Materials

18 pages, 16179 KiB

Open AccessArticle

Barium Titanate-Based Glass–Ceramics Crystallized from Multicomponent Oxide Glasses: Phase Composition and Microstructure

by Ruzha Harizanova, Wolfgang Wisniewski, Dragomir M. Tatchev, Georgi Avdeev, Svetlozar Nedev and Christian Rüssel

Materials 2025, 18(16), 3783; https://doi.org/10.3390/ma18163783 (registering DOI) - 12 Aug 2025

Abstract

The interest in synthesizing new dielectric materials is caused by their potential application in various electronic and sensor devices as well as in a large variety of electronic components. The present work reports the synthesis of glasses in the Na₂O/Al₂ [...] Read more.

The interest in synthesizing new dielectric materials is caused by their potential application in various electronic and sensor devices as well as in a large variety of electronic components. The present work reports the synthesis of glasses in the Na₂O/Al₂O₃/BaO/ZrO₂/TiO₂/B₂O₃/SiO₂ system prepared by melt-quenching. These glasses were then crystallized to glass–ceramics by a controlled thermal treatment. X-ray diffraction experiments reveal the precipitation of Ba₂TiSi₂O₈ (fresnoite) and BaTiO₃, which probably forms a BaZr_xTi_1−xO₃ solid solution. The microstructure is studied by scanning electron microscopy and shows the presence of mulberry-shaped, crystallized structures with a densely-branching morphology. Microcomputed X-ray tomography is used to gather information on the volume fraction and average size of the crystallized volume as an effect of the applied temperature–time schedule. Longer annealing times lead to a higher volume fraction and increasing average size of the crystallization structures obtained. The dielectric properties analyzed by impedance spectroscopy are insulating and show relatively high dielectric constants ≥ 100 and moderate loss tangent values at 10 kHz. Full article

(This article belongs to the Special Issue New Generation Materials for Advanced Electronic and Biomedical Applications)

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23 pages, 8548 KiB

Open AccessArticle

Optimization of the Elastic Modulus of the Filler in High-Rib Thin-Web Grid-Stiffened Panels with Bending Forming Process

by Siyu Nan and Xinlong Zhang

Materials 2025, 18(16), 3782; https://doi.org/10.3390/ma18163782 (registering DOI) - 12 Aug 2025

Abstract

Grid-stiffened panels are indispensable in aerospace applications, valued for their lightweight nature, high strength, and excellent deformation resistance. However, the roll-bending forming process of these panels is plagued by critical defects such as rib buckling and uneven skin deformation, which undermine structural quality [...] Read more.

Grid-stiffened panels are indispensable in aerospace applications, valued for their lightweight nature, high strength, and excellent deformation resistance. However, the roll-bending forming process of these panels is plagued by critical defects such as rib buckling and uneven skin deformation, which undermine structural quality and performance. Fillers are commonly employed to mitigate these issues, yet there remains a lack of systematic guidance for optimizing filler parameters—particularly the elastic modulus—that is tailored to high-rib thin-web configurations. This study focuses on high-rib thin-web grid-stiffened panels, aiming to address this gap by exploring the optimization of filler elastic modulus. By delving into this critical parameter, the research seeks to lay the groundwork for enhancing forming precision in roll bending, offering valuable insights for advancing high-quality manufacturing of aerospace components. Full article

(This article belongs to the Special Issue Artificial Intelligence in Materials Science and Engineering)

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12 pages, 1572 KiB

Open AccessArticle

Impact of Airborne Particle Morphology on Filtration Processes

by Franco Furgiuele, Lucija Boskovic and Igor E. Agranovski

Materials 2025, 18(16), 3781; https://doi.org/10.3390/ma18163781 (registering DOI) - 12 Aug 2025

Abstract

This study explores the critical role of airborne nanoparticle shape in air filtration performance, with direct relevance to the field of nanomaterials production. Aerosol particles ranging from 40 to 250 nm—including spherical Fe₂O₃, cubic MgO, straight rod-shaped ZnO, and [...] Read more.

This study explores the critical role of airborne nanoparticle shape in air filtration performance, with direct relevance to the field of nanomaterials production. Aerosol particles ranging from 40 to 250 nm—including spherical Fe₂O₃, cubic MgO, straight rod-shaped ZnO, and curved or clustered COOH-functionalized nanotubes—were synthesized and tested to assess shape-dependent filtration behavior. The results indicate that the effect of particle morphology on filtration efficiency becomes markedly pronounced at larger particle sizes. For instance, at 250 nm, filtration efficiency differed by as much as 30% between spherical Fe₂O₃ and rod-shaped ZnO particles. These findings have substantial implications for industries engaged in large-scale nanomaterial synthesis, particularly where anisotropic or rod-like particles are prevalent. The potential for higher-than-anticipated atmospheric release of such particles underscores the need for refined environmental controls and monitoring. Furthermore, the current practice of using primarily spherical particles in air filter certification tests may require reconsideration to ensure accuracy and applicability to real-world scenarios involving non-spherical nanomaterials. Full article

