Tungsten has the highest melting point (3410ˇăC) with a density of 19.3 gm/ cc, it is only surpassed by rhenium and osmium in weight. Tungsten has a long history of use for filaments in the lamp industry.Tungsten has the best high-temperature strength of all the refractory metals. For this reason, it is used in very high temperature vacuum furnaces.
Tungsten is practically the only material used for electron emitters. Even though other more electropositive metals would have higher emission rates, the advantage of tungsten is its extremely low vapor pressure even at high temperatures.
This property is also important for electrical contact materials. While more conductive metals like copper or silver evaporate under the conditions of electric arc, tungsten withstands these.
The following illustrates some of tungsten's applications:
- Directly heated cathodes or heater coils for indirectly heated cathodes in cathode ray tubes for TV sets or computer displays, X-ray tubes, electron tubes, klystrons, magnetrons for microwave ovens.
- Thoria or rare earth oxide alloyed electrodes for inert gas welding, as well as High Intensity Discharge (HID) lamps.
- Tungsten disks for substrate of high power semiconductor rectifying devices; Electrical contacts.
- High temperature furnace parts such as tungsten heating coils, reflectors and structural material.
- Tungsten / tungsten-rhenium thermocouples for measuring the temperature in such furnaces.
- X-ray tubes for medical use are not only equipped with a tungsten emitter coil, but also a static anode made of tungsten or tungsten-rhenium. Important here are not only the low vapor pressure, but also tungsten's good heat conductivity and the wavelength of the resulting X-rays.
- Modern business machines, such as photocopiers, facsimile machines, laser printers and air cleaners are equipped with tungsten charger wires. Not only drawn tungsten wire, but also electro-polished, gold-plated or platinum clad tungsten wires are used for this application.
- Modern computer processors generate a heat output per square centimeter similar to that of a household cook top. Tungsten-copper heat sinks and the processor fan remove the heat.