•Copper protection in 3.5 wt.%NaCl by 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol (PyODT).•High inhibitive efficacy of PyODT on Cu corrosion was reached at long exposure.•A uniform and compact inhibitor ...film was formed on copper surface.•Interaction between Cu and PyODT proceeded through thiol and oxadiazole groups.•Machine learning algorithms and Raman data were firstly applied in corrosion study.
An oxadiazole derivative with functional groups favouring its adsorption on copper surface, namely 5-(4-pyridyl)-1,3,4-oxadiazole-2-thiol, has been explored as potential inhibitor of copper corrosion in 3.5 wt.% NaCl. Electrochemical evaluation by electrochemical impedance spectroscopy, potentiodynamic polarization and SVET reveals high inhibition efficiencies. Surface microscopy inspection and spectroscopic analysis by Raman, SEM-EDX and XPS highlight the formation of a compact barrier film responsible for long-lasting protection, that is mainly composed of the organic molecules. Machine learning algorithms used in combination with Raman spectroscopy data were applied successfully for the first time in corrosion studies to allow discrimination between corroded and inhibitor-protected metal surfaces. Quantum Chemistry calculations in aqueous solution and Molecular Dynamic studies predict a strong interaction between copper and the thiol group and an extensive coverage of the metal surface, responsible for the excellent protection against corrosion.
Display omitted .
•The physico-chemical model of galvanic corrosion AA2024-Ti was developed.•Local corrosion effects and formation of porous corrosion products were considered.•The diffusion layer for O2 was ...introduced, although convection was not considered.•A qualitative agreement was found between the model and experiment.
This study focuses on the development of a physico-chemical model based on mechanistic and kinetics understanding of the corrosion process in galvanic couple Ti6Al4V-AA2024. Proposed model provides deeper insights at macro level for initiation and propagation of localized corrosion of AA2024 in galvanically coupled multi-material assemblies. The model is able to reveal the localized corrosion, related to heterogeneity of AA2024 microstructure, including local pH changes, the deposition of the reaction products, and emphasizes the important role of AA2024 self-corrosion in galvanic assemblies. The validation of the developed model was performed using relevant data collected by advanced in situ localized techniques.
•Intermetallic compounds Mg2Ca and MgZn2 were successfully fabricated.•Real-time in situ monitoring of the current density, pH value and Mg2+ concentration of galvanic couples were ...conducted.•Self-forming cathodes on the anode along with anodic reaction were recorded.•Corrosion behavior of intermetallic MgZn2 in Hank’s solution was evaluated.•A mechanism involving galvanic corrosion and corrosion products forming was illustrated.
The purpose of this study is to comparatively investigate on intermetallic compounds Mg2Ca and MgZn2 in galvanic corrosion of magnesium alloy by using real-time in situ monitoring techniques. The results indicated Mg2Ca functioned as an anode with higher anodic current density, higher Mg2+ concentration and higher pH values than the Mg cathode, while MgZn2 worked as a cathode with a cathodic current density, lower Mg2+ concentration and higher pH value than the anodic Mg. The results also suggested a corrosion forming mechanism involving solubility product constant (Ksp) in which Zn-based corrosion products were easier to form than their Mg counterparts.
Since 2010, China's economic growth has stagnated due to an unbalanced regional industrial structure and lack of sufficient qualified technical personnel. A nonlinear autoregressive distributed lag ...(NARDL) model has been used in this study to examine the asymmetric effects of secondary vocational education and training (SVET) and higher vocational education and training (HVET) and their interaction with high-tech industries on economic growth over the period 1980–2020. The findings show that an increase in secondary vocational education and training (SVET) significantly boosts long-term economic growth, while a decrease in secondary vocational education and training (SVET) insignificantly reduces long-term China economic growth. Likewise, the upward change in higher vocational education and training (HVET) promotes and the downward fluctuation in higher vocational education and training (HVET) significantly reduces China's long-term economic growth. The moderating role of secondary vocational education in the impact of high-tech industries on China's economic growth is positive, but not significant. However, higher vocational education plays a significant positive moderating role in high technology industries impact on economic growth. Strategically, the study analysis suggests that economic transition prosperity can be achieved by encouraging higher vocational education and the equal development of high-tech industries in all regions. In addition, this study also proposes to cultivate high-quality talents related to high-tech development and modern industrial innovation and upgrading through higher vocational education, improve productivity, and promote the country's intensive development.
