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A nanometric (thickness ≤200 nm) composite hybrid coating consisting of alternating laminate layers of aluminium and titanium oxides deposited by atomic layer deposition (ALD) onto a thin graphene layer of reduced graphene oxide (rGO) nanoplatelets applied on AISI 304 stainless steel, was developed and its electrochemical properties were studied. The rGO by itself has not revealed significant effects in terms of protection, whereas the laminate reinforced the passivity by decreasing the passive current. The best performance was obtained by the complete system, in which the rGO film acts as a primer for the anchoring of the ceramic layer, as a barrier for corrosive ions, and as a shield for local electrical fields if these are generated by starting local corrosion, thus, decreases the tendency to metastable pitting.

The effect of biaxial strain on the electrochemical behaviour of a thin weldable primer containing zinc-aluminium particles applied to galvanized steel was studied by assessing both the integral behavior of the system and the micro-currents on the heterogeneous surface. The ionic currents near the surface were measured by the SVET and revealed to be sensitive to the shape and lifetime of micro-active areas of the coating. The EIS data on intact coatings revealed that immersion time caused a drop of the low frequency resistance while the capacitive slope remained constant; on elongated samples, a similar trend in low frequency was observed along with an increase of the capacitance. A model is proposed, based upon an electrical equivalent electric circuit that includes distinct elements mimicking the electrochemical behaviour of the exposed and embedded metal particles and for the polymer phase.

In this work, the applicability of localized electrochemical impedance spectroscopy (LEIS) to characterize metal-corrosion inhibitor systems has been investigated. Copper corrosion inhibition by benzotriazole (BTA) and 2-mercaptobenzimidazole (MBI) has been studied, and compared to the electrochemical behaviour of the non inhibited metal. A rather wide frequency range of the AC potential signal was employed, namely 50 mHz ≤ f ≤ 65 kHz. The measurements were conducted for different probe-substrate distances in order to explore the effect of the different component of the localized impedance. Nyquist diagrams exhibit inductive loops in the high frequency range, and capacitive semicircles at intermediate and low frequencies for all the systems investigated, though they were affected in a different extent by the variation of the probe-substrate distance depending on the surface condition of the metal samples, this effect being more notorious for distances smaller than the dimensions of the bi-electrode probe.

The corrosion distribution along a coil-coating sample formed by deep-drawing is reported. The formed rectangular cup was divided in five different regions and their impedance response investigated independently. The response of each region was compared with the overall sample response and the morphology of degradation was studied by scanning electron microscopy. Severe attack was observed in the most strained regions (corners and edges). Micro-defects in the shape of pinholes and cracks developed as a consequence of the forming process, apparently nucleating in the vicinity of the inorganic particles present in the paint. Immersion increased the size and number of defects. The overall impedance was reconstructed from the impedance measured in the local regions by two methods: (a) calculation using the local experimental data and (b) simulation using an equivalent electrical circuit with the values taken from the fitting of the local experimental data.

