Electrochemical Impedance Spectroscopy Investigation on the Corrosive Behaviour of Waterborne Silicate Micaceous Iron Oxide Coatings in Seawater

The anticorrosive composite coatings based on waterborne silicate were prepared to replace existing solvent-based coatings suitable for ships. A series of composite coatings were prepared by adding zinc powder and micaceous iron oxide to the waterborne silicate resin. The adhesion, pencil hardness and impact resistance of the coatings were investigated and corrosion performance in seawater is characterized by electrochemical impedance spectroscopy (EIS). The results show that coatings have excellent adhesion and impact resistance and their pencil hardness can reach up to 4H. During the immersion of composite coatings in seawater for 8 h, only one time constant appears in the Bode plot, coating capacitance (Qc) gradually increases but dispersion coefficient (n) and coating resistance (Rc) gradually decrease. The breakpoint frequency formula was deduced, considering the dispersion effect. With the increase of micaceous iron oxide, the fluctuation of breakpoint frequency with immersion time is weakened. It can be used to evaluate the corrosion resistance of inorganic anticorrosive coatings in seawater. In addition, different penetration models of corrosive media were proposed for the coatings with low or high content of micaceous iron oxide.