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29 décembre 2011 4 29 /12 /décembre /2011 02:08

Rhenium is a chemical element with the symbol Re and atomic number 75. It is a silvery-white, heavy, third-row transition metalin group 7 of the periodic table. With an average concentration of 1 part per billion (ppb), rhenium is one of the rarest elements in the Earth's crust. Sony VAIO VGN-CR11H/B Battery

The free element has the third-highestmelting point and highest boiling point of any element. Rhenium resembles manganese chemically and is obtained as a by-product of molybdenum and copper refinement. Rhenium shows in its compounds a wide variety of oxidation states ranging from ?1 to +7. Sony VAIO VGN-CR11S/L Battery

Discovered in 1925, rhenium was the last stable element to be discovered. It was named after the river Rhine in Europe.

Nickel-based superalloys for use in jet engines contain up to 6% rhenium, making jet engine construction the largest use for the element, with chemical industry catalytic uses being next-most important. Sony VAIO VGN-CR11H/B Battery

Because of the low availability relative to demand, rhenium is among the most expensive industrial metals, with an average price of approximately US$4,575 perkilogram, on 1 August 2011.[1]

Rhenium (Latin: Rhenus meaning: "Rhine")[2] was the last element to be discovered having a stable isotope (other new radioactive elements have been discovered in nature since then, such as neptunium and plutonium). Sony VAIO VGN-CR11S/L Battery

The existence of a yet undiscovered element at this position in the periodic table had been first predicted by Dmitry Mendeleev. Other calculated information was obtained by Henry Moseley in 1914.[4] It is generally considered to have been discovered byWalter Noddack, Ida Tacke, and Otto Berg in Germany. Sony VAIO VGN-CR11S/P Battery

In 1925 they reported that they detected the element in platinum ore and in the mineral columbite. They also found rhenium in gadolinite and molybdenite.[5] In 1928 they were able to extract 1 g of the element by processing 660 kg of molybdenite.[6] The process was so complicated and expensive that production was discontinued until early 1950 when tungsten-rhenium and molybdenum-rhenium alloys were prepared. Sony VAIO VGN-CR11S/W Battery

These alloys found important applications in industry that resulted in a great demand for the rhenium produced from the molybdenite fraction of porphyry copper ores.

In 1908, Japanese chemist Masataka Ogawa announced that he discovered the 43rd element and named it nipponium (Np) afterJapan (which is Nippon in Japanese). Sony VAIO VGN-CR11Z/R Battery

However, later analysis indicated the presence of rhenium (element 75), not element 43.[7] The symbol Np was later used for the element neptunium.

Characteristics

Rhenium is a silvery-white metal with one of the highest melting points of all elements, exceeded by only tungsten andcarbon. It is also one of the densest, exceeded only by platinum, iridium and osmium. Sony VAIO VGN-CR120E/L Battery

Sony VAIO VGN-CR120E/P Battery

Its usual commercial form is a powder, but this element can be consolidated by pressing and sintering in a vacuum orhydrogenatmosphere. This procedure yields a compact solid having a density above 90% of the density of the metal. Sony VAIO VGN-CR120E/R Battery

Whenannealed this metal is very ductile and can be bent, coiled, or rolled.[8] Rhenium-molybdenum alloys are superconductiveat 10 K; tungsten-rhenium alloys are also superconductive[9] around 4-8 K, depending on the alloy. Rhenium metal superconducts at 2.4 K.[10][11] Sony VAIO VGN-CR120E/W Battery

Rhenium has a stable isotope, rhenium-185, which nevertheless occurs in minority abundance, a situation found only in one other element (indium). Naturally occurring rhenium is 37.4% 185Re, which is stable, and 62.6% 187Re, which is unstablebut has a very long half-life (~1010 years). Sony VAIO VGN-CR125E/B Battery

This lifetime is affected by the charge state of rhenium atom.[12][13] Thebeta decay of 187Re is used for rhenium-osmium dating of ores. The available energy for this beta decay (2.6 keV) is one of the lowest known among all radionuclides. There are twenty-six other recognized radioactive isotopes of rhenium.[14] Sony VAIO VGN-CR13/B Battery

Compounds

Rhenium has nine known oxidation states: ?1, 0, +1, +2, +3, +4, +5, +6 and +7.[15] The oxidation states +7, +6, +4, and +2 are the most common.[15] Sony VAIO VGN-CR13/L Battery

The most common rhenium compounds are the oxides and the halides exhibiting a broad oxidation number spectrum: Re2O7, ReO3, Re2O5, ReO2, and Re2O3 are the known oxides, and ReF7, ReCl6, ReCl5, ReCl4 and ReCl3 are a few of the known halogen derivatives.[16] Known sulfides are ReS2 and Re2S7.[16] Sony VAIO VGN-CR13/P Battery

