The filament of an electron gun is made of which material and coated with which material? Why?

(N/A) The filament of an electron gun is typically made of $Tungsten$ $(W)$.
It is coated with $Barium$ $Oxide$ $(BaO)$ or $Strontium$ $Oxide$ $(SrO)$.
Reason: $Tungsten$ has a very high melting point $(3695 \ K)$,which allows it to withstand high temperatures without melting. However,its work function is high,meaning it requires a lot of energy to emit electrons. By coating the filament with $Barium$ $Oxide$ or $Strontium$ $Oxide$,the work function of the surface is significantly reduced. This allows for the emission of a large number of electrons at relatively lower temperatures,a process known as thermionic emission.