Adsorption of corrosion inhibitors (SA, HEDP) using EQCM: chloride effect and synergic behavior

摘要

The adsorption of inhibitor molecules, ascorbic acid (SA), and 1-hydroxyethane-1,1-diphosphonic acid (HEDP), was studied using electrochemical quartz crystal microbalance. Adsorption on iron was studied compared with gold in the presence of chloride ions and at E OP and cathodic potential. Each of these parameters significantly affects monolayer adsorption following the Langmuir isotherm. HEDP was adsorbed more rapidly than SA. The novelty in this study concerns the influence of chloride concentration on the inhibition efficiency. Indeed, the rate of inhibition also depends on the concentration ratio of chloride/inhibitor, which is an important factor for the practical implementation of these compounds. Adding a small quantity of chloride ions can increase adsorption rate as well as degree of coverage. Optimum behavior was noted for a HEDP/Cl− ratio about 500. Passivation of the electrode to cathodic potential influenced HEDP adsorption and promoted that of SA. A low adsorption current proportional to the concentration of the inhibitor was recorded. A synergic inhibition by the two molecules was observed for a concentration relationship of 1.16. The study showed that SA was not adsorbed at the interface but its presence made a reduction in lateral tensions possible between adsorbed HEDP, leading to a better coverage.