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Materials, Volume 14, Issue 8 (April-2 2021) – 274 articles

Cover Story (view full-size image): All-solid-state supercapacitors have gained increasing attention as wearable energy storage devices, partially due to their flexible, safe, and lightweight natures. However, their electrochemical performances are largely hampered by the low flexibility and durability of current polyvinyl alcohol (PVA) based electrolytes. Herein, a novel polyvinyl alcohol-polyethyleneimine (PVA-PEI) based, conductive and elastic hydrogel was devised as an all-in-one electrolyte platform for wearable supercapacitor (WSC). For proof-of-concept, we assembled all-solid-state supercapacitors based on boron nitride nanosheets (BNNS) intercalated graphene electrodes and PVA-PEI based gel electrolyte. View this paper
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15 pages, 4797 KiB  
Article
Microstructure, Micro-Mechanical and Tribocorrosion Behavior of Oxygen Hardened Ti–13Nb–13Zr Alloy
by Alicja Łukaszczyk, Sławomir Zimowski, Wojciech Pawlak, Beata Dubiel and Tomasz Moskalewicz
Materials 2021, 14(8), 2088; https://doi.org/10.3390/ma14082088 - 20 Apr 2021
Cited by 2 | Viewed by 2649
Abstract
In the present work, an oxygen hardening of near-β phase Ti–13Nb–13Zr alloy in plasma glow discharge at 700–1000 °C was studied. The influence of the surface treatment on the alloy microstructure, tribological and micromechanical properties, and corrosion resistance is presented. A strong influence [...] Read more.
In the present work, an oxygen hardening of near-β phase Ti–13Nb–13Zr alloy in plasma glow discharge at 700–1000 °C was studied. The influence of the surface treatment on the alloy microstructure, tribological and micromechanical properties, and corrosion resistance is presented. A strong influence of the treatment on the hardened zone thickness, refinement of the α’ laths and grain size of the bulk alloy were found. The outer hardened zone contained mainly an oxygen-rich Ti α’ (O) solid solution. The microhardness and elastic modulus of the hardened zone decreased with increasing hardening temperature. The hardened zone thickness, size of the α’ laths, and grain size of the bulk alloy increased with increasing treatment temperature. The wear resistance of the alloy oxygen-hardened at 1000 °C was about two hundred times, and at 700 °C, even five hundred times greater than that of the base alloy. Oxygen hardening also slightly improved the corrosion resistance. Tribocorrosion tests revealed that the alloy hardened at 700 °C was wear-resistant in a corrosive environment, and when the friction process was completed, the passive film was quickly restored. The results show that glow discharge plasma oxidation is a simple and effective method to enhance the micromechanical and tribological performance of the Ti–13Nb–13Zr alloy. Full article
(This article belongs to the Collection Microstructure and Corrosion Behavior of Advanced Alloys)
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Figure 1
<p>Microstructure of the as-received alloy.</p> Full article ">Figure 2
<p>Schematic of the tribological device with parallel corrosion potential measurement during wear tests of the titanium alloy in sliding contact with a ball.</p> Full article ">Figure 3
<p>Microstructure of the Ti–13Nb–13Zr alloy after oxygen hardening at 700 °C (<b>a</b>,<b>b</b>), 850 °C (<b>c</b>,<b>d</b>) and 1000 °C (<b>e</b>,<b>f</b>). LM (<b>a</b>) and SEM (<b>b</b>–<b>f</b>), cross-section samples. The zone with voids is marked with a dashed line in <a href="#materials-14-02088-f003" class="html-fig">Figure 3</a>f. An arrow in <a href="#materials-14-02088-f003" class="html-fig">Figure 3</a>f indicates a microcrack developed in the near-surface zone.</p> Full article ">Figure 4
<p>TEM image of the near-surface region in the Ti–13Nb–13Zr alloy after oxygen hardening at 700 °C. SAED patterns of α’ (hcp) and α’’ (orthorhombic, Cmcm) were taken from areas marked with 1 and 2, respectively. In the SAED pattern no. 2, the spots belonging to the three [100] α‘‘ zone axes are marked with black, green and red color. Indices of green spots are given.</p> Full article ">Figure 5
<p>STEM image of the microstructure of the near-surface region in the Ti–13Nb–13Zr alloy cross-section after oxygen hardening at a temperature of 700 °C (<b>a</b>) and concentration profile of oxygen obtained by TEM-EDS microanalysis performed in points 1–16 (<b>b</b>). The exemplary grains of the α‘ and β phases, as well as the areas 1 and 2 given in <a href="#materials-14-02088-f004" class="html-fig">Figure 4</a>, are marked in <a href="#materials-14-02088-f005" class="html-fig">Figure 5</a>a.</p> Full article ">Figure 6
<p>COF of the alloy oxygen hardened at 700 °C (<b>a</b>), 850 °C (<b>b</b>) and 1000 °C (<b>c</b>) compared to as-received alloy (<b>d</b>) in dry friction condition as well as the alloy hardened at 700 °C in Ringer’s solution (<b>e</b>) against alumina ball.</p> Full article ">Figure 7
<p>Cross-section profile of wear track of as-received Ti–13Nb–13Zr alloy (<b>a</b>) and hardened Ti–13Nb–13Zr alloy (<b>b</b>) after dry friction.</p> Full article ">Figure 8
<p>Electrochemical measurements of as-received and oxygen hardened alloy (Ti–13Nb–13Zr/700 °C) in Ringer’s solution at 37 °C, (<b>a</b>) evolution of the corrosion potential vs. time and (<b>b</b>) polarization curves at 1 mV/s.</p> Full article ">Figure 9
<p>Electrochemical impedance curves of the as-received and oxygen hardened alloy in Ringer’s solution. (<b>a</b>) Bode impedance and phase angle plot, (<b>b</b>) Nyquist impedance plot.</p> Full article ">Figure 10
<p>Equivalent circuit used for fitting EIS data.</p> Full article ">Figure 11
<p>Change in the corrosion potential during the tribological test in Ringer’s solution at 25 °C of the alloy hardened at 700 °C.</p> Full article ">
15 pages, 4637 KiB  
Article
Microstructure, Mineralogical Characterization and the Metallurgical Process Reconstruction of the Zinc Calcine Relics from the Zinc Smelting Site (Qing Dynasty)
by Ya Xiao, Wenli Zhou, Linheng Mo, Jianli Chen, Meiying Li and Shaojun Liu
Materials 2021, 14(8), 2087; https://doi.org/10.3390/ma14082087 - 20 Apr 2021
Cited by 1 | Viewed by 2121
Abstract
The smelting of zinc is considered as one of the most challenging technologies in ancient civilization. Compared with non-sulfide zinc ores, the smelting of zinc sulfide ores is more complicated since they have to be roasted before smelting. The technological smelting process of [...] Read more.
The smelting of zinc is considered as one of the most challenging technologies in ancient civilization. Compared with non-sulfide zinc ores, the smelting of zinc sulfide ores is more complicated since they have to be roasted before smelting. The technological smelting process of the ancient zinc metallurgy technology has been studied and partly reconstructed. However, the roasting technology, including the roasting conditions and involved metallurgical processes, is still unclear. The discovery of the zinc smelting site of Doulingxia dates back to the Qing dynasty (CE 1636–1912), and for the first time provides us with critical archeological evidence to gain an insight into the roasting technology in ancient zinc metallurgy technology. In this paper, the microstructure and mineralogical features of the zinc calcine relics found at the Doulingxia site were characterized by X-ray diffraction (XRD) and scanning electron microscopy coupled with X-ray energy dispersive spectrometer (SEM-EDS). To reconstruct the metallurgical process, the original roasting temperature of the unearthed zinc calcine was estimated by thermogravimetric analysis and differential thermal analysis (TG-DTA), combined with reheating experiments and phase composition analysis as well as microstructural analysis. The simulation experiments were conducted to reconstruct the roasting process. The results indicated that the original roasting temperature of the unearthed zinc calcine should be in a range of 650–850 °C, most probably near 750 °C. As long as the retention time is long enough, all sphalerite can be oxidized when the roasting temperature is above 650 °C. The final roasting products mainly include tiny porous particles of ZnFe2O4, Fe2O3, PbSO4, and ZnO. These findings are helpful to reconstruct the ancient zinc metallurgy technology of zinc sulfide ores. Full article
(This article belongs to the Section Advanced Materials Characterization)
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<p>Archaeological evidence found in the Doulingxia site. (<b>a</b>) Cylindrical roasting hearths; (<b>b</b>) the unearthed zinc calcine.</p> Full article ">Figure 2
<p>Backscattered electron images showing the morphology of the zinc calcine found at the Doulingxia site. (<b>a</b>) Low magnification, (<b>b</b>) tiny particles.</p> Full article ">Figure 3
<p>X-ray maps showing the distributions of O, S, Zn, Fe, Pb, and Si in a partially reacted sphalerite particle. (<b>a</b>) The secondary electron (SE) image shows the morphology of the grain; (<b>b</b>) Different grey levels in the backscattered electron (BSE) image imply different compositions. A—lightly reacted sphalerite (core), B—Fe-Pb-Zn-Si-O phase (brighter rim), C—Fe-Zn-Si-O phase (dark grey rim), D—a mixture of ZnFe<sub>2</sub>O<sub>4</sub> and Zn<sub>2</sub>SiO<sub>4</sub> (grey rim), E—a mixture of ZnFe<sub>2</sub>O<sub>4</sub> and Zn<sub>2</sub>SiO<sub>4</sub> (porous portion); (<b>c</b>) O Kα map; (<b>d</b>) S Kα map; (<b>e</b>) Zn Kα map; (<b>f</b>) Fe Kα map; (<b>g</b>) Pb Lα map; and (<b>h</b>) Si Kα map.</p> Full article ">Figure 4
<p>TG-DTA analysis result of the zinc calcine (DZC-1).</p> Full article ">Figure 5
<p>XRD analysis results showing the phase transformation of the zinc calcine (DZC-1) reheated at different temperatures.</p> Full article ">Figure 6
<p>Backscattered electron image showing the morphology of the zinc calcine reheated at 900 °C. 1—PbZnSiO<sub>4</sub> (light), 2—ZnFe<sub>2</sub>O<sub>4</sub> (grey), 3—Zn<sub>2</sub>SiO<sub>4</sub> (dark grey), 4—pore (black), 5—Pb<sub>10</sub>(SiO<sub>4</sub>)<sub>3</sub>(SO<sub>4</sub>)<sub>3</sub>F<sub>2</sub> (light), 6—CaSO<sub>4</sub> (dark).</p> Full article ">Figure 7
<p>Degree of desulfurization of the products obtained under different conditions. (<b>a</b>) Products roasted at 650 °C for different roasting times, (<b>b</b>) products roasted for 48 h at different temperatures.</p> Full article ">Figure 8
<p>Backscattered electron images showing the morphology of the final products obtained under different simulated (<b>a</b>) 650 °C; (<b>b</b>) 750 °C; (<b>c</b>) 850 °C.</p> Full article ">
13 pages, 7154 KiB  
Article
Preparation and Characterization of Silica Nanoparticles and of Silica-Gentamicin Nanostructured Solution Obtained by Microwave-Assisted Synthesis
by Violeta Purcar, Valentin Rădiţoiu, Cornelia Nichita, Adriana Bălan, Alina Rădiţoiu, Simona Căprărescu, Florentina Monica Raduly, Raluca Manea, Raluca Şomoghi, Cristian-Andi Nicolae, Iuliana Raut and Luiza Jecu
Materials 2021, 14(8), 2086; https://doi.org/10.3390/ma14082086 - 20 Apr 2021
Cited by 39 | Viewed by 3758
Abstract
In this research work, silica nanoparticles and silica-gentamicin nanostructured solution were synthesized by using the microwave-assisted synthesis, in basic medium, using two silane precursors (tetraethylorthosilicate and octyltriethoxysilane) and the antibiotic (gentamicin sulfate). The prepared materials were characterized through Fourier transform infrared (FTIR) spectroscopy, [...] Read more.
In this research work, silica nanoparticles and silica-gentamicin nanostructured solution were synthesized by using the microwave-assisted synthesis, in basic medium, using two silane precursors (tetraethylorthosilicate and octyltriethoxysilane) and the antibiotic (gentamicin sulfate). The prepared materials were characterized through Fourier transform infrared (FTIR) spectroscopy, TGA analysis, transmission electron microscopy (TEM), and atomic force microscopy (AFM) to investigate the morphology and structure. Antimicrobial studies of the silica-gentamicin nanostructured solution versus silica nanoparticles were performed against Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. FTIR spectra showed that the gentamicin has been loaded to the silica nanoparticles. AFM analysis showed that the morphology of the silica-gentamicin nanostructured solution has changed, and agglomerations of particles are present at the surface. Antimicrobial testing, performed using the diffusion method through spot inoculation, indicates that the silica-gentamicin nanostructured solution exhibited activity against the resistant strain. The obtained silica-gentamicin solution can be used as biochemical agent for the prevention and treatment of microorganisms which are deposited on different surfaces (e.g., glass, plastic, ceramic). Full article
(This article belongs to the Special Issue Nano-Composite Coatings: Processing, Characterization, Properties, and Applications)
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<p>FTIR spectra of gentamicin sulfate (GS), SiO<sub>2</sub> NPs (sample G0), and silica-gentamicin nanostructured solution (sample G1), obtained as powders.</p> Full article ">Figure 2
<p>Thermogravimetric analysis curves of: (<b>a</b>) gentamicin sulfate (GS), (<b>b</b>) SiO<sub>2</sub> NPs (sample G0) and silica-gentamicin nanostructured solution (sample G1), obtained as powders.</p> Full article ">Figure 3
<p>TEM images of SiO<sub>2</sub> NPs (sample G0) and silica-gentamicin nanostructured solution (sample G1), obtained as dispersions.</p> Full article ">Figure 4
<p>Three-dimensional (3D) AFM images of SiO<sub>2</sub> NPs (sample G0) and silica-gentamicin nanostructured solution (sample G1) deposited on glass substrates.</p> Full article ">Figure 5
<p>Optical microscope images of SiO<sub>2</sub> NPs (sample G0) and silica-gentamicin nanostructured solution (sample G1).</p> Full article ">Figure 6
<p>Antimicrobial activity of SiO<sub>2</sub> NPs (sample G0) and of silica-gentamicin nanostructured solution (sample G1) using the diffusion method through spot inoculation.</p> Full article ">Scheme 1
<p>Preparation of silica nanoparticles and of silica-gentamicin nanostructured solution by microwave-assisted synthesis.</p> Full article ">
12 pages, 3073 KiB  
Article
Development of Precipitation-Strengthened Al0.8NbTiVM (M = Co, Ni) Light-Weight Refractory High-Entropy Alloys
by Kangjin Lee, Yunjong Jung, Junhee Han, Sung Hwan Hong, Ki Buem Kim, Peter K. Liaw, Chanho Lee and Gian Song
Materials 2021, 14(8), 2085; https://doi.org/10.3390/ma14082085 - 20 Apr 2021
Cited by 16 | Viewed by 3430
Abstract
Single-phase solid-solution refractory high-entropy alloys (RHEAs) have been receiving significant attention due to their excellent mechanical properties and phase stability at elevated temperatures. Recently, many studies have been reported regarding the precipitation-enhanced alloy design strategy to further improve the mechanical properties of RHEAs [...] Read more.
Single-phase solid-solution refractory high-entropy alloys (RHEAs) have been receiving significant attention due to their excellent mechanical properties and phase stability at elevated temperatures. Recently, many studies have been reported regarding the precipitation-enhanced alloy design strategy to further improve the mechanical properties of RHEAs at elevated temperatures. In this study, we attempted to develop precipitation-hardened light-weight RHEAs via addition of Ni or Co into Al0.8NbTiV HEA. The added elements were selected due to their smaller atomic radius and larger mixing enthalpy, which is known to stimulate the formation of precipitates. The addition of the Ni or Co leads to the formation of the sigma precipitates with homogeneous distribution. The formation and homogeneous distribution of sigma particles plays a critical role in improvement of yield strength. Furthermore, the Al0.8NbTiVM0.2 (M = Co, Ni) HEAs show excellent specific yield strength compared to single-phase AlNbTiV and NbTiVZr RHEA alloys and conventional Ni-based superalloy (Inconel 718) at elevated temperatures. Full article
(This article belongs to the Special Issue Structure and Mechanical Properties of Alloys)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Microstructure of the as-cast Al<sub>X</sub>NbTiV alloys: (<b>a</b>) XRD patterns, (<b>b</b>) SEM-BSE images.</p> Full article ">Figure 2
<p>Stress–strain curves of as-cast Al<sub>X</sub>NbTiV (X = 0, 0.4, 0.8, 1) alloys at room temperature.</p> Full article ">Figure 3
<p>Microstructure of the as-cast Al<sub>0.8</sub>NbTiVM<sub>0.2</sub> (M = Co, Ni) alloys: (<b>a</b>) XRD patterns, (<b>b</b>) SEM-BSE images.</p> Full article ">Figure 4
<p>Stress–strain curves of as-cast Al<sub>0.8</sub>NbTiVM<sub>0.2</sub> (M = Co, Ni) alloys at room temperature.</p> Full article ">Figure 5
<p>Microstructure of the Al<sub>0.8</sub>NbTiVM<sub>0.2</sub> (M = Co, Ni) alloys heat-treated at 1100 °C for 1 h: (<b>a</b>) XRD patterns, (<b>b</b>) SEM-BSE images.</p> Full article ">Figure 6
<p>Stress–strain curves of the Al<sub>0.8</sub>NbTiVM<sub>0.2</sub> (M = Co, Ni) alloys heat-treated at 1100 °C for 1 h at elevated temperatures.</p> Full article ">Figure 7
<p>Specific yield strength of the Al<sub>0.8</sub>NbTiVM<sub>0.2</sub> (M = Co, Ni) alloys, AlNbTiV [<a href="#B19-materials-14-02085" class="html-bibr">19</a>], AlCrNbTiV [<a href="#B17-materials-14-02085" class="html-bibr">17</a>], CrNbTiVZr [<a href="#B23-materials-14-02085" class="html-bibr">23</a>], NbTiZrV [<a href="#B23-materials-14-02085" class="html-bibr">23</a>], and Al<sub>0.5</sub>CrNbTi<sub>2</sub>V<sub>0.5</sub> [<a href="#B36-materials-14-02085" class="html-bibr">36</a>] HEAs and Inconel 718 [<a href="#B35-materials-14-02085" class="html-bibr">35</a>].</p> Full article ">
21 pages, 8901 KiB  
Article
Multiple-Criteria Decision-Making and Sensitivity Analysis for Selection of Materials for Knee Implant Femoral Component
by Raman Kumar, Rohit Dubey, Sehijpal Singh, Sunpreet Singh, Chander Prakash, Yadaiah Nirsanametla, Grzegorz Królczyk and Roman Chudy
Materials 2021, 14(8), 2084; https://doi.org/10.3390/ma14082084 - 20 Apr 2021
Cited by 77 | Viewed by 4357
Abstract
Total knee replacement (TKR) is a remarkable achievement in biomedical science that enhances human life. However, human beings still suffer from knee-joint-related problems such as aseptic loosening caused by excessive wear between articular surfaces, stress-shielding of the bone by prosthesis, and soft tissue [...] Read more.
