Surface damage occurring during surgery can compromise coating integrity, leaving exposed areas susceptible to bacterial colonization. However, the impact of partial coating loss on antibacterial performance has not yet been investigated. In this work, a multifunctional UV-activated coating composed of hydroxyapatite, magnesium phosphate, and zinc oxide (HMZ) was developed and electrodeposited onto AZ31 and MgCa magnesium alloys. Its antibacterial efficacy against Staphylococcus aureus and Escherichia coli was evaluated under three conditions: adhered bacteria, planktonic cells, and biofilm. In the absence of UV activation, coated surfaces exhibited no significant antibacterial activity. In contrast, fully coated and UV-activated surfaces achieved bacterial reductions above 98% in all scenarios. Surfaces with 60% coverage showed antibacterial efficacy equivalent to that of fully coated surfaces, even against established biofilm. Surfaces with 30% coverage also exhibited moderate activity, particularly against adhered and planktonic bacteria. These results demonstrate that full surface coverage is not required to preserve the coating’s antibacterial effectiveness. This strategy provides a clinically relevant solution to maintain antibacterial protection even when coating integrity is compromised.

This study reports the development of novel, sustainable bionanocomposite coatings for AA2024-T3 aluminium alloy, achieved by integrating eco-friendly carbon-sepiolite nanofillers within chitosan and zein biopolymer matrices. The carbon-clay filler was prepared by impregnating a suspension containing multiwalled carbon nanotubes and liquid caramel into sepiolite clay, being the graphitization of caramel performed by hydrothermal treatment (180 degrees C for 18 h) followed by pyrolysis (550 degrees C for 1 h). The resultant carbon-sepiolite filler was blended with chitosan or zein matrices to obtain bionanocomposite suspensions. Thin bionanocomposite layers were deposited by dip-coating on the metal aluminium alloy surfaces, and selected samples were sealed with a hybrid organic-inorganic sol-gel topcoat to eliminate inherent porosity and boost passive corrosion resistance. The hybrid coating was prepared from a mixture of tetramethyl orthosilicate (TMOS) and gamma-methacryloxypropyltrimethoxysilane (MAPTMS), used as alkoxysilane precursors. Electrochemical impedance spectroscopy (EIS) as a rigorous, non-destructive methodology for assessing the coatings' protective performance against corrosion. EIS analysis revealed a clear two-stage degradation and protection mechanism: initially, the sol-gel layer provides a robust passive barrier, and upon its gradual deterioration, the underlying bionanocomposite film activates active corrosion inhibition via physical obstruction and controlled release of functional additives. Field-emission scanning electron microscopy confirmed the integrity, uniformity, and adherence of both monolayer and bilayer systems before and after immersion tests. Electrochemical studies revealed that the degradation process of these coatings occurs in two distinct stages. In the initial stage, the top sol-gel coating primarily provides a barrier effect. Once this layer deteriorates, an active corrosion protection mechanism from the bionanocomposite film is activated. These results demonstrate that the synergy between advanced material design and electrochemical characterization can yield high-performance, environmentally responsible coatings. The innovative carbon-sepiolite bionanocomposite approach, validated by EIS, offers superior corrosion resistance and represents a promising alternative to conventional chromate-based inhibitors in demanding engineering applications.

