Prevention of iron corrosion at scratched surfaces in NaCl solutions by thin organosiloxane polymer films containing octylthiopropionate

Films of 1,2-bis(triethoxysilyl)ethane (C2H5O)3Si(CH2)2Si(OC2H5)3 polymer containing a nonchromate corrosion inhibitor, sodium octylthiopropionate C8H17S(CH2)2COONa (NaOTP) prevented corrosion of iron at a scratched surface in aerated NaCl solutions. The healing ability of the film at the scratch was evaluated by polarization measurement. The protective efficiencies of the films for iron corrosion at the scratched electrodes in 0.1 M NaCl were significantly high, more than 97% in many cases, indicating that the scratches were healed with NaOTP diffusing from the scratched films. X-ray photoelectron spectroscopy and electron-probe microanalysis of the surface after immersion of the electrode in 0.1 M NaCl revealed that iron corrosion at the scratch was suppressed by the formation of an iron oxide layer containing a small amount of a compound derived from NaOTP, probably a Fe3+ complex with octylthiopropionate ion.