[iron]]. [[Mammal]]s require small amounts of cobalt [[salt]]s.
  
−
== Notable characteristics ==
+
Metallic cobalt commonly presents a mixture of two [[crystallographic structure]]*s: "[[hcp]]*" and "[[Face-centered cubic|fcc]]*." The [[transition]]* temperature in going from hcp to fcc is 722 K.
  
−
In chemistry, cobalt is a member of a group of [[transition metal]]s. It is located in period 4 of the [[periodic table]], situated between [[iron]] and [[nickel]]. In addition, it lies at the top of group 9 (former group 8B). Iron, cobalt, and nickel have a number of similar properties and were once grouped together as group 8B.
+
=== Isotopes ===
  
−
Cobalt is [[ferromagnetic]]. The [[Curie temperature]] is of 1388 K with 1.6~1.7 [[Bohr magneton]]s per [[atom]]. It is frequently associated with [[nickel]], and both are characteristic ingredients of [[meteoric iron]]. [[Mammals]] require small amounts of cobalt [[salt]]s. [[Cobalt-60 (isotope)|Cobalt-60]], an artificially produced [[radioactive isotope]] of cobalt, is an important radioactive tracer and [[cancer]]-treatment agent. Cobalt has a [[Permeability (electromagnetism)|relative permeability]] two thirds that of iron.
+
Naturally occurring cobalt is composed of 1 stable [[isotope]], <sup>59</sup>Co. In addition, 22 [[radioisotope]]*s have been characterized, of which the most stable is <sup>60</sup>Co, with a [[half-life]]* of 5.2714 years. Cobalt-60 is useful as a gamma-ray source partially because it can be produced&mdash;in known quantity and large amounts&mdash;by simply exposing natural cobalt to [[neutron]]s in a reactor for a given time. It is used as a radioactive tracer and agent for treating [[cancer]].
−
[[Metallic]] cobalt commonly presents a mixture of two [[crystallographic structure]]s [[hcp]] and [[Face-centered cubic|fcc]] with a [[transition]] temperature hcp→fcc of 722 K.  
 
  
−
Common [[oxidation states]] of cobalt include +2, and +3, though +1 is also seen.
+
Other radioisotopes include <sup>57</sup>Co, with a half-life of 271.79 days; <sup>56</sup>Co, with a half-life of 77.27 days; and <sup>58</sup>Co, with a half life of 70.86 days. All the remaining radioisotopes 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 state]]*s, all of which have half-lives less than 15 minutes.
  
−
=== Isotopes ===
+
The isotopes of cobalt range in [[atomic weight]]* from 50 [[atomic mass unit|amu]]* (<sup>50</sup>Co) to 73 amu (<sup>73</sup>Co). The primary [[decay mode]]* before the most abundant stable isotope, <sup>59</sup>Co, is [[electron capture]]* and the primary mode after is [[beta decay]]*. The primary [[decay product]]*s before <sup>59</sup>Co are element 26 ([[iron]]) isotopes, and the primary products after are element 28 ([[nickel]]) isotopes.
  
−
Naturally occurring cobalt is composed of 1 stable [[isotope]], <sup>59</sup>Co. 22 [[radioisotope]]s have been characterized with the most stable being <sup>60</sup>Co with a [[half-life]] of 5.2714 years, <sup>57</sup>Co with a half-life of 271.79 days, and <sup>56</sup>Co with a half-life of 77.27 days, and <sup>58</sup>Co with a half life of 70.86 days.  All of the remaining [[radioactive]] isotopes have half-lifes 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 state]]s, all of which have half lives less than 15 minutes.
+
== Compounds ==
  
−
The isotopes of cobalt range in [[atomic weight]] from 50 [[atomic mass unit|amu]] (<sup>50</sup>Co) to 73 amu (<sup>73</sup>Co). The primary [[decay mode]] before the most abundant stable isotope, <sup>59</sup>Co, is [[electron capture]] and the primary mode after is [[beta decay]]. The primary [[decay product]]s before <sup>59</sup>Co are element 26 ([[iron]]) isotopes and the primary products after are element 28 ([[nickel]]) isotopes.
+
There is a wide variety of cobalt compounds. The +2 and +3 [[oxidation state]]*s  are most prevalent, but cobalt(I) complexes are also fairly common. Cobalt(II) salts form the red-pink [Co(OH<sub>2</sub>)<sub>6</sub>]<sup>2+</sup> complex in aqueous solution. Addition of excess chloride changes the color from pink to blue, due to the formation of [CoCl<sub>4</sub>]<sup>2-</sup>. Cobalt oxides are [[Magnetism|antiferromagnetic]] at low [[temperature]]: CoO ([[Neel temperature]]* 291 K) and Co<sub>3</sub>O<sub>4</sub> (Neel temperature 40 K).
  
