AskDefine | Define osmium

Dictionary Definition

osmium n : a hard brittle blue-gray or blue-black metallic element that is one of the platinum metals; the heaviest metal known [syn: Os, atomic number 76]

User Contributed Dictionary

see Osmium



οσμή, smell (because of the strong smell of its oxide) + -ium


  1. a heavy metallic chemical element (symbol Os) with an atomic number of 76.


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  1. osmium



  1. osmium

Extensive Definition

Osmium () is a chemical element that has the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-black transition metal in the platinum family, and is the densest natural element, beating iridium by 0.19  g·cm−3. Osmium is used in alloys with platinum, iridium and other platinum group metals. Osmium is found in nature as an alloy in platinum ore. Alloys of osmium are employed in fountain pen tips, electrical contacts and in other applications where extreme durability and hardness are needed.

Notable characteristics

Osmium in a metallic form is extremely dense, blue-white, brittle, and lustrous even at high temperatures. It is so dense in fact, that it is estimated that a football sized chunk would be too heavy for a man to lift by himself. It proves to be extremely difficult to make. Powdered osmium is easier to make, but powdered osmium exposed to air leads to the formation of osmium tetroxide (OsO4), which is very toxic. The tetroxide is a powerful oxidizing agent, very volatile, water-soluble, pale yellow, crystalline solid with a strong smell that boils at 130°C. By contrast osmium dioxide (OsO2) is black, non-volatile and much less reactive and toxic.
Due to its very high density, osmium is generally considered to be the densest known element, narrowly defeating iridium. However, calculations of density from the space lattice may produce more reliable data for these elements than actual measurements and give a density of 22650 kg/m3 for iridium versus 22610 kg/m³ for osmium. Definitive selection between the two is therefore not possible at this time. If one distinguishes different isotopes, then the highest density ordinary substance would be 192Os. The extraordinary density of osmium is a consequence of the lanthanide contraction.
Osmium has a very low compressibility. Correspondingly, its bulk modulus is extremely high—commonly quoted as 462 GPa, which is higher than that of diamond but lower than that of aggregated diamond nanorods—although there is some debate in the academic community about whether it is in fact this high. A paper by Cynn et al reported that osmium had this bulk modulus, based on an experimental result, but other authors have cast doubt upon this ( and references therein).
Osmium metal has the highest melting point and the lowest vapor pressure of the platinum family. Common oxidation states of osmium are +4 and +3, but oxidation states from +1 to +8 are observed.


Because of the volatility and extreme toxicity of its oxide, osmium is rarely used in its pure state, and is instead often alloyed with other metals that are used in high-wear applications. Osmium alloys such as osmiridium are very hard and, along with other platinum group metals, is almost entirely used in alloys employed in the tips of fountain pens, instrument pivots, and electrical contacts, as they can resist wear from frequent use. The stylus (needle) in early phonograph designs was also made of osmium, especially for 78-rpm phonograph recordings, until industrial diamond replaced the metal in later designs.
Osmium tetroxide has been used in fingerprint detection and in staining fatty tissue for microscope slides. As a strong oxidant, it cross-links lipids mainly by reacting with unsaturated carbon-carbon bonds, and thereby both fixes biological membranes in place in tissue samples and simultaneously stains them, since osmium atoms are extremely electron dense, making OsO4 an important stain for transmission electron microscopy (TEM) studies of many biological materials. An alloy of 90% platinum and 10% osmium (90/10) is used in surgical implants such as pacemakers and replacement pulmonary valves.
The tetroxide (and a related compound, potassium osmate) are important oxidants for chemical synthesis, despite being very poisonous.
In 1898 an Austrian chemist, Auer von Welsbach, developed the Oslamp with a filament made of osmium, which he introduced commercially in 1902. After only a few years, osmium was replaced by the more stable metal tungsten (originally known as wolfram). Tungsten has the highest melting point of any metal, and using it in light bulbs increases the luminous efficacy and life of incandescent lamps.
The light bulb manufacturer OSRAM (founded in 1906 when three German companies; Auer-Gesellschaft, AEG and Siemens & Halske combined their lamp production facilities), derived its name from the elements of OSmium and wolfRAM.
Like palladium, powdered osmium will densely absorb hydrogen atoms, perhaps making it a potential candidate as a metal hydride battery electrode substance, but it will react with potassium hydroxide, the most common battery electrolyte.


