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16 décembre 2011 5 16 /12 /décembre /2011 02:10

Niobiumor columbium, is a chemical element with the symbol Nband atomic number 41. It's a soft, grey, ductile transition metal, which is often found in the pyrochlore mineral, the main commercial source for niobium, and columbite. The name comes from Greek mythology: Niobe, daughter of Tantalus.Sony VGP-BPL18 Battery

Niobium has physical and chemical properties similar to those of the element tantalum, and the two are therefore difficult to distinguish. The English chemist Charles Hatchett reported a new element similar to tantalum in 1801, and named it columbium. In 1809, the English chemist William Hyde Wollaston wrongly concluded that tantalum and columbium were identical.Sony VGP-BPS18 Battery

The German chemist Heinrich Rose determined in 1846 that tantalum ores contain a second element, which he named niobium. In 1864 and 1865, a series of scientific findings clarified that niobium and columbium were the same element (as distinguished from tantalum), and for a century both names were used interchangeably.Sony VGP-BPL20 Battery

The name of the element was officially adopted as niobium in 1949.

It was not until the early 20th century that niobium was first used commercially. Brazil is the leading producer of niobium and ferroniobium, an alloy of niobium and iron. Niobium is used mostly in alloys, the largest part in special steel such as that used in gas pipelines.Sony VGP-BPS20/B Battery

Although alloys contain only a maximum of 0.1%, that small percentage of niobium improves the strength of the steel. The temperature stability of niobium-containing superalloys is important for its use in jet and rocket engines. Niobium is used in various superconducting materials.Sony VGP-BPS20/S Battery

These superconducting alloys, also containing titanium andtin, are widely used in the superconducting magnets of MRI scanners. Other applications of niobium include its use in welding, nuclear industries, electronics, optics, numismatics and jewelry. In the last two applications, niobium's low toxicity and ability to be colored by anodization are particular advantages.Sony VGP-BPL21 Battery

Niobium was discovered by the English chemist Charles Hatchett in 1801.[1]He found a new element in a mineral sample that had been sent to England from Massachusetts, United States in 1734 by a John Winthrop,[2]and named the mineral columbiteand the new element columbiumafter Columbia, the poetical name for America.Sony VGP-BPS21 Battery

The columbiumdiscovered by Hatchett was probably a mixture of the new element with tantalum.

Subsequently, there was considerable confusion[4]over the difference between columbium (niobium) and the closely related tantalum.Sony VGP-BPS21/S Battery

In 1809, the English chemist William Hyde Wollaston compared the oxides derived from both columbium—columbite, with a density 5.918 g/cm3, and tantalum—tantalite, with a density over 8 g/cm3, and concluded that the two oxides, despite the significant difference in density, were identical; thus he kept the name tantalum.Sony VGP-BPS21A Battery

This conclusion was disputed in 1846 by the German chemist Heinrich Rose, who argued that there were two different elements in the tantalite sample, and named them after children of Tantalus: niobium(from Niobe), and pelopium(from Pelops).[5][6]This confusion arose from the minimal observed differences between tantalum and niobium.Sony VGP-BPS21A/B Battery

The claimed new elements pelopium, ilmeniumanddianium[7]were in fact identical to niobium or mixtures of niobium and tantalum.[8]

The differences between tantalum and niobium were unequivocally demonstrated in 1864 by Christian Wilhelm Blomstrand,and Henri Etienne Sainte-Claire Deville,Sony VGP-BPS21B Battery

as well as Louis J. Troost, who determined the formulas of some of the compounds in 1865[8][9]and finally by the Swiss chemist Jean Charles Galissard de Marignac[10]in 1866, who all proved that there were only two elements. Articles on ilmeniumcontinued to appear until 1871.Sony VGP-BPL22 Battery

De Marignac was the first to prepare the metal in 1864, when he reduced niobium chloride by heating it in an atmosphere of hydrogen.Although de Marignac was able to produce tantalum-free niobium on a larger scale by 1866, it was not until the early 20th century that niobium was first used commercially, inincandescent lamp filaments.Sony VGP-BPS22 Battery

This use quickly became obsolete through the replacement of niobium withtungsten, which has a higher melting point and thus is preferable for use in incandescent lamps. The discovery that niobium improves the strength of steel was made in the 1920s, and this application remains its predominant use.Sony VGP-BPS22/A Battery

In 1961 the American physicist Eugene Kunzler and coworkers at Bell Labsdiscovered that niobium-tin continues to exhibit superconductivity in the presence of strong electric currents and magnetic fields,making it the first material to support the high currents and fields necessary for useful high-power magnets and electrically powered machinery.Sony VGP-BPS22A Battery

This discovery would allow — two decades later — the production of long multi-strand cables that could be wound into coils to create large, powerful electromagnets for rotating machinery, particle accelerators, or particle detectors.

