Niobium is achemical element; it hassymbolNb (formerlycolumbium,Cb) andatomic number 41. It is a light grey, crystalline, andductiletransition metal. Pure niobium has aMohs hardness rating similar to puretitanium,[8] and it has similar ductility toiron. Niobium oxidizes in Earth's atmosphere very slowly, hence its application in jewelry as ahypoallergenic alternative tonickel. Niobium is often found in the mineralspyrochlore andcolumbite. Its name comes from Greek mythology:Niobe, daughter ofTantalus, the namesake oftantalum. The name reflects the great similarity between the two elements in their physical and chemical properties, which makes them difficult to distinguish.[9]
English chemistCharles Hatchett reported a new element similar to tantalum in 1801 and named it columbium. In 1809, English chemistWilliam Hyde Wollaston wrongly concluded that tantalum and columbium were identical. German chemistHeinrich 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. Niobium was officially adopted as the name of the element in 1949, but the name columbium remains in current use in metallurgy in the United States.
It was not until the early 20th century that niobium was first used commercially. Niobium is an important addition to high-strength low-alloy steels. Brazil is the leading producer of niobium andferroniobium, an alloy of 60–70% niobium with iron. Niobium is used mostly in alloys, the largest part in special steel such as that used in gas pipelines. Although these alloys contain a maximum of 0.1%, the small percentage of niobium enhances the strength of the steel by scavengingcarbide andnitride. The temperature stability of niobium-containingsuperalloys is important for its use in jet and rocket engines.
Niobium is used in varioussuperconducting materials. These alloys, also containing titanium and tin, are widely used in the superconducting magnets ofMRI scanners. Other applications of niobium include welding, nuclear industries, electronics, optics, and jewelry. In the last application, the low toxicity and iridescence produced byanodization are highly desired properties.[citation needed]
English chemistCharles Hatchett identified the elementcolumbium in 1801 within a mineral discovered in Connecticut, US.Picture of a Hellenistic sculpture representingNiobe byGiorgio Sommer
Niobium was identified by English chemist Charles Hatchett in 1801.[10][11][12] He found a new element in a mineral sample that had been sent to England from Connecticut, United States in 1734 by John WinthropFRS (grandson ofJohn Winthrop the Younger) and named the mineral "columbite"" and the new element "columbium" afterColumbia, the poetic name for the United States.[13][14][15] Thecolumbium discovered by Hatchett was probably a mixture of the new element with tantalum.[13]
Subsequently, there was considerable confusion[16] over the difference between columbium (niobium) and the closely related tantalum. In 1809, English chemistWilliam 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.[16] This conclusion was disputed in 1846 by German chemistHeinrich Rose, who argued that there were two different elements in the tantalite sample, and named them after children of Tantalus:niobium (from Niobe) andpelopium (fromPelops).[17][18] This confusion arose from the minimal observed differences between tantalum and niobium. The claimed new elementspelopium,ilmenium, anddianium[19] were in fact identical to niobium or mixtures of niobium and tantalum.[20]
Christian Wilhelm Blomstrand was the first to prepare the metal in 1866, when hereduced niobium chloride by heating it in an atmosphere of hydrogen.[24] 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 used in incandescent lamp filaments, the first commercial application.[21] This use quickly became obsolete through the replacement of niobium withtungsten, which has a higher melting point. That niobium improves the strength of steel was first discovered in the 1920s, and this application remains its predominant use.[21] In 1961, the American physicistEugene Kunzler and coworkers atBell Labs discovered thatniobium–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 electrical power machinery. This discovery enabled—two decades later—the production of long multi-strand cables wound into coils to create large, powerful electromagnets for rotating machinery, particle accelerators, and particle detectors.[25][26]
Columbium (symbol Cb)[27] was the name originally given by Hatchett upon his discovery of the metal in 1801.[11] The name reflected that the type specimen of theore came from the United States of America (Columbia).[28] This name remained in use in American journals—the last paper published byAmerican Chemical Society withcolumbium in its title dates from 1953[29]—while niobium was used in Europe. To end this confusion, the name niobium was chosen for element 41 at the 15th Conference of the Union of Chemistry in Amsterdam in 1949.[30] A year later this name was officially adopted by theInternational Union of Pure and Applied Chemistry (IUPAC) after 100 years of controversy, despite the chronological precedence of the namecolumbium.[30] This was a compromise of sorts;[30] the IUPAC accepted tungsten instead of wolfram in deference to North American usage; and niobium instead ofcolumbium in deference to European usage. While many US chemical societies and government organizations typically use the official IUPAC name, some metallurgists and metal societies still use the original American name,columbium.[31][32][33][34][excessive citations]
Niobium is a lustrous, grey, ductile,paramagnetic metal ingroup 5 of the periodic table (see table), with an electron configuration in the outermostshells atypical for group 5. Similarly atypical configurations occur in the neighborhood ofruthenium (44) andrhodium (45).[35]
Although it is thought to have abody-centered cubic crystal structure from absolute zero to its melting point, high-resolution measurements of the thermal expansion along the three crystallographic axes reveal anisotropies which are inconsistent with a cubic structure.[36][37] Therefore, further research and discovery in this area is expected.
