From the CRC handbook of Chemistry and Physics, CRC Press, Cleveland, 55th ed., 1974-75 "The Elements" by C.R. Hammond. page B-32
Tantalum (Gr. tantalos, mythological character - father of Niobe), Ta; at. wt. 180.9479; at. no. 73; m.p. 2996 C; b.p. 5425 +/- 100 C; sp.gr. 16.654; valence 2?, 3, 4?, or 5. Discovered in 1802 by Ekeberg, but many chemists thought niobium and tantalum were identical elements until Rose, in 1844, and Marignac, in 1866, indicated and showed that niobic and tantalic acids were two different acids. The early investigators only isolated the impure metal. The first relatively pure ductile tantalum was produced by von Bolton in 1903. Tantalum occurs principally in the mineral columbite-tantalite (Fe, Mn)(Nb, Ta)2O6. Tantalum ores are found in the Republic of Congo, Brazil, Mozambique, Thailand, Portugal, Nigeria, and Canada. The new mine at Bernic Lake, Manitoba, has reserves of more than a million tons of ore averaging about .25% tantalum oxide. Separation of tantalum from niobium requires several complicated steps. Several methods are commercially used to produce the element including: electrolysis of molten potassium fluotantalate, reduction of potassium fluotantalate with sodium, or reacting tantalum carbide with tantalum oxide. Sixteen isotopes of tantalum are known to exist. Natural tantalum contains two isotopes; one of these, Ta(180), is present in very small quantity (0.0123%) and is unstable with a very long half-life of > 10^13 yrs. Tantalum is a gray, heavy, and very hard metal. When pure, it is ductile and can be drawn into fine wire, which is used as a filament for evaporating metals, such as aluminum. Tantalum is almost completely immune to chemical attack at temperatures below 150 C, and is attacked only by hydrofluoric acid, acidic solutions containing fluoride ion, and free sulfur trioxide. Alkalis attack only slowly. At higher temperatures, tantalum becomes much more reactive. The element has a melting point exceeded only by tungsten and rhenium. Tantalum is used to make a variety of alloys with desirable properties, such as high-melting point, high strength, good ductility, etc. The metal has good "gettering" ability at high temperatues, and tantalum oxide films are stable, and have good rectifying and dielectric properties. Tantalum is used to make electrolytic capacitors and vacuum furnace parts, which account for about 70% of its use. The metal is also widely used to fabricate chemical process equipment, nuclear reactors, and aircraft and missle parts. Tantalum is completely immune to body liquids and is a nonirritating metal. It has, therefore, found wide use in making surgical appliances. Tantalum oxide is used to make special glass with a high index of refraction for camera lenses. The metal has many other uses. The metal in powdered form costs about $35/lb. Sheet tantalum and fabricated forms are more expensive.
