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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 4 | Viewed by 2643
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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<p>Outline of nanoarchitectonics, which combines nanotechnology with organic chemistry, inorganic chemistry, polymer chemistry, coordination chemistry, supramolecular chemistry, material chemistry, biochemistry, and microfabrication techniques.</p> Full article ">Figure 2
<p>Two-dimensional nanoarchitectonics of binaphthyl molecules with an axial chirality in its racemic form (<b>left</b>) and its optically active S-isomer form (<b>right</b>). Reprinted with permission from [<a href="#B369-materials-17-00271" class="html-bibr">369</a>]. Copyright 2023, Chemical Society of Japan.</p> Full article ">Figure 3
<p>The nanoarchitectonics of the highly conductive charge transfer complex of (phthalocyaninato)cobalt iodide through a cobalt phthalocyanine crystal phase transition method by simply mixing a KI solution containing CF<sub>3</sub>COOH and cobalt phthalocyanine with a CH<sub>2</sub>Cl<sub>2</sub> solution at the interface. Reprinted with permission from [<a href="#B370-materials-17-00271" class="html-bibr">370</a>]. Copyright 2023, Chemical Society of Japan.</p> Full article ">Figure 4
<p>A new principle, submarine luminescence, as a luminescence control, involving molecular manipulation of double-paddle platinum complexes through compression at the air–water interface. Reprinted with permission from [<a href="#B375-materials-17-00271" class="html-bibr">375</a>]. Copyright 2020, Wiley-VCH.</p> Full article ">Figure 5
<p>A flexible control of the intensity and signature of circularly polarized emissions from molecular aggregates of an achiral trans-bis(salicylaldiminato)platinum(II) complex upon precisely controlled clockwise and counterclockwise vortex motions at the air–water interface. Reprinted with permission from [<a href="#B376-materials-17-00271" class="html-bibr">376</a>]. Copyright 2022, Wiley-VCH.</p> Full article ">Figure 6
<p>Aggregation behavior of bottlebrush polymers at dynamic interfaces, as formed by electrostatic interaction of carboxylate (poly(acrylic acid)) and ammonium (aminopropylisobutyl polyhedral oligomeric silsesquioxane). Reprinted with permission from [<a href="#B377-materials-17-00271" class="html-bibr">377</a>]. Copyright 2023, American Chemical Society.</p> Full article ">Figure 7
<p>Dynamic covalent bonding controlled through modulating the droplet shape at the dynamic interface, where anisotropic compartmentalization of the liquid–liquid interface thus occurs, and the pH dependence of the Schiff base reaction leads to reversible toggling from jamming to unjamming in the interfacial assembly. Reprinted with permission from [<a href="#B381-materials-17-00271" class="html-bibr">381</a>]. Copyright 2022, American Chemical Society.</p> Full article ">Figure 8
<p>Covalent two-dimensional polymer under ambient temperature conditions at the air–water interface with the thickness of the sheet corresponding to that for its monolayer. Reprinted with permission from [<a href="#B382-materials-17-00271" class="html-bibr">382</a>]. Copyright 2016, Wiley-VCH.</p> Full article ">Figure 9
<p>Effect of the type of solvent (methanol or <span class="html-italic">N</span>,<span class="html-italic">N</span>-dimethylformamide) in the ligand diffusion solution to control the formation of MOF nanosheets synthesized through spreading the ligand 2,3,6,7,10,11-hexaiminotriphenylene on an aqueous solution containing Ni<sup>2+</sup>. Reprinted with permission from [<a href="#B388-materials-17-00271" class="html-bibr">388</a>]. Copyright 2023, Chemical Society of Japan.</p> Full article ">Figure 10
<p>Fabrication of mesoporous thin films with both uniformity and many tens of nanometer pores through a simple method in which a vortex flow is created in a beaker filled with water and carbon nanorings that float on the water surface and are then transferred to a substrate. The resulting thin films were carbonized under an inert gas atmosphere to synthesize carbon nanosheets. Reprinted with permission from [<a href="#B392-materials-17-00271" class="html-bibr">392</a>]. Copyright 2018, Wiley-VCH.</p> Full article ">Figure 11
<p>Dynamic liquid crystal transition using interfaces designed to spontaneously delay bulk crystallization and release residual strain at the interface in situ during annealing, spontaneously healing the interface via a dynamic transition to give better perovskite materials. Reprinted with permission from [<a href="#B393-materials-17-00271" class="html-bibr">393</a>]. Copyright 2022, Wiley-VCH.</p> Full article ">Figure 12
<p>Self-adaptive polydimethylsiloxane/TiO<sub>2−x</sub> coating that can dynamically adapt to volume changes and inhibit dendrite growth with high dynamic adaptability due to the micro-crosslinking of the B-O bonds. Reprinted with permission from [<a href="#B406-materials-17-00271" class="html-bibr">406</a>]. Copyright 2022, Wiley-VCH.</p> Full article ">Figure 13
<p>The kinetically controlled liquid–liquid interfacial precipitation (KC-LLIP) strategy, where ethylenediamine was selected as a covalent cross-linker of C<sub>60</sub> and the formation of C<sub>60</sub>-ethylenediamine products was controlled by the addition of isopropyl alcohol. To introduce the hollow structure, ethylenediamine-sulfur was used as an in situ generated droplet to form the yoke–shell structure, giving porous spheres, string hollow spheres, hollow spheres, and aperture hollow spheres. Reprinted with permission from [<a href="#B418-materials-17-00271" class="html-bibr">418</a>]. Copyright 2022, Wiley-VCH.</p> Full article ">Figure 14
<p>The in situ reaction method to the self-assembly process of C<sub>60</sub> molecules and mela-mine/ethylenediamine components in solution, producing a new fullerene assembly, a micron-sized, two-dimensional, amorphous-shaped, regular object, a fullerene rosette (<b>a</b>–<b>d</b>). Reproduced under terms of the CC-BY license [<a href="#B420-materials-17-00271" class="html-bibr">420</a>]. Copyright 2022, MDPI.</p> Full article ">Figure 15
<p>Cone–husk fullerene C<sub>60</sub> crystals prepared by dynamic liquid–liquid interface precipitation under ambient temperature (<b>a</b>–<b>e</b>) and pressure with high sensitivity to acetic acid in quartz crystal resonator sensor electrodes modified with cone–husk fullerene C<sub>60</sub> crystals (bottom). Reproduced under terms of the CC-BY license [<a href="#B421-materials-17-00271" class="html-bibr">421</a>]. Copyright 2022, MDPI.</p> Full article ">Figure 16
<p>Supramolecular assembly of fullerene C<sub>60</sub> into high aspect ratio quasi-two-dimensional microbelts at room temperature at the dynamic liquid–liquid interface of a carbon disulfide solution of fullerene C<sub>60</sub> and isopropyl alcohol. The formed fullerene microbelt can be converted to a mesoporous carbon microbelt with amorphous or graphite backbone structure through carbonizing at 900 °C or 2000 °C, respectively. Reprinted with permission from [<a href="#B422-materials-17-00271" class="html-bibr">422</a>]. Copyright 2017, American Chemical Society.</p> Full article ">
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 2 | Viewed by 1585
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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Figure 1
<p>SE-SEM photomicrograph of the Zn-3Mg heat-treated alloy. The darker contrast phase is the Mg-rich phase, and the lighter contrast phase is the Zn-rich phase.</p> Full article ">Figure 2
<p>SE-SEM images corresponding to the cross-sections of the HPT Zn-3Mg (<b>a</b>) hybrid and (<b>b</b>) alloy where the number of turns is indicated and (<b>a</b>) shows the 30-turn sample along with the 30-turn sample after post-deformation annealing (PDA). It is noted that the PDA treatment homogenized the distribution of the Mg (dark content) throughout the microstructure compared to the 30-turn sample without the PDA. Adapted from [<a href="#B49-materials-17-00270" class="html-bibr">49</a>].</p> Full article ">Figure 3
<p>(<b>a</b>–<b>c</b>) SE-SEM photomicrographs of the Zn-3Mg HPT hybrid near the sample edge after 30 turns of HPT + PDA (200 °C, 1 h). The blue-dashed circles show Mg-rich regions, constituting the Mg<sub>2</sub>Zn<sub>11</sub> phase. (<b>d</b>–<b>f</b>) BSE-SEM photomicrographs of the HPT Zn-3Mg alloy near the edge of the sample after 1 turn, at 0.9 mm from the center after 5 turns, and at 1 mm from the center after 15 turns, respectively. The Zn-rich (lighter contrast) and Mg<sub>2</sub>Zn<sub>11</sub> (darker contrast) phases constituted approximately 68% and 32%, respectively, by volume. Adapted from [<a href="#B49-materials-17-00270" class="html-bibr">49</a>].</p> Full article ">Figure 4
<p>SE-SEM micrograph corresponding to (<b>a</b>) low-magnification and (<b>b</b>) higher-magnification SE-SEM photomicrographs of the Zn-10Mg HPT hybrid after 15 turns, where image b was acquired near the edge of the disk; (<b>c</b>) the Zn-30Mg hybrid after 15 turns.</p> Full article ">Figure 5
<p>XRD patterns taken from the mid-thickness plane at the periphery of the disk surface area of the Zn-10Mg HPT hybrids after 1 and 15 turns.</p> Full article ">Figure 6
<p>Effect of Mg content on the corrosion behavior of Zn-xMg, where x = 3, 10, or 30, HPT hybrid specimens after 15 turns: (<b>a</b>) OCP, (<b>b</b>) PDP, (<b>c</b>) Nyquist plot, (<b>d</b>) Bode plot, and (<b>e</b>) equivalent circuit.</p> Full article ">Figure 7
<p>Effect of the number of turns on the corrosion behavior of the Zn-3Mg HPT alloy specimens: (<b>a</b>) OCP, (<b>b</b>) PDP, (<b>c</b>) Nyquist plot, and (<b>d</b>) Bode plot. 1T, 3T, and 15T indicate 1 turn, 3 turns, and 15 turns, respectively.</p> Full article ">Figure 8
<p>Effect of the number of turns on the corrosion behavior of Zn-3Mg HPT hybrid specimens: (<b>a</b>) OCP, (<b>b</b>) PDP, (<b>c</b>) Nyquist plot, and (<b>d</b>) Bode plot. 1T, 3T, and 15T indicate 1 turn, 3 turns, and 15 turns, respectively.</p> Full article ">Figure 9
<p>Effect of material processing (HPT alloy versus HPT hybrid) on the corrosion behavior of Zn-3Mg specimens: (<b>a</b>) OCP, (<b>b</b>) PDP, (<b>c</b>) Nyquist plot, and (<b>d</b>) Bode plot.</p> Full article ">
23 pages, 32864 KiB   99 wt.%) in Suspension: Methodology Design and Verification" data-journal="materials">
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 1331
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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Figure 1

Figure 1
<p>Reaction vessels in a six-position Weflon-PTFE holder mounted in an UltraCLAVE IV reactor.</p> Full article ">Figure 2
<p>Particle size distribution of the LED sample: (<b>a</b>) histogram and cumulative sum curve; (<b>b</b>) quantification of the limit values of the size intervals x, their frequency q3, and the cumulative values Q.</p> Full article ">Figure 3
<p>(<b>a</b>–<b>d</b>) SEM images of LED fly ash.</p> Full article ">Figure 4
<p>SEM image of LED sample supplemented with ED XRF spot analyses of the (red cross): (<b>a</b>) cenosphere; (<b>b</b>) microparticles on the microsphere surface.</p> Full article ">Figure 5
<p>XRD patterns of the (<b>a</b>) LED; (<b>b</b>) PRU; (<b>c</b>) MEL_II; (<b>d</b>) MEL_III; (<b>e</b>) TRM_E; (<b>f</b>) TRM_M; (<b>g</b>) DET_E; (<b>h</b>) DET_M; (<b>i</b>) TUS fly ashes.</p> Full article ">Figure 5 Cont.
