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Materials, Volume 17, Issue 1 (January-1 2024) – 271 articles

Cover Story (view full-size image): MXene is a promising candidate for the next generation of lightweight electromagnetic interference (EMI) materials owing to its low density, excellent conductivity, etc. However, MXene lacks interlayer support and tends to agglomerate, leading to a shorter service life and limiting its development in thin-layer electromagnetic shielding material. We designed self-assembled TiO2-Ti3C2Tx materials with a ball–plate structure to mitigate agglomeration and obtain thin-layer and multiple absorption porous materials for high-efficiency EMI shielding. Research results demonstrated that the ball–plate structure generates additional interlayer cavities and an internal interface, increasing the propagation path for an electromagnetic wave, which, in turn, raises the capacity of materials to absorb and dissipate the wave. These effects improve the overall EMI shielding performance of MXene. View this paper
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38 pages, 8389 KiB  
Review
Materials Nanoarchitectonics at Dynamic Interfaces: Structure Formation and Functional Manipulation
by Katsuhiko Ariga
Materials 2024, 17(1), 271; https://doi.org/10.3390/ma17010271 - 4 Jan 2024
Cited by 5 | Viewed by 2870
Abstract
The next step in nanotechnology is to establish a methodology to assemble new functional materials based on the knowledge of nanotechnology. This task is undertaken by nanoarchitectonics. In nanoarchitectonics, we architect functional material systems from nanounits such as atoms, molecules, and nanomaterials. In [...] Read more.
The next step in nanotechnology is to establish a methodology to assemble new functional materials based on the knowledge of nanotechnology. This task is undertaken by nanoarchitectonics. In nanoarchitectonics, we architect functional material systems from nanounits such as atoms, molecules, and nanomaterials. In terms of the hierarchy of the structure and the harmonization of the function, the material created by nanoarchitectonics has similar characteristics to the organization of the functional structure in biosystems. Looking at actual biofunctional systems, dynamic properties and interfacial environments are key. In other words, nanoarchitectonics at dynamic interfaces is important for the production of bio-like highly functional materials systems. In this review paper, nanoarchitectonics at dynamic interfaces will be discussed, looking at recent typical examples. In particular, the basic topics of “molecular manipulation, arrangement, and assembly” and “material production” will be discussed in the first two sections. Then, in the following section, “fullerene assembly: from zero-dimensional unit to advanced materials”, we will discuss how various functional structures can be created from the very basic nanounit, the fullerene. The above examples demonstrate the versatile possibilities of architectonics at dynamic interfaces. In the last section, these tendencies will be summarized, and future directions will be discussed. Full article
(This article belongs to the Special Issue Nanoarchitectonics in Materials Science)
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17 pages, 4082 KiB  
Article
The Microstructural Evolution and Corrosion Behavior of Zn-Mg Alloys and Hybrids Processed Using High-Pressure Torsion
by Ayoub Tanji, Hendra Hermawan and Carl J. Boehlert
Materials 2024, 17(1), 270; https://doi.org/10.3390/ma17010270 - 4 Jan 2024
Cited by 3 | Viewed by 1730
Abstract
Zinc (Zn) alloys, particularly those incorporating magnesium (Mg), have been explored as potential bioabsorbable metals. However, there is a continued need to enhance the corrosion characteristics of Zn-Mg alloys to fulfill the requirements for biodegradable implants. This work involves a corrosion behavior comparison [...] Read more.
Zinc (Zn) alloys, particularly those incorporating magnesium (Mg), have been explored as potential bioabsorbable metals. However, there is a continued need to enhance the corrosion characteristics of Zn-Mg alloys to fulfill the requirements for biodegradable implants. This work involves a corrosion behavior comparison between severe-plastic-deformation (SPD) processed cast Zn-Mg alloys and their hybrid counterparts, having equivalent nominal compositions. The SPD processing technique used was high-pressure torsion (HPT), and the corrosion behavior was studied as a function of the number of turns (1, 5, 15) for the Zn-3Mg (wt.%) alloy and hybrid and as a function of composition (Mg contents of 3, 10, 30 wt.%) for the hybrid after 15 turns. The results indicated that HPT led to multimodal grain size distributions of ultrafine Mg-rich grains containing MgZn2 and Mg2Zn11 nanoscale intermetallics in a matrix of coarser dislocation-free Zn-rich grains. A greater number of turns resulted in greater corrosion resistance because of the formation of the intermetallic phases. The HPT hybrid was more corrosion resistant than its alloy counterpart because it tended to form the intermetallics more readily than the alloy due to the inhomogeneous conditions of the materials before the HPT processing as well as the non-equilibrium conditions imposed during the HPT processing. The HPT hybrids with greater Mg contents were less corrosion resistant because the addition of Mg led to less noble behavior. Full article
(This article belongs to the Special Issue Corrosion of Metals for Biomedical Applications)
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23 pages, 32864 KiB  
Article
Microwave-Assisted Hydrothermal Synthesis of Pure-Phase Sodalite (>99 wt.%) in Suspension: Methodology Design and Verification
by Kamila Rouchalová, Dana Rouchalová, Vladimír Čablík and Dalibor Matýsek
Materials 2024, 17(1), 269; https://doi.org/10.3390/ma17010269 - 4 Jan 2024
Viewed by 1458
Abstract
Despite numerous studies focused on the hydrothermal (HT) synthesis of fly ash zeolites (FAZs), this method still has many limitations, the main of which is the low yield of zeolites. Hydrothermally synthesized zeolites are typically multiphase and exhibit low purity, which limits their [...] Read more.
Despite numerous studies focused on the hydrothermal (HT) synthesis of fly ash zeolites (FAZs), this method still has many limitations, the main of which is the low yield of zeolites. Hydrothermally synthesized zeolites are typically multiphase and exhibit low purity, which limits their applicability. Pure-phase zeolites have been primarily prepared from filtrates after alkaline mineralization of fly ashes, not directly in suspension. In addition, the published methodologies have not been tested in a wider set of samples, and thus their reproducibility is not confirmed. The aim of the study is to propose a reproducible methodology that overcomes the mentioned limitations. The influence of the Si/Al ratio (1.3:1–1:2), the type and concentration of the activator (2/4 M NaOH/KOH/LiOH), the reagent (30% LiCl), the duration (24–168 h), and the temperature (50–180 °C) of the synthesis phases were studied. The sequence of the synthesis phases was also optimized, depending on the type of heat transfer. The fly ashes were analyzed by wavelength-dispersive X-ray fluorescence (WD XRF), flame atomic absorption spectrometry (F-AAS), and X-ray diffraction (XRD). The energy intensity of the synthesis was reduced through the application of unique microwave digestion technology. Both microwave and combined (microwave and convection) syntheses were conducted. FAZs were identified and quantified by XRD analysis. This study presents a three-stage (TS) hydrothermal synthesis of pure-phase sodalite in suspension. Sodalite (>99 wt.%) was prepared from nine fly ashes under the following conditions: I. microwave phase: 120 °C, 150 min, solid-to-liquid ratio (S/L) 1:5, Si/Al ratio 1:1.5, and 4 M NaOH; II. convection phase: 120 °C, 24 h, S/L 1:40, and the addition of 30 mL of 30% LiCl; and III. crystallization: 70 °C for 24 h. The formation of rhombododecahedral sodalite crystals was confirmed by scanning electron microscope (SEM) images. Full article
(This article belongs to the Special Issue Zeolites and Related Materials: Synthesis, Properties and Applications)
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30 pages, 433 KiB  
Review
Esters in the Food and Cosmetic Industries: An Overview of the Reactors Used in Their Biocatalytic Synthesis
by Salvadora Ortega-Requena, Claudia Montiel, Fuensanta Máximo, María Gómez, María Dolores Murcia and Josefa Bastida
Materials 2024, 17(1), 268; https://doi.org/10.3390/ma17010268 - 4 Jan 2024
Cited by 8 | Viewed by 4968
Abstract
Esters are versatile compounds with a wide range of applications in various industries due to their unique properties and pleasant aromas. Conventionally, the manufacture of these compounds has relied on the chemical route. Nevertheless, this technique employs high temperatures and inorganic catalysts, resulting [...] Read more.
