Rhenium
Symbol: Re
Atomic Number: 75
Atomic Mass: 186.207 amu (atomic mass units)
Melting Point: 3180.0°C (3453.15 K, 5756.0°F)
Boiling Point: 5627.0°C (5900.15 K, 10160.6°F)
Number of Protons: 75
Number of Electrons: 75
Number of Neutrons: 111
Classification: Transition Metal
Crystal Structure: Hexagonal
Density @ 293 K: 21.02 grams per cubic centimeter
Color: Silver with a metallic luster.
Rhenium’s name comes from the Latin name for the River Rhine “Rhenus”. Its name relates to the country in which it was first discovered by the German chemists Ida Tacke-Noddack, Walter Noddack and Otto Carl Berg in the year 1925. They used spectroscopic methods to find the mineral in the minerals columbite, gadolinite and molybdenite as well as in some platinum ores. Only trace amounts of rhenium can be found in these minerals and, in 1928, the same scientists were able to extract only 1 gram of pure rhenium metal from 660 kilograms of the mineral ore molybdenite.
The element has never been found in a pure state in nature. Today it is produced as a valuable byproduct by industries involved in the refining of the minerals copper and molybdenum. Pure rhenium metal is produced by reducing ammonium perrhentate with hydrogen at high temperatures.
Rhenium has two naturally occurring isotopes rhenium-185 and rhenium-187. There are also 26 unstable isotopes recognized. Rhenium-185 and rhenium-187 can be used to produce two unstable rhenium isotopes which are of use in medicine. Rhenium-186 is produced from rhenium-185 and has been found useful in the palliative care of bone pain. Rhenium-188, which is used in cancer therapy, can be produced from rhenium-187 although it is more commonly made from the tungsten isotope tungsten-186.
Its high melting point has made rhenium a valuable mineral in the production of thermocouples in conjunction with tungsten. These thermocouples are used for measuring temperatures up to 2000°C (2273 K, 3632°F). At the other end of the temperature spectrum alloys of rhenium and molybdenum have been found to be superconductors at minus 263°C (10 K, minus 441°F).
Rhenium wire is used to produce the filaments used in flash photography. Rhenium filaments are also used in mass spectrographs and ion gauges. It has also found a use as an electrical contact material as it resists arc corrosion and has good wear resistance.
Catalysts made from rhenium are used in the chemical industry for the hydrogenation of fine chemicals. These catalysts have been found to resist poisoning by nitrogen, sulphur and phosphorous which has impaired the use of other catalysts.
