Materials

11 pages, 3428 KiB

Open AccessEditor’s ChoiceArticle

Study on the Crystallization Behavior of Neodymium Rare-Earth Butadiene Rubber Blends and Its Effect on Dynamic Mechanical Properties

by Xiaohu Zhang, Wenbin Zhu, Xiaofan Li, Xinzheng Xie, Huan Ji, Yanxing Wei and Jifu Bi

Materials 2024, 17(1), 256; https://doi.org/10.3390/ma17010256 - 3 Jan 2024

Cited by 1 | Viewed by 1510

Abstract

Utilizing neodymium-based butadiene rubber as a baseline, this study examines the effect of eco-friendly aromatic TDAE oil, fillers, and crosslinking reactions on neodymium-based rare-earth butadiene rubber (Nd-BR) crystallization behavior. The findings suggest that TDAE oil hinders crystallization, resulting in decreased crystallization temperatures and [...] Read more.

Utilizing neodymium-based butadiene rubber as a baseline, this study examines the effect of eco-friendly aromatic TDAE oil, fillers, and crosslinking reactions on neodymium-based rare-earth butadiene rubber (Nd-BR) crystallization behavior. The findings suggest that TDAE oil hinders crystallization, resulting in decreased crystallization temperatures and heightened activation energies (E_a). The crystallization activation energies for 20 parts per hundreds of rubber (PHR) and 37.5 PHR oil stand at −116.8 kJ/mol and −48.1 kJ/mol, respectively, surpassing the −264.3 kJ/mol of the unadulterated rubber. Fillers act as nucleating agents, hastening crystallization, which in turn elevates crystallization temperatures and diminishes E_a. In samples containing 20 PHR and 37.5 PHR oil, the incorporation of carbon black and silica brought the E_a down to −224.9 kJ/mol and −239.1 kJ/mol, respectively. Crosslinking considerably restricts molecular motion and crystallization potential. In the examined conditions, butadiene rubber containing 37.5 PHR oil displayed no crystallization following crosslinking, albeit crystallization was discernible with filler inclusion. Simultaneously, the crystallinity level sharply declined, manifesting cold crystallization behavior. The crosslinking process elevates E_a, while the equilibrium melting point (

T_{m}^{0}

) noticeably diminishes. For instance, the

T_{m}^{0}

of pure Nd-BR is approximately −0.135 °C. When blended with carbon black and silica, the

T_{m}^{0}

values are −3.13 °C and −5.23 °C, respectively. After vulcanization, these values decrease to −21.6 °C and −10.16 °C. Evaluating the isothermal crystallization kinetics of diverse materials via the Avrami equation revealed that both the oil and crosslinking process can bring about a decrease in n values, with the Avrami index n for various samples oscillating between 1.5 and 2.5. Assessing the dynamic mechanical attributes of different specimens reveals that Nd-BR crystallization notably curtails its glass transition, marked by a modulus shift in the transition domain and a decrement in loss factor. The modulus in the rubbery state also witnesses a substantial augmentation. Full article

(This article belongs to the Section Polymeric Materials)

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13 pages, 2529 KiB

Open AccessEditor’s ChoiceArticle

Design, Synthesis, and Spectral Properties of Novel 2-Mercaptobenzothiazole Derivatives

by Agnieszka Skotnicka and Janina Kabatc-Borcz

Materials 2024, 17(1), 246; https://doi.org/10.3390/ma17010246 - 2 Jan 2024

Cited by 2 | Viewed by 2122

Abstract

This paper is focused on the optimalization of methods for the synthesis, isolation, and purification of 2-mercaptobenzothiazole-based acrylic and methacrylic monomers. The structures of the newly synthesized compounds were confirmed through infrared (IR) and nuclear magnetic resonance spectroscopy (NMR). Spectroscopic properties of the [...] Read more.

This paper is focused on the optimalization of methods for the synthesis, isolation, and purification of 2-mercaptobenzothiazole-based acrylic and methacrylic monomers. The structures of the newly synthesized compounds were confirmed through infrared (IR) and nuclear magnetic resonance spectroscopy (NMR). Spectroscopic properties of the resulting 2-mercaptobenzothiazole derivatives were determined based on their absorption spectra and molar absorption coefficients in solvents with varying polarities. A correlation was established between the calculated density functional theory (DFT) energies and Frontier Molecular Orbitals and the experimental observations, confirming their consistency. The practical utility of the synthesized compounds, particularly in future polymerization processes, hinges on a thorough understanding of these properties. Full article

(This article belongs to the Special Issue Feature Paper in the Section 'Polymeric Materials' (2nd Edition))

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47 pages, 7700 KiB

Open AccessEditor’s ChoiceReview

On the Durability of Icephobic Coatings: A Review

by Andrés Nistal, Benjamín Sierra-Martín and Antonio Fernández-Barbero

Materials 2024, 17(1), 235; https://doi.org/10.3390/ma17010235 - 31 Dec 2023

Cited by 12 | Viewed by 3799

Abstract

Ice formation and accumulation on surfaces has a negative impact in many different sectors and can even represent a potential danger. In this review, the latest advances and trends in icephobic coatings focusing on the importance of their durability are discussed, in an [...] Read more.

Ice formation and accumulation on surfaces has a negative impact in many different sectors and can even represent a potential danger. In this review, the latest advances and trends in icephobic coatings focusing on the importance of their durability are discussed, in an attempt to pave the roadmap from the lab to engineering applications. An icephobic material is expected to lower the ice adhesion strength, delay freezing time or temperature, promote the bouncing of a supercooled drop at subzero temperatures and/or reduce the ice accretion rate. To better understand what is more important for specific icing conditions, the different types of ice that can be formed in nature are summarized. Similarly, the alternative methods to evaluate the durability are reviewed, as this is key to properly selecting the method and parameters to ensure the coating is durable enough for a given application. Finally, the different types of icephobic surfaces available to date are considered, highlighting the strategies to enhance their durability, as this is the factor limiting the commercial applicability of icephobic coatings. Full article

(This article belongs to the Special Issue Surface Modifications and Coatings: Processing, Characterization, and Applications)

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14 pages, 6311 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Rapid Growth of Metal–Metal Oxide Core–Shell Structures through Joule Resistive Heating: Morphological, Structural, and Luminescence Characterization

by Juan Francisco Ramos-Justicia, Ana Urbieta and Paloma Fernández

Materials 2024, 17(1), 208; https://doi.org/10.3390/ma17010208 - 30 Dec 2023

Cited by 1 | Viewed by 1402

Abstract

The aim of this study is to prove that resistive heating enables the synthesis of metal/metal oxide composites in the form of core–shell structures. The thickness and morphology of the oxide layer depends strongly on the nature of the metal, but the influences [...] Read more.

The aim of this study is to prove that resistive heating enables the synthesis of metal/metal oxide composites in the form of core–shell structures. The thickness and morphology of the oxide layer depends strongly on the nature of the metal, but the influences of parameters such as the time and current profiles and the presence of an external field have also been investigated. The systems chosen for the present study are Zn/ZnO, Ti/TiO₂, and Ni/NiO. The characterization of the samples was performed using techniques based on scanning electron microscopy (SEM). The thicknesses of the oxide layers varied from 10 μm (Zn/ZnO) to 50 μm (Ni/NiO). In the case of Zn- and Ti-based composites, the growth of nanostructures on the oxide layer was observed. Micro- and nanoneedles formed on the ZnO layer while prism-like structures appeared on the TiO₂. In the case of the NiO layer, micro- and nanocrystals were observed. Applying an external electric field seemed to align the ZnO needles, whereas its effect on TiO₂ and NiO was less appreciable, principally affecting the shape of their grain boundaries. The chemical compositions were analysed using X-ray spectroscopy (EDX), which confirmed the existence of an oxide layer. Structural information was obtained by means of X-ray diffraction (XRD) and was later checked using Raman spectroscopy. The oxide layers seemed to be crystalline and, although some non-stoichiometric phases appeared, the stoichiometric phases were predominant; these were wurtzite, rutile, and cubic for Zn, Ti, and Ni oxides, respectively. The photoluminescence technique was used to study the distribution of defects on the shell, and mainly visible bands (2–2.5 eV), attributed to oxygen vacancies, were present. The near-band edges of ZnO and TiO₂ were also observed around 3.2–3.3 eV. Full article

(This article belongs to the Special Issue Advantages and Perspectives of ZnO Nanostructured Materials)

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13 pages, 3193 KiB

Open AccessEditor’s ChoiceArticle

High Emissivity MoSi₂-SiC-Al₂O₃ Coating on Rigid Insulation Tiles with Enhanced Thermal Protection Performance

by Xukun Yang, Yange Wan, Jiancun Li, Jiachen Liu, Mingchao Wang and Xin Tao

Materials 2024, 17(1), 220; https://doi.org/10.3390/ma17010220 - 30 Dec 2023

Cited by 6 | Viewed by 2177

Abstract

High emissivity coatings with sol as the binder have the advantages of room temperature curing, good thermal shock resistance, and high emissivity; however, only silica sol has been used in the current systems. In this study, aluminum sol was used as the binder [...] Read more.

High emissivity coatings with sol as the binder have the advantages of room temperature curing, good thermal shock resistance, and high emissivity; however, only silica sol has been used in the current systems. In this study, aluminum sol was used as the binder for the first time, and MoSi₂ and SiC were used as emittance agents to prepare a high emissivity MoSi₂-SiC-Al₂O₃ coating on mullite insulation tiles. The evolution of structure and composition at 1000–1400 °C, the spectral emissivity from 200 nm to 25 μm, and the insulation performance were studied. Compared with the coating with silica sol as a binder, the MoSi₂-SiC-Al₂O₃ coating has better structural uniformity and greater surface roughness and can generate mullite whiskers at lower temperatures. The total emissivity is 0.922 and 0.897, respectively, at the wavelength range of 200–2500 nm and 2.5–25 μm, and the superior emissivity at a low wavelength (<10 μm) is related to a higher surface roughness and reduced feature absorption. The emissivity reduction related to the oxidation of emittance agents at a high temperature (−10.2%) is smaller than that of the silica-sol-bonded coating (−18.6%). The cold surface temperature of the coated substrate is 215 °C lower than the bare substrate, suggesting excellent thermal insulation performance of the coating. Full article

(This article belongs to the Special Issue Advanced Ceramic and Glass Materials: Preparation, Characterization and Applications—2nd Edition)

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24 pages, 11690 KiB

Open AccessEditor’s ChoiceArticle

Crashworthiness of Additively Manufactured Auxetic Lattices: Repeated Impacts and Penetration Resistance

by Paolo Franzosi, Ivan Colamartino, Alessandro Giustina, Marco Anghileri and Marco Boniardi

Materials 2024, 17(1), 186; https://doi.org/10.3390/ma17010186 - 29 Dec 2023

Cited by 4 | Viewed by 1673

Abstract

Auxetic materials have recently attracted interest in the field of crashworthiness thanks to their peculiar negative Poisson ratio, leading to densification under compression and potentially being the basis of superior behavior upon impact with respect to conventional cellular cores or standard solutions. However, [...] Read more.

Auxetic materials have recently attracted interest in the field of crashworthiness thanks to their peculiar negative Poisson ratio, leading to densification under compression and potentially being the basis of superior behavior upon impact with respect to conventional cellular cores or standard solutions. However, the empirical demonstration of the applicability of auxeticity under impact is limited for most known geometries. As such, the present work strives to advance the investigation of the impact behavior of auxetic meta-materials: first by selecting and testing representative specimens, then by proceeding with an experimental and numerical study of repeated impact behavior and penetration resistance, and finally by proposing a new design of a metallic auxetic absorber optimized for additive manufacturing and targeted at high-performance crash applications. Full article

(This article belongs to the Special Issue Mechanical Performance of Advanced Composite Materials and Structures)

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23 pages, 5067 KiB

Open AccessEditor’s ChoiceArticle

Green Synthesis of Silver Nanoparticles Using the Cell-Free Supernatant of Haematococcus pluvialis Culture

by Maria G. Savvidou, Evgenia Kontari, Styliani Kalantzi and Diomi Mamma

Materials 2024, 17(1), 187; https://doi.org/10.3390/ma17010187 - 29 Dec 2023

Cited by 7 | Viewed by 2060

Abstract

The green synthesis of silver nanoparticles (AgNPs) using the cell-free supernatant of a Haematococcus pluvialis culture (CFS) was implemented in the current study, under illumination conditions. The reduction of Ag⁺ to AgNPs by the CFS could be described by a pseudo-first-order kinetic [...] Read more.