Esters are versatile compounds with a wide range of applications in various industries due to their unique properties and pleasant aromas. Conventionally, the manufacture of these compounds has relied on the chemical route. Nevertheless, this technique employs high temperatures and inorganic catalysts, resulting in undesired additional steps to purify the final product by removing solvent residues, which decreases environmental sustainability and energy efficiency. In accordance with the principles of “Green Chemistry” and the search for more environmentally friendly methods, a new alternative, the enzymatic route, has been introduced. This technique uses low temperatures and does not require the use of solvents, resulting in more environmentally friendly final products. Despite the large number of studies published on the biocatalytic synthesis of esters, little attention has been paid to the reactors used for it. Therefore, it is convenient to gather the scattered information regarding the type of reactor employed in these synthesis reactions, considering the industrial field in which the process is carried out. A comparison between the performance of the different reactor configurations will allow us to draw the appropriate conclusions regarding their suitability for each specific industrial application. This review addresses, for the first time, the above aspects, which will undoubtedly help with the correct industrial implementation of these processes. Full article
(This article belongs to the Section Catalytic Materials)
16 pages, 5728 KiB  
Article
Enhanced Degradation of Ethylene in Thermo-Photocatalytic Process Using TiO2/Nickel Foam
by Maciej Trzeciak, Piotr Miądlicki and Beata Tryba
Materials 2024, 17(1), 267; https://doi.org/10.3390/ma17010267 - 4 Jan 2024
Cited by 3 | Viewed by 1334
Abstract
The photocatalytic decomposition of ethylene was performed under UV-LED irradiation in the presence of nanocrystalline TiO2 (anatase, 15 nm) supported on porous nickel foam. The process was conducted in a high-temperature chamber with regulated temperature from ambient to 125 °C, under a [...] Read more.
The photocatalytic decomposition of ethylene was performed under UV-LED irradiation in the presence of nanocrystalline TiO2 (anatase, 15 nm) supported on porous nickel foam. The process was conducted in a high-temperature chamber with regulated temperature from ambient to 125 °C, under a flow of reacted gas (ethylene in synthetic air, 50 ppm, flow rate of 20 mL/min), with simultaneous FTIR measurements of the sample surface. Ethylene was decomposed with a higher efficiency at elevated temperatures, with a maximum of 28% at 100–125 °C. The nickel foam used as support for TiO2 enhanced ethylene decomposition at a temperature of 50 °C. However, at 50 °C, the stability of ethylene decomposition was not maintained in the following reaction run, but it was at 100 °C. Photocatalytic measurements conducted in the presence of certain radical scavengers indicated that a higher efficiency of ethylene decomposition was obtained due to the improved separation of charge carriers and the increased formation of superoxide anionic radicals, which were formed at the interface of the thermally activated nickel foam and TiO2. Full article
(This article belongs to the Topic New Materials and Advanced Applications in Photocatalysis)
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12 pages, 16320 KiB  
Article
The Synergistic Impact of Crystal Seed and Fluoride Ion in the Synthesis of Silicalite-1 Zeolite in Low-Template Systems
by Xiaojing Meng, Yanjie Qin, Yang Zhang, Min Li, Huibang Huang, Jiaqin Peng, Liangxu Zhou and Jian Feng
Materials 2024, 17(1), 266; https://doi.org/10.3390/ma17010266 - 4 Jan 2024
Viewed by 1240
Abstract
Silicalite-1 zeolites are widely applied in gas adsorption, catalysis, and separation due to their excellent hydrothermal stability and unique pore structure. However, traditional preparation methods have inherent drawbacks such as high pollution, high cost, etc. Therefore, this work proposed a green and efficient [...] Read more.
Silicalite-1 zeolites are widely applied in gas adsorption, catalysis, and separation due to their excellent hydrothermal stability and unique pore structure. However, traditional preparation methods have inherent drawbacks such as high pollution, high cost, etc. Therefore, this work proposed a green and efficient route for preparing Silicalite-1 zeolite by adding NH4F (F/Si = 0.1) and seeds (10 wt%) in a much shorter time (8 h) in a low-template system (TPA+/Si = 0.007). It was found that NH4F is beneficial for inhibiting the formation of SiO2. The S-1 seeds could drastically induce the formation of the zeolite skeleton structure. Noteworthy, the morphology of zeolites was determined by the relative content of NH4F and seeds. The crystal morphology is determined by the higher content of the two substances; however, when the content is similar, the crystal morphology is determined by NH4F. The results showed that simultaneous control of NH4F and seeds can suppress SiO2 formation, can improve the relative crystallinity of products, and can be precisely regulated via the synergistic effect of both in zeolite morphology. This work not only provides new ideas for regulating the morphology of silicate-1 crystals but also offers a new path for industrial large-scale production of low-cost and efficient zeolites. Full article
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13 pages, 25089 KiB  
Article
Theoretical and Experimental Studies of the Shock-Compressed Gas Parameters in the Welding Gap
by Andrey Malakhov, Igor Denisov, Nemat Niyozbekov, Ivan Saikov, Denis Shakhray, Vasily Sosikov and Andrey Emelyanov
Materials 2024, 17(1), 265; https://doi.org/10.3390/ma17010265 - 4 Jan 2024
Cited by 3 | Viewed by 1281
Abstract
This work is devoted to the study of the processes that take place in the welding gap during explosive welding (EW). In the welding gap, when plates collide, a shock-compressed gas (SCG) region is formed, which moves at supersonic speed and has a [...] Read more.
