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.     

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.     

Preparation of a 16-hydroxyhexadecanoate ion self-assembled monolayer on a zinc electrode coated with hydrated cerium(III) oxide

A self-assembled monolayer (SAM) of 16-hydroxyhexadecanoate ion was prepared on a zinc electrode coated with a hydrated cerium(III) oxide Ce₂O₃ layer. The protective efficiency, P of the duplex film composed of the Ce₂O₃ layer and the SAM was examined by polarization measurement of the zinc electrode in aerated 0.5 M NaCl. The P value of the HOC₁₆A⁻ SAM on the Ce₂O₃-coated electrode was only a little higher than that of the Ce₂O₃-coated one. The contact angle of the surface covered with the film with a drop of water was far higher than the value of the HOC₁₆A⁻ SAM on passivated iron, suggesting that HOC₁₆A⁻ was partly adsorbed on the Ce₂O₃ surface via both and OH groups in a looped orientation. Because this orientation must be changed to an extended orientation during immersion in 0.5 M NaCl, some defects appeared within the SAM in places, resulting in a poor enhancement of P. The film structure was characterized by X-ray photoelectron and FTIR reflection spectroscopies.     

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.     

Self-healing protective films prepared on zinc by treatments with cerium(III) nitrate and sodium phosphate

Chromate-free, self-healing protective films were prepared on a surface of zinc electrode previously treated in a solution of cerium(III) nitrate Ce(NO₃)₃ by coverage of the surface with a layer of sodium phosphate Na₃PO₄. The self-healing ability of the film was examined by polarization measurements of the electrode after scratching the surface with a knife-edge crosswise and immersed in an aerated 0.5 M NaCl solution for many hours and by observation of pit formation at the scratches. A thin film containing 0.0552 mg/cm² of Na₃PO₄·12H₂O prepared on the electrode previously treated in 1×10⁻³ M Ce(NO₃)₃ at 30 °C for 30 min and dried at 90 °C for 23 h was highly self-healing and protective against corrosion of zinc in 0.5 M NaCl at the scratches. No pit was detected at the scratches on the electrode coated with this film after immersion for 72 h.     

Synergistic inhibition of zinc corrosion in 0.5 M NaCl by combination of cerium(III) chloride and sodium silicate

The synergistic inhibition effects of cerium(III) chloride, CeCl₃ and sodium silicate, Na₂Si₂O₅ (water glass) on corrosion of zinc in an aerated 0.5 M NaCl solution at 30°C were examined by polarization measurements. Equimolar mixtures of these inhibitors were markedly effective, indicating that the inhibition efficiencies of the mixture at 1×10⁻⁴ of each inhibitor were 95.9 and 93.6 after immersion of a zinc electrode in the solution for 3 and 120 h, respectively. X-ray photoelectron spectra revealed that a protective layer composed of hydroxylated or hydrated cerium-rich oxide and small amounts of zinc hydroxide and silicate formed on the zinc surface. A high inhibition efficiency of 1×10⁻³ M Na₂Si₂O₅, 97.7% was obtained for corrosion of a zinc electrode which was previously treated in the NaCl solution of 1×10⁻³ M CeCl₃ at 30°C for 30 min.     

Cerium(III) chloride and sodium octylthiopropionate as an effective inhibitor mixture for zinc corrosion in 0.5 M NaCl

It has been reported that cerium(III) chloride CeCl₃ and sodium octylthiopropionate C₈H₁₇S(CH₂)₂COONa (NaOTP) are effective inhibitors for zinc corrosion in 0.5 M NaCl. In this study, synergistic inhibition of zinc corrosion in an aerated 0.5 M NaCl solution by a mixture of these inhibitors was investigated by polarization measurements after immersion of a zinc electrode in the solution for many hours. The inhibition efficiency of 1×10⁻⁴ M CeCl₃ plus 1×10⁻⁵ M NaOTP mixture was high, 95.1% after both 3 and 120 h. X-ray photoelectron spectroscopy and electron-probe microanalysis for the inhibited electrode revealed that the zinc surface was covered with a protective film composed of an hydrated or hydroxylated Ce-rich oxide, a small amount of Zn(OH)₂ and a trace of Zn(OTP)₂ chelate. The inhibition effect of 1×10⁻⁵ M NaOTP in the NaCl solution for the zinc electrode previously treated in 1×10⁻³ M CeCl₃ for 30 min was also examined, indicating a higher inhibition efficiency, 96.3% after immersion of the electrode in the solution for 120 h.     

Preparation of self-healing protective films on a zinc electrode treated in a cerium(III) nitrate solution and modified with sodium phosphate and cerium(III) nitrate

Self-healing protective films were prepared on a zinc electrode previously treated in a Ce(NO₃)₃ solution by modification with Na₃PO₄ and Ce(NO₃)₃. The protective and self-healing abilities of the films were examined by polarization measurements and observation of pit formation after the electrode was scratched with a knife-edge crosswise and immersed in oxygenated 0.5 M NaCl at 30 °C for many hours. Mechanisms of the protective and self-healing activities were discussed using X-ray photoelectron spectroscopy and electron-probe microanalysis. The protective and self-healing abilities of the films prepared on the zinc electrode by treatment in the Ce(NO₃)₃ solution and modification with Na₃PO₄ plus Ca(NO₃)₂, Mg(NO₃)₂, Zn(NO₃)₂ or Ce(NO₃)₃ were summarized.     

