EVALUATION OF GALVANIC CORROSION OF COPPER COUPLED TO STAINLESS STEELS BY TWO ELECTROCHEMICAL TECHNIQUES IN LiBr SOLUTIONS AT DIFFERENT TEMPERATURES

摘要

The galvanic behaviour of copper when coupled to three Stainless Steels was analyzed in LiBr media (with and without chromate inhibitor). The galvanic potential and the galvanic current were measured by a Zero-Resistance Ammeter (ZRA) during a temperature cycle. Potentiodynamic curves of the materials were obtained and the Mixed Potential Theory was applied in order to evaluate the galvanic corrosion and to compare the results to those obtained by the ZRA technique. Images of the electrode surfaces were captured simultaneously with the recorded electrochemical signal caused by corrosion processes without disturbing the electrochemical system. Copper is always the anodic element of the pairs in solutions without additives, while it behaves cathodically at room temperature when the couples are immersed in commercial LiBr solution. Chromate inhibits copper corrosion when coupled to the stainless steels by means of diminishing the galvanic current between the pairs and shifting the galvanic potential to less negative values. Materials with high passivation character generate lower galvanic current values when Mixed Potential Theory is applied compared to the values obtained with the ZRA technique.