This study aims to develop new environmentally compliant coatings as surface pretreatments for the protection of light alloys. To achieve this goal, chitosan and zein biopolymers were combined with eco-friendly carbon-clay fillers to produce bionanocomposite thin films. Chitosan- and zein-based suspensions were prepared for the synthesis of the bionanocomposite thin films. For the chitosan-based suspension, carbon-sepiolite fillers and/or caffeic acid were dispersed in an acetic acid solution [1]. For the zein suspension, the carbon-sepiolite and/or caffeic acid additives were dispersed in an ethanol/water mixture. The carbon-clay fillers were prepared by impregnating natural sepiolite clay with liquid caramel, followed by thermal treatment under N2 flow at 550ºC for graphitization [2,3]. The resulting suspensions were then deposited on AA2024-T3 aluminium alloy and AZ61 magnesium alloy samples using the dip-coating technique. A post-treatment involving the application of an organic-inorganic hybrid top-coat on a series of bionanocomposite thin films. The purpose was to seal the inherent pores within these layers and enhance their corrosion resistance. The hybrid matrix was prepared by co-hydrolysis and polycondensation of a mixture of γ-methacryloxypropyltrimethoxysilane and tetramethyl orthosilicate by using the sol-gel process. The resulting coatings were characterized using field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis and differential scanning calorimetry (TGA/DSC). The corrosion protection of these coatings was evaluated by open circuit potential (OCP) measurements and electrochemical impedance spectroscopy (EIS) during immersion tests in a 0.06 M NaCl solution. FESEM images acquired on the corrosion test areas confirmed the corrosion protection offered by the bionanocomposite thin films. Electrochemical studies showed that the degradation process of these coatings goes through two stages. Initially, a barrier effect exerted by the sol-gel top-coat predominates. Once this layer has failed, an active protection mechanism against corrosion engaged by the bionanocomposite thin film is activated. As a remarkable conclusion of the study, it should be noted that these bionanocomposite thin films exhibit relevant properties that make them promising green candidates for applications in the automotive and aeronautical industries. Acknowledgements: This work was developed within the scope of the projects CICECO UIDB/50011/2020, UIDP/50011/2020 & LA/P/0006/2020, financed by national funds through the FCT/MEC (PIDDAC) as well as MCIN/AEI/10.13039/501100011033 - PID2019-105479RB-I00 and PID2022-139920OB-I00 projects, Spain. AB and PF are thankful to FCT for grant SFRH/BD/148856/2019 and the Investigator FCT (IF/00300/2015), respectively. CN is grateful to Portuguese national funds (DL 57/2016/CP1482/CT0031). References: [1] A. Barra, J.K. Wychowaniec, D. Winning, M.M. Cruz, L.P. Ferreira, B.J. Rodriguez, H. Oliveira, E. Ruiz-Hitzky, C. Nunes, D.F. Brougham, P. Ferreira. Magnetic Chitosan Bionanocomposite Films as a Versatile Platform for Biomedical Hyperthermia. Advanced Healthcare Materials, 2303861 (2023). [2] A. Barra, C. Nunes, E. Ruiz-Hitzky, P Ferreira. Green Carbon Nanostructures for Functional Composite Materials. International Journal of Molecular Sciences, 23 (3), art. no. 1848 (2022). [3] A. Barra, O. Lazăr, G. Mihai, C. Bratu, C. Ruiz-García, M. Darder, P. Aranda, M. Enăchescu, C. Nunes, P. Ferreira, E. Ruiz-Hitzky, Graphene-like materials supported on sepiolite clay synthesized at relatively low temperature. Carbon, 218, art. no. 118767, (2024).

Additive manufacturing, heralded for its ability to produce intricate geometries with unparalleled precision while potentially minimizing material and energy consumption compared to traditional methods, has garnered significant attention in recent years. Magnesium, with its density of around 1.74 g/cm³ and appropriate mechanical strength, is an appealing lightweight structural material widely employed in industries such as automotive and aerospace. Despite these advantages, the corrosion behavior of additively manufactured magnesium alloys remains relatively unexplored, posing challenges for their widespread adoption. In this work, the corrosion behavior of AZ91 Mg alloy obtained through additive manufacturing was investigated. Cylindrical AZ91 Mg alloy samples were fabricated using the Powder Bed Laser Fusion (PBLF) technique. Analysis was conducted in both the transverse and longitudinal planes, where the transverse plane represents the top plane of the cylinder and the longitudinal plane represents a section through the center of the cylinder. This comparative approach, allowed a comprehensive examination of corrosion kinetics and behavior across different orientations. Furthermore, cast AZ91 Mg alloy was also studied for comparative purposes. Potenciodynamic polarization (PDP) tests, including both cathodic and anodic polarization, revealed similar kinetics for both the longitudinal and transverse planes studied, indicating consistent corrosion behavior across different orientations. Simultaneous gravimetric hydrogen collection and electrochemical impedance spectroscopy measurements (EIS) were performed to elucidate the underlying mechanisms governing corrosion processes. Furthermore, galvanodynamic polarization tests were employed to investigate the anomalous hydrogen evolution (AHE) intrinsic to Mg alloys. These tests were conducted in both planes, with concurrent hydrogen collection. Additionally, the role of the beta-Mg17Al12 phase on the electrochemical response of the additively manufactured AZ91 Mg alloy was investigated. The results of this study have significant implications for various industries, particularly automotive and aerospace applications, where Mg corrosion resistance is crucial for ensuring structural integrity and component longevity. Understanding the corrosion behavior of additively manufactured Mg alloys is paramount for optimizing their performance and facilitating widespread adoption in critical applications.

