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Materials, Volume 18, Issue 18 (September-2 2025) – 212 articles

Cover Story (view full-size image): Substrate orientation-engineered ZnO optoelectronic synaptic devices fabricated by a sol–gel process exhibit tunable synaptic plasticity and visual memory, advancing neuromorphic computing applications. Polar ZnO on c-plane sapphire exhibits strong internal polarization fields, which accelerate recombination and limit persistent photoconductivity. In contrast, nonpolar ZnO on m-plane sapphire suppresses polarization fields, enabling longer carrier lifetimes and stronger memory retention. The brain-inspired schematic highlights the analogy between presynaptic/post-synaptic signaling and optoelectronic synapse operation, where UV light triggers synaptic responses. This work demonstrates that substrate orientation serves as an effective strategy for enhancing neuromorphic performance in oxide-based optoelectronic devices. View this paper
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28 pages, 597 KB  
Review
Ab Initio Calculations of Spin Waves: A Review of Theoretical Approaches and Applications
by Michael Neugum and Arno Schindlmayr
Materials 2025, 18(18), 4431; https://doi.org/10.3390/ma18184431 - 22 Sep 2025
Viewed by 440
Abstract
Spin waves represent an important class of low-energy excitations in magnetic solids, which influence the thermodynamic properties and play a major role in technical applications, such as spintronics or magnetic data storage. Despite the enormous advances of ab initio simulations in materials science, [...] Read more.
Spin waves represent an important class of low-energy excitations in magnetic solids, which influence the thermodynamic properties and play a major role in technical applications, such as spintronics or magnetic data storage. Despite the enormous advances of ab initio simulations in materials science, quantitative calculations of spin-wave spectra still pose a significant challenge, because the collective nature of the spin dynamics requires an accurate treatment of the Coulomb interaction between the electrons. As a consequence, simple lattice models like the Heisenberg Hamiltonian are still widespread in practical investigations, but modern techniques like time-dependent density-functional theory or many-body perturbation theory also open a route to material-specific spin-wave calculations from first principles. Although both are in principle exact, actual implementations necessarily employ approximations for electronic exchange and correlation as well as additional numerical simplifications. In this review, we recapitulate the theoretical foundations of ab initio spin-wave calculations and analyze the common approximations that underlie present implementations. In addition, we survey the available results for spin-wave dispersions of various magnetic materials and compare the performance of different computational approaches. In this way, we provide an overview of the present state of the art and identify directions for further developments. Full article
(This article belongs to the Special Issue Recent Advances in Magnetic and Electronic Materials and Their Applications)
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24 pages, 5525 KB  
Article
Compositional Effects on the Performance of High-Permeability Emulsified Asphalt for Prime Coat Applications
by Zhen Qin, Xiang Liu, Shaopeng Zheng, Simiao Pan, Xiaolong Li, Jingpeng Jia and Hang Xiong
Materials 2025, 18(18), 4430; https://doi.org/10.3390/ma18184430 - 22 Sep 2025
Viewed by 395
Abstract
High-permeability emulsified asphalt has emerged as a promising prime coat for enhancing interlayer bonding in semi-rigid pavement structures. However, its widespread adoption remains limited by insufficient permeability and inconsistent mechanical properties. This study systematically investigated the effects of emulsifier ionic type (cationic or [...] Read more.
High-permeability emulsified asphalt has emerged as a promising prime coat for enhancing interlayer bonding in semi-rigid pavement structures. However, its widespread adoption remains limited by insufficient permeability and inconsistent mechanical properties. This study systematically investigated the effects of emulsifier ionic type (cationic or anionic), kerosene dosage (0–20%), and diluted asphalt content (corresponding to oil-water ratios of 5:5 and 4:6) on the comprehensive performance of high-permeability emulsified asphalt. Fundamental physical tests (sieve residue, evaporation residue, penetration, softening point, ductility), permeability evaluation, rotational viscosity measurements, and adhesion performance tests were conducted. Grey relational analysis (GRA) was employed to quantify the influence of each factor and their interactions on key performance metrics. The results reveal that anionic emulsifiers significantly improved low-temperature ductility and permeability. A low kerosene dosage (<10%) enhanced permeability and viscosity but compromised thermal stability at higher levels. Reducing the diluted asphalt content partially offset these adverse effects. GRA identified kerosene dosage as the dominant factor influencing permeability, softening point, and adhesion performance while emulsifier ionic type primarily affected ductility, and oil-water ratio strongly governed emulsification quality and viscosity. These findings provide quantitative insights for optimizing the composition of high-permeability emulsified asphalt and serve as a theoretical foundation for its engineering application in durable prime coats. Full article
(This article belongs to the Special Issue Mechanical Property Research of Advanced Asphalt-Based Materials—Second Edition)
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22 pages, 4725 KB  
Article
Data-Driven Optimization and Mechanical Assessment of Perovskite Solar Cells via Stacking Ensemble and SHAP Interpretability
by Ruichen Tian, Aldrin D. Calderon, Quanrong Fang and Xiaoyu Liu
Materials 2025, 18(18), 4429; https://doi.org/10.3390/ma18184429 - 22 Sep 2025
Viewed by 363
Abstract
Perovskite solar cells (PSCs) have emerged as promising photovoltaic technologies owing to their high power conversion efficiency (PCE) and material versatility. Conventional optimization of PSC architectures largely depends on iterative experimental approaches, which are often labor-intensive and time-consuming. In this study, a data-driven [...] Read more.
Perovskite solar cells (PSCs) have emerged as promising photovoltaic technologies owing to their high power conversion efficiency (PCE) and material versatility. Conventional optimization of PSC architectures largely depends on iterative experimental approaches, which are often labor-intensive and time-consuming. In this study, a data-driven modeling strategy is introduced to accelerate the design of efficient and mechanically robust PSCs. Seven supervised regression models were evaluated for predicting key photovoltaic parameters, including PCE, short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF). Among these, a stacking ensemble framework exhibited superior predictive accuracy, achieving an R2 of 0.8577 and a root mean square error of 2.084 for PCE prediction. Model interpretability was ensured through Shapley Additive exPlanations(SHAP) analysis, which identified precursor solvent composition, A-site cation ratio, and hole-transport-layer additives as the most influential parameters. Guided by these insights, ten device configurations were fabricated, achieving a maximum PCE of 24.9%, in close agreement with model forecasts. Furthermore, multiscale mechanical assessments, including bending, compression, impact resistance, peeling adhesion, and nanoindentation tests, were conducted to evaluate structural reliability. The optimized device demonstrated enhanced interfacial stability and fracture resistance, validating the proposed predictive–experimental framework. This work establishes a comprehensive approach for performance-oriented and reliability-driven PSC design, providing a foundation for scalable and durable photovoltaic technologies. Full article
(This article belongs to the Section Energy Materials)
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18 pages, 4842 KB  
Article
Positron Annihilation Studies of Hydrostatically Extruded AA1050 Aluminum
by Ewa Dryzek, Mirosław Wróbel, Maciej Sarnek and Jacek Skiba
Materials 2025, 18(18), 4428; https://doi.org/10.3390/ma18184428 - 22 Sep 2025
Viewed by 283
Abstract
AA1050 aluminum was hydrostatically extruded at room temperature to true strains of 0.9 and 3.2, and at cryogenic temperature to a true strain of 0.9. As a result of the extrusion process, the yield strength (YS) increased by 130–160% to 120–130 MPa, and [...] Read more.