Naming of the element

Columbium(symbol Cb ) was the name originally given to this element by Hatchett,Sony VGP-BPL23 Battery

and this name remained in use in American journals—the last paper published by American Chemical Society with columbium in its title dates from 1953[17]—while niobiumwas used in Europe. To end this confusion, the name niobiumwas chosen for element 41 at the 15th Conference of the Union of Chemistry in Amsterdam in 1949.Sony VGP-BPS23 Battery

A year later this name was officially adopted by the International Union of Pure and Applied Chemistry (IUPAC) after 100 years of controversy, despite the chronological precedence of the name Columbium.[18]The latter name is still sometimes used in US industry.Sony VGP-BPS23/B Battery

This was a compromise of sorts; the IUPAC accepted tungsteninstead of wolfram, in deference to North American usage; and niobium instead of columbium, in deference to European usage. Not everyone agreed, and while many leading chemical societies and government organizations refer to it by the official IUPAC name, many leading metallurgists, metal societies, and the United States Geological Survey still refer to the metal by the original "columbium".Sony VGP-BPS23/D Battery

Physical

Niobium is a lustrous, grey, ductile, paramagnetic metal in group 5 of the periodic table (see table), although it has an atypical configuration in its outermost electron shells compared to the rest of the members. (This can be observed in the neighborhood of ruthenium (44), rhodium (45), and palladium (46).)Sony VGP-BPS23/G Battery

Niobium becomes a superconductor at cryogenic temperatures. At atmospheric pressure, it has the highest critical temperature of the elemental superconductors: 9.2 K.[22]Niobium has the largest magnetic penetration depth of any element.Sony VGP-BPS23/P Battery

In addition, it is one of the three elemental Type II superconductors, along with vanadium andtechnetium. The superconductive properties are strongly dependent on the purity of the niobium metal.[23]When very pure, it is comparatively soft and ductile, but impurities make it harder.Sony VGP-BPS23/W Battery

The metal has a low capture cross-section for thermal neutrons;[25]thus it is used in the nuclear industries.[26]

Chemical

The metal takes on a bluish tinge when exposed to air at room temperature for extended periods.[27]Despite presenting a high melting point in elemental form (2,468 °C), it has a low density in comparison to other refractory metals.Sony Limited Edition 007 Battery

Furthermore, it is corrosion resistant, exhibits superconductivity properties, and forms dielectric oxide layers.

Niobium is slightly less electropositive and more compact than its predecessor in the periodic table, zirconium, whereas it is virtually identical in size to the heavier tantalum atoms, owing to the lanthanide contraction.Sony VAIO VGC-LB15 Battery

As a result, niobium's chemical properties are very similar to those for tantalum, which appears directly below niobium in the periodic table.Although its corrosion resistance is not as outstanding as that of tantalum, its lower price and greater availability make niobium attractive for less demanding uses such as linings in chemical plants.Sony VGN-AR Series Battery

Naturally occurring niobium is composed of one stable isotope, 93Nb.As of 2003, at least 32 radioisotopes have also been synthesized, ranging in atomic massfrom 81 to 113. The most stable of these is 92Nb with a half-life of 34.7 million years. One of the least stable is 113Nb, with an estimated half-life of 30 milliseconds.Sony VGN-CR Series Battery

Isotopes that are lighter than the stable 93Nb tend to decay by ?+decay, and those that are heavier tend to decay by ?-decay, with some exceptions. 81Nb, 82Nb, and 84Nb have minor ?+delayed proton emission decay paths, 91Nb decays by electron capture and positron emission, and 92Nb decays by both ?+and ?-decay.Sony VIAO VGN-G Series Battery

At least 25 nuclear isomers have been described, ranging in atomic mass from 84 to 104. Within this range, only 96Nb, 101Nb, and 103Nb do not have isomers. The most stable of niobium's isomers is 93mNb with a half-life of 16.13 years. The least stable isomer is 84mNb with a half-life of 103 ns.Sony VIAO VGN-G118 Battery

All of niobium's isomers decay byisomeric transition or beta decay except 92m1Nb, which has a minor electron capture decay chain.[28]

Occurrence

Niobium is estimated to be 33rd on the list of the most common elements in the Earth’s crust with 20 ppm.[Sony VIAO VGN-G118CN/B Battery

Some think that the abundance on Earth should be much greater, but that the “missing” niobium may be located in the Earth’s core due to the metal's high density.The free element is not found in nature, but it does occur in minerals.Minerals that contain niobium often also contain tantalum, such as columbite ((Fe,Mn)(Nb,Ta)2O6) and columbite-tantalite (or coltan, (Fe,Mn)(Ta,Nb)2O6).Sony VIAO VGN-G118CN/T Battery

Columbite-tantalite minerals are most usually found as accessory minerals in pegmatite intrusions, and in alkaline intrusive rocks. Less common are the niobates of calcium, uranium, thorium and the rare earth elements such as pyrochlore ((Na,Ca)2Nb2O6(OH,F)) and euxenite ((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6).Sony VIAO VGN-G218 Battery

These large deposits of niobium have been found associated with carbonatites (carbonate-silicate igneous rocks) and as a constituent of pyrochlore.[31]

The two largest deposits of pyrochlore were found in the 1950s in Brazil and Canada, and both countries are still the major producers of niobium mineral concentrates.Sony VGN-TZ121 Battery

The largest deposit is hosted within a carbonatite intrusion at Araxá, Minas Gerais Brazil, owned by CBMM (Companhia Brasileira de Metalurgia e Mineração); the other deposit is located at Goiás owned by Anglo American plc (through its subsidiary Mineração Catalão), also hosted within a carbonatite intrusion.Sony VGN-TZ13 Battery

Altogether these two Brazilian mines produce around 75% of world supply. The third largest producer of niobium is the carbonatite-hosted Niobec Mine,Saint-Honoré near Chicoutimi, Quebec owned by Iamgold Corporation Ltd, which produces around 7% of world supply.Sony VGN-TZ131 Battery

Extensive unexploited resources are located in Nigeria, Democratic Republic of Congo, Tanzania, Malawi, Australia, Afghanistan, Russia and Colombia.