Improvement in the self-healing ability of a protective film consisting of hydrated cerium(III) oxide and sodium phosphate layers on zinc

A self-healing protective film prepared on a zinc electrode by previous treatment in a Ce(NO₃)₃ solution and coverage with a Na₃PO₄ layer was improved by the addition of Zn(NO₃)₂. The protective and self-healing abilities of the films against corrosion of zinc in an aerated 0.5 M NaCl solution were examined by polarization measurements and observation of pit-like anodic dissolution feature (plf) and pit formation after the electrode was scratched with a knife-edge crosswise and immersed in the solution for many hours. The film prepared on the pretreated electrode coated with 9.98 or 19.9 μg/cm² of Zn(NO₃)₂ · 6H₂O and 55.2 μg/cm² of Na₃PO₄ · 12H₂O was significantly protective and self-healing against zinc corrosion on the scratched electrode. The protective efficiency of the film was more than 96% in the region of the immersion time between 72 and 360 h. No plf was observed at the scratches after immersion for 120 h. Results of Fourier transform infrared reflection and X-ray photoelectron spectroscopies revealed that the film was composed of Na₃PO₄, Zn₃(PO₄)₂ and Ce₂O₃ layers.     

Self-healing protective films prepared on zinc electrodes by treatment in a cerium(III) nitrate solution and modification with sodium phosphate and calcium or magnesium nitrate

Self-healing protective films were prepared on a zinc electrode by treatment in a Ce(NO₃)₃ solution and modification with Na₃PO₄ and Ca(NO₃)₂ or Mg(NO₃)₂. The protective and self-healing abilities of the films were examined by polarization measurements and observation of pit formation after the electrode was scratched with a knife-edge and immersed in aerated 0.5 M NaCl for many hours. The protective efficiency of the film modified with Ca(NO₃)₂ was higher than that of the film without Ca(NO₃)₂ but the self-healing ability of the former film was not sufficiently high during the prolonged immersion. Mechanisms of the protective and self-healing activities were discussed using X-ray photoelectron spectroscopy and electron-probe microanalysis.     

Self-healing mechanism of an organosiloxane polymer film containing sodium silicate and cerium(III) nitrate for corrosion of scratched zinc surface in 0.5 M NaCl

A highly protective and self-healing film of 1,2-bis(triethoxysilyl)ethane (C₂H₅O)₃Si(CH₂)₂Si(OC₂H₅)₃ polymer containing sodium silicate (water glass) Na₂Si₂O₅ and cerium(III) nitrate Ce(NO₃)₃ was prepared on a zinc electrode previously treated in a Ce(NO₃)₃ solution. The film was examined by polarization measurement of the electrode in an aerated 0.5 M NaCl solution after the electrode was scratched and immersed in the solution for 4-72 h. Self-healing mechanism of the film was investigated by X-ray photoelectron spectroscopy and electron-probe microanalysis for the coated electrode surface after scratched and immersed in the NaCl solution. A passive film composed of Zn(OH)₂, ZnSi₂O₅ and Ce³⁺-Si₂O₅²⁻ salt or complex was formed on the scratched surface and preferential deposition of Si₂O₅²⁻ compounds occurred at a defect of the passive film where Cl⁻ accumulated, resulting in suppression of pitting corrosion at the scratch.     

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.     

Corrosion behaviour of steel in the presence of Y(III) salts: Kinetic and mechanistic studies

The corrosion resistance of carbon steel after deposition of yttrium rich (hydr)oxide films on its surface was evaluated as a function of the Y(III) concentration in the solution, the immersion time and the presence of oxygen. During film formation in an aerated solution, two different cathodic reactions are involved: oxygen reduction and water reduction.The rate of oxygen reduction is lowered, whereas water reduction is activated in the presence of Y(III) in the solution. In the absence of oxygen, activated water reduction gets the main cathodic reaction, leading to polarization resistance values which are lower in the presence than in the absence of Y(III) ions.     

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.     

Direct modification of a passivated iron electrode with alkyltriethoxysilanes for preventing passive film breakdown in a borate buffer containing 0.1 M of chloride ion

A passive film on an iron electrode was modified with alkyltriethoxysilanes directly. In order to examine the protective ability of the modified passive film against breakdown, the pitting potential, E_pit was measured by anodic polarization of the modified electrode in a borate buffer solution (pH 8.49) containing 0.1 M of Cl⁻. The value of E_pit for the modified electrode shifted in the positive direction from that of the unmodified electrode, indicating prevention of passive film breakdown. The modified passive film was not broken down in the passive and transpassive regions of polarization curve in some cases. However, many current spikes appeared in the all curves of the modified electrodes. The modified surface of passivated electrode was characterized by X-ray photoelectron and FTIR reflection spectroscopies and contact angle measurement. There were defects and clusters of associated water within the modified film and hence, Cl⁻ could permeate through the defects, leading to appearance of current spikes and occurrence of breakdown.     