Total knee replacement (TKR) is a remarkable achievement in biomedical science that enhances human life. However, human beings still suffer from knee-joint-related problems such as aseptic loosening caused by excessive wear between articular surfaces, stress-shielding of the bone by prosthesis, and soft tissue development in the interface of bone and implant due to inappropriate selection of TKR material. The choice of most suitable materials for the femoral component of TKR is a critical decision; therefore, in this research paper, a hybrid multiple-criteria decision-making (MCDM) tactic is applied using the degree of membership (DoM) technique with a varied system, using the weighted sum method (WSM), the weighted product method (WPM), the weighted aggregated sum product assessment method (WASPAS), an evaluation based on distance from average solution (EDAS), and a technique for order of preference by similarity to ideal solution (TOPSIS). The weights of importance are assigned to different criteria by the equal weights method (EWM). Furthermore, sensitivity analysis is conducted to check the solidity of the projected tactic. The weights of importance are varied using the entropy weights technique (EWT) and the standard deviation method (SDM). The projected hybrid MCDM methodology is simple, reliable and valuable for a conflicting decision-making environment. Full article
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<p>Proposed hybrid decision-making methodology.</p> Full article ">Figure 2
<p>Applicant Femoral Component Material for TKR.</p> Full article ">Figure 3
<p>Qualitative degree of the attribute in the format of a 9-point scale.</p> Full article ">Figure 4
<p>Ranks of FC material for TKR by different MCDM methods and DoM with EWM.</p> Full article ">Figure 5
<p>Ranks of FC material for TKR by different MCDM methods and DoM with SDM.</p> Full article ">Figure 6
<p>Ranks of FC material for TKR by different MCDM methods and DoM with EWT.</p> Full article ">Figure 7
<p>Ranks of FC material for TKR by different MCDM methods and DoM with Fuzzy AHP.</p> Full article ">Figure 8
<p>Final ranks with DoM with all weighting criteria.</p> Full article ">
14 pages, 4358 KiB  
Article
Evaluation of Wood Composite Sandwich Panels as a Promising Renewable Building Material
by Mostafa Mohammadabadi, Vikram Yadama and James Daniel Dolan
Materials 2021, 14(8), 2083; https://doi.org/10.3390/ma14082083 - 20 Apr 2021
Cited by 14 | Viewed by 3886
Abstract
During this study, full-size wood composite sandwich panels, 1.2 m by 2.4 m (4 ft by 8 ft), with a biaxial corrugated core were evaluated as a building construction material. Considering the applications of this new building material, including roof, floor, and wall [...] Read more.
During this study, full-size wood composite sandwich panels, 1.2 m by 2.4 m (4 ft by 8 ft), with a biaxial corrugated core were evaluated as a building construction material. Considering the applications of this new building material, including roof, floor, and wall paneling, sandwich panels with one and two corrugated core(s) were fabricated and experimentally evaluated. Since primary loads applied on these sandwich panels during their service life are live load, snow load, wind, and gravity loads, their bending and compression behavior were investigated. To improve the thermal characteristics, the cavities within the sandwich panels created by the corrugated geometry of the core were filled with a closed-cell foam. The R-values of the sandwich panels were measured to evaluate their energy performance. Comparison of the weight indicated that fabrication of a corrugated panel needs 74% less strands and, as a result, less resin compared to a strand-based composite panel, such as oriented strand board (OSB), of the same size and same density. Bending results revealed that one-layer core sandwich panels with floor applications under a 4.79 kPa (100 psf) bending load are able to meet the smallest deflection limit of L/360 when the span length (L) is 137.16 cm (54 in) or less. The ultimate capacity of two-layered core sandwich panels as a wall member was 94% and 158% higher than the traditional walls with studs under bending and axial compressive loads, respectively. Two-layered core sandwich panels also showed a higher ultimate capacity compared to structural insulated panels (SIP), at 470% and 235% more in bending and axial compression, respectively. Furthermore, normalized R-values, the thermal resistance, of these sandwich panels, even with the presence of thermal bridging due to the core geometry, was about 114% and 109% higher than plywood and oriented strand board, respectively. Full article
(This article belongs to the Special Issue Advances in Construction and Building Materials)
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<p>(<b>a</b>) Full size biaxial corrugated panel used as a core to fabricate (<b>b</b>) one-layered (<b>c</b>) two-layered core sandwich panels.</p> Full article ">Figure 2
<p>(<b>a</b>) Wood strands and (<b>b</b>) frequency distribution graph of their thickness.</p> Full article ">Figure 3
<p>(<b>a</b>) Wood-strand mat (<span class="html-italic">preform</span>), and (<b>b</b>) Aluminum matched-die mold.</p> Full article ">Figure 4
<p>(<b>a</b>) Filling two-layered core sandwich panels with spray foam (<b>b</b>) trimmed foam and wall prepared to use.</p> Full article ">Figure 5
<p>Experimental testing; (<b>a</b>) small scale bending of 559 mm long and 1-UC wide specimen from a one-layered core, large scale (<b>b</b>) bending, and (<b>c</b>) compression testing of a commercial-size two-layered core sandwich panel.</p> Full article ">Figure 6
<p>Thermal test (<b>a</b>) samples of both sandwich panels (<b>b</b>) heat flow meter.</p> Full article ">Figure 7
<p>Failure mode of one-layered core sandwich panel (<b>a</b>) interfacial debonding (<b>b</b>) tension or compression in face-sheet.</p> Full article ">Figure 8
<p>Bending stiffness per unit width for one-layered core sandwich panel (values in parenthesis are COV).</p> Full article ">Figure 9
<p>(<b>a</b>) Maximum bending load for different span lengths without passing the deflection limits (<b>b</b>) a blow-up of the circle area in part a.</p> Full article ">Figure 10
<p>Load-deflection curves for two-layered core sandwich panels under (<b>a</b>) bending and (<b>b</b>) axial compression tests.</p> Full article ">Figure 11
<p>Typical failure of two-layered core sandwich panel under (<b>a</b>) bending: tension and (<b>b</b>) compression: crushing.</p> Full article ">Figure 12
<p>Comparison between normalized R-value of sandwich panel with corrugated core to those of commercially available wood-based and insulator products provided by Kawasaki and Kawai [<a href="#B42-materials-14-02083" class="html-bibr">42</a>].</p> Full article ">
16 pages, 6033 KiB  
Article
Heterostructural Mixed Oxides Prepared via ZnAlLa LDH or ex-ZnAl LDH Precursors—Effect of La Content and Its Incorporation Route
by Katarzyna Antoniak-Jurak, Paweł Kowalik, Wiesław Próchniak, Robert Bicki and Grzegorz Słowik
Materials 2021, 14(8), 2082; https://doi.org/10.3390/ma14082082 - 20 Apr 2021
Cited by 6 | Viewed by 2531
Abstract
The effect of La content and its incorporation route on physicochemical properties of ZnO/Zn(Al,La)2O4 or La2O3–ZnO/ZnAl2O4 mixed oxides with a spinel structure obtained from ZnAlLa Layered double hydroxides (LDHs) or ex-ZnAl LDH materials [...] Read more.
The effect of La content and its incorporation route on physicochemical properties of ZnO/Zn(Al,La)2O4 or La2O3–ZnO/ZnAl2O4 mixed oxides with a spinel structure obtained from ZnAlLa Layered double hydroxides (LDHs) or ex-ZnAl LDH materials was investigated. The heterostructural nanocomposites with the similar Zn/Al molar ratio and varied La content were prepared by two techniques: via co-precipitation and thermal treatment of ZnAlLa LDHs at 500 °C or via incipient wetness impregnation of ex-ZnAl LDHs with aqueous solutions of lanthanum nitrate and subsequent thermal treatment. The obtained series of materials were characterized by the following techniques: X-ray fluorescence (XRF), N2 adsorption (BET), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis with evolved gas analysis (TG/DTG/EGA), scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM) and Fourier-transform infrared spectroscopy (FFT). The evaluation of activity toward the high-temperature water gas shift (HT-WGS) within the temperature range of 350–420 °C was carried out on the basis of rate constant measurements in the kinetic mode using a differential reactor. The co-precipitation technique allowed for a better distribution of La in bulk and on the spinel surface than in case of lanthanum incorporation via impregnation. ZnO/Zn(Al,La)2O4 or La2O3–ZnO/ZnAl2O4 mixed oxides were characterized by moderate activity in the HT-WGS reaction. The results reveal that introduction of lanthanum oxide over 2.4–2.8 wt% induces the phase separation of the ZnAl2O4 spinel, forming ZnO on the ZnAl2O4 spinel surface. Full article
(This article belongs to the Special Issue Nanoparticles and Nanotechnology: From the Synthesis to Application)
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<p>DTG (<b>a</b>) and EGA (<b>b</b>) curves for the series of ZnAl_W_xLa materials.</p> Full article ">Figure 2
<p>DTG (<b>a</b>) and EGA (<b>b</b>) curves for the series of ZnAl_I_xLa materials.</p> Full article ">Figure 3
<p>XRD patterns of ZnAl_W_xLa (<b>a</b>) and ZnAl_W<sub>k</sub>_xLa (<b>b</b>) materials: Zn<sub>0.6</sub>Al<sub>0.4</sub>(OH)<sub>0.2</sub>·0.5H<sub>2</sub>O phase peaks at 2θ 11.7° (003), 23.6° (006), 34.7° (012), 39.1° (015), 46.6° (018), 60.5° (110) and 61.6° (113); 11.79°, 23.69°, 34.78°, 39.47° (015), 46.6° (018), 60.5° (110), 61.6° (113); (*) Zn<sub>5</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>6</sub> phase peaks at 2θ 12.8°, 19.2° and 26.5°; ZnO phase peaks at angles 2θ 31.8° (100), 36.1° (101).</p> Full article ">Figure 4
<p>XRD pattern of the ZnAl_I_xLa (<b>a</b>) and ZnAl_I<sub>k</sub>_xLa (<b>b</b>) materials.</p> Full article ">Figure 5
<p>FT-IR spectra of the ZaAl_W<sub>k</sub>_1La (<b>a</b>) and ZnAl_I<sub>k</sub>_xLa (<b>b</b>) series of materials.</p> Full article ">Figure 6
<p>HRTEM image and FFT with phase identification of ZnAl_W<sub>k</sub>_1La (<b>a</b>,<b>b</b>) and ZnAl_I<sub>k</sub>_1La (<b>c</b>,<b>d</b>).</p> Full article ">Figure 7
<p>HRTEM images and FFT with phase identification of ZnAl_W<sub>k</sub>_3La (<b>a</b>,<b>b</b>) and ZnAl_I<sub>k</sub>_3La (<b>c</b>,<b>d</b>).</p> Full article ">Figure 8
<p>HRTEM images and FFT with phase identification of ZnAl_W<sub>k</sub>_5La (<b>a</b>,<b>b</b>) and ZnAl_I<sub>k</sub>_5La (<b>c</b>,<b>d</b>).</p> Full article ">
13 pages, 8470 KiB  
Article
Biological Response Induced in Primary Human Gingival Fibroblasts upon Exposure to Various Types of Injectable Astringent Retraction Agents
by Danuta Nowakowska, Julita Kulbacka, Joanna Wezgowiec, Anna Szewczyk, Dagmara Baczynska, Marek Zietek, Wlodzimierz Wieckiewicz and Jolanta Saczko
Materials 2021, 14(8), 2081; https://doi.org/10.3390/ma14082081 - 20 Apr 2021
Cited by 5 | Viewed by 2522
Abstract
Traditional chemo-mechanical retraction/displacement materials can impact the gingival margin tissues. This study was undertaken to analyze biological responses induced in human gingival fibroblasts (HGFs) upon application of injectable astringent-based agents used in the cordless retraction technique. HGFs were exposed to hemostatic agents (five [...] Read more.
Traditional chemo-mechanical retraction/displacement materials can impact the gingival margin tissues. This study was undertaken to analyze biological responses induced in human gingival fibroblasts (HGFs) upon application of injectable astringent-based agents used in the cordless retraction technique. HGFs were exposed to hemostatic agents (five gels, three pastes, and one foam) based on aluminium chloride, aluminium sulphate and ferric sulphate. Changes in cell viability and proliferation were evaluated using an MTT assay and a BrdU assay. The cytoskeleton structure organization (zyxin and F-actin) was visualized by confocal laser scanning microscopy. Oxidative stress was determined using the Griess Reagent System. The RNA expression levels of antioxidant enzymes were quantified by real-time RT-PCR. The statistical significance was evaluated using Student’s t-test and one-way ANOVA with post-hoc Tukey HSD test. The evaluated agents did not downregulate fibroblast viability or proliferation. No significant cytoskeleton reorganization was observed. Only one agent (Expasyl) induced oxidative stress, demonstrated by the increased level of nitrites. Incubation with the studied agents significantly increased the RNA expression of some antioxidant enzymes (SOD1, SOD3, GPX1). However, no significant influence on the expression of SOD2 and HMOX1 was detected. The injectable forms of chemical retraction agents revealed biocompatibility with HGFs, suggesting their potential clinical usefulness in gingival margin retraction. Full article
(This article belongs to the Special Issue Biomaterials and Technologies in Dentistry)
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<p>The viability evaluated by MTT assay in human gingival fibroblasts after various time points of incubation (5, 10, and 30 min, and 24 h), with the gingival retraction agents diluted in the cell culture medium to 1 mg/mL and 0.5 mg/mL concentrations; * <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.005.</p> Full article ">Figure 2
<p>The cell proliferation detected by BrdU incorporation assay in human gingival fibroblasts after various time points of incubation (5 min, 10 min, and 24 h), with the gingival retraction agents diluted in the cell culture medium to 1 mg/mL concentration; * <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.005.</p> Full article ">Figure 3
<p>Confocal microscopy evaluation of zyxin and F-actin distribution in human gingival fibroblasts after 24 h of incubation with the gingival retraction agents diluted in the cell culture medium to 1 mg/mL concentration; green colour—zyxin, red colour—F-actin; magnification: 60×.</p> Full article ">Figure 4
<p>The oxidative stress detected by nitrite (NO<sup>2−</sup>) concentration assay in human gingival fibroblasts after various time points of incubation (10 min and 24 h), with the gingival retraction agents diluted in the cell culture medium to 1 mg/mL concentration; * <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.005.</p> Full article ">Figure 5
<p>The RNA expression levels of: (<b>A</b>) SOD1, SOD2, and SOD3; and (<b>B</b>) HMOX1 and GPX1 detected by real-time RT-PCR in human gingival fibroblasts after 24 h of incubation with the gingival retraction agents diluted in the cell culture medium to 1 mg/mL concentration; * <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.005.</p> Full article ">
18 pages, 10101 KiB  
Article
Sustainable and Clean Utilization of Yellow Phosphorus Slag (YPS): Activation and Preparation of Granular Rice Fertilizer
by Cuihong Hou, Luyi Li, Lishuang Hou, Bingbing Liu, Shouyu Gu, Yuan Yao and Haobin Wang
Materials 2021, 14(8), 2080; https://doi.org/10.3390/ma14082080 - 20 Apr 2021
Cited by 7 | Viewed by 3230
Abstract
Yellow phosphorus slag (YPS) is a typical industrial solid waste, while it contains abundant silicon micronutrient required for the growth of rice. The key scientific problem to use the YPS as rice fertilizer is how to activate the slag efficiently during the phosphorite [...] Read more.
