Review of LaB6, Re-W Dispenser, and BaHfO3-W Cathode Development

Results of development, emission properties investigations, and applications of cathode materials based on lanthanum hexaboride (LaB6), LaB6-Me(IV-VI)1B(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 LaB6-Me(IV-VI)1B(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 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/cm(2) at T = 2000 K. Cathodes with a rhenium-tungsten sponge with 3BaO center dot 0.5CaO center dot Al2O3 as the emissive active substance have higher emission properties in comparison to cathodes with a tungsten sponge with normal impregnation.