AA1050 aluminum was hydrostatically extruded at room temperature to true strains of 0.9 and 3.2, and at cryogenic temperature to a true strain of 0.9. As a result of the extrusion process, the yield strength (YS) increased by 130–160% to 120–130 MPa, and the ultimate tensile strength (UTS) rose by 64–81% to 125–140 MPa. The hardness reached 46–49 HV. YS and UTS values correspond to mechanical properties typical of the H6 or H8 temper designations, with unusually high elongation at break ranging from 15% to 16.4%. Differences in lattice parameters, crystallite size, and lattice strain between samples deformed under various conditions—as well as those annealed after deformation—were within the margin of measurement uncertainty. This indicated that differences in defect density between the samples were relatively small, due to dynamic recovery occurring during extrusion. However, positron annihilation spectroscopy demonstrated that the cryo-cooled material extruded at a true strain of 0.9, as well as the one extruded at RT at a true strain of 3.2, exhibited significantly higher mean lattice defect concentrations compared to the sample extruded at RT at a true strain of 0.9. The predominant defects detected were vacancies associated with dislocations. The extrusion parameters also significantly affected the crystallographic texture. In particular, they altered the relative proportions of the <111> and <100> components in the axial texture, with the <100> component becoming dominant in cryogenically extruded samples. This trend was further intensified during recrystallization, which enhanced the <100> component even more. Recrystallization of the deformed materials occurred in the temperature range of 520–570 K. The activation energy for grain boundary migration during recrystallization was estimated to be approximately 1.5 eV. Full article
(This article belongs to the Section Metals and Alloys)
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22 pages, 15273 KB  
Article
Investigation on the Microstructure and Mechanical Properties of FeGa3 Surface Film on SKD11 Substrate
by Roonie Protasius, Masaki Tanaka, Shigeto Yamasaki, Tatsuya Morikawa, Kazuyuki Yagi, Masahiko Tezuka, Yasufumi Yoshida, Yukinari Yoshida and Makoto Higashionna
Materials 2025, 18(18), 4427; https://doi.org/10.3390/ma18184427 - 22 Sep 2025
Viewed by 291
Abstract
Gallium-based liquid metal is corrosive to steel alloys, forming FeGa3 surface films which can potentially be applied as a solid lubricant to enhance wear resistance and mitigate liquid metal-induced corrosion. However, the characteristics of these films remain insufficiently explored. In this study, [...] Read more.
Gallium-based liquid metal is corrosive to steel alloys, forming FeGa3 surface films which can potentially be applied as a solid lubricant to enhance wear resistance and mitigate liquid metal-induced corrosion. However, the characteristics of these films remain insufficiently explored. In this study, Ga-In-Sn alloy was ultrasonically soldered onto annealed and decarburised substrates, followed by heating in a vacuum chamber to form a 30 μm thick FeGa3 reaction layer. The film on the annealed samples with an alpha-ferrite microstructure exhibited high porosity and a surface roughness of 1.97 Ra. In contrast, the film on the decarburised samples with a ferritic microstructure showed minimal porosity and a lower surface roughness of 1.29 Ra. Nanoindentation tests revealed Young modulus values of 231 GPa and 242 GPa and hardness values of 11.4 GPa and 12.7 GPa for the annealed and decarburised samples, respectively. The high porosity in the annealed samples is attributed to the suppression of FeGa3 formation in regions containing chromium carbides. Shear stress for fracture, measured by microcantilever tests at the interface between the substrate and the inner matrix of the surface film, showed lower fracture shear stress in the annealed sample, attributed to the presence of larger pores within its microstructure. Full article
(This article belongs to the Section Thin Films and Interfaces)
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20 pages, 6771 KB  
Article
A Comparative Analysis of the Fatigue Strength of Aluminium and Copper Wires Used for Power Cables
by Tadeusz Knych, Beata Smyrak and Bartosz Jurkiewicz
Materials 2025, 18(18), 4426; https://doi.org/10.3390/ma18184426 - 22 Sep 2025
Viewed by 510
Abstract
Recent studies have demonstrated that the utilisation of aluminium in electrical applications has increased substantially, particularly in the context of power cables. The substitution of copper with aluminium in cable fabrication is predominantly driven by economic considerations. When designing such cables, it is [...] Read more.
Recent studies have demonstrated that the utilisation of aluminium in electrical applications has increased substantially, particularly in the context of power cables. The substitution of copper with aluminium in cable fabrication is predominantly driven by economic considerations. When designing such cables, it is imperative to ascertain their functional properties, including their electrical conductivity and mechanical properties, and their operational properties, which include rheological, thermal, and material fatigue resistance. This is to ensure that the aluminium and copper cables are compatible. The primary challenge confronting researchers in this domain pertains to predicting and forecasting the failure of overhead cables during their operational lifecycle. One of the most significant and prevalent operational hazards is fatigue damage. This article presents the experimental results of fatigue tests on single Al and Cu wires in various states of mechanical reinforcement. The parameters of the Wöhler curve were determined, and a comparative analysis of the morphology of fatigue damage in single copper and aluminium wires was performed. It was found that copper wires are more fatigue-resistant than aluminium wires. In the case of high-cycle fatigue, this difference can amount to 106 cycles. An analysis of fatigue fracture morphology showed that fractures have a developed surface and that plastic deformation makes a significant contribution in the case of low-cycle fatigue. In the case of high-cycle fatigue, many cracks were observed in the copper wires. No such cracks were observed in the aluminium wires. Full article
(This article belongs to the Special Issue High-Performance Applications of Advanced Materials: Material Properties, Behaviour Modeling, Optimal Design and Advanced Processes)
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24 pages, 8575 KB  
Article
Molecular Dynamics Study on Silane Coupling Agent Grafting to Optimize the Interfacial Microstructure and Physical Properties of Polyimide/Nano-Si3N4 Composites
by Qikun Yang, Jinxin Huang, Li Zhang, Nurbek N. Kurbonov and Shengrui Zhou
Materials 2025, 18(18), 4425; https://doi.org/10.3390/ma18184425 - 22 Sep 2025
Viewed by 615
Abstract
Polyimide (PI) is widely used in aerospace, electronic packaging, and other fields due to its excellent dielectric and thermophysical properties. However, the performance of traditional PI materials under extreme conditions has become increasingly inadequate to meet the growing demands. To address this, this [...] Read more.
Polyimide (PI) is widely used in aerospace, electronic packaging, and other fields due to its excellent dielectric and thermophysical properties. However, the performance of traditional PI materials under extreme conditions has become increasingly inadequate to meet the growing demands. To address this, this study designed a PI/Nano-Si3N4 advanced composite material and, based on molecular dynamics simulations, thoroughly explored the influence of silane coupling agents with different grafting densities on the interfacial microstructure and their correlation with the overall material’s physical properties. The results show that when the grafting density is 10%, the interfacial bonding of the PI/Nano-Si3N4 composite is optimized: non-bonded interaction energy increases by 18.4%, the number of hydrogen bonds increases by 32.5%, and the free volume fraction decreases to 18.13%. These changes significantly enhance the overall performance of the material, manifested by an increase of about 30 K in the glass transition temperature and a 49.5% improvement in thermal conductivity compared to pure PI. Furthermore, the system maintains high Young’s modulus and shear modulus in the temperature range of 300–700 K. The study reveals that silane coupling agents can effectively enhance the composite material’s overall performance by optimizing the interfacial structure and controlling the free volume, providing an efficient computational method for the design and performance prediction of advanced high-performance PI composites. Full article
(This article belongs to the Special Issue Innovations in Modelling and Simulations: Bridging Microstructures to Macroscopic Properties in Advanced Materials)
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32 pages, 8677 KB  
Review
Advances in Dealloying of Ti and Ti-Based Alloys for Biomedical Applications
by Kirti Tiwari, Deepti Raj, Paola Rizzi and Federico Scaglione
Materials 2025, 18(18), 4424; https://doi.org/10.3390/ma18184424 - 22 Sep 2025
Viewed by 293
Abstract
Dealloying technique has been used for centuries as an attractive method for producing porous surfaces by removing one or more undesirable elements from the surface. Since early 2000s, the technique has been further developed for understanding the dealloying mechanism and tailoring it to [...] Read more.