Yellow phosphorus slag (YPS) is a typical industrial solid waste, while it contains abundant silicon micronutrient required for the growth of rice. The key scientific problem to use the YPS as rice fertilizer is how to activate the slag efficiently during the phosphorite reduction smelting process. In this work, an alkaline rice fertilizer from the activated YPS was successfully prepared to use the micronutrients. Thermodynamic analyses of SiO2-CaO, SiO2-CaO-Al2O3, and SiO2-CaO-Al2O3-MgO systems were discussed to optimize the acidity for reduction smelting. Results showed that the reduction smelting followed by the water quenching process can realize the reduction of phosphorite and activation of YPS synchronously. Ternary acidity m(SiO2)/(m(CaO) + m(MgO)) of 0.92 is suitable for the reduction smelting and activation of the slag. After smelting, the molten YPS can be effectively activated by water quenching, and 78.28% P, 90.03% Ca, and 77.12% Si in the YPS are activated, which can be readily absorbed by the rice roots. Finally, high-strength granular rice fertilizers with a particle size of Φ2–4 mm were successfully prepared from the powdery nitrogen-phosphorus-potassium (NPK) and activated YPS mixture. Full article
(This article belongs to the Special Issue Advances in Processing and Characterization of Mineral Materials)
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Figure 1
<p>XRD patterns of phosphate ore.</p> Full article ">Figure 2
<p>Schematic diagram of the reduction smelting furnace.</p> Full article ">Figure 3
<p>Preparation process of granular rice fertilizer.</p> Full article ">Figure 4
<p>Phase diagrams of SiO<sub>2</sub>-CaO system and SiO<sub>2</sub>-CaO-Al<sub>2</sub>O<sub>3</sub>-MgO system at atmospheric pressure. (<b>a</b>) SiO<sub>2</sub>-CaO system; (<b>b</b>) SiO<sub>2</sub>-CaO-Al<sub>2</sub>O<sub>3</sub> system; (<b>c</b>) SiO<sub>2</sub>-CaO-Al<sub>2</sub>O<sub>3</sub>-MgO system.</p> Full article ">Figure 5
<p>Effect of cooling regimes on the phase transformation of the mixtures with an acidity of 0.92 smelted at different temperatures for 60 min in pure N<sub>2</sub> (99.99%) atmosphere. (<b>a</b>) Air cooling; (<b>b</b>) Water quenching; (<b>c</b>) Phase comparison of the mixture smelted at 1450 °C for 60 min under different cooling regimes; (<b>d</b>) Glass structure of YPS after water quenching.</p> Full article ">Figure 6
<p>SEM-EDS analyses of the mixtures with an acidity of 0.92 smelted at 1450 °C for 60 min in pure N<sub>2</sub> (99.99%) atmosphere. (<b>a</b>) Water quenching; (<b>b</b>) Air cooling.</p> Full article ">Figure 7
<p>Nutrient activities of the slag obtained under different conditions. (<b>a</b>) Smelting at 1450 °C for 60 min under different acidity; (<b>b</b>) Smelting at 1450 °C for 60 min with an acidity of 0.92 under different cooling methods; (<b>c</b>) Smelting at 1450 °C with an acidity of 0.92 under different reaction time; (<b>d</b>) Smelting for 60 min with an acidity of 0.92 under different reaction temperature.</p> Full article ">Figure 8
<p>(<b>a</b>) Heavy metals leaching toxicity test for active slag; (<b>b</b>) Limits of heavy metals content in fertilizers.</p> Full article ">Figure 9
<p>(<b>a</b>) Effective conversion of the nutrients in the prepared rice fertilizer (dotted line left is Sample A1, and right is Sample A2); (<b>b</b>) Schematic diagram of absorption by the rice roots.</p> Full article ">Figure 10
<p>(<b>a</b>) Average crush strength of the granular rice fertilizer; (<b>b</b>) Appearance of the granular rice fertilizer.</p> Full article ">Figure 11
<p>(<b>a</b>) Flowsheet and elements distribution in the treatment of phosphorite; (<b>b</b>) Possible and recommended industrial equipment for the granular fertilizer preparation from activated YPS in the existing yellow phosphorus smelting factory.</p> Full article ">
19 pages, 7914 KiB  
Article
Dimensional Analysis and Optimization of IsoTruss Structures with Outer Longitudinal Members in Uniaxial Compression
by Hanna B. Opdahl and David W. Jensen
Materials 2021, 14(8), 2079; https://doi.org/10.3390/ma14082079 - 20 Apr 2021
Cited by 4 | Viewed by 2323
Abstract
This study analyzes the buckling behavior of 8-node IsoTruss® structures with outer longitudinal members. IsoTruss structures are light-weight composite lattice columns with diverse structural applications, including the potential to replace rebar cages in reinforced concrete. In the current work, finite element analyses [...] Read more.
This study analyzes the buckling behavior of 8-node IsoTruss® structures with outer longitudinal members. IsoTruss structures are light-weight composite lattice columns with diverse structural applications, including the potential to replace rebar cages in reinforced concrete. In the current work, finite element analyses are used to predict the critical buckling loads of structures with various dimensions. A dimensional analysis is performed by: deriving non-dimensional Π variables using Buckingham’s Π Theorem; plotting the Π variables with respect to critical buckling loads to characterize trends between design parameters and buckling capacity; evaluating the performance of the outer longitudinal configuration with respect to the traditional, internal longitudinal configuration possessing the same bay length, outer diameter, longitudinal radius, helical radius, and mass. The dimensional analysis demonstrates that the buckling capacity of the inner configuration exceeds that of the equivalent outer longitudinal structure for the dimensions that are fixed and tested herein. A gradient-based optimization analysis is performed to minimize the mass of both configurations subject to equivalent load criteria. The optimized outer configuration has about 10.5% less mass than the inner configuration by reducing the outer diameter whilst maintaining the same global moment of inertia. Full article
(This article belongs to the Special Issue Advances in Construction and Building Materials)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>End view of IsoTruss structure [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 2
<p>Side view of IsoTruss structure with outer longitudinal members (i.e., OLC) [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 3
<p>Global buckling of an inner longitudinal IsoTruss structure [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 4
<p>Local buckling of an outer longitudinal IsoTruss structure (side view) [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 5
<p>Local buckling of an outer longitudinal IsoTruss structure (end view) [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 6
<p>OLC <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>1</mn> </msub> </semantics></math> [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 7
<p>OLC <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>2</mn> </msub> </semantics></math> [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 8
<p>OLC <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>3</mn> </msub> </semantics></math> [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 9
<p>OLC <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>1</mn> </msub> </semantics></math> Analytical and FE predictions [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 10
<p>OLC <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>1</mn> </msub> </semantics></math> Percent deviation of analytical predictions from FE predictions [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 11
<p>OLC <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>2</mn> </msub> </semantics></math> Analytical and FE predictions [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 12
<p>OLC <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>2</mn> </msub> </semantics></math> Percent deviation of analytical predictions from FE predictions [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 13
<p>OLC <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>3</mn> </msub> </semantics></math> Analytical and FE predictions [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 14
<p>OLC <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>3</mn> </msub> </semantics></math> Percent deviation of analytical predictions from FE predictions [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 15
<p><math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>1</mn> </msub> </semantics></math> of OLC and ILC [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 16
<p><math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>2</mn> </msub> </semantics></math> of OLC and ILC [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 17
<p><math display="inline"><semantics> <msub> <mo>Π</mo> <mn>0</mn> </msub> </semantics></math> vs. <math display="inline"><semantics> <msub> <mo>Π</mo> <mn>3</mn> </msub> </semantics></math> of OLC and ILC [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 18
<p>Local buckling of Set 2 OLC with two carbon tows in helical members [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 19
<p>Local buckling of Set 2 OLC with thirteen carbon tows in helical members [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 20
<p>Rotation at the nodes of an IsoTruss structure with two carbon tows per helical member [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">Figure 21
<p>Rotation at the nodes of an IsoTruss structure with thirteen carbon tows per helical member [<a href="#B26-materials-14-02079" class="html-bibr">26</a>].</p> Full article ">
22 pages, 6297 KiB  
Article
Incorporation of Wheat Straw Ash as Partial Sand Replacement for Production of Eco-Friendly Concrete
by Shazim Ali Memon, Usman Javed, Muhammad Haris, Rao Arsalan Khushnood and Jong Kim
Materials 2021, 14(8), 2078; https://doi.org/10.3390/ma14082078 - 20 Apr 2021
Cited by 10 | Viewed by 4313
Abstract
The depletion of natural sand resources occurs due to excessive consumption of aggregate for concrete production. Continuous extraction of sand from riverbeds permanently depletes fine aggregate resources. At the same time, a major ecological challenge is the disposal of agricultural waste ash from [...] Read more.
The depletion of natural sand resources occurs due to excessive consumption of aggregate for concrete production. Continuous extraction of sand from riverbeds permanently depletes fine aggregate resources. At the same time, a major ecological challenge is the disposal of agricultural waste ash from biomass burning. In this study, an environmental friendly solution is proposed to investigate the incorporation of wheat straw ash (WSA) by replacing 0, 5, 10, 15, and 20% of sand in concrete. Characterization results of WSA revealed that it was well-graded, free from organic impurities, and characterized by perforated and highly porous tubules attributed to its porous morphology. A decrease in fresh concrete density and an increase in slump values were attained by an increase in WSA replacement percentage. An increasing trend in compressive strength, hardened concrete density, and ultrasonic pulse velocity was observed, while a decrease was noticed in the values of water absorption with the increase in WSA replacement percentages and the curing age. The WSA incorporation at all replacement percentages yielded concrete compressive strength values over 21 MPa, which complies with the minimum strength requirement of structural concrete as specified in ACI 318-19. Acid resistance of WSA incorporated concrete improved due to the formation of pozzolanic hydrates as evident in Chappelle activity and thermogravimetric analysis (TGA) results of WSA modified composites. Thus, the incorporation of WSA provides an environmentally friendly solution for its disposal. It helps in conserving natural aggregate resources by providing a suitable alternative to fine aggregate for the construction industry. Full article
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<p>Gradation curves of sand and WSA along with ASTM C33 limits.</p> Full article ">Figure 2
<p>Morphology of wheat straw in longitudinal section (<b>a</b>–<b>c</b>) and cross section (<b>d</b>–<b>f</b>).</p> Full article ">Figure 3
<p>SEM of WSA at varying magnification levels, (<b>a</b>–<b>d</b>): The fibrous nature of WSA at the macroscopic scale has also been retained at the microscopic level; (<b>e</b>,<b>f</b>): WSA particles containing micro-perforations, micro-tubules’ of diameter between 0.25 to 2 μm and 2 to 7 μm, respectively.</p> Full article ">Figure 4
<p>X-ray diffraction of wheat straw ash.</p> Full article ">Figure 5
<p>Pozzolanic potential of WSA using Chapelle activity.</p> Full article ">Figure 6
<p>Linear shrinkage response of WSA-incorporated concrete.</p> Full article ">Figure 7
<p>Comparison of the slump of different concrete mixes.</p> Full article ">Figure 8
<p>Fresh concrete densities of concrete mix.</p> Full article ">Figure 9
<p>Compressive strength of WSA incorporated concrete mixes.</p> Full article ">Figure 10
<p>Hardened concrete density containing WSA at varying curing ages.</p> Full article ">Figure 11
<p>Regression correlation between hardened density and WSA content at various curing ages.</p> Full article ">Figure 12
<p>Regression relation between concrete hardened density and compressive strength.</p> Full article ">Figure 13
<p>Water absorption of WSA incorporated concrete.</p> Full article ">Figure 14
<p>Regression relation between compressive strength and UPV of WSA incorporated mixes.</p> Full article ">Figure 15
<p>Relation between hardened density and UPV of concrete.</p> Full article ">Figure 16
<p>Deterioration of concrete mixes in terms of weight loss after exposure to the acid solution.</p> Full article ">Figure 17
<p>Thermogravimetric analysis and derivative weight loss curves of W0 and W10 mixes.</p> Full article ">
13 pages, 5390 KiB  
Article
Assessment of the Deterioration State of Post-Installed Bonded Anchors Using Ultrasonic
by Oliver Zeman, Michael Schwenn, Martin Granig and Konrad Bergmeister
Materials 2021, 14(8), 2077; https://doi.org/10.3390/ma14082077 - 20 Apr 2021
Cited by 2 | Viewed by 1878
Abstract
The assessment of already installed anchorages for a possible exceeding of the service load level is a question that is gaining more and more importance, especially in building maintenance. Bonded anchors are of particular interest here, as the detection of a capacity reduction [...] Read more.
The assessment of already installed anchorages for a possible exceeding of the service load level is a question that is gaining more and more importance, especially in building maintenance. Bonded anchors are of particular interest here, as the detection of a capacity reduction or load exceedance can cause damage to the concrete-bonded mortar behavior. This article investigates the extent to which ultrasonic methods can be used to make a prediction about the condition of anchorages in concrete and about their load history. A promising innovative assessment method has been developed. The challenges in carrying out the experimental investigations are the arrangement of the transducers, the design of the test set-up and the applicability of direct, indirect or semidirect ultrasonic transmission. The experimental investigations carried out on a test concrete mix and a bonded anchor system show that damage to the concrete structure can be detected by means of ultrasound. The results indicate the formation of cracks and therefore a weakening of the response determined by means of direct, indirect and semidirect ultrasonic transmission. However, for application under non-laboratory conditions and on anchors with unknown load history, the calibration with a reference anchor and the identification of the maximum load is required. This enables a referencing of the other loaded anchors to the unloaded conditions and allows an estimation of the load history of individual anchors. Full article
(This article belongs to the Special Issue Concrete and Concrete Structures Monitored by Ultrasound)
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<p>Overview of ultrasonic measurement configurations: (<b>a</b>) used ultrasound device Pundit Lab+; (<b>b</b>) test setup for load application.</p> Full article ">Figure 2
<p>Overview of ultrasonic measurement configurations (<span class="html-italic">T—</span>transmitter; <span class="html-italic">R—</span>receiver). (<b>a</b>) direct transmission; (<b>b</b>) indirect transmission; (<b>c</b>) semidirect transmission.</p> Full article ">Figure 3
<p>Test setups for different ultrasonic measurement configurations: (<b>a</b>) test setup for all types of transmission, top side; (<b>b</b>) test setup for direct transmission, bottom side; (<b>c</b>) test setup for indirect transmission, top side.</p> Full article ">Figure 4
<p>Overview of the bonded anchor system used in the test series. (<b>a</b>) installation of anchor system; (<b>b</b>) typical failure mode.</p> Full article ">Figure 5
<p>Schematic loading procedure for the conducted investigations, see [<a href="#B2-materials-14-02077" class="html-bibr">2</a>] for additional information.</p> Full article ">Figure 6
<p>Results based on signal propagation time for different longitudinal wave transducers (54 kHz, 54 kHz (exponential transducer), 150 kHz and 250 kHz) and transverse wave transducer (250 kHz with different configuration) for direct transmission. (<b>a</b>) 54 kHz; (<b>b</b>) 54 kHz Exp.; (<b>c</b>) 150 kHz; (<b>d</b>) 250 kHz; (<b>e</b>) 250 kHz transverse orthogonal; (<b>f</b>) 250 kHz transverse parallel</p> Full article ">Figure 6 Cont.
<p>Results based on signal propagation time for different longitudinal wave transducers (54 kHz, 54 kHz (exponential transducer), 150 kHz and 250 kHz) and transverse wave transducer (250 kHz with different configuration) for direct transmission. (<b>a</b>) 54 kHz; (<b>b</b>) 54 kHz Exp.; (<b>c</b>) 150 kHz; (<b>d</b>) 250 kHz; (<b>e</b>) 250 kHz transverse orthogonal; (<b>f</b>) 250 kHz transverse parallel</p> Full article ">Figure 7
<p>Examples of ultrasonic signals after different load steps, the area is defined between the abszissa and the wave, the procedure is described in [<a href="#B2-materials-14-02077" class="html-bibr">2</a>]. (<b>a</b>) example of ultrasonic respond after unloading the 60 kN load step; (<b>b</b>) example of ultrasonic respond after unloading the 60 kN load step.</p> Full article ">Figure 8
<p>Results based on wave shape for different longitudinal wave transducers (54 kHz, 54 kHz (exponential transducer), 150 kHz and 250 kHz) and transverse wave transducer (250 kHz with different configuration) for direct transmission. (<b>a</b>) 54 kHz; (<b>b</b>) 54 kHz Exp.; (<b>c</b>) 150 kHz; (<b>d</b>) 250 kHz; (<b>e</b>) 250 kHz transverse orthogonal; (<b>f</b>) 250 kHz transverse parallel</p> Full article ">Figure 8 Cont.
<p>Results based on wave shape for different longitudinal wave transducers (54 kHz, 54 kHz (exponential transducer), 150 kHz and 250 kHz) and transverse wave transducer (250 kHz with different configuration) for direct transmission. (<b>a</b>) 54 kHz; (<b>b</b>) 54 kHz Exp.; (<b>c</b>) 150 kHz; (<b>d</b>) 250 kHz; (<b>e</b>) 250 kHz transverse orthogonal; (<b>f</b>) 250 kHz transverse parallel</p> Full article ">Figure 9
<p>Results based on signal propagation time for different longitudinal wave transducers 54 kHz (exponential transducer) and 250 kHz. (<b>a</b>) 54 kHz Exp.; (<b>b</b>) 250 kHz.</p> Full article ">Figure 10
<p>Results based on wave shape for different longitudinal wave transducers 54 kHz (exponential transducer) and 250 kHz. (<b>a</b>) 54 kHz Exp.; (<b>b</b>) 250 kHz.</p> Full article ">Figure 11
<p>Schematically evaluation based on signal propagation time and wave shape for direct, indirect and semidirect transmission.</p> Full article ">
17 pages, 4058 KiB  
Article
Annealing of Al-Zn-Mg-Cu Alloy at High Pressures: Evolution of Microstructure and the Corrosion Behavior
by Chuanjun Suo, Pan Ma, Yandong Jia, Xiao Liu, Xuerong Shi, Zhishui Yu and Konda Gokuldoss Prashanth
Materials 2021, 14(8), 2076; https://doi.org/10.3390/ma14082076 - 20 Apr 2021
Cited by 7 | Viewed by 2661
Abstract
Extruded Al-Zn-Mg-Cu alloy samples with grains aligned parallel to the extrusion direction were subjected to high-pressure annealing. The effects of annealing pressure on the microstructure, hardness, and corrosion properties (evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS)) were investigated. Phase analysis [...] Read more.
