Effect of annealing and polishing on flashover characteristics of ceramic in vacuum

Experiments were carried out to study the effects of surface polishing and annealing ceramic parts on the dielectric breakdown characteristics of their surfaces. It was discovered that when the samples were annealed at 1000°C, allowing the residual stresses in their surfaces to decrease, breakdown voltages rose, whereas with the polished samples, reductions of residual stresses resulted in slight rises of breakdown voltages. Prior to dielectric breakdown, a surface glow was observed, presumably luminescence due to insulator surface defects. The starting voltage of luminescence rose when residual stresses were reduced. It is presumed that mechanical strain due to surface defects contribute to dielectric breakdowns on ceramic surfaces