Online Visualization of Corrosion Processes of Zinc and a Cu/Zn Galvanic Pair in Lithium Bromide Solutions

A new method has been developed for online visualization of corrosion processes. The system allows surface images of the tested electrode to be captured simultaneously with the recorded electrochemical signal caused by corrosion processes without disturbing the electrochemical system. The experimental device consists of an electrochemical system with a horizontal electrochemical cell coupled to optical equipment. The horizontal position of the electrodes tested permitted the direct observation of surface modifications with time and of the experimental conditions by means of a triocular microscope stereoscope assembled to an image acquisition system. The new methodology was applied in the study of zinc corrosion and galvanic behavior when coupled to copper in lithium bromide (LiBr) media. Zinc exfoliation was observed in potentiodynamic tests. Zero-resistance ammetry was the electrochemical technique used to evaluate the galvanic corrosion in the Cu/Zn pair. The online visualization of the electrodes allowed the measurement of the corroded area of zinc and the study of how it grows with time. Hydrogen evolution was produced on the localized cathodic sites of the zinc surface when the Cu/Zn pair was immersed during 24 h at room temperature in the LiBr solution. This hydrogen generation was accelerated by the effect of temperature when the samples were subjected to a temperature cycle. The goal of the present research was to complement the conventional electrochemical methods with an online image analysis, which allows the identification of real corrosion processes developing on the electrodes.