Materials

16 pages, 8169 KiB

Open AccessArticle

The Wear Resistance of NiCrSiB-20%CaF₂ Sinters in the Temperature Range 23–600 °C

by Adam Piasecki, Mateusz Kotkowiak, Oleksandr Tisov, Bartosz Gapiński, Michał Jakubowicz, Julia Sobkowiak, Maciej Tuliński and Stanisław Legutko

Materials 2025, 18(7), 1405; https://doi.org/10.3390/ma18071405 (registering DOI) - 21 Mar 2025

Abstract

In this work, powder metallurgy was used in order to produce self-lubricating composite materials. The NiCrSiB alloy as a matrix of the sinters and 20 wt. % CaF₂ as a solid lubricant were used. The sinters were subjected to wear tests using [...] Read more.

In this work, powder metallurgy was used in order to produce self-lubricating composite materials. The NiCrSiB alloy as a matrix of the sinters and 20 wt. % CaF₂ as a solid lubricant were used. The sinters were subjected to wear tests using the pin-on-disc method at four different temperatures (room temperature (RT), 200, 400, and 600 °C). The coefficients of friction of the friction pairs were determined, and research on their wear mechanism was carried out. For this purpose, research techniques such as Light Microscopy (LM), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), and profilometer were used. Based on the conducted tests, it was found that CaF₂ was smeared on the surfaces of the samples and counter-specimens, particularly at elevated temperatures. Moreover, it was found that micro-cutting and micro-ploughing are the major wear of the friction pairs at room temperature, while with the increasing temperature, they were dominated by the reduction of such mechanisms, which is associated with the formation of a tribofilm composed of CaF₂ and oxidation wear. Full article

20 pages, 1024 KiB

Open AccessArticle

Computationally Efficient p-Version Finite Element Analysis of Composite-Reinforced Thin-Walled Cylindrical Shells with Circumferential Cracks

by Jae S. Ahn

Materials 2025, 18(7), 1404; https://doi.org/10.3390/ma18071404 (registering DOI) - 21 Mar 2025

Abstract

Cylindrical shells are extensively employed in fluid transport, pressure vessels, and aerospace structures, where they endure mechanical and environmental stresses. However, under high pressure or external loading, circumferential cracks may develop, threatening structural integrity. Composite patch reinforcement is an effective method to mitigate [...] Read more.

Cylindrical shells are extensively employed in fluid transport, pressure vessels, and aerospace structures, where they endure mechanical and environmental stresses. However, under high pressure or external loading, circumferential cracks may develop, threatening structural integrity. Composite patch reinforcement is an effective method to mitigate crack propagation and restore structural performance. This study presents a finite element model using p-refinement techniques to analyze cylindrical shells with circumferential cracks reinforced by composite patches. The approach integrates equivalent single-layer (ESL) and layer-wise (LW) theories within a unified single-element mesh, significantly reducing the degrees of freedom compared to conventional LW models. Fracture analysis is conducted using the virtual crack closure technique (VCCT) to evaluate stress intensity factors. The model’s accuracy and efficiency are verified through benchmark and patch reinforcement simulations. Additionally, a parametric study examines how patch material, thickness, and adhesive properties affect reinforcement efficiency across varying crack angles. This study provides an effective methodology for analyzing composite-reinforced thin-walled cylindrical shells, offering valuable insights for aerospace, marine, and pipeline engineering. Full article

(This article belongs to the Special Issue Mechanics of Thin-Walled Structures and Other Lightweight Constructions)

14 pages, 787 KiB

Open AccessArticle

Crystallization Phase Regulation of BaO-CaO-SiO₂ Glass-Ceramics with High Thermal Expansion Coefficient

by Haonan Hu, Yongyuan Liang, Qifan Guan, Feng Liu, Mingsheng Ma, Yongxiang Li and Zhifu Liu

Materials 2025, 18(7), 1403; https://doi.org/10.3390/ma18071403 - 21 Mar 2025

Abstract

In this work, the influence of Ba/Ca ratios on the BaO-CaO-SiO₂ (BCS) glass network structure, crystallization phases, and coefficient of thermal expansion (CTE) was investigated. As the Ba/Ca ratio increases, the Qⁿ units in the glass network structure have undergone significant [...] Read more.

