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Corrosion of reinforcing steel in concrete is a worldwide problem. An important factor affecting such process is the concrete composition and, especially the presence of additives. In fact, the kinetics of water absorption and water evaporation are affected both by the environment conditions and by the nature of the additives. This is important for powdered additives, which can partially occlude the porous structure, changing porosity and permeability of concrete too. Reinforced concrete samples were modified by adding spent fluid cracking catalyst powders (SFCC) and an environment friendly commercial inhibitor. The samples were submitted to consecutive cycles of 15 day of immersion (in saturated NaCl electrolyte) followed by 15 day of drying. Samples were regularly monitored by electrochemical Impedance Spectroscopy (EIS). The results revealed that the additives interfere with the water adsorption/evaporation kinetics in concrete, a process resulting from the joint effect of diffusion and capillary processes. These interferences occur due to three combined mechanisms: two related to pore blocking and pozzolanic activity, which are the result of structural changes in concrete and affect the diffusion processes/mechanism; the third one is the capillary mechanism, which is strongly dependent from the chemical nature of the additives, but can also be influenced by structure modifications. This mechanism can increase, reduce or eliminate the capillary processes. [ABSTRACT FROM AUTHOR]

A silane-based coating modified with titanium IV iso-propoxide was developed to slow down the corrosion rate of AZ31 and ZE41 magnesium alloys intended as biodegradable implants materials. Electrochemical impedance spectroscopy (EIS) was used to monitor the corrosion evolution over 7 weeks in simulated body fluid at 37 °C. A homogeneous crack-free 3 μm-thick coating provided corrosion protection for 2 and 3 weeks to the ZE41 and the AZ31, respectively. The corrosion mechanisms and the nature of the corrosion products of the coated systems are discussed and correlated to the coating morphology before and after the immersion tests. [ABSTRACT FROM AUTHOR]

Coatings tailored to corrosion protection of metallic substrates are of the utmost relevance to ensure reliability and long-term performance of coated parts as well as the product value of the coated materials. Presently, there is a strong emphasis on the development of advanced functional and smart coatings for corrosion protection in different technological applications. On the one hand, there is a need for more advanced coatings for conventional applications and, on the other hand, there is a need to answer the requirements of several new Hi-Tech applications. Thus, this review highlights the most recent trends in the field of functional coatings for corrosion protection of metallic materials in a wide range of technical applications. Emphasis is given to self-healing coatings and smart coatings combining multiple functionalities for increased corrosion protection. Recent developments on the introduction of functionalities based on encapsulation of corrosion inhibitors, anti-fouling agents and superhydrophobic additives or modification of organic and hybrid matrices via chemical manipulation are reviewed. Special attention is dedicated to functional coatings for corrosion protection of bioresorbable metallic implants that have an important impact in biomedical applications. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the elaboration of 3-glycidoxypropyltrimethoxysilane (3-GPTMS) films onto AA2024-T3 aluminum alloy for corrosion protection. The dependence of sol–gel morphology on both precipitation under cathodic polarization and nitrate incorporation was investigated via scanning electron microscopy (SEM). Once added into silanization solution, sodium nitrate promoted the reaction of silane condensation and enhanced the film compactness. Electrochemical impedance spectroscopy results (EIS) indicated that doping silane film with NaNO3 ameliorated its barrier property and protectiveness. Silane films applied onto AA2024-T3 surface by using potentiostatic method, exhibited obviously higher corrosion resistance than those obtained by conventional “dip-coating” method. The resistance of coating is accentuated when not very negative potential was applied. [Copyright &y& Elsevier]

Abstract: Nowadays, there is a strong demand on the search of thinner, but more effective organic coatings for corrosion protection of metallic substrates, like galvanised steel, used in the automotive industry. In order to guarantee effective corrosion protection of these coatings, and because chromate-based pigments cannot be used, one of the most attractive strategies consists on the modification of the organic matrix with nano-additives filled with corrosion inhibitors, which can be released to the active sites. In this work, two different nano-additives are explored as potential self-healing materials for the development of active protective coatings. These additives are layered double hydroxides and cerium molybdate hollow nanospheres loaded with mercaptobenzothiazole, as a corrosion inhibitor. These additives were added to epoxy primers, individually, or combining the two nanoadditives in the same layer. The electrochemical behaviour and the potential of self-healing ability were studied by electrochemical impedance spectroscopy, scanning vibrating electrode technique and scanning ion-selective electrode technique. The results reveal that both types of nanocontainers can provide effective corrosion inhibition on artificial induced defects, at different stages of the degradation process. Moreover, the results also show that there is a synergistic effect concerning corrosion inhibition and self-healing potential when a mixture of the two nanocontainers is used. The mechanism of self healing is presented and discussed in terms of effect of organic inhibitor and role of the nanocontainers, including effect of cerium ions released from cerium molibdate nanoparticles. [Copyright &y& Elsevier]

