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17 pages, 9744 KB  
Article
Effect of Secondary Aging Conditions on Mechanical Properties and Microstructure of AA7150 Aluminum Alloy
by Fei Chen, Han Wang, Yanan Jiang, Yu Liu, Qiang Zhou and Quanqing Zeng
Materials 2025, 18(20), 4763; https://doi.org/10.3390/ma18204763 - 17 Oct 2025
Abstract
Al-Zn-Mg-Cu alloys are widely used as heat-treatable ultra-high-strength materials in aerospace structural applications. While conventional single-stage aging enables high strength, advanced performance demands call for precise microstructural control via multi-stage aging. In this study, we employ a combination of scanning transmission electron microscopy [...] Read more.
Al-Zn-Mg-Cu alloys are widely used as heat-treatable ultra-high-strength materials in aerospace structural applications. While conventional single-stage aging enables high strength, advanced performance demands call for precise microstructural control via multi-stage aging. In this study, we employ a combination of scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) to investigate the microstructural evolution and its correlation with mechanical properties of AA7150 aluminum alloy subjected to two-step aging treatments, following a 6 h pre-aging at 120 °C. Through atomic-scale STEM imaging along the [110]Al zone axis, we systematically characterize the precipitation behavior of GPII zones, η′ phases, and equilibrium η phases both within the grains and at grain boundaries under varying secondary aging (SA) conditions. Our results reveal that increasing the SA temperature from 140 °C to 180 °C leads to coarsening and reduced number density of intragranular precipitates, while promoting the continuous and coarse precipitation of η phases along grain boundaries, accompanied by a widening of the precipitation-free zone (PFZ). Notably, SA at 160 °C induces the formation of fine, uniformly dispersed nanoscale η′ precipitates in the alloy, as confirmed by XRD phase analysis. Aging at this temperature markedly enhances the mechanical properties, achieving an ultimate tensile strength (UTS) of 613 MPa and a yield strength (YS) of 598 MPa, while presenting an exceptionally broad peak-aging plateau. Owing to this feature, a moderate extension of the SA duration does not reduce strength and can further improve ductility, increasing the elongation (EL) to 14.26%. These results demonstrate a novel two-step heat-treatment strategy that simultaneously achieves ultra-high strength and excellent ductility, highlighting the critical role of advanced electron microscopy in elucidating phase-transformation pathways that inform microstructure-guided alloy design and processing. Full article
(This article belongs to the Section Metals and Alloys)
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15 pages, 4121 KB  
Article
The Effects of Soft-Segment Molecular Weight on the Structure and Properties of Poly(trimethylene terephthalate)-block-poly(tetramethylene glycol) Copolymers
by Hailiang Dong, Yuchuang Tian, Junyu Li, Jiyou Shi, Jun Kuang, Wenle Zhou and Ye Chen
Polymers 2025, 17(20), 2781; https://doi.org/10.3390/polym17202781 - 17 Oct 2025
Viewed by 28
Abstract
A series of PTT-b-PTMG copolyesters was synthesized via direct esterification followed by melt polycondensation using purified terephthalic acid (PTA), bio-based 1,3-propanediol (PDO), and poly(tetramethylene glycol) (PTMG) of varying molecular weights (650–3000 g/mol). The resulting materials were comprehensively characterized in terms of [...] Read more.
