Characterization of scandia doped pressed cathode fabricated by spray drying method

Abstract

Scandia doped pressed cathode was prepared by a new method of spray drying combined with two-step hydrogen reduction process. The Sc 2O 3 and barium–calcium aluminate co-doped powders have sub-micrometer size in the range of 0.1–1 μm and scandium oxide and barium–calcium aluminate are distributed evenly in the powders. The cathodes sintered by powder metallurgy at 1600 °C b have a smooth surface and sub-micrometer grain structure with homogeneous distribution of scandium, barium, calcium and aluminum which are dispersed over and among the tungsten grains. This cathode has good emission, e.g., the current density of this cathode reaches 31.50 A/cm 2 at 850 °C b. After proper activation, the cathode surface is covered by a Ba–Sc–O active substances layer with a preferable atomic ratio, leading to its good emission property. The evaporation activation energy of SDP cathode with 4.58 eV is the highest among the Ba–W, M-type and SDP cathodes, and the average evaporation velocity v t of SDP cathode with 1.28 × 10 −8 g cm −2 s −1 at 1150 °C b is the lowest one.