Materials

20 pages, 4685 KB

Open AccessArticle

Non-Invasive Rayleigh, Raman, and Chromium-Fluorescence Study of Phase Transitions: β-Alumina into γ-Alumina ‘Single’ Crystal and Then to α-Alumina

by Juliette Redonnet, Gulsu Simsek-Franci and Philippe Colomban

Materials 2025, 18(20), 4682; https://doi.org/10.3390/ma18204682 (registering DOI) - 12 Oct 2025

Abstract

In many advanced materials production processes, the analysis must be non-invasive, rapid, and, if possible, operando. The Raman signal of the various forms of alumina, especially transition alumina, is very weak due to the highly ionic nature of the Al-O bond, which [...] Read more.

In many advanced materials production processes, the analysis must be non-invasive, rapid, and, if possible, operando. The Raman signal of the various forms of alumina, especially transition alumina, is very weak due to the highly ionic nature of the Al-O bond, which requires long exposure times that are incompatible with monitoring transitions. Here, we explore the use of the fluorescence signal of chromium, a natural impurity in alumina, and the Rayleigh wing to follow the crystallization process up to alpha alumina. To clarify the assignment of the fluorescence components, we compare the transformation of beta alumina single crystals into transition (gamma and theta) alumina and then into alpha alumina with the transformation of optically transparent alumina xerogel and glass, obtained by very slow hydrolysis-polycondensation of aluminum sec-butoxide, into alpha alumina. Vibrational modes are better resolved in thermally treated single crystals than in thermally treated xerogels. Measurements of the Rayleigh wing, the Boson peak, and the fluorescence signal are easier than those of vibrational modes for studying the evolution from amorphous to alpha alumina phases. The fluorescence spectra allow almost instantaneous (<1 s) quantitative control of the phases present. Full article

(This article belongs to the Special Issue Functionalized Ceramics and Their Composites: Preparation, Properties and Applications—2nd Edition)

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12 pages, 7399 KB

Open AccessArticle

The Influence of Reactive Ion Etching Chemistry on the Initial Resistance and Cycling Stability of Line-Type (Bridge) Phase-Change Memory Devices

by Abbas Espiari, Henriette Padberg, Alexander Kiehn, Kristoffer Schnieders, Jiayuan Zhang, Gregor Mussler, Stefan Wiefels, Abdur Rehman Jalil and Detlev Grützmacher

Materials 2025, 18(20), 4681; https://doi.org/10.3390/ma18204681 (registering DOI) - 12 Oct 2025

Abstract

Phase-change memory (PCM) is a promising candidate for in-memory computation and neuromorphic computing due to its high endurance, low cycle-to-cycle variability, and low read noise. However, among other factors, its performance strongly depends on the post-lithography fabrication steps. This study examines the impact [...] Read more.

Phase-change memory (PCM) is a promising candidate for in-memory computation and neuromorphic computing due to its high endurance, low cycle-to-cycle variability, and low read noise. However, among other factors, its performance strongly depends on the post-lithography fabrication steps. This study examines the impact of reactive ion etching (RIE) on PCM device performance by evaluating different etching gas mixtures, CHF

_{3}

:O

_{2}

, H

_{2}

:Ar, and Ar, and determining their impact on key device characteristics, particularly initial resistance and cycling stability. The present study demonstrates that a two-step etching approach in which the capping layer is first removed using H

_{2}

:Ar and the underlying GST layer is subsequently etched using physical Ar sputtering ensures stable and reliable PCM operation. In contrast, chemically reactive gases negatively impact the initial resistance, cycling stability, and device lifetime, likely due to alterations in the material composition. For the cycling stability evaluation, an advanced measurement algorithm utilizing the aixMATRIX setup by aixACCT Systems is employed. This algorithm enables automated testing, dynamically adjusting biasing parameters based on cell responses, ensuring a stable ON/OFF ratio and high-throughput characterization. Full article

(This article belongs to the Section Materials Physics)

18 pages, 7555 KB

Open AccessArticle

Considering γ’ and Dislocation in Constitutive Modeling of Hot Compression Behavior of Nickel-Based Powder Superalloy

by Liwei Xie, Jinhe Shi, Jiayu Liang, Dechong Li, Lei Zhao, Qian Bai, Kailun Zheng and Yaping Wang

Materials 2025, 18(20), 4680; https://doi.org/10.3390/ma18204680 (registering DOI) - 12 Oct 2025

Abstract

The deformation mechanism during the hot compression of PM nickel-based superalloy FGH99 and its micro-structural evolution, especially the evolution of γ’ phases, are the key factors affecting the final molding quality of aero-engine hot forged turbine disks. In this study, a new constitutive [...] Read more.

The deformation mechanism during the hot compression of PM nickel-based superalloy FGH99 and its micro-structural evolution, especially the evolution of γ’ phases, are the key factors affecting the final molding quality of aero-engine hot forged turbine disks. In this study, a new constitutive model of viscoplasticity with micro-structures as physical internal parameters were developed to simulate the hot compression behavior of FGH99 by incorporating the strengthening effect of the γ’ phase. The mechanical behavior of high-temperature (>1000 K) compressive deformation of typical superalloys under a wide strain rate (0.001~1 s⁻¹) is investigated using the Gleeble thermal-force dynamic simulation tester. The micro-structure after the hot deformation was characterized using EBSD and TEM. Work hardening as well as dynamic softening were observed in the hot compression tests. Based on the mechanical responses and micro-structural features, the model considered the coupled effects of dislocation density, DRX, and γ’ phase during hot flow. The model is programmed into a user subroutine based on the Fortran language and called in the simulation of the DEFORM-3D V6.1 software, thus realizing the multiscale predictive simulation of FGH99 alloy by combining macroscopic deformation and micro-structural evolution. The established viscoplastic constitutive model shows a peak discrepancy of 10.05% between its predicted hot flow stresses and the experimental values. For the average grain size of FGH99, predictions exhibit an error below 7.20%. These results demonstrate the high accuracy of the viscoplastic constitutive model developed in this study. Full article

(This article belongs to the Special Issue Additive Manufacturing and Forming Technologies of Alloy: Mechanical Properties and Microstructure Evaluation)

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13 pages, 6127 KB

Open AccessArticle

The Influence of Laser Shock Peening on the Microstructure and Mechanical Properties of AH32 Steel

by Xu Pei, Yiming Shen, Zhaomei Xu, Pengfei Li and Yuchun Peng

Materials 2025, 18(20), 4679; https://doi.org/10.3390/ma18204679 (registering DOI) - 12 Oct 2025

Abstract

The mechanical integrity of shipbuilding steel under demanding maritime service conditions is a pivotal factor for ensuring the structural safety and operational longevity of vessels. This research employs laser shock peening (LSP) to augment the surface performance of AH32 steel and carries out [...] Read more.

