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Materials, Volume 15, Issue 17 (September-1 2022) – 383 articles

Cover Story (view full-size image): Peptide-based hydrogels have attracted increasing attention for biological applications and diagnostic research due to their impressive features, including biocompatibility, biodegradability, injectability, mechanical stability, high water absorption capacity, and tissue-like elasticity. Such properties are extremely interesting for biomedical applications, such as drug delivery and tissue engineering. Recently, in the literature, many papers have focused their attention on peptide-based hydrogels, especially in the field of anticancer drug delivery, antimicrobial and wound healing materials, 3D bioprinting, tissue engineering, and vaccines. Moreover, some hydrogel-based materials possess the very intriguing ability to function as biosensing tools, receiving attention for cancer detection purposes. View this paper
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32 pages, 3128 KiB  
Review
Lignin as a Renewable Building Block for Sustainable Polyurethanes
by Fernanda Rosa Vieira, Sandra Magina, Dmitry V. Evtuguin and Ana Barros-Timmons
Materials 2022, 15(17), 6182; https://doi.org/10.3390/ma15176182 - 5 Sep 2022
Cited by 35 | Viewed by 6491
Abstract
Currently, the pulp and paper industry generates around 50–70 million tons of lignin annually, which is mainly burned for energy recovery. Lignin, being a natural aromatic polymer rich in functional hydroxyl groups, has been drawing the interest of academia and industry for its [...] Read more.
Currently, the pulp and paper industry generates around 50–70 million tons of lignin annually, which is mainly burned for energy recovery. Lignin, being a natural aromatic polymer rich in functional hydroxyl groups, has been drawing the interest of academia and industry for its valorization, especially for the development of polymeric materials. Among the different types of polymers that can be derived from lignin, polyurethanes (PUs) are amid the most important ones, especially due to their wide range of applications. This review encompasses available technologies to isolate lignin from pulping processes, the main approaches to convert solid lignin into a liquid polyol to produce bio-based polyurethanes, the challenges involving its characterization, and the current technology assessment. Despite the fact that PUs derived from bio-based polyols, such as lignin, are important in contributing to the circular economy, the use of isocyanate is a major environmental hot spot. Therefore, the main strategies that have been used to replace isocyanates to produce non-isocyanate polyurethanes (NIPUs) derived from lignin are also discussed. Full article
(This article belongs to the Special Issue Synthesis and Application of New Lignin-Based Polymers and Composites)
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Figure 1
<p>Schematic representation of the reaction between a polyol and a diisocyanate to form the urethane linkage.</p> Full article ">Figure 2
<p>Polyurethane products from lignin-based polyol (LBP).</p> Full article ">Figure 3
<p>Lignin as a renewable building block to produce sustainable polyurethanes.</p> Full article ">Figure 4
<p>Example of hardwood lignin structure representation [<a href="#B30-materials-15-06182" class="html-bibr">30</a>].</p> Full article ">Figure 5
<p>(<b>Left</b>) LignoBoost process; (<b>right</b>) LignoForce<sup>TM</sup> [<a href="#B45-materials-15-06182" class="html-bibr">45</a>].</p> Full article ">Figure 6
<p>Scheme of oxypropylation reaction of biomass with PO [<a href="#B18-materials-15-06182" class="html-bibr">18</a>].</p> Full article ">Figure 7
<p>Scheme of oxypropylation of lignin with PC [<a href="#B18-materials-15-06182" class="html-bibr">18</a>].</p> Full article ">Figure 8
<p>Proposed reaction scheme of lignin with glycerol during wood liquefaction using PTSA (ρ-toluene sulfonic acid) as a catalyst based on carbon assignments, adapted from [<a href="#B81-materials-15-06182" class="html-bibr">81</a>].</p> Full article ">Figure 9
<p>Scheme of the general formula of polyol, adapted from [<a href="#B2-materials-15-06182" class="html-bibr">2</a>].</p> Full article ">Figure 10
<p>Chemical routes to produce PU by (<b>a</b>) conventional route, NIPU by (<b>b</b>) polycondensation, and (<b>c</b>) polyaddition.</p> Full article ">Figure 11
<p>Strategy for the functionalization of kraft lignin to produce NIPU [<a href="#B192-materials-15-06182" class="html-bibr">192</a>].</p> Full article ">Figure 12
<p>Summary of lignin-based polyurethane patents from 2013 to June 2022 obtained at the WIPO.</p> Full article ">
11 pages, 3825 KiB  
Article
Effect of Multi-Walled Carbon Nanotubes and Carbon Fiber Reinforcements on the Mechanical and Tribological Behavior of Hybrid Mg-AZ91D Nanocomposites
by G. U. Raju, Vinod Kumar V. Meti, N. R. Banapurmath, T. M. Yunus Khan, I. G. Siddhalingeshwar, Vishal Vaikunte, Chandramouli Vadlamudi, Sanjay Krishnappa, A. M. Sajjan and Adarsh Patil
Materials 2022, 15(17), 6181; https://doi.org/10.3390/ma15176181 - 5 Sep 2022
Cited by 8 | Viewed by 2181
Abstract
Magnesium matrix composites are extensively used in automotive and structural applications due to their low density, high strength, and wear-resistant properties. To reach the scope of industry needs, research is carried out regarding enhancing the mechanical and tribological behavior of the magnesium composites [...] Read more.
