Materials

25 pages, 7777 KB

Open AccessArticle

Influence of S and Mn Initial Concentrations on the Graphite Branching in Gray Cast Iron as Quantified by 2D Image Analysis

by Luis Filiberto De Santiago-Méndez, Manuel de Jesús Castro-Román, Martín Herrera-Trejo, Hector Mancha-Molinar and Beñat Bravo

Materials 2025, 18(21), 4837; https://doi.org/10.3390/ma18214837 (registering DOI) - 22 Oct 2025

Abstract

The morphology changes in graphite flakes due to the difference in S and Mn contents were analyzed in gray iron samples with a Carbon Equivalent (CE) of 4.0. Although these Mn and S contents are within the range of industrial usage, the morphological [...] Read more.

The morphology changes in graphite flakes due to the difference in S and Mn contents were analyzed in gray iron samples with a Carbon Equivalent (CE) of 4.0. Although these Mn and S contents are within the range of industrial usage, the morphological characteristics of graphite flakes among the different samples show significant changes in their size and distribution. Graphite flake size was estimated using the Feret diameter, and the flake’s distribution was visually characterized following established standards. As it was observed that graphite flakes also differ in branching, a new procedure was developed to quantify such branching. Based on a skeletonization technique, this new procedure provides data to obtain additional microstructural parameters of the graphite flakes, such as the percentage of branched flakes and the longest shortest path (LSP) of each graphite flake. Microstructural characterization included measuring the eutectic cell count. The results indicate that Feret values and LSP show only weak correlations with concentration estimates from initial S and Mn. The most notable relationships are between sulfur content and Feret or LSP values. In contrast, the branching percentage correlates well with free sulfur at 1150 °C and eutectic cell count and is also linked to graphite distribution types (A or B). Notably, branching percentage offers a straightforward morphological parameter that enhances graphite flake characterization. Full article

(This article belongs to the Special Issue Characterization of Metallic Materials: Solidification, Deformation, Heat Treatment and Other Related Phenomena—Third Edition)

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20 pages, 5750 KB

Open AccessArticle

Bone Formation and Anti-Inflammatory Properties of Iodine-Loaded Titanium Implants: An Animal Study

by Kazuto Yamada, Kazuya Inoue, Nanako Shimada, Tatsuya Kakutani, Yasuhisa Sawai, Naoko Imagawa-Fujimura, Kayoko Yamamoto, Nahoko Kato-Kogoe, Seiji Yamaguchi and Takaaki Ueno

Materials 2025, 18(21), 4836; https://doi.org/10.3390/ma18214836 (registering DOI) - 22 Oct 2025

Abstract

Titanium implants are subjected to various surface treatments to improve their in vivo function. In this study, we evaluated the usefulness of titanium implants treated with acid, NaOH, CaCl₂, heat, and ICl₃ (Ac-NaCaThIo) in terms of in vivo bone-bonding strength, [...] Read more.

Titanium implants are subjected to various surface treatments to improve their in vivo function. In this study, we evaluated the usefulness of titanium implants treated with acid, NaOH, CaCl₂, heat, and ICl₃ (Ac-NaCaThIo) in terms of in vivo bone-bonding strength, bone formation, and histological anti-inflammatory properties. Iodine-loaded experimental dental implants and commercial control dental implants were placed in rabbit femurs, and bone-bonding strength was evaluated by measuring the implant stability quotient (ISQ), bone formation using tissue specimens, and the effect of iodine using thyroid-stimulating hormone (TSH) levels. Iodine-loaded titanium plates and untreated titanium plates were placed on rat skulls and inoculated with Streptococcus mitis (S. mitis) solution to evaluate anti-inflammatory properties. Consequently, the experimental implants did not demonstrate non-inferiority in bone-bonding strength (ISQ) compared with the controls; however, histological specimens revealed dense bone contact and favorable bone formation. TSH levels showed no differences at 13 weeks, indicating no long-term adverse effects of iodine. The experimental tissue specimens of the soft tissue had fewer inflammatory cells than the control at 2 weeks after placement, demonstrating an anti-inflammatory effect. These results suggest that, although non-inferiority in ISQ was not demonstrated, Ac-NaCaThIo-treated implants showed favorable bone formation, dense bone contact, anti-inflammatory properties, and biosafety, indicating potential for future applications. Full article

(This article belongs to the Special Issue Materials for Drug Delivery and Medical Engineering)

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18 pages, 1328 KB

Open AccessArticle

Effect of Ultrasonic Condensation Time on Void Formation and Microhardness of Well-Root^TM PT Apical Plugs in 3D-Printed Immature Teeth

by Krasimir Hristov and Ralitsa Bogovska-Gigova

Materials 2025, 18(21), 4835; https://doi.org/10.3390/ma18214835 (registering DOI) - 22 Oct 2025

Abstract

Background: This study aimed to evaluate the impact of varying durations of ultrasonic condensation on the formation of internal and external voids and the microhardness of apical plugs created with premixed bioceramic putty Well-Root^TM PT in standardized 3D-printed immature permanent teeth using [...] Read more.