Production

After the separation from the other minerals, the mixed oxides of tantalum Ta2O5and niobium Nb2O5are obtained. The first step in the processing is the reaction of the oxides with hydrofluoric acid:Sony VGN-TZ132N Battery

Ta2O5+ 14 HF ? 2 H2[TaF7] + 5 H2O

Nb2O5+ 10 HF ? 2 H2[NbOF5] + 3 H2O

The first industrial scale separation, developed by de Marignac, exploits the differing solubilities of the complex niobium and tantalum fluorides, dipotassium oxypentafluoroniobate monohydrate (K2[NbOF5]·H2O) and dipotassium heptafluorotantalate (K2[TaF7]) in water.Sony VGN-TZ132/N Battery

Newer processes use the liquid extraction of the fluorides from aqueoussolution by organic solvents like cyclohexanone. The complex niobium and tantalum fluorides are extracted separately from the organic solvent with water and either precipitated by the addition of potassium fluoride to produce a potassium fluoride complex, or precipitated with ammonia as the pentoxide:Sony VGN-TZ17N Battery

H2[NbOF5] + 2 KF ? K2[NbOF5]? + 2 HF

Followed by:

2 H2[NbOF5] + 10 NH4OH ? Nb2O5? + 10 NH4F + 7 H2O

Several methods are used for the reduction to metallic niobium. The electrolysis of a molten mixture of K2[NbOF5] and sodium chloride is one;Sony VGN-TZ16N Battery

the other is the reduction of the fluoride with sodium. With this method niobium with a relatively high purity can be obtained. In large scale production the reduction of Nb2O5with hydrogen or carbon is used. In the process involving the aluminothermic reaction a mixture of iron oxide and niobium oxide is reacted with aluminium:Sony VGN-TZ18N Battery

3 Nb2O5+ Fe2O3+ 12 Al ? 6 Nb + 2 Fe + 6 Al2O3

To enhance the reaction, small amounts of oxidizers like sodium nitrate are added. The result is aluminium oxide and ferroniobium, an alloy of iron and niobium used in the steel production. The ferroniobium contains between 60 and 70% of niobium.Sony VAIO VGN-AR47G/E1 Battery

Without addition of iron oxide, aluminothermic process is used for the production of niobium. Further purification is necessary to reach the grade for superconductive alloys. Electron beam melting under vacuum is the method used by the two major distributors of niobium.  Sony VAIO VGN-AR520E Battery

The United States Geological Survey estimates that the production increased from 38,700 tonnes in 2005 to 44,500 tonnes in 2006. The worldwide resources are estimated to be 4,400,000 tonnes.During the ten-year period between 1995 and 2005, the production more than doubled, starting from 17,800 tonnes in 1995.Sony VAIO VGN-AR53DB Battery

Compounds

Niobium is in many ways similar to tantalum and zirconium. It reacts with most nonmetals at high temperatures: niobium reacts with fluorine at room temperature, withchlorine and hydrogen at 200 °C, and with nitrogen at 400 °C, giving products that are frequently interstitial and nonstoichiometric.Sony VAIO VGN-AR54DB Battery

The metal begins tooxidize in air at 200 °C,  and is resistant to corrosion by fused alkalis and by acids, including aqua regia, hydrochloric, sulfuric, nitric and phosphoric acids. Niobium is attacked by hydrofluoric acid and hydrofluoric/nitric acid mixtures.Sony VAIO VGN-AR550E Battery

Although niobium exhibits all of the formal oxidation states from +5 to -1, in most commonly encountered compounds, it is found in the +5 state.[24]Characteristically, compounds in oxidation states less than 5+ display Nb-Nb bonding.

Oxides and sulfides

Niobium forms oxides with the oxidation states +5 (Nb2O5), +4 (NbO2), and +3 (Nb2O3),Sony VAIO VGN-AR55DB Battery

as well as with the rarer oxidation state +2 (NbO).[41]Most commonly encountered is the pentoxide, precursor to almost all niobium compounds and alloys. Niobates are generated by dissolving the pentoxide in basic hydroxidesolutions or by melting it in alkali metal oxides. Examples are lithium niobate (LiNbO3) and lanthanum niobate (LaNbO4).Sony VAIO VGN-AR630E Battery

In the lithium niobate is a trigonally distorted perovskite-like structure, whereas the lanthanum niobate contains lone NbO43?ions.[33]The layered niobium sulfide (NbS2) is also known.

Halides

Niobium forms halides in the oxidation states of +5 and +4 as well as diverse substoichiometric compounds.Sony VAIO VGN-AR64DB Battery

The pentahalides (NbX5) feature octahedral Nb centres. Niobium pentafluoride (NbF5) is a white solid with a melting point of 79.0 °C and niobium pentachloride (NbCl5) is yellow (see image at left) with a melting point of 203.4 °C. Both are hydrolyzed to give oxides and oxyhalides, such as NbOCl3.Sony VAIO VGN-AR65DB Battery

The pentachloride is a versatile reagent being used to generate the organometallic compounds, such asniobocene dichloride ((C5H5)2NbCl2).[43]The tetrahalides (NbX4) are dark-coloured polymers with Nb-Nb bonds, for example the blackhygroscopic niobium tetrafluoride (NbF4) and brown niobium tetrachloride (NbCl4).Sony VAIO VGN-AR660U Battery

