Effect of CaO on Phase Composition and Properties of Aluminates for Barium Tungsten Cathode.

Jinglin Li,Jianjun Wei,Yongbao Feng,Xiaoyun Li

doi:10.3390/ma11081380

Abstract

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).

Highlights

As the main electron source for vacuum electronic devices, the impregnated barium-tungsten (Ba-W) cathode has the desirable characteristics of high emission current density, long lifetime, resistance to ion bombardment, and so on [1,2]
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 Ba3 CaAl2 O7, and the diffraction peak shifts to a higher angle
To improve the properties of aluminates for Ba-W cathodes, researchers have focused on the effects of the synthesis process [8,11,12], the phase composition [6,13], the scandium element doping [14,15,16], and porous tungsten matrix [17] on the properties of aluminates

Summary

Introduction

As the main electron source for vacuum electronic devices, the impregnated barium-tungsten (Ba-W) cathode has the desirable characteristics of high emission current density, long lifetime, resistance to ion bombardment, and so on [1,2]. It is prepared by impregnating a molten electron emission salt into the porous tungsten matrix, followed by processing and coating with a film [3]. CaO cannot provide emission electrons, but it has an important influence on the environmental stability, melting characteristics, and phase composition of aluminates, which has an indirect effect on the emission and evaporation properties of aluminates for Materials 2018, 11, 1380; doi:10.3390/ma11081380 www.mdpi.com/journal/materials

Methods

Results

Conclusion