IMPEDANCE SPECTROSCOPIC STUDY OF ALUMINUM AND AL-ALLOYS IN ACID-SOLUTION - INHIBITORY-ACTION OF NITROGEN-CONTAINING COMPOUNDS

The adsorption behaviour of triethanolamine (TEA) on aluminium, AlMgSi and AlZnMg alloys covered with naturally formed oxide films was inves tigated in 0.5 m NaCl solution, pH 1.3, by means of potentiodynamic an d electrochemical impedance spectroscopy techniques. The results of po larization measurements show that in all cases the addition of TEA ind uces a decrease in the cathodic currents without affecting the anodic polarization behaviour, and, accordingly, TEA can be treated as a cath odic type inhibitor. The adsorption behaviour of TEA on the electrode surface follows a Frumkin isotherm with constants: a = 1.74, B = 18.41 dm3 mol-1. The results of impedance measurements presented in Nyquist plots show a high frequency capacitive loop related to the dielectric properties of the oxide film and a low-frequency inductive part which was determined by the faradaic process and attributed to the localize d corrosion.