 
== Applications ==
 
== Applications ==
  
 
* [[Alloy]]s, such as:
 
* [[Alloy]]s, such as:
−
** [[Superalloy]]s, for parts in gas [[turbine]] [[aircraft]] [[engine]]s.  
+
** [[Superalloy]]*s, for parts in gas [[turbine]]* [[aircraft]] [[engine]]s.
−
** [[Corrosion]]- and wear-resistant alloys.
+
** [[Corrosion]]*- and wear-resistant alloys.
−
** [[High speed steel]]s.
+
** [[High speed steel]]*s.
−
** Cemented [[carbide]]s (also called hard metals) and [[diamond]] tools.
+
** Cemented [[carbide]]*s (also called hard metals) and [[diamond]] tools.
−
* [[Magnet]]s and magnetic [[recording media]].
+
* [[Magnetism|Magnet]]s and magnetic [[recording media]]*.
−
** [[Alnico]] magnets.
+
** [[Alnico]]* magnets.
 
* [[Catalyst]]s for the [[petroleum]] and chemical industries.
 
* [[Catalyst]]s for the [[petroleum]] and chemical industries.
−
* [[electroplating]] because of its appearance, hardness, and resistance to oxidation.  
+
* [[Electroplating]], because of its appearance, hardness, and resistance to oxidation.  
 
* Drying agents for [[paint]]s, varnishes, and inks.
 
* Drying agents for [[paint]]s, varnishes, and inks.
−
* Ground coats for [[porcelain]] [[vitreous enamel|enamel]]s.
+
* Ground coats for [[porcelain]] [[vitreous enamel|enamel]]*s.
 
* Pigments (cobalt blue and cobalt green).
 
* Pigments (cobalt blue and cobalt green).
 
[[image:bristol.blue.glass.arp.750pix.jpg|thumb|left|145px|Cobalt blue glass]]
 
[[image:bristol.blue.glass.arp.750pix.jpg|thumb|left|145px|Cobalt blue glass]]
 
<br clear="left" style="clear:left" />
 
<br clear="left" style="clear:left" />
 
* [[Battery (electricity)|Battery]] electrodes.
 
* [[Battery (electricity)|Battery]] electrodes.
−
* Steel-belted radial [[tire]]s.
+
* Steel-belted radial [[tire]]*s.
−
* [[Cobalt-60 (isotope)|Cobalt-60]] has multiple uses as a [[gamma ray]] source:
+
* The isotope cobalt-60 has multiple uses as a source of [[gamma ray]]*s:
−
** It is used in [[Radiation therapy|radiotherapy]].
+
** [[Radiation therapy|Radiotherapy]].
−
** It is used in radiation treatment of [[Food irradiation|foods for sterilization]] (cold [[pasteurization]]).
+
** Radiation treatment of [[Food irradiation|foods for sterilization]]* (cold [[pasteurization]]*).
−
** It is used in industrial [[radiography]] to detect structural flaws in metal parts.
+
** Industrial [[radiography]]*, to detect structural flaws in metal parts.
−
 
 
−
Co-60 is useful as a gamma ray source partially because it can be produced - in known quantity, and very large amounts - by simply exposing natural cobalt to [[neutron]]s in a reactor for a given time. 
 
