Question

Mention the reason why tungsten is a suitable metal for Thermionic emission

Answer 1

Undesrtanding the thermal chemistry of Tungsten.

• Tungsten has a high melting point of $3655\mathrm{K}$ with a high work function of about $4.52\mathrm{eV}$.
• Tungsten starts electronic emission at $2500\mathrm{K}$.
• Thoriated tungsten i.e., Tungsten coated with Carbon and Thorium has a work function of $2.6\mathrm{eV}$ and in Thoriated Tungsten electronic emission begins at $2000\mathrm{K}$.
• Infact when Tungsten is coated with Barium and Strontium Oxide, the work function of this material reduces to $1\mathrm{eV}$ and electronic emission begins at $1000\mathrm{K}$.
• For these reasons Tungsten is suiatble for thermionic emission.