In this work, the influence of Ba/Ca ratios on the BaO-CaO-SiO₂ (BCS) glass network structure, crystallization phases, and coefficient of thermal expansion (CTE) was investigated. As the Ba/Ca ratio increases, the Qⁿ units in the glass network structure have undergone significant changes. The Q⁴ units in the BCS glass network transform into Q³ units, indicating the reduction of the glass network connectivity. The variation in the Ba/Ca ratio leads to a change in the crystallization phases of BCS glass-ceramics sintered at a temperature higher than Tc (crystallization temperature). The addition of α-SiO₂(quartz) could regulate the crystallization phases and their ratio of the barium silicates (BaSi₂O₅, Ba₂Si₃O₈, and Ba₅Si₈O₂₁) in the BCS glass-ceramics. An abundant orthorhombic BaSi₂O₅ phase can be obtained in the BCS glass-ceramics with 15 wt% α-SiO₂ calcinated over 875 °C. The α-SiO₂ modified BCS glass-ceramics exhibited excellent properties (CTE = 12.10 ppm/°C, ε_r = 7.49 @ 13.4 GHz, tanδ = 4.96 × 10⁻⁴, Q × f = 27,034 GHz) sintered at optimized conditions, making it a promising candidate material for RF module and electronic packaging substrate. Full article

25 pages, 2739 KiB

Open AccessArticle

Analysis of the Strength of Polyamide Used for High Pressure Transmission of Hydrogen on the Example of Reinforced Plastic Hoses

by Natalia Dawicka, Beata Kurc, Xymena Gross, Jakub Tomasz, Katarzyna Siwińska-Ciesielczyk and Agnieszka Kołodziejczak-Radzimska

Materials 2025, 18(7), 1402; https://doi.org/10.3390/ma18071402 - 21 Mar 2025

Abstract

The purpose of this study is to evaluate the strength of polyamide utilized in high pressure hydrogen transmission, exemplified by reinforced plastic hoses. The research encompasses a comprehensive investigation of materials employed in hydrogen infrastructure, focusing on their barrier and mechanical properties. It [...] Read more.

The purpose of this study is to evaluate the strength of polyamide utilized in high pressure hydrogen transmission, exemplified by reinforced plastic hoses. The research encompasses a comprehensive investigation of materials employed in hydrogen infrastructure, focusing on their barrier and mechanical properties. It addresses challenges associated with hydrogen storage and transport, presenting various types of tanks and hoses commonly used in the industry and detailing the materials used in their construction, such as metals and polymers. Two materials were analyzed in the study; one new material and one material exposed to hydrogen. Key mechanisms and factors affecting gas permeation in materials are discussed, including an analysis of parameters such as fractional free volume (FFV), solubility coefficient (S), diffusion coefficient, and permeability coefficient. Methods for evaluating material permeation were outlined, as they are essential for assessing suitability in hydrogen infrastructure. Experimental analyses included Fourier Transform Infrared Spectroscopy (ATR), differential thermal analysis (DTA), scanning electron microscopy (SEM), and Energy dispersive X-ray spectroscopy (EDS). These techniques provided detailed insights into the structure and properties of polyamide, allowing for an assessment of its performance under high pressure hydrogen conditions. Pressure was identified as a critical factor influencing both the material’s mechanical strength and its hydrogen transport capability, as it affects the quantity of adsorbed particles. According to the DTA investigation, the polyamide demonstrates minimal mass loss at lower temperatures, indicating a low risk of material degradation. However, its performance declines significantly at higher temperatures (above 350 °C). Up to 250 °C, the material shows no notable decomposition occurred, suggesting its suitability for certain applications. The presence of functional groups was found to play a significant role in gas permeation, highlighting the importance of detailed physicochemical analysis. XRD studies revealed that hydrogen exposure did not significantly alter the internal structure of polyamide. These findings suggest that the structure of polyamide is well-suited for operation under specific conditions, making it a promising candidate for use in hydrogen infrastructure. However, the study also highlights areas where further research and optimization are needed. Overall, this work provides valuable insights into the properties of polyamide and its potential applications in hydrogen systems. Full article

(This article belongs to the Special Issue Advanced Polymers and Composites for Multifunctional Applications)

17 pages, 6753 KiB

Open AccessArticle

Microstructure of CuCrZrV and ODS(Y₂O₃)-Cu Alloys After Neutron Irradiation at 150, 350, and 450 °C to 2.5 dpa

by Michael Klimenkov, Carsten Bonnekoh, Ute Jaentsch, Michael Rieth, Hans-Christian Schneider, Dmitry Terentyev, Koray Iroc and Wouter Van Renterghem

Materials 2025, 18(7), 1401; https://doi.org/10.3390/ma18071401 - 21 Mar 2025

Abstract

In this study, the results of transmission electron microscopy (TEM) examinations of neutron-irradiated (2.5 dpa at 150 °C, 350 °C, and 450 °C) CuCrZrV and ODS(Y₂O₃)-Cu alloys are presented. These materials were developed for application as heat sink materials [...] Read more.

