Preparation of ultrathin polymer coatings adsorbed on iron via a covalent bond by multistep modification of a hydroxymethylbenzene SAM with ethoxysilanes and alkanediol for preventing iron corrosion in 0.5 M NaCl

The film thickness, d of a p-hydroxymethylbenzene - C₆H₄CH₂OH (HOMB) self-assembled monolayer (SAM) adsorbed on iron via a covalent bond was increased by multistep modification with tetraethoxysilane (C₂H₅O)₄Si (TES) and 1,8-octanediol HO(CH₂)₈OH (C₈DO) and subsequently with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ (BTESE) and akyltriethoxysilane C_nH_2n+1Si(OC₂H₅)₃ (C_nTES, n = 8 or 18). The protective ability of the film against iron corrosion was examined by polarization measurement of the iron electrode coated with the film in an oxygenated 0.5 M NaCl after immersion in the solution for many hours. The values of protective efficiency, P for the films, the HOMB SAM modified with TES and C₈DO twice and subsequently with BTESE and C_nTES were high, more than 81% at n = 8 and 85% at n = 18 in the range of the immersion time, t up to 240 h, respectively. The maximal P values of the respective films were 88.0% and 92.2%, of which approximate d values were 4.6 and 5.8 nm. The high protection of iron against corrosion was attributed to increases in the film thickness and interconnection between the adsorbed molecules with Si-O polymer linkages. The protective ability of the film was remarkably persistent during immersion in the solution for many hours. A slight enhancement of P was observed by additional modification of the modified HOMB SAM with C₈TES due to increases in interconnection and close packed arrangement. The formation of strong adsorption bonds, σ-covalent bond and back-donating π-bond, between the carbon atom of HOMB moiety and iron atom was discussed.     

Preparation of one-dimensional polymer films by modification of a hydroxymethylbenzene self-assembled monolayer on iron with alkyltriethoxysilanes for preventing iron corrosion

A self-assembled monolayer (SAM) of p-hydroxymethylbenzene HOCH₂C₆H₄ - (HOMB) moiety adsorbed on iron by the formation of a covalent bond between carbon and iron atoms was prepared by electrochemical derivatization of an iron electrode with p-hydroxymethylbenzenediazonium tetrafluoroborate HOCH₂C₆H₄N₂BF₄. The electrode covered with the HOMB SAM was modified with alkyltriethoxysilanes C_nH_2n+1Si(OC₂H₅)₃ (C_nTES, n = 8 or 18) to prepare a film of one-dimensional polymer. The protective ability of the polymer film was determined by polarization measurement of the covered electrode in an aerated 0.5 M NaCl solution. The ability was enhanced by modification of the HOMB SAM with C_nTES markedly. The iron surface coated with the one-dimensional polymer film of the HOMB SAM modified with C₈TES was characterized by contact angle measurement and FTIR reflection and X-ray photoelectron spectroscopies. The persistence in the protective ability of the polymer film against iron corrosion in 0.5 M NaCl may be associated with the strong adsorption via the covalent bond, revealed by electron-probe microanalysis.     

Additional modification to two-dimensional polymer films of a hydroxymethylbenzene self-assembled monolayer with alkyltriethoxysilanes for enhancing the protective abilities against iron corrosion

Additional modification of the ultrathin two-dimensional polymer film, a p-hydroxymethylbenzene C₆H₄CH₂OH self-assembled monolayer modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ (BTESE) and alkyltriethoxysilane C_nH_2n+1Si(OC₂H₅)₃ (C_nTES, n = 8 or 18), was attempted to improve the protective ability of the film against iron corrosion. The ability of the film was examined by polarization measurement of an iron electrode coated with the film in an oxygenated 0.5 M NaCl solution after immersion in the solution for 1.5 to 72 h. Marked improvement of the protective efficiency, P was not obtained by additional modification to the polymer film with BTESE. The P values of the two-dimensional polymer films were markedly increased by additional modification with C₈TES. The increases in P were ascribable to improvement of alkyl tail arrangement and additional interconnection in the polymer films. The film on the iron surface was characterized by contact angle measurement, FTIR reflection spectroscopy and X-ray photoelectron spectroscopy. The protective abilities of the two-dimensional polymer films additionally modified with C₈TES were persistent during immersion for 72 h.     