Extruded Al-Zn-Mg-Cu alloy samples with grains aligned parallel to the extrusion direction were subjected to high-pressure annealing. The effects of annealing pressure on the microstructure, hardness, and corrosion properties (evaluated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS)) were investigated. Phase analysis showed the presence of MgZn2 and α-Al phases, the MgZn2 phase dissolved into the matrix, and its amount decreased with the increasing annealing pressure. The recrystallization was inhibited, and the grains were refined, leading to an increase in the Vickers hardness with increasing the annealing pressure. The corrosion resistance was improved after high-pressure treatment, and a stable passivation layer was observed. Meanwhile, the number of corrosion pits and the width of corrosion cracks decreased in the high-pressure annealed samples. Full article
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<p>A schematic diagram showing (<b>a</b>) high-pressure equipment and (<b>b</b>) cell assembly sample for high-pressure synthesis: 1—pyrophillite, 2—conducting ring, 3—graphite crucible, 4—BN (clad), 5—sample, and 6—Top ram.</p> Full article ">Figure 2
<p>The X-ray diffraction patterns of the (<b>a</b>) extruded Al-Zn-Mg-Cu-based alloys annealed at different pressures (atmospheric pressure 1 and 2 GPa) and (<b>b</b>) plot showing the presence of MgZn<sub>2</sub> phase.</p> Full article ">Figure 3
<p>The optical microstructures of the extruded Al-Zn-Mg-Cu-based alloy: (<b>a</b>) along the extrusion direction and (<b>b</b>) perpendicular to the extrusion direction.</p> Full article ">Figure 4
<p>The optical microstructures of the extruded Al-Zn-Mg-Cu-based alloy annealed under (<b>a</b>) atmospheric pressure, (<b>b</b>) 2 GPa, and (<b>c</b>) 3 GPa, respectively.</p> Full article ">Figure 5
<p>The grain size distribution statistics chart of the Al-Zn-Mg-Cu-based alloy annealed under (<b>a</b>) atmospheric pressure, (<b>b</b>) 2 GPa, and (<b>c</b>) 3 GPa, respectively.</p> Full article ">Figure 6
<p>The scanning electron microscopy images of the (<b>a</b>) extruded Al-Zn-Mg-Cu-based alloy annealed under (<b>b</b>) atmospheric pressure, (<b>c</b>) 2 GPa, and (<b>d</b>) 3 GPa, respectively.</p> Full article ">Figure 7
<p>The Nyquist impedance plots for the extruded Al-Zn-Mg-Cu-based samples annealed as a function of pressure in 3.5 wt.% NaCl solution.</p> Full article ">Figure 8
<p>Equivalent circuit models used for impedance data fitting for the Al-Zn-Mg-Cu-based alloy after extrusion and annealing under (<b>a</b>) atmospheric and (<b>b</b>) 2 and 3 GPa.</p> Full article ">Figure 9
<p>Potentiodynamic polarization plots for the extruded Al-Zn-Mg-Cu alloy annealed under different pressures.</p> Full article ">Figure 10
<p>Autocatalytic mechanism of pitting corrosion.</p> Full article ">Figure 11
<p>The scanning electron microscopy images of the (<b>a</b>) extruded Al-Zn-Mg-Cu samples annealed as a function of pressure and tested for corrosion in a 3.5 wt.% NaCl solution: (<b>b</b>) atmospheric pressure, (<b>c</b>) 2 GPa, and (<b>d</b>) 3 GPa, respectively.</p> Full article ">Figure 12
<p>The scanning electron microscopy images of the Al-Zn-Mg-Cu alloy as a function of annealing pressure and after corrosion in 3.5 wt.% NaCl solution: (<b>a</b>) sample annealed at atmospheric pressure, (<b>b</b>) 2 GPa, and (<b>c</b>,<b>d</b>) 3 GPa, respectively.</p> Full article ">
13 pages, 3783 KiB  
Article
Thermoelectric Properties of Cu2Se Nano-Thin Film by Magnetron Sputtering
by Liangliang Yang, Jiangtao Wei, Yuanhao Qin, Lei Wei, Peishuai Song, Mingliang Zhang, Fuhua Yang and Xiaodong Wang
Materials 2021, 14(8), 2075; https://doi.org/10.3390/ma14082075 - 20 Apr 2021
Cited by 31 | Viewed by 3756
Abstract
Thermoelectric technology can achieve mutual conversion between thermoelectricity and has the unique advantages of quiet operation, zero emissions and long life, all of which can help overcome the energy crisis. However, the large-scale application of thermoelectric technology is limited by its lower thermoelectric [...] Read more.
Thermoelectric technology can achieve mutual conversion between thermoelectricity and has the unique advantages of quiet operation, zero emissions and long life, all of which can help overcome the energy crisis. However, the large-scale application of thermoelectric technology is limited by its lower thermoelectric performance factor (ZT). The thermoelectric performance factor is a function of the Seebeck coefficient, electrical conductivity, thermal conductivity and absolute temperature. Since these parameters are interdependent, increasing the ZT value has always been a challenge. Here, we report the growth of Cu2Se thin films with a thickness of around 100 nm by magnetron sputtering. XRD and TEM analysis shows that the film is low-temperature α-Cu2Se, XPS analysis shows that about 10% of the film’s surface is oxidized, and the ratio of copper to selenium is 2.26:1. In the range of 300–400 K, the maximum conductivity of the film is 4.55 × 105 S m−1, which is the maximum value reached by the current Cu2Se film. The corresponding Seebeck coefficient is between 15 and 30 µV K−1, and the maximum ZT value is 0.073. This work systematically studies the characterization of thin films and the measurement of thermoelectric properties and lays the foundation for further research on nano-thin-film thermoelectrics. Full article
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<p>Scanning electron microscopic (SEM) image of the surface of the film. (<b>a</b>–<b>c</b>) Surface topography at different magnifications. (<b>d</b>) False cross-sectional SEM analysis of the film on Si substrate.</p> Full article ">Figure 2
<p>(<b>a</b>) Atomic force microscopy (AFM) images of Cu<sub>2</sub>Se. (<b>b</b>) X-ray diffraction (XRD) patterns of Cu<sub>2</sub>Se.</p> Full article ">Figure 3
<p>Structural characterization of the Cu<sub>2</sub>Se thin films. (<b>a</b>) The high-resolution transmission electron microscopic (TEM) image of the cross-sectional view of the thin film. (<b>b</b>) Fast Fourier-transform (FFT) of the TEM image in (<b>a</b>). (<b>c</b>) Inverse Fourier-transform of (060) crystal plane. (<b>d</b>) High-angle annular dark-field (HAADF) imaging technique in scanning TEM (STEM). (<b>e</b>,<b>f</b>) X-ray energy spectrum (EDS) analysis maps of Cu and Se taken from the Cu<sub>2</sub>Se.</p> Full article ">Figure 4
<p>X-ray photoelectron spectroscopy (XPS) analysis of the Cu<sub>2</sub>Se thin film. (<b>a</b>) Survey. (<b>b</b>) Cu 2p. (<b>c</b>) Cu(Ι):Cu(ΙΙ). (<b>d</b>) Se 3d.</p> Full article ">Figure 5
<p>Thermoelectric properties of Cu<sub>2</sub>Se film on glass substrate prepared at various temperatures. (<b>a</b>) Seebeck coefficient <span class="html-italic">S</span>, (<b>b</b>) electrical conductivity <span class="html-italic">σ</span>, and (<b>c</b>) power factor (<span class="html-italic">PF</span>) <span class="html-italic">σS</span><sup>2</sup> of the film measured in the helium atmosphere.</p> Full article ">Figure 6
<p>(<b>a</b>) Thermal conductivity values measured in multiple samples prepared at different temperatures, (<b>b</b>) The calculated ZT for the Cu<sub>2</sub>Se thin film.</p> Full article ">
19 pages, 7345 KiB  
Article
An Experimental Study on the Dynamic Mechanical Properties of Epoxy Polymer Concrete under Ultraviolet Aging
by Yutian Liao, Dongpeng Ma, Yiping Liu, Zhenyu Jiang, Zejia Liu, Licheng Zhou and Liqun Tang
Materials 2021, 14(8), 2074; https://doi.org/10.3390/ma14082074 - 20 Apr 2021
Cited by 5 | Viewed by 2314
Abstract
Epoxy polymer concrete (EPC) is widely applied in engineering for its excellent mechanical properties. The impact loads and severe climatic conditions such as ultraviolet radiation, temperature change and rain erosion are in general for its engineering practice, potentially degrading the performance of EPC. [...] Read more.
Epoxy polymer concrete (EPC) is widely applied in engineering for its excellent mechanical properties. The impact loads and severe climatic conditions such as ultraviolet radiation, temperature change and rain erosion are in general for its engineering practice, potentially degrading the performance of EPC. In this paper, a procedure of accelerated aging for EPC, imitating the aging effect of ultraviolet radiation and hygrothermal conditions based on the meteorological statistics of Guangzhou city, was designed. After various periods of accelerated aging, the dynamic behaviors of EPC were studied by using a Split Hopkinson Pressure Bar (SHPB). The verification of the experimental data was performed. The two-stage dynamic compression stress-strain curves were obtained: (a) linear growth stage following by strain hardening stage at impact velocity 12.2 m/s and 18.8 m/s, (b) linear growth stage and then a horizontal stage when impact velocity is 25.0 m/s, (c) linear growth stage following by strain softening stage at impact velocity 29.2 m/s. The experimental results show that the specimens after longer accelerated aging tend to be more easily broken, especially at impact velocity 12.2 m/s and 18.8 m/s, while the strain rate is the main factor affecting the compression strength and stiffness. Ultimately the influence of strain rate and equivalent aging time on dynamic increase factor was revealed by a fitting surface. Full article
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<p>Percentage passing rate of aggregate.</p> Full article ">Figure 2
<p>(<b>a</b>) Metal mold and (<b>b</b>) specimen after demolding.</p> Full article ">Figure 3
<p>Right cone SHPB system: (<b>a</b>) schematic diagram, (<b>b</b>) photo.</p> Full article ">Figure 4
<p>Time history curve of parameters: (<b>a</b>) UV-light, (<b>b</b>) temperature, (<b>c</b>) humidity.</p> Full article ">Figure 5
<p>Reflection and transmission of elastic wave at specimen interface: (<b>a</b>) <math display="inline"><semantics> <mrow> <mi>t</mi> <mo>&lt;</mo> <msub> <mi>τ</mi> <mi>S</mi> </msub> </mrow> </semantics></math>, (<b>b</b>) <math display="inline"><semantics> <mrow> <msub> <mi>τ</mi> <mi>S</mi> </msub> <mo>&lt;</mo> <mi>t</mi> <mo>&lt;</mo> <mn>2</mn> <msub> <mi>τ</mi> <mi>S</mi> </msub> </mrow> </semantics></math>, (<b>c</b>) <math display="inline"><semantics> <mrow> <mn>2</mn> <msub> <mi>τ</mi> <mi>S</mi> </msub> <mo>&lt;</mo> <mi>t</mi> <mo>&lt;</mo> <mn>3</mn> <msub> <mi>τ</mi> <mi>S</mi> </msub> </mrow> </semantics></math>.</p> Full article ">Figure 6
<p>Pulse signal with different impact velocities: (<b>a</b>) 12.2 m/s, (<b>b</b>) 18.8 m/s, (<b>c</b>) 25.0 m/s, (<b>d</b>) 29.2 m/s.</p> Full article ">Figure 7
<p>Compression Stress-strain curves of specimens without aging treatment under different impact velocities: (<b>a</b>) 12.2 m/s, (<b>b</b>) 18.8 m/s, (<b>c</b>) 25.0 m/s, (<b>d</b>) 29.2 m/s.</p> Full article ">Figure 8
<p>Average compression stress-strain curves with different equivalent aging time under different impact velocities: (<b>a</b>) 12.2 m/s, (<b>b</b>) 18.8 m/s, (<b>c</b>) 25.0 m/s, (<b>d</b>) 29.2 m/s.</p> Full article ">Figure 9
<p>Average compression stress-strain curves with different equivalent aging time: (<b>a</b>) 0 years, (<b>b</b>) 1 year, (<b>c</b>) 2 years, (<b>d</b>) 4 years, (<b>e</b>) 6 years.</p> Full article ">Figure 10
<p>Strain rate-equivalent aging time curves with different impact velocities.</p> Full article ">Figure 11
<p>Failure phenomenon under different impact velocities and equivalent aging time.</p> Full article ">Figure 11 Cont.
<p>Failure phenomenon under different impact velocities and equivalent aging time.</p> Full article ">Figure 12
<p>Maximal compression stress under different impact velocity with different equivalent aging time.</p> Full article ">Figure 13
<p>The scatter of the maximal compression stress with different strain rate.</p> Full article ">Figure 14
<p>The scatter of the DIF with <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>log</mi> </mrow> <mrow> <mn>10</mn> </mrow> </msub> <mo stretchy="false">(</mo> <mrow> <mrow> <msub> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> <mi>d</mi> </msub> </mrow> <mo>/</mo> <mrow> <msub> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> <mi>s</mi> </msub> </mrow> </mrow> <mo stretchy="false">)</mo> </mrow> </semantics></math>.</p> Full article ">Figure 15
<p>Variation of DIF with strain rate and the equivalent aging time.</p> Full article ">
23 pages, 13731 KiB  
Article
Effect of Waste Glass on the Properties and Microstructure of Magnesium Potassium Phosphate Cement
by Qiubai Deng, Zhenyu Lai, Rui Xiao, Jie Wu, Mengliang Liu, Zhongyuan Lu and Shuzhen Lv
Materials 2021, 14(8), 2073; https://doi.org/10.3390/ma14082073 - 20 Apr 2021
Cited by 16 | Viewed by 2291
Abstract
Waste glass is a bulk solid waste, and its utilization is of great consequence for environmental protection; the application of waste glass to magnesium phosphate cement can also play a prominent role in its recycling. The purpose of this study is to evaluate [...] Read more.
Waste glass is a bulk solid waste, and its utilization is of great consequence for environmental protection; the application of waste glass to magnesium phosphate cement can also play a prominent role in its recycling. The purpose of this study is to evaluate the effect of glass powder (GP) on the mechanical and working properties of magnesium potassium phosphate cement (MKPC). Moreover, a 40mm × 40mm × 40mm mold was used in this experiment, the workability, setting time, strength, hydration heat release, porosity, and microstructure of the specimens were evaluated. The results indicated that the addition of glass powder prolonged the setting time of MKPC, reduced the workability of the matrix, and effectively lowered the hydration heat of the MKPC. Compared to an M/P ratio (MgO/KH2PO4 mass ratio) of 1:1, the workability of the MKPC with M/P ratios of 2:1 and 3:1 was reduced by 1% and 2.1%, respectively, and the peak hydration temperatures were reduced by 0.5% and 14.6%, respectively. The compressive strength of MKPC increased with an increase in the glass powder content at the M/P ratio of 1:1, and the addition of glass powder reduced the porosity of the matrix, effectively increased the yield of struvite-K, and affected the morphology of the hydration products. With an increase in the M/P ratio, the struvite-K content decreased, many tiny pores were more prevalent on the surface of the matrix, and the bonding integrity between the MKPC was weakened, thereby reducing the compressive strength of the matrix. At less than 40 wt.% glass powder content, the performance of MKPC improved at an M/P ratio of 1:1. In general, the addition of glass powders improved the mechanical properties of MKPC and reduced the heat of hydration. Full article
(This article belongs to the Special Issue Processing of End-of-Life Materials and Industrial Wastes)
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<p>Particle size distribution of dead-burnt MgO and glass powder.</p> Full article ">Figure 2
<p>Setting time and workability of the MKPC specimens as a function of glass powder content (0, 10, 20, and 40 wt.%) and M/P ratio (1:1, 2:1, and 3:1), (<b>a</b>) Setting time; (<b>b</b>) workability.</p> Full article ">Figure 3
<p>Hydration heat of the MKPC specimens as a function of glass powder content (0, 10, 20, and 40 wt.%) and M/P ratio of (<b>a</b>) 1:1, (<b>b</b>) 2:1, and (<b>c</b>) 3:1.</p> Full article ">Figure 3 Cont.
<p>Hydration heat of the MKPC specimens as a function of glass powder content (0, 10, 20, and 40 wt.%) and M/P ratio of (<b>a</b>) 1:1, (<b>b</b>) 2:1, and (<b>c</b>) 3:1.</p> Full article ">Figure 4
<p>Compressive strength of the MKPC specimens with various glass powder contents (0, 10, 20, and 40 wt.%) and M/P ratios of (<b>a</b>) 1:1, (<b>b</b>) 2:1, and (<b>c</b>) 3:1.</p> Full article ">Figure 4 Cont.
<p>Compressive strength of the MKPC specimens with various glass powder contents (0, 10, 20, and 40 wt.%) and M/P ratios of (<b>a</b>) 1:1, (<b>b</b>) 2:1, and (<b>c</b>) 3:1.</p> Full article ">Figure 5
<p>The MIP results for the hardened pastes at an M/P ratio of 1:1 after curing for 28 d: (<b>a</b>) pore size distribution and (<b>b</b>) total porosity and pore volume fraction.</p> Full article ">Figure 6
<p>XRD patterns of the samples hydrated for 28 d: (<b>a</b>) samples with different glass powder concentrations and an M/P ratio of 3:1, and (<b>b</b>) samples with different M/P ratios and a glass powder concentration of 40 wt.%.</p> Full article ">Figure 7
<p>TG/DTG curves of the MKPC pastes with an M/P ratio of 1:1, containing 0 to 40 wt.% glass powder cured for 28 d, where (<b>a</b>) shows all curves and (<b>b</b>) and (<b>c</b>) are expanded graphs of areas 1 and 2 in (<b>a</b>).</p> Full article ">Figure 8
<p>TG/DTG curves of samples cured for 28 d with different M/P ratios and 40 wt.% glass powder concentration, where (<b>a</b>) shows all curves and (<b>b</b>,<b>c</b>) are expanded graphs of areas 1 and 2 in (<b>a</b>).</p> Full article ">Figure 8 Cont.
