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nickel, metallic chemical element; symbol Ni; at. no. 28; at. wt. 58.6934; m.p. about 1,453℃; b.p. about 2,732℃; sp. gr. 8.902 at 25℃; valence 0, +1, +2, +3, or +4.
Nickel is a hard, malleable, ductile, lustrous, silver-white metal with a face-centered cubic crystalline structure. It takes a high polish. In its magnetic properties and chemical activity it resembles iron and cobalt, the elements preceding it in Group 10 of the periodic table. It is a fairly good conductor of heat and electricity. In its familiar compounds nickel is bivalent, although it assumes other valences. It also forms a number of complex compounds. Most nickel compounds are blue or green. Nickel dissolves slowly in dilute acids but, like iron, becomes passive when treated with nitric acid. Finely divided nickel adsorbs hydrogen.
Commercially, the most important compound is the sulfate, which is used in electroplating, as a mordant in dyeing, in preparation of other nickel compounds, and in paints, varnishes, and ceramics. The nickel oxides are also important; they are used in ceramic glazes, in glass manufacture, in the preparation of alloys, and in the Edison battery. Pure wrought nickel in the form of sheets and wire has many uses. Finely divided nickel is used as a catalyst, e.g., in the hydrogenation of oils. Nickel is used as a protective and ornamental coating for less corrosion resistant metals, especially iron and steel; it is applied by electroplating and by other methods (see plating). It is used in the nickel-cadmium (NiCad) storage battery.
The major use of nickel is in the preparation of alloys. The chief attributes of nickel alloys are strength, ductility, and resistance to corrosion and heat. Many stainless steels contain nickel. Nickel steels are used in safes and armor plate. Alloys of nickel and copper are widely used, e.g., Monel metal, nickel bronze, and nickel silver. The so-called German silver is a nickel-copper alloy. Nickel-copper alloys are used in coinage; the American “nickel” coin is about one-fourth nickel. Constantan is a nickel-copper alloy used in thermocouples. Other alloys of nickel include nickel-chromium alloys (such as Nichrome) used for electric heating elements; alloys of aluminum, nickel, cobalt, and iron (such as Alnico) used to make magnets; and alloys of nickel, chromium, and cobalt used structurally in jet engines. Nitinol, a nickel-titanium alloy, exhibits shape memory and is used in temperature control products, stents, and frames for eyeglasses.
Nickel occurs in a number of minerals; its chief ores are pentlandite and pyrrhotite (nickel-iron sulfides) and garnierite (nickel-magnesium silicate). Nickel is present in most meteorites. It is also found in trace amounts in plants and animals. Nickel sulfide ores are concentrated by the flotation process, then smelted or roasted to partially convert them to the oxide form, and further treated in a Bessemer converter to form a matte. The metal is separated from copper and other metals present in the Bessemer matte by electrorefining or chemical methods (see Mond process under Mond, Ludwig). The end product is in the form of nickel cathodes, pellets, or powder. Nickel was discovered in 1751 by A. F. Cronstedt in kupfernickel (niccolite), a copper-colored nickel arsenide mineral.
(Latin, niccolum), a chemical element of the first triad of Group VIII in the Mendeleev periodic system. Atomic number, 28; atomic weight, 58.70. A silver-white metal, malleable and plastic. Natural nickel consists of a mixture of five stable isotopes: 58Ni (67.76 percent), 60Ni (26.16 percent), 61Ni (1.25 percent), 63Ni (3.66 percent), and 64Ni (1.16 percent).
History. Metallic nickel was first isolated in an impure state in 1751 by the Swedish chemist A. Cronstedt, who also proposed the name of the element. The metal was isolated in a considerably purer state by the German chemist I. Richter in 1804. The name “nickel” is derived from the German Kupfernickel (niccolite, NiAs), which has been known since the 17th century and which caused confusion among the miners because of its external resemblance to copper ore (in German, Kupfer means copper and Nickel is a mine spirit that was believed to slip barren rock to the miners instead of ore). Beginning in the mid-18th century, nickel was used only as a constituent of alloys that resembled silver in appearance. Vigorous development of the nickel industry in the 19th century was connected with the discovery of large deposits of nickel ores in New Caledonia and Canada, as well as with the discovery of nickel’s “ennobling” effect on steels.
