(From the
Latin Rhenus, the river
Rhine) A very rare,
metallic
chemical element that is a silver-white
solid or a gray-to-black
powder. Its
density is exceeded only by that of
platinum,
iridium, and
osmium; and its
melting point is exceeded only by that of
tungsten and
carbon. Rhenium does not occur freely in nature, but is found in small amounts in
gadolinite and
molybdenite. Commercial production of rhenium is by extraction from the
flue dusts of
molybdenum smelters. Rhenium is used as a trace alloying agent for hardening metal compounds that are subjected to continuous frictional forces. It is mixed with
tungsten or
platinum to make
filaments for
mass spectrographs. It is also used as an electrical contact material as it has good resistance to wear and withstands
arc corrosion. Rhenium
catalysts are exceptionally resistant to
poisoning and are used for the
hydrogenation of fine chemicals. The metal and its
alloys are also used in
thermocouples and in electrical components. Rhenium resists
corrosion and
oxidation but slowly
tarnishes in moist
air. It is not soluble in
hydrochloric acid and dissolves only slowly in other
acids.
Rhenium was discovered in 1925 by Ida and Walter Noddack and Otto Carl Berg in Berlin, Germany but was predicted in 1869 by Dmitri Mendeleev as chemically related to manganese.
Symbol: Re
Atomic number: 75
Atomic weight: 186.207
Density (at room temperature and pressure): 21.02 g/cc
Melting point: 3,180°C
Boiling point: 5,627°C
Main valences: +3, +4, +5, +7
Ground state electron configuration: [Xe]4f145d56s2