The role of acetylacetone in alkaline surface modification bath of electro-galvanized steel to enhance protective functioning of a hybrid silane coating

Abstract

The current work outlines the impact of acetylacetone (AcAc) in the alkaline surface treatment bath on durability and the anti-corrosion properties of electro-galvanized steel (EGS) coated with a hybrid silane composition. The surface characteristics of the EGS samples before and after modifications were appraised using atomic force microscopy, field emission scanning electron microscopy, and contact angle measurements confirming the changes in roughness, morphology and wettability properties imposed by surface treatments. To elucidate the chemical composition of the protecting layer developed on the surface of EGS, X-ray photoelectron spectroscopy was utilized which evidently endorsed forming a film consisting of zinc hydroxide, zinc oxide, and zinc acetylacetonate. The corrosion resistance of the specimens during immersion in 3.5 % NaCl medium was determined using electrochemical impedance spectroscopy and polarization experiments. The low-frequency impedance (at 0.01 Hz) of silane-coated samples modified in the optimal condition (0.5 M NaOH bath) in the presence and absence of AcAc was respectively ca. 15,900, 5800 Ω·cm2. The electrochemical results corroborated the overriding role of a trace amount of AcAc in the corrosion protection of silane-coated EGS samples. The novel surface treatment proposed in this work provides improved corrosion protection of silane coating on EGS having the lowest icorr and presenting inhibition efficiency of 74 % in polarization experiment.