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.
Novel Fe–Cr SS alloys were fabricated by alloying with 0, 0.10 and 0.20 wt-% Sn respectively to investigate the effect of the Sn addition on the microstructure, passive characteristics and localized ...corrosion behavior in chloride medium at room temperature. The advanced scanning micro-electrochemical techniques along with the traditional electrochemical methods were used for in-depth investigations. Potentiodynamic and potentiostatic test results exhibited that the addition of Sn in SS alloys increased the resistance against pitting corrosion in NaCl medium. The acquired dynamic impedance data confirmed the effective electrochemical stability of the alloy SS3 (SS with 0.20 wt-% Sn) at applied anodic potential, suggesting the presence of a compact and stable passive film in Sn containing alloys, which contributed to their improved localized corrosion resistance in chloride solution. The scanning electrochemical microscopic results corroborated that the alloy SS3 remained stable even after 24 h of exposure and displayed no noticeable surface heterogeneity. A reduced anodic current density in scanning vibrative electrode technique mapping images was observed even after 24-h of exposure in alloy SS3 compared to other samples, indicating that the anodic metal dissolution was successfully obstructed by forming a compact and dense passive film on this alloy.
The galvanic corrosion of the Q-phase/Al couple in 0.1 M NaCl solutions has been studied using the scanning vibrating electrode technique (SVET), the scanning ion-selective electrode technique (SIET) ...and energy dispersive X-ray spectroscopy (EDX). The galvanic corrosion of the Q-phase/Al couple was found to be dependent on pH and immersion time. Current density maps obtained by SVET shows that the anodic oxidation processes emerge from Al in a localized manner in pH 2 and 6 solutions but is initiated in a uniform manner in pH 13 solution, whereas, the cathodic processes are more homogeneously distributed over the Q-phase at pH 2, 6 and 13. It is seen that the Q-phase remains cathodic in the Q-phase/Al couple in acidic, neutral and alkaline solutions indicating that the galvanic polarity of the Q-phase is independent of pH. The effect of the galvanic corrosion was largest at pH 2 and 13 compared to pH 6. The pH map obtained by SIET indicates that the galvanic activity of the Q-phase/Al couple proceeds via heavy alkalization of the Q-phase surface with the generation of appreciable amounts of OH− ions. The enrichment of Cu indicated by EDX is responsible for the observed cathodic activity of the Q-phase in the Q-phase/Al couple.
In this study, sol-gel technique was used to prepare Ca10(PO4)6(OH)2 (HA) coating on Micro arc oxidation (MAO) coated degradable Mg matrix composites to reduce their primary degradation and enhance ...biocompatibility in simulated body fluid (SBF). The microstructure and phase composition were analyzed using Scanning electron microscopy (SEM) and X-ray diffraction (XRD). Potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were used to examine their global corrosion behavior. Scanning vibrating electrode technique (SVET) and local electrochemical impedance spectroscopy (LEIS) were used to evaluate the potential distribution and impedance differences among the different zones. The global measurements show that the sol-gel/MAO coating has much better corrosion resistance than MAO coating, since the sol-gel coating sealed the pores produced in the MAO process. The post-corrosion microstructures of sol-gel/MAO composite coating on magnesium alloy are in agreement with the results of local corrosion performances. The corrosion mechanism is explained by proposing an empirical model.
•Sol-gel/MAO composite coating was prepared on Mg alloy to improve corrosion resistance.•SVET and LEIS were used to study the local corrosion behavior of Sol-gel/MAO coating.•A phenomenological model for the mechanism of the localized corrosion was proposed.
The corrosion mechanism of two AA2024-T3/graphite galvanic couples, with different electrodes area ratio, was studied in 12.00 mM NaCl solution using the Scanning Vibrating Electrode Technique (SVET) ...and the Scanning Ion-Selective Electrode Technique (SIET). Both techniques were used, quasi-simultaneously, to monitor the current density distribution and the pH associated to the corrosion process occurring in the galvanic couples. The morphological features and the elemental composition of the electrodes' surfaces, after 20 h of immersion, were analysed by Scanning Electron microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDX). The results show that the area of the electrodes in the galvanic couple significantly influences the corrosion mechanism. For the couple, with the highest AA2024/graphite area ratio (M1), both anodic and cathodic processes developed on the alloy surface, resulting in localised corrosion (trenching of the matrix around intermetallics) at the cathodic zones as detected by SVET and SIET. A more generalised anodic dissolution of AA2024 (corrosion of the matrix and grain boundaries) was observed for the sample with the lowest area ratio (M2), however.
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•Two AA2024/graphite model galvanic couples with different area ratio were studied.•Complementary use of SVET/SIET and SEM-EDX revealed distinct corrosion mechanisms.•AA2024 of M1 (anod/cat ratio = 10): trenching of the Al matrix around Cu-rich IMPs.•Alloy of M2 (anod/cat ratio = 1.5): generalised dissolution (matrix, grain boundaries).•Trenching/IGC were respectively referred to the more/less active breakdown potentials.