(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)

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16 pages, 2926 KiB

Open AccessArticle

Efficient Conversion of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid by the Magnetic Laccase Nanoflowers-2,2,6,6-Tetramethylpiperidin-1-Oxyl System

by Lei Yang, Anbang Duan, Zhanyin Liu, Tingying Wei and Chunzhao Liu

Materials 2025, 18(16), 3780; https://doi.org/10.3390/ma18163780 (registering DOI) - 12 Aug 2025

Abstract

Aiming to address the key challenges of poor enzyme stability, difficult recovery, and difficult synergistic optimization of catalytic efficiency in high-value conversion of biomass, this study utilizes mineralization self-assembly technology to combine laccase with Fe₃O₄@SiO₂-PMIDA-Cu²⁺ composite, [...] Read more.

Aiming to address the key challenges of poor enzyme stability, difficult recovery, and difficult synergistic optimization of catalytic efficiency in high-value conversion of biomass, this study utilizes mineralization self-assembly technology to combine laccase with Fe₃O₄@SiO₂-PMIDA-Cu²⁺ composite, constructing magnetic laccase nanoflower (MLac-NFs) materials with a porous structure and superparamagnetism. This synthetic material can efficiently catalyze the selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). The characterization results indicated that MLac-NFs exhibit optimal catalytic activity (63.4 U mg⁻¹) under conditions of pH 6.0 and 40 °C, with significantly enhanced storage stability (retaining 94.26% of activity after 30 days of storage at 4 °C). Apparent kinetic analysis reveals that the substrate affinity and maximum reaction rate of MLac-NFs were increased by 38.3% and 439.6%, respectively. In the laccase–mediator system (LMS), MLac-NFs mediated by 30 mM TEMPO could achieve complete conversion of HMF to FDCA within 24 h. Moreover, due to the introduction of magnetic nanoparticles, the MLac-NFs could be recovered and reused via an external magnetic field, maintaining 53.26% of the initial FDCA yield after six cycles. Full article

(This article belongs to the Section Catalytic Materials)

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24 pages, 5729 KiB

Open AccessArticle

Prediction of Elastic Modulus of Leached Fly Ash Concrete Based on Non-Uniform ITZ Model

by Xiaoping Zhao, Misha Zhan, Zhiwei Chen, Jian Zhang, Qiang Li and Wenbing Song

Materials 2025, 18(16), 3779; https://doi.org/10.3390/ma18163779 (registering DOI) - 12 Aug 2025

Abstract

The incorporation of fly ash into concrete reduces cement consumption by 10–30%, lowers CO₂ emissions by 30–50%, cuts costs by 15–25%, and enhances durability, thus reducing maintenance expenses. However, the predictive model for the elastic modulus of fly ash concrete subjected to [...] Read more.

The incorporation of fly ash into concrete reduces cement consumption by 10–30%, lowers CO₂ emissions by 30–50%, cuts costs by 15–25%, and enhances durability, thus reducing maintenance expenses. However, the predictive model for the elastic modulus of fly ash concrete subjected to calcium leaching is still lacking. Regarding the theoretical method, the content of calcium hydroxide and calcium silicate hydrate in fly ash–cement systems is quantitatively calculated according to the hydration reaction relationship between cement, fly ash, and water, and then the porosity of the fly ash–cement matrix and interface transition zone (ITZ) after calcium leaching can be obtained. Based on the theory of two-phase composite spheres and the non-uniform ITZ model, the prediction method for the elastic modulus of leached fly ash concrete can be constructed, which comprehensively considers key parameters such as fly ash content, non-uniform characteristics of the ITZ, and the water–binder ratio (w/b). Additionally, the corresponding experimental investigation is also designed to study the variation regulation of the leaching depth, leaching extent, and elastic modulus of fly ash concrete with leaching time. The prediction method for the elastic modulus of leached fly ash concrete is validated via self-designed experimental methods and third-party experiments. This study further delves into the specific effects of w/b, aggregate volume fraction (f_a), fly ash content, and ITZ thickness (h_ITZ) on the elastic modulus of leached concrete (E). The research findings indicate that an appropriate amount of fly ash can effectively enhance the leaching resistance of concrete. For a leaching degree of 10.0%, 30.0%, and 50.0%, E at w/b = 0.40 exceeds that of w/b = 0.60 by 26.71%, 28.43%, and 30.28%, respectively; E at h_ITZ = 10 μm exceeds that of h_ITZ = 50 μm by 16.96%, 15.80%, and 15.11%, respectively; and E at f_a = 65% is 39.82%, 43.15%, and 46.12% higher, respectively, than that of concrete with f_a = 45%. Furthermore, a linear correlation exists between the elastic modulus and the degree of leaching. The prediction method for the elastic modulus offers a theoretical foundation for in-depth exploration of the durability of leached mineral admixture concrete and its scientific application in practical engineering. Full article

