Effect of Na-Montmorillonite sonication on the protective properties of hybrid silica coatings

This work deals with the effect of the sonication treatment applied to an aqueous suspension of sodiummontmorillonite nanoparticles used to prepare hybrid clay-organosilane derived sol-gel films. The sol-gelfilms were obtained from a mixture of 3-glycidoxypropyltrimethoxysilane (GPTMS), tetraethoxysilane(TEOS) and methyltriethoxysilane (MTES) adding 2 wt% of sodium montmorillonite suspension aftersonication. The sol-gel layers were applied onto hot dip galvanized (HDG) steel plates. The influenceof the duration of the sonication treatment (i.e. 0, 1, 3 and 12 hours) on both the structure as well ason the electrochemical properties of the sol-gel films was analyzed in details. The effect of differentsonication times on the structure of the sol-gel film was investigated by means of solid state NuclearMagnetic Resonance (NMR), X-Ray diffraction (XRD) and Infra-Red (FT-IR) spectroscopy. The corrosionprotection properties of the different sol-gel layers were investigated mainly by means of electrochemicaltechniques. The structural characterization (NMR, XRD, FT-IR) of the coating proved that interactionsbetween the montmorillonite plates and the silica-based sol-gel network take place, with changing thelocal environment of Al sites in the clay. The potentiodynamic measurements as well as the EIS confirmedthe beneficial effects of the presence of the Na-MMT and of the sonication treatment.