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===Other uses===
===Other uses===
Niobium and some niobium alloys are used in medical devices such as pacemakers, because they are physiologically inert (and thus [[hypoallergenic]]).<ref>{{cite journal | last = Mallela| first = Venkateswara Sarma | coauthors = Ilankumaran, V.; Srinivasa Rao, N.| title = Trends in Cardiac Pacemaker Batteries | journal = Indian Pacing Electrophysiol J. | volume = 4 | issue = 4 | pages = 201–212 | url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1502062 | format = PDF | accessdate = | year =2004 | pmid = 16943934 | month = Jan | day = 01 }}</ref> Niobium treated with [[sodium hydroxide]] forms a porous layer that aids [[osseointegration]].<ref>{{cite journal | last = Godley | first = Reut | coauthors = Starosvetsky, David; Gotman, Irena | year = 2004 | title = Bonelike apatite formation on niobium metal treated in aqueous NaOH | journal = Journal of Materials Science: Materials in Medicine | volume = 15 | pages = 1073–1077 | doi = 10.1023/B:JMSM.0000046388.07961.81 | url = http://www.springerlink.com/content/l5613670648017wp/ | format = PDF }}</ref> Along with titanium, tantalum, and aluminium, niobium can also be electrically heated and [[anodize]]d, resulting in a wide array of colours using a process known as reactive metal [[anodizing]] which is useful in making jewelry,<ref>{{cite journal | journal = Journal of Applied Electrochemistry | volume = 21 | issue = 11 | doi = 10.1007/BF01077589 | pages = 1023–1026 | year = 1991 | title = Anodization of niobium in sulphuric acid media | first = M. A. | last = Biason Gomes | coauthors = Onofre, S.; Juanto, S.; Bulhões, L. O. de S. }}</ref><ref>{{cite journal | journal = Thin Solid Films | volume = 8 | issue = 4 | doi = 10.1016/0040-6090(71)90027-7 | pages = R37–R39 | year = 1971 | title = A note on the thicknesses of anodized niobium oxide films | first = Y. L. | last = Chiou }}</ref> The fact that niobium is hypoallergenic also benefits the use in jewelry.<ref>{{cite journal | last = Azevedo | first = C. R. F. | coauthors = Spera, G.; Silva, A. P. | title = Characterization of metallic piercings that caused adverse reactions during use | journal = Journal of Failure Analysis and Prevention | volume = 2 | issue = 4 | pages = 47–53 | doi = 10.1007/BF02715453 | year =2002 | doi_brokendate = 2008-11-12}}</ref>
Niobium and some niobium alloys are used in medical devices such as pacemakers, because they are physiologically inert (and thus [[hypoallergenic]]).<ref>{{cite journal | last = Mallela| first = Venkateswara Sarma | coauthors = Ilankumaran, V.; Srinivasa Rao, N.| title = Trends in Cardiac Pacemaker Batteries | journal = Indian Pacing Electrophysiol J. | volume = 4 | issue = 4 | pages = 201–212 | url = http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1502062 | format = PDF | accessdate = | year =2004 | pmid = 16943934 | month = Jan | day = 01 }}</ref> Niobium treated with [[sodium hydroxide]] forms a porous layer that aids [[osseointegration]].<ref>{{cite journal | last = Godley | first = Reut | coauthors = Starosvetsky, David; Gotman, Irena | year = 2004 | title = Bonelike apatite formation on niobium metal treated in aqueous NaOH | journal = Journal of Materials Science: Materials in Medicine | volume = 15 | pages = 1073–1077 | doi = 10.1023/B:JMSM.0000046388.07961.81 | url = http://www.springerlink.com/content/l5613670648017wp/ | format = PDF }}</ref> Along with titanium, tantalum, and aluminium, niobium can also be electrically heated and [[anodize]]d, resulting in a wide array of colours using a process known as reactive metal [[anodizing]] which is useful in making jewelry.<ref>{{cite journal | journal = Journal of Applied Electrochemistry | volume = 21 | issue = 11 | doi = 10.1007/BF01077589 | pages = 1023–1026 | year = 1991 | title = Anodization of niobium in sulphuric acid media | first = M. A. | last = Biason Gomes | coauthors = Onofre, S.; Juanto, S.; Bulhões, L. O. de S. }}</ref><ref>{{cite journal | journal = Thin Solid Films | volume = 8 | issue = 4 | doi = 10.1016/0040-6090(71)90027-7 | pages = R37–R39 | year = 1971 | title = A note on the thicknesses of anodized niobium oxide films | first = Y. L. | last = Chiou }}</ref> The fact that niobium is hypoallergenic also benefits the use in jewelry.<ref>{{cite journal | last = Azevedo | first = C. R. F. | coauthors = Spera, G.; Silva, A. P. | title = Characterization of metallic piercings that caused adverse reactions during use | journal = Journal of Failure Analysis and Prevention | volume = 2 | issue = 4 | pages = 47–53 | doi = 10.1007/BF02715453 | year =2002 | doi_brokendate = 2008-11-12}}</ref>