<p>XRD patterns of the (<b>a</b>) LED; (<b>b</b>) PRU; (<b>c</b>) MEL_II; (<b>d</b>) MEL_III; (<b>e</b>) TRM_E; (<b>f</b>) TRM_M; (<b>g</b>) DET_E; (<b>h</b>) DET_M; (<b>i</b>) TUS fly ashes.</p> Full article ">Figure 6
<p>SEM images: microwave products (<b>a</b>,<b>b</b>) M2_C—garronite-Ca, (<b>c</b>,<b>d</b>) M5_C—sodalite and nepheline hydrate I; (<b>e</b>,<b>f</b>) product of three-stage synthesis under optimal conditions (sample LED)—sodalite.</p> Full article ">Figure 7
<p>SEM image of one L_20 product with ED XRF spot analysis (red cross).</p> Full article ">Scheme 1
<p>Three-stage HT synthesis of FAZs.</p> Full article ">Scheme 2
<p>FAZs determined by XRD in microwave products depend on temperature, concentration and type of activator, and Si/Al ratio.</p> Full article ">Scheme 3
<p>Results of XRD analysis of products depending on the Si/Al ratio and sample type.</p> Full article ">
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 5 | Viewed by 4188
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 2 | Viewed by 1191
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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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>A</b>) Praying Mantis<sup>TM</sup> Diffuse Reflection Accessory with high-temperature reaction chamber in FTIR spectrometer. (<b>B</b>) The optical fibre with UV LED diode; (<b>C</b>) the emission spectrum of UV LED diode.</p> Full article ">Figure 2
<p>XRD pattern of TiO<sub>2</sub> and patterns representing the standard diffraction data from the JCPDS file for anatase (No. 01-071-1168) and rutile (No. 01-088-117).</p> Full article ">Figure 3
<p>SEM images of nickel foam at different magnifications: (<b>a</b>) 50, (<b>b</b>) 100, (<b>c</b>) 200 and (<b>d</b>) 500 times.</p> Full article ">Figure 4
<p>SEM images of TiO<sub>2</sub> powder at different magnifications: (<b>a</b>) 20, (<b>b</b>) 50, (<b>c</b>) 100 and (<b>d</b>) 200 times.</p> Full article ">Figure 5
<p>Photocatalytic decomposition of ethylene under UV irradiation at various reaction temperatures in the presence of TiO<sub>2</sub>/KBr.</p> Full article ">Figure 6
<p>Photocatalytic decomposition of ethylene under UV irradiation at various reaction temperatures in the presence of TiO<sub>2</sub>/nickel foam.</p> Full article ">Figure 7
<p>Photocatalytic decomposition of ethylene in the presence of TiO<sub>2</sub>/nickel foam at 100 °C with the addition of some radical scavengers.</p> Full article ">Figure 8
<p>In situ FTIR spectra of titania surface during the photocatalytic decomposition of ethylene using TiO<sub>2</sub>.</p> Full article ">Figure 9
<p>In situ FTIR spectra of titania surface recorded during the photocatalytic decomposition of ethylene using TiO<sub>2</sub>/nickel foam (<b>A</b>) at 50 °C and (<b>B</b>) at 100 °C.</p> Full article ">Figure 10
<p>In situ FTIR spectra of titania surface during the photocatalytic decomposition of ethylene using TiO<sub>2</sub>-p-BQ/nickel foam at 100 °C.</p> Full article ">Figure 11
<p>In situ FTIR spectra of titania surface during the photocatalytic decomposition of ethylene using TiO<sub>2</sub>-p-BQ/nickel foam at 25 °C.</p> Full article ">Figure 12
<p>In situ FTIR spectra of titania surface during the photocatalytic decomposition of ethylene using TiO<sub>2</sub>-EDTA/nickel foam at 100 °C.</p> Full article ">Figure 13
<p>In situ FTIR spectra of titania surface during the photocatalytic decomposition of ethylene using TiO<sub>2</sub>-TA/nickel foam at 100 °C.</p> Full article ">
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 1136
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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Figure 1

Figure 1
<p>XRD and SEM of (<b>a</b>,<b>e</b>) S-1 seeds; (<b>b</b>,<b>f</b>) S1 (without NH<sub>4</sub>F or S-1 seeds); (<b>c</b>,<b>g</b>) S1-0.1 (with only NH<sub>4</sub>F); and (<b>d</b>,<b>h</b>) S1-10 wt% (with only S-1 seeds); N<sub>2</sub> adsorption–desorption isotherms and pore size distribution of different Silicalite-1: (<b>i</b>) S1-0.1 (with only NH<sub>4</sub>F); and (<b>j</b>) S1-10 wt% (with only S-1 seeds).</p> Full article ">Figure 2
<p>RC and SRV of the products in the system: (<b>a</b>) NH<sub>4</sub>F alone and (<b>b</b>) individual S-1 seeds; SEM of with different S-1 seed contents: (<b>c</b>) 5 wt%, (<b>d</b>) 10 wt%, and (<b>e</b>) 15 wt%; XRD of (<b>f</b>) Silicalite-1 zeolites with different S-1 seed contents.</p> Full article ">Figure 3
<p>SEM of Silicalite-1 zeolites with a F/Si of 0.1 under different S-1 seeds contents: (<b>a</b>) 1 wt%, (<b>b</b>) 5 wt%, (<b>c</b>) 10 wt%, and (<b>d</b>) 20 wt%; RC and SRV of the products with different system: (<b>e</b>) F/Si = 0.1 under different S-1 seeds contents; and (<b>f</b>) S-1 seeds = 10 wt% with different NH<sub>4</sub>F contents.</p> Full article ">Figure 4
<p>XRD and SEM of products synthesized with different crystallization times in the system: (<b>a</b>,<b>b</b>) NH<sub>4</sub>F system alone, (<b>c</b>,<b>d</b>) S-1 seeds solely, and (<b>e</b>,<b>f</b>) both NH<sub>4</sub>F and S-1 seeds.</p> Full article ">Scheme 1
<p>The role of different crystallization stages for synthesizing Silicalite-1 crystals in the system: (<b>a</b>) NH<sub>4</sub>F alone and (<b>b</b>) only S-1 seeds.</p> Full article ">Scheme 2
<p>Schematic diagram of different crystallization stages for producing Silicalite-1 zeolite crystals in a system containing both NH<sub>4</sub>F and S-1 seeds.</p> Full article ">
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 1181
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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<p>The schematic diagram of EW process [<a href="#B15-materials-17-00265" class="html-bibr">15</a>].</p> Full article ">Figure 2
<p>Photographs of configurations: (<b>a</b>) configuration 1; (<b>b</b>) configuration 2.</p> Full article ">Figure 3
<p>The measurement of the denotation velocity: (<b>a</b>) scheme of arrangement of probes; (<b>b</b>) photograph the steel plate with probes; (<b>c</b>) scheme of the assembly: 1—sand, 2—steel plate, 3—primary charge, 4—detonator, 5—secondary charge, 6—electrical contact probes, 7—ceramic probes.</p> Full article ">Figure 4
<p>The photograph of NANOGATE-22/16 high-speed electronic camera.</p> Full article ">Figure 5
<p>Schematic diagram of configuration 1.</p> Full article ">Figure 6
<p>Configuration 2 for high-speed photography of SCG: (<b>a</b>) schematic diagram: 1—post; 2—base plate (acrylic glass); 3—flyer plate; 4—secondary charge; 5—primary charge; 6—detonator; 7—screw, (<b>b</b>) photograph of configuration 2.</p> Full article ">Figure 7
<p>Schematic diagram of measurement of the SCG temperature.</p> Full article ">Figure 8
<p>Photography of the scheme of location optical fibers for measurement of the SCG temperature (the numbers indicate optical fibers).</p> Full article ">Figure 9
<p>Photograph of the scheme of calibration of silicon photodiodes: 1—current source; 2—tungsten filament lamp; 3—collecting lens; 4—chopper; 5—optic fiber holder.</p> Full article ">Figure 10
<p>Oscillograms of detonation process.</p> Full article ">Figure 11
<p>High-speed photography images (in configuration 1) over time: (<b>a</b>) 57.38 µs and (<b>b</b>) 91.75 µs.</p> Full article ">Figure 12
<p>High-speed photography images of SCG region (in configuration 2) over time.</p> Full article ">Figure 13
<p>The length of the SCG region vs. length of the plate vs. time.</p> Full article ">Figure 14
<p>The oscillograms of the SCG region temperature.</p> Full article ">Figure 15
<p>The scheme for determining the distance of maximum light collection from SCG region: 1—base plate; 2—flyer plate; 3—SCG region; 4—acceptance cone; 5—first field of view of the optical fibers; 6—second field; 7—optical fiber.</p> Full article ">
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 3 | Viewed by 1494
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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<p>Process flow diagram.</p> Full article ">Figure 2
<p>Morphology of Ni60–35WC hybrid powder at different magnifications. (<b>a</b>) Microstructure at low magnification (<b>b</b>) Microstructure at high magnification.</p> Full article ">Figure 3
<p>Schematic diagram of laser cladding processing.</p> Full article ">Figure 4
<p>Schematic diagram of friction wear test.</p> Full article ">Figure 5
<p>XRD pattern of laser-melted Ni60–WC composite coating.</p> Full article ">Figure 6
<p>Variation of standard ΔG with temperature for reactions (1)–(5).</p> Full article ">Figure 7
<p>EDS surface scanning results of Ni60/WC composite coating with a scanning speed of 12 mm/s.</p> Full article ">Figure 8
<p>SEM image of the intermediate coating with a scanning speed of 12 mm/s.</p> Full article ">Figure 9
<p>SEM images of Ni60/WC coating bonding areas at (<b>a</b>) 8 mm/s; (<b>b</b>) 10 mm/s; (<b>c</b>) 12 mm/s; (<b>d</b>) 14 mm/s.</p> Full article ">Figure 10
<p>SEM images of a dendrite microstructure in the middle region of the Ni60/WC coating at (<b>a</b>) 8 mm/s; (<b>b</b>) 10 mm/s; (<b>c</b>) 12 mm/s; (<b>d</b>) 14 mm/s.</p> Full article ">Figure 11
<p>Microhardness of fused coatings with different scanning speeds.</p> Full article ">Figure 12
<p>Coating friction coefficient at various scanning speeds.</p> Full article ">Figure 13
<p>Coating and substrate wear weight loss plots at various scanning speeds.</p> Full article ">Figure 14
<p>Wear surfaces of Ni60/WC coating with Ti6Al4V substrate. (<b>a</b>) Scanning speed 8 mm/s coating; (<b>b</b>) Scanning speed 10 mm/s coating; (<b>c</b>) Scanning speed 12 mm/s coating; (<b>d</b>) Scanning speed 14 mm/s coating; (<b>e</b>) Ti6Al4V substrate.</p> Full article ">Figure 15
<p>Schematic diagram of frictional wear of Ni60/WC composite coating.</p> Full article ">
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 1348
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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<p>View of the simulated clinical setting with a missing mandibular first molar. The first and second premolars served as abutment teeth (44 and 45, according to FDI notation, 8 mm distance between the abutment tooth axes).</p> Full article ">Figure 2
<p>Different views of the cFDP show (<b>A</b>) the connector design and (<b>B</b>) the modified occlusal surface of the pontic.</p> Full article ">Figure 3
<p>Nesting position of the cFDPs in the multilayer zirconia blanks, consisting of a 3 mm high enamel layer (E), a 4 mm high transition layer (T), and a dentine layer (D) forming the rest of the blank height. According to the manufacturer’s instructions, cFDP was positioned 1 mm from the upper surface.</p> Full article ">Figure 4