(This article belongs to the Special Issue High-Performance Concrete: Synergies Between Material Innovation and Structural Health Monitoring)

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18 pages, 4233 KiB

Open AccessArticle

Structure–Property Linkage in Alloys Using Graph Neural Network and Explainable Artificial Intelligence

by Benjamin Rhoads, Abigail Hogue, Lars Kotthoff and Samrat Choudhury

Materials 2025, 18(16), 3778; https://doi.org/10.3390/ma18163778 (registering DOI) - 12 Aug 2025

Abstract

Deep learning tools have recently shown significant potential for accelerating the prediction of microstructure–property linkage in materials. While deep neural networks like convolution neural networks (CNNs) can extract physics information from 3D microstructure images, they often require a large network architecture and substantial [...] Read more.

Deep learning tools have recently shown significant potential for accelerating the prediction of microstructure–property linkage in materials. While deep neural networks like convolution neural networks (CNNs) can extract physics information from 3D microstructure images, they often require a large network architecture and substantial training time. In this research, we trained a graph neural network (GNN) using phase field generated microstructures of Ni-Al alloys to predict the evolution of mechanical properties. We found that a single GNN is capable of accurately predicting the strengthening of Ni-Al alloys with microstructures of varying sizes and dimensions, which cannot otherwise be done with a CNN. Additionally, GNN requires significantly less GPU utilization than CNN and offers more interpretable explanation of predictions using saliency analysis as features are manually defined in the graph. We also utilize explainable artificial intelligence tool Bayesian Inference to determine the coefficients in the power law equation that governs coarsening of precipitates. Overall, our work demonstrates the ability of the GNN to accurately and efficiently extract relevant information from material microstructures without having restrictions on microstructure size or dimension and offers an interpretable explanation. Full article

(This article belongs to the Special Issue AI-Driven Modeling and Monitoring Towards Advanced Additive Manufacturing)

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14 pages, 4256 KiB

Open AccessCommunication

Characterization of Hard Coatings Using Acoustic Emission

by Ivana Sára Škrobáková, Peter Gogola, Marián Palcut and Ľubomír Čaplovič

Materials 2025, 18(16), 3777; https://doi.org/10.3390/ma18163777 (registering DOI) - 12 Aug 2025

Abstract

Acoustic emission (AE) testing is a non-destructive method used in various applications. In our work we demonstrate its capabilities and potential in studying the functional properties of physical vapor deposited (PVD) coatings. The goal was to classify the coating damage during indentation testing [...] Read more.

Acoustic emission (AE) testing is a non-destructive method used in various applications. In our work we demonstrate its capabilities and potential in studying the functional properties of physical vapor deposited (PVD) coatings. The goal was to classify the coating damage during indentation testing more objectively by quantifying specific imprint features. The AE response was systematically recorded in nine sample conditions and 27 individual imprints, allowing us to identify correlations between the numerical values derived from the SEM observations and the characteristics of the AE signal. An increase in the delaminated coating area was found to correspond to an exponential increase in the AE signal energy. These findings suggest that AE analysis could reduce the reliance on SEM-based evaluation and help accelerate systematic research in the field of PVD coatings. The advantages of AE testing are discussed and conclusions for practical applications are provided. Full article

(This article belongs to the Special Issue Surface Engineering in Materials (2nd Edition))

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16 pages, 2694 KiB

Open AccessArticle

Study on the Performance and Service Life Prediction of Corrosion-Resistant Concrete Cut-Corner Square Piles

by Rui Sheng, Kang Wang, Hua Wei, Hao Lu and Chunhe Li

Materials 2025, 18(16), 3776; https://doi.org/10.3390/ma18163776 (registering DOI) - 12 Aug 2025

Abstract

This paper addresses the issue of reduced lifespan of coastal concrete piles due to chloride ion corrosion. A combination of concrete mix optimization and pile geometry improvement measures is proposed. Based on the diffusion coefficient optimization of Fick’s second law, the service life [...] Read more.

This paper addresses the issue of reduced lifespan of coastal concrete piles due to chloride ion corrosion. A combination of concrete mix optimization and pile geometry improvement measures is proposed. Based on the diffusion coefficient optimization of Fick’s second law, the service life prediction of concrete piles in corrosive environments is completed. The results show that, compared to single slag incorporation and the “slag-fly ash” dual-component mix, the “slag-fly ash-corrosion inhibitor” triple-component concrete achieves a 28-day compressive strength of 67.4 MPa, and the chloride ion diffusion coefficient is reduced to 1.14 × 10⁻¹² m²/s, significantly improving overall performance. Finite element simulations reveal that, compared to ordinary square piles, cut-corner square piles can effectively alleviate stress concentration at the pile tip and reduce settlement. The maximum stress is 3.94 MPa, and the settlement is 22.64 mm, representing reductions of about 16.3% and 15.5%, respectively, compared to ordinary square piles. Concrete service life prediction confirms that the concrete with corrosion inhibitors has a predicted service life of 31.5 years, extending 7.4 years and 13.3 years longer than the single slag and the “slag-fly ash” dual-component groups, respectively. The “material-structure” optimization theory proposed in this study provides a theoretical basis and technical path for the long-life design of coastal engineering pile foundations. Full article

