Materials

16 pages, 6799 KB

Open AccessArticle

Sodium Alginate-Encapsulated Oregano Essential Oil Microcapsules for the Conservation of Waterlogged Archaeological Wood

by Biao Wang, Bingjian Zhang and Yulan Hu

Materials 2026, 19(4), 827; https://doi.org/10.3390/ma19040827 - 23 Feb 2026

Viewed by 477

Abstract

Waterlogged archaeological wood is highly vulnerable to degradation by wood-degrading microorganisms. Oregano essential oil (OEO) shows excellent antimicrobial activity against such microbes, but its high volatility and poor stability restrict direct application in cultural relic protection. This study aims to optimize the preparation [...] Read more.

Waterlogged archaeological wood is highly vulnerable to degradation by wood-degrading microorganisms. Oregano essential oil (OEO) shows excellent antimicrobial activity against such microbes, but its high volatility and poor stability restrict direct application in cultural relic protection. This study aims to optimize the preparation of sodium alginate (SA)-based OEO microcapsules (OEO@SAM), characterize their structural and physicochemical properties, and evaluate their sustained-release antimicrobial performance for waterlogged archaeological wood conservation. OEO@SAM was fabricated via ionic crosslinking, with orthogonal experiments optimizing three key parameters: OEO:SA ratio, SA concentration, and CaCl₂ concentration. The microcapsules were characterized by morphological observation, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), etc. Encapsulation efficiency (EE), in vitro sustained-release kinetics, and antimicrobial activity against dominant wood-degrading microorganisms (isolated from waterlogged archaeological sites) were tested. The OEO:SA ratio was the dominant factor regulating EE: EE decreased sharply as the OEO:SA ratio increased, with the highest EE (24.05%) achieved at OEO:SA = 0.5, SA = 2%, and CaCl₂ = 3%. Meanwhile, only 0.71 g/L of OEO@SAM is required to inhibit bacterial growth and achieve the conservation of waterlogged archaeological wood. OEO@SAM exhibited stable sustained release (fitting the zero-order kinetic model) and significant antimicrobial activity against target microorganisms. It provides a new type of antibacterial and antifungal material for the in situ conservation of waterlogged archaeological wood. Full article

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14 pages, 3984 KB

Open AccessArticle

Novel Acetal Rotating Tool Improving Surface Quality in Incremental Sheet Forming

by Hongsong Song, Kai Han, Peng Xu, Jinxin Zang, Xiaoqiang Li and Shaohua Wang

Materials 2026, 19(4), 826; https://doi.org/10.3390/ma19040826 - 23 Feb 2026

Viewed by 443

Abstract

Surface quality remains a critical factor limiting the widespread adoption of incremental sheet forming (ISF). This study proposes a novel acetal wheel-type rotating tool and systematically investigates the influence of tool structure and material on surface quality through experimental and numerical analyses. The [...] Read more.

Surface quality remains a critical factor limiting the widespread adoption of incremental sheet forming (ISF). This study proposes a novel acetal wheel-type rotating tool and systematically investigates the influence of tool structure and material on surface quality through experimental and numerical analyses. The results demonstrate that the acetal tool significantly improves surface quality by 32–40% compared to conventional metal ball tools, primarily due to enhanced sheet–tool contact area that effectively suppresses the formation of surface waviness topography. Furthermore, the wheel-type tool reduces contact stress by over 37.5% while improving surface quality by 21.1% relative to traditional metal ball tools. Notably, the acetal rotating wheel achieves a 32.0% surface quality enhancement while eliminating tool wear, highlighting its industrial applicability. These findings provide both a mechanistic understanding and a practical tooling solution, highlighting significant potential for improving surface quality in ISF industrial applications. Full article

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

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19 pages, 5504 KB

Open AccessArticle

Finite Element Analysis of Anterior Odontoid Screw Fixation for Type II Odontoid Fractures

by Pedro Miguel González-Vargas, Antía Millán, José Luis Thenier-Villa, Aida Badaoui, Cesáreo Conde, Juan Pou and Antonio Riveiro

Materials 2026, 19(4), 825; https://doi.org/10.3390/ma19040825 - 23 Feb 2026

Viewed by 428

Abstract

Introduction: Type II odontoid process fractures are common in the adult population, and anterior screw fixation aims to restore C1–C2 complex stability while preserving cervical motion. This study focuses on the numerical analysis of odontoid fractures, evaluating the structural behavior after anterior screw [...] Read more.

Introduction: Type II odontoid process fractures are common in the adult population, and anterior screw fixation aims to restore C1–C2 complex stability while preserving cervical motion. This study focuses on the numerical analysis of odontoid fractures, evaluating the structural behavior after anterior screw fixation using finite element simulations. Methods: Forty-eight patients (males, females, 74 years old on average) diagnosed with type II odontoid fractures and treated surgically between 2015 and 2023 were included in the study. Various loading conditions (magnitude and direction) were simulated to analyze displacements and stress distributions after screw insertion. Results: Screw fixation significantly fixes fractured vertebrae, but stress and deformation are considerably larger than in unfractured cases. Posterior oblique loads produced the highest stress concentrations, particularly at the base of the odontoid and the screw-bone interface. Male models exhibited greater total deformations and stresses under the same loading conditions, suggesting relevant biomechanical differences based on sex. Conclusions: Anterior odontoid screw fixation provides effective stabilization in type II odontoid fractures, although its performance depends on factors such as load vector and patient-specific anatomical characteristics. These findings support the use of FEM simulation as a valuable tool for personalized surgical analysis. Full article

(This article belongs to the Section Biomaterials)

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17 pages, 8329 KB

Open AccessArticle

The Influence of Al Content on the Ignition and Flame Propagation Behavior of Ti_1−xAl_x Alloys in Enriched-Oxygen Environment

by Cheng Zhang, Qiwei Ran, Jianjun Li, Pengfei Jin, Guangyu He, Jinfeng Huang and Congzhen Wang

Materials 2026, 19(4), 824; https://doi.org/10.3390/ma19040824 - 23 Feb 2026

Viewed by 436

Abstract

Titanium aluminide intermetallics have gained considerable attention as high-temperature structural materials for aerospace applications, but are susceptible to “titanium fire” under extreme service conditions. The role of Al elements on the combustion behavior of titanium aluminide intermetallics remains not fully understood. Herein, the [...] Read more.