This work is devoted to the study of the processes that take place in the welding gap during explosive welding (EW). In the welding gap, when plates collide, a shock-compressed gas (SCG) region is formed, which moves at supersonic speed and has a high temperature that can affect the quality of the weld joint. Therefore, this work focuses on a detailed study of the parameters of the SCG. A complex method of determining the SCG parameters included: determination of the detonation velocity using electrical contact probes, ceramic probes, and an oscilloscope; calculation of the SCG parameters; high-speed photography of the SCG region; measurement of the SCG temperature using optical pyrometry. As a result, it was found that the head front of the SCG region moved ahead of the collision point at a velocity of 3000 ± 100 m/s, while the collision point moved with a velocity of 2500 m/s. The calculation of the SCG temperature showed that the gas was heated up to 2832 K by the shock compression, while the measured temperature was in the range of 4100–4400 K. This is presumably due to the fact that small metal particles that broke off from the welded surfaces transferred their heat to the SCG region. Thus, the results of this study can be used to optimize the EW parameters and improve the weld joint quality. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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17 pages, 5708 KiB  
Article
Microstructure and Wear Resistance of Ti6Al4V Titanium Alloy Laser-Clad Ni60/WC Composite Coating
by Mingjia Feng, Yunhai Ma, Yitong Tian and Hongtu Cao
Materials 2024, 17(1), 264; https://doi.org/10.3390/ma17010264 - 4 Jan 2024
Cited by 4 | Viewed by 1640
Abstract
In this paper, Ni60/WC wear-resistant coatings have been created on the Ti6Al4V substrate surface using a pre-layered powder laser cladding method by deploying various scanning speeds of 8, 10, 12, and 14 mm/s. The coatings are characterized through X-ray diffraction (XRD), scanning electron [...] Read more.
In this paper, Ni60/WC wear-resistant coatings have been created on the Ti6Al4V substrate surface using a pre-layered powder laser cladding method by deploying various scanning speeds of 8, 10, 12, and 14 mm/s. The coatings are characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), and a high-speed reciprocating fatigue wear tester. It is found that the phase composition of the coating comprises the synthesized, hard phase TiC and TiB2, the silicides WSi2 and W5Si3, and NiTi and γ-Ni solid solutions. At different scanning speeds, there is a metallurgical fusion line in the bonding area of the fused cladding layer, indicating a good metallurgical bonding between the substrate and the powder. At a low scanning speed, the coating develops into coarse dendrites, which shows significant improvement with scanning speed. The microhardness first increases and then decreases with the scanning speed, and the coating’s average microhardness was 2.75–3.13 times higher than that of the substrate. The amount of mass wear has been reduced by 60.1–79.7% compared to the substrate. The wear behavior of the coatings was studied through detailed analysis of wear surfaces’ microstructures and the amount of wear to identify the optimum scanning speed. Full article
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15 pages, 2799 KiB  
Article
Fracture Resistance of Posterior Tooth-Supported Cantilever Fixed Dental Prostheses of Different Zirconia Generations and Framework Thicknesses: An In Vitro Study
by Anna-Luisa Klotz, Janina Halfmann, Stefan Rues, Wolfgang Bömicke, Peter Rammelsberg and Andreas Zenthöfer
Materials 2024, 17(1), 263; https://doi.org/10.3390/ma17010263 - 4 Jan 2024
Cited by 3 | Viewed by 1466
Abstract
The rehabilitation of free-end situations is a frequent indication in prosthetic dentistry. Cantilever fixed dental prostheses (cFDPs) made of 1st and 2nd generation zirconia are one treatment option. Due to a unique gradient technology, combinations of different zirconium dioxide generations are thus feasible [...] Read more.
The rehabilitation of free-end situations is a frequent indication in prosthetic dentistry. Cantilever fixed dental prostheses (cFDPs) made of 1st and 2nd generation zirconia are one treatment option. Due to a unique gradient technology, combinations of different zirconium dioxide generations are thus feasible in one restoration. However, data about these materials are rare. The purpose of this study was therefore to investigate the fracture resistance and fracture modes of tooth-supported cFDPs fabricated from different zirconia materials (gradient technology) and different framework thicknesses. A total of 40 cFDPs were fabricated using the CAD/CAM approach and belonged to five test groups. The different groups differed in the yttria content, the proportion of the tetragonal/cubic phases, or in wall thickness (0.7 mm or 1 mm). After completion, the cFDPs were subjected to thermal cycling and chewing simulation (1.2 × 106 load cycles, 108 N load). Afterwards, cFDPs were statically loaded until fracture in a universal testing machine. A non-parametric ANOVA was compiled to determine the possible effects of group membership on fracture resistance. In addition, post-hoc Tukey tests were used for bivariate comparisons. The mean fracture loads under axial load application ranged from 288 to 577 N. ANOVA detected a significant impact of the used material on the fracture resistances (p < 0.001). Therefore, the use of cFDPs fabricated by gradient technology zirconia may not be unreservedly recommended for clinical use, whereas cFPDs made from 3Y-TZP exhibit fracture resistance above possible masticatory loads in the posterior region. Full article
(This article belongs to the Special Issue Ceramic Dental Restorations: From Materials Sciences to Applications)
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12 pages, 11824 KiB  
Article
Nondestructive Evaluation of Tensile Stress-loaded GFRPs Using the Magnetic Recording Method
by Ryszard D. Łukaszuk, Tomasz Chady, Marek J. Żwir and Krzysztof Gorący
Materials 2024, 17(1), 262; https://doi.org/10.3390/ma17010262 - 4 Jan 2024
Viewed by 1124
Abstract
This paper presents the results of inspecting tensile stress-loaded GFRP (glass fiber-reinforced polymer) samples using the Magnetic Recording Method (MRM). The MRM can be utilized solely to examine ferromagnetic materials. The modification was proposed in order to examine nonmagnetic composites. Ferromagnetic strips made [...] Read more.
This paper presents the results of inspecting tensile stress-loaded GFRP (glass fiber-reinforced polymer) samples using the Magnetic Recording Method (MRM). The MRM can be utilized solely to examine ferromagnetic materials. The modification was proposed in order to examine nonmagnetic composites. Ferromagnetic strips made of low-carbon steel DC01 were bonded to the surface using an adhesive composed of epoxy resin with the addition of triethylenetetramine. The modified method’s feasibility was tested on six samples made of GFRP. The research procedure consisted of three steps. In the first step, a metal strip is glued at the top surface of each sample, and an array of 100 cylindrical permanent magnets is used to record a sinusoidal magnetic pattern on the strip. The initial residual magnetization is measured in the second step, and the samples are subjected to static stress. In the third step, the residual magnetization is measured one more time. Ultimately, the measurement results from the second and third steps are compared. Generally, the applied stress causes changes in the amplitude and frequency of the sinusoidal magnetization pattern. In the case of GFRP, the frequency changes have not been used for evaluation due to minimal variations. The statistical parameters (mean, median, max, and mode) of the RMS (root mean square) value of the sinusoidal pattern were calculated and analyzed. The analysis demonstrates that the modified method is suitable for providing unequivocal and exact information on the load applied to a nonmagnetic composite material. For the presented results, the applied load can be assessed unambiguously for the samples elongated up to 0.6%. Full article
(This article belongs to the Special Issue Advances in Nondestructive Evaluation of Materials and Structures)
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13 pages, 4485 KiB  
Article
Antimicrobial Activity of Morphology-Controlled Cu2O Nanoparticles: Oxidation Stability under Humid and Thermal Conditions
by Jeong Yeon Park, Siwoo Lee, Yangdo Kim and Young Bok Ryu
Materials 2024, 17(1), 261; https://doi.org/10.3390/ma17010261 - 4 Jan 2024
Cited by 3 | Viewed by 1750
Abstract
Metal oxides can be used as antimicrobial agents, especially since they can be fabricated into various forms such as films, masks, and filters. In particular, the durability of antimicrobial agents and the duration of their antimicrobial activity are important factors that determine their [...] Read more.