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

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18 pages, 4250 KiB

Open AccessArticle

Highly Efficient Electrocatalyst of 2D–2D gC₃N₄–MoS₂ Composites for Enhanced Overall Water Electrolysis

by Sankar Sekar, Atsaya Shanmugam, Youngmin Lee and Sejoon Lee

Materials 2025, 18(16), 3775; https://doi.org/10.3390/ma18163775 (registering DOI) - 12 Aug 2025

Abstract

For future clean and renewable energy technology, designing highly efficient and robust electrocatalysts is of great importance. Particularly, creating efficient bifunctional electrocatalysts capable of effectively catalyzing both hydrogen- and oxygen-evolution reactions (HERs and OERs) is vital for overall water electrolysis. In this study, [...] Read more.

For future clean and renewable energy technology, designing highly efficient and robust electrocatalysts is of great importance. Particularly, creating efficient bifunctional electrocatalysts capable of effectively catalyzing both hydrogen- and oxygen-evolution reactions (HERs and OERs) is vital for overall water electrolysis. In this study, we employ 2D molybdenum disulfide (MoS₂) nanosheets and pyrolytically fabricated 2D graphitic carbon nitride (gC₃N₄) nanosheets to create 2D gC₃N₄-decorated 2D MoS₂ (2D–2D gC₃N₄–MoS₂) nanocomposites using a facile sonochemical method. The 2D–2D gC₃N₄–MoS₂ nanocomposites show an interconnected and agglomerated structure of 2D gC₃N₄ nanosheets decorated on 2D MoS₂ nanosheets. For water electrolysis, the gC₃N₄–MoS₂ nanocomposites exhibit low overpotentials (OER: 225 mV, HER: 156 mV), small Tafel slope values (OER: 49 mV/dec, HER: 101 mV/dec), and excellent durability (up to 100 h for both OER and HER) at 10 mA/cm² in 1 M KOH. Furthermore, the gC₃N₄–MoS₂ nanocomposites show excellent overall water electrolysis performance with a low full-cell voltage (1.52 V at 10 mA/cm²) and outstanding long-term cell stability. The superb bifunctional activities of the gC₃N₄–MoS₂ nanocomposites are attributed to the synergistic effects of 2D gC₃N₄ (i.e., low charge-transfer resistance) and 2D MoS₂ (i.e., a large electrochemically active surface area). These findings suggest that the 2D–2D gC₃N₄–MoS₂ nanocomposites could serve as excellent bifunctional catalysts for overall water electrolysis. Full article

(This article belongs to the Special Issue Advanced Nanomaterials for Energy Storage and Conversion)

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18 pages, 19489 KiB

Open AccessArticle

Oxidation Kinetics, Morphology Evolution, and Formation Mechanisms of the High-Temperature Oxide Scale for Cr-Alloyed Automotive Beam Steels

by Jiang Chang, Yuantao Hu, Yonggang Yang, Chen Jiang, Jianling Liu, Borui Zhang, Xiong Yang and Zhenli Mi

Materials 2025, 18(16), 3774; https://doi.org/10.3390/ma18163774 - 12 Aug 2025

Abstract

The oxidation behaviors of varying Cr-alloyed automotive beam steels—0.015 wt.% Cr, 0.15 wt.% Cr, and 1 wt.% Cr—were investigated using isothermal oxidation experiments. The morphologies of the oxide scale were characterized, and the formation mechanisms were analyzed to understand the change in the [...] Read more.

The oxidation behaviors of varying Cr-alloyed automotive beam steels—0.015 wt.% Cr, 0.15 wt.% Cr, and 1 wt.% Cr—were investigated using isothermal oxidation experiments. The morphologies of the oxide scale were characterized, and the formation mechanisms were analyzed to understand the change in the oxidation kinetics of the investigated steels. The results show that a small amount of Cr, up to 0.15 wt.%, can reduce oxidation kinetics; the addition of Cr at 1 wt.% causes the oxidation rate to decline at a low isothermal temperature, but the hindrance effect expires when the oxidation temperature is above 1050 °C. The oxidation scale, including the inner FeO layer, the intermediate Fe₃O₄ layer, and the outer Fe₂O₃ layer, exhibits a morphological evolution from marble-like to pore-like, then whisker-like, flocculation-like, fine oxide grains, and finally coarse oxide grains. With increasing Cr addition, the thickness of the FeO layer decreases significantly, leading to a reduction in the total thickness of the oxidation scale. During the oxidation process of the investigated steel with 0.15 wt.% Cr, a Cr-rich layer and FeO-(Cr, Fe, Mn)₃O₄ eutectic form; meanwhile, FeO-(Cr, Fe)₂O₃ eutectic and Si-rich oxides, as well as a (Cr, Si)-rich layer, occur in the oxidation scale when 1 wt.% Cr is added to the steel. The occurrence of voids in the (Cr, Si)-rich layer is responsible for the increasing oxidation kinetics of the 1 wt.% Cr steel when the isothermal temperature is above 1050 °C, and the optimal Cr concentration in automotive beam steel is 0.15 wt.%, considering both oxidation resistance and cost. Full article