A series of PTT-b-PTMG copolyesters was synthesized via direct esterification followed by melt polycondensation using purified terephthalic acid (PTA), bio-based 1,3-propanediol (PDO), and poly(tetramethylene glycol) (PTMG) of varying molecular weights (650–3000 g/mol). The resulting materials were comprehensively characterized in terms of chemical structure, molecular weight, thermal behavior, phase morphology, crystalline architecture, and mechanical performance using a range of analytical techniques: Fourier-transform infrared spectroscopy (FTIR), 1H-NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), dynamic mechanical thermal analysis (DMA), tensile testing, and other standard physical methods. FTIR, 1H-NMR, and GPC data confirmed the successful incorporation of both PTT-hard and PTMG-soft segments into the copolymer backbone. As the PTMG molecular weight increased, the average sequence length of the PTT-hard segments (Ln,T) also increased, leading to higher melting (Tm) and crystallization (Tc) temperatures, albeit with a slight reduction in overall crystallinity. DMA results indicated enhanced microphase separation between hard and soft domains with increasing PTMG molecular weight. WAXS and SAXS analyses further revealed that the crystalline structure and long-range ordering were strongly dependent on the copolymer composition and block architecture. Mechanical testing showed that tensile strength at break remained relatively constant across the series, while Young’s modulus increased significantly with higher PTMG molecular weight—concurrently accompanied by a decrease in elongation at break. Furthermore, the elastic deformability and recovery behavior of PTT-b-PTMG block copolymers were evaluated through cyclic tensile testing. TGA confirmed that all copolyesters exhibited excellent thermal stability. This study demonstrates that the physical and mechanical properties of bio-based PTT-b-PTMG elastomers can be effectively tailored by adjusting the molecular weight of the PTMG-soft segment, offering valuable insights for the rational design of sustainable thermoplastic elastomers with tunable performance. Full article
(This article belongs to the Section Polymer Chemistry)
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29 pages, 9861 KB  
Article
Multiscale Investigation of Interfacial Behaviors in Rubber Asphalt–Aggregate Systems Under Salt Erosion: Insights from Laboratory Tests and Molecular Dynamics Simulations
by Yun Li, Youxiang Si, Shuaiyu Wang, Peilong Li, Ke Zhang and Yuefeng Zhu
Materials 2025, 18(20), 4746; https://doi.org/10.3390/ma18204746 - 16 Oct 2025
Viewed by 138
Abstract
Deicing salt effectively melts ice and snow to maintain traffic flow in seasonal freezing zones, but its erosion effect compromises the water stability and structural integrity of asphalt pavements. To comprehensively explore the impacts of salt erosion on the interfacial behaviors of rubber [...] Read more.
Deicing salt effectively melts ice and snow to maintain traffic flow in seasonal freezing zones, but its erosion effect compromises the water stability and structural integrity of asphalt pavements. To comprehensively explore the impacts of salt erosion on the interfacial behaviors of rubber asphalt–aggregate systems, this study developed a multiscale characterization method integrating a macroscopic mechanical test, microscopic tests, and molecular dynamics (MD) simulations. Firstly, laboratory-controlled salt–freeze–thaw cycles were employed to simulate field conditions, followed by quantitative evaluation of interfacial bonding properties through pull-out tests. Subsequently, the atomic force microscopy (AFM) and Fourier transform infrared spectrometer (FTIR) tests were conducted to characterize the microscopic morphology evolution and chemical functional group transformations, respectively. Moreover, by combining the diffusion coefficients of water molecules, salt solution ions, and asphalt components, the mechanism of interfacial salt erosion was elucidated. The results demonstrate that increasing NaCl concentration and freeze–thaw cycles progressively reduces interfacial pull-out strength and fracture energy, with NaCl-induced damage becoming limited after twelve salt–freeze–thaw cycles. In detail, with exposure to 15 freeze–thaw cycles in 6% NaCl solution, the pull-out strength and fracture energy of the rubber asphalt–limestone aggregate decrease by 50.47% and 51.57%, respectively. At this stage, rubber asphalt exhibits 65.42% and 52.34% increases in carbonyl and sulfoxide indexes, respectively, contrasted by 49.24% and 42.5% decreases in aromatic and aliphatic indexes. Long-term exposure to salt–freeze–thaw conditions promotes phase homogenization, ultimately reducing surface roughness and causing rubber asphalt to resemble matrix asphalt morphologically. At the rubber asphalt–NaCl solution–aggregate interface, the diffusion of Na+ is faster than that of Cl. Meanwhile, compared with other asphalt components, saturates exhibit notably enhanced mobility under salt erosion conditions. The synergistic effects of accelerated aging, salt crystallization pressure, and enhanced ionic diffusion jointly induce the deterioration of interfacial bonding, which accounts for the decrease in macroscopic pull-out strength. This multiscale investigation advances understanding of salt-induced deterioration while providing practical insights for developing durable asphalt mixtures in cold regions. Full article
(This article belongs to the Section Construction and Building Materials)
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22 pages, 4743 KB  
Article
Investigation into the Multiphase Product Distribution and Evolution During Biomass Pyrolysis Using Wheat Straw and Pine Sawdust
by Jishuo Li, Kaili Xu, Xiwen Yao and Xingyu Luo
Energies 2025, 18(20), 5397; https://doi.org/10.3390/en18205397 - 13 Oct 2025
Viewed by 147
Abstract
Understanding the formation mechanisms of three-phase products during biomass pyrolysis is essential for optimizing thermochemical conversion and enhancing the efficient utilization of renewable resources. In this study, wheat straw (WS) and pine sawdust (PS) were selected as representative feedstocks to investigate the thermal [...] Read more.
