Search Results (431)

The Alaunian–Sevatian (Norian) substage boundary, originally defined in the marine realm by ammonoid biostratigraphy, is now widely defined by conodont biostratigraphy (first occurrence of Mockina bidentata), particularly in the Tethyan realm. Although the taxon used is cosmopolitan, the zone base appears to be diachronous between Tethys and Panthalassa. The biostratigraphically anchored composite magnetostratigraphy for the marine Triassic places the base of the Mo. bidentata Zone at the base of the UT21n or high in the UT20r magnetochron as defined in the Geomagnetic Polarity Time Scale. When correlated to the terrestrial Newark Basin magnetostratigraphy, this zone appears equivalent to the base of the E15n or upper E14r magnetochron. The current version of the Newark Astronomic Polarity Time Scale, based on fitting the cyclicity of Newark Basin strata to established orbital cycle frequencies, places the E15n magnetochron base at an age of ca. 213.4 Ma. The Manicouagan impact event in eastern Canada is well-dated to 215.5 Ma, and an ejecta layer in Japan linked to the Manicouagan structure occurs very near the base of the Mo. bidentata conodont zone. If the age of the Manicouagan impact is accurately dated, the Newark time scale is inaccurate by as much as ca. 2.1 Myr. Full article

Inconel superalloys are employed in demanding components of different equipment. However, they can be exposed to atmospheric corrosion systems, such as marine and industrial environments. This research is focused on studying the localized corrosion susceptibility of Inconel 600, 690 and 718 exposed to H₂SO₄, 1 wt.% and 3.5 wt. % NaCl solutions, simulating marine and industrial atmospheres at 25 ± 0.5 °C. Localized corrosion behavior was characterized by electrochemical noise (EN) and cyclic potentiodynamic polarization (CPP) curves according to ASTM 6-199 ASTM G61 standards. The EN technique was analyzed through time series and analysis for chaotic systems, such as Hurst, Lyapunov and Husdorff coefficients, to determine the corrosion type of each system to reduce the uncertainty in common statistical analysis. The EN results show how Inconel superalloys tend to present localized attacks, being more notorious in NaCl. The application of specialized methods such as Hurst and Lyapunov helped to determine the corrosion system when alloys were characterized by EN. The results indicated that all superalloys exhibit positive hysteresis under CPP, indicating susceptibility to localized pitting corrosion. Full article

The corrosion behavior of copper and a Cu-Fe-P alloy in 3.5% NaCl solution was studied in this paper. This study focused on the influence of microalloying in the Cu-Fe-P alloy containing 0.003 wt% Fe and 0.014 wt% P on corrosion resistance in chloride media. Additionally, the effect of 2-mercapto-1-methylimidazole as an inhibitor was evaluated using electrochemical techniques, including potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy. According to the potentiodynamic polarization results, 2-mercapto-1-methylimidazole can be classified as a mixed-type inhibitor. The inhibition efficiency also increases with increasing concentration. The results indicate that the Cu-Fe-P alloy has improved corrosion resistance compared to copper, and a higher inhibition efficiency of 2-mercapto-1-methylimidazole was observed for the Cu alloy. Full article