Titanium aluminide intermetallics have gained considerable attention as high-temperature structural materials for aerospace applications, but are susceptible to “titanium fire” under extreme service conditions. The role of Al elements on the combustion behavior of titanium aluminide intermetallics remains not fully understood. Herein, the influence of Al content on the ignition critical condition and burning rate of Ti_1−xAl_x alloys was investigated by using promoted ignition combustion (PIC) tests under oxygen-enriched atmosphere. Results indicated that the critical oxygen pressure of Ti_1−xAl_x alloys increases from 0.11 MPa to 0.23 MPa, and the ignition temperature under oxygen pressure of 0.41 MPa increases from 1059.5 ± 4.8 K to 1120.4 ± 2.5 K as Al content increases from 20 at% to 70 at%. However, the combustion rate increases from 11.85 ± 0.13 mm·s⁻¹ to 14.05 ± 0.09 mm·s⁻¹ as Al content increases from 20 at% to 70 at%. Moreover, the activation energy for ignition increases from 105.44 kJ·mol⁻¹ to 153.04 kJ·mol⁻¹ as Al content increases from 20 at% to 70 at%. According to the microstructure analysis after combustion, the influence of Al content on the ignition activation energy and burning rate is attributed to multiple factors involving bonding energy, melting temperature, and heat release. Full article

(This article belongs to the Special Issue Advances in Lightweight Alloys: Microstructure, Mechanical Properties and Applications)

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22 pages, 3288 KB

Open AccessArticle

Assessing the Porosity-Binder Ratio and Machine Learning Models for Predicting the Strength and Durability of Soil-Cement-Glass Powder Geomaterial

by Jair Arrieta Baldovino, Oscar E. Coronado-Hernández and Yamid E. Nuñez de la Rosa

Materials 2026, 19(4), 823; https://doi.org/10.3390/ma19040823 - 21 Feb 2026

Viewed by 403

Abstract

This study evaluates the mechanical behavior and durability of a silty soil stabilized with Portland cement and recycled ground glass powder (GGP). The porosity–cement index (η/C_iv) was applied to predict unconfined compressive strength (

q_{u}

), splitting tensile [...] Read more.

This study evaluates the mechanical behavior and durability of a silty soil stabilized with Portland cement and recycled ground glass powder (GGP). The porosity–cement index (η/C_iv) was applied to predict unconfined compressive strength (

q_{u}

), splitting tensile strength (

q_{t}

), and accumulated mass loss (ALM) under wetting–drying cycles. Mixtures were prepared with cement contents of 3%, 6%, and 9%, GGP contents of 5%, 15%, and 30%, and dry unit weights of 13.5, 14.5, and 15.5 kN/m³, and were cured for 7, 28, and 90 days. The experimental program consisted of a large dataset, comprising 486 mechanical tests (unconfined compressive and splitting tensile strength) and 81 durability tests, providing a robust basis for both empirical modeling and machine learning analysis. The results confirmed a strong power-law relationship between η/C_iv and both

q_{u}

and

q_{t}

, achieving high coefficients of determination (R² > 0.98). The strength coefficient (A) increased consistently with curing time and GGP addition, indicating enhanced pozzolanic reactivity and matrix densification. After 90 days,

q_{u}

increased by over 250% and

q_{t}

by nearly 700%. Durability tests revealed exponential reductions in ALM with higher density and binder content, achieving values below 0.5% for the densest mixtures, which contained 30% GGP. These findings validate the η/C_iv index as an effective predictor of strength and durability in soil–cement–GGP geomaterials, establishing a solid basis for future integration with machine learning models. The implementation of twenty-eight machine learning presets for predicting

q_{u}

,

q_{t}

, and ALM demonstrated that the Matern 5/2 Gaussian Process Regression and the trilayered neural network are the most suitable algorithms, achieving R² values higher than 0.987 in both the validation and testing stages. Full article

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

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53 pages, 17273 KB

Open AccessReview

Research Progress on Interfacial Design and Mechanical Optimization of Graphene-Reinforced Titanium Matrix Composites

by Yongkang Fu, Shilong Xing, Zongan Li, Shuo Wu, Liran Sun, Xiaohua Yang, Wei Shen, Zhikun Li and Xiaocong Li

Materials 2026, 19(4), 822; https://doi.org/10.3390/ma19040822 - 21 Feb 2026

Viewed by 451

Abstract

Graphene (GR) demonstrates significant potential in enhancing the mechanical performance of titanium matrix composites (TMCs), particularly by improving their tensile strength, fracture toughness, and fatigue resistance, thereby optimizing the overall structural integrity and durability of the composites; however, their practical implementation confronts two [...] Read more.

Graphene (GR) demonstrates significant potential in enhancing the mechanical performance of titanium matrix composites (TMCs), particularly by improving their tensile strength, fracture toughness, and fatigue resistance, thereby optimizing the overall structural integrity and durability of the composites; however, their practical implementation confronts two fundamental challenges: achieving uniform dispersion and mitigating excessive interfacial TiC formation, which compromises mechanical properties. This review comprehensively explores progress in the fabrication, interfacial design, and mechanical optimization of TMCs reinforced with graphene-based materials. Various processing techniques, such as powder metallurgy (PM) and spark plasma sintering (SPS), are critically analyzed in terms of their advantages and limitations for producing high-performance TMCs. This article analyzes how key parameters in processes like PM and SPS affect graphene structure, dispersion, and interfacial reactions. It outlines strategies—including surface modification, 3D structural design, and multiscale interface engineering—that enhance both strength and toughness. While progress has been made in microscale performance, challenges remain in engineering stability and long-term reliability. Future work should focus on intelligent process optimization and architectured composite manufacturing. By systematically synthesizing existing research findings, this article clarifies the advantages and limitations of current technological approaches, providing a theoretical foundation and technical roadmap for the subsequent development of graphene-reinforced TMCs that exhibit high strength, high toughness, and excellent reliability. Full article

(This article belongs to the Section Advanced Composites)

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23 pages, 1743 KB

Open AccessArticle

Antioxidant Constituents of Hops (Humulus lupulus L.) as Functional Raw Materials for Cosmetic Applications

by Magdalena Dzienisik, Marta Marzec and Izabela Nowak

Materials 2026, 19(4), 821; https://doi.org/10.3390/ma19040821 - 21 Feb 2026

Viewed by 462

Abstract

Humulus lupulus L. (hops) is best known for its application in the brewing industry; however, growing scientific interest has revealed its high content of natural antioxidants, including flavonoids and polyphenols. These compounds exhibit pronounced anti-inflammatory activity, positioning hops as a promising plant-derived ingredient [...] Read more.

Humulus lupulus L. (hops) is best known for its application in the brewing industry; however, growing scientific interest has revealed its high content of natural antioxidants, including flavonoids and polyphenols. These compounds exhibit pronounced anti-inflammatory activity, positioning hops as a promising plant-derived ingredient for cosmetic use. The present study evaluates the antioxidant properties of Humulus lupulus L. (HL) extract and cosmetic formulations loaded with hop-based active substances. Antioxidant capacity was determined using ABTS, Folin–Ciocâlteu, and FRAP methods. The hop extract showed limited free radical scavenging activity and reducing power; however, these results still confirm its antioxidant potential. Importantly, cosmetic emulsions enriched with the HL extract maintained substantial antioxidant activity, demonstrating successful incorporation and stability of the bioactive compounds within the formulations. Physicochemical stability tests, including pH monitoring and visual evaluation during storage, indicated good stability under different conditions. In vivo studies confirmed the effectiveness of cosmetics containing HL extracts as natural anti-irritant agents, demonstrated by a 10% reduction in erythema after a three-week application period. These findings provide evidence supporting the use of Humulus lupulus L. in the development of plant-based cosmetic products designed to improve the health of skin prone to irritation. Full article

(This article belongs to the Section Green Materials)

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7 pages, 221 KB

Open AccessEditorial

Nanoarchitectonics in Materials Science, Second Edition

by Katsuhiko Ariga and Rawil Fakhrullin

Materials 2026, 19(4), 820; https://doi.org/10.3390/ma19040820 - 21 Feb 2026

Viewed by 444

Abstract

There are many social needs that nanoarchitectonics, as an emerging technology, can meet, such as converting and storing energy [...] Full article

