Where Found (Encyclopedia of Global Resources)
Rhenium is widely distributed in the Earth’s crust in small amounts. In the United States, the richest concentrations of rhenium are found in molybdenum ores in Arizona, Utah, and New Mexico. The major world producer is Chile, followed by Kazakhstan, the United States, and Peru.
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Primary Uses (Encyclopedia of Global Resources)
Technical Definition (Encyclopedia of Global Resources)
Rhenium (abbreviated Re), atomic number 75, belongs to Group VIIB of the periodic table of the elements and resembles manganese in its chemical and physical properties. It has two naturally occurring isotopes and an average atomic weight of 186.2. Pure rhenium is a hard, dense, silvery-white metal. Its density is 21.04 grams per cubic centimeter; it has a melting point of 3,170° Celsius and a boiling point of 5,630° Celsius.
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Description, Distribution, and Forms (Encyclopedia of Global Resources)
Rhenium is a rare but widely distributed element resembling manganese. It usually occurs in a concentration of about 1 part per billion, but in molybdenum ores it may be found in a concentration as high as 20 parts per million. It is used with tungsten, iridium, molybdenum, or platinum to manufacture high-temperature thermocouples that can measure and control temperatures up to about 2,500° Celsius.
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History (Encyclopedia of Global Resources)
Obtaining Rhenium (Encyclopedia of Global Resources)
Rhenium is produced as a by-product of molybdenum production. When molybdenum ore is heated it releases dust and gas containing rhenium. These substances are treated with water to dissolve the rhenium oxide present. This solution is treated with potassium chloride to form potassium perrhenate or with ammonia to form ammonium perrhenate. These compounds are purified by repeated crystallization.
The perrhenate is treated with hydrogen to produce free rhenium. Ammonium perrhenate is usually used because it produces a purer rhenium. The rhenium is produced in the form of a black powder. It may then be compressed and heated with hydrogen to produce bars of metallic rhenium. This metal may be cold-worked and annealed into wire or foil.
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Uses of Rhenium (Encyclopedia of Global Resources)
About 70 percent of rhenium is used in superalloys built to withstand high temperatures, such as those for turbine engines and their components. About 20 percent is used in petroleum-reforming catalysts. Rhenium is also used as a catalyst in various other chemical reactions; in petroleum refining, to produce lead-free gasoline; in electronic components, because of its resistance to electrical erosion; in boat engines, because of its resistance to seawater; and in fountain pen points.
An important use of rhenium is in producing thermocouples that operate at high temperatures. A thermocouple is a device consisting of two wires of different metals connected at both ends. One end of the thermocouple is placed in a sample, and the other is kept at a constant, cooler temperature. An electric current produced in the thermocouple is used to measure the temperature of the sample. A thermocouple can also be used to control temperatures like a thermostat.
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Further Reading (Encyclopedia of Global Resources)
Natural Resources Canada. Canadian Minerals Yearbook, 2005: Rhenium. http://www.nrcan.gc.ca/smm-mms/busi-indu/cmy-amc/content/2005/rhenium.pdf
U.S. Geological Survey. Mineral Information: Rhenium Statistics and Information. http://minerals.usgs.gov/minerals/pubs/commodity/rhenium/
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Rhenium (Chemical Elements)
Rhenium was discovered by a German research team that included Walter Noddack (1893-1960), Ida Tacke (1896-1979) and Otto Berg. These scientists knew that there were two empty boxes in the periodic table that represented elements that had not yet been discovered. The periodic table is a chart that shows how chemical elements are related to one another. In 1925, the German team announced that they had found both elements. They were correct about one (element number 75) but wrong about the other (element number 43).
Rhenium is one of the rarest elements in the world. At one time it sold for about $10,000,000 a kilogram (about $5,000,000 a pound). It is no longer that expensive, although it is still very costly.
Rhenium has some unusual properties. For example, it is one of the most dense elements known. It also has one of the highest boiling points of all elements.
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