  
 
=== Use in medicine ===
 
=== Use in medicine ===
  
−
The radioactive isotope cobalt-60 (Co-60 or <sup>60</sup>Co) is used in [[Radiation therapy|radiotherapy]]*. It produces gamma rays at two energy levels: 1.17 [[MeV]]* and 1.33 MeV. The <sup>60</sup>Co source is about 2 centimeters (cm) in diameter and as a result produces a [[geometric]]* [[penumbra]]*, which means that the edge of the radiation field is fuzzy. The metal has the unfortunate habit of producing a fine dust, causing problems with radiation protection. The <sup>60</sup>Co source is useful for about 5 years, but even after this point it is still very radioactive. For these reasons, cobalt machines have fallen from favor in the Western world where [[linacs]] are common.
+
The radioactive isotope cobalt-60 (Co-60 or <sup>60</sup>Co) is used in [[Radiation therapy|radiotherapy]]*. It produces gamma rays at two energy levels: 1.17 [[MeV]]* and 1.33 MeV. The <sup>60</sup>Co source is about 2 centimeters (cm) in diameter and as a result produces a [[geometric]]* [[penumbra]]*, which means that the edge of the radiation field is fuzzy. The metal has the unfortunate habit of producing a fine dust, causing problems with radiation protection. The <sup>60</sup>Co source is useful for about 5 years, but even after this point it is still very radioactive. For these reasons, cobalt machines have fallen from favor in the Western world where [[linacs]]* are common.
  
 
== Biological role ==
 
== Biological role ==
−
Cobalt in small amounts is essential to many living [[organism]]s, 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 B-12]].
 
−
 
−
== Compounds ==
 
  
−
There is a wide variety of cobalt compounds.  The +2 and +3 [[oxidation state]]s are most prevalent, however cobalt(I) complexes are also fairly common. Cobalt(II) salts form the red-pink [Co(OH<sub>2</sub>)<sub>6</sub>]<sup>2+</sup> complex in aqueous solution. Adding excess chloride will also change the colour from pink to blue, due to the formation of [CoCl<sub>4</sub>]<sup>2-</sup>. Cobalt oxides are [[antiferromagnetic]] at low [[temperature]]: CoO ([[Neel temperature]] 291 K) and Co<sub>3</sub>O<sub>4</sub> (Neel temperature: 40 K).
+
Cobalt in small amounts is essential to many living [[organism]]s, including [[human]]s. The presence of 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 B-12]]*.
−
; see also [[:Category:Cobalt compounds]]
 
  
 
== Precautions ==
 
== Precautions ==
Line 127: Line 123:
 
Powdered cobalt in metal form is a fire hazard. Cobalt compounds should be handled with care due to cobalt's slight toxicity.
 
Powdered cobalt in metal form is a fire hazard. Cobalt compounds should be handled with care due to cobalt's slight toxicity.
  
−
[[Cobalt-60 (isotope)|<sup>60</sup>Co]] is a powerful gamma ray emitter and exposure to it is therefore a cancer risk. Ingestion of <sup>60</sup>Co will lead to incorporation of some cobalt into tissues, which is released very slowly. <sup>60</sup>Co is a risk factor in a nuclear confrontation because neutron emissions will convert <sup>59</sup>Co into this isotope. Some [[nuclear weapon design]]s could intentionally increase the amount of <sup>60</sup>Co dispersed as [[nuclear fallout]] &ndash; this is sometimes called a [[dirty bomb]] or [[cobalt bomb]], once predicted by a leading scientist as being capable of wiping out all life on earth. The risk in the absence of a [[nuclear war]] comes from improper handling (or theft) of medical radiotherapeutic units.  Nevertheless, the gamma radiation emitted from <sup>60</sup>Co is used to kill bacteria on fruit and vegetables thus increasing their shelf life.  This process is referred to as [[food irradiation|irradiation]].
+
The radioisotope [[Cobalt-60 (isotope)|<sup>60</sup>Co]]* is a powerful gamma-ray emitter and exposure to it is therefore a cancer risk. Ingestion of <sup>60</sup>Co leads to incorporation of some cobalt into tissues, which is released very slowly. <sup>60</sup>Co is a risk factor in a nuclear confrontation because neutron emissions will convert <sup>59</sup>Co into this isotope. Some [[nuclear weapon]]s may be designed to increase the amount of <sup>60</sup>Co dispersed in [[nuclear fallout]]*. Such a weapon is sometimes called a [[dirty bomb]]* or [[cobalt bomb]]*, which a leading scientist predicted as being capable of wiping out all life on earth. The risk in the absence of a [[nuclear war]]* comes from improper handling (or theft) of medical radiotherapeutic units.
  