Dealloying technique has been used for centuries as an attractive method for producing porous surfaces by removing one or more undesirable elements from the surface. Since early 2000s, the technique has been further developed for understanding the dealloying mechanism and tailoring it to produce chemically homogeneous materials with nanoporous (np) morphology. Dealloying has found numerous applications such as sensors, catalysts, as well as in the biomedical field, which is fairly recent and has attracted great attention on this topic. This review investigates the dealloying technique for preparing nanoporous materials and nanoporous surfaces by using different modification routes on various types of Ti-based alloys for biomedical implant application. There has been significant growth in studying dealloying of crystalline, amorphous, shape memory, and composites-based Ti alloys. This review aims to summarise the findings from literature and discuss the scope of this technique and challenges involved for future aspects. Full article
(This article belongs to the Special Issue Advances in Implant Materials and Biocompatibility)
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15 pages, 5434 KB  
Article
Experimental Study on Mechanical Property of Cemented Backfill in Coal Mine
by Haigang Yang, Rui Wang, Qiang Zhang, Wencheng Ma and Yukai Wang
Materials 2025, 18(18), 4423; https://doi.org/10.3390/ma18184423 - 22 Sep 2025
Viewed by 303
Abstract
In response to the insufficiency of shear strength and severe segregation of cemented backfilling material in coal mines, a shear strength test, static segregation index test, and homogeneity degree test were carried out, taking slurry concentration (SC) as the main control factor. The [...] Read more.
In response to the insufficiency of shear strength and severe segregation of cemented backfilling material in coal mines, a shear strength test, static segregation index test, and homogeneity degree test were carried out, taking slurry concentration (SC) as the main control factor. The effect law of SC on shear strength, the static segregation index, and the homogeneity degree was discussed. The relationship between the static segregation index and homogeneity degree and shear strength was analyzed, and the action mechanism of SC on shear strength was revealed. The research results show that for cemented backfill in coal mines, with a suspending agent content of 0 and a curing age of 28 d, when SC increases from 77% to 80%, shear strength increases by 31.43%, the static segregation index of the backfilling slurry decreases by 40.29%, and the homogeneity degree of the backfill increases by 69.23%. The increase in SC can enhance shear strength, reduce the segregation degree of backfilling slurry, and improve the homogeneity of backfill. The reason for the increase in shear strength lies in the fact that SC reduces the segregation degree of the backfilling slurry. The research in this paper has certain guiding significance for the timely support of the surrounding rock in the working face and the effective control of surface settlement. Full article
(This article belongs to the Section Construction and Building Materials)
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21 pages, 3539 KB  
Article
Study of Properties and Characteristics of a Foam Glass from a Mixture of Glass Shards and Perlite
by Ilja Horonko, Pavels Tihomirovs and Aleksandrs Korjakins
Materials 2025, 18(18), 4422; https://doi.org/10.3390/ma18184422 - 22 Sep 2025
Viewed by 345
Abstract
The current study presents the development and optimisation of foam glass manufactured from recycled glass shards and expanded ground perlite, targeting enhanced structural and thermal performance for sustainable building applications. By investigating various particle size fractions (“125 μm”, “250 μm”, “500 μm”) and [...] Read more.
The current study presents the development and optimisation of foam glass manufactured from recycled glass shards and expanded ground perlite, targeting enhanced structural and thermal performance for sustainable building applications. By investigating various particle size fractions (“125 μm”, “250 μm”, “500 μm”) and sintering temperatures (800–850 °C), we achieved a foam glass with superior compressive strength and uniform porosity. Notably, samples utilising a homogeneous 500 μm particle fraction sintered at 850 °C exhibited the highest compressive strength of 2.17 MPa, coupled with open porosity uniformity and stable structural matrix formation. Density values in this fraction decreased from 321 to 263 kg/m3, indicating effective foaming and well-developed open porosity that balances mechanical integrity and thermal insulation. The optimised thermal regime minimised crystalline phase formation, preserving low thermal conductivity and mechanical stability. Compared to heterogeneous composites, the homogeneous fractions demonstrated significantly improved strength-to-porosity ratios, ensuring predictable mechanical performance and competitive thermal insulation properties. These findings underline the material’s potential as a cost-effective, environmentally friendly insulation solution that meets or exceeds existing standards, with promising applications in energy-efficient construction. Full article
(This article belongs to the Special Issue Processing of End-of-Life Materials and Industrial Wastes (3rd Edition))
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23 pages, 2095 KB  
Article
Advanced Platelet-Rich Fibrin Plus Sealed Exclusively with Glass Ionomer Cement: Setting a New Standard for Healing, Aesthetics and Predictive Modelling in Regenerative Endodontics
by Dubravka Turjanski, Dragutin Lisjak, Petra Bučević Sojčić, Jelena Valpotić, Tea Borojević Renić, Kristina Goršeta and Domagoj Glavina
Materials 2025, 18(18), 4421; https://doi.org/10.3390/ma18184421 - 22 Sep 2025
Viewed by 383
Abstract
Regenerative endodontic approaches for immature necrotic permanent teeth must balance biological efficacy, clinical practicality and long-term aesthetic outcomes. This study evaluates a novel regenerative protocol using autologous advanced platelet-rich fibrin plus (A-PRF+) scaffold sealed exclusively with glass ionomer cement (GIC) and compares it [...] Read more.
Regenerative endodontic approaches for immature necrotic permanent teeth must balance biological efficacy, clinical practicality and long-term aesthetic outcomes. This study evaluates a novel regenerative protocol using autologous advanced platelet-rich fibrin plus (A-PRF+) scaffold sealed exclusively with glass ionomer cement (GIC) and compares it to conventional calcium hydroxide apexification used as the control. Twenty-eight patients were prospectively enrolled and followed for 12 months alongside a retrospectively selected historical control group. Outcomes were evaluated through standardised blinded clinical, radiographic and vitality assessments. The A-PRF+ protocol demonstrated significantly faster periapical healing, superior root lengthening, increased dentinal wall thickness and apical closure (p < 0.0001), with excellent aesthetic outcomes and no reported tooth discolouration. Pulpal blood flow measured by laser Doppler flowmetry indicated vitality restoration in 93% of cases. Preliminary linear regression identified treatment duration as a significant predictor of apical closure (p < 0.0001), with possible enhancement by additional patient-specific variables. These findings validate the A-PRF+ protocol as a highly effective, aesthetically favourable and predictable regenerative strategy, establishing a new benchmark for the management of immature necrotic teeth and laying the foundation for personalised predictive endodontic care. Future studies should include multicentre randomised controlled trials to confirm long-term clinical sustainability and generalisability. Full article
(This article belongs to the Special Issue Advanced Scaffold Biomaterials in Tissue Engineering)
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26 pages, 4522 KB  
Article
Durability Assessment of Cement Mortars with Recycled Ceramic Powders
by Anna Tokareva and Danièle Waldmann
Materials 2025, 18(18), 4420; https://doi.org/10.3390/ma18184420 - 22 Sep 2025
Viewed by 459
Abstract
Although substantial knowledge exists regarding the use of ceramic powders as pozzolanic supplementary cementitious materials, a notable gap remains in the literature concerning the durability properties of cement with ceramics. This research aims to address this gap by evaluating the effects of ceramic [...] Read more.
