Effect of BaO on the phase composition and properties of aluminates for Ba-W cathodes

Abstract

In this study, we prepared (4.8+x)BaO·CaO·2Al2O3 (0 ≤ x ≤ 1.6) aluminates by calcining the precursors under static air at 1500 °C for 120 min. The precursor powders were prepared using a liquid phase co-precipitation method. The effects of the molar content of BaO on the phase composition (before and after melting), melting properties, environmental stability, evaporation, and emission properties of the aluminates was investigated systematically The results showed that the phase of the aluminates completely transformed from Ba5CaAl4O12 to Ba3CaAl2O7 with an increase in the BaO content. After melting, the phase changed from Ba5CaAl4O12 to a mixed phase of Ba5CaAl4O12 and Ba3CaAl2O7. In the high-temperature molten state, the aluminates were in the ionic state, which generated a relatively low-energy Ba5CaAl4O12 phase during cooling crystallization. With every 0.4 mol increase in the BaO content, the initial melting temperature of the aluminates decreased by 10–20 °C, while the environmental stability deteriorated gradually. When the aluminates reacted with H2O and CO2 in the air, the original phase still existed and the characteristic peaks gradually broadened, but with the formation of Ca(OH)2, CaCO3, and BaCO3. At 1050 °C, with an increase in the BaO content, the evaporation rate of the Ba-W cathodes increased and the emission current density first increased and then decreased. The main components of the Ba-W cathode evaporation were Ba and BaO. At n(BaO):n(CaO):n(Al2O3) = 6:1:2, the Ba-W cathode showed the best emission performance, and its pulse emission current density at 1050 °C was as high as 35.31 A/cm2.