AC-IMPEDANCE MEASUREMENTS ON ALUMINUM IN CHLORIDE CONTAINING SOLUTIONS AND BELOW THE PITTING POTENTIAL

Impedance measurements were performed on aluminium in 0.5M NaCl in the frequency range 5×10-4-104 Hz and before the onset of pitting corrosion. The behaviour of the system was characterized by a high frequency capacitive loop related to the thickness of the oxide film, an inductive loop at medium frequency, which was interpreted on the basis of the dielectric relaxation model proposed by Dignam, and a second capacitive loop obtained at low frequencies which was ascribed to the film dissolution through the formation of a soluble chloride containing aluminium salt. © 1990 Chapman and Hall Ltd.