The mechanical integrity of shipbuilding steel under demanding maritime service conditions is a pivotal factor for ensuring the structural safety and operational longevity of vessels. This research employs laser shock peening (LSP) to augment the surface performance of AH32 steel and carries out a comprehensive analysis of the influence and underlying mechanisms of LSP on both the microstructural evolution and mechanical properties of the material. The results indicate that the LSP treatment successfully introduced a high magnitude residual compressive stress (−162 MPa) at the surface of AH32 steel. Additionally, the surface hardness of LSP-1 and LSP-2 increased by 7.3% and 14.7%, respectively. The tensile test results indicate that Sample LSP-2 achieved a 25.8% improvement in elongation while exhibiting only a 5.9% reduction in ultimate tensile strength. Friction and wear tests demonstrated that the average coefficient of friction for the samples treated with LSP decreased by approximately 18%, while the wear rate reduced significantly by over 40%. Full article

(This article belongs to the Special Issue Corrosion, Fatigue and Corrosion Protection of Metals and Their Alloys in Various Environments (2nd Edition))

19 pages, 1200 KB

Open AccessArticle

Evaluating Biochar’s Role in Dye Adsorption and Wheat Performance Under Saline Conditions

by Ghenwa Kataya, Dalia El Badan, David Cornu, Assi Al Mousawi, Mikhael Bechelany and Akram Hijazi

Materials 2025, 18(20), 4678; https://doi.org/10.3390/ma18204678 (registering DOI) - 12 Oct 2025

Abstract

This research explores the dual role of biochar in addressing the escalating challenges of water salinity and pollution, focusing on its potential for both wastewater treatment and agricultural resilience. We investigated the adsorption capacity and efficiency of various biochar treatments to remove crystal [...] Read more.

This research explores the dual role of biochar in addressing the escalating challenges of water salinity and pollution, focusing on its potential for both wastewater treatment and agricultural resilience. We investigated the adsorption capacity and efficiency of various biochar treatments to remove crystal violet dye from contaminated water. Biochar treated with H₂SO₄ demonstrated the highest adsorption capacity (450 mg/g). It consistently achieved 100% removal efficiency in all crystal violet concentrations tested, while silver-modified biochar showed a 99.95% removal rate at 50 ppm and an adsorption capacity of 5 mg/g. In agricultural applications, we evaluated the impact of biochar applications at concentrations of 1% and 3% on wheat crops irrigated with saline water of varying conductivity levels (0.63 and 10 dS/m). Wheat plants treated with 1% biochar exhibited the highest yield (26.6 cm) under 0.63 dS/m water conductivity, significantly outperforming the control group (17 cm). Biochar also resulted in elevated chlorophyll levels, with chlorophyll a ranging from 29.8 to 20.9 µg/mL and chlorophyll b ranging from 54 to 23 µg/mL, showing a marked improvement over the control. These findings demonstrate biochar’s potential to mitigate salinity-induced damage, with lower salinity conditions further enhancing chlorophyll a levels, while untreated plants showed reduced chlorophyll under high salinity. Full article

(This article belongs to the Section Green Materials)

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Graphical abstract

18 pages, 6499 KB

Open AccessArticle

Physicochemical Properties of Hematite Nanoparticles Obtained via Thermogravimetric Conversion of Biosynthesized Nanomaghemite

by Juan A. Ramos-Guivar, Mercedes del Pilar Marcos-Carrillo, Renzo Rueda-Vellasmin, Erich V. Manrique-Castillo, Noemi-Raquel Checca-Huaman, Bruno L. D. Santos, Waldemar A. A. Macedo and Edson C. Passamani

Materials 2025, 18(20), 4677; https://doi.org/10.3390/ma18204677 (registering DOI) - 12 Oct 2025

Abstract

Hematite nanoparticles (

α - {Fe}_{2} O_{3} NPs

) were synthesized through a thermal conversion of synthetic and biosynthesized nanomaghemite (

γ - {Fe}_{2} O_{3} NPs

) precursors. X-ray diffraction data confirmed phase-pure hematite with crystallite sizes [...] Read more.

Hematite nanoparticles (

α - {Fe}_{2} O_{3} NPs

) were synthesized through a thermal conversion of synthetic and biosynthesized nanomaghemite (

γ - {Fe}_{2} O_{3} NPs

) precursors. X-ray diffraction data confirmed phase-pure hematite with crystallite sizes of 54 and 56 nm for the H1 and H2 samples, respectively. Transmission electron microscopy (TEM) revealed a bimodal-like distribution feature (peaks at 18.5 and 35.5 nm) for the H1 sample, while the histogram plot of the H2 sample displayed a homogeneous particle size distribution with a mean size of 28 nm. X-ray photoelectron spectroscopy confirmed Fe³⁺ ions as the dominant oxidation state in both samples. In addition, while ⁵⁷Mössbauer spectroscopy indicated relaxation effects and line broadening for the H1 sample at both 300 K and 16 K, consistent with incomplete

γ \to α

transformation, the H2 sample exhibited spectra at the same temperatures resembling a bulk-like hematite. Magnetometry supported these findings since the H1 sample showed enhanced coercivity (2.2 kOe) and remanence (0.23 emu/g), features attributed to a residual ferrimagnetic contribution of

γ - {Fe}_{2} O_{3} NPs

, and the H2 sample exhibited weaker ferromagnetism, as typically found in nanoscale hematite. These results highlight the synergistic use of X-ray photoelectron and Mössbauer spectroscopies, and magnetic measurements to reveal subtle multiphase coexistence, demonstrating that precursor chemistry and biosynthetic functionalization decisively govern the structural and magnetic evolution of

γ \to α - {Fe}_{2} O_{3} NPs

. Full article

(This article belongs to the Special Issue Synthesis and Characterization Techniques for Nanomaterials)

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20 pages, 3922 KB

Open AccessArticle

Both Benzannulation and Heteroatom-Controlled Photophysical Properties in Donor–π–Acceptor Ionic Dyes: A Combined Experimental and Theoretical Study

by Przemysław Krawczyk and Beata Jędrzejewska

Materials 2025, 18(20), 4676; https://doi.org/10.3390/ma18204676 (registering DOI) - 12 Oct 2025

Abstract

Donor–π–acceptor (D–π–A) dyes have garnered significant attention due to their unique optical properties and potential applications in various fields, including optoelectronics, chemical sensing and bioimaging. This study presents the design, synthesis, and comprehensive photophysical investigation of a series of ionic dyes incorporating five- [...] Read more.

Donor–π–acceptor (D–π–A) dyes have garnered significant attention due to their unique optical properties and potential applications in various fields, including optoelectronics, chemical sensing and bioimaging. This study presents the design, synthesis, and comprehensive photophysical investigation of a series of ionic dyes incorporating five- and six-membered heterocyclic rings as electron-donating and electron-withdrawing units, respectively. The influence of the dye structure, i.e., (a) the systematically varied heteroatom (NMe, S and O) in donor moiety, (b) benzannulation of the acceptor part and (c) position of the donor vs. acceptor, on the photophysical properties was evaluated by steady-state and time-resolved spectroscopy across solvents of varying polarity. To probe solvatochromic behavior, the Reichardt parameters and the Catalán four-parameter scale, including polarizability (SP), dipolarity (SdP), acidity (SA) and basicity (SB) parameters, were applied. Emission dynamics were further analyzed through time-resolved fluorescence spectroscopy employing multi-exponential decay models to accurately describe fluorescence lifetimes. Time-dependent density functional theory (TDDFT) calculations supported the experimental findings by elucidating electronic structures, charge-transfer character, and dipole moments in the ground and excited states. The experimental results show the introduction of O or S instead of NMe causes substantial hypsochromic shifts in the absorption and emission bands. Benzannulation enhances the photoinduced charge transfer and causes red-shifted absorption spectra to be obtained without deteriorating the emission properties. Hence, by introducing an appropriate modification, it is possible to design materials with tunable photophysical properties for practical applications, e.g., in opto-electronics or sensing. Full article

(This article belongs to the Special Issue Size-Dependent Effects in Materials for Environmental Protection and Energy Application (3rd Edition))

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19 pages, 3322 KB

Open AccessArticle

The Use of Metal/ZSM-5 Nanosheet for Efficient Catalytic Cracking of Cross-Linked Polyethylene for High-Voltage Cable Insulation

by Zhenfei Fu, Yuqi Pan, Rui Wang, Shilong Suo, Zheng Wang, Xiangyang Peng and Pengfei Fang

Materials 2025, 18(20), 4675; https://doi.org/10.3390/ma18204675 (registering DOI) - 11 Oct 2025

Abstract

Cross-linked polyethylene (XLPE) has been widely used in high-voltage cables due to its superior properties, but its thermoset cross-linked structure makes it difficult to recycle. Catalytic pyrolysis offers a feasible pathway for converting XLPE into high-value chemicals. In this study, a systematic study [...] Read more.

