Niobium

Niobium (or columbium) 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.

Notable characteristics

Niobium is a shiny grey, 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 and its oxidation states are +2, +3, +5.

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;

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.

Because of its bluish color, niobium is also used in body piercing jewelry (usually as an alloy).

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.

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. 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.

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 metal. He did this by 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. Many leading chemical societies and government organizations refer to it by the official IUPAC name but most 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.

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 mega electron volts 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.

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 biological role.

References

Los Alamos National Laboratory – Niobium

External links

WebElements.com – Niobium

EnvironmentalChemistry.com – Niobium

Tantalum-Niobium International Study Center

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