TANTALUM

(Ta), chemical element, very hard, silver-gray metal of Group Vb of the periodic table, characterized by its high density, extremely high melting point, and excellent resistance to all acids except hydrofluoric at ordinary temperatures. Closely associated with niobium in ores and in properties, tantalum was discovered (1802) by the Swedish chemist Anders Gustaf Ekeberg and named after the mythological character Tantalus because of the tantalizing problem of dissolving the oxide in acids. It was soon identified with niobium (then called columbium) until the German chemist Heinrich Rose demonstrated (1844) their distinct characters. Although some of the impure metal was isolated earlier, the Russian chemist Werner Bolton prepared (1903) the first ductile tantalum, which was used briefly as incandescent lamp-filament material. Relatively rare, tantalum is about as abundant as uranium. It occurs, with niobium, in the columbitetantalite and the pyrochloremicrolite series of minerals. Native tantalum metal with some niobium and traces of manganese and gold occurs sparingly in Russia in placers in the Ural and possibly the Altai mountains in Central Asia. For mineralogical properties, see native element (table). Tantalum is separated from niobium compounds by solvent extraction and is then reduced to metallic tantalum powder. The massive metal is produced by powder metallurgy techniques. The most important uses for tantalum are in electrolytic capacitors and corrosion-resistant chemical equipment. Tantalum capacitors have the highest capacitance per unit volume of any capacitors and are used extensively in miniaturized electrical circuitry. Other uses include getters and components in electron tubes, rectifiers, and prosthetic devices. Tantalum is chemically much like niobium because both have similar electronic configurations and because the radius of the tantalum ion is nearly the same as that of niobium as a result of the lanthanide contraction (q.v.). Tantalum is usually pentavalent; lower oxidation states, especially from +2 to +4, have been prepared. Tantalum compounds are relatively unimportant commercially, although the carbide TaC is used in cemented-carbide tools for machining hard metals. The only naturally occurring isotope, tantalum-181, is stable. atomic number 73 atomic weight 180.948 melting point 2,996 C (5,425 F) boiling point 5,425 C (9,797 F) specific gravity 16.6 (20 C) valence 2, 3, 4, 5 electronic config. 2-8-18-32-11-2 or (Xe)4f 145d36s2