Cross-linked polyethylene (XLPE) has been widely used in high-voltage cables due to its superior properties, but its thermoset cross-linked structure makes it difficult to recycle. Catalytic pyrolysis offers a feasible pathway for converting XLPE into high-value chemicals. In this study, a systematic study on the catalytic cracking of XLPE using metal ion-loaded ZSM-5 nanosheets was conducted, and ZSM-5 nanosheets loaded with Ag, Mo, Ni, and Ce were prepared via ion exchange. After metal loading, ZSM-5 retained the MFI framework structure, but the specific surface area and mesopore volume varied depending on the type of metal. Temperature-Programmed Desorption of Ammonia results indicated that metal–support interactions enhanced the acidity of ZSM-5. Among the catalysts, Ag-loaded ZSM-5 exhibited the highest efficiency: with 10 wt% Ag, at 380 °C, the conversion reached 94.1%, with 52.5% light olefins in the gas phase and 59.4% benzene, toluene, and xylene (BTX) in the liquid products. Further studies on different Ag loadings revealed that moderate Ag loading (5 wt%) provided the best overall balance, maintaining 92.3% conversion, 56.1% selectivity to light olefins, and 58.2% BTX in the liquid fraction. These findings demonstrate that tuning the metal loading effectively optimizes the acidity and pore structure of ZSM-5, thereby enabling controlled regulation of XLPE pyrolysis product distribution. Full article

(This article belongs to the Special Issue Recycling Conductive and Electrical Insulating Polymer Composites)

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15 pages, 2086 KB

Open AccessArticle

Effect of Adhesive Bonding Process Parameters on the Joint Quality of the Middle Layer in Floorboards

by Agnieszka Kujawińska, Michał Rogalewicz, Magdalena Hryb and Krzysztof Żywicki

Materials 2025, 18(20), 4674; https://doi.org/10.3390/ma18204674 (registering DOI) - 11 Oct 2025

Abstract

The quality and durability of adhesive joints in wood flooring are determined by both the type of adhesive and the parameters of the bonding process. This study examines the effects of pressing time and seasoning time on the bending strength of adhesive joints [...] Read more.

The quality and durability of adhesive joints in wood flooring are determined by both the type of adhesive and the parameters of the bonding process. This study examines the effects of pressing time and seasoning time on the bending strength of adhesive joints in the middle layer of floorboards manufactured using innovative block-bonding technology. Experimental trials were conducted with two adhesive systems—polyvinyl acetate (PVAC) and polyurethane (PUR)—using a full factorial design and statistical evaluation of joint strength in terms of pressing time and seasoning time. For PVAC, an overall tendency toward increased strength with extended pressing time was observed; however, the strongest effects were associated with interactions between pressing and seasoning times, with the most favorable results obtained for short pressing (5 min) combined with extended seasoning (5 h). In the case of PUR, the relationships were non-linear, and the only statistically significant factor was the interaction between pressing and seasoning times, confirming the necessity of joint optimization. The findings demonstrate that simple one-factor analyses are insufficient to explain adhesive performance, as non-linear and interaction effects are critical in defining joint strength. The results provide new insights for optimizing bonding processes in floorboard production, supporting improvements in material efficiency and mechanical reliability of wood flooring. Full article

(This article belongs to the Special Issue Advanced Materials, Machinability and Intelligent Manufacturing Systems)

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20 pages, 5763 KB

Open AccessArticle

Layer Thickness Effects on Residual Stress, Microstructure, and Tensile Properties of Cu18150/Al1060/Cu18150 Multilayered Composites: An Integrated EBSD-KAM Approach

by Yuchao Zhao, Mahmoud Ebrahimi, Shokouh Attarilar, Qiang Lu, Haiyan Jiang and Qudong Wang

Materials 2025, 18(20), 4673; https://doi.org/10.3390/ma18204673 (registering DOI) - 11 Oct 2025

Abstract

This study examines the influence of layer thickness (0.9, 1.6, 2.4, and 4 mm) on the distribution of residual stress, microstructural evolution, and tensile properties of Cu18150/Al1060/Cu18150 multilayered composites fabricated via a combined cast-rolling and hot-rolling technique. The grain refinement, dislocation density, and [...] Read more.

This study examines the influence of layer thickness (0.9, 1.6, 2.4, and 4 mm) on the distribution of residual stress, microstructural evolution, and tensile properties of Cu18150/Al1060/Cu18150 multilayered composites fabricated via a combined cast-rolling and hot-rolling technique. The grain refinement, dislocation density, and residual stress gradients across the interfaces were characterized and analyzed using integrated electron backscatter diffraction and kernel average misorientation mapping. The results demonstrated that specimens with a lower layer thickness (0.9–1.6 mm) possess a significantly improved tensile strength of 351 MPa, which is mainly due to the significant grain refinement and the presence of compressive residual stresses at the region of the Al/Cu interfaces. However, tensile strength decreased to 261 MPa in specimens with thicker layers (4 mm), accompanied by improved ductility, e.g., elongation of 30%. This is associated with a reduction in the degrees of interfacial constraint and the formation of more homogeneous deformation structures that accommodate a larger strain. The intermediate layer thickness of 2.4 mm offers an optimal compromise, achieving a tensile strength of 317 MPa while maintaining balanced mechanical performance. These results emphasize the importance of layer thickness in controlling such stress profiles and optimizing the mechanical behavior of hybrid metal composites, providing useful guidance on the design and fabrication of superior structural-form materials. Full article

(This article belongs to the Special Issue Advances in Mechanical Behavior of Laminated Materials)

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14 pages, 2691 KB

Open AccessArticle

Evaluation of the Effect of Post-Processing Methods on the Surface Parameters of Parts Produced by FFF/FDM Technology

by Marek Kočiško, Lukáš Štafura, Karol Goryl and Zuzana Mitaľová

Materials 2025, 18(20), 4672; https://doi.org/10.3390/ma18204672 (registering DOI) - 11 Oct 2025

Abstract

This article focuses on evaluating selected roughness parameters on samples created by material extrusion, specifically FFF (Fused Filament Fabrication). The experiment was divided into two separate phases. The first phase of the experiment involved creating a four-level model A from PLA (poly (lactic [...] Read more.

