Materials

15 pages, 6097 KB

Open AccessEditor’s ChoiceArticle

Crack Initiation in Compacted Graphite Iron with Random Microstructure: Effect of Volume Fraction and Distribution of Particles

by Xingling Luo, Konstantinos P. Baxevanakis and Vadim V. Silberschmidt

Materials 2024, 17(13), 3346; https://doi.org/10.3390/ma17133346 - 6 Jul 2024

Cited by 5 | Viewed by 1670

Abstract

Thanks to the distinctive morphology of graphite particles in its microstructure, compacted graphite iron (CGI) exhibits excellent thermal conductivity together with high strength and durability. CGI is extensively used in many applications, e.g., engine cylinder heads and brakes. The structural integrity of such [...] Read more.

Thanks to the distinctive morphology of graphite particles in its microstructure, compacted graphite iron (CGI) exhibits excellent thermal conductivity together with high strength and durability. CGI is extensively used in many applications, e.g., engine cylinder heads and brakes. The structural integrity of such metal-matrix materials is controlled by the generation and growth of microcracks. Although the effects of the volume fraction and morphology of graphite inclusions on the tensile response of CGI were investigated in recent years, their influence on crack initiation is still unknown. Experimental studies of crack initiation require a considerable amount of time and resources due to the highly complicated geometries of graphite inclusions scattered throughout the metallic matrix. Therefore, developing a 2D computational framework for CGI with a random microstructure capable of predicting the crack initiation and path is desirable. In this work, an integrated numerical model is developed for the analysis of the effects of volume fraction and nodularity on the mechanical properties of CGI as well as its damage and failure behaviours. Finite-element models of random microstructure are generated using an in-house Python script. The determination of spacings between a graphite inclusion and its four adjacent particles is performed with a plugin, written in Java and implemented in ImageJ. To analyse the orientation effect of inclusions, a statistical analysis is implemented for representative elements in this research. Further, Johnson–Cook damage criteria are used to predict crack initiation in the developed models. The numerical simulations are validated with conventional tensile-test data. The created models can support the understanding of the fracture behaviour of CGI under mechanical load, and the proposed approach can be utilised to design metal-matrix composites with optimised mechanical properties and performance. Full article

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

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21 pages, 5652 KB

Open AccessEditor’s ChoiceArticle

Dynamic Adhesive Behavior and Biofilm Formation of Staphylococcus aureus on Polylactic Acid Surfaces in Diabetic Environments

by María Fernández-Grajera, Miguel A. Pacha-Olivenza, María Coronada Fernández-Calderón, María Luisa González-Martín and Amparo M. Gallardo-Moreno

Materials 2024, 17(13), 3349; https://doi.org/10.3390/ma17133349 - 6 Jul 2024

Cited by 1 | Viewed by 1544

Abstract

Interest in biodegradable implants has focused attention on the resorbable polymer polylactic acid. However, the risk of these materials promoting infection, especially in patients with existing pathologies, needs to be monitored. The enrichment of a bacterial adhesion medium with compounds that are associated [...] Read more.

Interest in biodegradable implants has focused attention on the resorbable polymer polylactic acid. However, the risk of these materials promoting infection, especially in patients with existing pathologies, needs to be monitored. The enrichment of a bacterial adhesion medium with compounds that are associated with human pathologies can help in understanding how these components affect the development of infectious processes. Specifically, this work evaluates the influence of glucose and ketone bodies (in a diabetic context) on the adhesion dynamics of S. aureus to the biomaterial polylactic acid, employing different approaches and discussing the results based on the physical properties of the bacterial surface and its metabolic activity. The combination of ketoacidosis and hyperglycemia (GK2) appears to be the worst scenario: this system promotes a state of continuous bacterial colonization over time, suppressing the stationary phase of adhesion and strengthening the attachment of bacteria to the surface. In addition, these supplements cause a significant increase in the metabolic activity of the bacteria. Compared to non-enriched media, biofilm formation doubles under ketoacidosis conditions, while in the planktonic state, it is glucose that triggers metabolic activity, which is practically suppressed when only ketone components are present. Both information must be complementary to understand what can happen in a real system, where planktonic bacteria are the ones that initially colonize a surface, and, subsequently, these attached bacteria end up forming a biofilm. This information highlights the need for good monitoring of diabetic patients, especially if they use an implanted device made of PLA. Full article

(This article belongs to the Special Issue Synthesis, Degradation and Biocompatibility of Bioresorbable Materials)

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11 pages, 9639 KB

Open AccessEditor’s ChoiceArticle

Ferrovalley and Quantum Anomalous Hall Effect in Janus TiTeCl Monolayer

by Yufang Chang, Zhijun Zhang, Li Deng, Yanzhao Wu and Xianmin Zhang

Materials 2024, 17(13), 3331; https://doi.org/10.3390/ma17133331 - 5 Jul 2024

Cited by 3 | Viewed by 1309

Abstract

Ferrovalley materials are garnering significant interest for their potential roles in advancing information processing and enhancing data storage capabilities. This study utilizes first-principles calculations to determine that the Janus monolayer TiTeCl exhibits the properties of a ferrovalley semiconductor. This material demonstrates valley polarization [...] Read more.

Ferrovalley materials are garnering significant interest for their potential roles in advancing information processing and enhancing data storage capabilities. This study utilizes first-principles calculations to determine that the Janus monolayer TiTeCl exhibits the properties of a ferrovalley semiconductor. This material demonstrates valley polarization with a notable valley splitting of 80 meV. Additionally, the Berry curvature has been computed across the first Brillouin zone of the monolayer TiTeCl. The research also highlights that topological phase transitions ranging from ferrovalley and half-valley metals to quantum anomalous Hall effect states can occur in monolayer TiTeCl under compressive strains ranging from −1% to 0%. Throughout these strain changes, monolayer TiTeCl maintains its ferromagnetic coupling. These characteristics make monolayer TiTeCl a promising candidate for the development of new valleytronic and topological devices. Full article

(This article belongs to the Special Issue Research on Interfaces and Transportation Phenomena in Materials Under Extreme Conditions)

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33 pages, 13446 KB

Open AccessEditor’s ChoiceReview

Doping Engineering in Manganese Oxides for Aqueous Zinc-Ion Batteries

by Fanjie Ji, Jiamin Yu, Sen Hou, Jinzhao Hu and Shaohui Li

Materials 2024, 17(13), 3327; https://doi.org/10.3390/ma17133327 - 5 Jul 2024

Cited by 6 | Viewed by 2760

Abstract

Manganese oxides (Mn_xO_y) are considered a promising cathode material for aqueous zinc-ion batteries (AZIBs) due to their high theoretical specific capacity, various oxidation states and crystal phases, and environmental friendliness. Nevertheless, their practical application is limited by their intrinsic [...] Read more.

Manganese oxides (Mn_xO_y) are considered a promising cathode material for aqueous zinc-ion batteries (AZIBs) due to their high theoretical specific capacity, various oxidation states and crystal phases, and environmental friendliness. Nevertheless, their practical application is limited by their intrinsic poor conductivity, structural deterioration, and manganese dissolution resulting from Jahn–Teller distortion. To address these problems, doping engineering is thought to be a favorable modification strategy to optimize the structure, chemistry, and composition of the material and boost the electrochemical performance. In this review, the latest progress on doped Mn_xO_y-based cathodes for AZIBs has been systematically summarized. The contents of this review are as follows: (1) the classification of Mn_xO_y-based cathodes; (2) the energy storage mechanisms of Mn_xO_y-based cathodes; (3) the synthesis route and role of doping engineering in Mn_xO_y-based cathodes; and (4) the doped Mn_xO_y-based cathodes for AZIBs. Finally, the development trends of Mn_xO_y-based cathodes and AZIBs are described. Full article

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

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18 pages, 3698 KB

Open AccessEditor’s ChoiceArticle

Electronic Properties of Group-III Nitride Semiconductors and Device Structures Probed by THz Optical Hall Effect

by Nerijus Armakavicius, Philipp Kühne, Alexis Papamichail, Hengfang Zhang, Sean Knight, Axel Persson, Vallery Stanishev, Jr-Tai Chen, Plamen Paskov, Mathias Schubert and Vanya Darakchieva

Materials 2024, 17(13), 3343; https://doi.org/10.3390/ma17133343 - 5 Jul 2024

Cited by 3 | Viewed by 2120

Abstract

Group-III nitrides have transformed solid-state lighting and are strategically positioned to revolutionize high-power and high-frequency electronics. To drive this development forward, a deep understanding of fundamental material properties, such as charge carrier behavior, is essential and can also unveil new and unforeseen applications. [...] Read more.

Group-III nitrides have transformed solid-state lighting and are strategically positioned to revolutionize high-power and high-frequency electronics. To drive this development forward, a deep understanding of fundamental material properties, such as charge carrier behavior, is essential and can also unveil new and unforeseen applications. This underscores the necessity for novel characterization tools to study group-III nitride materials and devices. The optical Hall effect (OHE) emerges as a contactless method for exploring the transport and electronic properties of semiconductor materials, simultaneously offering insights into their dielectric function. This non-destructive technique employs spectroscopic ellipsometry at long wavelengths in the presence of a magnetic field and provides quantitative information on the charge carrier density, sign, mobility, and effective mass of individual layers in multilayer structures and bulk materials. In this paper, we explore the use of terahertz (THz) OHE to study the charge carrier properties in group-III nitride heterostructures and bulk material. Examples include graded AlGaN channel high-electron-mobility transistor (HEMT) structures for high-linearity devices, highlighting the different grading profiles and their impact on the two-dimensional electron gas (2DEG) properties. Next, we demonstrate the sensitivity of the THz OHE to distinguish the 2DEG anisotropic mobility parameters in N-polar GaN/AlGaN HEMTs and show that this anisotropy is induced by the step-like surface morphology. Finally, we present the temperature-dependent results on the charge carrier properties of 2DEG and bulk electrons in GaN with a focus on the effective mass parameter and review the effective mass parameters reported in the literature. These studies showcase the capabilities of the THz OHE for advancing the understanding and development of group-III materials and devices. Full article

(This article belongs to the Special Issue Feature Papers in Electronic Materials Section (Volume 2)—15th Anniversary of Materials)

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18 pages, 3469 KB

Open AccessEditor’s ChoiceArticle

On the Feasibility of an LCD-Based Real-Time Converter for Ionizing Radiation Imaging

by Adam Januszko, Eugeniusz Zych, Wiktor Piecek, Witalis Pellowski, Krzysztof A. Bogdanowicz and Agnieszka Iwan

Materials 2024, 17(13), 3320; https://doi.org/10.3390/ma17133320 - 4 Jul 2024

Viewed by 1135

Abstract

Here we present the cascade converter (CC), which provides real-time imaging of ionizing radiation (IoR) distribution. It was designed and manufactured with the simplest architecture, utilizing liquid crystal display (LCD) technology. Based on two merged substrates with transparent electrodes, armed with functional layers, [...] Read more.

Here we present the cascade converter (CC), which provides real-time imaging of ionizing radiation (IoR) distribution. It was designed and manufactured with the simplest architecture, utilizing liquid crystal display (LCD) technology. Based on two merged substrates with transparent electrodes, armed with functional layers, with the cell filled with nematic liquid crystal, a display-like, IoR-stimulated CC was achieved. The CC comprises low-absorbing polymer substrates (made of polyethylene terephthalate—PET) armed with a transparent ITO electrode covered with a thin semipermeable membrane of polymer (biphenylperfluorocyclobutyl: BP-PFCB) doped with functional nanoparticles (NPs) of Lu₂O₃:Eu. This stack was covered with a photoconductive layer of α-Se and finally with a thin polyimide (PI) layer for liquid crystal alignment. The opposite substrate was made of LCD-type glass with ITO and polyimide aligning layers. Both substrates form a cell with a twisted structure of nematic liquid crystal (TN) driven with an effective electric field

E_{e f f}

. An effective electric field driving TN structure is generated with a sum of (1) a bias voltage

V_{B I A S}

applied to ITO transparent electrodes and (2) the photogenerated additional voltage

V_{X r a y}

induced between ITO and α-Se layers with a NPs-doped BP-PFCB polymer layer in-between. The IoR (here, X-ray) conversion into real imaging of the IoR distribution was achieved in the following stages: (1) conversion of IoR distribution into non-ionizing red light emitted with functional NPs, (2) transformation of red light into an electric charge distributed in a layer of the photoconductive α-Se, which is what results in the generation of distributed voltage

V_{X r a y}

, and (3) a voltage-mediated, distributed switching of the TN structure observed with the naked eye. The presented imaging device is characterized by a simple structure and a simple manufacturing process, with the potential for use as a portable element of IoR detection and as a dosimeter. Full article

(This article belongs to the Special Issue Visualizing Electronic and Structural Properties of Materials Using X-ray and Electron Beam Technique)

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19 pages, 4345 KB

Open AccessEditor’s ChoiceArticle

Electrical, Optical and Thermal Properties of Ge-Si-Sn-O Thin Films

by Femina Vadakepurathu and Mukti Rana

Materials 2024, 17(13), 3318; https://doi.org/10.3390/ma17133318 - 4 Jul 2024

Viewed by 4112

Abstract

This work evaluates the electrical, optical and thermal properties of Sn-doped Ge_xSi_1-xO_y thin films for use as microbolometer sensing materials. The films were prepared using a combination of a radio frequency (RF) magnetron and direct current (DC) sputtering [...] Read more.