Introduction: Ischemic stroke is the leading cause of mortality in Portugal, with around 30 to 50% of cases being of cardioembolic etiology. Transesophageal echocardiography (TEE) has assumed growing importance in the detection of cardiac sources of embolism. However, there is controversy regarding the implications of TEE findings for the therapeutic approach to patients with ischemic stroke. Objectives: To analyze TEE findings in the diagnostic work-up of patients with ischemic cerebral events and to determine their infl uence on therapeutic strategy. Methods: We retrospectively studied patients with stroke or transient ischemic attack (TIA) before the age of 65, of no apparent cause after carotid ultrasound, electrocardiogram and transthoracic echocardiography, who underwent TEE between 1992 and 2009. The following diagnoses on TEE were considered as potential embolic sources: atrial septal defect; patent foramen ovale (PFO); atrial septal aneurysm (ASA); vegetations; tumors; intracavitary thrombi; and aortic plaques >2 mm (ascending aorta and arch). Results: We analyzed 294 patients, mean age 45 years, 56.8% men. TEE revealed a potential cardioembolic source in 36.7% of the patients, PFO and ASA being the most frequent. Throughout the period considered, there was an increase in the number of exams performed, as well as in diagnoses, mainly PFO and ASA. Comparison of patients with and without a diagnosis on TEE showed that the former were older and were more often prescribed oral anticoagulation. By multivariate analysis, the presence of a positive TEE finding was shown to be an independent predictor of treatment with oral anticoagulation (OR=2.48; CI 95%: 1.42-4.34; p=0.001). Conclusion: In the population under analysis, TEE was useful in identifying potential cardioembolic sources and influenced the therapeutic strategy. : Introdução: O acidente vascular cerebral (AVC) isquémico é a principal causa de morte em Portugal, estimando-se que cerca de 30 a 50% dos casos sejam de etiologia embólica cardíaca. O ecocardiograma transesofágico (ETE) tem assumido um papel cada vez mais importante na identificação de potenciais fontes cardíacas de embolização. No entanto, o seu papel na orientação terapêutica tem sido mais controverso. Objectivos: Analisar os dados obtidos pelo ETE na avaliação diagnóstica dos doentes internados com AVC, assim como a influência dos mesmos na orientação terapêutica. Métodos: Estudo retrospectivo de doentes com AVC ou acidente isquémico transitório (AIT) até aos 65 anos, sem diagnóstico após ecodoppler dos vasos do pescoço, electrocardiograma (ECG) e ecocardiograma transtorácico (ETT), submetidos à realização de ETE entre 1992 e 2009. Relativamente aos achados do ETE, foram considerados como potenciais fontes embólicas os seguintes diagnósticos: defeito do septo interauricular (SIA) ou comunicação interauricular; foramen ovale patente (FOP); aneurisma do SIA (ASIA); vegetação; trombo intracavitário; tumor; placas aórticas > 2 mm (aorta ascendente e arco). Resultados: Foram avaliados 294 doentes com idade média de 45 anos, sendo 56,8% do sexo masculino. O ETE diagnosticou potenciais fontes embólicas cardíacas em 36,7% dos casos, sendo o FOP e o ASIA os diagnósticos mais frequentes. Ao longo do período avaliado, verificou-se um aumento do número de exames realizados assim como do número de diagnósticos, principalmente de FOP e ASIA. Quando comparados os doentes com achado diagnóstico no ETE com os restantes, verificou-se que os primeiros eram mais idosos e mais frequentemente medicados com hipocoagulação oral. Através de análise multivariada, a presença de um achado diagnóstico no ETE foi confirmada como preditor independente da instituição de hipocoagulação oral (OR = 2,48; IC 95%: 1,42-4,34; p = 0,001). Conclusão: Na população avaliada, o ETE revelou-se útil na pesquisa de potenciais fontes embólicas cardíacas e infl uenciou a subsequente orientação terapêutica. Keywords: Cardioembolic source, Transesophageal echocardiogram, Oral anticoagulation, Palavras-chave: Fonte embólica cardíaca, Ecocardiograma transesofágico, Hipocoagulação oral

The object of this paper was to formulate a two-pack wash primer employing aluminium phosphosilicate as active anticorrosive pigment instead of basic zinc chromate. The anticorrosive action of the primer was evaluated by the polarization technique and the scanning vibrating electrode technique (SVET). The exposed surface was then examined by scanning electron microscopy (SEM) and the surface composition determined by energy dispersive X-ray (EDX) analysis. The primer was finally integrated in a complete paint scheme whose anticorrosive performance was evaluated by the salt spray chamber and electrochemical impedance spectroscopy. The adhesion of the primer plus a painting system was also evaluated by standard ASTM D 3359-90 test method. The wash primer pigmented with zinc chromate was used as reference. Results indicated that basic zinc chromate could be replaced by the more eco-friendly wash-primer containing aluminium phosphosilicate.

The work deals with the effect of sodium phosphate on the corrosion at the cut edge of electrogalvanized steel, studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and the scanning vibrating electrode technique (SVET). Mapping of the ionic currents revealed that in non-inhibiting solution, the cathode shifts away from the anode as zinc corrosion products precipitate along concentric whitish lines that result from the location of the peak cathodic current. Sodium phosphate inhibits corrosion at the cut edge by precipitation of gel-like zinc phosphate clusters with barrier properties. Breakdown and repassivation of this layer can occur under certain conditions.

