Doping is that in order to prevent or control recrystallization or grain growth in sintering or using, adding a few other elements or compounds, making materials produce certain electrical, magnetic and optical properties.
Manufactured by adding potassium to tungsten. It is normally used as wire. At recrystalization temperature, tungsten with high purity forms series of small grains. Crystal boundaries running through tungsten wire and rod could lead to deformation or breakage. By adding 30 - 100 ppm potassium, it can raise the recrystalization temperature, and dope hole can help elongate the size of crystal grains. As a result, crystal grains on crystal boundaries are interlocked, and less likely to sag or deform.
Car and motorbike lamps are one of the most important applications of non-sag tungsten wire. When used non-sag tungsten wire as filament in such bulbs, the wire can have the most effective effects for the cars and motorbikes to achieve stable light from the lamps. The application in incandescent lamps has the same effects.
The Distinction of Doped Tungsten Wire and Undoped Tungsten Wire
The term undoped also refers to sag, pure wire and doped may refer to as non-sag tungsten wire. Doped tungsten wire refer to industry standard doping of commercially pure tungsten wire with small amounts of aluminum, potassium and silicate. Filaments doped in this way have added strength to counteract operational stresses in unsupported applications.
1. In Chemistry
| Materials | Potassium | Aluminum | Silicon | Tungsten |
| Undoped tungsten wire | 20ppm max | 25ppm max | 40ppm max | 99.95%min |
| Doped tungsten wire | 20ppm max | 60ppm max | 60ppm max | 99.95%min |
2. In Properties
Doped tungsten wire have good resistance to drop ability, good resistance to high temperature and vibration and void reformation.
However, undoped tungsten wire have low ability to vibration resistance and reformation, the recrystallization temperature is lower than that of doped tungsten wire, and it is less resistant to sag at high temperatures.
3. In Application
Doped tungsten wire are good for coiled filaments and used as supports in all incandescent, infrared, and high-temperature halogen lamps. Further more, it is also used for electronic tube and heater applications as well as electric-furnace elements.It is available in the broadest range of standard process for the widest variety of applications.
Undoped tungsten wire are used for lamp coils in which sag is not important item as in supported coils.
