Ultrathin protective films of two-dimensional polymers on passivated iron against corrosion in 0.1 M NaCl

Prevention of iron corrosion in an aerated 0.1 M NaCl solution was investigated by polarization and mass-loss measurements of a passivated iron electrode covered with ultrathin and ordered films of two-dimensional polymers. The films were prepared on the passivated 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 alkyltriethoxysilane C_nH_{2n + 1}Si(OC ₂H₅)₃ (n = 8 or 18). Because crevice corrosion occurred at the initial stage of immersion in the solution preferentially, the edge of electrode covered with the polymer film was coated with epoxy resin. The open-circuit potentials of the covered electrodes in the solution were maintained high, more than -0.2 V/SCE for several hours, indicating that no breakdown of the passive film occurred on the surface. The protective efficiencies of the films were extremely high, more than 99.9% unless the passive film was broken down. The efficiencies after immersion for 24 h almost agreed with those obtained by mass-loss measurements. X-ray photoelectron spectroscopy and electron-probe microanalysis of the passivated surface covered with the polymer film after immersion in the solution for 4 h revealed that pit initiation on the passive film was suppressed by coverage with the polymer film completely.