Although substantial knowledge exists regarding the use of ceramic powders as pozzolanic supplementary cementitious materials, a notable gap remains in the literature concerning the durability properties of cement with ceramics. This research aims to address this gap by evaluating the effects of ceramic powders on mortar durability, specifically focusing on resistance to freeze–thaw, high temperatures, and 1% sulphuric acid. The study also investigates the use of recycled ceramic demolition waste as a replacement for calcined clay in limestone calcined clay (LC3) formulations. This research demonstrates the potential of using ceramic waste to enhance mortar durability. The results show significant improvements in freeze–thaw resistance, with strength losses of 1.91% to 2.61% for modified mortars, compared to 6.31% for the reference mortar. Fire resistance also improves, with strength gains of up to 13.9% at 200 °C for LC3 mortars with ceramic powder. At 500 °C, strength losses ranged from 2.8% to 31.9%, with ceramic-containing mortars showing better performance than the reference. At 900 °C, substantial strength losses occurred across all mixes (72.0% to 90.0%), with mortars containing ultrafine ceramic powder showing the best resistance. Resistance to 1% sulphuric acid is enhanced, with strength losses decreasing from 9.37% in the reference mortar to 1.38% in LC3 mortar with ceramic powder. Full article
(This article belongs to the Section Construction and Building Materials)
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17 pages, 2756 KB  
Article
Effects of Thermal Activation on Mechanical Performance and Sustainability of Slag-Based Geopolymers
by Lais Alves, Nordine Leklou, Fábio de Simone e Souza and Silvio de Barros
Materials 2025, 18(18), 4419; https://doi.org/10.3390/ma18184419 - 22 Sep 2025
Viewed by 396
Abstract
Ground granulated blast furnace slag (GBFS)-based geopolymers represent a viable binder system that combines mechanical efficiency with a significantly lower carbon footprint when compared to conventional Portland cement. This work examines how thermal curing between 20 °C and 80 °C affects setting time, [...] Read more.
Ground granulated blast furnace slag (GBFS)-based geopolymers represent a viable binder system that combines mechanical efficiency with a significantly lower carbon footprint when compared to conventional Portland cement. This work examines how thermal curing between 20 °C and 80 °C affects setting time, mechanical performance, shrinkage, and porosity of GBFS-based geopolymers. Curing at 40 °C accelerated gel formation, yielding compressive strengths up to 71.9 MPa. This regime also reduced shrinkage and porosity. In contrast, curing at ≥60 °C caused structural degradation and reduced long-term performance. Statistical analysis (ANOVA and Tukey post hoc) confirmed significant effects of curing regime and age on performance. These findings provide key insights for optimizing thermal curing of slag-based geopolymers, supporting their deployment in environmentally responsible construction practices. Full article
(This article belongs to the Special Issue Sustainable Materials for Construction Applications)
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20 pages, 8741 KB  
Article
Experimental and Numerical Studies of “Wood–Composite” Reinforcement in Bending Sheared Wooden Beams Using Pre-Stressed Natural and Artificial Fibers
by Agnieszka Katarzyna Wdowiak-Postulak, Grzegorz Świt, Aleksandra Krampikowska and Luong Minh Chinh
Materials 2025, 18(18), 4418; https://doi.org/10.3390/ma18184418 - 22 Sep 2025
Viewed by 462
Abstract
Recent studies have confirmed the effectiveness of using natural fibers and fiber-reinforced polymer (FRP) composites as methods to improve the mechanical properties of timber structures. This improvement is particularly evident in static and dynamic flexural and shear performance. Moreover, there is a paucity [...] Read more.
Recent studies have confirmed the effectiveness of using natural fibers and fiber-reinforced polymer (FRP) composites as methods to improve the mechanical properties of timber structures. This improvement is particularly evident in static and dynamic flexural and shear performance. Moreover, there is a paucity of literature pertaining to numerical models that predict the non-linear behaviour of low-quality timber beams reinforced with natural and man-made fibers. The present article expounds upon a shear bending study of timber beams reinforced with bars in addition to other materials. The experimental study yielded the following findings: the best properties were obtained with hybrid reinforcement, in comparison to the reference beams. The enhancement of load-bearing capacity and stiffness for beams that have been reinforced with pre-stressed basalt bars was found to be the most advantageous, with increases of approximately 17% and 8%, respectively. Natural fibers exhibited slightly lower values, with an increase in load-bearing capacity and stiffness of approximately 14% and 3%, respectively, when compared to beams that had not been reinforced. Moreover, the numerical analyses yielded analogous results to those obtained from the experimental study. The numerical models thus proved to be a valid tool with which to study the influence of the reinforcement factor. Full article
(This article belongs to the Section Advanced Composites)
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14 pages, 3363 KB  
Article
Selective Etching of Multi-Stacked Epitaxial Si1-xGex on Si Using CF4/N2 and CF4/O2 Plasma Chemistries for 3D Device Applications
by Jihye Kim, Joosung Kang, Dongmin Yoon, U-in Chung and Dae-Hong Ko
Materials 2025, 18(18), 4417; https://doi.org/10.3390/ma18184417 - 22 Sep 2025
Viewed by 414
Abstract
The SiGe/Si multilayer is a critical component for fabricating stacked Si channel structures for next-generation three-dimensional (3D) logic and 3D dynamic random-access memory (3D-DRAM) devices. Achieving these structures necessitates highly selective SiGe etching. Herein, CF4/O2 and CF4/N2 [...] Read more.
The SiGe/Si multilayer is a critical component for fabricating stacked Si channel structures for next-generation three-dimensional (3D) logic and 3D dynamic random-access memory (3D-DRAM) devices. Achieving these structures necessitates highly selective SiGe etching. Herein, CF4/O2 and CF4/N2 gas chemistries were employed to elucidate and enhance the selective etching mechanism. To clarify the contribution of radicals to the etching process, a nonconducting plate (roof) was placed just above the samples in the plasma chamber to block ion bombardment on the sample surface. The CF4/N2 gas chemistries demonstrated superior etch selectivity and profile performance compared with the CF4/O2 gas chemistries. When etching was performed using CF4/O2 chemistry, the SiGe etch rate decreased compared to that obtained with pure CF4. This reduction is attributed to surface oxidation induced by O2, which suppressed the etch rate. By minimizing the ion collisions on the samples with the roof, higher selectivity, and a better etch profile were obtained even in the CF4/N2 gas chemistries. Under high-N2-flow conditions, X-ray photoelectron spectroscopy revealed increased surface concentrations of GeFx species and confirmed the presence of Si–N bond, which inhibited Si etching by fluorine radicals. A higher concentration of GeFx species enhanced SiGe layer etching, whereas Si–N bonds inhibited etching on the Si layer. The passivation of the Si layer and the promotion of adhesion of etching species such as F on the SiGe layer are crucial for highly selective etching in addition to etching with pure radicals. This study provides valuable insights into the mechanisms governing selective SiGe etching, offering practical guidance for optimizing fabrication processes of next-generation Si channel and complementary field-effect transistor (CFET) devices. Full article
(This article belongs to the Section Materials Physics)
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29 pages, 10965 KB  
Article
Influence of Hydration and Natural Carbonation Evolution on the Gas Permeability and Microstructure of Blended Cement Pastes
by Tomasz Tracz, Tomasz Zdeb, Krzysztof Witkowski and Daniel Szkotak
Materials 2025, 18(18), 4416; https://doi.org/10.3390/ma18184416 - 22 Sep 2025
Viewed by 404
Abstract
The high density of the internal structure of new-generation cementitious composites, such as high-performance and ultra-high-performance concretes, necessitates the use of advanced methods for evaluating their transport properties, particularly those employing a gaseous medium. The developed gas permeability method for cement pastes, based [...] Read more.