Occurrence in nature. Nickel is an element of the depths of the earth (its content in the ultrabasic rocks of the mantle is 0.2 percent by weight). There is a hypothesis that the earth’s core consists of nickel-containing iron; according to this hypothesis, the total nickel content of the earth is estimated at 3 percent. In the earth’s crust, which contains 5.8 × 10-3 percent nickel, the element also gravitates toward a deeper layer, called the basaltic layer. In the earth’s crust, nickel is an associated element of iron and magnesium; this is explained by the similarity in their valences (II) and ionic radii. Nickel is present as an isomorphic impurity in minerals of divalent iron and magnesium.
There are 53 known nickel minerals. Most of them were formed at high temperatures and pressures, either during the solidification of magma or from hot aqueous solutions. Deposits of nickel are associated with processes in the magma and the crust of weathering. Commercial nickel deposits (sulfide ores) usually contain nickel and copper minerals. Nickel is a relatively weak migrant on the earth’s surface and in the biosphere. There is relatively little nickel in surface waters and in living matter. In areas where ultrabasic formations predominate, the soil and plants are rich in nickel.
Physical and chemical properties. Under ordinary conditions nickel exists in the form of the β-modification, which has a face-centered cubic lattice (a = 3.5236 angstroms [Å]). However, nickel that undergoes cathode sputtering in an atmosphere of H2 forms the α-modification, with a hexagonal close-packed lattice (a = 2.65 Å c = 4.32 Å), which passes into the cubic modification upon heating to temperatures above 200°C. Compact cubic nickel has a density of 8.9 g/cm3 (at 20°C) and an atomic radius of 1.24 Å. The ionic radii are as follows: for Ni2+, 0.79 Å for Ni3+, 0.72 Å Melting point, 1453°C; boiling point, about 3000°C; specific heat at 20°C, 0.440 kilojoule per (kg-°K), or 0.105 cal/(g-°C); temperature coefficient of linear expansion, 13.3×10-6 (0°-100°C); thermal conductivity, 90.1 watts per (m-°K), or 0.215 cal/(cm-sec.°C), at 25°C and 60.01 W/(m.°K), or 0.148 cal/(cm•sec•°C), at 500°C; specific electric resistance, 68.4 nanohm•m, or 6.84 microhm•cm, at 20°C; temperature coefficient of electric resistance, 6.8 × 10-3(0°-100°C).
Nickel is a malleable and ductile metal, from which extremely thin sheets and tubes may be made. Tensile strength, 400–500 meganewtons per sq m (MN/m2), or 40–50 kilograms-force per sq mm (kgf/mm2); elastic limit, 80 MN/m2; yield stress, 120 MN/m2; relative elongation, 40 percent; modulus of normal elasticity, 205 GN/m2; Brinell hardness, 600–800 MN/m2. Nickel is ferromagnetic in the temperature range of 0°-631°K (the upper limit corresponds to the Curie point).
The ferromagnetism of nickel is caused by special structural features of the outer electron shells (3d84s2) of its atoms. Along with iron (3d64s2) and cobalt (3d74s2), which are also ferromag-nets, nickel belongs to the elements with an incomplete 3d electron shell (the 3d transition metals). The electrons of the incomplete shell generate an uncompensated spin magnetic moment with an effective value of 6 μB, where μB is a Bohr magneton. A positive value of the exchange interaction in crystals of nickel leads to parallel orientation of the atomic magnetic moments—that is, to ferromagnetism. For the same reason, alloys and a number of compounds of nickel (oxides, halides, and so on) are magnetically ordered (they have ferromagnetic or, less frequently, ferrimagnetic structure). Nickel is a component of the most important magnetic materials and alloys, with minimum values of the coefficient of thermal expansion (such as Permalloy, Monel metal, and Invar).
Nickel is chemically similar not only to iron and cobalt but also to copper and the noble metals. In its compounds, nickel has variable valence (it is most frequently divalent). Nickel is a moderately active metal. It absorbs large quantities of gases (H2, CO, and so on), particularly in the finely divided state; saturation with gases degrades its mechanical properties. Reaction with oxygen begins at 500°C; in the finely dispersed state nickel is pyrophoric (it ignites spontaneously in air). The most important oxide is the monoxide NiO, which consists of greenish crystals that are virtually insoluble in water (the mineral bunsenite). Upon addition of alkalies, the hydroxide precipitates from solutions of nickel salts as a voluminous apple-green precipitate. Nickel combines with halogens upon heating to give NiX2. Burning in sulfur vapor yields the sulfide, which is similar in composition to Ni3 S2. The monosulfide NiS may be prepared by heating NiO with sulfur.