<p>(<b>A</b>) Design of the pontic and connector of the cFDP with a 1.0 mm wall thickness based on the geometry of the cFDP with a 0.7 mm wall thickness; (<b>B</b>) test setup and load application (red arrow) of the cFDP cemented to resiliently embedded metal stumps.</p> Full article ">Figure 5
<p>Picture taken during the fracture tests of the cFDPs in the universal-testing machine with a sensor enabling body-borne sound signals.</p> Full article ">Figure 6
<p>Results of the fracture load test of the different test series: (<b>a</b>) fracture resistance and (<b>b</b>) ranks according to failure during aging and respective fracture resistance. <span class="html-italic">p</span>-values were calculated by unifactorial ANOVA.</p> Full article ">Figure 7
<p>Localization of the fractures of the cFDPs (<b>a</b>–<b>d</b>): The localization of the fracture was the distal wall at the connector area. (<b>a</b>,<b>b</b>) as well as (<b>c</b>,<b>d</b>) each show one sample, abutment-sided and pontic-sided.</p> Full article ">
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 1047
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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<p>Stress–strain curve for the laminate.</p> Full article ">Figure 2
<p>A photo of a GFRP sample with the strip sensor.</p> Full article ">Figure 3
<p>An array of permanent magnets as the magnetizing system. The samples are magnetized by moving the system along the <span class="html-italic">y</span>-axis.</p> Full article ">Figure 4
<p>Positioning system with a sample and the HMC5883L magnetometer.</p> Full article ">Figure 5
<p>A photo of a sample after the stress test (the star mark was used to keep the same orientation of the sample during all tests).</p> Full article ">Figure 6
<p>Mean residual magnetic field components before stress test (green curves) and after stress test (red curves): (<b>a1</b>–<b>a6</b>) <span class="html-italic">B<sub>x</sub></span> for samples S01–S06, (<b>b1</b>–<b>b6</b>) <span class="html-italic">B<sub>z</sub></span> for samples S01–S06.</p> Full article ">Figure 7
<p>The plot of the 2D distribution of relative change in the RMS residual magnetization Δ<span class="html-italic">RMS<sub>x</sub></span> (<b>a1</b>–<b>a6</b>) and Δ<span class="html-italic">RMS<sub>z</sub></span> (<b>b1</b>–<b>b6</b>) measured in case of samples S01–S06.</p> Full article ">Figure 8
<p>Statistical parameters (mean—(<b>a1</b>,<b>b1</b>); median—(<b>a2</b>,<b>b2</b>); maximum—(<b>a3</b>,<b>b3</b>); mode—(<b>a4</b>,<b>b4</b>)) calculated for the relative change in the RMS residual magnetization Δ<span class="html-italic">RMS<sub>x</sub></span> (<b>a1</b>–<b>a4</b>) and Δ<span class="html-italic">RMS<sub>z</sub></span> (<b>b1</b>–<b>b4</b>).</p> Full article ">
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 1571
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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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Flowchart and a schematic of the synthesis process of Cu<sub>2</sub>O NPs (A: Spherical Cu<sub>2</sub>O, B: Octahedral Cu<sub>2</sub>O, C: Cubic Cu<sub>2</sub>O).</p> Full article ">Figure 2
<p>SEM images of Cu<sub>2</sub>O NPs with (<b>a</b>) spherical, (<b>b</b>) octahedral, and (<b>c</b>) cubic morphologies showing the effect of zero-, two-, four-, and eight-week exposure to humid conditions (temperature of 20 ± 5 °C and RH of 85 ± 5%).</p> Full article ">Figure 3
<p>SEM images of as-synthesized (<b>a1</b>) octahedral and (<b>b1</b>) cubic Cu<sub>2</sub>O; HRTEM images of as-synthesized (<b>a2</b>,<b>a3</b>) octahedral and (<b>b2</b>,<b>b3</b>) cubic Cu<sub>2</sub>O.</p> Full article ">Figure 4
<p>(<b>a</b>) BET specific surface area of Cu<sub>2</sub>O NPs obtained from conditions of not being exposed to humid conditions and (<b>b</b>) bactericidal rate (%) of Cu<sub>2</sub>O NPs with different morphologies exposed to humid conditions for 0 (raw), 2, 4, and 8 weeks.</p> Full article ">Figure 5
<p>XRD patterns of Cu<sub>2</sub>O NPs: (<b>a</b>) 0W samples (●: Cu<sub>2</sub>O) and (<b>b</b>) spherical Cu<sub>2</sub>O, (<b>c</b>) octahedral Cu<sub>2</sub>O, and (<b>d</b>) cubic Cu<sub>2</sub>O exposed to humid conditions for 0, 4, and 8 weeks (●: Cu<sub>2</sub>O; ○: CuO; ▲: Cu(OH)<sub>2</sub>).</p> Full article ">Figure 6
<p>(<b>a</b>) Cu 2p region of the XPS spectra of samples and high-resolution XPS spectrum of the Cu 2p peak: (<b>b</b>) spherical Cu<sub>2</sub>O, (<b>c</b>) octahedral Cu<sub>2</sub>O, and (<b>d</b>) cubic Cu<sub>2</sub>O in humid conditions for zero and four weeks; (A: Spherical Cu<sub>2</sub>O, B: Octahedral Cu<sub>2</sub>O, C: Cubic Cu<sub>2</sub>O).</p> Full article ">Figure 7
<p>(<b>a</b>) TGA-DSC curves at 250 °C for 2 h, (<b>b</b>) bactericidal rate of Cu<sub>2</sub>O NPs in raw samples and following TGA, and (<b>c</b>) XRD patterns of Cu<sub>2</sub>O NPs (●: Cu<sub>2</sub>O; ○: CuO); (A: Spherical Cu<sub>2</sub>O, B: Octahedral Cu<sub>2</sub>O, C: Cubic Cu<sub>2</sub>O).</p> Full article ">
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 1131
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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Figure 1
<p>(<b>a</b>) General geometry and directions of vectors of electric (<b>E</b>) and magnetic (<b>H</b>) fields and wavevector (<b>k</b>) in case of TE polarization; in case of TM polarization, <b>E</b> is along the cylinder axis while <b>H</b> lays in (<span class="html-italic">x</span>,<span class="html-italic">y</span>)-plane; (<b>b</b>) schematic demonstrating the principle of thermally tunable scattering.</p> Full article ">Figure 2
<p>Total SCS, <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>t</mi> </msub> </semantics></math>, as a function of <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> </mrow> </semantics></math>, for <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>=</mo> <mn>80</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>: (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>0.5</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>, TE polarization, (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>0.5</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>, TM polarization, (<b>c</b>) <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>2</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>, TE polarization, (<b>d</b>) <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>2</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>, TM polarization. Conductivity of <math display="inline"><semantics> <msub> <mrow> <mi>V</mi> <mi>O</mi> </mrow> <mn>2</mn> </msub> </semantics></math>, <math display="inline"><semantics> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> </msub> </semantics></math>, takes the following values: <math display="inline"><semantics> <mrow> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>1.4</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>2.5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>2.5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math> (blue lines). Arrows indicate the increase in <math display="inline"><semantics> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> </msub> </semantics></math>; for comparison, <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>t</mi> </msub> </semantics></math> is shown in the shell-free case (red line).</p> Full article ">Figure 3
<p>Total SCS, <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>t</mi> </msub> </semantics></math>, as a function of <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> </mrow> </semantics></math>, for <math display="inline"><semantics> <mrow> <mi>b</mi> <mo>=</mo> <mn>60</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>: (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>0.2</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>, TE polarization; (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>0.2</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>, TM polarization; (<b>c</b>) <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>2</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>, TE polarization; (<b>d</b>) <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>=</mo> <mn>2</mn> <mspace width="3.33333pt"/> <mi mathvariant="sans-serif">μ</mi> <mi mathvariant="normal">m</mi> </mrow> </semantics></math>, TM polarization. Conductivity of <math display="inline"><semantics> <msub> <mrow> <mi>VO</mi> </mrow> <mn>2</mn> </msub> </semantics></math>, <math display="inline"><semantics> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> </msub> </semantics></math>, takes the values <math display="inline"><semantics> <mrow> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>1.4</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>2.5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>2.5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mn>5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math> (blue lines). Arrows schematically show the changes of <math display="inline"><semantics> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> </msub> </semantics></math> from smaller to larger values; for comparison, <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>t</mi> </msub> </semantics></math> is shown in the case without shell (red line).</p> Full article ">Figure 4
<p>Magnitude of magnetic field, <math display="inline"><semantics> <mrow> <mrow> <mo>|</mo> </mrow> <msub> <mi>H</mi> <mi>z</mi> </msub> <mrow> <mo>|</mo> </mrow> </mrow> </semantics></math>, at (<b>a</b>–<b>e</b>) <math display="inline"><semantics> <mrow> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <mi>O</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, (<b>f</b>–<b>j</b>) <math display="inline"><semantics> <mrow> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <mi>O</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>, (<b>k</b>–<b>o</b>) <math display="inline"><semantics> <mrow> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <mi>O</mi> <mn>2</mn> </mrow> </msub> <mo>=</mo> <mn>5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>; (<b>a</b>,<b>f</b>,<b>k</b>) <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> <mo>=</mo> <mn>1.023</mn> </mrow> </semantics></math>, (<b>b</b>,<b>g</b>,<b>l</b>) <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> <mo>=</mo> <mn>1.21</mn> </mrow> </semantics></math>, (<b>c</b>,<b>h</b>,<b>m</b>) <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> <mo>=</mo> <mn>1.39</mn> </mrow> </semantics></math>, (<b>d</b>,<b>i</b>,<b>n</b>) <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> <mo>=</mo> <mn>1.52</mn> </mrow> </semantics></math>, (<b>e</b>,<b>j</b>,<b>o</b>) <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> <mo>=</mo> <mn>1.768</mn> </mrow> </semantics></math>; TE polarization; axes’ directions shown in the inset are the same for all plots from (<b>a</b>–<b>o</b>). Dashed white circles show location of the shell.</p> Full article ">Figure 5
