Tantalum

2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements

73 hafnium ← tantalum → tungsten Nb ↑ Ta ↓ Db Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	tantalum, Ta, 73
Chemical series	transition metals
Group, Period, Block	5, 6, d
Appearance	gray blue
Standard atomic weight	180.94788 (2)  g·mol−1
Electron configuration	[Xe] 4f14 5d3 6s2
Electrons per shell	2, 8, 18, 32, 11, 2
Physical properties
Phase	solid
Density (near r.t.)	16.69  g·cm−3
Liquid density at m.p.	15  g·cm−3
Melting point	3290  K (3017 ° C, 5463 ° F)
Boiling point	5731  K (5458 ° C, 9856 ° F)
Heat of fusion	36.57   kJ·mol−1
Heat of vaporization	732.8   kJ·mol−1
Specific heat capacity	(25 °C) 25.36  J·mol−1·K−1
Vapor pressure P(Pa) 1 10 100 1 k 10 k 100 k at T(K) 3297 3597 3957 4395 4939 5634
Atomic properties
Crystal structure	cubic body centered
Oxidation states	5, 4, 3 (mildly acidic oxide)
Electronegativity	1.5 (Pauling scale)
Ionization energies	1st: 761 kJ/mol
	2nd: 1500 kJ/mol
Atomic radius	145   pm
Atomic radius (calc.)	200  pm
Covalent radius	138  pm
Miscellaneous
Magnetic ordering	no data
Electrical resistivity	(20 °C) 131 n Ω·m
Thermal conductivity	(300 K) 57.5  W·m−1·K−1
Thermal expansion	(25 °C) 6.3  µm·m−1·K−1
Speed of sound (thin rod)	(20 °C) 3400 m/s
Young's modulus	186  GPa
Shear modulus	69  GPa
Bulk modulus	200  GPa
Poisson ratio	0.34
Mohs hardness	6.5
Vickers hardness	873  MPa
Brinell hardness	800  MPa
CAS registry number	7440-25-7
Selected isotopes
Main article: Isotopes of tantalum iso NA half-life DM DE ( MeV) DP 177Ta syn 56.56 h ε 1.166 177Hf 178Ta syn 2.36 h ε 1.910 178Hf 179Ta syn 1.82 a ε 0.110 179Hf 180Ta syn 8.125 h ε 0.854 180Hf 180Ta syn 8.125 h β- 0.708 180W 180 mTa 0.012% >1.2×1015 y ε 0.929 180Hf β- 0.783 180W IT 0.075 180Ta 181Ta 99.988% 181Ta is stable with 108 neutrons 182Ta syn 114.43 d β- 1.814 182W 183Ta syn 5.1 d β- 1.070 183W
References

Tantalum (pronounced /ˈtæntələm/) (formerly tantalium /tænˈtæliəm/) is a chemical element with the symbol Ta and atomic number 73. A rare, hard, blue-gray, lustrous, transition metal, tantalum is highly corrosion-resistant and occurs naturally in the mineral tantalite.

Characteristics

Tantalum is dark, 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 be dissolved with hydrofluoric acid or acidic solutions containing the fluoride ion and sulfur trioxide, as well as with a solution of potassium hydroxide. Tantalum's high melting point of 3017 °C (boiling point 5458 °C) is exceeded only by tungsten and rhenium for metals, and carbon.

Applications

The major use for tantalum, as the metal powder, is in the production of electronic components, mainly capacitors and some high-power resistors. Tantalum electrolytic capacitors exploit the tendency of tantalum to form a protective oxide surface layer, using tantalum powder, pressed into a pellet shape, as one "plate" of the capacitor, the oxide as the dielectric, and an electrolytic solution or conductive solid 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, tantalum can be drawn into fine wires or filaments, which are used for evaporating metals such as aluminium.

Due to the fact that it resists attack by body fluids and is nonirritating, tantalum is widely used in making surgical instruments and implants. For example, porous tantalum coatings are used in the construction of orthopedic implants due to tantalum's ability to form a direct bond to hard tissue. The oxide is used to make special high refractive index glass for camera lenses. The metal is also used to make vacuum furnace parts.

Shaped charge and explosively formed penetrator liners have been constructed from tantalum.

History

Tantalum 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. The English word tantalize was named after Tantalus, and tantalum was named after the tantalizing problems posed by the inertness of the element and its compounds.

For many years, the commercial technology for separating tantalum from niobium involved the fractional crystallization of potassium heptafluorotantalate away from potassium oxypentafluoroniobate monohydrate, that had been discovered by Marignac in the 1860s. The method has been supplanted by solvent extraction from fluoride-containing solutions.

Occurrence

Tantalum occurs principally in the minerals tantalite [(Fe, Mn) Ta₂O₆], microlite, and euxenite (other minerals: samarskite, and fergusonite).

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

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-copper alloy which is more flexible and two to three times stronger than traditional steel alloys.

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.