Effect of Molar Ratio and Resin Modification on the Protection Properties of Zinc-rich Alkali Silicate Primer

The influence of increasing the SiO2/K2O molar ratio on the electrochemical action of a waterborne potassium silicate zinc-rich coating was investigated by means of electrochemical impedance spectroscopy (EIS) and corrosion potential (Ecorr) measurements. The EIS results showed that increasing the SiO2/K2O molar ratio in the range of 3.135 to 5 by the addition of nano-SiO2 to the resins improved the resistance of coatings; however, higher molar ratios showed an adverse effect. Moreover, the alkali silicate binder of the sample with a SiO2/K2O molar ratio of 5 was improved by adding 5, 10, and 15 wt.% of acrylic resin and acrylic/styrene copolymer to potassium silicate resin. These formulated coatings were sprayed over carbon steel plates and the adhesion and morphology of these primers were evaluated by pull-off, cross cut, and scanning electron microscopy tests. Electrochemical measurements showed that the sample with a SiO2/K2O molar ratio of 5 had better corrosion properties than the other samples. Adhesion and SEM tests also showed that B1 and C2 with respectively 5 and 10% acrylic derivatives had less holes, cracks, and better adhesive properties.