Tungsten filament is mainly used in electric light sources such as incandescent lamps and halogen tungsten lamps. The tungsten wire used as a various luminous body in the bulb also needs to be doped with a small amount of potassium, silicon and aluminum oxides in the smelting process, and this tungsten wire is called doped tungsten wire (DopedTungstenWire), also known as 218 tungsten wire or non-sagTungsten wire (Non-sagTungstenWire).
Tungsten wire is generally drawn from various drawing dies. The main use is to make filament and high-speed cutting alloy steel, and also used in optical instruments, chemical instruments, etc.
The resistivity of tungsten filament is 5.3*10^-8, tungsten has high melting point, high resistivity, good strength and low vapor pressure, which is the best material for making incandescent filament among all pure metals. However, tungsten is hard and brittle, making it difficult to process. When the current is heated to a certain temperature through the tungsten wire, the resistance value of the tungsten wire also increases to a certain value (the resistance value of the wire increases with the increase of temperature). In 1909, Kulich invented the process of processing tungsten filament, which played a decisive role in the production and promotion of incandescent light bulbs, and its basic principles are still used today.
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