The electrodes in some high pressure [[sodium vapor lamp]]s are made from niobium, or niobium with 1% of [[zirconium]], because niobium is resistant to the corrosive sodium vapors within the lamp.<ref>{{cite journal | title = Refractory metals: crucial components for light sources | last = Eichelbrönner | first = G. | year =1998 | journal = International Journal of Refractory Metals and Hard Materials | volume = 16 | issue = 1 | pages = 5–11 | doi = 10.1016/S0263-4368(98)00009-2 | format = PDF | accessdate = }}</ref><ref>{{cite journal | title = Niobium and Niobium 1% Zirconium for High Pressure Sodium (HPS) Discharge Lamps | first = Christopher A. | last = Michaluk | coauthors = Huber, Louis E.; Ford, Robert B.| url = http://www.cbmm.com.br/portug/sources/techlib/science_techno/table_content/sub_3/images/pdfs/017.pdf | accessdate = | journal = Niobium Science & Technology: Proceedings of the International Symposium Niobium 2001 (Orlando, Florida, USA) | date = 2001 | isbn = 9780971206809 |publisher = Niobium 2001 Ltd, 2002 | editor=Minerals, Metals and Materials Society, Metals and Materials Society Minerals | year = 2001 | format = {{dead link|date=November 2008}} – <sup>[http://scholar.google.co.uk/scholar?hl=en&lr=&q=author%3AMichaluk+intitle%3ANiobium+and+Niobium+1%25+Zirconium+for+High+Pressure+Sodium+%28HPS%29++Discharge+Lamps&as_publication=Niobium+Science+%26+Technology%3A+Proceedings+of+the+International+Symposium+Niobium+2001+%28Orlando%2C+Florida%2C+USA%29&as_ylo=2001&as_yhi=2001&btnG=Search Scholar search]</sup> }}</ref> The metal is also used in [[arc welding]] rods for some stabilized grades of stainless steel.<ref>{{US patent reference | number = 5254836 | y = 1993 | m = 10 | d = 19 | inventor = Okada, Yuuji; Kobayashi, Toshihiko; Sasabe, Hiroshi; Aoki, Yoshimitsu; Nishizawa, Makoto; Endo, Shunji | title = Method of arc welding with a ferrite stainless steel welding rod}}</ref><!--<ref>{{cite web | url=http://www.jxmetals.com/sdp/316680/4/cp-1271725.html | publisher=Shanghai Jiangxi Metals Co. Ltd | accessdate=2008-10-14 | title=Niobium - Properties & Uses}}</ref>-->
The electrodes in some high pressure [[sodium vapor lamp]]s are made from niobium, or niobium with 1% of [[zirconium]], because niobium is resistant to the corrosive sodium vapors within the lamp.<ref>{{cite journal | title = Refractory metals: crucial components for light sources | last = Eichelbrönner | first = G. | year =1998 | journal = International Journal of Refractory Metals and Hard Materials | volume = 16 | issue = 1 | pages = 5–11 | doi = 10.1016/S0263-4368(98)00009-2 | format = PDF | accessdate = }}</ref><ref>{{cite journal | title = Niobium and Niobium 1% Zirconium for High Pressure Sodium (HPS) Discharge Lamps | first = Christopher A. | last = Michaluk | coauthors = Huber, Louis E.; Ford, Robert B.| url = http://www.cbmm.com.br/portug/sources/techlib/science_techno/table_content/sub_3/images/pdfs/017.pdf | accessdate = | journal = Niobium Science & Technology: Proceedings of the International Symposium Niobium 2001 (Orlando, Florida, USA) | date = 2001 | isbn = 9780971206809 |publisher = Niobium 2001 Ltd, 2002 | editor=Minerals, Metals and Materials Society, Metals and Materials Society Minerals | year = 2001 | format = {{dead link|date=November 2008}} – <sup>[http://scholar.google.co.uk/scholar?hl=en&lr=&q=author%3AMichaluk+intitle%3ANiobium+and+Niobium+1%25+Zirconium+for+High+Pressure+Sodium+%28HPS%29++Discharge+Lamps&as_publication=Niobium+Science+%26+Technology%3A+Proceedings+of+the+International+Symposium+Niobium+2001+%28Orlando%2C+Florida%2C+USA%29&as_ylo=2001&as_yhi=2001&btnG=Search Scholar search]</sup> }}</ref> The metal is also used in [[arc welding]] rods for some stabilized grades of stainless steel.<ref>{{US patent reference | number = 5254836 | y = 1993 | m = 10 | d = 19 | inventor = Okada, Yuuji; Kobayashi, Toshihiko; Sasabe, Hiroshi; Aoki, Yoshimitsu; Nishizawa, Makoto; Endo, Shunji | title = Method of arc welding with a ferrite stainless steel welding rod}}</ref><!--<ref>{{cite web | url=http://www.jxmetals.com/sdp/316680/4/cp-1271725.html | publisher=Shanghai Jiangxi Metals Co. Ltd | accessdate=2008-10-14 | title=Niobium - Properties & Uses}}</ref>-->

