Cerium salt activated nanoparticles as fillers for silane films: Evaluation of the corrosion inhibition performance on galvanised steel substrates

The present work investigates the electrochemical behaviour of galvanised steel substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane (BTESPT) solutions modified with SiO₂ or CeO₂ nanoparticles activated with cerium ions. The electrochemical behaviour of the pre-treated substrates was evaluated via electrochemical impedance spectroscopy in order to assess the role of the nanoparticles in the silane film resistance and capacitance. The ability of the Ce-activated nanoparticles to mitigate corrosion activity at the microscale level in artificial induced defects was studied via scanning vibrating electrode technique (SVET). Complementary studies were performed using potentiodynamic polarisation. The results show that the presence of nanoparticles reinforces the barrier properties of the silane films and that a synergy seems to be created between the activated nanoparticles and the cerium ions, reducing the corrosion activity. The addition of CeO₂ nanoparticles was more effective than the addition of SiO₂ nanoparticles.     

The synergistic combination of bis-silane and CeO2·ZrO2 nanoparticles on the electrochemical behaviour of galvanised steel in NaCl solutions

Bis-1,2-[triethoxysilylpropyl]tetrasulfide silane films containing CeO₂·ZrO₂ nanoparticles were deposited by dip-coating on galvanised steel substrates. The morphological features of the coated substrates were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The anti-corrosion performance of the modified silane film applied on galvanised steel substrates was studied by electrochemical impedance spectroscopy (EIS). The ability of nanoparticles to mitigate localized corrosion activity at artificially induced defects was investigated via the scanning vibrating electrode technique (SVET) and by the scanning ion-selective electrode technique (SIET). The results showed that the addition of nanoparticles provides good corrosion protection of the galvanised steel substrates pre-treated with the modified silane solutions. The corrosion activity was reduced by more than one order of magnitude. Complementary d.c. experiments, using zinc electrodes exposed to NaCl solutions containing the nanoparticles were also performed in order to better understand the role of the nanoparticles. An ennoblement of the corrosion potential and polarisation of the anodic reactions could be detected.     

Surface evaluation and electrochemical behaviour of doped silane pre-treatments on galvanised steel substrates

The present work aims at evaluating the surface morphology and the corrosion resistance of galvanised steel substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane (BTESPT) solutions doped with cerium nitrate or zirconium nitrate. The silane pre-treatment leads to the formation of a silane coating in the metallic surface. The surface morphology of this coating was studied by atomic force microscopy (AFM) and scanning electron microscopy (SEM).     

A comparative study on the corrosion resistance of AA2024-T3 substrates pre-treated with different silane solutions: Composition of the films formed

This work reports a comparative study on the corrosion resistance of AA2024-T3 pre-treated with three different silane solutions. The silanes used for the pre-treatments of the AA2024-T3 panels were: 1,2-bis(triethoxysilyl)ethane (BTSE), bis-[triethoxysilylpropyl]tetrasulfide (BTESPT) and γ-mercaptopropyltrimethoxysilane (γ-MPS). The analytical characterisation of the silane films was performed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The corrosion performance of the pre-treated substrates was evaluated by electrochemical impedance spectroscopy (EIS). The results show that the pre-treatments based on silanes provide good corrosion protection of unpainted AA2024-T3. Painted substrates, previously pre-treated with the silane solutions also revealed improved corrosion resistance and good adhesion properties. Fatigue tests show that the silane pre-treatments do not affect the fatigue behaviour of the AA2024-T3. The work also discusses the formation of the protective silane films.     

The corrosion resistance of 316L stainless steel coated with a silane hybrid nanocomposite coating

The present work aims at evaluating the corrosion resistance of 316L stainless steel pre-treated with an organic–inorganic silane hybrid coating. The latter was prepared via a sol–gel process using 3-glycidoxypropyl-trimethoxysilane as a precursor and bisphenol A as a cross-linking agent. The corrosion resistance of the pre-treated substrates was evaluated by neutral salt spray tests, linear sweep voltammetry and electrochemical impedance spectroscopy techniques during immersion in a 3.5% NaCl solution. In addition, the effect of the drying method as an effective parameter on the microscopic features of the hybrid coatings was studied using Fourier transform infrared spectroscopy and scanning electron microscopy. Results show that the silane hybrid coatings provide a good coverage and an additional corrosion protection of the 316L substrate.     

