Effect of metal oxide additives on the structural and barrier properties of a hybrid organosilicon sol-gel coating in 3.5% NaCl medium

Hybrid sol-gel materials provide a favorable alternative to the use of toxic phosphate and chromate conversion coating to protect metal substrates from corrosion attack. Herein, a systematic study was performed to investigate the effect of metal oxide additives i.e niobium(V) oxide), titanium(IV) ethoxide, and zirconium(IV) propoxide on the structural and corrosion protection properties of novel hybrid sol-gel coatings applied on a mild steel (MS) surface. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) analyses revealed the introduction of structural changes on the parent hybrid polymer upon loading it with the metal oxide additives. Moreover, the gel permeation chromatography (GPC) studies of the functionalized hybrid polymeric materials proved higher polymerization extent in these materials in comparison with the parent polymer. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests have shown that the metal oxide additives displayed; to various extents, an enhancement in the barrier properties of the base hybrid coating for a MS substrate in a 3.5 wt.% NaCl medium. Zirconium(IV) propoxide additive showed the highest corrosion resistance as compared to parent sol-gel coating or other metal oxide additives. Scanning electron microscope (SEM) analyses indicate an excellent homogeneous coverage of the functionalized coatings on the MS surface with no signs of defects, delamination, or micro cracks behaviors. The present study gains deeper insights into the interactions nature between the oxide additive and the host polymer matrix.