Rhenium (Re)
Rhenium (Re) is a rare, silvery-white metal known for its remarkable high melting point of 3,170°C and a boiling point of 5,630°C, making it valuable in high-temperature applications. With an atomic number of 75, it belongs to Group VIIB of the periodic table and resembles manganese in its properties. Rhenium is primarily sourced from molybdenum ores, particularly concentrated in regions of the United States such as Arizona, Utah, and New Mexico, with Chile being the largest global producer.
About 70% of rhenium is utilized in superalloys for turbine engines, while 20% is employed in catalysts for petroleum refining and other chemical reactions. Its unique characteristics also lend themselves to use in electronic components and high-temperature thermocouples, devices essential for measuring and controlling temperatures in various industrial settings. Discovered in 1925, rhenium was first isolated in free form in 1929. The metal is produced as a by-product during molybdenum extraction, where it is recovered through a series of chemical processes. Overall, rhenium’s versatility and high-performance capabilities make it an essential material across multiple industries.
Rhenium (Re)
Where Found
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.
Primary Uses
Rhenium is mostly used for applications in which a high melting point and strength at high temperatures are important, as in high-temperature thermocouples. It has also found use as a catalyst and in electronic components.
Technical Definition
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.
Description, Distribution, and Forms
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.
History
Rhenium was discovered in 1925 by the German chemists Ida Tacke, Walter Noddack, and Otto Berg. It was not produced in a free form until 1929, when Tacke and Noddack produced a gram of it from 600 kilograms of molybdenum ore.
Obtaining Rhenium
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.
Uses of Rhenium
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.
Bibliography
Natural Resources Canada.
U.S. Geological Survey.