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Tungsten

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                74              tantalum ← tungsten → rhenium
                Mo
                ↑
                W
                ↓
                Sg

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                      Name, Symbol, Number tungsten, W, 74
                                         Chemical series transition metals
                                              Group, Period, Block 6, 6, d
                                        Appearance grayish white, lustrous
                                              Atomic mass 183.84 (1) g/mol
                               Electron configuration [Xe] 4f^14 5d^4 6s^2
                                   Electrons per shell 2, 8, 18, 32, 12, 2
                                                       Physical properties
                                                               Phase solid
                                      Density (near r.t.) 19.25 g·cm^−3
                                    Liquid density at m.p. 17.6 g·cm^−3
                                                     Melting point 3695  K
                                                    (3422 ° C, 6192 ° F)
                                                      Boiling point 5828 K
                                                   (5555 ° C, 10031 ° F)
                                         Heat of fusion 52.31 kJ·mol^−1
                                   Heat of vaporization 806.7 kJ·mol^−1
                          Heat capacity (25 °C) 24.27 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 3477 3773 4137 4579 5127 5823

                                                         Atomic properties
                                     Crystal structure cubic body centered
                                Oxidation states 6, 5, 4, 3, 2, 1, 0, −1
                                                     (mildly acidic oxide)
                                    Electronegativity 2.36 (Pauling scale)
                                       Ionization energies 1st: 770 kJ/mol
                                                          2nd: 1700 kJ/mol
                                                      Atomic radius 135 pm
                                              Atomic radius (calc.) 193 pm
                                                    Covalent radius 146 pm
                                                             Miscellaneous
                                                 Magnetic ordering no data
                               Electrical resistivity (20 °C) 52.8 nΩ·m
                        Thermal conductivity (300 K) 173 W·m^−1·K^−1
                        Thermal expansion (25 °C) 4.5 µm·m^−1·K^−1
                              Speed of sound (thin rod) ( r.t.) (annealed)
                                                          4620   m·s^−1
                                                   Young's modulus 411 GPa
                                                     Shear modulus 161 GPa
                                                      Bulk modulus 310 GPa
                                                        Poisson ratio 0.28
                                                         Mohs hardness 7.5
                                                 Vickers hardness 3430 MPa
                                                 Brinell hardness 2570 MPa
                                             CAS registry number 7440-33-7
                                                         Selected isotopes

                 CAPTION: Main article: Isotopes of tungsten

                              iso    NA    half-life  DM  DE ( MeV)   DP
                             ^180W 0.12%  1.8×10^18 y α   2.516     ^176Hf
                             ^181W syn    121.2 d     ε   0.188     ^181Ta
                             ^182W 26.50% W is stable with 108 neutrons
                             ^183W 14.3%  W is stable with 109 neutrons
                             ^184W 30.64% W is stable with 110 neutrons
                             ^185W syn    75.1 d      β^- 0.433     ^185Re
                             ^186W 28.43% W is stable with 112 neutrons

                                                                References

   Tungsten ( IPA: /ˈtʊŋstən/), also called wolfram ( IPA: /ˈwʊlfrəm,
   -am/) is a chemical element that has the symbol W ( New Latin:
   wolframium) and atomic number 74. A very hard, heavy, steel-gray to
   white transition metal, tungsten is found in several ores including
   wolframite and scheelite and is remarkable for its robust physical
   properties, especially the fact that it has the highest melting point
   of all the non- alloyed metals and the second highest of all the
   elements after Carbon. The pure form is used mainly in electrical
   applications but its many compounds and alloys are widely used in many
   applications (most notably in light bulb filaments, and as both the
   filament and target in most X-ray tubes and in superalloys).

Notable characteristics

   Pure tungsten is steel-gray to tin-white and is a hard metal. Tungsten
   can be cut with a hacksaw when it is very pure (it is brittle and hard
   to work when impure) and is otherwise worked by forging, drawing,
   extruding, or sintering. This element has the highest melting point
   (3422 ° C) (6192 ° F), lowest vapor pressure and the highest tensile
   strength at temperatures above 1650 °C (3000 °F) of all metals. Its
   corrosion resistance is excellent and it can only be attacked slightly
   by most mineral acids. Tungsten metal forms a protective oxide when
   exposed to air but can be oxidized at high temperature. Steel alloyed
   with small quantities of tungsten greatly increases in toughness.