Abstract: The effect of incorporated Mo and Nb on the electronic properties of oxide films formed on AISI 304L was investigated by Mott–Schottky analysis. The films show a bi-layer structure and behave as n-type and p-type semiconductors at potentials above and below the flat band potential. The inner p-type layer is Cr-enriched, while the outer n-type layer shows a slight increase in Fe-content close to the outer surface, where NbO3+-oxalate or MoO4 2− incorporation occurred. The observed enhancement of pitting corrosion resistance of anodized steels is most probably related to compositional changes and thickness increase of the film after the surface treatments. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

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: 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. [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: This work aims to develop and study new anticorrosion films for AZ31B magnesium alloy based on the sol–gel coating approach. Hybrid organic–inorganic sols were synthesized by copolymerization of epoxy-siloxane and titanium or zirconium alkoxides. Tris(trimethylsilyl) phosphate was also used as additive to confer additional corrosion protection to magnesium-based alloy. A sol–gel coating, about 5-μm thick, shows good adhesion to the metal substrate and prevents corrosion attack in 0.005M NaCl solution for 2 weeks. The sol–gel coating system doped with tris(trimethylsilyl)-phosphate revealed improved corrosion protection of the magnesium alloy due to formation of hydrolytically stable Mg–O–P chemical bonds. The structure and the thickness of the sol–gel film were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The corrosion behaviour of AZ31B substrates pre-treated with the sol–gel derived hybrid coatings was tested by electrochemical impedance spectroscopy (EIS). The chemical composition of the silylphosphate-containing sol–gel film at different depths was investigated by X-ray photoelectron spectroscopy (XPS) with depth profiling. [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: In situ monitoring of the chloride content is one of the most important procedures in preventing and controlling chloride-induced corrosion in reinforced concrete structures. Thus, the development of chloride sensors is of paramount importance for the continuous monitoring of concrete structures. The sensors must present long lifetime and reliability and operate in a wide range of chloride concentrations. The present work aims at developing and testing a sensor based on Ag/AgCl electrodes for in situ monitoring of chloride ions in reinforced concrete structures. Although these electrodes are widely used in analytical experiments due to their sensitivity to the chloride ion, little is known on their behaviour during exposure to alkaline environments, such as those existing in concrete. The multiprobe sensor presented in this work was tested in mortar and concrete specimens, revealing good stability. The results reveal that the Ag/AgCl sensor presents good sensitivity in a wide range of chloride concentrations. [Copyright &y& Elsevier]

Abstract: The present work aims at understanding the corrosion behaviour of hot dip galvanized steel pretreated with either bis-1,2-[triethoxysilyl]ethane silane (BTSE) or bis-[triethoxysilylpropyl] tetrasulfide (BTESPT) modified with microparticles of SiO2. The corrosion resistance was evaluated by electrochemical impedance spectroscopy, potentiodynamic polarization and by the scanning vibrational electrode technique (SVET) during immersion in dilute NaCl solutions. The films formed on the galvanized steel substrate were characterized by X-ray photoelectron spectroscopy, Auger electron spectroscopy and atomic force microscopy. The results show that the pretreatments based on silane films modified with silica particles provide corrosion protection for hot dip galvanized steel during immersion in NaCl-containing solutions. [Copyright &y& Elsevier]

The present work aims at correlating the evolution of the analytical composition of bis-1,2-(triethoxysilyl)ethane films formed on hot dip galvanised steel substrate during immersion in NaCl solution with the corrosion performance of the pre-treated substrates. The electrochemical tests were carried out by electrochemical impedance spectroscopy and the analytical characterisation was performed by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and infrared spectroscopy (FT-IR). The electrochemical results show that the functional silane provides temporary corrosion protection for hot dip galvanised steel during immersion in NaCl-containing solutions. The analytical results show that the chemical composition of the silane film changes during immersion in the aggressive solution. During the first days of immersion these changes improve the corrosion resistance of the pre-treated substrate. [Copyright &y& Elsevier]

Laboratory investigations were performed in order to assess the effectiveness and the inhibition mechanism of an amino alcohol-based inhibitor currently used as admixture to prevent corrosion of steel in concrete. The investigation was performed in the presence of chloride ions, using solutions simulating the concrete interstitial solution. Electrochemical measurements allowed to conclude that, an inhibitor film is formed on the surface hindering the anodic activity. Furthermore, the analytical investigation through the use of X-ray photoelectron spectroscopy (XPS) shows that the inhibitor film is able to complex with the chloride ion. [Copyright &y& Elsevier]

One of the most important causes for reinforcing steel corrosion is the presence of chloride ions. They cause localised breakdown of the passive film that initially forms on steel as a result of the alkaline nature of the pore solution in concrete. The harmful chloride ions can be originated from the use of contaminated mix constituents or from the surrounding environment. The determination of a critical level, above which serious problems can occur, has been one of the main goals of investigation. Unfortunately, it is difficult to establish such a value since the chloride level is influenced by several factors. Thus, after concrete contamination, it is of fundamental importance to follow the activity of chlorides and the state of the reinforcing rebars. In this respect, the use of electrochemical techniques such as polarisation resistance, electrochemical impedance, galvanostatic pulse and potential measurements have shown to be powerful tools. Nevertheless, the interpretation of the results becomes sometimes a difficult task. A large number of authors have dedicated several studies to the interpretation of such measurements and a highly dispersed number of interpretations can be found in literature. The aim of this paper is to present an overview on the state-of-the-art of the most important aspects of the corrosion process initiated by chlorides, its development and monitoring techniques. [Copyright &y& Elsevier]