This work evaluates the electrical, optical and thermal properties of Sn-doped Ge_xSi_1-xO_y thin films for use as microbolometer sensing materials. The films were prepared using a combination of a radio frequency (RF) magnetron and direct current (DC) sputtering using a Kurt J Leskar Proline PVD-75 series sputtering machine. Thin films were deposited in an O₂+Ar environment at a chamber pressure of 4 mTorr. The thicknesses of the thin films were varied between 300 nm–1.2 µm by varying the deposition time. The morphology and microstructure of thin films were investigated by atomic force microscope (AFM) imaging and X-ray diffraction (XRD), while the atomic composition was determined using the energy dispersive spectroscopy (EDS) function of a scanning electron microscope. The thin film with an atomic composition of Ge_0.45Si_0.05Sn_0.15O_0.35 was found to be amorphous. We used the Arrhenius relationship to determine the activation energy as well as temperature coefficient of resistance of the thin films, which were found to be 0.2529 eV and −3.26%/K, respectively. The noise voltage power spectral density (PSD) of the film was analyzed using a Primarius—9812DX noise analyzer using frequencies ranging from 2 Hz to 10 kHz. The noise voltage PSD of the film was found to be 1.76 × 10⁻¹¹ V²/Hz and 2.78 × 10⁻¹⁴ V²/Hz at 2 Hz and

1 K H z

frequencies, respectively. The optical constants were determined using the ellipsometry reflection data of samples using an RC2 and infrared (IR) VASE Mark-II ellipsometer from J A Woollam. Absorption, transmission and reflection data for a wavelength range of 900 nm–5000 nm were also determined. We also determined the optical constant values such as the real and imaginary parts of refractive index (n and k, respectively) and real and imaginary part of permittivity (

ε_{1}

and

ε_{2,}

respectively) for wavelength ranges between 193 nm to 35 µm. An optical band gap of 1.03 eV was determined from absorption data and using Tauc’s equation. In addition, the thermal conductivity of the film was analyzed using a Linseis thin film analyzer employing the 3ω method. The thermal conductivity of a 780 nm thick film was found to be 0.38 Wm⁻¹K⁻¹ at 300 K. From the data, the Ge-Si-Sn-O alloy was found to be a promising material for use as a sensing material for microbolometers. Full article

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

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14 pages, 4390 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Photoinduced Phase Transitions of Imine-Based Liquid Crystal Dimers with Twist–Bend Nematic Phases

by Yuki Arakawa and Yuto Arai

Materials 2024, 17(13), 3278; https://doi.org/10.3390/ma17133278 - 3 Jul 2024

Cited by 3 | Viewed by 1572

Abstract

Photoisomerizable molecules in liquid crystals (LCs) allow for photoinduced phase transitions, facilitating applications in a wide variety of photoresponsive materials. In contrast to the widely investigated azobenzene structure, research on the photoinduced phase-transition behavior of imine-based LCs is considerably limited. We herein report [...] Read more.

Photoisomerizable molecules in liquid crystals (LCs) allow for photoinduced phase transitions, facilitating applications in a wide variety of photoresponsive materials. In contrast to the widely investigated azobenzene structure, research on the photoinduced phase-transition behavior of imine-based LCs is considerably limited. We herein report the thermal and photoinduced phase-transition behaviors of photoisomerizable imine-based LC dimers with twist–bend nematic (N_TB) phases. We synthesize two homologous series of ester- and thioether-linked N-(4-cyanobenzylidene)aniline-based bent-shaped LC dimers with an even number of carbon atoms (n = 2, 4, 6, 8, and 10) in the central alkylene spacers, namely, CBCOOnSBA(CN) and CBOCOnSBA(CN), possessing oppositely directed ester linkages, C=OO and OC=O, respectively. Their thermal phase-transition behavior is examined using polarizing optical microscopy and differential scanning calorimetry. All dimers form a monotropic N_TB phase below the temperature of the conventional nematic (N) phase upon cooling. Remarkably, the N_TB phases of CBCOOnSBA(CN) (n = 2, 4, 6, and 8) and CBOCOnSBA(CN) (n = 6 and 8) supercool to room temperature and vitrify without crystallization. In addition, the phase-transition temperatures and entropy changes of CBCOOnSBA(CN) are lower than those of CBOCOnSBA(CN) at the same n. Under UV light irradiation, the N_TB and N phases transition to the N and isotropic phases, respectively, and reversibly return to their initial LC phases when the UV light is turned off. Full article

(This article belongs to the Special Issue Structural and Physical Properties of Liquid Crystals)

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16 pages, 4533 KB

Open AccessEditor’s ChoiceArticle

Structural Defects on Graphene Generated by Deposition of CoO: Effect of Electronic Coupling of Graphene

by Cayetano Hernández-Gómez, Pilar Prieto, Carlos Morales, Aida Serrano, Jan Ingo Flege, Javier Méndez, Julia García-Pérez, Daniel Granados and Leonardo Soriano

Materials 2024, 17(13), 3293; https://doi.org/10.3390/ma17133293 - 3 Jul 2024

Viewed by 1471

Abstract

Understanding the interactions in hybrid systems based on graphene and functional oxides is crucial to the applicability of graphene in real devices. Here, we present a study of the structural defects occurring on graphene during the early stages of the growth of CoO, [...] Read more.

Understanding the interactions in hybrid systems based on graphene and functional oxides is crucial to the applicability of graphene in real devices. Here, we present a study of the structural defects occurring on graphene during the early stages of the growth of CoO, tailored by the electronic coupling between graphene and the substrate in which it is supported: as received pristine graphene on polycrystalline copper (coupled), cleaned in ultra-high vacuum conditions to remove oxygen contamination, and graphene transferred to SiO₂/Si substrates (decoupled). The CoO growth was performed at room temperature by thermal evaporation of metallic Co under a molecular oxygen atmosphere, and the early stages of the growth were investigated. On the decoupled G/SiO₂/Si samples, with an initial low crystalline quality of graphene, the formation of a CoO wetting layer is observed, identifying the Stranski-Krastanov growth mode. In contrast, on coupled G/Cu samples, the Volmer-Weber growth mechanism is observed. In both sets of samples, the oxidation of graphene is low during the early stages of growth, increasing for the larger coverages. Furthermore, structural defects are developed in the graphene lattice on both substrates during the growth of CoO, which is significantly higher on decoupled G/SiO₂/Si samples mainly for higher CoO coverages. When approaching the full coverage on both substrates, the CoO islands coalesce to form a continuous CoO layer with strip-like structures with diameters ranging between 70 and 150 nm. Full article

(This article belongs to the Special Issue Current Research in Thin-Film Deposition: From Principles and Technologies to Film Properties and Applications)

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28 pages, 13227 KB

Open AccessEditor’s ChoiceReview

Nanoindentation Test of Ion-Irradiated Materials: Issues, Modeling and Challenges

by Hailiang Ma, Ping Fan, Qiuyu Qian, Qiaoli Zhang, Ke Li, Shengyun Zhu and Daqing Yuan

Materials 2024, 17(13), 3286; https://doi.org/10.3390/ma17133286 - 3 Jul 2024

Cited by 3 | Viewed by 2351

Abstract

Exposure of metals to neutron irradiation results in an increase in the yield strength and a significant loss of ductility. Irradiation hardening is also closely related to the fracture toughness temperature shift or the ductile-to-brittle transition temperature (DBTT) shift in alloys with a [...] Read more.

Exposure of metals to neutron irradiation results in an increase in the yield strength and a significant loss of ductility. Irradiation hardening is also closely related to the fracture toughness temperature shift or the ductile-to-brittle transition temperature (DBTT) shift in alloys with a body-centered cubic (bcc) crystal structure. Ion irradiation is an indispensable tool in the study of the radiation effects of materials for nuclear energy systems. Due to the shallow damage depth in ion-irradiated materials, the nanoindentation test is the most commonly used method for characterizing the changes in mechanical properties after ion irradiation. Issues that affect the analysis of irradiation hardening may arise due to changes in the surface morphology and mechanical properties, as well as the inherent complexities in nanoscale indentation. These issues, including changes in surface roughness, carbon contamination, the pile-up effect, and the indentation size effect, with corresponding measures, were reviewed. Modeling using the crystal plasticity finite element method of the nanoindentation of ion-irradiated materials was also reviewed. The challenges in extending the nanoindentation test to high temperatures and to multiscale simulation were addressed. Full article

(This article belongs to the Special Issue Characterisation and Testing of Materials: Advancing the State of the Art)

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20 pages, 7739 KB

Open AccessEditor’s ChoiceArticle

Resistance Analysis of Crack Propagation in Concrete Subjected to Hydraulic Pressure

by Yang Wang, Jingshan Sun, Gaohui Wang, Yongzhen Li and Weiqi Xiong

Materials 2024, 17(13), 3243; https://doi.org/10.3390/ma17133243 - 2 Jul 2024

Cited by 1 | Viewed by 1147

Abstract

The K_R resistance curve for hydraulic crack propagation in a concrete beam was determined and discussed. A semi-analytical method was introduced to calculate the hydraulic crack propagation in concrete. A series of concrete beams with various hydraulic pressures and initial crack depths [...] Read more.

The K_R resistance curve for hydraulic crack propagation in a concrete beam was determined and discussed. A semi-analytical method was introduced to calculate the hydraulic crack propagation in concrete. A series of concrete beams with various hydraulic pressures and initial crack depths were tested, and the hydraulic crack propagation in these beams was calculated. The calculated P-CMOD curves were first verified, and then the calculated K_R resistance curve for hydraulic crack propagation was determined. Based on the test results and calculation results, the following conclusions can be drawn: The proposed analysis method can accurately predict the hydraulic crack propagation process in concrete. The K_R resistance to hydraulic crack propagation in concrete decreases with the increase in hydraulic pressure but is less influenced by the initial crack depth of the test beams. In addition, the concrete beams collapse immediately under hydraulic fracturing once the K_Iw curve reaches the K_R resistance curve. This indicates that the failure of concrete structures under hydraulic fracturing occurs immediately once the driving force of crack propagation, dominated by the hydraulic pressure in the crack, becomes significant. Full article

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

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15 pages, 11104 KB

Open AccessEditor’s ChoiceArticle

FEM-Based Conductive Heat Transfer Analytical Description of Solidification Rate and Temperature Gradient during Lateral Laser Beam Oscillation Welding of Aluminum Alloy

by Jason Cheon, Cheolhee Kim, Sanghoon Kang and Minjung Kang

Materials 2024, 17(13), 3248; https://doi.org/10.3390/ma17133248 - 2 Jul 2024

Viewed by 1716

Abstract

This study investigates the feasibility of utilizing the finite element method (FEM)-based conductive heat transfer (CHT) analysis simulation to determine temperature gradients and solidification rates at the solid–liquid interface during laser beam oscillation welding. By comparing experimental observations with FEM-based CHT analysis, the [...] Read more.

