The Effect of Chromium Oxide Coatings on Surface Flashover of Alumina Spacers in Vacuum

An experimental investigation of the effect of chromium oxide coatings upon the surface flashover of high-density alumina in vacuum is reported. It is shown that such coatings improve the withstand voltage for dc, 60-Hz, and impulse voltages by significant amounts. The coatings are simply applied, effective, and durable. It is postulated that the improvement in insulation is due to the elimination of positive surface charging by the use of a coating with a secondary-electron emission coefficient less than unity for all incident electron energies.