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29 décembre 2011 4 29 /12 /décembre /2011 02:11

Isotopes with masses below 191 decay by some combination of ?+ decay, ? decay, and proton emission, with the exceptions of 189Ir, which decays byelectron capture, and 190Ir, which decays by positron emission. Synthetic isotopes heavier than 191 decay by ??decay, although 192Ir also has a minor electron capture decay path.[22] Sony VAIO VGN-CS190NBB Battery

All known isotopes of iridium were discovered between 1934 and 2001; the most recent is 171Ir.[24]

At least 32 metastable isomers have been characterized, ranging in mass number from 164 to 197. Sony VAIO VGN-CS190NCA Battery

The most stable of these is 192m2Ir, which decays by isomeric transition with a half-life of 241 years,[22] making it more stable than any of iridium's synthetic isotopes in their ground states. The least stable isomer is190m3Ir with a half-life of only 2 µs.[22] The isotope 191Ir was the first one of any element to be shown to present a Mössbauer effect. Sony VAIO VGN-CS190NCB Battery

This renders it useful forMössbauer spectroscopy for research in physics, chemistry, biochemistry, metallurgy, and mineralogy.[25]

The discovery of iridium is intertwined with that of platinum and the other metals of the platinum group. Sony VAIO VGN-CS190NCC Battery

Native platinum used by ancient Ethiopians[26] and by South American cultures[27] always contained a small amount of the other platinum group metals, including iridium. Platinum reached Europe as platina ("small silver"), found in the 17th century by the Spanish conquerors in a region today known as the department of Chocó in Colombia.[ Sony VAIO VGN-CS50B/W Battery

The discovery that this metal was not an alloy of known elements, but instead a distinct new element, did not occur until 1748.[29]

Chemists who studied platinum dissolved it in aqua regia (a mixture of hydrochloric and nitric acids) to create soluble salts. Sony VAIO VGN-CS51B/W Battery

Sony VAIO VGN-CS52JB/W Battery

They always observed a small amount of a dark, insoluble residue.[4] Joseph Louis Proust thought that the residue was graphite.[4]The French chemists Victor Collet-Descotils, Antoine François, comte de Fourcroy, and Louis Nicolas Vauquelin also observed the black residue in 1803, but did not obtain enough for further experiments.[4] Sony VAIO VGN-CS60B/P Battery

In 1803, British scientist Smithson Tennant (1761–1815) analyzed the insoluble residue and concluded that it must contain a new metal. Vauquelin treated the powder alternately with alkali and acids[10] 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.[30][31] Sony VAIO VGN-CS60B/Q Battery

Tennant, who had the advantage of a much greater amount of residue, continued his research and identified the two previously undiscovered elements in the black residue, iridium and osmium.[4][10] He obtained dark red crystals (probably of Na2[IrCl6]·nH2O) by a sequence of reactions withsodium hydroxide and hydrochloric acid.[31] Sony VAIO VGN-CS60B/R Battery

He named iridium after Iris (????), the Greek winged goddess of the rainbow and the messenger of the Olympian gods, because many of the salts he obtained were strongly colored.[note 2][32] Discovery of the new elements was documented in a letter to the Royal Society on June 21, 1804.[4][33] Sony VAIO VGN-CS61B/P Battery

British scientist John George Children was the first to melt a sample of iridium in 1813 with the aid of "the greatest galvanic battery that has ever been constructed" (at that time).[4] The first to obtain high purity iridium was Robert Hare in 1842. He found that it had a density of around 21.8 g/cm3 and noted that the metal is nearly unmalleable and very hard. Sony VAIO VGN-CS61B/Q Battery

The first melting in appreciable quantity was done by Henri Sainte-Claire Deville and Jules Henri Debray in 1860. They required burning more than 300 L of pure O2and H2 for each kilogram of iridium.[4]

These extreme difficulties in melting the metal limited the possibilities for handling iridium. Sony VAIO VGN-CS61B/R Battery

John Isaac Hawkins was looking to obtain a fine and hard point for fountain pen nibs and in 1834 managed to create an iridium-pointed gold pen. In 1880 John Hollandand William Lofland Dudley were able to melt iridium by adding phosphorus and patented the process in the United States; Sony VAIO VGN-CS62JB/P Battery

British company Johnson Matthey later stated that they had been using a similar process since 1837 and had already presented fused iridium at a number of World Fairs.[4] The first use of an alloy of iridium with ruthenium in thermocouples was made by Otto Feussner in 1933. These allowed for the measurement of high temperatures in air up to 2000 °C.[4] Sony VAIO VGN-CS62JB/Q Battery

In 1957 Rudolf Mössbauer, in what has been called one of the "landmark experiments in twentieth century physics",[34] discovered the resonant and recoil-free emission and absorption of gamma rays by atoms in a solid metal sample containing only 191Ir.[35]Sony VAIO VGN-CS62JB/R Battery

This phenomenon, known as the Mössbauer effect (which has since been observed for other nuclei, such as 57Fe), and developed asMössbauer spectroscopy, has made important contributions to research in physics, chemistry, biochemistry, metallurgy, and mineralogy.[25] Mössbauer received the Nobel Prize in Physics in 1961, just three years after he published his discovery.[36] Sony VAIO VGN-CS71B/W Battery