Metal oxides can be used as antimicrobial agents, especially since they can be fabricated into various forms such as films, masks, and filters. In particular, the durability of antimicrobial agents and the duration of their antimicrobial activity are important factors that determine their suitability for a specific purpose. These factors are related to the morphology and size of particles. The metal oxide Cu2O is often oxidized to CuO in various conditions, which reduces its antimicrobial activity. This study focused on the oxidation of nanoparticles of Cu2O with three morphologies, namely, spherical, octahedral, and cubic morphologies, in excessively humid and excessive-thermal environments for a specific duration and the antimicrobial activity of the NPs. Cu2O nanoparticles were prepared using the chemical reduction method, and their morphology could be varied by adjusting the molar ratio of OH− to Cu2+ and changing the reducing agent. It was found that cubic Cu2O was the most stable against oxidation and had the smallest reduction in antimicrobial activity. This study examined the antimicrobial activity and the oxidation stability of Cu2O NPs with different morphologies but similar particle sizes. Full article
(This article belongs to the Section Materials Chemistry)
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14 pages, 1542 KiB  
Article
Using Thin Films of Phase-Change Material for Active Tuning of Terahertz Waves Scattering on Dielectric Cylinders
by Atilla Ozgur Cakmak, Evrim Colak and Andriy E. Serebryannikov
Materials 2024, 17(1), 260; https://doi.org/10.3390/ma17010260 - 4 Jan 2024
Cited by 2 | Viewed by 1212
Abstract
The scattering of electromagnetic waves by isotropic dielectric cylinders can be dramatically modified by means of vanadium dioxide (VO2) thin-film coatings. Efficient dynamic control of scattering is achieved due to the variations in material parameters realizable by means of external [...] Read more.
The scattering of electromagnetic waves by isotropic dielectric cylinders can be dramatically modified by means of vanadium dioxide (VO2) thin-film coatings. Efficient dynamic control of scattering is achieved due to the variations in material parameters realizable by means of external biasing. In this paper, we study the scattering of terahertz waves in a case where the coating shells are made of VO2, a phase-change material, whose thin films may work rather as electromagnetic phase screens in the insulator material phase, but as lossy quasi-metallic components in the metallic material phase. The shells that uniformly cover the dielectric cylinders are investigated. Attention will be paid to the demonstration of the potential of VO2 in the external control of diverse scattering regimes of the dielectric-VO2 core–shell scatterer, while conductivity of VO2 corresponds to rather insignificant variations in temperature. In line with the purposes of this work, it is shown that the different resonant and nonresonant regimes have different sensitivity to the variations in VO2 conductivity. Both the total scattering cross section and field distributions inside and around the core are studied, as well as the angle-dependent scattering cross section. Full article
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18 pages, 4440 KiB  
Article
Mechanical Properties of Epoxy Compounds Based on Unmodified Epoxy Resin Modified with Boric Acid as an Antiseptic
by Anna Rudawska
Materials 2024, 17(1), 259; https://doi.org/10.3390/ma17010259 - 3 Jan 2024
Cited by 2 | Viewed by 1501
Abstract
The objective of this study was to compare the selected mechanical properties of epoxy compounds based on an unmodified epoxy resin with those containing an antiseptic as a modifying agent. Experiments were carried out on twelve epoxy compounds made of an epoxy resin [...] Read more.
The objective of this study was to compare the selected mechanical properties of epoxy compounds based on an unmodified epoxy resin with those containing an antiseptic as a modifying agent. Experiments were carried out on twelve epoxy compounds made of an epoxy resin based on bisphenol A (BPA) with a basic epoxide amount of 0.48–0.51 mol/100 g. Three curing agents were used: one polyamide (a polyaminoamide curing agent) and two amines (one was an adduct of aliphatic amine and aromatic glycidyl ether, and the other was an adduct of cycloaliphatic amine). The epoxy compounds were modified by adding an antiseptic in the form of powdered boric acid (H3BO3) in three amounts: 0.5 g, 1.0 g, and 1.5 g. The cured modified and unmodified epoxy compounds were subjected to compressive strength testing and microscopic examination. The experimental results showed that the epoxy compounds containing adduct of aliphatic amine (triethylenetetramine) and aromatic glycidyl ether as the amine curing agent, i.e., E5/ET/100:18, had the highest compressive strength out of all the tested epoxy compounds, with the highest value of 119 MPa obtained for the epoxy compound modified by the addition of 1.0 g boric acid. The epoxy compounds modified with boric acid acquired antiseptic properties and, for most cases, exhibited a higher compressive strength than the unmodified epoxy compounds (not lower than that specified by the manufacturer for unmodified epoxy compounds). Full article
(This article belongs to the Special Issue Modification, Properties and Application of Epoxy Adhesives/Materials)
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16 pages, 10186 KiB  
Article
The Impact of NaOH on the Micro-Mechanical Properties of the Interface Transition Zone in Low-Carbon Concrete
by Yue Li, Hailong Wang, Lisi Wei, Haolong Guo and Kuo Ma
Materials 2024, 17(1), 258; https://doi.org/10.3390/ma17010258 - 3 Jan 2024
Cited by 2 | Viewed by 1593
Abstract
To tackle carbon emissions from cement production and address the decline in concrete’s mechanical properties due to the substitution of cement with solid waste (glass powder) and natural mineral admixture (zeolite powder) materials, we employed glass powder and zeolite powder to create composite [...] Read more.