<p>Angle-dependent scattering cross section, <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>ϕ</mi> </msub> </semantics></math> (a.u.), for TE-polarization at <math display="inline"><semantics> <mrow> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> </msub> <mo>=</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>: (<b>a</b>) axial field pattern plotted on (<math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> </mrow> </semantics></math>,<math display="inline"><semantics> <mi>ϕ</mi> </semantics></math>)-plane; <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>ϕ</mi> </msub> </semantics></math> vs. <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> </mrow> </semantics></math> at (<b>b</b>) <math display="inline"><semantics> <mrow> <mi>ϕ</mi> <mo>=</mo> <mn>0</mn> <mo>°</mo> </mrow> </semantics></math> (forward scattering), (<b>c</b>) <math display="inline"><semantics> <mrow> <mi>ϕ</mi> <mo>=</mo> <mn>180</mn> <mo>°</mo> </mrow> </semantics></math> (backscattering), (<b>d</b>) <math display="inline"><semantics> <mrow> <mi>ϕ</mi> <mo>=</mo> <mn>135</mn> <mo>°</mo> </mrow> </semantics></math>, (<b>e</b>) <math display="inline"><semantics> <mrow> <mi>ϕ</mi> <mo>=</mo> <mn>45</mn> <mo>°</mo> </mrow> </semantics></math> (side scattering), (<b>f</b>) <math display="inline"><semantics> <mrow> <mi>ϕ</mi> <mo>=</mo> <mn>90</mn> <mo>°</mo> </mrow> </semantics></math>; <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>ϕ</mi> </msub> </semantics></math> vs. <math display="inline"><semantics> <mi>ϕ</mi> </semantics></math> at (<b>g</b>) <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> <mo>=</mo> <mn>1.48</mn> </mrow> </semantics></math> and (<b>h</b>) <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> <mo>=</mo> <mn>1.584</mn> </mrow> </semantics></math>. In plots (<b>b</b>–<b>f</b>), <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>ϕ</mi> </msub> </semantics></math> is shown by red solid line; <math display="inline"><semantics> <mrow> <msub> <mi>σ</mi> <mi>t</mi> </msub> <mo>≠</mo> <mrow> <mi>f</mi> <mo>(</mo> <mi>ϕ</mi> <mo>)</mo> </mrow> </mrow> </semantics></math> is shown by blue dashed line for comparison; observation angle, <math display="inline"><semantics> <mi>ϕ</mi> </semantics></math>, is shown at the ordinate axis in plot (<b>a</b>) and at the abscissa axis in plots (<b>g</b>,<b>h</b>) in units of <math display="inline"><semantics> <mi>π</mi> </semantics></math>; note that the different normalizations are used for <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>t</mi> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>ϕ</mi> </msub> </semantics></math>, for the sake of simplicity of simulations; arbitrary units used for <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>ϕ</mi> </msub> </semantics></math> are the same in all plots.</p> Full article ">Figure 6
<p>Angle-dependent scattering cross section, <math display="inline"><semantics> <msub> <mi>σ</mi> <mi>ϕ</mi> </msub> </semantics></math> plotted on (<math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> </mrow> </semantics></math>,<math display="inline"><semantics> <mi>ϕ</mi> </semantics></math>)-plane for (<b>a</b>) TE-polarization at <math display="inline"><semantics> <mrow> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> </msub> <mo>=</mo> <mn>2.5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>; (<b>b</b>) TM-polarization at <math display="inline"><semantics> <mrow> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> </msub> <mo>=</mo> <msup> <mn>10</mn> <mn>2</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>; (<b>c</b>) TM-polarization at <math display="inline"><semantics> <mrow> <msub> <mi>σ</mi> <mrow> <mi>V</mi> <msub> <mi>O</mi> <mn>2</mn> </msub> </mrow> </msub> <mo>=</mo> <mn>2.5</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>3</mn> </msup> <mspace width="3.33333pt"/> <mrow> <mi mathvariant="normal">S</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>; normalized frequency has units of <math display="inline"><semantics> <mrow> <mi>k</mi> <mi>a</mi> </mrow> </semantics></math>.</p> Full article ">
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 1390
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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Figure 1
<p>Orthoboric acid form <a href="https://pl.wikipedia.org/wiki/Kwas_borowy" target="_blank">https://pl.wikipedia.org/wiki/Kwas_borowy</a> (accessed on 28 February 2023).</p> Full article ">Figure 2
<p>Epoxy compound samples for: (<b>a</b>) strength tests; (<b>b</b>) microscopic examination (dimensions in mm).</p> Full article ">Figure 3
<p>Compressive strength of modified and unmodified (reference) epoxy compound samples.</p> Full article ">Figure 4
<p>Compression modulus of modified and unmodified (reference) epoxy compounds.</p> Full article ">Figure 5
<p>Compressive strain of the modified and unmodified (reference) epoxy compounds.</p> Full article ">Figure 6
<p>(<b>a</b>) Examples of failure modes obtained for the compressed samples of epoxy compound treated with polyamide curing agent (E5/PAC/H<sub>3</sub>BO<sub>3</sub>/100:80:0.5). (<b>b</b>) Examples of failure modes obtained for the compressed samples of epoxy compound treated with amine curing agent (E5/ET/H<sub>3</sub>BO<sub>3</sub>/100:18:0.5).</p> Full article ">Figure 7
<p>Microscopic examination results of E5/PAC/100:80: (<b>a</b>) reference, (<b>b</b>) with 0.5 g of boric acid (0.28% mass fraction of boric acid in the epoxy compound), (<b>c</b>) with 1.0 g of boric acid (0.55% mass fraction of boric acid in the epoxy compound), (<b>d</b>) with 1.5 g of boric acid (0.83% mass fraction of boric acid in the epoxy compound).</p> Full article ">Figure 8
<p>Microscopic examination results of E5/ET/100:18: (<b>a</b>) reference, (<b>b</b>) with 0.5 g of boric acid (0.42% mass fraction of boric acid in the epoxy compound), (<b>c</b>) with 1.0 g of boric acid (0.84% mass fraction of boric acid in the epoxy compound), (<b>d</b>) with 1.5 g of boric acid (1.26% mass fraction of boric acid in the epoxy compound).</p> Full article ">Figure 8 Cont.
<p>Microscopic examination results of E5/ET/100:18: (<b>a</b>) reference, (<b>b</b>) with 0.5 g of boric acid (0.42% mass fraction of boric acid in the epoxy compound), (<b>c</b>) with 1.0 g of boric acid (0.84% mass fraction of boric acid in the epoxy compound), (<b>d</b>) with 1.5 g of boric acid (1.26% mass fraction of boric acid in the epoxy compound).</p> Full article ">Figure 9
<p>Microscopic examination results of E5/IDA/100:40: (<b>a</b>) reference, (<b>b</b>) with 0.5 g of boric acid (0.33% mass fraction of boric acid in the epoxy compound), (<b>c</b>) with 1.0 g of boric acid (0.66% mass fraction of boric acid in the epoxy compound), (<b>d</b>) with 1.5 g of boric acid (0.99% mass fraction of boric acid in the epoxy compound).</p> Full article ">
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 1500
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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Figure 1
<p>SEM images of (<b>a</b>) zeolite powder and (<b>b</b>) glass powder. (<b>a</b>) ZP; (<b>b</b>) GP.</p> Full article ">Figure 2
<p>XRD patterns and quantitative phase analysis of (<b>a</b>,<b>c</b>) zeolite powder and (<b>b</b>,<b>d</b>) glass powder. (<b>a</b>) ZP; (<b>b</b>) GP; (<b>c</b>) ZP; (<b>d</b>) GP.</p> Full article ">Figure 3
<p>Particle size distribution diagrams of (<b>a</b>) ZP and (<b>b</b>) GP.</p> Full article ">Figure 4
<p>Indentation matrix and load displacement curve of low-carbon concrete samples. (<b>a</b>) Indentation matrix; (<b>b</b>) load displacement curve.</p> Full article ">Figure 5
<p>Apparent morphology of each group of concrete; (<b>a</b>) 3D apparent morphology; (<b>b</b>) 2D apparent morphology.</p> Full article ">Figure 6
<p>Indentation modulus and indentation hardness of each group. (<b>a</b>) Modulus/GPa; (<b>b</b>) hardness/GPa; (<b>c</b>) modulus/GPa; (<b>d</b>) hardness/GPa; (<b>e</b>) modulus/GPa; (<b>f</b>) Hardness/GPa.</p> Full article ">Figure 7
<p>Analysis of elastic modulus contours for (<b>a</b>) WLCC-5-5 and (<b>b</b>) LCC-5-5. (<b>a</b>) Contour analysis diagram of LCC-5-5; (<b>b</b>) contour analysis diagram of WLCC-5-5.</p> Full article ">Figure 8
<p>Accumulated pore volumes and volume fractions of (<b>a</b>) WLCC-5-5 and (<b>b</b>) LCC-5-5. (<b>a</b>) Contour analysis diagram; (<b>b</b>) pore volume fraction.</p> Full article ">Figure 9
<p>Typical p–h curves of different phases [<a href="#B43-materials-17-00258" class="html-bibr">43</a>].</p> Full article ">Figure 10
<p>Probability distribution functions of hydration products in WLCC-5-5 and LCC-5-5 phases. (<b>a</b>) Modulus of hydrate phase in LCC-5-5; (<b>b</b>) modulus of hydrate phase in WLCC-5-5; (<b>c</b>) hardness of hydrate phase in LCC-5-5; (<b>d</b>) hardness of hydrate phase in WLCC-5-5.</p> Full article ">Figure 11
<p>Probability distribution functions of hydration products in (<b>a</b>) WLCC-5-5 and (<b>b</b>) LCC-5-5 phases. (<b>a</b>) Graph of peak elastic modulus of each hydrate phase; (<b>b</b>) graph of peak elastic hardness of each hydrate phase.</p> Full article ">Figure 12
<p>Volume fractions of hydration products in WLCC-5-5 and LCC-5-5.</p> Full article ">
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 1181
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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<p>Improved WOL specimen (unit: mm).</p> Full article ">Figure 2
<p>Molecular dynamics models (α-Fe in blue, hydrogen in red): (<b>a</b>) hydrogen-free model; (<b>b</b>) uniformly distributed hydrogen model; (<b>c</b>) hydrogen concentrated at the crack tip.</p> Full article ">Figure 3
<p>Load curve used in molecular dynamics simulation (T = 10.32 ps).</p> Full article ">Figure 4
<p>d<span class="html-italic">a</span>/d<span class="html-italic">N-</span>Δ<span class="html-italic">K</span> curves of different experimental conditions: (<b>a</b>) un-corroded and pre-corroded specimen under the loading condition of stress ratio <span class="html-italic">R</span> = 0.1, loading frequency <span class="html-italic">f</span> = 100 Hz; (<b>b</b>) un-corroded and corrosion fatigue specimen under the loading condition of stress ratio <span class="html-italic">R</span> = 0.1, loading frequency <span class="html-italic">f</span> = 0.01 Hz.</p> Full article ">Figure 5
<p>Crack propagation of three models: (<b>a</b>) hydrogen-free; (<b>b</b>) uniformly distributed hydrogen; (<b>c</b>) hydrogen concentrated at the crack tip.</p> Full article ">Figure 6
<p>The relationship between cycle number and crack growth length under different environments.</p> Full article ">Figure 7
<p>Crack growth curves before and after pre-corrosion (<span class="html-italic">R</span> = 0.1).</p> Full article ">Figure 8