The corrosion performance and the composition of galvanised steel treated by immersion in nitrate solutions of rare-earth metals (cerium, yttrium and lanthanum) were evaluated by electrochemical techniques and surface analysis. The surface film consists of a mixture of rare-earth oxides/hydroxides, which hinders the corrosion reactions of the substrate by reducing the rate of both the cathodic and the anodic reactions. Although all the films provide corrosion protection, the effect seems to be more pronounced for lanthanum. The behaviour of the films formed on the surface is dependent on the rare-earth cation and on the treatment time. [Copyright &y& Elsevier]

Addition of fly ash has beneficial effects on some mechanical properties of concrete, as well as on the corrosion process induced by the chloride ion. The aim of this study was to investigate the effect of fly ash addition on the corrosion process occurring in reinforced concrete exposed simultaneously to carbon dioxide and chloride. The corrosion process of steel rebars embedded in mortar with 15% and 30% of fly ash was tested under carbon dioxide and sodium chloride contamination. Monitoring of open circuit potential and electrochemical impedance spectroscopy (EIS) were used to follow the corrosion process. Results have shown that under accelerated carbonation fly ash mortar shows higher corrosion rates. The chloride content in mortar exposed to accelerated carbonation increases with the amount of fly ash. However, under natural carbonation it decreases with the addition of fly ash. [Copyright &y& Elsevier]

• Materials conservation utilizes alkoxysilanes with VOC's. • Sonocatalysis creates eco-friendlier, water-based inorganic sonogels. • Water reduces gelling time and affects gel rate deposition in miscible mixtures. • Sonogels are capable to enhance stone hardness and depth resistance of stone. • Potential for inorganic-organic sonogels with dual-roles (protection and consolidation). Products designed to form continuous inorganic networks from alkoxysilanes frequently include organic solvents because of the necessity to turning the precursors miscible with water and because dilution is required for certain applications. Thus, there is a demand for efficient mixtures employing eco-design strategies. This study explores the feasibility of sonocatalysis to prepare homogeneous mixtures with water to initiate sol-gel reactions and as the dilution agent. The approach allowed to design and prepare viable mixtures with unique tetraethoxysilane(TEOS):H2O ratios (1:4 to 1:32). By managing the ultrasonic irradiation parameters, it was possible to formulate mixtures with high degree of hydrolysis, appropriate condensation ratios, and capable to create sonogel materials containing other desired features for stone conservation. The water content manages the gelling times and gel deposition rates through a dilution effect, which might be useful to minimize undesirable side effects of conservation treatments, such as excessive pore occlusion. For instance, a TEOS:H2O ratio of 1:32 results in a very low gel deposition rate. Furthermore, the applicability and efficacy of successful mixtures was preliminary assessed, and it was demonstrated that the resulting inorganic networks, primarily composed of Si O Si bonds, can enhance the hardness and surface resistance of soft stones. This potential strengthening effect improves gradually with increasing TEOS:H2O ratios. The mixtures deserve further studies aimed at enhancing understanding of their consolidation characteristics. The advances achieved also opens the door for producing innovative dual-role hybrid inorganic-organic sonogels that can be used for materials protection and surface consolidation. [ABSTRACT FROM AUTHOR]

The deposition of γ-glycidoxypropyltrimethoxysilane (γ-GPTMS) film onto AA2024-T3 aluminum alloy surface was performed via two techniques: dip-coating and electrodeposition. The electrodeposited coatings were performed under potentiostatic control at different cathodic potentials (namely −0.80, −1.30 and −1.70 V vs.SCE). γ-GPTMS films were characterized by physical, microscopic and spectroscopic techniques: Pull-off test, Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Fourier Transform Infrared Attenuated Total Reflectance (FTIR-ATR) and X-Ray Photoelectron Spectroscopy (XPS). The electrochemical behaviors of coatings were assessed in chloride solution by means of Electrochemical Impedance Spectroscopy (EIS). The synthesis conditions have shown a key role in the morphology and the anticorrosion performance of γ-GPTMS coating. Results revealed the uneven nature of the dip-coated film that resulted in a non-satisfactory anticorrosion performance. For the electrodeposited coatings, the protectiveness was dictated by the imposed potential value. The film electrogenerated at −0.80 V vs.SCE possessed the best protective performance. Moreover, it was found to be uniform, compact and proved superior adhesion strength when compared to the dip-coated film. [ABSTRACT FROM AUTHOR]

