Preparation and characterisation of scandia doped dispenser cathodes

Abstract

Scandia doped dispenser cathodes were prepared by powder metallurgy method using mixed powder of scandia doped tungsten, barium–calcium aluminates obtained by sol–gel method. The scanning electron microscope observation results indicate that the cathode has submicron quasi–spherical tungsten grains structure with homogeneous distribution of Sc2O3 and barium–calcium aluminates which dispersed over and among W grains. The cathode exhibits good emission property, i.e. the current density of this cathode can reach more than 40A/cm² at 850°Cb. The cathode has low work function of 1.43 eV. Active substance of Sc, Ba and O diffuse from the inner part of cathode to the surface to form a Ba–Sc–O multilayer having certain ratios of Ba:Sc:O which contains much more Ba than normal dispenser cathode at the surface of Sc2O3–W matrix cathode during the activation period. This active–multi–layer is considered to be responsible for copious emission capability.