Magnesium matrix composites are extensively used in automotive and structural applications due to their low density, high strength, and wear-resistant properties. To reach the scope of industry needs, research is carried out regarding enhancing the mechanical and tribological behavior of the magnesium composites by reinforcing the nano-sized reinforcements. In the present work, research has been carried out to enhance the properties of the magnesium AZ91D hybrid composite by reinforcing carbon fibers (CFs) and multi-walled carbon nanotubes (MWCNTs) with varying weight percentages (AZ91D + 0.5% CF’s + 0.5% MWCNT and AZ91D + 0.75% CF’s + 0.75% MWCNT, respectively). The experimental tests were carried out to evaluate the mechanical and tribological behavior of the composites. The test results showed that the addition of CF and MWCNT reinforcements improved the hybrid Mg composite’s hardness, tensile strength, and impact strength compared to the base Mg matrix. The AZ91D + 0.75% CF’s + 0.75% MWCNT hybrid composite showed a 19%, 35%, and 66% increased hardness, tensile strength, and impact strength, respectively, compared to the base Mg AZ91D. The wear test results also showed the improved wear resistance of the Mg composite compared to the base matrix. The enhanced wear resistance of the composite is due to the addition of hard MWCNT and CF reinforcements. The wear rate of the AZ91D + 0.75%CF’s + 0.75% MWCNT composite for a load of 30 N at a sliding distance of 1500 m is lower as compared to the base matrix. The SEM micrographs of the worn surfaces revealed the existence of abrasive wear. The improved mechanical and tribological behavior of the magnesium composite is also due to the homogeneous distribution of the hard reinforcement particles along the grain boundaries. Full article
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<p>Sample of nano reinforcements; (<b>a</b>) carbon fibers and (<b>b</b>) MWCNT.</p> Full article ">Figure 2
<p>Mechanical characterization as ASTM standards used: (<b>a</b>) hardness test specimen dimension [ASTM E92-82]; (<b>b</b>) tensile test sample dimension [ASTM E8]; (<b>c</b>) wear test specimen dimension [ASTM G99]; (<b>d</b>) impact test sample dimension [ASTM E23-16a].</p> Full article ">Figure 3
<p>SEM micrographs of AZ91D composite with varying weight percentages of CF and MWCNT reinforcements. (<b>a</b>,<b>b</b>): AZ91D + 0.5% CF’s + 0.5% MWCNT composite and (<b>c</b>,<b>d</b>): AZ91D + 0.75% CF’s + 0.75% MWCNT composite.</p> Full article ">Figure 4
<p>Variation of Vickers hardness number in the Mg AZ91D hybrid composite with varying weight percentages of CF and MWCNT reinforcements.</p> Full article ">Figure 5
<p>(<b>a</b>) Variation of yield strength, ultimate tensile strength, and elongation of Mg AZ91D hybrid composite with varying weight percentages of CF and MWCNT reinforcements; (<b>b</b>) stress–strain curves of all composites.</p> Full article ">Figure 6
<p>The analysis of the tensile strength of the AZ91D composite reinforced with CF and MWCNT reinforcements. (<b>a</b>,<b>b</b>): AZ91D + 0.5% CF’s + 0.5% MWCNT composite and (<b>c</b>,<b>d</b>): AZ91D + 0.75% CF’s + 0.75% MWCNT composite.</p> Full article ">Figure 7
<p>Variation of impact strength of Mg AZ91D hybrid composite with varying weight percentages of CF and MWCNT reinforcements.</p> Full article ">Figure 8
<p>Wear rate of the Mg AZ91D hybrid composite with varying weight percentages of CF and MWCNT reinforcements.</p> Full article ">Figure 9
<p>SEM micrographs of the worn surfaces of the Mg AZ91D hybrid composites (<b>a</b>) AZ91D + 0.5% CFs + 0.5% MWCNT composite with magnification 10.00 KX; (<b>b</b>) AZ91D + 0.5% CFs + 0.5% MWCNT composite with magnification 5.00 KX; (<b>c</b>) AZ91D + 0.75% CF’s + 0.75% MWCNT composite with magnification 10.00 KX; and (<b>d</b>) AZ91D + 0.75% CF’s + 0.75% MWCNT composite with magnification 5.00 KX.</p> Full article ">Figure 10
<p>SEM-EDS analysis of the worn surfaces of the Mg AZ91D hybrid composite with varying weight percentages of CF and MWCNT reinforcements. (<b>a</b>): AZ91D + 0.5% CFs + 0.5% MWCNT composite; (<b>b</b>): AZ91D + 0.75% CFs + 0.75% MWCNT composite.</p> Full article ">Figure 11
