Nickel

iso	NA	half-life	DM	DE (MeV)	DP
⁵⁸Ni	68.077%	⁵⁸Ni is stable with 30 neutrons
⁵⁹Ni	trace	76000 y	ε	-	⁵⁹Co
⁶⁰Ni	26.223%	⁶⁰Ni is stable with 32 neutrons
⁶¹Ni	1.14%	⁶¹Ni is stable with 33 neutrons
⁶²Ni	3.634%	⁶²Ni is stable with 34 neutrons
⁶³Ni	syn	100.1 y	β⁻	0.0669	⁶³Cu
⁶⁴Ni	0.926%	⁶⁴Ni is stable with 36 neutrons

Nickel ( /ˈnɪkəl/ ni-kəl) is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal. Nickel belongs to the transition metals and is hard and ductile. Pure nickel shows a significant chemical activity that can be observed when nickel is powdered to maximize the exposed surface area on which reactions can occur, but larger pieces of the metal are slow to react with air at ambient conditions due to the formation of a protective oxide surface. Even then, however, nickel is reactive enough with oxygen that native nickel is rare on Earth's surface, being mostly confined to the interiors of larger nickel–iron meteorites that were protected from oxidation during their time in space. On Earth, such native nickel is always found in combination with iron, in keeping with those elements' origin as major end products of the nucleosynthesis process in supernovas. An iron–nickel mixture is thought to compose Earth's inner core.

The use of nickel (as a natural meteoric nickel–iron alloy) has been traced as far back as 3500 BC. Nickel was first isolated and classified as a chemical element in 1751 by Axel Fredrik Cronstedt, who initially mistook its ore for a copper mineral. Its most important ore minerals are laterites, including limonite, garnierite, and pentlandite. Major production sites include Sudbury region in Canada (which is thought to be of meteoric origin), New Caledonia and Norilsk in Russia.

Because of nickel's slow rate of oxidation at room temperature, it is considered corrosion-resistant. Historically this has led to its use for plating metals such as iron and brass, to its use for chemical apparatus, and its use in certain alloys that will retain a high silvery polish, such as German silver. About 6% of world nickel production is still used for corrosion-resistant pure-nickel plating. Nickel was once a common component of coins, but has largely been replaced by cheaper iron for this purpose, especially since the metal has proven to be a skin allergen for some people.

Nickel is one of the four elements that are ferromagnetic around room temperature. Alnico permanent magnets based partly on nickel are of intermediate strength between iron-based permanent magnets and rare earth magnets. The metal is chiefly valuable in the modern world for the alloys it forms; about 60% of world production is used in nickel-steels (particularly stainless steel). Other common alloys, as well as some new superalloys, make up most of the remainder of world nickel use, with chemical uses for nickel compounds consuming less than 3% of production.^[3] As a compound, nickel has a number of niche chemical manufacturing uses, such as a catalyst for hydrogenation. Enzymes of some microorganisms and plants contain nickel as an active center, which makes the metal an essential nutrient for them.

Characteristics

Atomic and physical properties

Nickel is a silvery-white metal with a slight golden tinge that takes a high polish. It is one of only four elements that are magnetic at or near room temperature, the others being iron, cobalt and gadolinium. Its Curie temperature is 355 °C, meaning that bulk nickel is non-magnetic above this temperature.^[4] The unit cell of nickel is a face centered cube with the lattice parameter of 0.352 nm giving an atomic radius of 0.124 nm. Nickel belongs to the transition metals and is hard and ductile.

