I.

Introduction

Nickel, symbol Ni, silvery white, magnetic metallic element used chiefly in making alloys. Nickel is one of the transition elements of the periodic table (see Periodic Law). The atomic number of nickel is 28.

Nickel was used as coinage in nickel-copper alloys for several thousand years, but was not recognized as an elemental substance until 1751 when the Swedish chemist Baron Axel Frederic Cronstedt isolated the metal from niccolite ore. The element’s name comes from the German Kupfernickel, “demon copper,” so-called because it was often found mixed with valuable copper ore as if done through mischief by a goblin (“Old Nick”).

II.

Properties of Nickel

Nickel is a hard, malleable, ductile metal, capable of taking a high polish. It is magnetic below 345°C (653°F). It exists in five stable isotopic forms. Metallic nickel is not very active chemically. It is soluble in dilute nitric acid and becomes passive (nonreactive) in concentrated nitric acid; it does not react with alkalis. Nickel melts at about 1455°C (about 2651°F), boils at about 2913°C (about 5275°F), and has a specific gravity of 8.9. The atomic weight of nickel is 58.69.

III.

Occurrence of Nickel

Nickel occurs as a metal in meteorites. Combined with other elements, it occurs in minerals such as garnierite, millerite, niccolite, pentlandite, and pyrrhotite; the latter two minerals are the principal ores of nickel. Nickel ranks about 22nd in natural abundance among elements in crustal rock.

Nickel ores usually contain impurities, chief among which is copper. Sulfide ores, such as pentlandite and nickeliferous pyrrhotite, are usually smelted in a blast furnace and shipped in the form of a matte of copper and nickel sulfide to refineries, where the nickel is removed by various processes. In the electrolytic process, the nickel is deposited in pure metallic form after the copper has been preferentially removed by deposition at a different voltage and in a different electrolyte. In the Mond process, copper is removed by dissolution in dilute sulfuric acid, and the nickel residue is reduced to impure metallic nickel. Carbon monoxide is passed over the impure nickel, forming nickel carbonyl (Ni(CO)₄), a volatile gas. The nickel carbonyl is heated to 200°C (392°F) and decomposes, depositing pure metallic nickel.

IV.

Uses and Production

Nickel is used as a protective and ornamental coating for metals, particularly iron and steel, that are susceptible to corrosion. The nickel plate is deposited by electrolysis in a nickel solution. Finely divided nickel absorbs 17 times its own volume of hydrogen and is used as a catalyst in many processes, including the hydrogenation of oils.

Nickel is used chiefly in the form of alloys. It imparts great strength and corrosion resistance to steel. Nickel steel, containing about 2 to 4 percent nickel, is used in automobile parts such as axles, crankshafts, gears, valves, and rods; in machine parts; and in armor plate. Some of the most important nickel-containing alloys are German silver, Invar, Monel metal, Nichrome, and Permalloy. The nickel coins used for currency in the United States are an alloy of 25 percent nickel and 75 percent copper. Nickel is also a key component of nickel-cadmium batteries.

V.

Compounds of Nickel

Nickel forms primarily divalent (nickelous) compounds, although examples of compounds with formal oxidation states ranging from -1 to +4 are known. Most of the salts of nickel, such as nickel chloride (NiCl ₂), nickel sulfate (NiSO₄), and nickel nitrate (Ni(NO₃)₂), are green or blue in color, and they are most commonly hydrated. Nickel ammonium sulfate (NiSO₄·(NH₄)₂SO₄·6H₂O) is used in nickel-electroplating solutions. Nickel compounds are often identified by adding an organic reagent, dimethylgloxime, which reacts with nickel to form a red, flocculent precipitate.