Niobium becomes a superconductor atcryogenic temperatures. At atmospheric pressure, it has the highest critical temperature of the elemental superconductors at 9.2 K (−263.95 °C; −443.11 °F). Niobium has the greatestmagnetic penetration depth of any element.[38] 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.[39]
When very pure, it is comparatively soft and ductile, but impurities make it harder.[40]
The metal has a lowneutron capture cross-section for thermal neutrons; thus it is used in the nuclear industries where neutron transparent structures are desired.[41][42]
The metal takes on a bluish tinge when exposed to air at room temperature for extended periods.[43] Despite a high melting point in elemental form (2,468 °C (4,474 °F)), it is less dense than otherrefractory metals. Furthermore, it is corrosion-resistant, exhibits superconductivity properties, and formsdielectricoxide layers.[citation needed]
Niobium is slightly lesselectropositive and more compact than its predecessor in the periodic table, zirconium, whereas it is virtually identical in size to the heavier tantalum atoms, as a result of thelanthanide contraction.[40] As a result, niobium's chemical properties are very similar to those for tantalum, which appears directly below niobium in the periodic table.[21] Although its corrosion resistance is not as outstanding as that of tantalum, the lower price and greater availability make niobium attractive for less demanding applications, such as vat linings in chemical plants.[40]
Almost all of the niobium in Earth's crust is the one stableisotope,93Nb. The most stableradioisotope is92Nb withhalf-life 34.7 million years.92Nb, along with the next most stable one,94Nb (20,400 years), has been detected in refined samples of terrestrial niobium and may originate from bombardment bycosmic raymuons in Earth's crust.[44] Isotopes lighter than the stable93Nb tend toβ+ decay, and those that are heavier tend to β− decay, with some exceptions: β+-delayedproton emission is observed for isotopes as heavy as84Nb, and92Nb alone can decay by bothβ+ andβ− modes.[citation needed]
The most stable of isomeric state of a niobium isotope is93mNb with half-life16.12 years. The long-lived fission product93Zr decays, mainly through this isomer, to stable niobium.[citation needed]
Niobium is estimated to be the33rd most abundant element in the Earth's crust, at20 ppm.[45] Some believe that the abundance on Earth is much greater, and that the element's high density has concentrated it in Earth's core.[32] The free element is not found in nature, but niobium occurs in combination with other elements in minerals.[40] Minerals that contain niobium often also contain tantalum. Examples includeferrocolumbite ((Fe,Mn)Nb2O6) andcoltan ((Fe,Mn)(Ta,Nb)2O6).[46] Columbite–tantalite minerals (the most common species being columbite-(Fe) and tantalite-(Fe)[47][48][49]) that are most usually found as accessory minerals inpegmatite intrusions, and in alkalineintrusive rocks. Less common are the niobates ofcalcium,uranium,thorium and therare earth elements. Examples of such niobates arepyrochlores ((Na,Ca)2Nb2O6(OH,F))[50] andeuxenite ((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6). These large deposits of niobium have been found associated withcarbonatites (carbonate-silicate igneous rocks) and as a constituent ofpyrochlore.[51][52]
The three largest currently mined deposits of pyrochlore, two in Brazil and one in Canada, were found in the 1950s, and are still the major producers of niobium mineral concentrates.[21] The largest deposit is hosted within a carbonatite intrusion in Araxá, state of Minas Gerais, Brazil, owned by CBMM (Companhia Brasileira de Metalurgia e Mineração); the other active Brazilian deposit is located near Catalão, state of Goiás, and owned byChina Molybdenum, also hosted within a carbonatite intrusion.[53] Together, those two mines produce about 88% of the world's supply.[54] Brazil also has a large but still unexploited deposit near São Gabriel da Cachoeira, state of Amazonas, as well as a few smaller deposits, notably in the state of Roraima.[54][55]
The third largest producer of niobium is the carbonatite-hostedNiobec mine, in Saint-Honoré, Quebec, Canada, owned by Magris Resources.[56] It produces between 7% and 10% of the world's supply.[53][54]
