Nanostructured silane coatings for corrosion resistance of low carbon steel

The overall aim of this work is to design an alternative metal pre-treatment with improved corrosion resistance and low environmental impact. Hybrid silane pre-treatments with nano-additives and corrosion inhibitors as fillers for corrosion protection of low carbon steels using sol-gel processing technique were developed. Multifunctional silane molecules used to design the hybrid silane films were based on cross-condensation between an epoxy-silane, 3-glycidoxy-propyl-trimethoxy-silane (GPTMS) and methyl-triethoxy-silane (MTES) in acid catalysis condition. The silane films thus developed on low carbon steel surface also showed good adhesion, verified by Fourier Transform Infra-red Spectroscopy (FTIR). The corrosion resistance of the silane films modified with impregnation of corrosion inhibitors (i.e. rare earth salts) and/or silica nanoparticles was evaluated by electrochemical measurements using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The corrosion studies were complimented by investigation of surface topography and wetting properties using scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDX) and contact angle measurements, respectively. This work aided the identification of the synergistic effects of both additives in efficient retardation of corrosion kinetics of the low carbon steel. The direct addition of active lanthanum triflate species, was found to have detrimental effects effect on corrosion resistance of the steel. The investigation also included cerium and yttrium triflates, for activation of silica nanoparticles within hybrid silane network for corrosion protection of low carbon steel. The electrochemical investigations elucidate the superior corrosion resistance of cerium activated systems on low carbon steel, as compared to lanthanum and yttrium triflates. It is proposed that the cerium triflates within the silane films on coated steels, forms cerium oxides or hydroxides on cathodic and anodic regions as a result of increase in pH during corrosion, thus hindering further progression of the corrosion onset. Optimum concentration of the cerium activated systems for the best corrosion resistance of low carbon steel was also established in this study.