Cobalt

Cobalt
Pronunciation	/ˈkoʊbɒlt/ ⓘ[1]
Appearance	Hard lustrous bluish gray metal
Standard atomic weight Ar°(Co)
	58.933194±0.000003[2] 58.933±0.001 (abridged)[3]
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 [4]
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)
Specific heat capacity	420.987 J/(kg·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,[5] −1,[7] 0,[7] +1,[7] +4,[7] +5[6]
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)[4]
Thermal expansion	12.9×10−6/K (at 20 °C)[a]
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
Naming	from the kobelt ore, possibly named after Kobolds
Discovery and first isolation	Georg Brandt (1735)
Isotopes of cobalt v e
Main isotopes[8] Decay Isotope abun­dance half-life (t1/2) mode pro­duct 56Co synth 77.24 d β+ 56Fe 57Co synth 271.81 d ε 57Fe 58Co synth 70.84 d β+ 58Fe 59Co 100% stable 60Co trace 5.2714 y β− 60Ni
Category: Cobalt view talk edit | references

Cobalt is a chemical element; it has symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, produced by reductive smelting, is a hard, lustrous, somewhat brittle, gray metal.

Cobalt-based blue pigments (cobalt blue) have been used since antiquity for jewelry and paints, and to impart a distinctive blue tint to glass. The color was long thought to be due to the metal bismuth. Miners had long used the name kobold ore (German for goblin ore) for some of the blue pigment-producing minerals. They were so named because they were poor in known metals and gave off poisonous arsenic-containing fumes when smelted.[9] In 1735, such ores were found to be reducible to a new metal (the first discovered since ancient times), which was ultimately named for the kobold.

Today, cobalt is usually produced as a by-product of copper and nickel mining, but sometimes also from one of a number of metallic-lustered ores such as cobaltite (CoAsS). The Copperbelt in the Democratic Republic of the Congo (DRC) and Zambia yields most of the global cobalt production. World production in 2016 was 116,000 tonnes (114,000 long tons; 128,000 short tons) according to Natural Resources Canada, and the DRC alone accounted for more than 50%.[10] In 2024, production exceeded 300,000 tons, of which DRC accounted for more than 80%.[11]

Cobalt is primarily used in lithium-ion batteries, and in the manufacture of magnetic, wear-resistant. and high-strength alloys. The compounds cobalt silicate and cobalt(II) aluminate (CoAl2O4, cobalt blue) give a distinctive deep blue color to glass, ceramics, inks, paints and varnishes. Cobalt occurs naturally as only one stable isotope, cobalt-59. Cobalt-60 is a commercially important radioisotope, used as a radioactive tracer and for the production of high-energy gamma rays. Cobalt is also used in the petroleum industry as a catalyst when refining crude oil. This is to purge it of sulfur, which is very polluting when burned and causes acid rain.[12]

Cobalt is the active center of a group of coenzymes called cobalamins. Vitamin B12, the best-known example of the type, is an essential vitamin for all animals. Cobalt in inorganic form is also a micronutrient for bacteria, algae, and fungi.

The name cobalt derives from a type of ore considered a nuisance by 16th century German silver miners, which in turn may have been named from a spirit or goblin held superstitiously responsible for it; this spirit is considered equitable to the kobold (a household spirit) by some, or categorized as a gnome (mine spirit) by others.

Cobalt is a ferromagnetic metal with a specific gravity of 8.9. The Curie temperature is 1,115 °C (2,039 °F)[13] and the magnetic moment is 1.6–1.7 Bohr magnetons per atom.[14] Cobalt has a relative permeability two-thirds that of iron.[15] Metallic cobalt occurs as two crystallographic structures: hcp and fcc. The ideal transition temperature between the hcp and fcc structures is 450 °C (842 °F), but in practice the energy difference between them is so small that random intergrowth of the two is common.[16][17][18]

Cobalt is a weakly reducing metal that is protected from oxidation by a passivating oxide film. It is attacked by halogens and sulfur. Heating in oxygen produces Co3O4 which loses oxygen at 900 °C (1,650 °F) to give the monoxide CoO.[19] The metal reacts with fluorine (F2) at 520 K to give CoF3; with chlorine (Cl2), bromine (Br2) and iodine (I2), producing equivalent binary halides. It does not react with hydrogen gas (H2) or nitrogen gas (N2) even when heated, but it does react with boron, carbon, phosphorus, arsenic and sulfur.[20] At ordinary temperatures, it reacts slowly with mineral acids, and very slowly with moist, but not dry, air.[citation needed]