Understanding the formation mechanisms of three-phase products during biomass pyrolysis is essential for optimizing thermochemical conversion and enhancing the efficient utilization of renewable resources. In this study, wheat straw (WS) and pine sawdust (PS) were selected as representative feedstocks to investigate the thermal decomposition behavior and evolution characteristics of gas, liquid (tar), and solid (char) products during pyrolysis. Thermogravimetric analysis and kinetic modeling revealed that PS exhibited higher activation energy (75.44 kJ/mol) than WS (65.63 kJ/mol), indicating greater thermal resistance. Tar yield increased initially and then declined with temperature, peaking at 700 °C (37.79% for PS and 32.82% for WS), while the composition shifted from oxygenated compounds to polycyclic aromatic hydrocarbons as temperature rose. FTIR analysis demonstrated that most functional group transformations in char occurred below 400 °C, with aromatic structures forming above 300 °C and stabilizing beyond 700 °C. Gas product evolution showed that WS produced higher CO and H2 yields due to its composition, with CH4 generated in relatively lower amounts. These findings provide insights into biomass pyrolysis mechanisms and offer a theoretical basis for targeted regulation of product distributions in bioenergy applications. Full article
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39 pages, 19794 KB  
Article
Cylindrical Coordinate Analytical Solution for Axisymmetric Consolidation of Unsaturated Soils: Dual Bessel–Trigonometric Orthogonal Expansion Approach to Radial–Vertical Composite Seepage Systems
by Yiru Hu and Lei Ouyang
Symmetry 2025, 17(10), 1714; https://doi.org/10.3390/sym17101714 - 13 Oct 2025
Viewed by 184
Abstract
This study develops a novel analytical solution for three-dimensional axisymmetric consolidation of unsaturated soils incorporating radial–vertical composite seepage mechanisms and anisotropic permeability characteristics. A groundbreaking dual orthogonal expansion framework is established, utilizing innovative Bessel–trigonometric function coupling to solve the inherently complex spatiotemporal coupled [...] Read more.
This study develops a novel analytical solution for three-dimensional axisymmetric consolidation of unsaturated soils incorporating radial–vertical composite seepage mechanisms and anisotropic permeability characteristics. A groundbreaking dual orthogonal expansion framework is established, utilizing innovative Bessel–trigonometric function coupling to solve the inherently complex spatiotemporal coupled partial differential equations in cylindrical coordinate systems. The mathematical approach synergistically combines modal expansion theory with Laplace transform methodology, achieving simultaneous spatial expansion of gas–liquid two-phase pressure fields through orthogonal function series, thereby transforming the three-dimensional problem into solvable ordinary differential equations. Rigorous validation demonstrates exceptional accuracy with coefficient of determination R2 exceeding 0.999 and relative errors below 2% compared to numerical simulations, confirming theoretical correctness and practical applicability. The analytical solutions reveal four critical findings with quantitative engineering implications: (1) dual-directional drainage achieves 28% higher pressure dissipation efficiency than unidirectional drainage, providing design optimization criteria for vertical drainage systems; (2) normalized matric suction variation exhibits characteristic three-stage evolution featuring rapid decline, plateau stabilization, and slow recovery phases, while water phase follows bidirectional inverted S-curve patterns, enabling accurate consolidation behavior prediction under varying saturation conditions; (3) gas-water permeability ratio ka/kw spanning 0.1 to 1000 produces two orders of magnitude time compression effect from 10−2 s to 10−4 s, offering parametric design methods for construction sequence control; (4) initial pressure gradient parameters λa and λw demonstrate opposite regulatory mechanisms, where increasing λa retards consolidation while λw promotes the process, providing differentiated treatment strategies for various geological conditions. The unified framework accommodates both uniform and gradient initial pore pressure distributions, delivering theoretical support for refined embankment engineering design and construction control. Full article
(This article belongs to the Section Engineering and Materials)
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34 pages, 18226 KB  
Article
The Vanadium Micro-Alloying Effect on the Microstructure of HSLA Steel Welded Joints by GMAW
by Giulia Stornelli, Bryan Ramiro Rodríguez-Vargas, Anastasiya Tselikova, Rolf Schimdt, Michelangelo Mortello and Andrea Di Schino
Metals 2025, 15(10), 1127; https://doi.org/10.3390/met15101127 - 10 Oct 2025
Viewed by 328
Abstract
Structural applications that use High-Strength Low-Alloy (HSLA) steels require detailed microstructural analysis to manufacture welded components that combine strength and weldability. The balance of these properties depends on both the chemical composition and the welding parameters. Moreover, in multi-pass welds, thermal cycling results [...] Read more.