The nickel atom has two electron configurations, [Ar] 4s² 3d⁸ and [Ar] 4s¹ 3d⁹, which are very close in energy, where the symbol [Ar] refers to the argon-like core structure. There is some disagreement as to which should be considered the lowest energy configuration.^[5] Chemistry textbooks quote the electron configuration of nickel as [Ar] 4s² 3d⁸,^[6] or equivalently as [Ar] 3d⁸ 4s².^[7] This configuration agrees with the Madelung energy ordering rule, which predicts that 4s is filled before 3d. It is supported by the experimental fact that the lowest energy state of the nickel atom is a 4s² 3d⁸ energy level, specifically the 3d⁸(³F) 4s² ³F, J=4 level.^[8]

However each of these two configurations in fact gives rise to a set of states at different energies.^[8] The two sets of energies overlap, and the average energy of states having configuration [Ar] 4s¹ 3d⁹ is in fact lower than the average energy of states having configuration [Ar] 4s² 3d⁸. For this reason the research literature on atomic calculations quotes the ground state configuration of nickel as 4s¹ 3d⁹.^[5]

Isotopes

Main article: Isotopes of nickel

Naturally occurring nickel is composed of 5 stable isotopes; ⁵⁸Ni, ⁶⁰Ni, ⁶¹Ni, ⁶²Ni and ⁶⁴Ni with ⁵⁸Ni being the most abundant (68.077% natural abundance). ⁶²Ni is the "most stable" nuclide of all the existing elements, with binding energy greater than both ⁵⁶Fe, often incorrectly cited as "most stable", and ⁵⁸Fe.^[9] 18 radioisotopes have been characterised with the most stable being ⁵⁹Ni with a half-life of 76,000 years, ⁶³Ni with a half-life of 100.1 years, and ⁵⁶Ni with a half-life of 6.077 days. All of the remaining radioactive isotopes have half-lives that are less than 60 hours and the majority of these have half-lives that are less than 30 seconds. This element also has 1 meta state.^[10]

Nickel-56 is produced by the silicon burning process and later set free in large quantities during type Ia supernovae. Indeed, the shape of the light curve of these supernovae at intermediate to late-times corresponds to the decay via electron capture of nickel-56 to cobalt-56 and ultimately to iron-56.^[11] Nickel-59 is a long-lived cosmogenic radionuclide with a half-life of 76,000 years. ⁵⁹Ni has found many applications in isotope geology. ⁵⁹Ni has been used to date the terrestrial age of meteorites and to determine abundances of extraterrestrial dust in ice and sediment. Nickel-60 is the daughter product of the extinct radionuclide ⁶⁰Fe, which decays with a half-life of 2.6 million years. Because ⁶⁰Fe has such a long half-life, its persistence in materials in the solar system at high enough concentrations may have generated observable variations in the isotopic composition of ⁶⁰Ni. Therefore, the abundance of ⁶⁰Ni present in extraterrestrial material may provide insight into the origin of the solar system and its early history. Nickel-62 has the highest binding energy per nucleon of any isotope for any element (8.7946 Mev/nucleon).^[12] Isotopes heavier than ⁶²Ni cannot be formed by nuclear fusion without losing energy. Nickel-48, discovered in 1999, is the most proton-rich heavy element isotope known. With 28 protons and 20 neutrons ⁴⁸Ni is "double magic" (like ²⁰⁸Pb) and therefore unusually stable.^[10]^[13]

The isotopes of nickel range in atomic weight from 48 u (⁴⁸Ni) to 78 u (⁷⁸Ni). Nickel-78's half-life was recently measured to be 110 milliseconds and is believed to be an important isotope involved in supernova nucleosynthesis of elements heavier than iron.^[14]

Occurrence

See also: Ore genesis and Category:Nickel minerals

On Earth, nickel occurs most often in combination with sulfur and iron in pentlandite, with sulfur in millerite, with arsenic in the mineral nickeline, and with arsenic and sulfur in nickel galena.^[15] Nickel is commonly found in iron meteorites as the alloys kamacite and taenite.

The bulk of the nickel mined comes from two types of ore deposits. The first are laterites where the principal ore minerals are nickeliferous limonite: (Fe, Ni)O(OH) and garnierite (a hydrous nickel silicate): (Ni, Mg)₃Si₂O₅(OH)₄. The second are magmatic sulfide deposits where the principal ore mineral is pentlandite: (Ni, Fe)₉S₈.

