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
. Cobalt blue
(cobalt(II) aluminate, CoAl2
) gives a distinctive deep blue color to glass
, and varnishes
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 amounts of it are found in most rocks, soil, plants, and animals. It is the element of atomic number 27. The Curie temperature
is 1388 K with 1.6~1.7 Bohr magnetons
. In nature, it is frequently associated with nickel
, and both are characteristic ingredients of meteoric iron
require small amounts of cobalt which is the basis of vitamin B
, an artificially produced radioactive isotope
of cobalt, is an important radioactive tracer
-treatment agent. Cobalt has a relative permeability
two thirds that of iron. Metallic
cobalt commonly presents a mixture of two crystallographic structures hcp
with a transition
temperature hcp→fcc of 722 K. 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 well developed.
Co is the only stable cobalt isotope
. 22 radioisotopes
have been characterized with the most stable being 60
Co with a half-life
of 5.2714 years, 57
Co with a half-life of 271.79 days, 56
Co with a half-life of 77.27 days, and 58
Co 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 60
Co source is about 2 cm
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 B uptake. It is useful for the Schilling test.
Industrial uses for radioactive isotopes
Cobalt-60 (Co-60 or 60
Co) 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
Cobalt-59 is used as a source in Mössbauer spectroscopy.
Cobalt compounds have been used for centuries to impart a rich blue color to glass
, 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; 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.
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.
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
complex in aqueous solution. Adding excess chloride will also change the color from pink to blue, due to the formation of [CoCl4
. Cobalt oxides are antiferromagnetic
at low temperature
: CoO (Neel temperature
291 K) and Co3
(Neel temperature: 40 K), which is analogous to magnetite
), with a mixture of +2 and +3 oxidation states. The oxide Co2
is probably unstable; it has never been synthesized. Other than Co3
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 Cobalt compounds
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 B
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.
Although cobalt is an essential element for life in minute amounts, at higher levels of exposure it shows mutagenic
effects similar to nickel
(see Cobalt Poisoning
Powdered cobalt in metal form is a fire hazard.
References & notes