Development and application of a holistic model for the steady state growth of porous anodic alumina films

• Published in: Electrochimica acta 2009-03, Vol.54 (9), p.2434-2443
• Main Authors: Patermarakis, G., Moussoutzanis, K.
• Format: Article
• Language: English
• Subjects: Applied sciences; Corrosion; Corrosion mechanisms; Exact sciences and technology; Holistic model; Lattice density and form variability; Metals. Metallurgy; Porous anodic alumina; Steady state growth
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2008.11.064

A holistic model was developed and applied to anodic alumina films galvanostatically grown in sulphuric acid solution at different anodising conditions thus characterised by different structural characteristics. The O 2− and Al 3+ species transport numbers near the metal|oxide interface were determined that depended on both temperature and current density. The rate of film thickness growth was found to be proportional to the O 2− anionic current through the barrier layer near the metal|oxide interface. The results introduced a new growth mechanism theory embracing the rarefaction of barrier layer oxide lattice towards the metal|oxide interface. The oxide density near the metal|oxide is closely independent of anodising conditions and is related to the transformation of Al lattice to a transient oxide lattice about 37% rarer than that of γ-Al 2O 3 that is further suitably transformed to denser, amorphous or nanocrystalline material as this oxide is shifted to the oxide|electrolyte interface and becomes the pore wall material. This gradual lattice density variability can explain many peculiar properties of anodic alumina films.