This study investigates the feasibility of utilizing the finite element method (FEM)-based conductive heat transfer (CHT) analysis simulation to determine temperature gradients and solidification rates at the solid–liquid interface during laser beam oscillation welding. By comparing experimental observations with FEM-based CHT analysis, the underlying microstructural evolution and grain formation during welding were examined. FEM-based CHT enables the calculation of temperature gradients (G) and solidification rates (R), offering insights into the formation of equiaxed structures, which are crucial for suppressing hot cracking. Columnar-to-equiaxed structure transition thresholds, such as G/R and G³/R, accurately predict the emergence of fully equiaxed grain structures, validated by electron backscatter diffraction. This research provides valuable insights into temperature gradients and solidification rates in oscillation welding, guiding process design for achieving refined equiaxed structures and minimizing hot cracks. Full article

(This article belongs to the Special Issue Study on the Microstructure and Mechanical Properties of Welding Alloys and Steels)

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44 pages, 22443 KB

Open AccessEditor’s ChoiceArticle

Assessment of Methods to Derive Tensile Properties of Ultra-High-Performance Fiber-Reinforced Cementitious Composites

by Tamás Mészöly and Norbert Randl

Materials 2024, 17(13), 3259; https://doi.org/10.3390/ma17133259 - 2 Jul 2024

Viewed by 1702

Abstract

There is no unified method for deriving the tensile properties of fiber-reinforced ultra-high-performance cementitious composites (UHPCC). This study compares the most common material tests based on a large series of laboratory tests performed on a self-developed UHPCC mixture. The cementitious matrix, with a [...] Read more.

There is no unified method for deriving the tensile properties of fiber-reinforced ultra-high-performance cementitious composites (UHPCC). This study compares the most common material tests based on a large series of laboratory tests performed on a self-developed UHPCC mixture. The cementitious matrix, with a compressive strength of over 150 MPa and a matrix tensile strength of 8–10 MPa, was reinforced with 2% by volume of 15 mm long and 0.2 mm diameter straight high-strength steel microfibers. Over 100 uniaxial tensile tests were performed on three test configurations using cylindrical cores drilled out from larger prismatic specimens in three perpendicular directions. In addition to uniaxial tests, flexural tests on prismatic elements and flexural tests on thin plates were conducted, and the tensile properties were derived through digital image correlation (DIC) measurements and inverse analysis. Furthermore, splitting tensile tests on cylindrical specimens were employed to ascertain the tensile properties of the matrix. The outcomes of the diverse laboratory tests are presented and discussed in detail. The relationships between crack width and deflection in the context of flexural tests were developed and presented. In conjunction with compression tests and modulus of elasticity tests, the constitutive law is presented for the investigated materials. Full article

(This article belongs to the Special Issue Advances in Fiber-Reinforced Cementitious Composites for Concrete and Masonry Structures)

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12 pages, 5704 KB

Open AccessEditor’s ChoiceArticle

Evaluation of the Modal Parameters of a Unidirectional Carbon-Based Composite Structure Using the Influential Factor of Static Loading

by Seunghwan Chung and Chan-Jung Kim

Materials 2024, 17(13), 3209; https://doi.org/10.3390/ma17133209 - 1 Jul 2024

Cited by 1 | Viewed by 999

Abstract

Static loading can significantly alter the dynamics of unidirectional carbon-based composites (UCBCs), with modal parameters varying depending on the orientation of the carbon fibers. In this study, the sensitivity of modal parameters of UCBC structures under uniaxial static loading was investigated. The theoretical [...] Read more.

Static loading can significantly alter the dynamics of unidirectional carbon-based composites (UCBCs), with modal parameters varying depending on the orientation of the carbon fibers. In this study, the sensitivity of modal parameters of UCBC structures under uniaxial static loading was investigated. The theoretical static load influential factor was derived from a linearized UCBC model and corresponded to the transformed decoupled response over the mass-normalized static load. Three rectangular UCBC specimens (carbon fiber orientation of 0°, 45°, and 90°) were prepared under fixed–fixed boundary conditions using a jig fixture. Uniaxial static loads between 0 N and 1000 N were applied, and the first three modes of the UCBC specimens were analyzed. An isotropic SUS304 specimen was used as a reference. The linearization assumption about the UCBC structure was preliminarily validated with the Modal Assurance Criterion (MAC). A high influential factor was found for the UCBC specimen when carbon fibers were aligned with the static load direction at the first two resonance frequencies. Therefore, the proposed influential factor is an efficient indicator for determining the sensitivity of the dynamic response of a UCBC structure over a static load case. The variations in the influential factors for the UCBC specimens were more pronounced than for the isotropic specimens. Full article

(This article belongs to the Section Carbon Materials)

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13 pages, 4101 KB

Open AccessEditor’s ChoiceArticle

Phosphor Ceramic Composite for Tunable Warm White Light

by Ross A. Osborne, Nerine J. Cherepy, Peter S. Bleier, Romain M. Gaume and Stephen A. Payne

Materials 2024, 17(13), 3187; https://doi.org/10.3390/ma17133187 - 29 Jun 2024

Cited by 2 | Viewed by 1526

Abstract

Composite phosphor ceramics for warm white LED lighting were fabricated with K₂SiF₆:Mn⁴⁺ (KSF) as both a narrowband red phosphor and a translucent matrix in which yellow-emitting Y₃Al₅O₁₂:Ce³⁺ (YAG) particles were dispersed. [...] Read more.

Composite phosphor ceramics for warm white LED lighting were fabricated with K₂SiF₆:Mn⁴⁺ (KSF) as both a narrowband red phosphor and a translucent matrix in which yellow-emitting Y₃Al₅O₁₂:Ce³⁺ (YAG) particles were dispersed. The emission spectra of these composites under blue LED excitation were studied as a function of YAG loading and thickness. Warm white light with a color temperature of 2716 K, a high CRI of 92.6, and an R9 of 77.6 was achieved. A modest improvement in the thermal conductivity of the KSF ceramic of up to 9% was observed with the addition of YAG particles. In addition, a simple model was developed for predicting the emission spectra based on several parameters of the composite ceramics and validated with the experimental results. The emission spectrum can be tuned by varying the dopant concentrations, thickness, YAG loading, and YAG particle size. This work demonstrates the utility of KSF/YAG composite phosphor ceramics as a means of producing warm white light, which are potentially suitable for higher-drive applications due to their increased thermal conductivity and reduced droop compared with silicone-dispersed phosphor powders. Full article

(This article belongs to the Special Issue Study on Rare Earth Doped Luminescent Materials and Transparent Ceramics)

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19 pages, 6679 KB

Open AccessEditor’s ChoiceArticle

Cu- and Fe-Doped Ni-Mn-Sn Shape Memory Alloys with Enhanced Mechanical and Magnetocaloric Properties

by Siyao Ma, Xuexi Zhang, Guangping Zheng, Mingfang Qian and Lin Geng

Materials 2024, 17(13), 3172; https://doi.org/10.3390/ma17133172 - 28 Jun 2024

Cited by 1 | Viewed by 1603

Abstract

Ni-Mn-Sn-based ferromagnetic shape memory alloys (FSMAs) are multifunctional materials that are promising for solid-state refrigeration applications based on the magnetocaloric effect (MCE) and elastocaloric effect (eCE). However, a combination of excellent multi-caloric properties, suitable operating temperatures, and mechanical properties cannot be well achieved [...] Read more.

Ni-Mn-Sn-based ferromagnetic shape memory alloys (FSMAs) are multifunctional materials that are promising for solid-state refrigeration applications based on the magnetocaloric effect (MCE) and elastocaloric effect (eCE). However, a combination of excellent multi-caloric properties, suitable operating temperatures, and mechanical properties cannot be well achieved in these materials, posing a challenge for their practical application. In this work, we systematically study the phase transformations and magnetic properties of Ni_50−xMn₃₈Sn₁₂Cu_x (x = 0, 2, 3, 4, 5, and 6) and Ni_50−yMn₃₈Sn₁₂Fe_y (y = 0, 1, 2, 3, 4, and 5) alloys, and the magnetic-structural phase diagrams of these alloy systems are reported. The influences of the fourth-element doping on the phase transitions and magnetic properties of the alloys are elucidated by first-principles calculations. This work demonstrates that the fourth-element doping of Ni-Mn-Sn-based FSMA is effective in developing multicaloric refrigerants for practical solid-state refrigeration. Full article

(This article belongs to the Special Issue Physical Metallurgy of Metals and Alloys (3rd Edition))

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21 pages, 4863 KB

Open AccessEditor’s ChoiceArticle

Antifungal Hybrid Graphene–Transition-Metal Dichalcogenides Aerogels with an Ionic Liquid Additive as Innovative Absorbers for Preventive Conservation of Cultural Heritage

by George Gorgolis, Maria Kotsidi, Elena Messina, Valentina Mazzurco Miritana, Gabriella Di Carlo, Elsa Lesaria Nhuch, Clarissa Martins Leal Schrekker, Jeniffer Alves Cuty, Henri Stephan Schrekker, George Paterakis, Charalampos Androulidakis, Nikos Koutroumanis and Costas Galiotis

Materials 2024, 17(13), 3174; https://doi.org/10.3390/ma17133174 - 28 Jun 2024

Cited by 4 | Viewed by 1824

Abstract

The use and integration of novel materials are increasingly becoming vital tools in the field of preventive conservation of cultural heritage. Chemical factors, such as volatile organic compounds (VOCs), but also environmental factors such as high relative humidity, can lead to degradation, oxidation, [...] Read more.

The use and integration of novel materials are increasingly becoming vital tools in the field of preventive conservation of cultural heritage. Chemical factors, such as volatile organic compounds (VOCs), but also environmental factors such as high relative humidity, can lead to degradation, oxidation, yellowing, and fading of the works of art. To prevent these phenomena, highly porous materials have been developed for the absorption of VOCs and for controlling the relative humidity. In this work, graphene and transition-metal dichalcogenides (TMDs) were combined to create three-dimensional aerogels that absorb certain harmful substances. More specifically, the addition of the TMDs molybdenum disulfide and tungsten disulfide in such macrostructures led to the selective absorption of ammonia. Moreover, the addition of the ionic liquid 1-hexadecyl-3-methylimidazolium chloride promoted higher rates of VOCs absorption and anti-fungal activity against the fungus Aspergillus niger. These two-dimensional materials outperform benchmark porous absorbers in the absorption of all the examined VOCs, such as ammonia, formic acid, acetic acid, formaldehyde, and acetaldehyde. Consequently, they can be used by museums, galleries, or even storage places for the perpetual protection of works of art. Full article

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

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9 pages, 2034 KB

Open AccessEditor’s ChoiceArticle

Anisotropic Optical Response of Ti-Doped VO₂ Single Crystals

by Salvatore Macis, Lorenzo Mosesso, Annalisa D’Arco, Andrea Perucchi, Paola Di Pietro and Stefano Lupi

Materials 2024, 17(13), 3121; https://doi.org/10.3390/ma17133121 - 25 Jun 2024

Cited by 2 | Viewed by 1478

Abstract

This study delves into the effects of titanium (Ti) doping on the optical properties of vanadium dioxide (VO₂), a material well known for its metal–to–insulator transition (MIT) near room temperature. By incorporating Ti into VO₂’s crystal lattice, we aim [...] Read more.

This study delves into the effects of titanium (Ti) doping on the optical properties of vanadium dioxide (VO₂), a material well known for its metal–to–insulator transition (MIT) near room temperature. By incorporating Ti into VO₂’s crystal lattice, we aim to uncover the resultant changes in its physical properties, crucial for enhancing its application in smart devices. Utilizing polarized infrared micro–spectroscopy, we examined Ti_xV_1−xO₂ single crystals with varying Ti concentrations (x = 0.059, x = 0.082, and x = 0.187) across different crystal phases (the conductive rutile phase and insulating monoclinic phases M1 and M2) from the far–infrared to the visible spectral range. Our findings reveal that Ti doping significantly influences the phononic spectra, introducing absorption peaks not attributed to pure VO₂ or TiO₂. This is especially notable with polarization along the crystal growth axis, mainly in the x = 0.187 sample. Furthermore, we demonstrate that the electronic contribution to optical conductivity in the metallic phase exhibits strong anisotropy, higher along the c axis than the a–b plane. This anisotropy, coupled with the progressive broadening of the zone center infrared active phonon modes with increasing doping, highlights the complex interplay between structural and electronic dynamics in doped VO₂. Our results underscore the potential of Ti doping in fine-tuning VO₂’s electronic and thermochromic properties, paving the way for its enhanced application in optoelectronic devices and technologies. Full article

(This article belongs to the Section Advanced Materials Characterization)

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11 pages, 10922 KB

Open AccessEditor’s ChoiceArticle

Model of Shape Memory Alloy Actuator with the Usage of LSTM Neural Network

by Waldemar Rączka and Marek Sibielak

Materials 2024, 17(13), 3114; https://doi.org/10.3390/ma17133114 - 25 Jun 2024

Cited by 5 | Viewed by 1648

Abstract

Shape Memory Alloys (SMAs) are used to design actuators, which are one of the most fascinating applications of SMA. Usually, they are on-off actuators because, in the case of continuous actuators, the nonlinearity of their characteristics is the problem. The main problem, especially [...] Read more.

