Exploration for the Self-ordering of Porous Alumina Fabricated via Anodizing in Etidronic Acid

Abstract

Ordered porous alumina (OPA) with large-scale circular and hexagonal pores was fabricated via etidronic acid anodizing. High-purity aluminum plates were anodized in 0.2–4.2M etidronic acid solution at 145–310V and 288–323K. Self-ordering of porous alumina was observed at 165V and 313K in 4.2M, at 205V and 303K in 1.0M, and at 260V and 298K in 0.2M, and the cell diameter was measured to be 400–640nm. The ordering potential difference decreased with the electrolyte concentration increasing. OPA without an intercrossing nanostructure could be fabricated on a nanostructured aluminum surface via two-step anodizing. Subsequent pore-widening in etidronic acid solution caused the circular dissolution of anodic oxide and the expansion of pore diameters to 470nm. The shape of the pores was subsequently changed to a hexagon from a circle via long-term pore-widening, and a honeycomb structure with narrow alumina walls and hexagonal pores measuring 590nm in its long-axis was formed in the porous alumina. Transition of the nanostructure configuration during pore-widening corresponded to differences in the incorporated phosphorus distribution originating from the etidronic acid anions.