Background: This study aimed to evaluate the impact of varying durations of ultrasonic condensation on the formation of internal and external voids and the microhardness of apical plugs created with premixed bioceramic putty Well-Root^TM PT in standardized 3D-printed immature permanent teeth using micro-CT imaging and Vickers microhardness testing. Methods: Forty-eight 3D-printed upper incisors with simulated open apices (2 mm canal diameter) were divided into four groups (n = 12 each) based on apical plug condensation technique as follows: Group 1 (control, manual condensation), Group 2 (3-s Ultrasonic at 25 kHz), Group 3 (9-s Ultrasonic at 25 kHz), and Group 4 (15-s Ultrasonic at 25 kHz). Well-Root^TM PT was used to form 5 mm apical plugs under a microscope. Samples were stored at 37 °C and 100% humidity for one week. Micro-CT imaging was used to quantify internal, external, and total void volumes (% of total material volume), while microhardness was measured using a Vickers tester (1 kgf load, 10 s) on polished apical plug sections. Statistical analysis was performed using ANOVA and Tukey post hoc tests. Results: Group 4 (15-s Ultrasonic) exhibited significantly higher external and total void volumes compared to Groups 1–3 (p < 0.001), with no significant differences in internal voids across groups (p > 0.05). Microhardness was highest in Group 1 (mean VHN: 76.95 ± 3.73), followed by Group 2 (73.11 ± 4.82), Group 3 (55.11 ± 5.28), and Group 4 (51.25 ± 7.73) (p < 0.05). Shorter ultrasonic durations (3-s Ultrasonic) resulted in fewer voids and higher microhardness compared to longer durations (15-s Ultrasonic). There was no statistically significant difference in void size among the groups compared (p > 0.05). Fractal dimension analysis showed that prolonged ultrasonic condensation results in less complex voids compared to shorter activation. Conclusion: Manual condensation of premixed bioceramic putty, by promoting denser particle packing without ultrasonic-induced disruptions, leads to higher microhardness. Brief ultrasonic activation (3-s Ultrasonic) optimizes the quality of Well-Root^TM PT apical plugs by minimizing voids and maintaining higher microhardness, thus enhancing the apical seal. Prolonged ultrasonic activation (15-s Ultrasonic) increases void formation and reduces microhardness, potentially compromising the long-term integrity of the apical barrier. Full article

(This article belongs to the Special Issue Mechanical Properties of Dental Materials)

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16 pages, 2675 KB

Open AccessArticle

The Use of Acoustic Emission to Determine the Safe Range of Operational Stresses of 3D-Printed ABS Polymer Components

by Krzysztof Dudzik, Patryk Krawulski, Robert Starosta and Burkhard Ziegler

Materials 2025, 18(21), 4834; https://doi.org/10.3390/ma18214834 (registering DOI) - 22 Oct 2025

Abstract

This work proposes using acoustic emission during a static tensile test to determine the stress characteristics of the initial phase of the destruction process of elements printed using the material extrusion (MEX) additive method at various printing parameters. The changed parameters were layer [...] Read more.

This work proposes using acoustic emission during a static tensile test to determine the stress characteristics of the initial phase of the destruction process of elements printed using the material extrusion (MEX) additive method at various printing parameters. The changed parameters were layer height, print orientation, filling ratio, and nozzle temperature. ABS material was chosen for printing. The experiment was carried out according to the Taguchi plan. The analysis of the results showed that changes in printing parameters significantly impact the mechanical properties of the tested elements. The parameter that had the greatest impact on strength was the filling ratio. Maximum tensile strength was achieved with the following printing parameters: 0.24 mm layer, 30°, 100% infill, 275 °C, concentric pattern. The results can be the basis for optimizing the additive printing process and improving the efficiency and reliability of manufactured components. The results of recorded acoustic emissions during strength tests allow the identification of stresses characteristic of the initial phase of the destruction process of the tested material. This phase is the elastic-visco-plastic transition, and the use of the AE method enables its detection 2–5 s earlier than the static tensile test. This allows us to determine the safe range of stresses when using the mentioned materials, which is particularly helpful in designing structures or spare parts. The test results showed that the critical stress for the investigated components is approximately 6 MPa, and exceeding this value is associated with the risk of unsafe operation. Full article

(This article belongs to the Special Issue Design and Application of Additive Manufacturing: 4th Edition)

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10 pages, 498 KB

Open AccessArticle

Tensile Strength Characterization of Alkaline-Treated and Untreated Banana Fibres Using Weibull Statistics

by Maryam Sodagar, Nassim Edouard Lagrou and Thomas Gries

Materials 2025, 18(21), 4833; https://doi.org/10.3390/ma18214833 (registering DOI) - 22 Oct 2025

Abstract

Banana fibres (BFs), derived from the pseudo-stems of Musa acuminata, represent a widely available agricultural residue with strong potential as an eco-friendly reinforcement in composite materials—particularly in bio-based epoxy or thermoplastic systems used in automotive interiors, packaging, and lightweight construction. However, their inherent [...] Read more.