<p>EDS analysis (<b>a</b>) depicts the presence of carbon (from CFs and CNTs) and oxygen, and (<b>b</b>) depicts other metals, such as Mg and Al.</p> Full article ">
15 pages, 2829 KiB  
Article
Effect of the Composition of Hybrid Sands on the Change in Thermal Expansion
by Filip Radkovský, Martina Gawronová, Václav Merta, Petr Lichý, Ivana Kroupová, Isabel Nguyenová, Šimon Kielar, Martin Folta, Josef Bradáč and Radim Kocich
Materials 2022, 15(17), 6180; https://doi.org/10.3390/ma15176180 - 5 Sep 2022
Cited by 5 | Viewed by 2123
Abstract
In the foundry industry, silica sands are the most commonly used type of sands for the production of sand foundry moulds using various types of binders. Their greatest disadvantage is their significant volume changes at elevated temperatures, which are associated with the formation [...] Read more.
In the foundry industry, silica sands are the most commonly used type of sands for the production of sand foundry moulds using various types of binders. Their greatest disadvantage is their significant volume changes at elevated temperatures, which are associated with the formation of many foundry defects from stress, such as veining, and thus have a direct influence on the final quality of the casting. In the case of non-silica sands and synthetic sands, the volume stability is more pronounced, but this is accompanied by a higher purchase price. Therefore, a combination of silica sand and synthetic sand CERABEADS is considered in order to influence and reduce the thermal expansion. The hybrid mixtures of sands, and their most suitable ratios, were evaluated in detail using sieve analysis, log W and cumulative curve of granularity. It was found that the addition of 50% CERABEADS achieves a 32.2% reduction in dilatation but may increase the risk of higher stresses. The measurements showed a significant effect of the granulometric composition of the sand on the resulting thermal expansion, where the choice of grain size and sorting can achieve a significant reduction in dilatation with a small addition of CERABEADS. Full article
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<p>Detailed view of the sands used captured on a Keyence VHX 6000 digital microscope: (<b>a</b>) silica sand BG 27, (<b>b</b>) NCB 650, (<b>c</b>) NCB 950, (<b>d</b>) NCB 1450.</p> Full article ">Figure 2
<p>The trend of bulk density of hybrid mixtures as a function of CERABEADS content and its mean grain size.</p> Full article ">Figure 3
<p>Cumulative curves of granularity for all pure and hybrid sands with various NCB contents.</p> Full article ">Figure 4
<p>Detailed cumulative curves of granularity for individual NCB types compared with BG 27 100%: (<b>a</b>) 100% content of all sands. (<b>b</b>) NCB 650 addition. (<b>c</b>) NCB 950 addition. (<b>d</b>) NCB 1450 addition.</p> Full article ">Figure 5
<p>Dilatation curves for: (<b>a</b>) original silica and NCB sands in 100% content, (<b>b</b>) all tested pure and hybrid sand mixtures with various NCB contents.</p> Full article ">Figure 6
<p>Detailed dilatation curves for individual NCB types compared with BG 27 100%: (<b>a</b>) NCB 650 hybrid sands, (<b>b</b>) NCB 950 hybrid sands, (<b>c</b>) NCB 1450 hybrid sands.</p> Full article ">Figure 7
<p>Comparison of thermal expansion coefficient of tested hybrid sands.</p> Full article ">
12 pages, 3907 KiB  
Communication
Effects of Endic Anhydride Grafted PPC on the Properties of PHBV Blends
by Qing Zhang, Yongguang Gao, Huiyuan Liu, Shili Shu and Wei Chen
Materials 2022, 15(17), 6179; https://doi.org/10.3390/ma15176179 - 5 Sep 2022
Cited by 3 | Viewed by 1839
Abstract
Poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PHBV) was modified with endic anhydride grafted poly(propylene carbonate) (EA–PPC), and then PHBV/EA–PPC composite polymers were prepared by melt blending under the catalysis of stannous octoate (Sn(Oct)2). The blends were characterized by an electronic universal testing machine, cantilever [...] Read more.
