BOILING POINT: ∼4,740°C
DENSITY : 8.57g/cm 3 at room temperature
MOST COMMON IONS : Nb 3+
Niobium metal is typically gray or dull silver in color. It is one of the refractory metals along with tantalum, tungsten, molybdenum, and rhenium, due to its very high melting point. It is estimated that niobium has a natural occurrence in Earth's crust of approximately 20 parts per million (ppm). The largest niobium-containing mineral reserves are located in Brazil and Canada.
English chemist Charles Hatchett originally discovered niobium in 1801 while examining an ore sample obtained in Connecticut. Since the ore sample came from the United States, he named the unknown material columbium (at the time, Columbia was another name for America). In the 1840s German chemist Heinrich Rose rediscovered the element and named it niobium. Chemically, niobium and the element tantalum are very similar, so niobium was named for Niobe, a daughter of Tantulus (root name for the element tantalum) in ancient mythology. It was not until 1950, at a meeting of the International Union of Pure and Applied Chemistry, that it was finally settled that the element would be called niobium. Many metallurgists and engineers, especially in the United States, still refer to the element as columbium.
Pure niobium has relatively poor mechanical properties and readily oxidizes in air to niobium pentoxide (Nb 2 O 5 ) at elevated temperatures. Various niobium-containing alloys such as Nb-1Zr and C-103 have been successfully used in specific liquid-metal based nuclear applications and in the fabrication of various rocket components.
SEE ALSO Inorganic Chemistry .
Daniel P. Kramer
American Society for Metals (1998). Metals Handbook, Vol. 2: Properties and Selection: Nonferrous Alloys and Pure Metals . Metals Park, OH: American Society for Metals.