Occurrence

The Willamette Meteorite, the sixth-largest meteorite found in the world, has 4.7 ppm iridium.[37]

Iridium is one of the least abundant elements in the Earth's crust, having an average mass fraction of 0.001 ppm in crustal rock; Sony VAIO VGN-CS72JB/W Battery

goldis 40 times more abundant, platinum is 10 times more abundant, and silver and mercury are 80 times more abundant.[3]Telluriumis about as abundant as iridium, and only three naturally occurring elements are less abundant: rhenium, ruthenium, andrhodium, iridium being 10 times more abundant than the last two.[3] Sony VAIO VGN-CS90HS Battery

In contrast to its low abundance in crustal rock, iridium is relatively common in meteorites, with concentrations of 0.5 ppm or more.[38] It is thought that the overall concentration of iridium on Earth is much higher than what is observed in crustal rocks, but because of the density and siderophilic ("iron-loving") character of iridium, it descended below the crust and into the Earth's core when the planet was still molten.[18] Sony VAIO VGN-CS90NS Battery

Iridium is found in nature as an uncombined element or in natural alloys; especially the iridium–osmium alloys, osmiridium(osmium rich), and iridiosmium (iridium rich).[10] In the nickel and copper deposits the platinum group metals occur as sulfides(i.e. (Pt,Pd)S), tellurides (i.e. PtBiTe), antimonides (PdSb), and arsenides (i.e. PtAs2). Sony VAIO VGN-CS90S Battery

In all of these compounds platinum is exchanged by a small amount of iridium and osmium. As with all of the platinum group metals, iridium can be found naturally in alloys with raw nickel or raw copper.[39]

Within the Earth's crust, iridium is found at highest concentrations in three types of geologic structure: Sony VAIO VGN-CS91HS 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,[40] though the large copper–nickel deposits near Norilsk inRussia, and the Sudbury Basin in Canada are also significant sources of iridium. Sony VAIO VGN-CS91NS Battery

Smaller reserves are found in the United States.[40] Iridium is also found in secondary deposits, combined with platinum and other platinum group metals in alluvialdeposits. The alluvial deposits used by pre-Columbian people in the Chocó Department of Colombia are still a source for platinum-group metals. As of 2003 the world reserves had not been estimated.[10]Sony VAIO VGN-CS91S Battery

K–T boundary presence

The K–T boundary of 65 million years ago, marking the temporal border between the Cretaceous and Tertiary periods of geological time, was identified by a thin stratum of iridium-rich clay.[41] Sony VAIO VGN-CS92DS Battery

A team led by Luis Alvarez proposed in 1980 an extraterrestrial origin for this iridium, attributing it to an asteroid or comet impact.[41] Their theory, known as the Alvarez hypothesis, is now widely accepted to explain the demise of the dinosaurs. A large buried impact crater structure with an estimated age of about 65 million years was later identified under what is now the Yucatán Peninsula (the Chicxulub crater).[42][43] Sony VAIO VGN-CS92JS Battery

Dewey M. McLean and others argue that the iridium may have been of volcanic origin instead, as the Earth's core is rich in iridium, and active volcanoes such as Piton de la Fournaise, in the island of Réunion, are still releasing iridium.[44][45] Sony VAIO VGN-CS92XS Battery

Production

Iridium 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 as well as selenium and tellurium settle to the bottom of the cell as anode mud, which forms the starting point for their extraction. Sony VAIO VGN-FW11E 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 in aqua regia, and dissolution in a mixture of chlorinewith hydrochloric acid.[18][40] Sony VAIO VGN-FW11L Battery

After it is dissolved, iridium is separated from the other platinum group metals by precipitating (NH4)2IrCl6 or by extracting IrCl2?
6with organic amines.[50] The first method is similar to the procedure Tennant and Wollaston used for their separation. Sony VAIO VGN-FW11M Battery

The second method can be planned as continuous liquid–liquid extraction and is therefore more 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 metallurgytechniques.[51][52] Sony VAIO VGN-FW11S Battery

Annual production of iridium circa 2000 was around 3 tonnes or about 100,000 troy ounces (ozt).[note 3][10] The price of iridium as of 2007 was $440 USD/ozt,[46] but the price fluctuates considerably, as shown in the table. Sony VAIO VGN-FW11ZU Battery

The high volatility of the prices of the platinum group metals has been attributed to supply, demand, speculation, and hoarding, amplified by the small size of the market and instability in the producing countries.[53] Sony VAIO VGN-FW139E/H Battery

Applications

The global demand for iridium in 2007 was 119,000 troy ounces (3,700 kg), out of which 25,000 ozt (780 kg) were used for electrical applications such as spark plugs; 34,000 ozt (1,100 kg) for electrochemical applications such as electrodes for the chloralkali process; 24,000 ozt (750 kg) for catalysis; and 36,000 ozt (1,100 kg) for other uses.[54] Sony VAIO VGN-FW140AE Battery

