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•Novel cerium tri(bis(2-ethylhexyl)phosphate) corrosion inhibition additive.•High compatibility with epoxy coatings.•Increased corrosion resistance of coated steel panels.•Corrosion ...healing in defects.•Synergistic cathodic and anodic corrosion inhibitors.
In this work cerium tri(bis(2-ethylhexyl)phosphate) (Ce(DEHP)3) particles were used as anti-corrosion pigments in epoxy coatings applied on steel coupons. The composition of the corrosion inhibitor was designed to introduce pH-stimulated corrosion healing in the coating. Electrochemical Impedance measurements demonstrated very high compatibility between the inhibitor and the coating, and effective and stable corrosion protection. Localized electrochemical measurements carried out using the Scanning Vibrating Electrode Technique and Localised Electrochemical Impedance revealed efficient corrosion inhibition of steel exposed in artificially damaged coatings.
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.
In the present work corrosion inhibition in microdefects of protective coatings on magnesium alloy was studied by SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective ...electrode technique) in 0.05
M NaCl. Mg
2+- and pH-selective microelectrodes were developed to be used by SIET. The microelectrodes were characterized from the standpoint of properties important for corrosion applications, aiming at the reliable functioning during measurements. The combination of SVET and SIET demonstrated to be a useful approach to investigate the inhibition of corrosion processes in microdefects on coated AZ31. In this paper the corrosion inhibiting properties of 1,2,4,-triazole, F
− and Ce
3+ on AZ31 alloy were analyzed. According to the results, 1,2,4-triazole in concentration of 0.01
M showed the highest inhibition efficiency among the studied inhibitors and was able to prevent the increase of pH in the corroding defects, by keeping the corrosion activity on a very low level during the tested immersion period.
This work aims at developing a new complex anticorrosion protection system for ZK30 magnesium alloy. This protective coating is based on an anodic oxide layer loaded with corrosion inhibitors in its ...pores, which is then sealed with a sol–gel hybrid polymer. The porous oxide layer is produced by spark anodizing. The sol–gel film shows good adhesion to the oxide layer as it penetrates through the pores of the anodized layer forming an additional transient oxide–sol–gel interlayer.
The thickness of this complex protective coating is about 3.7–7.0
μm. A blank oxide–sol–gel coating system or one doped with Ce
3+ ions proved to be effective corrosion protection for the magnesium alloy preventing corrosion attack after exposure for a relatively long duration in an aggressive NaCl solution.
The structure and the thickness of the anodized layer and the sol–gel film were characterized by scanning electron microscopy (SEM). The corrosion behaviour of the ZK30 substrates pre-treated with the complex coating was tested by electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET), and scanning ion-selective electrode techniques (SIET).
•Localized electrochemical techniques are applied to study the corrosion of Al2CuMg phase.•Al2CuMg phase reveals high level of self-dissolution.•The alkalization of S phase can lead to the trenching ...of Al matrix around it.
The coupling of pure Al, Cu and Mg wires and the coupling of Al2CuMg intermetallic rod and Al wire were used to study the corrosion process of Al2CuMg phase particles in 2024-T3 aluminium alloy, by means of scanning vibrating electrode technique (SVET) and scanning ion-selective electrode technique (SIET). The results show the preferential dissolution of Mg in the coupling of Al, Cu and Mg. Al2CuMg was found to show self-dissolution when coupled with Al, rather than anodic dissolution. According to the results, a mechanism of early corrosion of S phase in AA2024-T3 is proposed.