The corrosion resistance of 316L stainless steel coated with a silane hybrid nanocomposite coating

The present work aims at evaluating the corrosion resistance of 316L stainless steel pre-treated with an organic–inorganic silane hybrid coating. The latter was prepared via a sol–gel process using 3-glycidoxypropyl-trimethoxysilane as a precursor and bisphenol A as a cross-linking agent. The corrosion resistance of the pre-treated substrates was evaluated by neutral salt spray tests, linear sweep voltammetry and electrochemical impedance spectroscopy techniques during immersion in a 3.5% NaCl solution. In addition, the effect of the drying method as an effective parameter on the microscopic features of the hybrid coatings was studied using Fourier transform infrared spectroscopy and scanning electron microscopy. Results show that the silane hybrid coatings provide a good coverage and an additional corrosion protection of the 316L substrate.     

Chemical composition and corrosion protection of silane films modified with CeO2 nanoparticles

The present work aims at understanding the role of CeO₂ nanoparticles (with and without activation in cerium(III) solutions) used as fillers for hybrid silane coatings applied on galvanized steel substrates.The work reports the improved corrosion protection performance of the modified silane films and discusses the chemistry of the cerium-activated nanoparticles, the mechanisms involved in the formation of the surface coatings and its corrosion inhibition ability.The anti-corrosion performance was investigated using electrochemical impedance spectroscopy (EIS), the scanning vibrating electrode technique (SVET) and d.c. potentiodynamic polarization. The chemical composition of silanised nanoparticles and the chemical changes of the silane solutions due to the presence of additives were studied using X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance spectroscopy (NMR), respectively.The NMR and XPS data revealed that the modified silane solutions and respective coatings have enhanced cross-linking and that silane-cerium bonds are likely to occur.Electrochemical impedance spectroscopy showed that the modified coatings have improved barrier properties and the SVET measurements highlight the corrosion inhibition effect of ceria nanoparticles activated with Ce(III) ions. Potentiodynamic polarization curves demonstrate an enhanced passive domain for zinc, in the presence of nanoparticles, in solutions simulating the cathodic environment.     

Analytical characterization of silane films modified with cerium activated nanoparticles and its relation with the corrosion protection of galvanised steel substrates

Galvanised steel substrates were pre-treated in bis-1,2-[triethoxysilyilpropyl]tetrasulphide silane solutions containing SiO₂ or CeO₂ nanoparticles activated with cerium ions. The surface composition was investigated by infrared spectroscopy. The film thickness was determined by scanning electron microscopy. The results showed that the barrier properties of silane films modified with nanoparticles depend upon the concentration of nanoparticles. The results also showed that the silane film thickness increases when the nanoparticles are activated with cerium ions. The anti-corrosion behaviour of the cerium activated nanoparticles was also investigated at the microscale level, in artificial induced defects, using the scanning vibrating electrode technique (SVET). The substrates treated with the silane coating modified with CeO₂ nanoparticles revealed improved corrosion behaviour comparatively to the coatings modified with SiO₂ nanoparticles. X-ray photoelectron spectroscopy and Auger electron spectroscopy experiments carried out on the defects after immersion in NaCl solutions revealed the presence of a surface film containing zinc corrosion products and cerium/ceria compounds.     

Tailoring of the practical adhesion between polyethylene and galvanised steel

The practical adhesion of maleic anhydride grafted polyethylene (MAH-PE) to galvanised steel was studied using 3-point flexure tests, before and after hydrothermal ageing. Before bonding, the electro-galvanised steel was treated with γ-aminopropyltriethoxysilane (γ-APS). The influence of the silane coating thickness and deposition pH on the practical adhesion of MAH-PE to steel was investigated. FT-IR spectroscopy and microscopy enabled to gain understanding of the interphase formation between the silane and the metal substrate. It was found that, at the natural pH of the γ-APS, Zn ions dissolved in the silane coating with subsequent formation of crystals. This interphase could be held responsible for the better durability of the bonds than for silane coatings applied at quasi-neutral pH, for which dissolution of Zn ions was not observed.     