Applications

   Tungsten is a metal with a wide range of uses, the largest of which is
   as tungsten carbide (W[2]C, WC) in cemented carbides. Cemented carbides
   (also called hardmetals) are wear-resistant materials used by the
   metalworking, mining, petroleum and construction industries. Tungsten
   is widely used in light bulb and vacuum tube filaments, as well as
   electrodes, because it can be drawn into very thin metal wires that
   have a high melting point. Other uses:
     * A high melting point also makes tungsten suitable for
       space-oriented and high temperature uses which include electrical,
       heating, and welding applications, notably in the GTAW process
       (also called TIG welding).
     * Hardness and density properties make this metal ideal for making
       heavy metal alloys that are used in armaments, heat sinks, and
       high-density applications, such as weights, counterweights, ballast
       keels for yachts and tail ballast for commercial aircraft.
     * The high density makes it an ideal ingredient for darts, normally
       80% and sometimes up to 97 %.
     * High speed steel contains tungsten and some tungsten steels contain
       as much as 18 % tungsten.
     * Superalloys containing tungsten are used in turbine blades and
       wear-resistant parts and coatings. Examples are Hastelloy and
       Stellite.
     * Tungsten powder is used as a filler material in thermoplastic
       composites which are used as a nontoxic substitute for lead, in
       bullets, shot, and radiation shields.
     * Tungsten chemical compounds are used in catalysts, inorganic
       pigments, and tungsten disulfide high-temperature lubricants which
       are stable to 500 °C (930 °F).
     * Since this element's thermal expansion is similar to borosilicate
       glass, it is used for making glass-to-metal seals.
     * It is used in kinetic energy penetrators, usually alloyed with
       nickel and iron or cobalt to form tungsten heavy alloys, as an
       alternative to depleted uranium.
     * Tungsten is used as an interconnect material in integrated
       circuits. Contact holes are etched in silicon dioxide dielectric
       material, filled with tungsten and polished to form connections to
       transistors. Typical contact holes can be as small as 65 nm.
     * Tungsten carbide is one of the hardest substances in existence and
       is used in, among other things, machine tools such as milling
       cutters. Tungsten carbide is the most common material used to make
       milling and turning tools, and used together with cobalt and carbon
       is often the best choice for such applications.
     * Used extensively for shielding in the Radiopharmaceutical industry.
       It is often employed when transporting individual FDG doses (called
       'pigs') - the high energy of Fluorine-18 makes lead much less
       effective.
     * Tungsten is used in the emitters of focused ion beam and electron
       microscopes.
     * Tungsten is also beginning to see uses in jewelry. Its hardness
       makes it ideal for rings that will never scratch, and will in turn
       not need polishing (this is especially good for brushed designs).

   Miscellaneous: Oxides are used in ceramic glazes and calcium/magnesium
   tungstates are used widely in fluorescent lighting. Crystal tungstates
   are used as scintillation detectors in nuclear physics and nuclear
   medicine. The metal is also used in X-ray targets and heating elements
   for electrical furnaces. Salts that contain tungsten are used in the
   chemical and tanning industries. Tungsten 'bronzes' (so-called due to
   the colour of the tungsten oxides) along with other compounds are used
   in paints. Tungsten Carbide has recently been used in the fashioning of
   jewelry due to its hypoallergenic nature and the fact that due to its
   extreme hardness it is not apt to lose its luster like other polished
   metals. Some types of strings for musical instruments are wound with
   tungsten wire.

History

   Tungsten ( Swedish tung sten meaning "heavy stone"), even though the
   current name for the element in Swedish is Wolfram (sometimes spelled
   in Swedish as volfram), from the denomination volf rahm by Wallerius in
   1747, translated from the description by Agricola in 1546 as Lupi
   spuma, meaning "wolf's froth" after the way tin is eaten up like a wolf
   after sheep in the process of its extraction^ .

   It was first hypothesized to exist by Peter Woulfe in 1779 who examined
   wolframite and concluded that it must contain a new substance. In 1781
   Carl Wilhelm Scheele ascertained that a new acid could be made from
   tungstenite. Scheele and Torbern Bergman suggested that it could be
   possible to obtain a new metal by reducing tungstic acid. In 1783 José
   and Fausto Elhuyar found an acid in wolframite that was identical to
   tungstic acid. In Spain later that year the brothers succeeded in
   isolating tungsten through reduction of this acid with charcoal. They
   are credited with the discovery of the element.