Structural applications that use High-Strength Low-Alloy (HSLA) steels require detailed microstructural analysis to manufacture welded components that combine strength and weldability. The balance of these properties depends on both the chemical composition and the welding parameters. Moreover, in multi-pass welds, thermal cycling results in a complex Heat-Affected Zone (HAZ), characterized by sub-regions with a multitude of microstructural constituents, including brittle phases. This study investigates the influence of Vanadium addition on the microstructure and performance of the HAZ. Multi-pass welded joints were manufactured on 15 mm thick S355 steels with different Vanadium contents using a robotic GMAW process. A steel variant containing both Vanadium and Niobium was also considered, and the results were compared to those of standard S355 steel. Moving through the different sub-regions of the welded joints, the results show a heterogeneous microstructure characterized by ferrite, bainite and martensite/austenite (M/A) islands. The presence of Vanadium reduces carbon solubility during the phase transformations involved in the welding process. This results in the formation of very fine (average size 11 ± 4 nm) and dispersed precipitates, as well as a lower percentage of the brittle M/A phase, in the variant with a high Vanadium content (0.1 wt.%), compared to the standard S355 steel. Despite the presence of the brittle phase, the micro-alloyed variants exhibit strengthening without loss of ductility. The combined presence of both hard and soft phases in the HAZ provides stress-damping behavior, which, together with the very fine precipitates, promises improved resistance to crack propagation under different loading conditions. Full article
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21 pages, 5514 KB  
Article
Dynamic Constitutive Model of Basalt Fiber Concrete After High Temperature Based on Fractional Calculus
by Wenbiao Liang, Kai Ding, Yan Li, Yue Zhai, Lintao Li and Yi Tian
Materials 2025, 18(20), 4657; https://doi.org/10.3390/ma18204657 - 10 Oct 2025
Viewed by 316
Abstract
Concrete materials undergo a series of physical and chemical changes under high temperature, leading to the degradation of mechanical properties. This study investigates basalt fiber-reinforced concrete (BFRC) through high-temperature testing using the split Hopkinson pressure bar (SHPB) apparatus. Impact compression tests were conducted [...] Read more.
Concrete materials undergo a series of physical and chemical changes under high temperature, leading to the degradation of mechanical properties. This study investigates basalt fiber-reinforced concrete (BFRC) through high-temperature testing using the split Hopkinson pressure bar (SHPB) apparatus. Impact compression tests were conducted on specimens after exposure to elevated temperatures to analyze the effects of varying fiber content, temperature levels, and impact rates on the mechanical behaviors of BFRC. Based on fractional calculus theory, a dynamic constitutive equation was established to characterize the viscoelastic properties and high-temperature damage of BFRC. The results indicate that the dynamic compressive strength of BFRC decreases significantly with increasing temperature but increases gradually with higher impact rates, demonstrating fiber-toughening effects, thermal degradation effects, and strain rate strengthening effects. The proposed constitutive model aligns well with the experimental data, effectively capturing the dynamic mechanical behaviors of BFRC after high-temperature exposure, including its transitional mechanical characteristics across elastic, viscoelastic, and viscous states. The viscoelastic behaviors of BFRC are fundamentally attributed to the synergistic response of its multi-phase composite system across different scales. Basalt fibers enhance the material’s elastic properties by improving the stress transfer mechanism, while high-temperature exposure amplifies its viscous characteristics through microstructural deterioration, chemical transformations, and associated thermal damage. Full article
(This article belongs to the Section Construction and Building Materials)
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14 pages, 2513 KB  
Article
Long-Term Chemical Solubility of 2.3Y-TZP Dental Ceramics
by Lidija Ćurković, Sanja Štefančić, Irena Žmak, Vilko Mandić, Ivana Gabelica and Ketij Mehulić
J. Funct. Biomater. 2025, 16(10), 374; https://doi.org/10.3390/jfb16100374 - 8 Oct 2025
Viewed by 543
Abstract
In this study, the chemical solubility (stability) of yttria-partially stabilized zirconia (2.3Y-TZP) dental ceramics, both glazed (Group 2) and non-glazed samples (Group 1), was evaluated using a modified testing protocol based on ISO 6872:2024. Chemical stability was assessed by measuring ion release with [...] Read more.