This work contributes to the development of new feedback-active anticorrosion systems. Inhibitor-doped hydroxyapatite microparticles (HAP) are used as reservoirs, storing corrosion inhibitor to be ...released on demand. Release of the entrapped inhibitor is triggered by redox reactions associated with the corrosion process. HAP were used as reservoirs for several inhibiting species: cerium(III), lanthanum(III), salicylaldoxime, and 8-hydroxyquinoline. These species are effective corrosion inhibitors for a 2024 aluminum alloy (AA2024), used here as a model metallic substrate. Dissolution of the microparticles and release of the inhibitor are triggered by local acidification resulting from the anodic half-reaction during corrosion of AA2024. Calculated values and experimentally measured local acidification over the aluminum anode (down to pH = 3.65) are presented. The anticorrosion properties of inhibitor-doped HAP were assessed using electrochemical impedance spectroscopy. The microparticles impregnated with the corrosion inhibitors were introduced into a hybrid silica−zirconia sol−gel film, acting as a thin protective coating for AA2024, an alloy used for aeronautical applications. The protective properties of the sol−gel films were improved by the addition of HAP, proving their applicability as submicrometer-sized reservoirs of corrosion inhibitors for active anticorrosion coatings.
pH-sensitive calcium carbonate microparticles were loaded with polyethyleneimine (PEI), a corrosion inhibitor, and used as anti-corrosion additive in epoxy coatings applied on carbon steel. The ...presence of PEI in the CaCO3 particles was confirmed by Fourier-Transform Infra-Red Spectroscopy (FTIR) and the loading was quantified by Thermal Gravimetric Analysis (TGA). The protective performance of the modified coatings applied on carbon steel was investigated by Electrochemical Impedance Spectroscopy (EIS) and the results evidenced that the modified coatings provided high corrosion protection and very stable barrier properties over time. The self-healing ability was investigated by Localized Electrochemical Impedance Spectroscopy (LEIS) and by the Scanning Vibrating Electrode Technique (SVET) on coated samples artificially damaged and immersed in NaCl solutions. The results revealed an important corrosion inhibition effect, stable over time, in the coatings modified with the PEI loaded particles. The corrosion inhibition effect involves the dissolution of the calcium carbonate microparticles in the local acid media formed at the anodic sites and subsequent release of the corrosion inhibitor that forms a protective film on the steel surface.
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•Nanostructured pH sensitive CaCO3 particles were successfully loaded with Polyethyleneimine (PEI).•Electrochemical impedance spectroscopy demonstrated the high compatibility of the PEI loaded particles with epoxy coatings.•Localized electrochemical tests in presence of defects evidenced corrosion healing ability.
Aluminium-rich metallic coated steels were found to be especially sensitive to cut-edge corrosion in various climates for both painted and unpainted material. The aim of this work is to study the ...corrosion process in the cut-edge and the effect of aluminium presence in the metallic coating. In this frame, painted zinc metallic coated steel samples with different amount of Al were studied by scanning vibrating electrode technique coupled with a scanning ion-selective electrode technique (SVET/SIET). SVET and micro-potentiometric pH measurements were performed quasi simultaneously. The experiments were performed in continuous immersion in 0.05
M NaCl. As a result, differences in pH and activity for the studied systems could be linked to the presence of aluminium. Formed corrosion products were identified by Raman spectroscopy, FTIR spectroscopy, SEM-EDX and by analyzing the local pH in the area of precipitation.
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•Microstructural studies of 2524-T3 Al alloy welded by FSW were performed.•Corrosion resistance of the base material and nugget zone was assessed by EIS and SVET.•Base material and ...nugget zone possess a cathodic behaviour.•The influence of FSW process on FCG curves in nugget and base material was studied.
The corrosion processes and its influence on the FCG curves of the 2524-T3 alloy joined by FSW was studied in the nugget and BM. To assess the corrosion process, SVET, pH micro-potentiometry and EIS were used. The localised corrosion results showed similar BM and nugget zone electrochemical behaviour, while the TMAZ/HAZ region was electrochemically the weakest zone, susceptible to anodic dissolution. The FSW process and saline environment was found to modify the BM and nugget FCG resistance, being more detrimental for the BM due to the primary IM particles that are not present in the nugget, making it chemically more homogeneous.
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.
