Niobium (Chemical symbol: Nb) or Columbium (Chemical symbol: Cb)
Niobium (aka Columbium) is one of the lesser-known, but nevertheless important, elements. Metallurgists tend to use the word Niobium; chemists Columbium.
Discovered in 1801, Columbium was found in an unknown ore by Charles Hatchet, an American scientist from Connecticut. He called this mineral columbite and the corresponding element "columbium." In 1844, H. Rose found two elements in a sample of columbite. One, tantalum, he named after the mythical Greek king Tantalus. The other, niobium, he named after the king’s daughter, Niobe, the goddess of tears. Sainte-Claire Deville and Troost made the chemical distinction between tantalum and niobium and determined the formulas of some of their compounds. Niobium was first prepared in 1864 by Blomstrand, who reduced the chloride by heating it in a hydrogen atmosphere.
Niobium is a shiny, white, soft and ductile metal. It takes on a bluish tinge when exposed to air at room temperatures for a long time. The metal starts to oxidize in air at high temperatures and must be handled hot under a protective atmosphere to minimize oxide formation. Niobium is available in many forms, including foil, sheet, wire, insulated wire, powder, rod, turnings and tube.
Niobium occurs in nature in columbite (or niobite), niobite-tantalite, parochlore and euxenite. Large deposits of niobium have been found associated with carbonatites (carbon-silicate rocks). Extensive ore reserves are found in Canada, Brazil, Nigeria, Zaire and Russia. Niobium metal (99.5% pure) is priced at about $75 per pound.
Niobium is used in arc-welding rods for stabilized grades of stainless steel. It is also considered a critical strategic metal. Thousands of pounds have been used in superalloys in the aerospace industry for military applications, such as missiles (Fig. 2) and jets, and for advanced airframe systems such as those used in the Gemini space program. The element has superconductive properties. Superconductive magnets have been made with Nb-Zr wire, which retains its superconductivity in strong magnetic fields. Niobium is also commonly used for jewelry.
Here are a few important facts about niobium.
- Atomic number: 41
- Density (g/ml): 8.55
- Atomic weight (u): 92.9064
- Melting point (K): 2740
- Boiling point (K): 5017
- Atomic radius (A): 2.08
- Heat of vaporization (kJ/mole): 682.0
- Ionization potential, first (V): 6.88
- Heat of fusion (kJ/mole): 26.40
- Electronegativity: 1.60
- Oxidation states: 5, 3
- Specific heat (J/gK): 0.26
- Electron configuration: [Kr] 4d4 5s1