Reaction of rhenium with hydrogen produces the negatively charged hydride [ReH9]2? ion, which is isostructural with [TcH9]2?. It consists of a trigonal prism with Re atom in the center and six hydrogen atoms at the corners. Sony VAIO VGN-CR13/R Battery

Three more hydrogens make a triangle lying parallel to the base and crossing the prism in its center (see figure). Although those hydrogen atoms are not equivalent geometrically, their electronic structure is almost the same. The coordination number 9 in this complex is the highest for a rhenium complex. Sony VAIO VGN-CR13/W Battery

Sony VAIO VGN-CR131E/L Battery

Two protons in it can be replaced by sodium (Na+) or potassium (K+) ions.[17]

Rhenium is most available commercially as the sodium and ammonium perrhenates. It is also readily available as dirhenium decacarbonyl; these three compounds are common entry points to rhenium chemistry. Sony VAIO VGN-CR13G Battery

Various perrhenate salts may be easily converted to tetrathioperrhenate by the action of ammonium hydrosulfide.[18] It is possible to reduce the dirhenium decacarbonylRe2(CO)10 by reacting it with sodium amalgam to Na[Re(CO)5] with rhenium in the formal oxidation state ?1.[19Sony VAIO VGN-CR13G/B Battery

]Dirhenium decacarbonyl may be oxidatively cleaved with bromine to givebromopentacarbonylrhenium(I),[20] then reduced with zincand acetic acid topentacarbonylhydridorhenium:[21] Sony VAIO VGN-CR13G/L Battery

Re2(CO)10 + Br2 ? 2 Re(CO)5Br

Re(CO)5Br + Zn + HOAc ? Re(CO)5H + ZnBr(OAc)

Bromopentacarbonylrhenium(I) may be decarbonylated to give the rhenium tricarbonyl fragment either by refluxing in water:[22]Sony VAIO VGN-CR13G/P Battery

Re(CO)5Br + 3 H2O ? [Re(CO)3(H2O)3]Br + 2 CO

or by reacting with tetraethylammonium bromide:[23]

Re(CO)5Br + 2 NEt4Br ? [NEt4]2[Re(CO)3Br3] + 2 CO

Rhenium diboride (ReB2) is a hard compound having the hardness similar to that of tungsten carbide, silicon carbide, titanium diboride or zirconium diboride.[24] Sony VAIO VGN-CR13G/R Battery

Rhenium was originally thought to form the rhenide anion, Re?
, in which it has the ?1 oxidation state. This was based on the product of the reduction of perrhenatesalts, such as the reduction of potassium perrhenate (KReO4) by potassium metal.[25] "Sony VAIO VGN-CR13G/W Battery

Potassium rhenide" was shown to exist as a tetrahydrated complex, with the postulated chemical formula KRe·4H2O.[26] This compound exhibits strongly reducing properties, and slowly yields hydrogen gas when dissolved in water. The lithium and thallous salts were also reported. Sony VAIO VGN-CR13T/L Battery

Later rese

"Potassium rhenide" was shown to be in fact the nonahydridorhenate, K2ReH9, containing the ReH92? anion in which the oxidation state of rhenium is actually +7.[27][28] Other methods of reduction of perrhenate salts yield compounds containing other hydrido- complexes, including ReH3(OH)3(H2O)?. arch, however, indicates that the "rhenide" ion is actually a hydridorhenate complex. Sony VAIO VGN-CR13T/P Battery

Occurrence

Rhenium is one of the rarest elements in Earth's crust with an average concentration of 1 ppb;[16] other sources quote the number of 0.5 ppb making it the 77th most abundant element in Earth's crust.[30] Rhenium is probably not found free in nature (its possible natural occurrence is uncertain), but occurs in amounts up to 0.2%[1Sony VAIO VGN-CR13T/R Battery

6] in the mineral molybdenite (which is primarily molybdenum disulfide), the major commercial source, although single molybdenite samples with up to 1.88% have been found.[31]Chile has the world's largest rhenium reserves, part of the copper ore deposits, and was the leading producer as of 2005.[32] Sony VAIO VGN-CR13T/W Battery

It was only recently that the first rhenium mineral was found and described (in 1994), a rhenium sulfide mineral (ReS2) condensing from a fumaroleon Russia's Kudriavy volcano, Iturup island, in the Kurile Islands.[33] Kudryavy discharges up to 20–60 kg rhenium per year mostly in the form of rhenium disulfide. Sony VAIO VGN-CR15/B Battery