Comparative EIS and XPS studies of the protective character of thin lacquer films containing CR or P salts formed on galvanised steel, galvanneal and galfan substrates

X-ray photoelectron spectroscopy (XPS) is used to analyse variations during exposure to humidity and UV radiation (UVCON test) in the chemical composition of the outer surface of organic coatings (lacquers) containing phosphating or chromating reagents applied on galvanised steel, galvanneal and galfan substrates. By means of electrochemical impedance spectroscopy (EIS) measurements the protective character of the coatings analysed by XPS is studied and an attempt is made to establish possible relationships between the chemical composition of the surface of the lacquered substrates after exposure to the UVCON test and their electrochemical characterisation in immersion in a 3% NaCl solution. In general, the formation of defects or the loss of adhesion of the lacquer film leads to a significant reduction in charge transfer resistance values and, at the same time, an increase in interfacial capacitance values. The special behaviour of the galfan/lacquer “with chromating reagents” system is associated with the presence of a thin insulating film of chromium and aluminium oxides at the base of the pores in the lacquer. Interfacial capacitance values tend to evolve in close correspondence with the content of some elements on the surface of the materials.     

Corrosion resistance of steel treated with different silane/paint systems

This article reports on a comparative study on the corrosion resistance of low-carbon steel substrates pretreated with different silane solutions and painted. The pure silanes used to pretreat the steel panels were 3-aminopropyltriethoxysilane (γ-APS), 3-glycidoxypropyltrimethoxysilane (γ-GPS), and bis(3-triethoxysilylpropyl)amine. The study also considered other silane solutions with ureido, amino, and epoxy organofunctional groups, and two bis-functional silanes: bis(γ-trimethoxysilylpropyl)amine (BAS) and 1,2-bis(triethoxysilyl)ethane (BTSE). A conventional phosphate-type pretreatment was also applied for reference purposes. The pretreated panels were then finished with an alkyd/polyester aminoplast base paint. As a branch test, an acrylic/urethane paint was also applied. Different tests were conducted to evaluate the anticorrosive ability of the different silane/paint systems: outdoor exposure in an atmosphere of moderate aggressivity; accelerated corrosion test (salt fog test); and electrochemical impedance spectroscopy (EIS). The results show that the steel pretreated with certain silanes, especially γ-APS, yields similar results to steel subjected to conventional phosphate pretreatment.     

Electrochemical study of modified bis-[triethoxysilylpropyl] tetrasulfide silane films applied on the AZ31 Mg alloy

This work investigates the protective behaviour of bis-[triethoxysilylpropyl] tetrasulfide silane pre-treatments on the AZ31 Mg alloy. The silane solution was modified by the addition of cerium nitrate or lanthanum nitrate in order to introduce corrosion inhibition properties in the silane film.The corrosion behaviour of the pre-treated AZ31 magnesium alloy was studied during immersion in 0.005 M NaCl solution, using electrochemical impedance spectroscopy and the scanning vibrating electrode technique (SVET). The electrochemical experiments showed that the presence of cerium ions or lanthanum ions improve the protective behaviour of the silane film. The SVET experiments evidenced that the presence cerium in the silane film led to an important reduction of the corrosion activity.The results demonstrate that either cerium ions or lanthanum ions can be used as additives to the silane solutions to improve the performance of the pre-treatments for the AZ31 magnesium alloy.     

Electrochemical impedance spectroscopy study of the effect of curing time on the early barrier properties of silane systems applied on steel substrates

Silane-based pretreatments have emerged as a valuable ecologically acceptable alternative to the chromating process. The application process of these pretreatments involves a series of fundamental variables whose optimisation is imperative in order to form a silane layer with good behaviour properties at the interface. One of the most important variables is the silane layer curing process, during which an interfacial network that delays the entry of aggressive species to the metallic surface is formed. The present work studies the effect of curing time on the barrier properties of two types of silane, 3-aminopropyltriethoxysilane and bis-3-triethoxysilylpropylamine, applied on steel substrates, with or without the subsequent application of an alkyd-base paint. Electrochemical impedance spectroscopy (EIS) shows how the silane layer curing process influences its barrier properties and thus its corrosion protection properties.     

EIS study of the effect of high levels of SO2 on the corrosion of polyester-coated galvanised steel at different relative humidities

The effect of SO₂ on the degradation of polyester-coated galvanised steel at different relative humidities was investigated using electrochemical impedance spectroscopy. Measurements were performed on specimens which had been tested in an accelerated gaseous corrosion test. For this purpose the samples were subjected to SO₂ gas for 16 days in atmospheric test cells with adjusted relative humidity (RH) from 60 to 100%. Subsequently, the impedance response of the coated material was measured and evaluated. The results indicated that the coating performance varies with RH. Thus, under condensing conditions, the organic coating and galvanised layer was totally removed, the impedance response being interpreted as the formation of an iron sulphide film on the surface. At lower RH, remarkably, the coating remained effectively intact with the coating resistance varying inversely with RH. This work is relevant to the application of such organic-coated products adjacent to combustion flues where high levels of SO₂ occur in association with high humidity.     