In this study, the results of transmission electron microscopy (TEM) examinations of neutron-irradiated (2.5 dpa at 150 °C, 350 °C, and 450 °C) CuCrZrV and ODS(Y₂O₃)-Cu alloys are presented. These materials were developed for application as heat sink materials in fusion technology. This study includes TEM imaging and quantitative analysis of neutron radiation-induced defects such as dislocation loops and voids as well as the determination of the conditions for their formation. It was found that dislocation loops of a₀½⟨110⟩ type form in both alloys at all irradiation temperatures. The formation of voids in CuCrZrV alloy is effectively suppressed. The neutron irradiation causes a redistribution of Cr, Zr, and V in the CuCrZrV alloy. A particular focus was on the investigation of the distribution of the transmutation products Ni and Zn. Ni tends to segregate at the Cr-rich clusters and forms a shell around them, while Zn is evenly distributed. Full article

(This article belongs to the Special Issue Mechanical Behavior and Radiation Response of Materials)

12 pages, 5015 KiB

Open AccessArticle

6-(4-Pyridyl)Azulene Derivatives as Hole Transport Materials for Perovskite Solar Cells

by Yuanqing Sun, Zhangyan Wang, Tianyi Geng, Xinyue Liu, Yangyang Su, Yi Tian, Ming Cheng and Hongping Li

Materials 2025, 18(7), 1400; https://doi.org/10.3390/ma18071400 - 21 Mar 2025

Abstract

Azulene has been attracting much attention as a charge transfer material in organic electronics due to its inherent large dipole moment and small band gap, but its application in perovskite solar cells (PSCs) is very limited. Herein, azulene was applied as the core [...] Read more.

Azulene has been attracting much attention as a charge transfer material in organic electronics due to its inherent large dipole moment and small band gap, but its application in perovskite solar cells (PSCs) is very limited. Herein, azulene was applied as the core acceptor for hole transport materials (HTMs), and two molecules named Azu-Py-DF and Azu-Py-OMeTPA were designed and synthesized, in which 4-pyridyl was introduced on the 6-position of the 1,3-substituted azulene core to adjust energy levels. The different spatial orientations of pyridine and the azulene core improve the solubility and reduce the crystallinity of the material, which is conducive to creating a thin film morphology. Azu-Py-OMeTPA exhibited good hole and electron mobility compared with standard Spiro-OMeTAD. Applied as an HTM in PSCs, the Azu-Py-OMeTPA-based device achieved a power conversion efficiency (PCE) of 18.10%, which is higher than that of the 6-position unsubstituted counterpart. Nevertheless, the anticipated passivation effect of the 4-pyridyl group was diminished due to the electron-deficient nature of azulene’s seven-membered ring. These results demonstrate that optimizing the structure of azulene-based HTMs can significantly alter molecular spatial structure, film formation properties, electron delocalization characteristics and charge transport, and can lead to improved device performance, providing insights for the future design of novel HTMs. Full article

(This article belongs to the Section Energy Materials)

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13 pages, 7667 KiB

Open AccessArticle

The Effect of B₂O₃ Doping on the Properties of Electrical and Thermal Conductivity for SnO₂ Varistors

by Siqiao Gong and Hongfeng Zhao

Materials 2025, 18(7), 1399; https://doi.org/10.3390/ma18071399 - 21 Mar 2025

Abstract

This study investigates SnO₂-based varistors in the SnO₂-Co₃O₄-Cr₂O₃-Nb₂O₅ system with varying B₂O₃ doping concentrations to optimize both electrical properties and thermal conductivity. The experimental formulation [...] Read more.

