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n smithson tennant 1803 isotopes of osmium v e main isotopes 11 decay isotope abun dance half life t 1 2 mode pro duct 184 os 0 02 1 12 10 13 y α 180 w 185 os synth 92 95 d ε 185 re 186 os 1 59 2 0 10 15 y α 182 w 187 os 1 96 stable 188 os 13 2 stable 189 os 16 1 stable 190 os 26 3 stable 191 os synth 14 99 d β 191 ir 192 os 40 8 stable 193 os synth 29 83 h β 193 ir 194 os synth 6 0 y β 194 ir category osmium view talk edit references osmium from ancient greek ὀσμή osmḗ smell is a chemical element it has symbol os and atomic number 76 it is a hard brittle bluish white transition metal in the platinum group it was discovered in 1803 by smithson tennant who named it for the characteristic smell of its volatile oxide osmium has the highest density of any stable element and one of the lowest abundances in the earth s crust where it is mainly found alongside other platinum group metals and in ores of copper and nickel while its metallic applications are limited manufacturers use alloys of osmium with platinum iridium and other platinum group metals for fountain pen nib tipping electrical contacts and other applications that require extreme durability and hardness 12 its chemical applications are more prominent with major applications in electron microscopy and laboratory scale production of vicinal diols characteristics edit physical properties edit osmium remelted pellet osmium is a hard brittle blue gray metal and the densest stable element about twice as dense as lead the density of osmium is slightly greater than that of iridium the two are so similar 22 587 versus 22 562 g cm 3 at 20 c that each was at one time considered to be the densest element only in the 1990s were measurements made accurately enough by means of x ray crystallography to be certain that osmium is the denser of the two 13 14 osmium has a blue gray tint 12 the reflectivity of single crystals of osmium is complex and strongly direction dependent with light in the red and near infrared wavelengths being more strongly absorbed when polarized parallel to the c crystal axis than when polarized perpendicular to the c axis the c parallel polarization is also slightly more reflected in the mid ultraviolet range reflectivity reaches a sharp minimum at around 1 5 ev near infrared for the c parallel polarization and at 2 0 ev orange for the c perpendicular polarization and peaks for both in the visible spectrum at around 3 0 ev blue violet 15 osmium remains lustrous even at high temperatures it has a very low compressibility correspondingly its bulk modulus is extremely high reported to be between 395 and 462 gpa which rivals that of diamond 443 gpa the hardness of osmium is moderately high at 4 gpa 16 17 18 because of its hardness brittleness low vapor pressure the lowest of the platinum group metals and very high melting point the fourth highest of all elements after carbon tungsten and rhenium solid osmium is difficult to machine form or work chemical properties edit main article osmium compounds oxidation states of osmium 2 na 2 os co 4 1 k 2 os 2 co 8 0 os 3 co 12 1 osi 2 osi 2 3 osbr 3 4 oso 2 oscl 4 5 osf 5 6 osf 6 7 osof 5 8 oso 4 os nch 3 4 osmium forms compounds with oxidation states ranging from 2 to 8 the most common oxidation states are 2 3 4 and 8 19 examples of the 1 and 2 oxidation states are na 2 os 4 co 13 mixed 0 and 1 oxidation states and na 2 os co 4 respectively these reactive compounds are used to synthesize osmium cluster compounds 20 21 another example of the 1 oxidation state of osmium is k 2 os 2 co 8 6 osmium tetroxide oso 4 the most common compound exhibiting the 8 oxidation state osmium tetroxide oso 4 is a toxic volatile and water soluble solid with a pronounced and nauseating smell 22 osmium tetroxide forms red perosmates oso 4 oh 2 2 upon reaction with alkali with ammonia it forms the nitrido osmates oso 3 n 23 24 25 the 4 oxide osmium dioxide oso 2 is a darkly colored non volatile and much less reactive compound osmium pentafluoride osf 5 is known but osmium trifluoride osf 3 has not yet been synthesized the lower oxidation states are stabilized by the larger halogens so that the trichloride tribromide triiodide and even diiodide are known the oxidation state 1 is known only for osmium monoiodide osi whereas several carbonyl complexes of osmium such as triosmium dodecacarbonyl os 3 co 12 represent oxidation state 0 23 24 26 27 in general the lower oxidation states of osmium are stabilized by ligands that are good σ donors such as amines and π acceptors heterocycles containing nitrogen the higher oxidation states are stabilized by strong σ and π donors such as o 2 and n 3 28 despite its broad range of compounds in numerous oxidation states osmium in bulk form at ordinary temperatures and pressures is inert it resists attack by most acids and