The green synthesis of silver nanoparticles (AgNPs) using the cell-free supernatant of a Haematococcus pluvialis culture (CFS) was implemented in the current study, under illumination conditions. The reduction of Ag⁺ to AgNPs by the CFS could be described by a pseudo-first-order kinetic equation at the temperature range tested. A high reaction rate during synthesis and stable AgNPs were obtained at 45 °C, while an alkaline pH (pH = 11.0) and a AgNO₃ aqueous solution to CFS ratio of 90:10 (v/v) proved to be the most effective conditions in AgNPs synthesis. A metal precursor (AgNO₃) at the concentration range tested (1–5 mM) was the limited reactant in the synthesis process. The synthesis of AgNPs was accomplished under static and agitated conditions. Continuous stirring enhanced the rate of reaction but induced aggregation at prolonged incubation times. Zeta potential and polydispersity index measurements indicated stable AgNPs and the majority of AgNPs formation occurred in the monodisperse phase. The X-ray diffraction (XRD) pattern revealed the face-centered cubic structure of the formed AgNPs, while TEM analysis revealed that the AgNPs were of a quasi-spherical shape with a size from 30 to 50 nm. The long-term stability of the AgNPs could be achieved in darkness and at 4 °C. In addition, the synthesized nanoparticles showed antibacterial activity against Escherichia coli. Full article

(This article belongs to the Special Issue Eco-Nanotechnology in Materials)

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20 pages, 15729 KiB

Open AccessEditor’s ChoiceArticle

Atomistic-Continuum Study of an Ultrafast Melting Process Controlled by a Femtosecond Laser-Pulse Train

by Yu Meng, An Gong, Zhicheng Chen, Qingsong Wang, Jianwu Guo, Zihao Li and Jiafang Li

Materials 2024, 17(1), 185; https://doi.org/10.3390/ma17010185 - 29 Dec 2023

Cited by 4 | Viewed by 1781

Abstract

In femtosecond laser fabrication, the laser-pulse train shows great promise in improving processing efficiency, quality, and precision. This research investigates the influence of pulse number, pulse interval, and pulse energy ratio on the lateral and longitudinal ultrafast melting process using an experiment and [...] Read more.

In femtosecond laser fabrication, the laser-pulse train shows great promise in improving processing efficiency, quality, and precision. This research investigates the influence of pulse number, pulse interval, and pulse energy ratio on the lateral and longitudinal ultrafast melting process using an experiment and the molecular dynamics coupling two-temperature model (MD-TTM model), which incorporates temperature-dependent thermophysical parameters. The comparison of experimental and simulation results under single and double pulses proves the reliability of the MD-TTM model and indicates that as the pulse number increases, the melting threshold at the edge region of the laser spot decreases, resulting in a larger diameter of the melting region in the 2D lateral melting results. Using the same model, the lateral melting results of five pulses are simulated. Moreover, the longitudinal melting results are also predicted, and an increasing pulse number leads to a greater early-stage melting depth in the melting process. In the case of double femtosecond laser pulses, the pulse interval and pulse energy ratio also affect the early-stage melting depth, with the best enhancement observed with a 2 ps interval and a 3:7 energy ratio. However, pulse number, pulse energy ratio, and pulse interval do not affect the final melting depth with the same total energies. The findings mean that the phenomena of melting region can be flexibly manipulated through the laser-pulse train, which is expected to be applied to improve the structural precision and boundary quality. Full article

(This article belongs to the Section Materials Physics)

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14 pages, 6019 KiB

Open AccessEditor’s ChoiceArticle

Multiscale Analysis of Composite Structures with Artificial Neural Network Support for Micromodel Stress Determination

by Wacław Kuś, Waldemar Mucha and Iyasu Tafese Jiregna

Materials 2024, 17(1), 154; https://doi.org/10.3390/ma17010154 - 27 Dec 2023

Cited by 7 | Viewed by 1875

Abstract

Structures made of heterogeneous materials, such as composites, often require a multiscale approach when their behavior is simulated using the finite element method. By solving the boundary value problem of the macroscale model, for previously homogenized material properties, the resulting stress maps can [...] Read more.

Structures made of heterogeneous materials, such as composites, often require a multiscale approach when their behavior is simulated using the finite element method. By solving the boundary value problem of the macroscale model, for previously homogenized material properties, the resulting stress maps can be obtained. However, such stress results do not describe the actual behavior of the material and are often significantly different from the actual stresses in the heterogeneous microstructure. Finding high-accuracy stress results for such materials leads to time-consuming analyses in both scales. This paper focuses on the application of machine learning to multiscale analysis of structures made of composite materials, to substantially decrease the time of computations of such localization problems. The presented methodology was validated by a numerical example where a structure made of resin epoxy with randomly distributed short glass fibers was analyzed using a computational multiscale approach. Carefully prepared training data allowed artificial neural networks to learn relationships between two scales and significantly increased the efficiency of the multiscale approach. Full article

(This article belongs to the Special Issue Computational Modelling and Design of Novel Engineering Materials (Second Edition))

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35 pages, 6148 KiB

Open AccessEditor’s ChoiceReview

Titanium Alloy Implants with Lattice Structures for Mandibular Reconstruction

by Khaled M. Hijazi, S. Jeffrey Dixon, Jerrold E. Armstrong and Amin S. Rizkalla

Materials 2024, 17(1), 140; https://doi.org/10.3390/ma17010140 - 27 Dec 2023

Cited by 9 | Viewed by 2644

Abstract

In recent years, the field of mandibular reconstruction has made great strides in terms of hardware innovations and their clinical applications. There has been considerable interest in using computer-aided design, finite element modelling, and additive manufacturing techniques to build patient-specific surgical implants. Moreover, [...] Read more.

In recent years, the field of mandibular reconstruction has made great strides in terms of hardware innovations and their clinical applications. There has been considerable interest in using computer-aided design, finite element modelling, and additive manufacturing techniques to build patient-specific surgical implants. Moreover, lattice implants can mimic mandibular bone’s mechanical and structural properties. This article reviews current approaches for mandibular reconstruction, their applications, and their drawbacks. Then, we discuss the potential of mandibular devices with lattice structures, their development and applications, and the challenges for their use in clinical settings. Full article

(This article belongs to the Section Biomaterials)

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17 pages, 3801 KiB

Open AccessEditor’s ChoiceArticle

A Machine Learning Approach for Modelling Cold-Rolling Curves for Various Stainless Steels

by Julia Contreras-Fortes, M. Inmaculada Rodríguez-García, David L. Sales, Rocío Sánchez-Miranda, Juan F. Almagro and Ignacio Turias

Materials 2024, 17(1), 147; https://doi.org/10.3390/ma17010147 - 27 Dec 2023

Cited by 2 | Viewed by 1771

Abstract

Stainless steel is a cold-work-hardened material. The degree and mechanism of hardening depend on the grade and family of the steel. This characteristic has a direct effect on the mechanical behaviour of stainless steel when it is cold-formed. Since cold rolling is one [...] Read more.

Stainless steel is a cold-work-hardened material. The degree and mechanism of hardening depend on the grade and family of the steel. This characteristic has a direct effect on the mechanical behaviour of stainless steel when it is cold-formed. Since cold rolling is one of the most widespread processes for manufacturing flat stainless steel products, the prediction of their strain-hardening mechanical properties is of great importance to materials engineering. This work uses artificial neural networks (ANNs) to forecast the mechanical properties of the stainless steel as a function of the chemical composition and the applied cold thickness reduction. Multiple linear regression (MLR) is also used as a benchmark model. To achieve this, both traditional and new-generation austenitic, ferritic, and duplex stainless steel sheets are cold-rolled at a laboratory scale with different thickness reductions after the industrial intermediate annealing stage. Subsequently, the mechanical properties of the cold-rolled sheets are determined by tensile tests, and the experimental cold-rolling curves are drawn based on those results. A database is created from these curves to generate a model applying machine learning techniques to predict the values of the tensile strength (Rm), yield strength (Rp), hardness (H), and elongation (A) based on the chemical composition and the applied cold thickness reduction. These models can be used as supporting tools for designing and developing new stainless steel grades and/or adjusting cold-forming processes. Full article

(This article belongs to the Special Issue Machine Learning Techniques in Materials Science and Engineering)

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19 pages, 2944 KiB

Open AccessEditor’s ChoiceArticle

Particleboards with Recycled Material from Hemp-Based Panels

by Electra Papadopoulou, Iouliana Chrysafi, Konstantina Karidi, Andromachi Mitani and Dimitrios N. Bikiaris

Materials 2024, 17(1), 139; https://doi.org/10.3390/ma17010139 - 27 Dec 2023

Cited by 2 | Viewed by 2447

Abstract

This research addresses the current need for sustainable solutions in the construction and furniture industries, with a focus on environmentally friendly particleboard. Particleboards were made from a mixture of virgin wood chips and hemp shives, which were then mechanically recycled and used to [...] Read more.

This research addresses the current need for sustainable solutions in the construction and furniture industries, with a focus on environmentally friendly particleboard. Particleboards were made from a mixture of virgin wood chips and hemp shives, which were then mechanically recycled and used to make new lightweight particleboards. Phenol–formaldehyde resin with 25% w/w phenol replacement by soybean flour (PFS) was used as the binder for the lignocellulosic materials. Laboratory analyses determined the resin properties, and FTIR confirmed the structure of the experimental PFS resin. The thermal properties of all the resins were evaluated using thermogravimetric analysis (TGA). The panels were manufactured using industrial simulation and tested for mechanical and physical properties in accordance with European standards. The FTIR study confirmed good adhesion, and the TGA showed improved thermal stability for the recycled biomass panels compared to virgin biomass panels. The study concludes that lightweight particleboards can be successfully produced from recycled hemp shive-based panels, providing a sustainable alternative to traditional materials in the construction industry. Full article

(This article belongs to the Special Issue Towards a Sustainable and Recyclable Future with Wood and Wood-Based Composites)

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14 pages, 5431 KiB

Open AccessEditor’s ChoiceArticle

Advanced Integration of Glutathione-Functionalized Optical Fiber SPR Sensor for Ultra-Sensitive Detection of Lead Ions

by Jiale Wang, Kunpeng Niu, Jianguo Hou, Ziyang Zhuang, Jiayi Zhu, Xinyue Jing, Ning Wang, Binyun Xia and Lei Lei

Materials 2024, 17(1), 98; https://doi.org/10.3390/ma17010098 - 24 Dec 2023

Cited by 7 | Viewed by 1862

Abstract

It is crucial to detect Pb²⁺ accurately and rapidly. This work proposes an ultra-sensitive optical fiber surface plasmon resonance (SPR) sensor functionalized with glutathione (GSH) for label-free detection of the ultra-low Pb²⁺ concentration, in which the refractive index (RI) sensitivity of [...] Read more.

It is crucial to detect Pb²⁺ accurately and rapidly. This work proposes an ultra-sensitive optical fiber surface plasmon resonance (SPR) sensor functionalized with glutathione (GSH) for label-free detection of the ultra-low Pb²⁺ concentration, in which the refractive index (RI) sensitivity of the multimode-singlemode-multimode (MSM) hetero-core fiber is largely enhanced by the gold nanoparticles (AuNPs)/Au film coupling SPR effect. The GSH is modified on the fiber as the sensing probe to capture and identify Pb²⁺ specifically. Its working principle is that the Pb²⁺ chemically reacts with deprotonated carboxyl groups in GSH through ligand bonding, resulting in the formation of stable and specific chelates, inducing the variation of the local RI on the sensor surface, which in turn leads to the SPR wavelength shift in the transmission spectrum. Attributing to the AuNPs, both the Au substrates can be fully functionalized with the GSH molecules as the probes, which largely increases the number of active sites for Pb²⁺ trapping. Combined with the SPR effect, the sensor achieves a sensitivity of 2.32 × 10¹¹ nm/M and a limit of detection (LOD) of 0.43 pM. It also demonstrates exceptional specificity, stability, and reproducibility, making it suitable for various applications in water pollution, biomedicine, and food safety. Full article

(This article belongs to the Section Materials Chemistry)

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14 pages, 8542 KiB

Open AccessEditor’s ChoiceArticle

Electrophysical Properties of the Three-Component Multiferroic Ceramic Composites

by Dariusz Bochenek, Przemysław Niemiec, Dagmara Brzezińska, Grzegorz Dercz and Marcin Wąs

Materials 2024, 17(1), 49; https://doi.org/10.3390/ma17010049 - 22 Dec 2023

Cited by 2 | Viewed by 1086

Abstract

Using the free (pressureless) sintering method, multiferroic ceramic composites based on two ferroelectric materials, i.e., BaTiO₃ (B) and Pb_0.94Sr_0.06 (Zr_0.46Ti_0.54)_0.99Cr_0.01O₃ (P), and magnetic material, i.e., zinc–nickel ferrite (F) were obtained. [...] Read more.