The high density of the internal structure of new-generation cementitious composites, such as high-performance and ultra-high-performance concretes, necessitates the use of advanced methods for evaluating their transport properties, particularly those employing a gaseous medium. The developed gas permeability method for cement pastes, based on a modified RILEM-Cembureau approach, has proven to be highly accurate, reliable, and extremely sensitive to changes in the porosity characteristics of such composites. The article contains the results of a study of the mass transport capabilities of blended cement pastes, characterised by variable water–cement ratios. Two types of cements were used in the study: with the addition of fly ash and blast furnace slag. Ordinary Portland cement was used as the reference binder. The tests were conducted after long-term curing under natural conditions, i.e., after 90 days and 2 years. The assessment of open porosity was carried out through three techniques: helium pycnometry, mercury intrusion porosimetry, and water saturation. Permeability, on the other hand, was measured using a customized approach tailored for uniform paste materials. Microstructural changes were also analysed in the context of natural hydration carbonation progress. The results presented allowed a quantitative description of the effects of the w/c ratio, the presence of additives, and the progress of hydration and carbonation on the porosity of pastes and their permeability to gas flow. The two-year curing period of the pastes exposed to natural CO2 resulted in a reduction of the permeability coefficient k ranging from 11% to 74%, depending on the type of cement and the water-to-cement (w/c) ratio. This decrease was caused by the continued progress of hydration and simultaneous carbonation. The results of the research presented are of interest from both an engineering and scientific point of view in the context of long-term microstructural changes and the mass transport abilities of cement pastes associated with these processes. The extensive range of materials compositions investigated makes it possible to analyse the durability and tightness of many cementitious composites over long periods of service. Full article
(This article belongs to the Section Construction and Building Materials)
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17 pages, 3704 KB  
Article
Study on the Charge Characteristics and Migration Characteristics of Amorphous Alloy Core Debris
by Wenxu Yu and Xiangyu Guan
Materials 2025, 18(18), 4415; https://doi.org/10.3390/ma18184415 - 22 Sep 2025
Viewed by 317
Abstract
Compared with a traditional distribution transformer with silicon steel sheet as the core material, the no-load loss of an amorphous alloy transformer is greatly reduced due to its core using iron-based amorphous metal material, which has been applied in many countries. However, due [...] Read more.
Compared with a traditional distribution transformer with silicon steel sheet as the core material, the no-load loss of an amorphous alloy transformer is greatly reduced due to its core using iron-based amorphous metal material, which has been applied in many countries. However, due to the brittleness of its amorphous strip, an amorphous alloy transformer is prone to debris in the process of production, transportation and work. The charge and migration characteristics of these debris will reduce the insulation strength of the transformer oil and endanger the safe operation of the transformer. In this paper, a charge measurement platform of amorphous alloy debris is set up, and the charging characteristics of amorphous alloy core debris under different flow velocities, particle radius and plate electric field strength are obtained. The results show that with an increase in pipeline flow velocity, the charge-to-mass ratio of the debris increases first and then decreases. With an increase in electric field strength, the charge-to-mass ratio of the debris increases; with an increase in the number of debris, the charge-to-mass ratio of the debris decreases; with an increase in debris size, the charge-to-mass ratio of the debris increases. The debris with different charge-to-mass ratios and types obtained from the above experiments are added to the simulation model of an amorphous alloy transformer. The lattice Boltzmann method (LBM) coupled with the discrete element method (DEM) is used to simulate the migration process of metal particles in an amorphous alloy transformer under the combined action of gravity, buoyancy, electric field force and oil flow resistance under electrothermal excitation boundary. The results show that the trajectory of the debris is related to the initial position, electric field strength and oil flow velocity. The LBM–DEM calculation model and charge measurement platform proposed in this paper can provide a reference for studying the charge mechanism and migration characteristics of amorphous alloy core debris in insulating oil. Full article
(This article belongs to the Section Metals and Alloys)
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13 pages, 3515 KB  
Article
A Dual-Layer Frequency Selective Surfaces with Tunable Transmission and Fixed Absorption Bands
by Zhiming Zhang, Qingyang Wang, Qiyuan Wang, Pei Liu, Yun He and Mingyu Li
Materials 2025, 18(18), 4414; https://doi.org/10.3390/ma18184414 - 22 Sep 2025
Viewed by 352
Abstract
This paper presents dual-layer frequency selective surfaces (FSSs) with frequency division control function through an integrated tunable transmission window at a lower frequency and an absorption performance at a higher frequency. The bottom frequency selective surface (FSS) layer, configured as a bandpass structure, [...] Read more.
This paper presents dual-layer frequency selective surfaces (FSSs) with frequency division control function through an integrated tunable transmission window at a lower frequency and an absorption performance at a higher frequency. The bottom frequency selective surface (FSS) layer, configured as a bandpass structure, incorporates a gradient gap square-ring element loaded with varactor diodes. This configuration enables dynamic tuning of the L-band transmission window from 1.26 GHz to 1.9 GHz via varactor capacitance modulation. Simultaneously, the top FSS layer utilizes a square-ring-cross-slot topology. Leveraging the strong reflection characteristic of the bottom FSS at higher frequencies in conjunction with dielectric loss mechanisms, the structure achieves absorption performance within the 5.56 GHz to 5.72 GHz band. Measurement results indicate insertion loss at operational frequencies within the transmission window remains below 1.41 dB, while the absorption peak reaches approximately −30 dB. Close agreement between simulated and measured results validates the proposed design. Full article
(This article belongs to the Special Issue Intelligent Metasurfaces and Metamaterials: From Computational Design to Dynamic Absorption)
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15 pages, 2928 KB  
Article
Bio-Based Grease from Agricultural Waste: Modified Cellulose from Corn Stover for Sustainable Lubrication
by Yuhao Fang, Gaobo Lou, Qiang Wu, Xingguo Cheng and Yifan Chen
Materials 2025, 18(18), 4413; https://doi.org/10.3390/ma18184413 - 22 Sep 2025
Viewed by 366
Abstract
In this study, a green lubricating grease was prepared based on cellulose and epoxidized soybean oil (ESO). The cellulose extracted from the corn stover was functionalized using diphenylmethane diisocyanate (MDI), which enhances its compatibility and thickening ability in non-polar oil, and subsequently dispersed [...] Read more.
In this study, a green lubricating grease was prepared based on cellulose and epoxidized soybean oil (ESO). The cellulose extracted from the corn stover was functionalized using diphenylmethane diisocyanate (MDI), which enhances its compatibility and thickening ability in non-polar oil, and subsequently dispersed in ESO to form a stable gel-like bio-based grease. The functionalized surface of cellulose was characterized by FTIR, SEM, and XRD. And the rheological and tribological characteristics of the prepared bio-based grease were discussed. The superior lubricity and anti-wear properties of our bio-based grease are demonstrated by its lower friction and diminished wear relative to commercial lithium-based formulations. This work provides practical guidance for designing environmentally friendly grease for sustainable lubrication. Full article
(This article belongs to the Section Green Materials)
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12 pages, 7222 KB  
Communication
Experimental Performance Analysis of Large-Format 304 Stainless Steel Surface Laser Matting Process
by Qianqian Ding, Mingdi Wang, Xihuai Wang, Peijiao Huang, Zirui Wang and Yeyi Ji
Materials 2025, 18(18), 4412; https://doi.org/10.3390/ma18184412 - 22 Sep 2025
Viewed by 323
Abstract
In response to the demand for rapid matte finishing on large-format 304 stainless steel surfaces, this study utilized four fiber laser devices (output wavelength: 1064 nm, output power: 100 W, maximum modulation frequency: 4 kHz) to simultaneously perform surface matte finishing experiments on [...] Read more.
