Type:scheelite,wolframite,ferberite,hubnerite
Listing description
A
steel-gray metal
under standard conditions when uncombined, tungsten is found naturally on Earth
only combined in chemical compounds. Its important ores
include wolframite and scheelite.
The free element 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.
Also remarkable is its very high density of 19.3 times that of water. This
density is slightly more than that of uranium
and 71% more than that of lead.[3]
Tungsten with minor amounts of impurities is often brittle[4]
and hard, making it difficult to work.
However, very pure tungsten is more ductile, and can be cut with a hacksaw.[5]
Detailed description
This density is
slightly more than that of uranium and 71% more than that of lead.[3] Tungsten with minor amounts of
impurities is often brittle[4] and hard, making it difficult to work. However, very pure tungsten is more ductile,
and can be cut with a hacksaw.[5]
The unalloyed
elemental form is used mainly in electrical applications. Tungsten's many
alloys have numerous applications, most notably in incandescent light bulb filaments, X-ray tubes (as both the filament and target),
and superalloys. Tungsten's hardness and high density
give it military applications in penetrating projectiles. Tungsten compounds
are most often used industrially as catalysts.
Tungsten is the
only metal from the third transition series that is known to occur in biomolecules, and is the heaviest element known to
be used by living organisms.[6][7]
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History
In 1781, Carl
Wilhelm Scheele
discovered that a new acid, tungstic acid, could be made from scheelite (at the time named tungstenite).
Scheele and Torbern
Bergman suggested that
it might be possible to obtain a new metal by reducing this acid.[8] In 1783, José and Fausto Elhuyar found an acid made from wolframite
that was identical to tungstic acid. Later that year, in Spain, the brothers succeeded in isolating tungsten
by reduction of this acid with charcoal, and they are credited with the
discovery of the element.[9][10]
In World War II, tungsten played a significant role
in background political dealings. Portugal, as the main European source of the
element, was put under pressure from both sides, because of its deposits of
wolframite ore. Tungsten's resistance to high temperatures and its strength in
alloys made it an important raw material for the weaponry industry.[11]
Characteristics
Physical properties
In its raw form,
tungsten is a steel-gray metal that is often brittle and hard to work, but, if pure, it can be worked easily.[5] It is worked by forging, drawing, extruding or sintering. Of all metals in pure form, tungsten has the
highest melting
point (3,422 °C, 6,192 °F), lowest vapor pressure and (at temperatures above
1,650 °C, 3,000 °F) the highest tensile strength.[13] Tungsten has the lowest coefficient of thermal expansion of any pure metal. The low thermal
expansion and high melting point and strength of tungsten are due to strong covalent bonds formed between tungsten atoms by the
5d electrons.[14] Alloying small quantities of tungsten
with steel greatly increases its toughness.[3]
Occurrence
Tungsten is found
in the minerals wolframite (iron-manganese tungstate, (Fe,Mn)WO4), scheelite (calcium tungstate, (CaWO4), ferberite (FeWO4) and hübnerite (MnWO4). China produced over 75% of this total, with most of
the remaining production coming from Austria, Bolivia, Portugal, Russia, and Colombia.[20] Wolframite is also considered to be a
conflict
mineral due to the
unethical mining practices observed in the Democratic Republic of the Congo.[citation needed]
Biological role
Tungsten, at
atomic number 74, is the heaviest element known to be biologically functional,
with the next heaviest being iodine (Z = 53). Although not in
eukaryotes, tungsten is used by some bacteria. For example, enzymes called oxidoreductases use tungsten similarly to molybdenum by using it in a tungsten-pterin complex with
molybdopterin (molybdopterin, despite its name,
does not contain molybdenum, but may complex with either molybdenum or tungsten
in use by living organisms). Tungsten-using enzymes typically reduce carboxylic
acids to aldehydes.[21] However, the tungsten oxidoreductases may also catalyse oxidations. The
first tungsten-requiring enzyme to be discovered also requires selenium, and in
this case the tungsten-selenium pair may function analogously to the
molybdenum-sulfur pairing of some molybdenum
cofactor-requiring
enzymes.[22] One of the enzymes in the
oxidoreductase family which sometimes employ tungsten (bacterial formate
dehydrogenase
H) is known to use a selenium-molybdenum version of molybdopterin.[23] Although a tungsten-containing
xanthine dehydrogenase from bacteria has been found to contain
tungsten-molydopterin and also non-protein bound selenium, a tungsten-selenium
molybdopterin complex has not been definitively described.[24]
Other effects on biochemistry
In soil, tungsten
metal oxidizes to the tungstate anion. It may substitute for molybdenum in certain enzymes, and in such cases the resulting enzyme in
eukaryotes would presumably be inert. The soil's chemistry determines how the
tungsten polymerizes; alkaline soils cause monomeric tungstates; acidic soils cause polymeric tungstates.[25]
Sodium
tungstate and lead have been studied for their effect on earthworms. Lead was found to be lethal at low
levels and sodium tungstate was much less toxic, but the tungstate completely
inhibited their reproductive
ability.[26]
Production
From its ores,
about 37,400 tonnes of tungsten concentrates are produced per year in 2000.[20] Tungsten is extracted from its ores
in several stages. The ore is eventually converted to tungsten(VI)
oxide (WO3),
which is heated with hydrogen or carbon to produce powdered tungsten.[8] It can be used in that state or
pressed into solid bars.
