Evaluation of cathodic protection behavior of waterborne inorganic zinc-rich silicates containing various contents of MIO pigments

Purpose - The aim of this paper is to study the corrosion protection behavior of water-borne inorganic zinc-rich coatings based on potassium silicate/nanosilica developed with various zinc and micaceous iron oxide (MIO) contents during cathodic protection stage. Design/methodology/approach - The formulated coatings were applied on carbon steel panels and were subjected to electrochemical impedance spectroscopy (EIS) and free corrosion potential measurements for characterization of corrosion protection behavior. Also atomic force microscopy (AFM) and optical microscopy were used to investigate the surface topography of coatings. Findings - All of the coatings preserved the cathodic protection ability throughout 75 days of exposure to 3.5% NaCl solution. Supporting results of electrochemical tests and microscopic observations revealed that replacement of zinc by MIO particles reduced both the rate of reactivity and the duration of cathodic protection of inorganic zinc-rich coatings. It was observed that the coatings demonstrated a reactivation step after a dry-wet cycle implying that cyclic immersion can change the overall duration of cathodic protection stage. Originality/value - The paper describes formulation and investigation of corrosion protection behavior of an environmentally friendly zero-VOC coating as well as providing an insight into EIS of zinc-rich coatings.