Industrial and medical

The high melting point, hardness and corrosion resistance of iridium and its alloys determine most of its applications. Iridium and especially iridium–platinum alloys or osmium–iridium alloys have a low wear and are used, for example, for multi-pored spinnerets, through which a plastic polymer melt is extruded to form fibers, such as rayon.[55] Sony VAIO VGN-FW140D Battery

Osmium–iridium is used for compass bearings and for balances.[10]

Corrosion and heat resistance makes iridium an important alloying agent. Certain long-life aircraft engine parts are made of an iridium alloy and an iridium–titanium alloy is used for deep-water pipes because of its corrosion resistance.[10] Sony VAIO VGN-FW140E Battery

Iridium is also used as a hardening agent in platinum alloys. The Vickers hardness of pure platinum is 56 HV while platinum with 50% of iridium can reach over 500 HV.[56][57]

Devices that must withstand extremely high temperatures are often made from iridium. Sony VAIO VGN-FW140E/H Battery

For example, high-temperature cruciblesmade of iridium are used in the Czochralski process to produce oxide single-crystals (such as sapphires) for use in computer memory devices and in solid state lasers.[58][59] The crystals, such as gadolinium gallium garnet and yttrium gallium garnet, are grown by melting pre-sintered charges of mixed oxides under oxidizing conditions at temperatures up to 2100 °C.[4] Sony VAIO VGN-FW140E/W Battery

Its resistance to arc erosion makes iridium alloys ideal for electrical contacts for spark plugs.[59][60]

Iridium compounds are used as catalysts in the Cativa process for carbonylation of methanol to produce acetic acid.[61] Iridium itself is used as a catalyst in a type of automobile engine introduced in 1996 called the direct-ignition engine.[10] Sony VAIO VGN-FW140FE Battery

The radioisotope iridium-192 is one of the two most important sources of energy for use in industrial ?-radiography for non-destructive testing of metals.[62][63]Additionally, 192Ir is used as a source of gamma radiation for the treatment of cancer using brachytherapy, a form of radiotherapy where a sealed radioactive source is placed inside or next to the area requiring treatment. Sony VAIO VGN-FW140N Battery

Specific treatments include high dose rate prostate brachytherapy, bilary duct brachytherapy, and intracavitary cervix brachytherapy.[10]

Scientific

An alloy of 90% platinum and 10% iridium was used in 1889 to construct the International Prototype Meter and kilogram mass, kept by the International Bureau of Weights and Measures near Paris.[10] Sony VAIO VGN-FW140N/W Battery

The meter bar was replaced as the definition of the fundamental unit of length in 1960 by a line in the atomic spectrum of krypton,[note 4][64] but the kilogram prototype is still the international standard of mass.[65]

Iridium has been used in the radioisotope thermoelectric generators of unmanned spacecraft such as the Voyager, Viking, Pioneer,Cassini, Galileo, and New Horizons. Sony VAIO VGN-FW145E Battery

Iridium was chosen to encapsulate the plutonium-238 fuel in the generator because it can withstand the operating temperatures of up to 2000 °C and for its great strength.[4]

Another use concerns X-ray optics, especially X-ray telescopes.[66] The mirrors of the Chandra X-ray Observatory are coated with a layer of iridium 60 nm thick. Sony VAIO VGN-FW145E/W Battery

Iridium proved to be the best choice for reflecting X-rays after nickel, gold, and platinum were also tested. The iridium layer, which had to be smooth to within a few atoms, was applied by depositing iridium vapor under high vacuumon a base layer of chromium.[67] Sony VAIO VGN-FW160AE Battery

Iridium is used in particle physics for the production of antiprotons, a form of antimatter. Antiprotons are made by shooting a high-intensity proton beam at aconversion target, which needs to be made from a very high density material. Although tungsten may be used instead, iridium has the advantage of better stability under the shock waves induced by the temperature rise due to the incident beam.[68] Sony VAIO VGN-FW160D Battery

Carbon–hydrogen bond activation (C–H activation) is an area of research on reactions that cleave carbon–hydrogen bonds, which were traditionally regarded as unreactive. The first reported successes at activating C–H bonds in saturated hydrocarbons, published in 1982, used organometallic iridium complexes that undergo an oxidative addition with the hydrocarbon.[69][70] Sony VAIO VGN-FW160E Battery

Iridium complexes are being investigated as catalysts for asymmetric hydrogenation. These catalysts have been used in the synthesis of natural products and able to hydrogenate certain difficult substrates, such as unfunctionalized alkenes, enantioselectively (generating only one of the two possible enantiomers).[71][72]

Iridium forms a variety of complexes of fundamental interest in triplet harvesting.[73][74][75] Sony VAIO VGN-FW160E/H Battery

Historical

Iridium–osmium alloys were used to tip fountain pen nibs. The first major use of iridium was in 1834 in nibs mounted on gold.[4]Since 1944, the famous Parker 51 fountain pen was fitted with a nib tipped by a ruthenium and iridium alloy (with 3.8% iridium). Sony VAIO VGN-FW160F/E Battery

The tip material in modern fountain pens is still conventionally called "iridium," although there is seldom any iridium in it; other metals such as tungsten have taken its place.[76]