This study investigates SnO₂-based varistors in the SnO₂-Co₃O₄-Cr₂O₃-Nb₂O₅ system with varying B₂O₃ doping concentrations to optimize both electrical properties and thermal conductivity. The experimental formulation involved doping B₂O₃ with fixed concentration ratios of Co₃O₄, Cr₂O₃, and Nb₂O₅ (ranging from 0 mol% to 0.35 mol%), and the microstructure, electrical properties, and thermoelectric coefficient of the samples were measured in order to identify the optimal doping proportion. The varistor doped with 0.25 mol% B₂O₃ exhibited optimal performance, demonstrating a maximum voltage gradient of 525 V/mm, a minimum leakage current density of 11.2 μA/cm², and a peak nonlinear coefficient of 36. Furthermore, the optimized formulation achieved enhanced thermal performance with a maximum thermal conductivity of 6.13 W·m⁻¹·K⁻¹. Full article

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18 pages, 74287 KiB

Open AccessArticle

Graining and Texturing of Metal Surfaces by Picosecond Laser Treatment

by Carmelo Corsaro, Fortunato Neri, Paolo Maria Ossi, Domenico Bonanno, Priscilla Pelleriti and Enza Fazio

Materials 2025, 18(7), 1398; https://doi.org/10.3390/ma18071398 - 21 Mar 2025

Abstract

Different approaches have been proposed to control the tribological behavior of materials under different conformal and non-conformal contact conditions with influenced surface texturing. The ever-increasing demand to improve material friction, erosion wear, and adhesion bond strength of coatings is a major concern for [...] Read more.

Different approaches have been proposed to control the tribological behavior of materials under different conformal and non-conformal contact conditions with influenced surface texturing. The ever-increasing demand to improve material friction, erosion wear, and adhesion bond strength of coatings is a major concern for the contact interface of surfaces. Laser texturing is considered a promising approach to tuning materials’ tribological properties. The latter are strongly influenced by the texture density and shape imprinted on the engineered materials and vary in dry or lubricating conditions. In this work, the physicochemical properties of picosecond laser-textured surfaces of metallic materials have been systematically analyzed. Specifically, the wettability character of laser-textured materials was correlated with their morphological/compositional features. Full article

(This article belongs to the Section Materials Physics)

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19 pages, 6167 KiB

Open AccessReview

Additive Manufacturing and Influencing Factors of Lattice Structures: A Review

by Jinlin Yang, Hui Liu, Gaoshen Cai and Haozhe Jin

Materials 2025, 18(7), 1397; https://doi.org/10.3390/ma18071397 - 21 Mar 2025

Abstract

Lattice structures have the characteristics of light weight, excellent heat dissipation and mechanical properties. Because of excellent properties, lattice structures have been widely used in aerospace, automobile manufacturing, biomedical and other fields. At present, additive manufacturing is the mainstream method for manufacturing lattice [...] Read more.

Lattice structures have the characteristics of light weight, excellent heat dissipation and mechanical properties. Because of excellent properties, lattice structures have been widely used in aerospace, automobile manufacturing, biomedical and other fields. At present, additive manufacturing is the mainstream method for manufacturing lattice structures. This study reviews the existing literature on additive manufacturing of lattice structures, introduces manufacturing methods, and summarizes the influencing factors of forming quality. In addition, the topology optimization of the unit cell and the gradient design of the lattice structure are discussed, and the future research direction of the lattice structure is proposed. Full article

(This article belongs to the Special Issue Design and Application of Additive Manufacturing: 3rd Edition)

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18 pages, 7109 KiB

Open AccessArticle

Study on the Process Parameters and Corrosion Resistance of FeCoNiCrAl High Entropy Alloy Coating Prepared by Atmospheric Plasma Spraying

by Miao Zhang, Yu Zhang, Pengyu Dai, Lin Zhao, Liping Wu and Shendian Li

Materials 2025, 18(7), 1396; https://doi.org/10.3390/ma18071396 - 21 Mar 2025

Abstract

FeCoNiCrAl high-entropy alloy (HEA) coating was prepared by air plasma spraying, and the coating’s morphology and properties under different power parameters were analyzed. The results show that the spraying power significantly affects the morphology of the coating during plasma spraying. The molten droplets [...] Read more.

FeCoNiCrAl high-entropy alloy (HEA) coating was prepared by air plasma spraying, and the coating’s morphology and properties under different power parameters were analyzed. The results show that the spraying power significantly affects the morphology of the coating during plasma spraying. The molten droplets formed during the preparation process of HEA coatings tend to combine with oxygen, with aluminum bonding particularly strongly with oxygen, resulting in the presence of aluminum oxide within the coating, while other elements exhibit weaker bonding with oxygen. The optimal spraying power is 12 kW, and coatings prepared at this optimal power exhibit advantages such as low porosity, uniform element distribution, and excellent corrosion resistance. The aluminum in the HEA coating forms a relatively stable compound with oxygen, creating a Cr-depleted and Al-enriched region. This region is less prone to passivation during corrosion and more susceptible to reacting with corrosive media, leading to localized corrosion of the coating. Full article

