Open Circuit Potential Measurements Research Articles

Insight into patina formed on beryllium-bronze after 29 years of exposure in an industrial environment and DFT research

This research explores the corrosion behavior of beryllium bronze over a period of 29 years in an industrial atmosphere, revealing an average corrosion rate of 0.557 μm·a−1. The skyward patina layer primarily consists of Cu2O, Cu4SO4(OH)6 and CuSO4, while the field-ward patina layer contains Cu2O, CuO, Cu4SO4(OH)6 and CuSO4. Density functional theory (DFT) calculations and XPS analysis show that Be oxidizes preferentially, providing early-stage corrosion protection. DFT and open circuit potential measurements suggest that the patina layer on the field-ward surface is more thermodynamically stable, but cracks serve as pathways for mass transport, accelerating corrosion.

Mechanism and rate of anomalous extraction of chloride salts from water to 1,2-dichloroethane

Open circuit potential (OCP) measurements, potentiostatic pulse (PP) amperometry and cyclic voltammetry (CV), were used to investigate and to sort by rate the anomalous extraction of the chloride salts RCl of the cations R+ = tetrabutylammonium (TBA+), tetrapentylammonium (TPeA+), tetrahexylammonium (THexA+), tetraheptylammonium (THepA+) and bis(triphenyl-phosphoranylidene)ammonium (BA+) from water to 1,2-dichloroethane (DCE). A tentative mechanism is proposed comprising (a) the diffusion-controlled transport of the ion-pairs (RCl)ip from the aqueous to the organic solvent phase providing a major contribution to the chloride extraction, (b) decomposition of the multiple ion-pairs or clusters (RCl)ipx, which are formed by agglomeration of the single ion-pairs (RCl)ip in the aqueous phase (w), and (c) the exponential decay of the ion-pairs (RCl)ip accumulated on the organic solvent side of the interface at the beginning of the OCP measurements. This model enables to simulate successfully the experimental time dependence of the chloride concentration. A conclusion is made that the effect of the composition of the organic solvent electrolyte RX, where X- = tetraphenylborate (TPB-) or tetrakis(pentafluorophenyl) borate (TB-), on the rate and extent of the anomalous accumulation of the chloride anion in the phase (o) of the two-phase liquid system LiCl(w)/RX(o) can be related to the hydrophobicity of the electrolytes RCl and RX. The latter property can be characterized by the standard Gibbs energy of transfer from the aqueous (w) to the organic solvent (o) phase. The accumulation of the chloride anion in the phase (o) appears to be promoted by the decreasing value of the transfer Gibbs energy of RCl in the sequence TBACl > TPeACl > THexACl > THepACl > BACl, while the decreasing value of the transfer Gibbs energy of RX in the sequence TBATPB > TPeATPB > THexATPB > THepATPB > BATPB > BATB starts to block the cycle combining the energetically unfavorable extraction of RX from the phase (o) to the phase (w) with the energetically favorable extraction of RCl in the opposite direction. IR spectroscopy provides evidence of the formation of the water clusters in the organic solvent phase equilibrated with the aqueous phase in the presence of the tetraalkylammonium cation in both phases, which are supposed to drive the anomalous accumulation of the chloride anion in the phase (o).

Understanding the corrosion and structural potential of 95Al-RHA-PSA composite for advance application