Anionic halide compounds of niobium are well known, owing in part to the Lewis acidity of the pentahalides. The most important is [NbF7]2-, which is an intermediate in the separation of Nb and Ta from the ores. This heptafluoride tends to form the oxopentafluoride more readily than does the tantalum compound.Sony VAIO VGN-AR690U Battery

Other halide complexes include octahedral [NbCl6]-:

Nb2Cl10+ 2 Cl-? 2 [NbCl6]-

As for other early metals, a variety of reduced halide clusters are known, the premier example being [Nb6Cl18]4-.Sony VAIO VGN-AR71ZU Battery

Nitrides and carbides

Other binary compounds of niobium include the niobium nitride (NbN), which becomes a superconductor at low temperatures and is used in detectors for infrared light. The main niobium carbide is NbC, an extremely hard, refractory, ceramic material, commercially used intool bits for cutting tools.Sony VAIO VGN-AR730E/B Battery

Applications

It is estimated that out of 44,500 metric tons of niobium mined in 2006, 90% was used in the production of high-grade structural steel, followed by its use in superalloys. The use of niobium alloys for superconductors and in electronic components account only for a small share of the production.Sony VAIO VGN-AR73DB Battery

Steel production

Niobium is an effective microalloying element for steel. Adding niobium to the steel causes the formation of niobium carbide andniobium nitride within the structure of the steel. These compounds improve the grain refining, retardation of recrystallization, and precipitation hardening of the steel.Sony VAIO VGN-AR74DB Battery

These effects in turn increase the toughness, strength, formability, and weldability of the microalloyed steel.Microalloyed stainless steels have a niobium content of less than 0.1%. It is an important alloy addition to high strength low alloy steels which are widely used as structural components in modern automobiles.Sony VAIO VGN-AR75UDB Battery

These niobium-containing alloys are strong and are often used in pipeline construction.

Superalloys

Appreciable amounts of the element, either in its pure form or in the form of high-purity ferroniobium and nickel niobium,Sony VAIO VGN-AR790U/B Battery

are used in nickel-, cobalt-, and iron-based superalloys for such applications as jet engine components, gas turbines, rocket subassemblies, and heat resisting and combustion equipment. Niobium precipitates a hardening ?''-phase within the grain structure of the superalloy.Sony VAIO VGN-AR820E Battery

The alloys contain up to 6.5% niobium.  One example of a nickel-based niobium-containing superalloy is Inconel 718, which consists of roughly 50% nickel, 18.6% chromium, 18.5% iron, 5% niobium, 3.1% molybdenum, 0.9%titanium, and 0.4% aluminium.These superalloys are used, for example, in advanced air frame systems such as those used in the Gemini program.Sony VAIO VGN-AR830E Battery

An alloy used for liquid rocket thruster nozzles, such as in the main engine of the Apollo Lunar Modules, is C103, which consists of 89% niobium, 10% hafnium and 1% titanium. Another niobium alloy was used for the nozzle of the Apollo Service Module.Sony VAIO VGN-AR83S Battery

As niobium is oxidized at temperatures above 400 °C, a protective coating is necessary for these applications to prevent the alloy from becoming brittle.

Superconducting magnets

Niobium-germanium (Nb3Ge), niobium-tin (Nb3Sn), as well as the niobium-titanium alloys are used as a type II superconductor wire for superconducting magnets.Sony VAIO VGN-AR83US Battery

These superconducting magnets are used in magnetic resonance imaging and nuclear magnetic resonance instruments as well as in particle accelerators.For example, the Large Hadron Collider uses 600 tons of superconducting strands, while the International Thermonuclear Experimental Reactor is estimated to use 600 tonnes of Nb3Sn strands and 250 tonnes of NbTi strands.Sony VAIO VGN-AR84S Battery

In 1992 alone, niobium-titanium wires were used to construct more than US$1 billion worth of clinical magnetic resonance imaging systems.

Superconducting, other

The Superconducting Radio Frequency (RF) cavities used in the free electron lasers TESLA and XFEL are made from pure niobium.Sony VAIO VGN-AR84US Battery

The high sensitivity of superconducting niobium nitride bolometers make them an ideal detector for electromagnetic radiation in the THz frequency band. These detectors were tested at the Heinrich Hertz Submillimeter Telescope, the South Pole Telescope, theReceiver Lab Telescope, and at APEX and are now used in the HIFI instrument on board the Herschel Space Observatory.Sony VAIO VGN-AR85S Battery

Electroceramics

Lithium niobate, which is a ferroelectric, is used extensively in mobile telephones and optical modulators, and for the manufacture of surface acoustic wave devices. It belongs to the ABO3structure ferroelectrics like lithium tantalate and barium titanate.Sony VAIO VGN-AR85US Battery

Niobium was evaluated as a cheaper alternative to tantalum incapacitors, but tantalum capacitors are still predominant. Niobium is added to glass in order to attain a higher refractive index, a property of use to the optical industry in making thinner corrective glasses.Sony VAIO VGN-AR870EA Battery

Hypoallergenic applications: medicine and jewelry

Niobium and some niobium alloys are physiologically inert and thus hypoallergenic. For this reason, niobium is found in many medical devices such as pacemakers.[62]Niobium treated with sodium hydroxide forms a porous layer that aids osseointegration.Sony VAIO VGN-AR890U Battery