The effect of benzotriazole (BTAH) in high concentration on the cut edge corrosion of galvanized steel in sodium chloride solution was studied, using electrochemical polarization, EIS, SVET and XPS. It was observed that there is the formation of a BTAH surface film on both steel and zinc, which polarizes anodically both metals, greatly reducing their electrochemical activity and changing the rate control from diffusion at the cathode to mixed control. The protective film undergoes numerous events of local activation and repassivation. The XPS data revealed that the BTAH becomes differently bound to zinc depending on the metal being under self-corrosion or coupled to steel. Although the BTAH reduces the electrochemical activity of both materials, there is significant reduction of the cathodic protection effect of zinc.

In order to lower the excessive costs of metallic prosthesis materials alternatives to Ti and Ti alloys have been searched. In this study, the corrosion resistance of the DIN 1.4575 superferritic stainless steel, either solution annealed or solution annealed and aged at 475 °C for periods varying from 100 to 1080 h, was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods in Hanks' solution. The solution annealed and the aged for 1080 h samples were also tested using scanning electrochemical microscopy (SECM) in a 0.1 mol/L NaCl solution at 25 °C. The EIS results showed that the corrosion resistance of the DIN 1.4575 steel decreases with heat treatment time at 475 °C probably due to alpha prime formation. Besides the diminution of the overall impedance values, the low frequency limit of the Nyquist diagrams show a progressive change from an almost capacitive response to a resistive behavior as the heat treatment time increases. Pitting corrosion resistance also decreased with aging time at 475 °C.

The corrosion mechanisms and the inhibiting effect of sodium phosphate at cut edges on galvanized steel was studied by potentiodynamic polarization, EIS and monitoring of local ionic currents made by means of the scanning vibrating electrode technique (SVET). Assessment of zinc and of iron single electrodes was also made for comparison. In the absence of phosphate, corrosion of electrogalvanized steel at the cut edge is cathodically inhibited by the precipitation of zinc corrosion products over the steel surface. Mapping of the ionic currents revealed that the cathodic area becomes laterally shifted away from the anode as zinc corrosion products precipitate along parallel lines that are dictated by the location of the maximum cathodic currents. Sodium phosphate revealed inhibiting properties on the cut edge by precipitation of zinc phosphate, in the form of gel-like zinc phosphate clusters. Estimated inhibiting efficiencies for the cut edge were slightly above 80%.

Magnesium-rich coatings have the capability of providing sacrificial corrosion protection to aluminium substrates and therefore present a new and challenging field of development. In this work the mechanism of protection of an aluminium substrate by a Mg-rich coating was investigated using the scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM). The SVET has shown the evolution of the pit activity with time under sacrificial protection, whereas the SECM allowed indirect sensing of the cathodic activity above the electrodes. The study was complemented by classical electrochemical techniques, namely electrochemical impedance spectroscopy and open circuit potential measurement. The results show that magnesium acts in a first stage by both preventing nucleation of pits and inhibiting the growth of the already existing ones, whereas at a later stage the precipitation of a porous layer of magnesium oxide at defective areas leads to some degree of barrier protection.