In this study, the chemical solubility (stability) of yttria-partially stabilized zirconia (2.3Y-TZP) dental ceramics, both glazed (Group 2) and non-glazed samples (Group 1), was evaluated using a modified testing protocol based on ISO 6872:2024. Chemical stability was assessed by measuring ion release with inductively coupled plasma mass spectrometry (ICP-MS) and by analyzing phase composition with X-ray diffraction (XRD). While ISO 6872 prescribes chemical stability testing in a 4 wt.% aqueous acetic acid solution at 80 °C for 16 h, the exposure duration in this study was extended to 768 h (32 days) to allow a more accurate determination of long-term solubility behavior. Additionally, the surface roughness parameters (Ra, Rmax, Rz, Sa, Sq) were analyzed and evaluated before and after solubility testing. Kinetic analysis revealed that degradation followed a near-parabolic rate law, with power-law exponents of n = 2.261 for Group 1 and n = 1.935 for Group 2. The corresponding dissolution rate constants were 3.85 × 10−5 µgn·cm−2n·h−1 for Group 1 and 132.3 µgn·cm−2n·h−1 for Group 2. XRD results indicated that the long exposure to acetic acid induced a partial phase transformation of zirconia from the tetragonal to the monoclinic phase. Under prolonged acetic exposure, the glaze layer on 2.3Y-TZP exhibited significantly higher dissolution, whereas the zirconia (polished, unglazed) showed low ion release. The temporal change in the total amount of dissolved ions was statistically analyzed for Group 1 and Group 2. The samples showed a strong correlation, but ANOVA confirmed significant differences between them. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Functional Biomaterials (2nd Edition))
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15 pages, 3727 KB  
Article
In Situ High-Temperature and High-Pressure Spectroscopic Study of the Thermal and Pressure Behavior of Hydrous Fe-Rich Ringwoodite
by Jiayi Yu, Tianze Chen and Li Zhang
Minerals 2025, 15(10), 1053; https://doi.org/10.3390/min15101053 - 4 Oct 2025
Viewed by 214
Abstract
In situ high-temperature Raman spectroscopy (up to 550 °C) and infrared spectroscopy (up to 700 °C) were employed to analyze hydrous Fe-rich ringwoodite (Fo76 composition containing 0.69 wt% H2O). The results demonstrate that the hydrous Fe-rich ringwoodite sample undergoes irreversible structural [...] Read more.
In situ high-temperature Raman spectroscopy (up to 550 °C) and infrared spectroscopy (up to 700 °C) were employed to analyze hydrous Fe-rich ringwoodite (Fo76 composition containing 0.69 wt% H2O). The results demonstrate that the hydrous Fe-rich ringwoodite sample undergoes irreversible structural transformation above 300 °C at ambient pressure, converting to an amorphous phase. This indicates a lower thermal stability threshold compared to Fe-bearing ringwoodite (Fo90) with equivalent water content. Notably, identical infrared spectral evolution patterns were observed during heating (25–500 °C) for the studied Fo76 sample and previously reported Fo82/Fo90 specimens, suggesting minimal influence of iron content variation on hydroxyl group behavior. The material derived from Fe-rich ringwoodite through structural transformation at ~350 °C retains the capacity to preserve water within a defined temperature window (400–550 °C). In situ high-pressure Raman spectroscopy experiments conducted up to 20 GPa detected no notable structural modifications, suggesting that hydrous Fe-rich ringwoodite, hydrous Fe-bearing ringwoodite, and hydrous Mg-endmember ringwoodite exhibit comparable structural stability within this pressure range. Full article
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24 pages, 3808 KB  
Article
Study of Soliton Solutions, Bifurcation, Quasi-Periodic, and Chaotic Behaviour in the Fractional Coupled Schrödinger Equation
by Manal Alharbi, Adel Elmandouh and Mamdouh Elbrolosy
Mathematics 2025, 13(19), 3174; https://doi.org/10.3390/math13193174 - 3 Oct 2025
Viewed by 278
Abstract
This study presents a qualitative analysis of the fractional coupled nonlinear Schrödinger equation (FCNSE) to obtain its complete set of solutions. An appropriate wave transformation is applied to reduce the FCNSE to a fourth-order dynamical system. Due to its non-Hamiltonian nature, this system [...] Read more.
