Niobium – facts and properties

Position in the periodic table

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Occurrence and extraction

Niobium never occurs as the pure metal. Its main ore is pyrochlore, a mineral of niobium, calcium and sodium with oxygen and fluorine. Another is columbite, which holds niobium and tantalum together and is the source of the mixed ore known as coltan. By far the largest part of the world supply comes from Brazil, where pyrochlore is mined in open pits. Smaller amounts come from Canada.

The element was discovered in 1801 by the English chemist Charles Hatchett in a mineral from North America. He called it columbium, after Columbia, an old name for the United States. The mix-up with tantalum lasted a long time because the two metals behave so alike. Only in 1844 did Heinrich Rose in Berlin show that they are two different elements, and he named one niobium after Niobe. A clean separation method came about twenty years later from Jean Charles de Marignac. In the United States the name columbium stayed in use for many years, until niobium prevailed internationally.

Industrially the ore is first turned into niobium pentoxide, which is reduced with aluminium in a thermite-type process. For steel an iron alloy called ferroniobium is enough. Superconductors need very pure metal, which is remelted under vacuum.

Properties and reactions

Niobium is in period 5 and group 5, below vanadium. Its electron configuration is [Kr] 4d⁴ 5s¹ and its electronegativity is 1.6. The metal has a density of 8.57 g/cm³, melts at 2477 °C and boils at 4744 °C. It melts only at a very high temperature, yet it is easy to shape and can be rolled into sheet and drawn into wire. Its atomic mass is 92.906 u.

In compounds niobium usually has oxidation number plus five, and its most important oxide has the formula Nb₂O₅. In air a thin, dense oxide layer forms on the metal and protects it against almost all acids, although hot alkalis attack it. At higher temperatures, however, the metal absorbs oxygen, nitrogen and hydrogen and turns brittle, so it is often worked under protective gas or in vacuum.

The oxide layer can be thickened on purpose. If niobium is placed in an electrolytic bath and a voltage is applied, a clear oxide film forms. Light reflected from its top and bottom surfaces interferes, and depending on the thickness different colours are reinforced. The metal then looks blue, violet, green or golden, with no dye at all. This is used for jewellery, rings and coins.

Uses in everyday life and technology

Most niobium goes into steelmaking. Very little of it, usually well under one percent, makes steel stronger and tougher because it keeps the grains in the structure fine. Such microalloyed steels are found in gas pipelines, bridges, car bodies and ship hulls. Thinner plate is enough, so structures can be lighter.

The second large field is superconductors. An alloy of niobium and titanium, NbTi, loses its electrical resistance at temperatures close to absolute zero. Cooled with liquid helium, coils made of it carry very strong currents and produce powerful magnetic fields. They sit in most medical MRI scanners and in the magnets of the Large Hadron Collider at CERN, which accelerates particles to almost the speed of light. For even stronger fields the compound Nb₃Sn of niobium and tin is used, for instance in NMR spectrometers and in the ITER fusion project. The cavities of modern particle accelerators are also made of pure niobium.

Further uses are superalloys for jet engines and rocket parts, and capacitors. Because the body tolerates it well, niobium and its alloys also serve in implants and body piercings.

Molecules containing this element

• Ammonium hexafluoroniobate NH₄NbF₆View in 3D

Quick question

What is the atomic number of niobium (Nb)?

FAQ