Inhibition of acid undercutting of inorganic/organic hybrid polyurethane coatings

Abstract

This study investigated the corrosion resistance of inorganic/organic hybrid polyurethane based coatings by using a mixture of sol-gel precursors. Four sol-gel precursor, tetraethyl orthosilicate (TEOS), titanium(IV) isopropoxide (TIP), and zirconium(IV) propoxide (ZRP), were utilized in this study. Salt spray, acid undercutting, and electrochemical impedance spectroscopy (EIS) were conducted to study the anticorrosion behavior of the coatings. Generally, samples based on mixed sol-gel precursors exhibited better protection compared to the urethane coating without sol-gel precursors or the coating with only TEOS as the single sol-gel precursor. In acid undercutting experiments, mixed sol-gel precursor samples provided the best results compared to the control and TEOS-based samples. Comparison of parameters extracted by EIS describing water uptake indicates mixed sol-gel precursor composition had the best anticorrosion performance, which was consistent with acid undercutting results. The impedance of the hybrid coatings, at the order of 1010 ohms cm2 at 0.01 Hz, were ca. 3 orders higher than the control sample. Coating capacitance for all the hybrid coatings were stable throughout the immersion time while that for the control sample had a significant change after short time. The water uptake for the control sample was close to 2.5% while that for all the hybrid coatings were about or lower than 0.5%. Morphology from SEM revealed that the organic inorganic sample with TEOS/TIP/ZRP mixed precursors maintained the coating integrity while higher porosity was developed in the control sample.