(This article belongs to the Special Issue High-Performance Alloys and Steels: Design, Processing, and Applications)

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16 pages, 1656 KiB

Open AccessArticle

Evaluation of Hazel-Derived Particleboard as a Substitute for Conventional Wood-Based Composites

by Marta Wronka, Damian Wojnicz, Anita Wronka and Grzegorz Kowaluk

Materials 2025, 18(16), 3773; https://doi.org/10.3390/ma18163773 - 12 Aug 2025

Abstract

This study investigated the potential of hazelnut wood (Corylus avellana L.) as an alternative raw material in the production of single-layer structural particleboards. Boards with a target density of 700 kg m⁻³ and thickness of 13 mm were manufactured using varying [...] Read more.

This study investigated the potential of hazelnut wood (Corylus avellana L.) as an alternative raw material in the production of single-layer structural particleboards. Boards with a target density of 700 kg m⁻³ and thickness of 13 mm were manufactured using varying substitution levels (5%, 10%, 25%, 50% and 100%) of hazel wood particles relative to industrial pine (Pinus sylvestris L.) particles. Phenol-formaldehyde (PF) resin was used as the adhesive at a 15% resination rate. Mechanical and physical properties, including modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB), screw withdrawal resistance (SWR), water absorption (WA), and thickness swelling (TS), were evaluated according to relevant European standards. Density profiles (DP) were also assessed. The results showed that while higher hazel content reduced bending strength (from 23.3 N mm⁻² for reference to 18.7 N mm⁻² for 100% hazel wood board) and stiffness (from 3515 N mm⁻² for reference to 2520 N mm⁻² for 100% hazel wood board), most boards met standard mechanical requirements of EN 312 for P3 and P5 boards. Notably, IB strength improved significantly at higher hazel content, with the 100% variant (2.07 N mm⁻²) exceeding the reference board (1.57 N mm⁻²). Screw withdrawal resistance also increased with hazel wood addition (from 235 N mm⁻¹ for reference to 262 N mm⁻¹ for 100% hazel wood board), linked to its higher density. However, water resistance and dimensional stability worsened with increasing hazel content, particularly in bark-containing particles, leading to excessive thickness swelling after prolonged water exposure. Thickness swelling after 24 h of soaking rose from 16.36% for the reference board to 20.13% for the 100% hazel wood board. Density profiles revealed a more uniform internal structure in boards with higher hazel content. Overall, hazelnut wood shows promise as a partial substitute for pine in particleboard production, especially at moderate substitution levels, though limitations in moisture resistance must be addressed for broader industrial application. Full article

(This article belongs to the Special Issue Modern Wood-Based Materials for Sustainable Building)

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12 pages, 923 KiB

Open AccessArticle

Effect of Ultraviolet Light on the Shear Bond Strength of Commercial Dental Adhesives

by Markus Heyder, Stefan Kranz, Johanna Sandra Woelfel, Tabea Raabe, André Guellmar, Anna Mrozinska, Michael Gottschaldt, Ulrich S. Schubert, Bernd W. Sigusch and Markus Reise

Materials 2025, 18(16), 3772; https://doi.org/10.3390/ma18163772 (registering DOI) - 12 Aug 2025

Abstract

Background: In adhesive dentistry, debonding-on-demand is attractive for situations where no permanent attachment is required. Due to its destructive nature, ultraviolet (UV) light may be of interest for attenuating bond forces. The aim of this study was to investigate the impact of UV [...] Read more.

Background: In adhesive dentistry, debonding-on-demand is attractive for situations where no permanent attachment is required. Due to its destructive nature, ultraviolet (UV) light may be of interest for attenuating bond forces. The aim of this study was to investigate the impact of UV light on the shear bond strength (SBS) of etch-and-rinse (n = 4) and universal adhesives (n = 3). Methods: Glass-ceramic samples were bonded to bovine enamel surfaces (n = 10/adhesive) and subjected to shear bond testing before and after exposure to UV light (320–390 nm, 126 Jcm⁻²). Data was statistically analyzed by Mann–Whitney U test. Results: Initial photopolymerized etch-and-rinse adhesives showed superior SBS compared to universal adhesives. Highest values were recorded for iBOND^® Total etch (15.48 MPa) and Syntac classic© (17.60 MPa). Lowest SBS was obtained for Ecosite Bond^® (2.63 MPa). Additional UV exposure caused a significant decrease in SBS among iBOND Total etch (5.24 MPa, p = 0.009) and Solobond M© (3.65 MPa, p = 0.005), while for Syntac classic©, an increase (24.12 MPa, p = 0.047) was recorded. Among all other tested adhesives, no significant changes were observed. Conclusions: UV radiation impacted SBS of etch-and-rinse adhesives only (decrease: iBOND Total Etch, Solobond M; enhancement: Syntac classic©). Further research should focus on introducing sufficient light-triggered debonding mechanisms. Full article

