O rhenium (chemical symbol Re, atomic number 75) it is a transition metal, obtained as a by-product of processing molybdenum minerals. It was discovered in Germany around 1925.
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With atomic mass of 186.2 u, the element is located in the group 7 of the periodic classification of elements. The name of rhenium comes from the Latin rhenus, in honor of the river Rhine, located in Germany.
Regarding obtaining, the element cannot be found freely in nature, nor in any mineral in particular. Rhenium can be found in small amounts all over the Earth's crust, around 0.001 ppm (part per million).
Commercial rhenium extraction comes from the by-products of molybdenum minerals present in some copper ores. Some of them contain from 0.002% to 0.2% rhenium.
The preparation of the metal is carried out at high temperatures, from the reduction of ammonium perrhenate (NH4ReO4) with hydrogen.
Rhenium was the last natural element to be discovered. Those responsible for the discovery were Walter Noddack, Ida Tacke and Otto Berg, in Germany.
In 1925, chemists and physicist Ida Tacke reported the detection of the element in a platinum ore and in the mineral columbite. They also recorded the presence of rhenium in gadolinite and molybdenite.
However, only in 1928, three years later, was it possible to extract 1 gram of the element, from the processing of 660 kilograms of molybdenite.
Since the extraction of the metal was complex and required a lot of financial resources, production was suspended until 1950, when tungsten-rhenium and molybdenum-rhenium alloys were produced.
The alloys had important industrial applications and the demand resulted in an increase in the consumption of rhenium, extracted mainly from molybdenite present in porphyry (copper) ores.
To this day, no traces of rhenium have been found in Brazilian territory.
Natural rhenium is the result of a mixture of two isotopes, Re-185 (stable) with an abundance of 37.4% and Re-187 (radio-unstable) with an abundance of 62.6%. In addition to these, there are also 26 known unstable isotopes.
Rhenium is a shiny, silvery-white metal with atomic number 75 (75 protons and 75 electrons). It has one of the highest melting points, second only to tungsten and carbon. It is also one of the densest, surpassed only by platinum, iridium, and osmium.
It is usually marketed in powder form, however, it can be obtained in compact form, with up to 90% of its theoretical density. When annealed, the element becomes very ductile, giving the possibility of bending it into a spiral or a ring.
Furthermore, rhenium-molybdenum alloys are considered to be superconducting at 10K.
Rhenium catalysts are highly used to obtain superalloys resistant to high temperatures, used for the manufacture of jet engine parts. They are also used to obtain high-octane gasoline and metallic lead.
Because they are very resistant to chemical poisoning, rhenium catalysts are still used in some types of hydrogenation reactions.
It can be added to tungsten or molybdenum-based alloys to improve their properties. Rhenium wires are often used in photo flash lamps.
Due to good resistance to wear and corrosion, another very common use is in electrical contact materials.
In medicine, Rhenium-188 can be used in bacteria to fight pancreatic cancer.
atomic mass – 186.207(1)u
electronic configuration – 4f14 5d5 6s2
electrons – 2, 8, 18, 32, 13, 2
state of matter – solid
Fusion point – 3459 K (3185.85 °C)
Boiling point – 5 869 K (5595.85 °C)
enthalpy of fusion – 33.2 kJ/mol
enthalpy of vaporization – 715 kJ/mol