<p>Fracture morphology under different corrosion environments: (<b>a</b>) fatigue crack growth fracture morphology in non-corrosive environment; (<b>b</b>) fatigue crack growth fracture morphology after pre-corrosion.</p> Full article ">Figure 9
<p>Dislocation emission during crack propagation: (<b>a</b>) hydrogen-free; (<b>b</b>) uniformly distributed hydrogen.</p> Full article ">Figure 10
<p>Crack growth rate curves under different corrosion modes (<span class="html-italic">R</span> = 0.1).</p> Full article ">Figure 11
<p>Fatigue crack growth fracture morphology in corrosion environment.</p> Full article ">Figure 12
<p>Dislocation emission from a hydrogen-containing α-Fe model at the crack tip.</p> Full article ">Figure 13
<p>Crack growth rates at different frequencies.</p> Full article ">Figure 14
<p>The relationship between cycle number and crack growth length at different frequencies (high-frequency T = 10.32 ps and low-frequency T = 20.64 ps): (<b>a</b>) hydrogen-free; (<b>b</b>) uniformly distributed hydrogen; (<b>c</b>) hydrogen concentrated at the crack tip.</p> Full article ">Figure 15
<p>Atomic configuration diagrams of the hydrogen-free model: (<b>a</b>) the maximum load in a cycle, high-frequency (T = 10.32 ps); (<b>b</b>) the minimum load in a cycle, high-frequency (T = 10.32 ps); (<b>c</b>) the maximum load in a cycle, low-frequency (T = 20.64 ps); (<b>d</b>) the minimum load in a cycle, low-frequency (T = 20.64 ps).</p> Full article ">Figure 16
<p>Dislocation distribution extracted from the uniformly distributed hydrogen model: (<b>a</b>) the maximum load in a cycle, high-frequency (T = 10.32 ps); (<b>b</b>) the minimum load in a cycle, high-frequency (T = 10.32 ps); (<b>c</b>) the maximum load in a cycle, low-frequency (T = 20.64 ps); (<b>d</b>) the minimum load in a cycle, low-frequency (T = 20.64 ps).</p> Full article ">Figure 17
<p>Dislocation distribution extracted from the hydrogen concentrated at the crack tip model: (<b>a</b>) the maximum load in a cycle, high-frequency (T = 10.32 ps); (<b>b</b>) the minimum load in a cycle, high-frequency (T = 10.32 ps); (<b>c</b>) the maximum load in a cycle, low-frequency (T = 20.64 ps); (<b>d</b>) the minimum load in a cycle, low-frequency (T = 20.64 ps).</p> Full article ">
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 1061
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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<p>Crystallization (<b>a</b>) and melting (<b>b</b>) curves of Nd-BR/silica compounds.</p> Full article ">Figure 2
<p>Crystallization (<b>a</b>) and melting (<b>b</b>) curves of Nd-BR/CB compounds.</p> Full article ">Figure 3
<p>Crystallization curves of Nd-BR compounds with different maximum heating temperatures.</p> Full article ">Figure 4
<p>Relationship of <span class="html-italic">E</span><sub>a</sub> with <span class="html-italic">T</span><sub>c,peak</sub>. ▪, non-crosslinked samples; <span style="color:red">●</span>, cured sample.</p> Full article ">Figure 5
<p>DMA curves of Nd-BR compounds. (<b>a</b>) Storage modulus <span class="html-italic">G</span>′, shifted vertically by 10<sup>×</sup>; (<b>b</b>) loss modulus <span class="html-italic">G</span>″, shifted vertically by 10<sup>×</sup>; (<b>c</b>) loss tangent, tan <span class="html-italic">δ</span>.</p> Full article ">
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 1446
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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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>PBF-LB SS 316L steel deposit on an AISI 1020 steel substrate.</p> Full article ">Figure 2
<p>Schematic of the locations of n.3 MIIT on the Y-Z and X-Y planes (dark diamonds); the inset shows the n.9 nIIT (3 × 3 matrix in the 26 × 26 µm<sup>2</sup> square in yellow) locations over the X-Y plane.</p> Full article ">Figure 3
<p>Microstructures from optical microscopy obtained after etching with aqua regia: (<b>a</b>) Etched micrograph at a magnification of 5× from OM revealing curved and semi-circular trace features; (<b>b</b>) Details of columnar grains at a magnification of 10×, with an embedded cellular structure; a narrow region along the solidification front appears relatively brighter, likely due to a greater content of passivating elements (Cr and Mo); (<b>c</b>,<b>d</b>) SEM images of the characteristic cellular structure of either an equiaxed or elongated morphology; (<b>e</b>,<b>f</b>) Unetched nano-polished PBF-LB 316L samples at a magnification of 5× before and after MIIT, respectively, with a peak load of 700 N in the core of the deposit and after nIIT (not shown).</p> Full article ">Figure 3 Cont.
<p>Microstructures from optical microscopy obtained after etching with aqua regia: (<b>a</b>) Etched micrograph at a magnification of 5× from OM revealing curved and semi-circular trace features; (<b>b</b>) Details of columnar grains at a magnification of 10×, with an embedded cellular structure; a narrow region along the solidification front appears relatively brighter, likely due to a greater content of passivating elements (Cr and Mo); (<b>c</b>,<b>d</b>) SEM images of the characteristic cellular structure of either an equiaxed or elongated morphology; (<b>e</b>,<b>f</b>) Unetched nano-polished PBF-LB 316L samples at a magnification of 5× before and after MIIT, respectively, with a peak load of 700 N in the core of the deposit and after nIIT (not shown).</p> Full article ">Figure 4
<p>Nano-indentation curves (load control, 5 mN peak load) in the X-Y plane at the core of the deposit face.</p> Full article ">Figure 5
<p>(<b>a</b>) Macro-ICs (150 N peak load) at corner locations of the deposit face in the X-Y plane. Although the loading of the three ICs is comparable, ICs 1 and 3 exhibit abnormal behavior, which was ascribed to an incorrect touching of the two indenter-sensors against the deposit during complete release of the load (see discussion in the text). (<b>b</b>) Macro-ICs (150 N peak load) at the core of the deposit face in the Y-Z plane.</p> Full article ">Figure 5 Cont.
<p>(<b>a</b>) Macro-ICs (150 N peak load) at corner locations of the deposit face in the X-Y plane. Although the loading of the three ICs is comparable, ICs 1 and 3 exhibit abnormal behavior, which was ascribed to an incorrect touching of the two indenter-sensors against the deposit during complete release of the load (see discussion in the text). (<b>b</b>) Macro-ICs (150 N peak load) at the core of the deposit face in the Y-Z plane.</p> Full article ">Figure 6
<p>Multi-cycle (10 cycles) plots of (<b>a</b>) EIT for each cycle on the X−Y and Y−Z planes, (<b>b</b>) HIT for each cycle of the six indents on the X−Y and Y−Z planes, (<b>c</b>) the progressive increase in EIT, with respect to the increase in the first cycle (diff-EIT), and (<b>d</b>) the progressive decrease in HIT with respect to the decrease in the first cycle (diff-HIT).</p> Full article ">Figure 7
<p>Three-dimensional schematic illustration of in-plane and in-depth residual stresses with reference to the macro-indents in XY and YZ planes (which are highlighted in <a href="#materials-17-00255-f002" class="html-fig">Figure 2</a>) and detail of indent 2D cross section in both planes underlining the effect of residual stress.</p> Full article ">
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 906
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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<p>From Koch’s 1940 paper [<a href="#B9-materials-17-00254" class="html-bibr">9</a>]. Its caption (translated from German) reads: <span class="html-italic">“Electrons moving from the interior outward due to the temperature gradient (<math display="inline"><semantics> <mrow> <msub> <mi>T</mi> <mn>1</mn> </msub> <mo>&gt;</mo> <msub> <mi>T</mi> <mn>2</mn> </msub> </mrow> </semantics></math>) are deflected by the magnetic field <math display="inline"><semantics> <mi mathvariant="script">H</mi> </semantics></math>. The figure on the side shows the direction of the Lorentz force for an electron moving to the right. The resulting circular current is depicted in the Figure in the conventional sense (positive charge carriers). Its magnetic field <math display="inline"><semantics> <msub> <mi mathvariant="script">H</mi> <mi>S</mi> </msub> </semantics></math> is in direction opposite to that of the primary field (<math display="inline"><semantics> <mi mathvariant="script">H</mi> </semantics></math>)”</span>. “Nerst-Strom” in the figure means “Nerst current”.</p> Full article ">Figure 2
<p>Schematic picture of the charge distribution in the ground state of a superconducting body, from Ref. [<a href="#B21-materials-17-00254" class="html-bibr">21</a>] of 2001. The figure caption in Ref. [<a href="#B21-materials-17-00254" class="html-bibr">21</a>] says <span class="html-italic">“Negative charge is expelled from the bulk to the surface”</span>, but no connection to the Meissner effect is made in that paper.</p> Full article ">Figure 3
<p>Schematic picture of the charge flow during the superconducting transition proposed to explain the Meissner effect, from Ref. [<a href="#B24-materials-17-00254" class="html-bibr">24</a>] of 2008. The figure caption in Ref. [<a href="#B24-materials-17-00254" class="html-bibr">24</a>] reads <span class="html-italic">“Superfluid electrons flow from the interior towards the surface and are deflected to the left by the magnetic field pointing up. Normal electrons backflow from the surface towards the interior and are deflected to the right by the magnetic field. The momentum in this normal current is transferred to the ions by collisions with impurities”</span>. It was only 8 years later that I realized that the last sentence in this caption is incorrect.</p> Full article ">Figure 4
<p>An electron expanding its orbit in the presence of a magnetic field B perpendicular to the orbit acquires an azimuthal velocity that generates a magnetic field opposite to the applied field.</p> Full article ">Figure 5
<p>The top left panel, from Ref. [<a href="#B32-materials-17-00254" class="html-bibr">32</a>], shows how superconducting domains with surface currents are created that exclude the magnetic field (black dots) from their interior; the top right panel shows the final state after the superconducting domains grow and merge. The bottom panel, from Ref. [<a href="#B24-materials-17-00254" class="html-bibr">24</a>], shows a single domain where the enlarged orbits lead to expulsion of negative charge and a radial outgoing electric field.</p> Full article ">Figure 6
<p>Upper panels show schematically orbits in the superconducting and normal regions. As normal electrons enter the superconducting region, their orbits expand causing a forward thrust of negative charge over a distance <math display="inline"><semantics> <msub> <mi>λ</mi> <mi>L</mi> </msub> </semantics></math>, as shown in the lower panel left side. This gives rise to a backflow of normal charge shown on the right side of the lower panel.</p> Full article ">Figure 7