An iridium–platinum alloy was used for the touch holes or vent pieces of cannon. Sony VAIO VGN-FW170J/H Battery

According to a report of the Paris Exhibition of 1867, one of the pieces being exhibited by Johnson and Matthey "has been used in a Withworth gun for more than 3000 rounds, and scarcely shows signs of wear yet. Those who know the constant trouble and expense which are occasioned by the wearing of the vent-pieces of cannon when in active service, will appreciate this important adaptation".[77] Sony VAIO VGN-FW180AE Battery

The pigment iridium black, which consists of very finely divided iridium, is used for painting porcelain an intense black; it was said that "all other porcelain black colors appear grey by the side of it".[78]

Precautions

Iridium in bulk metallic form is not biologically important or hazardous to health due to its lack of reactivity with tissues; Sony VAIO VGN-FW180D Battery

there are only about 20 parts per trillion of iridium in human tissue.[10] However, finely divided iridium powder can be hazardous to handle, as it is an irritant and may ignite in air.[40] Very little is known about the toxicity of iridium compounds because they are used in very small amounts, but soluble salts, such as the iridium halides, could be hazardous due to elements other than iridium or due to iridium itself.[23] Sony VAIO VGN-FW180E Battery

However, most iridium compounds are insoluble, which makes absorption into the body difficult.[10]

A radioisotope of iridium, 192Ir, is dangerous like other radioactive isotopes. The only reported injuries related to iridium concern accidental exposure to radiation from 192Ir used in brachytherapy.[23] Sony VAIO VGN-FW180E/H Battery

High-energy gamma radiation from 192Ir can increase the risk of cancer. External exposure can cause burns, radiation poisoning, and death. Ingestion of 192Ir can burn the linings of the stomach and the intestines.[79] 192Ir, 192mIr, and 194mIr tend to deposit in the liver, and can pose health hazards from both gamma and beta radiation. Sony VAIO VGN-FW180FU Battery

Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River."[1]It is a dense, malleable, ductile, precious, gray-white transition metal. Sony VAIO VGN-FW190EBH Battery

Even though it has six naturally occurring isotopes, platinum is one of the rarest elements in the Earth's crust and has an average abundance of approximately 0.005 mg/kg. It is the least reactive metal. It occurs in some nickeland copper ores along with some native deposits, mostly in South Africa, which accounts for 80% of the world production. Sony VAIO VGN-FW190ECH Battery

As a member of the platinum group of elements, as well as of the group 10 of the periodic table of elements, platinum is generally non-reactive. It exhibits a remarkable resistance to corrosion, even at high temperatures, and as such is considered a noble metal. As a result, platinum is often found chemically uncombined as native platinum. Sony VAIO VGN-FW190EDH Battery

Because it occurs naturally in the alluvial sands of various rivers, it was first used by pre-Columbian South American natives to produce artifacts. It was referenced in European writings as early as 16th century, but it was not until Antonio de Ulloa published a report on a new metal of Colombian origin in 1748 that it became investigated by scientists. Sony VAIO VGN-FW190NAH Battery

Platinum is used in catalytic converters, laboratory equipment, electrical contacts and electrodes, platinum resistance thermometers, dentistry equipment, and jewelry. Because only a few hundred tonnes are produced annually, it is a scarce material, and is highly valuable and is a major precious metal commodity. Sony VAIO VGN-FW190NBH Battery

Being a heavy metal, it leads to health issues upon exposure to its salts, but due to its corrosion resistance, it is not as toxic as some metals. Its compounds, most notablycisplatin, are applied in chemotherapy against certain types of cancer.[2]

Physical

As a pure metal, platinum is silvery-white, lustrous, ductile, and malleable.[ Sony VAIO VGN-FW190NCH Battery

Platinum is more ductile than gold, silver and copper, thus being the most ductile of pure metals, but gold is still more malleable than platinum [4] [5] It does not oxidize at any temperature, although it is corroded by halogens, cyanides, sulfur, and caustic alkalis. Platinum is insoluble in hydrochloricand nitric acid, but dissolves in aqua regia to form chloroplatinic acid, H2PtCl6.[6] Sony VAIO VGN-FW190NDH Battery

Platinum's resistance to wear and tarnish is well suited for making fine jewelry. The metal has an excellent resistance to corrosion and high temperature and has stable electrical properties. All of these characteristics have been used for industrial applications.[7]

Chemical

The most common oxidation states of platinum are +2 and +4. Sony VAIO VGN-FW190NEH Battery

The +1 and +3 oxidation states are less common, and are often stabilized by metal bonding in bimetallic (or polymetallic) species. As is expected, tetracoordinate platinum(II) compounds tend to adopt 16-electronsquare planar geometries. While elemental platinum is generally unreactive, it dissolves in aqua regia to give soluble hexachloroplatinic acid ("H2PtCl6", formally (H3O)2PtCl6·nH2O ):[8]Sony VAIO VGN-FW198U/H Battery

Pt + 4 HNO3 + 6 HCl ? H2PtCl6 + 4 NO2 + 4 H2O

As a soft acid, platinum has a great affinity for sulfur, such as on dimethyl sulfoxide(DMSO); numerous DMSO complexes have been reported and care should be taken in the choice of reaction solvent.[9] Sony VAIO VGN-FW260J/B Battery

