Dielectric breakdown and healing of anodic oxide films on aluminium under single pulse anodizing

Single pulse anodizing of aluminium micro-electrode has been employed to study the behaviour of dielectric breakdown and subsequent oxide formation on aluminium in alkaline silicate and pentaborate electrolytes. Current transients during applying pulse voltage have been measured, and surface has been observed by scanning electron microscopy. Two types of current transients are observed, depending on the electrolyte and applied voltage. There is a good correlation between the current transient behaviour and the shape of discharge channels. In alkaline silicate electrolyte, circular open pores are healed by increasing the pulse width, but such healing is not obvious in pentaborate electrolyte.

Research highlights► We examined dielectric breakdown of anodic alumina by single pulse anodizing. ► Current transients and morphology of discharge channels are dependent upon electrolyte and voltage. ► There is a good correlation between current transient and morphology of discharge channel. ► Healing of open discharge pores occurs in alkaline silicate, but not in pentaborate electrolyte.