Wallid Guergour | Information on materials, tungsten

Metallurgy

21/01/2022


Wallid Guergour | Information on materials, tungsten.

Tungsten, with the chemical symbol W, is the most refractory of the metals, and consolidation techniques by arc melting or electron beam are relatively recent and limited to the laboratory. Unfortunately, they lead to a highly recrystallised metal that is exceptionally brittle at grain boundaries. As a result, current commercial production of wrought tungsten relies mainly on powder metallurgy techniques, a path brilliantly opened up for this metal in 1910 by Coolidge.


few informations on tungsten

The quality of the sintered products depends on the characteristics of the starting tungsten powder: purity, particle size, shape and porosity, lattice defects, specific surface area, particle size distribution, bulk density, tapped density, flowability, compressibility.


Some non-volatile substitute impurities are not removed during sintering and affect the ductility and workability of the metal. The trend is therefore to use high purity powders. Powders with an average grain size of 0.02 to 500 µm can be produced, but commercial powders are in the 0.3 to 10 µm range. Fine powders are more difficult to compress than coarse powders.


Unalloyed and doped tungsten


In wire form its main use is in the incandescent lamp industry. It is also used as a heating element for fluorescent tubes, lamp filament holders, electronic transmitters, electronic tube elements, vacuum metallization filaments (especially for aluminium: car headlights, capacitors, etc.), heating elements for high temperature furnaces. Tungsten rod is also used to make glass-to-metal joints, the electrode of arc lamps or welding machines. The sheet is used in the manufacture of resistors and screens for high-temperature industrial furnaces, under vacuum or hydrogen. Finally, tungsten is used in the manufacture of anticathodes for X-ray tubes and space rocket nozzles.


Here is an article about zinc

Alloys and composites


Alloys W-3 Re and W-25 Re are used specifically for the manufacture of high-temperature thermocouples (up to 2600°C). W-Re wires, which are more resistant to external stresses (e.g. vibration) than tungsten, are used in the manufacture of special electronic tubes and incandescent lamps. All other things being equal, W-Re anticathodes can dissipate two to three times more power per unit area than unalloyed tungsten. W-Re electrical contacts are more stable and resistant to erosion than tungsten in saline or tropical atmospheres.