Shape Memory Alloys (SMAs) are used to design actuators, which are one of the most fascinating applications of SMA. Usually, they are on-off actuators because, in the case of continuous actuators, the nonlinearity of their characteristics is the problem. The main problem, especially in control systems in these actuators, is a hysteretic loop. There are many models of hysteresis, but from a control theory point of view, they are not helpful. This study used an artificial neural network (ANN) to model the SMA actuator hysteresis. The ANN structure and training method are presented in the paper. Data were generated from the Preisach model for training. This approach allowed for quick and controllable data generation, making experiments thoroughly planned and repeatable. The advantage and disadvantage of this approach is the lack of disturbances. The paper’s main goal is to model an SMA actuator. Additionally, it explores whether and how an ANN can describe and model the hysteresis loop. A literature review shows that ANNs are used to model hysteresis, but to a limited extent; this means that the hysteresis loop was modelled with a hysteretic element. Full article

(This article belongs to the Special Issue Modeling and Design Based on Shape Memory Behavior)

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24 pages, 11093 KB

Open AccessEditor’s ChoiceArticle

Experimental Study on the Flexural Performance of Steel–Polyvinyl Alcohol Hybrid Fiber-Reinforced Concrete

by Jingjiang Wu, Wenjie Zhang, Juhong Han, Zheyuan Liu, Jie Liu and Yafei Huang

Materials 2024, 17(13), 3099; https://doi.org/10.3390/ma17133099 - 25 Jun 2024

Cited by 2 | Viewed by 1148

Abstract

This paper explores the impact of steel–PVA hybrid fibers (S-PVA HF) on the flexural performance of panel concrete via three-point bending tests. Crack development in the concrete is analyzed through Digital Image Correlation (DIC) and Scanning Electron Microscope (SEM) experiments, unveiling the underlying [...] Read more.

This paper explores the impact of steel–PVA hybrid fibers (S-PVA HF) on the flexural performance of panel concrete via three-point bending tests. Crack development in the concrete is analyzed through Digital Image Correlation (DIC) and Scanning Electron Microscope (SEM) experiments, unveiling the underlying mechanisms. The evolution of cracks in concrete is quantitatively analyzed based on fractal theory, and a predictive model for flexural strength (PMFS) is established. The results show that the S-PVA HF exhibits a synergistic effect in enhancing and toughening the concrete at multi-scale. The crack area of steel–PVA hybrid fiber concrete (S-PVA HFRC) is linearly correlated with deflection (δ), and it further reduces the crack development rate and crack area compared to steel fiber-reinforced concrete (SFRC). The S-PVA HF improves the proportional ultimate strength (f_L) and residual flexural strength (f_R,j) of concrete, and the optimal flexural performance of concrete is achieved when the steel fiber dosage is 1.0% and the PVA fiber dosage is 0.2%. The established PMFS of hybrid fiber-reinforced concrete (HFRC) can effectively predict the flexural strength of concrete. Full article

(This article belongs to the Special Issue Numerical Modeling and Mechanical Properties of Fiber-Reinforced Cementitious Composites)

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91 pages, 19320 KB

Open AccessEditor’s ChoiceReview

Ammonothermal Crystal Growth of Functional Nitrides for Semiconductor Devices: Status and Potential

by Thomas Wostatek, V. Y. M. Rajesh Chirala, Nathan Stoddard, Ege N. Civas, Siddha Pimputkar and Saskia Schimmel

Materials 2024, 17(13), 3104; https://doi.org/10.3390/ma17133104 - 25 Jun 2024

Cited by 4 | Viewed by 3194

Abstract

The state-of-the-art ammonothermal method for the growth of nitrides is reviewed here, with an emphasis on binary and ternary nitrides beyond GaN. A wide range of relevant aspects are covered, from fundamental autoclave technology, to reactivity and solubility of elements, to synthesized crystalline [...] Read more.

The state-of-the-art ammonothermal method for the growth of nitrides is reviewed here, with an emphasis on binary and ternary nitrides beyond GaN. A wide range of relevant aspects are covered, from fundamental autoclave technology, to reactivity and solubility of elements, to synthesized crystalline nitride materials and their properties. Initially, the potential of emerging and novel nitrides is discussed, motivating their synthesis in single crystal form. This is followed by a summary of our current understanding of the reactivity/solubility of species and the state-of-the-art single crystal synthesis for GaN, AlN, AlGaN, BN, InN, and, more generally, ternary and higher order nitrides. Investigation of the synthesized materials is presented, with a focus on point defects (impurities, native defects including hydrogenated vacancies) based on GaN and potential pathways for their mitigation or circumvention for achieving a wide range of controllable functional and structural material properties. Lastly, recent developments in autoclave technology are reviewed, based on GaN, with a focus on advances in development of in situ technologies, including in situ temperature measurements, optical absorption via UV/Vis spectroscopy, imaging of the solution and crystals via optical (visible, X-ray), along with use of X-ray computed tomography and diffraction. While time intensive to develop, these technologies are now capable of offering unprecedented insight into the autoclave and, hence, facilitating the rapid exploration of novel nitride synthesis using the ammonothermal method. Full article

(This article belongs to the Special Issue Feature Papers in Electronic Materials Section (Volume 2)—15th Anniversary of Materials)

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27 pages, 17029 KB

Open AccessEditor’s ChoiceArticle

Influence of the Addition of TiO₂ Nanoparticles on the Self-Cleaning Capacity of Cementitious Composites

by Carmen Teodora Florean, Alexandra Csapai, Horatiu Vermesan, Timea Gabor, Andreea Hegyi, Vlad Stoian, Willi Andrei Uriciuc, Cristian Petcu and Marius Cîmpan

Materials 2024, 17(13), 3098; https://doi.org/10.3390/ma17133098 - 25 Jun 2024

Cited by 2 | Viewed by 4549

Abstract

This study evaluated the potential of incorporating TiO₂ nanoparticles (NT) into cementitious composites to provide self-cleaning and self-sanitising properties, as well as the partial replacement of natural aggregates with recycled glass (RGA), ceramic brick (RBA), granulated blast furnace slag (GBA), and textolite [...] Read more.

This study evaluated the potential of incorporating TiO₂ nanoparticles (NT) into cementitious composites to provide self-cleaning and self-sanitising properties, as well as the partial replacement of natural aggregates with recycled glass (RGA), ceramic brick (RBA), granulated blast furnace slag (GBA), and textolite waste (RTA) from electronic equipment on these properties. Based on the research results, the addition of NT to cementitious composites led to a significant reduction in contact angle, which means an increase in surface hydrophilicity. At the same time, Rhodamine B stain fading was highlighted, with the degree of whiteness recovery of NT composites exceeding that of the control by up to 11% for natural aggregate compositions, 10.6% for RGA compositions, 19.9% for RBA compositions, 15% for GBA compositions, and 13% for RTA compositions. In a mould-contaminated environment, it was shown that the introduction of NT allowed the material to develop a biocidal surface capacity which is also influenced by the nature of the aggregates used. Furthermore, the study revealed that, under controlled conditions, certain recycled waste aggregates, such as textolite, promoted mould growth, while others, such as brick and slag, inhibited it, highlighting not just the effect of the addition of NT, but also the significant influence of the aggregate type on the microbial resistance of cementitious composites. These improvements in the performance of cementitious composites are particularly advantageous when applied to prefabricated elements intended for the finishing and decorative surfaces of institutional (schools, administrative buildings, religious structures, etc.) or residential buildings. Full article

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

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14 pages, 6961 KB

Open AccessEditor’s ChoiceArticle

Oxide Scale Microstructure and Scale Growth Kinetics of the Hot-Pressed SiBCN-Ti Ceramics Oxidized at 1500 °C

by Hao Peng, Haobo Jiang, Daxin Li, Zhihua Yang, Wenjiu Duan, Dechang Jia and Yu Zhou

Materials 2024, 17(13), 3118; https://doi.org/10.3390/ma17133118 - 25 Jun 2024

Viewed by 1388

Abstract

In this study, the SiBCN-Ti series ceramics with different Ti contents were fabricated, and the oxidation resistance and microstructural evolution of the ceramics at 1500 °C for different times were explored. The results show that with the increase in oxidation time, pores and [...] Read more.

In this study, the SiBCN-Ti series ceramics with different Ti contents were fabricated, and the oxidation resistance and microstructural evolution of the ceramics at 1500 °C for different times were explored. The results show that with the increase in oxidation time, pores and bubbles are gradually formed in the oxide layer. When the oxidation time is less than or more than 4 h, the Ti(C, N) in the ceramics will maintain its initial structure or mostly transform to TiN. The introduction of Ti content can promote the formation of rutile silicate glass, thus healing the cracks and improving the oxidation resistance of the ceramics effectively. Full article

(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications, Volume II)

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20 pages, 4483 KB

Open AccessEditor’s ChoiceArticle

Modern Rare Earth Imprinted Membranes for the Recovery of Rare Earth Metal Ions from Coal Fly Ash Extracts

by Aleksandra Rybak, Aurelia Rybak, Sławomir Boncel, Anna Kolanowska, Agata Jakóbik-Kolon, Joanna Bok-Badura and Waldemar Kaszuwara

Materials 2024, 17(13), 3087; https://doi.org/10.3390/ma17133087 - 24 Jun 2024

Cited by 9 | Viewed by 2000

Abstract

The need to identify secondary sources of REEs and their recovery has led to the search for new methods and materials. In this study, a novel type of ion-imprinted adsorption membranes based on modified chitosan was synthesized. Their application for the recovery of [...] Read more.

The need to identify secondary sources of REEs and their recovery has led to the search for new methods and materials. In this study, a novel type of ion-imprinted adsorption membranes based on modified chitosan was synthesized. Their application for the recovery of chosen REEs from synthetic coal fly ash extracts was analyzed. The examined membranes were analyzed in terms of adsorption kinetics, isotherms, selectivity, reuse, and their separation abilities. The experimental data obtained were analyzed with two applications, namely, REE 2.0 and REE_isotherm. It was found that the adsorption of Nd³⁺ and Y³⁺ ions in the obtained membranes took place according to the chemisorption mechanism and was significantly controlled by film diffusion. The binding sites on the adsorbent surface were uniformly distributed; the examined ions showed the features of regular monolayer adsorption; and the adsorbents showed a strong affinity to the REE ions. The high values of K_d (900–1472.8 mL/g) demonstrate their high efficiency in the recovery of REEs. After five subsequent adsorption–desorption processes, approximately 85% of the value of one cycle was reached. The synthesized membranes showed a high rejection of the matrix components (Na, Mg, Ca, Al, Fe, and Si) in the extracts of the coal fly ashes, and the retention ratio for these Nd and Y ions was 90.11% and 80.95%, respectively. Full article

(This article belongs to the Special Issue Current and Future Trends in Mineral Processing and Extractive Metallurgy)

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16 pages, 1564 KB

Open AccessEditor’s ChoiceReview

Piezoelectric Charge Coefficient of Halide Perovskites

by Raja Sekhar Muddam, Joseph Sinclair and Lethy Krishnan Jagadamma

Materials 2024, 17(13), 3083; https://doi.org/10.3390/ma17133083 - 23 Jun 2024

Cited by 3 | Viewed by 2069

Abstract

Halide perovskites are an emerging family of piezoelectric and ferroelectric materials. These materials can exist in bulk, single-crystal, and thin-film forms. In this article, we review the piezoelectric charge coefficient (d_ij) of single crystals, thin films, and dimension-tuned halide perovskites based [...] Read more.