(This article belongs to the Special Issue Metallic and Ceramic Materials Integrity—Surface Engineering for Wear, Corrosion and Erosion Prevention (2nd Edition))

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26 pages, 7318 KiB

Open AccessArticle

A Modified Trilinear Post-Cracking Model for Fiber-Reinforced Concrete to Improve the Evaluation of the Serviceability Limit State Performance

by Fan Zhang, Wouter De Corte, Xian Liu, Yihai Bao and Luc Taerwe

Materials 2025, 18(7), 1395; https://doi.org/10.3390/ma18071395 - 21 Mar 2025

Abstract

An accurate constitutive model for fiber-reinforced concrete (FRC) is fundamental for analyzing and designing FRC structures. The recently released fib Model Code 2020 (MC2020) includes significant modifications to the tensile constitutive model for FRC, enhancing its accuracy. However, it has been observed that [...] Read more.

An accurate constitutive model for fiber-reinforced concrete (FRC) is fundamental for analyzing and designing FRC structures. The recently released fib Model Code 2020 (MC2020) includes significant modifications to the tensile constitutive model for FRC, enhancing its accuracy. However, it has been observed that the applicability of this model for certain types of FRC is limited due to its overly simplified post-cracking mechanical assumptions. This is particularly evident in structural FRC, where the fiber pull-out force reaches its maximum at a large fiber slip, resulting in a load decrease before increasing again after the notched beam cracks. In that case, the bilinear assumption in the stress–strain model of MC2020 for post-cracking is insufficient to reflect the fiber mechanism and the mechanical properties of FRC at small crack widths. Therefore, based on the characteristics of fiber pull-out in structural FRC, this paper proposes a trilinear post-cracking stress–strain model to reflect the fiber pull-out mechanism more accurately and better analyze the performance of FRC structures in the serviceability limit state. Through an analysis of experimental data and numerical simulation studies on steel fiber-reinforced concrete (SFRC) notched beams, the parameters for the proposed trilinear constitutive model are determined and validated, and the results indicate that the stress value at the new inflection point in the post-cracking trilinear model should be 0.8f_Fts (the serviceability residual strength of the FRC). Although the proposed trilinear model seems similar to the trilinear model provided in MC2020, it is developed based on fiber pull-out behavior, whereas the trilinear model in MC2020 was mainly developed to eliminate numerical singularities. Finally, while the models in MC2020 perform well in evaluating the ultimate limit state performance, the proposed constitutive model can serve as a supplement, especially when serviceability limit state performance is considered. Full article

(This article belongs to the Special Issue Advanced Computational Methods in Manufacturing Processes)

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15 pages, 3912 KiB

Open AccessArticle

Treatment of Aqueous Amoxicillin Solutions with Sunlight Using a Pelletized Macrocomposite Photocatalyst

by Saad Slimani Tlemcani, Zenydia Marín, J. Arturo Santaballa and Moisés Canle

Materials 2025, 18(7), 1394; https://doi.org/10.3390/ma18071394 - 21 Mar 2025

Abstract

We report on the preparation and characterization of a cost-effective, durable, and reusable macrocomposite, prepared in the form of pellets and designed for the photodegradation of water pollutants, using amoxicillin (AMX) as a model compound. Using the wet impregnation method, kaolin clay and [...] Read more.

We report on the preparation and characterization of a cost-effective, durable, and reusable macrocomposite, prepared in the form of pellets and designed for the photodegradation of water pollutants, using amoxicillin (AMX) as a model compound. Using the wet impregnation method, kaolin clay and TiO₂-P25 composites were doped with copper (Cu²⁺) and cobalt (Co²⁺). The produced materials were characterized by SEM-EDS, XRD, XRF, textural property analysis, and their potential lixiviation of components by ICP-MS. The photodegradation efficiency under solar irradiation was evaluated by varying the acidity of the medium, the concentration of AMX, and the amount of catalyst. The performance of the recycled photocatalysts was also studied. The photodegradation of AMX was monitored by UV–Vis and UV–Vis/HPLC spectrophotometry. The optimal formulations, Cu (0.1%)/TiO₂ and Co (0.1%)/TiO₂, achieved up to 95% degradation of 5 mg·L⁻¹ AMX in 3 h at pH 5.9, with a catalyst loading of 1 g·L⁻¹. The Cu-doped material showed a slightly faster reaction rate and higher total-organic-carbon removal (80.4%) compared to the Co-doped material (59%) under identical conditions. The same photodegradation intermediates were identified by LC-MS/MS for both doped macrocomposites, and a reaction mechanism is proposed. These macrocomposites showed efficient and consistent recyclability over more than five reuse cycles, showing their potential to be used for antibiotic pollution abatement in water-treatment facilities. Full article