Self-assembled monolayers of p-toluene and p-hydroxymethylbenzene moieties adsorbed on iron by the formation of covalent bonds between carbon and iron atoms for protection of iron from corrosion

An iron electrode was modified by electrolytic reduction in deaerated acetonitrile solution of p-toluenediazonium tetrafluoroborate CH₃C₆H₄N₂BF₄ (TDFB) or p-hydroxymethylbenzenediazonium tetrafluoroborate HOCH₂C₆H₄N₂BF₄ (HOTDFB) below 10 °C to form a self-assembled monolayer (SAM) of toluene CH₃C₆H₄- or hydroxymethylbenzene HOCH₂C₆H₄- (HOMB) moiety, probably adsorbed on the electrode by the formation of a covalent bond between carbon and iron atoms, as shown in references. The protective ability of the layer was examined by polarization measurement of the electrode in an aerated 0.5 M NaCl solution. The protective efficiencies of these two SAMs were not high, around 30%, a little higher than that of the toluenethiol CH₃C₆H₄SH SAM which was anchored on iron via a coordinate bond between sulfur and iron atoms. The iron surfaces modified with TDFB and HOTDFB were characterized by contact angle measurement, FTIR reflection spectroscopy and X-ray photoelectron spectroscopy. The persistence in protection of iron against corrosion by coverage with the HOMB SAM was confirmed by polarization measurements after immersion in 0.5 M NaCl for a long period of the time.     

Protection of zinc from corrosion by coverage with a hydrated cerium(III) oxide layer and ultrathin polymer films of a carboxylate self-assembled monolayer modified with alkyltriethoxysilanes

Ultrathin films of one- and two-dimensional polymers were prepared on a zinc electrode coated with a hydrated cerium(III) oxide Ce₂O₃ layer by modification of a 16-hydroxyhexadecanoate ion self-assembled monolayer (SAM) with alkyltriethoxysilanes. The protective efficiency, P of the film was determined by polarization measurements of the electrodes bare and covered with the polymer films in an oxygenated 0.5 M NaCl solution. The respective P values for the one-dimensional polymers of the HOC₁₆A⁻ SAM modified with octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃ (C₈TES) and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃ (C₁₈TES) were 94.4 and 95.1%. The values for the two-dimensional polymers of the HOC₁₆A⁻ SAM modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅)₃Si(CH₂)₂Si(C₂H₅)₃ plus C₈TES and C₁₈TES were 95.4 and 96.5%, respectively, indicating higher than those of the one-dimensional polymers. Structures of the polymer films were characterized by contact angle measurement with a drop of water and X-ray photoelectron and FTIR reflection spectroscopies.     

Improvement of the film thickness by modification of the hydroxymethylbenzene SAM with tetraethoxysilane and octanediol for protection of iron from corrosion in 0.5 M NaCl

For enhancing the protective efficiency, P of a film prepared by modification of a p-hydroxymethylbenzene HOC₆H₄ (HOMB) self-assembled monolayer (SAM) adsorbed on iron by the formation of a covalent bond, an increase in the film thickness, d was attempted. The HOMB SAM was modified with tetraethoxysilane (C₂H₅O)₄Si (TES), 1,8-octanediol HO(CH₂)₈OH (C₈DO), 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ (BTESE) and alkyltriethoxysilane C_nH_2n+1Si(OC₂H₅)₃ (C_nTES, n = 8 or 18). The P value of the film was determined by polarization measurement of a covered iron electrode in an aerated 0.5 M NaCl solution after immersion in the solution for 1.5–72 h of the immersion time, t. High values of P, more than 82% were obtained for the films of HOMB SAM modified with TES, C₈DO and C_nTES and with TES, C₈DO, BTESE and C_nTES in the range of t up to 72 h. The highest value was 93.2%, for the film of HOMB SAM modified with TES, C₈DO, BTESE and C₁₈TES, of which d was 4.7 nm. The film of HOMB SAM modified with TES, C₈DO and C₈TES was characterized by contact angle measurement, X-ray photoelectron spectroscopy and FTIR reflection spectroscopy.     