Platinum has six naturally occurring isotopes: 190Pt, 192Pt, 194Pt, 195Pt, 196Pt, and 198Pt. The most abundant of these is195Pt, comprising 33.83% of all platinum. It is the only stable isotope with a non-zero spin; with a spin of 1/2, 195Pt satellite peaks are often observed in 1H and 31P NMR spectroscopy (i.e. Pt-phosphine and Pt-alkyl complexes). Sony VAIO VGN-FW280J/H Battery

190Pt is the least abundant at only 0.01%. Of the naturally occurring isotopes, only 190Pt is unstable, though it decays with a half-life of 6.5×1011 years. 198Pt undergoes alpha decay, but because its half-life is estimated at longer than 3.2×1014 years, it is considered stable. Sony VAIO VGN-FW290JRB Battery

Platinum also has 31 synthetic isotopes ranging in atomic mass from 166 to 202, making the total number of known isotopes 37. The least stable of these is 166Pt with a half-life of 300 µs, while the most stable is 193Pt with a half-life of 50 years. Most platinum isotopes decay by some combination of beta decay and alpha decay. 188Pt, 191Pt, and 193Pt decay primarily by electron capture. 190Pt and 198Pt have double beta decay paths.[10] Sony VAIO VGN-FW290JTB Battery

Occurrence

Platinum is an extremely rare metal,[11] occurring at a concentration of only 0.005 ppm in the Earth's crust.[12][13] It is sometimes mistaken for silver (Ag). Platinum is often found chemically uncombined as native platinum and alloyed with iridium as platiniridium. Sony VAIO VGN-FW290JTH Battery

Most often the native platinum is found in secondary deposits; platinum is combined with the other platinum group metals in alluvial deposits. The alluvial deposits used by pre-Columbian people in the Chocó Department, Colombia are still a source for platinum group metals. Another large alluvial deposit is in the Ural Mountains, Russia, and it is still mined.[6] Sony VAIO VGN-FW290JTW Battery

In nickel and copper deposits, platinum group metals occur as sulfides (e.g., (Pt,Pd)S),tellurides (e.g., PtBiTe), antimonides (PdSb), and arsenides (e.g., PtAs2), and as end alloys with nickel or copper. Platinum arsenide, sperrylite (PtAs2), is a major source of platinum associated with nickel ores in the Sudbury Basin deposit in Ontario, Canada. Sony VAIO VGN-FW355J/H Battery

AtPlatinum, Alaska, about 545,000 troy ounces had been mined between 1927 and 1975. The mine ceased operations in 1990.[14]The rare sulfide mineral cooperite, (Pt,Pd,Ni)S, contains platinum along with palladium and nickel. Cooperite occurs in theMerensky Reef within the Bushveld complex, Gauteng, South Africa.[15] Sony VAIO VGN-FW373J/B Battery

In 1865, chromites were identified in the Bushveld region of South Africa, followed by the discovery of platinum in 1906.[16]The largest known primary reserves are in the Bushveld complex in South Africa.[17] The large copper–nickel deposits nearNorilskin Russia, and the Sudbury Basin, Canada, are the two other large deposits. Sony VAIO VGN-FW30B Battery

In the Sudbury Basin, the huge quantities of nickel ore processed make up for the fact platinum is present as only 0.5 ppm in the ore. Smaller reserves can be found in the United States,[17]for example in the Absaroka Range in Montana.[18] In 2009, South Africa was the top producer of platinum, with an almost 80% share, followed by Russia at 11%.[19] Sony VAIO VGN-FW50B Battery

In 2010 July its been announced that Platinum is present in the state of Tamil nadu, India[20] and a MOU has been signed between Geological Survey of India with TAMIN - Tamilnadu Minerals Ltd.[21]

Platinum exists in higher abundances on the Moon and in meteorites. Sony VAIO VGN-FW51B/W Battery

Correspondingly, platinum is found in slightly higher abundances at sites of bolide impact on the Earth that are associated with resulting post-impact volcanism, and can be mined economically; the Sudbury Basin is one such example.[22] Sony VAIO VGN-FW51MF Battery

Compounds

Hexachloroplatinic acid mentioned above is probably the most important platinum compound, as it serves as the precursor for many other platinum compounds. By itself, it has various applications in photography, zinc etchings, indelible ink, plating, mirrors, porcelain coloring, and as a catalyst.[23] Sony VAIO VGN-FW51MF/H Battery

Treatment of hexachloroplatinic acid with an ammonium salt, such as ammonium chloride, gives ammonium hexachloroplatinate,[8]which is relatively insoluble in ammonium solutions. Heating this ammonium salt in the presence of hydrogen reduces it to elemental platinum. Sony VAIO VGN-FW51ZF Battery

Potassium hexachloroplatinate is similarly insoluble, and hexachloroplatinic acid has been used in the determination of potassium ions by gravimetry.[24]

When hexachloroplatinic acid is heated, it decomposes through platinum(IV) chloride and platinum(II) chloride to elemental platinum, although the reactions do not occur stepwise:[25] Sony VAIO VGN-FW51ZF/H Battery