This study investigates the microstructural evolution of the CoCrFeNi system after incorporating Gallium (Ga) at varying concentrations (0, 15, and 20 at.%). The systems were synthesized by Vacuum Arc Melting (VAM) and characterized through X-ray Diffraction diffraction (XRD) and Scanning Electron Microscopy (SEM/EDS). Findings showed that the CoCrFeNi medium medium-entropy alloy stabilizes in a single-phase Face-Centered Cubic (FCC) structure. Upon the addition of 15 at.% Ga a dendritic morphology with a transition towards a duplex FCC + BCC microstructure was induced, a trend which was further solified in the equiatomic FeCoNiCrGa system. In this case the proportion of the Ga-rich BCC phase was increased from 18–22% to 31–34% for the Ga15 and Ga20 systems respectively. A combined approach of Electrochemical Frequency Modulation (EFM), Cyclic Potentiodynamic Polarization (CPP), and Electrochemical Impedance Spectroscopy (EIS) was selected for studying the electrochemical corrosion behavior of the produced systems. EFM results indicated a progressive deterioration of corrosion resistance when increasing Ga concentration (Icorr: 4.142, 5.619 and 10.01 μA/cm², and Rp: 12,035, 10,736 and 7254 Ω for the Ga0, Ga15 and Ga20 alloys respectively). Surface inhomogeneity, rapid passivation, and diffusion-controlled processes caused deviations from the ideal causality factors’ values. CPP measurements revealed increasing corrosion current densities with Ga addition within the Tafel region (2.81 × 10⁻⁷, 3.72 × 10⁻⁷ and 5.11 × 10⁻⁷A/cm² for the Ga0, Ga15 and Ga20 alloys respectively). All alloys showed positive hysteresis loops and an absence of repassivation, indicating susceptibility to pitting corrosion. Nevertheless, detailed analysis of the forward polarization region highlighted a more complex aspect. Reverse polarization scans confirmed stable pit growth in all alloys, with the absence of a repassivation tendency. EIS tests, performed after the completion of CPP measurements, further clarified the corrosion mechanisms. Equivalent circuit modeling revealed that although Ga-containing alloys exhibited relatively improved film characteristics in the forward polarization stage, the charge transfer resistance (Rct) was highest for the CoCrFeNi alloy, followed by Ga15 and Ga20 (22,620, 11,380, 10,060 Ω respectively). The overall impedance ranking (Ga0 > Ga15 > Ga20, i.e., 27,139 > 20,279.5 > 16,341 ohms respectively) showed that, despite microstructural and entropic effects enhancing certain passivation aspects, the reduced Cr content highly impacted long-term corrosion resistance. This holistic electrochemical approach showcases the complex interactions between compositional alterations, phase structure, grain refinement, passive film chemistry, and diffusion trends in establishing the corrosion performance of Ga-modified CoCrFeNi HEAs. Full article

The present work compares the corrosion performance of additively manufactured (AM) Ti-6Al-4V ELI (Extra-Low Interstitials) alloy manufactured by Laser-Powder Bed Fusion (L-PBF) using virgin powder (Cycle 1/C1 sample) and reused powder feedstock after up to 34 cycles (Cycle 34/C34 sample) of manufacturing. The effect of powder reuse is also evaluated for anodizing and Flash-PEO-coated specimens in Harrison’s (25 °C) and Hanks’ solutions (37 °C), representing simulated atmospheric precipitation and physiological conditions, respectively. Specimens were characterized using common metallographic techniques, X-ray diffraction, scanning electron microscopy and optical profilometry. Corrosion resistance was evaluated using cyclic potentiodynamic polarization (PDP) tests. The oxygen content in the Ti-6Al-4V reaches 0.14 wt.% after 34 cycles (C34) of powder reuse, enhancing its passivity in both Harrison’s and Hanks’ solutions. Both virgin and reused powder builds are susceptible to localized corrosion in Hanks’ solution at potentials above 1.75 V. Melt pool borders are thought to be the preferential sites for localized corrosion, as indicated by Volta potential measurements (ΔV = 100 mV). The number of cycles does not significantly affect the current–voltage responses for anodizing and flash-Plasma Electrolytic Oxidation (Flash-PEO) treatments, although anodizing is slightly more responsive to variations in surface roughness (i.e., real specimen area). Anodizing and Flash-PEO reduce the passive current density by nearly two orders of magnitude. Even after surface treatment, the alloy printed with reused powder revealed better passivity. Flash-PEO coatings yielded significant protection against localized corrosion. This unlocks Flash-PEO processing as a successful protection approach for AM biomedical components. Full article

