|
General |
Name, Symbol, Number | Tungsten, W, 74 |
Chemical series | Transition metals |
Group, Period, Block | 6 (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]4f14 5d4 6s2 |
e- 's per energy level | 2, 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 ×10-3 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 |
|
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).
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. Common
oxidation states of tungsten are +2, +3, +4, +5, +6, but it exhibits all oxidation states from -2 to 6. Tungsten metal forms a protective
oxide when exposed to air. When alloyed in small quantities with
steel, it greatly increases its hardness.
Tungsten is a metal with a wide range of uses, the largest of which is as tungsten carbide (W
2C, WC) in cemented
carbides. Cemented carbides (also called hardmetals) are wear-resistant materials used by the metalworking,
mining, and
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.
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.
José[?] and
Fausto Elhuyar[?] found an acid in wolframite that was identical to the tungstic acid in 1783. In
Spain later that year the brothers succeeded in isolating tungsten through reduction of this acid with
charcoal. They are credited for the discovery of the element.
Enzymes called
oxidoreductases[?] use tungsten in a way that is similar to
molybdenum by using it in a tungsten-
pterin[?] complex.
Tungsten is found in the
minerals wolframite (
iron-
manganese tungstate, FeW
O4/MnWO
4) ,
scheelite[?] (
calcium tungstate, CaWO
4),
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.
Naturally occurring tungsten is made of three stable
isotopes and two
radioisotopes that have such absurdly long
half lifes that for most practical purposes are considered stable. In addition to this, there are twenty-one unstable isotopes with W-181 being the longest lived (t
˝ = 121.2 days).