Niobium (pronounced /naɪˈoʊbiəm/ nye-OH-bee-əm) (Greek mythology: Niobe, daughter
of Tantalus),
or columbium (/kəˈlʌmbiəm/ kə-LUM-bee-əm), is the chemical element with the symbol Nb and the
atomic
number 41. A rare, soft, grey, ductile transition
metal, niobium is found in the minerals pyrochlore,
the main commercial source for niobium, and columbite.
Etaild descrption
Etaild descrption
Niobium
has physical and chemical properties similar to those of the element tantalum, and
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 tantalum and columbium were identical. The German chemist Heinrich
Rose determined in 1846 that tantalum ores contain a second element, which
he named niobium. In 1864 and 1865, a series of scientific findings clarified
that niobium and columbium were the same element (as distinguished from
tantalum), and for a century both names were used interchangeably. The name of
the element was officially adopted as niobium in 1949.
History
Niobium was discovered by the English
chemist Charles Hatchett in 1801.[1]
He found a new element in a mineral sample that had been sent to England from Massachusetts,
United
States in 1734 by a John Winthrop,[2]
and named the mineral columbite and the new element columbium after
Columbia, the poetical name for America.[3]
The columbium discovered by Hatchett was probably a mixture of the new
element with tantalum.[3]
Subsequently,
there was considerable confusion[4]
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.[4]
elements in the tantalite sample, and named them after children of Tantalus: niobium
(from Niobe), and pelopium
(from Pelops).[5][6]
Characteristics
Niobium
is a lustrous, grey, ductile, paramagnetic
metal in group
5 of the periodic table (see table), although it
has an atypical configuration in its outermost electron
shells compared to the rest of the members. (This can be observed in the
neighborhood of niobium (41), ruthenium (44), rhodium (45), and
palladium
(46).)
The
metal takes on a bluish tinge when exposed to air at room temperature for
extended periods.[22]
Despite presenting a high melting point in elemental form (2,468 °C), it
has a low
Chemistry
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Niobium
is in many ways similar to its predecessors in group
5. It reacts with most nonmetals at high temperatures: niobium reacts with fluorine at
room temperature, with chlorine and hydrogen at 200 °C, and with nitrogen at
400 °C, giving products that are frequently interstitial and
nonstoichiometric.[24]
The metal begins to oxidize in air at 200 °C,[26]
and is resistant to corrosion by fused alkalis
and by acids, including aqua regia, hydrochloric,
sulfuric,
nitric
and phosphoric acids.[24]
Niobium is attacked by hot, concentrated mineral
acids, such as hydrofluoric acid and hydrofluoric/nitric acid
mixtures. Although niobium exhibits all the formal oxidation states from +5
down to -1, its most stable state is +5.[24]
Occurrence
According
to estimates, niobium is 33rd on the list of the most common elements in the
Earth’s crust with 20 ppm.[38]
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.[20]
The free element is not found in nature, but it does occur in minerals.[24]
Minerals that contain niobium often also contain tantalum, such as columbite
((Fe,Mn)(Nb,Ta)2O6) and columbite-tantalite (or coltan,
(Fe,Mn)(Ta,Nb)2O6).[32]
Columbite-tantalite minerals are most usually found as accessory minerals in pegmatite
intrusions, and in alkaline intrusive rocks. Less common are the niobates of calcium, uranium, thorium and the rare earth elements such as pyrochlore
((Na,Ca)2Nb2O6(OH,F)) and euxenite
((Y,Ca,Ce,U,Th)(Nb,Ta,Ti)2O6). These large deposits of
niobium have been found associated with carbonatites
(carbonate-silicate igneous
rocks) and as a constituent of pyrochlore.[39]
Production
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:[32]
Ta2O5 + 14
HF → 2 H2[TaF7] + 5 H2O
Nb2O5 + 10
HF → 2 H2[NbOF5] + 3 H2O
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.[32]
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:[26]
Applications
It
is estimated that out of 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.[47]
The use of niobium alloys for superconductors and in electronic components
account only for a small share of the production.[47]
Steel production
Niobium
is an effective microalloying element for steel. Adding niobium
to the steel causes the formation of niobium
carbide and niobium nitride within the structure of
the steel.[20]
These compounds improve the grain refining, retardation of recrystallization,
and precipitation hardening of the steel. These effects in turn increase the
toughness, strength, formability, and weldability of the microalloyed steel.[20]
Microalloyed stainless steels have a niobium content of less
than 0.1%.[48]
It is an important alloy addition to high strength
low alloy steels which are widely used as structural components in modern
automobiles.[20]
These niobium containing alloys are strong and are often used in pipeline
construction.[49][50]
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-based 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.[51]
The alloys contain up to 6.5% niobium.[48]
One example of a nickel-based niobium-containing superalloy is Inconel 718,
which consists of roughly 50% nickel, 18.6% chromium, 18.5% iron, 5% niobium, 3.1% molybdenum,
0.9% titanium,
and 0.4% aluminium.[52][53]
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 C103, which
consists of 89% niobium, 10% hafnium and 1% titanium.[54]
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.[54]
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.[55]
Niobium has the largest magnetic penetration depth of any element.[55]
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 particle accelerators.[56]
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.[57]
In 1992 alone, niobium-titanium wires were used to construct more than US$1 billion worth
of clinical magnetic resonance imaging systems.
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