The effect of pretreatments with siloxanes on the corrosion resistance of aluminium in NaCl solution

The inhibitory action of different pretreatments with metacryloxypropylmethoxysilane (MAOS) on the corrosion of aluminium in NaCl aqueous 3.5% solutions has been examined. Free corrosion and electrochemical tests (potentiodynamic polarisation and electrochemical impedance spectroscopy) were performed to characterise the resistance to general and localised corrosion of pretreated specimens. The surfaces of uncorroded pretreated samples were characterised by SEM and AFM. Their surfaces were also examined with XPS technique before and after corrosion attack. It was found that the inhibitory action of MAOS against general and localised corrosion depends on the nature of the solvent in which it is dispersed. The siloxane polymeric film formed by MAOS aqueous dispersion acts as a good corrosion inhibitor in the whole exposure time range, whereas the inhibitory power of the polymeric film formed by MAOS methanol solutions decreases with increasing immersion time. (C) 1999 Elsevier Science S.A. All rights reserved.