Tungsten

For other uses, see Tungsten (disambiguation).

74 tantalum ← tungsten → rhenium Mo ↑ W ↓ Sg 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] 4f14 5d4 6s2
Electrons per shell	2, 8, 18, 32, 12, 2
Physical properties
Phase	solid
Density (near r.t.)	19.25 g/cm³
Liquid density at m.p.	17.6 g/cm³
Melting point	3683 K (3410 °C, 6192 °F)
Boiling point	5828 K (5555 °C, 10031 °F)
Heat of fusion	52.31 kJ/mol
Heat of vaporization	806.7 kJ/mol
Heat capacity	(25 °C) 24.27 J/(mol·K)
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 (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·K)
Thermal expansion	(25 °C) 4.5 µm/(m·K)
Speed of sound (thin rod)	(r.t.) (annealed) 4620 m/s
Speed of sound (thin rod)	(r.t.) 411 m/s
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
Notable isotopes
Main article: Isotopes of tungsten iso NA half-life DM DE (MeV) DP 180W 0.12% 1.8×1018 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

Tungsten (formerly wolfram) is a chemical element that has the symbol W (L. 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 a higher melting point than any other non-alloy in existence. 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 space-age superalloys).

History

Tungsten powder

Tungsten was first hypothesized to exist by Peter Woulfe in 1779, when he examined the mineral wolframite and concluded 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 the possibility of obtaining a new metal by reducing this acid, named tungstic acid. In 1783, two brothers, 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 from the acid, through a chemical process called reduction, using charcoal. They are credited with discovering the element.

In World War II, tungsten played an enormous role in background political dealings. The metal's resistance to high temperatures, as well as the extreme strength of its alloys, made tungsten a very important raw material for the weapons industry. Thus both sides in the war sought the element, putting pressure on Portugal, the main European source of wolframite ore.

• (Swedish, Danish and Norwegian tung sten meaning "heavy stone", even though the current name for the element in all three languages 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)

Occurrence

Tungsten is found in the minerals wolframite (iron-manganese tungstate, FeWO₄/MnWO₄), scheelite (calcium tungstate, CaWO₄), ferberite, and hübnerite. Important deposits of these minerals have been found in California and Colorado in the United States, and in the nations of Bolivia, China, Portugal, Russia, and South Korea. China produces 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. It has been suggested that 30% of the reserves are wolframite and 70% are scheelite ores. Unfortunately, most of these reserves are not economically workable, so far. At our current annual consumption rate, these reserves will last for only about 140 years. Another factor that controls the tungsten supply is scrap recycling of tungsten, which has been proven to be a very valuable source.

Notable characteristics

Tungsten is a chemical element classified as a transition metal. In the periodic table, it lies in period 6, between tantalum (Ta) and rhenium (Re).

The pure metal is hard, with a steel-gray to tin-white color. When impure, it is brittle and hard to work with, but in the pure form it can be cut with a hacksaw. In addition, it can be worked by forging, drawing, or extruding.

Of all metals, this element has the highest melting point (3422 °C or 6192 °F) and lowest vapor pressure. It also has the highest tensile strength (the maximum stress it can withstand before deformation or breakage) at temperatures above 1650 °C (3000 °F). It is extremely resistant to corrosion and can be attacked only slightly by most mineral acids. When exposed to air, a protective oxide is formed on the surface of the metal, but tungsten can be oxidized more fully at high temperature. When alloyed in small quantities with steel, tungsten greatly increases the hardness of steel.

Isotopes

Naturally occurring tungsten consists of five radioactive isotopes, but they have such long half-lives that they can be considered stable. All five can decay into isotopes of hafnium-72 by the emission of alpha particles (corresponding to nuclei of helium-4). Alpha decay has been observed (in 2003) in only ¹⁸⁰W, the lightest and rarest of these isotopes. On average, two alpha decays of ¹⁸⁰W occur in one gram of natural tungsten per year.

In addition, 27 artificial radioisotopes of tungsten have been characterized. The most stable of these 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 the other artificial isotopes have half-lives of less than 24 hours, and most of these have half-lives under 8 minutes. Tungsten also has four "metastable" states, of which the most stable is ^179mW (half-life of 6.4 minutes). (A metastable state of an atom is an unstable state in which a proton or neutron in the nucleus is in an energetically higher, or excited, state.)

Applications

Tungsten metal is widely used in filaments for light bulbs and vacuum tubes, as well as for electrodes, because it can be drawn into very thin metal wires with a high melting point. Its largest use, however, is in the form of tungsten carbide (W₂C, WC), classified as a "cemented carbide." Cemented carbides (also called hard metals) are wear-resistant materials used in the metalworking, mining, petroleum, and construction industries.

Additional uses of tungsten are as follows:

• Its high melting point makes tungsten suitable for space-oriented and high-temperature applications, such as electrical, heating, and welding purposes. One notable use is in the "gas tungsten arc welding" (GTAW) process, also called "TIG" welding.
• Based on its hardness, tungsten is ideal for making heavy metal alloys for armaments.
• Given its high density, it is used in weights, counterweights, and ballast keels for yachts, and it is also used in darts (normally 80 % and sometimes up to 97 % tungsten).
• "High speed steel" (which can cut material at higher speeds than carbon steel) contains tungsten, and some tungsten steels contain as much as 18 % tungsten.
• Turbine blades and wear-resistant parts and coatings use "superalloys" containing tungsten. (Superalloys are high-performance alloys that function well at elevated temperatures.)
• Composites containing tungsten are used as substitutes for lead in bullets and shot.
• Tungsten chemical compounds are used as catalysts and inorganic pigments. Tungsten disulfide is useful in high-temperature lubricants, as it is 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 65nm.
• 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 to make milling and turning tools from and often the best choice for such applications.

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.

Biological role

In the body, a class of enzymes called oxidoreductases use tungsten in a complex with the organic compound pterin. (This is similar to the use of molybdenum by these enzymes.)

On August 20, 2002, officials representing the U.S.-based Centers for Disease Control and Prevention (CDC) 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 most of the cancer victims were not long-time residents of Fallon. In addition, Dr. Carol H. Rubin, a branch chief at the CDC, said data demonstrating a link between tungsten and leukemia is not available at present.

Compounds

The most common oxidation state of tungsten is +6, 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.

See also tungsten compounds.

References

ISBN links support NWE through referral fees

• Los Alamos National Laboratory - Tungsten

DC/AC Circuits and Electronics: Principles & Applications by Robert K. Herrick, Published by Delmar Learning 2003 for Purdue University

External links

• WebElements.com – Tungsten
• Properties, Photos, History, MSDS
• ScienceLab.com – Tungsten
• Picture in the collection from Heinrich Pniok
• Tungsten-Scrap.com – Articles about Tungsten and applications for Tungsten scrap
• Elementymology & Elements Multidict by Peter van der Krogt – Tungsten

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