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Abstract: In the present paper, a shape-memory polyurethane (SMPU) film consisting of a two-segmented block co-polymer is presented as a novel organic coating for the protection of metals against corrosion. When the coating is damaged, a physical self-healing and consequent recovery of the barrier properties are induced after an increase of the temperature. Indeed, thermal treatment leads to the relaxation of the soft matrix in the polymer and subsequent coverage of the damaged area. The scanning vibrating electrode technique (SVET) is employed to visualize local variations of the electrochemical activity in the damaged area of the SMPU coating, proving that the physical-repairing of the film during the thermal treatment leads to a recovery of the protective properties of the coated system. By using laser scanning confocal microscopy (LSCM), observation of the coating defect before and after the thermal healing allowed to establish the efficiency of the polymer to cover the coating defect qualitatively. Complementary experiments using dynamic mechanical analysis (DMA) allowed to study the mechanical properties of the co-polymer under a gradient of temperature and to prove its stability during the healing treatment. [Copyright &y& Elsevier]

A detailed microstructural and electrochemical analysis of electroless nickel phosphorous (NiP) coatings with P contents of 13.2 ± 1.2 wt%, 12.9 ± 0.7 wt%, and 8.3 ± 0.8 wt% on a copper substrate was performed to study the corrosion behaviour of electroless NiP/Cu systems. The P content of the electroless NiP coatings plays an essential role in the microstructure of the coatings in terms of crystallinity. The crystallinity variations, representing the extent of crystalline and amorphous phases within the material, with P content, affect the local electrochemical characteristics and, hence, the corrosion protection behaviour of electroless NiP coatings. The coatings with the highest P content showed the best corrosion performance in a 3.5 wt-% NaCl solution. In contrast, the surface of the electroless NiP coatings with low P content is more susceptible to corrosion due to the presence of locations with heterogeneous electronic properties that initiate localised corrosion. Microgalvanic interactions with a high cathode-to-anode surface ratio govern the localised corrosion kinetics of the low P-content samples. A high concentration of nodule boundaries and/or other existing structural defects on the surface serve as anodic sites, whereas the remainder of the surface serves as cathodic sites. • P content influences the localised corrosion mechanism of electroless NiP coatings. • P contents are associated with changes in NiP microstructure and topography. • Electrochemical and microstructural analyses offer insight into the corrosion mechanism. [ABSTRACT FROM AUTHOR]

Transients in electrochemical noise (EN) signals that are associated with localized corrosion typically contain frequency information that is quite localized in time. The study of these transients is therefore preferably performed using analysis procedures with high discrimination ability in both time and frequency simultaneously. The present work studies the combination of the Hilbert-Huang transform with the continuous wavelet transform, as data analysis methods that operate in time as well as in frequency, for the identification of localized corrosion. Additionally it incorporates fast Fourier transform as a technique to determine the distribution of power over frequency. Finally, it integrates the study of transient shape into the analysis of (time-) frequency properties. It is shown that the maxima in instantaneous frequency amplitudes of transients with otherwise different shapes can be similar. In the case of the presence of multiple transients in the EN signal, the cut-off frequency obtained from power spectral density plots is related to maxima in instantaneous frequency amplitudes of only a limited number of transients. [ABSTRACT FROM AUTHOR]

Abstract: The interfacial bondings formed between succinic acid and myristic acid, as well as succinic anhydride molecules with a set of differently treated zinc substrates have been investigated using infrared reflection absorption spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The compounds were selected to model typically used carboxylic-based adhesives and coatings. Moreover, the adsorption kinetic has been evaluated by means of chronoamperometry (CA) and chronovoltammetry measurements. XPS results showed a relation between the amount of carboxylates formed by adsorption of succinic acid/myristic acid and the hydroxyl fraction presented on the surfaces as proved by a higher electron transfer in CA. On the other hand a set of oxidative/reductive interactions was detected during the adsorption of succinic anhydride, in turn proving a spontaneous ring opening and adsorption mechanism. A clear relationship between the amount of adsorbents and surface hydroxyls/carbonates was detected for the adsorption of succinic anhydride. The extent to which the formed carboxylates resisted negative potentials was also investigated by cyclic voltammetry (CV) in an aqueous solution. The coordinative bonding of a bifunctional carboxylic acid group to the oxide surface was found to be not stable in the presence of a negative potential, while a monofunctional carboxylic acid group could resist displacement by water for a prolonged period of time. On the other hand, a low double layer capacitance was obtained after the adsorption of succinic anhydride, which was related to a change in potential of zero charge (PZC) upon the adsorption. [Copyright &y& Elsevier]

