Beneficial role of manganese dioxide for reducing surface resistivity to increase surface flashover voltage of vacuum insulating ceramics

Electric vacuum insulated devices generate surface flashover and breakdown under instantaneous high voltage. Flashover voltage can be increased through coating without changing the structure of the ceramic device. Herein, multiphase coatings with different manganese dioxide contents are prepared on alpha-Al2O3 insulating ceramic surface by screen printing and solid-state sintering methods to yield an average film thickness of about 12.38 mu m with good bonding strength. X-ray diffraction shows that the crystal phases of the coating are (Al0.9Cr0.1)(2)O-3 and MnAl2O4. Scanning electron micrographs and atomic force microscopy reveal that greater surface height difference and deeper surface depth are more conducive to increasing the surface roughness and the formation of "pores", and decreasing the surface potential decay rate. When MnO2 content is 0.0069 mol, the deep trap center energy level on the material surface reaches its maximum, increasing from 1.506 eV to 1.550 eV, and the surface resistivity of ceramics decreases from 10(16) Omega to 10(13) Omega. The formation of deep trap centers on the surface makes it difficult for surface charges to detach, which reduces the charge mobility and surface potential decay rate, and leads to decrease in surface resistivity and increase in surface flashover voltage.