(This article belongs to the Special Issue Photocatalysis for a Green Future: Breaking Barriers in Energy, Environment, and Healthcare)

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17 pages, 2516 KiB

Open AccessArticle

Seed-Assisted Crystallization in the Hydrothermal Synthesis of FAU Zeolite from Acid-Treated Residue Glass Powder

by Paulla B. F. Sousa, Lindiane Bieseki and Sibele B. C. Pergher

Materials 2025, 18(7), 1393; https://doi.org/10.3390/ma18071393 - 21 Mar 2025

Abstract

A simple and low-cost synthesis assisted by seed crystals has been proposed to convert residual colorless glass powder into a Na-X zeolite. For this purpose, the optimal parameters for acid leaching of glass powder were studied to remove impurities that could interfere with [...] Read more.

A simple and low-cost synthesis assisted by seed crystals has been proposed to convert residual colorless glass powder into a Na-X zeolite. For this purpose, the optimal parameters for acid leaching of glass powder were studied to remove impurities that could interfere with the crystallization process. Then, the hydrothermal syntheses were supported by Na-X seed crystals (0% to 5%, wt.) to induce the growth of zeolite X, evaluating the crystallization time (12 h to 48 h) and the variation of the silicon source (acid-treated and untreated residues). The formation of the faujasite as the main phase, with a higher degree of structural order and microporosity, was observed with the previous treatment in the residue, a higher seed loading, and a shorter crystallization time. On the other hand, a phase competition between faujasite, gismondine, Linde type-A, and sodalite structures was observed in the zeolites synthesized from the untreated residue. In this case, the high seed loading and the longer synthesis time allowed the correct targeting of the faujasite structure with low structural order and micro/mesoporous properties. Furthermore, interzeolite transformations occur in all syntheses, where the framework type synthesized was influenced by the presence of a specific ion as a mineralizing agent. Full article

(This article belongs to the Special Issue Research on Zeolites and Zeolite-Like Materials: Synthesis, Structure, Properties and Application)

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11 pages, 6318 KiB

Open AccessArticle

Polydimethylsiloxane-Zinc Oxide Nanorod-Based Triboelectric Nanogenerator for Compression Applications

by Shiyu Zhao, Guanghui Han, Huaxia Deng, Mengchao Ma and Xiang Zhong

Materials 2025, 18(7), 1392; https://doi.org/10.3390/ma18071392 - 21 Mar 2025

Abstract

In this study, to enhance the output performance of a contact-separation mode triboelectric nanogenerator (TENG), a zinc oxide nanorod (ZnO NR) film with piezoelectric properties was integrated into a Polydimethylsiloxane (PDMS) film as the dielectric layer. The working mechanism of the PDMS-ZnO NR-based [...] Read more.

In this study, to enhance the output performance of a contact-separation mode triboelectric nanogenerator (TENG), a zinc oxide nanorod (ZnO NR) film with piezoelectric properties was integrated into a Polydimethylsiloxane (PDMS) film as the dielectric layer. The working mechanism of the PDMS-ZnO NR-based TENG was theoretically analyzed in two stages: charge transfer during contact electrification on the material surface and charge movement in the electrostatic induction process. The output characteristics of the PDMS-ZnO NR-based TENG were investigated and compared with those of a PDMS-based TENG. The experimental results demonstrate that the PDMS-ZnO NR-based TENG reached an open-circuit voltage of 39.34 V, representing an increase of 64.5% compared to the PDMS-based TENG. The maximum output power of a 4 cm × 4 cm PDMS-ZnO NR-based TENG reached 82.2 μW. Using a specially designed energy-harvesting circuit, the generated electrical energy was stored in a capacitor, which was charged to 1.47 V within 1 min and reached 3 V in just 2.78 min. This voltage was sufficient to power over 20 LEDs and small sensors. Additionally, the TENG was integrated into the sole of footwear, where the electrical signals generated by compression could be utilized for step counting and gait analysis. Full article

(This article belongs to the Special Issue Advances in Transition Metal and Rare-Earth Metal Based Alloys, Oxides, Chalcogenides, MXenes, and 2D-Materials)

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20 pages, 5677 KiB

Open AccessArticle

Thermo-Mechanical Analysis for Composite Cylindrical Shells with Temperature-Dependent Material Properties Under Combined Thermal and Mechanical Loading

by Junjie Li, Hai Qian and Chunhua Lu

Materials 2025, 18(7), 1391; https://doi.org/10.3390/ma18071391 - 21 Mar 2025

Abstract

Composite laminated structures, comprising various engineering materials, are extensively utilized in engineering structures due to their superior design flexibility and enhanced mechanical performance. This study investigates the mechanical behavior of laminated cylindrical shells under combined thermal and mechanical loads. Using the theory of [...] Read more.