Banana fibres (BFs), derived from the pseudo-stems of Musa acuminata, represent a widely available agricultural residue with strong potential as an eco-friendly reinforcement in composite materials—particularly in bio-based epoxy or thermoplastic systems used in automotive interiors, packaging, and lightweight construction. However, their inherent variability presents challenges for consistent and reliable mechanical characterisation. This study investigates the effect of wood ash treatment, an eco-friendly alternative to conventional alkaline processing, on the tensile strength of single BFs. Fibres were treated in aqueous wood ash solutions at two pH levels (12.4 and 13.5) and soaking durations of 3 h and 24 h, and then tested according to ASTM C1557. At least 50 valid tensile tests per series were performed, and the results were analysed using a two-parameter Weibull distribution to quantify characteristic strength and variability, complemented by reliability analysis to assess survival probability. Untreated fibres exhibited low characteristic strength (396.6 MPa) and a Weibull modulus of 1.79, confirming significant scatter. Treated fibres showed marked improvements: the highest characteristic strength was achieved at pH 13.5 for 3 h (552.8 MPa, m = 3.17), while the greatest uniformity was observed at pH 13.5 for 24 h (m = 4.62). Reliability curves confirmed superior performance of treated fibres, with 75% survival strengths up to 373 MPa compared to 198 MPa for untreated. These findings demonstrate that wood ash treatment enhances both the strength and reliability of BFs for sustainable composite applications. Full article

(This article belongs to the Special Issue Bio-Based Natural Fiber Composite Materials)

17 pages, 2086 KB

Open AccessArticle

The Impact of Storage Conditions on the Gas-Forming Tendency of Moulds and Cores Made with Resole-Type Phenol Formaldehyde Resin

by Artur Bobrowski, Faustyna Woźniak, Sylwia Żymankowska-Kumon, Hubert Ziętal, Kacper Januszek and Beata Grabowska

Materials 2025, 18(21), 4832; https://doi.org/10.3390/ma18214832 (registering DOI) - 22 Oct 2025

Abstract

The article presents the results of a study aimed at determining the impact of storage conditions on the gas-forming tendency of standard samples (cores) made from moulding sand using a two-component binder based on resole-type phenolic resin, cured with a dedicated ester mixture. [...] Read more.

The article presents the results of a study aimed at determining the impact of storage conditions on the gas-forming tendency of standard samples (cores) made from moulding sand using a two-component binder based on resole-type phenolic resin, cured with a dedicated ester mixture. The objective of the research was to determine the total volume of gases released as a result of contact between the cores or moulds and the high temperature of molten casting alloys, as well as the rate of gas release, which can influence the tendency for gas-related casting defects. Additionally, the influence of storage conditions on the gas-forming tendency of the samples was evaluated in terms of their environmental and occupational health impact, based on the emission of BTEX compounds (benzene, toluene, ethylbenzene, and xylenes), which serve as key indicators of the harmfulness of moulding and core sands to the surrounding environment. Full article

(This article belongs to the Special Issue Achievements in Foundry Materials and Technologies)

13 pages, 1075 KB

Open AccessArticle

Influence of Surface Treatments and Thermocycling on Wettability, Roughness, and Bond Strength of Lithium Disilicate CAD/CAM Ceramics

by Serpil Demiroğlu and Salim Ongun

Materials 2025, 18(21), 4831; https://doi.org/10.3390/ma18214831 (registering DOI) - 22 Oct 2025

Abstract

This study evaluated the effects of surface treatments and thermal aging on the surface properties and bonding performance of three CAD/CAM lithium disilicate ceramics: Amber Mill, Vita Suprinity, and IPS e.max CAD. A total of 150 specimens were divided into five groups: control, [...] Read more.

This study evaluated the effects of surface treatments and thermal aging on the surface properties and bonding performance of three CAD/CAM lithium disilicate ceramics: Amber Mill, Vita Suprinity, and IPS e.max CAD. A total of 150 specimens were divided into five groups: control, hydrofluoric acid etching, airborne-particle abrasion, and Er,Cr:YSGG laser irradiation at 2 W and 3 W. Half of the samples underwent thermocycling (10,000 cycles, 5–55 °C). Surface roughness, water contact angle, and microshear bond strength were measured, and failure modes were analyzed. Ceramic type and surface treatment significantly affected outcomes. Amber Mill generally exhibited higher roughness, while IPS e.max CAD achieved the greatest bond strength. Hydrofluoric acid etching consistently enhanced bonding in Vita Suprinity and IPS e.max CAD, whereas 2 W laser irradiation improved bond strength without notably changing roughness. In contrast, 3 W laser treatment increased contact angle, reducing wettability. Thermocycling raised bond strength in control and sandblasted groups but overall increased contact angle. Adhesive failures predominated, though cohesive and mixed failures became more common after aging. Overall, ceramic type, surface treatment, and thermal aging interactively influenced adhesion. Hydrofluoric acid etching remains the most effective treatment, while low-power laser irradiation offers a promising, less invasive alternative. Full article