Magnesium (Mg) and its alloys are the lightest structural metallic materials with a high strength/weight ratio, which makes them desirable materials in the transportation industry. However, the widespread use of Mg alloys remains limited by their poor corrosion resistance. Electrochemical impedance spectroscopy (EIS) has emerged as a highly applicable in situ electrochemical technique used in Mg corrosion research due to its “non-destructive” character, and its capability to provide information on the electrode/electrolyte interface. This paper includes a brief review of some basic aspects of EIS. In addition, we discuss various applications of EIS techniques in the study of Mg corrosion.

The urgent need to address the challenges posed by climate change has led to increased research and development efforts aimed at creating lightweight materials to reduce greenhouse gas emissions. This study focuses on corrosion protection of the commercial magnesium alloy AZ61, valued for its wide-ranging applications in engineering and industry, including automotive, aeronautics, and biomedical engineering. Despite its interesting mechanical properties, the AZ61 alloy exhibits poor corrosion resistance in saline aqueous environments, prompting significant research into coatings to enhance its durability. This research aims to design and prepare organic-inorganic hybrid sol-gel coatings for corrosion protection of the AZ61 alloy. The inorganic phase, mainly based on tetramethyl orthosilicate (TMOS), serves as a cross-linking agent, while four organofunctionalized silanes containing hydrolysable methoxy groups and functional organic groups into the same molecule are used as precursors for the organic component of these hybrid coatings. Specifically, the organofunctionalized silanes selected are γ-methacryloxypropyltrimethoxysilane (MAPTMS), γ -glycidoxypropyltrimethoxysilane (GPTMS), γ -aminopropyltrimethoxysilane (AMPTMS), and γ -mercaptopropyltrimethoxysilane (MPTMS). These silanes are chosen for their ability to create organopolysiloxane coatings with sufficient chemical compatibility and flexibility to accommodate other species without phase segregation or cracking. These properties are essential to create a suitable structural environment to encapsulate the selected ecofriendly corrosion inhibitors that are added in later stages of the study, thereby yielding a processable system that serves as a functional phase of active corrosion protection coatings for magnesium alloys. Physicochemical characterization techniques are employed to understand the chemical environment within the hybrid networks and confirm the successful formation of organopolysiloxane networks. Thermogravimetry and differential thermal analysis (TG/DTA), Fourier transform infrared spectroscopy (FTIR), and high-resolution solid-state 13C and 29Si nuclear magnetic resonance spectroscopies are used for these purposes. The performance of coated AZ61 samples is analysed using the aforementioned organic-inorganic hybrid gels. These sol-gel coatings are applied using immersion techniques (dip-coating) on unpolished (as-received) and polished AZ61 samples, to determine the influence of surface conditions on their behaviour during immersion tests in 0.6, 0.06 and 0.006 M NaCl aqueous solutions. Open circuit potential (OCP) measurements and global and localized electrochemical impedance spectroscopies (EIS, LEIS) are applied with this purpose. The microstructure and texture of the coatings, both before and after the corrosion tests, are observed by optical microscopy (OM) and scanning electron microscopy (SEM). Moreover, Energy dispersive X-ray (EDX) microanalyses are performed on several areas of the coated samples after the corrosion tests. In the last phase of the study, modifications to the sol-gel formulations are explored by incorporating environmentally friendly corrosion inhibitors such as cysteine (L-Cys) and benzotriazole (BTA), as well as cross-linking agents like hexamethoxymethylmelamine (HMMM) in presence of an acid catalysts, specifically p-toluenesulfonic acid (p-TSA), to facilitate the cross-linking reaction within the organosilicon network. These modifications aim to enhance the protective properties of the sol-gel coatings. EIS and LEIS are used to assess their effectiveness. Films formulated with HMMM demonstrate robust passive protection against corrosion, while those doped with L-Cys and BTA exhibit self-healing and active protection properties, offering a promising alternative to traditional chemical conversion pretreatments based on hexavalent chromium. Funding Sources This work has been supported by the Project PID2022-139920OB-I00 (Ministry of Science, Innovation and Universities, MICINN, Spain).