Revision as of 23:39, 29 November 2008

Niobium, 41Nb
A lump of gray shining crystals with hexagonal facetting
Niobium
Pronunciation/naɪˈoʊbiəm/ ​(ny-OH-bee-əm)
AppearanceGray metallic, bluish when oxidized
Standard atomic weight Ar°(Nb)
Niobium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
V
↑
Nb
↓
Ta
zirconium ← niobium → molybdenum
Atomic number (Z)41
Groupgroup 5
Periodperiod 5
Block  d-block
Electron configuration[Kr] 4d4 5s1
Electrons per shell2, 8, 18, 12, 1
Physical properties
Phase at STPsolid
Melting point2750 K ​(2477 °C, ​4491 °F)
Boiling point5017 K ​(4744 °C, ​8571 °F)
Density (at 20° C)8.582 g/cm3[3]
Heat of fusion30 kJ/mol
Heat of vaporization689.9 kJ/mol
Molar heat capacity24.60 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 2942 3207 3524 3910 4393 5013
Atomic properties
Oxidation states−3, −1, 0, +1, +2, +3, +4, +5 (a mildly acidic oxide)
ElectronegativityPauling scale: 1.6
Ionization energies
  • 1st: 652.1 kJ/mol
  • 2nd: 1380 kJ/mol
  • 3rd: 2416 kJ/mol
Atomic radiusempirical: 146 pm
Covalent radius164±6 pm
Color lines in a spectral range
Spectral lines of niobium
Other properties
Natural occurrenceprimordial
Crystal structure ​body-centered cubic (bcc) (cI2)
Lattice constant
Cubic body-centered crystal structure for niobium
a = 330.05 pm (at 20 °C)[3]
Thermal expansion7.07×10−6/K (at 20 °C)[3]
Thermal conductivity53.7 W/(m⋅K)
Electrical resistivity152 nΩ⋅m (at 0 °C)
Magnetic orderingparamagnetic
Young's modulus105 GPa
Shear modulus38 GPa
Bulk modulus170 GPa
Speed of sound thin rod3480 m/s (at 20 °C)
Poisson ratio0.40
Mohs hardness6.0
Vickers hardness870–1320 MPa
Brinell hardness735–2450 MPa
CAS Number7440-03-1
History
Namingafter Niobe in Greek mythology, daughter of Tantalus (tantalum)
DiscoveryCharles Hatchett (1801)
First isolationChristian Wilhelm Blomstrand (1864)
Recognized as a distinct element byHeinrich Rose (1844)
Isotopes of niobium
Main isotopes[4] Decay
abun­dance half-life (t1/2) mode pro­duct
91Nb synth 680 y ε 91Zr
92Nb trace 3.47×107 y β+ 92Zr
93Nb 100% stable
93mNb synth 16.12 y IT 93Nb
94Nb trace 2.04×104 y β− 94Mo
95Nb synth 34.991 d β− 95Mo
 Category: Niobium
| references