Xanthophylls are oxygenated carotenoids widely distributed in photosynthetic microorganisms, plants, algae, and certain invertebrates, where they function as key photoprotective and antioxidant pigments. Among them, xanthophylls containing vicinal 1,2-diol moieties exhibit unique chemical reactivity that enables reversible coordination with boron species naturally present in marine and terrestrial environments. The formation of cyclic borate esters between boron and diol-containing xanthophylls induces structural and electronic modifications that may enhance pigment stability and functional performance. Emerging evidence suggests that boron–xanthophyll complexes display improved resistance to photooxidative degradation, enhanced singlet oxygen quenching capacity, and increased radical-scavenging activity compared with their uncomplexed counterparts. In addition, boron coordination can influence molecular conformation, polarity, and supramolecular organization within lipid bilayers, thereby promoting membrane stabilization under conditions of high light exposure and oxidative stress. Together, these effects indicate a cooperative role of boron complexation in amplifying the intrinsic photoprotective and antioxidant properties of xanthophylls. A deeper understanding of the structural basis and biological implications of boron–xanthophyll interactions may provide new insights into adaptive stress tolerance in marine and photosynthetic organisms, as well as guide the development of advanced photoprotective systems for biomedical and technological applications. Full article

The corrosion behavior and time-dependent mechanism of 22MnB5 steel featuring a thinned Al-Si coating (60 g/m²) were systematically investigated in a chloride ion wet–dry cyclic environment, motivated by the demand for thinning and toughening development of aluminum-silicon coatings. A periodic immersion accelerated corrosion test using 3.5% NaCl solution was conducted, together with macro/microscopic morphology observation (SEM/EDS), phase analysis (XRD, FTIR), and electrochemical measurements (polarization curves, EIS). The Al-Si coated steel was studied over corrosion periods of 1, 8, 10, and 20 days to elucidate its corrosion behavior, interfacial evolution, and failure mechanism. The results indicated that the corrosion process exhibited a three-stage evolution: stable protection, rapid failure, and dynamic equilibrium. At the initial stage (1 day), a dense Al₂O₃ passive film formed on the coating surface, providing excellent substrate protection, with a corrosion current density of only 1.77 µA/cm² and a maximum charge-transfer resistance (R₂) of 652 Ω·cm². In the middle stage (8 days), Cl⁻ permeated through the cracked film, triggering selective dissolution of Al, while Si was enriched in situ to form a porous residual layer; the corrosion current density (I_corr) sharply increased to 13.25 µA/cm², and R₂ dropped to its minimum of 156.6 Ω·cm². Corrosion products at this stage were mainly Al₂O₃ and SiO₂, accompanied by small amounts of iron oxyhydroxides and hydroxides, and local coating failure began to appear. During the later stage (10–20 days), the corrosion products evolved into γ-FeOOH, α-FeOOH, and Fe₂O₃, which, together with an amorphous SiO₂ gel network enriched at the interface, formed a dual-layer composite rust layer. R2 consequently recovered from 156.6 Ω·cm² at 8 days to 424 Ω·cm² at 20 days, indicating a reduced corrosion rate and entry into a stable inhibition stage. The critical failure mechanism is that Cl⁻ preferentially penetrates the surface of the Al₂O₃ passive film, disrupting the metastable state of the coating and thereby creating pathways for corrosive media intrusion. The findings of this study can provide technical support for the safe application of such as-received coatings in non-load-bearing components with heat and corrosion resistance requirements. Full article