<p>TG/DTG curves of samples cured for 28 d with different M/P ratios and 40 wt.% glass powder concentration, where (<b>a</b>) shows all curves and (<b>b</b>,<b>c</b>) are expanded graphs of areas 1 and 2 in (<b>a</b>).</p> Full article ">Figure 9
<p>SEM images of the MKPC pastes cured for 28 days: (<b>a</b>) G1-0 (<b>b</b>) G1-1 (<b>c</b>) G1-2 (<b>d</b>) G1-4 (<b>e</b>) G2-4 and (<b>f</b>) G3-4.</p> Full article ">Figure 10
<p>SEM-EDS analyses on spots of (<b>a</b>) G1-1, (<b>b</b>) G1-2, and (<b>c</b>) G1-4 cured for 28 days.</p> Full article ">Figure 11
<p>SEM images of the MPC pastes mixed with glass fragments: (<b>a</b>) M/P ratio = 1:1, 20%; (<b>b</b>) 2:1, 40%; (<b>c</b>) 3:1, 40%.</p> Full article ">Figure 12
<p>SEM images and elemental maps along lines 1–2 of the MKPC pastes cured after 7 days: M/P ratio = 1:1 and 40 wt.% content of glass fragments, (<b>a</b>) SEM image; (<b>b</b>) Intensity of each element distribution along line 1-2; (<b>c</b>) EDS elemental distribution along lines 1–2; (<b>d</b>) EDS elemental maps.</p> Full article ">Figure 13
<p>SEM images and element maps along lines 1–2 of the MKPC pastes cured after 7 days: M/P ratio = 2:1 and 40 wt.% content of glass fragments, (<b>a</b>) SEM image; (<b>b</b>) Intensity of each element distribution along line 1-2; (<b>c</b>) EDS elemental distribution along lines 1–2; (<b>d</b>) EDS elemental maps; (<b>e</b>) EDS elemental area 3.</p> Full article ">Figure 14
<p>SEM images and element maps along lines 1–2 of the MKPC pastes cured after 7 days: M/P ratio = 3:1 and 40 wt.% content of glass fragments, (<b>a</b>) SEM image; (<b>b</b>) Intensity of each element distribution along line 1-2; (<b>c</b>) EDS elemental distribution along line 1-2; (<b>d</b>) EDS elemental maps.</p> Full article ">
14 pages, 2785 KiB  
Article
Improving the Solid Fuel Properties of Non-Lignocellulose and Lignocellulose Materials through Torrefaction
by Nwokolo Nwabunwanne, Tonga Vuyokazi, Adeniji Olagoke, Ojemaye Mike, Mukumba Patrick and Okoh Anthony
Materials 2021, 14(8), 2072; https://doi.org/10.3390/ma14082072 - 20 Apr 2021
Cited by 8 | Viewed by 2335
Abstract
Biomass torrefaction is a thermal pre-treatment technique that improves solid fuel properties in relation to its efficient utilization for energy generation. In this study, the torrefaction performance of sewage sludge, a non-lignocellulose biomass and sugarcane bagasse, a lignocellulose biomass were investigated in an [...] Read more.
Biomass torrefaction is a thermal pre-treatment technique that improves solid fuel properties in relation to its efficient utilization for energy generation. In this study, the torrefaction performance of sewage sludge, a non-lignocellulose biomass and sugarcane bagasse, a lignocellulose biomass were investigated in an electric muffle furnace. The influence of torrefaction temperature on the physiochemical properties of the produced biomaterial were examined. Characterization of the raw and torrefied biomass material were studied using thermogravimetric analysis, Fourier transform infrared spectroscopy (FTIR) analysis and scanning electron microscopy. From the result obtained, it was evident that an increase in torrefaction temperature up to 350 °C caused a 33.89% and 45.94% decrease in volatile matter content of sewage sludge and sugarcane bagasse, respectively. At a higher temperature of 350 °C, the peak corresponding to OH stretching of hydroxyl group decreased in intensity for both biomasses, showing a decomposition of the hydroxyl group as a result of torrefaction. This enriched the lignin content of the torrefied samples, thus making these solid fuels good feedstock for energy production. Full article
(This article belongs to the Section Energy Materials)
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<p>TG curves for raw and torrefied sewage sludge at heating 25 °C/min (SST 200—sewage sludge torrefied at 200 °C, SST 250—sewage sludge torrefied at 250 °C, SST 300—sewage sludge torrefied at 300 °C, SST 350—sewage sludge torrefied at 350 °C, and SS Raw—raw sewage sludge).</p> Full article ">Figure 2
<p>TG curves for raw and torrefied sugarcane bagasse at heating 25 °C/min (BGT200—bagasse torrefied at 200 °C, BGT250—bagasse torrefied at 250 °C, BGT300—bagasse torrefied at 300 °C, BGT350—bagasse torrefied at 350 °C, and BG Raw—raw bagasse).</p> Full article ">Figure 3
<p>FTIR spectra of raw and torrefied sewage sludge at varying temperature.</p> Full article ">Figure 4
<p>FTIR spectra of raw and torrefied sugarcane bagasse at varying temperature.</p> Full article ">Figure 5
<p>SEM images of raw sewage sludge (SSRaw) and torrefied sewage sludge at 200 °C (SST200), 250 °C (SST250), 300 °C (SST300) and 350 °C (SST350).</p> Full article ">Figure 6
<p>SEM images of raw bagasse (BGRaw) and torrefied bagasse at 200 °C (BGT200), 250 °C (BGT250), 300 °C (BGT300) and 350 °C (BGT350).</p> Full article ">
62 pages, 12239 KiB  
Review
Applications of Ceramic/Graphene Composites and Hybrids
by Cristina Ramírez, Manuel Belmonte, Pilar Miranzo and Maria Isabel Osendi
Materials 2021, 14(8), 2071; https://doi.org/10.3390/ma14082071 - 20 Apr 2021
Cited by 33 | Viewed by 6636
Abstract
Research activity on ceramic/graphene composites and hybrids has increased dramatically in the last decade. In this review, we provide an overview of recent contributions involving ceramics, graphene, and graphene-related materials (GRM, i.e., graphene oxide, reduced graphene oxide, and graphene nanoplatelets) with a primary [...] Read more.
Research activity on ceramic/graphene composites and hybrids has increased dramatically in the last decade. In this review, we provide an overview of recent contributions involving ceramics, graphene, and graphene-related materials (GRM, i.e., graphene oxide, reduced graphene oxide, and graphene nanoplatelets) with a primary focus on applications. We have adopted a broad scope of the term ceramics, therefore including some applications of GRM with certain metal oxides and cement-based matrices in the review. Applications of ceramic/graphene hybrids and composites cover many different areas, in particular, energy production and storage (batteries, supercapacitors, solar and fuel cells), energy harvesting, sensors and biosensors, electromagnetic interference shielding, biomaterials, thermal management (heat dissipation and heat conduction functions), engineering components, catalysts, etc. A section on ceramic/GRM composites processed by additive manufacturing methods is included due to their industrial potential and waste reduction capability. All these applications of ceramic/graphene composites and hybrids are listed and mentioned in the present review, ending with the authors’ outlook of those that seem most promising, based on the research efforts carried out in this field. Full article
(This article belongs to the Special Issue Graphene-Based Materials, Their Composites and Potential Applications )
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<p>(<b>a</b>) Publications per year in the subject of ceramic/graphene composites (data collected from WOS, Clarivate Analytics); (<b>b</b>) Number of patents per year and cumulative in the same topic in either the title or the abstract (source Espacenet, EPO).</p> Full article ">Figure 2
<p>(<b>a</b>) Coulombic efficiency and specific capacity (at 100 mA·g<sup>−1</sup>) of SiOx and three SiOx/G composite electrodes (2 wt.%, 5 wt.%, 10 wt.%); (<b>b</b>–<b>e</b>) SEM micrographs of the surface of SiOx and the composite electrodes after 120 cycles. SiOx sample (<b>b</b>) shows large cracks in comparison to the smooth surface exhibited by the electrodes with graphene filler (<b>c</b>–<b>e</b>). Reprinted from [<a href="#B21-materials-14-02071" class="html-bibr">21</a>], Copyright (2019), with permission from Elsevier.</p> Full article ">Figure 3
<p>R-TiO<sub>2</sub>@rGO hybrid for LIB anode. (<b>a</b>) SEM image of GO, (<b>b</b>) SEM image of titanium hydroxide/GO after hydrothermal synthesis, (<b>c</b>,<b>d</b>) TEM images showing the morphology of R-TiO<sub>2</sub>@rGO hybrid; (<b>e</b>) cycling performance of R-TiO<sub>2</sub>@RGO and R-TiO<sub>2</sub> at 10 C, (<b>f</b>) rate capacities. Adapted from [<a href="#B27-materials-14-02071" class="html-bibr">27</a>], Copyright (2019), with permission from Elsevier.</p> Full article ">Figure 4
<p>(<b>a</b>) Schematics of MnO<sub>2</sub>@G-CNF hybrid supercapacitor architecture, (<b>b</b>) SEM micrographs of the material. The electrostatic double-layer is composed of carbon nanofiber substrate and vertically oriented graphene sheets (VG). The pseudocapacitor consists of the MnO nanosheets grown on VG. (<b>c</b>) Performance of samples with different treatments and MnO<sub>2</sub> contents. Reprinted from [<a href="#B43-materials-14-02071" class="html-bibr">43</a>], Copyright (2018), with permission from Elsevier.</p> Full article ">Figure 5
<p>(<b>a.1</b>) Schematics of faster charge transport via graphene microplatelets in SnO<sub>2<sup>−</sup></sub>TiO<sub>2</sub>/graphene anode; (<b>a.2</b>) diagram of an electronic band in DSSC with SnO<sub>2<sup>−</sup></sub>TiO<sub>2</sub>/graphene anode. Reprinted from [<a href="#B62-materials-14-02071" class="html-bibr">62</a>], Copyright (2020) with permission from Elsevier; (<b>b.1</b>) SEM image of MoS<sub>2</sub>/rGO counter electrode; and (<b>b.2</b>) J–V curves of DSSC using Pt counter electrode compared to those based on MoS<sub>2</sub>/rGO composites and pure MoS<sub>2</sub>, under simulated illumination (AM 1.5G, 100 mWcm<sup>−2</sup>). Reprinted from [<a href="#B59-materials-14-02071" class="html-bibr">59</a>], copyright (2019), with permission from Elsevier.</p> Full article ">Figure 6
<p>MAPbI<sub>3</sub>/CuInS<sub>2</sub> QDs@Graphene PSC. (<b>a</b>) Diagram showing charge transfer energy levels; (<b>b</b>) J-V curve of PSC with different active layer compositions; and (<b>c</b>) performance of solar cell exposed to air. Reprinted from [<a href="#B71-materials-14-02071" class="html-bibr">71</a>], Copyright (2020), with permission from Elsevier.</p> Full article ">Figure 7
<p>(<b>a</b>) Pt/TiC@GNS hybrid. (<b>a.1</b>,<b>a.2</b>) HRTEM images showing TiC core covered by graphene shell and Pt nanoparticles; (<b>a.3</b>) power densities obtained with Pt/TiC@GNS, Pt/rGO and Pt/C electrodes. Reprinted from [<a href="#B84-materials-14-02071" class="html-bibr">84</a>], Copyright (2017), with permission from Elsevier. (<b>b.1</b>) TEM image of rGO@SiO<sub>2</sub> hybrid, (<b>b.2</b>) DMFC performance using CS/SiO<sub>2</sub>@rGO membrane at 80 °C. Reprinted from [<a href="#B89-materials-14-02071" class="html-bibr">89</a>], Copyright (2019), with permission of Elsevier.</p> Full article ">Figure 8
<p>Strength and piezoelectric properties of PDMS/BCZT/rGO: (<b>a</b>) Stretching of PDMS/BCZT and PDMS/BCZT/rGO composites; (<b>b</b>) stress- strain curve; (<b>c</b>) piezoelectric constant at different rGO contents; (<b>d</b>) schematic diagram of dipole formation; (<b>e</b>) open-circuit voltage and (<b>f</b>) short circuit current under finger tapping. Reprinted from [<a href="#B112-materials-14-02071" class="html-bibr">112</a>], Copyright (2018), with permission from Elsevier.</p> Full article ">Figure 9
<p>Examples of performance for different sensors: (<b>a</b>) Comparison of the sensing response for detection of SO<sub>2</sub> gas of SnO<sub>2</sub>, SnO<sub>2</sub>/rGO and SnO<sub>2</sub>/MWCNT sensors as a function of temperature. Reprinted from reference [<a href="#B156-materials-14-02071" class="html-bibr">156</a>], Copyright (2017), with permission from Elsevier; (<b>b</b>) Selectivity of the SnO<sub>2</sub> quantum wire/rGO gas sensor for SH<sub>2</sub> detection compared to other gases, reprinted with permission from [<a href="#B155-materials-14-02071" class="html-bibr">155</a>], Copyright (2016) American Chemical Society; (<b>c</b>) linear response of In<sub>2</sub>O<sub>3</sub> nanofibers/GO hybrid sensor to the NH3 concentration. Reprinted from reference [<a href="#B168-materials-14-02071" class="html-bibr">168</a>], Copyright (2019), with permission from Elsevier; (<b>d</b>) time response/recovery curves of an In<sub>2</sub>O<sub>3</sub>/rGO composite sensor to successive cycles of 100 ppm TMA at RT. Reprinted from reference [<a href="#B170-materials-14-02071" class="html-bibr">170</a>], Copyright (2019), with permission from Elsevier.</p> Full article ">Figure 10
<p>Example of microstructures of sensors prepared by hydrothermal synthesis: (<b>a</b>) transmission electron microscopy (TEM) image of WO<sub>3</sub>/rGO sensor reprinted from reference [<a href="#B163-materials-14-02071" class="html-bibr">163</a>] published by the Royal Society of Chemistry; (<b>b.1</b>) FESEM and (<b>b.2</b>) TEM views of Fe<sub>2</sub>O<sub>3</sub>-1.0 wt.% rGO composites reprinted from reference [<a href="#B180-materials-14-02071" class="html-bibr">180</a>], Copyright (2017), with permission from Elsevier.</p> Full article ">Figure 11
<p>(<b>a</b>) Plots of the resistance of a strain-sensitive MnO<sub>2</sub> <span class="html-italic">np</span>/CNT/GO film at various bending angles and (<b>b</b>) resistence changes with strain. (<b>c</b>,<b>d</b>) A photograph of a sensor attached to a sole and the corresponding current signals for detecting the walking motion of a human, reprinted from reference [<a href="#B184-materials-14-02071" class="html-bibr">184</a>], copyright (2020), with permission from Elsevier.</p> Full article ">Figure 12
<p>A chart summarizing the main types of ceramic/graphene-based sensors with the indication of the different tested analytes.</p> Full article ">Figure 13
<p>Schematics of the procedures for preparing (<b>a</b>) SiO<sub>2</sub>/rGO and (<b>b</b>) mullite/rGO composites for EMI applications, adapted with permission from references [<a href="#B195-materials-14-02071" class="html-bibr">195</a>], copyright (2020), American Chemical Society and [<a href="#B196-materials-14-02071" class="html-bibr">196</a>], copyright (2018), American Chemical Society, respectively.</p> Full article ">Figure 14
<p>Microwave absorption performance of (<b>a</b>) LAS/CoFe<sub>2</sub>O<sub>4</sub>/rGO composites. Reprinted from [<a href="#B209-materials-14-02071" class="html-bibr">209</a>], Copyright (2019), with permission from Elsevier; and (<b>b</b>) SiC@rGO aerogels. Reprinted from [<a href="#B213-materials-14-02071" class="html-bibr">213</a>], Copyright (2017) with permission from Elsevier.</p> Full article ">Figure 15
<p>Schematic illustration of the photocatalytic mechanism for the degradation of methyl violet (MV) solutions using BFO/rGO composites. Reprinted from [<a href="#B217-materials-14-02071" class="html-bibr">217</a>], Copyright (2017) The American Ceramic Society, with permission from John Wiley and Sons, Inc.</p> Full article ">Figure 16
<p>Scheme showing the possible role of graphene-based materials (GDs) in BTE applications. Reprinted from reference [<a href="#B234-materials-14-02071" class="html-bibr">234</a>].</p> Full article ">Figure 17
<p>(<b>a</b>) Maximum toughness increment, and (<b>b</b>) relative strength increase data for ceramic/graphene composites (full and empty symbols correspond to GO and GNP fillers, respectively), adapted from [<a href="#B4-materials-14-02071" class="html-bibr">4</a>], copyright (2017), with permission from Elsevier. Numbers in brackets show the corresponding references in that work. Shadowed blue area in (<b>a</b>) encircle data for GO and the green area for GNP, whereas shadowed area in (<b>b</b>) indicates the general observed trend.</p> Full article ">Figure 18
<p>(<b>a</b>) Schematic of the self-assembly fabrication procedure for nano-HA@rGO scaffolds; (<b>b</b>) SEM micrographs of the developed materials with different amounts of nano-HA. Adapted from [<a href="#B241-materials-14-02071" class="html-bibr">241</a>], copyright (2017), with permission from Elsevier.</p> Full article ">Figure 19
<p>(<b>a</b>) Example of thermal management results for thick graphitic networks on porous Al<sub>2</sub>O<sub>3</sub> and AlN ceramics processed by APCVD: (<b>a.1</b>) SEM images of the graphitic networks, (<b>a.2</b>) Schematics of the Joule heating test setup, based on a thick film resistor attached to a DBC substrate, and backside hot spot temperature profiles of both the coated Al<sub>2</sub>O<sub>3</sub> and bare AlN DBC substrates; and (<b>a.3</b>) temperature distribution during heating of both coated substrates. Adapted with permission from reference [<a href="#B263-materials-14-02071" class="html-bibr">263</a>], copyright (2019) American Chemical Society. (<b>b</b>) Schematics of the APCVD procedure used to develop thermal conductive fillers for silicone oil-based non-curing TIM: highly oriented thick graphitic network flakes delaminated from quartz substrates and graphitic network-coated Al<sub>2</sub>O<sub>3</sub> spherical particles. Adapted from [<a href="#B265-materials-14-02071" class="html-bibr">265</a>], copyright (2020) American Chemical Society. (<b>c</b>) SEM image of a highly oriented BN/rGO hybrid aerogel (GO/BN initial ratio: 1/15) adapted from reference [<a href="#B266-materials-14-02071" class="html-bibr">266</a>]. Copyright (2017), with permission from Elsevier.</p> Full article ">Figure 20
<p>(<b>a</b>) Electro-thermal performance by Joule heating of a mullite/G-coated CF composite: (<b>a.1</b>) schematic of the processing and (<b>a.2</b>) temperature changes versus time and images of temperature distribution during testing Adapted from [<a href="#B269-materials-14-02071" class="html-bibr">269</a>]. Copyright (2020), with permission from Elsevier. (<b>b</b>) Ablation performance of thermal sprayed glass-ceramic/GNP coatings: (<b>b.1</b>) assembly of SEM images of the top and cross-section surfaces, detail of the microstructure of the fracture surface by SEM, and Raman analysis was done on the polished cross-section Adapted from reference [<a href="#B271-materials-14-02071" class="html-bibr">271</a>], copyright (2015) American Chemical Society. (<b>b.2</b>) The thickness of the degraded top layer versus the maximum temperature reached during ablation tests at 900 °C and 1200 °C for the glass-ceramic/GNP and plain glass-ceramic coatings. Adapted from reference [<a href="#B273-materials-14-02071" class="html-bibr">273</a>], copyright (2016) The American Ceramic Society, with permission from John Wiley and Sons, Inc.</p> Full article ">Figure 21
<p>(<b>a</b>) Schematics and image of a B<sub>4</sub>C/GNP ceramic plate tested as armor target. Reprinted from reference [<a href="#B275-materials-14-02071" class="html-bibr">275</a>], copyright (2019), with permission from Elsevier. (<b>b</b>) SEM images of the damage underneath Hertzian contact for monolithic SiC, and SiC/GNP and SiC/rGO composites with 5 vol.% of nanofillers. Arrows point the cone cracks whereas the dashed lines demarcate the quasi-plastic damage zones. Reprinted from reference [<a href="#B277-materials-14-02071" class="html-bibr">277</a>], copyright (2017), with permission from Elsevier.</p> Full article ">Figure 22
<p>(<b>a</b>) Illustration of the roll formation in graphene stacks, (<b>b</b>) exfoliated graphene flake on the tested surface, (<b>c</b>) carbon-based tribofilm, (<b>d</b>) long carbon roll, (<b>e</b>) twisted roll formed by the combination of different rolls and, (<b>f</b>) accumulation of rolls trapped into a cavity. Reprinted from [<a href="#B281-materials-14-02071" class="html-bibr">281</a>], copyright (2019), with permission from Elsevier.</p> Full article ">Figure 23
<p>SEM images of micro-thruster section of t-YSZ/GNP composite, showing the overall configuration (<b>a.1</b>) and a detail of the micro-nozzle (<b>a.2</b>); and (<b>b</b>) damping characteristics (tan δ) of the composites and plain YSZ at different frequencies, adapted from [<a href="#B288-materials-14-02071" class="html-bibr">288</a>].</p> Full article ">Figure 24
<p>(<b>a</b>) Schematics showing fabrication of 3D printed SiCN/rGO structure by impregnation of a DIW rGO with a preceramic polymer; (<b>b</b>) tomographic image of the treated structure (800 °C); (<b>c</b>) cyclic voltammogram at different scan rates from 1 to 200 mV·s<sup>−1</sup> with an ideal capacitive behavior. Reprinted from reference) [<a href="#B328-materials-14-02071" class="html-bibr">328</a>], copyright (2019), with permission from Elsevier.</p> Full article ">Figure 25
<p>(<b>a.1</b>) Printing of a kaolin/rGO cavity; (<b>a.2</b>) infrared camera images of a LED module within the 3D printed cavity reprinted from reference [<a href="#B340-materials-14-02071" class="html-bibr">340</a>], copyright (2020), with permission from Elsevier; (<b>b</b>) Illustration of an inkjet deposition process on a CMOS platform of a ZnO/graphene mix for a sensory device, reprinted from reference [<a href="#B341-materials-14-02071" class="html-bibr">341</a>].</p> Full article ">Figure 26
<p>(<b>a</b>) Illustration of the printing of the Li-ion battery cell (LTO/GO anode, LFP/GO cathode and electrolyte); (<b>b</b>–<b>d</b>) images of the actual miniaturized cells reprinted from reference [<a href="#B349-materials-14-02071" class="html-bibr">349</a>], copyright (2016), with permission of John Wiley and Sons, Inc.</p> Full article ">
17 pages, 5777 KiB  
Article
Studies of Nickel-Rich LiNi0.85Co0.10Mn0.05O2 Cathode Materials Doped with Molybdenum Ions for Lithium-Ion Batteries
by Francis Amalraj Susai, Daniela Kovacheva, Tatyana Kravchuk, Yaron Kauffmann, Sandipan Maiti, Arup Chakraborty, Sooraj Kunnikuruvan, Michael Talianker, Hadar Sclar, Yafit Fleger, Boris Markovsky and Doron Aurbach
Materials 2021, 14(8), 2070; https://doi.org/10.3390/ma14082070 - 20 Apr 2021
Cited by 19 | Viewed by 5218
Abstract
In this work, we continued our systematic investigations on synthesis, structural studies, and electrochemical behavior of Ni-rich materials Li[NixCoyMnz]O2 (x + y + z = 1; x ≥ 0.8) for advanced lithium-ion batteries (LIBs). We focused, [...] Read more.