In this work, the study of the time-dependent behaviour of lithium carbonate based inhibitor technology for the active corrosion protection of aluminium alloy 2024-T3 is presented. Odd random phase electrochemical impedance spectroscopy (ORP-EIS) is selected as the electrochemical tool to study the corrosion protective properties of a model organic coating with and without lithium carbonate as a function of immersion time, by examination of the non-linearities and non-stationarities in the system. A dedicated qualitative and quantitative analysis allows linking the presence of non-stationarities in a certain frequency range with the (un)stable behaviour of different electrochemical processes. Monitoring of the system with and without lithium corrosion inhibitors during the first 12 h after immersion in a 0.05 M NaCl aqueous solution and modelling the ORP-EIS data with equivalent electrical circuit (EEC) models revealed a relation between the trends in the parameter evolution and the (un)stable behaviour of the morphological changes taking place. This paper shows that the ORP-EIS based methodology allows us to study the behaviour of corrosion inhibitors in an alternative way; the time-dependent behaviour of corrosion inhibitor containing electrochemical systems is highlighted, proving that this a useful approach for further corrosion inhibitor and active protective coating research. [ABSTRACT FROM AUTHOR]

Zirconium-based conversion treatment of zinc, aluminium and magnesium oxides have been studied in-situ using ATR-FTIR in a Kretschmann geometry. This set-up was coupled to an electrochemical cell, which allowed to obtain chemical and electrochemical information simultaneously as a function of conversion time. This elucidated the strong relation between physico-chemical surface properties and zirconium-based conversion kinetics. Whereas the surface hydroxyl density of zinc and aluminium increased during conversion, magnesium (hydr)oxide was shown to dissolve in the acid solution. Due to this dissolution, strong surface alkalization can be expected, explaining the rapid conversion kinetics. AES depth profiling was used to determine the final oxide thickness and elemental composition. This confirmed that magnesium is most active and forms a zirconium oxide layer approximately 10 times thicker than zinc. On the other hand, the presence of zirconium oxide on aluminium is very low and can be considered as not fully covering the metal oxide. Additionally, the converted oxide chemistry was related to the bonding mechanisms of amide functionalized molecules using ATR-FTIR and XPS. It was shown that inclusion of zirconium altered the acid-base properties, increasing the substrate proton donating capabilities in case of magnesium oxide and increasing hydrogen bonding and Bronsted interactions due to increased surface hydroxide fractions on zinc and aluminium substrates. [ABSTRACT FROM AUTHOR]

Highlights: [•] Transients are identified effectively through Hilbert spectra of electrochemical current noise. [•] Transient analysis reveals local frequency characteristics of electrochemical current noise. [•] Corrosion inhibition can be effectively analysed by electrochemical noise using transient analysis. [ABSTRACT FROM AUTHOR]

Abstract: The local electrochemical reactivity of high purity copper as a function of the grain orientation in the microstructure has been investigated. The different crystal orientations were determined by means of Electron backscatter diffraction (EBSD) followed by in-situ Scanning electrochemical microscopy (SECM) measurements operating in feedback mode across the very same copper surface. With this procedure it is possible to characterize in-situ the reactivity of selected grains in the polycrystalline microstructure of the copper. The study is focused on monitoring differences in the electrochemical response on <001>//ND and <111>//ND oriented grains. The behaviour of these selected orientations was studied under two surface conditions: passive state of copper after the formation of an anodic oxide layer, and corrosion or active state of the copper by immersion in chloride solution. In the case of the passivated copper it was observed that the grain with an orientation closer to <111>//ND shows a lower reactivity compared to the grain where the orientation is nearer to <001>//ND, which confirmed that grain orientation has an influence on the electrochemical reactivity of the passive layer formed on the metal. It was found that for the copper in the active state, the reactivity of a <111>//ND oriented grain is higher when compared to a <001>//ND oriented grain, which is contrary to the expected behaviour. This discrepancy could be explained by possible neighbouring effects between both grains. [Copyright &y& Elsevier]