(This article belongs to the Section Advanced and Functional Ceramics and Glasses)

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25 pages, 1021 KB

Open AccessArticle

Hardness Characterization of Simultaneous Aging and Surface Treatment of 3D-Printed Maraging Steel

by Zsuzsa Szabadi Olesnyovicsné, Attila Széll, Richárd Horváth, Mária Berkes Maros and Mihály Réger

Materials 2025, 18(21), 4830; https://doi.org/10.3390/ma18214830 (registering DOI) - 22 Oct 2025

Abstract

The primary objective of this research is to simplify and make the industrial manufacturing process of coated maraging steels more economical by combining the advantages of additive manufacturing with simultaneous bulk (aging) and surface (nitriding) treatment in an effective manner. With this aim, [...] Read more.

The primary objective of this research is to simplify and make the industrial manufacturing process of coated maraging steels more economical by combining the advantages of additive manufacturing with simultaneous bulk (aging) and surface (nitriding) treatment in an effective manner. With this aim, preliminary experiments were performed that demonstrated the hardness (and related microstructure) of an as-built MS1 maraging steel, produced by selective laser melting (SLM), is comparable to that of the bulk maraging steel products treated by conventional solution annealing. The direct aging of the solution-annealed and as-built 3D printed maraging steel resulted in similar hardness, indicating that the kinetics of the precipitation hardening process are identical for the steel in both conditions. This assumption was strengthened by a thermodynamic analysis of the kinetics and determination of the activation energy for precipitation hardening using Differential Scanning Calorimetry (DSC) measurements. Industrial target experiments were performed on duplex-coated SLM-printed MS1 steel specimens, which were simultaneously aged and salt-bath nitrided, followed by PVD coating with three different ceramic layers: DLC, CrN, and TiN. For reference, similar duplex-coated samples were used, featuring a bulk Böhler W720 maraging steel substrate that was solution annealed, precipitation hardened, and salt-bath nitrided in separate steps, following conventional procedures. The technological parameters (temperature and time) of the simultaneous nitriding and aging process were optimized by modeling the phase transformations of the entire heat treatment procedure using DSC measurements. A comparison was made based on the in-depth hardness profile estimated by the so-called expanding cavity model (ECM), demonstrating that the hardness of the surface layer of the coated composite material systems is determined solely by the type of the coatings and does not influenced by the type of the applied substrate materials (bulk or 3D printed) or its heat treatment (whether it is a conventional, multi-step treatment or a simultaneous nitriding + aging process). Based on the research work, a proposal is suggested for modernizing and improving the cost-effectiveness of producing aged, duplex-treated, wear-resistant ceramic-coated maraging steel. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

36 pages, 96985 KB

Open AccessArticle

Fire Resistance and Colorimetric Analysis of Lightweight Fiber-Reinforced Foamed Alkali-Activated Hybrid Binders

by Magdalena Rudziewicz, Katarzyna Mróz, Marcin Maroszek, Paweł Wołkanowski and Marek Hebda

Materials 2025, 18(21), 4829; https://doi.org/10.3390/ma18214829 (registering DOI) - 22 Oct 2025

Abstract

In response to escalating environmental concerns, the construction industry is under growing pressure to adopt sustainable practices. As a major consumer of natural resources and a significant emitter of greenhouse gases, it paradoxically holds the potential to become a leader in green transformation. [...] Read more.

In response to escalating environmental concerns, the construction industry is under growing pressure to adopt sustainable practices. As a major consumer of natural resources and a significant emitter of greenhouse gases, it paradoxically holds the potential to become a leader in green transformation. This study investigates the development of innovative, fire-resistant, and alkali-activated hybrid binder foams incorporating recycled materials: fly ash, coal slag, and ground brick waste, as sustainable alternatives to traditional building materials. The fire resistance performance at a technical scale and the thermal behavior of fiber-reinforced, alkali-activated hybrid binder foams synthesized from recycled aluminosilicate precursors were determined. The properties of unreinforced composite were compared with the composites reinforced with merino wool, basalt fibers, polypropylene fibers, and coconut fiber. Small-scale fire-resistance tests revealed that merino wool-reinforced composites exhibited the best thermal insulation performance, maintaining structural integrity, that is, retaining shape and continuity without delamination or collapse for 83 min under fire exposure. Analyses combining chemical characterization (X-ray fluorescence) with microstructural methods (computed tomography and colorimetry) confirmed that fire performance is strongly influenced not only by fiber type but also by pore distribution, phase composition, and oxide migration under thermal loading. These findings demonstrate the potential of fiber-reinforced foamed, alkali-activated hybrid binder as eco-efficient, printable materials for fire-safe and thermally demanding construction applications. Full article

(This article belongs to the Special Issue Green and Sustainable Infrastructure Construction Materials (3rd Edition))