Osmium (Greek osme meaning "a smell") was discovered in 1803 by Smithson Tennant and William Hyde Wollaston in London, England.
Wollaston and Tennant were looking for a way to purify platinum by dissolution of native platinum ore in aqua regia. Large amounts of insoluble black powder remained as a byproduct of this operation.
Wollaston concentrated on the soluble portion and discovered palladium (in 1802) and rhodium (in 1804), while Tennant examined the insoluble residue. In the summer of 1803, Tennant identified two new elements, osmium and iridium. Discovery of the new elements was documented in a letter to the Royal Society on June 21, 1804.


Turkey, with 127,000 tons, has the world's largest known reserve of osmium. Bulgaria also has substantial reserves of about 2500 tons. This transition metal is also found in iridiosmium, a naturally occurring alloy of iridium and osmium, and in platinum-bearing river sands in the Ural Mountains, and North and South America. It also occurs in nickel-bearing ores found in the Sudbury, Ontario region with other platinum group metals. Even though the quantity of platinum metals found in these ores is small, the large volume of nickel ores processed makes commercial recovery possible.


Osmium has seven naturally occurring isotopes, 6 of which are stable: 184Os, 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. 186Os undergoes alpha decay with enormously long half-life of (2.0±1.1)×1015 yr and for many practical purposes can be considered to be stable as well. Alpha decay is predicted for all 7 naturally occurring isotopes, but due to very long half-lives, it was observed only for 186Os. It is predicted also that 184Os and 192Os can undergo double beta decay but this radioactivity is not yet observed.
187Os is the daughter of 187Re (half-life 4.56×1010 years) and is used extensively in dating terrestrial as well as meteoric rocks (see Rhenium-osmium dating). It has also been used to measure the intensity of continental weathering over geologic time and to fix minimum ages for stabilization of the mantle roots of continental cratons. This decay is a reason why rhenium-rich minerals contain an abnormally high isotopic abundance of 187Os. However, the most notable application of Os in dating has been in conjunction with iridium, to analyze the layer of shocked quartz along the K-T boundary that marks the extinction of the dinosaurs 65 million years ago.


Osmium tetroxide is highly volatile and penetrates skin readily, and is very toxic by inhalation, in contact with skin, and if swallowed. Airborne low concentrations of osmium vapour can cause lung congestion and skin or eye damage, and should therefore be used in a fume hood. Osmium tetroxide is rapidly reduced to relatively inert compounds by polyunsaturated vegetable oils, such as corn oil.


osmium in Arabic: أوزميوم
osmium in Bengali: অসমিয়াম
osmium in Belarusian: Осмій
osmium in Bosnian: Osmijum
osmium in Bulgarian: Осмий
osmium in Catalan: Osmi
osmium in Czech: Osmium
osmium in Corsican: Osmiu
osmium in Danish: Osmium
osmium in German: Osmium
osmium in Estonian: Osmium
osmium in Modern Greek (1453-): Όσμιο
osmium in Spanish: Osmio
osmium in Esperanto: Osmio
osmium in Basque: Osmio
osmium in Persian: اسمیوم
osmium in French: Osmium
osmium in Friulian: Osmi
osmium in Manx: Osmium
osmium in Galician: Osmio
osmium in Korean: 오스뮴
osmium in Armenian: Օսմիում
osmium in Croatian: Osmij
osmium in Ido: Osmio
osmium in Indonesian: Osmium
osmium in Icelandic: Osmín
osmium in Italian: Osmio
osmium in Hebrew: אוסמיום
osmium in Javanese: Osmium
osmium in Kurdish: Osmiyûm
osmium in Latin: Osmium
osmium in Latvian: Osmijs
osmium in Luxembourgish: Osmium
osmium in Lithuanian: Osmis
osmium in Lojban: jinmrbosmi
osmium in Hungarian: Ozmium
osmium in Malayalam: ഓസ്മിയം
osmium in Dutch: Osmium
osmium in Japanese: オスミウム
osmium in Norwegian: Osmium
osmium in Norwegian Nynorsk: Osmium
osmium in Occitan (post 1500): Òsmi
osmium in Polish: Osm
osmium in Portuguese: Ósmio
osmium in Romanian: Osmiu
osmium in Russian: Осмий
osmium in Sicilian: Òsmiu
osmium in Simple English: Osmium
osmium in Slovak: Osmium
osmium in Slovenian: Osmij
osmium in Serbian: Осмијум
osmium in Serbo-Croatian: Osmijum
osmium in Finnish: Osmium
osmium in Swedish: Osmium
osmium in Thai: ออสเมียม
osmium in Turkish: Osmiyum
osmium in Ukrainian: Осмій
osmium in Chinese: 锇
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