To tackle carbon emissions from cement production and address the decline in concrete’s mechanical properties due to the substitution of cement with solid waste (glass powder) and natural mineral admixture (zeolite powder) materials, we employed glass powder and zeolite powder to create composite cementitious materials. These materials underwent alkali activation treatment with a 4% NaOH dosage, replacing 50% of cement to produce low-carbon concrete. Nanoindentation tests and mercury intrusion porosimetry (MIP) were employed to uncover the micro-mechanical properties and influencing mechanisms of alkali-activated low-carbon concrete. The results indicate a notable enhancement in the indentation modulus (19.9%) and hardness (25.9%) of alkali-activated low-carbon concrete compared to non-activated concrete. Simultaneously, the interfacial transition zone thickness decreased by 10 µm. The addition of NaOH led to a reduced volume fraction of pores (diameter >100 nm) and an increased fraction of pores (diameter < 100 nm), thereby reducing porosity by 2.6%, optimizing the pore structure of low-carbon concrete. The indentation modulus, hardness and volume fraction of the hydrated phase derived from Gaussian fitting analysis of the nanoindentation statistics showed that NaOH significantly improved the modulus and hardness of the hydration products of low-carbon concrete. This activation resulted in decreased LDC-S-H gel (low-density hydrated calcium silicate Ca5Si6O16(OH)·4H2O) and pore content, while the HD C-S-H gel (high-density hydrated calcium silicate Ca5Si6O16(OH)·4H2O) and CH (calcium hydroxide crystals Ca(OH)2) content increased by 13.91% and 23.46%, respectively. Consequently, NaOH influenced the micro-mechanical properties of low-carbon concrete by generating more high-density hydration products, reducing pore content, enhancing the pore indentation modulus and hardness, and shortening the interfacial transition zone. This study offers novel insights into reducing carbon emissions and promoting the use of solid waste (glass powder) and natural mineral admixture (zeolite powder) materials in concrete, contributing to the advancement of sustainable construction practices. Full article
(This article belongs to the Special Issue Advance in Sustainable Construction Materials)
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17 pages, 12801 KiB  
Article
The Study on Fatigue Crack Growth Rate of 4130X Material under Different Hydrogen Corrosion Conditions
by Shaolei Jiang, Jing Wang, Bo Zhao and Enfeng Zhang
Materials 2024, 17(1), 257; https://doi.org/10.3390/ma17010257 - 3 Jan 2024
Cited by 1 | Viewed by 1269
Abstract
In this paper, the fatigue crack growth rates of typical pressure vessel material 4130X under different corrosion conditions are investigated, and the effects of corrosion modes and loading frequency on the fatigue crack growth rate of 4130X are discussed. The results show that [...] Read more.
In this paper, the fatigue crack growth rates of typical pressure vessel material 4130X under different corrosion conditions are investigated, and the effects of corrosion modes and loading frequency on the fatigue crack growth rate of 4130X are discussed. The results show that under the same loading conditions, the pre-corroded crack propagation rate is increased by 1.26 times compared with the uncorroded specimens. The plastic deformation mechanism of the crack tip in air is dominated by phase transformation but the hydrogen introduced by pre-corrosion causes a small number of dislocations at the crack tip. The crack growth rate obtained by corrosion fatigue is four times that of the uncorroded specimen, and the fracture surface shows a strong corrosion effect. The molecular dynamics simulation shows that the hydrogen atoms accumulated at the crack tip make the plastic deformation mechanism dominated by dislocation in the crack propagation process, and the coupling interaction between low frequency and the corrosion environment aggravates the hydrogen embrittlement of the crack tip. In the air condition, the loading frequency has no obvious effect on the crack growth rate: when the frequency decreases from 100 Hz to 0.01 Hz and other conditions remain unchanged, the fatigue crack growth rate increases by 1.5 times. The parameter n in the Paris expression is mainly influenced by frequency. The molecular dynamics simulation shows that low frequency promotes crack tip propagation. Full article
(This article belongs to the Section Corrosion)
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11 pages, 3428 KiB  
Article
Study on the Crystallization Behavior of Neodymium Rare-Earth Butadiene Rubber Blends and Its Effect on Dynamic Mechanical Properties
by Xiaohu Zhang, Wenbin Zhu, Xiaofan Li, Xinzheng Xie, Huan Ji, Yanxing Wei and Jifu Bi
Materials 2024, 17(1), 256; https://doi.org/10.3390/ma17010256 - 3 Jan 2024
Cited by 1 | Viewed by 1158
Abstract
Utilizing neodymium-based butadiene rubber as a baseline, this study examines the effect of eco-friendly aromatic TDAE oil, fillers, and crosslinking reactions on neodymium-based rare-earth butadiene rubber (Nd-BR) crystallization behavior. The findings suggest that TDAE oil hinders crystallization, resulting in decreased crystallization temperatures and [...] Read more.
Utilizing neodymium-based butadiene rubber as a baseline, this study examines the effect of eco-friendly aromatic TDAE oil, fillers, and crosslinking reactions on neodymium-based rare-earth butadiene rubber (Nd-BR) crystallization behavior. The findings suggest that TDAE oil hinders crystallization, resulting in decreased crystallization temperatures and heightened activation energies (Ea). The crystallization activation energies for 20 parts per hundreds of rubber (PHR) and 37.5 PHR oil stand at −116.8 kJ/mol and −48.1 kJ/mol, respectively, surpassing the −264.3 kJ/mol of the unadulterated rubber. Fillers act as nucleating agents, hastening crystallization, which in turn elevates crystallization temperatures and diminishes Ea. In samples containing 20 PHR and 37.5 PHR oil, the incorporation of carbon black and silica brought the Ea down to −224.9 kJ/mol and −239.1 kJ/mol, respectively. Crosslinking considerably restricts molecular motion and crystallization potential. In the examined conditions, butadiene rubber containing 37.5 PHR oil displayed no crystallization following crosslinking, albeit crystallization was discernible with filler inclusion. Simultaneously, the crystallinity level sharply declined, manifesting cold crystallization behavior. The crosslinking process elevates Ea, while the equilibrium melting point (Tm0) noticeably diminishes. For instance, the Tm0 of pure Nd-BR is approximately −0.135 °C. When blended with carbon black and silica, the Tm0 values are −3.13 °C and −5.23 °C, respectively. After vulcanization, these values decrease to −21.6 °C and −10.16 °C. Evaluating the isothermal crystallization kinetics of diverse materials via the Avrami equation revealed that both the oil and crosslinking process can bring about a decrease in n values, with the Avrami index n for various samples oscillating between 1.5 and 2.5. Assessing the dynamic mechanical attributes of different specimens reveals that Nd-BR crystallization notably curtails its glass transition, marked by a modulus shift in the transition domain and a decrement in loss factor. The modulus in the rubbery state also witnesses a substantial augmentation. Full article
(This article belongs to the Section Polymeric Materials)
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21 pages, 4123 KiB  
Article
Nanoscale and Tensile-Like Properties by an Instrumented Indentation Test on PBF-LB SS 316L Steel
by Giovanni Maizza, Faisal Hafeez, Alessandra Varone and Roberto Montanari
Materials 2024, 17(1), 255; https://doi.org/10.3390/ma17010255 - 3 Jan 2024
Viewed by 1566
Abstract
The mechanical properties of a defect-free laser melting (PBF-LB) deposit of an AISI 316L steel alloy were assessed by means of an instrumented indentation test (IIT), at both the macro- and nano-scales. The inherent non-equilibrium microstructure of the alloy was chemically homogenous and [...] Read more.
