|Name, Symbol, Number||niobium, Nb, 41|
|Chemical series||transition metals|
|Group, Period, Block||5, 5, d|
|Appearance||gray metallic |
|Atomic mass||92.90638(2) g/mol|
|Electron configuration||[Kr] 4d4 5s1|
|Electrons per shell||2, 8, 18, 12, 1|
|Density (near r.t.)||8.57 g/cm³|
|Melting point||2750 K|
(2477 °C, 4491 °F)
|Boiling point||5017 K|
(4744 °C, 8571 °F)
|Heat of fusion||30 kJ/mol|
|Heat of vaporization||689.9 kJ/mol|
|Heat capacity||(25 °C) 24.60 J/(mol·K)|
|Crystal structure||cubic body centered|
|Oxidation states||5, 3|
(mildly acidic oxide)
|Electronegativity||1.6 (Pauling scale)|
|1st: 652.1 kJ/mol|
|2nd: 1380 kJ/mol|
|3rd: 2416 kJ/mol|
|Atomic radius||145 pm|
|Atomic radius (calc.)||198 pm|
|Covalent radius||137 pm|
|Magnetic ordering||no data|
|Electrical resistivity||(0 °C) 152 nΩ·m|
|Thermal conductivity||(300 K) 53.7 W/(m·K)|
|Thermal expansion||(25 °C) 7.3 µm/(m·K)|
|Speed of sound (thin rod)||(20 °C) 3480 m/s|
|Speed of sound (thin rod)||(r.t.) 105 m/s|
|Shear modulus||38 GPa|
|Bulk modulus||170 GPa|
|Vickers hardness||1320 MPa|
|Brinell hardness||736 MPa|
|CAS registry number||7440-03-1|
Niobium or columbium (chemical symbol Nb, atomic number 41) is a rare, soft, gray metal. It was discovered in a variety of columbite (now called niobite) and was at first named after this mineral. It is used in alloys to make special steels and strong welded joints. At extremely low temperatures, it acts as a superconductor.
The element is never found as a free element but does occur in the minerals columbite ((Fe,Mn)(Nb,Ta)2O6), columbite-tantalite or coltan ((Fe,Mn)(Ta,Nb)2O6), pyrochlore ((Na,Ca)2Nb2O6OH,F), and euxenite ((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6). Minerals that contain niobium often also contain tantalum. Large deposits of niobium have been found associated with carbonatites (carbon-silicate igneous rocks) and as a constituent of pyrochlore. Brazil and Canada are the major producers of niobium mineral concentrates and extensive ore reserves are also in Nigeria, Democratic Republic of Congo, and Russia.
Niobium (Greek mythology: Niobe, daughter of Tantalus) was discovered by Charles Hatchett in 1801. Hatchett found niobium in columbite ore that was sent to England in the 1750s by John Winthrop, the first governor of Connecticut. Hatchett named the element columbium (symbol Cb).
Around that time, there was considerable confusion about the difference between this element and the closely related tantalum. This confusion was not resolved until 1846 by Heinrich Rose and Jean Charles Galissard de Marignac, who rediscovered the element. Rose was unaware of Hatchett's work and gave the element a different name, niobium. In 1864, Christian Blomstrand was the first to prepare the pure metal, reducing niobium chloride by heating it in a hydrogen atmosphere.
The International Union of Pure and Applied Chemistry (IUPAC) officially adopted "niobium" as the name for element 41 in 1950, after 100 years of controversy. This was a compromise of sorts; 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 most leading American commercial producers still refer to the metal by the original "columbium."
Niobium is a transition metal that lies in period 5 of the periodic table, between zirconium and molybdenum. It is also located in group 5 (former group 5B), between vanadium and tantalum. Its chemical properties are almost identical to those of tantalum.
This shiny gray, ductile metal takes on a bluish tinge when exposed to air at room temperature for extended periods. When it is processed at even moderate temperatures, it must be placed in a protective atmosphere. The metal begins to oxidize in air at 200° C. Its most common oxidation states are +3, and +5, although others are also known.
Naturally occurring niobium is composed of one stable isotope: Nb-93. The most stable radioisotopes are Nb-92, with a half-life of 34.7 million years; Nb-94, with a half-life of 20,300 years; and Nb-91, with a half-life of 680 years. There is also a meta state at 0.031 megaelectronvolts, with a half-life is 16.13 years. Many other radioisotopes have been characterized, with mass numbers ranging from 81 to 113. Most of these have half-lives that are less than two hours, except Nb-95 (35 days), Nb-96 (23.4 hours), and Nb-90 (14.6 hours).