 
== External links ==
 
== External links ==
Line 134: Line 130:
 
* [http://www.webelements.com/webelements/elements/text/Co/key.html WebElements.com &ndash; Cobalt]
 
* [http://www.webelements.com/webelements/elements/text/Co/key.html WebElements.com &ndash; Cobalt]
 
* [http://www.caro-acro.ca/caro/educ/publ/vig/vignettes/cobalt/Interactions.pdf London celebrates 50 years of Cobalt-60 Radiotherapy ]
 
* [http://www.caro-acro.ca/caro/educ/publ/vig/vignettes/cobalt/Interactions.pdf London celebrates 50 years of Cobalt-60 Radiotherapy ]
 +
* [http://minerals.usgs.gov/minerals/pubs/commodity/cobalt/ USGS - Cobalt]
  
−
{{ChemicalSources}}
+
==References==
  
−
==References==
 
 
*[http://periodic.lanl.gov/elements/27.html Los Alamos National Laboratory - Cobalt]
 
*[http://periodic.lanl.gov/elements/27.html Los Alamos National Laboratory - Cobalt]
−
*[http://www.chevrolet.com/cobalt/ Cobalt] is the name of a current line of cars from [[Chevrolet]].
 
  
 
===Footnotes===
 
===Footnotes===
Line 147: Line 142:
 
[[Category:Chemistry]]
 
[[Category:Chemistry]]
 
[[Category:Chemical elements]]
 
[[Category:Chemical elements]]
−
[[Category:Transition metals]]
 
  
 
{{credit|76949126}}
 
{{credit|76949126}}

Revision as of 20:37, 26 September 2006

For other uses, see Cobalt (disambiguation).
27 iron ← cobalt → nickel
-
↑
Co
↓
Rh
Co-TableImage.png
periodic table
General
Name, Symbol, Number cobalt, Co, 27
Chemical series transition metals
Group, Period, Block 9, 4, d
Appearance metallic with gray tinge
Co,27.jpg
Atomic mass 58.933195(5) g/mol
Electron configuration [Ar] 3d7 4s2
Electrons per shell 2, 8, 15, 2
Physical properties
Density (near r.t.) 8.90 g/cm³
Liquid density at m.p. 7.75 g/cm³
Melting point 1768 K
(1495 °C, 2723 °F)
Boiling point 3200 K
(2927 °C, 5301 °F)
Heat of fusion 16.06 kJ/mol
Heat of vaporization 377 kJ/mol
Heat capacity (25 °C) 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
Crystal structure hexagonal
Oxidation states 2, 3
(amphoteric oxide)
Electronegativity 1.88 (Pauling scale)
Ionization energies
(more) 		1st: 760.4 kJ/mol
2nd: 1648 kJ/mol
3rd: 3232 kJ/mol
Atomic radius 135 pm
Atomic radius (calc.) 152 pm
Covalent radius 126 pm
Miscellaneous–
Electrical resistivity (20 °C) 62.4 nΩ·m
Thermal conductivity (300 K) 100 W/(m·K)
Thermal expansion (25 °C) 13.0 µm/(m·K)
Speed of sound (thin rod) (20 °C) 4720 m/s
Speed of sound (thin rod) (r.t.) 209 m/s
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
Notable 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

Cobalt (chemical symbol Co, atomic number 27) is a hard, lustrous, silver-gray metal. 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.

Occurrence

Cobalt ore.

Cobalt is not found as a free metal but is generally found in the form of ores. It is usually produced as a byproduct of nickel and copper mining activities. The main ores of cobalt are:

  • cobaltite - cobalt arsenic sulfide (CoAsS)
  • erythrite - hydrated cobalt arsenate (Co3(AsO4)2·8H2O)
  • glaucodot - cobalt, iron arsenic sulfide ((Co,Fe)AsS), in which the cobalt:iron(II) ratio is typically 3:1
  • skutterudite - a cobalt arsenide mineral in which variable amounts of nickel and iron substitute for cobalt ((Co,Ni,Fe)As3)

The world's major producers of cobalt are the Democratic Republic of the Congo, China, Zambia, Russia, and Australia. It is also found in Finland, Azerbaijan, and Kazakhstan. In the town of Cobalt, Ontario, it is a byproduct of silver mining.