Our laboratory recently began work on the use of room temperature ionic liquids ((RTIL's) to enhance our capabilities for the electrochemical characterization of organic coatings [A.M. Simoes, D. Tallman, G.P. Bierwagen, The use of ionic liquids for the electrochemical characterization of water transport in organic coatings, Electrochem. Solid-State Lett. 8 (2005) 60]. The RTIL's are electrically conductive liquids consisting of large molecules that can be used to investigate the electrochemical properties of coatings in a non-aqueous medium. The enhancement of coating characterization comes from the fact that RTIL's have sufficient conductivity to be an immersion medium for electrochemical measurements, but they do not directly penetrate and effect organic coatings as do aqueous electrolyte solutions. This allows the separate examination of the effects of water on coatings in immersion or cyclic exposure. Indeed, our initial studies showed that a hydrophilic RTIL could be used to electrochemically characterize the drying of a coating after immersion, a process which heretofore had not been followed electrochemically. Thus, electrochemical measurements of coatings based on aqueous electrolyte immersion can be enhanced by the use of RTIL's and the effects of water on the coatings under study isolated and analyzed separately, especially the diffusion of water out of coatings during drying processes. Recent papers from our group have introduced the methodology whereby RTIL's in conjunction with capacitance monitoring via electrochemical impedance spectroscopy (EIS) can be used to determine the diffusion coefficient of water out of a non-pigmented, additive free coating [A.M. Simoes, D. Tallman, G.P. Bierwagen, The use of ionic liquids for the electrochemical characterization of water transport in organic coatings, Electrochem. Solid-State Lett. 8 (2005) 60; K. Allahar, B. Hinderliter, A. Simoes, D. Tallman, G. Bierwagen, S. Croll, Simulation of wet–dry cycling of organic coatings using ionic liquids, J. Electrochem. Soc. 154 (2007) 177–185; B. Hinderliter, K. Allahar, O. Stafford, S. Croll, Using Ionic Liquids to Measure Coating Properties via Electrochemical Impedance Spectroscopy, Presented the 2006 International Coatings Exposition, Federation of Societies for Coatings Technology, New Orleans, LA, 2006 Oct.; B.R. Hinderliter, K.N. Allahar, G.P. Bierwagen, D.E. Tallman, S.G. Croll, Thermal cycling of epoxy coatings using room temperature ionic liquids, J. Electrochem. Soc. 155 (3) (2008) 1]. The technique has been extended to several types of coatings as well as the study of the cyclic wetting and drying of coatings [K. Allahar, B. Hinderliter, A. Simoes, D. Tallman, G. Bierwagen, S. Croll, Simulation of wet–dry cycling of organic coatings using ionic liquids, J. Electrochem. Soc. 154 (2007) 177–185]. This latter set of processes is one of the key set of events in exterior exposure that causes the failure of exterior protective coatings. Recently, RTIL's have been used to simulate the alternate wetting and drying of a Zn-rich epoxy coating system. EIS experiments were conducted on the Zn-rich epoxy under constant immersion in 0.05 M NaCl and RTIL. The experimental results were analyzed to determine the dielectric response and changes due to Zn oxidation within the Zn-rich system.

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 0.005 M 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.

A model cut edge consisting of a zinc anode and a split iron cathode was used for studying corrosion mechanisms and assessing the suitability of scanning electrochemical techniques for corrosion studies at the microscale. Scanning electrochemical microscope (SECM), localized electrochemical impedance spectroscopy (LEIS) and scanning vibrating electrode technique coupled with the scanning ion-selective electrode technique (SVET/SIET) were applied. The corrosion products precipitated on the cathode once the critical pH and solubility limits were reached, which resulted from the diffusion of hydroxyl and zinc ions across the cathode. There was no evidence of self-healing by the corrosion products.

The galvanic corrosion of an iron/zinc pair immersed in aqueous 0.1 M Na 2 SO 4 solution has been investigated by using the scanning vibrating electrode technique (SVET). In this way, investigations in the micrometer range of the progress of the electrochemical reactions involved in galvanic process were performed. The anodic oxidation process is observed to be initiated on the zinc sample in a localized manner, whereas the cathodic reaction involving the electroreduction of dissolved oxygen is homogeneously distributed over the iron sample. This later process is the rate determining step in the overall corrosion process, as demonstrated by the changes in the ionic and galvanic currents measured in the system when the area of the iron specimen is varied relative to that of zinc. The occurrence of coupled chemical reactions in the solution phase involving the products of the corrosion reactions could also be deduced from the integration of the ionic currents measured for each half-reaction during a SVET scan. Thus, the corrosion processes involved in the galvanic coupling of iron and zinc have been further understood by using this microelectrochemical technique appropriately, helping to better interpret large scale measurements.

The mechanism of cathodic protection of an aluminium substrate by a Mg-rich coating was investigated using localized techniques. Both scanning vibrating electrode techniques (SVET) and scanning electrochemical microscopy (SECM) were used to investigate the processes occurring at the surface of exposed metal when electrically connected or disconnected in a galvanic couple with the Mg-rich coating. The SVET has shown the evolution of the pit activity with time under conditions of sacrificial protection, whereas the SECM allowed indirect sensing of the cathodic activity above the electrodes. It was shown that the cathodic protection provided by magnesium to aluminium substrates acts by both preventing pit nucleation and inhibiting the growth of the pre-existing pits.

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 0.005 M 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.