The sustainability and corrosion protection are two critical factors in the field of materials for mobility. Lightweight alloys, such as the AZ61 magnesium alloy, are gaining recognition for their potential applications in the aerospace, automotive, and marine industries. The use of these alloys not only contributes to weight reduction and consequent fuel and CO2 emission savings, but also opens up new possibilities for innovative design and performance enhancements [1]. In search for sustainable corrosion protection, we have focused our research towards the development of environmentally acceptable sol-gel coatings enriched with green corrosion inhibitors. These coatings not only prolong the lifespan of materials made with the AZ61 magnesium alloy but also align with the commitment to environmental stewardship, offering promising prospects for effective corrosion protection [2]. The sol-gel coatings were synthesized using tetraethyl orthosilicate (TEOS) and 3-(trimethoxysilyl)propyl methacrylate (MAPTMS) as precursors. Four different organic inhibitors - L-cysteine (CYS), N-acetyl-cysteine (N-A-CYS), curcumin (CUR), and methylene blue (MB) - that are environmentally friendly, non-toxic, inexpensive and contain S, N heteroatoms, O and/or OH groups and/or conjugated double bonds - were selected for the study. These compounds were incorporated into the sol as dopants. A set of sols was doped with a common corrosion inhibitor, benzotriazole (BTA), for comparison purposes. The resulting sols were processed and deposited on AZ61 substrates using the dip-coating technique. The thickness of the coatings was determined using the interference fringe method in the ultraviolet-visible and near-infrared ranges [2]. Transmission spectra of coated glass samples were also obtained to determine the wavelength of each coating at 50% transmission. The hydrophilic character of the coatings was characterized by measuring the contact angle. To study the corrosion behaviour of the coated surfaces, weathering tests, based on a variation of the ISO 11130 [3], were conducted. The samples were weighed before and after the corrosion test to examine weight variations. Optical microscopy provided insights into the surface of the samples both before and after the corrosion test. Detailed observations of the surface morphologies of the samples were made using SEM, and EDX analyses were performed to verify the compositions of the compounds found. Confocal Raman microscopy was also employed to provide accurate compositional information at a local microscale level, shedding light on the compounds formed considering the chemical strategies developed in the protective sol-gel coating [4,5]. The study was concluded by applying global and localized electrochemical impedance spectroscopies (EIS, LEIS) to study the corrosion protection behaviour of the sol-gel coatings during immersion tests in 0.006 M and 0.6 M NaCl aqueous solutions. As a concluding remark, it is noteworthy that in several of the tested sol-gel coatings, micro-cracks and defects formed during weathering tests self-seal, thanks to oxy-hydroxides adhering to the Mg alloy substrate. Additionally, in response to the corrosive anions of the aqueous solution, due to the release of the organic inhibitors that were nanoencapsulated in the sol-gel matrix, an active corrosion protection is initiated beneath the coatings. In conclusion, the tested eco-friendly coatings, applicable by dip-coating or spray at room temperature, offer potential for broad industrial use and economic feasibility, suggesting industrial scale-up feasibility. Funding Sources This work has been supported by the Projects PID2022-139920OB-I00, PID2021-126323OA-I00 and TED2021-129688-CT21 (Ministry of Science, Innovation and Universities, MICINN, Spain). The team extends its acknowledgements to Miguel Romero Martín of the ECORR Group for his help with impedance measurements and result analysis. References 1. Kumar, D., Phanden, R.K., Thakur, L. A review on environment friendly and lightweight Magnesium-Based metal matrix composites and alloys. Materials Today: Proceedings, 38, pp. 359-364 (2020). 2. Domínguez-Martínez, J., López-Sánchez, J., García-Galván, F., Serrano, A., Barranco, V., Galván, J.C., Rodríguez de la Fuente, O., Carmona, N. Eco-Friendly Sol-Gel Coatings with Organic Corrosion Inhibitors for Lightweight AZ61 Alloy. Gels 10 (3), art. no. 168 (2024). 3. ISO Standard 11130 ; Corrosion of Metals and Alloys – Alternate Immersion Test in Salt Solution. Available online: https://www.iso.org/standard/71867.html (accessed on 18 April 2023). 4. Aparicio, M., Mosa, J., Rodriguez, G., Guzman, J., Picard, Q., Klein, L.C., Jitianu, A. Consolidated Melting Gel Coatings on AZ31 Magnesium Alloy with Excellent Corrosion Resistance in NaCl Solutions: An Interface Study. ACS Applied Materials and Interfaces 11 (3), pp. 3493-3505 (2019) 5. López-Sánchez, J., Serrano, A., del Campo, A., Muñoz-Noval, Á., Salas-Colera, E., Cabero, M., Varela, M., Abuín, M.,Castro, G.R., Rubio-Zuazo, J., Rodríguez de la Fuente, O., Carmona, N. A combined micro-Raman, X-ray absorption and magnetic study to follow the glycerol-assisted growth of epsilon-iron oxide sol-gel coatings. Journal of Alloys and Compounds 892, art. no. 162061 (2022).