Since 2010, China's economic growth has stagnated due to an unbalanced regional industrial structure and lack of sufficient qualified technical personnel. A nonlinear autoregressive distributed lag ...(NARDL) model has been used in this study to examine the asymmetric effects of secondary vocational education and training (SVET) and higher vocational education and training (HVET) and their interaction with high-tech industries on economic growth over the period 1980-2020. The findings show that an increase in secondary vocational education and training (SVET) significantly boosts long-term economic growth, while a decrease in secondary vocational education and training (SVET) insignificantly reduces long-term China economic growth. Likewise, the upward change in higher vocational education and training (HVET) promotes and the downward fluctuation in higher vocational education and training (HVET) significantly reduces China's long-term economic growth. The moderating role of secondary vocational education in the impact of high-tech industries on China's economic growth is positive, but not significant. However, higher vocational education plays a significant positive moderating role in high technology industries impact on economic growth. Strategically, the study analysis suggests that economic transition prosperity can be achieved by encouraging higher vocational education and the equal development of high-tech industries in all regions. In addition, this study also proposes to cultivate high-quality talents related to high-tech development and modern industrial innovation and upgrading through higher vocational education, improve productivity, and promote the country's intensive development.
In order to study the effect of defects on the corrosion behavior of MAO coatings, global electrochemical method including potentiodynamic polarization (PDP) and electrochemical impedance ...spectroscopy (EIS) was used to measure the corrosion resistance of MAO coatings. Local electrochemical measurements including local impedance spectroscopy (LEIS) and scanning vibrating electrode technique (SVET) were used to study the local corrosion mechanism. The confocal microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe the microstructure and phases of the samples. Results of global electrochemical measurement demonstrate that the scratches cause the reduction of the impedance and the increase of the corrosion current density. LEIS results show the impedance value distribution of the coating with the scratch. With the changes over time, the minimum impedance value of the scratch decreases first and then increases from the third hour. SVET results show the corrosion current density distribution of the scratched coating. The maximum corrosion current density at the scratch increases first and then decreases. The results of local electrochemical measurements show that the corrosion rate at the scratch decreases when the reaction lasted 3 h. Confocal microscopy found that the scratch is expanding with increasing time, and the depth and cross-sectional area of the coating is 5 times deeper and 10 times larger than that of 7075Al with scratch at the first 6 h. The 6-day immersion test proved that the scratch coating still has the protective effect on the substrate. The main corrosion product is Al(OH)3. A physical model reflecting the mechanism of the scratch propagation and the formation of the corrosion product film is proposed.
•Global and local electrochemical corrosion of scratched MAO coating on Al Alloy was studied.•The electrochemical impedance and current distribution of scratches were analyzed by LEIS and SVET.•A phenomenological model for the influence of scratch on the local corrosion of the MAO coated Al alloy was proposed.
Display omitted
•GO with different aspect ratios were prepared and the uniform GO/epoxy composite coatings were fabricated.•Anti-corrosion performance of composite coatings containing GO sheets with ...different aspect ratio were investigated.•Anti-corrosion mechanism of different GO/epoxy composite coatings were studied.•The aspect ratio of GO sheets was a significant factor for enhancing corrosion resistance of GO/epoxy coatings.
Graphene oxide (GO) has a wide application prospect in the field of metal protection due to its good dispersion, chemical activity and physical barrier property. Herein, graphene oxide sheets with different aspect ratio were first prepared by simply controlling the procedure of chemical exfoliation and then used to fabricate GO/epoxy composite coatings. The morphology and structural features of as-prepared GO sheets were characterized by Raman spectroscopy, X-ray diffraction and atomic force microscopy. The dispersion and anticorrosive performances of GO with different aspect ratios incorporated in epoxy-based waterborne composite coatings were investigated by Raman spectroscopic mapping, electrochemical measurements and scanning vibrating electrode technique. The results demonstrated that the different types of GO showed homogeneous dispersion in epoxy resin and GO with higher aspect ratio exhibited larger corrosion protection potential. Furthermore, the anti-corrosion mechanisms for composite coatings enhanced via GO with different aspect ratio were tentatively proposed, which indicating that the GO sheets with higher aspect ratio provided a more tortuous permeation path for corroding medium and thus displayed better corrosion resistance.