This work aims to investigate the corrosion resistance of AZ31 magnesium alloy protected by hybrid films based on tetraethylorthosilane (TEOS) and (3-glycidoxypropyl)trimethoxysilane (GPTMS) with the addition of different amounts of SiO 2 nanoparticles. The electrochemical techniques used to evaluate the corrosion resistance in 0.1 mol l l− 1 NaCl electrolyte were open circuit potential (EOC) measurements and electrochemical impedance spectroscopy (EIS), which diagrams were fitted using equivalent electrical circuits (EEC). Surface and cross-section analyses of the bare and coated samples were performed by means of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) before and after electrochemical studies. The results showed that the coatings protected the Mg alloy against corrosion, and that the addition of the nanoparticles improves the corrosion resistance. The morphological characterization showed, for the coated systems, the presence of corrosion products adhered to the metal surface, a process that seems to be hindered in the presence of the SiO 2 nanoparticles. The results demonstrate that an optimum amount of nanoparticles must be added to the coating in order to optimize the anticorrosion protection and that only early stages protection can be achieved. [ABSTRACT FROM AUTHOR]

[Display omitted] • Direct microwave plasma deposition of self-standing VCNs on nickel foils, analyzed by SEM, Raman and XPS. • Optimal plasma growth parameters P=800 W, Q CH4 = 10 sccm, U= − 400 V, t = 60 min. • N-doping (2.3 at% N) of VCNs using an Ar-N 2 plasma treatment. • VCNs integrated as electrodes in high-frequency AC filtering capacitors. • Overall capacitance 481 and 477 µF at 100 Hz, for doped and pure VCN. Self-standing vertically oriented carbon nanostructures (VCNs) were synthesized using a large-scale microwave plasma under low-pressure conditions, employing methane as a carbon precursor. The influence of plasma operational and substrate conditions on nanostructure growth and morphology were systematically studied. Furthermore, post-synthesis N-doping of VCNs with nitrogen content of 2.4 at% N was achieved using an Ar-N 2 microwave plasma. Plasma-enabled direct deposition of VCNs, both doped and un-doped, onto nickel foils has been accomplished. The assessment of the developed nanostructures as electrodes in high-frequency AC filtering capacitors, has demonstrated an overall capacitance of approximately 480 µF at 100 Hz, with a cut-off frequency of 4 kHz for a phase angle of −45°. The excellent electrochemical performance can be attributed to the appropriate structural and morphological properties peculiar for the directly deposited on nickel foil VCNs providing binder-free electrode fabrication, thus enhancing the electrode's conductivity and charge transfer kinetics. This plasma-enabled approach for electrode design on a large scale, coupled with excellent filtering performance, paves the way for many applications in high-frequency scenarios, offering an environmentally friendly alternative to conventional electrolytic capacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ball milling is a cost-effective, one-step, and solvent-free approach to preparing electrode materials and shows advantages such as no use of heat treatment, harmful solvents, long processes, and high energy consumption required by the common methods such as solvothermal, sol–gel, hydrothermal, and precipitation. • Functional materials applied in supercapacitors can be produced via planetary ball milling. • Transition metal carbonates and nanocomposite were mechanochemically synthesized without additional process. • MnCO 3 and CoCO 3 resulted in excellent performance in 1 M KOH electrolyte. • High storage, remarkable rate capability, and outstanding capacitance retention were achieved. Transition metals are known for their enormous potential as electrode materials for supercapacitor applications, however anhydrous carbonate minerals, namely Mn-carbonate, and Co-carbonate, are less explored and exhibit competitive energy storage performance compared to oxide and hydroxide forms. For the first time, MnCO 3 (Rhodochrosite), CoCO 3 (Spherocobaltite) and MnCo mixture (Mn 1-x Co x CO 3) were synthesized via mechanochemistry by a one-pot approach and used to prepare pseudocapacitive electrode materials for electrochemical energy storage. In this work, these materials were tested in alkaline electrolyte, and the morphological and structural features of the materials were examined using SEM (Scanning Electron Microscope), Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). The surface composition was studied by X-ray photoelectron spectroscopy (XPS). After milling, the microstructures showed an increase in dislocations and microstrains in their crystal lattices which influenced the electrochemical performance. The crystallinity of the carbonate materials was also affected by grinding. In 1 M KOH electrolyte, milled MnCO 3 evidenced the highest specific capacitance (354.3 F/g at 1.0 A/g), while milled CoCO 3 , revealed impressive capacitance retention of 94.8 % after 20000 continuous charge–discharge cycles at 10 A/g. Interestingly, the composite (Mn-Co)CO 3 evidenced superior rate capability (58.8 %) and enhanced capacitance retention under cycling compared to the individual cobalt and manganese carbonates. The results evidence the excellent electrochemical behavior of Mn and Co carbonates prepared by a simple, low-cost, and green route and prove their potential as electroactive electrode materials for electrochemical energy storage applications, particularly pseudocapacitors. [ABSTRACT FROM AUTHOR]