XPS and EPMA studies on self-healing mechanism of a protective film composed of hydrated cerium(III) oxide and sodium phosphate on zinc

A thin, protective film was prepared on a zinc electrode by coverage with a hydrated Ce₂O₃ layer and 0.0552 mg/cm² of a Na₃PO₄·12H₂O deposit layer and by drying the layers at 90 °C for 23 h, as has been reported in the preceding paper. This film was highly self-healing at the scratched electrode in an aerated 0.5 M NaCl solution for many hours. The present investigation deals with elucidation on self-healing mechanism of this film by X-ray photoelectron spectroscopy and electron-probe microanalysis. The scratched surface was covered with deposits of Zn(OH)₂, ZnO and small amount of Zn₃(PO₄)₂. Both cathodic and anodic processes of zinc corrosion were markedly suppressed by coverage of the scratches with the deposits, resulting in the self-healing activity at the scratched electrode in 0.5 M NaCl.     

Influence on the anticorrosive properties of the use of erbium (III) trifluoromethanesulfonate as initiator in an epoxy powder clearcoat

New low curing temperature epoxy powder coatings cured cationically by the use of erbium (III) trifluoromethanesulfonate as initiator have been formulated. Their curing kinetics and anticorrosive properties have been studied and compared with a system commonly used in industry (o-tolylbiguanide/epoxy resin). Three different tests of anticorrosive properties (EIS, AC/DC/AC, and salt fog spray) have been used together with an adherence test, in order to establish the optimal system. Results show that a system employing 1 phr of erbium triflate presents good anticorrosive properties. The technique AC/DC/AC has shown its ability to evaluate properly, much faster, and in accordance to anticorrosive properties results’ of powder coatings obtained by other techniques.     

Influence of Ce surface treatments on corrosion behaviour of A3xx.x/SiCp composites in 3.5 wt.% NaCl

The influence of silicon carbide particles (SiCp) proportion and matrix composition on aluminium metal matrix composites A3xx.x/SiCp modified by cerium-based conversion or electrolysis coating was evaluated in 3.5 wt.% NaCl at 22 °C using potentiodynamic polarization and gravimetric measurements. Ce-treated surfaces presented better corrosion behaviour in chloride media than original composite surfaces without treatment. Both treatments preferentially covered the intermetallic compounds and SiCp. The electrolysis afforded a higher degree of protection than conversion treatment because the coating was more extensive. Coating microstructure and nature of corrosion products were analysed by scanning electron and atomic force microscopy (SEM, AFM) and low angle X-ray diffraction (XRD).     

The effect of post-treatment time and temperature on cerium-based conversion coatings on Al 2024-T3

Corrosion performance, morphology, and electrochemical characteristics of cerium-based conversion coatings on Al 2024-T3 were examined as a function of phosphate post-treatment time and temperature. Corrosion resistance improved after post-treatment in 2.5 wt.% NH₄H₂PO₄ for times up to 10 min or temperatures up to 85 °C. Electrochemical impedance spectroscopy and polarization testing correlated to neutral salt spray corrosion performance. Hydrated cerium oxide and peroxide species present in the as-deposited coatings were transformed to CePO₄·H₂O for post-treatments at longer times and/or higher temperatures. Based on these results, processes active during post-treatment are kinetically dependent and strongly influenced by the post-treatment time and temperature.     

Investigation of the corrosion for Mg-xGd-3Y-0.4Zr (x = 6, 8, 10, 12 wt%) alloys in a peak-aged condition

The corrosion behaviour of Mg-6Gd-3Y-0.4Zr (GW63K), Mg-8Gd-3Y-0.4Zr (GW83K), Mg-10Gd-3Y-0.4Zr (GW103K) and Mg-12Gd-3Y-0.4Zr (GW123K) were investigated in peak-aged condition using immersion and salt spraying tests and electrochemical measurements in 5% NaCl solution. The corrosion resistances of Mg-xGd-3Y-0.4Zr alloys were found to decrease with the increase of Gd content from 6% to 10% and then increase from 10% to 12%. The corrosion products of Mg-xGd-3Y-0.4Zr alloys were discovered to be composed of voluminous tiny erect flakes by FE-SEM, and the compactness of the corrosion films decreases with the increase of Gd content. The results of AES revealed that the corrosion film is enriched with Gd and Y. The potentiodynamic polarization curves showed that the overpotentials of cathodic hydrogen evolution on GW63K and GW83K are much higher than on GW103K and GW123K. The results of EIS are in good agreement with the morphologies of the corrosion products and the corrosion rates of the corrosion tests.