pH sensitive gel pads for the visualization of anodes and cathodes on zinc

• A pH indicator was added to the agar gels • The gels visualize anodic and cathodic areas on zinc samples during the reaction • The influence of the pH indicator on the electrochemical behaviour was tested • The gels enable the water drop theory to be examined on a real sample • Even when using a defined anode, the water drop theory is contradicted Zinc and zinc alloys have many applications. Zinc corrosion takes place in the atmosphere and is assumed to follow the water drop theory (a macroelement), in which the anode is at the centre of the drop and is surrounded by a cathode. This paper is the first to use gel electrolytes made of agar to visualize anodic and cathodic areas on zinc samples in order to examine the water drop theory. For that, agar gels were added with universal pH indicators, as the anode and cathode exhibit different pH values. In this paper, different amounts of pH indicators were tested to determine whether the indicator influences the potential, the impedance, phase shift, corrosion current and potential and corrosion layer resistance.