Properties Of Anodic Alumina Films Research Articles

Stored Charge and its Influence on Properties of Anodic Alumina Films

Stored Charge and its Influence on Properties of Anodic Alumina Films

Influence of the anodizing process variables on the acidic properties of anodic alumina films

Abstract In the present work, the effect of the different variables involved in the process of aluminum anodizing on the total surface acidity of the samples obtained was studied. Aluminum foils were treated by the electro-chemical process of anodic anodizing within the following variable ranges: concentration = 1.5-2.5 M; temperature = 303-323 K; voltage = 10-20 V; time = 30-90 min. The total acidity of the samples was characterized by two different methods: acid-base titration using Hammett indicators and potentiometric titration. The results showed that anodizing time, temperature and concentration were the main variables that determined the surface acid properties of the samples, and to a lesser extent voltage. Acidity increased with increasing concentration of the electrolytic bath, whereas the rest of the variables had the opposite effect. The results obtained provide a novel tool for variable selection in order to use synthetized materials as catalytic supports, adding to previous research based on the morphology of alumina layers.

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

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.