Adhesion enhancement of powder coatings on galvanised steel by addition of organo-modified silica particles

The addition of organo-modified silica particles (OSP) to organic monolayer coatings has been investigated as an alternative to the use of primers or surface pretreatments in galvanised steel substrates. A commercial additive consisting of trifunctional organosilane (alkyl-triethoxysilane) grafted on silica particles was directly incorporated at different concentrations (1, 2.5, 3.5 and 4.5 wt%) as an integral additive in a polyester powder coating. The OSP were characterised physicochemically by means of FTIR and TGA, and the coating formulated by DSC. The anticorrosive properties of the systems were evaluated by means of electrochemical impedance spectroscopy (EIS), showing improvements with all the formulations containing the OSP, especially in the coating with 2.5% OSP. In order to explain this behaviour, morphological (using SEM) and adhesion studies were done. The formation of agglomerates in the powder coatings was detected when the concentration was over 2.5%. There was an improvement in the adhesion of the coating to the substrate for all the samples containing the OSP but especially for that containing 2.5%. The impact resistance was increased too, especially in the formulations with 2.5% and 3.5%.     

Adhesion of Injection Molded PVC to Steel Substrates

Interactions occurring at the interface between injection-molded poly (vinyl chloride) (PVC) and steel substrates that were coated with thin films of aminosilanes were investigated by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The silane films were formed by adsorption of γ-aminopropyltriethoxysilane (γ-APS) or N-(2-aminoethyl-3-aminopropyl)trimethoxysilane (γ-AEAPS) from 2% aqueous solutions onto polished steel substrates. PVC was injection molded onto the silane-primed steel substrates and annealed at temperatures up to 170°C for times as long as 30 min. PVC was peeled off of the primed steel substrates using a 90° peel test and the substrate failure surfaces were thoroughly rinsed with tetrahydrofuran (THF) and distilled water to remove PVC and other compounds that were not strongly bonded to the substrates. The PVC failure surfaces were characterized by attenuated total reflection infrared spectroscopy (ATR) and PVC rinsed off of the substrate failure surfaces was characterized by transmission infrared spectroscopy. The resulting transmission and ATR spectra showed an absorption band near 1650 cm^-1 that was attributed to unsaturation in PVC. The substrate failure surfaces were characterized by XPS; curve-fitting of N(1s) and Cl(2p) high-resolution spectra showed the formation of amine hydrochloride complexes by protonation of amino groups of the silanes with HCl that was liberated from PVC during the onset of thermal dehydrochlorination. Furthermore, quaternization or nucleophilic substitution of labile pendent allylic chloride groups by amino groups on the silanes took place, thus grafting PVC onto the aminosilanes. It was determined that PVC that had β-chloroallyl groupings along its chains showed better adhesion with steel primed with aminosilanes and that generation of allylic chloride groups in PVC chains was the rate-limiting step in the reaction between PVC and aminosilane. Moreover, the effect of crosslinking of silane films on adhesion between PVC and aminosilane primed steel was investigated and it was concluded that interdiffusion of the polymer phase and the silane phase was also critical in obtaining good adhesion.     

Adhesion of Injection Molded PVC to Steel Substrates

Interactions occurring at the interface between injection-molded poly (vinyl chloride) (PVC) and steel substrates that were coated with thin films of aminosilanes were investigated by X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy (FTIR). The silane films were formed by adsorption of γ-aminopropyltriethoxysilane (γ-APS) or N-(2-aminoethyl-3-aminopropyl)trimethoxysilane (γ-AEAPS) from 2% aqueous solutions onto polished steel substrates. PVC was injection molded onto the silane-primed steel substrates and annealed at temperatures up to 170°C for times as long as 30 min. PVC was peeled off of the primed steel substrates using a 90° peel test and the substrate failure surfaces were thoroughly rinsed with tetrahydrofuran (THF) and distilled water to remove PVC and other compounds that were not strongly bonded to the substrates. The PVC failure surfaces were characterized by attenuated total reflection infrared spectroscopy (ATR) and PVC rinsed off of the substrate failure surfaces was characterized by transmission infrared spectroscopy. The resulting transmission and ATR spectra showed an absorption band near 1650 cm^?1 that was attributed to unsaturation in PVC. The substrate failure surfaces were characterized by XPS; curve-fitting of N(1s) and Cl(2p) high-resolution spectra showed the formation of amine hydrochloride complexes by protonation of amino groups of the silanes with HCl that was liberated from PVC during the onset of thermal dehydrochlorination. Furthermore, quaternization or nucleophilic substitution of labile pendent allylic chloride groups by amino groups on the silanes took place, thus grafting PVC onto the aminosilanes. It was determined that PVC that had β-chloroallyl groupings along its chains showed better adhesion with steel primed with aminosilanes and that generation of allylic chloride groups in PVC chains was the rate-limiting step in the reaction between PVC and aminosilane. Moreover, the effect of crosslinking of silane films on adhesion between PVC and aminosilane primed steel was investigated and it was concluded that interdiffusion of the polymer phase and the silane phase was also critical in obtaining good adhesion.     