- Niobium carbide (NbC and Nb2C): It is an extremely hard, refractory ceramic material. It has the appearance of a brown-gray metallic powder with purple luster and is highly resistant to corrosion. It is usually processed by sintering and is a frequent additive in cemented carbides. Commercially, it is used in tool bits for cutting tools. In addition, it is a frequent intentional product in microalloyed steels, and it can be used in refractory coatings for nuclear reactors.
- Niobium(V) chloride or niobium pentachloride (NbCl5): It is a yellow crystalline solid often used as a starting material in niobium chemistry. It is prepared by heating niobium metal in chlorine. Often contaminated with small amounts of niobium(V) oxychloride (NbOCl3), it may be purified by sublimation. It is useful for certain reactions in organic chemistry.
- Niobium-tin (Nb3Sn): It is a metallic chemical compound of niobium (Nb) and tin (Sn), used industrially as a type II superconductor. It is usually used at 4.2 K, the boiling point of liquid helium. It is more expensive than niobium-titanium (NbTi), but can withstand magnetic field intensity values up to 30 tesla (T), whereas NbTi can withstand only up to roughly 10 T.
- Niobium is a component of some stainless steels and an alloy of other nonferrous metals. These alloys are strong and are often used in pipeline construction.
- The metal has a low capture cross-section for thermal neutrons and so finds use in the nuclear industries.
- It is also the metal used in arc welding rods for some stabilized grades of stainless steel.
- Appreciable amounts of niobium 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, rocket subassemblies, and heat-resisting and combustion equipment. Advanced air-frame systems such as those used in the Gemini program used this metal.
- Niobium is being evaluated as an alternative to tantalum in capacitors.
- Because niobium metal and some niobium alloys are physiologically inert (and thus hypoallergenic), they are used in jewelry and medical devices. Niobium metal treated with sodium hydroxide forms a porous layer that aids osseointegration.
- Along with titanium, tantalum, and aluminum, niobium can also be electrically heated and anodized to a wide array of colors using a process known as reactive metal anodizing. This makes it very attractive for use in jewelry.
- Niobium is also added to glass in order to attain a higher refractive index, a property used in the optical industry to make thinner corrective glasses.
- At cryogenic temperatures, niobium becomes a superconductor. At atmospheric pressure, it has the highest critical temperature of the elemental superconductors: 9.3 Kelvin (K). In addition, it is one of three elemental superconductors that are Type II (the others being vanadium and technetium), meaning it remains a superconductor when subjected to high magnetic fields. Niobium-tin and niobium-titanium alloys are used as wires for superconducting magnets capable of producing exceedingly strong magnetic fields. Niobium is also used in its pure form to make superconducting accelerating structures for particle accelerators.
Niobium has no known biological role. Dust of the metal is an eye and skin irritant and can also be a fire hazard. Niobium-containing compounds are relatively rarely encountered by most people, but many are highly toxic and should be handled with care.
- Godley, Reut and David Starosvetsky, and Irena Gotman (2004). Bonelike apatite formation on niobium metal treated in aqueous NaOH. Journal of Materials Science: Materials in Medicine 15: 1073–1077.
- Andrade, C. K. Z.; Rocha, R. O.; Russowsky, D.; and Godoy, M. N. 2005. "Studies on the Niobium Pentachloride-Mediated Nucleophilic Additions to an Enantiopure Cyclic N-acyliminium Ion Derived from (S)-malic acid." J. Braz. Chem. Soc. 16:535–539. Online Article (.PDF file). Retrieved August 7, 2007.
- Chang, Raymond. 2006. Chemistry (ninth ed.). New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
- Cotton, F. Albert and Wilkinson, Geoffrey. 1980. Advanced Inorganic Chemistry (4th ed.). New York: Wiley. ISBN 0-471-02775-8
- Fairbrother, F. 1967. The Chemistry of Niobium and Tantalum. New York: Elsevier Publishing Company. ASIN B0006BQA7U
- Greenwood, N. N. and Earnshaw, A. 1998. Chemistry of the Elements (2nd Edition). Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654. Online version available at . Accessed on November 25, 2006.
- Niobium Los Alamos National Laboratory. Accessed on November 25, 2006.
All links retrieved December 5, 2018.
- WebElements.com – Niobium.
- Tantalum-Niobium International Study Center.
- Niobium for particle accelerators.
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