Along with titanium, tantalum, and aluminium, niobium can also be electrically heated and anodized, resulting in a wide array of colours using a process known as reactive metal anodizing which is useful in making jewelry. The fact that niobium is hypoallergenic also benefits its use in jewelry.Sony VAIO VGN-AR93S Battery

Numismatics

Niobium is used as a precious metal in commemorative coins, often with silver or gold. For example, Austria produced a series of silver niobium euro coins starting in 2003; the colour in these coins is created by the diffraction of light by a thin oxide layer produced by anodising.Sony VAIO VGN-AR93US Battery

In 2008, six coins are available showing a broad variety of colours in the centre of the coin: blue, green, brown, purple, violet, or yellow. Two more examples are the 2004 Austrian €25 150 Years Semmering Alpine Railway commemorative coin, and the 2006 Austrian €25 European Satellite Navigation commemorative coin.Sony VAIO VGN-AR94S Battery

Latvia produced a similar series of coins starting in 2004, with one following in 2007. In 2011, the Royal Canadian Mint started production of a $5 sterling silver and niobium coin named Hunter's Moonin which the niobium was selectively oxidized, thus creating unique finishes where no two coins are exactly alike.Sony VAIO VGN-AR94US Battery

Other

The arc-tube seals of high pressure sodium vapor lamps are made from niobium, or niobium with 1% of zirconium, because niobium has a very similar coefficient of thermal expansion to the sintered alumina arc tube ceramic, a translucent material which resists chemical attack or reduction by the hot liquid sodium and sodium vapour contained inside the operating lamp.Sony VAIO VGN-AR95S Battery

The metal is also used in arc welding rods for some stabilized grades of stainless steel.

Precautions

Niobium has no known biological role. While niobium dust is an eye and skin irritant and a potential fire hazard, elemental niobium on a larger scale is physiologically inert (and thus hypoallergenic) and harmless.Sony VAIO VGN-AR95US Battery

It is frequently used in jewelry and has been tested for use in some medical implants.

Niobium-containing compounds are rarely encountered by most people, but some are toxic and should be treated with care. The short and long term exposure to niobates and niobium chloride, two chemicals that are water soluble, have been tested in rats.Sony VAIO VGN-AW110J/H Battery

Rats treated with a single injection of niobium pentachloride or niobates show a median lethal dose (LD50) between 10 and 100 mg/kg. For oral administration the toxicity is lower; a study with rats yielded a LD50after seven days of 940 mg/kg.Sony VAIO VGN-AW11M/H Battery

Molybdenumis a Group 6 chemical element with the symbol Moand atomic number 42. The name is from Neo-Latin Molybdaenum, from Ancient Greek ???????? molybdos, meaning lead, itself proposed as a loanword from Anatolian Luvian and Lydian languages,[3]since its ores were confused with lead ores.Sony VAIO VGN-AW11S/B Battery

The free element, which is a silvery metal, has the sixth-highest melting point of any element. It readily forms hard, stable carbides, and for this reason it is often used in high-strength steel alloys. Molybdenum does not occur as a free metal on Earth, but rather in various oxidation states in minerals.Sony VAIO VGN-AW11XU/Q Battery

Industrially, molybdenum compounds are used in high-pressure and high-temperature applications, as pigments and catalysts.

Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from the mineral salts of other metals) in 1778 by Carl Wilhelm Scheele. The metal was first isolated in 1781 byPeter Jacob Hjelm.Sony VAIO VGN-AW11Z/B Battery

Most molybdenum compounds have low solubility in water, but the molybdate ion MoO42?is soluble and forms when molybdenum-containing minerals are in contact with oxygen and water.

Molybdenum-containing enzymes are used as catalysts by some bacteria to break the chemical bond in atmospheric molecularnitrogen, allowing biological nitrogen fixation.Sony VAIO VGN-AW120J/H Battery

At least 50 molybdenum-containing enzymes are now known in bacteria and animals, though only the bacterial and cyanobacterial enzymes are involved in nitrogen fixation. Owing to the diverse functions of the remainder of the enzymes, molybdenum is a required element for life in higher organisms (eukaryotes), though not in all bacteria.Sony VAIO VGN-AW150Y/H Battery

Physical properties

In its pure form, molybdenum is a silvery-white metal with a Mohs hardness of 5.5. It has a melting point of 2,623 °C(4,753 °F); of the naturally occurring elements, only tantalum, osmium, rhenium, tungsten, and carbon have higher melting points.Sony VAIO VGN-AW160J/Q Battery

Molybdenum burns only at temperatures above 600 °C (1,112 °F).[5]It has one of the lowest coefficients ofthermal expansion among commercially used metals.[6]The tensile strength of molybdenum wires increases about 3 times, from about 10 to 30 GPa, when their diameter decreases from ~50–100 nm to 10 nm.Sony VAIO VGN-AW170Y/Q Battery

There are 35 known isotopes of molybdenum, ranging in atomic mass from 83 to 117, as well as four metastable nuclear isomers. Seven isotopes occur naturally, with atomic masses of 92, 94, 95, 96, 97, 98, and 100. Of these naturally occurring isotopes, only molybdenum-100 is unstable.Sony VAIO VGN-AW180Y/Q Battery

All unstable isotopes of molybdenum decay into isotopes of niobium,technetium, and ruthenium.