Highly porous iron‑nickel foams, including the first-ever reported pure iron foam, were prepared by the dynamic hydrogen bubble template electrodeposition method and studied regarding their electrochemical stability and mechanical properties. Changes on the morphology, microstructure, and electrochemical resistance of the foams were investigated as a function of the Fe:Ni ratio by scanning electron microscopy (SEM), d.c. polarization and electrochemical impedance spectroscopy (EIS). Tensile and bending tests were carried out to evaluate the mechanical behavior of the prepared foams. Both crystalline structure and morphology are affected by the increase of Ni content, evolving from a highly porous foam with a body-centered cubic (bcc) structure to a denser material with open pores and face-centered cubic (fcc) structure. Polarization curves reveal an ennoblement of the corrosion potential as the nickel content increases. The impedance response revealed a dependence on the foam porosity. An increased number of pores was found more detrimental to the mechanical properties of the foams, as fractures seem to propagate, preferentially by cracks due to connecting pores. As result, foams with higher Ni contents displayed better mechanical performance for both tensile and bending assays. Results show that this innovative and powerfull technique enables to design iron foams with the adequate properties required for industrial applications. [Display omitted] • Fe and FeNi nanofoams are prepared by Dynamic Hydrogen Bubble Template Electrodeposition. • Pure iron foam is obtained for the first time. • Foams morphology change for higher Ni contents. • Faradaic resistance depends on both %Fe and the pore availability. • Improved mechanical resistance is observed for the less porous foams. [ABSTRACT FROM AUTHOR]

Electrodeposited Co and Mn spinel phase oxides for application as coatings for metallic interconnectors in Solid Oxide Fuel Cells were prepared. The study aims at understanding the initial stages of transformation of the metallic layers into the spinel phase. Co and Mn metallic layers were sequentially deposited over AISI 430 stainless steel substrate from acidic sulfate solutions and annealed in oxidizing and inert atmospheres between 600 °C and 800 °C. The coatings obtained showed a thickness above 20 μm. After 1 h of isothermal aging the coatings were composed of layers of un-reacted metallic elements and Mn based oxides. The spinel phase was studied by XRD and revealed Mn based tetragonal structure Mn3O4 with Co in solid solution and a non-determined Co/Mn ratio. According to EDS measurements this ratio should vary with depth. Full conversion was not obtained at these time frames with the presence other Mn oxides (MnO and Mn2O3). In inert atmosphere, the allotropic Mn transformation from α to β phase was detected. No outward diffusion of Cr was detected, due to the short exposure times. [ABSTRACT FROM AUTHOR]

Corrosion remains a critical issue for steel structures, leading to costly repairs and potential failures in industrial sectors. This study presents the development and characterization of polyolefin coatings for enhanced corrosion protection. Initially, the porous TiO 2 nanoparticles were synthesized using the sol-gel method, followed by their modification through the encapsulation of sodium benzoate (SB) as a corrosion inhibitor. Modified Polyolefin coatings were prepared by incorporating modified nanoparticles (TiO 2 loaded with sodium benzoate) into the polyolefin matrix, and an unmodified/blank polyolefin coating was prepared without any additive in the polyolefin matrix. The loading of the inhibitor into porous TiO 2 was 10 % analyzed using thermogravimetric analysis. Furthermore, the electrochemical analysis revealed significant improvements in the corrosion resistance and barrier properties of the modified coatings compared to the unmodified blank coatings. Specifically, after 7 days in a corrosive environment, the blank coating pore resistance dropped from 1 × 1010 Ω·cm2 to 5 × 108 Ω·cm2, while the modified coating maintained a high pore resistance of 5 × 1011 Ω·cm2. A localized corrosion study for scratched blank polyolefin coatings showed growing corrosion activity from 5 h of immersion, while modified coatings ceased the detectable activity before 4 h of immersion, which evidenced the improved corrosion inhibition efficiency of the modified coating. This stability in corrosive environments was attributed to the successful loading of modified nanoparticles (TiO 2 /SB), where SB served as an active agent by forming a protective film on the steel substrate. Which inhibits the corrosion processes along with Ti-based compounds and prevents corrosion propagation under the damaged coating. The enhanced hydrophobic nature of 99° and electrochemical properties support the suitability of these coatings for corrosion protection of steel in various industries. [Display omitted] • Developing anticorrosive pigment by synthesis of porous TiO 2 and encapsulation with sodium benzoate (SB). • Formulation of modified polyolefin coatings by incorporating TiO 2 /SB, showing a higher impedance value of 100 GΩ. • Incorporation of TiO 2 /SB nanoparticles filled the pore effectively and enhanced the barrier property of the coating. • Localized corrosion revealed blank coatings showed growing corrosion activity, while modified coatings ceased it. • SB forms a protective film on the steel substrate, inhibiting corrosion and preventing propagation under damaged coating. [ABSTRACT FROM AUTHOR]