The latest advances in technology and materials science have catalyzed a transformative shift towards the adoption of environmentally conscious and lightweight materials across key sectors such as aeronautics, biomedical, and automotive industries. Noteworthy among these innovations are the magnesium-aluminum (Mg-Al) alloys employed in aeronautical applications, contributing to the overall reduction in aircraft weight and subsequently diminishing fuel consumption and mitigating atmospheric emissions. The present work delves into a study of the anti-corrosive properties inherent in various sol-gel coatings, leveraging a range of environmentally friendly corrosion inhibitors, specifically tailored for samples of the AZ61 alloy. Methodologically, the work involves the synthesis and application of sol-gel coatings on AZ61 alloy containing eco-friendly inhibitors: L-cysteine, N-acetyl-cysteine, curcumin and methylene blue. Subsequently, an accelerated corrosion test in a simulated saline environment is performed. Through microstructural and compositional analyses, the best inhibitors responses are achieved with inhibitors containing S, N heteroatoms and conjugated double bonds in their structure, probably due to the creation of a continuous MgCl2 layer. This research contributes to the ongoing discourse on protective eco-coatings, aligning with the broader paradigm shift towards sustainable and lightweight materials in key industries.

(FeXNi1−X)0.8 (X, Y)0.2 metallic glasses were obtained by a rapid solidification technique. Reversible oxide layers of variable thickness were generated in a alkaline medium on the surface of these metallic glasses, using an electrochemical technique of potential triangular sweeps. The composition of the metallic matrix as well as the oxide layers electrochemically generated have been studied both by X-ray photoelectron spectroscopy and specular reflactance spectroscopy. Pitting corrosion susceptibility tests were realised inNaCl solution 0.05 M, pH 6.8 ± 0.1 at room temperature on the basis of a study of anodic polarisation curves. The generated layers are not only stable in the medium in which they were generated, but also in other corrosive media with different pH, such as a NaCl neutral solution. The glass with a generation of layers of maximum thickness substantially improve pitting resistance in comparison to control specimens in reception state. The best behaviour corrosion was found in the Fe38.5Ni38.5Mo2Si13B8 glass, with a typical curve for material in a passive state. Finally, the different peaks observed in the SRS spectra of this last glass insinuate the existence of different chemical species and/ or different state oxidation of the elements of these layers when they were generated after 200 or 400 potential cycles.

Metallic corrosion is an all-time dangerous and extremely expensive problem. Here, we present an autonomous self-healing polymer coating based on an epoxy resin and superabsorbent polymer (SAP) blend as an anticorrosion coating. Tailor-made coatings were manufactured by controlling the location of the SAP on the surface, middle, and bottom of the coating. The corrosion behavior and self-healing process of the coatings were analyzed at the macro, micro, and sub-micro scales using Electrochemical Impedance Spectroscopy (EIS). The SAP preferentially located at the bottom showed coating resistance values higher than 1 x 1011 omega cm2 over 10 days of immersion with 3-point defects. This configuration provided the best anticorrosion performance, preventing coating delamination, and protecting the metal from corrosion after surface damage, indicating better barrier properties. The SAP enabled local repair of the crack when in contact with water, minimizing the diffusion of oxygen and electroactive species, which are responsible for the corrosion of a metal.

