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 (LaB₆), LaB₆-Me^IV-VIB₂, 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 LaB₆-Me^IV-VIB₂ 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 LaB₆-VB₂. 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% BaHfO₃-37% W (by mass) is enables a thermionic current density of 230 A/cm² at T = 2000 K. Cathodes with a rhenium-tungsten sponge with 3BaOldr0.5CaOmiddotAl₂O₃ as the emissive active substance have higher emission properties in comparison to cathodes with a tungsten sponge with normal impregnation.