In response to the demand for rapid matte finishing on large-format 304 stainless steel surfaces, this study utilized four fiber laser devices (output wavelength: 1064 nm, output power: 100 W, maximum modulation frequency: 4 kHz) to simultaneously perform surface matte finishing experiments on 304 stainless steel, with the aim of fabricating anti-reflective micro-nano structures. During the experiments, by systematically investigating the influence of parameters—including laser power, scanning speed, frequency, and idle speed of a single laser head—on the matte finishing process, the optimal processing parameters for a single laser head were determined as follows: laser power of 20 W, scanning speed of 11,000 mm/s, and frequency of 80 kHz. For large-area high-speed laser matte finishing, the delay of laser on/off was adjusted to compensate for the galvanometer’s motion trajectory, thereby ensuring uniform ablation at both the start and end positions of the processing path. Furthermore, in the context of large-area rapid multi-head laser matte finishing on 304 stainless steel, the overlapping of surface regions processed by different galvanometers was achieved by calibrating the motion start and end points of each galvanometer. The optimal overlapping parameters were successfully obtained. This study provides technical support for environmentally friendly matte finishing of stainless steel and offers valuable insights for its application in the stainless steel home appliance industry. Full article
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15 pages, 5165 KB  
Article
Carbon-Induced Structural Evolution and Synergistic Enhancement of Wear and Corrosion Resistance in (AlFeCoNi)C High-Entropy Alloy Carbide Films
by Duoli Chen, Yefeng Zhou, Xianting Yang, Mengyuan Guo, Jun Liang, Deming Huang, Yu Ni, Yurong Zhou, Yantao Li and Xin Jiang
Materials 2025, 18(18), 4411; https://doi.org/10.3390/ma18184411 - 22 Sep 2025
Viewed by 281
Abstract
The (AlFeCoNi)C high-entropy alloy carbide films (HECFs) with tunable carbon contents were fabricated by magnetron sputtering to investigate the carbon-driven structural evolution and its coupling effects on mechanical and chemical properties. With increasing carbon incorporation (0–47.6 at.%), the HECFs formed a composite structure [...] Read more.
The (AlFeCoNi)C high-entropy alloy carbide films (HECFs) with tunable carbon contents were fabricated by magnetron sputtering to investigate the carbon-driven structural evolution and its coupling effects on mechanical and chemical properties. With increasing carbon incorporation (0–47.6 at.%), the HECFs formed a composite structure of amorphous phase and BCC nanocrystalline phase, as evidenced by XRD and TEM. Atom probe tomography (APT) reveals Al segregation in the film. Remarkably, the wear rate decreases exponentially from 4.8 × 10−5 to 6.7 × 10−6 mm3/N·m, attributed to the amorphous carbon phase acting as solid lubricant. Simultaneously, the corrosion current density reduces by two orders of magnitude (7.2 × 10−8 A/cm2 in 3.5% NaCl), benefiting from the amorphous network inhibiting ion diffusion pathways. This work establishes a carbon-content–property correlation paradigm for designing multifunctional HEA films in extreme environments. Full article
(This article belongs to the Special Issue New Advances in High Entropy Alloys)
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23 pages, 3198 KB  
Article
High-Temperature and Acid Resistance of Concrete with Recycled, Desert Sand, and Crumb Rubber Blends
by Mohammad Nadeem Akhtar, Khaldoon A. Bani-Hani and Jan Nisar Akhtar
Materials 2025, 18(18), 4410; https://doi.org/10.3390/ma18184410 - 22 Sep 2025
Viewed by 374
Abstract
Natural sand extraction for concrete manufacturing is a global issue for ecological balance and environmental concerns. This study introduced three mixes with three newly developed sand types to replace natural sand in concrete manufacturing. Additionally, three more mixes were made by incorporating optimized [...] Read more.
Natural sand extraction for concrete manufacturing is a global issue for ecological balance and environmental concerns. This study introduced three mixes with three newly developed sand types to replace natural sand in concrete manufacturing. Additionally, three more mixes were made by incorporating optimized 10% silica fume. The durability of the prepared mixes was evaluated at high temperatures of (150–750 °C) at the interval of 150 °C and against immersion in a 5% sulfuric acid solution for 28, 56, 91, and 182 days, respectively. The study’s results reported the stability of the samples up to 300 °C, and then the fall of the samples started at 450 °C. Severe damage in the samples was formed at about 600 °C, and finally, a total collapse was seen at 750 °C. From (150 to 750 °C), the mix TYPE-3SSFC with a sustainable sand combination (50% recycled sand + 45% desert sand + 5% crumb rubber) and 10% silica fume showed better resistance than the other mixes. The compressive strength in the mix TYPE-3SSFC was 20.6%, 16.3%, 14.7%, 21.3%, 26.5%, and 43.2% higher than the mix TYPE-3SC with 10% silica fume. The mix TYPE-3SSFC with optimized 10% silica fume content showed better resistance against 5% sulfuric acid solution than those without silica fume. By morphological analysis, the mix TYPE-3SSFC showed that the interface improved due to the dense interconnectivity of the concrete mix between the crumb rubber paste and silica fume content. A dense calcite crystal was also seen in the mixture, which confirmed the study’s results. The mix with TYPE 2-Sand (100% recycled sand) revealed inferior results, low stability, and high damage. Thus, 100% recycled sand is not recommended for structural concrete. Full article
(This article belongs to the Special Issue Microstructural, Mechanical, and Durability Characteristics of Cementitious Materials (2nd Edition))
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28 pages, 1805 KB  
Systematic Review
Characteristics of Acrylic Produced Additively by 3D Printing in Dentistry: Comparison of Mechanical and Surface Parameters—A Systematic Review with Meta-Analysis of Novel Reports
by Paweł Szymlet, Maciej Jedliński, Wojciech Frąckiewicz, Aleksandra Jankowska, Aleksandra Wdowiak-Szymanik and Ewa Sobolewska
Materials 2025, 18(18), 4409; https://doi.org/10.3390/ma18184409 - 21 Sep 2025
Viewed by 555
Abstract
Background/Objectives: This systematic review and meta-analysis aimed to compare the mechanical and surface properties of three-dimensional (3D) printed and conventionally polymerized acrylic resins. Methods: A comprehensive search of four electronic databases (PubMed, Embase, Scopus, and Web of Science) was conducted to identify in [...] Read more.
Background/Objectives: This systematic review and meta-analysis aimed to compare the mechanical and surface properties of three-dimensional (3D) printed and conventionally polymerized acrylic resins. Methods: A comprehensive search of four electronic databases (PubMed, Embase, Scopus, and Web of Science) was conducted to identify in vitro studies evaluating impact strength, elastic modulus, surface hardness, and surface roughness. Study quality was assessed using design-specific evaluation tools. When sufficient homogeneous data were available, a meta-analysis was performed. Results: The initial search yielded 942 potentially relevant records. Fifteen studies met the criteria for qualitative synthesis, and 13 were included in the meta-analysis. All studies were in vitro and were rated as having moderate to high methodological quality. Conclusions: Although conventional acrylic resins currently demonstrate superior mechanical strength, 3D-printed materials exhibit comparable surface properties and continue to evolve rapidly. Additive manufacturing technologies show promise as a viable and effective alternative for future prosthodontic applications. Full article
(This article belongs to the Section Biomaterials)
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13 pages, 2592 KB  
Article
Reduction Study of Carbon-Bearing Briquettes in the System of Multiple Reductants
by Xiaojun Ning, Zheng Ren, Nan Zhang, Guangwei Wang, Xueting Zhang, Junyi Wu, Jiangbin Liu, Andrey Karasev and Chuan Wang
Materials 2025, 18(18), 4408; https://doi.org/10.3390/ma18184408 - 21 Sep 2025
Viewed by 354
Abstract
Against the backdrop of escalating global carbon emissions, the steel industry urgently requires a transition toward green and low-carbon practices. As a conditionally carbon-neutral renewable energy source, biochar holds potential for replacing traditional fossil-based reducing agents. This study aims to investigate the mechanism [...] Read more.