Common oxidation states of cobalt include +2 and +3, although compounds with oxidation states ranging from −3 to +5 are also known. A common oxidation state for simple compounds is +2 (cobalt(II)). These salts form the pink-colored metal aquo complex [Co(H
2O)
6]2+
in water. Addition of chloride gives the intensely blue [CoCl
4]2−
.[6] In a borax bead flame test, cobalt shows deep blue in both oxidizing and reducing flames.[21]

Several oxides of cobalt are known. Green cobalt(II) oxide (CoO) has rocksalt structure. It is readily oxidized with water and oxygen to brown cobalt(III) hydroxide (Co(OH)3). At temperatures of 600–700 °C, CoO oxidizes to the blue cobalt(II,III) oxide (Co3O4), which has a spinel structure.[6] Black cobalt(III) oxide (Co2O3) is also known.[22] Cobalt oxides are antiferromagnetic at low temperature: CoO (Néel temperature 291 K) and Co3O4 (Néel temperature: 40 K), which is analogous to magnetite (Fe3O4), with a mixture of +2 and +3 oxidation states.[23]

The principal chalcogenides of cobalt are the black cobalt(II) sulfides, CoS2 (pyrite structure), Co2S3 (spinel structure), and CoS (nickel arsenide structure).[6]: 1118 

Four dihalides of cobalt(II) are known: cobalt(II) fluoride (CoF2, pink), cobalt(II) chloride (CoCl2, blue), cobalt(II) bromide (CoBr2, green), cobalt(II) iodide (CoI2, blue-black). These halides exist in anhydrous and hydrated forms. Whereas the anhydrous dichloride is blue, the hydrate is red.[24]

The reduction potential for the reaction Co3+
+ e− → Co2+
is +1.92 V, beyond that for chlorine to chloride, +1.36 V. Consequently, cobalt(III) chloride would spontaneously reduce to cobalt(II) chloride and chlorine. Because the reduction potential for fluorine to fluoride is so high, +2.87 V, cobalt(III) fluoride is one of the few simple stable cobalt(III) compounds. Cobalt(III) fluoride, which is used in some fluorination reactions, reacts vigorously with water.[19]

The inventory of complexes is very large. Starting with higher oxidation states, complexes of Co(IV) and Co(V) are rare. Examples are found in caesium hexafluorocobaltate(IV) (Cs2CoF6) and potassium percobaltate (K3CoO4).[19]

Cobalt(III) forms a wide variety of coordination complexes with ammonia and amines, which are called ammine complexes. Examples include [Co(NH3)6]3+, [Co(NH3)5Cl]2+ (chloropentamminecobalt(III)), and cis- and trans-[Co(NH3)4Cl2]+. The corresponding ethylenediamine complexes are also well known. Analogues are known where the halides are replaced by nitrite, hydroxide, carbonate, etc. Alfred Werner worked extensively on these complexes in his Nobel-prize winning work.[25] The robustness of these complexes is demonstrated by the optical resolution of tris(ethylenediamine)cobalt(III) ([Co(en)
3]3+
).[26]

Cobalt(II) forms a wide variety of complexes, but mainly with weakly basic ligands. The pink-colored cation hexaaquocobalt(II) [Co(H2O)6]2+ is found in several routine cobalt salts such as the nitrate and sulfate. Upon addition of excess chloride, solutions of the hexaaquo complex converts to the deep blue CoCl2−4, which is tetrahedral.[citation needed]

Softer ligands like triphenylphosphine form complexes with Co(II) and Co(I), examples being bis- and tris(triphenylphosphine)cobalt(I) chloride, CoCl2(PPh3)2 and CoCl(PPh3)3. These Co(I) and Co(II) complexes represent a link to the organometallic complexes described below.[citation needed]

Cobaltocene is a structural analog to ferrocene, with cobalt in place of iron. Cobaltocene is much more sensitive to oxidation than ferrocene.[27] Cobalt carbonyl (Co2(CO)8) is a catalyst in carbonylation and hydrosilylation reactions.[28] Vitamin B12 (see below) is an organometallic compound found in nature and is the only vitamin that contains a metal atom.[29] An example of an alkylcobalt complex in the otherwise uncommon +4 oxidation state of cobalt is the homoleptic complex tetrakis(1-norbornyl)cobalt(IV) (Co(1-norb)4), a transition metal-alkyl complex that is notable for its resistance to β-hydrogen elimination,[30] in accord with Bredt's rule. The cobalt(III) and cobalt(V) complexes [Li(THF)
4]+
[Co(1-norb)
4]−
and [Co(1-norb)
4]+
[BF
4]−
are also known.[31]

59Co is the only stable cobalt isotope and the only isotope that exists naturally on Earth. Twenty-two radioisotopes have been characterized: the most stable, 60Co, has a half-life of 5.2714 years; 57Co has a half-life of 271.81 days; 56Co has a half-life of 77.24 days; and 58Co has a half-life of 70.84 days. All the other radioactive isotopes of cobalt have half-lives shorter than 18 hours, and in most cases shorter than 1 second. This element also has 4 meta states, all of which have half-lives shorter than 15 minutes.[32]