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

7 pages, 217 KB

Open AccessEditorial

Obtaining and Characterization of New Materials, Volume V

by Andrei Victor Sandu

Materials 2026, 19(4), 819; https://doi.org/10.3390/ma19040819 - 21 Feb 2026

Viewed by 386

Abstract

Volume V of the Special Issue “Obtaining and Characterization of New Materials” continues to provide a multidisciplinary venue for reporting cutting-edge breakthroughs in materials science and engineering, building on the success of earlier volumes [...] Full article

(This article belongs to the Special Issue Obtaining and Characterization of New Materials (5th Edition))

15 pages, 3338 KB

Open AccessArticle

Increased Thermal Conductivity of Liquid-Phase Sintering Silicon Carbide with Ytterbium Oxide and Magnesium Oxide

by Ziting Yuan, Yuhong Chen, Fan Yang, Chaofan He, Wanxiu Hai and Meiling Liu

Materials 2026, 19(4), 818; https://doi.org/10.3390/ma19040818 - 21 Feb 2026

Viewed by 402

Abstract

Using α-SiC powder as a raw material, with ytterbium oxide and magnesium oxide as liquid-phase sintering aids, silicon carbide ceramics were prepared via spark plasma sintering (SPS) at 1900, 2000, and 2050 °C with a 10 min dwell. As the sintering temperature increased, [...] Read more.

Using α-SiC powder as a raw material, with ytterbium oxide and magnesium oxide as liquid-phase sintering aids, silicon carbide ceramics were prepared via spark plasma sintering (SPS) at 1900, 2000, and 2050 °C with a 10 min dwell. As the sintering temperature increased, the grain size grew from 0.54 μm to 17.59 μm, while the thermal conductivity correspondingly increased from 122.4 W/(m·K) to 231.8 W/(m·K). Microstructural analyses revealed that elevated sintering temperatures significantly accelerated the dissolution–precipitation process, thereby inducing abnormal grain growth. Grain size is identified as the dominant factor governing the thermal conductivity of SiC ceramics. Larger grains reduce grain boundary density and interfacial thermal resistance, thereby facilitating phonon transport. Full article

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

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22 pages, 4147 KB

Open AccessArticle

Optimization of Microbial-Induced Carbonate Precipitation Parameters for Strength, Durability, and Environmental Safety of Phosphogypsum Road Base Materials

by Peiyao Sun, Xiaodi Hu, Jiaxi He, Quantao Liu and Pan Pan

Materials 2026, 19(4), 817; https://doi.org/10.3390/ma19040817 - 20 Feb 2026

Viewed by 443

Abstract

This study investigates the mechanical properties, moisture stability, and environmental safety of microbial-induced carbonate precipitation (MICP)-treated phosphogypsum (PG)-based mixtures (MPGT) for road base utilization. Optimal cementation solution concentrations and bacterial-to-cementation solution ratios were determined via unconfined compressive strength (UCS), California bearing ratio (CBR), [...] Read more.

This study investigates the mechanical properties, moisture stability, and environmental safety of microbial-induced carbonate precipitation (MICP)-treated phosphogypsum (PG)-based mixtures (MPGT) for road base utilization. Optimal cementation solution concentrations and bacterial-to-cementation solution ratios were determined via unconfined compressive strength (UCS), California bearing ratio (CBR), and splitting tensile strength tests. Durability was compared with untreated mixtures, and enhancement mechanisms were analyzed using XRD, SEM, and FTIR. Additionally, toxicity leaching tests evaluated environmental safety. Results indicated optimal parameters of 2.0 mol/L cementation solution and a 2:1 bacterial/cementation solution ratio for maximum mechanical strength. Under these conditions, MPGT durability significantly improved compared to untreated mixtures. Mechanism analysis revealed that MICP-generated calcium carbonate coats PG particles and fills voids, enhancing strength and durability. Furthermore, F⁻ and PO₄³⁻ leaching concentrations were significantly reduced. In summary, MICP improves the mechanical performance, durability, and environmental safety of PG-based mixtures, promoting PG recycling in road engineering. Full article

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

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20 pages, 4323 KB

Open AccessArticle

Influence of Infill Density on the Fatigue Performance of FDM-Manufactured Orthopaedic Plates

by Aleksa Milovanović, Simon Sedmak, Aleksandar Sedmak, Filip Vučetić and Katarina Monkova

Materials 2026, 19(4), 816; https://doi.org/10.3390/ma19040816 - 20 Feb 2026

Cited by 1 | Viewed by 583

Abstract

Orthopaedic plates are long-established medical devices conventionally manufactured from metals, most notably titanium alloys. The introduction of Additive Manufacturing (AM) has created new opportunities to design implants with complex internal architectures, enabling precise control over infill patterns and densities that directly influence mechanical [...] Read more.

Orthopaedic plates are long-established medical devices conventionally manufactured from metals, most notably titanium alloys. The introduction of Additive Manufacturing (AM) has created new opportunities to design implants with complex internal architectures, enabling precise control over infill patterns and densities that directly influence mechanical properties and fatigue performance. Biodegradable polymers such as polylactic acid (PLA) have attracted growing interest in biomedical engineering, potentially reducing the need for secondary implant-removal surgery if degradation rates are carefully controlled and clinically approved. Additionally, AM offers the ability to customise internal structure for improved mechanical performance and load-bearing, while also providing the possibility of integrating advanced functionalities, such as controlled drug delivery. Building on previous work by our research group at the University of Belgrade, this study investigates the fatigue behaviour of the best-performing AM-optimised orthopaedic plate design. Numerical models incorporating honeycomb infill structures with the full range of achievable densities were developed to assess structural integrity under fatigue loading. Fatigue crack growth was simulated in ANSYS Mechanical (ANSYS Inc., Canonsburg, PA, USA) software, employing a four-point bending configuration in accordance with the ASTM F382 standard. A validated PLA material model was implemented at a reduced load level (10%) relative to previous studies. Direct comparison with titanium plates was avoided due to fundamentally different material properties, focusing instead on infill architecture to identify optimal AM design strategies for orthopaedic plates. Full article

(This article belongs to the Special Issue Novel Materials for Additive Manufacturing)

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17 pages, 2239 KB

Open AccessArticle

Research on Toughening and Damping Application of Epoxy Resin-Based Carbon Fiber-Reinforced Composite Material

by Wei Wang, Xueping Gao, Zhimin Li, Yishi Wang and Bo Zhu

Materials 2026, 19(4), 815; https://doi.org/10.3390/ma19040815 - 20 Feb 2026

Viewed by 583

Abstract

Carbon fiber-reinforced resin matrix composites (CFRC) are extensively used in aerospace, automotive manufacturing, and sports equipment. However, the brittle nature of the resin matrix causes CFRC to exhibit severe vibrations and noise under dry friction conditions. Enhancing the intrinsic damping properties of the [...] Read more.

