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http://hdl.handle.net/10261/319
2024-03-19T07:08:32Z(Invited) Multiscale Electrochemical Analysis of Sol-Gel Films Modified with Eco-Friendly Corrosion Inhibitors for Active Corrosion Protection of AZ61 Magnesium Alloy
http://hdl.handle.net/10261/350844
Título: (Invited) Multiscale Electrochemical Analysis of Sol-Gel Films Modified with Eco-Friendly Corrosion Inhibitors for Active Corrosion Protection of AZ61 Magnesium Alloy
Autor: Garcia-Galvan, Federico R.; Martín Cordón, Jesús; Carmona, Noemí; Llorente, Irene; Fajardo, Santiago; Feliú Jr., Sebastián; Galván Sierra, Juan Carlos; Barranco, Violeta
Resumen: The use of magnesium and its alloys has increased in recent years due to their low weight, high strength, excellent machinability, and high dimensional durability. Therefore, they have found applications in communications, automotive and aerospace industries, among others. However, their high negative reduction potentials, low chemical stability, and unstable native oxide films have limited their use, particularly in applications that require high corrosion resistance.1-3 The application of sol-gel coatings has shown to be an effective method to overcome this problem. In this context, this study aimed to develop sol-gel thin films doped with ecological corrosion inhibitors for corrosion protection of AZ61 alloy surfaces. The objective was to determine whether these new systems could provide an alternative to the replacement of chromates, surface pre-treatments and chemical conversion coatings that contain conventional corrosion inhibitors, which are currently being questioned for their harmfulness to health and the environment.4
Methyltriethoxysilane (MTEOS) and tetraethylorthosilicate (TEOS) were used as precursors to produce sols, which were then modified with active corrosion protection dopants. Eco-benign corrosion inhibitors, such as L-cysteine (L-Cys), lanthanum (III) acetate hydrate, and lanthanum (III) isopropoxide were incorporated in the sol-gel matrix as dopants. A set of sol-gel coatings was modified with a common dopant, benzotriazole (BTA), for comparison purposes, as it is a well-known effective corrosion inhibitor. However, this chemical compound is known to be carcinogenic and toxic to flora and fauna, and its use is currently being restricted today in compliance with environmental protection regulations.5,6
The resulting sols were processed and deposited on AZ61 substrates by dip-coating technique, producing transparent sol-gel thin-films. The thickness of the films was evaluated by interference of reflection spectra. Their chemical composition was characterized by X-ray fluorescence (XRF), while surface chemical composition and oxidation state of elements present at the outermost surface nanolayers was also analysed by X-ray photoelectron spectroscopy (XPS). The structural and thermal characterization of the doped thin-films were respectively analysed by Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry and differential thermal analysis (TG/DTA).
The corrosion protection behaviour of the sol-gel coatings during immersion tests in 0.006 M and 0.6 M NaCl aqueous solutions was studied using a multiscale electrochemical approach. Global electrochemical impedance spectroscopy (EIS) was used for macroscopic scale characterisation. Localised electrochemical impedance spectroscopy (LEIS and LEIM) was used for the characterisation at micro- and sub-microscopic scales using an electrochemical minicell system and a scanning electrochemical workstation.
The texture and microstructure of coated samples before and after corrosion tests were observed by optical and scanning electron microscopies (OM and SEM), while topography and coating roughness were analysed by atomic force microscopy (AFM).
In terms of corrosion resistance, similar results were obtained with sol-gel thin-films doped with lanthanum acetate or lanthanum isopropoxide. The synthesis method of the acetate-doped gels is much simpler and cheaper, so from a practical standpoint, these sol-gel thin-films could be more interesting. On the other hand, highly satisfactory results were obtained with gels doped with non-toxic L-Cys compared with those doped with BTA. Finally, it is noteworthy that an interesting synergistic effect was observed in the corrosion protection of the AZ61 alloy in sol-gel coatings that were doped with metal-organic inhibitors and loaded with organic inhibitors (L-Cys or BTA).
