Properties of hybrid sol-gel coatings with the incorporation of lanthanum 4-hydroxy cinnamate as corrosion inhibitor on carbon steel with different surface finishes

• La(4-OHCin) 3 improves the corrosion protection of two sol-gel synthesized coatings. • The concentration of La(4-OHCin) 3 was optimised and 5 wt.% showed best performance. • EIS show a high capacitive behaviour specially in coatings with 5 wt.% La(4-OHCin) 3 . • High concentrations of La(4-OHCin) 3 gave place to coatings with higher porosity. • Solid-state NMR showed that La(4-OHCin) 3 affects the structure of the sol-gel. In recent years, sol-gel chemistry has been of increasing interest for the development of hybrid organic-inorganic coatings as conversion coating replacements for carbon steel. They provide passive corrosion protection through the creation of a highly adhered coating with a barrier effect to the ionic movement, however, they do not offer active corrosion protection. Lanthanum 4-hydroxy cinnamate [La(4-OHCin) 3 ] has been extensively studied and has demonstrated corrosion inhibition for carbon steel substrates. In this work, different concentrations of La(4-OHCin) 3 have been directly incorporated into two sol-gel formulations with the aim of improving the overall corrosion protection provided by the hybrid coatings. The effect of La(4-OHCin) 3 on the structure of the coating has been studied by 29 Si MAS NMR. The effect on the corrosion protection of coatings deposited on carbon steel with different surface finishes has been examined by EIS and the surface analysis of these coatings has been characterised with techniques such as SEM-EDX and ATR/FT-IR. The better anticorrosion performance of the coatings containing La(4-OHCin) 3 has been demonstrated independently of the surface finish. Also, optimum coating and inhibitor concentrations have been found and a correlation between the structural and morphological properties of the coatings and their anticorrosion performance has been identified.