Composite laminated structures, comprising various engineering materials, are extensively utilized in engineering structures due to their superior design flexibility and enhanced mechanical performance. This study investigates the mechanical behavior of laminated cylindrical shells under combined thermal and mechanical loads. Using the theory of thermoelasticity, exact solutions are derived for temperature, displacement, and stress distributions in axisymmetric cylindrical shells with arbitrary numbers of layers and varying thicknesses, considering the temperature-dependent properties of the component materials. An iterative method and a slice model are introduced to address the interplay between temperature variations and material properties with the transfer matrix method on the basis of Fourier’s law of heat conduction. Stresses and displacements are used to formulate the state-space equation. Continuity conditions at the interfaces are applied to recursively establish the relationships between internal and external surfaces by the state-space method. Unique solutions for temperature, displacement, and stress, which are dependent on temperature, are determined by the surface conditions. The high accuracy and effectiveness of the proposed method are validated through convergence and comparative studies. Notably, neglecting temperature dependence leads to significant differences, with temperature increasing by 11.28%, displacement by 17.35%, and stress by 33.74%. Furthermore, the effects of surface temperature, thickness-to-radius ratio, layer numbers, and component materials on the temperature, displacement, and stress distributions within laminated cylindrical shells are thoroughly explored. Full article

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7 pages, 1255 KiB

Open AccessCommunication

Effect of Electrode Surface Microstructuring on Electrochemical Biosensor Performance

by Amal Kabalan and Maliheh Azimi Roueini

Materials 2025, 18(7), 1390; https://doi.org/10.3390/ma18071390 - 21 Mar 2025

Abstract

Electrode surface microstructuring involves the engineering of the topographical features of an electrode to enhance its performance in electrochemical sensing applications. By creating controlled micro- or nano-scale patterns, the active surface area can significantly increase, which leads to improved electron transfer and enhanced [...] Read more.

Electrode surface microstructuring involves the engineering of the topographical features of an electrode to enhance its performance in electrochemical sensing applications. By creating controlled micro- or nano-scale patterns, the active surface area can significantly increase, which leads to improved electron transfer and enhanced sensitivity to target analytes in devices such as biosensors. Geometrical parameters such as diameter, height, pitch, and position of the patterns can be optimized to enhance sensor detection. This paper introduces an electrochemical biosensor designed to detect Moraxella catarrhalis, a respiratory pathogen affecting young children. This paper investigates the effects of the radius of micropillars on adsorption in the electrochemical biosensor using COMSOL Multiphysics (Version: 6.0). The model demonstrates that the rate of surface adsorption depends on the position of the micropillars on the electrode. The paper also presents the effects of analyte concentration on the detection current of the biosensor using Cottrell’s equation. Full article

(This article belongs to the Topic Advanced Manufacturing and Surface Technology)

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12 pages, 5767 KiB

Open AccessArticle

Microstructure and Optical Properties of Y_1.8La_0.2O₃ Transparent Ceramics Prepared by Spark Plasma Sintering

by Junming Luo, Xu Huang and Liping Deng

Materials 2025, 18(7), 1389; https://doi.org/10.3390/ma18071389 - 21 Mar 2025

Abstract

Yttrium oxide ceramic is an excellent optical material widely used in lasers, scintillators, and upconversion luminescence. In this study, LiF was employed as an additive to generate volatile gases (CF)_n to effectively inhibit carbon contamination and act as a sintering aid to [...] Read more.

