Effect of CaO on phase composition and properties of aluminates for barium tungsten cathode

6BaO·xCaO·2Al₂O₃ (x = 0.8, 1.2, 1.6, 2, and 2.2) aluminates were synthesized via a liquid phase co-precipitation method. Effects of the molar amount of CaO on the phase of aluminates before and after melting and their hygroscopic phase, melting properties, environmental stability, evaporation, and emission properties were systematically studied. The results show that with the increase of the molar amount of CaO, the aluminates change from a mixture phase to a single phase of Ba₃CaAl₂O₇, and the diffraction peak shifts to a higher angle. The melted phase of the aluminates changed from a single phase to a mixed phase of Ba₅CaAl₄O₁₂ and Ba₃CaAl₂O₇. Meanwhile, the comprehensive properties of the aluminates are improved. The weight gain of 6BaO·2CaO·2Al₂O₃ aluminates is only 10.88% after exposure to air for 48 h; the pulse emission current density of barium tungsten cathodes impregnated with 6BaO·2CaO·2Al₂O₃ aluminates in the porous tungsten matrix can reach 28.60 A/cm² at 1050 °C, and the evaporation rate is 2.52 × 10^-10 g/(cm²·s).