Against the backdrop of escalating global carbon emissions, the steel industry urgently requires a transition toward green and low-carbon practices. As a conditionally carbon-neutral renewable energy source, biochar holds potential for replacing traditional fossil-based reducing agents. This study aims to investigate the mechanism and performance differences between biochar (wood char, bamboo char) and conventional reducing agents (semi-coke, coke powder, anthracite) in the direct reduction process of carbon-bearing briquettes. Through reduction experiments simulating rotary kiln conditions, combined with analysis of reducing agent gasification characteristics, carbon-to-oxygen (C/O) molar ratio control, X-ray diffraction (XRD), and microstructural examination, the high-temperature behavior of different reducing agents was systematically evaluated. Results indicate that biochar exhibits superior gasification reactivity due to its high specific surface area and developed pore structure: wood char and bamboo char show significantly enhanced reaction rates above 1073 K, approaching complete conversion at 1173 K. In contrast, anthracite and coke powder, characterized by dense structures and low specific surface areas, failed to achieve complete gasification even at 1273 K. Pellets containing bamboo char achieved the highest metallization rate (90.16%) after calcination at 1373 K. The compressive strength of the pellets first decreased and then increased with rising temperature, consistent with the trend in metallization rate. The mechanism analysis indicates that the high reactivity and porous structure of biochar promote rapid CO diffusion and synergistic gas–solid reactions, significantly accelerating the reduction of iron oxides and the formation of metallic iron. Full article
(This article belongs to the Special Issue Advances in Process Metallurgy and Metal Recycling)
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16 pages, 2793 KB  
Article
Bacterial Tolerance and Bioleaching in the Presence of Chloride
by Narine Vardanyan, Anna Khachatryan, Zaruhi Melkonyan, Nelli Abrahamyan, Sona Barseghyan, Ruiyong Zhang and Arevik Vardanyan
Materials 2025, 18(18), 4407; https://doi.org/10.3390/ma18184407 - 21 Sep 2025
Viewed by 982
Abstract
Chloride ions can enhance the bioleaching of copper minerals, yet most biomining microorganisms are highly sensitive to chloride and cannot survive or colonize mineral surfaces in saline environments. Chloride tolerance varies among acidophilic iron-oxidizing bacteria, but the concentrations at which they remain active [...] Read more.
Chloride ions can enhance the bioleaching of copper minerals, yet most biomining microorganisms are highly sensitive to chloride and cannot survive or colonize mineral surfaces in saline environments. Chloride tolerance varies among acidophilic iron-oxidizing bacteria, but the concentrations at which they remain active are generally too low to permit the industrial use of seawater. Therefore, identifying highly chloride-tolerant leaching microorganisms and studying their bioleaching potential in chloride-containing systems is of utmost importance. This study investigated chloride tolerance and adaptability of bacteria from different genera, with a focus on Sulfobacillus thermosulfidooxidans subsp. asporogenes 41, a moderately thermophilic strain that can oxidize both Fe (II) and reduced inorganic sulfur compounds (RISCs). This dual activity makes it advantageous for bioleaching by facilitating sulfur removal, generating acidity, and preventing mineral passivation. Comparative experiments on the bioleaching of pyrite and chalcopyrite demonstrated that adaptation to 0.3 M NaCl enhanced the chloride tolerance of S. thermosulfidooxidans subsp. asporogenes 41. The adapted strain exhibited significantly improved copper extraction under saline conditions compared with the native culture. Maximum copper recovery was achieved at 0.4 M NaCl, highlighting the potential of chloride-adapted moderate thermophiles for biomining applications in saline environments. In contrast the minimal inhibitory concentration for Acidithiobacillud ferrooxidans Dr was 0.005 M (causing 41.2% inhibition), while Leptospirillum ferriphilum CC was unaffected by lower concentrations (0.01–0.02 M) and only showed severe inhibition (86.5%) at 0.1 M NaCl, defining its minimal inhibitory concentration (MIC) at 0.05 M. Full article
(This article belongs to the Special Issue The Interactions of Microorganisms and Materials: Biocorrosion and Bioleaching)
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16 pages, 4093 KB  
Article
Damage Localization and Sensor Layout Optimization for In-Service Reinforced Concrete Columns Using Deep Learning and Acoustic Emission
by Tao Liu, Aiping Yu, Zhengkang Li, Menghan Dong, Xuelian Deng and Tianjiao Miao
Materials 2025, 18(18), 4406; https://doi.org/10.3390/ma18184406 - 21 Sep 2025
Viewed by 364
Abstract
As the main load-bearing components of engineering structures, regular health assessment of reinforced concrete (RC) columns is crucial for improving the service life and overall performance of the structures. This study focuses on the health detection problem of in-service RC columns. By combining [...] Read more.
As the main load-bearing components of engineering structures, regular health assessment of reinforced concrete (RC) columns is crucial for improving the service life and overall performance of the structures. This study focuses on the health detection problem of in-service RC columns. By combining deep learning algorithms and acoustic emission (AE) technology, the AE sources of in-service RC columns are located, and the optimal sensor layout form for the health monitoring of in-service RC columns is determined. The results show that the data cleaning method based on the k-means clustering algorithm and the voting selection concept can significantly improve the data quality. By comparing the localization performance of the Back Propagation (BP), Radial Basis Function (RBF) and Support Vector Regression (SVR) models, it is found that compared with the RBF and SVR models, the MAE of the BP model is reduced by 7.513 mm and 6.326 mm, the RMSE is reduced by 9.225 mm and 8.781 mm, and the R2 is increased by 0.059 and 0.056, respectively. The BP model has achieved good results in AE source localization of in-service RC columns. By comparing different sensor layout schemes, it is found that the linear arrangement scheme is more effective for the damage location of shallow concrete matrix, while the hybrid linear-volumetric arrangement scheme is better for the damage location of deep concrete matrix. The hybrid linear-volumetric arrangement scheme can simultaneously detect damage signals from both shallow and deep concrete matrix, which has certain application value for the health monitoring of in-service RC columns. Full article
(This article belongs to the Section Construction and Building Materials)
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34 pages, 9541 KB  
Article
Formability and Electromagnetic Performance Comparison of Fe-P-Based SMC and Fe-5.0 wt.%Si Powders
by Seongsu Kang and Seonbong Lee
Materials 2025, 18(18), 4405; https://doi.org/10.3390/ma18184405 - 21 Sep 2025
Viewed by 314
Abstract
This study investigates the comparative applicability of Somaloy 700HR 5P and Fe-5.0 wt.%Si powders for axial flux permanent magnet (AFPM) motor cores in low-speed electric vehicles. Optimal forming conditions were derived through Taguchi-based simulations, considering corner radius, forming temperature, and forming speed, followed [...] Read more.
