Cobalt
Cobalt is a transition metal, one of the elements that occurs in the middle of the periodic table, between Groups 2 and 13. It is located between iron and nickel, with whom it shares many common properties. Cobalt's atomic number is 27, its atomic mass is 58.9332, and its chemical symbol is Co.
Properties
Cobalt is a hard, gray metal that looks much like iron and nickel. It is ductile, but only moderately malleable. Cobalt is one of three naturally occurring magnetic elements, the other two being iron and nickel. The melting point of cobalt is 2,719°F (1,493°C), its boiling point is about 5,250°F (2,900°C), and its density is 8.9 grams per cubic centimeter. Cobalt is a moderately reactive element that combines slowly with oxygen in the air. It does not react with water at room temperature, but it does react with most acids to produce hydrogen.
Occurrence and Extraction
Cobalt is a relatively abundant element with an abundance of about 10-30 parts per million in the Earth's crust. It usually occurs in the form of a compound with its most common minerals being cobaltite, smaltite, chloranthite, and linnaeite. The major supplies of cobalt in the world are in Zambia, Canada, Russia, Australia, Zaire, and Cuba. No cobalt is mined in the United States. Cobalt is obtained from its ores by converting the naturally-occurring minerals to cobalt oxide (Co2O3) and then reducing the oxide with aluminum: 2Al + Co2O3 Al2O3 + 2Co.
Discovery and Naming
Cobalt was discovered in 1735 by the Swedish chemist Georg Brandt (1694-1768) who was analyzing a dark blue pigment found in copper ore. Chemists later found that cobalt often appears in conjunction with copper ores.
The element was given a name that had been associated with cobalt minerals for many years, Kobold. That word is German for "goblin" or "evil spirit." The name arose because certain cobalt minerals are very difficult to mine and, when refined, give off an offensive gas that can cause illness. The gas was later identified as arsenic trioxide (As4O6), which often occurs with cobalt minerals in the earth.
Uses
About 65% of the cobalt used in the United States is used to make alloys, primarily superalloys. Superalloys consist primarily of iron, cobalt, or nickel with smaller amounts of other metals, such as chromium, tungsten, aluminum, and titanium. Superalloys are so-called because they are very resistant to corrosion and retain their properties at high temperatures. Superalloys are used in the manufacture of jet engines and gas turbines, where temperatures in the thousands of degrees are produced routinely. Cobalt alloys are also widely used in the manufacture of strong electromagnets.
The most important use of cobalt compounds is as coloring agents in glass, glazes, cosmetics, paints, rubber, inks, and pottery. Some of the compounds frequently used are cobalt oxide, or cobalt black (Co2O3); cobalt potassium nitrite, or cobalt yellow [CoK3(NO2)6]; cobalt aluminate, or cobalt blue (Co(AlO2)2); and cobalt ammonium phosphate, or cobalt violet (CoNH4PO4).
Health Issues
Cobalt is needed in very small amounts to maintain good health in animals. It is used in the synthesis of certain enzymes in the body. Rare examples have been observed of cobalt deficiency disorders, such as a condition known as Coast disease, which appears among sheep in Australia in areas where the soil is deficient in cobalt. An excess of cobalt may cause health problems. For example, people who work with the metal may inhale its dust or get dust on their skin, producing vomiting, diarrhea, or skin rashes.
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