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•A novel dendrimer like mesoporous silica nanocontainer (DMSN) was prepared by the emulsion method.•The DMSN containing 8- hydroxyquinoline act as an inhibitor at the onset of ...corrosion.•The BET surface area of DMS nanoparticles is 1322.4 m2g-1, the pore volume is 1.39 cc/g and pore diameter is ∼ 4.2 nm.•The SVET technique confirmed the superior corrosion-resistant and self-healing properties of the DMSN coating.•The artificially defeated DMSN coating was completely passivated to 1200 min of immersion assessed by the SIM technique.
A new generation smart self-healing coating possessing both passive matrix functionality and rapid response to local changes in the environment is of great industrial importance. In the present work, a stimulus responsive smart self -healing anticorrosion coating was developed based on acrylic resin, incorporated with Dendrimer like Mesoporous Silica Nanoparticles (DMSN) loaded inside with 8-hydroxyquinoline inhibitor. FESEM and TEM analysis showed that the dendrimer like mesoporous silica (DMS) nanoparticles synthesized were of spherical and fibrous form with size less than 200 nm. The BET surface area, pore volume and average pore diameter of the nanoparticles were found to be 1322.4 m2 g−1, 1.39 cc/g and 4.2 nm respectively. The corrosion protection performance of the coatings was evaluated via Electrochemical Impedance Spectroscopy (EIS) in 3.5 % NaCl. The acrylic coating with dendrimer like silica nano containers showed improved and long-term corrosion protection than the coating without nano containers. The smart self-healing property of the coating was studied by Scanning Vibrating Electrode Technique (SVET). The SVET showed a smartness activity of DMSN by release of inhibitor triggered by corrosion phenomena in the defect area. Further, to reassert the smartness of the coating, impedance mapping of the surface was carried out at a fixed frequency.
•ATAT in smart microcontainers was used to develop anticorrosion coatings for AA20204-T3.•The release of ATAT from microcontainers protected the oxide layer of the substrate.•Direct addition of ATAT ...in the epoxy coating formula causes the loss of inhibition of ATAT.
Using organic coatings with high barrier property in combination with active corrosion protection can improve corrosion protection of aluminum alloys. In this work, 3-Amino-1,2,4-triazole-5-thiol (ATAT) was used as organic inhibitor in developing anticorrosion coatings for AA2024-T3. The delivery of ATAT was achieved by using smart microcontainers with ATAT that respond to pH change caused by corrosion reaction at the coating-substrate interface. The developed coatings with low concentration of smart microcontainers showed a slight reduction of barrier properties, but gained active corrosion protection capability. The resistance of the coatings reduced the rate of penetration of corrosive species and the active corrosion protection stopped the damaging reactions at the coating-substrate interface. The active corrosion protection is also evident in the case of coatings with mechanical damages, when the barrier property of coatings is compromised. Waterborne coatings with smart microcontainers for delivery of ATAT exhibited enhanced performance for corrosion protection of AA2024-T3.
This study delved into the potential application of Platanus acerifolia leaf extract (PALE) as an environmentally benign corrosion inhibitor. Evaluation of corrosion inhibition was conducted using ...electrochemical methods, field emission scanning electron microscopy equipped with energy dispersive spectrometer. The results reveal that PALE offers efficient protection for Q235 steel across the temperature range of 298 K–318 K, achieving a maximum corrosion inhibition efficiency of approximately 93%. Furthermore, Density functional theory (DFT) calculations and molecular dynamics (MD) simulations were performed to elucidate the spontaneous and stable adsorption of PALE molecules onto the surface of Q235 steel. This adsorption impedes the diffusion of corrosive substances towards the steel surface, thereby endowing Q235 steel with robust corrosion resistance.
This study aimed to systematically investigate the heterogeneous microstructures and corrosion resistance of the EH36 welded joint fabricated through vertical electro-gas welding (VEGW) at a high ...heat input (about 308 kJ/cm). In addition to the conventional electrochemical measurement techniques, the scanning vibrating electrode technique (SVET) was also employed to examine the localized corrosion behavior of the welded joint. Our results suggested that, the welded joint consisted of four different distinguishable microstructures, which were the coarse-grain heat affected zones, fine-grain heat affected zones, incomplete heat affected zone and weld metal zones. Meanwhile, these different zones were easily distinguished in the SVET map. Besides, the WM showed positive corrosion resistance compared with the other regions, except in the root layer. The highest Rct value (226.6 Ω·cm2) was obtained in WM of the top layer, and the most negative corrosion resistance appeared in BM of the middle layer. Additionally, results of SVET current density distribution map, micro-hardness and Charpy impact test also confirmed the varying tendency of the heterogeneous microstructures of the welded joint. Finally, it was discovered that the corrosion resistance in various regions of this VEGW joint was determined by its microstructure and chemical composition.
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