Using the free (pressureless) sintering method, multiferroic ceramic composites based on two ferroelectric materials, i.e., BaTiO₃ (B) and Pb_0.94Sr_0.06 (Zr_0.46Ti_0.54)_0.99Cr_0.01O₃ (P), and magnetic material, i.e., zinc–nickel ferrite (F) were obtained. Three composite compositions (BP-F) were obtained with a constant 90/10 content (ferroelectric/magnetic) and a variable content of the ferroelectric component (B/P), i.e., 70/30, 50/50, and 30/70. Crystalline structure, microstructural, DC electrical conductivity, dielectric, and ferroelectric properties of multiferroic composites were investigated. The concept of a composite consisting of two ferroelectric components ensures the preservation of sufficiently high ferroelectric properties of multiferroic composites sintered by the free sintering method. Research has shown that the percentage of individual ferroelectric components in the composite significantly affects the functional properties and the entire set of physical parameters of the multiferroic BP-F composite. In the case of the dielectric parameters, the best results were obtained for the composition with a more significant amount of BaTiO₃; i.e., permittivity is 1265, spontaneous polarization is 7.90 µC/cm², and remnant polarization is 5.40 µC/cm². However, the most advantageous set of performance parameters shows the composite composition of 50BP-F. Full article

(This article belongs to the Special Issue Advanced Materials and Technologies for Thermal Sprayed Coatings)

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22 pages, 7099 KiB

Open AccessEditor’s ChoiceArticle

Reprocessing Possibilities of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)–Hemp Fiber Composites Regarding the Material and Product Quality

by Wiesław Frącz, Andrzej Pacana, Dominika Siwiec, Grzegorz Janowski and Łukasz Bąk

Materials 2024, 17(1), 55; https://doi.org/10.3390/ma17010055 - 22 Dec 2023

Cited by 3 | Viewed by 1368

Abstract

An important issue addressed in research on the assessment of the quality of polymer products is the quality of the polymer material itself and, in accordance with the idea of waste-free management, the impact of its repeated processing on its properties and the [...] Read more.

An important issue addressed in research on the assessment of the quality of polymer products is the quality of the polymer material itself and, in accordance with the idea of waste-free management, the impact of its repeated processing on its properties and the quality of the products. In this work, a biocomposite, based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with short hemp fibers, was obtained and repeatedly processed, which is a continuation of the research undertaken by the team in the field of this type of biocomposites. After subsequent stages of processing, the selected mechanical, processing and functional properties of the products were assessed. For this purpose, microscopic tests were carried out, mechanical properties were tested in static tensile and impact tests, viscosity curves were determined after subsequent processing cycles and changes in plastic pressure in the mold cavity were determined directly during processing. The results of the presented research confirm only a slight decrease in the mechanical properties of the produced type of biocomposite, even after it has been reprocessed five times, which gives extra weight to arguments for its commercialization as a substitute for petrochemical-based plastics. No significant changes were found in the used parameters and processing properties with the stages of processing, which allows for a predictable and stable manufacturing process using, for example, the injection molding process. Full article

(This article belongs to the Special Issue Qualitative-Environmental Aspects to Improve Materials and Processes of Their Formation)

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30 pages, 7029 KiB

Open AccessEditor’s ChoiceReview

Development and Future Trends of Protective Strategies for Magnesium Alloy Vascular Stents

by Dexiao Liu, Ke Yang and Shanshan Chen

Materials 2024, 17(1), 68; https://doi.org/10.3390/ma17010068 - 22 Dec 2023

Cited by 8 | Viewed by 2665

Abstract

Magnesium alloy stents have been extensively studied in the field of biodegradable metal stents due to their exceptional biocompatibility, biodegradability and excellent biomechanical properties. Nevertheless, the specific in vivo service environment causes magnesium alloy stents to degrade rapidly and fail to provide sufficient [...] Read more.

Magnesium alloy stents have been extensively studied in the field of biodegradable metal stents due to their exceptional biocompatibility, biodegradability and excellent biomechanical properties. Nevertheless, the specific in vivo service environment causes magnesium alloy stents to degrade rapidly and fail to provide sufficient support for a certain time. Compared to previous reviews, this paper focuses on presenting an overview of the development history, the key issues, mechanistic analysis, traditional protection strategies and new directions and protection strategies for magnesium alloy stents. Alloying, optimizing stent design and preparing coatings have improved the corrosion resistance of magnesium alloy stents. Based on the corrosion mechanism of magnesium alloy stents, as well as their deformation during use and environmental characteristics, we present some novel strategies aimed at reducing the degradation rate of magnesium alloys and enhancing the comprehensive performance of magnesium alloy stents. These strategies include adapting coatings for the deformation of the stents, preparing rapid endothelialization coatings to enhance the service environment of the stents, and constructing coatings with self-healing functions. It is hoped that this review can help readers understand the development of magnesium alloy cardiovascular stents and solve the problems related to magnesium alloy stents in clinical applications at the early implantation stage. Full article

(This article belongs to the Special Issue Advances in the Corrosion and Protection of Metals (Second Volume))

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16 pages, 4984 KiB

Open AccessEditor’s ChoiceArticle

N-Doped Carbon Nanowire-Modified Macroporous Carbon Foam Microbial Fuel Cell Anode: Enrichment of Exoelectrogens and Enhancement of Extracellular Electron Transfer

by Ke Liu, Zhuo Ma, Xinyi Li, Yunfeng Qiu, Danqing Liu and Shaoqin Liu

Materials 2024, 17(1), 69; https://doi.org/10.3390/ma17010069 - 22 Dec 2023

Cited by 13 | Viewed by 1805

Abstract

Microbial fuel cell (MFC) performance is affected by the metabolic activity of bacteria and the extracellular electron transfer (EET) process. The deficiency of nanostructures on macroporous anode obstructs the enrichment of exoelectrogens and the EET. Herein, a N-doped carbon nanowire-modified macroporous carbon foam [...] Read more.

Microbial fuel cell (MFC) performance is affected by the metabolic activity of bacteria and the extracellular electron transfer (EET) process. The deficiency of nanostructures on macroporous anode obstructs the enrichment of exoelectrogens and the EET. Herein, a N-doped carbon nanowire-modified macroporous carbon foam was prepared and served as an anode in MFCs. The anode has a hierarchical porous structure, which can solve the problem of biofilm blockage, ensure mass transport, favor exoelectrogen enrichment, and enhance the metabolic activity of bacteria. The microscopic morphology, spectroscopy, and electrochemical characterization of the anode confirm that carbon nanowires can penetrate biofilm, decrease charge resistance, and enhance long-distance electron transfer efficiency. In addition, pyrrolic N can effectively reduce the binding energy and electron transfer distance of bacterial outer membrane hemin. With this hierarchical anode, a maximum power density of 5.32 W/m³ was obtained, about 2.5-fold that of bare carbon cloth. The one-dimensional nanomaterial-modified macroporous anodes in this study are a promising strategy to improve the exoelectrogen enrichment and EET for MFCs. Full article

(This article belongs to the Special Issue Nanoarchitectonics in Materials Science)

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33 pages, 5643 KiB

Open AccessEditor’s ChoiceReview

Research Progress in Special Engineering Plastic-Based Electrochromic Polymers

by Yixuan Liu, Zhen Xing, Songrui Jia, Xiangfu Shi, Zheng Chen and Zhenhua Jiang

Materials 2024, 17(1), 73; https://doi.org/10.3390/ma17010073 - 22 Dec 2023

Cited by 13 | Viewed by 2041

Abstract

SPECPs are electrochromic polymers that contain special engineering plastic structural characteristic groups (SPECPs). Due to their high thermal stability, mechanical properties, and weather resistance, they are also known as high-performance electrochromic polymer (HPEP or HPP). Meanwhile, due to the structural characteristics of their [...] Read more.

SPECPs are electrochromic polymers that contain special engineering plastic structural characteristic groups (SPECPs). Due to their high thermal stability, mechanical properties, and weather resistance, they are also known as high-performance electrochromic polymer (HPEP or HPP). Meanwhile, due to the structural characteristics of their long polymer chains, these materials have natural advantages in the application of flexible electrochromic devices. According to the structure of special engineering plastic groups, SPECPs are divided into five categories: polyamide, polyimide, polyamide imide, polyarylsulfone, and polyarylketone. This article mainly introduces the latest research on SPECPs. The structural design, electrochromic properties, and applications of these materials are also introduced in this article, and the challenges and future development trends of SPECPs are prospected. Full article

(This article belongs to the Section Polymeric Materials)

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20 pages, 1543 KiB

Open AccessEditor’s ChoiceReview

Production, Recycling and Economy of Palladium: A Critical Review

by Tomasz Michałek, Volker Hessel and Marek Wojnicki

Materials 2024, 17(1), 45; https://doi.org/10.3390/ma17010045 - 21 Dec 2023

Cited by 14 | Viewed by 5602

Abstract

Platinum group metals (PGMs), including palladium, play a pivotal role in various industries due to their unique properties. Palladium is frequently employed in technologies aimed at environmental preservation, such as catalytic converters that reduce harmful emissions from vehicles, and in the production of [...] Read more.

Platinum group metals (PGMs), including palladium, play a pivotal role in various industries due to their unique properties. Palladium is frequently employed in technologies aimed at environmental preservation, such as catalytic converters that reduce harmful emissions from vehicles, and in the production of clean energy, notably in the hydrogen evolution process. Regrettably, the production of this vital metal for our environment is predominantly centered in two countries—Russia and South Africa. This centralization has led to palladium being classified as a critical raw material, emphasizing the importance of establishing a secure and sustainable supply chain, as well as employing the most efficient methods for processing materials containing palladium. This review explores techniques for palladium production from primary sources and innovative recycling methods, providing insights into current technologies and emerging approaches. Furthermore, it investigates the economic aspects of palladium production, including price fluctuations influenced by emission regulations and electric vehicle sales, and establishes connections between palladium prices, imports from major producers, as well as copper and nickel prices, considering their often co-occurrence in ores. Full article

(This article belongs to the Special Issue Advanced Metallurgy Technologies: Physical and Numerical Modelling)

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45 pages, 10823 KiB

Open AccessEditor’s ChoiceReview

Progress in Gallium Oxide Field-Effect Transistors for High-Power and RF Applications

by Ory Maimon and Qiliang Li

Materials 2023, 16(24), 7693; https://doi.org/10.3390/ma16247693 - 18 Dec 2023

Cited by 10 | Viewed by 4188

Abstract

Power electronics are becoming increasingly more important, as electrical energy constitutes 40% of the total primary energy usage in the USA and is expected to grow rapidly with the emergence of electric vehicles, renewable energy generation, and energy storage. New materials that are [...] Read more.

