Anodising of aluminium in formate solutions with formation of porous alumina arrays

Abstract

ABSTRACT New applications of porous anodic aluminium oxide (alumina) structures for the fabrication of photonic devices, etching masks, and periodic pore templates with prospective magnetic, photoluminescent, anti-reflecting properties recently are of high interest. In this respect, new anodising processes for controllable formation of periodic structures in unconventional solutions at low voltages might be challenging. In this study, the anodic behaviour of aluminium in aqueous formate solutions was studied within a wide range of concentrations, pH, electrolyte temperatures, anodising times, and voltages. It was established that the thickness of porous anodic films depended on the concentration of solution applied (c), pH, bath temperature (T), and voltage (U a) increasing with increase in c, U a, and T. The thickest films were formed in the solution containing 0.2 mol L−1 formic acid at a pH of 2.5. These films contained up to 5.8 at% of entrapped carbon. The transition of porous anodising to the ‘burning’ type occurred at 22–25 V. Under appropriate anodising conditions ordered hexagonal cell arrays can be formed.