Named rheniite, this rare mineral commands high prices among collectors.[36]

Production

Commercial rhenium is extracted from molybdenum roaster-flue gas obtained from copper-sulfide ores. Some molybdenum ores contain 0.001% to 0.2% rhenium.[ Sony VAIO VGN-CR150E/B Battery

Rhenium(VII) oxide and perrhenic acid readily dissolve in water; they are leached from flue dusts and gasses and extracted by precipitating with potassium or ammonium chloride as the perrhenate salts, and purified byrecrystallization.[37] Total world production is between 40 and 50 tons/year; the main producers are in Chile, the United States, Peru, and Kazakhstan.[38] Sony VAIO VGN-CR190 Battery

Recycling of used Pt-Re catalyst and special alloys allow the recovery of another 10 tons per year. Prices for the metal rose rapidly in early 2008, from $1000–$2000 per kg in 2003-2006 to over $10,000 in February 2008.[39][40]The metal form is prepared by reducing ammonium perrhenate with hydrogen at high temperatures:[37] Sony VAIO VGN-CR190E/L Battery

2 NH4ReO4 + 7 H2 ? 2 Re + 8 H2O + 2 NH3

Applications

The F-15 engine uses rhenium-containing second-generation superalloys

Rhenium is added to high-temperature superalloys that are used to make jet engine parts, making 70% of the worldwide rhenium production.[41] Sony VAIO VGN-CR190E/P Battery

Another major application is in platinum-rhenium catalysts, which are primarily used in making lead-free, high-octane gasoline.[42]

Alloys

The nickel-based superalloys have improved creep strength with the addition of rhenium. The alloys normally contain 3% or 6% of rhenium.[43] Sony VAIO VGN-CR190E/R Battery

Second generation alloys contain 3%; these alloys were used in the engines of the F-16 and F-15, while the newer single-crystal third generation alloys contain 6% of rhenium; they are used in the F-22 and F-35 engines.[42][44] Rhenium is also used in the superalloys, such as CMSX-4 (2nd gen) and CMSX-10 (3rd gen) that are used in industrial gas turbine engines like the GE 7FA. Sony VAIO VGN-CR190E/W Battery

Rhenium can cause superalloys to become microstructurally unstable, forming undesirable TCP (topologically close packed)phases. In 4th and 5th generation superalloys, ruthenium is used to avoid this effect. Among others the new superalloys are EPM-102 (with 3 % Ru) and TMS-162 (with 6 % Ru), both containing 6 % rhenium,[45] as well as TMS-138[46] and TMS-174.[47][48] Sony VAIO VGN-CR19VN/B Battery

For 2006, the consumption is given as 28% for General Electric, 28% Rolls-Royce plc and 12% Pratt & Whitney, all for superalloys, while the use for catalysts only accounts for 14% and the remaining applications use 18%.[41] In 2006, 77% of the rhenium consumption in the United States was in alloys.[42] Sony VAIO VGN-CR19XN/B Battery

The rising demand for military jet engines and the constant supply made it necessary to develop superalloys with a lower rhenium content. For example the newer CFM International CFM56 high-pressure turbine (HPT) blades will use Rene N515 with a rhenium content of 1.5 % instead of Rene N5 with 3 %.[49][50] Sony VAIO VGN-CR20 Battery

Rhenium improves the properties of tungsten and is therefore the most important alloying material for tungsten. Tungsten-rhenium alloys are more ductile at low temperature making them easier to machine, while the high-temperature stability is also improved.Sony VAIO VGN-CR21/B Battery

The effect increases with the rhenium concentration, and therefore tungsten alloys are produced with up to 27% of Re, which is the solubility limit.[51] One application for the tungsten-rhenium alloys is X-ray sources. The high melting point of both compounds, together with the high atomic mass, makes them stable against the prolonged electron impact.[52] Sony VAIO VGN-CR21E/L Battery

Rhenium tungsten alloys are also applied as thermocouples to measure temperatures up to 2200 °C.[53]

The high temperature stability, low vapor pressure, good wear resistance and ability to withstand arc corrosion of rhenium are useful in self-cleaning electrical contacts. In particular, the discharge occurring during the switching oxidizes the contacts. Sony VAIO VGN-CR21E/P Battery

However, rhenium oxide Re2O7 has poor stability (sublimates at ~360 °C) and therefore is removed during the discharge.[41]

Rhenium has a high melting point and a low vapor pressure similar to tantalum and tungsten, however, rhenium forms no volatile oxides. Sony VAIO VGN-CR21E/W Battery

