•A hybrid coating with duplex-layered structure was developed on magnesium.•The hybrid coating contains effective corrosion inhibitor of 3-methylsalicylate.•The corrosion performance of hybrid ...coatings was studied by EIS.•Active corrosion protection mechanism by inhibitor was characterized by SVET.
A hybrid PEO-epoxy coating was developed for magnesium. A highly-efficient corrosion inhibitor (3-methysalicylate) was impregnated into the anodized layer, which was sealed by an epoxy layer through dip-coating process. Influence of dip-coating parameters on coating properties was investigated. The corrosion performance was evaluated through general and localized electrochemical techniques. As a result, the epoxy layers registered superior resistance, whereas the anodized layer suppressed corrosion expansion. Longer immersion and triple-dipping favored the production of better sealed epoxy layer. The active protection mechanism was achieved by suppression the re-deposition of detrimental impurity and/or adsorption upon the exposed surface from incorporated inhibitor.
In this work, antifouling copper-containing PEO coatings were produced on zinc-aluminized steels and their antifouling properties in circulating seawater were tested at the Hydrobiological Station ...Umberto D'Ancona located in Chioggia (Venice, Italy). The effect of the presence of the copper particles on the localized corrosion properties of the PEO coatings was also investigated in depth. In detail, the PEO-coated samples were produced and characterized in terms of microstructure and phase composition through SEM and XRD analysis. The antifouling properties of the samples were evaluated through stereo-microscope and SEM observations after up to 28 days of immersion and the corrosion properties were analyzed with EIS and SVET tests. The results, besides the successful incorporation of the copper particles into the coatings, evidenced the remarkable antifouling effect of the copper particles which also produced a clear selection in the type of algae that can colonize the samples. Considering the corrosion properties, the copper particles were found to be detrimental, due to the galvanic coupling with the substrate. Considering both results, the copper-containing PEO coating can be suggested only in combination with a topcoat which further increases the corrosion performance.
Despite several studies on Mg-Ca alloys as bone implants, the understanding of its early degradation in the first hours of immersion is still lacking. To overcome this gap, advanced localized ...electrochemical techniques were used to study the corrosion onset of Mg-2Ca alloy 2 h upon immersion. The presence of the nobler β-phase induced Mg dissolution from the matrix, an event supporting the positive response of osteoblast stem cells. This, together with apatite precipitation within the corrosion layer highlights the potential of Mg-2Ca for bone implants. The data gathered in this work contribute to tailoring the design of new Mg-Ca alloys.
Display omitted
•Degradation events that can modulate material-cell interaction were observed during the first 2 h of immersion.•The potential difference between less noble Mg matrix and more noble Mg2Ca guided the onset of degradation.•Mg dissolution from the matrix, induced by the nobler β-phase, can be related to an increase in fibroblasts viability.•Alkaline pH spreading in a range of ~50 µm from the β-phases can influence cells’ adhesion on the surface
Additions of 1 wt.% Ca were made to Zn (Zn-1Ca) to generate favourable chemical conditions during corrosion for enhanced performance of phosphate inhibitors. Zn-1Ca displayed a reduced corrosion rate ...in 0.17 M NaCl measured using the Scanning Vibrating Electrode Technique and polarisation. In-situ timelapse microscopy and SEM-EDS demonstrated that intermetallic CaZn13 preferentially corroded releasing Ca2+ that increased corrosion product precipitation, cathodically deactivating the system. 1 × 10−3 mol dm−3 phosphate additions to 0.17 M NaCl decreased the corrosion rate of Zn and Zn-1Ca. Inhibition was greater for Zn-1Ca where uniform precipitation of mixed metal phosphates produced anodic and cathodic inhibition.
•Addition of 1 wt.% Ca to Zn (Zn-1Ca) reduced its corrosion rate compared to Zn.•Distributed CaZn13 phases are preferentially corroded producing Ca2+ ions.•Zn-1Ca had increased corrosion products, cathodically deactivating the system.•Additions of phosphate ions inhibit the corrosion of both Zn and Zn-1Ca.•Inhibition is increased for Zn-1Ca due to precipitation of mixed metal phosphates.
The damage to a metal is significantly enhanced when simultaneously exposed to a corrosive solution and a cyclic mechanical stress. However, decoupling the contributions from each damage mechanisms ...is difficult. Localised electrochemical techniques, in particular scanning electrochemical microscopy (SECM), scanning electrochemical cell microscopy (SECCM), scanning kelvin probe force microscopy (SKPFM), and scanning vibrating electrode technique (SVET), can be advantageous when determining corrosion fatigue damage mechanisms and local phenomena, such as the transition between a corrosion pit and a fatigue crack. The recent corrosion fatigue literature is reviewed to highlight the usefulness of each localised electrochemical technique and how they can contribute to advancing the corrosion fatigue field.
