Rhodium



Rhodium is a chemical element with symbol Rh and atomic number 45.

Appearance
It is a rare, silvery-white, hard, and chemically inert transition metal. It is a member of the platinum group. It is composed of only one naturally-occurring isotope, Rh103. Naturally occurring rhodium is usually found as the free metal, alloyed with similar metals, and rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It is one of the rarest and most valuable precious metals.

Rhodium is a so-called noble metal, resistant to corrosion, found in platinum- or nickel ores together with the other members of the platinum group metals. It was discovered on Earth in 1803 by William Hyde Wollaston in one such ore, and named for the rose color of one of its chlorine compounds, produced after it reacted with the powerful acid mixture aqua regia.

Rhodium is a fission product of uranium 235; therefore, each kilogram of fission products contains significant amounts of the lighter platinum group metals including rhodium. Used nuclear fuel might be a possible source for rhodium. However, the extraction is complex,expensive, and the radioactive isotopes of rhodium would require a storage for several half-lives of the longest-lived decaying isotope (i.e. about 10 years).

Uses of Rhodium
The element's major Pre Astro use (approximately 80% of Earth rhodium production) was as one of the catalysts in the three-way catalytic converters in automobiles. Because rhodium metal is inert against corrosion and most aggressive chemicals, and because of its rarity, rhodium is usually alloyed with platinum or palladium and applied in high-temperature and corrosion-resistive coatings. White gold is often plated with a thin rhodium layer to improve its appearance while sterling silver is often rhodium plated for tarnish resistance.

Rhodium detectors are used in nuclear reactors to measure the neutron flux level.