Power electronics are becoming increasingly more important, as electrical energy constitutes 40% of the total primary energy usage in the USA and is expected to grow rapidly with the emergence of electric vehicles, renewable energy generation, and energy storage. New materials that are better suited for high-power applications are needed as the Si material limit is reached. Beta-phase gallium oxide (β-Ga₂O₃) is a promising ultra-wide-bandgap (UWBG) semiconductor for high-power and RF electronics due to its bandgap of 4.9 eV, large theoretical breakdown electric field of 8 MV cm⁻¹, and Baliga figure of merit of 3300, 3–10 times larger than that of SiC and GaN. Moreover, β-Ga₂O₃ is the only WBG material that can be grown from melt, making large, high-quality, dopable substrates at low costs feasible. Significant efforts in the high-quality epitaxial growth of β-Ga₂O₃ and β-(Al_xGa_1−x)₂O₃ heterostructures has led to high-performance devices for high-power and RF applications. In this report, we provide a comprehensive summary of the progress in β-Ga₂O₃ field-effect transistors (FETs) including a variety of transistor designs, channel materials, ohmic contact formations and improvements, gate dielectrics, and fabrication processes. Additionally, novel structures proposed through simulations and not yet realized in β-Ga₂O₃ are presented. Main issues such as defect characterization methods and relevant material preparation, thermal studies and management, and the lack of p-type doping with investigated alternatives are also discussed. Finally, major strategies and outlooks for commercial use will be outlined. Full article

(This article belongs to the Special Issue Ultra-Wide Bandgap Semiconductor Materials and Devices)

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14 pages, 5786 KiB

Open AccessEditor’s ChoiceArticle

Nitrogen- and Sulfur-Codoped Strong Green Fluorescent Carbon Dots for the Highly Specific Quantification of Quercetin in Food Samples

by Kandasamy Sasikumar, Ramar Rajamanikandan and Heongkyu Ju

Materials 2023, 16(24), 7686; https://doi.org/10.3390/ma16247686 - 17 Dec 2023

Cited by 13 | Viewed by 2043

Abstract

Carbon dots (CDs) doped with heteroatoms have garnered significant interest due to their chemically modifiable luminescence properties. Herein, nitrogen- and sulfur-codoped carbon dots (NS-CDs) were successfully prepared using p-phenylenediamine and thioacetamide via a facile process. The as-developed NS-CDs had high photostability against photobleaching, [...] Read more.

Carbon dots (CDs) doped with heteroatoms have garnered significant interest due to their chemically modifiable luminescence properties. Herein, nitrogen- and sulfur-codoped carbon dots (NS-CDs) were successfully prepared using p-phenylenediamine and thioacetamide via a facile process. The as-developed NS-CDs had high photostability against photobleaching, good water dispersibility, and excitation-independent spectral emission properties due to the abundant amino and sulfur functional groups on their surface. The wine-red-colored NS-CDs exhibited strong green emission with a large Stokes shift of up to 125 nm upon the excitation wavelength of 375 nm, with a high quantum yield (QY) of 28%. The novel NS-CDs revealed excellent sensitivity for quercetin (QT) detection via the fluorescence quenching effect, with a low detection limit of 17.3 nM within the linear range of 0–29.7 μM. The fluorescence was quenched only when QT was brought near the NS-CDs. This QT-induced quenching occurred through the strong inner filter effect (IFE) and the complex bound state formed between the ground-state QT and excited-state NS-CDs. The quenching-based detection strategies also demonstrated good specificity for QT over various interferents (phenols, biomolecules, amino acids, metal ions, and flavonoids). Moreover, this approach could be effectively applied to the quantitative detection of QT (with good sensing recovery) in real food samples such as red wine and onion samples. The present work, consequently, suggests that NS-CDs may open the door to the sensitive and specific detection of QT in food samples in a cost-effective and straightforward manner. Full article

(This article belongs to the Special Issue State-of-the-Art Nanomaterials in Energy and Environmental Applications)

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14 pages, 1971 KiB

Open AccessEditor’s ChoiceReview

A Review on Carrier Mobilities of Epitaxial Graphene on Silicon Carbide

by Wataru Norimatsu

Materials 2023, 16(24), 7668; https://doi.org/10.3390/ma16247668 - 15 Dec 2023

Cited by 6 | Viewed by 2170

Abstract

Graphene growth by thermal decomposition of silicon carbide (SiC) is a technique that produces wafer-scale, single-orientation graphene on an insulating substrate. It is often referred to as epigraphene, and has been thought to be suitable for electronics applications. In particular, high-frequency devices for [...] Read more.

Graphene growth by thermal decomposition of silicon carbide (SiC) is a technique that produces wafer-scale, single-orientation graphene on an insulating substrate. It is often referred to as epigraphene, and has been thought to be suitable for electronics applications. In particular, high-frequency devices for communication technology or large quantum Hall plateau for metrology applications using epigraphene are expected, which require high carrier mobility. However, the carrier mobility of as-grown epigraphene exhibit the relatively low values of about 1000 cm²/Vs. Fortunately, we can hope to improve this situation by controlling the electronic state of epigraphene by modifying the surface and interface structures. In this paper, the mobility of epigraphene and the factors that govern it will be described, followed by a discussion of attempts that have been made to improve mobility in this field. These understandings are of great importance for next-generation high-speed electronics using graphene. Full article

(This article belongs to the Special Issue Research Progress on Two-Dimensional Materials)

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14 pages, 8247 KiB

Open AccessEditor’s ChoiceArticle

SrTiO₃-SrVO₃ Ceramics for Solid Oxide Fuel Cell Anodes: A Route from Oxidized Precursors

by Javier Macías, Jorge R. Frade and Aleksey A. Yaremchenko

Materials 2023, 16(24), 7638; https://doi.org/10.3390/ma16247638 - 14 Dec 2023

Cited by 3 | Viewed by 1771

Abstract

Perovskite-type Sr(Ti,V)O_3-δ ceramics are promising anode materials for natural gas- and biogas-fueled solid oxide fuel cells, but the instability of these phases under oxidizing conditions complicates their practical application. The present work explores approaches to the fabrication of strontium titanate-vanadate electrodes from [...] Read more.

Perovskite-type Sr(Ti,V)O_3-δ ceramics are promising anode materials for natural gas- and biogas-fueled solid oxide fuel cells, but the instability of these phases under oxidizing conditions complicates their practical application. The present work explores approaches to the fabrication of strontium titanate-vanadate electrodes from oxidized precursors. Porous ceramics with the nominal composition SrTi_1−yV_yO_z (y = 0.1–0.3) were prepared in air via a solid state reaction route. Thermal processing at temperatures not exceeding 1100 °C yielded composite ceramics comprising perovskite-type SrTiO₃, pyrovanadate Sr₂V₂O₇ and orthovanadate Sr₃(VO₄)₂ phases, while increasing firing temperatures to 1250–1440 °C enabled the formation of SrTi_1−yV_yO₃ perovskites. Vanadium was found to substitute into the titanium sublattice predominantly as V⁴⁺, even under oxidizing conditions at elevated temperatures. Both perovskite and composite oxidized ceramics exhibit moderate thermal expansion coefficients in air, 11.1–12.1 ppm/K at 30–1000 °C, and insignificant dimensional changes induced by reduction in a 10%H₂-N₂ atmosphere. The electrical conductivity of reduced perovskite samples remains comparatively low, ~10⁻¹ S/cm at 900 °C, whereas the transformation of oxidized vanadate phases into high-conducting SrVO_3−δ perovskites upon reduction results in enhancement in conductivity, which reaches ~3 S/cm at 900 °C in porous composite ceramics with nominal composition SrTi_0.7V_0.3O_z. The electrical performance of the composite is expected to be further improved by optimization of the processing route and microstructure to facilitate the reduction of the oxidized precursor and attain better percolation of the SrVO₃ phase. Full article

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

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16 pages, 6994 KiB

Open AccessEditor’s ChoiceArticle

Point-Contact Spectroscopy in Bulk Samples of Electron-Doped Cuprate Superconductors

by Angela Nigro, Anita Guarino, Antonio Leo, Gaia Grimaldi, Francesco Avitabile and Paola Romano

Materials 2023, 16(24), 7644; https://doi.org/10.3390/ma16247644 - 14 Dec 2023

Cited by 1 | Viewed by 1454

Abstract

Point-contact spectroscopy was performed on bulk samples of electron-doped high temperature superconductor Nd_2−xCe_xCuO_4−δ. The samples were characterized using X-ray diffraction and scanning electron microscopy equipped with a wavelength-dispersive spectrometer and an electron backscatter diffraction detector. Samples with [...] Read more.

Point-contact spectroscopy was performed on bulk samples of electron-doped high temperature superconductor Nd_2−xCe_xCuO_4−δ. The samples were characterized using X-ray diffraction and scanning electron microscopy equipped with a wavelength-dispersive spectrometer and an electron backscatter diffraction detector. Samples with Ce content x = 0.15 showed the absence of spurious phases and randomly oriented grains, most of which had dimensions of approximately 220 µm². The low-bias spectra in the tunneling regime, i.e., high-transparency interface, exhibited a gap feature at about ±5 meV and no zero-bias conductance, despite the random oriented grains investigated within our bulk samples, consistent with most of the literature data on oriented samples. High-bias conductance was also measured in order to obtain information on the properties of the barrier. A V-shape was observed in some cases, instead of the parabolic behavior expected for tunnel junctions. Full article

(This article belongs to the Special Issue Physics and Application of Superconductivity)

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18 pages, 12761 KiB

Open AccessEditor’s ChoiceArticle

Preparation and Characterization of Modified ZrO₂/SiO₂/Silicone-Modified Acrylic Emulsion Superhydrophobic Coating

by Jiaxin Ben, Peipei Wu, Yancheng Wang, Jie Liu and Yali Luo

Materials 2023, 16(24), 7621; https://doi.org/10.3390/ma16247621 - 13 Dec 2023

Cited by 4 | Viewed by 2244

Abstract

Superhydrophobic coatings have increasingly become the focal point of research due to their distinctive properties like water resistance, wear resistance, and acid-base resilience. In pursuit of maximizing their efficiency, research has primarily revolved around refining the fabrication process and the composition of emulsion/nanoparticle [...] Read more.

Superhydrophobic coatings have increasingly become the focal point of research due to their distinctive properties like water resistance, wear resistance, and acid-base resilience. In pursuit of maximizing their efficiency, research has primarily revolved around refining the fabrication process and the composition of emulsion/nanoparticle coatings. We innovatively devised a superhydrophobic coating by employing a spraying technique. This involved integrating a γ-Methacryloyloxypropyltrimethoxysilane (KH570)-modified ZrO₂/SiO₂/silicone-modified acrylic emulsion. A comprehensive evaluation of this coating was undertaken using analytical instruments such as Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and confocal laser scanning microscopy (CLSM). The coating demonstrated exceptional performance across a range of tests, including wear, immersion, and anti-icing cleaning, showcasing notable wear resistance, sodium chloride corrosion resistance, self-cleaning efficiency, and thermal stability. In particular, one coating exhibited super-hydrophobic properties, with a high contact angle of 158.5 degrees and an impressively low rolling angle of 1.85 degrees. This remarkable combination of properties is attributed to the judicious selection of components, which significantly reinforced the mechanical strength of the coating. These enhancements make it highly suitable for industrial applications where self-cleaning, anti-icing, and anti-contamination capabilities are critical. Full article

(This article belongs to the Section Thin Films and Interfaces)

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13 pages, 1684 KiB

Open AccessEditor’s ChoiceArticle

Facile Synthesis of Platinum Nanoparticle-Embedded Reduced Graphene Oxide for the Detection of Carbendazim

by Suthira Pushparajah, Shinichi Hasegawa, Tien Song Hiep Pham, Mahnaz Shafiei and Aimin Yu

Materials 2023, 16(24), 7622; https://doi.org/10.3390/ma16247622 - 13 Dec 2023

Cited by 3 | Viewed by 1529

Abstract

In recent years, there has been a significant interest in the advancement of electrochemical sensing platforms to detect pesticides with high sensitivity and selectivity. Current research presents a novel approach utilising platinum nanoparticles (NPs) and reduced graphene oxide deposited on a glassy carbon [...] Read more.

