Tungsten

General
Name, Symbol, NumberTungsten, W, 74
Chemical series Transition metals
Group, Period, Block6 (VIB), 6 , d
Density, Hardness 19250 kg/m3, 7.5
Appearance grayish white, lustrous
Atomic properties
Atomic weight 183.84 amu
Atomic radius(calc.) 135 (193) pm
Covalent radius 146 pm
van der Waals radius no data
Electron configuration [Xe]44f14 5d4 6s2
e- 's per energy level2, 8, 18, 32, 12, 2
Oxidation states (Oxide) 6, 5, 4, 3, 2 (mildly acidic)
Crystal structure Cubic body centered
Physical properties
State of matter solid
Melting point 3695 K (6192 °F)
Boiling point 5828 K (10031 °F)
Molar volume 9.47 ×1010-3 m3/mol
Heat of vaporization 824 kJ/mol
Heat of fusion 35.4 kJ/mol
Vapor pressure 4.27 Pa at 3680 K
Speed of sound 5174 m/s at 293.15 K
Miscellaneous
Electronegativity 2.36 (Pauling scale)
Specific heat capacity 130 J/(kg*K)
Electrical conductivity 18.9 106/m ohm
Thermal conductivity 174 W/(m*K)
1st ionization potential 770 kJ/mol
2nd ionization potential 1700 kJ/mol
Most stable isotopes
isoNAhalf-life DMDE MeVDP
180W0.12%7.4 E16 y&alphano datano data
182W26.50%8.3 E18 yαno datano data
183W14.3%1.1 E17 yisono datano data
184W30.64%4 E18 yαno data180Hf
186W28.43%6.5 E18 yαno datano data
SI units & STP are used except where noted.
Tungsten (formerly wolfram) is a chemical element in the periodic table that has the symbol W 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. 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 in space-age superalloys).

Table of contents
1 Notable characteristics
2 Applications
3 History
4 Biological role
5 Occurrence
6 Compounds
7 Isotopes
8 External links

Notable characteristics

Pure tungsten is a steel-gray to tin-white 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, drawning, or extruding. This element has the highest melting point (3422 °C), lowest vapor pressure and the highest tensile strength at temperatures above 1650 °C 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. When alloyed in small quantities with steel, it greatly increases its hardness.

Applications

Tungsten is a metal with a wide range of uses, the largest of which is as tungsten carbide (W2C, 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 television tube filaments, as well as electrodes, because it can be drawn into very thin metal wires that have 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.
  • 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 and counterweights.
  • High speed tool steels (Hastelloy ®, Stellite ®) are often alloyed with tungsten, with tungsten steels containing as much as 18% tungsten.
  • Superalloys containing this metal are used in turbine blades, tool steels, and wear-resistant alloy parts and coatings.
  • Composites are used as a substitute for lead in bullets and shot.
  • Tungsten chemical compounds are used in catalysts, inorganic pigments, and tungsten disulfide high-temperature lubricants which is stable to 500 °C.
  • Since this element's thermal expansion is similar to borosilicate glass, it is used for making glass-to-metal seals.

Miscellaneous: Oxides are used in ceramic glazes and calcium/magnesium tungstates are used widely in fluorescent lighting. The metal is also used in X-ray targets, 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.

History

Tungsten (Swedish tung sten meaning "heavy stone") was first hypothesized to exist by Peter Woulfe in 1779 who examined wolframite (which was later named for Woulfe) 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 Berman 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.

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 US 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. 16 recent cases of cancer in children were discovered in the Fallon area which has now been identified as a "Cancer Cluster." Dr. Carol H. Rubin, a branch chief at the CDC, said data demonstrating a link between tungsten and leukemia are not available at present.

Occurrence

Tungsten is found in the minerals wolframite (iron-manganese tungstate, FeWO4/MnWO4) , scheelite (calcium tungstate, CaWO4), ferberite and huebnerite. Important deposits of these minerals are in Bolivia, California, China, Colorado, Portugal, Russia, 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.

Compounds

The most common oxidation state of tungsten is +6. Other oxidation states of tungsten are +2, +3, +4, +5, but it exhibits all oxidation states from -2 to 6. Tungsten typically combines with oxygen to form the yellow tungstic oxide, WO3, which dissolves in aqueous alkaline solutions to form tungstate ions, WO42-.

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, W7O246-, which over hours or days converts to the less soluble "paratungstate B" anion, H2W12O4210-. Further acidification produces the very soluble metatungstate anion, H2W12O406-, 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 is made of five radioisotopes that have such absurdly long half lifes that for most practical purposes are considered stable. 27 other radioisotopes have been characterized, with the most stable being W-181 with a half-life of 121.2 days, W-185 with a half-life of 75.1 days, W-188 with a half-life of 69.4 days and W-178 with a half-life of 21.6 days. All of the remaining radioactive isotopes have half-lifes that are less than 24 hours, and the majority of these have half-lifes that are less than 8 minutes. This element also has 4 meta states, with the most stable being W-179m (t˝ 6.4 minutes).

The isotopes of tungsten range in atomic weight from 157.974 amu (W-158) to 189.963 amu (W-190). The primary decay mode before the most abundant isotope, W-184, is electron capture, and the primary mode after is beta decay. The primary decay products before W-184 are element 73 (tantalum) isotopes, and the primary products after are element 75 (rhenium) isotopes.

External links


">
" size=20>

 
 

Browse articles alphabetically:
#0">0 | #1">1 | #2">2 | #3">3 | #4">4 | #5">5 | #6">6 | #7">7 | #8">8 | #9">9 | #_">_ | #A">A | #B">B | #C">C | #D">D | #E">E | #F">F | #G">G | #H">H | #I">I | #J">J | #K">K | #L">L | #M">M | #N">N | #O">O | #P">P | #Q">Q | #R">R | #S">S | #T">T | #U">U | #V">V | #W">W | #X">X | #Y">Y | #Z">Z