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 application in communications, automotive and aerospace industries, among others. However, their high negative reduction potentials, low chemical stability, and the 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, the aim of this study was 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. Funding Sources This work has been supported by the Ministry of Science and Innovation (MCINN, Spain) through the Project PID2019-104717RB-I00. References Feliu Jr., S., Maffiotte, C., Samaniego, A., Galván, J.C., Barranco, V. Acta, 56 (12) (2011) 4554-4565 Stojadinović, S., Vasilić, R., Radić-Perić, J., Perić, M. Coat. Technol., 273 (1) (2015), pp. 1-11 Toorani, M., Aliofkhazraei, M., Naderi, R., Golabadi, M., Sabour Rouhaghdam, A. Ind. Eng. Chem., 53, (2017) pp. 213-227 Vaghefinazari, B., Wierzbicka, E., Visser, P., Posner, R., Arrabal, R., Matykina, E., Mohedano, M., Blawert, C., Zheludkevich, M., Lamaka, S. Materials, 15 (23) (2022), art. no. 8676 Albini, M., Letardi, P., Mathys, L., Brambilla, L., Schröter, J., Junier, P., Joseph, E. Corrosion Sci., 143 (2018), pp. 84-92 Tan, L., Sun, Y., Li, J., Han, S., Zhou, X., Tang, Y., Zeng, X. Langmuir, 39 (2023), 2579-2588

Magnesium alloys possess many interesting properties, including high strength-to-weight ratios, good castability, and excellent biocompatibility. However, its use has been limited because they are also highly reactive and susceptible to corrosion in aqueous environments. As a result, the development of effective corrosion protection strategies for Mg alloys represents a significant challenge for many industrial applications, particularly in the aerospace, automotive, and biomedical industries. Sacrificial cathodic protection is a commonly used strategy to enhance the durability of metallic materials. This method involves the use of an active metal (known as the sacrificial anode) in galvanic contact with the metal to be protected from corrosion, which acts as the cathode. Due to their low corrosion potential, Mg alloys have traditionally served as sacrificial anodes to protect more noble metals such as steel, aluminum, and zinc. However, the growing interest in Mg alloys for industrial applications has led to the development of effective corrosion protection alternatives for Mg alloy components. Among them, the use of Mg alloy coatings as the anode material for the sacrificial protection of other Mg alloys is an interesting strategy. This approach offers several advantages such as minimized galvanic corrosion due to their comparable electrochemical behavior, as well as enhanced adhesion between the anode and the substrate. One of the key requirements for a metallic material to be used as a sacrificial anode is that its electrode potential must be more negative than that of the metal being protected. Additionally, the anode material must be chemically stable in the environment in which it will be located. These conditions are largely dependent on the composition of the anode material. Although recent studies have aimed to enhance the cathodic protection properties of Mg alloys for their use in industrial applications, such work remains restricted. This is due to the limited number of alloying elements with lower standard reduction potentials than Mg that are stable in solution, thereby decreasing the anode corrosion potential. In addition, Mg exhibits enhanced hydrogen evolution rates with increasing anodic polarization, which contradicts expectations of standard electrochemical kinetics and leads to significantly increased rates of self-dissolution. This phenomenon is termed anomalous hydrogen evolution (HE). This work investigates the potential of Mg-3Pb alloy as possible sacrificial anode material for the corrosion protection of three industrially important Mg alloys: AZ31, AM60, and AZ91. For that purpose, a Mg-3Pb alloy was casted in-house and its microstructural characteristics and electrochemical behavior were studied. Furthermore, galvanic corrosion between the Mg-3Pb alloy and the industrially relevant Mg alloys, AZ31, AM60, and AZ91, was evaluated in 0.1 M NaCl solution. The choice of Pb as an alloying element was motivated by its extremely low exchange current density for the HE reaction (i0,H2,Pb) on the order of 10-12 A/cm2. This was expected to result in reduced HE rates under cathodic polarization, which shifts the corrosion potential (Ecorr) to more negative values, and during anodic polarization, hindering anomalous HE and reducing self-dissolution. The microstructural characterization of the Mg-3Pb alloy revealed that it consisted of large α-Mg grains with the presence of a small amount of secondary phases, including Al, Si, Mn, Fe-containing intermetallics and oxide particles. Additionally, scanning electron microscopy revealed the occurrence of remarkable Pb segregation at grain boundaries. Electrochemical measurements showed that the Ecorr associated with the Mg-3Pb alloy was consistently lower than those of the AZ31, AM60, and AZ91 alloys during 24 hours of immersion in the test solution. Moreover, potentiodynamic polarization confirmed that the Mg-3Pb alloy exhibited the lowest cathodic kinetics. In terms of anomalous HE, which is directly related to the self-dissolution rate of the Mg alloy anode material, galvanostatic polarization at different anodic current densities showed that the HE current densities were linear with respect to the applied current density. Additionally, the charge associated with the HE was in the range of 40–50% of the applied anodic charge, which is consistent with previous findings for high purity Mg. Finally, ZRA measurements indicated that the galvanic current of the Mg-3Pb alloy remained anodic for 24 hours of immersion with no polarity reversal, indicating that the Pb-containing alloy served as sacrificial anode for the AZ31, AM60, and AZ91 alloys. In conclusion, the use of Mg-3Pb alloy in cathodic protection systems for Mg alloys has proved to be a viable option in 0.1 M NaCl solution, offering new possibilities for its use in various applications. Funding: This work was supported by the State Research Agency (MICINN), the Spanish National Research Council (CSIC) and European Regional Development Fund (ERDF) under the project RYC2019-027006-I (AEI/FEDER/UE).