<p>Motion of electrons becoming superconducting (s carriers) and backflowing normal electrons (n carriers) as the S-N phase boundary moves up in the figure. The magnetic Lorentz force acts to the left on s carriers and to the right on n carriers. However, the backflowing electrons are <math display="inline"><semantics> <mrow> <mi>n</mi> <mi>o</mi> <mi>t</mi> </mrow> </semantics></math> deflected to the right as the figure shows. The explanation is given in <a href="#materials-17-00254-f008" class="html-fig">Figure 8</a>.</p> Full article ">Figure 8
<p>Explanation of how momentum is conserved in the normal to superconductor transition. Backflowing electrons of negative effective mass experience a force <math display="inline"><semantics> <msub> <mi>F</mi> <mi>L</mi> </msub> </semantics></math> from the lattice to balance electric (from Faraday’s law) and magnetic forces acting on them. The resulting force <math display="inline"><semantics> <mrow> <mo>−</mo> <msub> <mi>F</mi> <mi>L</mi> </msub> </mrow> </semantics></math> from electrons acting on the ions transfers momentum to the body as a whole.</p> Full article ">Figure 9
<p>Meissner transition for a cylinder. The magnetic field points out of the paper, Meissner current flows clockwise. <math display="inline"><semantics> <msub> <mi>E</mi> <mi>F</mi> </msub> </semantics></math> is the Faraday electric field. The backflowing carriers are shown both as electrons moving in (upper part) or equivalently as holes moving out (lower part). For holes, electric and magnetic forces <math display="inline"><semantics> <msub> <mi>F</mi> <mi>E</mi> </msub> </semantics></math> and <math display="inline"><semantics> <msub> <mi>F</mi> <mi>H</mi> </msub> </semantics></math> are balanced. For backflowing electrons, they are balanced by the force <math display="inline"><semantics> <msub> <mi>F</mi> <mrow> <mi>l</mi> <mi>a</mi> <mi>t</mi> <mi>t</mi> </mrow> </msub> </semantics></math> exerted by the lattice on electrons with negative effective mass. Associated with it there is a force on the lattice, <math display="inline"><semantics> <msub> <mi>F</mi> <mrow> <mi>o</mi> <mi>n</mi> <mo>−</mo> <mi>l</mi> <mi>a</mi> <mi>t</mi> <mi>t</mi> </mrow> </msub> </semantics></math>, that transfers momentum to the body that rotates with angular momentum equal and opposite to that of the Meissner current [<a href="#B34-materials-17-00254" class="html-bibr">34</a>].</p> Full article ">Figure 10
<p>Cross-section of a superconducting wire connected to normal metal leads carrying a current from right to left (opposite to the horizontal arrows). The magnetic field generated by the current points into (out of) the paper in the upper (lower) half of the wire. The upper panel shows streamlines of electrons obtained through solution of London’s equation [<a href="#B29-materials-17-00254" class="html-bibr">29</a>]. Note the discontinuous change in the vertical component of the velocity as electrons enter and leave the superconducting regions. This is explained through the same orbit expansion and contraction discussed earlier, as illustrated in the lower panels and explained in the text.</p> Full article ">
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 1151
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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<p>Thermal–mechanical coupling test device. (<b>a</b>) Axonometric view; (<b>b</b>) Plan view.</p> Full article ">Figure 2
<p>Measuring point layout (unit: mm).</p> Full article ">Figure 3
<p>Temperature distribution of concrete with 40% coarse aggregate content. (<b>a</b>) Temperature curve at 1 h; (<b>b</b>) Temperature distribution at 2 h.</p> Full article ">Figure 4
<p>Temperature distribution of concrete with different coarse aggregate contents along the thickness direction.</p> Full article ">Figure 5
<p>Compressive strength of concrete with different coarse aggregate contents.</p> Full article ">Figure 6
<p>Concrete failure characteristics.</p> Full article ">Figure 7
<p>Change rate of concrete strength with different coarse aggregate contents.</p> Full article ">Figure 8
<p>Strength loss of 40% coarse aggregate concrete under different fire exposure times.</p> Full article ">Figure 9
<p>Strength loss of different coarse aggregate concretes under 1 h fire exposure time.</p> Full article ">Figure 10
<p>Three-dimensional reconstruction of concrete and the representative layers selection. (<b>a</b>) Layers selected at room temperature; (<b>b</b>) Layers selected after the coupling test.</p> Full article ">Figure 11
<p>CT scans at room temperature.</p> Full article ">Figure 12
<p>CT images of 40% coarse aggregate concrete under different fire exposure times.</p> Full article ">Figure 13
<p>CT images of different coarse aggregate concretes under 1 h fire exposure.</p> Full article ">Figure 14
<p>Relation between crack ratio and coarse aggregate content.</p> Full article ">Figure 15
<p>Relation between D and fire exposure time (40% coarse aggregate concrete).</p> Full article ">Figure 16
<p>Change in damage variable with the content of coarse aggregate (1 h fire exposure).</p> Full article ">Figure 17
<p>Relationship between D and strength loss.</p> Full article ">
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 1155
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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<p>2D visualization of fibers randomly oriented in space.</p> Full article ">Figure 2
<p>Infinite randomly oriented fibers in a parallelepipedal REV (<math display="inline"><semantics> <msub> <mi>L</mi> <mi>x</mi> </msub> </semantics></math> = <math display="inline"><semantics> <msub> <mi>L</mi> <mi>y</mi> </msub> </semantics></math> ≈ <math display="inline"><semantics> <msub> <mi>L</mi> <mi>z</mi> </msub> </semantics></math>).</p> Full article ">Figure 3
<p>Infinite randomly oriented fibers in a slice REV (<math display="inline"><semantics> <msub> <mi>L</mi> <mi>x</mi> </msub> </semantics></math> = <math display="inline"><semantics> <msub> <mi>L</mi> <mi>y</mi> </msub> </semantics></math> &gt;&gt; <math display="inline"><semantics> <msub> <mi>L</mi> <mi>z</mi> </msub> </semantics></math>).</p> Full article ">Figure 4
<p>Fiber orientation coordinate system.</p> Full article ">Figure 5
<p>(<b>a</b>) Mixed boundary condition (MBC); (<b>b</b>) uniform thermal gradient condition (UTGC); (<b>c</b>) quadratic mesh.</p> Full article ">Figure 6
<p>Illustration of the successive steps for the model generation in <b>ABAQUS CAE</b>.</p> Full article ">Figure 6 Cont.
<p>Illustration of the successive steps for the model generation in <b>ABAQUS CAE</b>.</p> Full article ">Figure 7
<p>Influence of mesh size for a volume fraction of 4%.</p> Full article ">Figure 8
<p>Influence of mesh size for a volume fraction of 15%.</p> Full article ">Figure 9
<p>Influence of cubic REV size at 4% volume fraction.</p> Full article ">Figure 10
<p>Geometry and meshing of a 3D slice (<math display="inline"><semantics> <msub> <mi>L</mi> <mi>x</mi> </msub> </semantics></math> = <math display="inline"><semantics> <msub> <mi>L</mi> <mi>y</mi> </msub> </semantics></math> = 10 and <math display="inline"><semantics> <msub> <mi>L</mi> <mi>z</mi> </msub> </semantics></math> = 1).</p> Full article ">Figure 11
<p>3D fiber temperature fields (<math display="inline"><semantics> <msub> <mi>L</mi> <mi>x</mi> </msub> </semantics></math> = <math display="inline"><semantics> <msub> <mi>L</mi> <mi>y</mi> </msub> </semantics></math> = 10 and <math display="inline"><semantics> <msub> <mi>L</mi> <mi>z</mi> </msub> </semantics></math> = 1).</p> Full article ">Figure 12
<p>Influence of REV size at 4% volume fraction.</p> Full article ">Figure 13
<p>Influence of REV size at 15% volume fraction.</p> Full article ">Figure 14
<p>Influence of volume fraction.</p> Full article ">Figure 15
<p>Comparison of numerical and analytical models for increasing the size of REV fibers in air, <math display="inline"><semantics> <msub> <mi>k</mi> <mrow> <mi>f</mi> <mi>i</mi> <mi>b</mi> </mrow> </msub> </semantics></math> = 1 W.K<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>.m<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math> with a volume fraction of 4%.</p> Full article ">Figure 16
<p>Comparison of numerical and analytical models for increasing the size of REV fibers in air, <math display="inline"><semantics> <msub> <mi>k</mi> <mrow> <mi>f</mi> <mi>i</mi> <mi>b</mi> </mrow> </msub> </semantics></math> = 1 W.K<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>.m<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math> with a volume fraction of 15%.</p> Full article ">Figure 17
<p>Comparison of numerical and analytical models for increasing the size of REV fibers in air, <math display="inline"><semantics> <msub> <mi>k</mi> <mrow> <mi>f</mi> <mi>i</mi> <mi>b</mi> </mrow> </msub> </semantics></math> = 0.472 W.K<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>.m<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math> with a volume fraction of 4%.</p> Full article ">Figure 18
<p>Comparison of numerical and analytical models for increasing the size of REV fibers in air, <math display="inline"><semantics> <msub> <mi>k</mi> <mrow> <mi>f</mi> <mi>i</mi> <mi>b</mi> </mrow> </msub> </semantics></math> = 0.472 W.K<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>.m<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math> with a volume fraction of 15%.</p> Full article ">Figure 19
<p>Comparison of the effective thermal conductivities of JM/mortar composites obtained experimentally and numerically for short and long fibers with the Glicksman model calculated using the estimate <math display="inline"><semantics> <msub> <mi>k</mi> <mrow> <mi>J</mi> <mi>M</mi> <mo>,</mo> <mi>f</mi> <mi>i</mi> <mi>b</mi> </mrow> </msub> </semantics></math> = 0.472 W.K<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>.m<math display="inline"><semantics> <msup> <mrow/> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>.</p> Full article ">
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 1173
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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<p>VLPC mixing process.</p> Full article ">Figure 2
<p>Measuring instrument for porosity and permeability coefficient. (<b>a</b>) Porosity measuring instrument; (<b>b</b>) permeability coefficient measuring instrument.</p> Full article ">Figure 3
<p>pH Testing. (<b>a</b>) Broken sample; (<b>b</b>) Grinding sample; (<b>c</b>) Sample sieving; (<b>d</b>) Mix with distilled water; (<b>e</b>) Filter mixture; (<b>f</b>) pH measurement.</p> Full article ">Figure 4
<p>Concrete bulk weight test results.</p> Full article ">Figure 5
<p>Effective porosity test results.</p> Full article ">Figure 6
