Review of $\hbox{LaB}_{6}$, Re-W Dispenser, and $\hbox{BaHfO}_{3}$-W Cathode Development

Results of development, emission properties investigations, and applications of cathode materials based on lanthanum hexaboride (LaB
₆
), LaB
₆
-Me
^IV-VI
B
₂
, and also rhenium-tungsten (Re-W) dispenser and pressed-oxide cathodes are presented. Emission properties of a novel class of directionally crystallized lanthanum hexaboride-based eutectics have been studied. The LaB
₆
-Me
^IV-VI
B
₂
composites exhibit improved emission properties and thermal cycling reliability as compared with the source lanthanum hexaboride. The most promising effective thermionic material is the eutectic composition LaB
₆
-VB
₂
. The techniques for producing pressed cathodes based on barium hafnate with tungsten and dispenser cathodes with a rhenium-tungsten matrix have been developed. It is shown that a cathode of 63% BaHfO
₃
-37% W (by mass) is enables a thermionic current density of 230 A/cm
²
at T = 2000 K. Cathodes with a rhenium-tungsten sponge with 3BaOldr0.5CaOmiddotAl
₂
O
₃
as the emissive active substance have higher emission properties in comparison to cathodes with a tungsten sponge with normal impregnation.