Carbon fiber-reinforced resin matrix composites (CFRC) are extensively used in aerospace, automotive manufacturing, and sports equipment. However, the brittle nature of the resin matrix causes CFRC to exhibit severe vibrations and noise under dry friction conditions. Enhancing the intrinsic damping properties of the resin matrix serves as a fundamental and effective strategy to mitigate vibration and noise radiation in composite components. This study systematically investigates high-temperature co-curing damping composites using co-curing technology, aiming to improve the mechanical performance and damping characteristics of traditional fiber-reinforced epoxy resin composites. A novel carbon fiber-reinforced terminal carboxyl nitrile epoxy pre-polymer composite material demonstrates both stable chemical properties and excellent high-temperature resistance. Through formulation adjustments, the curing temperature and time of epoxy resin are matched with those of the terminal carboxyl nitrile epoxy pre-polymer. The performance of epoxy carbon fiber composites was evaluated through tensile tests, flexural tests, impact tests, infrared spectroscopy, thermogravimetric analysis, dynamic mechanical analysis, scanning electron microscopy, and X-ray diffraction. Results show that blending epoxy resin with terminal carboxyl nitrile liquid rubber enhances energy dissipation by increasing intermolecular friction and hydrogen bonding interactions. The damping ratio of epoxy resin-based carbon fiber composites reaches as high as 1.67%. Tensile strength, flexural strength, and impact strength reach 1968 MPa, 1343 MPa, and 127 kJ/m², respectively. The addition of terminal carboxylated nitrile liquid rubber facilitates the formation of continuous friction membranes, enhancing friction stability. Tensile tests demonstrate that carbon fiber composites containing 25% terminal carboxylated nitrile liquid rubber outperforms other formulations. As evidenced by impact tests, the performance of the prepared composites is superior to that of other configurations. Dynamic mechanical analysis indicates that the 25% rubber-containing composites exhibit enhanced damping characteristics and higher loss modulus. Experimental results confirm that this study advances the development of functional composites for vibration reduction and noise control applications. Full article

(This article belongs to the Section Advanced Composites)

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27 pages, 6756 KB

Open AccessArticle

Mechanical Properties and Microstructure of Environmentally Friendly Foam Concrete with Fly Ash Modified with Micro- and Nano-SiO₂

by Alexey N. Beskopylny, Sergey A. Stel’makh, Evgenii M. Shcherban’, Diana M. Shakhalieva, Andrei Chernil’nik, Natal’ya Shcherban’, Ivan Vyalikov and Aleksandr Budovskiy

Materials 2026, 19(4), 814; https://doi.org/10.3390/ma19040814 - 20 Feb 2026

Viewed by 476

Abstract

Currently, foam concrete is a prevalent energy-efficient building material, which is applicable for multiple purposes in a wide variety of buildings and structures. Improving the environmental performance of foam concrete and reducing its production costs through the use of industrial waste is a [...] Read more.

Currently, foam concrete is a prevalent energy-efficient building material, which is applicable for multiple purposes in a wide variety of buildings and structures. Improving the environmental performance of foam concrete and reducing its production costs through the use of industrial waste is a relevant and promising area. The goal of this study is to create innovative foam concrete (FC) mixtures using industrial waste, focusing on their environmentally friendly and energy-efficient properties for structural and thermal insulation purposes. The production of FC involved industrial waste products like fly ash (FA) and microsilica (MS). Nanosilica (NS) was used as an additional modifying additive. The study experimentally investigated the impact of the proposed formulation and process solutions on FC’s density, compressive strength (CS), and thermal conductivity (TC). The most effective FC modification parameters were identified for FA, MS, and NS. The best combination of 15% FA, 6% MS, and 0.4% NS produces environmentally friendly FC with improved properties: a density of 1142 kg/m³ and a TC of 0.268 W/m×°C, which are 3.8% and 15.2% lower than the control composition, respectively, and a CS of 15.1 MPa, which is 46.6% higher than the control value. Scanning Electron Microscopy (SEM) analysis validates that incorporating pozzolanic additives FA, MS, and NS into the FC composition fosters the development of more robust interpore partitions. This is due to the generation of a significant quantity of supplementary calcium hydrosilicates and a more homogenous pore structure. The structural quality factor of FC with 15% FA, 6% MS, and 0.4% NS increases to 52.4%. The structural and thermal insulation of FCs developed in this study are environmentally friendly building materials with reduced environmental impact and improved performance properties. Full article

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

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17 pages, 6063 KB

Open AccessArticle

Synergistic Effects of Steel Slag Powder and Ground Granulated Blast Furnace Slag on the Hydration and Performance of Alkali-Activated Magnesium Phosphate Cement

by Mingze Wang, Shixing Han and Guoqing Wang

Materials 2026, 19(4), 813; https://doi.org/10.3390/ma19040813 - 20 Feb 2026

Viewed by 412

Abstract

Magnesium phosphate cement (MPC) is widely used in rapid repair applications due to its fast setting, high early strength, and high-temperature resistance. However, the high cost of magnesium oxide (MgO) and the rapid hydration reaction make it challenging to control the setting time. [...] Read more.

Magnesium phosphate cement (MPC) is widely used in rapid repair applications due to its fast setting, high early strength, and high-temperature resistance. However, the high cost of magnesium oxide (MgO) and the rapid hydration reaction make it challenging to control the setting time. In this study, steel slag powder (SSP) and ground granulated blast furnace slag (GGBS) were incorporated to partially replace MgO. The reactivity of SSP and GGBS was enhanced by an alkaline activator, promoting the dissolution of their glassy phases, which facilitated the formation of C-(A)-S-H gels and improved the performance of MPC. Experimental methods, including compressive strength testing, water resistance measurements, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), mercury intrusion porosimetry (MIP), and thermogravimetric analysis (TG), were used to evaluate the 28-day compressive strength and the microstructural characteristics of the modified MPC. When both SSP and GGBS were incorporated at 10 wt.%, the modified MPC achieved a 7-day compressive strength of 37.2 MPa, with the 28-day strength increasing to 50.2 MPa. The addition of an alkali activator with a modulus of 1.3 significantly boosted the 28-day strength to 62.3 MPa, while maintaining high flowability (215 mm). Microscopic characterization revealed that C₂S and C₃S in SSP undergo continuous hydration under alkaline conditions, while reactive silica-aluminum in GGBS reacted with phosphate to form a water-resistant C-(A)-S-H gel phase, optimizing the pore structure of MPC. This study provides a novel approach to developing low-cost, high-durability modified MPC with improved performance. Full article

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

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17 pages, 5570 KB

Open AccessArticle

Microstructure and Corrosion Characteristics of IN 625 Coating on Additively Manufactured 316L Stainless Steel in As-Fabricated Condition

by Prithwish Tarafder, Lingyin Meng, Tunji Adetayo Owoseni and Johan Moverare

Materials 2026, 19(4), 812; https://doi.org/10.3390/ma19040812 - 20 Feb 2026

Viewed by 446

Abstract

The microstructure and corrosion properties of electron beam powder bed fusion (EB-PBF)-fabricated 316L stainless steel are evaluated in the as-fabricated condition with and without the deposition of IN 625 coating. Different surface profiles were achieved by introducing layer thickness and a contour scan [...] Read more.