Material reinforcement has become popular in improving properties, such as corrosion, mechanical and wear behaviour. Aluminium-base composite has found usefulness in the technology of automobiles, aerospace, and marine and designs of a wide range of components. The use of reinforcement materials increases the efficiency of composites products and reduces overall expenses. Aluminium alloy composite provides low-cost advantages over many other matrix composites. The use of agro-based waste material as reinforcement alternatives is becoming very important because of its close to nothing cost and availability to produce nanoparticles. This study aim to use agro based processed rice hulls (RHA) and periwinkle shells (PSA) to improve aluminium properties in an attempt to gain prominence in today's automotive advancements. SEM imaging was conducted at a magnification of 15,000 at 20 kV to evaluate structural properties, while X-ray Diffractometer (XRD) images were utilized to observe the crystallography peaks and phases of the developed alloys. Rockwell hardness testing, in accordance with ASTM E18 standards, involved subjecting the samples to a 30 kg/f load for 30 s using a hardened steel ball for indentation. Corrosion properties were assessed via linear polarization resistance and open circuit potential measurements. From the results, there is a higher corrosion resistance from 95Al-RHA-PSA composite samples compared to the control (aluminium alloy) samples. The lower values of jcorr and higher values of Pr of the 95Al-RHA-PSA composite samples also indicated that the RHA and PSA content of the composite minimized the penetration of chloride ions into the active sites of the composite samples. The 95Al-2RHA-3PSA composite sample exhibited the lowest Cr of 1.4172 mm/year, lowest jcorr of 1.220E-04 A/cm2 and highest Pr of 70.02 Ω, which indicated the 95Al-2RHA-3PSA composite sample provided the most significant passivation, leading higher corrosion resistance. The XRD of the control sample has several crystallographic phases, with AlNi3Al2SiO8 exhibiting the most elevated peak intensity at about 550 a.u (2θ = 39°). In comparison, the peak intensity of the other crystals is less than 200 a.u. However, the 95Al-RHA-PSA composite samples exhibited crystallites of higher peak intensities and better morphological strengthening characteristics. The findings suggest promising prospects for the development of sustainable and long-lasting aluminium alloy for automotive use.

Tuning the Thermochemistry and Reactivity of a Series of Cu-Based 4H+/4e- Electron-Coupled-Proton Buffers.

Electron-coupled-proton buffers (ECPBs) store and deliver protons and electrons in a reversible fashion. We have recently reported an ECPB based on Cu and a redox-active ligand that promoted 4H+/4e- reversible transformations (J. Am. Chem. Soc. 2022, 144, 16905). Herein, we report a series of Cu-based ECPBs in which the ability of these to accept and/or donate H• equivalents can be tuned via ligand modification. The thermochemistry of the 4H+/4e- ECPB equilibrium was determined using open-circuit potential measurements. The reactivity of the ECPBs against proton-coupled electron transfer (PCET) reagents was also analyzed, and the results obtained were rationalized based on the thermochemical parameters. Experimental and computational analysis of the thermochemistry of the H+/e- transfers involved in the 4H+/4e- ECPB transformations found substantial differences between the stepwise (namely, BDFE1, BDFE2, BDFE3, and BDFE4) and average bond dissociation free energy values (BDFEavg.). Our analysis suggests that this "redox unleveling" is critical to promoting the disproportionation and ligand-exchange reactions involved in the 4H+/4e- ECPB equilibria. The difference in BDFEavg. within the series of Cu-based ECPBs was found to arise from a substantial change in the redox potential (E1/2) upon modification of the ligand scaffold, which is not fully compensated for by a change in the acidity/basicity (pKa), suggesting "thermochemical decompensation".

Properties and corrosion protection of polypyrrole prepared by electrochemical polymerization on aluminum

AbstractIn a one‐step procedure that did not require any surface preparation, polypyrrole (PPy) films doped with 3‐nitrosalicylic acid (3Nisa) became effectively electropolymerized on the aluminum substrate in aqueous solutions. Fourier transform infrared, scanning electron microscopy, and thermal gravimetric analysis were used to analyze the properties of PPy‐based films. Open circuit potential (OCP), electrochemical impedance spectroscopy, Tafel polarization, and salt spray tests were used to study the corrosion‐resistant efficiency of the coatings. The as‐prepared PPy films performed corrosion resistance on aluminum in the 3% NaCl solution. However, the PPy films prepared in the 0.01 m solution of 3Nisa showed the best protection ability on aluminum. The self‐healing characteristic of the PPy films was recorded by varying the potential in the OCP measurement. The findings indicate the potential of using 3‐nitrosalicylic acid‐doped PPy films for applications as anti‐corrosion coatings for aluminum.

Long-Term Performance of Ag/AgCl Reference Electrodes for Corrosion Potential Monitoring in Radioactive Tank Waste at the Hanford Site

This work studied the exposure effects of radioactive tank waste on the long-term performance of single junction Ag/AgCl reference electrodes for corrosion potential monitoring at the Hanford Site. Electrodes from three manufacturers with very different designs were studied using open-circuit potential and electrochemical impedance measurements in radioactive tank waste. Post-test analyses were conducted on some failed electrodes using destructive and nondestructive techniques. The intrusion of the aggressive and radioactive chemicals in tank waste through the porous frit materials was the primary mechanism that led to the clogging of frit, physical and chemical degradation of AgCl bonded to Ag wire, and alteration of the internal electrolyte. Radiolytic chemical species such as H2O2 and HNO3 may have also induced the degradation of the Ag wire. The extent of electrode degradation and failure probability highly depended on the electrode design and environmental conditions. Chemicals in tank waste had stronger effects than radiation on the long-term performance of the Ag/AgCl reference electrodes.