Today's environmental needs require the reduction of the weight of vehicles, thus reducing fuel consumption and associated emissions. For this reason, the use of light alloys is being studied, which, due to their reactivity, must be protected before use. In this work, the effectiveness of a hybrid sol-gel coating doped with various organic environmentally friendly corrosion inhibitors applied to an AA2024 lightweight aluminium alloy is evaluated. Some of the inhibitors tested are pH indicators, acting as both corrosion inhibitors and optical sensors for the surface of the alloy. Samples are subjected to a corrosion test in a simulated saline environment and characterised before and after the test. The experimental results regarding their best inhibitor performance for their potential application in the transport industry are evaluated.

Physiological human fluid is a natural corrosive environment and can lead to serious corrosion and mechanical damages to light Mg–Al alloys used in prosthetics for biomedical applications. In this work, organic–inorganic hybrid coatings doped with various environmentally friendly and non-toxic corrosion inhibitors have been prepared by the sol-gel process for the corrosion protection of AZ61 magnesium alloys. Effectiveness has been evaluated by pH measurements, optical microscopy, and SEM during a standard corrosion test in a Hanks’ Balanced Salt Solution. The results showed that the addition of an inhibitor to the sol-gel coating can improve significantly the corrosion performance, being an excellent barrier for the L-cysteine-doped hybrid sol-gel films. The incorporation of TiO2 nanoparticles, 2-Aminopyridine and quinine organic molecules slowed down the corrosion rate of the Mg–Al alloy. Graphene oxide seemed to have the same response to corrosion as the hybrid sol-gel coating without inhibitors.

The deposition of bioactive hydroxyapatite (HAp) coatings on pure magnesium (Mg) surfaces was studied. A modification of the biomimetic deposition method was used, which consisted in the incorporation of a supersaturated calcification solution (SCS). Different preparation parameters were modulated to obtain HAp and/or doped apatite coatings with different characteristics. The influence of the surface pre-treatments and soaking time in SCS on the physicochemical properties and the corrosion performance of the biomimetic HAp coatings were evaluated. Two different pre-treatments were explored to condition the sample’s surface for the biomimetic HAp deposition. After the surface pre-treatments, the Mg samples were covered with HAp coatings by soaking in SCS during two immersion periods specifically chosen for this study: 2 h and 6 h, respectively. Scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman Spectroscopy, and Fourier transform infrared (FTIR), were applied for the chemical, morphological, and structural characterization of the resulting biomimetic HAp-coatings. The in vitro corrosion behavior was studied by open circuit potential (OCP) measurements and electrochemical impedance spectroscopy (EIS) during immersion tests in Ringer’s physiological solution for up to 14 days. The results showed that HAp coatings were successfully deposited on the pure Mg substrates. Furthermore, the corrosion studies in Ringer’s solution showed that HAp coating behavior depends not only on the pre-treatment type but also on the immersion time in SCS. These results open the door to propose different strategies to control—on demand—the corrosion rate of Mg coated with biomimetic HAp. These systems could be a promising alternative for designing and developing new temporary implants for the human body.