(H3O)2PtCl6·nH2O   PtCl4 + 2 HCl + (n + 2) H2O

PtCl4 PtCl2 + Cl2

PtCl2 Pt + Cl2

All three reactions are reversible. Platinum(II) and platinum(IV) bromides are known as well. Platinum hexafluoride is a strong oxidizer capable of oxidizing oxygen. Sony VAIO VGN-FW52JB Battery

Oxides

Platinum(IV) oxide, PtO2, also known as Adams' catalyst, is a black powder which is soluble in KOH solutions and concentrated acids.[26] PtO2 and the less common PtO both decompose upon heating.[3] Platinum(II,IV) oxide, Pt3O4, is formed in the following reaction: Sony VAIO VGN-FW54FB Battery

2 Pt2+ + Pt4+ + 4 O2? ? Pt3O4

Platinum also forms a trioxide, where it is present in the +4 oxidation state.

Other compounds

Unlike palladium acetate, platinum(II) acetate is not commercially available. Where a base is desired, the halides have been used in conjunction with sodium acetate.[9] The use of platinum(II) acetylacetonate has also been reported.[27] Sony VAIO VGN-FW70DB Battery

Several barium platinides have been synthesized in which platinum exhibits negative oxidation states ranging from ?1 to ?2. These include BaPt, Ba3Pt2, andBa2Pt.[28] Caesium platinide, Cs2Pt, a dark-red transparent crystalline compound[29] has been shown to contain Pt2?anions.[30] Sony VAIO VGN-FW71DB/W Battery

Platinum also exhibits negative oxidation states at surfaces reduced electrochemically.[31] The negative oxidation states exhibited by platinum are unusual for metallic elements, and they are attributed to the relativistic stabilization of the 6s orbitals.[30]

Zeise's salt, containing an ethylene ligand, was one of the first organometallic compounds discovered. Sony VAIO VGN-FW72JGB Battery

Dichloro(cycloocta-1,5-diene)platinum(II) is a commercially available olefin complex, which contains easily displaceable cod ligands ("cod" being an abbreviation of 1,5-cyclooctadiene). The cod complex and the halides are convenient starting points to platinum chemistry.[9] Sony VAIO VGN-FW73JGB Battery

Cisplatin, or cis-diamminedichloroplatinum(II) is the first of a series of square planar platinum(II)-containing chemotherapy drugs, including carboplatin andoxaliplatin. These compounds are capable of crosslinking DNA, and kill cells by similar pathways to alkylating chemotherapeutic agents.[32] Sony VAIO VGN-FW74FB Battery

Platinum occurs naturally in the alluvial sands of various rivers, though there is little evidence of its use by ancient people. However, the metal was used by pre-Columbian Americans near modern-day Esmeraldas, Ecuador to produce artifacts of a white gold-platinum alloy. Sony VAIO VGN-FW81HS Battery

The first European reference to platinum appears in 1557 in the writings of the Italian humanist Julius Caesar Scaliger as a description of an unknown noble metal found between Darién and Mexico, "which no fire nor any Spanish artifice has yet been able to liquefy."[33]

In 1741, Charles Wood, a British metallurgist, found various samples of Colombian platinum in Jamaica, which he sent to William Brownrigg for further investigation. Sony VAIO VGN-FW81NS Battery

Antonio de Ulloa, also credited with the discovery of platinum, returned to Spain from the French Geodesic Mission in 1746 after having been there for eight years. His historical account of the expedition included a description of platinum as being neither separable norcalcinable. Ulloa also anticipated the discovery of platinum mines. Sony VAIO VGN-FW81S Battery

After publishing the report in 1748, Ulloa did not continue to investigate the new metal. In 1758, he was sent to superintend mercury mining operations inHuancavelica.[33]

In 1750, after studying the platinum sent to him by Wood, Brownrigg presented a detailed account of the metal to the Royal Society, mentioning that he had seen no mention of it in any previous accounts of known minerals.[34Sony VAIO VGN-FW82DS Battery

Brownrigg also made note of platinum's extremely high melting point and refractoriness towardborax. Other chemists across Europe soon began studying platinum, including Torbern Bergman, Jöns Jakob Berzelius, William Lewis, and Pierre Macquer. In 1752, Henrik Scheffer published a detailed scientific description of the metal, which he referred to as "white gold", including an account of how he succeeded in fusing platinum ore with the aid of arsenic. Sony VAIO VGN-FW82JS Battery

Scheffer described platinum as being less pliable than gold, but with similar resistance to corrosion.[33]

Carl von Sickingen researched platinum extensively in 1772. He succeeded in making malleable platinum by alloying it with gold, dissolving the alloy in aqua regia,

precipitating the platinum with ammonium chloride, igniting the ammonium chloroplatinate, and hammering the resulting finely divided platinum to make it cohere. Franz Karl Achard made the first platinum crucible in 1784. He worked with the platinum by fusing it with arsenic, then later volatilizing the arsenic.[33] Sony VAIO VGN-FW82XS Battery