This research aims to develop a multifunctional, water-based product for protecting and consolidating stone materials. A new synthesis strategy using water-diluted silane formulations, composed of TEOS and an alkyl monomeric silane (ETES) or a polymeric siloxane (PDMS), homogenized by ultrasonic irradiation was followed to produce hybrid networks and overcome the limitations of current hydrophobic consolidants. These formulations gave rise to low dry residues and hydrophobic surfaces on various stones, including on low and high porosity stone varieties. Despite some formulations originated cracked films, optimal concentrations of ETES and PDMS showed high protection levels against capillary water absorption with minimal impacts on the color and water vapor permeability of the stones. Besides demonstrating the initial efficacy of these new hybrid materials in modifying the inherent hydrophilic and water-absorbing properties of stones, this work further confirmed their ability to penetrate within the stone pores and their initial efficacy in consolidating porous stones. Thus, new water-based multifunctional hybrid materials capable of consolidating and protecting various types of stones from water-related damage have been developed. These novel materials align with both technical and environmental requirements. • New hybrid sonogels were prepared successfully with water-based formulations of silanes. • Different concentrations of ETES and PDMS turn various stones hydrophobic. • Optimal concentrations also reduce drastically the water absorption of very porous stones. • Formulations preserve the original water vapor permeability while offering protection. • A multifunctional role was confirmed, as they also improve the cohesion of porous stones. [ABSTRACT FROM AUTHOR]

This study aims at preparing novel composite materials for the consolidation of damaged stone in built heritage from tetraethoxysilane(TEOS)based sols with nano-sized hydroxyapatite (HAp) with high crystallinity and high aspect ratio. Synthesis of nanostructures of hydroxyapatite (HAp) was carried out using hydrothermal precipitation methods at different reaction temperatures and periods. Rod-like HAp nanostructures with a diameter around 5–20 nm and length up to 125 nm were obtained. The samples of nano-HAp were characterised using powder X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and μ-Raman spectroscopy. The derived nanostructures were used to modify TEOS-based formulations after tuning their colloidal stability period to the needs of their application as stone consolidants. The chemical structure (μ -Raman), viscosity, macroscopic and microscopic morphologies – Scanning Electron Microscopy (SEM) and EDS – and Shore Hardness of the composite materials were studied. The potential of the composite materials containing nano-HAp-rods as stone consolidants revealed to be superior to the potential of reference materials. [ABSTRACT FROM AUTHOR]

• The novel consolidants analyzed can consolidate aged carbonate stones. • Brushing allow deep penetration of low viscosity consolidants. • Poor consolidation effect in aged marble and over-consolidation in aged limestone. • Consolidation effect can be optimized by managing application procedures. • Aging conditions influence the consolidation outcome in marble and limestone differently. This work aims at investigating and comparing the ability of novel products to act as consolidants for carbonate stones and how the lithotype and testing conditions influence the perception of their initial efficacy. Novel consolidants based in alkoxysilanes and ammonium phosphate can penetrate deeply, and have initial efficacy on porous limestone in a pre-collapse condition and on marble in granular disintegration, when applied by brushing until their apparent saturation is reached. Nevertheless, unsatisfactory consolidation outcomes can be obtained in both lithotypes due to opposite reasons, namely, insufficient strengthening ability in fissured media (marble) and over-consolidation in pore-shape stone (soft limestone). Simple strategies dealing with the treatment procedures to optimize the application processes revealed useful to "scale-up" or "scale-down" the treatments in order to better met the requirements of each lithotype. The assessment of the potential initial efficacy of consolidants requires broader approaches, since its perception depends on diverse testing parameters, such as, the pore-shape and the lithotype aging conditions. [ABSTRACT FROM AUTHOR]

Abstract: This work reports the temperature dependence of the corrosion potential of passive stainless steel rebars embedded in concrete or in alkaline media. The corrosion potential mirrored the temperature variations and the coefficient (mV/°C) increased as the average temperature range increased. These variations were observed in the long time-scale domain (several hours) and were interpreted based on temperature-induced changes in the chemistry of the passive layer. This behaviour and its interpretation have not been reported before and are of great importance from the point of view of understanding the electrochemical behaviour of stainless steel rebars and the inspection and durability of reinforced concrete structures. [Copyright &y& Elsevier]

