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ungsten is
a lustrous and silvery white metal. The bulk metal resists attack by
oxygen, acids and alkalis. Tungsten has the highest melting point of any
metal.
Applications
Tungsten
is used in filaments in incandescent light bulbs, it is also used in
electric contacts and arc-welding electrodes. Tungsten is used in
alloys, such as steel, to which it imparts great strength. Cement
carbide is the most important use for tungsten: its main component is
tungsten carbide (WC). It has the strength to our cast iron and it makes
excellent cutting tools for the machining of steel. X-ray tubes
for medical use have a tungsten emitter coil and the screen used to view
X-rays rely on calcium and magnesiumtungstate phosphors to convert
X-rays into blue visible light. Tungsten is also used in microchip
tecnology and liquid crystals displays.
Tungsten in the environment
Very
little tungsten has been detetced in the dew soils that have been
analysed for it, although around an ore-processin plant in Russia levels
as high as 2000 ppm were found. The concentration of the element in
natural waters is very low.
There are
several minerals of tungsten, the most important are scheelite and
wolframite. The main mining area is China, which today accounts for more
than two-thirds of the world's supply. Other places with active tungsten
mines are Russia, Austria, Bolivia, Peru and Portugal. World production
is around 40.000 tonnes per year and reserves are estimated to be around
5 million tonnes. Tungsten is also recycled and it meets 30% of demand.
Tungsten has been shown to act by antagonizing the
action of the essential trace element, Molybdenum. Long
industrial experience has indicated no pneumoconiosis to develop among
workers exposed solely to W or its insoluble compounds (at air
concentrations of the order of 5 mg/m3).
Acute
health effects: Irritating to the skin and eyes on contact.
Inhalation will cause irritation to the lungs and mucus membrane.
Irritation to the eyes will cause watering and redness. Reddening,
scaling, and itching are characteristics of skin inflammation. Follow
safe industrial hygiene practices and always wear protective equipment
when handling this compound.
Chronic
health effects: This product has no known chronic effects.
Repeated or prolong exposure to this compound is not known to aggravate
medical conditions.
All
tungsten compounds should be regarded as highly toxic. The metal dust
presents a fire and explosion hazard.
Tungsten metal powder administered to animals has
been shown in several studies as not altogether inert. One study found
that guinea pigs treated orally or intravenously with tungsten suffered
from anorexia, colic, incoordination of movement, trembling, dyspnea and
weight loss. This
product is not expected to be hazardous for the environment. No specific
ecotoxicity data is available for this product.
Back to periodic
table.
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