Abstract
The effects of a.c.-electrochemical graining and anodizing of an aluminium substrate on the layer properties of both barrier and porous alumina layers are examined using electrochemical impedance spectroscopy (EIS). In order to show the capabilities of the technique for a quantitative determination, results based on impedance data are compared with complementary information from surface analytical techniques. Though the results for the determination of barrier layer thickness and dielectric constant look promising, calculations are troubled by non-trivial dispersion phenomena. This problem is treated using a fractal description of surface roughness of the substrate and of the layer thicknesses. Information on pore structure of porous oxide films could not be obtained from the approach considered in this study.
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Abbreviations
- C b :
-
geometric barrier layer capacitance (μFcm−2)
- C p :
-
porous layer capacitance
- c d :
-
elementary surface capacitance of the double layer
- R p :
-
resistance of the solution in pores (Ωm−2)
- r e :
-
elementary resistance of the solution near the surface
- D f :
-
fractal dimension of the surface
- E a :
-
anodizing voltage (V)
- r a :
-
unit barrier thickness (nm V−1)
- A g :
-
geometric surface area (cm2)
- d b :
-
thickness of the barrier layer (nm)
- α:
-
fractional power frequency dependence
- ω:
-
angular frequency of the a.c.-voltage (rad s−1)
- ɛ 0 :
-
permittivity of free space (8.85×10−12 F m−2)
- ɛ:
-
dielectric constant of the anodic oxide
- σ:
-
surface roughness factor
- j:
-
unit on imaginary axis
- Z :
-
Z′−jZ″ (Ω m−2)
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Van der Linden, B., Terryn, H. & Vereecken, J. Investigation of anodic aluminium oxide layers by electrochemical impedance spectroscopy. J Appl Electrochem 20, 798–803 (1990). https://doi.org/10.1007/BF01094309
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DOI: https://doi.org/10.1007/BF01094309