Niobium (Template:PronEng) (Greek mythology: Niobe, daughter of Tantalus), or columbium (/kəˈlʌmbiəm/), is a chemical element that has the symbol Nb and atomic number 41. A rare, soft, gray, ductile transition metal, niobium is found in the minerals pyrochlore (the main source for niobium) and columbite.

Niobium has similar physical and chemical properties to tantalum; 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 two elements were identical. Eventually, the German chemist Heinrich Rose determined in 1846 that tantalum ores contain a second element, which he named niobium. After some time, it became clear that niobium and columbium were the same, and for a century, both names were used interchangeably. 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. Although alloys contain only a maximum of 0.1%, that small percentage improves the strength of the steel. The temperature stability of niobium-containing superalloys is important for its use in jet engines and rocket engines. The superconducting alloys that contain titanium and tin are widely used in MRI scanners. Other applications include use in welding, nuclear industries, electronics, optics, numismatics and jewelry. In the last two applications, niobium's low toxicity and ability to be coloured by anodization are particular advantages.

History

Charles Hatchett, discoverer of columbium

Niobium was discovered by the English chemist Charles Hatchett in 1801.[5] Hatchett found niobium in a mineral sample that had been sent to England from Massachusetts in 1734 by a John Winthrop.[6] Hatchett named the mineral columbite and the new element columbium after Columbia, the poetical name for America.[7] It is probable that the columbium discovered by Hatchett was a mixture of a new element with tantalum.[7]

Subsequently, there was considerable confusion[8] over the difference between columbium (niobium) and the closely-related tantalum. 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 7.935 g/cm3, and concluded that the two oxides, despite the significant difference in density, were identical; thus he kept the name tantalum.[8] 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, the goddess of tears), and pelopium (from Pelops).[9][10] This confusion arose from the minimal observed differences between tantalum and niobium. Both tantalum and niobium react with chlorine and traces of oxygen, including atmospheric concentrations, forming two compounds: the white volatile niobium pentachloride (NbCl5) and the non-volatile niobium oxychloride (NbOCl3). Scientists claimed to have discovered new elements: pelopium, ilmenium and dianium,[11] which were in fact identical to niobium or mixtures of niobium and tantalum. Other elements reported to be present included innibite.[11][12]

The differences between tantalum and niobium were unequivocally demonstrated in 1864 by Christian Wilhelm Blomstrand,[12] and Henri Etienne Sainte-Claire Deville, as well as Louis J. Troost, who determined the formulas of some of the compounds in 1865[13][12] and finally by the Swiss chemist Jean Charles Galissard de Marignac,[14] in 1866, who all proved that there were only two elements. These discoveries did not stop scientists from publishing articles about ilmenium until 1871.[15] In 1864, de Marignac was the first to prepare the metal, reducing niobium chloride by heating it in an atmosphere of hydrogen.[16]

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, in incandescent lamp filaments.[13] This use quickly became obsolete through the replacement of niobium with tungsten, 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 remains its predominant use.[13] In 1961 the American physicist Eugene Kunzler and coworkers at Bell Labs discovered that niobium-tin continues to exhibit superconductivity in the presence of strong electric currents and magnetic fields,[17] thus becoming the first known material to support the high currents and fields necessary for making useful high-power magnets and electrically powered machinery. 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.[18][19]