After the separation from the other minerals, the mixed oxides of tantalum (Ta2O5) and niobium (Nb2O5) are obtained. The first step in the processing is the reaction of the oxides with hydrofluoric acid:[46]
Ta2O5 + 14 HF → 2 H2TaF7 + 5 H2O
Nb2O5 + 10 HF → 2 H2NbOF5 + 3 H2O
The first industrial scale separation, developed by Swiss chemistJean Charles Galissard de Marignac, exploits the differing solubilities of the complex niobium and tantalum fluorides, dipotassium oxypentafluoroniobate monohydrate (K2NbOF5·H2O) and dipotassium heptafluorotantalate (K2TaF7) in water. Newer processes use the liquid extraction of the fluorides from aqueous solution by organic solvents likecyclohexanone.[46] The complex niobium and tantalum fluorides are extracted separately from the organic solvent with water and either precipitated by the addition ofpotassium fluoride to produce a potassium fluoride complex, or precipitated withammonia as the pentoxide:[57]
H2NbOF5 + 2 KF → K2NbOF5↓ + 2 HF
Followed by:
2 H2NbOF5 + 10 NH4OH → Nb2O5↓ + 10 NH4F + 7 H2O
Several methods are used for the reduction to metallic niobium. Theelectrolysis of a molten mixture ofK2NbOF5 and sodium chloride is one; the other is the reduction of the fluoride withsodium. With this method, a relatively high purity niobium can be obtained. In large scale production,Nb2O5 is reduced with hydrogen or carbon.[57] In thealuminothermic reaction, a mixture ofiron oxide and niobium oxide is reacted withaluminium:
3 Nb2O5 + Fe2O3 + 12 Al → 6 Nb + 2 Fe + 6 Al2O3
Small amounts of oxidizers likesodium nitrate are added to enhance the reaction. The result isaluminium oxide andferroniobium, an alloy of iron and niobium used in steel production.[58][59] Ferroniobium contains between 60 and 70% niobium.[53] Without iron oxide, the aluminothermic process is used to produce 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.[60][61]
As of 2013[update], CBMM from Brazil controlled 85 percent of the world's niobium production.[62] TheUnited States Geological Survey estimates that the production increased from 38,700 tonnes in 2005 to 44,500 tonnes in 2006.[63][64] Worldwide resources are estimated to be 4.4 million tonnes.[64] During the ten-year period between 1995 and 2005, the production more than doubled, starting from 17,800 tonnes in 1995.[65] Between 2009 and 2011, production was stable at 63,000 tonnes per year,[66] with a slight decrease in 2012 to only 50,000 tonnes per year.[67]
In many ways, niobium is similar to tantalum and zirconium. It reacts with most nonmetals at high temperatures; with fluorine at room temperature; withchlorine at 150 °C (302 °F) andhydrogen at 200 °C (392 °F); and withnitrogen at 400 °C (752 °F), with products that are frequently interstitial and nonstoichiometric.[40] The metal begins tooxidize in air at 200 °C (392 °F).[57] It resists corrosion by acids, includingaqua regia,hydrochloric,sulfuric,nitric andphosphoric acids.[40] Niobium is attacked by hot concentrated sulfuric acid,hydrofluoric acid and hydrofluoric/nitric acid mixtures. It is also attacked by hot, saturated alkali metal hydroxide solutions.[citation needed]
Although niobium exhibits all of the formaloxidation states from +5 to −1, the most common compounds have niobium in the +5 state.[40] Characteristically, compounds in oxidation states less than 5+ display Nb–Nb bonding. In aqueous solutions, niobium only exhibits the +5 oxidation state. It is also readily prone to hydrolysis and is barely soluble in dilute solutions of hydrochloric, sulfuric, nitric and phosphoric acids due to the precipitation of hydrous Nb oxide.[60] Nb(V) is also slightly soluble in alkaline media due to the formation of soluble polyoxoniobate species.[71][72]
Niobium forms oxides in the oxidation states +5 (Nb2O5),[73] +4 (NbO2), and the rarer oxidation state, +2 (NbO).[74] Most common is the pentoxide, precursor to almost all niobium compounds and alloys.[57][75] Niobates are generated by dissolving the pentoxide in basic hydroxide solutions or by melting it in alkali metal oxides. Examples arelithium niobate (LiNbO3) and lanthanum niobate (LaNbO4). Lithium niobate has a trigonally distortedperovskite-like structure, whereas the lanthanum niobate contains loneNbO3− 4 ions.[57] The layered niobium sulfide (NbS2) is also known.[40]
A very pure sample of niobium pentachlorideBall-and-stick model of niobium pentachloride, which exists as adimer