This study presents a qualitative analysis of the fractional coupled nonlinear Schrödinger equation (FCNSE) to obtain its complete set of solutions. An appropriate wave transformation is applied to reduce the FCNSE to a fourth-order dynamical system. Due to its non-Hamiltonian nature, this system poses significant analytical challenges. To overcome this complexity, the dynamical behavior is examined within a specific phase–space subspace, where the system simplifies to a two-dimensional, single-degree-of-freedom Hamiltonian system. The qualitative theory of planar dynamical systems is then employed to characterize the corresponding phase portraits. Bifurcation analysis identifies the physical parameter conditions that give rise to super-periodic, periodic, and solitary wave solutions. These solutions are derived analytically and illustrated graphically to highlight the influence of the fractional derivative order on their spatial and temporal evolution. Furthermore, when an external generalized periodic force is introduced, the model exhibits quasi-periodic behavior followed by chaotic dynamics. Both configurations are depicted through 3D and 2D phase portraits in addition to the time-series graphs. The presence of chaos is quantitatively verified by calculating the Lyapunov exponents. Numerical simulations demonstrate that the system’s behavior is highly sensitive to variations in the frequency and amplitude of the external force. Full article
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18 pages, 8195 KB  
Article
Phase Engineering of Cu2S via Ce2S3 Incorporation: Achieving Enhanced Thermal Stability and Mechanical Properties
by Boke Sun, Liang Li, Yitong Wang, Yuqi Chen, Zhaoshuai Song and Ming Han
Coatings 2025, 15(10), 1135; https://doi.org/10.3390/coatings15101135 - 1 Oct 2025
Viewed by 266
Abstract
Cu2S has wide-ranging applications in the energy field, particularly as electrode materials and components of energy storage devices. However, the migration of copper ions is prone to component segregation and copper precipitation, impairing long-term thermal stability and service performance. Ce2 [...] Read more.
Cu2S has wide-ranging applications in the energy field, particularly as electrode materials and components of energy storage devices. However, the migration of copper ions is prone to component segregation and copper precipitation, impairing long-term thermal stability and service performance. Ce2S3 not only possesses the unique 4f electron layer structure of Ce but also has high thermal stability and chemical inertness. Here, we report for the first time that the thermal stability and mechanical properties of Cu2S can be significantly enhanced by introducing the dispersed phase Ce2S3. Thermogravimetry—differential scanning calorimetry (TG-DSC) results show that the addition of 6 wt% Ce2S3 improves the thermal stability of Cu2S sintered at 400 °C. X-ray diffraction (XRD) results indicate that the crystal structure of Cu2S gradually transforms to tetragonal Cu1.96S and orthorhombic Cu1.8S phase at 400 °C with the increase of Ce2S3 addition. Scanning electron microscopy (SEM) results show that the particle size gradually decreased with the increase of Ce2S3 amount, indicating that the Ce2S3 addition increased the reactivity. The Ce content in Cu2S increased gradually with the increase of Ce2S3 amount at 400–600 °C. The 7 wt% Ce2S3-Cu2S exhibits paramagnetic behavior with a saturation magnetization of 1.2 µB/Ce. UV-Vis analysis indicates that the addition of Ce2S3 can reduce the optical energy gap and enrich the band structure of Cu2S. With increasing addition of Ce2S3 and rising sintering temperature, the density of Ce2S3-Cu2S gradually increases, and the hardness of Ce2S3-Cu2S increases by 52.5% at 400 °C and by 34.2% at 600 °C. The friction test results show that an appropriate addition amount of Ce2S3 can increase the friction coefficients of Cu2S. Ce2S3 modification offers a novel strategy to simultaneously enhance the structural and service stability of Cu2S by regulating Cu ion diffusion and suppressing compositional fluctuations. Full article
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15 pages, 4890 KB  
Article
Tunable Bandgap in Cobalt-Doped FeS2 Thin Films for Enhanced Solar Cell Performance
by Eder Cedeño Morales, Yolanda Peña Méndez, Sergio A. Gamboa-Sánchez, Boris Ildusovich Kharissov, Tomás C. Hernández García and Marco A. Garza-Navarro
Materials 2025, 18(19), 4546; https://doi.org/10.3390/ma18194546 - 30 Sep 2025
Viewed by 332
Abstract
Cobalt-doped iron disulfide (FeS2) thin films were synthesized via chemical bath deposition (CBD) followed by annealing at 450 °C, yielding phase-pure pyrite structures with multifunctional properties. A deposition temperature of 95 °C is critical for promoting Co incorporation, suppressing sulphur vacancies, [...] Read more.
