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Tantalum

2007 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
                                           Atomic mass 180.94788 (2) g/mol
                               Electron configuration [Xe] 4f^14 5d^3 6s^2
                                   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
                          Heat capacity (25 °C) 25.36 J·mol^−1·K^−1

   CAPTION: 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 (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 nΩ·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

                 CAPTION: 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%  >1.2×10^15 y ε   0.929     ^180Hf
                                                      β^- 0.783     ^180W
                                                      IT  0.075     ^180Ta
                        ^181Ta   99.988% Ta 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 ( IPA: /ˈtæntələm/), formerly tantalium ( IPA: /ˌtænˈtæliəm/)
   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.

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.

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.

   Due to the fact that it resists attack by body fluids and is
   nonirritating, tantalum is widely used in making surgical instruments
   and implants. The 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 [(Fe, Mn)
   Ta[2]O[6]] 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, 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-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 10^15 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.
   Retrieved from " http://en.wikipedia.org/wiki/Tantalum"
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   with only minor checks and changes (see www.wikipedia.org for details
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