The growing emphasis on environmental sustainability and the need for advanced manufacturing methods have accelerated progress in material processing. Aluminum powder metallurgy (APM) is particularly promising due to aluminum’s low density, high strength-to-weight ratio, and the inherent benefits of the powder metallurgy (PM) process. However, the corrosion resistance of sintered aluminum components remains a significant concern. In this study, shot peening (SP) was employed as a surface modification technique to improve the corrosion behavior of Alumix 321 PM alloy. Samples of the as-sintered and shot-peened Alumix 321 PM alloy, together with the wrought alloy counterpart AA6061, were characterized using non-contact optical profilometry, optical microscopy (OM), and scanning electron microscopy (SEM). Corrosion performance was evaluated in 3.5 wt.% NaCl solution using Tafel extrapolation (TE), cyclic polarization (CP), stair step polarization (SSP), and electrochemical impedance spectroscopy (EIS). The results revealed that shot peening increased surface roughness and significantly reduced the corrosion rate from 0.079 mmpy to 0.004 mmpy for the unpeened and peened samples, respectively. While pitting was the dominant corrosion mechanism in the wrought alloy, the PM alloy exhibited a combination of pitting, crevice, and intergranular corrosion. These findings highlight the potential of SP in enhancing the durability of aluminum-based PM components, offering valuable insights for industrial applications. Full article

This study evaluated the influence of scan rate (4.23 mm/s [S10] and 6.35 mm/s [S15]) on the localized corrosion and tribocorrosion behavior of a laser engineered net shaping (LENS)-produced stainless steel 316L (SS316L) in a phosphate-buffered saline (PBS) solution. Electrochemical impedance spectroscopy (EIS) was performed by applying an AC signal from 10⁵ to 10⁻² Hz and cyclic potentiodynamic polarization (CPP) was performed by sweeping from −150 mV to +1.5 V (vs. open circuit potential) and back to characterize passivation and pitting susceptibility. Potentiostatic tribocorrosion tests were conducted using a reciprocating tribometer integrated with a potentiostat to probe material response in passive and cathodic regimes. S15 exhibited manufacturing-related defects that served as preferential pit initiation sites, with pits in both S10 and S15 showing evidence of cell-interior dissolution. Electrochemical results indicated that the charge transfer resistance was reduced by 66% for S15 and that the repassivation potential decreased by 35% compared to S10. Under tribocorrosion, material degradation was dominated by mechanical wear for both samples. However, sliding significantly accelerated electrochemical dissolution in S15, with the corrosion rate affected by wear (V_c-w) increasing by 46.8%. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) of wear scars revealed plastic deformation, abrasive grooves, and bio-tribofilm formation composed primarily of phosphates. Micro-pits associated with processing defects were observed exclusively in S15. Overall, lower scan rate processing (S10) produced a more defect-resistant microstructure with improved resistance to localized corrosion and tribocorrosion in PBS. Full article

This paper presents a novel integration of quadrature amplitude modulation (QAM)-based fast optical orthogonal frequency-division multiplexing (F-OFDM) with machine learning (ML)-based equalization in spatial division multiplexing (SDM) applications, using few-mode fibers (FMFs). The FMFs support four LP modes, resulting in a total of 12 orthogonal modes, each accommodating two polarizations. A digital multiple-input multiple-output channel equalizer is employed at the receiver’s digital signal processing (DSP) unit to effectively mitigate channel crosstalk. The study harnesses supervised ML-DSP techniques, in particular recurrent neural networks (RNNs) and deep neural networks (DNNs), achieving substantial reductions in bit error rates (BERs). In addition, higher-complexity architectures, namely convolutional neural networks (CNNs) and long short-term memory (LSTM) networks, are evaluated to assess the impact of advanced spatial and temporal feature extraction. It is shown that F-OFDM demonstrates superior performance over conventional optical OFDM, particularly when supported by ML techniques. Simulation results reveal that RNNs achieve a BER of 0.0019 over 15 km at 12 Gbaud (worst-case selected channel), showcasing a remarkable 52.5% improvement compared to linear equalization. DNNs achieve a BER of 0.0025, reflecting a 37.5% enhancement. While RNNs perform better, their computational demands pose challenges for real-time applications, and the more complex models (CNN and LSTM) do not provide additional performance gains. The paper also explores cyclic prefix management and subcarrier number strategies in F-OFDM to optimize performance, paving the way for future advancements in SDM networks. Full article