Columbium (symbol Cb[20]) was the name originally given to this element by Hatchett, 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[21]—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.[22] 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.[22] The latter name is still sometimes used in US industry.[23] This was a compromise of sorts;[22] the IUPAC accepted tungsten instead 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".[24][25]

Characteristics

Niobium is a lustrous, grey, ductile metal in group 5 of the periodic table, that takes on a bluish tinge when exposed to air at room temperature for extended periods.[26] Niobium's chemical properties are very similar to the chemical properties of tantalum, which appears directly below niobium in the periodic table.[13]

Isotopes

Main article: Isotopes of niobium

Naturally occurring niobium is composed of one stable isotope, 93Nb.[27] Up to 2003 at least 32 radioisotopes have also been synthesized, ranging in atomic mass from 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 millisecond. Isotopes that are lighter than the stable 93Nb tend to decay by β+ decay, and those that are heavier tend to decay by β- decay, with some exceptions. 81Nb, 82Nb, and 84Nb have minor β+ delayed proton emission decay paths, 91Nb decays by electron capture and positron emission, and 92Nb decays by both β+ and β- decay.[27]

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 isotope is 84mNb with a half-life of 103 ns. All of niobium's isotopes decay by isomeric transition or beta decay except 92m1Nb, which has a minor electron capture decay path.[27]

Compounds

See also: Category:Niobium compounds

The metal begins to oxidize in air at 200 °C.[28] It is able to form oxides with the oxidation states +5 (Nb2O5), +4 (NbO2) and +3 (Nb2O3),[28] as well as with the rarer oxidation state +2 (NbO).[29] The most stable oxidation state is +5, the pentoxide which, along with the dark green non-stoichiometric dioxide, is the most common of the oxides.[28] Niobium pentoxide is used mainly in the production of capacitors, optical glass, and as starting material for several niobium compounds.[30] The compounds are created by dissolving the pentoxide in basic hydroxide solutions or by melting it in another metal oxide. Examples are lithium niobate (LiNbO3) and lanthan niobate (LnNbO4). In the lithium niobate, the niobate ion NbO3− is not alone but part of a perovskite-like structure, while the lantane niobate contains lone NbO43− ions.[28] 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 ABO3 structure ferroelectrics like lithium tantalate and barium titanate.[31]

Niobium pentachloride

Niobium forms halogen compounds in the oxidation states of +5, +4, and +3 of the type NbX
5, NbX
4, and NbX
3, although multi-core complexes and substoichiometric compounds are also formed.[28][32] Niobium pentafluoride (NbF5) is a white solid with a melting point of 79.0 °C and niobium pentachloride (NbCl5) is a white solid with a melting point of 203.4 °C. Both are hydrolyzed by water and react with additional niobium at elevated temperatures by forming the black and highly hygroscopic niobium tetrafluoride (NbF4) and niobium tetrachloride (NbCl4). While the trihalogen compounds can be obtained by reduction of the pentahalogens with hydrogen, the dihalogen compounds do not exist.[28] Spectroscopically, the monochloride (NbCl) has been observed at high temperatures.[33] The fluorides of niobium can be used after its separation from tantalum.[34] The niobium pentachloride is used in organic chemistry as a Lewis acid in activating alkenes for the carbonyl-ene reaction and the Diels-Alder reaction.[35] The pentachloride is also used to generate the organometallic compound niobocene dichloride ((C
5H
5)
2NbCl
2), which in turn is used as a starting material for other organoniobium compounds.[36]

Other binary compounds of niobium include niobium nitride (NbN), which becomes a superconductor at low temperatures and is used in detectors for infrared light,[37] and niobium carbide, an extremely hard, refractory, ceramic material, commercially used in tool bits for cutting tools. The compounds niobium-germanium (Nb
3Ge) and niobium-tin (Nb
3Sn), as well as the niobium-titanium alloy, are used as a type II superconductor wire for superconducting magnets.[38][39]

