Cobalt
Cobalt is a grayish, hard, brittle metal closely resembling iron and nickel. These three metals are the only naturally magnetic elements on Earth. Cobalt exists in two allotropic forms that interconvert slowly. This property accounts for the fact that different physical properties may be reported for the element. Its atomic number is 27, its atomic weight 58.9332, and its chemical symbol, Co. It has a melting point of 2723 °F (1495 °C) and a boiling point of 5301 °F (2927 °C).
Cobalt was the first isolated in about 1735 by the Swedish chemist Georg Brandt (1694-1768). Brandt had studied medicine and chemistry at the University of Leyden and mining and metallurgy at Harz. He spent most of his life working for the Swedish government, first at the Bureau of Mines and later at the Royal Mint.
Brandt discovered cobalt while investigating a group of substances known as the "half-metals." By half-metal, Brandt meant a substance that had most of the physical properties of a metal but was not malleable. He included mercury, bismuth, zinc, and the sulfides of antimony, arsenic, and cobalt in this group.
Cobalt got its name from the German term Kobald, for " underground gnome." The Kobalden were annoying little spirits that took delight in causing problems for miners. The connection of cobalt metal with the Kobalden is easy to understand. For centuries, miners disliked having to deal with ores that contained cobalt. The ores seemed to have no practical value and just interfered with the miners' productive work. In addition, since these ores usually contained arsenic, they often made miners ill.
Without realizing it, artisans had long been using cobalt compounds in the coloring of glass, pottery, porcelain, tile, and enamel. The element imparts a blue color that is more intense than that of the much more commonly used copper. Cobalt compounds were also used as bluing in laundries.
Ores of cobalt exist in commercial amounts in Canada, Zaire, and Morocco. The sulfide, arsenide, and mixed sulfide-arsenide ores are the most common. Cobalt makes up about 0.001 to 0.002 percent of the Earth 's crust. It also occurs in significant amounts in meteorites.
Metallic cobalt is used in alloys and electroplating. Perhaps the most important cobalt-containing alloy is alnico, a mixture of iron, aluminum, nickel, and cobalt. Alnico is strongly magnetic. Another alloy, stellite, consists of chromium, tungsten, and cobalt. Stellite has the property of remaining hard even when it gets very hot. This property makes it useful for drill bits and other high-speed cutting tools. Other cobalt alloys are used in jet engines and turbines. Cobalt is desirable for electroplating because it provides a hard, resistant, attractive covering for other metals.
Cobalt occurs in animals in the form of cobalamin, or vitamin B 12. The vitamin is necessary to prevent the condition known as pernicious anemia. Humans take in sufficient quantities of vitamin B 12 from a normal diet. When absorption does not occur normally, or under other circumstances, an individual may have to take a vitamin B 12 supplement. Cobalamin is apparently the only compound in which cobalt occurs normally in living organisms.
Elemental cobalt and its compounds can also be a health hazard. Ingestion of cobalt compounds may produce indigestion, nausea, and vomiting. Contact of cobalt powder with the skin may cause rash and dermatitis. Inhalation of cobalt dust may cause respiratory problems.
The radioactive isotope, cobalt-60, has two important applications. It is often used as a source of gamma radiation in the treatment of tumors. It is also a potentially powerful factor in the construction of nuclear weapons. When stable cobalt-59 is used in the casing of such weapons, it is converted to the radioactive form, cobalt-60, when the weapon detonates. Pulverized to a fine powder by the blast, the cobalt-60 settles out on land and produces a dangerously high level of radiation for many years. Bombs of this type are known as "dirty" nuclear weapons.
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