Investigation of Sc2 O3 contents for nano-sized Scandia doped dispenser cathode

Nano-sized Scandia Doped Dispenser cathode made from Scandia doped tungsten powder has been paid worldwide attention due to its high emission and satisfactory emission uniformity. Among the adopted doping techniques the liquid-liquid doping by Sol-Gel process is the most favorable for the performance of this kind of cathode. A further searching on the details of the processes is necessary for cathode manufacturing. In this study, Sc
₂
O
₃
contents of 1%wt., 3%wt., 5%wt. and 7%wt. (named Sc1, Sc3, Sc5 and Sc7) were added to the tungsten powder; their effects on microstructures and emission performance of the produced cathodes were investigated. The study proved that the nano-sized Sc
₂
O
₃
particles are getting richer from Sc1 to Sc7 but cover on the W grains in all cases. While there is a slight decrease in porosities from Sc1 to Sc7, the filled impregnant of Ba Ca aluminates for Sc1 to Sc5 is satisfied the requirement for dispenser cathode, but is obviously lower for Sc7. All cathodes made from Sc3, Sc5 and Sc7 reach a Space Charge Limited current density of about 50A/cm
²
at true temperature of 960°C except Sc1 of 33A/cm
²
. The knee points at initial current density of 30A/cm
²
are 830C, 875°C and 920°C for Sc5, Sc3 and Sc7, respectively. Almost no knee can be observed for Sc1. Therefore, Sc5 and Sc3 exhibit the best emission and emission uniformity, Sc7 comes second and Sc1 goes the worst.