The microstructure and corrosion properties of electron beam powder bed fusion (EB-PBF)-fabricated 316L stainless steel are evaluated in the as-fabricated condition with and without the deposition of IN 625 coating. Different surface profiles were achieved by introducing layer thickness and a contour scan strategy as process variables. A potentiodynamic polarization test was used for corrosion testing, while state-of-the-art microstructural investigation techniques were employed to elucidate a possible link between the microstructure and corrosion properties of the samples. Results from this pilot study showed that the corrosion response was dictated by the combined effects of surface roughness, coating depth, coating morphology, and passive film characteristics. For specimens for which a contour scan strategy was not used, the coating hinted to an improved corrosion potential while it increased the corrosion rate for both layer thicknesses. On the contrary, for specimens where a contour scan was applied, as-fabricated samples trended towards better corrosion resistance than the coated samples. It is shown that the dross particles that are formed during EB-PBF processing influence the flattening mechanism of the coating, ultimately resulting in a coating deposit that is characterized by surface defects, microcracks, cavities, and incoherent splat boundaries. Full article

(This article belongs to the Section Metals and Alloys)

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13 pages, 19654 KB

Open AccessArticle

Effect of Cu₂P₂O₇ on the Formation of Black Micro-Arc Oxidation Coating on AZ31 Magnesium Alloy

by Jian Chen, Hongtao Li, Bo Chen and Kun Wang

Materials 2026, 19(4), 811; https://doi.org/10.3390/ma19040811 - 20 Feb 2026

Viewed by 424

Abstract

Magnesium alloys require protective surface coatings for widespread application, with micro-arc oxidation (MAO) being a prominent technique. However, conventional MAO coatings are typically gray or light-colored, necessitating secondary treatments for specific colors like black, which complicates the process. This study aims to develop [...] Read more.

Magnesium alloys require protective surface coatings for widespread application, with micro-arc oxidation (MAO) being a prominent technique. However, conventional MAO coatings are typically gray or light-colored, necessitating secondary treatments for specific colors like black, which complicates the process. This study aims to develop a one-step method for fabricating black MAO coatings on AZ31 magnesium alloy by introducing cupric pyrophosphate (Cu₂P₂O₇) as a colorant into a silicate-based electrolyte. As the Cu₂P₂O₇ concentration increased from 0 to 5 g/L, the coating color transitioned from grayish-white to pink, then brownish-black, achieving a uniform black appearance at 4–5 g/L. XPS and EDS analyses confirmed the incorporation of copper as CuO, identified as the primary coloring agent. XRD indicated that the phase composition remained MgO, MgSiO₃, and Mg, although the MgO content decreased. Microstructural analysis showed that an optimal concentration of 4 g/L enhanced coating compactness by thickening the dense layer and reducing pore size. However, electrochemical tests revealed that the incorporation of CuO significantly increased the corrosion current density, thereby reducing the coating’s corrosion resistance compared to the unmodified coating. This work successfully demonstrates the one-step fabrication of black MAO coatings, elucidates the coloration mechanism involving CuO formation, and provides insights into the trade-off between aesthetic functionalization and corrosion performance. Full article

(This article belongs to the Special Issue Protective Coatings for Metallic Materials)

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24 pages, 7336 KB

Open AccessArticle

Effect of Waste Composite Plate Powders on the Mechanical, Durability and Microstructural Properties of Self-Compacting Mortars

by Yusuf Yıldırım, Alirıza İlker Akgönen and Serkan Etli

Materials 2026, 19(4), 810; https://doi.org/10.3390/ma19040810 - 20 Feb 2026

Viewed by 373

Abstract

This study investigates the effects of artificial plate powders with different compositions on the durability, physical, mechanical, and microstructural properties of self-compacting mortar (SCM). Waste quartz-based composite plate fragments and waste cultured marble pieces were ground into fine powders, and the resulting quartz-based [...] Read more.

This study investigates the effects of artificial plate powders with different compositions on the durability, physical, mechanical, and microstructural properties of self-compacting mortar (SCM). Waste quartz-based composite plate fragments and waste cultured marble pieces were ground into fine powders, and the resulting quartz-based plate powder (WQP) and cultured marble powder (WMP) were used as filler materials to partially replace cement at replacement levels of 0%, 5%, 10%, 15%, 20%, and 25% by mass. The workability of fresh mortars was evaluated using the mini slump flow test in accordance with EFNARC guidelines, while hardened specimens were tested for porosity, capillary water absorption, abrasion resistance, flexural strength, and compressive strength. In addition, specimens with a 25% replacement ratio that were exposed to temperatures of 300 °C, 600 °C, and 900 °C underwent mechanical testing, and their microstructures were analyzed using SEM and XRD. The results indicated that increasing replacement ratios generally reduced workability and mechanical strength, while increasing porosity and water absorption. However, low replacement levels slightly enhanced flexural strength due to the filler effect. SEM and XRD analyses revealed that the quartz in WQP maintained high thermal stability, and mortars containing WQP exhibited a denser, more coherent, and more homogeneous microstructure. Overall, the findings demonstrate that waste-based plate powders can serve as sustainable fillers in SCM, offering environmental benefits while maintaining acceptable mechanical and microstructural performance. Full article

(This article belongs to the Special Issue Sustainable Mortars and Concrete Produced with Recycled Binders, Aggregates or Water)

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29 pages, 6751 KB

Open AccessArticle

Preliminary Assessment of Quartz Sand Properties from Latvian Coastal Beaches for Potential Filtration Applications

by Yuri Dekhtyar, Renate Kalnina, Elizabete Skrebele, Hermanis Sorokins, Marks Gorohovs and Fricis Tenters

Materials 2026, 19(4), 809; https://doi.org/10.3390/ma19040809 - 20 Feb 2026

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Abstract

Understanding the environmental pathways and surface modification of beach sand grains is essential for reconstructing coastal dynamics and assessing the suitability of natural sands for engineering applications. This study applies a multiproxy approach—integrating grain roundness classification, SEM microtextural analysis, and XPS surface chemistry—to [...] Read more.

Understanding the environmental pathways and surface modification of beach sand grains is essential for reconstructing coastal dynamics and assessing the suitability of natural sands for engineering applications. This study applies a multiproxy approach—integrating grain roundness classification, SEM microtextural analysis, and XPS surface chemistry—to beach sediments from four coastal sectors of Latvia: Liepaja, Ventspils, Riga, and Salacgrīva. The results reveal clear spatial differences in grain maturity, abrasion signatures, biological imprinting, and nanoscale surface composition. Liepaja is characterised by sub-rounded to rounded grains with abundant percussion pits and abrasion surfaces, indicating prolonged high-energy wave reworking. Ventspils retains angular grains with fresh conchoidal fractures, reflecting rapid sediment renewal from glacial and coastal sources. Riga exhibits weak abrasion and hydrated particulate coatings typical of low-energy brackish environments. Salacgrīva displays strong fluvial influence, including persistent diatom and algal microtextural features and elevated oxygenated carbon and metal-associated XPS signals. These findings demonstrate strong coupling between grain-surface microtextures and surface chemistry and reveal distinct sedimentary fingerprints linked to environmental setting. The multiproxy framework presented here improves understanding of Baltic coastal sediment pathways and provides a preliminary basis for future evaluation of natural sands in filtration and other environmental engineering applications. Full article

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22 pages, 3924 KB

Open AccessArticle

Simulated Aging Studies on Porcelain Restoration Adhesives for Conservation in Chinese Museums

by Kaixun Chen, Guanqun Xu, Kai Wang, Maolin Zhang, Yanting Zhong, Feng Yuan and Zihan Li

Materials 2026, 19(4), 808; https://doi.org/10.3390/ma19040808 - 20 Feb 2026

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Abstract

The rapid development of archaeology in China has led to the excavation of numerous fragmented porcelain artifacts, for which adhesive materials play a critical role in conservation and restoration. The long-term stability of these adhesives directly affects the structural safety and visual integrity [...] Read more.