This work explores the response of additively manufactured Al alloys (AlSi10Mg and AlSi7Mg) to a strong alkaline environment (pH 12, 1 M KOH). The corrosion response was monitored through electrochemical techniques such as open-circuit potential (OCP), Electrochemical Impedance Spectroscopy (EIS), potentiodynamic polarization (PDP), and cyclic potentiodynamic polarization (CPP), providing insights into film stability and pitting tendency. Scanning Electron Microscopy (SEM) was employed to characterize the surface morphology and degradation features before and after immersion. The results showed clear contrasts in passive film stability and resistance to pitting. AlSi10Mg demonstrated stronger protection, linked to its fine cellular–dendritic structure and tightly connected Si network that supported more uniform oxide growth. Contrastingly, AlSi7Mg showed premature film breakdown and localized attack, driven by coarse Si particles and micro-galvanic coupling. Post-corrosion SEM revealed clear signs of selective dissolution and Si particle detachment as the main degradation features. This behavior is consistent with earlier studies showing that the morphology of Si strongly influences the corrosion pathways of Al–Si–Mg alloys in alkaline media. Full article

This study reports that titanium nanoparticles can be used as a surface coating to enhance the corrosion resistance of 316 stainless steel. It specifically examines the influence of the deposition temperature (T_dep) on the coating’s structural and morphological properties, including corrosion behavior. TiO₂ nanoparticles were thoughtfully deposited on steel substrates at temperatures of 300, 400, and 500 °C using a horizontal hot-wall tubular reactor. This equipment was expertly engineered at the CIDETEQ laboratory through the metal–organic chemical vapor deposition (MOCVD) concept. Titanium isopropoxide [Ti(OC₃H₇)₄] was used as the precursor for the coating synthesis. Structural analysis was conducted using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). Corrosion performance was evaluated under accelerated conditions in 0.5 M H₂SO₄ using potentiodynamic anodic polarization (AP), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The corrosion test indicates that increasing T_dep significantly differentiates the coating morphology and improves corrosion resistance. AP revealed that the pitting potential (E_pit) shifted to more positive values, ranging from +1.4 to +1.5 V. CV voltammograms indicated that coated samples had lower passive current densities (I_p ≈ 10⁴ to 10⁵ A/cm²) than the bare substrate. EIS analysis demonstrated that the coating deposited at 500 °C processed the most favorable electrochemical performance, resisting corrosion for over 28 days. This coating achieved the highest electrical resistance (297 kΩ·cm²) and the lowest capacitance (2.7 μF/cm²), attributed to the formation of a crystalline anatase phase composed of pyramidal-like nanoparticle agglomerates (~40 nm). The dense packing structure effectively blocks charge-transfer pathways, restricting electron and ion transfer. Finally, MOCVD-based chemical surface modification with TiO₂ nanoparticles is considered an innovative method to improve the corrosion resistance of stainless steel, thereby prolonging its durability under accelerated sulfuric acid exposure. Full article

Silicone food contact materials (FCMs) pose potential health risks due to the migration of siloxanes. This study presents a comprehensive migration profiling of 35 siloxanes (cyclic D3–D22 and linear L2–L14) from 30 silicone FCMs, with migration tests rigorously conducted under worst-case intended-use scenarios to ensure conservative and reliable exposure estimates. Methodological innovations include an expanded analytical scope, age-stratified exposure assessment across seven age groups, and a multi-tiered risk evaluation framework. The results reveal that migration behaviors were affected by simulant polarity, siloxane solubility, and silicone thermal stability. The risk evaluation framework integrates aggregate migration limits for total cyclic (D3–D13) and total cyclic plus linear siloxanes (D3–D13, L3–L13), complemented by individual siloxane assessment via Risk Quotient (RQ) and Threshold of Toxicological Concern (TTC) approaches. While the total migration of cyclic siloxanes exceeded the proposed action limit of 12 mg/kg for adults in several samples and 2 mg/kg for children in most samples, granular assessment revealed divergent risks: Cyclic D4 and D5 showed negligible risk (RQ < 5). In contrast, D3 migration posed a potential concern (RQ > 5), especially for individuals aged >13 years. Notably, the estimated exposures to 14 siloxanes with low molecular weight (<1000 Da), including highly prevalent D6 and L12 with detection frequency >90%, exceeded the TTC threshold across all age groups, highlighting unaddressed risks that are not captured by aggregate action limits. This work underscores the need for substance-specific, age-specific risk evaluations and regulatory updates for silicone FCMs. Full article