Abstract: Corrosion protection of aluminium alloys often relies on the application of a coating on the metallic surface. The coating normally combines a barrier effect that restricts the ingress of corrosive species, with an inhibitive role induced by corrosion inhibitor pigments added to the coating formulation. However, the direct addition of corrosion inhibitors to the coating can cause some detrimental interactions between components, as well as formation of preferential electrolyte pathways, compromising the barrier properties. Moreover, electrolyte uptake and ageing may result in leaching of those corrosion inhibitors. In order to extend the corrosion inhibition ability of organic coatings one possible solution is to store the inhibitors inside nano or microreservoirs compatible with the coating matrix and able to sense the local changes induced by the corrosion process. This strategy has led to the development of a new generation of “smart” coatings for anti-corrosion purposes. The aim of this work is to study the anti-corrosion properties of water-based epoxy coatings loaded with pH sensitive particles, acting as feedback active containers for corrosion inhibitors and applied on the aluminium alloy AA2024-T3. For this purpose micron size calcium carbonate beads were modified with different corrosion inhibitors: cerium nitrate, salicylaldoxime and 2,5-dimercapto-1,3,4-thiadiazolate. These particles act as pH sensitive reservoirs because they dissolve at acidic pH, releasing the corrosion inhibitor, which then suppresses the corrosion activity of the bare metal. Electrochemical impedance spectroscopy (EIS) was used to estimate the electrical parameters assigned to the barrier properties of the coating and corrosion inhibition ability in the presence of inhibitor loaded calcium carbonate beads. The most relevant corrosion inhibition effects were observed from CaCO3 microbeads modified with cerium ions. The self healing potential of this new system was corroborated by localised electrochemical impedance measurements (LEIS). [Copyright &y& Elsevier]

Abstract: This work describes a simple methodology to bio-functionalize flat Au(111) electrodes through the one-step reaction between gold nanoparticles (AuNPs), carbon disulfide and a secondary amine (epinephrine) and an aminoacid (tryptophan). The process relies on the in situ dithiocarbamate formation between carbon disulphide and amine groups and also on the strong linkage between sulfur and gold. The redox behavior of modified gold with epinephrine or tryptophan, prepared from both ethanolic and aqueous solutions confirms their covalent immobilization and reveals a significant increase of their amount on the electrode due to the presence of AuNPs. Electrochemical reductive desorption in basic solution provided qualitative information on the amount of sulfur linked the gold surface and complements the redox studies. The co-immobilization of an enzyme (glucose oxidase, GOx) and gold nanoparticles, using carbon disulfide has been also tested. The presence of GOx on modified Au(111) electrodes has been confirmed by electrochemical detection of the catalytic oxidation of glucose in the presence of a redox mediator and through the evaluation of H2O2 reduction, formed during the catalytic reaction. XPS analysis, topographic and phase imaging by atomic force microscopy (AFM) further confirmed surface modification by AuNPs and also their functionalization. The successful one-step amine adsorption, in the presence of AuNPs, from aqueous solutions reveals the potential of this method in the construction of nanostructured biosensing interfaces. [Copyright &y& Elsevier]

Abstract: This paper describes the electrosynthesis of polypyrrole (PPy) onto AA6061-T6 aluminum alloy from a sulfuric acid solution doped with molybdate anions (MoO4 2−) or 8-hydroxyquinoline (8HQ) species. These dopant compounds were chosen as they have been proven to be effective in mitigating the corrosion in chloride medium. The protectiveness of PPy coatings incorporating these corrosion inhibitors within the polymer matrix is discussed. The coatings were morphologically characterized via scanning electron microscopy (SEM) and evaluated electrochemically via polarization in 0.5M NaCl. The results show that doping PPy with molybdates or 8HQ changes its morphological properties and its effectiveness in preventing passivity loss for AA6061-T6 in chloride media. [Copyright &y& Elsevier]

Abstract: This work reports a new methodology to measure quasi-simultaneously the local electric fields and the distribution of specific ions in a solution via selective microelectrodes. The field produced by the net electric current was detected using the scanning vibrating electrode technique (SVET) with quasi-simultaneous measurements of pH with an ion-selective microelectrode (pH-SME). The measurements were performed in a validation cell providing a 48μm diameter Pt wire cross section as a source of electric current. A time lag between acquiring each current density and pH data-point was 1.5s due to the response time of pH-SME. The quasi-simultaneous SVET–pH measurements that correlate electrochemical oxidation–reduction processes with acid–base chemical equilibria are reported for the first time. No cross-talk between the vibrating microelectrode and the ion-selective microelectrode could be detected under given experimental conditions. [Copyright &y& Elsevier]

Abstract: This work investigates the influence of the addition of cerium (IV) ions on the anticorrosion properties of organic–inorganic hybrid coatings applied to passivated tin coated steel. In order to evaluate the specific effect of cerium (IV) addition on nanostructural features of the organic and inorganic phases of the hybrid coating, the hydrolytic polycondensation of silicon alkoxide and the radical polymerization of the methyl methacrylate (MMA) function were induced separately. The corrosion resistance of the coatings was evaluated by means of linear polarization, Tafel type curves and electrochemical impedance measurements. The impedance results obtained for the hybrid coatings were discussed based on an electrical equivalent circuit used to fit the experimental data. The electrochemical results clearly showed the improvement of the protective properties of the organic–inorganic hybrid coating mainly when the cerium (IV) was added to the organic phase solution precursor, which seemed to be due to the formation of a more uniform and densely reticulated siloxane-PMMA film. [Copyright &y& Elsevier]