17 pages, 5096 KB

Open AccessArticle

Hot-Pressed Reinforced Photocatalyzed TiO₂/Chitosan/SiO₂ Nanofibers

by Jingwen Wang, Zunzhi Liu, Jingmei Zhang, Yang Liu, Chunjing Hou, Hui Cheng, Yaru Wang and Xiang Liu

Materials 2025, 18(21), 4828; https://doi.org/10.3390/ma18214828 (registering DOI) - 22 Oct 2025

Abstract

This study introduces a novel fabrication method for high-strength, self-cleaning photocatalytic membranes through the integration of hot-pressing and TiO₂/chitosan/SiO₂ nanofibers. The innovation of this research lies in the hot-pressing technique, which significantly enhances the mechanical properties and photocatalytic efficiency by [...] Read more.

This study introduces a novel fabrication method for high-strength, self-cleaning photocatalytic membranes through the integration of hot-pressing and TiO₂/chitosan/SiO₂ nanofibers. The innovation of this research lies in the hot-pressing technique, which significantly enhances the mechanical properties and photocatalytic efficiency by improving the adhesion, dispersion, and uniformity of the TiO₂/chitosan coating on SiO₂ nanofibers. SiO₂ nanofibers with an initial diameter of 0.79 ± 0.29 μm were coated and hot-pressed, resulting in a final diameter of 1.07 ± 0.57 μm, which corresponds to an approximate increase of 35.4%. In addition, the 1 wt% TiO₂-CTS sample showed the highest adhesion and surface energy, with values of 0.1 nN/nm², indicating the closest intermolecular binding. 3 wt% SiO₂-CTS exhibits a maximum hardness of 5.23 Pa. The 3 wt% TiO₂-chitosan coating demonstrated outstanding mechanical performance, achieving a fracture stress of 0.53 MPa, approximately five times that of the untreated SiO₂ nanofibers, a Young’s modulus of 0.63 MPa, and a toughness to triple of 0.27 MJ/m³—representing substantial improvements over uncoated membranes. Photocatalytic efficiency was significantly enhanced, with grayscale values increasing approximately 36% UV light exposure, indicating the superior degradation of pollutants. Full article

(This article belongs to the Special Issue Surface Modification of Materials for Multifunctional Applications)

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27 pages, 4483 KB

Open AccessArticle

Advancing Viscoelastic Material Characterization Through Computer Vision and Robotics: MIRANDA and RELAPP

by Antonio Monleón-Getino, Victor Madarnás-Gómez, Mario Cobos-Soler, Eduard Almacellas, Juan Ramos-Castro, Xavier Bielsa, Pere López-Brosa, Àngels Sahuquillo-Estrugo, Inés Marsà-González and Alejandro Rodríguez-Mena

Materials 2025, 18(21), 4827; https://doi.org/10.3390/ma18214827 (registering DOI) - 22 Oct 2025

Abstract

This study introduces MIRANDA, a computer vision system, and RELAPP, a complementary force measurement system, developed for characterizing viscoelastic materials. Our aim was to evaluate their combined ability to predict key rheological parameters and demonstrate their utility in material analysis, offering an alternative [...] Read more.

This study introduces MIRANDA, a computer vision system, and RELAPP, a complementary force measurement system, developed for characterizing viscoelastic materials. Our aim was to evaluate their combined ability to predict key rheological parameters and demonstrate their utility in material analysis, offering an alternative to traditional methods. We analyzed five distinct flour dough samples, correlating MIRANDA and RELAPP variables with established rheological reference values. Support Vector Machine (SVM) regression models were trained using MIRANDA’s stable TR and elasticity data to predict industrially relevant parameters: baking strength (W), tenacity (P), extensibility (L), and final viscosity (RVU) from Chopin alveograph and viscosimeter. The predictive models showed promising results, with R² values of 0.594 (p = 0) for W, 0.575 (p = 0) for P, and 0.612 (p = 0.03763) for viscosity, all statistically significant. While these findings are promising, it is important to note that the small sample size may limit the generalizability of these models. The synergy between the systems was evident, exemplified by strong positive correlations, such as between MIRANDA’s Elasticity and RELAPP’s c_exp (parameter ‘c’ of its mathematical model m1, r = 0.858) and final resistive force (r = 0.839). Despite the limited sample size, these findings highlight MIRANDA’s versatility and speed for efficient material characterization. MIRANDA and RELAPP offer significant industrial implications for viscoelastic materials, including accelerating development cycles and enhancing continuous quality control. This approach has strong potential to reduce reliance on slower, traditional methods, warranting further validation with larger datasets. Full article

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32 pages, 5273 KB

Open AccessReview

A Comprehensive Review of Green Hydrogen Technology: Electrolysis Methods, Topologies and Control Strategies, Applications

by Ailitabaier Abudureyimu, Ayiguzhali Tuluhong, Qingpu Chang, Feng Wang and Bao Luo

Materials 2025, 18(21), 4826; https://doi.org/10.3390/ma18214826 (registering DOI) - 22 Oct 2025

Abstract

As a pivotal clean energy carrier for achieving carbon neutrality, green hydrogen technology has attracted growing global attention. This review systematically examines four mainstream water electrolysis technologies—alkaline electrolysis, proton exchange membrane electrolysis, solid oxide electrolysis, and anion exchange membrane electrolysis—analyzing their fundamental principles, [...] Read more.