The mechanical properties of a defect-free laser melting (PBF-LB) deposit of an AISI 316L steel alloy were assessed by means of an instrumented indentation test (IIT), at both the macro- and nano-scales. The inherent non-equilibrium microstructure of the alloy was chemically homogenous and consisted of equiaxed grains and large-elongated grains (under the optical microscope) with irregular outlines composed of a much finer internal cell structure (under the scanning electron microscope). Berkovich and Vickers indenters were used to assess the indentation properties across individual grains (nano) and over multiple grains (macro), respectively. The nano-indentation over the X-Y plane revealed nearly constant indentation modulus across an individual grain but variable on average within different grains whose value depended on the relative orientation of the individual grain. The macro-indentation test was conducted to analyze the tensile-like properties of the polycrystalline SS 316L alloy over the X-Y and Y-Z planes. The macro-indentation test provided a reliable estimate of the ultimate tensile strength (UTS-like) of the alloy. Other indentation properties gave inconsistent results, and a post factum analysis was, therefore, conducted, by means of a new approach, to account for the presence of residual stresses. The already existing indentation data were supplemented with new repeated indentation tests to conduct a detailed analysis of the relaxation ability of compressive and tensile residual stresses. The developed methodology allows the effect of residual stresses and the reliability of measured macro-indentation properties to be examined as a function of a small group of indentation parameters. Full article
(This article belongs to the Special Issue Instrumented Indentation Test: An Aiding Tool for Materials Science and Industry)
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16 pages, 1509 KiB  
Perspective
On Thermal and Electrodynamic Aspects of the Superconductive Transition Process
by J. E. Hirsch
Materials 2024, 17(1), 254; https://doi.org/10.3390/ma17010254 - 3 Jan 2024
Viewed by 992
Abstract
In a classic paper of 1960, W. H. Cherry and J. I. Gittleman discussed various thermal and electrodynamic aspects of the superconductive transition process relevant to practical applications. In a section of the paper that has remained unnoticed, they proposed a physical model [...] Read more.
In a classic paper of 1960, W. H. Cherry and J. I. Gittleman discussed various thermal and electrodynamic aspects of the superconductive transition process relevant to practical applications. In a section of the paper that has remained unnoticed, they proposed a physical model for the Meissner effect. Earlier in 1940–1943, in work that has also remained unnoticed, K. M. Koch had introduced related physical ideas to explain the Meissner effect. Still earlier in 1937, J. C. Slater proposed a model to explain the perfect diamagnetism of superconductors. None of these ideas are part of the conventional London-BCS understanding of superconductivity, yet I will argue that they are essential to understand the Meissner effect, the most fundamental property of superconductors. The unconventional theory of hole superconductivity unifies and extends these ideas. A key missing element in the conventional theory as well as in these early theories is electron-hole asymmetry. A proper understanding of the Meissner effect may help with practical applications of superconductors, as well as to find new superconducting materials with desirable properties. Full article
(This article belongs to the Special Issue Characterization and Application of Superconducting Materials)
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18 pages, 8770 KiB  
Article
Macro–Meso Damage Analysis of Tunnel Lining Concrete under Thermal–Mechanical Coupling Based on CT Images
by Xudong Zheng, Wei Wang, Yanfei Zhang, Jinhui Qi and Xuedan Yao
Materials 2024, 17(1), 253; https://doi.org/10.3390/ma17010253 - 3 Jan 2024
Cited by 1 | Viewed by 1227
Abstract
The mechanical properties and failure modes of concrete are controlled by its mesoscopic material composition and structure; therefore, it is necessary to study the deterioration characteristics of tunnel lining concrete under fire from a mesoscopic perspective. However, previous studies mostly analyzed the damage [...] Read more.
The mechanical properties and failure modes of concrete are controlled by its mesoscopic material composition and structure; therefore, it is necessary to study the deterioration characteristics of tunnel lining concrete under fire from a mesoscopic perspective. However, previous studies mostly analyzed the damage and failure process from a macro-homogeneous perspective, which has certain limitations. In this paper, a thermal–mechanical coupling test device was modified to simulate the state of concrete under tunnel fire conditions. Combined with CT technology, the macroscopic properties and mesoscopic characteristics of concrete were observed. Features were obtained, such as the change in compressive strength under fire, as well as mesoscopic deterioration characteristics. The damage variable D was defined to quantify mesoscopic damage, and the link between mesoscopic deterioration characteristics and macroscopic performance was established, which can be used to predict compressive strength loss through mesoscopic characteristics. Full article
(This article belongs to the Special Issue Novel Civil Engineering Materials Integrated with Structures)
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19 pages, 2084 KiB  
Article
Computational Model of Effective Thermal Conductivity of Green Insulating Fibrous Media
by Hamidou Sankara, Dominique Baillis, Ousmane Coulibaly, Rémi Coquard, Naïm Naouar and Zahia Saghrouni
Materials 2024, 17(1), 252; https://doi.org/10.3390/ma17010252 - 3 Jan 2024
Viewed by 1247
Abstract
Modelling effective thermal properties is crucial for optimizing the thermal performance of materials such as new green insulating fibrous media. In this study, a numerical model is proposed to calculate the effective thermal conductivity of these materials. The fibers are considered to be [...] Read more.
Modelling effective thermal properties is crucial for optimizing the thermal performance of materials such as new green insulating fibrous media. In this study, a numerical model is proposed to calculate the effective thermal conductivity of these materials. The fibers are considered to be non-overlapping and randomly oriented in space. The numerical model is based on the finite element method. Particular attention is paid to the accuracy of the results and the influence of the choice of the representative elementary volume (REV) for calculation (cubic or rectangular parallelepiped slice). The calculated effective thermal conductivity of fibrous media under different boundary conditions is also investigated. A set of usual mixed boundary conditions is considered, alongside the uniform temperature gradient conditions. The REV rectangular slice and uniform temperature gradient boundary conditions provide a more accurate estimate of the effective thermal conductivity and are therefore recommended for use in place of the usual cubic representative elementary volume and the usual mixed boundary conditions. This robust model represents a principal novelty of the work. The results are compared with experimental and analytical data previously obtained in the literature for juncus maritimus fibrous media, for different fiber volume fractions, with small relative deviations of 7%. Analytical laws are generally based on simplified assumptions such as infinitely long fibers, and may neglect heat transfer between different phases. Both short and long fiber cases are considered in numerical calculations. Full article
(This article belongs to the Section Materials Physics)
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15 pages, 3831 KiB  
Article
Study on the Preparation and Properties of Vegetation Lightweight Porous Concrete
by Qingyu Cao, Juncheng Zhou, Weiting Xu and Xiongzhou Yuan
Materials 2024, 17(1), 251; https://doi.org/10.3390/ma17010251 - 3 Jan 2024
Viewed by 1256
Abstract
The objective of this study is to formulate vegetated light porous concrete (VLPC) through the utilization of various cementing materials, the design of porosity, and the incorporation of mineral additives. Subsequently, the study aims to assess and analyze key properties, including the bulk [...] Read more.