Molybdenum-98 is the most abundant isotope, comprising 24.14% of all molybdenum. Molybdenum-100 has a half-life of about 1019y and undergoes double beta decay into ruthenium-100.Sony VAIO VGN-AW190JAH Battery

Molybdenum isotopes with mass numbers from 111 to 117 all have half-lives of approximately 150 ns.

As also noted below, the most common isotopic molybdenum application involves molybdenum-99, which is a fission product. It is a parent radioisotope to the short-lived gamma-emitting daughter radioisotope technetium-99m, a nuclear isomer used in various imaging applications in medicine.Sony VAIO VGN-AW190NAB Battery

In 2008, the Delft University of Technology applied for a patent on the molybdenum-98-based production of technetium-99

Compounds and chemistry

Molybdenum is a transition metal with an electronegativity of 1.8 on the Pauling scale and an atomic mass of 95.94 g/mol.Sony VAIO VGN-AW190NBB Battery

It does not visibly react with oxygen or water at room temperature, and the bulk oxidation occurs at temperatures above 790 °C, resulting inmolybdenum trioxide:

2 Mo + 3 O2? 2 MoO3

The trioxide is volatile and sublimates at high temperatures.Sony VAIO VGN-AW190NCB Battery

This prevents formation of a continuous protective oxide layer, which would stop the bulk oxidation of metal. Molybdenum has several oxidation states, the most stable being +4 and +6 (bolded in the table). The chemistry and the compounds show more similarity to those of tungsten than that of chromium.Sony VAIO VGN-AW190YAB Battery

An example is the instability of molybdenum(III) and tungsten(III) compounds as compared with the stability of the chromium(III) compounds. The highest oxidation state is common in themolybdenum(VI) oxide (MoO3), whereas the normal sulfur compound is molybdenum disulfide MoS2.Sony VAIO VGN-AW190YBB Battery

Molybdenum(VI) oxide is soluble in strong alkaline water, forming molybdates (MoO42?). Molybdates are weaker oxidants than chromates, but they show a similar tendency to form complex oxyanions by condensation at lower pH values, such as [Mo7O24]6?and [Mo8O26]4?.Sony VAIO VGN-AW190YCB Battery

Polymolybdates can incorporate other ions into their structure, forming polyoxometalates.[15]The dark-blue phosphorus-containing heteropolymolybdate P[Mo12O40]3?is used for thespectroscopic detection of phosphorus.[16]The broad range of oxidation states of molybdenum is reflected in various molybdenum chlorides:Sony VAIO VGN-AW190YDB Battery

  • Molybdenum(II) chloride MoCl2(yellow solid)
  • Molybdenum(III) chloride MoCl3(dark red solid)
  • Molybdenum(IV) chloride MoCl4(black solid)
  • Molybdenum(V) chloride MoCl5(dark green solid)
  • Molybdenum(VI) chloride MoCl6(brown solid)

The structure of the MoCl2is composed of Mo6Cl84+clusters with four chloride ions to compensate the charge.Sony VAIO VGN-AW220J/B Battery

Like chromium and some other transition metals, molybdenum is able to form quadruple bonds, such as in Mo2(CH3COO)4. This compound can be transformed into Mo2Cl84?, which also has a quadruple bond.

The oxidation state 0 is possible with carbon monoxide as ligand, such as in molybdenum hexacarbonyl, Mo(CO)6.Sony VAIO VGN-AW230J/H Battery

Molybdenite—the principal ore from which molybdenum is now extracted—was previously known as molybdena. Molybdena was confused with and often implemented as though it were graphite. Like graphite, molybdenite can be used to blacken a surface or as a solid lubricant.Sony VAIO VGN-AW235J/B Battery

Even when molybdena was distinguishable from graphite, it was still confused with a common leadore (now called galena), which took its name from Ancient Greek ???????? molybdos, meaning lead. Although apparent deliberate alloying of molybdenum with steel in one 14th-century Japanese sword (mfd. ca. 1330) has been reported,Sony VAIO VGN-AW290JFQ Battery

that art was never employed widely and was later lost. In 1754, Bengt Andersson Qvist examined molybdenite and determined that it did not contain lead and was thus not the same as galena.

It was not until 1778 that Swedish chemist Carl Wilhelm Scheele realized that molybdena was neither graphite nor lead.Sony VAIO VGN-AW41JF Battery

He and other chemists then correctly assumed that it was the ore of a distinct new element, named molybdenumfor the mineral in which it was discovered. Peter Jacob Hjelm successfully isolated molybdenum by using carbon and linseed oil in 1781.

For about a century after its isolation, molybdenum had no industrial use, owing to its relative scarcity, difficulty extracting the pure metal, and the immaturity of the metallurgical subfield.Sony VAIO VGN-AW41JF/H Battery

Early molybdenum steel alloys showed great promise in their increased hardness, but efforts were hampered by inconsistent results and a tendency toward brittleness and recrystallization. In 1906, William D. Coolidge filed a patent for rendering molybdenum ductile,Sony VAIO VGN-AW41MF Battery

leading to its use as a heating element for high-temperature furnaces and as a support for tungsten-filament light bulbs; oxide formation and degradation require that molybdenum be physically sealed or held in an inert gas. In 1913, Frank E. Elmore developed a flotation process to recover molybdenite from ores; flotation remains the primary isolation process.Sony VAIO VGN-AW41MF/H Battery

During the first World War, demand for molybdenum spiked; it was used both in armor plating and as a substitute for tungsten in high speed steels. Some British tanks were protected by 75 mm (3 in) manganese steel plating, but this proved to be ineffective.Sony VAIO VGN-AW41XH Battery

The manganese steel plates were replaced with 25 mm (1 in) molybdenum-steel plating allowing for higher speed, greater maneuverability, and better protection. After the war, demand plummeted until metallurgical advances allowed extensive development of peacetime applications.Sony VAIO VGN-AW41XH/Q Battery

In World War II, molybdenum again saw strategic importance as a substitute for tungsten in steel alloys.