In situ electrochemical studies of forming-induced defects of organic coatings on galvanised steel

A new electrochemical setup is presented for in situ measurements during uniaxial forming of thin film coated metal substrates. This approach allows the formability analysis of a zinc pigmented organic coating on a galvanised steel substrate. The aim is to monitor the formation of defects during the forming process. The setup comprises an electrochemical microcapillary cell in a three-electrode arrangement and a miniaturised linear stretching device. The development of forming-induced defects is monitored in situ by applying electrochemical impedance spectroscopy (EIS) and also microscopically analysed by means of field emission scanning electron microscopy (FE-SEM). The studies were supported by GOM^® grid measurements and finite element simulations of model sample forming degrees. The established technique enables the evaluation of the correlation between forming degree and degradation of the barrier properties of organic coatings.Finally a phosphating process on the unformed and formed specimen is electrochemically and microscopically analysed to correlate the respective defect size with its local reactivity. The results show that stretching-induced defects occur at the interface between spherical Zn particles and the epoxy binder matrix. The defect size increases with increasing strain values. The phosphating process leads to the nucleation of phosphate crystals especially in the forming-induced defects and thereby reduces the free zinc in the defect area. The kinetic of the phosphating is accelerated with increasing size of the defect.     

Effect of silane as surface modifier and coupling agent on rheological and protective performance of epoxy/nano-glassflake coating systems

Epoxy resin nanocomposites suspended with nano-glassflakes (NGFs) are studied in the present work. A bi-functional silane, i.e., epoxy propoxy propyl tri-methoxy silane, was used as coupling agent and NGFs’ surface modifier. Fourier transformed infrared spectroscopy and thermogravimetry techniques confirmed the successful surface treatment of the NGFs. Rheological studies of the polymer composites were carried out by measuring complex viscosity and storage and loss modulus values. The rheological results revealed that the presence of silane either as coupling agent or as surface modifier could decrease the nanocomposite viscosity. It is indicated that reduced filler–filler interaction resulted in better dispersion of NGFs. It can be due to soft layer formation on nano-glassflakes by silane groups which prevents the agglomeration of NGFs and subsequently improves their dispersion quality. Storage and loss modulus investigations showed that an inter-connected network structure in the solution might be formed in the presence of silane, probably due to the interaction between the NGFs and the polymer resin phase. Electrochemical impedance spectroscopies were carried out to study the protective performance of epoxy/nano-glassflakes coatings. Although the electrochemical impedance results revealed that the incorporation of silane as coupling agent and surface modifier in the epoxy/NGF coating systems applied on carbon steel substrates could improve the protective performance, the superiority of the epoxy coating formulated with 0.5 wt% of modified NGF was obviously visible during immersion period.     

Effect of deep drawing on the performance of coil-coatings assessed by electrochemical techniques

The effect of forming on the corrosion performance of coil-coated galvanised steel is studied. The study was made using the deep drawing geometry and the corrosion behaviour of formed and non-formed samples was compared, using electrochemical impedance spectroscopy (EIS). The responses of the various layers (zinc, phosphate and organic film) were observed separately. Formed samples suffer much faster degradation, in the form of blisters or of total delamination for phosphated and non-phosphated systems, respectively. The drop in the resistance values caused by forming in the phosphated samples revealed a transition from passive to active, whereas in the non-phosphated material the loss of resistance corresponds to an acceleration of the corrosion processes. The choice of the best equivalent circuits describing the impedance response is discussed.