The rapid development of archaeology in China has led to the excavation of numerous fragmented porcelain artifacts, for which adhesive materials play a critical role in conservation and restoration. The long-term stability of these adhesives directly affects the structural safety and visual integrity of restored objects. In this study, four adhesives widely used in Chinese conservation practice—epoxy resin Hezhong AAA, epoxy resin Hongxing 509, acrylic resin Paraloid B-72, and cyanoacrylate adhesive 502—were systematically investigated through simulated cyclic aging experiments. A multi-analytical approach was employed, including ultra-depth-of-field microscopy, CIE Lab* colorimetric analysis, pencil hardness testing, and Fourier transform infrared spectroscopy (FTIR). The results reveal distinct aging behaviors among different adhesive types. Epoxy resin adhesives exhibit high initial hardness and pronounced hardening during aging, with coating hardness increasing from the B range to the H range after 15 aging cycles; however, they also show significant yellowing, with total color differences (ΔE) exceeding 10 and dominated by increases in the b* parameter. Paraloid B-72 maintains excellent color stability throughout aging, with ΔE values consistently below 2, although it shows limited thermal stability and delayed physical stabilization. The cyanoacrylate adhesive 502 demonstrates rapid curing and minimal discoloration but undergoes embrittlement and interfacial debonding during aging, indicating reduced long-term bonding reliability. By correlating macroscopic performance evolution with molecular-level chemical changes, this study elucidates the aging mechanisms of commonly used restoration adhesives and provides a scientific basis for adhesive selection, risk assessment, and long–term preservation strategies in porcelain conservation. Full article

(This article belongs to the Special Issue Materials in Cultural Heritage: Analysis, Testing and Preservation (Second Edition))

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20 pages, 488 KB

Open AccessArticle

Environmental Life Cycle Assessment of Selected Materials—Building Façades in Poland

by Dorota Burchart and Krzysztof Schabowicz

Materials 2026, 19(4), 807; https://doi.org/10.3390/ma19040807 - 20 Feb 2026

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Abstract

The use of sustainable building materials is becoming increasingly important in order to reduce their environmental impact. This article draws attention to the lack of life cycle assessment (LCA) of building façades, which would take into account national conditions. The aim of the [...] Read more.

The use of sustainable building materials is becoming increasingly important in order to reduce their environmental impact. This article draws attention to the lack of life cycle assessment (LCA) of building façades, which would take into account national conditions. The aim of the work is to assess the environmental impact of various building façade solutions. The analysis concerned a ventilated façade on an aluminum substructure with a fiber cement board and external thermal insulation composite system (ETICS) with expanded polystyrene (EPS). The assessed façades differed with regard to the used insulation materials. The study aims to select more ecological façades, while at the same time taking into account national conditions, which is important at the stage of designing a building. The study also aims to fill a gap in the existing literature by providing information concerning the environmental analysis of building façades based on real data. Based on a comparative analysis, it was shown that ETICSs with EPS have higher façade-damage category indicators in all impact categories except for eutrophication, human toxicity (carcinogenic and non-carcinogenic), and resource use related to minerals and metals, for which the ventilated façade shows higher values. Additionally, hot-spots for the analyzed façades were also presented. In the case of a ventilated façade, the determinant is the used insulating material, which is mineral wool. In the case of ETICS, it is the finish coat. For the first time in Poland, the LCA of a ventilated façade and ETICS was presented based on real data. The results of this study can be used as the first step of a full cradle-to-grave LCA for buildings. Full article

(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering (4th Edition))

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21 pages, 14449 KB

Open AccessArticle

Effect of Internal Curing on Early Shrinkage and Crack Resistance of UHPC by SAP and Ceramsite

by Xianqiang Wang, Jinxu Wang, Xiaonan Feng, Zaixin Yang, Jiancheng Gu and Wenqin Deng

Materials 2026, 19(4), 806; https://doi.org/10.3390/ma19040806 - 20 Feb 2026

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Abstract

This study investigated the effects of varying water–binder (w/b) ratios and internal curing materials—superabsorbent polymer (SAP) and ceramsite—on the shrinkage behavior and crack resistance of ultra-high-performance concrete (UHPC). Although internal curing has been extensively studied, the comparative effectiveness of different internal curing materials [...] Read more.

This study investigated the effects of varying water–binder (w/b) ratios and internal curing materials—superabsorbent polymer (SAP) and ceramsite—on the shrinkage behavior and crack resistance of ultra-high-performance concrete (UHPC). Although internal curing has been extensively studied, the comparative effectiveness of different internal curing materials on early-age shrinkage and restrained cracking behavior of UHPC under consistent mixture proportions remains unclear. To address this gap, a systematic experimental comparison of SAP and ceramsite was conducted. The influences of w/b ratio and different amounts and addition methods (dry and pre-absorbed addition) of SAP and ceramsite on the flowability, mechanical properties, early autogenous shrinkage, drying shrinkage, and early crack resistance of UHPC were discussed. Findings indicate that increasing the w/b ratio reduces autogenous shrinkage but compromises mechanical properties, altering the cracking mode from primary microcracks to a few wider cracks. Pre-saturated ceramsite (less than 10% volume) and SAP effectively mitigate autogenous and drying shrinkage, enhancing crack resistance without significantly reducing mechanical properties. However, exceeding a ceramsite volume dosage of 10% or using the dry addition method increased the flowability of UHPC, while decreasing crack resistance. Microstructural analysis reveals that internal curing materials facilitate hydration and enhance structural density through the formation of ettringite and calcium silicate hydrate. To optimize shrinkage reduction while maintaining mechanical properties, SAP should be incorporated in a dry state, with a dosage limited to 0.4% of the mass of the cementitious material; ceramsite needs to be pre-saturated and limited to 5% of the total volume. Full article

(This article belongs to the Special Issue Cement-Based Materials and Construction Materials: Modeling, Characterization, and Mechanical Behavior (Second Edition))

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66 pages, 8586 KB

Open AccessReview

Polyurethane Recycling: Sustainable Development Perspectives and Innovative Approaches

by Konrad Polecki, Joanna Paciorek-Sadowska, Marcin Borowicz, Marek Isbrandt and Iwona Zarzyka

Materials 2026, 19(4), 805; https://doi.org/10.3390/ma19040805 - 19 Feb 2026

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Abstract

Polyurethanes are widely used polymeric materials; their crosslinked structure and compositional diversity significantly hinder effective end-of-life management. The review emphasizes polyurethane recycling technologies, with chemical aspects discussed only insofar as they directly affect recyclability. The influence of polyol and isocyanate structure on phase [...] Read more.