In recent years, there has been a significant interest in the advancement of electrochemical sensing platforms to detect pesticides with high sensitivity and selectivity. Current research presents a novel approach utilising platinum nanoparticles (NPs) and reduced graphene oxide deposited on a glassy carbon electrode (Pt-rGO/GCE) for direct electrochemical measurement of carbendazim (CBZ). A straightforward one-step electrodeposition process was applied to prepare the Pt-rGO sensing platform. The incorporation of conductive rGO nanosheets along with distinctive structured Pt NPs significantly enhanced the effective electrode surface area and electron transfer of CBZ. Additionally, when exposed to 50 µM CBZ, Pt-rGO/GCE exhibited a higher current response compared to the bare electrode. Further investigations were performed to analyse and optimise the experimental parameters that could influence pesticide detection. Under the optimised conditions of pH 7 and 5 min of accumulation time, the Pt-rGO/GCE sensor showed a linear concentration detection range from 0.1 µM to 50 µM, with a detection limit of 3.46 nM. The fabricated sensor was successfully employed for CBZ detection in milk and tap water with 98.88% and 98.57% recovery, respectively. The fabricated sensor showed higher sensitivity and reproducibility, thus indicating the potential of this technology in the development of reliable sensors for the detection of CBZ or similar pesticides in forthcoming applications. Full article

(This article belongs to the Special Issue Applications of Advanced Nanomaterials in Sensor Devices)

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19 pages, 2026 KiB

Open AccessEditor’s ChoiceArticle

Metal Organic Frameworks: Current State and Analysis of Their Use as Modifiers of the Vulcanization Process and Properties of Rubber

by Katarzyna Klajn, Tomasz Gozdek and Dariusz M. Bieliński

Materials 2023, 16(24), 7631; https://doi.org/10.3390/ma16247631 - 13 Dec 2023

Cited by 3 | Viewed by 1861

Abstract

The interest in and application of metal organic frameworks (MOF) is increasing every year. These substances are widely used in many places, including the separation and storage of gases and energy, catalysis, electrochemistry, optoelectronics, and medicine. Their use in polymer technology is also [...] Read more.

The interest in and application of metal organic frameworks (MOF) is increasing every year. These substances are widely used in many places, including the separation and storage of gases and energy, catalysis, electrochemistry, optoelectronics, and medicine. Their use in polymer technology is also increasing, focusing mainly on the synthesis of MOF-polymer hybrid compounds. Due to the presence of metal ions in their structure, they can also serve as a component of the crosslinking system used for curing elastomers. This article presents the possibility of using zeolitic imidazolate framework ZIF-8 or MOF-5 as activators for sulfur vulcanization of styrene-butadiene rubber (SBR), replacing zinc oxide in conventional (CV) or effective (EF) curing systems to different extents. Their participation in the curing process and influence on the crosslinking density and structure, as well as the mechanical and thermal properties of the rubber vulcanizates, were examined. Full article

(This article belongs to the Special Issue Advanced Rubber Composites II)

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15 pages, 5584 KiB

Open AccessEditor’s ChoiceArticle

Multi-Order Asymmetric Acoustic Metamaterials with Broad Bandgaps at Subwavelength Scales

by Xiaopeng Wang, Wenjiong Chen and Sheng Li

Materials 2023, 16(24), 7587; https://doi.org/10.3390/ma16247587 - 10 Dec 2023

Cited by 1 | Viewed by 1406

Abstract

Noise manipulation at the subwavelength scale remains a challenging problem. To obtain better broadband sound isolation within the subwavelength range, a class of asymmetric acoustic metamaterials (AAMs) based on rotation is proposed, and this class of AAMs can further improve subwavelength sound isolation [...] Read more.

Noise manipulation at the subwavelength scale remains a challenging problem. To obtain better broadband sound isolation within the subwavelength range, a class of asymmetric acoustic metamaterials (AAMs) based on rotation is proposed, and this class of AAMs can further improve subwavelength sound isolation performance by introducing multi-orders. The influences of changing the alternate propagation length of the coiled channel and the square cavity in the unit cell on the band frequency distribution and the omnidirectional band structure were investigated. The effective parameters are calculated with the S-parameter retrieval method, and the generation and change mechanisms of the bandgaps were elucidated. The calculation of sound transmission characteristics showed that, in the asymmetric mode, the overall sound isolation performance of the structure was greatly improved, and the relative bandwidth expanded as the alternate propagation length of the coiled channel and square cavity increased. The omnidirectional bandgaps from the first-order to the third-order AAMs occupied 63.6%, 75.96%, and 76.84% of the subwavelength range, respectively. In particular, the first bandgap moves to the low frequency and becomes wider. Both the experimental results and numerical analyses consistently showed that disrupting structural symmetry enhances acoustic metamaterials for superior broadband sound isolation, inspiring broader applications for asymmetry in this field. Full article

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

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29 pages, 26002 KiB

Open AccessEditor’s ChoiceArticle

Effective Mechanical Properties of Periodic Cellular Solids with Generic Bravais Lattice Symmetry via Asymptotic Homogenization

by Padmassun Rajakareyar, Mostafa S. A. ElSayed, Hamza Abo El Ella and Edgar Matida

Materials 2023, 16(24), 7562; https://doi.org/10.3390/ma16247562 - 8 Dec 2023

Cited by 1 | Viewed by 1498

Abstract

In this paper, the scope of discrete asymptotic homogenization employing voxel (cartesian) mesh discretization is expanded to estimate high fidelity effective properties of any periodic heterogeneous media with arbitrary Bravais’s lattice symmetry, including those with non-orthogonal periodic bases. A framework was developed in [...] Read more.

In this paper, the scope of discrete asymptotic homogenization employing voxel (cartesian) mesh discretization is expanded to estimate high fidelity effective properties of any periodic heterogeneous media with arbitrary Bravais’s lattice symmetry, including those with non-orthogonal periodic bases. A framework was developed in Python with a proposed fast–nearest neighbour algorithm to accurately estimate the periodic boundary conditions of the discretized representative volume element of the lattice unit cell. Convergence studies are performed, and numerical errors caused by both voxel meshing and periodic boundary condition approximation processes are discussed in detail. It is found that the numerical error in periodicity approximation is cyclically dependent on the number of divisions performed during the meshing process and, thus, is minimized with a refined voxel mesh. Validation studies are performed by comparing the elastic properties of 2D hexagon lattices with orthogonal and non-orthogonal bases. The developed methodology was also applied to derive the effective properties of several lattice topologies, and variation of their anisotropic macroscopic properties with relative densities is presented as material selection charts. Full article

(This article belongs to the Special Issue Characterizations, Mechanical Properties and Constitutive Modeling of Advanced Materials)

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22 pages, 3811 KiB

Open AccessEditor’s ChoiceArticle

Photocatalyst Based on Nanostructured TiO₂ with Improved Photocatalytic and Antibacterial Properties

by Roberta Irodia, Camelia Ungureanu, Veronica Sătulu and Vasilica Mihaela Mîndroiu

Materials 2023, 16(24), 7509; https://doi.org/10.3390/ma16247509 - 5 Dec 2023

Cited by 3 | Viewed by 1516

Abstract

This study shows an easy way to use electrochemistry and plasma layering to make Cobalt-Blue-TiO₂ nanotubes that are better at catalysing reactions. Once a titanium plate has been anodized, certain steps are taken to make oxygen vacancies appear inside the TiO₂ [...] Read more.

This study shows an easy way to use electrochemistry and plasma layering to make Cobalt-Blue-TiO₂ nanotubes that are better at catalysing reactions. Once a titanium plate has been anodized, certain steps are taken to make oxygen vacancies appear inside the TiO₂ nanostructures. To find out how the Co deposition method changed the final catalyst’s properties, it was put through electrochemical tests (to find the charge transfer resistance and flat band potential) and optical tests (to find the band gap and Urbach energy). The catalysts were also described in terms of their shape, ability to stick to surfaces, and ability to inhibit bacteria. When Cobalt was electrochemically deposited to Blue-TiO₂ nanotubes, a film with star-shaped structures was made that was hydrophilic and antibacterial. The band gap energy went down from 3.04 eV to 2.88 eV and the Urbach energy went up from 1.171 eV to 3.836 eV using this electrochemical deposition method. Also, photodegradation tests with artificial doxycycline (DOX) water were carried out to see how useful the study results would be in real life. These extra experiments were meant to show how the research results could be used in real life and what benefits they might have. For the bacterial tests, both gram-positive and gram-negative bacteria were used, and BT/Co-E showed the best response. Additionally, photodegradation and photoelectrodegradation experiments using artificial doxycycline (DOX) water were conducted to determine the practical relevance of the research findings. The synergistic combination of light and applied potential leads to 70% DOX degradation after 60 min of BT/Co-E irradiation. Full article

(This article belongs to the Special Issue Novel Green Nanotechnologies Applied in Environmental Protection and Health)

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14 pages, 8347 KiB

Open AccessEditor’s ChoiceArticle

Wire Electrochemical Etching of Superhydrophobic Nickel Surfaces with Enhanced Corrosion Protection

by Binghan Wu, Defeng Yan, Junyi Lin and Jinlong Song

Materials 2023, 16(23), 7472; https://doi.org/10.3390/ma16237472 - 1 Dec 2023

Cited by 16 | Viewed by 1825

Abstract

Superhydrophobic nickel surfaces have significant advantages in the field of corrosion protection compared with traditional nickel corrosion protection methods which need a toxic chemical corrosion inhibitor. Electrochemical etching, an ideal method for fabricating superhydrophobic nickel surfaces, was also limited by low current density, [...] Read more.

Superhydrophobic nickel surfaces have significant advantages in the field of corrosion protection compared with traditional nickel corrosion protection methods which need a toxic chemical corrosion inhibitor. Electrochemical etching, an ideal method for fabricating superhydrophobic nickel surfaces, was also limited by low current density, resulting in low processing efficiency. To overcome this limitation, we proposed a new method to fabricate a superhydrophobic nickel surface using a wire electrochemical etching method. The wire electrochemical etching method accomplished the etching process by sweeping a controlled wire cathode across the surface of the anode nickel plate in an environmentally friendly neutral electrolyte, NaCl. The superhydrophobic nickel sample with a contact angle of 153° and a rolling angle of 10° could be fabricated by wire electrochemical etching and modification. Additionally, the optimal parameters of the wire electrochemical etching and the principle of superhydrophobic surface formation had also been systematically investigated, respectively. Moreover, the superhydrophobic nickel surface had self-cleaning performance, antifouling performance, corrosion protection, and abrasion resistance. Wire electrochemical etching improves the current density of processing, which means that this method improves the processing efficiency for fabricating a superhydrophobic nickel surface. This work is expected to enrich the theory and technology for fabricating superhydrophobic nickel surfaces to improve the corrosion protection of nickel. Full article

(This article belongs to the Special Issue Recent Progress in Corrosion Protection and Electrochemical Characterization of New and Advanced Materials)

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18 pages, 19065 KiB

Open AccessEditor’s ChoiceArticle

Optical and Structural Properties of Aluminum Nitride Epi-Films at Room and High Temperature

by Yanlian Yang, Yao Liu, Lianshan Wang, Shuping Zhang, Haixia Lu, Yi Peng, Wenwang Wei, Jia Yang, Zhe Chuan Feng, Lingyu Wan, Benjamin Klein, Ian T. Ferguson and Wenhong Sun

Materials 2023, 16(23), 7442; https://doi.org/10.3390/ma16237442 - 30 Nov 2023

Cited by 8 | Viewed by 1990

Abstract

The high-quality aluminum nitride (AlN) epilayer is the key factor that directly affects the performance of semiconductor deep-ultraviolet (DUV) photoelectronic devices. In this work, to investigate the influence of thickness on the quality of the AlN epilayer, two AlN-thick epi-film samples were grown [...] Read more.

