Self-ordered Porous Alumina Fabricated via Phosphonic Acid Anodizing

Self-ordered periodic porous alumina with an undiscovered cell diameter was fabricated via electrochemical anodizing in a new electrolyte, phosphonic acid (H3PO3). High-purity aluminum plates were anodized in phosphonic acid solution under various operating conditions of voltage, temperature, concentration, and anodizing time. Phosphonic acid anodizing at 150-180 V caused the self-ordering behavior of porous alumina, and an ideal honeycomb nanostructure measuring 370-440 nm in cell diameter was successfully fabricated on the aluminum substrate. Conversely, disordered porous alumina grew at below 140 V, and anodizing at above 190 V caused local thickening due to oxide burning. Two-step phosphonic acid anodizing allows the fabrication of high aspect ratio ordered porous alumina. HPO32 anions originated from the electrolyte were incorporated into the porous oxide during anodizing. Consequently, a double-layered porous alumina consisting of a thick outer layer containing incorporated HPO32 anions, and a thin inner layer without anions was constructed via phosphonic acid anodizing. (C) 2015 Elsevier Ltd. All rights reserved.