The objective of this study is to formulate vegetated light porous concrete (VLPC) through the utilization of various cementing materials, the design of porosity, and the incorporation of mineral additives. Subsequently, the study aims to assess and analyze key properties, including the bulk density, permeability coefficient, mechanical characteristics, and alkalinity. The findings indicate a linear decrease in the volume weight of VLPC as the designed porosity increases. While higher design porosity elevates the permeability coefficient, the measured effective porosity closely aligns with the design values. The examined VLPC exhibits a peak compressive strength of 17.7 MPa and a maximum bending strength of 2.1 MPa after 28 days. Notably, an escalation in porosity corresponds to a decrease in both the compressive and the bending strength of VLPC. Introducing mineral additives, particularly silicon powder, is shown to be effective in enhancing the strength of VLPC. Furthermore, substituting slag sulfonate cement for ordinary cement significantly diminishes the alkalinity of VLPC, resulting in a pH below 8.5 at 28 days. Mineral additives also contribute to a reduction in the pH of concrete. Among them, silica fume, fly ash, fly ash + slag powder, and slag powder exhibit a progressively enhanced alkaline reduction effect. Full article
(This article belongs to the Special Issue Study on Crack Resistance of Concrete)
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13 pages, 8890 KiB  
Article
Investigation of the Chemical Composition, Microstructure, Density, Microhardness, and Elastic Modulus of the New β Ti-50Nb-xMo Alloys for Biomedical Applications
by José Roberto Severino Martins Junior, Pedro Akira Bazaglia Kuroda and Carlos Roberto Grandini
Materials 2024, 17(1), 250; https://doi.org/10.3390/ma17010250 - 3 Jan 2024
Cited by 1 | Viewed by 1446
Abstract
β-type titanium alloys with a body-centered cubic structure are highly useful in orthopedics due to their low elastic modulus, lower than other commonly used alloys such as stainless steel and Co-Cr alloys. The formation of the β phase in titanium alloys is achieved [...] Read more.
β-type titanium alloys with a body-centered cubic structure are highly useful in orthopedics due to their low elastic modulus, lower than other commonly used alloys such as stainless steel and Co-Cr alloys. The formation of the β phase in titanium alloys is achieved through β-stabilizing elements such as Nb, Mo, and Ta. To produce new β alloys with a low modulus of elasticity, this work aimed to produce our alloy system for biomedical applications (Ti-50Nb-Mo). The alloys were produced by arc-melting and have the following compositions Ti-50Nb-xMo (x = 0, 3, 5, 7, and 12 wt% Mo). The alloys were characterized by density, X-ray diffraction, scanning electron microscopy, microhardness, and elastic modulus. It is worth highlighting that this new set of alloys of the Ti-50Nb-Mo system produced in this study is unprecedented; due to this, there needs to be a report in the literature on the production and structural characterization, hardness, and elastic modulus analyses. The microstructure of the alloys has an exclusively β phase (with bcc crystalline structure). The results show that adding molybdenum considerably increased the microhardness and decreased the elastic modulus, with values around 80 GPa, below the metallic materials used commercially for this type of application. From the produced alloys, Ti-50Nb-12Mo is highlighted due to its lower elastic modulus. Full article
(This article belongs to the Section Biomaterials)
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1 pages, 132 KiB  
Correction
Correction: Bysiec et al. Numerical Analysis of Steel Geodesic Dome under Seismic Excitations. Materials 2021, 14, 4493
by Dominika Bysiec and Tomasz Maleska
Materials 2024, 17(1), 249; https://doi.org/10.3390/ma17010249 - 3 Jan 2024
Viewed by 664
Abstract
In the original publication [...] Full article
11 pages, 3690 KiB  
Article
Mechanical Properties of MiniBars™ Basalt Fiber-Reinforced Geopolymer Composites
by Gabriel Furtos, Doina Prodan, Codruta Sarosi, Marioara Moldovan, Kinga Korniejenko, Leonard Miller, Lukáš Fiala and Nováková Iveta
Materials 2024, 17(1), 248; https://doi.org/10.3390/ma17010248 - 2 Jan 2024
Cited by 10 | Viewed by 1906
Abstract
Fly ash-based geopolymers represent a new material, which can be considered an alternative to ordinary Portland cement. MiniBars™ are basalt fiber composites, and they were used to reinforce the geopolymer matrix for the creation of unidirectional MiniBars™ reinforced geopolymer composites (MiniBars™ FRBCs). New [...] Read more.
Fly ash-based geopolymers represent a new material, which can be considered an alternative to ordinary Portland cement. MiniBars™ are basalt fiber composites, and they were used to reinforce the geopolymer matrix for the creation of unidirectional MiniBars™ reinforced geopolymer composites (MiniBars™ FRBCs). New materials were obtained by incorporating variable amount of MiniBars™ (0, 12.5, 25, 50, 75 vol.% MiniBars™) in the geopolymer matrix. Geopolymers were prepared by mixing fly ash powder with Na2SiO3 and NaOH as alkaline activators. MiniBars™ FRBCs were cured at 70 °C for 48 h and tested for different mechanical properties. Optical microscopy and SEM were employed to investigate the fillers and MiniBars™ FRBC. MiniBars™ FRBC showed increasing mechanical properties by an increased addition of MiniBars™. The mechanical properties of MiniBars™ FRBC increased more than the geopolymer wtihout MiniBars™: the flexural strength > 11.59–25.97 times, the flexural modulus > 3.33–5.92 times, the tensile strength > 3.50–8.03 times, the tensile modulus > 1.12–1.30 times, and the force load at upper yield tensile strength > 4.18–7.27 times. SEM and optical microscopy analyses were performed on the fractured surface and section of MiniBars™ FRBC and confirmed a good geopolymer network around MiniBars™. Based on our results, MiniBars™ FRBC could be a very promising green material for buildings. Full article
(This article belongs to the Special Issue Geopolymers and Fiber-Reinforced Concrete Composites)
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13 pages, 4731 KiB  
Article
Effect of Surface Hydrophilized Plastic Waste Aggregates Made by Mixing Various Kinds of Plastic on Mechanical Properties of Mortar
by Kyung-Min Kim and Young-Keun Cho
Materials 2024, 17(1), 247; https://doi.org/10.3390/ma17010247 - 2 Jan 2024
Viewed by 1092
Abstract
The surface hydrophilization of mixed plastic waste aggregates (MPAs) was conducted to improve the bond between an MPA and the surrounding cement matrix using two types of coating agents: a silicone amine resin and acrylic binders. The coating agents formed a physical bond [...] Read more.
The surface hydrophilization of mixed plastic waste aggregates (MPAs) was conducted to improve the bond between an MPA and the surrounding cement matrix using two types of coating agents: a silicone amine resin and acrylic binders. The coating agents formed a physical bond with the MPAs, and the results of contact angle measurement also revealed that the surface of MPAs was hydrophilic. The workability of a mortar mix increased by up to 1.47 times with the surface hydrophilization of MPAs. Meanwhile, the compressive and flexural strengths of mortar mixes decreased by 29~43% and 72~86%, respectively, at 28 days with the surface hydrophilization of MPAs. Namely, the surface hydrophilization of MPAs was successively conducted, and the workability of mortar mixes was improved accordingly, but the compressive and flexural strengths of mortar mixes decreased as the physical bond was partially separated from not only the MPA but also the surrounding cement matrix and the surface friction was decreased. Full article
(This article belongs to the Special Issue Environmentally Friendly Materials in Construction, Volume II)
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13 pages, 2529 KiB  
Article
Design, Synthesis, and Spectral Properties of Novel 2-Mercaptobenzothiazole Derivatives
by Agnieszka Skotnicka and Janina Kabatc-Borcz
Materials 2024, 17(1), 246; https://doi.org/10.3390/ma17010246 - 2 Jan 2024
Cited by 1 | Viewed by 1490
Abstract
This paper is focused on the optimalization of methods for the synthesis, isolation, and purification of 2-mercaptobenzothiazole-based acrylic and methacrylic monomers. The structures of the newly synthesized compounds were confirmed through infrared (IR) and nuclear magnetic resonance spectroscopy (NMR). Spectroscopic properties of the [...] Read more.