This article focuses on evaluating selected roughness parameters on samples created by material extrusion, specifically FFF (Fused Filament Fabrication). The experiment was divided into two separate phases. The first phase of the experiment involved creating a four-level model A from PLA (poly (lactic acid)) material without any additives. The variable parameter was the height of the printed layer, where each level was printed at a different print height. Subsequently, the sandblasting method was applied to the samples using a selected abrasive. The roughness parameters were evaluated using a Mitutoyo Surftest SJ-400 roughness tester. Based on the results of the roughness parameters of model A, model B was prepared, using a constant print height. Each level of model B was made with different metallic additives based on PLA material. The findings demonstrate the effectiveness of mechanical post-processing in achieving the desired surface characteristics of additively manufactured components. The experiment confirms the suitability of sanding and grinding to improve surface quality at different layer heights and for PLA-based materials with metal additives. In addition, grinding and sanding of PLA-based composites filled with metal particles can create a realistic metallic appearance comparable to conventionally manufactured metals. Full article

(This article belongs to the Special Issue Advances in Surface Engineering Technologies and Their Impact on Surface Integrity and Functional Performance of Additively Manufactured Parts)

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20 pages, 6160 KB

Open AccessArticle

The Impact of Physical Form on the Biocompatibility of Poly(3-hexylthiophene-2,5-diyl)

by Daniela A. Tudor, Sorin David, Mihaela Gheorghiu and Szilveszter Gáspár

Materials 2025, 18(20), 4671; https://doi.org/10.3390/ma18204671 (registering DOI) - 11 Oct 2025

Abstract

Poly(3-hexylthiophene-2,5-diyl) (P3HT) is a semiconducting, electron donor polymer which, in addition to its intensive use in optoelectronic devices, is increasingly investigated in biological systems. However, there are conflicting reports about the biocompatibility of P3HT, and no direct comparison between P3HT films and P3HT [...] Read more.

Poly(3-hexylthiophene-2,5-diyl) (P3HT) is a semiconducting, electron donor polymer which, in addition to its intensive use in optoelectronic devices, is increasingly investigated in biological systems. However, there are conflicting reports about the biocompatibility of P3HT, and no direct comparison between P3HT films and P3HT nanoparticles has been conducted. In this context, we investigated the viability of bEnd.3 endothelial cells when such cells are grown onto P3HT films or incubated with P3HT nanoparticles and subjected to trains of moderate power density, relatively long light pulses. We observed that, while P3HT films do not decrease the viability of bEnd.3 cells at all, P3HT nanoparticles lower the viability of bEND.3 cells by ~20%, when the nanoparticles also contain [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) as electron acceptor, and by ~30%, when the nanoparticles do not contain PCBM. Interestingly, the used photoexcitation protocol did not impact the biocompatibility of the P3HT-based materials. The obtained results reveal that (i). nanostructuring has a detrimental impact on the compatibility of P3HT with bEND.3 endothelial cells, and (ii). P3HT-based materials can be safely combined with light when used in biological systems because light, as used in the present study, does not alter the biocompatibility of such materials. Full article

(This article belongs to the Special Issue Interaction Between Biomaterials and Biological Systems)

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12 pages, 608 KB

Open AccessArticle

Flux-Dependent Superconducting Diode Effect in an Aharonov–Bohm Interferometer

by Yu-Mei Gao, Hao-Yuan Yang, Feng Chi, Zi-Chuan Yi and Li-Ming Liu

Materials 2025, 18(20), 4670; https://doi.org/10.3390/ma18204670 (registering DOI) - 11 Oct 2025

Abstract

We theoretically investigate the supercurrent and superconducting diode effect (SDE) in an Aharonov–Bohm (AB) interferometer sandwiched between two aluminium-based superconducting leads. The interferometer features a quantum dot (QD), which is created in an indium arsenide (InAs) semiconductor nanowire by local electrostatic gating, inserted [...] Read more.

We theoretically investigate the supercurrent and superconducting diode effect (SDE) in an Aharonov–Bohm (AB) interferometer sandwiched between two aluminium-based superconducting leads. The interferometer features a quantum dot (QD), which is created in an indium arsenide (InAs) semiconductor nanowire by local electrostatic gating, inserted in one of its arms and a magnetic flux threading through the ring structure. The magnetic flux breaks the system time-reversal symmetry by modulating the quantum phase difference between electronic transport through the QD path and the direct arm, which enhances constructive interference in one direction and destructive interference in the other. This leads to a discrepancy between the magnitudes of the forward and reverse critical supercurrents and is the core mechanism that induces the SDE. We demonstrate that the critical supercurrents exhibit Fano line shapes arising from the interference between discrete Andreev bound states in the QD and continuous states in the direct arm. It is found that when electron transport is dominated by the QD-containing path as compared to the direct arm path of the interferometer, the diode efficiency reaches a maximum, with values as high as 80%. In contrast, when the direct arm path dominates transport, the diode efficiency becomes weak. This attenuation is attributed to the participation of higher-order quantum interference processes, which disrupt the nonreciprocal supercurrent balance. Importantly, the proposed AB interferometer system has a relatively simple structure, and the realization of the SDE within it is feasible using current nano-fabrication technologies. Full article

(This article belongs to the Special Issue Feature Papers in Materials Physics (2nd Edition))

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24 pages, 13489 KB

Open AccessReview

Review of Oxides Prepared by a Short Process Using Rare-Earth Chlorides

by Jing Wei, Xue Bian, Xinmiao Zhu, Hao Huang, Chunlin Ye, Shuchen Sun, Liqin Zhong and Ganfeng Tu

Materials 2025, 18(20), 4669; https://doi.org/10.3390/ma18204669 (registering DOI) - 11 Oct 2025

Abstract

Direct thermal decomposition of rare-earth chlorides into rare-earth oxides (REOs) in a single step presents a short-process, wastewater-free, and environmentally friendly alternative to the conventional precipitation–calcination method, which produces large amounts of saline wastewater. While earlier reviews have primarily focused on summarizing reaction [...] Read more.

Direct thermal decomposition of rare-earth chlorides into rare-earth oxides (REOs) in a single step presents a short-process, wastewater-free, and environmentally friendly alternative to the conventional precipitation–calcination method, which produces large amounts of saline wastewater. While earlier reviews have primarily focused on summarizing reaction conditions and thermodynamic parameters, they have seldom discussed the critical variations in pyrolysis behavior across different rare-earth elements. This review highlights a novel classification of rare-earth chlorides into fixed-valence and variable-valence groups, revealing how their respective oxidation states govern thermodynamic stability, reaction pathways, and chlorine release behavior. Furthermore, a systematic comparison is provided on the effects of additives, temperature, and gas partial pressure on product purity, particle size, and microstructure, with particular attention to the mechanisms underlying oxychloride intermediate formation. Beyond fundamental reaction principles, this work uniquely evaluates the design and performance of existing pyrolysis reactors, outlining both opportunities and challenges in scaling up direct rare-earth chloride (RECl_x) pyrolysis for industrial REO production. By integrating mechanistic insights with reactor engineering considerations, this review offers advancements over previous descriptive summaries and proposes a strategic pathway toward sustainable rare-earth processing. Full article

(This article belongs to the Section Materials Chemistry)

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21 pages, 5046 KB

Open AccessArticle

A Comprehensive Analysis of the Effectiveness of a Water-Based Extraction Method in Cement Bypass Dust Valorization

by Karolina Wojtacha-Rychter, Magdalena Król and Jakub Dechnik

Materials 2025, 18(20), 4668; https://doi.org/10.3390/ma18204668 (registering DOI) - 11 Oct 2025

Abstract

The solid by-product from cement kiln gas installations, known as cement bypass dust (CBPD), is rich in chlorides, which limits the reuse of materials in cement. In this study, three types of CBPD were subjected to an extraction process to obtain a low-chlorine [...] Read more.