Abstract: Microbiologically Influenced Corrosion (MIC) is the term used for the phenomenon in which corrosion is initiated and/or accelerated by the activities of microorganisms. MIC is a very serious problem for the ship industry as it reduces structural lifetime in combination with safety risks for crewmembers or inspection personal and increases maintenance costs. This review aims to focus on the importance and mechanisms of MIC in ship ballast tanks (SBTs). First section presents a literature review of general aspects of ballast tanks: structural properties including predominant environmental conditions. Second section summarizes the fundamental corrosion mechanisms within SBTs from an electrochemical point of view. Third section links microbial corrosion mechanism with electrochemical processes summarizing types of microorganisms, mechanisms of MIC and possible triggers for biofilm formation within this enclosed environment. For this an integral model, linking environmental parameters such as oxygen concentration, corrosion rate, nutrient availability and the microbial species of this environment is introduced in this paper. Fourth section gives an outlook on surface treatment and coating application in SBT. The last section considers the practical aspects of MIC detection and possible counterstrategies for engineers/operators and inspection personal. This paper gives a comprehensive overview of MIC processes in ship ballast tanks addressing engineers, equipment manufacturers and operators by offering practical solutions for an appropriate SBT management. [Copyright &y& Elsevier]

Highlights: [•] Hilbert spectra allow selection of instantaneous frequencies of corrosion phenomena. [•] Advanced data analysis distinguishes valuable frequency information from artefacts. [•] Advanced data analysis prevents domination of the analysis by the largest transient. [•] Improved definition of frequency characteristics of localized corrosion mechanisms. [ABSTRACT FROM AUTHOR]

Highlights: [•] SKPFM and FE-EPMA for a modified aluminium brazing sheet were performed. [•] Cross-sectional electrochemical properties of the material were measured. [•] Cross-sectional variation of microstructural chemistry was investigated. [•] The electrochemical responses were correlated to the microstructural features. [•] A solution for corrosion protection enhancement of the material was proposed. [ABSTRACT FROM AUTHOR]

Abstract: A quasi in situ method using a specially developed holder is presented to follow electrochemically induced microstructural changes on a nanometre scale using analytical transmission electron microscopy (TEM). By following a specific specimen area after repeated exposure to oxygen bubbled through aqueous HCl of pH=3, de-alloying of a grain-boundary precipitate of ∼200nm was observed by monitoring the changes in the EELS copper L2,3-edge and EFTEM elemental maps. These results, supporting the existing models of de-alloying of copper rich precipitates in aluminium alloys, demonstrate the effectiveness of the quasi in situ specimen holder for analytical TEM studies of corrosion. [Copyright &y& Elsevier]

Abstract: Macro- and micro-electrochemical properties of clad and core surfaces of a modified AA4xxx/AA3xxx brazing sheet material, before and after brazing, have been evaluated and compared. By scanning Kelvin probe force microscopy (SKPFM), the Volta potential distribution over the brazed and non-brazed clad surfaces was measured. The changes in the Volta potential maps were correlated to the macro-electrochemical responses of the surfaces and the microstructural features that evolve as a result of brazing. By performing potentiodynamic polarization experiments and microscopic analysis of the corroded surfaces and cross sections, the suitability of SKPFM analysis for corrosion performance prediction of the aluminium brazing sheet material in a sea water acidified accelerated test (SWAAT) environment was confirmed. Considering the purity of Si phase in the structures of both brazed and non-brazed material, it is suggested that Si can be applied as a reliable local reference in both structures to compare the changes in Volta potential differences as the result of different heat treatments of aluminium brazing sheet. Increasing the copper content of the re-solidified clad material as a result of brazing treatment was found to increase the Volta potential of the matrix which in turn reduces the cathodic protection power of the re-solidified clad material towards the core material. [Copyright &y& Elsevier]

Abstract: Hilbert spectra, calculated with the Hilbert–Huang transform, are presented here as an analysis technique for the characterization of electrochemical noise data in corrosion studies. A highly detailed decomposition of the original current and potential data is provided in time and frequency simultaneously. Results on the decomposition of individual transients into their instantaneous frequencies at each moment in time are presented for five different corrosion processes: AISI304 in HCl solutions at different concentrations and AISI304 as well as mild steel in a 3wt.% NaCl solution. The results demonstrate the potential of this technique to identify and distinguish different corrosion mechanisms. [Copyright &y& Elsevier]