Niobium forms halides in the oxidation states of +5 and +4 as well as diversesubstoichiometric compounds.[57][60] The pentahalides (NbX 5) feature octahedral Nb centres. Niobium pentafluoride (NbF5) is a white solid with a melting point of 79 °C (174 °F) andniobium pentachloride (NbCl5) is yellow (see image at right) with a melting point of 203.4 °C (398.1 °F). Both arehydrolyzed to give oxides and oxyhalides, such asNbOCl3. The pentachloride is a versatile reagent used to generate theorganometallic compounds, such asniobocene dichloride ((C 5H 5) 2NbCl 2).[78] The tetrahalides (NbX 4) are dark-coloured polymers with Nb-Nb bonds; for example, the blackhygroscopicniobium tetrafluoride (NbF4)[79] and dark violetniobium tetrachloride (NbCl4).[80]
Anionic halide compounds of niobium are well known, owing in part to theLewis acidity of the pentahalides. The most important isNbF7]2−, an intermediate in the separation of Nb and Ta from the ores.[46] This heptafluoride tends to form the oxopentafluoride more readily than does the tantalum compound. Other halide complexes include octahedral [NbCl6]−:
Nb2Cl10 + 2 Cl− → 2 [NbCl6]−
As with other metals with low atomic numbers, a variety of reduced halide cluster ions is known, the prime example being[Nb6Cl18]4−.[81]
Other binary compounds of niobium includeniobium nitride (NbN), which becomes a superconductor at low temperatures and is used in detectors for infrared light.[82] The mainniobium carbide is NbC, an extremely hard, refractory,ceramic material, commercially used in cutting tool bits.[citation needed]
Out of 44,500 tonnes (44,500,000 kg) of niobium mined in 2006, an estimated 90% was used in high-grade structural steel. The second-largest application is superalloys.[83] Niobium alloy superconductors and electronic components account for a very small share of the world production.[83]
Niobium is an effectivemicroalloying element for steel, within which it forms niobium carbide and niobium nitride.[32] These compounds improve thegrain refining, and retard recrystallization andprecipitation hardening. These effects in turn increase the toughness, strength, formability, and weldability.[32] Within microalloyedstainless steels, the niobium content is a small (less than 0.1%)[84] but important addition to high-strength low-alloy steels that are widely used structurally in modern automobiles.[32] Niobium is sometimes used in considerably higher quantities for highly wear-resistant machine components and knives, as high as 3% in Crucible CPM S110V stainless steel.[85]
These same niobium alloys are often used in pipeline construction.[86][87]
Quantities of niobium are used in nickel-, cobalt-, and iron-based superalloys in proportions as great as 6.5%[84] for such applications as jet engine components, gas turbines, rocket subassemblies,turbocharger systems, heat resisting, and combustion equipment. Niobium precipitates a hardening γ''-phase within the grain structure of the superalloy.[88]
These superalloys were used, for example, in advanced air frame systems for theGemini program. Another niobium alloy[clarification needed] was used for the nozzle of theApollo Service Module. Because niobium is oxidized at temperatures above 400 °C, a protective coating is necessary for these applications to prevent the alloy from becoming brittle.[91]
The reactivity of niobium with oxygen requires it to be worked in a vacuum or inert atmosphere, which significantly increases the cost and difficulty of production.Vacuum arc remelting (VAR) andelectron beam melting (EBM), novel processes at the time, enabled the development of niobium and other reactive metals. The project that yielded C-103 began in 1959 with as many as 256 experimental niobium alloys in the "C-series" that could be melted as buttons and rolled into sheet. Wah Chang Corporation had an inventory of hafnium, refined from nuclear-grade zirconium alloys, that it wanted to put to commercial use. The 103rd experimental composition of the C-series alloys, Nb-10Hf-1Ti, had the best combination of formability and high-temperature properties. Wah Chang fabricated the first 500 pounds (230 kg) of C-103 in 1961, ingot to sheet, using EBM and VAR. The intended applications includedturbine engines and liquid metalheat exchangers. Competing niobium alloys from that era included FS85 (Nb-10W-28Ta-1Zr) fromFansteel Metallurgical Corp., Cb129Y (Nb-10W-10Hf-0.2Y) from Wah Chang and Boeing, Cb752 (Nb-10W-2.5Zr) from Union Carbide, and Nb1Zr from Superior Tube Co.[91]