To insure that the corrosion protective behavior of Mg-rich primers over Al aircraft alloys is properly understood, multiple electrochemical techniques have been utilized to characterize the behavior of this class of Cr-free coatings. Many substitutes for Cr-containing pretreatments for Al alloys such as AA 2024 T-3 or AA7075 T-6 have been put forth as performing as well as the present Cr-containing materials, but none except Mg-rich primers (MRPs) have succeeded in passing the qualification testing required of these materials. The electrochemical testing was done in conjunction with the subjective “qualification” testing of the primer materials for US Air Force and Navy specifications so that as this new class of primers did not encounter any unexpected corrosion protection-related deficiencies. To confirm that the MRPs did indeed provide cathodic, sacrificial protection to these alloys, one measures the mixed corrosion potential of the Al–Mg system (E mixed ), also know as the open circuit potential (OCP). This parameter indicates when the potential of the alloy substrate is modified by contact with the Mg to yield a potential cathodic to the Al Alloy (E alloy corr ). This was done by a steady state measurement of the total system OCP in immersion and also by measuring the potential of the minimum/free corrosion current (icorr) in a potentiodynamic scan of the mixed system. Both methods yielded values in excellent agreement, but initial studies of a system with a high quality topcoat gave problems in OCP measurement due to an exceedingly high impedance causing steady-state measurement difficulties. Electrochemical impedance spectroscopy (EIS) and electrochemical noise methods (ENM) were also used to characterize the system in immersion. Further, the scanning vibrating electrode technique (SVET) was used to examine local damage protection by the MRP about a deliberately induced scratch in the coating system. These results for the MRP system yield a very interesting, self-consistent set of data showing cathodic protection of one reactive metal (Al) by another more reactive metal (Mg). © 2007 Elsevier B.V. All rights reserved.

The influence of the electrochemical hardening treatment on the composition and structure of coloured porous films formed by triangular current scan on AISI 304 stainless steel has been examined by impedance spectroscopy and also by SEM, AES, XPS and AFM. It was observed that the films, originally consisting of a porous chromium–iron oxide, became more compact and enriched in chromium after the hardening treatment. The development of a high frequency semi-circle in the impedance spectra is explained by the formation of an outer oxide layer.

The capacitance evolution of an organic coating undergoing cyclic wetting and drying conditions was monitored by single frequency electrochemical impedance spectroscopy. Monitoring of the drying condition was possible with the use of a hydrophilic room temperature ionic liquid and the methodology employed is presented. Experimental results associated with cyclic dilute NaCl wetting and ionic liquid drying are presented for an epoxy coating on an AA 2024-T3 substrate. The calculated capacitance evolutions associated with wetting and drying were generally consistent with Fick’s second law. The calculation of the water ingress and egress diffusion coefficients using a short-time approximate solution and a series solution to Fick’s second law are presented. The latter solution is shown to address the capacitance evolution better than the former with the ingress coefficient larger than the egress coefficient for a given exposed coating surface. There was agreement between the calculated diffusion coefficient ingress values for coating areas exposed to cyclic NaCl wetting—ionic liquid drying and cyclic NaCl wetting—natural drying conditions. Comparison of the impedance spectra for test areas indicated that the use of the ionic liquid as a drying medium influenced the electrochemical properties of the coating only after a number of cycles. © 2007 The Electrochemical Society. DOI: 10.1149/1.2764235 All rights reserved. The protection of metallic structures by organic coatings is primarily due to the isolation of the structure from the environment by the coating. The barrier protection provided by a coating is influenced by the absorption of water and ionic species from the environment. Literature associated with the measurement of water absorption of a polymer film has been reported using gravimetry. 1-7 A parameter that significantly influences the transport properties of a coating is the diffusion coefficient of water into the coating Din .A n idealized model that relates the mass changes associated with absorption to Din for an organic coating is based on the series solution of Fick’s second law. 3,4,8 An approximation to the series solution that is applicable for short times is employed in literature to calculate Din based on gravimetric measurements. 3,5,6 The series solution to Fick’s second law and the approximate solutions are also applicable to mass changes associated with desorption of water. The different dielectric properties of water and an organic coating result in changes in the capacitance of the coating that accompanies water absorption or desorption. 1,2 The monitoring of the capacitance by electrochemical impedance spectroscopy EIS has provided a convenient method for the volumetric evaluation of water absorption in organic coatings. 3,4,7,9-15 The capacitance evolution of an organic coating can be used to calculate Din by relating the volumetric changes associated with water absorption with the mass changes.