bases including aqua regia but is attacked by f 2 and cl 2 at high temperatures and by hot concentrated nitric acid to produce oso 4 it can be dissolved by molten alkalis fused with an oxidizer such as sodium peroxide na 2 o 2 or potassium chlorate kclo 3 to give osmates such as k 2 oso 2 oh 4 26 isotopes edit main article isotopes of osmium osmium has seven naturally occurring isotopes five of which are stable 187 os 188 os 189 os 190 os and most abundant 192 os at least 37 artificial radioisotopes and 20 nuclear isomers exist with mass numbers ranging from 160 to 203 the most stable of these is 194 os with a half life of 6 0 years 11 the two primordial radioisotopes 184 os and 186 os are known to undergo alpha decay but with such long half lives the current best values are 1 12 0 23 10 13 and 2 0 1 1 10 15 years approximately 140 000 times the age of the universe that for practical purposes it can be considered stable alpha decay is predicted for all the other naturally occurring isotopes but has not been observed presumably due to very long half lives 184 os and 192 os are also predicted to undergo double beta decay but this not been observed either 11 189 os has a spin of 3 2 11 131 but 187 os has a nuclear spin 1 2 11 131 its low natural abundance 1 64 and low nuclear magnetic moment mean that it is one of the most difficult natural abundance isotopes for nmr spectroscopy 29 187 os is the descendant of 187 re half life 4 12 10 10 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 are abnormally rich in 187 os 30 history edit osmium was discovered in 1803 by smithson tennant and william hyde wollaston in london england 31 its discovery is intertwined with that of platinum and the other metals of the platinum group platinum reached europe as platina small silver first encountered in the late 17th century in silver mines around the chocó department in colombia 32 the discovery that this metal was not an alloy but a new element was published in 1748 33 chemists who studied platinum dissolved it in aqua regia a mixture of hydrochloric and nitric acids to create soluble salts they always observed a small amount of a dark insoluble residue 34 joseph louis proust thought the residue was graphite 34 victor collet descotils antoine françois comte de fourcroy and louis nicolas vauquelin also observed iridium in the black platinum residue in 1803 but did not obtain enough material for further experiments 34 later the two french chemists fourcroy and vauquelin identified a metal in a platinum residue they called ptène 35 in 1803 smithson tennant analyzed the insoluble residue and concluded that it must contain a new metal vauquelin treated the powder alternately with alkali and acids 36 and obtained a volatile new oxide which he believed was of this new metal which he named ptene from the greek word πτηνος ptènos for winged 37 38 however tennant who had the advantage of a much larger amount of residue continued his research and identified two previously undiscovered elements in the black residue iridium and osmium 34 36 he obtained a yellow solution probably of cis os oh 2 o 4 2 by reactions with sodium hydroxide at red heat after acidification he was able to distill the formed oso 4 37 he named it osmium after greek osme meaning a smell because of the chlorine like and slightly garlic like smell of the volatile osmium tetroxide 39 discovery of the new elements was documented in a letter to the royal society on june 21 1804 34 40 uranium and osmium were early successful catalysts in the haber process the nitrogen fixation reaction of nitrogen and hydrogen to produce ammonia giving enough yield to make the process economically successful at the time a group at basf led by carl bosch bought most of the world s supply of osmium to use as a catalyst shortly thereafter in 1908 cheaper catalysts based on iron and iron oxides were introduced by the same group for the first pilot plants removing the need for the expensive and rare osmium 41 osmium is now obtained primarily from the processing of platinum and nickel ores 42 occurrence edit native platinum containing traces of the other platinum group metals osmium is one of the least abundant stable elements in earth s crust with an average mass fraction of 50 parts per trillion in the continental crust 43 44 osmium is found in nature as an uncombined element or in natural alloys especially the iridium osmium alloys osmiridium iridium rich and iridosmium osmium rich 36 in nickel and copper deposits the platinum group metals occur as sulfides i e pt pd s tellurides e g ptbite antimonides e g pdsb and arsenides e g ptas 2 in all these compounds platinum is exchanged by a small amount of iridium and osmium as with all of the platinum group metals osmium can be found naturally in alloys with nickel or copper 45 within earth s crust osmium like iridium is