Therefore, rhenium filaments exhibit a higher stability if the filament is operated not in vacuum, but in oxygen-containing atmosphere.[54] Those filaments are widely used in mass spectrometers, in ion gauges.[55] and in photoflash lamps in photography.[56] Sony VAIO VGN-CR21S/L Battery

Catalysts

Rhenium in the form of rhenium-platinum alloy is used as catalyst for catalytic reforming, which is a chemical process to convert petroleum refinery naphthas with low octane ratings into high-octane liquid products. Sony VAIO VGN-CR21S/P Battery

Worldwide, 30% of catalysts used for this process contain rhenium.[57] The olefin metathesis is the other reaction for which rhenium is used as catalyst. Normally Re2O7on alumina is used for this process.[58] Rhenium catalysts are very resistant to chemical poisoningfrom nitrogen, sulfur and phosphorus, and so are used in certain kinds of hydrogenation reactions. Sony VAIO VGN-CR21S/W Battery

Other uses

188Re and 186Re isotopes are radioactive and are used for treatment of liver cancer. They both have similar penetration depth in tissue (5 mm for 186Re and 11 mm for188Re), but 186Re has advantage of longer lifetime (90 hours vs. 17 hours). Sony VAIO VGN-CR21Z/N Battery

Related by periodic trends, rhenium has a similar chemistry with technetium; work done to label rhenium onto target compounds can often be translated to technetium. This is useful for radiopharmacy, where it is difficult to work with technetium – especially the 99m isotope used in medicine – due to its expense and short half-life. Sony VAIO VGN-CR21Z/R Battery

Precaution

Very little is known about the toxicity of rhenium and its compounds because they are used in very small amounts. Soluble salts, such as the rhenium halides or perrhenates, could be hazardous due to elements other than rhenium or due to rhenium itself.[ Sony VAIO VGN-CR220E/R Battery

Only a few compounds of rhenium have been tested for their acute toxicity; two examples are potassium perrhenate and rhenium trichloride, which were injected as a solution into rats. The perrhenate had an LD50 value of 2800 mg/kg after seven days (this is very low toxicity, similar to that of table salt) and the rhenium trichloride showed LD50 of 280 mg/kg. Sony VAIO VGN-CR23/B Battery

Sony VAIO VGN-CR23/L Battery

Osmium is a chemical element with 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. Osmium is twice as dense as lead. Sony VAIO VGN-CR23/N Battery

The density of osmium is 22.59 g/cm3, slightly greater than that of iridium, the second densest element. Osmium is found in nature as an alloy, mostly in platinum ores. Osmium is also used in alloys, with platinum, iridium and other platinum group metals. Those alloys are employed in fountain pen tips, electrical contacts and in other applications where extreme durability and hardness are needed.[2] Sony VAIO VGN-CR23/P Battery

Physical properties

Osmium has a blue-gray tint and is the densest stable element, slightly denser thaniridium.[3] Calculations of density from the X-ray diffraction data may produce the most reliable data for these elements, giving a value of 22.562±0.009 g/cm3 for iridium versus 22.587±0.009 g/cm3 for osmium.[4] The high density of osmium is a consequence of the lanthanide contraction.[4][5] Sony VAIO VGN-CR23/R Battery

Osmium is a hard but brittle metal that remains lustrous even at high temperatures. It has a very low compressibility. Correspondingly, its bulk modulus is extremely high, reported between 395 and 462 GPa, which rivals that of diamond (443 GPa).Sony VAIO VGN-CR23/W Battery

The hardness of osmium is moderately high at 4 GPa.[6][7][8] 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), solid osmium is difficult to machine, form or work. Sony VAIO VGN-CR240E/B Battery

Chemical properties

Osmium forms compounds with the oxidation states ranging from ?2 to +8. The most common oxidation states are +2, +3, +4, and +8. The +8 oxidation state is notable for being the highest attained by any chemical element, and aside from osmium, is encountered only inxenon, iron [9] and ruthenium.[10] Sony VAIO VGN-CR240N/B Battery

The oxidation state ?1 and ?2 represented by the two reactive compounds Na2[Os4(CO)13] and Na2[Os(CO)4] are used in the synthesis of osmiumcluster compounds.[11][12]

The most common compound exhibiting the +8 oxidation state is osmium tetroxide. Sony VAIO VGN-CR25G/N Battery

This toxic compound is formed when powdered osmium is exposed to air, and is a very volatile, water-soluble, pale yellow, crystalline solid with a strong smell. Therefore, osmium powder has a characteristic smell of osmium tetroxide.[13] Osmium tetroxide forms red osmates OsO4(OH)2?
2 upon reaction with a base. Sony VAIO VGN-CR290EAL Battery

With ammonia, it forms the nitrido-osmatesOsO3N?.[14][15][16] Osmium tetroxide boils at 130 °C and is a powerful oxidizing agent. By contrast, osmium dioxide (OsO2) is black, non-volatile, and much less reactive and toxic.

