Estimating the barrier layer thickness of porous aluminium oxide films with A.C. impedance measurements

EIS studies of anodic aluminum oxide films

“…For the sake of comparison, the thicknesses of unsealed anodic oxides measured by EC are also included in the table. For unsealed samples on both materials, the barrier layer thicknesses: 0.011μm d μm for AA 6061 and 0.017 d are in good agreement with those reported in the literature for unsealed anodic oxides on the AA 6061 alloy [1,2] and Al 5N [3,4]. On the other hand, comparing the porous oxide thicknesses calculated from EIS data with the oxide thicknesses measured by the EC technique (Table I) it can be seen that EIS values under estimated the thicknesses of the porous layers by one order of magnitude.…”

“…For both AA 6061 and Al 5N, the impedance modulus (|Z|) increased with an increase in the anodizing voltage. Several authors [1][2][3][4][5] have reported similar EIS spectra for anodic aluminum oxides obtained in sulfuric acid. Bode plots for sealed anodic oxides ( Fig.…”

“…0 / d (1) where C is the effective capacitance; 0 is the vacuum dielectric constant (8,85.10 -12 F.m -1 ); is the dielectric constant for the oxide layer and d is the oxide layer thickness. Values of =10 for the barrier layer [3] and =36 for the porous layer [2] were used, being this later value typical for hydrated porous oxides [2]. For the sake of comparison, the thicknesses of unsealed anodic oxides measured by EC are also included in the table.…”

“…Giovanardi [7] used equivalent circuits with capacitive and inductive elements that are related to the adsorption of ions into the oxide layer. Several other authors [1][2][3][4][5][6] used equivalent circuits with resistances and capacitances that represent the properties of barrier and porous layers. These later authors mentioned that sulfate ions can incorporate into the oxide layer, but they did not consider this effect on the analysis of EIS data.…”

“…Since these elements will be immersed in water for periods of time up to 30 years, it is important to study the properties of the oxide films that grow in such conditions. Electrochemical Impedance Spectroscopy technique (EIS) has been employed by several authors to investigate electrical properties of anodic oxides in aluminum alloys [1][2][3][4][5]. However, little research has been done about the properties of aluminum oxide films grown in water at open circuit potential conditions.…”