The solid by-product from cement kiln gas installations, known as cement bypass dust (CBPD), is rich in chlorides, which limits the reuse of materials in cement. In this study, three types of CBPD were subjected to an extraction process to obtain a low-chlorine waste material. The relationships between the process parameters, including extraction time (1, 2, 5, 10, and 30 min), temperature (21, 45, and 90 °C), and extraction efficiency, were investigated. The chlorine removal efficiency ranged from 70% to 90%, with the optimal time and temperature identified as 1 min and 21 °C, respectively. Furthermore, a comprehensive characterization of CBPD was conducted before and after the extraction process using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FT-IR); an approach not yet extensively reported in the literature. The results demonstrated that chloride removal corresponded to an increase in concentrations of Ca, Al, Si, Mg, and Fe oxides in the solid residue. For CBPD samples with initial chloride contents of 13.65% and 15.43%, calcium content in the residue increased by approximately 40%. No linear and predictable relationship was observed between the leaching time or temperature and the release of metals in the solid residue. Full article

(This article belongs to the Section Construction and Building Materials)

18 pages, 1644 KB

Open AccessArticle

Composting Poultry Feathers with Keratinolytic Bacillus subtilis: Effects on Degradation Efficiency and Compost Maturity

by Justyna Sobolczyk-Bednarek, Anna Choińska-Pulit and Wojciech Łaba

Materials 2025, 18(20), 4667; https://doi.org/10.3390/ma18204667 (registering DOI) - 11 Oct 2025

Abstract

The continuous advancement of the food industry is accompanied by increased generation of animal waste, including poultry feathers. Composting presents a sustainable alternative to disposal methods such as incineration by converting waste into valuable fertilizer products. This study aimed to evaluate the impact [...] Read more.

The continuous advancement of the food industry is accompanied by increased generation of animal waste, including poultry feathers. Composting presents a sustainable alternative to disposal methods such as incineration by converting waste into valuable fertilizer products. This study aimed to evaluate the impact of inoculation with the keratinolytic strain Bacillus subtilis P22 on the quality and maturity of compost produced from feathers combined with organic additives (wood shavings and lignite). The experiment involved evaluation of the keratinolytic potential of the tested strain, and characterization of its proteolytic enzymes, solid-state cultures and composting conducted at semi-technical scale. The B. subtilis P22 strain demonstrated the ability to solubilize 78% of feather material within 7 days of cultivation. The keratinolytic enzyme complex was likely dominated by polycatalytic alkaline serine proteases, i.e., subtilisins. The effectiveness of the inoculum was confirmed in laboratory solid-state cultures, where the dry mass loss in inoculated samples was twice that of the control containing only endogenous microflora. At the semi-technical scale, inoculation with B. subtilis P22 significantly accelerated compost maturation and mineralization (C/N = 10.2; N-NH₄⁺/N-NO₃⁻ = 0.4; Cw/Corg = 0.9) compared to the control. The final compost’s mineral composition indicates its potential for use as an organic soil amendment. Full article

(This article belongs to the Section Green Materials)

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19 pages, 7242 KB

Open AccessArticle

Influence of Fe Vacancy on the Bonding Properties of γ-Fe (111)/α-Al₂O₃ (0001) Interfaces: A Theoretical Study

by Xiaofeng Zhang, Renwei Li, Qicheng Chen, Dehao Kong and Haifeng Yang

Materials 2025, 18(20), 4666; https://doi.org/10.3390/ma18204666 (registering DOI) - 11 Oct 2025

Abstract

Here, the effects of Fe vacancy defects on the bonding properties of γ-Fe (111)/α-Al₂O₃ (0001) interfaces are studied in depth at the atomic and electronic levels using first-principles calculations. The first (V₁), second (V₂), third (V [...] Read more.

Here, the effects of Fe vacancy defects on the bonding properties of γ-Fe (111)/α-Al₂O₃ (0001) interfaces are studied in depth at the atomic and electronic levels using first-principles calculations. The first (V₁), second (V₂), third (V₃), and fourth (V₄) layers of vacancy structures within the Fe substrate, as well as the ideal Fe/Al₂O₃ interface structure, are proposed and contrasted, including their thermodynamic parameters and atomic/electronic properties. The results demonstrate that the presence of vacancies in the first atomic layer of Fe deteriorates the interfacial bonding strength, whereas vacancies situated in the third layer enhance the interfacial bonding strength. The effect of vacancy beyond the third layer becomes negligible. This occurs mainly because vacancy defects at different positions induce the relaxation behavior of atoms, resulting in bond-breaking and bond-forming reactions at the interface. Following that, the formation process of vacancies can cause the transfer and rearrangement of the electrons at the interface. This process leads to significant changes in the charge concentration of the interfaces, where V₃ is the largest and V₁ is the smallest, indicating that the greater the charge concentration, the stronger the bonding strength of the interface. Furthermore, it is discovered that vacancy defects can induce new electronic orbital hybridization between Fe and O at the interface, which is the fundamental reason for changes in the properties of the interface. Interestingly, it is also found that more electronic orbital hybridization will strengthen the bonding performance of the interface. It seems, then, that the existence of vacancy defects not only changes the electronic environment of the Fe/Al₂O₃ interface but also directly affects the bonding properties of the interface. Full article

(This article belongs to the Section Materials Simulation and Design)

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13 pages, 3953 KB

Open AccessArticle

Study on Restraint Effect of Post-Casting Belt in Full-Section Interval Casting Immersed Tube

by Bang-Yan Liang, Wen-Huo Sun, Yong-Hui Huang and Kai Wang

Materials 2025, 18(20), 4665; https://doi.org/10.3390/ma18204665 - 10 Oct 2025

Abstract

The Chebei integral Immersed Tunnel introduced an innovative full-section interval casting process, where post-casting belts impose restraint effects on the full-section casting segments. To mitigate concrete cracking, this study investigates the influence of the bottom steel plate and steel bars in the post-casting [...] Read more.

The Chebei integral Immersed Tunnel introduced an innovative full-section interval casting process, where post-casting belts impose restraint effects on the full-section casting segments. To mitigate concrete cracking, this study investigates the influence of the bottom steel plate and steel bars in the post-casting belts on the mechanical behavior of full-section casting segments through comparative analysis of field tests and numerical simulations. Requirements for post-casting belt length are proposed. Key findings include: under post-casting belt restraint, the full-section casting segment’s shrinkage strain reached 348 με, with hydration heat-induced cooling and drying shrinkage contributing 60% and 40%, respectively. A temperature-dependent thermal expansion coefficient model was developed to characterize the nonlinear relationship between concrete strain and hydration heat temperature. Restraint effects diminished with increasing post-casting belt length, and the post-casting belt length should be control. At 1.6 m (Chebei design), restraint-induced tensile stress was 1.4 MPa (restraint coefficient β = 0.12), with the bottom steel plate and steel bars contributing about 70% and 30%, respectively. Relationships between post-casting belt length, stress, and restraint coefficient are established for engineering reference. These research findings have been successfully applied in the Chebei Immersed Tunnel, enabling high-quality prefabrication of full-section interval casting immersed tubes. Full article

(This article belongs to the Special Issue The Development of Sustainable Concrete with Solid Waste and By-Products)

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18 pages, 6545 KB

Open AccessArticle

Temperature-Dependent Effects of Hydroxyethyl Methyl Cellulose on Rheological Properties and Microstructural Evolution of Robotic Plastering Mortars

by Guangjie Ling, Hongbin Yang and Sifeng Liu

Materials 2025, 18(20), 4664; https://doi.org/10.3390/ma18204664 - 10 Oct 2025

Abstract

Temperature-induced instability in early-age rheology poses a major challenge to the pumpability and application of robotic plastering mortars. This study systematically investigates the temperature-dependent effects of a high-viscosity (75,000 mPa·s) hydroxyethyl methyl cellulose (HEMC) on the rheological properties and early microstructural evolution of [...] Read more.