found at highest concentrations in three types of geologic structure igneous deposits crustal intrusions from below impact craters and deposits reworked from one of the former structures the largest known primary reserves are in the bushveld igneous complex in south africa 46 though the large copper nickel deposits near norilsk in russia and the sudbury basin in canada are also significant sources of osmium smaller reserves can be found in the united states 46 the alluvial deposits used by pre columbian people in the chocó department colombia are still a source for platinum group metals the second large alluvial deposit was found in the ural mountains russia which is still mined 42 47 production edit osmium crystals grown by chemical vapor transport osmium is obtained commercially as a by product from nickel and copper mining and processing during electrorefining of copper and nickel noble metals such as silver gold and the platinum group metals together with non metallic elements such as selenium and tellurium settle to the bottom of the cell as anode mud which forms the starting material for their extraction 48 42 separating the metals requires that they first be brought into solution several methods can achieve this depending on the separation process and the composition of the mixture two representative methods are fusion with sodium peroxide followed by dissolution in aqua regia and dissolution in a mixture of chlorine with hydrochloric acid 46 49 osmium ruthenium rhodium and iridium can be separated from platinum gold and base metals by their insolubility in aqua regia leaving a solid residue rhodium can be separated from the residue by treatment with molten sodium bisulfate the insoluble residue containing ruthenium osmium and iridium is treated with sodium oxide in which ir is insoluble producing water soluble ruthenium and osmium salts after oxidation to the volatile oxides ruo 4 is separated from oso 4 by precipitation of nh 4 3 rucl 6 with ammonium chloride after it is dissolved osmium is separated from the other platinum group metals by distillation or extraction with organic solvents of the volatile osmium tetroxide 50 the first method is similar to the procedure used by tennant and wollaston both methods are suitable for industrial scale production modern methods involve reducing ammonium hexachloroosmate iv using hydrogen yielding the metal as a powder or sponge that can be treated using powder metallurgy techniques 51 estimates of annual worldwide osmium production are on the order of several hundred to a few thousand kilograms 14 26 production and consumption figures for osmium are not well reported because demand for the metal is limited and can be fulfilled with the byproducts of other refining processes 26 to reflect this statistics often report osmium with other minor platinum group metals such as iridium and ruthenium us imports of osmium from 2014 to 2021 averaged 155 kg annually 52 53 applications edit because osmium is virtually unforgeable when fully dense and very fragile when sintered it is rarely used in its pure state but is instead often alloyed with other metals for high wear applications osmium alloys such as osmiridium are very hard and along with other platinum group metals are used in the tips of fountain pens instrument pivots and electrical contacts as they can resist wear from frequent operation they were also used for the tips of phonograph styli during the late 78 rpm and early lp and 45 record era circa 1945 to 1955 osmium alloy tips were significantly more durable than steel and chromium needle points but wore out far more rapidly than competing and costlier sapphire and diamond tips so they were discontinued 54 only two osmium compounds have major applications osmium tetroxide for staining tissue in electron microscopy and for the oxidation of alkenes in organic synthesis and the non volatile osmates for organic oxidation reactions 55 osmium tetroxide has been used in fingerprint detection 56 and in staining fatty tissue for optical and electron microscopy 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 because osmium atoms are extremely electron dense osmium staining greatly enhances image contrast in transmission electron microscopy tem studies of biological materials those carbon materials otherwise have very weak tem contrast 55 another osmium compound osmium ferricyanide osfecn exhibits similar fixing and staining action 57 the tetroxide and its derivative potassium osmate are important oxidants in organic synthesis for the sharpless asymmetric dihydroxylation which uses osmate for the conversion of a double bond into a vicinal diol karl barry sharpless was awarded the nobel prize in chemistry in 2001 58 59 oso 4 is very expensive for this use so kmno 4 is often used instead even though the yields are less for this cheaper chemical r...