Halide perovskites are an emerging family of piezoelectric and ferroelectric materials. These materials can exist in bulk, single-crystal, and thin-film forms. In this article, we review the piezoelectric charge coefficient (d_ij) of single crystals, thin films, and dimension-tuned halide perovskites based on different measurement methods. Our study finds that the (d_ij) coefficient of the bulk and single-crystal samples is mainly measured using the quasi-static (Berlincourt) method, though the piezoforce microscopy (PFM) method is also heavily used. In the case of thin-film samples, the (d_ij) coefficient is dominantly measured by the PFM technique. The reported values of d_ij coefficients of halide perovskites are comparable and even better in some cases compared to existing materials such as PZT and PVDF. Finally, we discuss the promising emergence of quasi-static methods for thin-film samples as well. Full article

(This article belongs to the Special Issue Piezoelectrics and Ferroelectrics for End Users)

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21 pages, 4887 KB

Open AccessEditor’s ChoiceReview

Recent Progress in Creep-Resistant Aluminum Alloys for Diesel Engine Applications: A Review

by Raul Irving Arriaga-Benitez and Mihriban Pekguleryuz

Materials 2024, 17(13), 3076; https://doi.org/10.3390/ma17133076 - 22 Jun 2024

Cited by 8 | Viewed by 1875

Abstract

Diesel engines in heavy-duty vehicles are predicted to maintain a stable presence in the future due to the difficulty of electrifying heavy trucks, mine equipment, and railway cars. This trend encourages the effort to develop new aluminum alloy systems with improved performance at [...] Read more.

Diesel engines in heavy-duty vehicles are predicted to maintain a stable presence in the future due to the difficulty of electrifying heavy trucks, mine equipment, and railway cars. This trend encourages the effort to develop new aluminum alloy systems with improved performance at diesel engine conditions of elevated temperature and stress combinations to reduce vehicle weight and, consequently, CO₂ emissions. Aluminum alloys need to provide adequate creep resistance at ~300 °C and room-temperature tensile properties better than the current commercial aluminum alloys used for powertrain applications. The studies for improving creep resistance for aluminum casting alloys indicate that their high-temperature stability depends on the formation of high-density uniform dispersoids with low solid solubility and low diffusivity in aluminum. This review summarizes three generations of diesel engine aluminum alloys and focuses on recent work on the third-generation dispersoid-strengthened alloys. Additionally, new trends in developing creep resistance through the development of alloy systems other than Al-Si-based alloys, the optimization of manufacturing processes, and the use of thermal barrier coatings and composites are discussed. New progress on concepts regarding the thermal stability of rapidly solidified and nano-structured alloys and on creep-resistant alloy design via machine learning-based algorithms is also presented. Full article

(This article belongs to the Special Issue Development of Advanced Aluminum and Magnesium Alloys: Microstructure, Mechanical Properties and Processing)

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21 pages, 3610 KB

Open AccessEditor’s ChoiceArticle

Examination of Beam Theories for Buckling and Free Vibration of Functionally Graded Porous Beams

by Shuaishuai Wu, Yilin Li, Yumei Bao, Jun Zhu and Helong Wu

Materials 2024, 17(13), 3080; https://doi.org/10.3390/ma17133080 - 22 Jun 2024

Cited by 10 | Viewed by 1866

Abstract

This paper examines the accuracy and effectiveness of various beam theories in predicting the critical buckling loads and fundamental frequencies of functionally graded porous (FGP) beams whose material properties change continuously across the thickness. The beam theories considered are classical beam theory (CBT), [...] Read more.

This paper examines the accuracy and effectiveness of various beam theories in predicting the critical buckling loads and fundamental frequencies of functionally graded porous (FGP) beams whose material properties change continuously across the thickness. The beam theories considered are classical beam theory (CBT), first-order shear deformation beam theory (FSDBT), third-order shear deformation beam theory (TSDBT), and the broken-line hypothesis-based shear deformation beam theory (BSDBT). Governing equations for those beam theories are formulated by using the Hamilton’s principle and are then solved by means of the generalised differential quadrature method. Finite element simulation solutions are provided as reference results to assess the predictions of those beam theories. Comprehensive numerical results are presented to evaluate the influences of the porosity distribution and coefficient, slenderness ratio, and boundary condition on the difference between theoretical predictions and simulation results. It is found that the differences significantly increase as the porosity coefficient rises, and this effect becomes more noticeable for the rigid beam with a smaller slenderness ratio. Nonetheless, the results produced by the BSDBT are always the closest to simulation ones. The findings in this paper will contribute to the establishment of more refined theories for the mechanical analysis of FGP structures. Full article

(This article belongs to the Section Porous Materials)

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27 pages, 17974 KB

Open AccessEditor’s ChoiceReview

Properties and Applications of Iron–Chalcogenide Superconductors

by Jianlong Zhao, Junsong Liao, Chiheng Dong, Dongliang Wang and Yanwei Ma

Materials 2024, 17(13), 3059; https://doi.org/10.3390/ma17133059 - 21 Jun 2024

Cited by 1 | Viewed by 1501

Abstract

Iron–chalcogenide superconductors continue to captivate researchers due to their diverse crystalline structures and intriguing superconducting properties, positioning them as both a valuable platform for theoretical investigations and promising candidates for practical applications. This review begins with a comprehensive overview of the fabrication techniques [...] Read more.

Iron–chalcogenide superconductors continue to captivate researchers due to their diverse crystalline structures and intriguing superconducting properties, positioning them as both a valuable platform for theoretical investigations and promising candidates for practical applications. This review begins with a comprehensive overview of the fabrication techniques employed for various iron–chalcogenide superconductors, accompanied by a summary of their phase diagrams. Subsequently, it delves into the upper critical field, anisotropy, and critical current density. Furthermore, it discusses the successful fabrication of meters-long coated conductors and explores their applications in superconducting radio-frequency cavities and coils. Finally, several prospective avenues for future research are proposed. Full article

(This article belongs to the Special Issue Advances in Cuprates and Iron-Based Superconductors: Physics, Properties, and Applications)

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18 pages, 5495 KB

Open AccessEditor’s ChoiceArticle

Accelerated Design for Perovskite-Oxide-Based Photocatalysts Using Machine Learning Techniques

by Xiuyun Zhai and Mingtong Chen

Materials 2024, 17(12), 3026; https://doi.org/10.3390/ma17123026 - 20 Jun 2024

Cited by 6 | Viewed by 1671

Abstract

The rapid discovery of photocatalysts with desired performance among tens of thousands of potential perovskites represents a significant advancement. To expedite the design of perovskite-oxide-based photocatalysts, we developed a model of ABO₃-type perovskites using machine learning methods based on atomic and [...] Read more.

The rapid discovery of photocatalysts with desired performance among tens of thousands of potential perovskites represents a significant advancement. To expedite the design of perovskite-oxide-based photocatalysts, we developed a model of ABO₃-type perovskites using machine learning methods based on atomic and experimental parameters. This model can be used to predict specific surface area (SSA), a key parameter closely associated with photocatalytic activity. The model construction involved several steps, including data collection, feature selection, model construction, web-service development, virtual screening and mechanism elucidation. Statistical analysis revealed that the support vector regression model achieved a correlation coefficient of 0.9462 for the training set and 0.8786 for the leave-one-out cross-validation. The potential perovskites with higher SSA than the highest SSA observed in the existing dataset were identified using the model and our computation platform. We also developed a webserver of the model, freely accessible to users. The methodologies outlined in this study not only facilitate the discovery of new perovskites but also enable exploration of the correlations between the perovskite properties and the physicochemical features. These findings provide valuable insights for further research and applications of perovskites using machine learning techniques. Full article

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

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13 pages, 2343 KB

Open AccessEditor’s ChoiceArticle

Thermodynamic Model for Hydrogen Production from Rice Straw Supercritical Water Gasification

by Zhigang Liu, Zhiyong Peng, Lei Yi, Le Wang, Jingwei Chen, Bin Chen and Liejin Guo

Materials 2024, 17(12), 3038; https://doi.org/10.3390/ma17123038 - 20 Jun 2024

Cited by 7 | Viewed by 1625

Abstract

Supercritical water gasification (SCWG) technology is highly promising for its ability to cleanly and efficiently convert biomass to hydrogen. This paper developed a model for the gasification of rice straw in supercritical water (SCW) to predict the direction and limit of the reaction [...] Read more.

Supercritical water gasification (SCWG) technology is highly promising for its ability to cleanly and efficiently convert biomass to hydrogen. This paper developed a model for the gasification of rice straw in supercritical water (SCW) to predict the direction and limit of the reaction based on the Gibbs free energy minimization principle. The equilibrium distribution of rice straw gasification products was analyzed under a wide range of parameters including temperatures of 400–1200 °C, pressures of 20–50 MPa, and rice straw concentrations of 5–40 wt%. Coke may not be produced due to the excellent properties of supercritical water under thermodynamic constraints. Higher temperatures, lower pressures, and biomass concentrations facilitated the movement of the chemical equilibrium towards hydrogen production. The hydrogen yield was 47.17 mol/kg at a temperature of 650 °C, a pressure of 25 MPa, and a rice straw concentration of 5 wt%. Meanwhile, there is an absorptive process in the rice straw SCWG process for high-calorific value hydrogen production. Energy self-sufficiency of the SCWG process can be maintained by adding small amounts of oxygen (ER < 0.2). This work would be of great value in guiding rice straw SCWG experiments. Full article

(This article belongs to the Special Issue Application of Biomass Materials in the Fields of Electrochemistry and Thermochemistry)

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21 pages, 10012 KB

Open AccessEditor’s ChoiceArticle

Numerical Simulation of Friction Stir Welding of Dissimilar Al/Mg Alloys Using Coupled Level Set and Volume of Fluid Method

by Guanlan Zhang, Jinqiang Gao and Chuansong Wu

Materials 2024, 17(12), 3014; https://doi.org/10.3390/ma17123014 - 19 Jun 2024

Cited by 4 | Viewed by 1170

Abstract

The coupled level set and volume of fluid (CLSVOF) method is proposed to simulate the material distribution and physical properties during dissimilar aluminum/magnesium friction stir welding (FSW) process more accurately. Combined with a computational fluid dynamics model, the FSW process is numerically simulated [...] Read more.

The coupled level set and volume of fluid (CLSVOF) method is proposed to simulate the material distribution and physical properties during dissimilar aluminum/magnesium friction stir welding (FSW) process more accurately. Combined with a computational fluid dynamics model, the FSW process is numerically simulated and the heat transfer and material flow are analyzed. The results show that heat transfer and material flow have great influence on the Al/Mg bonding. In order to verify the accuracy of the model, the calculated results based on different methods are compared with the experimental results, and the Al/Mg interface simulated by the CLSVOF method is in better agreement with the experimental results. Finally, the material distribution and interface evolution near the tool at different times were studied based on the CLSVOF method. Full article

(This article belongs to the Section Metals and Alloys)

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16 pages, 2744 KB

Open AccessEditor’s ChoiceArticle

Thermal Stability of Encapsulated Carbon-Based Multiporous-Layered-Electrode Perovskite Solar Cells Extended to Over 5000 h at 85 °C

by Ryuki Tsuji, Yuuma Nagano, Kota Oishi, Eiji Kobayashi and Seigo Ito

Materials 2024, 17(12), 3002; https://doi.org/10.3390/ma17123002 - 19 Jun 2024

Cited by 6 | Viewed by 2390

Abstract

The key to the practical application of organometal–halide crystals perovskite solar cells (PSCs) is to achieve thermal stability through robust encapsulation. This paper presents a method to significantly extend the thermal stability lifetime of perovskite solar cells to over 5000 h at 85 [...] Read more.

