Comparison of Formation Mechanism between Porous Anodic Sn Oxide and Anodic TiO2 Nanotubes

Porous anodic Sn oxide (PASO) and other porous anodic oxides have aroused worldwide scientific interest. However, the relationship between the complex porous structure and the current-time curve cannot be interpreted by the traditional dissolution theory. In particular, with the change of anodizing conditions of Sn, the current-time curve sometimes shows three stages, sometimes five stages. In order to study the relationship between current-time curve and the growth model of complex PASO structure during Sn anodization, this study compares the anodizing processes of Sn and Ti. Under normal circumstances, the current-time curve of Ti in anodizing process is three stages, which can be interpreted reasonably by electronic current and oxygen bubble model. By adjusting the anodizing processes of both metals, their current-time curves would be changed into five stages, which means that the formation mechanism of the two metal oxide porous structures may be inherently connected. Here, the current-time curves of three stages and five stages are carefully compared. The internal relationship between the structure of anodic TiO2 nanotubes and the complex porous structure of PASO is found, revealing that the complex porous structure of PASO is caused by excessive gas evolution which is the result of electronic current.