Electrochemical analysis of carbon steel embedded in mortars with pretreated copper tailings as supplementary cementitious material

The cement industry, responsible for 8% of global greenhouse gas emissions, necessitates developing sustainable materials to replace cement partially. This investigation examined the feasibility of using copper tailings, a byproduct of mining, as alternative materials for cement within mortars and reinforced mortars (0–15 wt%). The microstructural composition of the tailings was analyzed using scanning electron microscopy and X-ray diffraction. The corrosion resistance of mortars reinforced with copper tailings was elucidated through open-circuit potential measurements and electrochemical impedance spectroscopy. The results showed that incorporating 5 and 10 wt% of sieved copper tailings improved the mechanical strength and significantly enhanced the electrochemical stability, as indicated by more noble open-circuit potential values. Specifically, the sieved tailings played a crucial role in forming a more stable oxide film, which was confirmed by higher impedance values, suggesting a reduced corrosion rate. In contrast, mortars with 5 wt% of milled tailings exhibited properties like those of the control group. This electrochemical understanding highlights the potential of processed copper tailings in mitigating the environmental impact of cement production and enhancing the durability of cementitious composites.

Impact of Surface Ligand Identity and Density on the Thermodynamics of H Atom Uptake at Polyoxovanadate-Alkoxide Surfaces.

An understanding of how molecular structure influences the thermodynamics of H atom transfer is critical to designing efficient catalysts for reductive chemistries. Herein, we report experimental and theoretical investigations summarizing structure-function relationships of polyoxovanadate-alkoxides that influence bond dissociation free energies of hydroxide ligands located at the surface of the cluster. We evaluate the thermochemical descriptors of O-H bond strength for a series of clusters, namely [V6O13-x(OH)x(TRIOLR)2]-2 (x = 2, 4, 6; R = NO2, Me) and [V6O11-x(OMe)2(OH)x(TRIOLNO2)2]-2, via computational analysis and open circuit potential measurements. Our findings reveal that modifications to the TRIOL ligand (e.g., changing from the previously reported electron withdrawing nitro-backed ligand to the electron-donating methyl variant) have limited influence on the strength of surface O-H bonds as a result of near complete thermodynamic compensation in these systems (i.e., correlated changes in redox potential and cluster basicity). In contrast, changes in surface density of alkoxide ligands via direct alkoxylation of the polyoxovanadate-alkoxide surface result in measurable increases in bond dissociation free energies of surface O-H bonds for the mixed-valent derivatives. Our findings indicate that the extent of (de)localization of electron density across the cluster core has an impact on the bond dissociation free energies of surface O-H bonds across all oxidation states of the assembly.

Detailed DFT/MD simulation, QSAR modeling, electrochemical, and surface morphological studies of self-assembled surfactants as eco-friendly corrosion inhibitors for copper in 1 M HNO3 solution

Three novel self-assembled phenyl pyrazole cationic surfactant derivatives, coded as SA-6, SA-12, and SA-18, were synthesized, structure confirmed, and examined as eco-friendly corrosion inhibitors for Cu in 1 M HNO3 electrolyte using open circuit potential (OCP), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) measurements. The efficacy of these surfactants was pointedly influenced by dosage (5 × 10−5 M − 1 × 10−3 M), attaining a maximum of 90.9 %, 92.9 %, and 94.5 % for SA-6, SA-12, and SA-18, respectively, at 1 × 10−3 M. The fact that the highest shift in corrosion potential (Ecorr) is so minor suggests that the compounds under investigation are inhibitors of the mixed type (anodic/cathodic). The high value of Kads and the negative ΔGadso value (−35.0, −35.8, and −36.8 kJ mol−1) suggests that the SA-6, SA-12, and SA-18 inhibitors have a strong and spontaneous tendency to adsorbed onto the Cu substrate. The development of the self-assembled surfactant defensive film on the Cu substrate was morphologically verified by atomic force microscopy (AFM). The studied self-assembled surfactants adsorbed physically and chemically according to Langmuir isotherm model. Quantitative structure–activity relationship (QSAR) was used to construct the prediction model for SA-6, SA-12, and SA-18′s anti-corrosion properties, while density functional theory (DFT) calculations were used to determine the chemical descriptors linked to the frontier molecular orbitals (FMOs). It was shown that the results of the computational and electrochemical experiments were highly consistent.