Nickel does not react with nitrogen even at high temperatures (up to 1400°C). The solubility of nitrogen in solid nickel is about 0.07 percent by weight (at 445°C). The nitride Ni3N may be prepared by passing NH3 over NiF2, NiBr2 or the powdered metal at 445°C. Reaction with phosphorus vapor at high temperature yields the phosphide Ni3P2 in the form of a gray mass. The existence of three arsenides in the Ni-As system has been established: Ni5As2, Ni3As (the mineral maucherite), and NiAs. Many intermetallic compounds have the structure of the nickel arsenide type, in which the arsenic atoms form a hexagonal close-packed structure, whose octahedral voids are all occupied by nickel atoms. The unstable carbide Ni3C may be prepared by slow carburization (hundreds of hours) of nickel powder in a CO atmosphere at 300°C. In the liquid state, nickel dissolves an appreciable quantity of carbon, which precipitates as graphite upon cooling. Separation of graphite causes nickel to lose its malleability and its ability to undergo pressure working.
Nickel is located to the right of iron in the electromotive series (their normal potentials are –0.44 and –0.24 volts, respectively); therefore, it dissolves more slowly than iron in dilute acids. Nickel is stable with respect to water. Organic acids have an effect on it only upon prolonged exposure. It is dissolved slowly by hydrochloric and sulfuric acids but rapidly by dilute nitric acid. Concentrated HNO3 passivates nickel, but to a lesser degree than iron.
Reaction with acids leads to the formation of divalent nickel salts. Almost all salts of Ni (II) and strong acids are readily soluble in water, and their solutions have an acidic reaction because of hydrolysis. The salts of such relatively weak acids as carbonic and phosphoric acids are poorly soluble. Most salts decompose upon roasting (600°–800°C). One of the most useful salts is the sulfate NiSO4, which crystallizes from solution in the form of emerald-green crystals of NiSo4 . 7H2O, or nickel vitriol. Strong alkalies have no effect on nickel, but it dissolves in ammonia solutions in the presence of (NH4)2C03, with the formation of soluble ammoniates, which have an intense blue color. Most of these compounds are characterized by the complex structures [Ni (NH3)6]2+ and [Ni (OH) (NH3)4]. The selective nature of the formation of ammoniates is the basis of the hydrometallurgical methods for the extraction of nickel from ores. NaOCl and NaOBr precipitate the black hydroxide Ni (OH)3 from solutions of Ni (II) salts. In contrast to cobalt, nickel is usually divalent in its complexes. The complex of nickel with dimethylglyoxime, (C4H7O2N)2Ni, is used for analytical identification of nickel.
Nickel reacts with nitrogen oxides and with SO2 and NH3 at high temperatures. The carbonyl Ni (CO)4 is produced by heating finely divided nickel with CO. The purest grade of nickel is produced by thermal dissociation of the carbonyl.
Production. About 80 percent of the production of nickel (excluding the USSR) is derived from sulfide cupronickel ores. Selective concentration of the ore by flotation yields copper, nickel, and pyrrhotine concentrates. The nickel ore concentrate is smelted in the presence of fluxes in electric or reverberatory furnaces to isolate the barren ore and extract the nickel in the form of a sulfide melt (matte), which contains 10–15 percent Ni. Electric smelting (the main smelting method in the USSR) is usually preceded by partial oxidative roasting and breaking-up of the concentrate into pieces. In addition to nickel, part of the iron and cobalt, as well as virtually all of the copper and noble metals, pass into the matte. Separation of iron by oxidation (blowing of the liquid matte in converters) yields a melt of the sulfides of copper and nickel (nickel matte), which is cooled slowly, finely ground, and sent to flotation to separate the copper and nickel. The nickel concentrate is roasted in a fluidized bed to give NiO. The metal is produced by reduction of NiO in electric arc furnaces. Crude nickel is cast into anodes and refined electrolytically. The impurity content in electrolytic nickel (type 110) is 0.01 percent.