Only two osmium compounds have major applications: osmium tetroxide — for stainingtissue in electron microscopy and the non-volatile osmates for organic oxidation reactions.[17] Sony VAIO VGN-CR290EAN Battery

Osmium heptafluoride (OsF7) and osmium pentafluoride (OsF5) are known, but osmium trifluoride (OsF3) has not been synthesized yet. The lower oxidation states are stabilized by the larger halogens. Therefore, the trichloride, tribromide, triiodide and even osmium diiodide are known. Sony VAIO VGN-CR290EAP Battery

The oxidation state +1 is only known for the osmium iodide (OsI), whereas several carbonyl complexes of osmium, such as triosmium dodecacarbonyl (Os3(CO)12), represent the oxidation state 0.[14][15][18][19]

In general, the lower oxidation states of osmium are stabilized by ligands that are good ?-donors (such as amines) and ?-acceptors (heterocycles containing nitrogen).

The higher oxidation states are stabilized by strong ?- and ?-donors, such as O2? and N3?.[20]

Osmium has seven naturally occurring isotopes, six of which are stable: 184Os, 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. Sony VAIO VGN-CR290EAR Battery

186Os undergoes alpha decay with such long half-life ((2.0±1.1)×1015 years) that for practical purposes it can be considered stable. 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 that 184Os and 192Os can undergo double beta decay but this radioactivity has not been observed yet.[21] Sony VAIO VGN-CR290EAW Battery

187Os is the daughter of 187Re (half-life 4.56×1010 yr) and is used extensively in dating terrestrial as well as meteoricrocks(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. Sony VAIO VGN-CR29XN/B Battery

This decay is a reason why rhenium-rich minerals are abnormally rich in 187Os.[22] 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 thedinosaurs 65 million years ago.[23] Sony VAIO VGN-CR305E/RC Battery

Osmium (from Greek osme (????) meaning "smell") was discovered in 1803 by Smithson Tennant and William Hyde WollastoninLondon, England.[24] The discovery of osmium 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.[25] Sony VAIO VGN-CR31S/D Battery

The discovery that this metal was not an alloy, but a distinct new element, was published in 1748.[26]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.[27] Sony VAIO VGN-CR323/W Battery

Joseph Louis Proustthought that the residue was graphite.[27]Victor Collet-Descotils, Antoine François, comte de Fourcroy, and Louis Nicolas Vauquelin also observed the black residue in 1803, but did not obtain enough material for further experiments.[27]

In 1803, Smithson Tennant analyzed the insoluble residue and concluded that it must contain a new metal. Sony VAIO VGN-CR33 Battery

Vauquelin treated the powder alternately with alkali and acids[28] and obtained a volatile new oxide, which he believed to be of this new metal—which he named ptene, from the Greek word ?????? (ptènos) for winged.[29][30] 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.[27][28] Sony VAIO VGN-CR382 Battery

He obtained a yellow solution (probably of cis–[Os(OH)2O4]2?) by reactions with sodium hydroxide at red heat. After acidification he was able to distill the formed OsO4.[29] He named osmium after Greek osme meaning "a smell", because of the ashen and smoky smell of the volatile osmium tetroxide.[31]Discovery of the new elements was documented in a letter to the Royal Society on June 21, 1804.[27][32] Sony VAIO VGN-CR490EBL Battery

Uranium and osmium were early successful catalysts in the Haber process, the nitrogen fixation reaction of nitrogen andhydrogen to produce ammonia, giving enough yield to make the process economically successful. However, in 1908 cheaper catalysts based on iron and iron oxides were introduced for the first pilot plants.[33] Sony VAIO VGN-CR490EBN Battery

Nowadays, osmium is primarily obtained from the processing of platinum and nickel ores.[34]

Occurrence

Osmium is the least abundant stable element in the Earth's crust with an average mass fraction of 0.05 ppb in thecontinental crust.[35] Sony VAIO VGN-CR490EBP Battery

Osmium is found in nature as an uncombined element or in natural alloys; especially the iridium–osmium alloys, osmiridium(osmium rich), and iridiosmium (iridium rich).[28] In the 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., PtAs2); Sony VAIO VGN-CR490EBR Battery

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.[36]

Within the Earth's crust, osmium, like iridium, is found at highest concentrations in three types of geologic structure: Sony VAIO VGN-CR490EBT Battery

