|Boiling Point: 5900°K, 5627°C, 10161°F
Melting Point: 3453°K, 3180°C, 5756°F
Electrons Energy Level: 2, 8, 18, 32, 13, 2
Isotopes: 34 + 1 Stable
Heat of Vaporization: 715 kJ/mol
Heat of Fusion: 33.2 kJ/mol
Density: 21.04 g/cm3 @ 300°K
Specific Heat: 0.13 J/g°K
Atomic Radius: 1.97Å
Ionic Radius: 0.56Å
Electronegativity: 1.9 (Pauling); 1.46 (Allrod Rochow)
Vapor Pressure: 3.24 Pa @ 3180°C
1s2 2s2p6 3s2p6d10 4s2p6d10f14 5s2p6d5 6s2
Rhenium (Latin Rhenus meaning "Rhine") was the last naturally-occurring element to be discovered. The existence of an as-yet undiscovered element at this position in the periodic table had been predicted by Henry Moseley in 1914. It is generally considered to have been discovered by Walter Noddack, Ida Tacke, and Otto Berg in Germany. In 1925 they reported that they detected the element in platinum ore and in the mineral columbite. They also found rhenium in gadolinite and molybdenite. In 1928 they were able to extract 1 g of element by processing 660 kg of molybdenite.
The process was so complicated and the cost so high that production was discontinued until early 1950 when tungsten-rhenium and molybdenum-rhenium alloys were prepared. These alloys found important applications in industry that resulted in a great demand for the rhenium produced from the molybdenite fraction of porphyry copper ores.
In 1908, Japanese chemist Masataka Ogawa announced that he discovered the 43rd element, and named it nipponium (Np) after Japan (which is Nippon in Japanese). However, later analysis indicated the presence of rhenium (element 75), not element 43. The symbol Np was later used for the element neptunium.
Rhenium is a silvery white metal, lustrous, and has one of the highest melting points of all elements, exceeded by only tungsten and carbon. It is also one of the most dense, exceeded only by platinum, iridium, and osmium. Rhenium has the widest range of oxidation states of any known element: -3,-1,+1,+2,+3,+4,+5,+6 and +7. The oxidation states +7,+6,+4,+2 and -1 are the most common.
Its usual commercial form is a powder, but this element can be consolidated by pressing and resistance-sintering in a vacuum or hydrogen atmosphere. This procedure yields a compact shape that is in excess of 90 percent of the density of the metal. When annealed this metal is very ductile and can be bent, coiled, or rolled. Rhenium-molybdenum alloys are superconductive at 10oK; tungsten-rhenium alloys are also superconductive, around 4-8oK depending on the alloy.
Rhenium is not found free in nature, and it was only recently that the first rhenium mineral was found. In 1994, Nature published a letter describing a rhenium sulfide mineral found condensing from a fumarole on Russia's Kudriavy volcano. This is not an economically viable source of the element. Rhenium is widely spread through the Earth's crust at approximately 1 ppb.
Commercial rhenium is extracted from molybdenum roaster-flue gas obtained from copper-sulfide ores. Some molybdenum ores contain 0.002% to 0.2% rhenium. Total world production is between 40 and 50 tons/year; the main producers are in Chile, USA and Kazakhstan. Recycling of used Pt-Re catalyst and special alloys allow the recovery of another 10 tons/year.
This was the last naturally-occurring element to be discovered and belongs to the ten most expensive metals on Earth (over $4000/kg).
The metal form is prepared by reducing ammonium perrhenate with hydrogen at high temperatures.
This element is used in platinum-rhenium catalysts which in turn are primarily used in making lead-free, high-octane gasoline and in high-temperature superalloys that are used to make jet engine parts. Other uses:
Naturally occurring rhenium is a mix of 185Re, which is stable, 187Re, which is unstable but has a very long half-life. There are thirty-four unstable isotopes recognized.
|187Re||186.9557531||41.2 x 109 years|
|Little is known about rhenium toxicity so it should be handled with care.|
|Ionization Energy: 7.88 eV
Estimated Crustal Abundance: 7×10-4 milligrams per kilogram
Estimated Oceanic Abundance: 4×10-6 milligrams per liter