Abstract: The production of polyaniline films on aluminium alloy 6061-T6 in sulphuric acid was carried out by electrodeposition, using cyclic voltammetry and potentiostatic polarization. The films obtained were characterized by SEM and XPS analysis. Electrochemical techniques were also used to assess the anticorrosive properties of the coatings. The choice of the upper potential limits for potential cycling and of the fixed potential for potentiostatic production should take in consideration the balance between their effect on the minimum number of cycles (or time) needed to produce the film and on the rate of overoxidation. Polarization curves show a slight increase of the corrosion potential for polyaniline coated substrate as compared with bare metal, indicating that no significant protection is achieved by the polymer coating. The Bode diagrams show low impedance values for the alloy covered with polyaniline when compared with the results obtained for the bare metal. This can be attributed to the conductive character of the polyaniline films. [Copyright &y& Elsevier]

[Display omitted] • Zn and Zn-Cu were deposited by dynamic hydrogen bubble template (DHBT) technique. • DHBT resulted in 3D porous architectures of Zn and Cu x Zn y compounds. • Gradient top-Cu and bottom-Zn can be beneficial in several biological applications. • In vitro experiments produced common Zn and Cu degradation compounds. • Degradation compounds are biocompatible and some can impart biological benefits. New biomaterials for bone healing applications are crucial for our ageing populations. Three-dimensional (3D) Zn and ZnCu architectures on stainless steel were reinvented through dynamic hydrogen bubble template (DHBT) deposition. 3D Zn was formed by porous pure Zn structures, whereas an interconnected architecture composed of Cu x Zn y was detected in ZnCu foams, with the preferential deposition of Cu on the top and Zn on the bottom. These materials, with pore diameters ranging from 0.4 to 5 µm in 3D Zn and from 60 to 270 µm in ZnCu foams, have applications in drug delivery or scaffold systems, respectively. To evaluate the biomedical usage of these materials, their degradation in different biological media was assessed. Both materials were stable in cell culture medium and active in simulated body fluid solution, where typical Cu- and Zn-derived corrosion products were formed. The bioactivity of the degradation products formed, namely Zn and Cu oxides, hydrozincite, simonkolleite and hydroxyapatite, all most likely doped with Cu in the ZnCu foams, was related to their applicability in the biomedical field. Based on these findings, 3D Zn and ZnCu foams produced by DHBT proved their biomedical potential, an original approach reported herein for the first time. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, iron oxide thin layers formed on mild steel substrates in alkaline media by the application of different anodic potentials were studied in order to characterize their morphology, composition and electrochemical behaviour, in particular under conditions of cathodic protection. The surface composition was evaluated by X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). The morphology of the surface oxides was studied via Atomic Force Microscopy (AFM). The electrochemical behaviour of the surface oxides was studied using Electrochemical Impedance Spectroscopy (EIS). The results showed that the surface film is composed by Fe2+oxides and Fe3+ oxides and/or hydroxides. The contribution of Fe2+ species vanishes when the potential of film formation increases in the passive domain. Two distinct phases were differentiated in the outer layers of the surface film, which proves that film growing is topotactic in nature. [Copyright &y& Elsevier]

Abstract: Polypyrrole films on aluminium alloy 6061-T6 were prepared by electropolymerization of pyrrole in sulphuric acid using two different processes – cyclic voltammetry and potentiostatic polarization – and assessed through SEM observation and voltammetry. The anticorrosive properties of these films were studied by polarization curves and electrochemical impedance spectroscopy. The polypyrrole films formed by both methods are homogeneous and present a globular structure. However, it was found that the films produced by cyclic voltammetry are thicker than those produced potentiostatically at a potential equal to the upper limit of the cyclic voltammetry (E λa ). It was also found that there is an optimum value for the formation potential (E appl, in the case of the potentiostatic method or E λa for cyclic voltammetry). Above this value, overoxidation of the polymer occurs, which is found to be deleterious to the coated system behaviour. From polarization curves no major differences were detected between the PPy-coated alloy and the bare material, indicating that no significant protection is achieved by the polymer coating. On the other hand, Bode diagrams are typical of a system undergoing pitting corrosion and show lower impedance values for the alloy covered with polypyrrole than for the bare metal. This can be attributed to the conductive character of the polypyrrole films. [Copyright &y& Elsevier]

Abstract: The work aims at investigating the corrosion behavior of AA2024-T3 substrates pretreated with sol–gel derived hybrid coatings. The hybrid sols were prepared by copolymerization of 3-Glycidoxypropyltrimethoxysilane (GPTMS), tetraethylortosilicate (TEOS) and tetra-n-propoxyzirconium (TPOZ). Coatings with Zr/Si atomic ratios of 1:9 and 1:4 were also prepared. During the synthesis process, there is formation of ZrO2 nanoparticles, which content depends on the temperature and time of the TPOZ hydrolysis/condensation reactions. The results show that the ZrO2 nanoparticles have diameters ranging between 40 and 200 nm. These particles are amorphous and they improve the corrosion protection of the sol–gel coatings. The presence of ZrO2 nanoparticles seems to have a pore blocking effect in the coatings with higher content of particles. [Copyright &y& Elsevier]