The work makes use of the scanning vibrating electrode technique (SVET) and the scanning electrochemical microscope (SECM) to investigate microscopic aspects of the electrochemical reactions that occur in an iron–zinc galvanic couple immersed in aqueous sodium chloride solution. Detection of the corrosion processes was made by sensing the phenomena occurring in solution. The SVET provided information on the distribution of ionic currents arising from the metal surface, whereas the SECM measured the concentration of chemical species relevant to the corrosion processes. The two techniques had comparable sensitivity for the corrosion of iron but significant differences were observed concerning the detection of corrosion of zinc.

Corrosion inhibition of metallic substrates is an important and crucial step for great economical as well as environmental savings. In this paper, we introduce an extra thin effective corrosion inhibitive material having layered structure designed for protection and functionalization of Ti Grade 5 alloy substrates. The coating consists of a first layer made of thin graphene nanoplatelets, on top of which a multilayer Al2O3 and TiO2 films is applied by low-temperature atomic layer deposition. The amorphous structure of the metal oxide films was confirmed by micro-Raman and X-ray diffraction analysis. Corrosion inhibition ability of the prepared coatings was analyzed by open circuit potential, potentiodynamic plot and by voltammetric analysis, in aqueous potassium bromide solution. The open circuit potential of the graphene-metal oxide coated substrate showed much passive nature than bare substrate or graphene coated or only metal oxide coated substrates. The localized corrosion potential of the graphene-metal oxide coated, only metal oxide coated, and bare substrates were found 5.5, 3.0, and 1.1 V, respectively. In addition, corrosion current density values of the graphene-metal oxide and only metal oxide coated substrates showed much more passive nature than the bare and graphene coated substrates. Long immersion test in the salt solution further clarified the effective corrosion inhibition of the graphene-metal oxide coated substrate. The analyzed results reflect that the graphene-metal oxide films can be used to prepare better and effective corrosion inhibition coatings for the Ti Grade 5 alloy to increase their lifetime.

Magnesium-rich coatings present a new and challenging field of development for the corrosion protection of aluminium structures. These coatings are capable of sacrificial protection, but assessment of their efficiency and durability can be strongly affected by the testing environment. In this work two solutions commonly used in our studies are compared: 0.1% NaCl and dilute Harrison solution (DHS). The corrosion behaviour of two aluminium alloys coated with a magnesium-rich coating, of pure magnesium and of the bare aluminium substrates was assessed in the two solutions using electrochemical techniques. The corrosion rate of pure magnesium was higher in DHS, although the dissolution rate of the magnesium embedded in the polymer matrix was not significantly affected. The impedance spectra of the scribed samples resembled that of the bare substrates in NaCl solution but not in DHS.

The anticorrosive performance of zinc chromate and zinc phosphate, used as extracts in 0.1 M NaCl, was studied using electrochemical impedance spectroscopy (EIS), the scanning vibrating electrode technique (SVET) and open circuit potential (OCP) measurements. Neither of the pigments managed to totally prevent corrosion. Phosphate had a much lower inhibiting efficiency and acted at a very low rate, whereas chromate acted immediately after immersion, but lost some of its action after a few hours of continuous immersion. Iron corroded uniformly in the phosphate extract, whereas in the chromate extract nucleation of metastable pits occurred. Evolution of the chromate layer with time was revealed in the EIS spectra in the form of a relaxation constant that developed during immersion, which was interpreted as being due to the formation of a porous healing layer formed on repassivated pits. The joint use of open circuit potential measurements, EIS and SVET is illustrated as a means of assessing different phenomena on the metal surface.

The electrochemical behaviour of Mg-rich primer on Al Alloys, AA2024 and AA7075, has been studied via Electrochemical Impedance Spectroscopy (EIS), Open Circuit Potential (OCP) and potentiodynamic polarization. Results showed that the Mg-rich primer provides sacrificial protection to the Al substrate by a two-stage mechanism. In a first stage, corrosion of aluminium is prevented by cathodic polarization, whereas at a later stage the precipitation of a porous barrier layer of magnesium oxide was observed.