The key to the practical application of organometal–halide crystals perovskite solar cells (PSCs) is to achieve thermal stability through robust encapsulation. This paper presents a method to significantly extend the thermal stability lifetime of perovskite solar cells to over 5000 h at 85 °C by demonstrating an optimal combination of encapsulation methods and perovskite composition for carbon-based multiporous-layered-electrode (MPLE)-PSCs. We fabricated four types of MPLE-PSCs using two encapsulation structures (over- and side-sealing with thermoplastic resin films) and two perovskite compositions ((5-AVA)_x(methylammonium (MA))_1−xPbI₃ and (formamidinium (FA))_0.9Cs_0.1PbI₃), and analyzed the 85 °C thermal stability followed by the ISOS-D-2 protocol. Without encapsulation, FA_0.9Cs_0.1PbI₃ exhibited higher thermal stability than (5-AVA)_x(MA)_1−xPbI₃. However, encapsulation reversed the phenomenon (that of (5-AVA)_x(MA)_1−xPbI₃ became stronger). The combination of the (5-AVA)_x(MA)_1−xPbI₃ perovskite absorber and over-sealing encapsulation effectively suppressed the thermal degradation, resulting in a PCE value of 91.2% of the initial value after 5072 h. On the other hand, another combination (side-sealing on (5-AVA)_x(MA)_1−xPbI₃ and over- and side-sealing on FA_0.9Cs_0.1PbI₃) resulted in decreased stability. The FACs-based perovskite was decomposed from these degradation mechanisms by the condensation reaction between FA and carbon. For side-sealing, the space between the cell and the encapsulant was estimated to contain approximately 1,260,000 times more H₂O than in over-sealing, which catalyzed the degradation of the perovskite crystals. Our results demonstrate that MA-based PSCs, which are generally considered to be thermally sensitive, can significantly extend their thermal stability after proper encapsulation. Therefore, we emphasize that finding the appropriate combination of encapsulation technique and perovskite composition is quite important to achieve further device stability. Full article

(This article belongs to the Special Issue Advanced Perovskite Solar Cells: Compatible Materials and Processes)

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41 pages, 24667 KB

Open AccessEditor’s ChoiceReview

Titanium Alloy Materials with Very High Cycle Fatigue: A Review

by Yuhang Wu, Weifeng He, Haitao Ma, Xiangfan Nie, Xiaoqing Liang, Jile Pan, Shiguang Wang, Min Shang and Li Cheng

Materials 2024, 17(12), 2987; https://doi.org/10.3390/ma17122987 - 18 Jun 2024

Cited by 5 | Viewed by 2466

Abstract

As the reliability and lifespan requirements of modern equipment continues to escalate, the problems with very high cycle fatigue (VHCF) has obtained increasingly widespread attention, becoming a hot topic in fatigue research. Titanium alloys, which are the most extensively used metal materials in [...] Read more.

As the reliability and lifespan requirements of modern equipment continues to escalate, the problems with very high cycle fatigue (VHCF) has obtained increasingly widespread attention, becoming a hot topic in fatigue research. Titanium alloys, which are the most extensively used metal materials in the modern aerospace industry, are particularly prone to VHCF issues. The present study systematically reviewed and summarized the latest (since 2010) developments in VHCF research on titanium alloy, with special focus on the (i) experimental methods, (ii) macroscopic and microscopic characteristics of the fatigue fractures, and (iii) construction of fatigue fracture models. More specifically, the review addresses the technological approaches that were used, mechanisms of fatigue crack initiation, features of the S–N curves and Goodman diagrams, and impact of various factors (such as processing, temperature, and corrosion). In addition, it elucidates the damage mechanisms, evolution, and modeling of VHCF in titanium alloys, thereby improving the understanding of VHCF patterns in titanium alloys and highlighting the current challenges in VHCF research. Full article

(This article belongs to the Special Issue Mechanics Behavior, Fatigue Damage, and Microstructure Evolution of Metallic Material)

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26 pages, 15125 KB

Open AccessEditor’s ChoiceArticle

Fatigue Life Data Fusion Method of Different Stress Ratios Based on Strain Energy Density

by Changyin Wang, Jianyao Yao, Xu Zhang, Yulin Wu, Xuyang Liu, Hao Liu, Yiheng Wei and Jianqiang Xin

Materials 2024, 17(12), 2982; https://doi.org/10.3390/ma17122982 - 18 Jun 2024

Cited by 1 | Viewed by 1356

Abstract

To accurately evaluate the probabilistic characteristics of the fatigue properties of materials with small sample data under different stress ratios, a data fusion method for torsional fatigue life under different stress ratios is proposed based on the energy method. A finite element numerical [...] Read more.

To accurately evaluate the probabilistic characteristics of the fatigue properties of materials with small sample data under different stress ratios, a data fusion method for torsional fatigue life under different stress ratios is proposed based on the energy method. A finite element numerical modeling method is used to calculate the fatigue strain energy density during fatigue damage. Torsional fatigue tests under different stresses and stress ratios are carried out to obtain a database for research. Based on the test data, the

W_{t}

-

N_{f}

curves under a single stress ratio and different stress ratios are calculated. The reliability of the models is illustrated by the scatter band diagram. More than 85% of points are within ±2 scatter bands, indicating that the fatigue life under different stress ratios can be represented by the same

W_{t}

-

N_{f}

curve. Furthermore, P-

W_{t}

-

N_{f}

prediction models are established to consider the probability characteristics. According to the homogeneity of the

W_{t}

-

N_{f}

model under different stress ratios, we can fuse the fatigue life data under different stress ratios and different strain energy densities. This data fusion method can expand the small sample test data and reduce the dispersion of the test data between different stress ratios. Compared with the pre-fusion data, the standard deviations of the post-fusion data are reduced by a maximum of 21.5% for the smooth specimens and 38.5% for the notched specimens. And more accurate P-

W_{t}

-

N_{f}

curves can be obtained to respond to the probabilistic properties of the data. Full article

(This article belongs to the Special Issue Advances in Computation and Modeling of Materials Mechanics)

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13 pages, 2928 KB

Open AccessEditor’s ChoiceArticle

Study of Morphology Control of Electro-Deposited Silver on Electro-Chemically Exfoliated Graphene Electrode and Its Conductivity

by Siwon Bak and Jongwon Shim

Materials 2024, 17(12), 2988; https://doi.org/10.3390/ma17122988 - 18 Jun 2024

Cited by 2 | Viewed by 1173

Abstract

Solution-processed graphene is beneficial for large-scale, low-cost production. However, its small lateral size, variable layer thickness, and uncontrollable oxidation level still restrict its widespread electronic application. In this study, a newly developed electrochemical exfoliation process was introduced, and a graphene-patched film electrode was [...] Read more.

Solution-processed graphene is beneficial for large-scale, low-cost production. However, its small lateral size, variable layer thickness, and uncontrollable oxidation level still restrict its widespread electronic application. In this study, a newly developed electrochemical exfoliation process was introduced, and a graphene-patched film electrode was fabricated by interfacial self-assembly. We were able to minimize the deterioration of graphene colloids during exfoliation by voltage and electrolyte modulation, but the patched structure of the graphene electrode still showed low conductivity with numerous inter-sheet junctions. Therefore, we determined the optimal conditions for the growth of fully networked silver structures on the multi-stacked graphene film by direct current electro-deposition, and these silver–graphene composite films showed significantly lowered graphene-colloid-patched film surface resistance. Full article

(This article belongs to the Special Issue Advances in Research on Graphene and Related Materials: From Preparation and Tuning Properties to Applications)

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13 pages, 2619 KB

Open AccessEditor’s ChoiceArticle

High-Strain-Rate Deformation Behavior of Co_0.96Cr_0.76Fe_0.85Ni_1.01Hf_0.40 Eutectic High-Entropy Alloy at Room and Cryogenic Temperatures

by Kun Jiang, Zhiping Xiong and Xi Chen

Materials 2024, 17(12), 2995; https://doi.org/10.3390/ma17122995 - 18 Jun 2024

Cited by 3 | Viewed by 1505

Abstract

The deformation behaviors of Co_0.96Cr_0.76Fe_0.85Ni_1.01Hf_0.40 eutectic high-entropy alloy (EHEA) under high strain rates have been investigated at both room temperature (RT, 298 K) and liquid nitrogen temperature (LNT, 77 K). The current Co_0.96 [...] Read more.

The deformation behaviors of Co_0.96Cr_0.76Fe_0.85Ni_1.01Hf_0.40 eutectic high-entropy alloy (EHEA) under high strain rates have been investigated at both room temperature (RT, 298 K) and liquid nitrogen temperature (LNT, 77 K). The current Co_0.96Cr_0.76Fe_0.85Ni_1.01Hf_0.40 EHEA exhibits a high yield strength of 740 MPa along with a high fracture strain of 35% under quasi-static loading. A remarkable positive strain rate effect can be observed, and its yield strength increased to 1060 MPa when the strain rate increased to 3000/s. Decreasing temperature will further enhance the yield strength significantly. The yield strength of this alloy at a strain rate of 3000/s increases to 1240 MPa under the LNT condition. Moreover, the current EHEA exhibits a notable increased strain-hardening ability with either an increasing strain rate or a decreasing temperature. Transmission electron microscopy (TEM) characterization uncovered that the dynamic plastic deformation of this EHEA at RT is dominated by dislocation slip. However, under severe conditions of high strain rate in conjunction with LNT, dislocation dissociation is promoted, resulting in a higher density of nanoscale deformation twins, stacking faults (SFs) as well as immobile Lomer–Cottrell (L-C) dislocation locks. These deformation twins, SFs and immobile dislocation locks function effectively as dislocation barriers, contributing notably to the elevated strain-hardening rate observed during dynamic deformation at LNT. Full article

(This article belongs to the Section Advanced Materials Characterization)

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28 pages, 4517 KB

Open AccessEditor’s ChoiceArticle

Mobility of Zn and Cu in Bentonites: Implications for Environmental Remediation

by Edyta Nartowska, Anna Podlasek, Magdalena Daria Vaverková, Eugeniusz Koda, Aleksandra Jakimiuk, Robert Kowalik and Tomasz Kozłowski

Materials 2024, 17(12), 2957; https://doi.org/10.3390/ma17122957 - 17 Jun 2024

Cited by 9 | Viewed by 1675

Abstract

The aim of this study was to evaluate the mobility of copper (Cu) and zinc (Zn) and their impact on the properties of bentonites and unfrozen water content. Limited research in this area necessitates further analysis to prevent the negative effects of metal [...] Read more.

The aim of this study was to evaluate the mobility of copper (Cu) and zinc (Zn) and their impact on the properties of bentonites and unfrozen water content. Limited research in this area necessitates further analysis to prevent the negative effects of metal interactions on bentonite effectiveness. Tests involved American (SWy-3, Stx-1b) and Slovak (BSvk) bentonite samples with Zn or Cu ion exchange. Sequential extraction was performed using the Community Bureau of Reference (BCR) method. Elemental content was analyzed via inductively coupled plasma optical emission spectrometry (ICP-OES). Unfrozen water content was measured using nuclear magnetic resonance (¹H-NMR) and differential scanning calorimetry (DSC). Results showed a significant influence of the main cation (Zn or Cu) on ion mobility, with toxic metal concentrations increasing mobility and decreasing residual fractions. Mobile Zn fractions increased with larger particle diameters, lower clay content, and shorter interplanar spacing, while the opposite was observed for Cu. Zn likely accumulated in larger clay pores, while Cu was immobilized in the bentonite complex. The stability of Zn or Cu ions increased with higher clay content or specific surface area. Residual Zn or Cu fractions were highest in uncontaminated bentonites with higher unfrozen water content, suggesting the potential formation of concentrated solutions in sub-zero temperatures, posing a threat to the clay–water environment, especially in cold regions. Full article

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

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17 pages, 11490 KB

Open AccessEditor’s ChoiceArticle

Pulse Design of Constant Strain Rate Loading in SHPB Based on Pulse Shaping Technique

by Shengpeng Chen, Runqiang Chi, Wuxiong Cao, Baojun Pang, Zhenlong Chao, Longtao Jiang, Tian Luo and Runwei Zhang

Materials 2024, 17(12), 2931; https://doi.org/10.3390/ma17122931 - 14 Jun 2024

Cited by 2 | Viewed by 1401

Abstract

The Split Hopkinson pressure bar (SHPB) is widely used for characterizing the mechanical behavior of materials at high strain rates. One of the most challenging factors is achieving constant strain rate (CSR) loading of the specimen at a certain strain rate. Obtaining the [...] Read more.