As a pivotal clean energy carrier for achieving carbon neutrality, green hydrogen technology has attracted growing global attention. This review systematically examines four mainstream water electrolysis technologies—alkaline electrolysis, proton exchange membrane electrolysis, solid oxide electrolysis, and anion exchange membrane electrolysis—analyzing their fundamental principles, material challenges, and development trends. It further classifies and compares power electronic converter topologies, including non-isolated and isolated DC–DC converters as well as AC–DC converter architectures, and summarizes advanced control strategies such as dynamic power regulation and fault-tolerant operation aimed at enhancing system efficiency and stability. A holistic “electrolyzer–power converter–control strategy” integration framework is proposed to provide tailored technological solutions for diverse application scenarios. Finally, the challenges and future prospects of green hydrogen across the energy, transportation, and industrial sectors are discussed, underscoring its potential to accelerate the global transition toward a sustainable, low-carbon energy system. Full article

(This article belongs to the Section Quantum Materials)

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23 pages, 3482 KB

Open AccessArticle

Understanding the Limitations of Modifying Bitumen with Re-Refined Engine Oil Bottom (REOB)

by Lucas Mortier, Xueyan Liu, Sayeda N. Nahar and Hinrich Grothe

Materials 2025, 18(21), 4825; https://doi.org/10.3390/ma18214825 (registering DOI) - 22 Oct 2025

Abstract

The evolving bitumen market is increasingly complex due to variations in crude sources and transitions in refining processes, affecting the properties of bitumen. Unexpected additions of materials to alter bitumen’s properties could occur, where traditional PEN grade testing fails to detect modifications by [...] Read more.

The evolving bitumen market is increasingly complex due to variations in crude sources and transitions in refining processes, affecting the properties of bitumen. Unexpected additions of materials to alter bitumen’s properties could occur, where traditional PEN grade testing fails to detect modifications by inclusion of, for example, Re-refined Engine Oil Bottoms. This is the first study to comprehensively compare REOBs from European vs. North American sources and assess their effects on binder performance in a unified framework, performed by assessing the REOB-modified binders by identification, stability, compatibility, ageing susceptibility, and low-temperature properties. Two series of REOB-modified bitumen were prepared by blending 5, 10, and 15 wt.% REOB into hard grade bitumen. Results showed increased carbonyl formations (likely caused by lubricant additives) and phase instability during storage which can be attributed to saturates exudation. Rheological assessment demonstrated that REOB softens bitumen, although ageing causes a pronounced gain in stiffness. Low temperature rheological measurements showed that REOB-modified bitumen is prone to brittle fracture, suggesting a loss of relaxation properties. This study highlights that REOB is a material of inconsistent nature, with complex interactions with molecular groups of the base bitumen, causing increased ageing, phase instability, and brittle fracture susceptibilities. Full article

(This article belongs to the Special Issue Advances in Resilient, Sustainable, and Functional Materials for Road Infrastructure)

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18 pages, 3078 KB

Open AccessArticle

Multi-Parameter Modulation of Dirac Plasmons in Germanene via Doping and Strain: A DFT Insight

by Pengfei Li, Lijun Han, Lin Zhang and Ningju Hui

Materials 2025, 18(21), 4824; https://doi.org/10.3390/ma18214824 (registering DOI) - 22 Oct 2025

Abstract

Based on first-principles calculations and linear-response time-dependent density functional theory within the random phase approximation (LR-TDDFT-RPA), this work systematically investigates the modulation of Dirac plasmons in germanene via carrier doping, biaxial strain, and substrate effects. The results demonstrate that carrier doping induces highly [...] Read more.

Based on first-principles calculations and linear-response time-dependent density functional theory within the random phase approximation (LR-TDDFT-RPA), this work systematically investigates the modulation of Dirac plasmons in germanene via carrier doping, biaxial strain, and substrate effects. The results demonstrate that carrier doping induces highly tunable Dirac plasmons whose excitation energy follows the ω ∝ n^1/4 scaling relation, leading to a sublinear increase with doping concentration. Furthermore, biaxial strain effectively modulates the Fermi velocity, and the established ω ∝ √V_F relationship directly explains the observed linear tuning of plasmon energy with strain. More importantly, the combined modulation of carrier density and strain enables a significantly broader plasmon energy range (0.16–0.61 eV) than achievable through individual parameter control. When supported on hBN substrates, germanene maintains the characteristic √q plasmon dispersion despite band hybridization and a redshift in energy, a behavior well explained by the 2D free electron gas model. This study provides important theoretical insights into the multi-parameter control of Dirac plasmons and supports the design of germanene-based tunable nanophotonic devices. Full article

(This article belongs to the Section Quantum Materials)

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18 pages, 8517 KB

Open AccessArticle

Influence of Artificial Aging of ZnAlCu Alloys on Microstructure and Compressive Yield Strength

by Angelika Kiefel, Alexander Bezold and Christoph Broeckmann

Materials 2025, 18(21), 4823; https://doi.org/10.3390/ma18214823 (registering DOI) - 22 Oct 2025

Abstract

So far, the influence of aging on the mechanical properties of ZnAlCu alloys has primarily been investigated under tensile load. Since some applications, such as plain bearings, are subjected to compressive loads, the results presented in the literature do not fully encompass all [...] Read more.

