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Abstract: 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. [Copyright &y& Elsevier]

Abstract: The present work investigates the corrosion behaviour of AZ31 Magnesium alloy (Mg AZ31) substrates pre-treated with a water soluble bis-aminosilane modified with multiwall carbon nanotubes (CNTs). Prior addition to the silane solution, the CNTs were submitted to a treatment in an aqueous solution containing cerium nitrate or lanthanum nitrate. The chemical composition of the treated CNTs and of the modified silane coatings was assessed by X-ray Photoelectron spectroscopy (XPS). The thickness and the morphology of the silane coatings were investigated by scanning electron microscopy (FEG/SEM). The pre-treatment of the Mg AZ31 was performed by dipping the metallic coupons in the silane solution modified with the CNTs. The electrochemical behaviour of the silane coated coupons was studied during immersion in 0.05 M NaCl solutions, using the scanning vibrating electrode technique. The electrochemical investigation showed that the activation of the CNTs with the rare-earth salt delays the corrosion activity of the Mg AZ31 substrates. The analytical and microscopic study suggested that the CNTs are homogeneously dispersed in the silane coating and that the CNTs act as support for inhibitor storage. [Copyright &y& Elsevier]

Abstract: Pre-treatments based on different cerium salts were applied to the AZ31 Mg alloy. The pre-treatments were performed by immersion in solutions of various Ce(III) salts: cerium chloride, cerium nitrate, cerium sulphate and cerium phosphate. The chemical composition of the treated surfaces was investigated by X-ray photoelectron spectroscopy and Auger electron spectroscopy, whereas the corrosion behaviour of the pre-treated AZ31 substrates was investigated in 0.005M NaCl solutions using potentiodynamic polarisation and open circuit potential monitoring. The surface film contained a mixture of Ce(IV) and Ce(III) salts. The film thickness depends upon the cerium salt used. The electrochemical results show that all the conversion pre-treatments reduced the corrosion activity of the AZ31 Mg alloy substrates in the presence of chloride ions. The corrosion protection efficiency is related with the anion present in the cerium salt. [Copyright &y& Elsevier]

Abstract: 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 0.005M 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. [Copyright &y& Elsevier]

Abstract: In this work solutions of bis-[triethoxysilylpropyl] tetrasulphide silane modified with cerium nitrate are used as pre-treatments for the AZ31 Mg alloy. The silane films formed after the pre-treatment of the metallic substrates were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The films were studied before and after immersion in corrosive NaCl solutions in order to study the ageing of the silane film and to understand the role of the dopant in this process. The results demonstrate that the addition of cerium ions modifies the morphology of the surface film and leads to important changes in the film thickness and composition. Ageing in NaCl solutions decreases the film thickness and affects the chemistry of the surface film. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: Two pre-treatments were studied for AZ31 Mg alloy substrates, consisting of immersion in cerium nitrate and lanthanum nitrate solutions for various immersion times. The surface composition was investigated by X-ray photoelectron spectroscopy and Auger electron spectroscopy that revealed the presence of a surface film containing the rare-earth cation, with a composition which was time dependent in the case of the cerium pre-treatment. The corrosion behaviour of the pre-treated substrates in 0.005M NaCl solutions was assessed by potentiodynamic polarization, open circuit potential monitoring and the scanning vibrating electrode technique (SVET). The electrochemical results show that the pre-treatments reduced the corrosion activity of the AZ31 Mg alloy substrates in the presence of chloride ions. The corrosion protection efficiency is dependent on the treatment time. [Copyright &y& Elsevier]