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,[37] though the large copper–nickel deposits nearNorilsk in Russia, and the Sudbury Basin in Canada are also significant sources of osmium. Sony VAIO VGN-CR490EBW Battery

Smaller reserves can be found in the United States.[37] 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.[34][38] Sony VAIO VGN-CR50B/W Battery

Production

Osmium is obtained commercially as a by-product from nickel and copper mining and processing. During electrorefining of copperand nickel, noble metals such as silver, gold and the platinum group metals, together with non-metallic elements such as seleniumand tellurium settle to the bottom of the cell as anode mud, which forms the starting material for their extraction. Sony VAIO VGN-CR51B/W Battery

In order to separate the metals, they must first be brought into solution. Several methods are available depending on the separation process and the composition of the mixture; two representative methods are fusion with sodium peroxide followed by dissolution inaqua regia, and dissolution in a mixture of chlorine with hydrochloric acid.[37][41] Sony VAIO VGN-CR520E/J Battery

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 Ru, Os and Ir, is treated with sodium oxide, in which Ir is insoluble, producing water-soluble Ru and Os salts.Sony VAIO VGN-CR52B/W Battery

After oxidation to the volatile oxides,RuO4 is separated from OsO4 by precipitation of (NH4)3RuCl6 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.[42] Sony VAIO VGN-CR590EBL Battery

The first method is similar to the procedure used by Tennant and Wollaston. Both methods are suitable for industrial scale production. In either case, the product is reduced using hydrogen, yielding the metal as a powder or sponge that can be treated using powder metallurgy techniques.[43] Sony VAIO VGN-CR590EBN Battery

Neither the producers nor the United States Geological Survey published any production amounts for osmium. Estimations of the United States consumption date published from 1971,[44] which gives a consumption in the United States of 2000 troy ounces(62 kg), would suggest that the production is still less than 1 ton per year. Sony VAIO VGN-CR590EBP Battery

Applications

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. Those alloys are utilized in high-wear applications. Sony VAIO VGN-CR590EBR Battery

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. The stylus (needle) in early phonograph designs was also made of osmium, especially for 78-rpm records, until sapphire and synthetic diamond replaced the metal in later designs for 45-rpm and 33-rpmlong-playing records.[45] Sony VAIO VGN-CR590EBT Battery

Osmium tetroxide has been used in fingerprint detection[46] and in staining fattytissue 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. Sony VAIO VGN-CR590EBW Battery

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 have otherwise very weak TEM contrast (see image).[17]Another osmium compound, osmium ferricyanide (OsFeCN), exhibits similar fixing and staining action.[47] Sony VAIO VGN-CR60B/L Battery

An alloy of 90% platinum and 10% osmium is used in surgical implants such as pacemakers and replacement of pulmonaryvalves.[48]

The tetroxide and a related compound, potassium osmate, are important oxidants for chemical synthesis, despite being very poisonous. Sony VAIO VGN-CR60B/P Battery

For the Sharpless asymmetric dihydroxylation, which uses osmate for the conversion of a double bond into a vicinaldiol, Karl Barry Sharpless won the Nobel Prize in Chemistry in 2001.[49][50]

In 1898 an Austrian chemist, Auer von Welsbach, developed the Oslamp with a filament made of osmium, which he introduced commercially in 1902. Sony VAIO VGN-CR60B/R Battery

After only a few years, osmium was replaced by the more stable metal tungsten (also 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.[29] Sony VAIO VGN-CR61B/L Battery

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.[53]

Like palladium, powdered osmium effectively absorbs hydrogen atoms. Sony VAIO VGN-CR61B/N Battery

This could make osmium a potential candidate for a metal hydride battery electrode. However, osmium is expensive and would react with potassium hydroxide, the most common battery electrolyte.[54]

Osmium has high reflectivity in the ultraviolet range of the electromagnetic spectrum; for example, at 600 Å osmium has a reflectivity twice that of gold.[55] Sony VAIO VGN-CR61B/P Battery

This high reflectivity is desirable in space-based UV spectrometers which have reduced mirror sizes due to space limitations. Osmium-coated mirrors were flown in several space missions aboard the Space Shuttle, but it soon became clear that the oxygen radicals in the low earth orbit are abundant enough to significantly deteriorate the osmium layer.[56] Sony VAIO VGN-CR61B/R Battery

Precautions

Finely divided metallic osmium is pyrophoric.[44] Osmium reacts with oxygen at room temperature forming volatile osmium tetroxide. Some osmium compounds are also converted to the tetroxide if oxygen is present.[44] This makes osmium tetroxide the main source of contact with the environment. Sony VAIO VGN-CR62B/L Battery

