Resumen
The aim of this work was the investigation of corrosion protection of zinc substrates by compact and porous silica sol-gel coatings of different thicknesses. Coatings were deposited on zinc and, for comparison, on glass substrates by dip-coating. For preparing mesoporous layers, cationic or non-ionic surfactant templates were applied. Thickness and porosity of layers on glass were determined by analyzing the transmittance spectra in terms of thin layer optical models. Surface morphology was studied by scanning electron microscopy and it was found that silica coatings could not flatten out completely the surface of zinc. Corrosion tests were carried out in 0.2 g/L aqueous solution (pH=5) of Na2SO4. The electrochemical data (open-circuit potential, polarization resistance, corrosion potentials and the corrosion current densities) showed that all the coatings provided corrosion protection and it was found that two-layered coatings are more efficient that single ones. Interestingly, the porous coatings provided better protection than compact ones.