Abstract: Chemical formulations based on silane solutions are currently used for the pre-treatment of metallic substrates. These pre-treatments provide corrosion protection of the metallic substrates due to the good barrier properties of the silane films that form on the surface. The corrosion protection of silane-based pre-treatments can be improved by adding dopants to the silane solutions. The dopants must present corrosion inhibition properties and must keep or improve the barrier properties of the silane film without modification of surface functionality and bulk properties. The present work aims at assessing the corrosion behaviour of hot dip galvanised steel substrates pre-treated with bis-[triethoxysilylpropyl]tetrasulfide and bis-1,2[triethoxysilyl]ethane silane solutions doped with cerium nitrate or doped with lanthanum nitrate. The effect of the dopants on the barrier properties of the silane film and its corrosion-inhibition ability is studied via electrochemical impedance spectroscopy. Complementary studies using atomic force microscopy and surface analysis were also performed. The results show that the corrosion resistance of substrates pre-treated with the silane solutions doped with the rare-earth cations increases by more than one order of magnitude when compared with the non-doped pre-treatments. The results also show that the protective behaviour of the pre-treatment is dependent on the dopant and on the silane film. The work discusses the role of the dopant on the anti-corrosion properties of the pre-treated substrates. [Copyright &y& Elsevier]

Abstract: Nanostructured hybrid sol–gel coatings doped with cerium ions were investigated in the present work as pre-treatments for the AA2024-T3 alloy. The sol–gel films have been synthesized from tetraethylorthosilicate (TEOS) and 3-glycidoxypropyltrimethoxysilane (GPTMS) precursors. Additionally the hybrid sol was doped with zirconia nanoparticles prepared from hydrolyzed tetra-n-propoxyzirconium (TPOZ). Cerium nitrate, as corrosion inhibitor, was added into the hybrid matrix or into the oxide nanoparticles. The chemical composition and the structure of the hybrid sol–gel films were studied by XPS (X-ray photoelectron spectroscopy) and AFM (atomic force microscopy), respectively. The evolution of the corrosion protection properties of the sol–gel films was studied by EIS (electrochemical impedance spectroscopy), which can provide quantitative information on the role of the different pre-treatments. Different equivalent circuits, for different stages of the corrosion processes, were used in order to model the coating degradation. The models were supported by SEM (scanning electron microscopy) measurements. The results show that the sol–gel films containing zirconia nanoparticles present improved barrier properties. Doping the hybrid nanostructured sol–gel coatings with cerium nitrate leads to additional improvement of the corrosion protection. The zirconia particles present in the sol–gel matrix seem to act as nanoreservoirs providing a prolonged release of cerium ions. The nanostructured sol–gel films doped with cerium nitrate can be proposed as a potential candidate for substitution of the chromate pre-treatments for AA2024-T3. [Copyright &y& Elsevier]

Cr(VI)-based pre-treatments have been in use for long time on several materials, however, they are target of great criticism and in the near future they could be definitely banned. The actual alternatives to Cr(VI) show pros and cons when sets of key properties are considered such as: corrosion resistance, adhesion of organic coatings, fatigue resistance, reliability and quality control. However, some of the possible alternatives show high potential, if some improvements are carried out and the if mechanisms involved are more deeply understood.The present work focus on the use of rare earth (Ce, La) salts and bis-sulphur silane (BTESPT) as chromate substitutes for galvanised steel. These compounds when applied by immersion and subsequent curing originate films that improve corrosion resistance and paint adherence. The films were characterised by Auger and XPS spectroscopy. The corrosion resistance was assessed by electrochemical impedance spectroscopy and dc polarisation. Comparison with the chromate conversion pre-treatment is also carried out simultaneously with discussion of the possible mechanisms involved in the different processes. [Copyright &y& Elsevier]