Osmium tetroxide is highly volatile and penetrates skin readily, and is very toxic by inhalation, ingestion, and skin contact.[57]Airborne low concentrations of osmium tetroxide vapor can cause lung congestion and skin or eye damage, and should therefore be used in a fume hood.[13] Sony VAIO VGN-CR62B/N Battery

Osmium tetroxide is rapidly reduced to relatively inert compounds by polyunsaturated vegetable oils, such as corn oil.[58]

Price

Osmium is usually sold as a 99% pure powder. Like other precious metals, it is measured by troy weight and by grams. Sony VAIO VGN-CR62B/P Battery

Its price at 2010 is about $400 per Troy ounce (or about $13 per gram), depending on the quantity and its supplier.[

Iridium is the chemical element with atomic number 77, and is represented by the symbol Ir. Sony VAIO VGN-CR62B/R Battery

A very hard, brittle, silvery-white transition metal of the platinum family, iridium is the second-densest element (after osmium) and is the most corrosion-resistant metal, even at temperatures as high as 2000 °C. Although only certain molten salts andhalogens are corrosive to solid iridium, finely divided iridium dust is much more reactive and can be flammable. Sony VAIO VGN-CR70B/W Battery

Iridium was discovered in 1803 among insoluble impurities in natural platinum. Smithson Tennant, the primary discoverer, named the iridium for the goddess Iris, personification of the rainbow, because of the striking and diverse colors of its salts. Sony VAIO VGN-CR71B/W Battery

Iridium is one of the rarest elements in the Earth's crust, with annual production and consumption of only threetonnes. 191Ir and 193Ir are the only two naturally occurring isotopes of iridium as well as the only stable isotopes; the latter is the more abundant of the two. Sony VAIO VGN-CR72B/W Battery

The most important iridium compounds in use are the salts and acids it forms with chlorine, though iridium also forms a number of organometallic compounds used in industrial catalysis, and in research. Iridium metal is employed when high corrosion resistance at high temperatures is needed, Sony VAIO VGN-CR90HS Battery

as in high-end spark plugs, crucibles for recrystallization of semiconductors at high temperatures, and electrodes for the production of chlorine in the chloralkali process. Iridium radioisotopes are used in some radioisotope thermoelectric generators. Sony VAIO VGN-CR90NS Battery

The unusually high abundance of iridium in the clay layer at the K–T geologic boundary gave rise to the Alvarez hypothesisthat the impact of a massive extraterrestrial object caused the extinction of dinosaurs and many other species 65 million years ago. Sony VAIO VGN-CR90S Battery

Iridium is found in meteorites with an abundance much higher than its average abundance in the Earth's crust. It is thought that the total amount of iridium in the planet Earth is much higher than that observed in crustal rocks, but as with other platinum group metals, the high density and tendency of iridium to bond with iron caused most iridium to descend below the crust when the planet was young and still molten. Sony VAIO VGN-CR92HS Battery

Physical properties

A member of the platinum group metals, iridium is white, resembling platinum, but with a slight yellowish cast. Because of its hardness, brittleness, and very high melting point (the ninth highest of all elements), solid iridium is difficult to machine, form, or work, and thus powder metallurgy is commonly employed instead. Sony VAIO VGN-CR92NS Battery

It is the only metal to maintain good mechanical properties in air at temperatures above 1600 °C.[4] Iridium has a very high boiling point (10th among all elements) and becomes a superconductor at temperatures below 0.14 K.[5]

Iridium's modulus of elasticity is the second highest among the metals, only being surpassed by osmium.[4] Sony VAIO VGN-CR92S Battery

This, together with a high modulus of rigidity and a very low figure for Poisson's ratio (the relationship of longitudinal to lateral strain), indicate the high degree of stiffness and resistance to deformation that have rendered its fabrication into useful components a matter of great difficulty. Sony VAIO VGN-CS118E/Q Battery

Despite these limitations and iridium's high cost, a number of applications have developed where mechanical strength is an essential factor in some of the extremely severe conditions encountered in modern technology.[4]

The measured density of iridium is only slightly lower (by about 0.12%) than that of osmium, the densest element known.[6][7] Sony VAIO VGN-CS118E/R Battery

There had been some ambiguity regarding which of the two elements was denser, due to the small size of the difference in density and difficulties in measuring it accurately,[8] but, with increased accuracy in factors used for calculating densityX-ray crystallographicdata yielded densities of 22.56 g/cm3 for iridium and 22.59 g/cm3 for osmium.[9] Sony VAIO VGN-CS118E/W Battery

