Role of cathodic half-cycle on AC etch process of aluminium

The AC etch process effectively expands the surface area of aluminium foil as compared with DC etch process. This study explored the effect of cathodic half-cycle. The cathodic half-cycle enhanced passivation of pits developed during the preceding anodic half-cycle, making pit nucleation random. Anodic pulse without cathodic half-cycle produced hollows, due to preferential pit nucleation on pits produced in the preceding anodic half-cycle. The open circuit before the cathodic half-cycle does not largely influence the etch factor, but etch film formation is largely suppressed. The precipitation of aluminium hydroxide may not have a crucial role in porous layer formation.