Rhodium is a lustrous, silver-white, chemically resistant metal in the so-called platinum group of metals. It has a face-centered cubic crystalline structure.Rhodium does not normally form an oxide,even when heated.Oxygen is absorbed from the atmosphere at the melting point of rhodium, but on solidification the oxygen is realeased.Rhodium has a higher melting point and lower density than Platinum.It is insoluble in most acids, including aqua regia, but is dissolved in hot concentrated sulfuric acid. Rhodium compounds include halides, oxides, sulfates, sulfites, a nitrate, and a sulfide. The salts form rose-colored aqueous solutions.The major use of the metal is in alloys with platinum and iridium; it gives improved high-temperature strength and oxidation resistance. These alloys are used for laboratory equipment,high-temperature thermocouple and resistance wires,bushings for glass fiber production,bearings, and electrical contacts and as a catalyst. Rhodium is also used as an alloying agent for hardening and improving the corrosion resistance of platinum and palladium.