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. � 2006 Elsevier Ltd. All rights reserved.

The application of scanning electrochemical microscopy (SECM) for corrosion studies of organic coatings on reactive metals is presented. In this work, the SECM was used to monitor the electrochemical processes at painted galvanized steel substrates immersed in 0.1 M NaCl aqueous solution. The coatings were investigated both as obtained and scribed, to simulate a defect across the coating, down to the metal-substrate surface. The SECM was operated under either the feedback or a variation of the sample generation/tip collection modes. In the first case the variations in the feedback current measured at the SECM-tip when scanned at constant height over the sample allowed imaging of the topography of the coated surface with high local resolution. In the second case, chemical species participating in the corrosion reactions at the sample are detected at the SECM-tip by applying appropriate potential values to the microelectrode. Local concentration variations could be assessed in this way.

The anticorrosive performance of two inhibitive pigments, zinc chromate and zinc phosphate, was compared using electrochemical impedance spectroscopy (EIS) and the scanning vibrating electrode technique (SVET) in pigment extracts in 0.1 M NaCl. It was observed that zinc was protected from corrosion in both extracts. In tests using hot dip galvanised steel painted with an epoxy primer incorporating the pigments, the SVET detected the anodic and cathodic distribution along the scribes, although no significant differences were observed among the various primers. On the contrary, EIS was able to distinguish processes occurring on the metal surface exposed by the scribe in different samples. For primers with anticorrosive pigment, a time constant at high frequencies was attributed to a layer of protective nature, probably formed by metal ions from the substrate and inhibitive ions leached from the anticorrosive pigments.

The electrochemical behaviour of passive films formed on one austenitic stainless steel (AISI 304) and one ferritic stainless steel (AISI 446) in solutions with pH between 0.6 and 8.4 was studied by capacitance measurements and photocurrent spectroscopy. Compositional characterization of the passive films was done by X-ray photoelectron spectroscopy. The capacitance increases with decreasing pH. Doping densities evaluated from Mott–Schottky plots are in the range 2–6 × 10 20 cm −3 and increased with the pH in the neutral/alkaline range while in pH 0.6, values above 10 21 cm −3 were found. The bandgap energy indicates two transitions, at 2.5–2.8 and 3.2 eV. The analytical data reveal that, as the pH increased, the films become enriched in Fe(II) and Fe(III), whereas the Cr(III) gradually decreases. The films formed at very low pH had a behaviour that contrasts with that of the films formed in the neutral/alkaline media. The films are described by a bilayer structure, with hydroxides in the outer layer and a spinel type oxide in the inner layer.

Scanning electrochemical microscopy has been used to detect the redox species involved in a corrosion process at the open-circuit potential. During the immersion of pure iron in a neutral aqueous solution, the potential of the ultra microelectrode (tip) was set to either detect the Fe2+ ions originating from the electrodissolution of iron at the anodic sites on the metal surface, or the depletion of oxygen in the electrolyte in the proximity of the corresponding cathodic sites. Keywords: Scanning electrochemical microscopy, Corrosion, Iron dissolution, Oxygen reduction, Localized electrochemical measurements

Coil-coated samples of electrogalvanised steel were submitted to uniaxial, biaxial and plane strain of various magnitudes and tested by electrochemical impedance spectroscopy (EIS). A good correlation was encountered between the coating resistance and the equivalent plastic strain. Microscopic inspection of the coatings suggests that the decrease in the coating resistance is a consequence of defects originated by cracks on the phosphate and by loss of adhesion at the polymer/pigment interface.

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. © 2004 Elsevier Ltd. All rights reserved.

The semiconducting properties and electrochemical behaviour of thin chromium and iron oxide films produced by sputtering were investigated by capacitance and photoelectrochemical measurements. The films were deposited onto various substrates and submitted in some cases, to a thermal treatment. It appears that sputtered chromium oxide on iron substrate reveals both types of semiconductivity (p and n) and that the thermal treatment enhances the n-type character. Finally, a study is developed using a duplex film formed by sputtered layers of chromium and iron oxides. This system allows for the discussion of the problem of the electronic structure of the heterojunction created by the two kinds of oxides. Comparison is made with the case of passive films on stainless steel.