Structural, Electrical and Corrosion Properties of Bulk Ti-Cu Alloys Produced by Mechanical Alloying and Powder Metallurgy.

Binary Ti100-x-Cux (x = 1.6 and 3.0 wt.%) alloys were produced by the application of mechanical alloying and powder metallurgy processes. The influence of the copper concentration in titanium on the microstructure and properties of bulk alloys was investigated. The synthesized materials were characterized by an X-ray diffraction technique, scanning electron microscopy, and chemical composition determination. The electrochemical and corrosion properties were also investigated. Cold compaction and sintering reduced the content of α-Ti content in Ti98.4-Cu1.6 and Ti97-Cu3 alloys to 92.4% and 83.7%, respectively. Open Circuit Potential measurements showed a positive shift after the addition of copper, suggesting a potential deterioration in the corrosion resistance of the Ti-Cu alloys compared to pure Ti. Electrochemical Impedance Spectroscopy analysis revealed significant improvement in electrical conductivity after the addition of copper. Corrosion testing results demonstrated compromised corrosion resistance of Ti-Cu alloys compared to pure Ti. In summary, the comprehensive investigation of Ti100-x-Cux alloys provides valuable insights for potential applications in biosensing.

Potential-Rate Correlations of Supported Palladium-Based Catalysts for Aqueous Formic Acid Dehydrogenation.

Aqueous formic acid dehydrogenation (FAD) is a crucial process for hydrogen production, as hydrogen is a clean energy carrier. During this process, formic acid converts into hydrogen and carbon dioxide over a catalyst. Pd-based catalysts have exhibited significant potential in FAD due to their high activity and selectivity. In this study, we investigated aqueous thermal FAD in a mixture of formic acid and sodium formate using electrochemical open-circuit potential (OCP) measurement by loading the catalysts onto a conductive substrate as a working electrode. By varying the reaction conditions such as the concentration of reactants and modifying Pd with Ag, different FAD rates were obtained. Consequently, we revealed the correlation between the catalyst OCP and FAD rate; superior FAD rates reflected a more negative catalyst OCP. Furthermore, deactivation was observed across all catalysts during FAD, with a concurrent increase in catalyst OCP. Interestingly, we found that the logarithm of the FAD rate showed a linear correlation with the OCP of the catalyst during the decay phase, which we quantitatively explained based on the reaction mechanism. This study presents a new discovery that bridges thermal and electrocatalysis.

Development and electrochemical investigations of enhanced corrosion-resistant Polyvinylcarbazole-TiO2 hybrid nanocomposite coatings on 316L SS for marine applications

The present study focuses on evaluating the corrosion resistance of 316L stainless steel substrates with Polyvinylcarbazole (PVK)/TiO2 hybrid nanocomposite coatings (HNC). Using the chronoamperometry approach, the HNC were electrochemically synthesized on 316L stainless steel substrates, incorporating various weight (%) 1 %, 2 %, 3 % of TiO2 nanoparticles into the PVK matrix. The findings of the surface morphology investigation verified that the 316L SS had a dense and smooth PVK/TiO2 coating. A low surface roughness and high contact value of the PVK/TiO2 coatings are also responsible for the decrease in corrosion rate of the 316L SS. The corrosion protection efficiency of the PVK/TiO2 HNC were investigated through open circuit potential (OCP) measurement, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) analysis in 3.5 wt% NaCl solution. The corrosion rate obtained from the polarization studies of the HNC coatings as follows PVKT-2 < PVKT-3 < PVKT-1 < PVK < 316L SS. Results revealed that an optimal loading of 2 wt% TiO2 nanoparticles significantly enhanced the corrosion resistance of the coating. The enhanced electrochemical impedance response for PVK/TiO2 coatings was verified by EIS experiments. The study demonstrates that the incorporation of TiO2 nanoparticles into the PVK matrix effectively creates a barrier layer at the coating-metal interface, inhibiting the entry of aggressive ions. Microhardness studies revealed the increase in hardness value of the PVK and PVK/TiO2 coatings indicated the protective nature of the coating and provided high mechanical strength to 316L SS. The tape adhesion tests carried out on the coated specimens also indicated a good adhesion of the PVK/TiO2 on the 316L SS surface.

