Niobium

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Niobium (Template:PronEng), or columbium (Template:IPA) is a chemical element that has the symbol Nb and atomic number 41. A rare, soft, gray, ductile transition metal, niobium is found in pyrochlore and columbite. It was first discovered in the latter mineral and so was initially named columbium; now that mineral is also called "niobite". Niobium is used in special steel alloys as well as in welding, nuclear industries, electronics, optics and jewelry.

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.

Applications

Niobium has a number of uses: it is a component of some stainless steels and an alloy of other nonferrous metals. It is also a very important alloy addition in HSLA steels, which are widely used as structural components in modern automobiles. These alloys are strong and are often used in pipeline construction. Other uses;

  • 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. For example, 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 and some niobium alloys are physiologically inert (and thus hypoallergenic), they are used in jewelry and in medical devices such as pacemakers. Niobium treated with sodium hydroxide forms a porous layer that aids osseointegration.[1]
  • 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.
  • In 2005, the country of Sierra Leone made a coin honoring Pope John Paul II that contained a disc of 24 carat (100%) gold surrounded by a ring of purple-tinted Niobium.

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.

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."

Occurrence

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.

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 31 keV 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.

Only Nb-95 (35 days) and Nb-97 (72 minutes) and heavier isotopes (halflives in seconds) are fission products in significant quantity, as the other isotopes are shadowed by stable or very long-lived (Zr-93) isotopes of the preceding element zirconium from production via beta decay of neutron-rich fission fragments. Nb-95 is the decay product of Zr-95 (64 days), so disappearance of Nb-95 in used nuclear fuel is slower than would be expected from its own 35 day halflife alone.. Tiny amounts of the other isotopes may be produced as direct fission products.

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.

See also

References

  1. Godley, Reut (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 2006-09-07. Unknown parameter |coauthors= ignored (help)<templatestyles src="Module:Citation/CS1/styles.css"></templatestyles>

External links


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