Improvement of surface flashover performance in vacuum by co-firing Mo/Al_2O3 cermets and Al_2O3 ceramics

A new insulation structure of Mo/Al₂O₃ cermet-Al ₂O₃ ceramic-Mo/Al₂O₃ cermet was designed to improve the surface flashover performance in vacuum through co-firing, where the volume addition of metal Mo was managed from 2 vol% to 50 vol% and there could exist one or two layers with different Mo addition in Mo/Al₂O₃ cermet. The influences of Mo addition of Mo/Al₂O₃ cermet on the surface flashover voltage in vacuum of samples were experimentally investigated, indicating that the surface flashover voltage of three and five-layer structures were improved by 77 % and 117 %, respectively. Through electrostatic field simulation, it was found that the improvement is caused by the weakening of the electric field at vacuum-insulator-cathode triple junction. On the basis of an in-depth investigation, it was also concluded that Mo particles of Mo/Al ₂O₃ cermet layer can decline the surface charging and secondary electron emission near the triple junction. Then with a further increase of Mo addition, the decreasing trend of flashover voltage after the growing has been reasonably explained by investigating the configuration of Mo particles in Mo/Al₂O₃ cermet.