Chemical properties

Iridium is the most corrosion-resistant metal known:[10] it is not attacked by almost any acid, aqua regia, molten metals or silicates at high temperatures. It can, however, be attacked by some molten salts, such as sodium cyanide and potassium cyanide,[10] as well as oxygen and the halogens (particularly fluorine)[11] at higher temperatures.[12] Sony VAIO VGN-CS11S/P Battery

Compounds

Iridium forms compounds in oxidation states between ?3 to +6; the most common oxidation states are +3 and +4.[3] Well-characterized examples of the highest oxidation state are rare, but includeIrF6 and two mixed oxides Sr2MgIrO6and Sr2CaIrO6.[3][13] Sony VAIO VGN-CS11S/Q Battery

In addition, it was reported in 2009 that iridium(VIII) tetroxide (IrO4) was prepared under matrix isolation conditions (6 K in Ar) by UV irradiation of an iridium-peroxo complex. This species, however, is not expected to be stable as a bulk solid at higher temperatures.[14] Sony VAIO VGN-CS11S/W Battery

Iridium dioxide, IrO2, a brown powder, is the only well-characterized oxide of iridium.[3] Asesquioxide, Ir2O3, has been described as a blue-black powder which is oxidized to IrO2 byHNO3.[11] The corresponding disulfides, diselenides, sesquisulfides and sesquiselenides are known and IrS3 has also been reported.[3] Sony VAIO VGN-CS11Z/R Battery

Iridium also forms iridates with oxidation states +4 and +5, such as K2IrO3 and KIrO3, which can be prepared from the reaction of potassium oxide or potassium superoxide with iridium at high temperatures.[15] Sony VAIO VGN-CS120J/P Battery

While no binary hydrides of iridium, IrxHy are known, complexes are known that contain IrH4?5 and IrH3?6, where iridium has the +1 and +3 oxidation states, respectively.[16] The ternary hydride Mg6Ir2H11 is believed to contain both the IrH4?
5 and the 18-electron IrH5?4 anion.[17] Sony VAIO VGN-CS120J/Q Battery

No monohalides or dihalides are known, whereas trihalides, IrX3, are known for all of the halogens.[3] For oxidation states +4 and above, only the tetrafluoride, pentafluoride and hexafluoride are known.[3] Iridium hexafluoride, IrF6, is a volatile and highly reactive yellow solid, composed of octahedral molecules. Sony VAIO VGN-CS120J/R Battery

It decomposes in water and is reduced to IrF4, a crystalline solid, by iridium black.[3] Iridium pentafluoride has similar properties but it is actually a tetramer, Ir4F20, formed by four corner-sharing octahedra.[3]

Hexachloroiridic(IV) acid, H2IrCl6, and its ammonium salt are the most important iridium compounds from an industrial perspective.[18] Sony VAIO VGN-CS190JTB Battery

They are involved in the purification of iridium and used as precursors for most other iridium compounds, as well as in the preparation of anode coatings. The IrCl2?
6 ion has an intense dark brown color, and can be readily reduced to the lighter-colored IrCl3?6 and vice versa.[18] Sony VAIO VGN-CS190JTP Battery

Iridium trichloride,IrCl3, which can be obtained in anhydrous form from direct oxidation of iridium powder bychlorine at 650 °C,[18] or in hydrated form by dissolving Ir2O3 in hydrochloric acid, is often used as a starting material for the synthesis of other Ir(III) compounds.[3] Sony VAIO VGN-CS190JTQ Battery

Another compound used as a starting material is ammonium hexachloroiridate(III), (NH4)3IrCl6. Iridium(III) complexes are diamagnetic (low-spin) and generally have an octahedral molecular geometry.[3]

Organoiridium compounds contain iridium–carbon bonds where the metal is usually in lower oxidation states. Sony VAIO VGN-CS190JTR Battery

For example, oxidation state zero is found in tetrairidium dodecacarbonyl, Ir4(CO)12, which is the most common and stable binary carbonylof iridium.[3] In this compound, each of the iridium atoms is bonded to the other three, forming a tetrahedral cluster. Some organometallic Ir(I) compounds are notable enough to be named after their discoverers. Sony VAIO VGN-CS190JTW Battery

One is Vaska's complex,IrCl(CO)[P(C6H5)3]2, which has the unusual property of binding to the dioxygen molecule, O2.[19] Another one is Crabtree's catalyst, a homogeneous catalyst for hydrogenation reactions.[20] These compounds are both square planar, d8complexes, with a total of 16 valence electrons, which accounts for their reactivity.[21] Sony VAIO VGN-CS190NAB Battery

Iridium has two naturally occurring, stable isotopes, 191Ir and 193Ir, with natural abundances of 37.3% and 62.7%, respectively.[22] At leas

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