The Split Hopkinson pressure bar (SHPB) is widely used for characterizing the mechanical behavior of materials at high strain rates. One of the most challenging factors is achieving constant strain rate (CSR) loading of the specimen at a certain strain rate. Obtaining the effective incident pulse based on the experimental material for achieving CSR loading remains unresolved. This research focuses on obtaining the proper incident pulse for achieving constant strain rate loading using the pulse-shaping technique. A parameterized objective incident model in terms of the strain rate and quasi-static (or dynamic stress–strain) behavior of the material is established utilizing the three-wave method. Experimental pulses that closely resemble the desired objective pulses can be generated by adjusting parameters such as the geometry of the shaper, the shaper material, striker velocities, and the length of the striker according to the pulse-shaping model. The model is applied to the design of the incident pulse for B₄C_P/2024Al composite material, and the dynamic stress–strain curves at different strain rates are obtained under CSRs. This model provides effective guidance for selecting an appropriate shaper and achieving CSR loading in SHPB tests. Full article

(This article belongs to the Special Issue Impact Dynamic Response of Materials and Structures)

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16 pages, 22531 KB

Open AccessEditor’s ChoiceArticle

Aggregation–Growth and Densification Behavior of Titanium Particles in Molten Mg-MgCl₂ System

by Xin Yang, Kaihua Li, Jun Li, Zhuo Sheng and Ying Liu

Materials 2024, 17(12), 2904; https://doi.org/10.3390/ma17122904 - 13 Jun 2024

Cited by 1 | Viewed by 1091

Abstract

In this work, the preparation of titanium sponge by magnesium thermal method is regarded as the liquid-phase sintering process of titanium, and powder-metallurgy sintering technology is utilized to simulate the aggregation–growth and densification behavior of titanium particles in a high-temperature liquid medium (the [...] Read more.

In this work, the preparation of titanium sponge by magnesium thermal method is regarded as the liquid-phase sintering process of titanium, and powder-metallurgy sintering technology is utilized to simulate the aggregation–growth and densification behavior of titanium particles in a high-temperature liquid medium (the molten Mg-MgCl₂ system). It was found that compared with MgCl₂, Mg has better high-temperature wettability and reduction effect, which promotes titanium particles to form a sponge titanium skeleton at lower temperature. The aggregation degree of titanium particles and the densification degree of a sponge titanium skeleton can be improved by increasing the temperature and the relative content of Mg in the melting medium. The kinetics study shows that with the increase in temperature, the porosity of the titanium particle aggregates and the sponge titanium skeleton decreases, and their density growth rate increases. With the extension of time, the aggregation degree of titanium particles and the densification degree of sponge titanium gradually increase. This work provides a theoretical reference for controlling the density of titanium sponge in industry. Full article

(This article belongs to the Special Issue Porous Metals: Preparation, Microstructure, Properties and Performance)

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12 pages, 4984 KB

Open AccessEditor’s ChoiceArticle

Influence of the Polymerization Parameters on the Porosity and Thermal Stability of Polymeric Monoliths

by Małgorzata Maciejewska

Materials 2024, 17(12), 2860; https://doi.org/10.3390/ma17122860 - 12 Jun 2024

Cited by 3 | Viewed by 1403

Abstract

Rigid porous polymeric monoliths are robust, highly efficient, versatile stationary phases. They offer simple preparation and convenient modification provided by a whole range of synthesis factors, e.g., starting monomers, cross-linkers, initiators, porogens, polymerization techniques, and temperature. The main aim of this study was [...] Read more.

Rigid porous polymeric monoliths are robust, highly efficient, versatile stationary phases. They offer simple preparation and convenient modification provided by a whole range of synthesis factors, e.g., starting monomers, cross-linkers, initiators, porogens, polymerization techniques, and temperature. The main aim of this study was to synthesize polymeric monoliths and determine the correlation between polymerization parameters and the porosity and thermal stability of the obtained materials. Polymeric monoliths were synthesized directly in HPLC columns using N-vinyl-2-pyrrolidone (NVP) and 4-vinylpiridine (4VP) as functional monomers, with trimethylolpropane trimethacrylate (TRIM) serving as the cross-linking monomer. During copolymerization a mixture of cyclohexanol/decane-1-ol was used as the pore-forming diluent. Polymerization was carried out at two different temperatures: 55 and 75 °C. As a result, monoliths with highly developed internal structure were synthesized. The value of their specific surface area was in the range of 92 m²/g to 598 m²/g, depending on the monomer composition and polymerization temperature. Thermal properties of the obtained materials were investigated by means of thermogravimetry (TG). Significant differences in thermal behavior were noticed between monoliths synthesized at 55 and 75 °C. Additionally, the poly(NVP-co-TRIM) monolith was successfully applied in GC analyses. Full article

(This article belongs to the Special Issue Polymer Materials: Research, Development and Application)

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12 pages, 2219 KB

Open AccessEditor’s ChoiceArticle

Phosphorus-Doping Enables the Superior Durability of a Palladium Electrocatalyst towards Alkaline Oxygen Reduction Reactions

by Wen-Yuan Zhao, Miao-Ying Chen, Hao-Ran Wu, Wei-Dong Li and Bang-An Lu

Materials 2024, 17(12), 2879; https://doi.org/10.3390/ma17122879 - 12 Jun 2024

Cited by 1 | Viewed by 1343

Abstract

The sluggish kinetics of oxygen reduction reactions (ORRs) require considerable Pd in the cathode, hindering the widespread of alkaline fuel cells (AFCs). By alloying Pd with transition metals, the oxygen reduction reaction’s catalytic properties can be substantially enhanced. Nevertheless, the utilization of Pd-transition [...] Read more.

The sluggish kinetics of oxygen reduction reactions (ORRs) require considerable Pd in the cathode, hindering the widespread of alkaline fuel cells (AFCs). By alloying Pd with transition metals, the oxygen reduction reaction’s catalytic properties can be substantially enhanced. Nevertheless, the utilization of Pd-transition metal alloys in fuel cells is significantly constrained by their inadequate long-term durability due to the propensity of transition metals to leach. In this study, a nonmetallic doping strategy was devised and implemented to produce a Pd catalyst doped with P that exhibited exceptional durability towards ORRs. Pd₃P_0.95 with an average size of 6.41 nm was synthesized by the heat-treatment phosphorization of Pd nanoparticles followed by acid etching. After P-doping, the size of the Pd nanoparticles increased from 5.37 nm to 6.41 nm, and the initial mass activity (MA) of Pd₃P_0.95/NC reached 0.175 A mg_Pd⁻¹ at 0.9 V, slightly lower than that of Pd/C. However, after 40,000 cycles of accelerated durability testing, instead of decreasing, the MA of Pd₃P_0.95/NC increased by 6.3% while the MA loss of Pd/C was 38.3%. The durability was primarily ascribed to the electronic structure effect and the aggregation resistance of the Pd nanoparticles. This research also establishes a foundation for the development of Pd-based ORR catalysts and offers a direction for the future advancement of catalysts designed for practical applications in AFCs. Full article

(This article belongs to the Section Materials Chemistry)

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14 pages, 5499 KB

Open AccessEditor’s ChoiceArticle

Comparison of Magnetron-Sputtered and Cathodic Arc-Deposited Ti and Cr Thin Films on Stainless Steel for Bipolar Plates

by Nils Fredebeul-Beverungen, Maximilian Steinhorst and Teja Roch

Materials 2024, 17(12), 2864; https://doi.org/10.3390/ma17122864 - 12 Jun 2024

Cited by 2 | Viewed by 1563

Abstract

In this work, the potential of magnetron sputtering, as well as cathodic arc evaporation, is investigated with regard to its suitability as a bipolar plate coating of a PEM fuel cell. For this purpose, Cr and Ti thin films were deposited onto a [...] Read more.

In this work, the potential of magnetron sputtering, as well as cathodic arc evaporation, is investigated with regard to its suitability as a bipolar plate coating of a PEM fuel cell. For this purpose, Cr and Ti thin films were deposited onto a 0.1 mm SS316L by varying the power and bias voltage. The surface structure and thickness of the coatings are examined via SEM and tactile profilometry. Moreover, the coating variants are compared with each other based on the electrical and electrochemical properties relevant to bipolar plates. The sputtered Cr thin films achieve the lowest contact resistance values and exhibit a columnar structure with a smooth surface. Regarding the electrochemical properties, titanium deposited via cathodic arc evaporation has a low current density in the passive region and high breakthrough potential. All in all, both deposition techniques have their individual advantages for the preparation of bipolar plates’ coatings. However, Ti thin films prepared via cathodic arc seem to be the most suitable option due to the combination of a high deposition rate, a low cost and good coating properties. Full article

(This article belongs to the Special Issue Friction, Corrosion and Protection of Material Surfaces)

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14 pages, 2127 KB

Open AccessEditor’s ChoiceArticle

The Effect of Cesium Incorporation on the Vibrational and Elastic Properties of Methylammonium Lead Chloride Perovskite Single Crystals

by Syed Bilal Junaid, Furqanul Hassan Naqvi and Jae-Hyeon Ko

Materials 2024, 17(12), 2862; https://doi.org/10.3390/ma17122862 - 12 Jun 2024

Viewed by 1353

Abstract

Hybrid organic-inorganic lead halide perovskites (LHPs) have emerged as a highly significant class of materials due to their tunable and adaptable properties, which make them suitable for a wide range of applications. One of the strategies for tuning and optimizing LHP-based devices is [...] Read more.

Hybrid organic-inorganic lead halide perovskites (LHPs) have emerged as a highly significant class of materials due to their tunable and adaptable properties, which make them suitable for a wide range of applications. One of the strategies for tuning and optimizing LHP-based devices is the substitution of cations and/or anions in LHPs. The impact of Cs substitution at the A site on the structural, vibrational, and elastic properties of MA_xCs_1−xPbCl₃-mixed single crystals was investigated using X-ray diffraction (XRD) and Raman and Brillouin light scattering techniques. The XRD results confirmed the successful synthesis of impurity-free single crystals, which exhibited a phase coexistence of dominant cubic and minor orthorhombic symmetries. Raman spectroscopy was used to analyze the vibrational modes associated with the PbCl₆ octahedra and the A-site cation movements, thereby revealing the influence of cesium incorporation on the lattice dynamics. Brillouin spectroscopy was employed to investigate the changes in elastic properties resulting from the Cs substitution. The incorporation of Cs cations induced lattice distortions within the inorganic framework, disrupting the hydrogen bonding between the MA cations and PbCl₆ octahedra, which in turn affected the elastic constants and the sound velocities. The substitution of the MA cations with smaller Cs cations resulted in a stiffer lattice structure, with the two elastic constants increasing up to a Cs content of 30%. The current findings facilitate a fundamental understanding of mixed lead chloride perovskite materials, providing valuable insights into their structural and vibrational properties. Full article

(This article belongs to the Special Issue Terahertz Vibrational Spectroscopy in Advanced Materials)

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14 pages, 5388 KB

Open AccessEditor’s ChoiceArticle

Additively-Manufactured Broadband Metamaterial-Based Luneburg Lens for Flexible Beam Scanning

by Xuanjing Li, Rui Feng, Quilin Tan, Jianjia Yi, Shixiong Wang, Feng He and Shah Nawaz Burokur

Materials 2024, 17(12), 2847; https://doi.org/10.3390/ma17122847 - 11 Jun 2024

Viewed by 2353

Abstract

Multi-beam microwave antennas have attracted enormous attention owing to their wide range of applications in communication systems. Here, we propose a broadband metamaterial-based multi-beam Luneburg lens-antenna with low polarization sensitivity. The lens is constructed from additively manufactured spherical layers, where the effective permittivity [...] Read more.