Occurrence

See also: Category:Niobium minerals

According to estimates, niobium is 33rd on the list of the most common elements in the Earth’s crust with 20 ppm.[40] The abundance on Earth should be much greater, but the “missing” niobium may be located in the Earth’s core due to the metal's high density.[24] The free element is not found in nature, but it does occur in minerals. Minerals that contain niobium often also contain tantalum, for example, columbite ((Fe,Mn)(Nb,Ta)2O6), columbite-tantalite (or coltan, (Fe,Mn)(Ta,Nb)2O6) and pyrochlore ((Na,Ca)2Nb2O6(OH,F).[34] Less common, although they form the largest mined niobium deposits, are the niobates of calcium, uranium, thorium and the rare earth elements such as pyrochlore and euxenite ((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6). These large deposits of niobium have been found associated with carbonatites (carbon-silicate igneous rocks) and as a constituent of pyrochlore.[41]

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.[13] The largest deposits in Brazil are owned by CBMM (Companhia Brasileira de Metalurgia e Mineração) located in Araxá; Minas Gerais, the other deposit, is owned by Mineração Catalão located in Catalão, Goiás.Cite error: The opening <ref> tag is malformed or has a bad name (see the help page). The third largest producer of niobium is the Niobec Inc. mine in Saint-Honoré near Chicoutimi, Quebec.[42] Yet not mined extensive ore reserves are located in Nigeria, Democratic Republic of Congo, and in Russia.

Production

Niobium producers in 2007

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:[34]

Ta2O5 + 14HF → 2H2[TaF7] + 5H2O, and
Nb2O5 + 10HF → 2H2[NbOF5] + 3H2O

The first industrial scale separation, developed by de Marignac, used the difference in solubility between the complex niobium and tantalum fluorides, dipotassium oxypentafluoroniobate monohydrate (K2[NbOF5].H2O) and dipotassium heptafluorotantalate (K2[TaF7]) in water. Newer processes use the liquid extraction of the fluorides from aqueous solution by organic solvents like cyclohexanone.[34] 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:[28]

H2[NbOF5] + 2KF → K2[NbOF5]↓ + 2HF, then
2H2[NbOF5] + 10NH4OH → Nb2O5↓ + 10NH4F + 3H2O

Several methods are used for the reduction to metallic niobium. The electrolysis of a molten mixture of K2[NbOF5] and sodium chloride is one, 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 Nb2O5 with hydrogen or carbon,[28] is used. In the process involving the aluminothermic reaction a mixture of iron oxide and niobium oxide is reacted with aluminium:

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

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.[43][44] The ferroniobium contains between 60 and 70% of niobium.Cite error: The opening <ref> tag is malformed or has a bad name (see the help page). 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.[32][45]

The United States Geological Survey estimates that the production to increased from 38,700 metric tonnes in 2005 to 44,500 tonnes in 2006.[46][47] The world wide resources are estimated to be 4,400,000 tonnes.[47] In the ten years between 1995 and 2005 the production more than doubled starting from 17,800 tonnes in 1995.[48]

Applications

A niobium foil

It is estimated that of the 44,500 metric tons of niobium mined in 2006, 90% ended up in the production of high-grade structural steel, followed by its use in superalloys.[49] The use of niobium alloys for superconductors and in electronic components account only for a small share of the production.[49]

Steel production

Niobium is an effective microalloying element for steel. The increase in toughness and strength and the good formability and weldability of the microalloyed steel is due to improved grain refining, the retardation of recrystallization, and precipitation hardening. These effects are caused by the formation of niobium carbide and niobium nitride within the structure of the steel.[24] Microalloyed stainless steels have a niobium content of less than 0.1%.[50] It is an important alloy addition to High strength low alloy steels which are widely used as structural components in modern automobiles.[24] These niobium containing alloys are strong and are often used in pipeline construction.[51][52]

Apollo CSM with the dark rocket nozzle made from niobium titanium alloy
A 3 tesla clinical Magnetic resonance imaging scanner using niobium-superconducting alloy
An 150 Years Semmering Alpine Railway Coin made of niobium and silver