In this work, we continued our systematic investigations on synthesis, structural studies, and electrochemical behavior of Ni-rich materials Li[NixCoyMnz]O2 (x + y + z = 1; x ≥ 0.8) for advanced lithium-ion batteries (LIBs). We focused, herein, on LiNi0.85Co0.10Mn0.05O2 (NCM85) and demonstrated that doping this material with high-charge cation Mo6+ (1 at. %, by a minor nickel substitution) results in substantially stable cycling performance, increased rate capability, lowering of the voltage hysteresis, and impedance in Li-cells with EC-EMC/LiPF6 solutions. Incorporation of Mo-dopant into the NCM85 structure was carried out by in-situ approach, upon the synthesis using ammonium molybdate as the precursor. From X-ray diffraction studies and based on our previous investigation of Mo-doped NCM523 and Ni-rich NCM811 materials, it was revealed that Mo6+ preferably substitutes Ni residing either in 3a or 3b sites. We correlated the improved behavior of the doped NCM85 electrode materials in Li-cells with a partial Mo segregation at the surface and at the grain boundaries, a tendency established previously in our lab for the other members of the Li[NixCoyMnz]O2 family. Full article
(This article belongs to the Special Issue Nanostructured Materials for Electrochemical Energy Storage)
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<p>XRD patterns of NCM85 undoped and Mo-doped materials synthesized by solution-combustion method and annealed in a tubular furnace at 760 °C in pure oxygen for 6 h.</p> Full article ">Figure 2
<p>Schematic diagram for a probable configuration of undoped (<b>a</b>,<b>b</b>) and Mo-doped (<b>c</b>,<b>d</b>) NCM85 materials. (<b>a</b>,<b>c</b>) are shown in <span class="html-italic">bc-</span>plane, and (<b>b</b>,<b>d</b>) are shown in <span class="html-italic">ab-</span>plane.</p> Full article ">Figure 3
<p>(<b>a</b>) The depth profiles of Molybdenum obtained from ToF-SIMS studies of NCM85 Mo-doped material demonstrating the dopant segregation at the outermost surface layer of ~15–20 Å. Note that due to high roughness of the powder NCM85 samples, “surface” and “bulk” regions are shown only schematically, as an eye guide. (<b>b</b>,<b>c</b>) HAADF-STEM images and the corresponding EDX maps of the Mo-K<span class="html-italic"><sub>α</sub></span> measured from NCM85 Mo-doped material demonstrating the enrichment of the grain boundaries with the dopant. Spectral image areas are shown with green-line rectangles. The grain boundaries are marked with arrows.</p> Full article ">Figure 4
<p>Schematic representation of possible (<b>a</b>) granular Li-ion conduction pathways in NCM85 and (<b>b</b>) Li-ion conduction pathways along grain boundaries (GBs) in Mo-doped NCM85. In these samples, the dopant segregates to the surface and the GBs are enriched with the dopant as demonstrated in <a href="#materials-14-02070-f003" class="html-fig">Figure 3</a>.</p> Full article ">Figure 5
<p>(<b>a</b>) DSC profiles measured in reactions with EC-EMC/LiPF<sub>6</sub> battery solutions (LP57) of NCM85 undoped and molybdenum-doped materials, as indicated. The total heat evolved Q<sub>t</sub> and the onset temperatures (indicated with arrows) are also shown; (<b>b</b>) enlarged temperature range of 55–85 °C, demonstrating the characteristic exothermal peak at ~75 °C assigned to the possible reactions of surface species like Li<sub>2</sub>CO<sub>3</sub> and Li<sub>2</sub>MoO<sub>4</sub> with solution. The main thermo-chemical reactions between NCM85 and solution species take place at 220–320 °C.</p> Full article ">Figure 6
<p>(<b>a</b>) Cycling behavior of electrodes comprising undoped and 1 at. % Mo-doped NCM85 materials, at 30 °C. Indicated are C-rates used and the capacity retention values measured for cycles 6-th and 60-th; (<b>b</b>,<b>c</b>) Voltage profiles of the above electrodes registered during charge/discharge in cycles 10-th, 20-th and 50-th at a C/3 rate. They show higher capacities obtained from Mo-doped NCM85 as well as more reversible phase transitions at ~4.2 V of these electrodes compared to the undoped ones.</p> Full article ">Figure 7
<p>The voltage hysteresis measured from cycling performance (<a href="#materials-14-02070-f006" class="html-fig">Figure 6</a>a) of electrodes comprising undoped and 1 at. % Mo-doped NCM85 materials, at 30 °C. Evolution of the voltage hysteresis (δ, mV/cycle) is indicated.</p> Full article ">Figure 8
<p>Discharge capacities measured at various C-rates (C/10, C/5, C/2, 1C, and 2C) from electrodes comprising undoped and 1 at. % Mo-doped NCM85 materials, at 30 °C.</p> Full article ">Figure 9
<p>Differential capacity dQ/dV as a function of the cell voltage measured from electrodes comprising undoped and 1 at. % Mo-doped NCM85 materials, at 30 °C for cycles 2, 25, and 50.</p> Full article ">Figure 10
<p>Impedance spectra of NCM85 undoped and Mo-doped electrodes measured during charging at 4.0 V, 30 °C in three-electrode pouch-type cells with the Li-reference electrodes (as described in the text). Symbols are experimental points and solid lines are fitted data: (<b>a</b>) full scale spectra and (<b>b</b>) an enlarged view of the high-to-medium frequency regions of the spectra marked with the rose color rectangles. (<b>c</b>) An equivalent circuit model of the impedance of NCM85 electrodes.</p> Full article ">
17 pages, 2010 KiB  
Article
Rheological and the Fresh State Properties of Alkali-Activated Mortars by Blast Furnace Slag
by Markssuel Teixeira Marvila, Afonso Rangel Garcez de Azevedo, Paulo Ricardo de Matos, Sérgio Neves Monteiro and Carlos Maurício Fontes Vieira
Materials 2021, 14(8), 2069; https://doi.org/10.3390/ma14082069 - 20 Apr 2021
Cited by 93 | Viewed by 4245
Abstract
The fresh and rheological properties of alkali mortars activated by blast furnace slag (BFS) were investigated. Consistency tests, squeeze flow, dropping ball, mass density in the hardened state, incorporated air, and water retention were performed. Mortars were produced with the ratio 1:2:0.45 (binder:sand:water), [...] Read more.
The fresh and rheological properties of alkali mortars activated by blast furnace slag (BFS) were investigated. Consistency tests, squeeze flow, dropping ball, mass density in the hardened state, incorporated air, and water retention were performed. Mortars were produced with the ratio 1:2:0.45 (binder:sand:water), using not only ordinary Portland cement for control but also BFS, varying the sodium content of the activated alkali mortars from 2.5 to 15%. The results obtained permitted understanding that mortars containing 2.5 to 7.5% sodium present a rheological behavior similar to cementitious mortars by the Bingham model. In turn, the activated alkali mortars containing 10 to 15% sodium showed a very significant change in the properties of dynamic viscosity, which is associated with a change in the type of model, starting to behave similar to the Herschel–Bulkley model. Evaluating the properties of incorporated air and water retention, it appears that mortars containing 12.5% and 15% sodium do not have compatible properties, which is related to the occupation of sodium ions in the interstices of the material. Thus, it is concluded that the techniques used were consistent in the rheological characterization of activated alkali mortars. Full article
(This article belongs to the Special Issue Study on Advanced Cement-Based Materials and Their Applications)
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<p>Particle size distribution of the materials used: Blast Furnace Slag (BFS); Ordinary Portland Cement (OPC) and sand.</p> Full article ">Figure 2
<p>Consistency index results.</p> Full article ">Figure 3
<p>Squeeze flow results for different mixtures.</p> Full article ">Figure 4
<p>Dropping ball results.</p> Full article ">Figure 5
<p>Results of mass density in the fresh state as function of the sodium content.</p> Full article ">Figure 6
<p>Results of incorporated air content as a function of the sodium content.</p> Full article ">Figure 7
<p>Results of water retention as a function of the sodium content.</p> Full article ">Figure 8
<p>(<b>a</b>) XRD; (<b>b</b>) SEM of the composition with 10% sodium.</p> Full article ">
18 pages, 10487 KiB  
Article
Improving the Autogenous Self-Sealing of Mortar: Influence of Curing Condition
by Lianwang Yuan, Min Li, Yongbo Huang, Zonghui Zhou, Congqi Luan, Zunchao Ren, Yongyi Liu, Tongtong Zhou, Xin Cheng and Jinbang Wang
Materials 2021, 14(8), 2068; https://doi.org/10.3390/ma14082068 - 20 Apr 2021
Cited by 7 | Viewed by 1904
Abstract
With the construction of projects under severe environments, new and higher requirements are put forward for the properties of concrete, especially the autogenous self-sealing property, which is greatly affected by the curing environment and the state of the water. Herein, six types of [...] Read more.
With the construction of projects under severe environments, new and higher requirements are put forward for the properties of concrete, especially the autogenous self-sealing property, which is greatly affected by the curing environment and the state of the water. Herein, six types of curing conditions, including in air with a relative humidity of 30%, 60%, and 95%; flowing water; wet-dry cycles; and static water, are designed to investigate the autogenous self-sealing of mortar under different curing conditions. The results showed that the self-sealing ratios are higher than 60% and the cracks are closed for the mortar undergoing the wet-dry cycles and the static water. However, the self-sealing ratios of mortar are lower than 10% and the cracks are almost unchanged when the mortar is cured in the air with a relative humidity (RH) of 30% and 60%. The static liquid water is more conducive to the continued hydration of cement and the formation of CaCO3 than the flowing water. The research provides guidance for the design of concrete and the improvement of autogenous self-sealing when the concrete serves in different environments. Full article
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<p>Schematic diagram of a single crack preparation: (<b>a</b>) a single crack prepared in prisms by three-point bending procedure, (<b>b</b>) a single crack prepared in cylinders by split test procedure, (<b>c</b>) a single crack prepared in cubes by split test procedure.</p> Full article ">Figure 2
<p>Schematic diagram of water permeability test.</p> Full article ">Figure 3
<p>Schematic diagram of UPV test: (<b>a</b>) equipment; (<b>b</b>) sensor location; and (<b>c</b>) the mechanism of UPV test.</p> Full article ">Figure 4
<p>Schematic diagram of ultrasonic wave test: (<b>a</b>) the transmission mechanism of ultrasonic wave in concrete, (<b>b</b>) equipment, and (<b>c</b>) the wave attenuation.</p> Full article ">Figure 5
<p>Surface cracks closure for the samples cured in different conditions.</p> Full article ">Figure 6
<p>Water permeability for the samples cured in different self-sealing conditions.</p> Full article ">Figure 7
<p>UPV for the samples with different states (DC: dry condition with 30% RH, MC: mild condition with 60% RH, HC: humid condition with &gt;95% RH, FW: flowing water condition, WD: wet-dry cycles condition, SW: static water condition. The abbreviations are the same for the figures below).</p> Full article ">Figure 8
<p>Arrival time and amplitude of head waves for the samples cured in different conditions.</p> Full article ">Figure 9
<p>Self-sealing ratios based on the arrival time (<b>a</b>) and amplitude (<b>b</b>) of head waves.</p> Full article ">Figure 10
<p>Ultrasonic waveform of samples cured in different conditions.</p> Full article ">Figure 11
<p>Self-sealing ratios based on the maximum amplitude of ultrasonic waves.</p> Full article ">Figure 12
<p>Frequency of ultrasonic waves for the samples with different states: the black, red, and blue lines belong to the uncracked, cracked, and sealed samples, respectively.</p> Full article ">Figure 13
<p>Self-sealing ratio based on the amplitude of dominant frequency.</p> Full article ">Figure 14
<p>XRD of self-sealing products for the samples cured in different conditions.</p> Full article ">Figure 15
<p>TG analysis of self-sealing products for samples cured in different conditions.</p> Full article ">Figure 16
<p>SEM of self-sealing product for samples cured in different conditions.</p> Full article ">Figure 17
<p>Mechanisms of self-sealing for samples cured in different conditions.</p> Full article ">Figure 17 Cont.
<p>Mechanisms of self-sealing for samples cured in different conditions.</p> Full article ">
9 pages, 61375 KiB  
Article
Deformation Mechanism, Microstructure, and Mechanical Properties Evolution of Mg–Gd–Y–Zr Alloy during Cold Torsion
by Hongchao Xiao, Zhengjiang Yang, Jie Li and Yingchun Wan
Materials 2021, 14(8), 2067; https://doi.org/10.3390/ma14082067 - 20 Apr 2021
Cited by 3 | Viewed by 1640
Abstract
Mg–Gd–Y–Zr alloy was subjected to torsion of various strain levels at room temperature. Obvious traces of basal slip were observed in the twisted alloy. Dislocations of <c+a> were also observed, but there were no signs of significant sliding. Even in the sample whose [...] Read more.