The nozzle of the Merlin Vacuum series of engines developed bySpaceX for the upper stage of itsFalcon 9 rocket is made from a C-103 niobium alloy.[92][93]
Niobium-based superalloys are used to produce components ofhypersonic missile systems.[94]
Niobium-germanium (Nb3Ge),niobium–tin (Nb3Sn), as well as theniobium–titanium alloys are used as a type II superconductor wire for superconducting magnets.[95][96] These superconducting magnets are used in magnetic resonance imaging andnuclear magnetic resonance instruments as well as inparticle accelerators.[97] For example, theLarge Hadron Collider uses 600 short tons (540,000 kg) of superconducting strands, while theInternational Thermonuclear Experimental Reactor uses an estimated 600 long tons (610,000 kg) ofNb3Sn strands and 250 long tons (250,000 kg) of NbTi strands.[98] In 1992 alone, more than one billion US dollars' worth of clinical magnetic resonance imaging systems were constructed with niobium-titanium wire.[25]
Niobium and some niobium alloys are physiologically inert andhypoallergenic. For this reason, niobium is used in prosthetics and implant devices, such as pacemakers.[105] Niobium treated with sodium hydroxide forms a porous layer that aidsosseointegration.[106]
Like titanium, tantalum, and aluminium, niobium can be heated andanodized to produce a wide array ofiridescent colours for jewelry, where its hypoallergenic property is highly desirable.[107][108][109]
Niobium is used as a precious metal in commemorative coins, often withsilver orgold. For example, Austria produced a series of silver niobium euro (€) coins starting in 2003; the colour in these coins is created by thediffraction of light by a thin anodized oxide layer.[110] In 2012, ten 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 €25150-Year Semmering Alpine Railway commemorative coin,[111] and the 2006 Austrian €25European Satellite Navigation commemorative coin.[112] The Austrian mint produced for Latvia a similar series of coins starting in 2004,[113] with one following in 2007.[114] In 2011, the Royal Canadian Mint started production of a $5 sterling silver and niobium coin namedHunter's Moon in which the niobium was selectively oxidized, thus creating unique finishes where no two coins are exactly alike.[115]
A 150 Years Semmering Alpine Railway Coin made of niobium and silver
The arc-tube seals of high pressuresodium vapor lamps are made from niobium, sometimes alloyed with 1% of zirconium; niobium has a very similar coefficient of thermal expansion, matching thesinteredaluminaarc tube ceramic, a translucent material which resists chemical attack or reduction by the hot liquid sodium and sodium vapour contained inside the operating lamp.[116][117][118]
Niobium is used inarc welding rods for some stabilized grades of stainless steel[119][better source needed] and in anodes for cathodic protection systems on some water tanks, which are then usually plated with platinum.[120][121]
Niobium is a constituent of a lightfast chemically stable inorganic yellow pigment that has the trade name NTP Yellow. It is Niobium Sulfur Tin Zinc Oxide, apyrochlore, produced via high-temperaturecalcination. The pigment is also known as pigment yellow 227, commonly listed as PY 227 or PY227.[123]
Niobium is employed in the atomic energy industry for its high temperature and corrosion resistance, as well as its stability underradiation.[124] It is used innuclear reactors for components like fuel rods and reactor cores.[125][126]
Nickel niobium alloys are used in aerospace, oil and gas, construction. They are used in components of jet engines, in ground gas turbines, elements of bridges and high-rise buildings.[127][128]
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. It is often used in jewelry and has been tested for use in some medical implants.[129][130]
Short- and long-term exposure to niobates and niobium chloride, two water-soluble chemicals, have been tested in rats. Rats treated with a single injection of niobium pentachloride or niobates show amedian lethal dose (LD50) between 10 and 100 mg/kg.[131][132][133] For oral administration the toxicity is lower; a study with rats yielded a LD50 after seven days of940 mg/kg.[131]
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