Structural properties of electrochemically designed porous oxide films on AlMg1

The characteristics of electrochemically formed porous oxide layers on alum inium alloys were investigated. The anodizing conditions were varied in a b road range (electrolyte: sulfuric acid, phosphoric acid and mixtures from t hese, concentration: 0.3-2.0 M, voltage: 5-10 V, time: 30-90 s, temperature : 25-50 degrees C). The oxide layers were characterized via spectroscopic i nterference measurements to determine the oxide thickness. The morphology o f this layer was also observed by AFM. The structural parameters of the oxi de layer were characterized by electrochemical impedance spectroscopy (EIS) . An equivalent circuit comprising two layers of barrier and porous layers was used to determine the characteristic parameters. The growth rate of oxi de varied with electrolyte type, temperature and concentration. The proport ionality constant of the barrier him thickness in relation to the applied v oltage and the relative porosity of the film were calculated from this mode l. Three-dimensional response surfaces were constructed with the aid of an appropriate experimental design strategy which allows the study of not only the effects of the fabrication variables but also the interactions between these variables. (C) 1999 Elsevier Science S.A. All rights reserved.