So far, the influence of aging on the mechanical properties of ZnAlCu alloys has primarily been investigated under tensile load. Since some applications, such as plain bearings, are subjected to compressive loads, the results presented in the literature do not fully encompass all areas of application. Therefore, this publication focuses on the influence of artificial aging on the 0.2% compressive yield strength. Samples from ZnAl1Cu0.7, ZnAl11Cu0.7 and ZnAl11Cu2 were aged at different aging temperatures for up to 840 h. After different aging periods, compressive tests as well as microstructure investigations with SEM and XRD were carried out. Furthermore, the dimensional stability of ZnAl11Cu0.7 was investigated in a quenching dilatometer. Shrinkage of up to 0.08%, followed by swelling, was determined. Compressive tests revealed a decrease in the 0.2% compressive yield strength across all tested alloys, most pronounced at the beginning of the aging process, reaching an approximately constant strength level after an alloy- and temperature-dependent aging period. At the end, based on the results, a possible way to determine the constant strength level and the necessary aging time to reach this strength level for specific application temperatures is presented to ensure stable mechanical properties during operation. Full article

(This article belongs to the Special Issue Quality, Microstructure and Properties of Metal Alloys (Third Edition))

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15 pages, 2501 KB

Open AccessArticle

Biomechanical Comparison of Patient-Specific Temporomandibular Joint Prostheses Using Ti6Al4V and CoCrMo Alloys: A Finite Element Analysis

by Ezgi Yüceer-Çetiner, Yasin Doğu, Hakan Yurten and Altan Varol

Materials 2025, 18(21), 4822; https://doi.org/10.3390/ma18214822 (registering DOI) - 22 Oct 2025

Abstract

End-stage temporomandibular joint (TMJ) disorders often necessitate total joint replacement, and the selection of biomaterial directly impacts long-term outcomes. Ti6Al4V and CoCrMo are commonly used alloys, yet their biomechanical performance in patient-specific prostheses remains insufficiently compared. This study aimed to evaluate the mechanical [...] Read more.

End-stage temporomandibular joint (TMJ) disorders often necessitate total joint replacement, and the selection of biomaterial directly impacts long-term outcomes. Ti6Al4V and CoCrMo are commonly used alloys, yet their biomechanical performance in patient-specific prostheses remains insufficiently compared. This study aimed to evaluate the mechanical response of custom TMJ prostheses fabricated from these alloys using finite element analysis (FEA). A three-dimensional mandibular model was created from computed tomography data, and a patient-specific prosthesis was designed in SolidWorks (Dassault Systèmes, SolidWorks Corp., Waltham, MA, USA) and analyzed in ANSYS Workbench 2022 R1 (Ansys Inc., Canonsburg, PA, USA). Physiological loading was simulated by applying forces at the insertion sites of the temporalis, masseter, and medial pterygoid muscles. In the Ti6Al4V model, maximum von Mises stresses reached 192.18 MPa on the mandibular component and 92.004 MPa on the fossa prosthesis, whereas the CoCrMo model demonstrated higher stresses of 204.31 MPa and 94.182 MPa, respectively. Both alloys exhibited similar stress distributions, but Ti6Al4V generated lower stress magnitudes, indicating more favorable load transfer and a reduced risk of mechanical overload on articulating components. These findings underscore the significance of alloy selection in optimizing TMJ prostheses and demonstrate the value of FEA as a tool for guiding future patient-specific designs. Full article

(This article belongs to the Section Biomaterials)

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21 pages, 2799 KB

Open AccessArticle

Molecular Insights into the Kinetic Aging Mechanisms of SBS-Modified Asphalt

by Yunjing Nie, Ye Bai, Fang Liu, Pengfei Li and Zhidong Zhou

Materials 2025, 18(21), 4821; https://doi.org/10.3390/ma18214821 - 22 Oct 2025

Abstract

The aging of SBS-modified asphalt (SBSMA) is a kinetic process that significantly deteriorates pavement performance and shortens service life. Although previous studies have explored the evolution of SBSMA during aging, the underlying kinetic mechanisms remain unclear. In this study, SBSMA samples were subjected [...] Read more.