Superalloys

Appreciable amounts of the element, either in its pure form or in the form of high-purity ferroniobium and nickel niobium, are used in nickel-, cobalt-, and iron-base superalloys for such applications as jet engine components, gas turbines, rocket subassemblies, and heat resisting and combustion equipment. Niobium precipitates a hardening γ''-phase within the grain structure of the superalloy.[53] The alloys contain up to 6.5% niobium.[50] One example of a nickel-based niobium-containing superalloy is inconel 718, which consists of 18.6% chromium, 18.5% iron, 5% niobium, 3.1% molybdenum, 0.9% titanium, and 0.4% aluminium.[54][55] These superalloys are used, for example, in advanced air frame systems such as those used in the Gemini program.

An alloy used for liquid rocket thruster nozzles, such as in the main engine of the Apollo Lunar Modules, is C130, which consists of 89% niobium, 10% hafnium and 1% titanium.[56] Another niobium alloy was used for the nozzle of the Apollo Service Module. As niobium is oxidized at temperatures above 400 °C, a protective coating is necessary for these applications to prevent the alloy from becoming brittle.[56]

Superconducting magnets

Niobium becomes a superconductor when lowered to cryogenic temperatures. At atmospheric pressure, it has the highest critical temperature of the elemental superconductors: 9.2 K.[57] Niobium has the largest magnetic penetration depth of any element.Cite error: The opening <ref> tag is malformed or has a bad name (see the help page). In addition, it is one of the three elemental Type II superconductors, along with vanadium and technetium. Niobium-tin and niobium-titanium alloys are used as wires for superconducting magnets capable of producing exceedingly strong magnetic fields. These superconducting magnets are used in Magnetic resonance imaging and Nuclear magnetic resonance instruments as well as in for particle accelerators.[58] For example, the Large Hadron Collider uses 600 metric tons of superconducting strands, while the International Thermonuclear Experimental Reactor is estimated to use 600 metric tonnes of Nb3Sn strands and 250 metric tonnes of NbTi strands.[59] In 1992 alone niobium-titanium wires were used to construct more than 1 billion US dollar worth of clinical magnetic resonance imaging systems.[18]

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 coins starting in 2003; the colour in these coins is created by diffraction of light by a thin oxide layer produced by anodizing. 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 euro 150 Years Semmering Alpine Railway commemorative coin,[60] and the 2006 Austrian 25 euro European Satellite Navigation commemorative coin.[61] Latvia produced a similar series of coins starting 2004,[62] with one following in 2007.[63] In 2005, Sierra Leone made a coin honoring Pope John Paul II that contained a disc of 24 carat gold surrounded by a ring of purple-tinted niobium.[64]

Other uses

Niobium and some niobium alloys are used in medical devices such as pacemakers, because they are physiologically inert (and thus hypoallergenic).[65] Niobium treated with sodium hydroxide forms a porous layer that aids osseointegration.[66] 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.[67][68] The fact that niobium is hypoallergenic also benefits the use in jewelry.[69]

The electrodes in some high pressure sodium vapor lamps are made from niobium, or niobium with 1% of zirconium, because niobium is resistant to the corrosive sodium vapors within the lamp.[70][71] The metal is also used in arc welding rods for some stabilized grades of stainless steel.[72]

Niobium was evaluated as a cheaper alternative to tantalum in capacitors,[73] 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. The metal has a low capture cross-section for thermal neutrons;[74] thus it is used in the nuclear industries.[75]

The Superconducting Radio Frequency (RF) cavities used in the free electron lasers TESLA and XFEL are made from pure niobium.[76]

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, the Receiver Lab Telescope, and at APEX and are now used in the HIFI instrument on board the Herschel Space Observatory. [77]

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. It is frequently used in jewelry and has been tested for use in some medical implants.[78][79]

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. Rats treated with a single injection of niobium pentachloride or niobates show a median lethal dose (LD50) between 10 and 100 mg/kg.[80][81][82] For oral administration the toxicity is lower; a study with rats yielded a LD50 after seven days of 940 mg/kg.[80]

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