Impedance Measurements during Anodization of Aluminum

The impedance of a growing anodic oxide layer is inductive in a certain frequency range. This effect is related to the occurrence of transients after changes in current density or applied electric field. Measurements on aluminum samples in the frequency range 5 mHz‐10 kHz and the current density range 3 × 10 − 6 – 5 × 10 − 3 A / cm 2 and in various electrolytes are presented and compared with a theory in which the relaxation effect is ascribed to a buildup of surface charge at the metal‐oxide interface.