As a concluding remark, this study has provided an effective and environmentally friendly solution for the active corrosion protection of the AZ61 alloy. Sol-gel thin films doped with eco-friendly corrosion inhibitors have showed promising results in extending the durability of AZ61 alloy while being sustainable. The multiscale electrochemical approach used has provided a comprehensive understanding of the active corrosion protection behaviour and the self-healing properties of sol-gel coatings, which can be extended to other materials and systems.2024-03-18T21:32:25ZTesting protective coatings for metal conservation: the influence of the application method
http://hdl.handle.net/10261/350405
Título: Testing protective coatings for metal conservation: the influence of the application method
Autor: Molina, María Teresa; Cano Díaz, Emilio; Ramírez-Barat, Blanca
Resumen: The lack of a standardised methodology for the application of coatings on heritage metals can lead to non-comparable results. A careful and meaningful study requires considering the different application variables involved, especially in the preparation of the coupons. In this work, the effect that these application variables can have on the protective capacity of the coatings used has been studied. The influence of the thickness, number of layers and drying time (between layers and final) of Paraloid B-72, C80 microcrystalline wax and Incralac has been evaluated. Coatings have been applied on bare steel coupons, thickness measured with an induction probe, and subject to artificial ageing on UV light/water condensation cycles. The performance of the coatings has been studied by visual inspection and electrochemical impedance spectroscopy (EIS). Morphology of the layers has been characterised by optical microscopy and the composition of the corrosion products by Raman spectroscopy. Results show that the number of layers is not always proportional to the final thickness of the coating, and that drying time is a critical factor affecting the thickness and the protective properties of the coatings. After accelerated ageing, some coatings that had been left to dry for 14 days have a much better protective capacity than those that were left to dry for less time. Without taking into account these factors, performance measured can be wrong and comparison between materials misleading.2024-03-14T10:20:03ZMachine learning dislocation density correlations and solute effects in Mg-based alloys
http://hdl.handle.net/10261/350402
Título: Machine learning dislocation density correlations and solute effects in Mg-based alloys
Autor: Salmenjoki, H.; Papanikolaou, S.; Shi, D.F.; Tourret; D.; Cepeda-Jiménez, C.M.; Pérez-Prado, María Teresa; Laurson, L.; Alava, M. J.
Resumen: Magnesium alloys, among the lightest structural materials, represent excellent candidates for lightweight applications. However, industrial applications remain limited due to relatively low strength and ductility. Solid solution alloying has been shown to enhance Mg ductility and formability at relatively low concentrations. Zn solutes are significantly cost effective and common. However, the intrinsic mechanisms by which the addition of solutes leads to ductility improvement remain controversial. Here, by using a high throughput analysis of intragranular characteristics through data science approaches, we study the evolution of dislocation density in polycrystalline Mg and also, Mg–Zn alloys. We apply machine learning techniques in comparing electron back-scatter diffraction (EBSD) images of the samples before/after alloying and before/after deformation to extract the strain history of individual grains, and to predict the dislocation density level after alloying and after deformation. Our results are promising given that moderate predictions (coefficient of determination R ranging from 0.25 to 0.32) are achieved already with a relatively small dataset (∼ 5000 sub-millimeter grains).2024-03-14T10:10:06ZTesting protective coatings for metal conservation: the influence of the application method
http://hdl.handle.net/10261/350337
Título: Testing protective coatings for metal conservation: the influence of the application method
Autor: Molina, María Teresa; Cano Díaz, Emilio; Ramírez-Barat, Blanca
Resumen: The lack of a standardised methodology for the application of coatings on heritage metals can lead to non-comparable results. A careful and meaningful study requires considering the different application variables involved, especially in the preparation of the coupons. In this work, the effect that these application variables can have on the protective capacity of the coatings used has been studied. The influence of the thickness, number of layers and drying time (between layers and final) of Paraloid B-72, C80 microcrystalline wax and Incralac has been evaluated. Coatings have been applied on bare steel coupons, thickness measured with an induction probe, and subject to artificial ageing on UV light/water condensation cycles. The performance of the coatings has been studied by visual inspection and electrochemical impedance spectroscopy (EIS). Morphology of the layers has been characterised by optical microscopy and the composition of the corrosion products by Raman spectroscopy. Results show that the number of layers is not always proportional to the final thickness of the coating, and that drying time is a critical factor affecting the thickness and the protective properties of the coatings. After accelerated ageing, some coatings that had been left to dry for 14 days have a much better protective capacity than those that were left to dry for less time. Without taking into account these factors, performance measured can be wrong and comparison between materials misleading.2024-03-13T15:15:55Z