Graphical abstract Highlights • Inhibitive effects of CeCl 3 /triethanolamine on AA2024/graphite couples were revealed. • SVET/SIET tests showed that inhibition mechanisms depend on the electrodes area ratio. • CeCl 3 inhibited localised corrosion of AA2024-T3 (trenching, IGC) coupled to graphite. • Triethanolamine formed complexes with Cu ions when Cu-rich particles were active. Abstract The inhibition mechanism of cerium chloride and triethanolamine on the galvanic corrosion of AA2024-T3/graphite in NaCl electrolyte was investigated by localised electrochemical techniques. Quasi-simultaneous measurements of ionic current densities and pH were performed by the Scanning Vibrating Electrode Technique (SVET) and Scanning Ion-Selective Electrode Technique (SIET). Surfaces were analysed by Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM-EDX) and X-Ray Photoelectron Spectroscopy (XPS). This work follows a recent publication (Coelho et al. 2018) and discusses the effect of inhibitors on two AA2024-T3/graphite galvanic couples, constructed with two different areas ratio, evidencing that this parameter significantly influences the corrosion and corrosion inhibition process. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the performance of bis-1, 2-(triethoxysilyl) ethane (BTSE) as a pre-treatment to protect the AA 2024-T3 against corrosion has been investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and the scanning vibrating electrode technique (SVET). The microstructural and morphological characterizations were carried out via scanning electron microscopy and atomic force microscopy and the chemical composition evaluated using contact angle measurements and X-ray photoelectron spectroscopy (XPS). The electrochemical results showed that the additives improved the anticorrosion properties of the coating. The chemical characterization indicated that additives contribute to an increased degree of surface coverage, as well as to a more complete reticulation. The SVET results evidenced the self-healing abilities of Ce ions. [Copyright &y& Elsevier]

Abstract: 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). The corrosion behaviour of the pre-treated substrates during immersion in 0.05M NaCl was assessed by the scanning vibrating electrode technique (SVET) and by electrochemical impedance spectroscopy (EIS). The results show that the presence of dopant improves the protective properties of the silane pre-treatment. Moreover, it was found that pre-treatments based on silanes doped with cerium nitrate are more resistant against corrosion development due to the corrosion inhibition properties of the cerium ions. [Copyright &y& Elsevier]

Abstract: The present work aims at evaluating the corrosion resistance of galvanised steel substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane doped with cerium nitrate or zirconium nitrate. The corrosion resistance of the pre-treated substrates was evaluated by electrochemical impedance spectroscopy, during immersion in NaCl solutions. The chemical composition of the surface was assessed by X-ray photoelectron spectroscopy and the surface morphology was studied by atomic force microscopy. The electrochemical results show that pre-treatments based on doped silane solutions provide good corrosion protection of the galvanised steel substrates. The work also aims at discussing the role of the dopants on the protective properties of the silane coatings formed on galvanised steel substrates. [Copyright &y& Elsevier]

Abstract: The present work aims at assessing the electrochemical behaviour of galvanised steel (GS) substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane (BTESPT) doped with cerium nitrate. Furthermore, the work aims at evaluating the self-healing properties of the dopant and discussing the possible mechanisms involved in this process. The study was performed by electrochemical impedance spectroscopy (EIS) and by the scanning vibrating electrode technique (SVET), during immersion in NaCl solutions. X-ray photoelectron spectroscopy (XPS) was also used to complement the electrochemical results. The results show that the protective behaviour of the pre-treatments based on Ce-doped silane solutions is dependent on the concentration of the dopant. The results also show that the dopant improves the anti-corrosion performance of the silane coatings formed on galvanised steel substrates. [Copyright &y& Elsevier]

• pH sensitive hydroxyapatite particles were successfully loaded with cerium as corrosion inhibitor. • Electrochemical impedance spectroscopy showed longer term corrosion protection for the coatings modified with the cerium loaded particles. • The synergistic corrosion inhibition effect, resulting from the presence of cerium loaded in pH sensitive particles and polymer healing process was observed by localized electrochemical techniques combined with video imaging. • A remarkable healing effect in the modified coating was demonstrated. • Alkaline medium seems to facilitate the polymer healing process in the modified coating. pH-sensitive hydroxyapatite particles were loaded with cerium ions (Ce-HAP) and incorporated into polyolefin coatings applied on carbon steel. The Ce-modified hydroxyapatite particles were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The protective performance of modified and reference polyolefin coatings applied on carbon steel was studied by electrochemical impedance spectroscopy (EIS), and the self-healing capability was evidenced by combining the scanning vibrating electrode technique (SVET) and pH micro-potentiometry with video-imaging, SEM and Raman. The modified coatings showed significantly improved long-term corrosion protection compared to reference coatings. The effect was attributed to the synergistic combination of the corrosion inhibition effect of cerium ions loaded in the HAP particles and polyolefin healing capability. [Display omitted] [ABSTRACT FROM AUTHOR]