Multi-beam microwave antennas have attracted enormous attention owing to their wide range of applications in communication systems. Here, we propose a broadband metamaterial-based multi-beam Luneburg lens-antenna with low polarization sensitivity. The lens is constructed from additively manufactured spherical layers, where the effective permittivity of the constituting elements is obtained by adjusting the ratio of dielectric material to air. Flexible microstrip patch antennas operating at different frequencies are used as primary feeds illuminating the lens to validate the radiation features of the lens-antenna system. The proposed Luneburg lens-antenna achieves ±72° beam scanning angle over a broad frequency range spanning from 2 GHz to 8 GHz and presents a gain between 15.3 dBi and 22 dBi, suggesting potential applications in microwave- and millimeter-wave mobile communications, radar detection and remote sensing. Full article

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

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17 pages, 3917 KB

Open AccessEditor’s ChoiceArticle

Polyurethane Composites Recycling with Styrene–Acrylonitrile and Calcium Carbonate Recovery

by Jesús del Amo, Subramaniam Iswar, Thomas Vanbergen, Ana Maria Borreguero, Simon Dirk E. De Vos, Isabel Verlent, Jan Willems and Juan Francisco Rodriguez Romero

Materials 2024, 17(12), 2844; https://doi.org/10.3390/ma17122844 - 11 Jun 2024

Cited by 3 | Viewed by 1471

Abstract

The glycolysis process of flexible polyurethane foams containing styrene–acrylonitrile and calcium carbonate as fillers was explored in detail. The use of DABCO as a catalyst allowed us to reduce the catalyst concentration and the polyurethane-to-glycol mass ratio to 0.1% and 1:1, respectively. The [...] Read more.

The glycolysis process of flexible polyurethane foams containing styrene–acrylonitrile and calcium carbonate as fillers was explored in detail. The use of DABCO as a catalyst allowed us to reduce the catalyst concentration and the polyurethane-to-glycol mass ratio to 0.1% and 1:1, respectively. The glycolysis process allowed us to obtain a high-purity polyol (99%), which can totally replace raw polyols in the synthesis of new flexible polyurethane foams, maintaining the standard mechanical properties of the original one and modifying the ratio of isocyanates employed to correct the closed cell structure caused by the impurities present in the recovered polyol. This isocyanate mixture was also optimized, resulting in a ratio of 30 and 70% of the isocyanates TDI80 and TDI65, respectively. Additionally, the fillers incorporated in the glycolyzed foams were recovered. Both recovered fillers, styrene–acrylonitrile and calcium carbonate, were fully characterized, showing a quality very similar to that of commercial compounds. Finally, the replacement of commercial fillers by the recovered ones in the synthesis of new polyurethane foams was studied, demonstrating the feasibility of using them in the synthesis of new foams without significantly altering their properties. Full article

(This article belongs to the Special Issue Physics and Chemistry of Polymers and Sustainable Polymer-Based Materials)

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18 pages, 5494 KB

Open AccessEditor’s ChoiceArticle

Three-Dimensional-Printed Composite Structures: The Effect of LSCF Slurry Solid Loading, Binder, and Direct-Write Process Parameters

by Man Yang, Santosh Kumar Parupelli, Zhigang Xu and Salil Desai

Materials 2024, 17(12), 2822; https://doi.org/10.3390/ma17122822 - 10 Jun 2024

Cited by 3 | Viewed by 1364

Abstract

In this research, a direct-write 3D-printing method was utilized for the fabrication of inter-digitized solid oxide fuel cells (SOFCs) using ceramic materials. The cathode electrode was fabricated using the LSCF (La_0.6Sr_0.2Fe_0.8Co_0.2O_3-δ) slurry loading [...] Read more.

In this research, a direct-write 3D-printing method was utilized for the fabrication of inter-digitized solid oxide fuel cells (SOFCs) using ceramic materials. The cathode electrode was fabricated using the LSCF (La_0.6Sr_0.2Fe_0.8Co_0.2O_3-δ) slurry loading and the Polyvinyl butyral (PVB) binder. The rheological parameters of slurries with varying LSCF slurry loading and PVB binder concentration were evaluated to determine their effect on the cathode trace performance in terms of microstructure, size, and resistance. Additionally, the dimensional shrinkage of LSCF lines after sintering was investigated to realize their influence on cathode line width and height. Moreover, the effect of the direct-write process parameters such as pressure, distance between the nozzle and substrate, and speed on the cathode line dimensions and resistance was evaluated. LSCF slurry with 50% solid loading, 12% binder, and 0.2% dispersant concentration was determined to be the optimal value for the fabrication of SOFCs using the direct-write method. The direct-write process parameters, in addition to the binder and LSCF slurry concentration ratios, had a considerable impact on the microstructure of cathode lines. Based on ANOVA findings, pressure and distance had significant effects on the cathode electrode resistance. An increase in the distance between the nozzle and substrate, speed, or extrusion pressure of the direct writing process increased the resistance of the cathode lines. These findings add to the ongoing effort to refine SOFC fabrication techniques, opening the avenues for advanced performance and efficiency of SOFCs in energy applications. Full article

(This article belongs to the Special Issue 3D-Printed Composite Structures: Design, Properties and Application)

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22 pages, 3109 KB

Open AccessEditor’s ChoiceArticle

Determination of Fluorine by Ion-Selective Electrode and High-Resolution Continuum Source Graphite Furnace Molecular Absorption Spectrometry with Respect to Animal Feed Safety

by Zofia Kowalewska, Karolina Goluch, Waldemar Korol, Rafał Olchowski and Ryszard Dobrowolski

Materials 2024, 17(12), 2812; https://doi.org/10.3390/ma17122812 - 9 Jun 2024

Cited by 1 | Viewed by 1974

Abstract

Fluorine, depending on its concentration and chemical form, is essential or toxic to humans and animals. Therefore, it is crucial to be able to determine it reliably. In this study, fluorine was determined in animal feed after extraction with HCl (gastric juice simulation). [...] Read more.

Fluorine, depending on its concentration and chemical form, is essential or toxic to humans and animals. Therefore, it is crucial to be able to determine it reliably. In this study, fluorine was determined in animal feed after extraction with HCl (gastric juice simulation). The standard potentiometric method with a fluoride-selective electrode (ISE) and newly developed high-resolution continuum source graphite furnace molecular absorption spectrometry (HR-CS GFMAS) method was applied. Feed samples turned out to be a challenge for HR-CS GFMAS. Chemical interferences (formation of competing molecules, CaF, GaCl, and GaP, instead of the target GaF molecule) and spectral effects (including a phosphorous molecule spectrum and atomic lines) were identified. An additional difficulty was caused by reagent contamination with F and memory effects. Difficulties were eliminated/reduced. The quality of ISE analysis was multi-directionally verified (including comprehensive proficiency testing). A risk of inaccuracy at low F concentration, where the calibration relationship is nonlinear, was investigated. The results of both methods were consistent, which confirms the accuracy of the methods and informs that the extracted fluorine is in fluoride form. The results of extensive ISE tests conducted in Poland in 2021–2023 have shown that, in most cases, the fluoride content is significantly lower than the threshold values. Full article

(This article belongs to the Special Issue Electrochemical Material Science and Electrode Processes)

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12 pages, 3520 KB

Open AccessEditor’s ChoiceArticle

Comparative Study for Propranolol Adsorption on the Biochars from Different Agricultural Solid Wastes

by Wenjie Nie, Qianqian Che, Danni Chen, Hongyu Cao and Yuehua Deng

Materials 2024, 17(12), 2793; https://doi.org/10.3390/ma17122793 - 7 Jun 2024

Cited by 2 | Viewed by 1014

Abstract

Currently, large amounts of agricultural solid wastes have caused serious environmental problems. Agricultural solid waste is made into biochar by pyrolysis, which is an effective means of its disposal. As the prepared biochar has a good adsorption capacity, it is often used to [...] Read more.

Currently, large amounts of agricultural solid wastes have caused serious environmental problems. Agricultural solid waste is made into biochar by pyrolysis, which is an effective means of its disposal. As the prepared biochar has a good adsorption capacity, it is often used to treat pollutants in water, such as heavy metals and pharmaceuticals. PRO is an emerging contaminant in the environment today. However, there are limited studies on the interaction between biochars with PRO. Thus, in this study, we investigate the adsorption of PRO onto the biochars derived from three different feedstocks. The order of adsorption capacity was corn stalk biochar (CS, 10.97 mg/g) > apple wood biochar (AW, 10.09 mg/g) > rice husk biochar (RH, 8.78 mg/g). When 2 < pH < 9, the adsorption capacity of all the biochars increased as the pH increased, while the adsorption decreased when pH > 9, 10 and 10.33 for AW, CS and RH, respectively. The adsorption of PRO on biochars was reduced with increasing Na⁺ and Ca²⁺ concentrations from 0 to 200 mg·L⁻¹. The effects of pH and coexisting ions illustrated that there exist electrostatic interaction and cation exchange in the process. In addition, when HA concentration was less than 20 mg/L, it promoted the adsorption of PRO on the biochars; however, when the concentration was more than 20 mg/L, its promoting effect was weakened and gradually changed into an inhibitory effect. The adsorption isotherm data of PRO by biochars were best fitted with the Freundlich model, indicating that the adsorption process is heterogeneous adsorption. The adsorption kinetics were fitted well with the pseudo-second-order model. All the results can provide new information into the adsorption behavior of PRO and the biochars in the aquatic environment and a theoretical basis for the large-scale application of biochar from agricultural solid wastes. Full article

(This article belongs to the Special Issue Adsorption Materials and Their Applications)

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24 pages, 5331 KB

Open AccessEditor’s ChoiceReview

Material Extrusion Additive Manufacturing of Ceramics: A Review on Filament-Based Process

by Roberto Spina and Luigi Morfini

Materials 2024, 17(11), 2779; https://doi.org/10.3390/ma17112779 - 6 Jun 2024

Cited by 6 | Viewed by 3571

Abstract

Additive manufacturing is very important due to its potential to build components and products using high-performance materials. The filament-based 3D printing of ceramics is investigated, revealing significant developments and advancements in ceramic material extrusion technology in recent years. Researchers employ several typologies of [...] Read more.

Additive manufacturing is very important due to its potential to build components and products using high-performance materials. The filament-based 3D printing of ceramics is investigated, revealing significant developments and advancements in ceramic material extrusion technology in recent years. Researchers employ several typologies of ceramics and binders to achieve fully dense products. The design of the filament and the necessary technological adaptations for 3D printing are fully investigated. From a material perspective, this paper reviews and analyzes the recent developments in additive manufacturing of material-extruded ceramics products, pointing out the performance and properties achieved with different material-binder combinations. The main gaps to be filled and recommendations for future developments in this field are reported. Full article

(This article belongs to the Special Issue Advances in 3D Printing/Additive Manufacturing Technology of Materials)

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13 pages, 4593 KB

Open AccessEditor’s ChoiceArticle

Effect of Carbon Fiber Paper with Thickness Gradient on Electromagnetic Shielding Performance of X-Band

by Zhi Liu, Meiping Song, Weiqi Liang, Xueping Gao and Bo Zhu

Materials 2024, 17(11), 2767; https://doi.org/10.3390/ma17112767 - 6 Jun 2024

Cited by 3 | Viewed by 1509

Abstract

Flexible paper-based materials play a crucial role in the field of flexible electromagnetic shielding due to their thinness and controllable shape. In this study, we employed the wet paper forming technique to prepare carbon fiber paper with a thickness gradient. The electromagnetic shielding [...] Read more.

Flexible paper-based materials play a crucial role in the field of flexible electromagnetic shielding due to their thinness and controllable shape. In this study, we employed the wet paper forming technique to prepare carbon fiber paper with a thickness gradient. The electromagnetic shielding performance of the carbon fiber paper varies with the ladder-like thickness distribution. Specifically, an increase in thickness gradient leads to higher reflectance of the carbon fiber paper. Within the X-band frequency range (8.2–12.4 GHz), reflectivity decreases as electromagnetic wave frequency increases, indicating enhanced penetration of electromagnetic waves into the interior of the carbon fiber paper. This enhancement is attributed to an increased fiber content per unit area resulting from a greater thickness gradient, which further enhances reflection loss and promotes internal multiple reflections and scattering effects, leading to increased absorption loss. Notably, at a 5 mm thickness, our carbon fiber paper exhibits an impressive average overall shielding performance, reaching 63.46 dB. Moreover, it exhibits notable air permeability and mechanical properties, thereby assuming a pivotal role in the realm of flexible wearable devices in the foreseeable future. Full article

(This article belongs to the Special Issue Carbon-Based Functional Nanomaterials: Preparation, Properties and Applications)

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