The effect of n-alcohols on porous anodic alumina formed by self-organized two-step anodizing of aluminum in phosphoric acid

Self-ordered porous anodic alumina films were fabricated by a two-step anodization technique at potentials between 110 and 170 V using different n-alcohols and water mixtures containing 0.3 M H₃PO₄ at the electrolyte temperatures of 0 and − 5 °C. The morphology of the specimens was observed by a field emission scanning electron microscope (FE-SEM). Anodic aluminum oxide (AAO) films fabricated in the absence of n-alcohols exhibit a complex structure with sub-pores, independently of the anodizing potential. The sub-pore structure of films disappeared in the presence of n-alcohols probably due to the cooling effect of alcohol and extended time for the pore interaction (re-arrangement of pores). Additionally, with increasing anodizing potential, the regularity of pore arrangement, uniformity of pore shape and interpore distance of the AAO film increases independently of the electrolyte composition. The order of arrangement and circular shape of pores increases with increasing n-alcohol content for both anodizing temperatures. The best arranged porous structures were obtained in 1:1 methanol-water electrolyte containing 0.3 M H₃PO₄ (lower evaporating point than n-propanol and water) at 0 °C. The interpore distance of porous anodic alumina decreases with increasing n-alcohol content and increasing regularity of pore arrangement.