Temperature-induced instability in early-age rheology poses a major challenge to the pumpability and application of robotic plastering mortars. This study systematically investigates the temperature-dependent effects of a high-viscosity (75,000 mPa·s) hydroxyethyl methyl cellulose (HEMC) on the rheological properties and early microstructural evolution of mortars at 5 °C, 20 °C, and 40 °C. Mortars with HEMC dosages from 0 to 0.25 wt% were tested using rheological measurements, ultrasonic pulse velocity (UPV), and complementary microstructural analyses (XRD, FTIR, and SEM–EDS). Results show that HEMC reduced the initial static yield stress while monotonically increasing plastic viscosity, with the thickening effect more pronounced at higher temperatures. Notably, at 40 °C, the initial plastic viscosity of a 0.25% HEMC mix reached 14.4 Pa·s, a 133% increase compared to the control group. HEMC also effectively retarded the time-dependent increase in yield stress and stabilized plastic viscosity, thereby mitigating the adverse influence of elevated temperature. UPV confirmed that HEMC delayed microstructural formation, in agreement with the observed retardation of hydration reactions. At 40 °C, a 0.10% HEMC dosage postponed the percolation threshold from 67 min to 150 min, highlighting its strong retardation effect. Microstructural tests further revealed that HEMC delayed CH formation, refined C–S–H gels, and reduced the crystallinity of AFt, supporting the rheological and ultrasonic findings. A statistically significant, moderate-to-strong correlation (r = 0.88, R² = 0.77, p < 0.001) was established between static yield stress and UPV, indicating that macroscopic rheological resistance responds to microstructural evolution. Based on these results, the recommended HEMC dosages to achieve stable rheological performance are 0.05–0.10% at 5 °C, 0.10–0.15% at 20 °C, and 0.15–0.20% at 40 °C. Full article

(This article belongs to the Special Issue Eco-Friendly Materials for Sustainable Buildings)

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16 pages, 8519 KB

Open AccessArticle

The Oxidation and Corrosion Resistance of AlCrNbSiTiN Multi-Principal Element Nitride Coatings

by Zhenbo Lan, Jiangang Deng, Heng Xu, Zhuolin Xu, Zhengqi Wen, Wei Long, Lei Zhang, Ruoxi Wang, Jie Liu and Yanming Chen

Materials 2025, 18(20), 4663; https://doi.org/10.3390/ma18204663 - 10 Oct 2025

Abstract

Multi-principal element nitrides have great application potential in protective coatings. However, the investigation of the oxidation and corrosion resistance of multi-principal element nitride coatings is still insufficient. The synthesis and high-temperature performance of AlCrNbSiTiN multi-principal element nitride coatings fabricated through optimized arc ion [...] Read more.

Multi-principal element nitrides have great application potential in protective coatings. However, the investigation of the oxidation and corrosion resistance of multi-principal element nitride coatings is still insufficient. The synthesis and high-temperature performance of AlCrNbSiTiN multi-principal element nitride coatings fabricated through optimized arc ion plating (AIP) were explored. Leveraging the high ionization efficiency and ion kinetic energy characteristic of AIP, coatings with significantly fewer internal defects were obtained. These coatings demonstrate superior mechanical properties, including a maximum hardness of 36.5 GPa and critical crack propagation resistance (CPR) values approaching 2000 N². Optimal coatings exhibited exceptional water vapor corrosion resistance (5.15 at% O after 200 h). The coatings prepared at −150 V had the optimal corrosion resistance, with the coating resistance and corrosion current density being 1.68 × 10⁴ Ω·cm² and 0.79 μA·cm⁻², respectively. AlCrNbSiTiN coatings produced under these optimized AIP conditions exhibit remarkably high-temperature oxidation, highlighting their potential for use in demanding engineering applications. Full article

(This article belongs to the Special Issue Advanced Science and Technology of High Entropy Materials)

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22 pages, 6554 KB

Open AccessArticle

Mechanical Properties of Novel 3D-Printed Restorative Materials for Definitive Dental Applications

by Moritz Hoffmann, Andrea Coldea and Bogna Stawarczyk

Materials 2025, 18(20), 4662; https://doi.org/10.3390/ma18204662 - 10 Oct 2025

Abstract

The aim of this study is to evaluate the mechanical properties and long-term stability of 3D-printable resins for permanent fixed dental prostheses (FDPs), focusing on whether material performance is influenced by 3D-printer type or by differences in resin formulations. Specimens (N = 621) [...] Read more.

The aim of this study is to evaluate the mechanical properties and long-term stability of 3D-printable resins for permanent fixed dental prostheses (FDPs), focusing on whether material performance is influenced by 3D-printer type or by differences in resin formulations. Specimens (N = 621) were printed. CAD/CAM blocks (BRILLIANT Crios) served as control. Flexural strength (FS) with elastic modulus (E_calc), Weibull modulus (m), Martens’ hardness (HM), indentation modulus (EIT), elastic modulus (E_RFDA), shear modulus (G_RFDA), and Poisson’s Ratio (ν) were measured initially, after water storage (24 h, 37 °C), and after thermocycling (5–55 °C, 10,000×). SEM analysis assessed microstructure. Data were analyzed using Kolmogorov–Smirnov, ANOVA with Scheffe post hoc, Kruskal–Wallis with Mann–Whitney U, and Weibull statistics with maximum likelihood (α = 0.05). A ceramic crown printed with Midas showed higher FS, HM, and EIT values after thermocycling than with Pro55s, and higher E_calc scores across all aging regimes. A Varseo Smile Crown Plus printed with VarseoXS and AsigaMax showed a higher FS value than TrixPrint2, while AsigaMax achieved the highest initial E_calc and E_RFDA values, and VarseoXS did so after thermocycling. HM, EIT, and G_RFDA were higher for TrixPrint2 and AsigaMax printed specimens, while ν varied by system and aging. 3Delta Crown, printed with AsigaMax, showed the highest FS, E_calc, HM, EIT, and m values after aging. VarseoSmile triniQ and Bridgetec showed the highest E_RFDA and G_RFDA values depending on aging, and Varseo Smile Crown Plus exhibited higher ν initially and post-aging. Printer system and resin formulation significantly influence the mechanical and aging behaviors of 3D-printed FDP materials, underscoring the importance of informed material and printer selection to ensure long-term clinical success. Full article

(This article belongs to the Special Issue Dental Biomaterials: Synthesis, Characterization, and Applications)

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20 pages, 6936 KB

Open AccessArticle

Mechanistic Insights into Cooling-Rate-Governed Acicular Ferrite Transformation Kinetics and Strengthening-Toughening Synergy in EH36 Heavy Steel Plate

by Chunliang Yan, Fengming Wang, Rongli Sang and Qingjun Zhang

Materials 2025, 18(20), 4661; https://doi.org/10.3390/ma18204661 - 10 Oct 2025

Abstract

This study was focused on addressing the performance degradation in core microstructures of ultra-heavy steel plates (thickness ≥ 50 mm) caused by non-uniform cooling during thermo-mechanical controlled processing. Using microalloyed DH36 steel as the research subject, we systematically investigated the effects of cooling [...] Read more.

