Niobium

Niobium is a soft, grey, ductile transition metal in group 5, directly above tantalum. Its electron configuration, [Kr] 4d4 5s1, is an exception to the simple filling order: moving one electron from 5s into 4d gives a lower-energy arrangement. With five valence electrons, niobium's most stable oxidation state is +5, seen in the white oxide Nb2O5. A thin, tightly bonded layer of that oxide forms on the surface within moments of exposure to air, which is why the metal resists corrosion even though it is quite reactive underneath.

Because of the lanthanide contraction, niobium and tantalum have almost identical atomic radii and chemistry, and the two always occur together in ores; separating them took chemists more than forty years. Niobium's most valuable property appears in the cold. Below 9.2 K it becomes a superconductor, the highest such transition temperature of any element at ambient pressure. Alloys such as niobium-titanium and Nb3Sn carry enormous currents with zero resistance, making them the standard wire for superconducting magnets. Most niobium, though, goes into steel: about 0.1% refines the grain structure and makes pipelines and car frames stronger and lighter.

Discovery

In 1801 the English chemist Charles Hatchett analysed a black mineral that had been sent from Connecticut to the British Museum and found a new oxide, naming the element columbium after Columbia, a poetic name for America. Confusion with tantalum followed until Heinrich Rose showed in 1844 that the ores held two distinct elements; he called the new one niobium, after Niobe, daughter of Tantalus in Greek myth. Christian Wilhelm Blomstrand first produced the metal in 1864. IUPAC settled on 'niobium' in 1949, though some American metallurgists still say columbium.