Universidad de Sevilla: Escuela Politecnica Superior VII Jornada de Investigacion Desarrollo e Innovacion de la Escuela Politecnica Superior de la Universidad de Sevilla

The aim of this study was to develop new chrome-free surface pretreatments for AA2024-T3 aluminum alloy. These pretreatments were based on hybrid organic–inorganic sol–gel thin films prepared from mixtures of γ-methacryloxypropyltrimethoxysilane (MAPTMS) and tetramethylorthosilicate (TMOS). Different MAPTMS/TMOS molar ratios were used for optimizing the physical–chemical characteristics of the sol–gel films. The formulation of a set of these sols was modified by incorporating piperazine (1,4-diazacyclohexane) as a corrosion inhibitor. The resulting sol–gel films were characterized by using Fourier transform infrared spectroscopy (FTIR), liquid-state 29Si nuclear magnetic resonance spectroscopy (29Si-NMR) and viscosity measurements. The corrosion performance of the sol–gel films was analyzed by using electrochemical impedance spectroscopy (EIS) and local electrochemical impedance mapping (LEIM). The characterization techniques indicated that piperazine behaved as a catalyst for the condensation reaction during the formation of the MAPTMS/TMOS organopolysiloxane network and produces an increase of the crosslinking degree of the sol–gel films. EIS and LEIM results showed that piperazine is an effective corrosion inhibitor, which can be used to enhance the active corrosion protection performance of sol–gel films.

Zn-Ni alloys were electrodeposited on stainless steel from a sulphate bath in the presence of EDTA (ethylenediaminetetraacetic acid) as a complexing agent. The electrochemical behaviour of the bath was studied by cyclic voltammetry (CV), chronoamperometry (CA). Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis showed a change in surface morphology; the phase structure corresponds to the face centre cubic (fcc) structure attributed to the gamma phase (Ni5Zn21). The corrosion measurements of the obtained deposits with various EDTA concentrations were studied using potentiodynamic polarisation. Results showed that the deposit obtained in the presence of a low EDTA concentration (0.25 g L-1) exhibits better corrosion resistance.

The durability and long-term success of metallic implants are enhanced through the molecular scale design of biocompatible and corrosion resistant surface coatings. To pursue this hypothesis, we have developed a new class of organic-inorganic (O-I) hybrid nanocomposite coatings based on tetramethylorthosilicate (TMOS) and gamma-methacryloxypropyltrimethoxysilane (MAPTMS) as organofunctional alkoxysilanes precursors and dimethyltrimethylsilylphosphite (DMTMSP) as a phosphorus precursor. Addition of DMTMSP to TMOS-MAPTMS hybrids increased the extent of intermolecular condensation and cross-linking observed. Both normal human osteoblast in-vitro biocompatibility and corrosion resistance were enhanced in coatings containing DMTMSP. Though increasing phosphorous content correlated with biocompatibility, a compromise in the amount of phosphorus incorporated would be required if corrosion resistance was the most desirable parameter for optimization, at least for single coat systems. Evaluation of the electrochemical behaviour and the in-vitro biocompatibility show that films prepared using these materials by dip coating onto Ti6Al4V alloys offer a promising alternative to simpler coatings and wholly metallic prostheses.

Laser shock processing (ISP) is increasingly applied as an effective technology for improving the properties of different metallic components. This is done principally to enhance their corrosion and fatigue life behaviour, stress corrosion cracking resistance, etc. In this paper, LSP has been applied to a commercially pure Mg and a Mg-1Zn alloy (wt%) which is aimed to be used as a biodegradable material for biomedical applications. The rational for microalloying with Zn is not only influencing the bacterial response, but also enhancing corrosion resistance and mechanical strength of Mg without causing any toxic effect. The present work is focussed on the examination of the effects of the LSP treatment on the relevant surface related properties of the samples and their correlation with the surface and subsurface induced modifications such as residual stress state, microstructural, roughness, hardness, etc. Central to this investigation is the study of the corrosion response and antibacterial properties against Staphylococcus epidennidis of the different samples as a function of material and LSP parameters. The results show that the application of LSP introduces compressive residual stresses up to 1 mm deep. This occurs together with a significant improvement in corrosion resistance, and less bacterial colonization.