Poly(β-hydroxybutyrate-co-β-hydroxyvalerate) (PHBV) was modified with endic anhydride grafted poly(propylene carbonate) (EA–PPC), and then PHBV/EA–PPC composite polymers were prepared by melt blending under the catalysis of stannous octoate (Sn(Oct)2). The blends were characterized by an electronic universal testing machine, cantilever impact testing machine, and differential scanning calorimeter (DSC), as well as dynamic mechanical analysis (DMA) and field emission scanning electron microscopy (FESEM). Effects of the amount of Sn(Oct)2 on the mechanical properties, thermal properties, and morphology of the blends were discussed. The results showed that the addition of Sn(Oct)2 promoted the transesterification reaction between PHBV and EA–PPC, and the compatibility between PHBV and PPC was greatly improved. When the amount of Sn(Oct)2 was 3 wt%, the impact strength and elongation at break of the PHBV/EA–PPC blend increased from 3.7 kJ/m2 and 4.1% to 5.9 kJ/m2 and 387.5%, respectively, and there was no significant decrease in tensile strength. Additionally, four esterification reaction mechanisms for PHBV/EA–PPC blends were proposed. Full article
(This article belongs to the Special Issue Development and Application of Functional Polymer Materials)
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Figure 1
<p>TGA curves of PPC and EA–PPC.</p> Full article ">Figure 2
<p>Mechanical properties of PHBV/EA–PPC blends: (<b>a</b>) tensile strength, (<b>b</b>) impact strength, and (<b>c</b>) elongation at break.</p> Full article ">Figure 3
<p>DSC curves of neat PHBV, EA–PPC, and PHBV/EA–PPC blends with various amounts of Sn(Oct)<sub>2</sub>: (<b>a</b>) cooling, (<b>b</b>) the second heating.</p> Full article ">Figure 4
<p>DMA of neat polymers (<b>a</b>) and PHBV/EA–PPC blends (<b>b</b>).</p> Full article ">Figure 5
<p>SEM micrographs of tensile-fractured surfaces: (<b>a</b>) P70/EP30 and (<b>b</b>) P70/EP30/S3 blends.</p> Full article ">Figure 6
<p>Formation mechanism of PHBV/EA–PPC blends. (<b>i</b>) terminal hydroxyl group of PHBV attacked carbonyl carbon of EA–PPC, (<b>ii</b>) terminal carboxyl group of PHBV attacked carbonyl carbon of EA–PPC, (<b>iii</b>) terminal carboxyl group of EA–PPC attacked carbonyl carbon of PHBV, (<b>iv</b>) direct transesterification.</p> Full article ">Scheme 1
<p>Structures of (<b>a</b>) PHBV and (<b>b</b>) PPC.</p> Full article ">Scheme 2
<p>End-capping of PPC with EA.</p> Full article ">
11 pages, 10076 KiB  
Article
Controlling the Surface Morphology of ZnO Nano-Thin Film Using the Spin Coating Technique
by I. A. Elsayed and Ahmed S. Afify
Materials 2022, 15(17), 6178; https://doi.org/10.3390/ma15176178 - 5 Sep 2022
Cited by 9 | Viewed by 2432
Abstract
Zinc oxide (ZnO) thin films are significant in various electronic applications. This study introduced an efficient, simple, low cost and timesaving method to obtain an extended and uniform ZnO thin film with tunable surface morphology over the substrate using the spin coating technique. [...] Read more.
