Effects of Curing Temperature and Silica Content on the Structure and Properties of a Sol-Gel PU-Silica Hybrid Coating for Corrosion Protection

Abstract

Adjustments of the curing temperature and silica content were used to improve the corrosion protection properties of an organic-inorganic hybrid (OIH) coating based on a polyurethane-silica (SPU) system. Fourier transform infrared and nuclear magnetic resonance (C-13 and Si-29 NMR) spectroscopy analyses revealed the conversion of urethane groups to secondary amines, with concomitant condensation of Si-R to Si-O-Si, when the curing temperature was increased, while small-angle X-ray scattering analysis showed the formation of denser and less branched aggregates of the inorganic framework. The silica content influenced the roughness and thickness of the coatings, with values in the ranges 1.6-9.6 nm and 1.7-6.5 mu m, respectively. All the hybrid coatings deposited on steel presented impedance modulus at the lowest frequency (|Z(5)|) above 0.1 G Omega cm(2) throughout the 28 days of analysis. The SPU coating prepared using a TEOS/APTES ratio of 1 and a curing temperature of 167 degrees C presented the best performance as a corrosion protection barrier, characterized by predominant capacitive behavior and the invariance of |Z(5)| over 10 G Omega cm(2).