   In World War II, tungsten played an enormous role in background
   political dealings. Portugal, as the main European source of the
   element, was put under pressure from both sides, because of its sources
   of wolframite ore. The resistance to high temperatures, as well as the
   extreme strength of its alloys, made the metal into a very important
   raw material for the weaponry industry.

Biological role

   Enzymes called oxidoreductases use tungsten in a way that is similar to
   molybdenum by using it in a tungsten- pterin complex.

   On August 20, 2002, officials representing the U.S.-based Centers for
   Disease Control and Prevention announced that urine tests on leukemia
   patient families and control group families in the Fallon, Nevada area
   had shown elevated levels of the metal tungsten in the bodies of both
   groups. Sixteen recent cases of cancer in children were discovered in
   the Fallon area which has now been identified as a cancer cluster, (it
   should be noted, however, that the majority of the cancer victims are
   not long time residents of Fallon). Dr. Carol H. Rubin, a branch chief
   at the CDC, said data demonstrating a link between tungsten and
   leukemia is not available at present.

Occurrence

   Tungsten is found in the minerals wolframite (iron-manganese tungstate,
   FeWO[4]/MnWO[4]), scheelite (calcium tungstate, CaWO[4]), ferberite and
   hübnerite. There are important deposits of these minerals in Bolivia,
   California, China, Colorado, Portugal, Russia, Vietnam and South Korea
   (with China producing about 75 % of the world's supply). The metal is
   commercially produced by reducing tungsten oxide with hydrogen or
   carbon.

   World tungsten reserves have been estimated at 7 million t W.
   Unfortunately, most of these reserves are not economically workable so
   far. At our current annual consumption rate, these reserves will only
   last for about 140 years. China has been the largest supplier thus far.
   According to further estimates, it has been suggested that 30% of the
   reserves are Wolframite and 70% are Scheelite ores. Another factor that
   controls the tungsten supply is scrap recycling of tungsten and it has
   been proven to be a very valuable raw material in comparison to ore.

Compounds

   The most common formal oxidation state of tungsten is +6, but it
   exhibits all oxidation states from -1 to +6. Tungsten typically
   combines with oxygen to form the yellow tungstic oxide, WO[3], which
   dissolves in aqueous alkaline solutions to form tungstate ions,
   WO[4]^2−.

Aqueous polyoxoanions

   Aqueous tungstate solutions are noted for the formation of
   polyoxoanions under neutral and acidic conditions. As tungstate is
   progressively treated with acid, it first yields the soluble,
   metastable "paratungstate A" anion, W[7]O[24]^6−, which over hours or
   days converts to the less soluble "paratungstate B" anion,
   H[2]W[12]O[42]^10−. Further acidification produces the very soluble
   metatungstate anion, H[2]W[12]O[40]^6−, after equilibrium is reached.
   The metatungstate ion exists as a symmetric cluster of twelve
   tungsten-oxygen octahedra known as the " Keggin" anion. Many other
   polyoxoanions exist as metastable species. The inclusion of a different
   atom such as phosphorus in place of the two central hydrogens in
   metatungstate produces a wide variety of the so-called
   heteropolyanions.

Isotopes

   Naturally occurring tungsten consists of five isotopes whose half-lives
   are so long that they can be considered stable. All can decay into
   isotopes of element 72 (hafnium) by alpha emission; ^180W has been
   observed to have a half life of 1.8 +- 0.2 Ea. The other naturally
   occurring isotopes have not been observed to decay, constraining their
   half-lives to be: ^182W, T[1/2] > 8.3 Ea; ^184W, T[1/2] > 29 Ea; ^185W,
   T[1/2] > 13 Ea; ^186W, T[1/2] > 27 Ea. On average, two alpha decays of
   ^180W occur in one gram of natural tungsten per year.

   27 artificial radioisotopes of tungsten have been characterized, the
   most stable of which are ^181W with a half-life of 121.2 days, ^185W
   with a half-life of 75.1 days, ^188W with a half-life of 69.4 days and
   ^178W with a half-life of 21.6 days. All of the remaining radioactive
   isotopes have half-lives of less than 24 hours, and most of these have
   half-lives that are less than 8 minutes. Tungsten also has 4  meta
   states, the most stable being ^179mW (t[½] 6.4 minutes).
   Retrieved from " http://en.wikipedia.org/wiki/Tungsten"
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