Influence of Reducer on the Nanopore Structure of Porous Anodic Alumina

Abstract

In recent years, attention has been focused on adjustment and control of the nanostructures of porous anodic alumina (PAA) and porous anodic TiO2 nanotubes (PATNT). Because the formation mechanism of PAA and PATNT is still unclear, it is difficult to adjust the nanostructures of PAA and PATNT. To validate the novel viewpoint of the nanopore resulting from an oxygen bubble mold, an innovative chemical approach was used to adjust the PAA nanostructures. One successful approach is to use a reducer to absorb the oxygen bubbles in the nanopores. A novel anodic alumina film was obtained in a mixed solution of the reducer and oxalic acid. The influence of the reducer on the PAA nanostructures which formed in H3PO4 solution was investigated in detail. The experimental results showed that the regularity and the diameters of the nanopores in the PAA decreased as the reducer content increased. The differences in the voltage-time curves between electrolytes with and without the reducer were analyzed quantitatively. The results showed that the conductivity of the anodic oxide film that formed in the electrolyte with the reducer was better than that in the electrolyte without the reducer. When aluminum anodizes in a sealed case, oxygen bubbles are easily absorbed by the reducer, the oxygen bubble mold effect disappears, and a compact alumina film is obtained. Overall, these results clearly demonstrate that nanopores result from the oxygen bubble mold effect.