<p>Permeability coefficient test results.</p> Full article ">Figure 7
<p>Effect of porosity on compressive and flexural strengths. (<b>a</b>) Compressive strength; (<b>b</b>) flexural strength.</p> Full article ">Figure 8
<p>Effect of mineral admixtures on compressive and flexural strengths. (<b>a</b>) Compressive strength; (<b>b</b>) flexural strength.</p> Full article ">Figure 9
<p>pH value of VLPC at different ages.</p> Full article ">Figure 10
<p>SEM images of SSC hydrated with OPC for 28 days. (<b>a</b>) SSC; (<b>b</b>) OPC.</p> Full article ">
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 1331
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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<p>Monitoring, by EDS, of the elements that compose Ti-50Nb alloy, monitored region (<b>a</b>) and overlapping of the elements with micrograph (<b>b</b>).</p> Full article ">Figure 2
<p>Monitoring, by EDS, of the elements that compose Ti-50Nb-3Mo alloy, monitored region (<b>a</b>) and overlapping of the elements with micrograph (<b>b</b>).</p> Full article ">Figure 3
<p>Monitoring, by EDS, of the elements that compose Ti-50Nb-7Mo alloy, monitored region (<b>a</b>) and overlapping of the elements with micrograph (<b>b</b>).</p> Full article ">Figure 4
<p>Monitoring, by EDS, of the elements that compose Ti-50Nb-12Mo alloy, monitored region (<b>a</b>) and overlapping of the elements with micrograph (<b>b</b>).</p> Full article ">Figure 5
<p>The density of the Ti–50Nb–xMo alloys as a function of molybdenum content.</p> Full article ">Figure 6
<p>X-ray diffractograms for samples of alloys of Ti–50Nb–xMo system.</p> Full article ">Figure 7
<p>Ternary phase diagram of the Ti-Nb-Mo system alloys (<b>a</b>) and the influence of Mo content on β-transit and liquidus temperatures in Ti-50Nb-xMo system alloys (<b>b</b>).</p> Full article ">Figure 8
<p>Micrographs of samples of alloys of Ti–50Nb–xMo system after melting. Ti–50Nb (<b>a</b>), Ti–50Nb–3Mo (<b>b</b>), Ti–50Nb–7Mo (<b>c</b>), Ti– 50Nb–12Mo (<b>d</b>).</p> Full article ">Figure 9
<p>Microhardness values for Ti-50Nb-xMo system alloys (red) compared to other biomedical materials (black).</p> Full article ">Figure 10
<p>Elastic modulus values for the Ti-50Nb-xMo alloys (red) compared with alloys already used as biomaterials (black) [<a href="#B8-materials-17-00250" class="html-bibr">8</a>].</p> Full article ">Figure 11
<p>H/E ratio of the Ti–50Nb–Mo alloys as a function of Mo content.</p> Full article ">
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 601
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 8 | Viewed by 1773
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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<p>The photographs of: (<b>a</b>) fly ash powder; (<b>b</b>) MiniBars™.</p> Full article ">Figure 2
<p>(<b>a</b>) Optical microscopy of fly ash powder; (<b>b</b>) SEM micrographs of fly ash powder.</p> Full article ">Figure 3
<p>SEM micrographs of the surface of cured geopolymer.</p> Full article ">Figure 4
<p>Mechanical properties of MiniBars™ FRBCs: (<b>a</b>) flexural strength; (<b>b</b>) flexural modulus; (<b>c</b>) tensile strength; (<b>d</b>) tensile modulus; (<b>e</b>) force load at upper yield tensile strength.</p> Full article ">Figure 5
<p>The photographs of the sections of samples of MiniBars™ FRBCs: (<b>a</b>) MiniBars12.5; (<b>b</b>) MiniBars25; (<b>c</b>) MiniBars50; and (<b>d</b>) MiniBars75. Optical images of the sections of MiniBars™ FRBCs: (<b>e</b>) MiniBars12.5; (<b>f</b>) MiniBars25; (<b>g</b>) MiniBars50; and (<b>h</b>) MiniBars75.</p> Full article ">Figure 6
<p>The photographs of fractured MiniBars™ FRBCs at FS test: (<b>a</b>) MiniBars12.5; (<b>b</b>) MiniBars25; (<b>c</b>) MiniBars50; and (<b>d</b>) MiniBars75.</p> Full article ">Figure 7
<p>SEM images of: (<b>a</b>) MiniBars™; (<b>b</b>–<b>d</b>) transverse section of MiniBars75 after flexural test; (<b>e</b>,<b>f</b>) fracture of MiniBars75 after flexural test.</p> Full article ">
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 1032
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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<p>Manufacturing process of mixed plastic waste aggregates (MPAs).</p> Full article ">Figure 2
<p>Particle size and shape of MPA: (<b>a</b>) shape and (<b>b</b>) particle size distribution [<a href="#B19-materials-17-00247" class="html-bibr">19</a>].</p> Full article ">Figure 3
<p>Procedure of surface hydrophilization: (<b>a</b>) heating, (<b>b</b>) impregnation, and (<b>c</b>) drying.</p> Full article ">Figure 4
<p>Surface condition of MPA: (<b>a</b>) unmodified, (<b>b</b>) modified with CA1, (<b>c</b>) modified with CA2, and (<b>d</b>) modified with CA3.</p> Full article ">Figure 5
<p>Contact angle of MPA: (<b>a</b>) unmodified, (<b>b</b>) modified with CA1, (<b>c</b>) modified with CA2, and (<b>d</b>) modified with CA3.</p> Full article ">Figure 6
<p>Scanning electron microscopy (SEM) images of MPA: (<b>a</b>) unmodified, (<b>b</b>) modified with CA1, (<b>c</b>) modified with CA2, and (<b>d</b>) modified with CA3.</p> Full article ">Figure 6 Cont.
<p>Scanning electron microscopy (SEM) images of MPA: (<b>a</b>) unmodified, (<b>b</b>) modified with CA1, (<b>c</b>) modified with CA2, and (<b>d</b>) modified with CA3.</p> Full article ">Figure 7
<p>SEM images of mortar: (<b>a</b>) mix C1_MPA, (<b>b</b>) mix C2_MPA, and (<b>c</b>) mix C3_MPA.</p> Full article ">Figure 8
<p>Flow by the surface modification of MPA.</p> Full article ">Figure 9
<p>Strength by the surface modification of MPA: (<b>a</b>) compressive strength and (<b>b</b>) flexural strength.</p> Full article ">Figure 10
<p>Optical microscope image of mortar: (<b>a</b>) mix NC_MPA, (<b>b</b>) mix C1_MPA, (<b>c</b>) mix C2_MPA, and (<b>d</b>) mix C3_MPA.</p> Full article ">Figure 11
<p>SEM images of mortar: (<b>a</b>) mix NC_MPA, (<b>b</b>) mix C1_MPA, (<b>c</b>) mix C2_MPA, and (<b>d</b>) mix C3_MPA.</p> Full article ">
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 1360
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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<p>Examples of applications of 2-mercaptobenzothiazole.</p> Full article ">Figure 2
<p>New compounds based on 2-mercaptobenzothiazole and derivatives of (meth)acrylic acid.</p> Full article ">Figure 3
<p><sup>1</sup>H NMR spectrum (400 MHz) of 2-(2-(6-chlorobenzothiazolyl)thio)ethyl acrylate (<b>2</b>) (<b>A</b>) and 2-(2-(6-chlorobenzothiazolyl)thio)ethyl methacrylate (<b>5</b>) in CDCl<sub>3</sub> (<b>B</b>).</p> Full article ">Figure 4
<p>Normalized absorption spectra of: 2-(2-(6-chlorobenzothiazolyl)thio)ethyl acrylate (<b>2</b>) in solvents of different polarities (<b>A</b>), 2-(2-(6-chlorobenzothiazolyl)thio)ethyl acrylate (<b>2</b>) and 2-(2-(6-chlorobenzothiazolyl)thio)ethyl methacrylate (<b>5</b>) in dimethyl sulfoxide (<b>B</b>), and 2-(2-(6-chlorobenzothiazolyl)thio)ethyl acrylate (<b>2</b>) and 2-(2-(5-chlorobenzothiazolyl)thio)ethyl acrylate (<b>3</b>) in dimethyl sulfoxide (<b>C</b>).</p> Full article ">Figure 5
<p>Frontier molecular diagram of 2-(2-benzothiazolylthio)ethyl acrylate (<b>1</b>–<b>3</b>) and methacrylate derivatives (<b>4</b>–<b>6</b>) in dichloromethane.</p> Full article ">Scheme 1
<p>Synthesis procedure for 2-(2-benzothiazolylthio)ethyl acrylate (<b>1</b>–<b>3</b>) and methacrylate derivatives (<b>4</b>–<b>6</b>).</p> Full article ">
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 1046
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 2108
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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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic diagram of the wool sample preparation, from the dissolution process to the optical microscopy characterization.</p> Full article ">Figure 2
<p>Images showing how the cross-sectional size of the wool yarn reduced as the dissolution progressed (the blue and red outline the area measured using ImageJ). The top row images are for yarn dissolved at 65 °C for (<b>a</b>) 1 h, (<b>b</b>) 2 h, (<b>c</b>) 3 h, and (<b>d</b>) 4 h. The lower set of images are for yarn dissolved at 80 °C for (<b>e</b>) 1 h, (<b>f</b>) 2 h, (<b>g</b>) 3 h, and (<b>h</b>) 4 h.</p> Full article ">Figure 3
<p>Schematic diagram showing the cross-sectional area of wool yarn <math display="inline"><semantics> <mrow> <mi>A</mi> <mfenced separators="|"> <mrow> <mi>t</mi> </mrow> </mfenced> </mrow> </semantics></math> and the thickness loss <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>x</mi> </mrow> <mrow> <mi>r</mi> <mi>m</mi> <mi>s</mi> </mrow> </msub> <mfenced separators="|"> <mrow> <mi>t</mi> </mrow> </mfenced> </mrow> </semantics></math> of the wool yarn dissolved in [C2mim][OAc].</p> Full article ">Figure 4
<p>(<b>a</b>) The cross-sectional area of the processed wool yarn being dissolved in [C2mim][OAc] at different times and temperatures. (<b>b</b>) Shifting of the data set at 60 °C and 110 °C toward 70 °C data. (<b>c</b>) The time–temperature superposition plot after being shifted to the reference temperature (70 °C). (<b>d</b>) Cross-sectional area shift factor <math display="inline"><semantics> <mrow> <mrow> <mrow> <mi mathvariant="normal">ln</mi> </mrow> <mrow> <msub> <mrow> <mi>a</mi> </mrow> <mrow> <mi>T</mi> </mrow> </msub> </mrow> </mrow> </mrow> </semantics></math> as a function of inverse temperature, which indicates Arrhenius behavior of each process fitted with two straight lines and the crossover temperature at 70 °C. All the errors were calculated but in some cases these are smaller than the point size.</p> Full article ">Figure 5
<p>Schematic diagram of the rate of reaction vs. temperature of the interpretation of the dissolution activation energy of wool yarn in [C2mim][OAc].</p> Full article ">Figure 6
<p>(<b>a</b>) The cross-sectional area of the processed wool yarn being dissolved in [C2mim][OAc] at the low-temperature region. (<b>b</b>) The time–temperature superposition plot after being shifted to 65 °C. (<b>c</b>) The real dissolution time master curve at 65 °C. (<b>d</b>) A linear relation <math display="inline"><semantics> <mrow> <mrow> <mrow> <mi mathvariant="normal">ln</mi> </mrow> <mrow> <msub> <mrow> <mi>a</mi> </mrow> <mrow> <mi>T</mi> </mrow> </msub> </mrow> </mrow> </mrow> </semantics></math> as a function of inverse temperature showing Arrhenius-like behavior. All the errors were calculated but in some cases these are smaller than the point size.</p> Full article ">Figure 7
<p>(<b>a</b>) Cross-sectional area changes of each processed wool yarn at the high-temperature region. (<b>b</b>) Master curves of shifted cross-sectional area in <math display="inline"><semantics> <mrow> <mi mathvariant="normal">l</mi> <mi mathvariant="normal">n</mi> </mrow> </semantics></math> space using 90 °C as a reference temperature. (<b>c</b>) Linear time scale of the master curve. (<b>d</b>) Arrhenius plot for the set of the data at the high-temperature region. All the errors were calculated but in some cases these are smaller than the point size.</p> Full article ">Figure 8
