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

Previously, we studied the anodization of aluminum by adding alcohol to common acidic electrolytes with a focus on film formation efficiency and the hardness of the anodic oxide film. In this study, we focus on the difference in carbon number of monohydric alcohols and select propanol as an additive to confirm whether the effects of adding alcohol on anodization behavior and the growth rate of anodic film are universal regardless of the alcohol type. The tendency of propanol concentration dependence of conductivity and viscosity was generally consistent with results obtained using methanol and ethanol additives; however, unlike other alcohols, the steady state voltage during constant current anodization decreased with an increased amount of propanol. Unlike sulfuric acid only, the addition of propanol clearly improved film growth rate and current efficiency under mild conditions below 100 A‧m −2 and high current density conditions above 500 A‧m −2 .