In terms of supply, the Sudbury region of Ontario, Canada, produces about 30% of the world's supply of nickel. The Sudbury Basin deposit is theorized to have been created by a meteorite impact event early in the geologic history of Earth. Russia contains about 40% of the world's known resources at the Norilsk deposit in Siberia. The Russian mining company MMC Norilsk Nickel obtains the nickel and the associated palladium for world distribution. Other major deposits of nickel are found in New Caledonia, France, Australia, Cuba, and Indonesia. Deposits found in tropical areas typically consist of laterites, which are produced by the intense weathering of ultramafic igneous rocks and the resulting secondary concentration of nickel bearing oxide and silicate minerals.

Based on geophysical evidence, most of the nickel on Earth is postulated to be concentrated in the Earth's core. Kamacite and taenite are naturally occurring alloys of iron and nickel. For kamacite the alloy is usually in the proportion of 90:10 to 95:5 although impurities such as cobalt or carbon may be present, while for taenite the nickel content is between 20% and 65%. Kamacite and taenite occur in nickel iron meteorites.^[16]

Compounds

The most common oxidation state of nickel is +2, but compounds of Ni⁰, Ni⁺, and Ni³⁺ are well known, and Ni⁴⁺ has been demonstrated.^[17]

Nickel(0)

Tetracarbonylnickel (Ni(CO)₄), discovered by Ludwig Mond,^[18] is a volatile liquid at room temperature. On heating, the complex decomposes back to nickel and carbon monoxide:

Ni(CO)₄ $\overrightarrow{\leftarrow}$ Ni + 4 CO

This behavior is exploited in the Mond process for purifying nickel, as described above. The related nickel(0) complex bis(cyclooctadiene)nickel(0) is a useful catalyst in organonickel chemistry due to the easily displaced cod ligands.

Nickel(II)

Nickel(II) compounds are known with all common anions, i.e. the sulfide, sulfate, carbonate, hydroxide, carboxylates, and halides. Nickel(II) sulfate is produced in large quantities by dissolving nickel metal or oxides in sulfuric acid. It exists as both a hexa- and heptahydrates.^[19] This compound is useful for electroplating nickel.

The four halogens form nickel compounds, all of which adopt octahedral geometries. Nickel(II) chloride is most common, and its behavior is illustrative of the other halides. Nickel(II) chloride is produced by dissolving nickel residues in hydrochloric acid. The dichloride is usually encountered as the green hexahydrate, but it can be dehydrated to give the yellow anhydrous NiCl₂. Some tetracoordinate nickel(II) complexes form both tetrahedral and square planar geometries. The tetrahedral complexes are paramagnetic and the square planar complexes are diamagnetic. This equilibrium as well as the formation of octahedral complexes contrasts with the behavior of the divalent complexes of the heavier group 10 metals, palladium(II) and platinum(II), which tend to adopt only square-planar complexes.^[17]

Nickelocene is known; it has an electron count of 20, making it relatively unstable.

Nickel(I), (III), and (IV)

For simple compounds, nickel(III) and nickel(IV) only occurs with fluoride and oxides. Nickel(III) oxide is used as the cathode in many rechargeable batteries, including nickel-cadmium, nickel-iron, nickel hydrogen, and nickel-metal hydride, and used by certain manufacturers in Li-ion batteries.^[20]

History

Because the ores of nickel are easily mistaken for ores of silver, understanding of this metal and its use dates to relatively recent times. However, the unintentional use of nickel is ancient, and can be traced back as far as 3500 BC. Bronzes from what is now Syria had contained up to 2% nickel.^[21] Further, there are Chinese manuscripts suggesting that "white copper" (cupronickel, known as baitung) was used there between 1700 and 1400 BC. This Paktong white copper was exported to Britain as early as the 17th century, but the nickel content of this alloy was not discovered until 1822.^[22]

