Phase selectivity and environmental stability of 612‐aluminate synthesized by sintering Co‐precipitated precursor

Abstract

The environmental stability of barium calcium aluminate for impregnated cathodes is significant for storing impregnants and fabricating thermionic cathodes. In this work, two types of phase structures are obtained in the 612‐type aluminate. The Ba3CaAl2O7 single‐phase structure is obtained if the crucible is uncovered after sintering for 300 min at 1200°C. In contrast, the Ba3Al2O6 and BaCO3 dual‐phase structure is achieved by suppressing the solid‐state reaction by covering the crucible and reducing the sintering duration to 75 min. The dual‐phase sample exhibits superior environment stability to the single‐phase one when exposed to moist air. The reason could be attributed to the smaller specific surface area and total pore volume of the dual‐phase sample due to the incomplete liberty of gases in sintering. Because of their identical compositions, the cathodes impregnated with different sintered phases possess comparable electron emission capacities. This work provides an effective process to synthesize 612‐aluminate with good environmental stability and emissive capacity.