Mg–Gd–Y–Zr alloy was subjected to torsion of various strain levels at room temperature. Obvious traces of basal slip were observed in the twisted alloy. Dislocations of <c+a> were also observed, but there were no signs of significant sliding. Even in the sample whose equivalent strain became 0.294, 101¯0 twinning and 101¯2 twinning were rarely seen. The deformation mode with predominant basal <a> dislocations and subordinate <c+a> dislocations resulted in a modified Y fiber texture with a basal pole slightly dispersed at about 70° from the twist axis. Mechanical tests revealed that the tensile strength and compressive strengths increased simultaneously after twisting. Full article
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<p>Inverse pole figures of the twisted samples in the edge region (<b>a</b>) PT8, (<b>b</b>) PT28, (<b>c</b>) PT51.</p> Full article ">Figure 2
<p>Pole figures corresponding to the <math display="inline"><semantics> <mrow> <mfenced> <mrow> <mn>0001</mn> </mrow> </mfenced> </mrow> </semantics></math>, <math display="inline"><semantics> <mrow> <mfenced> <mrow> <mn>10</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>0</mn> </mrow> </mfenced> </mrow> </semantics></math>, and <math display="inline"><semantics> <mrow> <mfenced> <mrow> <mn>10</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>1</mn> </mrow> </mfenced> </mrow> </semantics></math> planes of the twisted samples in the edge region (<b>a</b>) PT8, (<b>b</b>) PT28, (<b>c</b>) PT51.</p> Full article ">Figure 3
<p>Local misorientation distributions of the twisted samples in the edge region (<b>a</b>) PT8, (<b>b</b>) PT28, (<b>c</b>) PT51.</p> Full article ">Figure 4
<p>Boundary distributions of the twisted samples in the edge region (<b>a</b>–<b>c</b>) PT8, (<b>d</b>–<b>f</b>) PT28, (<b>g</b>–<b>i</b>) PT51. (<b>a</b>,<b>d</b>,<b>g</b>) for 2~4°, (<b>b</b>,<b>e</b>,<b>h</b>) for 4~15°and (<b>c</b>,<b>f</b>,<b>i</b>) for tension twin and compression twin.</p> Full article ">Figure 5
<p>Transmission electron microscope image of sample PT51.</p> Full article ">Figure 6
<p>Transmission electron microscope images of sample PT51. (<b>a</b>) with a g vector of [0002], (<b>b</b>) with a g vector of <math display="inline"><semantics> <mrow> <mfenced close="]" open="["> <mrow> <mn>01</mn> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> <mn>0</mn> </mrow> </mfenced> </mrow> </semantics></math>.</p> Full article ">Figure 7
<p>Transmission electron microscope image of sample PT51.</p> Full article ">Figure 8
<p>Vickers hardness variation along the radius of the twisted samples.</p> Full article ">Figure 9
<p>Stress–strain curves of the alloys in (<b>a</b>) tensile and (<b>b</b>) compression tests.</p> Full article ">
13 pages, 2473 KiB  
Article
Improvement in the Carbonation Resistance of Construction Mortar with Cane Bagasse Fiber Added
by William A. Talavera-Pech, Diana Montiel-Rodríguez, Josefa de los A. Paat-Estrella, Ruth López-Alcántara, José T. Pérez-Quiroz and Tezozomoc Pérez-López
Materials 2021, 14(8), 2066; https://doi.org/10.3390/ma14082066 - 20 Apr 2021
Cited by 7 | Viewed by 2491
Abstract
In this work, sugarcane bagasse fiber, a waste product of agroindustry, was added to mortar mixes at different proportions looking to seal porosities so as to improve the resistance of concrete to carbonation and to improve its mechanical properties. To evaluate the behavior [...] Read more.
In this work, sugarcane bagasse fiber, a waste product of agroindustry, was added to mortar mixes at different proportions looking to seal porosities so as to improve the resistance of concrete to carbonation and to improve its mechanical properties. To evaluate the behavior of bagasse fibers in the alkaline media typical of mortars, bagasse fibers were subjected to solutions with alkaline pH values, and their chemical structure and morphological behavior was evaluated using FTIR (Fourier transform infrared spectroscopy) and SEM (Scanning Electron Microscopy). Using mortar cylinders in an accelerated carbonation chamber to obtain results in short lapses, the compressive strength and the carbonation were evaluated. The FTIR analysis results indicate that pH values of 11 and 12 causes a delignification, while at pH 9 and 10, a swelling of the molecule occurs because of the addition of hydroxyl ions, behavior that is confirmed with SEM images. A clear effect of the fiber addition on the performance of concrete was observed as the carbonation front of 35 mm for the sample without fibers was reduced to 2 mm for the sample with 2% fiber addition, resulting in an increase of 5 MPa in compressive strength. These results indicate that in the range of mortar pH, chemical changes occured over the sugarcane surface that could cause the growth of fibers and could partially seal the porosity in the mortars, thus enhancing its performance. Full article
(This article belongs to the Special Issue Sustainability in Construction and Building Materials)
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<p>(<b>a</b>) Cylinder sample for compressive resistance and (<b>b</b>) compressive resistance assay.</p> Full article ">Figure 2
<p>FTIR (Fourier transform infrared spectroscopy) spectra of the samples from the bagasse (blank) and subjected to different pH values: (<b>a</b>) 15 days of degradation and (<b>b</b>) 30 days of degradation.</p> Full article ">Figure 3
<p>Electron microscopies of the samples of bagasse: (<b>a</b>) as obtained (blank), (<b>b</b>) at pH 7 after 15 days of degradation, and at (<b>c</b>) pH 12 after 30 days of degradation.</p> Full article ">Figure 4
<p>Compressive strength as a function of time and fiber proportion.</p> Full article ">Figure 5
<p>Carbonation of concrete samples: (<b>a</b>) control, (<b>b</b>) 0.05%, (<b>c</b>) 1%, and (<b>d</b>) 2%.</p> Full article ">Figure 6
<p>Progress of carbonation for the concrete samples with different amount of fibers added: control (0%), 0.5%, 1% and 2%.</p> Full article ">
16 pages, 3131 KiB  
Article
An Insight into the Correlation between Chemical Composition Changes of Aluminum-Iron-Polyphosphate Glasses and Thermal Properties
by Pawel Goj, Aleksandra Wajda, Agata Stoch, Ireneusz Krakowiak and Pawel Stoch
Materials 2021, 14(8), 2065; https://doi.org/10.3390/ma14082065 - 20 Apr 2021
Cited by 11 | Viewed by 2372
Abstract
The present study aimed to investigate the influence of the gradual substitution of Fe2O3 by Al2O3 on the thermal properties of polyphosphate glasses. The conducted considerations based on differential scanning calorimetry (DSC) and heating microscopy thermal analysis [...] Read more.
The present study aimed to investigate the influence of the gradual substitution of Fe2O3 by Al2O3 on the thermal properties of polyphosphate glasses. The conducted considerations based on differential scanning calorimetry (DSC) and heating microscopy thermal analysis provided much essential information about the correlation between glass chemical composition and its characteristic parameters, such as transformation temperature, specific heat, crystallization temperature, crystallization enthalpy, the activation energy of crystal growth, melting temperature, and Angell glass thermal stability. The obtained estimation of viscosity changes as a function of temperature could be very helpful for researchers to correctly plan the vitrification process and thus radioactive waste immobilization. A precise analysis of DSC curves and X-ray diffraction patterns revealed the possibility of crystallization process design in order to create materials with different levels of crystallinity and phase composition. The drawn conclusions allow choosing the glass with the optimal concentration of Al2O3 and Fe2O3, which ensures the relatively low melting temperature, viscosity, and glass crystallization ability, with application potential in nuclear waste immobilization. Full article
(This article belongs to the Special Issue Advances in Glass and Glass-Ceramic Materials)
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<p>The confirmation of the amorphous nature of obtained glasses using XRD analysis.</p> Full article ">Figure 2
<p>Dependence of the glass shrinkage on temperature for the PFA1, PFA3, and PFA5 samples.</p> Full article ">Figure 3
<p>Examples of glass images at the selected temperatures for glasses: (<b>a</b>) PFA1, (<b>b</b>) PFA6.</p> Full article ">Figure 4
<p>Dependence of T<sub>S</sub> temperature on the glass composition.</p> Full article ">Figure 5
<p>DSC curves of the studied glasses.</p> Full article ">Figure 6
<p>Dependence of T<sub>g</sub> temperature on glass composition.</p> Full article ">Figure 7
<p>Dependence of T<sub>g</sub> temperature on Raman integral intensity of P-O-P bonds (the integral intensities from [<a href="#B12-materials-14-02065" class="html-bibr">12</a>]) (line for eye guides only).</p> Full article ">Figure 8
<p>Dependence of ΔC<sub>p</sub> on the glass composition (line for eye guides only).</p> Full article ">Figure 9
<p>Log total relaxation time τ versus Al<sub>2</sub>O<sub>3</sub> content (line for eye guides only).</p> Full article ">Figure 10
<p>Dependence of fragility parameter m on the glass composition.</p> Full article ">Figure 11
<p>The dependence of estimated viscosity on temperature and important technological points.</p> Full article ">Figure 12
<p>XRD analysis of the devitrified glasses.</p> Full article ">Figure 13
<p>Crystallization enthalpy (ΔH) versus Al<sub>2</sub>O<sub>3</sub> content.</p> Full article ">
21 pages, 8324 KiB  
Review
Research Status of High-Purity Metals Prepared by Zone Refining
by Liang Yu, Xiaoan Kang, Luona Chen, Kun Luo, Yanli Jiang and Xiuling Cao
Materials 2021, 14(8), 2064; https://doi.org/10.3390/ma14082064 - 20 Apr 2021
Cited by 12 | Viewed by 4592
Abstract
The zone refining method is a physical method for effectively purifying metals. Increasing yield and reducing impurity content have always been the focus of its research. This article systematically summarizes the relevant research on the production of high-purity metals by zone refining, including [...] Read more.
The zone refining method is a physical method for effectively purifying metals. Increasing yield and reducing impurity content have always been the focus of its research. This article systematically summarizes the relevant research on the production of high-purity metals by zone refining, including mechanisms, parameter optimization, zone refining types, analysis methods, limitations, and future development directions, and it provides relevant theoretical foundations for the production of high-purity metals as well. Full article
(This article belongs to the Special Issue Synthesis, Characterization, Theoretical Studies and Application of Nanofluids)
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<p>Binary system phase diagram; (<b>a</b>) <span class="html-italic">k</span><sub>0</sub> &gt; 1; (<b>b</b>) <span class="html-italic">k</span><sub>0</sub> &lt; 1.</p> Full article ">Figure 2
<p>Specific process of zone refining; (<b>a</b>) Single-pass zone refining; (<b>b</b>) Multi-pass melting zone refining.</p> Full article ">Figure 3
<p>Distribution of impurities along the ingot after the molten zone passes through the ingot; (<b>a</b>) Distribution curve of multiple zone molten impurities along the ingot when <span class="html-italic">k</span><sub>0</sub> &lt; 1; (<b>b</b>) Distribution curve of multiple zone molten impurities when <span class="html-italic">k</span><sub>0</sub> &gt; 1.</p> Full article ">Figure 4
<p>Relationship between <span class="html-italic">k<sub>eff</sub></span> and <span class="html-italic">fδ/D.</span></p> Full article ">Figure 5
<p>Relationship between impurity concentration and number of zone refining passes [<a href="#B35-materials-14-02064" class="html-bibr">35</a>].</p> Full article ">Figure 6
<p>(<b>a</b>) Optimal zone refining length of 1–10 passes; (<b>b</b>) Maximum solute removal rate during multi-pass zone refining.</p> Full article ">Figure 7
<p>Schematic diagram of the zone refining system under applied current.</p> Full article ">Figure 8
<p>(<b>a</b>) Horizontal zone refining technology; (<b>b</b>) Suspended zone refining technology.</p> Full article ">Figure 9
<p>Temperature cross-section: (<b>a</b>) SiC thermal conductor, (<b>b</b>) graphite electrothermal assembly.</p> Full article ">Figure 10
<p>Flow diagram of argon gas flow in the zone refining equipment.</p> Full article ">Figure 11
<p>Limiting distribution for the case of molten zone size <span class="html-italic">l</span> = 0.2 and impurity distribution factor (<b>a</b>) <span class="html-italic">k</span> = 2 and (<b>b</b>) <span class="html-italic">k</span> = 0.5.</p> Full article ">Figure 12
<p>Representative tree of possibilities.</p> Full article ">Figure 13
<p>(<b>a</b>) Schematic diagram of the melting zone; (<b>b</b>) Schematic diagram of the computation model.</p> Full article ">Figure 14
<p>Schematic diagram of vacuum refining-electromigration high-purity indium refining plant in multi-refining zone.</p> Full article ">Figure 15
<p>Vacuum zone refining/electromigration high-purity indium refining device designed with multiple furnace tubes.</p> Full article ">Figure 16
<p>Zone refining equipment diagram.</p> Full article ">
17 pages, 4928 KiB  
Article
An Electrochemical and Spectroscopic Study of Surfaces on Bronze Sculptures Exposed to Urban Environment
by Dajana Mikić, Helena Otmačić Ćurković, Tadeja Kosec and Neven Peko
Materials 2021, 14(8), 2063; https://doi.org/10.3390/ma14082063 - 20 Apr 2021
Cited by 7 | Viewed by 2872
Abstract
Polluted urban environment enhances dissolution of patina and underlying bronze material of recent and historical bronze sculptures exposed outdoors. In this work, two bronze statues, situated in one of the most polluted Croatian cities, were examined in order to characterize composition of patina [...] Read more.
Polluted urban environment enhances dissolution of patina and underlying bronze material of recent and historical bronze sculptures exposed outdoors. In this work, two bronze statues, situated in one of the most polluted Croatian cities, were examined in order to characterize composition of patina and its electrochemical stability. The composition of patina on several positions on each sculpture was determined by EDS, Raman spectroscopy, and FTIR measurements. Electrochemical impedance spectroscopy measurements were conducted in order to evaluate the corrosion stability of both patina and underlying bronze. Results obtained in this work show that the two examined bronze sculptures were covered with patina layer that was mainly composed of copper sulfides and sulphates, which is in accordance with the high concentrations of H2S and SO2 in the atmosphere. However, the variations in the appearance of FTIR and Raman spectra revealed that the amount of each species differed from spot to spot, as well as the fact that other compounds, such as carbonates, were present at some areas. This difference in patina composition was reflected in electrochemical behavior as observed by electrochemical impedance spectroscopy. Full article
(This article belongs to the Special Issue Surface Modification of Metallic Materials)
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<p>Sculpture <span class="html-italic">Nedovršena igra with indicated test areas 1–4</span>.</p> Full article ">Figure 2
<p>Sculpture at Memorial Cemetery with indicatedtest areas 1–3.</p> Full article ">Figure 3
<p>Optical microscopy of studied areas 1–4 on the NI sculpture, as shown in <a href="#materials-14-02063-f001" class="html-fig">Figure 1</a>.</p> Full article ">Figure 4
<p>Raman spectra collected on patina samples from NI: point 1 (<b>a</b>), point 2 (<b>b</b>), point 3 (<b>c</b>), and point 4 (<b>d</b>).</p> Full article ">Figure 5
<p>ATR-FTIR spectra collected on patina samples from NI.</p> Full article ">Figure 6
<p>Optical microscopy of studied areas 1–3 on the MC sculpture, as shown in <a href="#materials-14-02063-f002" class="html-fig">Figure 2</a>.</p> Full article ">Figure 7
<p>Raman spectra collected on patina samples from MC: position 1 (<b>a</b>), position 2 (<b>b</b>), and position 3 (<b>c</b>).</p> Full article ">Figure 8
<p>ATR-FTIR spectra collected on patina samples from MC.</p> Full article ">Figure 9
<p>Impedance spectra obtained on NI: (<b>a</b>) impedance modulus Bode plot, (<b>b</b>) phase angle Bode plot, and (<b>c</b>) Nyquist plot. Symbols represent measured and lines fitted data.</p> Full article ">Figure 10
<p>Electrical equivalent circuit used for analysis of EIS data in <a href="#materials-14-02063-f009" class="html-fig">Figure 9</a>.</p> Full article ">Figure 11
<p>Impedance spectra obtained on MC: (<b>a</b>) impedance modulus Bode plot, (<b>b</b>) phase angle Bode plot, and (<b>c</b>) Nyquist plot. Symbols represent measured and lines fitted data.</p> Full article ">Figure 11 Cont.
<p>Impedance spectra obtained on MC: (<b>a</b>) impedance modulus Bode plot, (<b>b</b>) phase angle Bode plot, and (<b>c</b>) Nyquist plot. Symbols represent measured and lines fitted data.</p> Full article ">Figure 12
<p>Electrical equivalent circuit used for analysis of EIS data in <a href="#materials-14-02063-f009" class="html-fig">Figure 9</a>.</p> Full article ">
17 pages, 7513 KiB  
Article
Milling Performance of CFRP Composite and Atomised Vegetable Oil as a Function of Fiber Orientation
by Tarek-Shaban-Mohamed Elgnemi, Martin Byung-Guk Jun, Victor Songmene and Agnes Marie Samuel
Materials 2021, 14(8), 2062; https://doi.org/10.3390/ma14082062 - 20 Apr 2021
Cited by 6 | Viewed by 2544
Abstract
Carbon fiber reinforced polymers (CFRPs) have found diverse applications in the automotive, space engineering, sporting goods, medical and military sectors. CFRP parts require limited machining such as detouring, milling and drilling to produce the shapes used, or for assembly purposes. Problems encountered while [...] Read more.