In medieval Germany, a red mineral was found in the Erzgebirge (Ore Mountains) that resembled copper ore. However, when miners were unable to extract any copper from it, they blamed a mischievous sprite of German mythology, Nickel (similar to Old Nick), for besetting the copper. They called this ore Kupfernickel from the German Kupfer for copper.^[23]^[24]^[25]^[26] This ore is now known to be nickeline or niccolite, a nickel arsenide. In 1751, Baron Axel Fredrik Cronstedt was attempting to extract copper from kupfernickel and obtained instead a white metal that he named after the spirit which had given its name to the mineral, nickel.^[27] In modern German, Kupfernickel or Kupfer-Nickel designates the alloy cupronickel.

After its discovery, the only source for nickel was the rare Kupfernickel, but, from 1824 on, the nickel was obtained as byproduct of cobalt blue production. The first large-scale producer of nickel was Norway, which exploited nickel-rich pyrrhotite from 1848 on. The introduction of nickel in steel production in 1889 increased the demand for nickel, and the nickel deposits of New Caledonia, which were discovered in 1865, provided most of the world's supply between 1875 and 1915. The discovery of the large deposits in the Sudbury Basin, Canada in 1883, in Norilsk-Talnakh, Russia in 1920, and in the Merensky Reef, South Africa in 1924 made large-scale production of nickel possible.^[22]

Nickel has been a component of coins since the mid-19th century. In the United States, the term "nickel" or "nick" was originally applied to the copper-nickel Flying Eagle cent, which replaced copper with 12% nickel 1857–58, then the Indian Head cent of the same alloy from 1859–1864. Still later in 1865, the term designated the three-cent nickel, with nickel increased to 25%. In 1866, the five-cent shield nickel (25% nickel, 75% copper) appropriated the designation. Along with the alloy proportion, this term has been used to the present in the United States. Coins of nearly pure nickel were first used in 1881 in Switzerland, and more notably 99.9% nickel five-cent coins were struck in Canada (the world's largest nickel producer at the time) during non-war years from 1922–1981, and their metal content made these coins magnetic.^[28] During the wartime period 1942–45, more or all nickel was removed from Canadian and U.S. coins, due to nickel's war-critical use in armor.^[24]^[29] Canada switched alloys again to plated steel during the Korean war, but was forced to stop making pure nickel "nickels" in 1981, reserving the pure 99.9% nickel alloy after 1968 only to its higher-value coins. Finally, in the 21st century, with rising nickel prices, most countries that formerly used nickel in their coins have abandoned the metal for cost reasons, and the U.S. five-cent coin remains one of the few in which the metal is still used, save for exterior plating.^[30]

Production

In 2005, Russia was the largest producer of nickel with about one-fifth world share closely followed by Canada, Australia, and Indonesia, as reported by the British Geological Survey. A nickel deposit in western Turkey had been exploited, with this location being especially convenient for European smelters, steelmakers, and factories. The one locality in the United States where nickel was commercially mined is Riddle, Oregon, where several square miles of nickel-bearing garnierite surface deposits are located. The mine closed in 1987.^[31]^[32] The Eagle mine project is a proposed new nickel mine in Michigan's upper peninsula.

Extraction and purification

Nickel is recovered through extractive metallurgy. Nickel is extracted from its ores by conventional roasting and reduction processes that yield a metal of greater than 75% purity. In many stainless steel applications, 75% pure nickel can be used without further purification, depending on the composition of the impurities.

Most sulfide ores have traditionally been processed using pyrometallurgical techniques to produce a matte for further refining. Recent advances in hydrometallurgy have resulted in significant nickel purification using these processes. Most sulfide deposits have traditionally been processed by concentration through a froth flotation process followed by pyrometallurgical extraction. In hydrometallurgical processes, nickel sulfide ores undergo flotation (differential flotation if Ni/Fe ratio is too low) and then smelted. After producing the nickel matte, further processing is done via the Sherritt-Gordon process. First, copper is removed by adding hydrogen sulfide, leaving a concentrate of only cobalt and nickel. Then, solvent extraction is used to separate the cobalt and nickel, with the final nickel concentration greater than 99%.

