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Chemical Elements

Cobalt

AsO4, erythrite, transition elements, cobalt steel, machining steel

Cobalt, symbol Co, silvery-white, magnetic, metallic element used chiefly for making alloys. The atomic number of cobalt is 27; it is one of the transition elements of the periodic table.

Cobalt was discovered in about 1735 by Swedish chemist George Brandt. It has a relatively low strength and little ductility at normal temperatures, but is ductile at high temperatures. Cobalt melts at about 1495C (about 2723F), boils at about 2927C (about 5301F), and has a specific gravity of 8.9; the atomic weight of cobalt is 58.933.

Of several known cobalt isotopes, the radioactive cobalt-60 is the most important. It has a half-life of 5.7 years and produces intense gamma radiation. Cobalt-60 is used extensively in industry and in radioisotope therapy.

Cobalt is about the 30th most abundant element in crustal rocks. Cobalt occurs as the arsenide CoAs2, known as smaltite or speiss cobalt; as cobalt sulfarsenide (CoAsS), known as cobalt glance or cobaltite; and as a hydrated arsenate of cobalt (Co(AsO4)2 8H 2O), known as cobalt bloom or erythrite. The chief commercial sources of cobalt are the cobaltite ores of Ontario in Canada, and the central African nations of the Democratic Republic of the Congo (DRC, formerly Zaire) and Zambia, which, along with Canada, are the world's leading producers of the metal.

Thermally resistant alloys, called superalloys, containing cobalt are used in industry and aircraft gas turbine engines. An alloy with steel known as cobalt steel is used for making permanent magnets. With tungsten carbide, cobalt forms Carboloy, a hard material used for cutting and machining steel; alloyed with chromium, cobalt produces Stellite, used for the same purpose. Cobalt is also used in ceramics and paint driers, and as a catalyst.



Article key phrases:

AsO4, erythrite, transition elements, cobalt steel, machining steel, metallic element, Stellite, superalloys, periodic table, tungsten carbide, normal temperatures, chromium, specific gravity, DRC, permanent magnets, half-life, Zaire, catalyst, ceramics, Congo, Zambia, symbol, high temperatures, Democratic Republic, metal, Canada, industry, years

 
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