Carbon fiber reinforced polymers (CFRPs) have found diverse applications in the automotive, space engineering, sporting goods, medical and military sectors. CFRP parts require limited machining such as detouring, milling and drilling to produce the shapes used, or for assembly purposes. Problems encountered while machining CFRP include poor tool performance, dust emission, poor part edge quality and delamination. The use of oil-based metalworking fluid could help improve the machining performance for this composite, but the resulting humidity would deteriorate the structural integrity of the parts. In this work the performance of an oil-in-water emulsion, obtained using ultrasonic atomization but no surfactant, is examined during the milling of CFRP in terms of fiber orientation and milling feed rate. The performance of wet milling is compared with that of a dry milling process. The tool displacement-fiber orientation angles (TFOA) tested are 0°, 30°, 45°, 60°, and 90°. The output responses analyzed were cutting force, delamination, and tool wear. Using atomized vegetable oil helps in significantly reducing the cutting force, tool wear, and fiber delamination as compared to the dry milling condition. The machining performance was also strongly influenced by fiber orientation. The interactions between the fiber orientation, the machining parameters and the tested vegetable oil-based fluid could help in selecting appropriate cutting parameters and thus improve the machined part quality and productivity. Full article
(This article belongs to the Special Issue Composites, Alloys and Advanced Processes for Manufacturing in Aeronautics and Aerospace)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Experimental set-up consisting of a workpiece mounted on table dynamometer, end mill cutting tool and cutting fluid application nozzles.</p> Full article ">Figure 2
<p>Procedure for measuring the tool nose radius. (<b>a</b>) New tool, (<b>b</b>) worn tool for a cutting distance of 66 mm with 0° TFOA at a feed rate of 3 µm/tooth and 20,000 rpm, in the dry condition.</p> Full article ">Figure 3
<p>Schematic representation of CFRP damage measurement technique.</p> Full article ">Figure 4
<p>Fiber length measurement technique.</p> Full article ">Figure 5
<p>Schematic representation of tool displacement-fibers orientation angle.</p> Full article ">Figure 6
<p>Influence of feed rate and fiber orientation on resultant cutting forces.in the (<b>a</b>) dry, and (<b>b</b>) ACF vegetable oil conditions (at 20,000 rpm speed).</p> Full article ">Figure 7
<p>Resultant cutting forces for all fiber orientations using 3 and 6 µm/tooth feed rates and different cutting conditions. (Speed: 20,000 rpm).</p> Full article ">Figure 8
<p>Comparison of measured friction angle as a function of fiber orientation at feed rates with 3 and 6 µm/tooth and different cutting conditions (at 20,000 rpm speed).</p> Full article ">Figure 9
<p>Progression of wear after milling 66 mm at 0°, 45°, and 90° fiber oriented at feed rate 3 µm/tooth, and 20,000 rpm using (<b>a</b>) atomization-based spray and (<b>b</b>) dry milling.</p> Full article ">Figure 10
<p>Comparison of measured edge rounding radius progress for all fiber orientations at feed rates 3 and 6 µm/tooth and speed of 20,000 rpm for (<b>a</b>) dry and (<b>b</b>) ACF vegetable oil conditions.</p> Full article ">Figure 11
<p>Variation in delamination percentage with fiber orientation angle at feed rates 3 and 6 µm/tooth and different cutting fluid conditions (at 20,000 rpm speed).</p> Full article ">Figure 12
<p>SEM images used for fiber length measurements for fiber orientations θ° = 0, 45, and 90 at feed rates 3 and 6 µm/tooth and dry milling condition (at 20,000 rpm speed).</p> Full article ">Figure 13
<p>Average fiber length measurements of 0°, 45°, and 90° fiber orientations at feed rates 3 and 6 µm/tooth and dry milling condition (at 20,000 rpm speed).</p> Full article ">Figure 14
<p>SEM images of a machined surface obtained after milling 0°, 45°, and 90° TFOA (feed rate µm/tooth and speed of 20,000 rpm): (<b>a</b>) ACF vegetable oil conditions and (<b>b</b>) dry.</p> Full article ">
24 pages, 16201 KiB  
Article
Design of Center Pillar with Composite Reinforcements Using Hybrid Molding Method
by Ji-Heon Kang, Jae-Wook Lee, Jae-Hong Kim, Tae-Min Ahn and Dae-Cheol Ko
Materials 2021, 14(8), 2047; https://doi.org/10.3390/ma14082047 - 20 Apr 2021
Cited by 10 | Viewed by 5218
Abstract
Recently, with the increase in awareness about a clean environment worldwide, fuel efficiency standards are being strengthened in accordance with exhaust gas regulations. In the automotive industry, various studies are ongoing on vehicle body weight reduction to improve fuel efficiency. This study aims [...] Read more.
Recently, with the increase in awareness about a clean environment worldwide, fuel efficiency standards are being strengthened in accordance with exhaust gas regulations. In the automotive industry, various studies are ongoing on vehicle body weight reduction to improve fuel efficiency. This study aims to reduce vehicle weight by replacing the existing steel reinforcements in an automobile center pillar with a composite reinforcement. Composite materials are suitable for weight reduction because of their higher specific strength and stiffness compared to existing steel materials; however, one of the disadvantages is their high material cost. Therefore, a hybrid molding method that simultaneously performs compression and injection was proposed to reduce both process time and production cost. To replace existing steel reinforcements with composite materials, various reinforcement shapes were designed using a carbon fiber-reinforced plastic patch and glass fiber-reinforced plastic ribs. Structural analyses confirmed that, using these composite reinforcements, the same or a higher specific stiffness was achieved compared to the that of an existing center pillar using steel reinforcements. The composite reinforcements resulted in a 67.37% weight reduction compared to the steel reinforcements. In addition, a hybrid mold was designed and manufactured to implement the hybrid process. Full article
(This article belongs to the Special Issue Advances in Manufacturing Technology of Metal/Composite Hybrid Structures)
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<p>(<b>a</b>) Center pillar with steel reinforcements and (<b>b</b>) concept design of center pillar with composite reinforcements.</p> Full article ">Figure 2
<p>Schematic of hybrid molding process: (<b>a</b>) insert steel center pillar outer and CFRTP laminate; (<b>b</b>) compression molding process for CFRTP laminate and injection molding process for GFRP; (<b>c</b>) demolding process.</p> Full article ">Figure 3
<p>FE model of hot stamping process for center pillar manufacture.</p> Full article ">Figure 4
<p>Results of FE simulation for hot stamping: (<b>a</b>) thinning distribution after forming stage and (<b>b</b>) temperature distribution after quenching stage.</p> Full article ">Figure 5
<p>Determination of thickness and lay-up angle of CFRTP part: (<b>a</b>) FE model for structural analysis and (<b>b</b>) result of structural analysis for various thinness and optimized lay-up angles.</p> Full article ">Figure 6
<p>FE model of forming process of CFRTP part.</p> Full article ">Figure 7
<p>Results of FE simulation for forming process of CFRTP: (<b>a</b>) shear angle distribution and (<b>b</b>) temperature distribution.</p> Full article ">Figure 8
<p>(<b>a</b>) Available rib design area and (<b>b</b>) topology optimization analysis conditions.</p> Full article ">Figure 9
<p>Analysis model concept for topology optimization of GFRP rib: (<b>a</b>) Definition of center line using nodes and (<b>b</b>) mechanical bonding points between steel outer part and GFRP design part.</p> Full article ">Figure 10
<p>Topology optimization process for GFRP structure according to the change of constraint combinations.</p> Full article ">Figure 11
<p>GFRP rib design with topology optimization results.</p> Full article ">Figure 12
<p>Center pillar employing CFRTP and GFRP reinforcement designs: (<b>a</b>) exploded view of center pillar with composite reinforcements and (<b>b</b>) details of mechanical bonding method.</p> Full article ">Figure 13
<p>Side impact standard of Insurance Institute for Highway Safety (IIHS) [<a href="#B20-materials-14-02047" class="html-bibr">20</a>].</p> Full article ">Figure 14
<p>Position of the upper and lower bending loads applied to the center pillar analysis model.</p> Full article ">Figure 15
<p>Components of center pillar with steel reinforcements.</p> Full article ">Figure 16
<p>Material properties and application information of hot-stamped steel outer part.</p> Full article ">Figure 17
<p>Von Mises stress contour results under upper and lower bending conditions. (<b>a</b>) Upper bending load condition—Steel outer only. (<b>b</b>) Lower bending load condition—Steel outer only. (<b>c</b>) Upper bending load condition—Center pillar with steel reinforcements. (<b>d</b>) Lower bending load condition—Center pillar with steel reinforcements. (<b>e</b>) Upper bending load condition—Center pillar with composite reinforcements. (<b>f</b>) Lower bending load condition—Center pillar with composite reinforcements.</p> Full article ">Figure 17 Cont.
<p>Von Mises stress contour results under upper and lower bending conditions. (<b>a</b>) Upper bending load condition—Steel outer only. (<b>b</b>) Lower bending load condition—Steel outer only. (<b>c</b>) Upper bending load condition—Center pillar with steel reinforcements. (<b>d</b>) Lower bending load condition—Center pillar with steel reinforcements. (<b>e</b>) Upper bending load condition—Center pillar with composite reinforcements. (<b>f</b>) Lower bending load condition—Center pillar with composite reinforcements.</p> Full article ">Figure 18
<p>Tsai–Hill criterion contour results of CFRTP patch.</p> Full article ">Figure 19
<p>Details of von Mises contour results for GFRP rib part.</p> Full article ">Figure 20
<p>Maximum deformation results: (<b>a</b>) under upper bending load condition and (<b>b</b>) under lower bending load condition.</p> Full article ">Figure 21
<p>Schematic of hybrid molding machine.</p> Full article ">Figure 22
<p>Two types of injection analysis models: (<b>a</b>) direct gate type and (<b>b</b>) side gate type.</p> Full article ">Figure 23
<p>Injection analysis results for direct gate and side gate conditions: Filling time, maximum clamp force, maximum injection force and maximum inner pressure.</p> Full article ">Figure 24
<p>Design of hybrid mold structure and operation method of upper mold pins for hole machining and ejection.</p> Full article ">Figure 25
<p>Final design of the hybrid mold: (<b>a</b>) top view of upper mold, (<b>b</b>) top view of lower mold, (<b>c</b>) isometric view of upper mold, (<b>d</b>) isometric view of lower mold, and (<b>e</b>) isometric view of entire mold.</p> Full article ">
13 pages, 7176 KiB  
Article
Application of Macro-Instrumented Indentation Test for Superficial Residual Stress and Mechanical Properties Measurement for HY Steel Welded T-Joints
by Junsang Lee, Kyungyul Lee, Seungha Lee, Oh Min Kwon, Won-Ki Kang, Jong-Il Lim, Hee-Keun Lee, Seong-Min Kim and Dongil Kwon
Materials 2021, 14(8), 2061; https://doi.org/10.3390/ma14082061 - 19 Apr 2021
Cited by 16 | Viewed by 3404
Abstract
HY-80 and HY-100 steels, widely used in constructing large ocean vessels and submarine hulls, contain mixed microstructures of tempered bainite and martensite and provide high tensile strength and toughness. Weld integrity in HY steels has been studied to verify and optimize welding conditions. [...] Read more.
HY-80 and HY-100 steels, widely used in constructing large ocean vessels and submarine hulls, contain mixed microstructures of tempered bainite and martensite and provide high tensile strength and toughness. Weld integrity in HY steels has been studied to verify and optimize welding conditions. In this study, the T-joint weld coupons, HY80 and HY100, were fabricated from HY-80 and HY-100 steel plates with a thickness of 30 mm as base metals by submerged-arc welding. Flux-cored arc welding was performed on an additional welding coupon consisting of HY-100 to evaluate the effect of repair welds (HY100RP). Microstructures in the heat-affected zones (HAZ) were thoroughly analyzed by optical observation. Instrumented indentation testing, taking advantage of local characterization, was applied to assess the yield strength and the residual stress of the HAZ and base regions. The maximum hardness over 400 HV was found in the HAZ due to the high volume fraction of untempered martensite microstructure. The yield strength of the weld coupons was evaluated by indentation testing, and the results showed good agreement with the uniaxial tensile test (within 10% range). The three coupons showed similar indentation residual stress profiles on the top and bottom surfaces. The stress distribution of the HY100 coupon was comparable to the results from X-ray diffraction. HY100RP demonstrated increased tensile residual stress compared to the as-welded coupon due to the effect of the repair weld (323 and 103 MPa on the top and bottom surfaces). This study verifies the wide applicability of indentation testing in evaluating yield strength and residual stress. Full article
(This article belongs to the Special Issue Instrumented Indentation Test: An Aiding Tool for Materials Science and Industry)
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<p>Effect of residual stress on (<b>a</b>) indentation curve; schematic diagram of contact morphology in (<b>b</b>) tensile stress state; (<b>c</b>) compressive stress state.</p> Full article ">Figure 2
<p>Schematic diagram of welding coupons (<b>a</b>) HY-80 and HY-100; (<b>b</b>) HY-100 repair weld.</p> Full article ">Figure 3
<p>Instruments used: (<b>a</b>) AIS 3000-HD; (<b>b</b>) Servohydraulic Test Systems; (<b>c</b>) Xstress 3000 G2R.</p> Full article ">Figure 4
<p>Microstructure of base metals: (<b>a</b>) HY-80; (<b>b</b>) HY-100 steels.</p> Full article ">Figure 5
<p>(<b>a</b>) Hardness distribution around the fusion line; overall microstructure of (<b>b</b>) HY80; (<b>c</b>) HY100; (<b>d</b>) HY100RP.</p> Full article ">Figure 6
<p>CGHAZ, FGHAZ, and ICHAZ microstructures of (<b>a</b>–<b>c</b>) HY80; (<b>d</b>–<b>f</b>) HY100; (<b>g</b>–<b>i</b>) HY100RP.</p> Full article ">Figure 7
<p>(<b>a</b>) Yield strength results in the uniaxial tensile test and the MIIT; (<b>b</b>) indentation load–depth curves for the base region and HAZ in HY80 coupon.</p> Full article ">Figure 8
<p>Indentation loading curves of HY100 for (<b>a</b>) stress-relieved state (black), stressed state (red) (<b>b</b>) enlarged curves at the maximum indentation load.</p> Full article ">Figure 9
<p>Residual stress distribution using the MIIT and X-ray diffraction method of three coupons on (<b>a</b>) top surface (<b>b</b>) bottom surface.</p> Full article ">
13 pages, 1075 KiB  
Article
A Comparison of Accuracy of Different Dental Restorative Materials between Intraoral Scanning and Conventional Impression-Taking: An In Vitro Study
by Jung-Hwa Lim, Utkarsh Mangal, Na-Eun Nam, Sung-Hwan Choi, June-Sung Shim and Jong-Eun Kim
Materials 2021, 14(8), 2060; https://doi.org/10.3390/ma14082060 - 19 Apr 2021
Cited by 24 | Viewed by 4309
Abstract
The properties of underlying substrates influence the quality of an intraoral scan, but few studies have compared the outcomes using common restorative materials. In this study, we aimed to compare the accuracy of digital and conventional impressions recorded for four different dental materials [...] Read more.
The properties of underlying substrates influence the quality of an intraoral scan, but few studies have compared the outcomes using common restorative materials. In this study, we aimed to compare the accuracy of digital and conventional impressions recorded for four different dental materials as the substrates. Experimental crowns were produced with a metallic surface (gold or cobalt-chromium alloy (Co-Cr)) or without a metallic surface (zirconia or PMMA (polymethyl methacrylate)). A conventional impression was made in the conventional group (CON group), and gypsum models were subsequently scanned with a tabletop scanner. An intraoral scanner was used to scan the crowns either after applying a powder spray to reduce the surface reflectivity (IOS-P group) or without the powder spray (IOS group). The scans were assessed in three dimensions for precision and trueness. The accuracy did not differ between the CON and IOS groups for the non-metallic crowns. However, it was statistically different for the Co-Cr metallic crown, reducing trueness observed between groups as CON > IOS > IOS-P. The study evidences the differences in outer surface accuracy observed with a change in the substrate material to be imaged using an oral scanner and with the impression method. These findings suggest that the restoration material present in the oral cavity should be considered when selecting an impression-taking method. Full article
(This article belongs to the Special Issue State-of-the-Art Biomaterials in Korea)
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Figure 1

Figure 1
<p>Flow chart of the study design for comparing accuracies between the two impression-taking protocols. Eight impressions were recorded for each material in accordance with the methodology of each group. CAD, computer-aided design; CAM, computer-aided manufacturing; CON, conventional; IOS, intraoral scan; and IOS-P, intraoral scan with powder.</p> Full article ">Figure 2
<p>Comparison of non-metallic restorative materials using different impression-taking protocols. (<b>A</b>) Precision; (<b>B</b>) trueness. Different uppercase letters indicate significant differences between groups within a category on the x-axis. Different lower-case letters indicate significant differences between two materials for the same impression-taking protocol. Each box plot shows the median, first and third quartiles, and range. CON, conventional; IOS, intraoral scan; and IOS-P, intraoral scan with powder.</p> Full article ">Figure 3
<p>Comparison of metallic restorative materials using different impression-taking protocols. (<b>A</b>) Precision; (<b>B</b>) trueness. Different uppercase letters indicate significant differences between groups within a category on the x-axis. Different lower-case letters indicate significant differences between two materials for the same impression-taking protocol. Each box plot shows the median, first and third quartiles, and range. CON, conventional; IOS, intraoral scan; and IOS-P, intraoral scan with powder.</p> Full article ">Figure 4
<p>(<b>A</b>) Trueness comparison between different restorative materials using the intraoral digital impression-taking protocol. The asterisk indicates a significant difference from the other groups (<span class="html-italic">p</span> &lt; 0.05); (<b>B</b>) Color maps showing the outcome of morphometric comparison, with positive deviations (larger than reference) and negative deviation (smaller than reference) between the materials for the different crown surfaces.</p> Full article ">
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