Zinc oxide (ZnO) thin films are significant in various electronic applications. This study introduced an efficient, simple, low cost and timesaving method to obtain an extended and uniform ZnO thin film with tunable surface morphology over the substrate using the spin coating technique. Different concentrations of zinc acetate dehydrate were used as precursor solutions mixed with polyvinyl alcohol as a binding polymer to obtain the film’s uniformity and to relieve thermal expansion that may cause a wrinkled surface. Synthesized films were characterized using X-ray diffraction (XRD), X-ray spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM) and ellipsometry. Findings show that the average size of ZnO particles was less than 50 nm in a uniform film over the whole substrate area regardless of the presence or absence of wrinkles. Additionally, this method was quite fast, attaining the desired viscosity in less than one hour in comparison with the time-consuming aging method, which requires approximately 24 h to achieve the required viscosity. Full article
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<p>XRD pattern of annealed ZnO film.</p> Full article ">Figure 2
<p>Overview spectrum of 0.5 M ZnO film with 1 eV resolution.</p> Full article ">Figure 3
<p>High resolution of XPS core level spectra of (<b>a</b>) O1s solid line: raw data, dotted line: fitting and (<b>b</b>) Zn2p.</p> Full article ">Figure 4
<p>SEM images of (<b>a</b>,<b>b</b>) 0.5 M RT film, dried and thermally dried, respectively, and (<b>c</b>,<b>d</b>) 1.0 M RT film, dried and thermally dried, respectively.</p> Full article ">Figure 5
<p>SEM images of (<b>a</b>,<b>b</b>) 0.5 M film, with and without wrinkles, and (<b>c</b>,<b>d</b>) 1 M film, with and without wrinkles.</p> Full article ">Figure 6
<p>SEM images of ZnO films coated at different spinning speeds: (<b>a</b>) 2000 rpm, (<b>b</b>) 2500 rpm, (<b>c</b>) 3000 rpm and (<b>d</b>) 3500 rpm.</p> Full article ">Figure 7
<p>SEM image of ZnO film coated at 3500 rpm.</p> Full article ">Figure 8
<p>(<b>a</b>–<b>d</b>) AFM images for the same films previous used for SEM imaging.</p> Full article ">Figure 9
<p>Three-dimensional AFM images of ZnO films coated at different spinning speeds: (<b>a</b>) 2000 rpm, (<b>b</b>) 2500 rpm, (<b>c</b>) 3000 rpm and (<b>d</b>) 3500 rpm.</p> Full article ">Figure 10
<p>Three-dimensional AFM image of nanostructured ZnO film.</p> Full article ">Figure 11
<p>Fitting of measured data for ellipsometric parameters Ψ and Δ for sample spinning speed of 3500 rpm using variable angle spectroscopic ellipsometric (VASE) data where the red line is the measured and the green line is the fitted.</p> Full article ">
20 pages, 4686 KiB  
Article
Meshless Chebyshev RPIM Solution for Free Vibration of Rotating Cross-Ply Laminated Combined Cylindrical-Conical Shells in Thermal Environment
by Zhen Li, Shuangwei Hu, Rui Zhong, Bin Qin and Xing Zhao
Materials 2022, 15(17), 6177; https://doi.org/10.3390/ma15176177 - 5 Sep 2022
Cited by 7 | Viewed by 1857
Abstract
This paper provides a numerical solution to the vibration of a rotating cross-ply laminated combined conical-cylindrical shell in the thermal environment. Its numerical discrete solution method uses the meshless method. The combined shell assumed the temperature independence of material property is divided to [...] Read more.