Electrorefining

A second common form of further refining involves the leaching of the metal matte into a nickel salt solution, followed by the electro-winning of the nickel from solution by plating it onto a cathode as electrolytic nickel.

Mond process

Main article: Mond process

Purification of nickel oxides to obtain the purest metal is performed via the Mond process, which increases the nickel concentrate to greater than 99.99% purity.^[33] This process was patented by L. Mond and has been in industrial use since before the beginning of the 20th century. In the process, nickel is reacted with carbon monoxide at around 40–80 °C to form nickel carbonyl in the presence of a sulfur catalyst. Iron gives iron pentacarbonyl too, but this reaction is slow. If necessary, it may be separated by distillation. Dicobalt octacarbonyl is also formed in this process, but it decomposes to tetracobalt dodecacarbonyl at the reaction temperature to give a non-volatile solid.^[3]

Nickel is re-obtained from the nickel carbonyl by one of two processes. It may be passed through a large chamber at high temperatures in which tens of thousands of nickel spheres, called pellets, are constantly stirred. It then decomposes depositing pure nickel onto the nickel spheres. Alternatively, the nickel carbonyl may be decomposed in a smaller chamber at 230 °C to create fine nickel powder. The resultant carbon monoxide is re-circulated and reused through the process. The highly pure nickel produced by this process is known as "carbonyl nickel."

Metal value

The market price of nickel surged throughout 2006 and the early months of 2007; as of April 5, 2007, the metal was trading at 52,300 USD/tonne or 1.47 USD/oz.^[34] The price subsequently fell dramatically from these peaks, and as of 19 January 2009 the metal was trading at 10,880 USD/tonne.^[34]

The US nickel coin contains 0.04 oz (1.25 g) of nickel, which at the April 2007 price was worth 6.5 cents, along with 3.75 grams of copper worth about 3 cents, making the metal value over 9 cents. Since the face value of a nickel is 5 cents, this made it an attractive target for melting by people wanting to sell the metals at a profit. However, the United States Mint, in anticipation of this practice, implemented new interim rules on December 14, 2006, subject to public comment for 30 days, which criminalize the melting and export of cents and nickels.^[35] Violators can be punished with a fine of up to $10,000 and/or imprisoned for a maximum of five years.

As of September 16, 2011, the melt value of a U.S. nickel is $0.0600409, which is 20% higher than the face value.^[36]

Applications

The fraction of global nickel production presently used for various applications is as follows: 60% for making nickel steels; 14% in nickel-copper alloys and nickel silver; 9% to make malleable nickel, nickel clad, Inconel, and other superalloys; 6% in plating; 3% for nickel cast irons; 3% in heat and electric resistance alloys, such as Nichrome; 2% for nickel brasses and bronzes; 3% in all other applications combined.^[37]^[38]

Nickel is used in many specific and recognizable industrial and consumer products, including stainless steel, alnico magnets, coinage, rechargeable batteries, electric guitar strings, microphone capsules, and special alloys. It is also used for plating and as a green tint in glass. Nickel is preeminently an alloy metal, and its chief use is in the nickel steels and nickel cast irons, of which there are many varieties. It is also widely used in many other alloys, such as nickel brasses and bronzes, and alloys with copper, chromium, aluminium, lead, cobalt, silver, and gold (Inconel, Incoloy, Monel, Nimonic).^[39]

Because of its resistance to corrosion, nickel has been occasionally used historically as a substitute for decorative silver. Nickel was also occasionally used in some countries after 1859 as a cheap coinage metal (see above) but beginning the later years of the 20th century has largely replaced by cheaper stainless steel (i.e., iron) alloys, except notably in the United States.

