Improvement of healing treatment with NaNO3 for a passivated iron electrode covered with an ultrathin polymer coating to prevent iron corrosion in some solutions containing aggressive anions

An ultrathin and ordered polymer coating was prepared on a passivated iron electrode by modification of a 16-hydroxyhexadecanoate ion HO(CH2)15CO2- self-assembled monolayer with 1,2-bis(triethoxysilyl)ethane (C2H5O)3Si(CH2)2Si(OC2H5)3 and octyltriethoxysilane C8H17Si(OC2H5)3. Further, the passivated and polymer-coated electrode was healed by treatment in 1.0 M NaNO3 for 4 h. Prevention of passive film breakdown and iron corrosion for the passivated, polymer-coated and healed electrode was examined by monitoring of the open-circuit potential and repeated polarization measurements in oxygenated 0.1 M KClO4, 0.1 M Na2SO4 and 0.1 M NaCl for many hours. The values of the time for passive film breakdown, tbd were >240, 22.2 and 9.5 h in these solutions, respectively. The protective efficiencies for the electrode were extremely high, more than 99.9% before tbd, indicating complete protection of substrate iron against corrosion in these solutions, unless passive film breakdown occurred. The presence of NO3- on the passive surface by treatment in 1.0 M NaNO3 was detected by X-ray photoelectron and FTIR reflection spectroscopies. The self-healing activity of adsorbed NO3- to suppress passive film breakdown was discussed.

► An ultrathin polymer film was prepared on a passivated iron electrode by a SAM.
► For the healing, the polymer-coated electrode was treated in 1.0 M NaNO3 for 4 h.
► This polymer film showed complete protection of iron against corrosion until tbd.