Rhenium

Rhenium was discovered in 1925 by the German chemists Walter Noddack, Ida Tacke and Otto Berg, who detected it in platinum ore and columbite. They named it after the river Rhine, from the Latin Rhenus. It was the last element with a stable isotope to be discovered in nature. Rhenium is a dense, silvery-white metal with one of the highest melting points of all, used in high-temperature superalloys for jet-engine turbine blades and in catalysts. One of the rarest and most costly of metals, rhenium is prized for the nickel-based superalloys of jet-engine and rocket parts, where its very high melting point resists extreme heat, and it serves as a catalyst in producing high-octane petrol.

Rhenium is never mined in its own right, recovered only as a trace byproduct of processing molybdenum and copper ores, and it ranks among the very scarcest elements in the Earth's crust, a scarcity that keeps its price among the highest of the industrial metals. The decay of rhenium-187 into osmium-187, occurring at an extremely slow, well-characterised rate, gives geochemists the rhenium-osmium dating method, used to date molybdenite ore deposits and some of the oldest meteorites in the solar system. The fumaroles of Kudryavy, a volcano on the Kuril island of Iturup, were found in the 1990s to deposit rheniite, a rare rhenium sulfide mineral and the only place on Earth where rhenium is known to concentrate naturally into a mineral of its own rather than merely occurring as a trace in other ores.

Rhenium closes a long chapter: it was the final element possessing a stable isotope to be discovered occurring naturally on Earth, all later additions to the periodic table being either radioactive or wholly synthetic. Its name is a plain geographical tribute to the Rhine, the great river of the German lands where its discoverers worked, one of the cluster of elements named for the homelands of their finders.

Ida Tacke, later Ida Noddack, who shared in the discovery, is also remembered for being among the first to suggest, years ahead of its acceptance, the possibility of nuclear fission. Rhenium has no ancient or esoteric tradition, being a twentieth-century discovery; its distinction is to mark the end of the search for stable elements in the natural world. The same team also claimed, controversially, to have detected element 43 in their samples, proposing the name masurium, but unlike rhenium this claim was never independently confirmed and is not accepted by the scientific community; element 43, technetium, was only genuinely produced artificially in 1937, and the Noddack-Tacke-Berg masurium claim remains one of the periodic table's disputed near-misses rather than an accepted discovery.