Polyurethanes are widely used polymeric materials; their crosslinked structure and compositional diversity significantly hinder effective end-of-life management. The review emphasizes polyurethane recycling technologies, with chemical aspects discussed only insofar as they directly affect recyclability. The influence of polyol and isocyanate structure on phase separation, network architecture and thermal stability is discussed in the context of degradation and depolymerization mechanisms. Mechanical, chemical, thermochemical and emerging biological recycling routes are compared, with emphasis on their respective advantages, limitations and technological maturity. Mechanical recycling remains the most accessible option on an industrial scale but typically leads to reduced mechanical and thermal-insulation performance. Chemical recycling—particularly glycolysis, hydrolysis and aminolysis—enables partial recovery of polyols suitable for reuse in new polyurethane formulations, albeit at the cost of higher energy demand and increased process complexity. The environmental impact of polyurethane recycling is considered in terms of energy consumption, greenhouse-gas emissions, waste-reduction potential and alignment with circular-economy principles. Emerging biological and hybrid recycling strategies are highlighted as promising low-temperature alternatives with potential environmental benefits, despite their current low technological readiness. Key structural and technological barriers to efficient polyurethane recycling are identified, and future research directions toward improved sustainability and resource efficiency are outlined. Full article

(This article belongs to the Section Polymeric Materials)

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15 pages, 2538 KB

Open AccessArticle

Effect of Duty Cycle on Amorphous Silicon Carbon Nitride Films Deposited by Microwave Sheath–Voltage Combination Plasma

by Ippei Tanaka, Yuki Hatae and Yasunori Harada

Materials 2026, 19(4), 804; https://doi.org/10.3390/ma19040804 - 19 Feb 2026

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Abstract

This study investigates the deposition of amorphous silicon carbon nitride (a-SiCN) films using a microwave sheath–voltage combination plasma (MVP) source under duty-cycle-controlled deposition conditions. Duty ratios of 10, 30, 50, and 70% resulted in substrate temperatures of 180, 600, 980, and 1040 °C, [...] Read more.

This study investigates the deposition of amorphous silicon carbon nitride (a-SiCN) films using a microwave sheath–voltage combination plasma (MVP) source under duty-cycle-controlled deposition conditions. Duty ratios of 10, 30, 50, and 70% resulted in substrate temperatures of 180, 600, 980, and 1040 °C, respectively. The deposition rate reached a maximum of approximately 208 μm/h at a duty ratio of 30%. The atomic ratios of C, N, and Si remained nearly constant for duty ratios from 30% to 70%. X-ray diffraction confirmed that all films were amorphous. Raman spectra revealed features characteristic of amorphous carbon (a-C) for duty ratios of 30% or higher, suggesting the incorporation of a-C-like structures into the a-SiCN matrix. The film hardness increased as the duty-cycle-controlled deposition conditions shifted from 10% to 50% (180 to 980 °C), reaching a maximum of 22.65 ± 6.78 GPa at a duty ratio of 50%, and then decreased at 70% (1040 °C). These variations in hardness are suggested to be associated with coupled changes in hydrogen incorporation, C–N bonding, and the evolution of sp²-rich carbon clustering (graphite-like short-range ordering) under elevated temperature and ion-bombardment conditions. Full article

(This article belongs to the Special Issue Properties and Applications of New Coating Materials)

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12 pages, 2453 KB

Open AccessArticle

Lightweight Ultra-Wideband Absorbing Metamaterials Based on Multi-Dimensional Structural Design

by Aixiong Ge, Shaobo Qu and Baocai Xu

Materials 2026, 19(4), 803; https://doi.org/10.3390/ma19040803 - 19 Feb 2026

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Abstract

Addressing the technical bottlenecks of excessive surface density in traditional magnetic metal powder absorbers and excessive thickness in conventional foam-based absorbers, this study proposes a novel lightweight, ultra-wideband microwave-absorbing metamaterial. This metamaterial, through multi-layer and multi-dimensional structural design, has constructed a composite structure [...] Read more.

Addressing the technical bottlenecks of excessive surface density in traditional magnetic metal powder absorbers and excessive thickness in conventional foam-based absorbers, this study proposes a novel lightweight, ultra-wideband microwave-absorbing metamaterial. This metamaterial, through multi-layer and multi-dimensional structural design, has constructed a composite structure composed of a resistive film frequency-selective surface, a foam wave-absorbing medium layer and a reflective layer, achieving the controllable regulation of microwave absorption performance and the integration of structure and function. The research results show that the fabricated absorbing metamaterial achieves efficient electromagnetic wave absorption over a wide frequency band of 94 GHz under the ultra-light and ultra-thin conditions with a density as low as 0.078 g/cm³ and a thickness of only 4.9 mm. This study provides an effective design concept and solution for developing new lightweight, thin-layer, wide-band, and highly microwave-absorbing materials. Full article

(This article belongs to the Section Materials Physics)

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11 pages, 3925 KB

Open AccessCommunication

Fabrication and Characterization of Binary Ti-Al and Ti-Si Thin-Film Metallic Glasses

by Vidžaja Knap, Petr Vlcak, Margit Žaloudková, Tomáš Horažďovský, Jan Drahokoupil, Ján Sovík, Jaroslav Fojt, Jaroslav Lukeš, Vojtěch Smola and Zdeněk Weiss

Materials 2026, 19(4), 802; https://doi.org/10.3390/ma19040802 - 19 Feb 2026

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Abstract

This study investigates the fabrication and characterization of binary Ti-Si and Ti-Al thin-film metallic glasses (TFMGs) deposited via electron beam evaporation on cp Ti and Si substrates. X-ray diffraction confirmed the amorphous structure of the Ti₈₉Si₁₁ and Ti₅₅Al [...] Read more.

This study investigates the fabrication and characterization of binary Ti-Si and Ti-Al thin-film metallic glasses (TFMGs) deposited via electron beam evaporation on cp Ti and Si substrates. X-ray diffraction confirmed the amorphous structure of the Ti₈₉Si₁₁ and Ti₅₅Al₄₅ thin films. AFM revealed differences in surface roughness, with Ti₈₉Si₁₁ exhibiting a smoother surface (Ra = 0.9 nm) than Ti₅₅Al₄₅ (Ra = 1.6 nm), likely due to differences in atomic size mismatch, heat of mixing, and potential oxidation effects. Electrochemical tests in Hank’s solution demonstrated the superior corrosion resistance of Ti₈₉Si₁₁, which had the lowest i_corr (0.123 µA/cm²) and widest passive region compared to Ti₅₅Al₄₅ and reference materials (cp Ti and SS316L). Mechanical properties revealed that both TFMGs exhibit higher indentation hardness and comparable reduced elastic modulus to cp Ti, with Ti₅₅Al₄₅ showing the highest hardness (5.93 ± 0.37 GPa). These findings highlight the potential of Ti-Si and Ti-Al TFMGs as high-performance materials for biomedical coatings. Full article

(This article belongs to the Special Issue Advanced Coatings and Films for Corrosion Resistance and Surface Engineering of Light Metal Alloys)

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20 pages, 2638 KB

Open AccessArticle

Spectroscopic Properties of Tb³⁺ Ions in TbF₃-Doped CaF₂ Crystals

by Irinuca Bodea, Marius Stef, Carla Schornig, Gabriel Buse, Philippe Veber and Daniel Vizman

Materials 2026, 19(4), 801; https://doi.org/10.3390/ma19040801 - 18 Feb 2026

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Abstract

Tb³⁺-doped CaF₂ single crystals are attractive materials for green photonic applications due to their low phonon energy, high optical transparency, and efficient Tb³⁺ emission. In this work, CaF₂ single crystals doped with different TbF₃ concentrations (1, 5, [...] Read more.

