Effects of the particle size distribution of zinc powder on the anticorrosion performance of water-borne inorganic zinc-rich coatings

Abstract

Due of their excellent cathodic protection, zinc-rich coatings are among the most important protective coatings for steel substrates used in extremely corrosive and harsh maritime environments. Unfortunately, very few investigations exist on the impact of the size distribution of zinc particle on the electrochemical performances of aqueous inorganic zinc-rich coatings. Herein, we statistically analysed the particle size distribution of two differently sourced zinc powders, named X1 and X2, for coating applications. Their micro-morphologies and particle size distribution within the cross-section of the prepared coatings (designated E06-1-1/X1 and E06-1-1/X2) were investigated by scanning electron microscopy and energy-dispersive spectrometry. While X1 exhibited a relatively uneven size distribution, X2 displayed a more distinct pattern with a step-down trend. After 2200 h, the open-circuit potential (OCP) of E06-1-1/X1coating was higher than that of the Q235 steel substrate (−0.72 V), and pitting corrosion was observed on its surface after 1000 h in a neutral salt spray test. The OCP of E06-1-1/X2 was lower than −0.72 V throughout the test duration of 2500 h, and the development of pits was observed after 1300 h. From the results of coating adhesion strength, OCP, electrochemical impedance spectra, and neutral salt spray tests, the effect of zinc particle size distribution on the anticorrosion performance of the two waterborne inorganic zinc-rich coatings was systematically investigated. The results show that improvements in zinc powder dispersion in coatings are related to the uniformity of zinc particle size distributions. Consequently, this increases the surface area at the interfaces between zinc powder and metal. Furthermore, zinc powders with consistent particle size distributions are better able to provide metal substrates with cathodic protection, while also affording water-based inorganic zinc-rich coatings prolonged anticorrosion effects. Therefore, this study advances the protection mechanism of zinc-rich coatings.