This paper provides a numerical solution to the vibration of a rotating cross-ply laminated combined conical-cylindrical shell in the thermal environment. Its numerical discrete solution method uses the meshless method. The combined shell assumed the temperature independence of material property is divided to the fundamental conical and cylindrical shell substructures, and the theoretical formulation for each substructure is derived based on the first order shear deformation theory (FSDT) and Hamilton’s principle. The effects of the initial hoop tension and temperature change are considered through the kinetic energy reflecting the effects of centrifugal and Coriolis forces and additional strain energy by the nonlinear part of the Green–Lagrange strains. The substructures are then assembled according to the continuity conditions. The boundary and continuity conditions are simulated by introducing artificial virtual spring technology. The displacement component in the theoretical formulation is approximated using a meshless Chebyshev-RPIM shape function. The reliability of the method is verified by comparing with mature and reliable results. The free vibration characteristics of the rotating combined conical-cylindrical shell structure under various sizes, speeds and temperatures are given by numerical examples. Full article
(This article belongs to the Special Issue Characterisation and Modelling of Manufacturing–Microstructure–Property–Mechanism Relationship for Advanced and Emerging Materials)
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<p>Geometry of rotating cross-ply combined conical-cylindrical shell in thermal environment.</p> Full article ">Figure 2
<p>Mode shapes of laminated combined conical-cylindrical shell with CC boundary condition (<span class="html-italic">m</span> = 1, <span class="html-italic">φ</span> = <span class="html-italic">π</span>/6) (<b>a</b>) ABAQUS (<b>b</b>) Present.</p> Full article ">Figure 3
<p>Mode shapes of laminated combined conical-cylindrical shell with FC boundary condition (<span class="html-italic">m</span> = 1, <span class="html-italic">φ</span> = <span class="html-italic">π</span>/4) (<b>a</b>) ABAQUS (<b>b</b>) Present.</p> Full article ">Figure 3 Cont.
<p>Mode shapes of laminated combined conical-cylindrical shell with FC boundary condition (<span class="html-italic">m</span> = 1, <span class="html-italic">φ</span> = <span class="html-italic">π</span>/4) (<b>a</b>) ABAQUS (<b>b</b>) Present.</p> Full article ">Figure 4
<p>Variation of dimensionless frequencies <math display="inline"><semantics> <mrow> <msup> <mi>ω</mi> <mo>*</mo> </msup> </mrow> </semantics></math> of rotating laminated combined conical-cylindrical shell with different semi-vertex angle (<span class="html-italic">m</span> = 1).</p> Full article ">Figure 5
<p>Variation of dimensionless frequencies <math display="inline"><semantics> <mrow> <msup> <mi>ω</mi> <mo>*</mo> </msup> </mrow> </semantics></math> of non-rotating laminated combined conical-cylindrical shell subjected to thermal effect (<span class="html-italic">m</span> = 1).</p> Full article ">Figure 6
<p>Variation of dimensionless frequencies <math display="inline"><semantics> <mrow> <msup> <mi>ω</mi> <mo>*</mo> </msup> </mrow> </semantics></math> of rotating laminated combined conical-cylindrical shell in the thermal environment.</p> Full article ">
17 pages, 6349 KiB  
Article
The Transverse Bearing Characteristics of the Pile Foundation in a Calcareous Sand Area
by Haibo Hu, Lina Luo, Gang Lei, Jin Guo, Shaoheng He, Xunjian Hu, Panpan Guo and Xiaonan Gong
Materials 2022, 15(17), 6176; https://doi.org/10.3390/ma15176176 - 5 Sep 2022
Cited by 2 | Viewed by 2107
Abstract
Reviewing literature revealed that the studies on the bearing characteristics of pile foundations mainly focuses on clay, ordinary sand, loess, saline soil, and other areas. However, few studies on the bearing characteristics of the pile foundation in calcareous sand were conducted. Besides, existing [...] Read more.
Reviewing literature revealed that the studies on the bearing characteristics of pile foundations mainly focuses on clay, ordinary sand, loess, saline soil, and other areas. However, few studies on the bearing characteristics of the pile foundation in calcareous sand were conducted. Besides, existing traditional studies ignored the variation of soil compression modulus with depth, and the effect of void ratio on the transverse bearing characteristics of the pile foundation in a calcareous sand area were not well understood. In response of these problems, this study conducted a theoretical investigation on the transverse bearing characteristics of the pile foundation in a calcareous sand area. The transverse bearing characteristics of the pile foundation were derived based on the Pasternak foundation model and the Winkler foundation model, incorporating the heterogeneous distribution of compressive modulus with buried depth. The calculation results of the Pasternak foundation model are closer