Yttrium oxide ceramic is an excellent optical material widely used in lasers, scintillators, and upconversion luminescence. In this study, LiF was employed as an additive to generate volatile gases (CF)_n to effectively inhibit carbon contamination and act as a sintering aid to accelerate densification during the spark plasma sintering (SPS) process. The effects of sintering temperature and annealing time on the transmittance of Y_1.8La_0.2O₃ transparent ceramics were systematically investigated. Results indicate that excessive LiF addition reduces the transmittance of Y_1.8La_0.2O₃ transparent ceramics due to the precipitation of F⁻ ions at grain boundaries, forming a secondary phase. For the Y_1.8La_0.2O₃ ceramics with 0.3 wt.% LiF, transmittance initially increases and then decreases with rising sintering temperature, reaching a maximum value of 78.10% in the UV region at 1550 °C. Under these conditions, the average particle size and relative density are 10–30 μm and 99.36%, respectively. Oxygen vacancies within the ceramics act as defects that degrade transmittance. Proper annealing in air reduces oxygen vacancy content, thereby improving transmittance. After annealing at 900 °C for 3 h, the maximum transmittance of Y_1.8La_0.2O₃ ceramics with 0.3 wt.% LiF increases to 82.67% in the UV region, accompanied by a 5.68% reduction in oxygen vacancy concentration. Full article

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19 pages, 4986 KiB

Open AccessArticle

Relationship Between Schmidt Hammer Rebound Hardness Test and Concrete Strength Tests for Limestone Aggregate Concrete Based on Experimental and Statistical Study

by Esra Tugrul Tunc

Materials 2025, 18(6), 1388; https://doi.org/10.3390/ma18061388 - 20 Mar 2025

Abstract

This study investigated the mechanical properties of concrete specimens produced with a limestone aggregate through laboratory testing. Destructive tests, specifically concrete compressive strength and splitting tensile strength tests, were conducted. Additionally, the Schmidt hammer rebound hardness test, a non-destructive method, was performed on [...] Read more.

This study investigated the mechanical properties of concrete specimens produced with a limestone aggregate through laboratory testing. Destructive tests, specifically concrete compressive strength and splitting tensile strength tests, were conducted. Additionally, the Schmidt hammer rebound hardness test, a non-destructive method, was performed on the same specimens. The experimental results, obtained from varying water-to-cement and limestone aggregate-to-cement ratios, yielded the following ranges: compressive strength from 23.6 to 42.6 MPa, splitting tensile strength from 3.2 to 5.1 MPa, and Schmidt hammer rebound values from 18 to 43 N. The correlation between the non-destructive and destructive test results was analyzed experimentally and statistically. Utilizing the experimental data, statistical models were developed, resulting in equations with a high determination coefficient (R² > 0.95) for accurately predicting concrete compressive and splitting tensile strengths. This approach offers the potential for significant labor and time savings in the production of sustainable conventional concrete that meets relevant standards. Furthermore, it aims to facilitate the estimation of concrete strength in existing structures. Full article

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

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13 pages, 5246 KiB

Open AccessArticle

Study on the Microstructure and Properties of AISI 304 Stainless Steel Corrugated Pipes by Aging and Solution Treatments

by Xiang Zhao, Anheng Wang, Jianbin Wang, Chuanwen Ling and Xiaolong Gui

Materials 2025, 18(6), 1387; https://doi.org/10.3390/ma18061387 - 20 Mar 2025

Abstract

This article focuses on the microstructural evolution and mechanical property changes of AISI 304 austenitic stainless steel corrugated pipes after aging treatment and solution treatment. The influence of different heat treatment processes on the microstructural evolution, second phase precipitation behavior, mechanical properties, and [...] Read more.

This article focuses on the microstructural evolution and mechanical property changes of AISI 304 austenitic stainless steel corrugated pipes after aging treatment and solution treatment. The influence of different heat treatment processes on the microstructural evolution, second phase precipitation behavior, mechanical properties, and corrosion resistance of corrugated pipes was analyzed through metallographic microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), fatigue testing, hardness testing, and corrosion resistance experiments. The results showed that after aging treatment at 600 °C, carbides precipitated at the grain boundaries and twin boundaries of the corrugated tube, leading to corrosion behavior. The average microhardness value was 266.08 HV, and the work hardening problem of the corrugated tube was not improved. After solution treatment at 1050 °C, a single-phase austenite structure was obtained in the corrugated tube, and the carbides at the grain boundaries were completely dissolved. The average microhardness value was 66.02 HV, significantly improving the work hardening problem of the corrugated tube. Simultaneously, excellent comprehensive fatigue performance and intergranular corrosion resistance were exhibited. The solid solution treatment process is more suitable for the manufacturing of corrugated pipes that require high formability and corrosion resistance, while the aging treatment requires strict temperature control to avoid the sensitization temperature zone. This study provides a theoretical basis for optimizing the heat treatment process of AISI 304 austenitic stainless steel corrugated pipes. Full article

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