(This article belongs to the Section Biomaterials)

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15 pages, 3654 KiB

Open AccessArticle

Kinetic Analysis of the Reaction of Silver with Elemental Sulfur in Mineral Insulating Oil

by Dejan Kolarski, Jelena Lukić, Jelena Janković and Sandra Glišić

Materials 2025, 18(16), 3771; https://doi.org/10.3390/ma18163771 - 12 Aug 2025

Abstract

Elemental sulfur (S₈) reacts readily with silver, forming highly conductive silver sulfide on silver-coated components of on-load tap changers (OLTCs), forming a highly conductive silver sulfide film at the surface of an OLTC, which can lead to the failure of critical [...] Read more.

Elemental sulfur (S₈) reacts readily with silver, forming highly conductive silver sulfide on silver-coated components of on-load tap changers (OLTCs), forming a highly conductive silver sulfide film at the surface of an OLTC, which can lead to the failure of critical components in power transformers. This study investigates the reaction between metallic silver and elemental sulfur dissolved in mineral insulating oil across temperatures from 60 °C to 180 °C. The process involves three stages: the diffusion of sulfur through oil, surface reaction, and product diffusion. For low-viscosity oil, diffusion is not the limiting factor, and sulfur does not react immediately on the silver’s surface, suggesting possible adsorption or intermediate formation. A kinetic analysis revealed that the reaction follows first-order kinetics, with a change in mechanism above 150 °C. The reaction follows the Arrhenius equation in two separate regions: 60–150 °C and 150–180 °C. Activation energy was calculated as 23.67 kJ mol⁻¹, and it can be concluded that the reaction is controlled by the diffusion of sulfur through mineral oil, and at higher temperatures (150 °C to 180 °C), the calculated activation energy is 160.69 kJ mol⁻¹, which leads to the conclusion that the combined chemisorption and diffusion through a silver sulfide–oil interface becomes the new limiting factor. Full article

(This article belongs to the Section Corrosion)

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20 pages, 691 KiB

Open AccessReview

Alloy Selection and Manufacturing Technologies for Total Ankle Arthroplasty: A Narrative Review

by Kishen Mitra, Arun K. Movva, Michael O. Sohn, Joshua M. Tennyson, Grayson M. Talaski, Samuel B. Adams and Albert T. Anastasio

Materials 2025, 18(16), 3770; https://doi.org/10.3390/ma18163770 - 11 Aug 2025

Abstract

Total ankle arthroplasty (TAA) has evolved significantly through advances in alloy selection and manufacturing technologies. This narrative review examines the metallurgical foundations of contemporary TAA implants, analyzing primary alloy systems and their mechanical properties. Cobalt-chromium alloys provide superior mechanical strength and durability but [...] Read more.

Total ankle arthroplasty (TAA) has evolved significantly through advances in alloy selection and manufacturing technologies. This narrative review examines the metallurgical foundations of contemporary TAA implants, analyzing primary alloy systems and their mechanical properties. Cobalt-chromium alloys provide superior mechanical strength and durability but present metal ion release concerns, while titanium alloys (Ti6Al4V) optimize biocompatibility with elastic modulus values (101–113 GPa) closer to bone, despite tribological limitations. Novel β-titanium formulations (Ti-35Nb-7Zr-5Ta, Ti10Mo6Zr4Sn3Nb) eliminate toxic aluminum and vanadium components while achieving lower elastic modulus values (50–85 GPa) that better match cortical bone properties. Manufacturing has transitioned from traditional methods (investment casting, forging, CNC machining) toward additive manufacturing technologies. Selective laser melting and electron beam melting enable patient-specific geometries, controlled porosity, and optimized microstructures, though challenges remain with residual stresses, surface finish requirements, and post-processing needs. Emerging biodegradable materials, composite structures, and hybrid implant designs represent promising future directions for addressing current material limitations. This review provides evidence-based insights for alloy selection and manufacturing approaches, emphasizing the critical role of materials engineering in TAA implant performance and clinical outcomes. Full article

(This article belongs to the Special Issue Microstructure and Mechanical Properties of Alloys (2nd Edition))

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25 pages, 5321 KiB

Open AccessArticle

Corrosion and Ion Release in 304L Stainless Steel Biomedical Stylets

by Lucien Reclaru, Alexandru Florian Grecu, Daniela Florentina Grecu, Cristian Virgil Lungulescu and Dan Cristian Grecu

Materials 2025, 18(16), 3769; https://doi.org/10.3390/ma18163769 (registering DOI) - 11 Aug 2025

Abstract

Styles are invasive medical devices that are visible on images and are used in several medical specialties, including cardiology, neurology, orthopaedics, anaesthesia, oto-rhino-laryngology (ENT), and dentistry. With their thin and flexible design, they allow for the optimal positioning and precise guidance of medical [...] Read more.

