Theory of electrical breakdown during formation of barrier anodic films

Abstract

The anodic formation of barrier oxide films on valve metals can be carried on till the electrode potential has attained the “breakdown voltage” ( U B , after which a sustained sparking appears. The systematization of the available data on this phenomenon revealed that U B depends fundamentally on the nature of the anodized metal, as well as on the composition and resistivity of the electrolyte. Many other factors like the current density, the surface topography of the electrode, the history of the film formation, etc do not affect U B noticeably. This phenomenology of the breakdowns, as well as their appearance, was explained by a breakdown model. According to this model, sparking is considered as an avalanching in the bulk of the anodic film, the initial electrons being injected into the film from the electrolyte. The peculiar features of the sparking were found to arise both from the specific injecting behaviour of the electrolyte and from the simultaneous oxide film formation.