Study of Electroless Nickel Plating on Super Duplex Stainless Steel for Lithium-Ion Battery Cases: Electrochemical Behaviour and Effects of Plating Time

With increasing demand for Li-ion batteries, studies are focusing on enhancing battery performance and safety. However, studies on battery cases remain scarce. Herein, we propose the use of super duplex stainless steel SAF2507, which is a two-phase (austenite + ferrite) steel, for battery casings. Unlike conventional AISI304, SAF2507 maintains its corrosion resistance and strength at high temperatures and precipitates a secondary phase at approximately 975 °C. However, the effects of Ni plating on this secondary phase are not well documented. Therefore, the electroless Ni plating of SAF2507 after secondary-phase precipitation was studied. Briefly, heat treatment at 1000 °C was used to induce precipitation, and the electroless Ni plating behaviour over varying plating periods was analysed using open-circuit potential, potentiodynamic polarisation, and electrochemical impedance spectroscopy measurements. The plating state and corrosion behaviour were examined using scanning electron microscopy. Heat-treated SAF2507 steel with a secondary phase exhibited excellent electroless Ni plating behaviour, which enhances the safety and durability of Li-ion batteries. Furthermore, uniform plating and electrochemical behaviour were achieved after 180 s, suggesting that SAF2507 is superior to AISI304. These findings contribute to the development of safer and more efficient batteries and address the growing demand for Li-ion battery case materials.

Flotation separation of chalcopyrite from molybdenite with sodium thioglycolate: Mechanistic insights from experiments and MD simulations

The pivotal roles of Cu and Mo in industrial applications accentuate the importance of effectively separating and recovering chalcopyrite and molybdenite. They commonly exist together in natural environments, necessitating their segregation prior to engaging in smelting processes. The separation is mainly accomplished through flotation. The inadequate comprehension of the mechanisms of thiol depressants, commonly used in the separation of chalcopyrite and molybdenite, poses challenges to both resource recovery and the development of depressants. Based on the bulk flotation practice of copper-molybdenum sulfide minerals, this study investigated the separation effect and mechanism of sodium thioglycolate (STG) on xanthate-treated chalcopyrite and molybdenite. Flotation and contact angle tests validate that STG enhances the hydrophilicity of chalcopyrite surfaces, leading to an 83.79% flotation separation efficiency for molybdenite. Various methodologies were employed to explore the mechanism of the depressant, encompassing open-circuit potential measurements, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, infrared and ultraviolet spectroscopy, time-of-flight secondary ion mass spectrometry, classical molecular dynamics and ab initio molecular dynamics simulations. The stable adsorption layer of STG is established by the interaction of thiol groups from STG with Cu and Fe sites on the chalcopyrite surface, resulting in the formation of Cu(I)-S and Fe(III)-S structures. The adsorption density of STG layer on the chalcopyrite surface is four times greater than that on molybdenite. Additionally, following the adsorption of STG, the previously adsorbed xanthate chalcopyrite surface is desorbed with an efficiency of 65.88%. These findings contribute to the elucidation of the mechanistic understanding of thiol-containing depressants in the flotation separation process of copper-molybdenum sulfide minerals and establish a basis for the prospective advancement of mineral processing reagents.

Structural Parameters and Behavior in Simulated Body Fluid of High Entropy Alloy Thin Films.

