Improvement of corrosion protection offered to galvanized steel by incorporation of lanthanide modified nanoclays in silane layer

Silane sol–gel based films are very promising alternatives to the traditional chromate pre-treatments. However, the protection offered by the silane films strongly decreaseswhenthe coating is damaged.Some previous studies showed that the barrier properties of the silane layer can be improved by incorporation of clay nanoparticles. Moreover, inhibitive metallic cations can be incorporated in the nanoclays by ion exchange, providing a way to prepare cheap corrosion inhibitors nanoreservoirs offering self-healing properties. Rare earth (RE) metal salts have been shown to be effective corrosion inhibitors on a wide range of metals, including hot dip galvanized (HDG) steel. For this study, montmorillonite clay is modified to obtain a Ce(III) montmorillonite clay (Ce-MMT). The amount of incorporated Ce(III) is characterized by means of XRF measurements. X-ray diffraction showed that the Ce(III) is located in the interlayer space. The influence of the ionic strength and of the nature of the counter ion on the kinetic of Ce(III) release is investigated in NaCl and ZnCl2 solutions. Either unmodified MMT or Ce-MMT nanoreservoirs are incorporated in a silane sol–gel treatment consisting in a combination of 3 different silanes (GPS, TEOS and MTES). The corrosion protection offered to HDG substrate by the modified silane layer was evaluated by means of electrochemical impedance spectroscopy in 0.1M NaCl.