Layered sodium transition-metal oxides are promising cathode materials for sodium-ion batteries due to their high theoretical capacity; however, their practical application is often limited by sluggish Na⁺ diffusion kinetics and structural instability during cycling. P2/O3 phase coexistence has been proposed as an effective strategy to balance capacity and stability, yet it is typically achieved through precise Na-content tuning or complex synthesis conditions, which restrict compositional flexibility. Herein, we demonstrate a phase-engineering approach that induces stable P2/O3 phase coexistence without adjusting the overall Na stoichiometry by controlling the dopant incorporation pathway. Using Na_0.8(Ni_0.25Fe_0.33Mn_0.33Cu_0.07)O₂ (NaNFMC) as a model system, Mg doping via a wet chemical route enables homogeneous dopant distribution, which triggers local stacking rearrangement and the formation of prismatic Na⁺ diffusion channels characteristic of the P2 phase. In contrast, dry-doped samples with identical Mg content retain a predominantly O3-type structure, highlighting the decisive role of dopant incorporation in governing phase evolution. As a result of the phase-engineered P2/O3 coexisting framework, the Mg wet-doped cathode exhibits enhanced initial reversibility, superior rate capability, and improved long-term cycling stability compared to pristine and dry-doped counterparts. Voltage-resolved dQ/dV and cyclic voltammetry analyses reveal stabilized redox behavior with reduced polarization, while electrochemical impedance spectroscopy confirms suppressed impedance growth and improved Na⁺ transport kinetics after cycling. This study establishes that phase engineering through controlled dopant incorporation provides an effective alternative to conventional Na-content tuning strategies for layered sodium cathodes. The findings offer a scalable and versatile design principle for optimizing the electrochemical performance and structural durability of next-generation sodium-ion battery cathode materials. Full article

Titanium alloys are widely used for biomedical implants due to their favorable mechanical properties, corrosion resistance, and biocompatibility. However, the development of multifunctional implant materials requires not only structural stability but also controlled electrochemical responsiveness, an important property for electrochemical sensing. This study developed ultrafine-grained Ti–xMo alloys (x = 28 and 31 wt.%) via mechanical alloying followed by powder metallurgy to investigate the effect of high Mo content on phase stability, corrosion behavior, and electrochemical sensing response. Both alloys exhibited predominantly β-phase microstructures, with β-phase fractions exceeding 93%, confirming effective stabilization at elevated Mo concentrations. Electrochemical tests conducted in 0.01 M PBS and Ringer’s solution revealed that pure Ti exhibited the highest impedance modulus and lowest corrosion current density, indicating superior passive film barrier properties. In contrast, high-Mo alloys showed reduced polarization resistance and increased charge-transfer contribution, associated with modifications in passive film defect chemistry and electronic properties induced by Mo enrichment. Among the investigated compositions, Ti-31 wt.% Mo demonstrated improved electrochemical stability compared to Ti-28 wt.% Mo, exhibiting lower corrosion current density and higher impedance values within the high-Mo regime. Cyclic voltammetry performed in 0.01 M PBS containing 1 mM K₃[Fe(CN)₆] confirmed enhanced heterogeneous electron-transfer capability for Mo-rich alloys relative to pure Ti. Overall, Ti-31 wt.% Mo provides a balanced combination of β-phase stabilization, moderate corrosion resistance, and improved electrochemical responsiveness potentially suitable for sensing interfaces. Full article