High Current Density and Long-Life Nanocomposite Scandate Dispenser Cathode Fabrication

A nano-Sc2O3-added W powder for use in high current density thermionic cathodes has been made using a solution-gel method with the following controllable uniform average particle sizes: ~72, 146, 272, and 587 nm. Using these powders, nanostructured Sc2O3-added tungsten matrices with uniform nanosized tungsten grains and homogenous pore distribution were obtained. Nanocomposite Sc2O3-added W impregnated cathodes have been prepared from these powders and have shown excellent emission properties. For example, space-charge-limited current densities of 40 ± 1 A · cm-2at 850°C and 170 ± 5 A · cm-2at 1050°C have been obtained using a 300-nm Sc2O3-added (4.77 wt.%) W powder. Life testing is ongoing with 50 ± 2.5 A · cm-2current density emission demonstrated at 1050°C after 10 680 h.