Selective Pore Sealing of Anodic Porous Alumina by Atomic Layer Deposition of TiO₂ Layer

Anodization and pore sealing are surface treatments used to impart corrosion resistance and mechanical durability to Al products. However, these treatments cannot preserve the ordered surface structure of anodic porous alumina after pore sealing, thereby preventing the imparting of functionality based on the surface nanostructures. In this study, we investigated novel methods for creating surface-protective films for Al products that combine corrosion resistance, mechanical durability, and functionality based on surface nanostructures. To maintain the ordered surface structure of an anodic porous alumina layer after the pore sealing treatment, a TiO₂ layer was formed by atomic layer deposition (ALD). This is because, in this study, we found that the TiO₂ layer formed on anodic porous alumina layer by ALD suppressed the progression of pore sealing in the alumina layer. Therefore, a two-layer anodic porous alumina was formed, featuring a TiO₂ layer applied only to the upper part of the sample. Pore sealing was performed on the resulting samples. Consequently, we obtained samples in which only the lower portion, which was not coated with TiO₂, was selectively pore-sealed. It was also confirmed that the surface structure of the anodic porous alumina remained intact after pore sealing. These findings indicate that this process is promising as a surface treatment technique capable of imparting corrosion resistance, mechanical durability, and functionality based on the surface structure of Al products.