Occurrence

The world's largest producers of molybdenum materials are the United States, China, Chile, Peruand Canada.Sony VAIO VGN-AW41ZF Battery

Though molybdenum is found in such minerals as wulfenite (PbMoO4) and powellite (CaMoO4), the main commercial source of molybdenum is molybdenite (MoS2). Molybdenum is mined as a principal ore, and is also recovered as a byproduct of copper and tungsten mining.Sony VAIO VGN-AW41ZF/B Battery

Large mines in Colorado (such as the Henderson mine and the now-inactiveClimax mine)  and in British Columbia yield molybdenite as their primary product, while manyporphyry copper deposits such as the Bingham Canyon Mine in Utah and the Chuquicamata mine in northern Chile produce molybdenum as a byproduct of copper mining.Sony VAIO VGN-AW50DB/H Battery

The Knaben mine in southern Norway was opened in 1885, making it the first molybdenum mine. It remained open until 1973.

Molybdenum is the 54th most abundant element in the Earth's crust and the 25th most abundant element in the oceans, with an average of 10 parts per billion; it is the 42nd most abundant element in the Universe.Sony VAIO VGN-AW51JGB Battery

The Russian Luna 24 mission discovered a molybdenum-bearing grain (1 × 0.6 µm) in a pyroxene fragment taken from Mare Crisium on the Moon.

Production

In molybdenite processing, the molybdenite is first heated to a temperature of 700 °C (1,292 °F) and the sulfide is oxidized into molybdenum(VI) oxide by air:Sony VAIO VGN-AW52JGB Battery

2 MoS2+ 7 O2? 2 MoO3+ 4 SO2

The oxidized ore is then either heated to 1,100 °C (2,010 °F) to sublimate the oxide, or leached with ammonia which reacts with the molybdenum(VI) oxide to form water-soluble molybdates:

MoO3+ 2 NH4OH ? (NH4)2(MoO4) + H2O

Copper, an impurity in molybdenite, is less soluble in ammonia. To completely remove it from the solution, it is precipitated with hydrogen sulfide.Sony VAIO VGN-AW53FB Battery

Pure molybdenum is produced by reduction of the oxide with hydrogen, while the molybdenum for steel production is reduced by the aluminothermic reaction with addition of iron to produce ferromolybdenum. A common form of ferromolybdenum contains 60% molybdenum.Sony VAIO VGN-AW70B/Q Battery

Molybdenum has a value of approximately $30,000 per tonne as of August 2009. It maintained a price at or near $10,000 per tonne from 1997 through 2003, and reached, due to increased demand, a peak of $103,000 per tonne in June 2005. In 2008 the London Metal Exchange announced that molybdenum would be traded as a commodity on the exchange.Sony VAIO VGN-AW71JB Battery

Applications

The ability of molybdenum to withstand extreme temperatures without significantly expanding or softening makes it useful in applications that involve intense heat, including the manufacture of armour, aircraft parts, electrical contacts, industrial motors and filaments.Sony VAIO VGN-AW72JB Battery

Most high-strength steel alloys (example 41xx steels) contain 0.25% to 8% molybdenum. Despite such small portions, more than 43,000 tonnes of molybdenum are used as an alloying agent each year in stainless steels, tool steels, cast irons and high-temperature superalloys.Sony VAIO VGN-AW73FB Battery

Molybdenum is also used in steel alloys for its high corrosion resistance and weldability. Molybdenum contributes further corrosion resistance to "chrome-moly" type-300 stainless steels (high-chromium steels that are corrosion-resistant already due to their chromium content) and especially so in the so-called superaustenitic stainless steels (such as alloy AL-6XN).Sony VAIO VGN-AW80NS Battery

Molybdenum acts by increasing lattice strain, thus increasing the energy required to dissolve out iron atoms from the surface.

Because of its lower density and more stable price, molybdenum is sometimes used instead of tungsten. An example is the 'M' series of high-speed steels such as M2, M4 and M42 as substitution for the 'T' steel series which contain tungsten.Sony VAIO VGN-AW80S Battery

Molybdenum can be implemented both as an alloying agent and as a flame-resistant coating for other metals. Although its melting point is 2,623 °C (4,753 °F), molybdenum rapidly oxidizes at temperatures above 760 °C (1,400 °F) making it better-suited for use in vacuum environments.Sony VAIO VGN-AW80US Battery

TZM (Mo (~99%), Ti (~0.5%), Zr (~0.08%) and some C) is a corrosion-resisting molybdenum superalloy that resists molten fluoride salts at temperatures above 1300C. It has about twice the strength of pure Mo, and is more ductile and more weldable, yet in tests it resisted corrosion of a standard eutectic salt (FLiBe) and salt vapors used in molten salt reactors for 1100 hours with so little corrosion that it was difficult to measure.Sony VAIO VGN-AW81DS Battery

