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Cobalt (pronouncedˈkoʊbɒlt}}) 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[edit | edit source]
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, water, plants, and animals. It is an 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. Cobalt has a hardness of 5.5 on the Mohs scale of mineral hardness.[How to reference and link to summary or text]
Isotopes[edit | edit source]
- 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 radioisotopes in medicine[edit | edit source]
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.
Occurrence[edit | edit source]
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.
Compounds[edit | edit source]
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
Biological role[edit | edit source]
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.
Precautions[edit | edit source]
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.
References[edit | edit source]
- Babb, T. L., Mitchell, A. G., & Crandall, P. H. (1974). Fastigiobulbar and dentatothalamic influences on hippocampal cobalt epilepsy in the cat: Electroencephalography & Clinical Neurophysiology Vol 36(2) Feb 1974, 141-154.
- Bourg, W. J., Nation, J. R., & Clark, D. E. (1985). The effects of chronic cobalt exposure on passive-avoidance performance in the adult rat: Bulletin of the Psychonomic Society Vol 23(6) Nov 1985, 527-530.
- Canfield, J. G., & Rose, G. J. (1996). Hierarchical sensory guidance of Mauthner-mediated escape responses in goldfish (Carassius auratus) and cichlids (Haplochromis burtoni): Brain, Behavior and Evolution Vol 48(3) Sep 1996, 137-156.
- Colasanti, B. K., Kosa, J. E., & Craig, C. R. (1975). Appearance of wet dog shake behavior during cobalt experimental epilepsy in the rat and its suppression by reserpine: Psychopharmacologia Vol 44(1) 1975, 33-36.
- Cunningham, T. J. (1976). Early eye removal produces excessive bilateral branching in the rat: Application of cobalt filling method: Science Vol 194(4267) Nov 1976, 857-859.
- Czarnota, M., Whitman, D., & Berman, R. (1998). Activity and passive-avoidance learning in cobalt-injected rats: International Journal of Neuroscience Vol 93(1-2) 1998, 29-34.
- Dong, C.-j., McReynolds, J. S., & Qian, H.-h. (1990). Time-dependent differential effects of cobalt ions on rod- and cone-driven responses in the isolated frog retina: Visual Neuroscience Vol 4(4) Apr 1990, 359-365.
- Finch, D. M. (1975). Visual evoked potential correlates of epilepsy in the cobalt focus of rat neocortex: Dissertation Abstracts International.
- Galbraith, R. A., Furukawa, M., & Li, M. (2006). Possible role of creatine concentrations in the brain in regulating appetite and weight: Brain Research Vol 1101(1) Jul 2006, 85-91.
- Hamann, S. R., Holtman, J. R., & Martin, W. R. (1992). Analgesic actions of local anesthetics and cobalt chloride in the rat brain stem: Pharmacology, Biochemistry and Behavior Vol 43(3) Nov 1992, 925-927.
- Harlow, H. F., Schlitz, K. A., & Settlage, P. H. (1955). Effect of cortical implanatations of radioactive cobalt on learned behavior of rhesus monkeys: Journal of Comparative and Physiological Psychology Vol 48(5) Oct 1955, 432-436.
- Hartman, E. R., Colasanti, B. K., & Craig, C. R. (1974). Epileptogenic properties of cobalt and related metals applied directly to cerebral cortex of rat: Epilepsia Vol 15(1) Mar 1974, 121-129.
- Jansen, H. M. L., Van Der Naalt, J., Van Zomeren, A. H., Paans, A. M. L., & et al. (1996). Cobalt-55 positron emission tomography in traumatic brain injury: A pilot study: Journal of Neurology, Neurosurgery & Psychiatry Vol 60(2) Feb 1996, 221-224.
- Nation, J. R., Bourgeois, A. E., Clark, D. E., & Hare, M. F. (1983). The effects of chronic cobalt exposure on behavior and metallothionein levels in the adult rat: Neurobehavioral Toxicology & Teratology Vol 5(1) Jan-Feb 1983, 9-15.
- Pearl, G. S., & Anderson, K. V. (1975). Use of cobalt impregnation as a method of identifying mammalian neural pathways: Physiology & Behavior Vol 15(5) Nov 1975, 619-622.
- Settlage, P. H., & Bogumill, G. P. (1955). Use of radioactive cobalt for the production of brain lesions in animals: Journal of Comparative and Physiological Psychology Vol 48(3) Jun 1955, 208-210.
- Shibuya, M., & et al. (1978). Cobalt injections into the substantia nigra of the rat: Effects on behavior and dopamine metabolism in the striatum: Experimental Neurology Vol 58(3) Feb 1978, 486-499.
- Turner, M. B., Corp, E. S., & Galbraith, R. A. (1994). Lack of NPY-induced feeding in cobalt protoporphyrin-treated rats is a postreceptor defect: Physiology & Behavior Vol 56(5) Nov 1994, 1009-1014.
- Van Gelder, N. M. (1972). Antagonism by taurine of cobalt induced epilepsy in cat and mouse: Brain Research Vol 47 1972, 157-165.
[edit | edit source]
- National Pollutant Inventory - Cobalt fact sheet
- WebElements.com – Cobalt
- London celebrates 50 years of Cobalt-60 Radiotherapy
- Los Alamos National Laboratory: Cobalt
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