Electrochemical behaviour of ceramic sol-gel coatings on mild steel

Sol-gel titania, silica and mixed thin films undoped and doped with cobalt, iron and tin ions were prepared on different substrates by spin-coating. Electrochemical techniques, X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to characterise the anticorrosion behaviour of the coatings in neutral medium. The results obtained prove that sol-gel TiO2 and SiO2 coatings act as a protective barrier against wet corrosion while mixed films provide lower corrosion protection. Moreover, it is shown that inserting dopants (Co, Fe, Sn) would improve anticorrosion properties but this is hindered in the case of cobalt and tin by a surface deterioration in marked contrast to the insertion of iron. The values of the electrochemical parameters provide an explanation of the role of each film in the increased resistance of mild steel against corrosion. (C) 2001 Elsevier Science B.V. All rights reserved.