This paper is focused on the optimalization of methods for the synthesis, isolation, and purification of 2-mercaptobenzothiazole-based acrylic and methacrylic monomers. The structures of the newly synthesized compounds were confirmed through infrared (IR) and nuclear magnetic resonance spectroscopy (NMR). Spectroscopic properties of the resulting 2-mercaptobenzothiazole derivatives were determined based on their absorption spectra and molar absorption coefficients in solvents with varying polarities. A correlation was established between the calculated density functional theory (DFT) energies and Frontier Molecular Orbitals and the experimental observations, confirming their consistency. The practical utility of the synthesized compounds, particularly in future polymerization processes, hinges on a thorough understanding of these properties. Full article
(This article belongs to the Special Issue Feature Paper in the Section 'Polymeric Materials' (2nd Edition))
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2 pages, 140 KiB  
Editorial
Special Issue: “Recent Developments in Geopolymers and Alkali-Activated Materials”
by Sujeong Lee
Materials 2024, 17(1), 245; https://doi.org/10.3390/ma17010245 - 2 Jan 2024
Viewed by 1110
Abstract
As efforts toward global sustainability converge with the imperative to reduce the environmental impact of construction materials, extensive research and development is underway in the field of geopolymers and alkali-activated materials (AAMs) [...] Full article
(This article belongs to the Special Issue Recent Developments in Geopolymers and Alkali-Activated Materials)
14 pages, 4910 KiB  
Article
Time–Temperature Superposition of the Dissolution of Wool Yarns in the Ionic Liquid 1-Ethyl-3-methylimidazolium Acetate
by Amjad Safar Alghamdi, Peter John Hine and Michael Edward Ries
Materials 2024, 17(1), 244; https://doi.org/10.3390/ma17010244 - 2 Jan 2024
Viewed by 2250
Abstract
The dissolution of wool yarns in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate [C2mim][OAc] has been investigated. Wool yarns were submerged into [C2mim][OAc] and dissolved for various times and temperatures before coagulating with water. Optical microscopy was used to track the yarn’s cross-sectional area. We [...] Read more.
The dissolution of wool yarns in the ionic liquid 1-ethyl-3-methyl-imidazolium acetate [C2mim][OAc] has been investigated. Wool yarns were submerged into [C2mim][OAc] and dissolved for various times and temperatures before coagulating with water. Optical microscopy was used to track the yarn’s cross-sectional area. We propose that there are two competing dissolution processes, one rate-limited by disulfide bonds at low temperatures (LTs), and a second by hydrogen bonds at high temperatures (HTs), with a crossover point between the two regimes at 70 ℃. The corresponding activation energies were ELT = 127 ± 9 kJ/mol and EHT = 34 ± 1 kJ/mol. The remaining area of the dissolved wool yarn could be shifted via time–temperature superposition to plot a single master curve of area against time for both regions. Finally, the dissolution could be modelled by a diffusion process, giving self-diffusion coefficients for the [C2mim][OAc] ions (0.64–15.31 × 10−13 m2/s). Full article
(This article belongs to the Section Biomaterials)
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11 pages, 1067 KiB  
Article
The Field-Dependent Magnetic Viscosity of FeNdB Permanent Magnets
by Thomas Kresse, Gerhard Martinek, Gerhard Schneider and Dagmar Goll
Materials 2024, 17(1), 243; https://doi.org/10.3390/ma17010243 - 2 Jan 2024
Viewed by 1242
Abstract
The time-dependent decrease of the magnetic polarization of magnet materials in the presence of an opposing field is well known as the magnetic viscosity or magnetic aftereffect. In previous studies, magnetic viscosity was usually measured in fields when in the vicinity of coercivity [...] Read more.
The time-dependent decrease of the magnetic polarization of magnet materials in the presence of an opposing field is well known as the magnetic viscosity or magnetic aftereffect. In previous studies, magnetic viscosity was usually measured in fields when in the vicinity of coercivity HcJ, and this was conducted in order to understand the coercivity mechanism in magnetic materials. In this study, the magnetic viscosity of commercial FeNdB magnets is determined at opposing fields weaker than HcJ and at different temperatures in the range from 303 to 433 K (i.e., from 30 to 160 °C) by means of a vibrating sample magnetometer (VSM). As a result, the parameter Sv, which describes the magnetic viscosity in the material, was found to increase with increases in the opposing field. Furthermore, both the parameter Sv and its dependence on the temperature were found to correlate with the coercivity HcJ of the material. Also, a difference with regard to the parameter Sv for the materials measured in this study with similar magnetic properties, but which had undergone different types of processing, could not be found. Knowledge of the field- and temperature-dependent behavior of the magnetic viscosity of FeNdB magnets allows for better estimations over the lifetime of a component under operating conditions with respect to the magnetic losses in FeNdB magnets that are used in electric components. Full article
(This article belongs to the Special Issue Advances in Multifunctional Magnetic Materials)
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20 pages, 13352 KiB  
Article
Valorisation of “La Palma” Volcanic Ash for Making Portland-Blended, Alkaline and Hybrid Portland–Alkaline Cements
by Pablo Martín-Rodríguez, Ana Fernández-Jiménez, María del Mar Alonso, Angel Palomo and Inés García-Lodeiro
Materials 2024, 17(1), 242; https://doi.org/10.3390/ma17010242 - 2 Jan 2024
Viewed by 1321
Abstract
The present work evaluates the feasibility of using volcanic fly ash (VFA) generated by the eruption of the Tajogaite volcano on the island of La Palma (Spain) in 2021, as a precursor in the preparation of cementitious materials with different Portland cement (PC) [...] Read more.
The present work evaluates the feasibility of using volcanic fly ash (VFA) generated by the eruption of the Tajogaite volcano on the island of La Palma (Spain) in 2021, as a precursor in the preparation of cementitious materials with different Portland cement (PC) replacement levels (0%, 30%, 70% and 100%), in the absence (Blended Cement, BC) and presence of an alkaline activator (Hybrid Alkaline Cement, HAC, and Alkaline Cements, AC). Hydration kinetics (isothermal conduction calorimetry), paste mechanical strengths and reaction products were characterised by XRD, FTIR, TG/DTG and BSEM/EDX. The results obtained indicate that the strengths developed by the hybrid alkaline cements (HAC) are higher than those of the blended cements (BC), especially at the age of 2 days, where 25 MPa were obtained with the replacement of 70% PC by VFA. Alkaline cements (AC, 100% VFA) that were prepared with 8 M NaOH solution as the activator reached 40 MPa after 2 days. It was observed that in all the binders, depending on the initial composition of the binder mixture and the percentage of replacement and/or activator, VFA reacts to form cementitious gels, C-A-S-H and N-A-S-H type, which supports its use as a mineral addition to blended cement or as a precursor in the preparation of alkaline and hybrid alkaline cements. Full article
(This article belongs to the Special Issue Science and Technology for Silicate-Based Construction and Building Materials)
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