Styles are invasive medical devices that are visible on images and are used in several medical specialties, including cardiology, neurology, orthopaedics, anaesthesia, oto-rhino-laryngology (ENT), and dentistry. With their thin and flexible design, they allow for the optimal positioning and precise guidance of medical devices such as nerve stimulation, defibrillation, electrode positioning, and catheter insertion. Generally, they are made of stainless steel, offering a combination of rigidity and flexibility. The aim of this study is to evaluate the sensitivity of austenitic stainless steel 304L used for the manufacture of J-stylets in uniform, pitting, crevice, and intergranular corrosion. We follow the manufacturing process step by step in order to analyse the risks of corrosion sensitisation and the cumulative effects of various forms of degradation, which could lead to a significant release of metal cations. Another objective of this study is to determine the optimal heat treatment temperature to minimise sensitivity to the intergranular corrosion of 304L steel. Uniform corrosion: Two samples were taken at each stage of the manufacturing process (eight steps in total), in the form of rods. After one hour of immersion, potentiodynamic polarisation curves were plotted up to ±400 mV vs. SCE. A coulometric analysis was also performed by integrating the anode zone between E (i = 0) and +400 mV vs. SCE. The values obtained by integration are expressed as mC/cm². The test medium used was a simulated artificial plasma solution (9 g/L NaCl solution). Intergranular corrosion: (a) Chemical test: Thirty rod-shaped samples were tested, representing the eight manufacturing steps, as well as heat treatments at 500 °C, 620 °C, and 750 °C, in accordance with ASTM A262 (F method). (b) Electrochemical Potentiokinetic Reactivation (EPR) according to ASTM G108–94 (2015). Two samples were tested for each condition: without heat treatment and after treatments at 500 °C, 620 °C, and 750 °C. Release of cations: The release of metal ions was evaluated in the following two media: artificial sweat, according to EN 1811:2011+A1:2015, and bone plasma, according to the Fitton-Jackson and Burks-Peck method. Six samples that had been heat-treated at 500 °C for one hour were analysed. Results, discussions: (a) Analysis of the polarisation curves revealed significant disturbances in the heat treatment steps, as well as the μC/cm² quantities, which were between 150,000 and 400,000 compared to only 40–180 for the other manufacturing steps; (b) Electrochemical Potentiokinetic reactivation (EPR) tests indicated that the temperature of 500 °C was a good choice to limit 304L steel sensitisation in intergranular corrosion; and (c) the quantities of cations released in EN 1811 sweat were of the order of a few μg/cm² week, as for Fe: 2.31, Cr: 0.05, and Ni: 0.12. Full article

(This article belongs to the Section Metals and Alloys)

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33 pages, 13817 KiB

Open AccessArticle

Comprehensive Analysis of Cutting-Force Components in Milling Using RQA: Effect of Edge Geometry and Process Parameters

by Marcin Płodzień, Łukasz Żyłka, Michał Wydra and Rafał Rusinek

Materials 2025, 18(16), 3768; https://doi.org/10.3390/ma18163768 - 11 Aug 2025

Abstract

This study investigates the influence of cutting edge geometry (continuous, serrated, and wavy) and selected machining parameters (cutting speed v_c, feed per tooth f_z, and radial infeed a_e) on cutting-force components and dynamic behavior during the milling [...] Read more.

This study investigates the influence of cutting edge geometry (continuous, serrated, and wavy) and selected machining parameters (cutting speed v_c, feed per tooth f_z, and radial infeed a_e) on cutting-force components and dynamic behavior during the milling of an AlZn5.5MgCu aluminum alloy. The analysis was based on box plots and Recurrence Quantification Analysis (RQA) applied to the cutting-force signal. The results demonstrated that serrated and wavy-edge tools generated significantly lower values of the normal force component F_fN—up to −57% on average—compared to the continuous-edge tool, particularly at lower f_z and v_c, indicating enhanced process dynamics. At higher a_e values, however, these tools induced increased signal variability—up to 300% greater—suggesting potential resonance excitation. RQA indicators, such as DET, Lmax, and LAM, revealed a strong dependence of system dynamics on tool edge geometry. Linear Discriminant Analysis (LDA) confirmed that RQA measures effectively distinguish between cutting-edge types. The study concludes that tooldge geometry substantially affects milling process stability and can be purposefully selected to optimize performance under varying machining conditions. Full article

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

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8 pages, 243 KiB

Open AccessEditorial

The 15th Anniversary of Materials—Recent Advances in Advanced Materials Characterization

by Sanichiro Yoshida, Luciano Lamberti and Giuseppe Lacidogna

Materials 2025, 18(16), 3767; https://doi.org/10.3390/ma18163767 - 11 Aug 2025

Abstract

Recent developments in materials science and technology have increased the structural complexity of materials and the level of sophistication in describing their properties, especially when the material under analysis is required to exhibit high multi-field performances [...] Full article

