Effect of Propanol on Growth Rate of Anodic Porous Alumina in Sulfuric Acid

Recently, we have investigated the anodization of aluminum in popular acidic electrolytes (e.g., sulfuric and oxalic acids) containing an alcohol as an additive with a focus on film formation efficiency and the hardness of the anodic films. In this study, to confirm whether the effects of alcohol on anodization behavior and anodic film growth are universal regardless of the type of alcohol, we focused on the difference in carbon number of the monohydric alcohols and selected propanol (n = 3 for C₃H₇OH) with a three carbon chain (C₃-alcohol) as an additive. Here, sulfuric acid was used as the electrolyte with concentrations of 0.3 and 1.5 mol‧dm⁻³. Propanol has two isomers, i.e., 1-propanol with the OH group on an end carbon and 2-propanol with the OH group on the middle carbon; thus, the difference of isomer on film formation was also investigated with a focus on the physical properties (e.g., viscosity and electric conductivity) of the mixed solution, the steady state voltage, and the anodic film’s growth rate. Adding propanol improved the film growth rate and current efficiency unlike sulfuric acid only, even under high current density conditions. However, there was no clear difference in the effect of different isomers on film growth rate.