Oxide density distribution across the barrier layer during the steady state growth of porous anodic alumina films: chronopotentiometry, kinetics of mass and thickness evolution and a high field ionic migration model

• Published in: Journal of solid state electrochemistry 2009-12, Vol.13 (12), p.1831-1847
• Main Authors: Patermarakis, G., Karayianni, H., Masavetas, K., Chandrinos, J.
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Condensed Matter Physics; Electrochemistry; Energy Storage; Original Paper; Physical Chemistry
• ISSN: 1432-8488; 1433-0768
• DOI: 10.1007/s10008-008-0745-6

The steady state growth of porous anodic alumina films in oxalate solutions at various conditions was studied by chronopotentiometry, mass balance and optical microscopy methods enabling determination of consumed Al, film mass and thickness, current efficiencies, Al 3+ and O 2− transport numbers across barrier layer, etc. The film thickness growth rate was found to be proportional to O 2− anionic current. A high field ionic migration model was developed. It predicted that, during anodising, the local oxide density across barrier layer rises from 2.6 in Al|oxide to 4.59–5.22 g cm −3 in oxide|electrolyte interface with mean value ≈3.21–3.52 g cm −3 . The field strength rises from the first to second interface. The mechanism of Al oxidation near the Al|oxide interface embraces the transformation of the Al lattice to a transient, rare oxide one sustained by field with comparable Al 3+ spacing parameter. The oxide near the Al|oxide interface and around the density maximum in the oxide|electrolyte interface are under different levels of electro-restriction stresses. During relaxation, the oxide behaves like a solid-fluid material suppressing the initial density distribution.