Tb³⁺-doped CaF₂ single crystals are attractive materials for green photonic applications due to their low phonon energy, high optical transparency, and efficient Tb³⁺ emission. In this work, CaF₂ single crystals doped with different TbF₃ concentrations (1, 5, and 10 mol%) were grown and systematically investigated in order to clarify the concentration-dependent spectroscopic behavior of Tb³⁺ ions in a fluorite host. Optical absorption spectroscopy, Judd–Ofelt analysis, steady-state and time-resolved photoluminescence, colorimetric evaluation, and emission cross-section and gain calculations were employed. Judd–Ofelt intensity parameters typical of fluoride hosts were obtained, enabling the calculation of radiative transition probabilities and lifetimes. The emission spectra are dominated by intense green luminescence from the ⁵D₄ → ⁷F₅ transition, while the absence of ⁵D₃ emission is attributed to efficient cross-relaxation processes. Fluorescence lifetimes in the millisecond range show slight changes with Tb³⁺ concentration. Quantum efficiency increases from low to intermediate concentrations and tends to saturate at higher doping levels. CIE 1931 chromaticity coordinates confirm stable green emission, while emission cross-sections and gain parameters reveal a highest value for orange emission of 10 mol% TbF₃-doped CaF₂ crystal. These results indicate that CaF₂:Tb³⁺ single crystals are promising materials for photonic applications. Full article

(This article belongs to the Section Optical and Photonic Materials)

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13 pages, 2885 KB

Open AccessArticle

Effect of Growth Orientation on the Standard Heat Treatment Microstructure of Nickel-Based Single-Crystal Superalloy DD6

by Zhenyu Yang, Xiaogong Liu, Ji Wang, Zhiqiang Yang, Songsong Hu, Jian Zhang, Yushi Luo and Shenglong Dai

Materials 2026, 19(4), 800; https://doi.org/10.3390/ma19040800 - 18 Feb 2026

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Abstract

Using the seeding method, nickel-based single-crystal superalloy DD6 specimens with different growth orientations were prepared in a liquid metal cooling (LMC) directional solidification furnace. Subsequent standard heat treatment was carried out, and the influence of growth orientation on the microstructure of the (001) [...] Read more.

Using the seeding method, nickel-based single-crystal superalloy DD6 specimens with different growth orientations were prepared in a liquid metal cooling (LMC) directional solidification furnace. Subsequent standard heat treatment was carried out, and the influence of growth orientation on the microstructure of the (001) crystal plane of the alloy after heat treatment was investigated. Results show that with the increase in growth orientation deviation angle from the <001> orientation, the area fraction of residual eutectic content is reduced, the average size and volume of pore and γ′ strengthening phase increase, and the cubicity of the γ′ strengthening phase decreases. The growth orientation does not significantly affect the morphology of residual eutectic content or the morphology of the strengthening phase of the γ′ in the dendrite cores and interdendrite regions. However, the size uniformity of the γ′ strengthening phase in dendrite cores and the width of the γ matrix channels decrease as the growth orientation deviation angle increases. Full article

(This article belongs to the Special Issue Advanced High-Performance Metals and Alloys: Microstructural Evolution, Mechanical Properties, and Strengthening Mechanisms)

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17 pages, 3585 KB

Open AccessArticle

Feasibility Study of Manufacturing Hydraulic Fittings Using Additive Manufacturing Technologies: Comparative Analysis of FDM and SLA Methods

by Jakub Backiel, Pawel Dzienis, Karol Golak, Przemysław Zamojski, Maciej Rećko, Rafał Grądzki, José Emiliano Martínez and Rogelio Valdés

Materials 2026, 19(4), 799; https://doi.org/10.3390/ma19040799 - 18 Feb 2026

Viewed by 375

Abstract

This paper investigates the feasibility of manufacturing hydraulic fittings using additive manufacturing (AM) technologies, specifically Fused Deposition Modeling (FDM) and Stereolithography (SLA). The study addresses the environmental challenge of material waste in conventional fitting production by exploring 3D printing as an alternative manufacturing [...] Read more.

This paper investigates the feasibility of manufacturing hydraulic fittings using additive manufacturing (AM) technologies, specifically Fused Deposition Modeling (FDM) and Stereolithography (SLA). The study addresses the environmental challenge of material waste in conventional fitting production by exploring 3D printing as an alternative manufacturing method. Hydraulic fittings were designed using CAD software: SolidWorks 2022 and fabricated using FDM with PETG (Polyethene Terephthalate Glycol) material and SLA with UV-sensitive photopolymer resin. In present studies, on-destructive leak testing was conducted in accordance with PN-EN 1254-4 and PN-EN 1254, at pressures ranging from 0.1 to 1.0 bar. Dimensional accuracy analysis revealed shrinkage of approximately 1% for SLA-printed parts and 2% for FDM-printed parts. Microscopic examination at 50× and 80× magnification showed superior thread quality in SLA samples compared to FDM, which exhibited visible layer separation and material porosity. Leak testing demonstrated that while the brass reference fitting maintained complete seal integrity, both 3D-printed variants failed to achieve leak tightness under operational pressures, with structural failure occurring at 1.0 bar during tightening. The study showed that FDM with PETG material and SLA with UV-sensitive photopolymer resin, despite achieving acceptable dimensional tolerances (±1–2%), do not meet hydraulic leak tightness requirements at pressures exceeding 0.5 bar in their raw state after printing. The results suggest that alternative material formulations (e.g., carbon fiber-reinforced PEEK for FDM or epoxy engineering resins for SLA) warrant further investigation. Potential avenues for improvement include advanced surface treatment, optimization of printing parameters, and modifications to thread geometry to reduce interthread gaps. Full article

(This article belongs to the Topic 3D Printing Materials: An Option for Sustainability)

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14 pages, 1385 KB

Open AccessArticle

Study on the Evolution Mechanism of Carbon Impurities in Polysilicon Production Based on HSC Simulation

by Yu Hou, Xueqian Lv and Guoqiang Huang

Materials 2026, 19(4), 798; https://doi.org/10.3390/ma19040798 - 18 Feb 2026

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Abstract

The existing forms and evolution mechanisms of carbon impurities constitute the core scientific issue in the optimization of polysilicon purification processes. The depth of research on this issue directly determines the targeting and effectiveness of directional impurity removal strategies, and is even a [...] Read more.

The existing forms and evolution mechanisms of carbon impurities constitute the core scientific issue in the optimization of polysilicon purification processes. The depth of research on this issue directly determines the targeting and effectiveness of directional impurity removal strategies, and is even a key prerequisite for improving the quality and reducing the cost of polysilicon products. Based on HSC simulation calculations and using the Gibbs free energy of reactions as the judgment criterion, this paper investigated the existing forms and evolution mechanism of carbon impurities during the production of polysilicon via the modified Siemens process. The results show that the evolution mechanism of carbon impurities is as follows: the solute carbon in silicon powder reacts with hydrogen to generate CH₄. Subsequently, CH₄ synergistically undergoes radical rearrangement and the Rochow reaction with methylchlorosilanes in chlorosilane and CH₄ in recovered hydrogen. Meanwhile, CH₃· radicals combine with radicals generated from chlorosilanes to form a mixture of methylchlorosilanes dominated by SiH(CH₃)Cl₂ as well as CH₄. After distillation purification, SiH(CH₃)Cl₂ enters the SiHCl₃ stream, and then synergistically undergoes cracking and radical rearrangement with CH₄ in high-purity hydrogen, the solid-soluble elemental carbon forms and deposits in polysilicon. Simultaneously, a mixture of methylchlorosilanes dominated by SiH(CH₃)Cl₂ along with CH₄ is generated and then fed into the tail gas system. This will provide the necessary theoretical foundation for the development of efficient and low-cost impurity removal strategies. Full article

(This article belongs to the Topic Advanced Materials in Chemical Engineering)

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