(This article belongs to the Special Issue The 15th Anniversary of Materials—Recent Advances in Advanced Materials Characterization)

24 pages, 15183 KiB

Open AccessArticle

Permittivity Measurement in Multi-Phase Heterogeneous Concrete Using Evidential Regression Deep Network and High-Frequency Electromagnetic Waves

by Zhaojun Hou, Hui Liu, Jianchuan Cheng, Qifeng Zhang and Zheng Tong

Materials 2025, 18(16), 3766; https://doi.org/10.3390/ma18163766 - 11 Aug 2025

Abstract

Permittivity measurements of concrete materials benefit from the application of high-frequency electromagnetic waves (HF-EMWs), but they still face the problem of being aleatory and exhibit epistemic uncertainty, originating from multi-phase heterogeneous materials and the limited knowledge of HF-EMW propagation. This limitation restricts the [...] Read more.

Permittivity measurements of concrete materials benefit from the application of high-frequency electromagnetic waves (HF-EMWs), but they still face the problem of being aleatory and exhibit epistemic uncertainty, originating from multi-phase heterogeneous materials and the limited knowledge of HF-EMW propagation. This limitation restricts the precision of non-destructive testing. This study proposes an evidential regression deep network for conducting permittivity measurements with uncertainty quantification. This method first proposes a finite-difference time-domain (FDTD) model with multi-phase heterogeneous concrete materials to simulate HF-EMW propagation in a concrete sample or structure, obtaining the HF-EMW echo that contains aleatory uncertainties owing to the limited knowledge of wave propagation. A U-net-based model is then proposed to denoise an HF-EMW, where the difference between a couple of observed and denoised HF-EMWs characterizes aleatory uncertainty owing to measurement noise. Finally, a Dempster–Shafer theory-based (DST-based) evidential regression network is proposed to compute permittivity, incorporating the quantification of two types of uncertainty using a Gaussian random fuzzy number (GRFN): a type of fuzzy set that has the characteristics of a Gaussian fuzzy number and a Gaussian random variable. An experiment with 1500 samples indicates that the proposed method measures permittivity with a mean square error of 7.50% and a permittivity uncertainty value of 74.70% in four types of concrete materials. Additionally, the proposed method can quantify the uncertainty in permittivity measurements using a GRFN-based belief measurement interval. Full article

(This article belongs to the Special Issue Sustainability in Asphalt, Concrete and Pavement Materials: Design, Performance, and Characterization)

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22 pages, 3629 KiB

Open AccessArticle

Pulse-Echo Ultrasonic Verification of Silicate Surface Treatments Using an External-Excitation/Single-Receiver Configuration: ROC-Based Differentiation of Concrete Specimens

by Libor Topolář, Lukáš Kalina, David Markusík, Vladislav Cába, Martin Sedlačík, Felix Černý, Szymon Skibicki and Vlastimil Bílek

Materials 2025, 18(16), 3765; https://doi.org/10.3390/ma18163765 - 11 Aug 2025

Abstract

This study investigates a non-destructive, compact pulse-echo ultrasonic method that combines an external transmitter with a single receiving sensor to identify different surface treatments applied to cementitious materials. The primary objective was to evaluate whether treatment-induced acoustic changes could be reliably quantified using [...] Read more.

This study investigates a non-destructive, compact pulse-echo ultrasonic method that combines an external transmitter with a single receiving sensor to identify different surface treatments applied to cementitious materials. The primary objective was to evaluate whether treatment-induced acoustic changes could be reliably quantified using time-domain signal parameters. Three types of surface conditions were examined: untreated reference specimens (R), specimens treated with a standard lithium silicate solution (A), and those treated with an enriched formulation containing hexylene glycol (B) intended to enhance pore sealing via gelation. A broadband piezoelectric receiver collected the backscattered echoes, from which the maximum amplitude, root mean square (RMS) voltage, signal energy, and effective duration were extracted. Receiver operating characteristic (ROC) analysis was conducted to quantify the discriminative power of each parameter. The results showed excellent classification performance between groups involving the B-treatment (AUC ≥ 0.96), whereas the R vs. A comparison yielded moderate separation (AUC ≈ 0.61). Optimal cut-off values were established using the Youden index, with sensitivity and specificity exceeding 96% in the best-performing scenarios. The results demonstrate that a single-receiver, one-sided pulse-echo arrangement coupled with straightforward amplitude metrics provides a rapid, cost-effective, and field-adaptable tool for the quality control of silicate-surface treatments. By translating laboratory ultrasonics into a practical on-site protocol, this study helps close the gap between the experimental characterisation and real-world implementation of surface-treatment verification. Full article

(This article belongs to the Special Issue Advances in the Nondestructive Testing of Construction and Building Materials)

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