The structure, composition and corrosion properties of thin films synthesized using the Pulsed Laser Deposition (PLD) technique starting from a three high entropy alloy (HEA) AlCoCrFeNix produced by vacuum arc remelting (VAR) method were investigated. The depositions were performed at room temperature on Si and mirror-like polished Ti substrates either under residual vacuum (low 10-7 mbar, films denoted HEA2, HEA6, and HEA10, which were grown from targets with Ni concentration molar ratio, x, equal to 0.4, 1.2, and 2.0, respectively) or under N2 (10-4 mbar, films denoted HEN2, HEN6, and HEN10 for the same Ni concentration molar ratios). The deposited films' structures, investigated using Grazing Incidence X-ray Diffraction, showed the presence of face-centered cubic and body-centered cubic phases, while their surface morphology, investigated using scanning electron microscopy, exhibited a smooth surface with micrometer size droplets. The mass density and thickness were obtained from simulations of acquired X-ray reflectivity curves. The films' elemental composition, estimated using the energy dispersion X-ray spectroscopy, was quite close to that of the targets used. X-ray Photoelectron Spectroscopy investigation showed that films deposited under a N2 atmosphere contained several percentages of N atoms in metallic nitride compounds. The electrochemical behavior of films under simulated body fluid (SBF) conditions was investigated by Open Circuit Potential (OCP) and Electrochemical Impedance Spectroscopy measurements. The measured OCP values increased over time, implying that a passive layer was formed on the surface of the films. It was observed that all films started to passivate in SBF solution, with the HEN6 film exhibiting the highest increase. The highest repassivation potential was exhibited by the same film, implying that it had the highest stability range of all analyzed films. Impedance measurements indicated high corrosion resistance values for HEA2, HEA6, and HEN6 samples. Much lower resistances were found for HEN10 and HEN2. Overall, HEN6 films exhibited the best corrosion behavior among the investigated films. It was noticed that for 24 h of immersion in SBF solution, this film was also a physical barrier to the corrosion process, not only a chemical one.

Effects of Passivation with Cu and W on the Corrosion Properties of Super Duplex Stainless Steel PRE 42

Carbon steel is subjected to several pretreatments to enable its use in highly corrosive environments, such as marine structures. However, its surface treatment is problematic owing to various processes, and these problems can be solved by replacing it with super duplex stainless steel (SDSS), which exhibits remarkable strength and corrosion resistance owing to its austenite and ferrite phases. EN 1.4410 and EN 1.4501 are the most extensively used SDSS grades in marine structures, as they exhibit exceptional strength and corrosion resistance in seawater. This study subjected EN 1.4410 and EN 1.4501 samples to specific heat treatment after casting and observed their structural alterations through field emission scanning electron microscopy. Their passivation states, with or without the Cu and W layers, were determined by examining their corrosion properties through open-circuit potential measurements, electrostatic polarisation tests, electrochemical impedance spectroscopy (EIS), and critical pitting temperature (CPT) analysis. The inclusion of Cu significantly improved the uniform corrosion resistance within the passivation layers, whereas the addition of W enhanced the pitting resistance (Epit, CPT). Additionally, the EIS analysis confirmed a double-layer structure in the passivation layer of EN 1.4501. Moreover, Cu did not act as a strengthening element of the passivation layer, whereas W significantly reinforced it.

Chromium/nickel-free conversion coating as cold post-treatment to anodized AA2024-T3 for corrosion resistance increase

The AA2024-T3 alloy exhibits significant properties for industrial applications, including low weight and high mechanical strength. However, its susceptibility to corrosion, attributed to precipitation hardening, requires effective surface treatments. Anodized aluminum alloys offer a robust protective structure; nevertheless, their porous layer must enable the anchoring of an additional coating or be adequately sealed. Boiling water sealing, though a non-toxic process, demands substantial energy consumption, while toxicity concerns limit the use of sealing with dichromate and Ni salts. Consequently, there is a pressing need to explore novel sealing methods capable of operating at lower temperatures for brief durations without Cr(VI) or Ni. This study proposes an alternative post-treatment for AA2024-T3 anodic layers generated in tartaric sulfuric acid (TSA). The method involves immersing the samples for 5 min in solutions containing H2ZrF6 alone, Na2MoO4 with KMnO4, and a combination of all three. The resulting layers underwent analysis using scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), open circuit potential (OCP) measurements during coating deposition, electrochemical impedance spectroscopy (EIS), and a visual examination post-immersion in a NaCl solution. The findings indicate that the Zr and Zr-Mo-Mn conversion coatings partially sealed the porous structure of the anodic oxide film, thereby enhancing its corrosion resistance in chloride medium. The incorporation of molybdate and permanganate ions intensified the precipitation of Zr oxide-fluorides within and on the porous layer, leading to improved corrosion resistance of the anodized alloy compared to Zr-only coating.