This study investigates the comparative applicability of Somaloy 700HR 5P and Fe-5.0 wt.%Si powders for axial flux permanent magnet (AFPM) motor cores in low-speed electric vehicles. Optimal forming conditions were derived through Taguchi-based simulations, considering corner radius, forming temperature, and forming speed, followed by prototype fabrication and validation. Simulation and SEM-EDS analyses confirmed consistent density distribution trends, and XRD verified phase stability during forming. While Fe-5.0 wt.%Si exhibited ~10% ± 2 superior electromagnetic performance in the powder state, its motor dynamo performance decreased by 19–25% (n = 1) compared to Somaloy 700HR 5P. This discrepancy was attributed to its ~4% lower target density (7.19 ± 0.02 g/cm3 vs. 7.51 ± 0.01 g/cm3, n = 3), assembly-induced mechanical losses, and non-uniform insulation layer caused by residual H3PO4 and Mo segregation. Somaloy 700HR 5P, despite a higher relative density variation (0.084 ± 0.002 g/cm3 vs. 0.063 ± 0.003 g/cm3 for Fe-5.0 wt.%Si), achieved an average density close to 7.5 g/cm3 and delivered more stable motor performance. Overall, Somaloy 700HR 5P was identified as a more suitable candidate for AFPM motor cores in low-speed EV applications, balancing formability and electromagnetic performance. Full article
(This article belongs to the Special Issue Soft Magnetic Materials: Synthesis, Properties and Applications)
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22 pages, 11310 KB  
Article
Mechanisms for Migration of Alkali in Dolomitic Limestones
by Xinyu Zhang, Wei Li, Xiaojun Huang, Zhixin Wang and Min Deng
Materials 2025, 18(18), 4404; https://doi.org/10.3390/ma18184404 - 21 Sep 2025
Viewed by 310
Abstract
The alkali–dolomite reaction (ADR) describes the interaction between alkalis in concrete and dolomite which results in dedolomitization, leading to cracking and deterioration of the concrete. A large number of research has explored the chemical products associated with the ADR, mechanisms of expansion, and [...] Read more.
The alkali–dolomite reaction (ADR) describes the interaction between alkalis in concrete and dolomite which results in dedolomitization, leading to cracking and deterioration of the concrete. A large number of research has explored the chemical products associated with the ADR, mechanisms of expansion, and methods of identification, but our understanding of the occurrence and progression of the ADR chemical reaction is substantially limited. Key factors controlling the ADR chemical reaction are generally not understood. This paper investigates the migration process of alkali ions in dolomitic limestone and reaction process with dolomite crystals and alkali. Dolomitic limestone samples were selected for experimentation. The amount of Sodium (Na+) was measured as a means of assessing alkali ion migration. We measured the degree of dedolomitization using X-ray diffraction (XRD). Microstructure was evaluated using field emission scanning electron microscopy (FESEM). This research provides new insights into dedolomitization. The pore network provides the physical pathway for alkali ion migration. Concentration gradients drive the migration of alkali ions, and their interactions control the efficiency of alkali ion migration. Full article
(This article belongs to the Special Issue Reaction Mechanism and Properties of Cement-Based Materials (2nd Edition))
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52 pages, 6335 KB  
Article
On Sampling-Times-Independent Identification of Relaxation Time and Frequency Spectra Models of Viscoelastic Materials Using Stress Relaxation Experiment Data
by Anna Stankiewicz, Sławomir Juściński and Marzena Błażewicz-Woźniak
Materials 2025, 18(18), 4403; https://doi.org/10.3390/ma18184403 - 21 Sep 2025
Viewed by 255
Abstract
Viscoelastic relaxation time and frequency spectra are useful for describing, analyzing, comparing, and improving the mechanical properties of materials. The spectra are typically obtained using the stress or oscillatory shear measurements. Over the last 80 years, dozens of mathematical models and algorithms were [...] Read more.
Viscoelastic relaxation time and frequency spectra are useful for describing, analyzing, comparing, and improving the mechanical properties of materials. The spectra are typically obtained using the stress or oscillatory shear measurements. Over the last 80 years, dozens of mathematical models and algorithms were proposed to identify relaxation spectra models using different analytical and numerical tools. Some models and identification algorithms are intended for specific materials, while others are general and can be applied for an arbitrary rheological material. The identified relaxation spectrum model always depends on the identification method applied and on the specific measurements used in the identification process. The stress relaxation experiment data consist of the sampling times used in the experiment and the noise-corrupted relaxation modulus measurements. The aim of this paper is to build a model of the spectrum that asymptotically does not depend on the sampling times used in the experiment as the number of measurements tends to infinity. Broad model classes, determined by a finite series of various basis functions, are assumed for the relaxation spectra approximation. Both orthogonal series expansions based on the Legendre, Laguerre, and Chebyshev functions and non-orthogonal basis functions, like power exponential and modified Bessel functions of the second kind, are considered. It is proved that, even when the true spectrum description is entirely unfamiliar, the approximate sampling-times-independent spectra optimal models can be determined using modulus measurements for appropriately randomly selected sampling times. The recovered spectra models are strongly consistent estimates of the desirable models corresponding to the relaxation modulus models, being optimal for the deterministic integral weighted square error. A complete identification algorithm leading to the relaxation spectra models is presented that requires solving a sequence of weighted least-squares relaxation modulus approximation problems and a random selection of the sampling times. The problems of relaxation spectra identification are ill-posed; solution stability is ensured by applying Tikhonov regularization. Stochastic convergence analysis is conducted and the convergence with an exponential rate is demonstrated. Simulation studies are presented for the Kohlrausch–Williams–Watts spectrum with short relaxation times, the uni- and double-mode Gauss-like spectra with intermediate relaxation times, and the Baumgaertel–Schausberger–Winter spectrum with long relaxation times. Models using spectrum expansions on different basis series are applied. These studies have shown that sampling times randomization provides the sequence of the optimal spectra models that asymptotically converge to sampling-times-independent models. The noise robustness of the identified model was shown both by analytical analysis and numerical studies. Full article
(This article belongs to the Special Issue Modelling of Viscoelastic Materials and Mechanical Behavior (2nd Edition))
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19 pages, 14535 KB  
Article
Corrosion Behaviors of ZrSi Coating by Laser Cladding on Zr-4 Alloy in High-Temperature Steam
by Dongliang Jin, Changda Zhu, Xiqiang Ma, Zhengxian Di and Shizhong Wei
Materials 2025, 18(18), 4402; https://doi.org/10.3390/ma18184402 - 21 Sep 2025
Viewed by 345
Abstract
Si powder was deposited onto the surface of Zr-4 alloy via laser cladding to enhance its high-temperature oxidation resistance. The high-power laser radiation and rapid solidification lead to a reaction between Si and Zr, resulting in the formation of a microstructure consisting of [...] Read more.
Si powder was deposited onto the surface of Zr-4 alloy via laser cladding to enhance its high-temperature oxidation resistance. The high-power laser radiation and rapid solidification lead to a reaction between Si and Zr, resulting in the formation of a microstructure consisting of lath-like ZrSi2 and Si-rich phases. The oxidation behavior of the laser-cladding ZrSi coating was evaluated at 1100–1300 °C in water steam. The weight gain follows a parabolic law, and the oxidation activation energy of the ZrSi coating is 182.7 kJ mol−1. The oxides produced by ZrSi2 oxidation are mainly ZrSiO4, ZrO2, and SiO2, and, under high-temperature conditions, the relative content of ZrSiO4 in the oxide decreases with increasing temperature. The oxidation of the ZrSi2 phase induces significant growth stresses, which are susceptible to causing cracks in the oxide, facilitating accelerated oxygen diffusion into the coating. However, the amorphous SiO2 formed at 1300 °C, which may be softened and fluidized to enable a self-healing effect, can heal the cracks to diminish oxygen permeation into the coating, improving its oxidation resistance. The oxidation resistance of the laser cladding ZrSi coating is better than that of the Zr-4 alloy. Full article
(This article belongs to the Section Metals and Alloys)
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