The high-quality aluminum nitride (AlN) epilayer is the key factor that directly affects the performance of semiconductor deep-ultraviolet (DUV) photoelectronic devices. In this work, to investigate the influence of thickness on the quality of the AlN epilayer, two AlN-thick epi-film samples were grown on c-plane sapphire substrates. The optical and structural characteristics of AlN films are meticulously examined by using high-resolution X-ray diffraction (HR-XRD), scanning electron microscopy (SEM), a dual-beam ultraviolet-visible spectrophotometer, and spectroscopic ellipsometry (SE). It has been found that the quality of AlN can be controlled by adjusting the AlN film thickness. The phenomenon, in which the thicker AlNn film exhibits lower dislocations than the thinner one, demonstrates that thick AlN epitaxial samples can work as a strain relief layer and, in the meantime, help significantly bend the dislocations and decrease total dislocation density with the thicker epi-film. The Urbach’s binding energy and optical bandgap (E_g) derived by optical transmission (OT) and SE depend on crystallite size, crystalline alignment, and film thickness, which are in good agreement with XRD and SEM results. It is concluded that under the treatment of thickening film, the essence of crystal quality is improved. The bandgap energies of AlN samples obtained from SE possess larger values and higher accuracy than those extracted from OT. The Bose–Einstein relation is used to demonstrate the bandgap variation with temperature, and it is indicated that the thermal stability of bandgap energy can be improved with an increase in film thickness. It is revealed that when the thickness increases to micrometer order, the thickness has little effect on the change of E_g with temperature. Full article

(This article belongs to the Special Issue Chemical Vapor Deposition (CVD) Techniques in Materials Science for Electronic Devices Applications)

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23 pages, 8459 KiB

Open AccessEditor’s ChoiceReview

Structural Relaxation, Rejuvenation and Plasticity of Metallic Glasses: Microscopic Details from Anelastic Relaxation Spectra

by Michael Atzmon, Jong Doo Ju and Tianjiao Lei

Materials 2023, 16(23), 7444; https://doi.org/10.3390/ma16237444 - 30 Nov 2023

Cited by 4 | Viewed by 1776

Abstract

The lack of periodicity and long-range order poses significant challenges in explaining and modeling the properties of metallic glasses. Conventional modeling of nonexponential relaxation with stretched exponents leads to inconsistencies and rarely offers information on microscopic properties. Instead, using quasi-static anelastic relaxation, we [...] Read more.

The lack of periodicity and long-range order poses significant challenges in explaining and modeling the properties of metallic glasses. Conventional modeling of nonexponential relaxation with stretched exponents leads to inconsistencies and rarely offers information on microscopic properties. Instead, using quasi-static anelastic relaxation, we have obtained relaxation-time spectra over >10 orders of magnitude of time for several metallic glasses. The spectra enable us to examine in microscopic detail the distribution of shear transformation zones and their properties. They reveal an atomically-quantized hierarchy of shear transformation zones, providing insights into the effect of structural relaxation and rejuvenation, the origin of plasticity and the mechanisms of the alpha and beta relaxation. Full article

(This article belongs to the Special Issue Advances in Glass and Glass-Ceramic Materials)

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21 pages, 4542 KiB

Open AccessEditor’s ChoiceReview

Poly(ethylene glycol)-Engrafted Graphene Oxide for Gene Delivery and Nucleic Acid Amplification

by Khushbu Chauhan, Jin Woo, Woong Jung and Dong-Eun Kim

Materials 2023, 16(23), 7434; https://doi.org/10.3390/ma16237434 - 29 Nov 2023

Cited by 3 | Viewed by 2080

Abstract

Graphene oxide (GO) is an oxidized form of graphene accommodating various oxygen-containing functional groups such as hydroxyl, epoxy, and carboxyl groups on its surface. GO has been extensively utilized in various biomedical applications including the delivery of biomolecules and the development of biosensors [...] Read more.

Graphene oxide (GO) is an oxidized form of graphene accommodating various oxygen-containing functional groups such as hydroxyl, epoxy, and carboxyl groups on its surface. GO has been extensively utilized in various biomedical applications including the delivery of biomolecules and the development of biosensors owing to its beneficial properties such as high surface area, nucleic acid adsorption, and fluorescence quenching through fluorescence resonance energy transfer (FRET). However, despite these favorable properties, the direct utilization of GO in these applications is often limited by low dispersibility in a physiological medium, cytotoxicity, low biocompatibility, and a strong binding affinity of nucleic acids to GO surface. The large surface area of GO and the presence of various functional groups on its surface make it highly amenable to facile surface modifications, offering scope for GO surface functionalization to overcome these limitations. When polyethylene glycol (PEG), which is a biocompatible polymer, is conjugated to GO, the PEGylated GO enhances the biocompatibility and dispersibility, reduces cytotoxicity, and allows controlled drug delivery with controllable binding affinity towards nucleic acid. PEG-engrafted GO retains the beneficial properties of GO while effectively addressing its limitations, rendering it suitable for various biomedical applications. In this review, we present the recent advancements of PEGylated GO in gene/drug delivery and the facilitation of nucleic acid amplification techniques, which aid in the development of therapeutic and diagnostic tools, respectively. Full article

(This article belongs to the Special Issue Preparation and Application of High-Performance Multifunctional Graphene Macroscopic Assemblies and Composites)

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14 pages, 10632 KiB

Open AccessEditor’s ChoiceArticle

On Impact Damage and Repair of Composite Honeycomb Sandwich Structures

by Hang Zhang, Xiaopei Wang, Zhenhan Guo, Yuan Qian, Yan Shang and Deng’an Cai

Materials 2023, 16(23), 7374; https://doi.org/10.3390/ma16237374 - 27 Nov 2023

Viewed by 2482

Abstract

This study is conducted on glass fiber-reinforced composite honeycomb sandwich structures by introducing delamination damage through low-velocity impact tests, establishing a three-dimensional progressive damage analysis model, and evaluating the delamination damage characteristics and laws of honeycomb sandwich structures under different impact energies through [...] Read more.

This study is conducted on glass fiber-reinforced composite honeycomb sandwich structures by introducing delamination damage through low-velocity impact tests, establishing a three-dimensional progressive damage analysis model, and evaluating the delamination damage characteristics and laws of honeycomb sandwich structures under different impact energies through experiments. Repair techniques and process parameters for delamination damage are explored. It is found that as the impact energy increases, the damage area of honeycomb sandwich panels also increases, and the delamination damage extends from the impact center to the surrounding areas, accompanied by damage such as fiber fracture and matrix cracking. The strength recovery rates of sandwich panels at impact energies of 5 J, 15 J, and 25 J after repair are 71.90%, 65.89%, and 67.10%, respectively, which has a considerable repair effect. In addition, a progressive damage model for low-velocity impact on the composite honeycomb sandwich structure is established, and its accuracy and reliability are verified. Full article

(This article belongs to the Special Issue Advanced Fiber-Reinforced Composites: Design, Properties and Applications)

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13 pages, 4908 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Yttrium Oxide Hollow Films for Efficient Passive Radiative Cooling

by Heegyeom Jeon, Sohyeon Sung, Jeehoon Yu, Hyun Kim, Yong Seok Kim and Youngjae Yoo

Materials 2023, 16(23), 7373; https://doi.org/10.3390/ma16237373 - 27 Nov 2023

Cited by 1 | Viewed by 1480

Abstract

In recent years, many parts of the world have researched the transition to renewable energy, reducing energy consumption and moving away from fossil fuels. Among the studies to reduce energy consumption, passive radiative cooling can reduce the energy used for building cooling, and [...] Read more.

In recent years, many parts of the world have researched the transition to renewable energy, reducing energy consumption and moving away from fossil fuels. Among the studies to reduce energy consumption, passive radiative cooling can reduce the energy used for building cooling, and to improve this, the optical properties of atmospheric window emissivity and solar reflectance must be increased. In this study, hollow yttrium oxide (H-Y₂O₃) was fabricated using melamine formaldehyde (MF) as a sacrificial template to improve the optical properties of passive radiative cooling. We then used finite-difference time-domain (FDTD) simulations to predict the optical properties of the fabricated particles. This study compares the properties of MF@Y(OH)CO₃ and H-Y₂O₃ particles derived from the same process. H-Y₂O₃ was found to have a solar reflectance of 70.73% and an atmospheric window emissivity of 86.24%, and the field tests revealed that the temperature of MF@Y(OH)CO₃ was relatively low during the daytime. At night, the temperature of the H-Y₂O₃ film was found to be 2.6 °C lower than the ambient temperature of 28.8 °C. The optical properties and actual cooling capabilities of the particles at each stage of manufacturing the hollow particles were confirmed and the cooling capabilities were quantified. Full article

(This article belongs to the Special Issue Advanced Electronic Devices for Biomedical Applications)

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20 pages, 1209 KiB

Open AccessEditor’s ChoiceArticle

Phase Transition and Point Defects in the Ferroelectric Molecular Perovskite (MDABCO)(NH₄)I₃

by Francesco Cordero, Floriana Craciun, Patrizia Imperatori, Venanzio Raglione, Gloria Zanotti, Antoniu Moldovan and Maria Dinescu

Materials 2023, 16(23), 7323; https://doi.org/10.3390/ma16237323 - 24 Nov 2023

Cited by 2 | Viewed by 1168

Abstract

We measured the anelastic, dielectric and structural properties of the metal-free molecular perovskite (ABX

_{3}

) (MDABCO)(NH

_{4}

)I

_{3}

, which has already been demonstrated to become ferroelectric below

T_{C} =

448 K. Both the dielectric permittivity measured in air on [...] Read more.

We measured the anelastic, dielectric and structural properties of the metal-free molecular perovskite (ABX

_{3}

) (MDABCO)(NH

_{4}

)I

_{3}

, which has already been demonstrated to become ferroelectric below

T_{C} =

448 K. Both the dielectric permittivity measured in air on discs pressed from powder and the complex Young’s modulus measured on resonating bars in a vacuum show that the material starts to deteriorate with a loss of mass just above

T_{C}

, introducing defects and markedly lowering

T_{C}

. The elastic modulus softens by 50% when heating through the initial

T_{C}

, contrary to usual ferroelectrics, which are stiffer in the paraelectric phase. This is indicative of improper ferroelectricity, in which the primary order parameter of the transition is not the electric polarization, but the orientational order of the MDABCO molecules. The degraded material presents thermally activated relaxation peaks in the elastic energy loss, whose intensities increase together with the decrease in

T_{C}

. The peaks are much broader than pure Debye due to the general loss of crystallinity. This is also apparent from X-ray diffraction, but their relaxation times have parameters typical of point defects. It is argued that the major defects should be of the Schottky type, mainly due to the loss of (MDABCO)

^{2 +}

and I

^{-}

, leaving charge neutrality, and possibly (NH

_{4}

)

^{+}

vacancies. The focus is on an anelastic relaxation process peaked around 200 K at ∼1 kHz, whose relaxation time follows the Arrhenius law with

τ

_{0}

∼

10^{- 13}

s and

E ≃ 0.4

eV. This peak is attributed to I vacancies (V

_{X}

) hopping around MDABCO vacancies (V

_{A}

), and its intensity presents a peculiar dependence on the temperature and content of defects. The phenomenology is thoroughly discussed in terms of lattice disorder introduced by defects and partition of V

_{X}

among sites that are far from and close to the cation vacancies. A method is proposed for calculating the relative concentrations of V

_{X}

, that are untrapped, paired with V

_{A}

or forming V

_{X}

–V

_{A}

–V

_{X}

complexes. Full article

(This article belongs to the Special Issue Piezoelectric, Ferroelectric and Dielectric Properties of Materials and Related Applications)

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39 pages, 8010 KiB

Open AccessEditor’s ChoiceReview

Advances in Structural and Morphological Characterization of Thin Magnetic Films: A Review

by Payel Aich, Carlo Meneghini and Luca Tortora

Materials 2023, 16(23), 7331; https://doi.org/10.3390/ma16237331 - 24 Nov 2023

Cited by 4 | Viewed by 3159

Abstract

The present review places emphasis on a comprehensive survey of experimental techniques to probe the structural and morphological features at the nanoscale range in thin magnetic films, incorporating those available at in-house laboratories as well as those at state-of-the-art synchrotron radiation facilities. This [...] Read more.

The present review places emphasis on a comprehensive survey of experimental techniques to probe the structural and morphological features at the nanoscale range in thin magnetic films, incorporating those available at in-house laboratories as well as those at state-of-the-art synchrotron radiation facilities. This elucidating the range of available techniques, and the information they can yield represents a step for advancing the understanding of and for unlocking new possibilities in the design and optimization of thin magnetic films across a wide range of applications. Full article

(This article belongs to the Special Issue Growth and Applications of Oxide Thin Films and Heterostructures)

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16 pages, 3301 KiB

Open AccessEditor’s ChoiceArticle

Lignin-Based Mesoporous Hollow Carbon@MnO₂ Nanosphere Composite as an Anodic Material for Lithium-Ion Batteries

by Shun Li, Jianguo Huang and Guijin He

Materials 2023, 16(23), 7283; https://doi.org/10.3390/ma16237283 - 23 Nov 2023

Cited by 4 | Viewed by 1753

Abstract

The lignin-based mesoporous hollow carbon@MnO₂ nanosphere composites (L-C-NSs@MnO₂) were fabricated by using lignosulfonate as the carbon source. The nanostructured MnO₂ particles with a diameter of 10~20 nm were uniformly coated onto the surfaces of the [...] Read more.