Cobalt-doped iron disulfide (FeS2) thin films were synthesized via chemical bath deposition (CBD) followed by annealing at 450 °C, yielding phase-pure pyrite structures with multifunctional properties. A deposition temperature of 95 °C is critical for promoting Co incorporation, suppressing sulphur vacancies, and achieving structural stabilization of the film. After annealing, the dendritic morphologies transformed into compact quasi-spherical nanoparticles (~100 nm), which enhanced the crystallinity and optoelectronic performance of the films. The films exhibited strong absorption (>50%) in the visible and near-infrared regions and tunable direct bandgaps (1.14 to 0.96 eV, within the optimal range for single-junction solar cells. Electrical characterization revealed a fourth-order increase in conductivity after annealing (up to 4.78 Ω−1 cm−1) and confirmed stable p-type behavior associated with Co2+-induced acceptor states and defect passivation. These results demonstrate that CBD enabled the fabrication of Co-doped FeS2 thin films with synergistic structural, electrical, and optical properties. The integration of earth-abundant elements and tunable electronic properties makes these films promising absorber materials for the next-generation photovoltaic devices. Full article
(This article belongs to the Special Issue The Optical, Ferroelectric and Dielectric Properties of Thin Films)
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21 pages, 57255 KB  
Article
Solidification Microstructure and Secondary-Phase Precipitation Behavior of 310S Austenitic Stainless Steel
by Jun Xiao, Di Wang, Shaoguang Yang, Kuo Cao, Siyu Qiu, Jianhua Wei and Aimin Zhao
Metals 2025, 15(10), 1091; https://doi.org/10.3390/met15101091 - 29 Sep 2025
Viewed by 259
Abstract
In this study, the solidification behavior of 310S stainless steel was systematically investigated by combining high-temperature confocal laser scanning microscopy (HT-CLSM), microstructural characterization, and thermodynamic calculations. The focus was on the formation and transformation of ferrite, secondary-phase precipitation, and elemental segregation behavior, with [...] Read more.
In this study, the solidification behavior of 310S stainless steel was systematically investigated by combining high-temperature confocal laser scanning microscopy (HT-CLSM), microstructural characterization, and thermodynamic calculations. The focus was on the formation and transformation of ferrite, secondary-phase precipitation, and elemental segregation behavior, with comparisons made with 304 stainless steel. The effects of an Al addition and cooling rate were also explored. The results show that the solidification sequence of 310S stainless steel is L → L + γ → L + γ + δ → δ + γ, in which austenite nucleates early and grows rapidly, followed by the precipitation of a small amount of δ-ferrite in the later stages of solidification. In contrast, 304 stainless steel solidifies according to L → L + δ → L + δ + γ → δ + γ, with a rapid δ → γ transformation occurring after solidification. Compared with 304, 310S stainless steel exhibits a reduced ferrite fraction and a significantly increased σ phase content. The σ phase primarily precipitates directly from δ-ferrite (δ → σ), while M23C6 preferentially forms at grain boundaries and δ/γ interfaces, where δ-ferrite not only provides fast diffusion pathways for Cr but also nucleation sites. The solidification segregation sequence in 310S stainless steel is Cr > Ni > Fe, with Cr and Ni showing positive segregation and Fe showing negative segregation. The addition of Al does not alter the solidification mode of 310S stainless steel but refines austenite grains, reduces interdendritic solute enrichment, decreases segregation, lowers both the size and fraction of ferrite, and suppresses the precipitation of σ and M23C6 phases. This effect is mainly attributed to the reduction of δ/γ interfaces, which weakens the preferred nucleation sites for M23C6. Increasing the cooling rate enhances non-equilibrium solute segregation, promotes ferrite formation, inhibits the δ → γ transformation, and ultimately retains more ferrite; the intensified segregation further accelerates the δ → σ transformation. Full article
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22 pages, 9045 KB  
Article
Weld Power, Heat Generation and Microstructure in FSW and SFSW of 11Cr-1.6W-1.6Ni Martensitic Stainless Steel: The Impact of Tool Rotation Rate
by Mohamed Ragab, Naser Alsaleh, Mohamed M. El-Sayed Seleman, Mohamed M. Z. Ahmed, Sabbah Ataya and Yousef G. Y. Elshaghoul
Crystals 2025, 15(10), 845; https://doi.org/10.3390/cryst15100845 - 28 Sep 2025
Viewed by 323
Abstract
Friction stir welding (FSW) is a leading technique for joining high-strength steel. This study investigates the relationship between weld power, heat generation (HG), cooling medium, and parent austenite grain (PAG) size during both FSW and submerged FSW (SFSW) processes on 11Cr-1.6W-1.6Ni Martensitic Stainless [...] Read more.