Since the other platinum family members were not discovered yet (platinum was the first in the list), Scheffer and Sickingen made the false assumption that due to it's hardness -which is slightly more than for pure iron , platinum was a relatively non pliable material, even brittle at times, when in fact it's ductility and malleability are close to that of gold. Sony VAIO VGN-FW83DS Battery

Their assumptions could not be avoided since the platinum they experimented with was highly contaminated with minute amounts of the platinum family elements such as Osmium and Iridium amongst others, which embrittled the platinum alloy. Sony VAIO VGN-FW83JS Battery

Alloying this impure platinum residue called "plyoxen" with gold was the only solution at the time to obtain a pliable compound, but nowadays, very pure platinum is available and extremely long wire can be drawn from pure platinum, very easily, due to it's crystalline structure which is similar to that of many soft metals.[35] Sony VAIO VGN-FW83XS Battery

In 1786, Charles III of Spain provided a library and laboratory to Pierre-François Chabaneau to aid in his research of platinum. Chabaneau succeeded in removing various impurities from the ore, including gold, mercury, lead, copper, and iron. This led him to believe he was working with a single metal, but in truth the ore still contained the yet-undiscovered platinum group metals. Sony VAIO VGN-FW90HS Battery

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This led to inconsistent results in his experiments. At times, the platinum seemed malleable, but when it was alloyed with iridium, it would be much more brittle. Sometimes the metal was entirely incombustible, but when alloyed with osmium, it would volatilize. After several months, Chabaneau succeeded in producing 23 kilograms of pure, malleable platinum by hammering and compressing the sponge form while white-hot. Sony VAIO VGN-FW90S Battery

Chabeneau realized the infusibility of platinum would lend value to objects made of it, and so started a business with Joaquín Cabezas producing platinum ingots and utensils. This started what is known as the "platinum age" in Spain.[33]

In 2007, Gerhard Ertl won the Nobel Prize in Chemistry for determining the detailed molecular mechanisms of the catalytic oxidation of carbon monoxide over platinum (catalytic converter).[36] Sony VAIO VGN-FW91NS Battery

Production

Platinum, along with the rest of the platinum metals, is obtained commercially as a by-product from nickel and copper mining and processing. During electrorefining of copper, noble metals such as silver, gold and the platinum group metals as well as seleniumand tellurium settle to the bottom of the cell as "anode mud", which forms the starting point for the extraction of the platinum group metals. Sony VAIO VGN-FW91S Battery

If pure platinum is found in placer deposits or other ores, it is isolated from them by various methods of subtracting impurities. Because platinum is significantly denser than many of its impurities, the lighter impurities can be removed by simply floating them away in a liquid. Platinum is also nonmagnetic, while nickel and iron are both magnetic. Sony VAIO VGN-FW92DS Battery

These two impurities are thus removed by running an electromagnet over the mixture. Because platinum has a higher melting point than most other substances, many impurities can be burned or melted away without melting the platinum. Finally, platinum is resistant to hydrochloric and sulfuric acids, while other substances are readily attacked by them. Sony VAIO VGN-FW92JS Battery

Metal impurities can be removed by stirring the mixture in either of the two acids and recovering the remaining platinum.[39]

One suitable method for purification for the raw platinum, which contains platinum, gold, and the other platinum group metals, is to process it with aqua regia, in which palladium, Sony VAIO VGN-FW93DS Battery

gold and platinum are dissolved, while osmium, iridium, ruthenium and rhodium stay unreacted. The gold is precipitated by the addition of iron(III) chloride and after filtering off the gold, the platinum is precipitated as ammonium chloroplatinate by the addition of ammonium chloride. Ammonium chloroplatinate can be converted to the metal by heating.[40] Sony VAIO VGN-FW93JS Battery

Applications

Of the 239 tonnes of platinum sold in 2006, 130 tonnes were used for vehicle emissions control devices, 49 tonnes for jewelry, 13.3 tonnes in electronics, and 11.2 tonnes in the chemical industry as a catalyst. The remaining 35.5 tonnes went to various other minor applications, such as electrodes, anticancer drugs, oxygen sensors, spark plugs and turbine engines.[41] Sony VAIO VGN-FW93XS Battery

Catalysis

The most common use of platinum is as a catalyst in chemical reactions, many times as platinum black. It has been employed in this application since the early 19th century, when platinum powder was used to catalyze the ignition of hydrogen. Sony VAIO VGN-FW94FS Battery

Its most important application is in automobiles as a catalytic converter, which allows the complete combustion of low concentrations of unburned hydrocarbons from the exhaust into carbon dioxide and water vapor. Platinum is also used in the petroleum industry as a catalyst in a number of separate processes, Sony VAIO VGN-FW94GS Battery

but especially in catalytic reforming of straight run naphthas into higher-octane gasoline which becomes rich in aromatic compounds. PtO2, also known as Adams' catalyst, is used as a hydrogenation catalyst, specifically for vegetable oils.[23] Platinum metal also strongly catalyzes the decomposition of hydrogen peroxide into water and oxygen gas.[42] Sony VAIO VGN-FW94HS Battery

