Question

Which metal is used as an electron emitter?

Answer 1

1. The metal or metallic substances used to construct a thermionic emitter should have some main features.
2. It should have a low work function.
3. A low work function helps to emit electrons from the cathode surface in a comparatively lower temperature.
4. It should have a high melting point.
5. Tungsten metal is used as an electron emitter as it has a very high melting point ($3655K$) and moderate work function.
6. It has a work function of about $4.52eV$. It starts emission at $2500K$.
7. If thoriated tungsten (which is coated with carbon and thorium) is used work function reduces to $2.6eV$ and emission begins at $2000K$.
8. If tungsten is coated with metals like barium and strontium oxide work, function reduces to $1eV$ and emission begins at $1000K$ and a good quality of electrons is obtained.

Thus, Tungsten is used as an electron emitter.