The lignin-based mesoporous hollow carbon@MnO₂ nanosphere composites (L-C-NSs@MnO₂) were fabricated by using lignosulfonate as the carbon source. The nanostructured MnO₂ particles with a diameter of 10~20 nm were uniformly coated onto the surfaces of the hollow carbon nanospheres. The obtained L-C-NSs@MnO₂ nanosphere composite showed a prolonged cycling lifespan and excellent rate performance when utilized as an anode for LIBs. The L-C-NSs@MnO₂ nanocomposite (24.6 wt% of MnO₂) showed a specific discharge capacity of 478 mAh g⁻¹ after 500 discharge/charge cycles, and the capacity contribution of MnO₂ in the L-C-NSs@MnO₂ nanocomposite was estimated ca. 1268.8 mAh g⁻¹, corresponding to 103.2% of the theoretical capacity of MnO₂ (1230 mAh g⁻¹). Moreover, the capacity degradation rate was ca. 0.026% per cycle after long-term and high-rate Li⁺ insertion/extraction processes. The three-dimensional lignin-based carbon nanospheres played a crucial part in buffering the volumetric expansion and agglomeration of MnO₂ nanoparticles during the discharge/charge processes. Furthermore, the large specific surface areas and mesoporous structure properties of the hollow carbon nanospheres significantly facilitate the fast transport of the lithium-ion and electrons, improving the electrochemical activities of the L-C-NSs@MnO₂ electrodes. The presented work shows that the combination of specific structured lignin-based carbon nanoarchitecture with MnO₂ provides a brand-new thought for the designation and synthesis of high-performance materials for energy-related applications. Full article

(This article belongs to the Section Materials Chemistry)

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16 pages, 7242 KiB

Open AccessEditor’s ChoiceArticle

Graphene-Based Composites for Thermoelectric Applications at Room Temperature

by Sonya Harizanova, Vassil Vulchev and Radostina Stoyanova

Materials 2023, 16(23), 7262; https://doi.org/10.3390/ma16237262 - 21 Nov 2023

Cited by 2 | Viewed by 1850

Abstract

The thermoelectric materials that operate at room temperature represent a scientific challenge in finding chemical compositions with three optimized, independent parameters, namely electrical and thermal conductivity and the Seebeck coefficient. Here, we explore the concept of the formation of hybrid composites between carbon-based [...] Read more.

The thermoelectric materials that operate at room temperature represent a scientific challenge in finding chemical compositions with three optimized, independent parameters, namely electrical and thermal conductivity and the Seebeck coefficient. Here, we explore the concept of the formation of hybrid composites between carbon-based materials and oxides, with the aim of modifying their thermoelectric performance at room temperature. Two types of commercially available graphene-based materials are selected: N-containing reduced graphene oxide (NrGO) and expanded graphite (ExGr). Although the NrGO displays the lowest thermal conductivity at room temperature, the ExGr is characterized by the lowest electrical resistivity and a negative Seebeck coefficient. As oxides, we choose two perspective thermoelectric materials: p-type Ca₃Co₄O₉ and n-type Zn_0.995Al_0.005O. The hybrid composites were prepared by mechanical milling, followed by a pelleting. The thermoelectric efficiency was evaluated on the basis of its measured electrical resistivity, Seebeck coefficient and thermal conductivity at room temperature. It was found that that 2 wt.% of ExGr or NrGO leads to an enhancement of the thermoelectric activity of Ca₃Co₄O₉, while, for Zn_0.995Al_0.005O, the amount of ExGr varies between 5 and 20 wt.%. The effect of the composites’ morphology on the thermoelectric properties is discussed on the basis of SEM/EDS experiments. Full article

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

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15 pages, 20857 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Sliding Speed on the Tribological Properties of Ceramic Materials

by Giovanni Paolo Alparone, David Penney, Eifion Jewell, James Sullivan and Christopher Mills

Materials 2023, 16(23), 7252; https://doi.org/10.3390/ma16237252 - 21 Nov 2023

Cited by 1 | Viewed by 2040

Abstract

Ceramics are considered to be candidate materials for galvanising pot bearing materials due to their excellent corrosion resistance in many molten metals. Galvanising pot roll bearings must have excellent wear resistance, and, therefore, it is important to understand the wear behaviour of prospective [...] Read more.

Ceramics are considered to be candidate materials for galvanising pot bearing materials due to their excellent corrosion resistance in many molten metals. Galvanising pot roll bearings must have excellent wear resistance, and, therefore, it is important to understand the wear behaviour of prospective bearing materials. This study investigates the friction- and wear-resistant properties of select ceramics, namely, pure hBN, BN M26, AlN-BN, Macor, 3YSZ, Al₂O₃ and Si₃N₄. The ceramics were tested at different sliding speeds using a pin-on-disc device equipped with SiC pins. The lowest coefficient of friction (COF) achieved was below 0.1, and it was measured for pure hBN at a 3.14 m/min sliding speed. However, a wear scar analysis showed that the BN grades suffered from severe wear. The highest wear rate was obtained for BN M26 at a 9.42 m/min sliding speed and was equal to 17.1 × 10⁻⁶ mm³ N⁻¹ m⁻¹. It was shown that the wear coefficient of the tested ceramics varied exponentially with hardness. The lowest wear was observed on the 3YSZ, Al₂O₃ and Si₃N₄ ceramics, which showed no volume loss, and, for this reason, they can be potentially used as bearing materials in continuous galvanising lines. Full article

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

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15 pages, 4525 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Flame Retarded Rigid Polyurethane Foams with Different Types of Blowing Agents

by Marcin Zemła, Sławomir Michałowski and Aleksander Prociak

Materials 2023, 16(22), 7217; https://doi.org/10.3390/ma16227217 - 17 Nov 2023

Cited by 7 | Viewed by 1631

Abstract

In this study, rigid polyurethane foams modified with non-halogenated flame retardant were obtained. The foams were synthesized using two systems containing different blowing agents. In the first one, cyclopentane and water were used as a mixture of blowing agents, and in the second [...] Read more.

In this study, rigid polyurethane foams modified with non-halogenated flame retardant were obtained. The foams were synthesized using two systems containing different blowing agents. In the first one, cyclopentane and water were used as a mixture of blowing agents, and in the second one, only water was used as a chemical blowing agent. The systems were modified with the additive phosphorus flame retardant Roflam F5. The obtained modified foams were tested for their flammability and basic properties, such as apparent density, closed-cell contents and analyses of the cell structures, thermal conductivity, mechanical properties, and water absorption. Increasing the content of Roflam F5 caused a decrease in temperature during the combustion of the material and extended the burning time. The addition of 1.0 wt.% phosphorus derived from Roflam F5 caused the modified rigid polyurethane foam to become a self-extinguishing material. The increase in the content of Roflam F5 caused a decrease in the total heat release and the maximum heat release rate during the pyrolysis combustion flow calorimetry. The foams with the highest content of flame retardant and foamed with a chemical-physical and chemical blowing agent had a lower total heat release by 19% and 11%, respectively, compared to reference foams. Full article

(This article belongs to the Special Issue Advances in Development and Characterization of Polyurethane Foams)

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18 pages, 2522 KiB

Open AccessEditor’s ChoiceArticle

Cell-Laden 3D Printed GelMA/HAp and THA Hydrogel Bioinks: Development of Osteochondral Tissue-like Bioinks

by Shahrbanoo Jahangir, Jana Vecstaudza, Adriana Augurio, Elena Canciani, Liga Stipniece, Janis Locs, Mauro Alini and Tiziano Serra

Materials 2023, 16(22), 7214; https://doi.org/10.3390/ma16227214 - 17 Nov 2023

Cited by 7 | Viewed by 2922

Abstract

Osteochondral (OC) disorders such as osteoarthritis (OA) damage joint cartilage and subchondral bone tissue. To understand the disease, facilitate drug screening, and advance therapeutic development, in vitro models of OC tissue are essential. This study aims to create a bioprinted OC miniature construct [...] Read more.

Osteochondral (OC) disorders such as osteoarthritis (OA) damage joint cartilage and subchondral bone tissue. To understand the disease, facilitate drug screening, and advance therapeutic development, in vitro models of OC tissue are essential. This study aims to create a bioprinted OC miniature construct that replicates the cartilage and bone compartments. For this purpose, two hydrogels were selected: one composed of gelatin methacrylate (GelMA) blended with nanosized hydroxyapatite (nHAp) and the other consisting of tyramine-modified hyaluronic acid (THA) to mimic bone and cartilage tissue, respectively. We characterized these hydrogels using rheological testing and assessed their cytotoxicity with live-dead assays. Subsequently, human osteoblasts (hOBs) were encapsulated in GelMA-nHAp, while micropellet chondrocytes were incorporated into THA hydrogels for bioprinting the osteochondral construct. After one week of culture, successful OC tissue generation was confirmed through RT-PCR and histology. Notably, GelMA/nHAp hydrogels exhibited a significantly higher storage modulus (G′) compared to GelMA alone. Rheological temperature sweeps and printing tests determined an optimal printing temperature of 20 °C, which remained unaffected by the addition of nHAp. Cell encapsulation did not alter the storage modulus, as demonstrated by amplitude sweep tests, in either GelMA/nHAp or THA hydrogels. Cell viability assays using Ca-AM and EthD-1 staining revealed high cell viability in both GelMA/nHAp and THA hydrogels. Furthermore, RT-PCR and histological analysis confirmed the maintenance of osteogenic and chondrogenic properties in GelMA/nHAp and THA hydrogels, respectively. In conclusion, we have developed GelMA-nHAp and THA hydrogels to simulate bone and cartilage components, optimized 3D printing parameters, and ensured cell viability for bioprinting OC constructs. Full article

(This article belongs to the Section Biomaterials)

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15 pages, 2984 KiB

Open AccessEditor’s ChoiceArticle

Turning Waste into Treasure: The Full Technological Process and Product Performance Characterization of Flushable Wet Wipes Prepared from Corn Stalk

by Lulu Liu, Yeying Wang, Ziying He, Yang Cai, Kai Meng, Ke-Qin Zhang and Huijing Zhao

Materials 2023, 16(22), 7189; https://doi.org/10.3390/ma16227189 - 16 Nov 2023

Cited by 2 | Viewed by 1983

Abstract

As a daily consumable, wet wipes are mostly synthetic fibers, which are incinerated or landfilled after use. The nanoplastics generated during this process will lead to environmental pollution. The application of flushable wet wipes, which are dispersible and fully degradable, is of great [...] Read more.

As a daily consumable, wet wipes are mostly synthetic fibers, which are incinerated or landfilled after use. The nanoplastics generated during this process will lead to environmental pollution. The application of flushable wet wipes, which are dispersible and fully degradable, is of great significance. The main raw material for flushable wipes is wood pulp, which has a long growth cycle and high cost. Corn is widely planted and has a short growth cycle. Currently most corn stalk is treated by incineration, which produces a lot of smoke that pollutes the environment. Therefore, using corn stalk as the raw material for flushable wet wipes, replacing wood pulp, is both cost-effective and environmentally friendly. In this study, aiming at industrial production, we explored the full process of producing flushable wet wipes from corn stalk to pulp board, then to the final wipes. The corn stalk was treated using alkali and a bleaching agent to obtain corn stalk pulp, which was then made into pulp board through the nonwoven wet-laid process. The optimal parameters for the alkali treatment and bleaching were obtained. The properties of the corn stalk pulp board were compared with the commercial wood pulp board. Further, we mixed the corn stalk pulp with Lyocell fiber to prepare wet-laid webs, which were then bonded using a chemical binder poloxamer. Then, the evenness of the web, mechanical properties, absorption, and dispersibility of the flushable wipes were characterized. Results showed that the pulp obtained using the optimal treatment process has a high yield and better whiteness. The properties of the corn stalk pulp board are comparable with the commercial wood pulp board, which can therefore potentially be replaced by the corn stalk board prepared in our study. The prepared flushable wet wipes had good evenness and their water absorption rate was more than 600%. The mechanical strength in dry and wet states achieved 595.94 N/m and 179.00 N/m, respectively. Most importantly, the wet wipes can completely disperse under the standardized testing method. A good balance of dispersibility and wet strength of the wet wipes was achieved. Full article

(This article belongs to the Special Issue Advances in High-Performance Functional Nonwovens)

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16 pages, 4193 KiB

Open AccessEditor’s ChoiceArticle

A Yield Stress and Work Hardening Model of Al-Mg-Si Alloy Considering the Strengthening Effect of β” and β’ Precipitates

by Xiaoyu Zheng, Qi Huang, Hong Mao, Kai Li, Namin Xiao, Xingwu Li, Yong Du, Yuling Liu and Yi Kong

Materials 2023, 16(22), 7183; https://doi.org/10.3390/ma16227183 - 16 Nov 2023

Cited by 1 | Viewed by 1995

Abstract

Precipitates are the primary source of strength for the Al-Mg-Si alloy. Aluminum alloy in the peak-aged state mainly contains β” and β’ precipitates. Most of the literature has only considered the strengthening effect of β”. Here, we develop a single-crystal intensity model including [...] Read more.