The separation of copper and nickel is also accomplished by the carbonyl process, based on the reversibility of the reaction Ni + 4CO ⇆2; Ni (CO)4. The preparation of nickel carbonyl is performed at 100–200 atmospheres and 200°–250°C, and its decomposition is accomplished in the absence of air at about 200°C, under atmospheric pressure. The decomposition of Ni (CO)4 is also used in the production of nickel coatings and various articles (decomposition on a hot matrix).
In modern “autogenous” processes, melting is produced by the heat evolved during the oxidation of sulfides by oxygen-enriched air. This process makes possible elimination of carbon-containing fuels and production of gases that are rich in SO2, which are suitable for the production of sulfuric acid or elemental sulfur; it also sharply reduces the cost of production. The highest efficiency and greatest promise are offered by oxidation of molten sulfides. Increasing acceptance is being gained by processes based on treatment of nickel concentrates with solutions of acids or ammonia in the presence of oxygen at high temperatures and pressures (autoclave processes). Nickel is usually dissolved and separated from the solution in the form of a rich sulfide concentrate or a metallic powder (reduction with hydrogen under pressure).
Nickel from silicate (oxidized) ores may also be concentrated in the form of a matte by introduction of fluxes (gypsum or pyrite) to the charge. Reduction sulfurizing smelting is usually performed in shaft furnaces. The resultant matte contains 16–20 percent Ni, 16–18 percent S, and the remainder Fe. The technology of extraction of nickel from the matte is analogous to that described above, except that the operation of copper separation is frequently dropped. The most expedient form of processing for oxidized ores with a low cobalt content is reductive smelting to give ferronickel, which is used in the production of steel. Hydrometallurgical methods, such as ammonia leaching of prereduced ore and sulfuric-acid autoclave leaching, are also used for the extraction of nickel from oxidized ores.
Use. Most nickel is used for the production of alloys with other metals (for example, iron, chromium, and copper), which are distinguished by outstanding mechanical, anticorrosion, magnetic, or electrical and thermoelectric properties. Heat- and oxidation-resistant nickel alloys with adequate strength at high temperatures have acquired special importance in connection with the development of reaction technology and gas-turbine engines. Nickel alloys are also used in the construction of atomic reactors.
A considerable quantity of nickel is used in the production of alkaline batteries and anticorrosion coatings. Malleable nickel in the pure state is used in the production of sheets, tubes, and other products. It is also used in the chemical industry for the fabrication of special chemical equipment and as a catalyst in many chemical reactions. Nickel is a very scarce material, which must be replaced by other less expensive and more readily available materials wherever possible.
The processing of nickel ores is accompanied by the evolution of toxic gases containing SO2 and frequently As2O3. A very toxic material is CO, which is used in the nickel refining process by the carbonyl method. Ni (CO)4 is very volatile and toxic; in a mixture with air it explodes at 60°C. Protective measures include the use of airtight equipment and strong ventilation.
A. V. VANIUKOV
Nickel in the organism. Nickel is an essential trace element in organisms. Its average content in plants is 5.0 × 10-5 percent, based on the weight of the raw material. The average nickel concentration in land animals is 1.0×10 -6 percent, and its concentration in marine animals is 1.6×10 -4 percent. In living organisms, nickel has been detected in the liver, skin, and endocrine glands. It accumulates in horny tissues, particularly feathers.
The physiological role of nickel has not been studied adequately. It was established that nickel activates the enzyme arginase and influences oxidative processes. In plants, nickel participates in a number of enzymatic reactions (carboxylation, hydrolysis of peptide linkages, and so on). Nickel-rich soils may increase the nickel content in plants by a factor of 30 or more, which leads to endemic diseases (distorted shapes of plants and eye diseases in animals, such as keratitis and keratoconjunctivitis, associated with increased concentrations of nickel in the cornea).
I. F. GRIBOVSKAIA
REFERENCESRipan, R., and I. Ceteanu. Neorganicheskaia khimiia. Vol. 2: Metally. Moscow, 1972. Pages 581–614. (Translated from Rumanian.)
Spravochnik metallurga po tsvetnym metallam. Vol. 2: Tsvetnye metally. Moscow, 1947. (Metallurgiia nikelia, pp. 269–392.)
Voinar, A. I. Biologicheskaia rol’mikroelementov v organizme zhivotnykh i cheloveka, 2nd ed. Moscow, 1960.
Biologicheskaia rol’ mikroelementov i ikh primenenie v sel’skom khoziaistve i meditsine, vols. 1–2. Leningrad, 1970.