Abstract: Electrochemical current and potential noise signals in many cases exhibit a DC drift that should be removed prior to further data analysis. The theoretical ability of wavelet analysis and empirical mode decomposition to effectively remove only the DC drift component is evaluated based on their mutual performance for the first time. The correlation coefficient between individual signals after both trend removal techniques proved to be superior compared to the correlation coefficients between these and the signals after moving average, polynomial and linear trend removal. The residual power of these signals was compared and again the two time–frequency methods acknowledged their theoretical ability of removing only a well-defined part of the data. [Copyright &y& Elsevier]

Abstract: Re-solidification of an AA4XXX cladding, particle formation, distribution and chemical composition in a modified AA3XXX core material before and after brazing was investigated. The cathodic and anodic electrochemical responses of the materials were investigated and correlated to the microstructural changes due to the brazing process. It is found that brazing causes copper accumulation in the eutectic phase which has resulted in a 50mV increase in the corrosion potential and inter-granular corrosion (IGC) susceptibility of the re-solidified clad material. Formation of α-Al(Fe–Mn)Si particles on the surface of the brazed material was found to increase the cathodic reactivity of the surface. [Copyright &y& Elsevier]

Abstract: A combinatorial matrix of four rare earth chlorides has been evaluated for the corrosion inhibition of aluminium alloy AA2024-T3 in aqueous solution. Two electrochemical techniques, potentiodynamic polarisation (PP) and electrochemical impedance spectroscopy (EIS), were used to evaluate AA2024-T3 corrosion in 0.1M NaCl with the addition of 10−3 M of rare earth chloride mixtures at time periods up to 18h. PP experiments showed rare earth inhibition of up to 98% within the first hour and thereafter corrosion rates were steadily decreased. The open-circuit potential (OCP) of AA2024-T3 decreased as a function of time for all solutions indicating predominantly cathodic inhibition. However, differing trends in the OCP were observed during PP and EIS experiments and are discussed in terms of likely time-dependent mechanisms. A comparative study of optimisation models indicated the best mixture at 10−3 M total inhibitor concentration was predicted to be 72% cerium (Ce) and 28% (praseodymium (Pr)/lanthanum (La)) ions. As the amount of Ce is decreased from this level the corrosion inhibition is predicted to decrease also, regardless of what other rare earths (La, Pr and Nd) are added alone or in combination. Individually, La, Pr and Nd show varying levels of corrosion inhibition activity, all of which are inferior to that of Ce. If Ce is absent entirely, then a mixture of approximately 50% Pr and 50% Nd is predicted to be preferred. This is one of the first applications of combinatorial design for the optimisation of corrosion inhibitor mixtures. [Copyright &y& Elsevier]

Abstract: The most common accelerated corrosion test used for aluminum brazing sheet is the Sea Water Acidified Accelerated Test (SWAAT). However, still some ambiguity exists, indicating that the test suffers from significant scattering of the results. Keeping the climatic parameters constant, this study elucidates how the variations of the test results are material dependent. Applying a new statistical reliability evaluation and interpretation method, it was shown that the SWAAT test is valid for product performance comparison purposes. Comparing the corrosion mechanism and morphology of attack it was proved that the SWAAT performance of the material can be reflected in potentiodynamic responses. [Copyright &y& Elsevier]

Abstract: In this paper a self-healing anticorrosive organic coating based on an encapsulated water reactive organic agent is presented. A reactive silyl ester is proposed as a new organic reactive healing agent and its synthesis, performance, incorporation into an organic coating and evaluation of self-healing capabilities is described. Such silyl esters are good candidates to be used in self-healing anticorrosive organic coating systems since they present the capability to react with water/humidity and metallic substrates, removing thus the need of presence of a crosslinker or catalyst in the system unlike traditional encapsulated approaches. In order to prove the self-healing ability and reactivity of the presented silyl ester encapsulated system, Fourier transform infrared spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and scanning vibrating electrode technique (SVET) were used, showing the high capability of these techniques to be used in the development and evaluation of self-healing anticorrosive organic coatings and the good results in corrosion protection offered by the proposed silyl ester healing agent. [Copyright &y& Elsevier]