This study was focused on addressing the performance degradation in core microstructures of ultra-heavy steel plates (thickness ≥ 50 mm) caused by non-uniform cooling during thermo-mechanical controlled processing. Using microalloyed DH36 steel as the research subject, we systematically investigated the effects of cooling rate on the nucleation and growth of acicular ferrite and its consequent microstructure-property relationships through an integrated approach combining in situ observation via high-temperature laser scanning confocal microscopy with multiscale characterization techniques. Results demonstrate that the cooling rate significantly affects acicular ferrite formation, with the range of 3–7 °C/s being most conducive to acicular ferrite formation. At 5 °C/s, the acicular ferrite volume fraction reached a maximum of 74% with an optimal aspect ratio (5.97). Characterization confirmed that TiOx-Al₂O₃·SiO₂-MnO-MnS complex inclusions act as effective nucleation sites for acicular ferrite, where the MnS outer layer plays a key role in reducing interfacial energy and promoting acicular ferrite radial growth. Furthermore, the interlocking acicular ferrite structure was shown to enhance microhardness by 14% (HV0.1 = 212.5) compared to conventional ferrite through grain refinement strengthening and dislocation strengthening (with a dislocation density of 2 × 10⁸ dislocations/mm²). These results provide crucial theoretical insights and a practical processing window for strengthening-toughening control of heavy plate core microstructures, offering a viable pathway for improving the comprehensive performance of ultra-heavy plates. Full article

(This article belongs to the Special Issue Physical Metallurgy of Metals and Alloys (4th Edition))

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15 pages, 6338 KB

Open AccessArticle

High-Strength Low-Alloy Steels for Automobiles: Microstructure and Mechanical Properties

by Guoqiang Ma, Bo Gao, Zhen Chen, Yuquan Li, Ruirui Wu, Hailian Gui and Zhibing Chu

Materials 2025, 18(20), 4660; https://doi.org/10.3390/ma18204660 - 10 Oct 2025

Abstract

High-strength low-alloy (HSLA) steel is widely used in automotive industry for reduction of consumption and emissions. The microstructure and mechanical properties of two automotive HSLA steels with different strength grades were systematically investigated in present study. Microstructural characterization was conducted using optical microscopy [...] Read more.

High-strength low-alloy (HSLA) steel is widely used in automotive industry for reduction of consumption and emissions. The microstructure and mechanical properties of two automotive HSLA steels with different strength grades were systematically investigated in present study. Microstructural characterization was conducted using optical microscopy (OM), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD), while mechanical properties were evaluated with Vickers hardness tester and tensile tests. Both steels exhibited a ferrite matrix with spheroidized carbides/pearlites. However, Sample A displayed equiaxed ferrite grains with localized pearlite colonies, while Sample B featured pronounced elongated ferrite grains with a band structure. Tensile testing revealed that Sample B had higher ultimate tensile stress and yield stress compared to Sample A. Texture analysis indicated that both steels were dominated by α-fiber and γ-fiber textures, with minor θ-fiber texture, resulting in minimal mechanical anisotropy between the rolling direction (RD) and transverse direction (TD). The quantitative assessment of strengthening mechanisms, based on microstructural parameters and experimental data, revealed that grain boundary strengthening dominates, with dislocation strengthening also contributing significantly. This work provides the first comprehensive quantification of individual strengthening contributions in automotive HSLA steels, offering critical guidance for developing further higher-strength automotive steels. Full article

(This article belongs to the Section Metals and Alloys)

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18 pages, 8027 KB

Open AccessArticle

Effect of Cementitious Capillary Crystalline Waterproof Material on the Resistance of Concrete to Sulfate Erosion

by Guangchuan Fu, Ke Tang, Dan Zheng, Bin Zhao, Pengfei Li, Guoyou Yao and Xinxin Li

Materials 2025, 18(20), 4659; https://doi.org/10.3390/ma18204659 - 10 Oct 2025

Abstract

Concrete structures are vulnerable to sulfate attacks during their service life, as sulfate ions react with cement hydration products to form expansive phases, generating internal stresses that cause mechanical degradation. In this study, a cementitious capillary crystalline waterproofing material (CCCW) was incorporated into [...] Read more.

Concrete structures are vulnerable to sulfate attacks during their service life, as sulfate ions react with cement hydration products to form expansive phases, generating internal stresses that cause mechanical degradation. In this study, a cementitious capillary crystalline waterproofing material (CCCW) was incorporated into concrete to mitigate sulfate ingress and enhance sulfate resistance. The evolution of compressive strength, ultrasonic pulse velocity, dynamic elastic modulus, and the microstructure of concrete was investigated in sulfate-exposed concretes with varying CCCW dosages and strength grades; the sulfate ion concentration profiles were also analyzed. The results indicate that the enhancement effect of CCCW on sulfate resistance declines progressively with increasing concrete strength. The formation of calcium silicate hydrate and calcium carbonate fills the pores of concrete, hindering the intrusion of sulfate solution. Moreover, the self-healing effect of concrete further inhibits the diffusion of sulfate ions through cracks, improving the sulfate resistance of concrete. These findings provide critical insights and practical guidance for improving concrete resistance to sulfate-induced deterioration. Full article

(This article belongs to the Section Construction and Building Materials)

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19 pages, 3385 KB

Open AccessArticle

Study on Dynamic Mechanical Behavior of 34CrNi3MoA Alloy Steel Considering the Coupling Effect of Temperature and Strain Rate

by Xiaoyan Guan, Zhengyuan Zhang, Hengheng Wu, Jianzhi Chen, Li Sun and Guochao Li

Materials 2025, 18(20), 4658; https://doi.org/10.3390/ma18204658 - 10 Oct 2025

Abstract

Temperature and strain rate play a crucial role in determining the mechanical properties of metals. These critical parameters are typically assessed using the split Hopkinson pressure bar (SHPB) test. However, previous studies have seldom considered the coupled influence of temperature and strain rate [...] Read more.

Temperature and strain rate play a crucial role in determining the mechanical properties of metals. These critical parameters are typically assessed using the split Hopkinson pressure bar (SHPB) test. However, previous studies have seldom considered the coupled influence of temperature and strain rate on dynamic mechanical behavior, thereby reducing the accuracy of constitutive models. To accurately characterize the dynamic mechanical behavior of 34CrNi3MoA low-alloy steel, a new constitutive model combining temperature and strain rate was developed. Firstly, SHPB experiments under varying temperatures and strain rates were designed to obtain actual stress–strain curves. The results indicate that the mechanical properties of 34CrNi3MoA low-alloy steel are significantly influenced by both temperature and strain rate. True stress has a significant temperature-softening effect within the temperature range of 25 °C to 600 °C, while the flow stress in the yield stage increases with rising strain rate. Secondly, a novel constitutive model was established by integrating a correction function. The model comprises three components: a strain rate-strengthening function influenced by temperature, a temperature-softening function influenced by strain rate, and a strain-hardening correction function accounting for the coupling of temperature and strain rate. Comparing the mean relative error, the new model significantly improves accuracy compared to the original Johnson–Cook (J-C) model. Full article

(This article belongs to the Special Issue Mechanical Properties and Structural Reliability of Advanced Materials)

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21 pages, 5514 KB

Open AccessArticle

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

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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15 pages, 3194 KB

Open AccessArticle

Influence and Mechanism of Azodicarbonamide Expansive Agent on the Workability, Mechanical Strength and Plastic Shrinkage of UHPC

by Haowen Zhan, Jing Yang, Haoran Guo, Caiqian Yang, Weigang Lu and Yuan Yao

Materials 2025, 18(20), 4656; https://doi.org/10.3390/ma18204656 - 10 Oct 2025

Abstract

This study introduces an innovative approach to addressing the plastic shrinkage of ultra-high-performance concrete (UHPC) using an azodicarbonamide (ADC) expansive agent. The influence of ADC on the workability, mechanical properties, and plastic shrinkage of UHPC were systematically investigated. The findings reveal that the [...] Read more.

