Special resistor materials: tungsten, Physics

Tungsten:

Atomic number

74

Symbol

W

Atomic weight

183.85

Discovery

Purified Tungsten in 1783.

Electronic configuration

[Xe] 6s2 4f14 5d4

Word origin

Swedish tungsten, heavy stone

Melting point

3410+/-200C

Boiling point

56600C

Electrical resistivity

5.5*10-8 ohm-m

Properties:

1.      Tungsten is a steel-gray to tin-white metal.

2.      Impure tungsten metal is quite brittle, although pure tungsten can be cut with a saw, spun, drawn, forged and extruded.

3.      Tungsten has the highest melting point and the lowest vapour pressure of the metals.

4.      At temperature exceeding 16500 C, it has the highest tensile strength.

5.      Tungsten oxidizes in air at elevated temperatures, although it generally has excellent corrosion resistance and is minimally attacked by most acids.

6.      It is resistant to destructive forces of arcing.

Uses:

1.      The thermal expansion of tungsten is similar to that of borosilicate glass, so the metal is used for glass/metal seals.

2.      Tungsten and its alloys are used to make filaments for electric lamps and television tubes, as electric contacts, X-ray targets, heating elements, for metal evaporation components, and for other numerous high temperature applications.

3.      Hastelloy, satellite, high speed tool steel, and numerous other alloys contain tungsten.

4.      Magnesium and calcium tungstenates are used in fluorescent lighting.

5.      Tungsten carbide is important in the mining, metalworking and petroleum industries.

6.      Tungsten disulphide is used as a dry high-temperature lubricant.

7.      Tungsten bronze and other tungsten compounds are used in paints.

Sources: Tungsten occurs in Wolframite, scheelite, ferberite and huebnerite. Tungsten is produced commercially by reducing tungsten oxide with carbon or hydrogen.

Posted Date: 7/21/2012 7:51:10 AM | Location : United States







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