KINETICS OF PURE ALUMINIUM DISSOLUTION IN H_3PO_4 AQUEOUS SOLUTIONS CONTAINING DIFFERENT AGGRESSIVE ANIONS AND ORGANIC INHIBITORS

摘要

Effects of aggressive anions additives on dissolution of pure aluminium have been investigated in aqueous 1M H_3PO_4 solution as a function of anion concentration using electrochemical impedance spectroscopy (EIS), potentiostatic and potentiodynamic methods. The addition of different aggressive anions (like as Cl~-, Br~-, I~-, SCN~-) lead to in all of the cases to an increase of the corrosion rate. The presence of halide ions creates pitting corrosion in all cases. Characteristic of all systems is that virtually no current flows before some definite potential is reached. The experimental results confirmed that even in solutions containing chloride ions the surface of the metal is covered by an oxide film which changes its properties with current density of anodic dissolution, being the less resistive the higher the current density. Impedance measurements showed a single capacitive loop in the complex plane plots and one maximum in the phase angle Bode plots at high frequencies. Electrochemical measurements showed that, the organic inhibitors, like as dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide and hexadecyltrimethylammonium bromide had good inhibiting properties. The best efficiencies appear to be obtained at concentrations around the critical micelle concentration (CMC). The adsorption of the organic inhibitor prevents the adsorption of aggressive anions and the destruction of the aluminium oxide layer.