Rhenium

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Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in the periodic table. With an estimated average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust. Rhenium has the third-highest melting point and second-highest boiling point of any element at 5869 K. Rhenium resembles manganese chemically and is mainly obtained as a by-product of the extraction and refinement of molybdenum and copper ores.

Properties

Rhenium has many unique properties that make it valuable in a variety of applications. It has an unusually high melting point, making it ideal for use in high-temperature superalloy engines for jet aircraft and industrial gas turbines. It is also used in filaments for mass spectrometers and in electrical contacts. Its density is one of the highest among all elements, surpassed only by platinum, iridium, and osmium.

History

Rhenium was the last naturally occurring element to be discovered. It was identified by Masataka Ogawa in 1908 in Japan in a mineral that also contained niobium and tantalum. However, he mistakenly identified it as element 43 (later named technetium), and the discovery was corrected to rhenium in 1925 by Walter Noddack, Ida Tacke, and Otto Berg in Germany. They named it after the Rhine River.

Occurrence

Rhenium is not found free in nature or as a compound in a distinct mineral, but is widely dispersed in small amounts in the Earth's crust. It is mostly obtained as a by-product of the extraction of molybdenum from porphyry copper mines. Chile and the United States are significant producers of rhenium.

Applications

Rhenium's high melting point and resistance to corrosion make it an important alloying element in superalloys that are used in high-temperature turbine engines. Alloys of rhenium with nickel and cobalt are used in jet engine parts and in gas turbines for power generation. Rhenium is also used in the production of lead-free, high-octane gasoline and in platinum-rhenium catalysts for the production of ethylene in the petrochemical industry. Additionally, rhenium is used in the medical field for the treatment of liver cancer through the use of rhenium-188 radiopharmaceuticals.

Isotopes

Rhenium has one stable isotope, rhenium-185, and one radioactive isotope, rhenium-187, with a very long half-life. This makes rhenium unique among the elements, as it has one of the longest detectable half-lives for its radioactive isotope.

See Also

• Transition metal
• Periodic table
• Molybdenum
• Copper

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