<p>Thickness loss <span class="html-italic">x<sub>rms</sub></span> of the processed wool yarn vs. the square root of time. (<b>a</b>) The low-temperature process at reference temperature 65 °C with the <math display="inline"><semantics> <mrow> <mi>D</mi> </mrow> </semantics></math> value. (<b>b</b>) The high-temperature process at reference temperature 90 °C with the <math display="inline"><semantics> <mrow> <mi>D</mi> </mrow> </semantics></math> value. All the errors were calculated but in some cases these are smaller than the point size.</p> Full article ">Figure 9
<p>The natural log of the self-diffusion coefficients of the [C2mim][OAc] in wool yarn as a function of <math display="inline"><semantics> <mrow> <mn>1000</mn> <mo>/</mo> <mi mathvariant="normal">T</mi> </mrow> </semantics></math>, which have Arrhenius behavior for each regime where the crossover temperature is at 70 °C. All the errors were calculated but in some cases these are smaller than the point size.</p> Full article ">
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 1153
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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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>VSM measurements for the determination of the magnetic viscosity parameter <math display="inline"><semantics> <msub> <mi>S</mi> <mi mathvariant="normal">v</mi> </msub> </semantics></math> at <math display="inline"><semantics> <mrow> <mi>T</mi> <mo>=</mo> <mn>303</mn> <mspace width="0.166667em"/> <mi mathvariant="normal">K</mi> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mi>H</mi> <mi>ext</mi> </msub> <mo>=</mo> <mo>−</mo> <mn>1870</mn> <mspace width="0.166667em"/> <mrow> <mi>kA</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math> (<math display="inline"><semantics> <mrow> <msub> <mi>μ</mi> <mn>0</mn> </msub> <mspace width="0.166667em"/> <msub> <mi>H</mi> <mi>ext</mi> </msub> <mo>=</mo> <mo>−</mo> <mn>2.35</mn> <mspace width="0.166667em"/> <mi mathvariant="normal">T</mi> </mrow> </semantics></math>) for the material M4. (<b>a</b>) Partial loop of the demagnetization curve starting at <math display="inline"><semantics> <mrow> <msub> <mi>H</mi> <mi>ext</mi> </msub> <mo>=</mo> <mo>−</mo> <mn>1870</mn> <mspace width="0.166667em"/> <mrow> <mi>kA</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>. The slope of the partial loop is <math display="inline"><semantics> <mrow> <msub> <mi>μ</mi> <mn>0</mn> </msub> <mspace width="0.166667em"/> <msubsup> <mi>χ</mi> <mi>ext</mi> <mi>rev</mi> </msubsup> </mrow> </semantics></math> with <math display="inline"><semantics> <mrow> <msubsup> <mi>χ</mi> <mi>ext</mi> <mi>rev</mi> </msubsup> <mo>=</mo> <mn>0.033</mn> <mo>±</mo> <mn>0.001</mn> </mrow> </semantics></math>. (<b>b</b>) Polarization decrease <math display="inline"><semantics> <mrow> <mo>Δ</mo> <mi>J</mi> </mrow> </semantics></math> caused by the thermally-activated demagnetization. After a certain time <math display="inline"><semantics> <msub> <mi>t</mi> <mn>0</mn> </msub> </semantics></math> the polarization <span class="html-italic">J</span> decreases logarithmically with time <span class="html-italic">t</span>. The slope of the logarithmic decrease of <span class="html-italic">J</span> (dashed line) is <math display="inline"><semantics> <mrow> <msub> <mi>μ</mi> <mn>0</mn> </msub> <mspace width="0.166667em"/> <mi>S</mi> </mrow> </semantics></math> with <math display="inline"><semantics> <mrow> <mi>S</mi> <mo>=</mo> <mo>(</mo> <mn>184</mn> <mo>±</mo> <mn>8</mn> <mo>)</mo> <mspace width="0.166667em"/> <mrow> <mi mathvariant="normal">A</mi> <mo>/</mo> <mi mathvariant="normal">m</mi> </mrow> </mrow> </semantics></math>.</p> Full article ">Figure 2
<p>Demagnetization curves of the investigated FeNdB magnets at selected temperatures. The respective positions for the demagnetizing field <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi mathvariant="normal">D</mi> <mn>5</mn> </mrow> </msub> </semantics></math> were determined in accordance with [<a href="#B23-materials-17-00243" class="html-bibr">23</a>], and they are marked with black squares. The decrease in polarization at the right side of the curves was caused by the demagnetization of the areas at the surface that exhibited a strongly reduced coercivity compared to those of the bulk type [<a href="#B24-materials-17-00243" class="html-bibr">24</a>,<a href="#B25-materials-17-00243" class="html-bibr">25</a>,<a href="#B26-materials-17-00243" class="html-bibr">26</a>].</p> Full article ">Figure 3
<p>Magnetic viscosity parameter <math display="inline"><semantics> <msub> <mi>S</mi> <mi mathvariant="normal">v</mi> </msub> </semantics></math>, which is dependent on the internal magnetic field <math display="inline"><semantics> <msub> <mi>H</mi> <mi>int</mi> </msub> </semantics></math> with regard to the demagnetizing field <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi mathvariant="normal">D</mi> <mn>5</mn> </mrow> </msub> </semantics></math> for selected temperatures.</p> Full article ">Figure 4
<p>The magnetic viscosity parameter <math display="inline"><semantics> <msub> <mi>S</mi> <mi mathvariant="normal">v</mi> </msub> </semantics></math> at the demagnetizing field <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi mathvariant="normal">D</mi> <mn>5</mn> </mrow> </msub> </semantics></math>, which is dependent on the temperature <span class="html-italic">T</span>. The values were determined by fitting the corresponding <math display="inline"><semantics> <mrow> <msub> <mi>S</mi> <mi mathvariant="normal">v</mi> </msub> <mrow> <mo>(</mo> <msub> <mi>H</mi> <mi>int</mi> </msub> <mo>)</mo> </mrow> </mrow> </semantics></math> values.</p> Full article ">Figure 5
<p>Activation volume <span class="html-italic">v</span> for the HREE-rich material M4 at 303 K, which is dependent on the internal magnetic field <math display="inline"><semantics> <msub> <mi>H</mi> <mi>int</mi> </msub> </semantics></math> with regard to the demagnetizing field <math display="inline"><semantics> <msub> <mi>H</mi> <mrow> <mi mathvariant="normal">D</mi> <mn>5</mn> </mrow> </msub> </semantics></math>. The values were calculated from the <math display="inline"><semantics> <msub> <mi>S</mi> <mi mathvariant="normal">v</mi> </msub> </semantics></math> values in <a href="#materials-17-00243-f003" class="html-fig">Figure 3</a>d in accordance with Equation (<a href="#FD7-materials-17-00243" class="html-disp-formula">7</a>), where <math display="inline"><semantics> <mrow> <msub> <mi>J</mi> <mi mathvariant="normal">s</mi> </msub> <mo>=</mo> <mn>1.24</mn> <mspace width="0.166667em"/> <mi mathvariant="normal">T</mi> </mrow> </semantics></math>.</p> Full article ">
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 1218
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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Figure 1

Figure 1
<p>Landscape generated after the eruption of the Tajogaite volcano (La Palma, Spain).</p> Full article ">Figure 2
<p>(<b>a</b>) Particle size distribution of both PC, original VFA and VFA after milling; (<b>b</b>) SEM photograph of original VFA; and (<b>c</b>) SEM photograph of milled VFA.</p> Full article ">Figure 3
<p>(<b>a</b>) XRD patterns and (<b>b</b>) FTIR spectra of Portland cement (PC) and the volcanic fly ash (VFA). Legend: d: diopside (MgCaSi<sub>2</sub>O<sub>6</sub>) (COD 9004319); a: augite (Ca,Mg,Fe)<sub>2</sub>(Si,Al)<sub>2</sub>O<sub>6</sub> (COD 9006247); q: cristobalita (SiO<sub>2</sub>) (COD 9001578); m: magnetite (Fe<sub>2</sub>O<sub>3</sub>) (COD 9006247); b: bytownite (Ca,Na)(Si,Al)<sub>4</sub>O<sub>8</sub>) (COD 9011200); i: ilmenite (FeTiO<sub>3</sub>) (COD 9000910); py: pyroxene (Fe<sub>0.44</sub>Mg<sub>0.56</sub>SiO<sub>3</sub>) (COD 9001577); A: alite (3CaO·SiO<sub>2</sub>) (COD 1540705)); B: belite (2CaO·SiO<sub>2</sub>) (COD 9012793)); C<sub>3</sub>A: tricalcium aluminate (3CaO·Al<sub>2</sub>O<sub>3</sub>) (COD 9014359)); C<sub>4</sub>AF: ferritic phase (4CaO·Al<sub>2</sub>O<sub>3</sub>·Fe<sub>2</sub>O<sub>3</sub>) (COD 9015955); g: anhydrite (CaSO<sub>4</sub>) (COD 5000040); c: calcite (CaCO<sub>3</sub>) (COD 9016022).</p> Full article ">Figure 4
<p>Compressive strengths (MPa) for all pastes: CEM, BC, HAC and AC cements.</p> Full article ">Figure 5
<p>XRD patterns of (<b>a</b>) CEM, (<b>b</b>) BC-3, (<b>c</b>) HAC-3, (<b>d</b>) BC-7, (<b>e</b>) HAC-7, (<b>f</b>) AC after 2 and 28 days of curing. <b>Legend:</b> d: diopside (MgCaSi<sub>2</sub>O<sub>6</sub>); a: augite (Ca,Mg,Fe)<sub>2</sub>(Si,Al)<sub>2</sub>O<sub>6</sub>); q: cristobalite (SiO<sub>2</sub>); b: bytownite ((Ca,Na)(Si,Al)<sub>4</sub>O<sub>8</sub>); i: ilmenite (FeTiO<sub>3</sub>); A: alite (3CaO·SiO<sub>2</sub>); B: belite (2CaO·SiO<sub>2</sub>); C<sub>3</sub>A:tricalcium aluminate; e:ettringite (Ca<sub>6</sub>Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>(OH)<sub>12</sub>(H<sub>2</sub>O)<sub>26</sub>) (COD 9015084); p: portlandite (Ca(OH)<sub>2</sub>) (COD 1008780); c: calcite (CaCO<sub>3</sub>); AFm: ((3CaO·Al<sub>2</sub>O<sub>3</sub>·CaSO<sub>4</sub>·12H<sub>2</sub>O) (COD 9013423), bs: basanite (Ca<sub>3</sub>H<sub>3</sub>.<sub>6</sub>O<sub>13</sub>.<sub>8</sub>S<sub>3</sub>) (COD 9012211), ms: magnesium silicate (MgSiO<sub>3</sub>) (COD 9016052).</p> Full article ">Figure 6
<p>FTIR patterns of CEM, BC-3, HAC-3, BC-7, HAC-7 and AC after 2 and 28 days of curing.</p> Full article ">Figure 7
<p>Thermogravimetric analysis of (<b>a</b>) CEM, (<b>b</b>) BC-3, (<b>c</b>) HAC-3, (<b>d</b>) BC-7, (<b>e</b>) HAC-7 and (<b>f</b>) AC after 2 days and 28 days of curing.</p> Full article ">Figure 8
<p>BSEM micrography of (<b>a</b>) AC after 2 days of curing (×500), (<b>b</b>) AC after 28 days of curing (×500), (<b>c</b>) partially attacked VFA particle in AC 28d (×3000).</p> Full article ">Figure 9
<p>BSEM micrography of (<b>a</b>) BC-3 after 2 days of curing (×500), (<b>b</b>) BC-3 after 28 days of curing (×500), (<b>c</b>) HAC-3 after 2 days of curing, (<b>d</b>) HAC-3 after 28 days of curing (×500).</p> Full article ">Figure 10
<p>BSEM micrography of (<b>a</b>) BC-7 after 2 days of curing (× 500), (<b>b</b>) BC-7 after 28 days of curing (× 500), (<b>c</b>) HAC-7 after 2 days of curing, (<b>d</b>) HAC-7 after 28 days of curing (× 500).</p> Full article ">Figure 11
<p>Ternary diagram CaO-SiO<sub>2</sub>-Al<sub>2</sub>O<sub>3</sub> of elemental EDX analysis of the gel phase.</p> Full article ">Figure 12
<p>(<b>a</b>) Heat Flow (J/g.h) (<b>b</b>) Total heat (J/g) for the different cementitious systems (CEM; BC and HAC) (where g represents the grams of binder (VFS+ CEM + Activator).</p> Full article ">
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