The aging of SBS-modified asphalt (SBSMA) is a kinetic process that significantly deteriorates pavement performance and shortens service life. Although previous studies have explored the evolution of SBSMA during aging, the underlying kinetic mechanisms remain unclear. In this study, SBSMA samples were subjected to varying degrees of aging to simulate the kinetic aging process. Changes in four components and chemical functional groups were characterized, supporting the construction of molecular models at different aging stages. Molecular dynamics simulations indicate that the oxidation rate of SBSMA and degradation rate of SBS molecular chains are significantly higher in the initial aging stage than later, leading to a pronounced increase in cohesive energy density and solubility parameters, along with a decrease in surface free energy, fractional free volume, and binding energies, predominantly occurring during the first aging stage. Aging also shortens intermolecular distance between asphaltene molecules while increasing the distances between asphaltene–resin and asphaltene–SBS. The adsorption competition between asphaltene and SBS for lightweight components intensifies initially, whereas asphaltene exhibits stronger adsorption in the later aging stage. Furthermore, the diffusion coefficients of asphaltene and SBS increase rapidly initially then slow, causing a corresponding rapid initial decline followed by decrease in resin, aromatic, and saturate components. Full article

(This article belongs to the Special Issue Road and Rail Construction Materials: Development and Prospects)

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22 pages, 8704 KB

Open AccessArticle

Cement-Based Grouting Materials Modified with GO/NS Hybrids

by Longfei Lu, Guoxiang Yang, Yan Ai, Jingkai Qu, Jinrui Duan, Kun Yang and Wenbin Sun

Materials 2025, 18(21), 4820; https://doi.org/10.3390/ma18214820 - 22 Oct 2025

Abstract

This study systematically investigates the effects of individual and combined incorporation of graphene oxide (GO) and nano-silica sol (NS) on the macroscopic properties and microstructure of cement-based grouting materials, with emphasis on their synergistic mechanisms. A series of macroscopic tests including setting time, [...] Read more.

This study systematically investigates the effects of individual and combined incorporation of graphene oxide (GO) and nano-silica sol (NS) on the macroscopic properties and microstructure of cement-based grouting materials, with emphasis on their synergistic mechanisms. A series of macroscopic tests including setting time, fluidity, bleeding rate, and mechanical strength were conducted, complemented by multi-scale microstructural characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and Fourier-transform infrared spectroscopy (FTIR). The results demonstrate that both NS and GO effectively reduce setting time and bleeding rate while enhancing mechanical strength; however, NS exhibits a more pronounced adverse effect on fluidity compared to GO. The hybrid system displays a distinct transition from synergy to antagonism: under low-dosage co-incorporation (2 wt% NS + 0.01 wt% GO), the flexural and compressive strengths increased by 13.5% and 45.5%, respectively, relative to the reference group. Microscopic analysis revealed that the synergistic interaction between the pozzolanic effect of NS and the templating effect of GO under this condition optimizes hydrate morphology and pore structure, leading to enhanced performance. Conversely, excessive dosage of either component induces agglomeration, resulting in microstructural deterioration and performance degradation. This study establishes optimal dosage ranges and combination principles for NS and GO in cement-based materials, providing a theoretical foundation for designing high-workability and high-strength cementitious composites. Full article

(This article belongs to the Special Issue Reaction Mechanism and Properties of Cement-Based Materials (2nd Edition))

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16 pages, 2720 KB

Open AccessArticle

Analysis of Quasi-Simultaneous Laser Welding in T-Joint Configuration for PMMA-ABS Using Circular Wobble Geometry

by Antonio Lezzoche, Giulia Mossotti, Carmelo Nicosia, Marco Baggi, Michele Perlo, Luciano Scaltrito and Andrea Ancillao

Materials 2025, 18(21), 4819; https://doi.org/10.3390/ma18214819 - 22 Oct 2025

Abstract

The focus of this study was the investigation of the quasi-simultaneous laser welding (QSW) technique of polymethyl methacrylate (PMMA) and acrylonitrile butadiene styrene (ABS) in a T-joint configuration using a circular wobble laser path. The main aim was to find how laser parameters, [...] Read more.

The focus of this study was the investigation of the quasi-simultaneous laser welding (QSW) technique of polymethyl methacrylate (PMMA) and acrylonitrile butadiene styrene (ABS) in a T-joint configuration using a circular wobble laser path. The main aim was to find how laser parameters, such as scanning speed, number of scans, and laser power, influence key indicators of weld quality: penetration depth and weld strength. A range of scanning speeds (1–2 m/s) and scan repetitions (20–70) was explored, with the goal of keeping the total welding time around 1 s, a time compatible with industrial mass production. The results demonstrated a clear correlation between linear energy density and penetration depth. Deeper penetrations were achieved at higher energy levels. Weld strength was maximized with a lower number of scans (20) and higher powers (above 130 W). The configuration offering the best combination of weld strength (1137 N) and total welding time (0.8 s) was identified, demonstrating the suitability of QSW for mass production. Full article

(This article belongs to the Special Issue Laser Welding and Surface Treatment of Advanced Materials)

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