History and etymology

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 B.C.E., in the ruins of Pompeii (destroyed CE 79), and in China dating from the Tang dynasty (CE 618–907) and Ming dynasty (CE 1368–1644)[1].

Swedish chemist Georg Brandt (1694–1768) is credited with isolating cobalt sometime between 1730 and 1737. He showed that cobalt was the source of the blue color in glass, which previously had been attributed to bismuth found with cobalt. During the nineteenth 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 the radioisotope cobalt-60.

The word cobalt is derived from the German kobalt, from kobold meaning "goblin." Miners used this term for the ore of cobalt, because they thought it worthless and found that it was poisonous and degraded other mined elements. The poisonous nature was mainly because of the presence of arsenic and sulfur in the ore[2].

Notable characteristics

In chemistry, cobalt is a member of a group of transition metals. It is located in period 4 of the periodic table, situated between iron and nickel. In addition, it lies at the top of group 9 (former group 8B). In combining with other elements, its common oxidation states are +2 and +3, but +1 is also seen.

Cobalt is ferromagnetic. The Curie temperature is 1388 K, with 1.6~1.7 Bohr magnetons per atom. It is frequently associated with nickel, and both are characteristic ingredients of meteoric iron. Mammals require small amounts of cobalt salts.

Metallic cobalt commonly presents a mixture of two crystallographic structures: "hcp" and "fcc." The transition temperature in going from hcp to fcc is 722 K.

Isotopes

Naturally occurring cobalt is composed of 1 stable isotope, 59Co. In addition, 22 radioisotopes have been characterized, of which the most stable is 60Co, with a half-life of 5.2714 years. Cobalt-60 is useful as a gamma-ray source partially because it can be produced—in known quantity and large amounts—by simply exposing natural cobalt to neutrons in a reactor for a given time. It is used as a radioactive tracer and agent for treating cancer.

Other radioisotopes include 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 the remaining radioisotopes 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 amu (50Co) to 73 amu (73Co). The primary decay mode before the most abundant stable isotope, 59Co, is electron capture and the primary mode after is beta decay. The primary decay products before 59Co are element 26 (iron) isotopes, and the primary products after are element 28 (nickel) isotopes.

Compounds

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

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.
  • Catalysts for the petroleum and chemical industries.
  • 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


  • Battery electrodes.
  • Steel-belted radial tires.
  • The isotope cobalt-60 has multiple uses as a source of gamma rays:
    • Radiotherapy.
    • Radiation treatment of foods for sterilization (cold pasteurization).
    • Industrial radiography, to detect structural flaws in metal parts.

Use in medicine

The radioactive isotope cobalt-60 (Co-60 or 60Co) is used in radiotherapy. It produces gamma rays at two energy levels: 1.17 MeV and 1.33 MeV. The 60Co source is about 2 centimeters (cm) in diameter and as a result produces a geometric penumbra, which means that the edge of the radiation field is 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 it is still very radioactive. For these reasons, cobalt machines have fallen from favor in the Western world where linacs are common.

Biological role

Cobalt in small amounts is essential to many living organisms, including humans. The presence of 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 B-12.

Precautions

Powdered cobalt in metal form is a fire hazard. Cobalt compounds should be handled with care due to cobalt's slight toxicity.

The radioisotope 60Co is a powerful gamma-ray emitter and exposure to it is therefore a cancer risk. Ingestion of 60Co leads to incorporation of some cobalt into tissues, which is released very slowly. 60Co is a risk factor in a nuclear confrontation because neutron emissions will convert 59Co into this isotope. Some nuclear weapons may be designed to increase the amount of 60Co dispersed in nuclear fallout. Such a weapon is sometimes called a dirty bomb or cobalt bomb, which a leading scientist predicted as being capable of wiping out all life on earth. The risk in the absence of a nuclear war comes from improper handling (or theft) of medical radiotherapeutic units.

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References
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Footnotes

  1. ↑ Encyclopedia Britannica Online.
  2. ↑ Oxford English Dictionary, Second Edition. 1989.

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