Structure and emission properties of barium calcium aluminates synthesized by room-temperature solid-state reaction approach

The two conventional aluminate precursor preparation methods are liquid-state co-precipitation and mechanical mixture, needing high temperature to fabricate thermionic cathodes for vacuum devices. Herein, we introduce the room temperature solid states (RTSS) approach to fabricate the precursors of barium calcium aluminates (BCA). For this, crystalline hydrates are used to prepare the precursor through mechanical grinding. The resulting product comprises of crystallized α-(Ba,Ca)CO3 solid solution and Al3+-contained amorphous precipitants. After sintering at 1200 °C, the active phases of Ba3CaAl2O7 and Ba3Al2O6 were obtained. The direct current (dc) emission measurements in a close-space diode configuration revealed that the divergent current density (Jdiv) of the test cathode reaches 7.2 A/cm2 at 1130 °CB, which is comparable to that of the co-precipitation liquid phase method. Considering the virtue of an environmentally-friendly and low-temperature preparation approach, the preparation of aluminates using the RTSS technique has great potential for the fabrication of dispenser cathodes for vacuum devices.