Corrosion prevention of passivated iron in 0.1 M NaCl by coverage with an ultrathin polymer coating and healing treatment in 0.1 M NaNO3

An ultrathin, ordered and two-dimensional polymer coating was prepared on a passivated iron electrode by modification of 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻ self-assembled monolayer with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. Subsequently, the electrode was healed in 0.1 M NaNO₃. Protection of passivated iron against passive film breakdown and corrosion of iron was examined by monitoring of the open-circuit potential and repeated polarization measurements of the polymer-coated and healed electrode in an aerated 0.1 M NaCl solution during immersion for many hours. Localized corrosion was markedly prevented by coverage with the polymer coating and the healing treatment in 0.1 M NaNO₃. Prominent protection of iron from corrosion in 0.1 M NaCl was observed before the breakdown occurred. The electrode surface covered with the healed passive film and polymer coating was analyzed by contact angle measurement, X-ray photoelectron spectroscopy and electron-probe microanalysis.     

Prevention of passive film breakdown and corrosion of iron in 0.1 M KClO4 with and without Cl by covering with an ultrathin two-dimensional polymer coating and healing treatment in 0.1 M NaNO3

A two-dimensional polymer coating, the self-assembled monolayer of 16-hydroxy hexadecanoate ion HO(CH₂)₁₅ modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃ was prepared on the passivated iron electrode and further, the passive film was healed by additional treatment in 0.1 M NaNO₃. This electrode was immersed in oxygenated 0.1 M KClO₄ solutions with and without 1 × 10⁻⁴ to 1 × 10⁻² M of Cl⁻. Protection of passive film against breakdown by covering the electrode with the polymer coating was examined by monitoring the open-circuit potential during immersion in the solutions for many hours to determine the time for passive film breakdown, t_bd. Repeated polarization measurements were carried out during immersion in these solutions for obtaining the protective efficiency, P. The t_bd value of the passivated, polymer-coated and healed electrode in 0.1 M KClO₄ solutions with and without Cl⁻ increased with a decrease in the concentration of Cl⁻. No breakdown occurred on the electrode during immersion in 0.1 M KClO₄ solutions with and without 1 × 10⁻⁴ of Cl⁻ for 360 h. The P values were extremely high, more than 99.9% before t_bd, indicating complete protection of iron from corrosion. The effect of healing treatment in 0.1 M NaNO₃ on passive film breakdown was investigated by electron-probe microanalysis.     

Preparation of a self-assembled monolayer on iron by the formation of a covalent bond between carbon and iron atoms

A self-assembled monolayer (SAM) of toluene moiety CH₃C₆H₄- was prepared on an iron electrode by electrochemical modification in a deaerated acetonitrile (AN) solution of p-toluenediazonium tetrafluoroborate CH₃C₆H₄N₂BF₄ (TDFB). The protection of the modified electrode was examined by polarization measurements in an oxygenated 0.5 M NaCl solution after immersion in the solution for 1.5 and 4.0 h. The average values of protective efficiency, P for the films prepared by modification in the TDFB solution at −1.013 V/Ag/Ag⁺AN for the modification time, t_m more than 5 min were fairly high, 78.1% and 53.6% at 1.5 and 4.0 h of the immersion time, t, respectively. However, X-ray photoelectron spectra of the iron surface modified with TDFB for 10 min revealed that the film thus prepared on iron was a polymer of the toluene moieties. A layer formed by the cathodic modification in the TDFB solution for 1 min seemed to be a monolayer of the toluene moiety, revealed by X-ray photoelectron spectra of the surface coated with the layer. The contact angle on the coated surface using a drop of water supported the formation of toluene SAM. The P values of the layer for iron corrosion in 0.5 M NaCl were 31.8% and 28.9% at 1.5 and 4.0 h of t, respectively, being a little higher than those of the toluenethiol CH₃C₆H₄SH SAM. The higher values may be attributed to the formation of a strong covalent bond between carbon and iron atoms.     

An ultrathin polymer coating of carboxylate self-assembled monolayer adsorbed on passivated iron to prevent iron corrosion in 0.1 M Na2SO4

For preparing an ultrathin two-dimensional polymer coating adsorbed on passivated iron, a 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻ self-assembled monolayer (SAM) was modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. Protection of passivated iron against passive film breakdown and corrosion of iron was investigated by monitoring of the open-circuit potential and repeated polarization measurements in an aerated 0.1 M Na₂SO₄ solution during immersion for many hours. The time required for passive film breakdown of the polymer-coated electrode was markedly higher in this solution than that of the passivated one, indicating protection of the passive film from breakdown by coverage with the polymer coating. The protective efficiencies of the passive film covered with the coating were extremely high, more than 99.9% in 0.1 M Na₂SO₄ before the passive film was broken down, showing prominent cooperative suppression of iron corrosion in the solution by coverage with the passive film and polymer coating. The polymer-coated surface was characterized by contact angle measurement and electron-probe microanalysis (EPMA). Prevention of passive film breakdown and iron corrosion for the polymer-coated electrode healed in 0.1 M NaNO₃ was also examined in 0.1 M Na₂SO₄.     