Standard

From 1889 to 1960, the meter was defined as the length of a platinum-iridium (90:10) alloy bar, known as the International Prototype Meter bar. The previous bar was made of platinum in 1799. The International Prototype Kilogram remains defined by a cylinder of the same platinum-iridium alloy made in 1879.[43] Sony VAIO VGN-G118CN Battery

The standard hydrogen electrode also uses a platinized platinum electrode due to its corrosion resistance, and other attributes.[44]

Precious metal

Platinum is a precious metal commodity; its bullion has the ISO currency code of XPT. Coins, bars, and ingots are traded or collected. Sony VAIO VGN-G118GN/B Battery

Platinum finds use in jewelry, usually as a 90–95% alloy, due to its inertness and shine. Jewelry trade publications advise jewelers to present minute surface scratches (which they term patina) as a desirable feature.[45][46]

In watchmaking, Vacheron Constantin, Patek Philippe, Rolex, Breitling, and other companies use platinum for producing their limited edition watch series. Sony VAIO VGN-G118GN/T Battery

Watchmakers appreciate the unique properties of platinum, as it neither tarnishes nor wears out (relative to gold).[47]

Average price of platinum from 1991 to 2007 in US$ per troy ounce(~$20/g)[48]

The price of platinum, like other industrial commodities, is more volatile than that of gold. Sony VAIO VGN-G118TN/B Battery

In 2008, the price of platinum dropped from $2,252 to $774 per oz,[49] a loss of nearly 2/3 of its value. By contrast, the price of gold dropped from ~$1,000 to ~$700/ozt during the same time frame, a loss of only 1/3 of its value.

During periods of sustained economic stability and growth, the price of platinum tends to be as much as twice the price of gold, Sony VAIO VGN-G118TN/S Battery

whereas during periods of economic uncertainty,[50] the price of platinum tends to decrease due to reduced industrial demand, falling below the price of gold. Gold prices are more stable in slow economic times, as gold is considered a safe haven and gold demand is not driven by industrial uses. In the 18th century, platinum's rarity made King Louis XV of France declare it the only metal fit for a king.[51] Sony VAIO VGN-G11VN/T Battery

Other uses

In the laboratory, platinum wire is used for electrodes; platinum pans and supports are used in thermogravimetric analysisbecause of the stringent requirements of chemical inertness upon heating to high temperatures (~1000 °C). Sony VAIO VGN-G11VN/TC Battery

Platinum is used as an alloying agent for various metal products, including fine wires, noncorrosive laboratory containers, medical instruments, dental prostheses, electrical contacts, and thermocouples. Platinum-cobalt, an alloy of roughly three parts platinum and one part cobalt, is used to make relatively strong permanent magnets.[23] Sony VAIO VGN-G11XN/B Battery

Platinum-based anodes are used in ships, pipelines, and steel piers.[6]

Symbol of prestige

Platinum's rarity as a metal has caused advertisers to associate it with exclusivity and wealth. "Platinum" debit cards have greater privileges than do "gold" ones.[52] Sony VAIO VGN-G1AAPS Battery

"Platinum awards" are the second highest possible, ranking above "gold"

, "silver" and "bronze", but below diamond. For example, in the United States, a musical album that has sold more than 1 million copies, will be credited as "platinum", whereas an album that sold more than 10 million copies will be certified as "diamond".[53] Sony VAIO VGN-G1AAPSA Battery

Some products, such as blenders and vehicles, with a silvery-white color are identified as "platinum". Platinum is considered a precious metal, although its use is not as common as the use of gold or silver. The frame of the Crown of Queen Elizabeth the Queen Mother, manufactured for her coronation as Consort of King George VI, is made of platinum. It was the first British crown to be made of this particular metal.[54] Sony VAIO VGN-G1AAPSB Battery

Health issues

According to the Centers for Disease Control and Prevention, short-term exposure to platinum salts may cause irritation of the eyes, nose, and throat, and long-term exposure may cause both respiratory and skin allergies. The current OSHA standard is 2 micrograms per cubic meter of air averaged over an 8-hour work shift.[55] Sony VAIO VGN-G1AAPSC Battery

Certain platinum complexes are used in chemotherapy, and show good activity against some tumors. Cisplatin is particularly effective against testicular cancer; the cure rate was improved from 10% to 85%.[56] However, the side effects are severe. Cisplatin causes cumulative, irreversible kidney damage and deafness.[57] Sony VAIO VGN-G1ABNS Battery

As with other ototoxic agents, deafness may be secondary to interactions with melanin in the stria vascularis. Binding of platinum to RNA has been reviewed.Sony VAIO VGN-G1KBN Battery

As platinum is a catalyst in the manufacture of the silicone rubber and gel components of several types of medical implants (breast implants, joint replacement prosthetics, artificial lumbar discs, vascular access ports, etc.), the possibility platinum could enter the body and cause adverse effects has merited study. Sony VAIO VGN-G1KAP Battery

TheFood and Drug Administration and other institutions have reviewed the issue and found no evidence to suggest toxicity in vivo.Sony VAIO VGN-G1KBNA Battery,Sony VAIO VGN-G1LAP Battery,Sony VAIO VGN-G1LBN Battery,Sony VAIO VGN-G218LN/T Battery,Sony VAIO VGN-G218N/B Battery

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