Niobium or columbium, 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. 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. It was not until the early 20th century
that niobium was first used commercially. Brazil is the leading
producer of niobium and ferroniobium, an alloy of niobium and iron.
Niobium is used mostly in alloys, the largest part in special steel
such as that used in gas pipelines. Although alloys contain only a
maximum of 0.1%, that small percentage of niobium improves the
strength of the steel. The temperature stability of
niobium-containing superalloys is important for its use in jet and
rocket engines. Niobium is used in various superconducting
materials. These superconducting alloys, also containing titanium
and tin, are widely used in the superconducting magnets of MRI
scanners. Other applications of niobium include its use in welding,
nuclear industries, electronics, optics, numismatics and jewelry.
In the last two applications, niobium's low toxicity and ability to
be coloured by anodisation are particular advantages.
Niobium was discovered by the English chemist Charles Hatchett
in 1801. 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, and named the mineral columbite and the new element
columbium after Columbia, the poetical name for America. The
columbium discovered by Hatchett was probably a mixture of the new
element with tantalum. Subsequently, there was considerable
confusion 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. This conclusion was disputed in 1846 by the German
chemist Heinrich Rose, who argued that there were two different
elements in the tantalite sample, and named them after children of
Tantalus: niobium (from Niobe), and pelopium (from Pelops). This
confusion arose from the minimal observed differences between
tantalum and niobium. The claimed new elements pelopium, ilmenium
and dianium were in fact identical to niobium or mixtures of
niobium and tantalum. The differences between tantalum and niobium
were unequivocally demonstrated in 1864 by Christian Wilhelm
Blomstrand, and Henri Etienne Sainte-Claire Deville, as well as
Louis J. Troost, who determined the formulas of some of the
compounds in 1865 and finally by the Swiss chemist Jean Charles
Galissard de Marignac in 1866, who all proved that there were only
two elements. Articles on ilmenium continued to appear until 1871.
De Marignac was the first to prepare the metal in 1864, when he
reduced niobium chloride by heating it in an atmosphere of
hydrogen. Although de Marignac was able to produce tantalum-free
niobium on a larger scale by 1866, it was not until the early 20th
century that niobium was first used commercially, in incandescent
lamp filaments. This use quickly became obsolete through the
replacement of niobium with tungsten, which has a higher melting
point and thus is preferable for use in incandescent lamps. The
discovery that niobium improves the strength of steel was made in
the 1920s, and this application remains its predominant use. In
1961 the American physicist Eugene Kunzler and coworkers at Bell
Labs discovered that niobium-tin continues to exhibit
superconductivity in the presence of strong electric currents and
magnetic fields, making it the first material to support the high
currents and fields necessary for useful high-power magnets and
electrically powered machinery. This discovery would allow —
two decades later — the production of long multi-strand
cables that could be wound into coils to create large, powerful
electromagnets for rotating machinery, particle accelerators, or
particle detectors.
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).)
Niobium becomes a superconductor at cryogenic temperatures. At
atmospheric pressure, it has the highest critical temperature of
the elemental superconductors: 9.2 K. Niobium has the largest
magnetic penetration depth of any element. In addition, it is one
of the three elemental Type II superconductors, along with vanadium
and technetium. The superconductive properties are strongly
dependent on the purity of the niobium metal. When very pure, it is
comparatively soft and ductile, but impurities make it harder. The
metal has a low capture cross-section for thermal neutrons; thus it
is used in the nuclear industries.