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)₁₅CO₂⁻ 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⁻.     

Protection of passivated iron against corrosion in a 0.1 M NaNO3 solution by coverage with an ultrathin polymer coating of carboxylate SAM

An ultrathin, ordered and two-dimensional polymer coating was prepared on passivated iron by modification of 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻ self-assembled monolayer (SAM) with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. Protection of passivated iron against passive film breakdown and corrosion of iron was examined by monitoring of the open-circuit potential and repeated polarization measurements in an aerated 0.1 M NaNO₃ solution during immersion for many hours. Passive film breakdown on the polymer-coated electrode in the solution was not observed during immersion for 480 h, whereas that of the passivated one occurred at 18.1 h, indicating protection of the passive film from breakdown by coverage with the polymer coating. The protective efficiencies of the passive film covered with the coating were extremely high, around 99.9% in the initial region of the immersion time up to 72 h and more than 98.3% thereafter, indicating prominent cooperative suppression of iron corrosion in 0.1 M NaNO₃ by coverage with the passive film and polymer coating. The polymer-coated surface was characterized by contact angle measurement and electron-probe microanalysis.     

Preparation of chromate-free, self-healing polymer films containing sodium silicate on zinc pretreated in a cerium(III) nitrate solution for preventing zinc corrosion at scratches in 0.5 M NaCl

Self-healing protective films of 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ (abbreviated to BTESE) polymer containing sodium silicate Na₂Si₂O₅ (water glass) and cerium(III) nitrate Ce(NO₃)₃ were prepared on a zinc electrode previously treated in a 1×10⁻³ M Ce(NO₃)₃ solution at 30 °C for 30 min. After the surface of coated electrode was crosswise scratched with a knife edge, the electrode was immersed in an aerated 0.5 M NaCl solution at 30 °C for many hours and polarization measurements of the scratched electrode were carried out for estimating the self-healing effects of the films on zinc corrosion at the scratches. The optimal quantities of Na₂Si₂O₅, Ce(NO₃)₃ and BTESE in the films were determined by polarization measurements and observation of pit formation at the scratches. No pitting corrosion occurred at the scratches on the zinc electrode covered with a film composed of their optimal quantities after immersion in the solution for 72 h.     

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 self-assembled monolayer with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and alkyltriethoxysilane C_nH_{2n + 1}Si(OC₂H₅)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.     

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 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, t_bd 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 t_bd, indicating complete protection of substrate iron against corrosion in these solutions, unless passive film breakdown occurred. The presence of 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 to suppress passive film breakdown was discussed.     

Limits determination of toleration of aggressive anions by a certain passivator on zinc surface

The open circuit potentials of Zn electrode were followed as a function of time in different concentrations Na₂B₄O₇ solutions until steady-state, E_st., values were attained. The potential shifts immediately towards positive values, indicating film thickening and repair. The effect of addition of NaCl, NaBr and NaI as aggressive agent on the steady-state potential of a Zn electrode previously equilibrated in a passivating borate solution was also established. For each Na₂B₄O₇ concentration, the variation in the potential with the quantity of aggressive anions follows an S-shaped relationship. The new potentials are established after an induction period which decreases with the increase in the concentration of the aggressive anion, C_agg., and/or decreases in that of the passivator anion, C_pass.. The concentration, C_agg., that can be tolerated by a certain concentration of the passivator anion, C_pass., is given by the relation: log C_pass. = k + n log C_agg., where k and n are constants. This is derived on the basis of competitive adsorption of both types of anion and the structure of the double layer at the metal/solution interface. The implications of the equations are briefly discussed.     

