Tungstenikatoodid

Tungstenikatoodid refers to the use of tungsten as a cathode material in vacuum tubes and other electronic devices. A cathode is a negatively charged electrode that emits electrons, a process known as thermionic emission. Tungsten is a suitable material for cathodes due to its high melting point and low vapor pressure, which allow it to withstand the high temperatures required for electron emission without degrading quickly.

Historically, pure tungsten was one of the earliest materials used for cathodes. When heated to a sufficiently high temperature, typically by a filament, the tungsten atoms on the surface gain enough thermal energy to overcome the work function of the material and escape into the surrounding vacuum as electrons. This process is essential for the operation of devices like X-ray tubes, vacuum tubes used in early radio and television, and certain types of electron guns.

However, pure tungsten cathodes have a relatively high work function, meaning they require very high operating temperatures to achieve adequate electron emission. This leads to significant power consumption and can reduce the lifespan of the cathode. To address these limitations, thoriated tungsten cathodes were developed. In thoriated tungsten, a small amount of thorium is added to the tungsten. Thorium has a lower work function than tungsten and migrates to the surface of the cathode, significantly increasing the electron emission efficiency at lower temperatures. This reduces power requirements and extends cathode life.

Later advancements led to oxide-coated cathodes, which typically use a nickel base coated with a mixture of barium and strontium oxides. These oxides have a very low work function, allowing for efficient electron emission at even lower temperatures than thoriated tungsten. While oxide-coated cathodes offer the highest efficiency and lowest operating temperatures, they are more susceptible to poisoning by residual gases in the vacuum. Therefore, the choice of tungsten-based cathodes or other types depends on the specific application requirements regarding operating temperature, current density, lifespan, and environmental factors.