Guide alphabétique, de la thermodynamique, amplification de chaleur, transfert de masse, et dynamique des fluides
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Tantalum —(Gr. Tantalos, mythological character, father of Niobe), Ta; atomic weight 180.9479; atomic number 73; melting point 2996°C; boiling point 5425 ± 100°C; specific gravity 16.654; valence 2,3,4, or 5.

Tantalum was discovered in 1802 by Ekeberg, but many chemists thought niobium and tantalum were identical elements until Rose, in 1844, and Marignac, in 1866, 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 Zaire, Brazil, Mozambique, Thailand, Portugal, Nigeria, and Canada. Mines at Bernic Lake, Manitoba, have reserves of 900,000 tons of ore averaging about 0.15% tantalum oxide. Separation of tantalum from niobium requires several complicated steps. Several methods are used to commercially 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, Ta180, is present in very small quantity (0.0123%) and is unstable with a very long half-life of > 1013 years. 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 the fluoride ion, and free sulfur trioxide. Alkalis attack it only slowly. At high 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. Scientists at Los Alamos have produced a tantalum carbide graphite composite material, which is said to be one of the hardest materials ever made. The compound has a melting point of 6760°F. Tantalum has good "gettering" ability at high temperatures, 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 60% of its use. The metal is also widely used to fabricate chemical process equipment, nuclear reactors, and aircraft and missile 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.

Nombre de vues : 16965 Article ajouté : 2 February 2011 Dernière modification de l'article : 9 February 2011 © Copyright 2010-2021 Retour en haut de page