Nickel is an excellent alloying agent for certain other precious metals, and so used in the so-called fire assay, as a collector of platinum group elements (PGE). As such, nickel is capable of full collection of all 6 PGE elements from ores, in addition to partial collection of gold. High-throughput nickel mines may also engage in PGE recovery (primarily platinum and palladium); examples are Norilsk in Russia and the Sudbury Basin in Canada.

Nickel foam or nickel mesh is used in gas diffusion electrodes for alkaline fuel cells.^[40]^[41]

Nickel and its alloys are frequently used as catalysts for hydrogenation reactions. Raney nickel, a finely-divided nickel-aluminium alloy, is one common form, however related catalysts are also often used, including related 'Raney-type' catalysts.

Nickel is a naturally magnetostrictive material, meaning that, in the presence of a magnetic field, the material undergoes a small change in length.^[42] In the case of nickel, this change in length is negative (contraction of the material), which is known as negative magnetostriction and is on the order of 50 ppm.

Nickel is used as a binder in the cemented tungsten carbide or hardmetal industry and used in proportions of six to 12% by weight. Nickel can make the tungsten carbide magnetic and adds corrosion-resistant properties to the cemented tungsten carbide parts, although the hardnesses are lower than those of parts made of the binder cobalt.^[43]

Biological role

Although not recognized until the 1970s, nickel plays important roles in the biology of microorganisms and plants.^[44] In fact, urease (an enzyme that assists in the hydrolysis of urea) contains nickel. The NiFe-hydrogenases contain nickel in addition to iron-sulfur clusters. Such [NiFe]-hydrogenases characteristically oxidise H₂. A nickel-tetrapyrrole coenzyme, Cofactor F430, is present in the methyl coenzyme M reductase, which powers methanogenic archaea. One of the carbon monoxide dehydrogenase enzymes consists of an Fe-Ni-S cluster.^[45] Other nickel-containing enzymes include a rare bacterial class of superoxide dismutase^[46] and glyoxalase I enzymes in bacteria and several parasitic eukaryotic trypanosomal parasites ^[47] (this enzyme in higher organisms, including yeast and mammals, uses divalent zinc, Zn²⁺).^[48]^[49]^[50]^[51]^[52]

Toxicity

Exposure to nickel metal and soluble compounds should not exceed 0.05 mg/cm³ in nickel equivalents per 40-hour work-week. Nickel sulfide fume and dust are believed to be carcinogenic, and various other nickel compounds may be as well.^[53]^[54] Nickel carbonyl, [Ni(CO)₄], is an extremely toxic gas. The toxicity of metal carbonyls is a function of both the toxicity of the metal as well as the carbonyl's ability to give off highly toxic carbon monoxide gas, and this one is no exception; nickel carbonyl is also explosive in air.^[55]^[56] Sensitized individuals may show an allergy to nickel, affecting their skin, also known as dermatitis. Sensitivity to nickel may also be present in patients with pompholyx. Nickel is an important cause of contact allergy, partly due to its use in jewellery intended for pierced ears.^[57] Nickel allergies affecting pierced ears are often marked by itchy, red skin. Many earrings are now made nickel-free due to this problem. The amount of nickel allowed in products that come into contact with human skin is regulated by the European Union. In 2002, researchers found amounts of nickel being emitted by 1 and 2 Euro coins far in excess of those standards. This is believed to be due to a galvanic reaction.^[58]

It was voted Allergen of the Year in 2008 by the American Contact Dermatitis Society.^[59]

Reports also showed that both the nickel-induced activation of hypoxia-inducible factor (HIF-1) and the up-regulation of hypoxia-inducible genes are due to depleted intracellular ascorbate levels. The addition of ascorbate to the culture medium increased the intracellular ascorbate level and reversed both the metal-induced stabilization of HIF-1- and HIF-1α-dependent gene expression.^[60]^[61]

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