Math Is Fun Forum

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 51,669

Rhenium

Rhenium

Gist

Rhenium (Re) is a rare, dense, silvery-white transition metal with atomic number 75, known for its extreme high-temperature stability and ductility. It is a critical component in high-temperature superalloys for jet engine parts, and also functions as a catalyst in petrochemical processes. Rhenium is primarily found in low concentrations in copper and molybdenum ores and is the last stable element to be discovered. 

Rhenium is primarily used in high-temperature superalloys for aircraft engine and gas turbine components, as well as a component in platinum-rhenium catalysts for petroleum reforming. Other applications include tungsten-rhenium alloys for high-temperature thermocouples and filaments, radioactive isotopes in cancer treatment, and as an additive to enhance the properties of other metals in alloys for electronics and welding.

Summary

Rhenium is a chemical element; it has symbol Re and atomic number 75. It is a silvery-gray, heavy, third-row transition metal in group 7 of 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. It has one of the highest melting and boiling points of any element. It resembles manganese and technetium chemically and is mainly obtained as a by-product of the extraction and refinement of molybdenum and copper ores. It shows in its compounds a wide variety of oxidation states ranging from −1 to +7.

Rhenium was originally discovered in 1908 by Masataka Ogawa, but he mistakenly assigned it as element 43 (now known as technetium) rather than element 75 and named it nipponium. It was rediscovered in 1925 by Walter Noddack, Ida Tacke and Otto Berg, who gave it its present name. It was named after the river Rhine in Europe, from which the earliest samples had been obtained and worked commercially.

Nickel-based superalloys of rhenium are used in combustion chambers, turbine blades, and exhaust nozzles of jet engines. These alloys contain up to 6% rhenium, making jet engine construction the largest single use for the element. The second-most important use is as a catalyst: it is an excellent catalyst for hydrogenation and isomerization, and is used for example in catalytic reforming of naphtha for use in gasoline (rheniforming process). Because of the low availability relative to demand, rhenium is expensive, with price reaching an all-time high in 2008–09 of US$10,600 per kilogram (US$4,800 per pound). As of 2018, its price had dropped to US$2,844 per kilogram (US$1,290 per pound) due to increased recycling and a drop in demand for rhenium catalysts.

Details

Rhenium (Re) is a chemical element, a very rare metal of Group 7 (VIIb) of the periodic table and one of the densest elements. Predicted by the Russian chemist Dmitry Ivanovich Mendeleyev (1869) as chemically related to manganese, rhenium was discovered (1925) by the German chemists Ida and Walter Noddack and Otto Carl Berg. The metal and its alloys have found limited application as turbine blades in fighter-jet engines, fountain pen points, high-temperature thermocouples (with platinum), catalysts, electrical contact points, and instrument-bearing points and in electrical components, such as in flashbulb filaments as an alloy with tungsten.

Rhenium does not occur free in nature or as a compound in any distinct mineral; instead it is widely distributed in small amounts in other minerals, usually in concentrations averaging about 0.001 parts per million. Chile is the world leader in rhenium recovery, followed by the United States, Poland, Uzbekistan, and Kazakhstan.

Rhenium occurs up to about 20 parts per million in molybdenite and to a lesser extent in sulfidic copper ores. The recovery of rhenium is aided by the concentration of its volatile heptoxide (Re2O7) in the flue dust and gases given off during the smelting of molybdenite ore or from its concentration with the platinum metals in the anode sludge during electrolytic copper refining. The black metal powder is extracted from the gases and dust by leaching or scrubbing them with water to dissolve the oxide, Re2O7, which in turn can be converted to ammonium perrhenate, NH4ReO4, and then reduced to the metal with hydrogen. The powder may be compressed and sintered into bars in hydrogen at elevated temperatures. Cold-working and annealing permit the fabrication of wire or foil.

Rhenium metal is silvery white and extremely hard; it resists wear and corrosion very well and has one of the highest melting points of the elements. (The melting point of rhenium, 3,180 °C [5,756 °F], is exceeded only by those of tungsten and carbon.) The metal powder slowly oxidizes in air above 150 °C (300 °F) and rapidly at higher temperatures to form the yellow heptoxide, Re2O7. The metal is not soluble in hydrochloric acid and dissolves only slowly in other acids. There is evidence for the existence of rhenium in each of the oxidation states from −1 to +7; the most common states are +3, +4, +5, and especially +7. Rhenium’s most characteristic and important compounds are formed in the oxidation states +4 and +7, although compounds are known in all formal oxidation states from −1 to +7. Perrhenic acid (HReO4) and its anhydride, the heptoxide, and the perrhenates are common stable compounds in which rhenium is in the +7 state. Natural rhenium is a mixture of the stable isotope rhenium-185 (37.4 percent) and the radioactive rhenium-187 (62.6 percent, 4.1 × {10}^{10}-year half-life).

Element Properties:

atomic number  :  75
atomic weight  :  186.2
melting point  :  3,180 °C (5,756 °F)
boiling point  :  5,627 °C (10,161 °F)
specific gravity  :  20.5 at 20 °C (68 °F)
oxidation states  :  +1, +2, +3, +4, +5, +6, +7.

Additional Information:

Appearance

A metal with a very high melting point.  Tungsten is the only metallic element with a higher melting point.

Uses

Rhenium is used as an additive to tungsten- and molybdenum-based alloys to give useful properties. These alloys are used for oven filaments and x-ray machines. It is also used as an electrical contact material as it resists wear and withstands arc corrosion.

Rhenium catalysts are extremely resistant to poisoning (deactivation) and are used for the hydrogenation of fine chemicals. Some rhenium is used in nickel alloys to make single-crystal turbine blades.

Biological role

Rhenium has no known biological role.

Natural abundance

Rhenium is among the rarest metals on Earth. It does not occur uncombined in nature or as a compound in a mineable mineral species. It is, however, widely spread throughout the Earth’s crust to the extent of about 0.001 parts per million. Commercial production of rhenium is by extraction from the flue dusts of molybdenum smelters.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.