The anti-corrosion performance of chaya leaf extracts on pure Mg substrates in Ringer´s solution

The chaya (Cnidoscolus aconitifolius) is a green, leafy vegetable domesticated since ancient Mayan culture, offering an abundance of valuable metabolites. This study investigated how three different extracts from Chaya leaves inhibit the corrosion of pure magnesium in Ringer's solution. Various techniques, such as scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction were employed to analyze the chemical, morphological, and structural aspects of the products formed on the magnesium surface after a 14-day exposure. The in vitro corrosion behavior was studied through open-circuit potential measurements and electrochemical impedance spectroscopy during immersion tests in physiological Ringer's solution with each extract. Polarization curves were also obtained to determine jcorr and Ecorr. Different morphologies were observed on the surfaces of the substrates due to each extract’s polarity. However, the results showed that the three chaya extracts retard, to some extent, the corrosion process, reducing the pH (from 9 to 6) and jcorr (from 18.2 to 1.12 µAcm−2) in comparison to untreated samples. The ethyl acetate-derived extract exhibited the highest percentage of inhibition (92.9%) according to the impedance results. These extracts could be a promising alternative for developing potential temporary implants for the human body and diverse industrial applications.

Crystalline to Amorphous: Unveiling the Potential of Transition Metal Oxide‐based Electrocatalysts for Facile Oxygen Evolution Reaction in Alkaline Media

AbstractTransition metal oxides/hydroxides exhibit reasonable oxygen activity in alkaline electrolytes and have been identified as potential electrocatalysts. Some highly active transition metal oxides or hydroxides can alter their surface chemistry in response to the electrolyte environment. This review presents the performance of some of the recently developed transition metal‐based oxides in electrocatalytic oxygen evolution reaction (OER). Despite the promising catalytic activity of many transition metals and their alloys due to their incompletely filled d orbitals, their low corrosion resistance in alkaline media barriers their use as electrocatalysts. Metallic glasses (MGs), with their disordered atomic structure, have many unique and exciting properties that cannot be found in crystalline metals. Metallic glasses′ unique chemical activity and corrosion resistance stem from their metastable and defective nature, as well as their structural and chemical homogeneity. In the case of Zr‐based MGs, the presence of MG−OHads and MG−Ox species on the surface for oxygen evolution enables rapid electron transfer to chemisorbed OH− with an “activated” MG surface leading to the generation of an amorphous Zr‐rich layer. Zr‐rich oxide layer formation favors the OER understood by decreased Tafel slope and highly stable nature during open circuit potential measurements in the alkaline solution. Unlike the as‐spun counterpart, the relatively small impedance magnitude and characteristic frequency for the post‐OER electrode corroborate the enhancement of oxygen evolution kinetics after electrochemistry. Compared with the early discovered electrodes, the MG‐oxide assembly outperforms many transition and precision metal‐based oxides and their composite forms regarding oxygen electroactivity and stability.

Influence of Hybrid Surface Modification on Biocompatibility and Physicochemical Properties of Ti-6Al-4V ELI Titanium.

Titanium-based materials are the most widely used materials in biomedical applications. However, according to literature findings, the degradation products of titanium have been associated with potential allergic reactions, inflammation, and bone resorption. The corrosion process of Ti-6Al-4V in the human body environment may be exacerbated by factors such as reduced pH levels and elevated concentrations of chloride compounds. Coatings made of biopolymers are gaining attention as they offer numerous advantages for enhancing implant functionality, including improved biocompatibility, bioactivity, wettability, drug release, and antibacterial activity. This study analyzes the physicochemical and electrochemical behavior of the Ti-6Al-4V ELI alloy subjected to PCL and PCL/TiO2 deposition by the electrospinning method. To characterize the polymer-based layer, tests of chemical and phase composition, as well as surface morphology investigations, were performed. Wetting angle tests were conducted as part of assessing the physicochemical properties. The samples were subjected to corrosion behavior analysis, which included open circuit potential measurements, potentiodynamic tests, and the electrochemical impedance spectroscopy method. Additionally, the quantification of released ions post the potentiodynamic test was carried out using the inductively coupled plasma atomic emission spectrometry (ICP-AES) method. Cytotoxicity tests were also performed. It was found that surface modification by depositing a polymer-based layer on the titanium substrate material using the electrospinning method provides improved corrosion behavior, and the samples exhibit non-toxic properties.