Friction stir welding (FSW) is a leading technique for joining high-strength steel. This study investigates the relationship between weld power, heat generation (HG), cooling medium, and parent austenite grain (PAG) size during both FSW and submerged FSW (SFSW) processes on 11Cr-1.6W-1.6Ni Martensitic Stainless Steel. Weld power and HG were determined by measuring plunge force and tool torque at various tool rotation rates (350–550 rpm). Additionally, the PAG size and microstructural phases in the base metal (BM), thermo-mechanically affected zone (TMAZ), and stir zone (SZ) were examined using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), and X-ray diffraction (XRD). The results indicated that the SFSW of martensitic steel required a plunge force twice that of the FSW process, along with greater weld power. The heat generated during SFSW was 130% higher than in FSW at 550 rpm. Despite this, the peak temperatures in the SZ were lower in SFSW as a result of the surrounding water’s high heat absorption. This difference in thermal behavior significantly affected the microstructure. While FSW resulted in a complete phase transformation to fine PAG, SFSW showed only minimal or partial transformation and a higher strain rate. Consequently, the SZ and TMAZ in SFSW exhibited a higher hardness than in FSW. Full article
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27 pages, 4484 KB  
Article
Formulation of Self-Emulsifying Microemulsion for Acemetacin Using D-Optimal Design: Enteric-Coated Capsule for Targeted Intestinal Release and Bioavailability Enhancement
by Zaineb Z. Abduljaleel and Khalid K. Al-Kinani
Pharmaceutics 2025, 17(10), 1270; https://doi.org/10.3390/pharmaceutics17101270 - 27 Sep 2025
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Abstract
Objectives: The current work aimed to formulate and optimize a self-emulsifying microemulsion drug delivery system (SEME) for acemetacin (ACM) to increase ACM’s aqueous solubility, improve oral bioavailability, and reduce gastrointestinal complications. Methods: Screening of components capable of enhancing ACM solubility was [...] Read more.
Objectives: The current work aimed to formulate and optimize a self-emulsifying microemulsion drug delivery system (SEME) for acemetacin (ACM) to increase ACM’s aqueous solubility, improve oral bioavailability, and reduce gastrointestinal complications. Methods: Screening of components capable of enhancing ACM solubility was performed. Pseudo-ternary phase diagrams were performed to choose the optimal formulation ratio. The ACM-SEME formulation’s composition was optimized using D-optimal design. Oil, Smix, and water percentages were used as independent variables, while globule size, polydispersity index, ACM content, and in vitro ACM release after 90 min were used as dependent variables. Also, thermodynamic stability and transmittance percentage tests were studied. Zeta potential was assessed for the optimized ACM-SEME formulation, which was then subjected to spray drying. The dried ACM-SEME was characterized using field-emission scanning electron microscope, Fourier-transform infrared spectroscopy, X-ray diffraction, and differential scanning calorimetry. The dried ACM-SEME formulation was filled into hard gelatin capsules and coated with Eudragit L100 to achieve pH-dependent release. Results: The antinociceptive activity of ACM-SEME was evaluated in vivo using Eddy’s hot plate test in rats, revealing a significant prolongation of the noxious time threshold compared to control groups. Ex vivo permeation studies across rat intestinal tissue confirmed the enhanced permeation potential of the ACM-SEME. Conclusions: It was concluded that the developed ACM-SEME system demonstrated improved physicochemical properties, enhanced release behavior, and superior therapeutic performance, highlighting its potential as a safer and more effective oral delivery platform for ACM. Full article
(This article belongs to the Special Issue Advances in Emulsifying Drug Delivery Systems)
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