The co-polymerization of aniline with p-nitroaniline has been synthesized in oxalic acid medium, here ammonium persulfate (APS) acts as an oxidant. TGA analysis was used to study the thermal ...stability of the copolymer, as well as FTIR, UV–Vis spectroscopy, and XRD. The synthetic poly (aniline-co-p-nitroaniline) (PANA) is used as a barrier/redox pigment for PANA coatings. The anti-corrosion study on PANA coatings was performed with a 3% NaCl solution for up to 35 days. The coating resistance of PANA coatings is three orders of magnitude more than that of pure epoxy coatings, according to the results of electrochemical impedance spectroscopy (EIS). The scanning vibrating electrode method (SVET) was used to investigate the self-healing characteristics of this PANA coating.
Display omitted
•The poly (aniline–co-p-nitroaniline) (PANA) is prepared by a chemical oxidation route.•The PANA doped oxalate ion acts as an inhibitor at the onset of corrosion.•The corrosion protector of PANA was studied by EIS.•The imitated corrosion process of PANA was studied by SVET.•The superior corrosion protection of PANA is better than epoxy coating.
Display omitted
•pH-dependent electrochemical behaviour of Al3Mg2 has been confirmed.•Galvanic corrosion currents versus pH of coupled Al3Mg2/Al were studied by SVET.•Dealloying element changes from ...Al to Mg as pH deviates from strong alkaline.•Three models were proposed to depict the corrosion process of Al3Mg2 at pH 2–12.
The effects of pH on the electrochemical behaviour of β-phase (Al3Mg2) and its role in corrosion of AA5000 series alloys in NaCl solution were investigated. The galvanic corrosion behaviour of synthesized Al3Mg2 intermetallic particle coupled with Al in 0.01 M NaCl solution over a wide pH window of 2–12 was studied using the scanning vibrating electrode technique (SVET). The results show that bulk Al3Mg2 acts as anode at pH 2–10.5, while cathode at pH 12. The corrosion resistance properties of bulk Al3Mg2 were then evaluated via potentiodynamic polarization and electrochemical impedance spectroscopy tests. Surface characterization were carried out by confocal laser scanning microscope (CLSM), scanning electron microscope (SEM) and X-ray photoelectron spectrometry (XPS). These results indicate that Al3Mg2 exhibits active dissolution of both Al and Mg elements at pH 2, while selective dissolution occurs at pH 3.5–12. At pH 3.5–10.5, any deviation from neutral pH causes a significant increase in the selective dissolution rate of Mg element, which results in a rough outer layer and a relatively compact inner layer of corrosive surface. At pH 12, the selective dissolution of Al element becomes dominant and the formation of compact Mg(OH)2 achieves complete passivity on the surface of Al3Mg2. This work contributes to further understanding of the electrochemical behaviour of β-phase in AA5000 series alloys.
Display omitted
•Synthesis of microcapsules (5−20 μm) containing isophorone diisocyanate using tris (p-isocyanatophenyl) thiophosphate as a shell forming agent.•Microcapsules show high encapsulation ...efficiency and high thermal and chemical resistance.•Microcapsules show high compatibility with epoxy coating formulations.•Electrochemical studies confirmed important healing ability of the microcapsules- containing coating.
This work aims at investigating the self-healing ability of epoxy coatings, modified with microcapsules containing highly reactive isocyanate in their core. Highly efficient, thermally and chemically stable isophorone diisocyanate microcapsules were prepared via emulsification followed by interfacial polymerization at the surface of oil droplets of the oil-in-water (O/W) emulsion. The microcapsules were incorporated into an epoxy coating to protect carbon steel from corrosion. Scanning Electron Microscopy (SEM) was used to assess the microcapsules̕ and coating morphology. The physico-chemical characterization of the microcapsules was studied by Fourier Transformed Infrared Spectroscopy (FTIR) and Thermogravimetric Analysis (TGA). Electrochemical Impedance Spectroscopy (EIS) was employed to evaluate the protective performance of coated steel samples and results confirmed that the barrier properties of modified coatings increased over time. The self-healing ability was studied via Localized Impedance Spectroscopy (LEIS), Scanning Vibrating Electrode Technique (SVET) and Scanning Ion-Selective Electrode Techniques (SIET) on coated steel samples containing artificial defects. This comprehensive study confirmed the ability of the capsules to heal damaged areas in the coating and to mitigate corrosion thanks to the formation of a protective polymeric barrier layer.
PDF