Precipitates are the primary source of strength for the Al-Mg-Si alloy. Aluminum alloy in the peak-aged state mainly contains β” and β’ precipitates. Most of the literature has only considered the strengthening effect of β”. Here, we develop a single-crystal intensity model including both precipitate enhancement effects for the first time. This model was subsequently implemented into a crystal plastic finite-element method to model the uniaxial tensile process of a polycrystalline aggregate model of Al-Mg-Si alloy. The simulation results for uniaxial stretching are in good agreement with the experimental results, confirming that the constitutive parameters used for the single-crystal strength model with two precipitates are based on realistic physical implications. Furthermore, by comparing the uniaxial tensile simulation results of a peak-aged alloy considering the actual precipitated phase composition of the alloy with those assuming that the precipitated phase is only the β” phase, the predicted tensile strength of the former is around 5.65% lower than that of the latter, suggesting that the two kinds of precipitation should be separately considered when simulating the mechanical response of Al-Mg-Si alloy. It is highly expected that the present simulation strategy is not limited to Al-Mg-Si alloys, and it can be equally applied to the other age-enhanced alloys. Full article

(This article belongs to the Special Issue Metallic Materials: Microstructure, Phase Equilibria and Thermodynamics)

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18 pages, 5364 KiB

Open AccessEditor’s ChoiceArticle

Study of the Chemical Vapor Deposition of Nano-Sized Carbon Phases on {001} Silicon

by Teodor Milenov, Dimitar Trifonov, Dobromir A. Kalchevski, Stefan Kolev, Ivalina Avramova, Stoyan Russev, Kaloyan Genkov, Georgi Avdeev, Dimitar Dimov, Desislava M. Karaivanova and Evgenia Valcheva

Materials 2023, 16(22), 7190; https://doi.org/10.3390/ma16227190 - 16 Nov 2023

Cited by 5 | Viewed by 2028

Abstract

Different nano-sized phases were synthesized using chemical vapor deposition (CVD) processes. The deposition took place on {001} Si substrates at about 1150–1160 °C. The carbon source was thermally decomposed acetone (CH₃)₂CO in a main gas flow of argon. We [...] Read more.

Different nano-sized phases were synthesized using chemical vapor deposition (CVD) processes. The deposition took place on {001} Si substrates at about 1150–1160 °C. The carbon source was thermally decomposed acetone (CH₃)₂CO in a main gas flow of argon. We performed experiments at two ((CH₃)₂CO + Ar)/Ar) ratios and observed that two visually distinct types of layers were deposited after a one-hour deposition process. The first layer type, which appears more inhomogeneous, has areas of SiO₂ (about 5% of the surface area substrates) beside shiny bright and rough paths, and its Raman spectrum corresponds to diamond-like carbon, was deposited at a (CH₃)₂CO+Ar)/Ar = 1/5 ratio. The second layer type, deposited at (CH₃)₂CO + Ar)/Ar = a 1/0 ratio, appears homogeneous and is very dark brown or black in color and its Raman spectrum pointed to defect-rich multilayered graphene. The performed structural studies reveal the presence of diamond and diamond polytypes and seldom SiC nanocrystals, as well as some non-continuously mixed SiC and graphene-like films. The performed molecular dynamics simulations show that there is no possibility of deposition of sp³-hybridized on sp²-hybridized carbon, but there are completely realistic possibilities of deposition of sp²- on sp²- and sp³- on sp³-hybridized carbon under different scenarios. Full article

(This article belongs to the Special Issue Silicon Carbide Materials: Crystal Growth, Device Processing and Functional Applications)

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14 pages, 2807 KiB

Open AccessEditor’s ChoiceArticle

Influence of NF₃ Plasma-Treated HfO₂ Gate Insulator Surface on Tin Oxide Thin-Film Transistors

by Christophe Avis and Jin Jang

Materials 2023, 16(22), 7172; https://doi.org/10.3390/ma16227172 - 15 Nov 2023

Cited by 2 | Viewed by 1719

Abstract

We studied the impact of NF₃ plasma treatment on the HfO₂ gate insulator of amorphous tin oxide (a-SnO_x) thin-film transistors (TFTs). The plasma treatment was for 0, 10, or 30 s. The HfO₂ insulator demonstrated a slightly higher [...] Read more.

We studied the impact of NF₃ plasma treatment on the HfO₂ gate insulator of amorphous tin oxide (a-SnO_x) thin-film transistors (TFTs). The plasma treatment was for 0, 10, or 30 s. The HfO₂ insulator demonstrated a slightly higher breakdown voltage, whereas the capacitance value remained almost constant (~150 nF/cm²). The linear mobility slightly increased from ~30 to ~35 cm²/Vs when the treatment time increased from 0 to 10 s, whereas a 30 s-treated TFT demonstrated a decreased mobility of ~15 cm²/Vs. The subthreshold swing and the threshold voltage remained in the 100–120 mV/dec. range and near 0 V, respectively. The hysteresis dramatically decreased from ~0.5 V to 0 V when a 10 s treatment was applied, and the 10 s-treated TFT demonstrated the best stability under high current stress (HCS) of 100 μA. The analysis of the tin oxide thin film crystallinity and oxygen environment demonstrated that the a-SnO_x remained amorphous, whereas more metal–oxygen bonds were formed with a 10 s NF₃ plasma treatment. We also demonstrate that the density of states (DOS) significantly decreased in the 10 s-treated TFT compared to the other conditions. The stability under HCS was attributed to the HfO₂/a-SnO_x interface quality. Full article

(This article belongs to the Special Issue High-Performance Materials for Thin-Film Transistors and Other Electronic Device Applications)

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19 pages, 6987 KiB

Open AccessEditor’s ChoiceArticle

Research on the Mechanical Model and Hysteresis Performance of a New Mild Steel-Rotational Friction Hybrid Self-Centering Damper

by Debin Wang, Ran Pang, Gang Wang and Guoxi Fan

Materials 2023, 16(22), 7168; https://doi.org/10.3390/ma16227168 - 15 Nov 2023

Cited by 2 | Viewed by 1502

Abstract

A mild steel-friction self-centering damper with a hybrid energy-dissipation mechanism (MS-SCFD) was proposed, which consisted of a mild steel, frictional, dual-energy-dissipation system and a disc spring resetting system. The structure and principle of the MS-SCFD were explained in detail while the restoring force [...] Read more.

A mild steel-friction self-centering damper with a hybrid energy-dissipation mechanism (MS-SCFD) was proposed, which consisted of a mild steel, frictional, dual-energy-dissipation system and a disc spring resetting system. The structure and principle of the MS-SCFD were explained in detail while the restoring force model was established. The hysteretic behavior of the MS-SCFD under low-cycle reciprocating loading was modeled. Then, the influence of parameters such as the disc spring preload, the friction coefficient, and the soft-steel thickness on the mechanical properties of the MS-SCFD was investigated. The results indicate that the simulation results are basically consistent with the theoretical prediction results, with a maximum error of only 9.46% for the key points of bearing capacity. Since the MS-SCFD is provided with a hysteretic curve in the typical flag type, it will obtain the capacity of excellent self-centering performance. It can effectively enhance the stiffness, bearing capacity, and self-centering capability of the damper after the pre-pressure of the disc spring is increased. The energy-dissipation capacity of the MS-SCFD increases with the increase in the friction coefficient. However, it also increases the residual deformation of the MS-SCFD. The energy dissipation of the MS-SCFD is particularly sensitive to the thickness of mild steel. After being loaded, all components of the MS-SCFD are not damaged except for the plastic deformation caused by the yielding of the mild steel. The normal function of the MS-SCFD can be restored simply by replacing the mild steel plates after the earthquake. Therefore, it can significantly enhance the economy and applicability of the damper. Full article

(This article belongs to the Special Issue Structure and Mechanical Properties of Alloys, Volume III)

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27 pages, 17279 KiB

Open AccessEditor’s ChoiceArticle

Support Structures Optimisation for High-Quality Metal Additive Manufacturing with Laser Powder Bed Fusion: A Numerical Simulation Study

by Antonios Dimopoulos, Mohamad Salimi, Tat-Hean Gan and Panagiotis Chatzakos

Materials 2023, 16(22), 7164; https://doi.org/10.3390/ma16227164 - 14 Nov 2023

Cited by 10 | Viewed by 3258

Abstract

This study focuses on Metal Additive Manufacturing (AM), an emerging method known for its ability to create lightweight components and intricate designs. However, Laser Powder Bed Fusion (LPBF), a prominent AM technique, faces a major challenge due to the development of high residual [...] Read more.

This study focuses on Metal Additive Manufacturing (AM), an emerging method known for its ability to create lightweight components and intricate designs. However, Laser Powder Bed Fusion (LPBF), a prominent AM technique, faces a major challenge due to the development of high residual stress, resulting in flawed parts and printing failures. The study’s goal was to assess the thermal behaviour of different support structures and optimised designs to reduce the support volume and residual stress while ensuring high-quality prints. To explore this, L-shaped specimens were printed using block-type support structures through an LPBF machine. This process was subsequently validated through numerical simulations, which were in alignment with experimental observations. In addition to block-type support structures, line, contour, and cone supports were examined numerically to identify the optimal solutions that minimise the support volume and residual stress while maintaining high-quality prints. The optimisation approach was based on the Design of Experiments (DOE) methodology and multi-objective optimisation. The findings revealed that block supports exhibited excellent thermal behaviour. High-density supports outperformed low-density alternatives in temperature distribution, while cone-type supports were more susceptible to warping. These insights provide valuable guidance for improving the metal AM and LPBF processes, enabling their broader use in industries like aerospace, medical, defence, and automotive. Full article

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

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15 pages, 4127 KiB

Open AccessEditor’s ChoiceArticle

Analysis of the Effect of Skew Rolling Parameters on the Surface Roughness of C60 Steel Products Using ML Methods

by Konrad Lis

Materials 2023, 16(22), 7136; https://doi.org/10.3390/ma16227136 - 12 Nov 2023

Viewed by 1481

Abstract

This paper presents results from experimental and numerical studies of the skew rolling process used to shape axisymmetric products made of C60-grade steel. An experimental study was carried out to investigate the effect of process parameters described by the forming angle α, [...] Read more.

This paper presents results from experimental and numerical studies of the skew rolling process used to shape axisymmetric products made of C60-grade steel. An experimental study was carried out to investigate the effect of process parameters described by the forming angle α, the skew angle θ, the reduction ratio δ, and the jaw chuck velocity V_u on the surface roughness Ra of the forgings. Stepped forgings made of C60-grade steel were rolled. Based on numerical calculations, a machine learning regression model was developed that uses process parameters to predict the surface roughness of produced parts. The random forest model was found to be the most effective based on the determined metrics (MAE, RMSE, R²). A more detailed analysis of this model was performed using the SHAP library. The application of ML methods will enable optimization of skew rolling through appropriate selection of process parameters affecting improvement in product quality. Full article

(This article belongs to the Special Issue Advanced Manufacturing Processes of Metal Forming)

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