Niobium

41 zirconiumniobiummolybdenum
V

Nb

Ta
Periodic Table - Extended Periodic Table
General
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
Physical properties
Phase solid
Density (near r.t.) 8.57 g·cm−3
Melting point 2750 K
(2477 °C, 4491 °F)
Boiling point 5017 K
(4744 °C, 8571 °F)
Heat of fusion 30 kJ·mol−1
Heat of vaporization 689.9 kJ·mol−1
Heat capacity (25 °C) 24.60 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 2942 3207 3524 3910 4393 5013
Atomic properties
Crystal structure cubic body centered
Oxidation states 5, 3
(mildly acidic oxide)
Electronegativity 1.6 (Pauling scale)
Ionization energies
(more)
1st: 652.1 kJ·mol−1
2nd: 1380 kJ·mol−1
3rd: 2416 kJ·mol−1
Atomic radius 145 pm
Atomic radius (calc.) 198 pm
Covalent radius 137 pm
Miscellaneous
Magnetic ordering no data
Electrical resistivity (0 °C) 152 nΩ·m
Thermal conductivity (300 K) 53.7 W·m−1·K−1
Thermal expansion (25 °C) 7.3 µm·m−1·K−1
Speed of sound (thin rod) (20 °C) 3480 m/s
Young's modulus 105 GPa
Shear modulus 38 GPa
Bulk modulus 170 GPa
Poisson ratio 0.40
Mohs hardness 6.0
Vickers hardness 1320 MPa
Brinell hardness 736 MPa
CAS registry number 7440-03-1
Selected isotopes
Main article: Isotopes of niobium
iso NA half-life DM DE (MeV) DP
91Nb syn 6.8×102 y ε - 91Zr
91mNb syn 60.86 d IT 0.104e 91Nb
92Nb syn 10.15 d ε - 92Zr
γ 0.934 -
92Nb syn 3.47×107y ε - 92Zr
γ 0.561, 0.934 -
93Nb 100% Nb is stable with 52 neutrons
93mNb syn 16.13 y IT 0.031e 93Nb
94Nb syn 2.03×104 y β- 0.471 94Mo
γ 0.702, 0.871 -
95Nb syn 34.991 d β- 0.159 95Mo
γ 0.765 -
95mNb syn 3.61 d IT 0.235 95Nb
References

Niobium (IPA: /niˈəʊbiəm, ˌnʌɪˈəʊbiəm/), or columbium (IPA: /kəˈlʌmbiəm/) is a chemical element in the periodic table that has the symbol Nb and atomic number 41. A rare, soft, gray, ductile transition metal, niobium is found in niobite and used in alloys. The most notable alloys are used to make special steels and strong welded joints. Niobium was discovered in a variety of columbite (now called niobite) and was at first named after this mineral.

Contents

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Notable characteristics

Niobium is a shiny gray, ductile metal that takes on a bluish tinge when exposed to air at room temperature for extended periods. Niobium's chemical properties are almost identical to the chemical properties of tantalum, which appears below niobium in the periodic table.

When it is processed at even moderate temperatures niobium 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.

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Applications

Niobium has a number of uses: it 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. Other uses;

Niobium becomes a superconductor when lowered to cryogenic temperatures. At atmospheric pressure, it has the highest critical temperature of the elemental superconductors: 9.3 K. Niobium has the largest magnetic penetration depth of any element. In addition, it is one of the 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.

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History

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. There was a considerable amount of confusion about the difference between the closely-related niobium and tantalum that wasn't resolved until 1846 by Heinrich Rose and Jean Charles Galissard de Marignac, who rediscovered the element. Since Rose was unaware of Hatchett's work, he 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.

Columbium (symbol Cb) was the name originally given to this element by Hatchett, but 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, however, 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."

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Occurrence

Niobium metal
Niobium metal

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 in Russia. A large producer in Brazil is CBMM located in Araxá, Minas Gerais.

See also niobium minerals.

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Isotopes

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 (half life: 20300 years), and Nb-91 with a half life of 680 years. There is also a meta state at 0.031 megaelectronvolts whose half-life is 16.13 years. Twenty three other radioisotopes have been characterized. 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). The primary decay mode before the stable Nb-93 is electron capture and the primary mode after is beta emission with some neutron emission occurring in the first mode of the two mode decay of Nb-104, 109 and 110. It is worth 4 dollars a gram

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Precautions

Niobium-containing compounds are relatively rarely encountered by most people, but many are highly toxic and should be treated with care. Metallic niobium dust is an eye and skin irritant and also can be a fire hazard. Niobium has no known biological role.

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See also

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References

  1. Godley, Reut, David Starosvetsky, and Irena Gotman (2004). "Bonelike apatite formation on niobium metal treated in aqueous NaOH" (PDF). Journal of Materials Science: Materials in Medicine 15: 1073–1077. DOI:10.1023/B:JMSM.0000046388.07961.81. Retrieved on 2006-09-07.
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External links

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