Other molybdenum-based alloys which do not contain iron have only limited applications. For example, because of the corrosion resistance against molten zinc, both pure molybdenum and the molybdenum/tungsten alloy (70%/30%) are used for piping, stirrers and pump impellers which come into contact with molten zinc.Sony VAIO VGN-AW81JS Battery

Other applications as catalyst and compounds

  • Molybdenum-99 is a parent radioisotope to the daughter radioisotope technetium-99m, which is used in many medical procedures.
  • Molybdenum disulfide (MoS2) is used as a solid lubricant and a high-pressure high-temperature (HPHT) antiwear agent.Sony VAIO VGN-AW81YS Battery
  • It forms strong films on metallic surfaces and is a common additive to HPHT greases—in case of a catastrophic grease failure, thin layer of molybdenum prevents contact of the lubricated parts. It also has semiconducting properties with distinct advantages over traditional silicon or graphene in electronics applications.Sony VAIO VGN-AW82DS Battery
  • MoS2is also used as a catalyst in hydrocracking of petroleum fractions which contain nitrogen, sulfur and oxygen.
  • Molybdenum disilicide (MoSi2) is an electrically conducting ceramic with primary use in heating elements operating at temperatures above 1500 °C in air.Sony VAIO VGN-AW82JS Battery
  • Molybdenum trioxide (MoO3) is used as an adhesive between enamels and metals. Lead molybdate (wulfenite) co-precipitated with lead chromate and lead sulfate is a bright-orange pigment used with ceramics and plastics.
  • Molybdenum powder is used as a fertilizer for some plants, such as cauliflower.Sony VAIO VGN-AW82YS Battery
  • The element is also used in NO, NO2, NOxanalyzers in power plants for pollution controls. At 350 °C (662 °F) the element acts as a catalyst for NO2/NOxto form only NO molecules for consistent readings by infrared light.
  • Ammonium heptamolybdate is used in biological staining procedures.Sony VAIO VGN-AW83FS Battery

Biochemistry

The most important role of the molybdenum in living organisms is as a metal heteroatom at the active site in certain enzymes. In nitrogen fixation in certain bacteria, the nitrogenase enzyme,Sony VAIO VGN-AW83GS Battery

which is involved in the terminal step of reducing molecular nitrogen, usually contains molybdenum in the active site (though replacement of Mo with iron or vanadium is also known). The structure of the catalytic center of the enzyme

is similar to that in iron-sulfur proteins: it incorporates a Fe4S3and multiple MoFe3S3clusters.Sony VAIO VGN-AW83HS Battery

n 2008, evidence was reported that a scarcity of molybdenum in the Earth's early oceans was a limiting factor for nearly two billion years in the further evolution of eukaryotic life (which includes all plants and animals) as eukaryotes cannot fix nitrogen, and must therefore acquire most of their organic nitrogen from prokaryotic bacteria.Sony VAIO VGN-AW90NS Battery

The scarcity of molybdenum resulted from the relative lack of oxygen in the early ocean. However, once oxygen dissolved in seawater it helped dissolve molybdenum from minerals on the sea bottom, making it available to nitrogen-fixing bacteria and allowing them to provide more nitrogen for higher forms of life.Sony VAIO VGN-AW90S Battery

Although oxygen once promoted nitrogen fixation via making molybdenum available in water, it also directly poisons nitrogenase enzymes, so that historically, after oxygen arrived in large quantities in Earth's air and water, organisms which continued to fix nitrogen in aerobic conditions were required to isolate their nitrogen-fixing enzymes in heterocysts, or similar structures which protect them from too much oxygen.Sony VAIO VGN-AW90US Battery

Though molybdenum forms compounds with various organic molecules, including carbohydrates and amino acids, it is transported throughout the human body as MoO42?. At least 50 molybdenum-containing enzymes were known by 2002, mostly in bacteria, and their number is increasing with every year;Sony VAIO VGN-AW91CDS Battery

those enzymes include aldehyde oxidase, sulfite oxidase and xanthine oxidase.I some animals, and in humans, the oxidation of xanthine to uric acid, a process of purine catabolism, is catalyzed by xanthine oxidase, a molybdenum-containing enzyme.Sony VAIO VGN-AW91CJS Battery

The activity of xanthine oxidase is directly proportional to the amount of molybdenum in the body. However, an extremely high concentration of molybdenum reverses the trend and can act as an inhibitor in both purine catabolism and other processes. Molybdenum concentrations also affect protein synthesis, metabolism and growth.Sony VAIO VGN-AW91CYS Battery

In animals and plants these enzymes use molybdenum bound at the active site in a tricyclic molybdenum cofactor. All molybdenum-using enzymes so far identified in nature use this cofactor, save for the phylogenetically ancient molybdenum nitrogenases, which fix nitrogen in some bacteria and cyanobacteria.Sony VAIO VGN-AW91DS Battery

Molybdenum enzymes in plants and animals catalyze the oxidation and sometimes reduction of certain small molecules, as part of the regulation of nitrogen, sulfur and carbon cycles.

 

Z Element No. of electrons/shell
23 vanadium 2, 8, 11, 2
41 niobium 2, 8, 18, 12, 1
73 tantalum 2, 8, 18, 32, 11, 2
105 dubnium 2, 8, 18, 32, 32, 11, 2

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medical device 21/12/2011 10:45

Great post for the molybednum and its properties. The toughed stainless steel made from the meatl is widely used in making the medical devices. Thanks for the share.