Prevention of passive film breakdown on iron by coverage with one-dimensional polymer films of a carboxylate ion self-assembled monolayer modified with alkyltriethoxysilanes

A film composed of a one-dimensional polymer was fabricated by modification of a 16-hydroxyhexadecanoate ion HO(CH2)(15)CO2- self-assembled monolayer (SAM) adsorbed on a passivated iron electrode with octadecyltriethoxysilane C18H37Si(OC2H5)(3). The pitting potential, E-pit of the passivated electrode coated with this film was measured by anodic polarization in a borate buffer solution containing 0.1 M of Cl-. The E-pit value of the electrode coated with the film was markedly shifted from the value of the bare electrode in the positive direction, indicating prevention of passive film breakdown. No breakdown occurred over the potential range of passive region in some cases. Structure of the modified SAM was discussed by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement of the electrode surface covered with the film. Suppression of Cl- accumulation at a defect of the passive film was revealed by electron-probe microanalyses of the surfaces uncoated and coated with the SAM modified with octyltriethoxysilane C8H17Si(OC2H5)(3) after anodic polarization in the borate buffer containing Cl-. (C) 2004 Elsevier Ltd. All rights reserved.