WF6 + 3 H2 → W +
6 HF
Tungsten is not
traded as a futures contract and cannot be tracked on exchanges like the London
Metal Exchange.
The price for pure metal is around $20,075 per tonne as of October 2008.[29]
Applications
Approximately
half of the tungsten is consumed for the production of hard materials (tungsten
carbide), with the remaining major use being its use in alloys and steels. Less
than 10% is used in chemical compounds.[30]
Hard materials
Tungsten is
mainly used in the production of hard materials based on tungsten carbide, one
of the hardest carbides, with a melting point of 2770 °C
for. WC is an efficient electrical
conductor, but W2C
is less so. WC is used to make wear-resistant abrasives and cutters and knives for drills, circular saws, milling and turning tools used by the metalworking,
woodworking, mining, petroleum and construction industries[3] and accounts for about 60% of current
tungsten consumption.[31]
Alloys
The hardness and
density of tungsten are applied in obtaining heavy
metal alloys. A good example is high speed steel, which can contain as much as 18%
tungsten.[32] Tungsten's high melting point makes
tungsten a good material for applications like rocket
nozzles, for example in
the UGM-27
Polaris Submarine-launched ballistic missile.[33] Superalloys containing tungsten, such as Hastelloy and Stellite, are used in turbine blades and wear-resistant parts and
coatings.
In armaments,
tungsten, usually alloyed with nickel and iron or cobalt to form heavy alloys, is used in kinetic
energy penetrators
as an alternative to depleted uranium, in applications where uranium's
additional pyrophoric properties are not required (for
example, in ordinary small arms bullets designed to penetrate body armor). Similarly,
tungsten alloys have also been used in cannon shells, grenades and missiles, to create supersonic shrapnel.
Niche uses
Applications
requiring its high density include heat sinks, weights, counterweights, ballast
keels for yachts, tail ballast for commercial aircraft, and as ballast in race
cars for NASCAR and Formula One. It is an ideal material to use as a dolly for riveting, where the mass necessary for good
results can be achieved in a compact bar. High-density alloys of tungsten with
nickel, copper or iron are used in high-quality darts[34] (to allow for a smaller diameter and
thus tighter groupings) or for fishing lures (tungsten beads allow the fly to sink
rapidly). Some types of strings for musical instruments are wound
with tungsten wires.
Electronics
Because it
retains its strength at high temperatures and has a high melting point, elemental tungsten is used in many
high-temperature applications,[37] such as light bulb, cathode-ray tube, and vacuum tube filaments, heating elements, and rocket engine nozzles.[5] Its high melting point also makes
tungsten suitable for aerospace and high-temperature uses such as electrical,
heating, and welding applications, notably in the gas
tungsten arc welding
process (also called tungsten inert gas (TIG) welding).
Because of its
conductive properties and relative chemical inertia, tungsten is also used in electrodes, and in the emitter tips in
electron-beam instruments that use field
emission guns,
such as electron
microscopes.
In electronics, tungsten is used as an interconnect material in integrated
circuits, between the silicon dioxide dielectric material and the transistors. It is
used in metallic films, which replace the wiring used in conventional
electronics with a coat of tungsten (or molybdenum) on silicon.[28]
The electronic
structure of tungsten makes it one of the main sources for X-ray targets,[38] and also for shielding from
high-energy radiations (such as in the radiopharmaceutical industry for shielding radioactive
samples of FDG). Tungsten powder is used as a filler
material in plastic composites, which are used as a
nontoxic substitute for lead in bullets, shot, and radiation shields. Since this element's
thermal expansion is similar to borosilicate
glass, it is used for
making glass-to-metal seals.
$51.74/KG
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