Display omitted
•Synthesis and characterization of three Schiff base derivatives for pitting corrosion inhibition of 304 stainless steel•Enhanced pitting corrosion resistance in neutral chloride solution was ...provided by these inhibitors•Inhibition efficiency increased with the concentration of sodium (E)-4-(nitrobenzylidene-amino)-benzoate up to 10 mM•SVET revealed the inhibitive action of the Schiff base on both metastable pit nucleation and stable pit growth regimes•Metal-inhibitor interaction happened upon breakdown of the chromium-enriched passive surface releasing iron ions
Three newly synthesized Schiff base derivatives, sodium (E)-4-(nitrobenzylideneamino)-benzoate (SNBB), sodium (E)-4-(benzylideneamino)-benzoate (SBB), and sodium (E)-4-(hydroxybenzylideneamino)-benzoate (SHBB) were investigated as pitting corrosion inhibitors for 304 stainless steel in neutral 0.1 M NaCl. Potentiodynamic polarization evidenced major shifts in pitting potential to more positive values with increasing inhibitor concentration. The scanning vibrating electrode technique (SVET) imaged metastable pitting in 0.1 M NaCl, but not in the presence of the inhibitor, indicating that it prevented pit nucleation. The inhibition performance was established under anodic polarization conditions, because only minute local anodic activity due to metastable pit formation could be observed when the steel was exposed to SNBB-containing solution, whereas the metal would undergo pit propagation at the same potential in the inhibitor-free solution. X-ray photoelectron spectroscopy (XPS) analysis evidenced chromium enrichment at weak points (pores) of the passive film at anodic polarization condition where sudden release of Fe cations is possible. In this way, the SNBB molecules will migrate to these sites to react with the Fe ions and form a chelate compound which will deposit finally at those sites and plug them, whereas no effect occurred at the open circuit potential (OCP).
The electrochemical corrosion of ductile pipes (DPs) in drinking water distribution systems (DWDS) has a crucial impact on cement-mortar lining (CML) failure and metal release, potentially leading to ...drinking water quality deterioration and posing a risk to public health. An in-situ scanning vibrating electrode technique (SVET) with micron-scale resolution, microscopic scale detection and water quality analysis were used to investigate the corrosion behavior and metal release from DPs throughout the whole CML failure process. Metal pollutants release occurred at three different stages of CML failure process, and there are potential risks of water quality deterioration exceeding the maximum allowable levels set by national standards in the partial failure stage and lining peeling stage. Furthermore, the effects of water chemistry (Cl−, SO42−, NO3−, and Ca2+) on corrosion scale growth and iron release activity, were investigated during the CML partial failure stage. Results showed that the CML failure process in DPs was accelerated by the autocatalysis of localized corrosion. Cl− was found to damage the uncorroded metal surface, while SO42− mainly dissolved the corrosion scale surface, increasing iron release. Both the oxidation of NO3− and selective sedimentation of Ca2+ were found to enhance the stability of corrosion scales and inhibit iron release.
Protection performance of zinc-rich coatings is generally ascribed to sacrificial anode protection and physical shielding derived from corrosion products, neglecting the contribution of zinc fillers’ ...self-corrosion. This work clarifies the fact that self-corrosion of zinc powders can induce active protection behaviour of zinc-rich coatings by chemical conversion for corrosive media, firstly building “chemical shielding” function, and then enhancing physical shielding protection during the formation of zinc corrosion products. Chemical and physical shielding effects enhance shielding performance of zinc-rich coatings and extend its cathodic protection life. The result is beneficial to enrich protection theory of zinc-rich coatings.
•Active protection of zinc-rich coatings is studied besides cathodic protection.•Self-corrosion of zinc actively traps corrosive media by chemical conversion.•Chemical conversion for oxygen dominates the “chemical shielding” function.•Chemical shielding function is the premise of enhanced physical shielding effect.•Chemical and physical shielding effects jointly endow active protection.
In situ localized electrochemical activity in the Al/Cu galvanic pair at the corrosion potential in an aggressive chloride electrolyte was investigated, along with the effect of the organic ...inhibitors 2-mercaptobenzimidazole (MBI) and octylphosphonic acid (OPA) on arresting the corresponding corrosion processes. Scanning electrochemical microscopy (SECM) and the scanning vibrating electrode technique (SVET) were used to discern local anodic and cathodic sites at the surface. The electrochemical activity in the galvanic pair was greatly reduced when the copper surface was covered with an MBI-containing film. SECM was successfully applied to visualize spatially resolved differences in local electrochemical activity related to the inhibitor action.
Display omitted
•Localized electrochemical activity in the Al/Cu galvanic pair was monitored in situ at the corrosion potential.•SECM and the SVET were used to discern local anodic and cathodic sites at the interface.•The electrochemical activity in the Al/Cu pair was greatly reduced when the Cu surface was covered with a 2-MBI film.•Measurements of key redox species, oxygen and hydrogen, as well as ion fluxes, were performed real-time and in situ.
Display omitted
•Self-healing ability based on hydrogen bonds of biobased coatings applied on aluminum alloy.•SVET/SIET and LEIS confirm the self-healing property of coating with higher polyester ...content.•Higher flexible segment ratio favors effective corrosion protection and self-healing effect.•Efficient, environmentally, and active protection of aluminum-based surfaces.
Biobased polyurethane coatings derived from vegetable oils, with 2 different compositions, were prepared and applied on the AA1200 aluminum alloy to confer corrosion protection. The influence of the ratio between the polyester (flexible segment) and the prepolymer (rigid segment) was investigated. Infrared spectroscopy studies evidenced the difference between the areas of the bands (NH) and optical and scanning electron microscopy evidenced the morphological features of the coating surface before and after immersion in aggressive medium. The barrier properties and anti-corrosion performance of the coatings were evaluated by electrochemical impedance spectroscopy and the results revealed an increase of impedance over the immersion time. Localized corrosion studies confirmed the self-healing effect in coatings formulated with the highest content of polyester.
PDF
