Tungsten metal was isolated in the year 1783 by J.J and F. Elhuyar in Spain. This metal is lustrous and silvery white in color and does not occur naturally. It is extracted from its ores, the two of the major ones being wolframite and scheelite. Tungsten metal is relatively inert and resists corrosion. This metal has the highest melting point of all metals and when it is in its pure form, it can be really easy to work with. But when there is presence of impurities, it becomes quite brittle and hence hard to use or work with.The high melting point of tungsten metal makes it useful for many applications under extreme conditions, as are discussed next.
2. Uses and applications of tungsten
· The fact that tungsten has a very high, infact the highest melting points makes it suitable for use as an electric filament in electric light bulbs, electrodes, etc.
· A number of tungsten-based alloys are further used in diverse applications, for instance, radiation shields since they provide 50% increase in density compared to lead.
· Tungsten and its alloys can be found military applications such as shells, armor, etc. These alloys also find usages in aerospace industry as well, i.e.aeronautics and astronautics.
· Tungsten carbide powder along with cobalt and nickel powder are often compressed and then sintered for the production of cemented carbides. These cemented carbides are then used in place of high speed steel to form the tip of cutting and drillingtools.
3. Occurrence and extraction of tungsten
Tungsten metal is found to be occurring in such minerals as wolframite, ferberite, scheelite and hubrenite ores. China is the largest producer of tungsten metal, followed by Russia, Bolivia and Canada. In order to extract tungsten from its ores, the ores are first crushed, then cleaned and treated with alkalis and this process results in tungsten trioxide. Finally, tungsten trioxide is heated with carbon or hydrogen gas in order to obtain the tungsten metal and carbon dioxide or water vapor and tungsten metal.
4. Properties of tungsten
Biological function: tungsten metal has no biological role and also has low toxicity.
· In pure form, it is very hard and malleable and hence easy to work with.If impure, it is brittle and difficult to fabricate.
· Tungsten has the highest melting point and lowest vapor pressure. It has really high tensile strength as well.
· Tungsten owns the lowest coefficient of thermal expansion amongall pure metals.
· It is of high resistance to corrosion and has 5 stable isotopes.
5. Sample material: radiation shield
Wolfmet tungsten alloy finds use as a shield against x rays as well as gamma rays. It is also used as a radiation shield because of the high density of Wolfmet tungsten by engineers and has been used like this for years. It is also often used as a collimator to focus radiation beams onto a target. This alloy of tungsten has 60% more density than lead and hence provides superior attenuation characteristics for x-ray and gamma radiations.
By Stanford Materials http://stanfordmaterials.com/
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