Structural and electrochemical characterization of zirconium and silicon based sol-gel coatings for corrosion protection

Oxide thin films based on the sol-gel technique are well-known for a number of favourable features, such as high hardness and chemical inertness, however, they tend to form holes and cracks. As they are chemically highly stable, they should be well-suited for corrosion protection. The drawback is that for this purpose, cracks might be detrimental. The study aimed at investigating the properties of sol-gel based oxide films for their corrosion protection ability. Thin films of zirconium oxide, partially mixed with silicon oxide, were prepared by spin depositing sols of zirconium tetrapropoxide and phenyltriethoxy silane onto silicon wafers and iron samples. The samples were heat treated to form the respective oxide coatings. Film thickness was determined as a function of spin speed, spin time, drying time and sintering temperature. The so-called critical film thickness for crack formation was determined. The films were characterized with scanning electron microscopy (SEM), IR spectroscopy, and secondary ion mass spectrometry (SIMS). Electrochemical measurements (cyclic voltammetry) were carried out to find a relation between film parameters and corrosion protection potential of the various coatings. The films showed a similar quality in corrosion protection ability as comparable films formed by physical vapour deposition