Rapid electrochemical separation of anodic porous alumina films from aluminum surfaces using a highly safe sodium chloride–ethylene glycol solution

Abstract

A rapid electrochemical separation of an anodic porous alumina (APA) film formed by anodizing an aluminum substrate was achieved using a highly safe sodium chloride (NaCl)/ethylene glycol (EG) mixture. A thick APA film (thickness: 20–80 µm) with an ordered pore structure was formed on the aluminum surface by anodizing the substrate in a 0.3 M sulfuric acid solution at 25 V, and the specimens were subsequently polarized anodically in a 1.0 M NaCl/EG solution. A large current density was measured when a voltage higher than the anodizing voltage of 25 V was applied, and the APA film was completely separated from the aluminum substrate. This may be due to the formation of extremely small through-holes at the bottom barrier oxide layer of the APA film and the subsequent dissolution of aluminum from the substrate. The separation time of the APA film decreased with increasing applied voltage in the NaCl/EG solution, and rapid separation within 0.5 s was successfully achieved via anodic polarization at 36 V. We demonstrate that large-area and thick APA films can also be isolated from the aluminum surface by anodic polarization in the benign NaCl/EG solution. Moreover, an APA through-hole membrane can be successfully fabricated by subsequent immersion in a 0.52 M H3PO4 solution.