Rhodium

Rhodium

Rhodium is a chemical element that is a rare, silvery-white, hard, and chemically inert transition metal and a member of the platinum group. It has the chemical symbol Rh and atomic number 45. It is composed of only one naturally-occurring isotope, 103Rh. 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 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 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.

The element's major use (more than 80% of world rhodium production) is 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 optical impression while sterling silver is often rhodium plated for tarnish resistance.
Rhodium detectors are used in nuclear reactors to measure the neutron flux level.

Occurrence

Rhodium is one of the rarest elements in the Earth's crust, of which it comprises an estimated 0.0002 parts per million (2 × 10−10). Its rarity affects its price, and thus its usage in commercial applications.

Symbol		Rh
Atomic Number		45
Atomic Weight		102.9055
Oxidation States		+3
Electronegativity, Pauling		2.28
State at RT		Solid, Metal
Melting Point, K		2239
Boiling Point, K		4000

Appearance and Characteristics

Harmful effects:

Rhodium is considered to be non-toxic. Some of its compounds are highly toxic and carcinogenic.

Characteristics:

• Rhodium is a rare, hard, silvery-white, lustrous metal.
• It is one of the of the six platinum group metals consisting of platinum, palladium, rhodium, osmium, iridium and ruthenium.
• It is highly reflective and extremely resistant to corrosion.
• It is not attacked by most acids.
• When present in compounds, rhodium exists mostly in the trivalent state, Rh3+.
• Rhodium’s salts form rose-colored aqueous solutions.

Uses of Rhodium

• The majority of rhodium is used as a catalyst in catalytic converters. It is also used to catalyze industrial processes.
• Rhodium is used as an alloying agent for hardening and improving the corrosion resistance of platinum and palladium.
• As a result of its low electrical resistance, low and stable contact resistance, and its stability against corrosion rhodium is used as an electrical contact material.
• The metal is used in jewelry and for decorations.