Tantalum

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Tantalum

Tantalum (formerly tantalium) is a chemical element in the periodic table that has the symbol Ta and atomic number 73. A rare, hard, blue-gray, lustrous, transition metal, tantalum is highly corrosion-resistant and occurs in the mineral tantalite. Tantalum is used in surgical instruments and implants because it does not react with body fluids.

Notable characteristics

Tantalum is gray, dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is renowned for its resistance to corrosion by acids; in fact, at temperatures below 150 °C tantalum is almost completely immune to attack by the normally aggressive aqua regia. It can only be dissolved with hydrofluoric acid or acidic solutions containing the fluoride ion and sulfur trioxide. Tantalum's high melting point of 3290 K (boiling point 5731 K) is exceeded only by tungsten and rhenium .

Applications

The major use for tantalum, as the metal powder, is in the production of electronic components, mainly capacitors and some high-end audio grade resistors. Tantalum electrolytic capacitors exploit the tendency of tantalum to form a protective oxide surface layer, using tantalum foil as one plate of the capacitor, the oxide as the dielectric, and an electrolytic solution as the other plate. Because the dielectric layer can be very thin (thinner than the similar layer in, for instance, an aluminium electrolytic capacitor), a high capacitance can be achieved in a small volume. Because of the size and weight advantages, tantalum capacitors are attractive for portable telephones, pagers, personal computers, and automotive electronics.

Tantalum is also used to produce a variety of alloys that have high melting points, are strong and have good ductility. Alloyed with other metals, it is also used in making carbide tools for metalworking equipment and in the production of superalloys for jet engine components, chemical process equipment, nuclear reactors, and missile parts. Because of its ductility, Ta can be drawn into fine wires or filaments, which are used for evaporating metals such as aluminium.

Because it resists attack by body liquids and is nonirritating, Ta is widely used in making surgical appliances. Tantalum oxide is used to make special high refractive index glass for camera lenses. The metal is also used to make vacuum furnace parts.

History

Tantalum (Greek Tantalus, mythological character) was discovered in Sweden in 1802 by Anders Ekeberg and isolated in 1820 by Jöns Berzelius. Many contemporary chemists believed niobium and tantalum were the same elements until 1844 and later 1866 when researchers showed that niobic and tantalic acids were different compounds. Early investigators were only able to isolate impure metal and the first relatively pure ductile metal was produced by Werner von Bolton in 1903. Wires made with tantalum metal were used for light bulbs until tungsten replaced it.

Its name is derived from the character Tantalus, father of Niobe in Greek mythology, who was punished after death by being condemned to stand knee-deep in water with perfect fruit growing above his head, both of which eternally tantalized him - if he bent to drink the water, it drained below the level he could reach, and if he reached for the fruit, the branches moved out of his grasp. This was considered similar to tantalum's general non-reactivity—it sits among reagents and is unaffected by them. Tantalum was named after the Greek myth due to being difficult to refine.

Occurrence

Tantalum occurs principally in the minerals tantalite href="http://articles.gourt.com/en/iron">Fe, Mn) Ta₂O₆ and euxenite (other minerals: samarskite, and fergusonite).

Tantalum ores are mined in Australia, Brazil, Egypt, Canada, the Democratic Republic of the Congo, Mozambique, Nigeria, Portugal, Malaysia and Thailand. A comprehensive, 2002 picture of non-Australian mines is reasonably current.

Tantalite is largely found mixed with columbite in an ore called coltan. Ethical questions have been raised about human rights and endangered wildlife, due to the exploitation of resources in the conflict regions of the Congo (see coltan).

Several complicated steps are involved in the separation of tantalum from niobium. Commercially viable production of this element can follow one of several different methods which includes; electrolysis of molten potassium fluorotantalate, reduction of potassium fluorotantalate with sodium, or by reacting tantalum carbide with tantalum oxide. Tantalum is also a byproduct from tin smelting.

Compounds

Los Alamos National Laboratory scientists have developed a tantalum carbide-graphite composite material that is one of the hardest materials ever synthesized. Korean researchers have developed an amorphous tantalum-tungsten-copperalloy which is more flexible and two to three times stronger than traditional steel alloys.

See also Tantalum compounds.

Isotopes

Natural tantalum consists of two isotopes. Ta-181 is a stable isotope, and Ta-180m has a half life of over 10¹⁵ years (see scientific notation) and is a nuclear isomer of Ta-180. Ta-180 has a ground state half life of only 8 hours.

Tantalum has been proposed as a "salting" material for nuclear weapons (cobalt is another, better-known salting material). A jacket of ¹⁸¹Ta, irradiated by the intense high-energy neutron flux from an exploding thermonuclear weapon, would transmute into the radioactive isotope ¹⁸²Ta with a half-life of 114.43 days and produce approximately 1.12 MeV of gamma radiation, significantly increasing the radioactivity of the weapon's fallout for several months. Such a weapon is not known to have ever been built, tested, or used.

Precautions

Compounds containing tantalum are rarely encountered, and the metal does not normally cause problems in the laboratory, but it should still be handled with care, taking the usual laboratory precautions. There is some evidence that tantalum compounds can cause tumors, and its metal dust is a fire and explosion hazard. However, refined tantalum is used in surgical instruments and implants because it does not react with body fluids.

References

Los Alamos National Laboratory - Tantalum

External links

Chemical elements | Transition metals

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