Preparation of a one-dimensional polymer film on passivated iron by modification of a carboxylate ion self-assembled monolayer with octyltriethoxysilane for preventing passive film breakdown

A self-assembled monolayer (SAM) of 16-hydroxyhexadecanoate ion HO(CH₂)₁₅CO₂⁻(HOC₁₆A⁻) has been prepared on an iron electrode passivated in a borate buffer solution (pH 8.49) in the preceding paper. In this work, the HOC₁₆A⁻ SAM on the passivated electrode was modified with octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃ to form a film composed of one-dimensional polymer. Prevention of passive film breakdown was examined by anodic polarization measurements of the electrodes uncoated and coated with the modified SAM in the borate buffer containing 0.1 M of Cl⁻. The pitting potential, E_pit of the coated electrode shifted from that of the uncoated electrode in the positive direction, indicating prevention of passive film breakdown. The anodic current density was decreased in the passive and transpassive regions by coverage with the modified SAM. Neither current spikes nor E_pit was observed in the curve of the passive region in some cases, demonstrating complete protection of the passive film against breakdown in the Cl⁻ solution. The modified SAM on the electrode was characterized by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement.     

Prevention of zinc corrosion in oxygenated 0.5 M NaCl by treatment in a cerium(III) nitrate solution and modification with sodium hexadecanoate

A self-assembled monolayer (SAM) of hexadecanoate ion (C₁₆A⁻) was prepared on a zinc electrode covered with a layer of hydrated cerium(III) oxide Ce₂O₃. The protection of zinc against corrosion was examined for the electrode coated with the Ce₂O₃ layer and the C₁₆A⁻ SAM in an oxygenated 0.5 M NaCl solution. A more positive open-circuit potential of the coated electrode was maintained during immersion in the solution for 4 h than that of the uncoated one and polarization curves showed marked suppression of the anodic process, implying that the layer modified with the SAM acted as a passive film. The protective efficiency of the modified layer was extremely high, more than 99%. The zinc surface coated with the Ce₂O₃ layer and the C₁₆A⁻ SAM was characterized by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement with a drop of water.     

Preparation of a two-dimensional polymer film on passivated iron by modification of a carboxylate ion self-assembled monolayer with alkyltriethoxysilanes for preventing passive film breakdown

The effect of an ultrathin, regularly arranged polymer film on prevention of passive film breakdown on iron in the presence of chloride ion was investigated. The film of two-dimensional polymer was prepared by modification of a 16-hydroxyhexadecanoate ion self-assembled monolayer adsorbed on a passivated iron electrode with 1,2-bis(triethoxysilyl)ethane(C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octyltriethoxysilane C₈H₁₇Si(OC₂H₅)₃. The pitting potentials of the passivated electrodes bare and covered with the polymer film were determined by anodic polarization measurements in a borate buffer solution containing 0.1 M of Cl⁻. The pitting potential of the coated electrode was higher than that of the uncoated one, indicating prevention of passive film breakdown. No breakdown was observed over the potential range in the passive and transpassive regions by covering the passive film with the well-arranged two-dimensional polymer film. The film was characterized by X-ray photoelectron and FTIR reflection spectroscopies and measurement of the contact angle with a drop of water.     

Protection of passivated iron from corrosion in 0.1 M KClO4 with and without Cl by coverage with a two-dimensional polymer film of carboxylate ion self-assembled monolayer

A film of two-dimensional polymer was prepared on an iron electrode passivated in a borate buffer solution at pH 8.49, derivatized with 16-hydroxyhexadecanoate ion and then modified with 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ and octadecyltriethoxysilane C₁₈H₃₇Si(OC₂H₅)₃. The protective ability of the polymer film adsorbed on passivated iron was examined by polarization measurement in oxygenated 0.1 M KClO₄ solutions with and without 1 × 10⁻⁴ and 1 × 10⁻³ M of Cl⁻. The values of the open-circuit potential, E_oc were monitored with the immersion time, t in these solutions. The E_oc value of the passivated electrode in 0.1 M KClO₄ was maintained high, more than −0.2 V/SCE in the initial region of t up to 10 h, indicating the presence of a passive film on the electrode. Thereafter, E_oc decreased to −0.4 V/SCE abruptly, exhibiting breakdown of the passive film. The value of the passivated electrode covered with the polymer film remained almost constant around −0.04 V/SCE during immersion for 45 h. The protective efficiency, P (%) of the polymer film on passivated iron was extremely high, more than 99.9% unless the passive film was broken down, indicating complete protection of iron against corrosion. The times for breakdown on the passivated electrode and polymer-coated one diminished with an increase in the concentration of Cl⁻. The polymer-coated surface was analyzed by electron-probe microanalysis after immersion in 0.1 M KClO₄ for 24 h.