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Encyclopedia :
O :
OS :
OSM :
Osmium |
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Osmium
Notable characteristicsOsmium in a metallic form is extremely dense, blue white, brittle and lustrous even at high temperatures, but 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 toxic. The oxide is also a powerful oxidizing agent, emits a strong smell and boils at 130°C. Due to its very high density osmium is generally considered to be the heaviest 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 22661 kg/m3 for osmium. Definitive selection between the two is therefore not possible at this time. It's just too close to call. If one distinguishes different isotopes, then the heaviest ordinary substance would be Osmium-192. This 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. ApplicationsBecause of the 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 are very hard and along with other platinum group metals is almost entirely used in alloys employed in the tips of fountain pens, phonograph needles, instrument pivots, and electrical contacts. Osmium tetroxide has been used in fingerprint detection and in staining fatty tissue for microscope slides. An alloy of 90% platinum and 10% osmium (90/10) is used in surgical implants such as pacemakerss and replacement pulmonary valves. The tetroxide (and a related compound, potassium osmate) are important oxidants for chemical synthesis. HistoryOsmium (Greek osme meaning "a smell") was discovered in 1803 by Smithson Tennant in London, England along with iridium in the residue of dissolving platinum in aqua regia. OccurrenceThis transition metal is 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 is 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. CompoundsOsmium tetroxide OsO4IsotopesOsmium has seven naturally-occurring isotopes, 5 of which are stable: Os-187, Os-188, Os-189, Os-190, and (most abundant) Os-192. Os-184, Os-186 have absurdly long half lifes and for practical purposes can be considered to be stable as well. Os-187 is the daughter of rhenium-187 (half-life 4.56 x 1010 years) and is most often measured in a Os-187/Os-186 ratio. This ratio, as well as the Re-187/Os-187 ratio, have been used extensively in dating terrestrial as well as meteoric rockss. 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. PrecautionsOsmium tetroxide is highly toxic. Airborne concentrations of osmium as low as 10-7 g/m³ can cause lung congestion, skin or eye damage.ReferencesExternal links
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