The isotopes of cobalt range from 50Co to 78Co. The primary decay mode for isotopes with atomic masses less than that of the only stable isotope, 59Co, is electron capture and the primary mode of decay in isotopes with atomic mass greater than that is beta decay. The primary decay products below 59Co are element 26 (iron) isotopes; above that the decay products are element 28 (nickel) isotopes.[32]

The 59Co nucleus is detectable using nuclear magnetic resonance[33] and has a magnetic quadrupole moment. Among all NMR active nuclei, 59Co has the largest chemical shift range and the chemical shift can be correlated with the spectrochemical series.[34] Resonances are observed over a range of 20000 ppm, the width of the signals being up to 20 kHz. A widely used standard is potassium hexacyanocobaltate (0.1M K3Co(CN)6 in D2O), which, due to its high symmetry, has a rather small line width. Systems of low symmetry can yield broadened signals to an extent that renders the signals unobservable in fluid phase NMR, but still observable in solid state NMR.

Many different stories about the origin of the word "cobalt" have been proposed. In one version the element cobalt was named after "kobelt", the name which 16th century German silver miners had given to a nuisance type of ore which occurred that was corrosive and issued poisonous gas.[35][36] Although such ores had been used for blue pigmentation since antiquity, the Germans at that time did not have the technology to smelt the ore into metal (cf. § History below).[37]

The authority on such kobelt ore (Latinized as cobaltum or cadmia[38][39]) at the time was Georgius Agricola.[35][37] He was also the oft-quoted authority on the mine spirits called "kobel" (Latinized as cobalus or pl. cobali) in a separate work.[40][41][42]

Agricola did not make a connection between the similarly named ore and spirit. However, a causal connection (ore blamed on "kobel") was made by a contemporary,[44] and a word origin connection (word "formed" from cobalus) made by a late 18th century writer.[45] Later, Grimms' dictionary (1868) noted the kobalt/kobelt ore was blamed on the mountain spirit (Bergmännchen [de][b]) which was also held responsible for "stealing the silver and putting out an ore that caused poor mining atmosphere (Wetter[46]) and other health hazards".[36]

Grimms' dictionary entries equated the word "kobel" with "kobold", and listed it as a mere variant diminutive,[48] but the latter is defined in it as a household spirit.[47] Some more recent commentators prefer to characterize the ore's namesake kobelt (recté kobel) as a gnome.[49][52]

The early 20th century Oxford English Dictionary (1st edition, 1908) upheld Grimm's etymology.[c][53] However, by around the same time in Germany, the alternate etymology not endorsed by Grimm (kob/kof "house, chamber" + walt "power, ruler") was being proposed as more convincing.[54][55]

Somewhat later, Paul Kretschmer (1928) explained that while this "house ruler" etymology was the proper one that backed the original meaning of kobold as household spirit, a corruption later occurred introducing the idea of "mine demon" to it.[56] The present edition of the Etymologisches Wörterbuch (25th ed., 2012) under "kobold" lists the latter, not Grimm's etymology, but still maintains, under its entry for "kobalt", that the cobalt ore may have gotten its name from "a type of mine spirit/demon" (daemon metallicus) while stating that this is "apparently" the kobold.[57]

Joseph William Mellor (1935) also stated that cobalt may derive from kobalos (κόβαλος), though other theories had been suggested.[58]

Several alternative etymologies that have been suggested, which may not involve a spirit (kobel or kobold) at all. Karl Müller-Fraureuth conjectured that kobelt derived from Kübel, a bucket used in mining, frequently mentioned by Agricola,[54] namely the kobel/köbel (Latinized as modulus).[59]

Another theory given by the Etymologisches Wörterbuch derives the term from kōbathium[57] or rather cobathia (κωβάθια, "arsenic sulfide"[60]) which occurs as noxious fumes.[37]

An etymology from Slavonic kowalti was suggested by Emanuel Merck (1902).[61][58]

W. W. Skeat and J. Berendes construed κόβαλος as "parasite", i.e. as an ore parasitic to nickel,[58] but this explanation is faulted for its anachronism since nickel was not discovered until 1751.[62][63]

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, Persian jewelry from the third millennium BC, in the ruins of Pompeii, destroyed in 79 AD, and in China, dating from the Tang dynasty (618–907 AD) and the Ming dynasty (1368–1644 AD).[64]