This study introduces an innovative approach to addressing the plastic shrinkage of ultra-high-performance concrete (UHPC) using an azodicarbonamide (ADC) expansive agent. The influence of ADC on the workability, mechanical properties, and plastic shrinkage of UHPC were systematically investigated. The findings reveal that the addition of ADC generates a substantial number of bubbles within the UHPC slurry, thereby reducing internal frictional resistance and cohesion of the mixture. Consequently, the fluidity and setting time of UHPC were enhanced to varying degrees with increasing ADC content. However, the introduction of these bubbles also reduced the density, leading to a noticeable decline in both compressive and flexural strength, particularly at later stages. Notably, ADC effectively mitigated early shrinkage and increased the vertical expansion rate within the first 24 h. When the ADC dosage ranged from 0.04% to 0.1%, the UHPC remained in an expanded state within 24 h, with a notable difference in expansion rate exceeding 0.02% from 3 to 24 h. Microstructural and pore structure analysis revealed that the ADC generated considerable gas during the mixing process, forming numerous micropores within the UHPC matrix. These dispersed pores contributed to reduced compactness of the UHPC hydrates, resulting in increased pore area, porosity, and average pore diameter. Full article

(This article belongs to the Section Construction and Building Materials)

11 pages, 1301 KB

Open AccessArticle

Artificial Neural Network Approach for Hardness Prediction in High-Entropy Alloys

by Makachi Nchekwube, A. K. Maurya, Dukhyun Chung, Seongmin Chang and Youngsang Na

Materials 2025, 18(20), 4655; https://doi.org/10.3390/ma18204655 - 10 Oct 2025

Abstract

High-entropy alloys (HEAs) are highly concentrated, multicomponent alloys that have received significant attention due to their superior properties compared to conventional alloys. The mechanical properties and hardness are interrelated, and it is widely known that the hardness of HEAs depends on the principal [...] Read more.

High-entropy alloys (HEAs) are highly concentrated, multicomponent alloys that have received significant attention due to their superior properties compared to conventional alloys. The mechanical properties and hardness are interrelated, and it is widely known that the hardness of HEAs depends on the principal alloying elements and their composition. Therefore, the desired hardness prediction to develop new HEAs is more interesting. However, the relationship of these compositions with the HEA hardness is very complex and nonlinear. In this study, we develop an artificial neural network (ANN) model using experimental data sets (535). The compositional elements—Al, Co, Cr, Cu, Mn, Ni, Fe, W, Mo, and Ti—are considered input parameters, and hardness is considered as an output parameter. The developed model shows excellent correlation coefficients (Adj R2) of 99.84% and 99.3% for training and testing data sets, respectively. We developed a user-friendly graphical interface for the model. The developed model was used to understand the effect of alloying elements on hardness. It was identified that the Al, Cr, and Mn were found to significantly enhance hardness by promoting the formation and stabilization of BCC and B2 phases, which are inherently harder due to limited active slip systems. In contrast, elements such as Co, Cu, Fe, and Ni led to a reduction in hardness, primarily due to their role in stabilizing the ductile FCC phase. The addition of W markedly increased the hardness by inducing severe lattice distortion and promoting the formation of hard intermetallic compounds. Full article

(This article belongs to the Special Issue Machine Learning for Materials Design)

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24 pages, 4912 KB

Open AccessArticle

Numerical Simulation and Prediction of Flexure Performance of PSC Girders with Long-Term Prestress Loss

by Jun-Hee Won, Woo-Ri Kwon and Jang-Ho Jay Kim

Materials 2025, 18(20), 4654; https://doi.org/10.3390/ma18204654 - 10 Oct 2025

Abstract

The purpose of this parametric study was to develop a numerical simulation model calibrated with experimental data to predict the flexural behavior of prestressed concrete (PSC) girders subjected to long-term prestress losses. The model is capable of accurately simulating the flexural behavior of [...] Read more.

The purpose of this parametric study was to develop a numerical simulation model calibrated with experimental data to predict the flexural behavior of prestressed concrete (PSC) girders subjected to long-term prestress losses. The model is capable of accurately simulating the flexural behavior of PSC girders using commercial finite-element (FE) software in the ABAQUS/Explicit program. The accuracy of the model was validated by comparing its results with flexural response test data from three post-tensioned girders, with the tendons ultimately having tensile strength capacities of 1860 MPa, 2160 MPa, and 2400 MPa. The comparison demonstrated generally excellent agreement between numerical and experimental results in terms of the load–deflection response and crack propagation behavior, from the onset of first cracking through the maximum load and into the ductile response range. Subsequently, a parametric study was conducted to evaluate the effects of tendon ultimate strength, amount of long-term prestress loss, grouting defects, degradation-induced reductions in concrete strength, and reductions in tendon cross-sectional area on girder flexural behavior. Through this parametric investigation, the study identified key factors with respect to long-term prestress loss that may influence the flexural behavior of aging PSC structures. Full article

(This article belongs to the Special Issue Modeling and Mechanical Analysis of Materials and Structures in Civil Engineering)

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27 pages, 3027 KB

Open AccessArticle

Production of Food-Grade Monocalcium Phosphate from Meat-Bone Meal

by Zygmunt Kowalski, Agnieszka Wilkosz-Język and Agnieszka Makara

Materials 2025, 18(20), 4653; https://doi.org/10.3390/ma18204653 - 10 Oct 2025

Abstract

The study presents a developed process for producing monocalcium phosphate from hydroxyapatite ash, a by-product of meat-bone meal incineration. The process integrates technological and environmental synergies, enabling efficient recycling of both materials and energy. Waste hydroxyapatite ash, obtained as an intermediate by-product of [...] Read more.

The study presents a developed process for producing monocalcium phosphate from hydroxyapatite ash, a by-product of meat-bone meal incineration. The process integrates technological and environmental synergies, enabling efficient recycling of both materials and energy. Waste hydroxyapatite ash, obtained as an intermediate by-product of the meat-bone meal process, is converted into high-quality monocalcium phosphate. Furthermore, waste heat from incineration is recovered, improving energy efficiency and reducing costs. Preliminary economic analysis indicates that the process is highly profitable, with an annual production capacity of 21,700 tons at a cost of $924 per ton, compared to a market price of $1400 per ton. The total production cost is estimated at $20,058,947, while total sales are projected to reach $30,380,000, yielding a profit of $10,321,053 (34% profit margin). The proposed method is consistent with the principles of the Circular Economy and Cleaner Production, promoting sustainability by reducing waste, lowering resource consumption, and enhancing energy efficiency. The developed technology is both environmentally friendly and economically viable, offering a promising pathway for efficient monocalcium phosphate production and a blueprint for industrial-scale implementation. Full article

(This article belongs to the Special Issue Calcium Phosphate Biomaterials with Medical Applications)

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