• Efficient corrosion protection of WE43 conferred by Ce(DEHP) 3. • Improved performance of Ce(DEHP) 3 in intact and damaged coatings. • Self-healing of corrosion activity in the presence of Ce(DEHP) 3. • pH-dependant activation of Ce(DEHP) 3. Ce(DEHP) 3 (cerium tri(bis(2-ethylhexyl)phosphate)) is proposed as a self-healing corrosion inhibitor for WE43. The use of Ce(DEHP) 3 in a 3.90 ± 0.54 µm hybrid epoxy-silane coating led to an improvement of the coating barrier properties. The presence of the inhibitor increased the corrosion resistance, and Electrochemical Impedance Spectroscopy tests carried out in 0.5 M NaCl revealed low frequency impedance modulus (0.01 Hz) around 109 Ω∙cm2. The pH-dependant self-healing effect of Ce(DEHP) 3 was evidenced by localized electrochemical techniques, which revealed inhibition of corrosion propagation in artificial defects and decreased net cathodic current densities compared to an unmodified reference coating. Protective behaviour of Ce(DEHP) 3 was related to the combined action of the cerium and organophosphate moieties of this inhibitor, in addition to the protective role of yttrium species derived from the yttrium present in the WE43 magnesium alloy. Image, graphical abstract [ABSTRACT FROM AUTHOR]

One of the main applications of SVET in corrosion research is the study of the corrosion inhibition effectiveness and the evaluation of the self-healing effect of inhibitor-containing coatings. The tip of the platinum/iridium vibrating electrode is electroplated with black platinum, which creates a large electrode surface and confers high capacitance to the tip. When studying organic inhibitors in aqueous solutions with SVET, inhibitor adsorption may occur at the tip, causing its contamination and the initial calibration conditions of the system might not be valid. This may lead to an incorrect interpretation of the results. This work is intended to study the effect of different inhibitors (cerium nitrate, 8-hydroxyquinoline, potassium 2,5-dimercapto-1,3,4-thiadiazolate, benzotriazole and mercaptobenzothiazole), typically used for corrosion protection of aluminum alloys, on the Pt probe signal during SVET measurements. The results reveal the detrimental effect of some corrosion inhibitors on the sensitivity of the vibrating probe, an effect that imposes a regular assessment of the electrode state during measurements. The increase of the signal noise was related to a decrease of the probe capacitance, while the false current density signal was a result of the potential drift between vibrating and reference electrodes. [ABSTRACT FROM AUTHOR]

• Novel cerium tri(bis(2-ethylhexyl)phosphate) corrosion inhibition additive. • High compatibility with epoxy coatings. • Increased corrosion resistance of coated steel panels. • Corrosion healing in defects. • Synergistic cathodic and anodic corrosion inhibitors. In this work cerium tri(bis(2-ethylhexyl)phosphate) (Ce(DEHP) 3) particles were used as anti-corrosion pigments in epoxy coatings applied on steel coupons. The composition of the corrosion inhibitor was designed to introduce pH-stimulated corrosion healing in the coating. Electrochemical Impedance measurements demonstrated very high compatibility between the inhibitor and the coating, and effective and stable corrosion protection. Localized electrochemical measurements carried out using the Scanning Vibrating Electrode Technique and Localised Electrochemical Impedance revealed efficient corrosion inhibition of steel exposed in artificially damaged coatings. [ABSTRACT FROM AUTHOR]