Cobalt has been used to color glass since the Bronze Age. The excavation of the Uluburun shipwreck yielded an ingot of blue glass, cast during the 14th century BC.[65][66] Blue glass from Egypt was either colored with copper, iron, or cobalt. The oldest cobalt-colored glass is from the eighteenth dynasty of Egypt (1550–1292 BC). The Egyptians sourced this cobalt from cobaltiferous alums found in Egypt's Western Oases.[67]

One possible origin of the word cobalt is the 16th century German "kobald", a type of ore. The first attempts to smelt those ores for copper or silver failed, yielding simply powder (cobalt(II) oxide) instead. Because the primary ores of cobalt always contain arsenic, smelting the ore oxidized the arsenic into the highly toxic and volatile arsenic oxide, adding to the notoriety of the ore.[68] Paracelsus, Georgius Agricola, and Basil Valentine all referred to such silicates as "cobalt".[69]

Swedish chemist Georg Brandt (1694–1768) is credited with discovering cobalt c. 1735, showing it to be a previously unknown element, distinct from bismuth and other traditional metals. Brandt called it a new "semi-metal",[70][71] naming it for the mineral from which he had extracted it.[72]: 153  He showed that compounds of cobalt metal were the source of the blue color in glass, which previously had been attributed to the bismuth found with cobalt. Cobalt became the first metal to be discovered since the pre-historical period. All previously known metals (iron, copper, silver, gold, zinc, mercury, tin, lead and bismuth) had no recorded discoverers.[73]

During the 19th century, a significant part of the world's production of cobalt blue (a pigment made with cobalt compounds and alumina) and smalt (cobalt glass powdered for use for pigment purposes in ceramics and painting) was carried out at the Norwegian Blaafarveværket.[74][75] The first mines for the production of smalt in the 16th century were located in Norway, Sweden, Saxony and Hungary. With the discovery of cobalt ore in New Caledonia in 1864, the mining of cobalt in Europe declined. With the discovery of ore deposits in Ontario, Canada, in 1904 and the discovery of even larger deposits in the Katanga Province in the Congo in 1914, mining operations shifted again.[68] When the Shaba conflict started in 1978, the copper mines of Katanga Province nearly stopped production.[76][77] The impact on the world cobalt economy from this conflict was smaller than expected: cobalt is a rare metal, the pigment is highly toxic, and the industry had already established effective ways for recycling cobalt materials. In some cases, industry was able to change to cobalt-free alternatives.[76][77]

In 1938, John Livingood and Glenn T. Seaborg discovered the radioisotope cobalt-60.[78] This isotope was famously used at Columbia University in the 1950s to establish parity violation in radioactive beta decay.[79][80]

After World War II, the US wanted to guarantee the supply of cobalt ore for military uses (as the Germans had been doing) and prospected for cobalt within the US. High purity cobalt was highly sought after for its use in jet engines and gas turbines.[81] An adequate supply of the ore was found in Idaho near Blackbird canyon. Calera Mining Company started production at the site.[82]

Cobalt demand has further accelerated in the 21st century as an essential constituent of materials used in rechargeable batteries, superalloys, and catalysts.[81] It has been argued that cobalt will be one of the main objects of geopolitical competition in a world running on renewable energy and dependent on batteries, but this perspective has also been criticised for underestimating the power of economic incentives for expanded production.[83]

The stable form of cobalt is produced in supernovae through the r-process.[84] It comprises 0.0029% of the Earth's crust. Except as recently delivered in meteoric iron, free cobalt (the native metal) is not found on Earth's surface because of its tendency to react with oxygen in the atmosphere. Small amounts of cobalt compounds are found in most rocks, soils, plants, and animals.[85] In the ocean cobalt typically reacts with chlorine.

In nature, cobalt is frequently associated with nickel. Both are characteristic components of meteoric iron, though cobalt is much less abundant in iron meteorites than nickel. As with nickel, cobalt in meteoric iron alloys may have been well enough protected from oxygen and moisture to remain as the free (but alloyed) metal.[86]

Cobalt in compound form occurs in copper and nickel minerals. It is the major metallic component that combines with sulfur and arsenic in the sulfidic cobaltite (CoAsS), safflorite (CoAs2), glaucodot ((Co,Fe)AsS), and skutterudite (CoAs3) minerals.[19] The mineral cattierite is similar to pyrite and occurs together with vaesite in the copper deposits of Katanga Province.[87] When it reaches the atmosphere, weathering occurs; the sulfide minerals oxidize and form pink erythrite ("cobalt glance": Co3(AsO4)2·8H2O) and spherocobaltite (CoCO3).[88][89]

Cobalt is also a constituent of tobacco smoke.[90] The tobacco plant readily absorbs and accumulates heavy metals like cobalt from the surrounding soil in its leaves. These are subsequently inhaled during tobacco smoking.[91]