Role of nano ZnO particles in the electrodeposition and growth mechanism of phosphate coatings for enhancing the anti-corrosive performance of low carbon steel in 3.5% NaCl aqueous solution

Abstract

In this work, nano ZnO powders were used in the electrodeposition of zinc phosphate coatings to mitigate the detrimental effects of corrosion on low carbon steel. Our results showed that nano ZnO powder promotes the formation of hopeite (Zn3(PO4)2·4H2O) and phosphophyllite (Zn2Fe(PO4)2·4H2O) phases which are the main constituents of phosphate conversion coatings. The surface morphology, chemical composition, the growth process and anticorrosive performance of these coatings are examined using SEM, EDS, XRD and electrochemical measurements. Electrochemical characterization results suggest, nano ZnO incorporated phosphate coatings exhibit a lower corrosion rate (∼1.89 mpy) in 3.5% NaCl solution against normal zinc phosphate coatings (∼5.68 mpy) which is well supported by microstructural examination. It is believed that positive shift in corrosion potential and marked reduction in the current density helps in the formation of compact coatings with full crystalline surface coverage suggesting the corrosion protection mechanism offered by these coatings is a diffusion controlled process.