Spontaneous grafting of iron surfaces by reduction of aryldiazonium salts in acidic or neutral aqueous solution. Application to the protection of iron against corrosion

The chemical grafting of iron surfaces at open-circuit potential by reduction of different aryldiazonium salts in aqueous acidic solution occurs spontaneously without the need of electrochemical assistance. X-ray photoelectron spectroscopy (XPS) and IR allowed to evidence the grafting of organic moieties without any adsorption of diazonium salts. The aryl groups are strongly bonded to the metal since they can withstand sonication in acetone. XPS measurements also show that spontaneous grafting in water is at least as efficient as electrochemical grafting and also indicate the presence of a multiphenyl layer coverage of the iron surface. The surface film of carboxyphenyl groups on iron was chemically derivatized further by octyltriethoxysilane. The anticorrosive effects of the different films were evaluated in 0.01 M H2SO4 aqueous solution, by polarization and impedance measurements. Grafting of the diazonium salt results in an inhibition efficiency up to 73%, which can be slightly increased up to 85% by derivatization of the film by octyltriethoxysilane. The inhibition efficiency can be significantly improved up to 97% when the grafted metal is left in the corrosion medium in the presence of the diazonium salt.