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.

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