An impedance model for the estimation of water absorption in organic coatings is presented. In part I, the model was developed taking a high frequency approximation. In part II the model is generalized by removing that approximation and by treating the film as a multicomponent system. Comparison with weight variation data has shown an improvement of the estimates made with the classical model of Brasher and Kingsbury. A low frequency approximation of the model has given good results with freestanding films.

A capacitance model for the estimation of water uptake in polymeric coatings is presented. The model is based upon a linear combination of the individual capacitances of the polymeric phase, the water and the air contained in the coating. Experimental comparison of the model with gravimetric data has revealed an improvement with respect to the classical equations.

The effect of uniaxial deformation on coil-coated galvanised steel was investigated. Samples with several degrees of uniaxial elongation were exposed to a corrosive solution and the loss of protective properties was monitored by electrochemical impedance spectroscopy (EIS). Protection rapidly decreased with the degree of elongation. After 16% the coating degradation introduced by elongation was so high that EIS was not able to distinguish different strained samples. The loss of protection was interpreted in terms of the morphological changes experienced by the coated system as a consequence of strain, supported by scanning electron microscopy (SEM) observations.

A model for the estimation of water uptake in polymeric coatings is presented. Experimental comparison of the model with the Brasher–Kingsbury equation using a PVC plastisol film revealed an improvement in the agreement with respect to the gravimetry. The influence of NaCl concentration of the outer solution revealed the same trend with both models.

The corrosion of electrogalvanized steel exposed to 0.1 M NaCl was studied using the SVET. Situations of localized corrosion, cathodic protection and corrosion protection due to surface pre-treatment were analyzed, putting in evidence the possibilities of the technique.

A model for the estimation of water uptake in polymeric coatings is presented, based upon a linear combination of the individual capacitances of the polymeric phase, the water and the air contained in the coating. Experimental comparison of the model with the Brasher–Kingsbury (BK) equation has revealed an improvement in the agreement with respect to the gravimetry.

Forming limit curves (FLCs) are useful tools to predict the safe forming limits of metal sheet. However, existing FLCs are limited to bare metal and the increasing use of pre-painted metal sheet (coil-coatings) requires new limits that take into account the corrosion resistance. In this work electrochemical impedance spectroscopy (EIS) was used to characterise the degradation of a coil-coated system in different states of deformation (uniaxial, biaxial and plane strain). The EIS data provided information about the condition of both paint and metal substrate and was used to devise criteria for minimum acceptable protection. A FLC was produced based on those criteria and its predictions were compared with the degradation of a model deep-drawn cup. (C) 2014 Elsevier B.V. All rights reserved.

Scanning electrochemical microscopy (SECM) and the Scanning vibrating electrode technique (SVET) were employed to identify the local reactivity and the cathodes and anodes on a cut edge of galvanized steel. The SECM was used in the amperometric feedback mode (for the oxidation of ferrocenemethanol as mediator) for sensing the conductivity of the surface and in the redox competition mode for locating the depletion of the cathodic reactant. Good agreement was observed in acidic solution between the location of the conductive regions of the surface and the depletion of oxygen estimated from amperometric lines across the cut edge. In neutral medium, non-uniform activity of the steel surface was observed and correlated well with the ionic current flows in solution and with the accumulation of zinc corrosion products on steel. In alkaline medium, the entire metallic surface operated as electron source for the regeneration cycle of the redox mediator. Irrespective of the pH of the solution, a maximum of the feedback observed over the cut edge is consentaneous with the thermodynamic stability of iron in the reduced form. SECM provided useful information regarding the steel conductivity, whereas the zinc anodes could only be resolved by the SVET

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.

The semiconductive behaviour of amorphous and crystalline Cr-oxide films deposited on stainless steels was studied by capacitance and photoelectrochemical measurements. The amorphous films presented metallic behaviour. For the crystalline films, bandgaps were determined for direct and indirect transitions. Doping densities evaluated from Mott–Schottky plots were below 1019 cm−3 for the films treated at high temperature, and decreased with the treatment temperature. The crystalline films were described as a thick layer of non-stoichiometric chromium oxide with a bi-polar character.

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.