Rh - Rhodium
|Chemical Element||Rhodium||Melting Point °C||1966|
|Chemical Symbol||Rh||Boiling Point °C||3725|
|Atomic Number||45||Density g/cm3||12.4|
|Atomic Weight||102.9055||Oxide||Rh2O3, RhO, RhO2|
Rhodium is a rare, lustrous, silvery, extremely hard metal, which is a member of Group 9 of the Periodic Table. It is the 79th most abundant element within the Earth’s crust. Rhodium is one of the platinum group elements (ruthenium, rhodium, palladium, osmium, iridium and platinum) and therefore is usually found within platinum ores. Rhodium is corrosion resistant, as it is unaffected by air and water up to 600°C, and unaffected by acids including aqua regia below 100°C. Despite this, rhodium is attacked by molten alkalis. It is a durable metal that has a high reflectance. Rhodium metal does not normally form an oxide, even when heated.
Rhodium was discovered in 1803 by William Hyde Wollaston. Wollaston dissolved in acid a sample of platinum emanating from South America. From the solution he recovered platinum and palladium. He was then left with a beautiful, red solution from which he obtained rose red crystals (he named the new element ‘rhodium’ after the Greek word “Rhodon” which means rose). These crystals were sodium rhodium chloride, Na3RhCl6, which he was able to reduce to the metal itself by heating with hydrogen gas, and eventually reported rhodium as a new element.
The industrial extraction of rhodium is complex, as the metal occurs in ores mixed with other metals such as palladium, silver, platinum, and gold. It is found in platinum ores and obtained free as a white inert metal which is very difficult to fuse. Principal sources of this element are located in South Africa, in river sands of the Ural Mountains, and in North America, including the copper-nickel sulfide mining area of the Sudbury, Ontario, region.The main exporter of rhodium is South Africa (>80%) followed by Russia. The annual world production of this element is only about 25 tons, and there are very few rhodium minerals.
The primary use of this element is as an alloying agent for hardening and improving the corrosion resistance of platinum and palladium. These alloys are used in furnace windings, bushings for glass fiber production, thermocouple elements, electrodes for aircraft spark plugs, and laboratory crucibles.
- Emsley, John. Nature’s Building Blocks, An A-Z Guide to the Elements, New Edition, Oxford University Press, 2011
- Gray, Theodore. The Elements, A Visual Exploration of Every Known Atom in the Universe, Black Dog & Leventhal Publishers, Inc, NY, 2009
- Stwertka, Albert. A Guide to the Elements, 3rd Edition, Oxford University Press, 2012