to the observed results than the Winkler foundation model. Therefore, the following research on the transverse bearing characteristics of the pile foundation in the calcareous sand area adopts the Pasternak foundation model. Then, the effects of the pile length, pile diameter, pile elastic modulus, horizontal load, bending moment, and void ratio on the transverse bearing characteristics of the pile foundation in a calcareous sand area were thoroughly analyzed. Furthermore, the difference between the transverse bearing characteristics of the pile foundation in a calcareous sand area and a quartz sand area was discussed. Results show that the horizontal displacement of the pile top in a calcareous sand area is greater than the quartz sand area under the same conditions. Full article
(This article belongs to the Topic New Trends in Rock Materials Mechanics and Engineering Geology)
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<p>Pasternak foundation model.</p> Full article ">Figure 2
<p>Discrete analysis model of pile.</p> Full article ">Figure 3
<p>Comparison of horizontal displacement of pile body.</p> Full article ">Figure 4
<p>Correlation between compressive modulus and confining pressure.</p> Full article ">Figure 5
<p>Horizontal displacement of pile body.</p> Full article ">Figure 6
<p>Effect of pile length on horizontal displacement of pile body in calcareous sand area.</p> Full article ">Figure 7
<p>Effect of pile diameter on horizontal displacement of pile body in calcareous sand area.</p> Full article ">Figure 8
<p>Effect of elastic modulus of pile on horizontal displacement of pile in calcareous sand area.</p> Full article ">Figure 9
<p>Effect of horizontal load on horizontal displacement of pile in calcareous sand area.</p> Full article ">Figure 10
<p>Effect of bending moment on horizontal displacement of pile in calcareous sand area.</p> Full article ">Figure 11
<p>Effect of void ratio on horizontal displacement of pile in calcareous sand area.</p> Full article ">Figure 12
<p>Effect of pile length on horizontal displacement of pile body. (<b>a</b>) L; (<b>b</b>) 2L; (<b>c</b>) 3L.</p> Full article ">Figure 13
<p>Effect of pile diameter on horizontal displacement of pile body. (<b>a</b>) D; (<b>b</b>) 2D; (<b>c</b>) 3D.</p> Full article ">Figure 13 Cont.
<p>Effect of pile diameter on horizontal displacement of pile body. (<b>a</b>) D; (<b>b</b>) 2D; (<b>c</b>) 3D.</p> Full article ">Figure 14
<p>Effect of elastic modulus of pile on horizontal displacement of pile. (<b>a</b>) E; (<b>b</b>) 2E; (<b>c</b>) 3E.</p> Full article ">Figure 15
<p>Effect of horizontal load on horizontal displacement of pile. (<b>a</b>) H; (<b>b</b>) 2H; (<b>c</b>) 3H.</p> Full article ">Figure 16
<p>Effect of bending moment on horizontal displacement of pile. (<b>a</b>) M; (<b>b</b>) 2M; (<b>c</b>) 3M.</p> Full article ">Figure 17
<p>Effect of void ratio on horizontal displacement of pile. (<b>a</b>) e; (<b>b</b>) 1.1e; (<b>c</b>) 1.2e.</p> Full article ">Figure 17 Cont.
<p>Effect of void ratio on horizontal displacement of pile. (<b>a</b>) e; (<b>b</b>) 1.1e; (<b>c</b>) 1.2e.</p> Full article ">
12 pages, 5196 KiB  
Article
Electrochemical Impedance Investigation of Dye-Sensitized Solar Cells Based on Electrospun TiO2 Nanofibers Photoanodes
by Hany M. Abd El-Lateef, Mai M. Khalaf, Van-Duong Dao and Ibrahim M. A. Mohamed
Materials 2022, 15(17), 6175; https://doi.org/10.3390/ma15176175 - 5 Sep 2022
Cited by 10 | Viewed by 2213
Abstract
This work investigates an electrochemical impedance analysis based on synthesized TiO2 nanofibers (NFs) photoanodes, which were fabricated via electrospinning and calcination. The investigated photoanode substrate NFs were studied in terms of physicochemical tools to investigate their morphological character, crystallinity, and chemical contents [...] Read more.
This work investigates an electrochemical impedance analysis based on synthesized TiO2 nanofibers (NFs) photoanodes, which were fabricated via electrospinning and calcination. The investigated photoanode substrate NFs were studied in terms of physicochemical tools to investigate their morphological character, crystallinity, and chemical contents via scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD) analyses. As a result, the studied photoanode substrate NFs were applied to fabricate dye-sensitized solar cells (DSCs), and the electrochemical impedance analysis (EIS) was studied in terms of equivalent circuit fitting and impacts of N-doping, the latter of which was approved via XPS analysis. N-doping has a considerable role in the enhancement of charge transfers, which could be due to the strong interactions between active-site N atoms and the used photosensitizer. Full article
(This article belongs to the Special Issue Development of Nano-Materials for Catalytic and Biomedical Applications)
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<p>Schematic diagram of the fabricated solar cell based on the synthesized nanofibers.</p> Full article ">Figure 2
<p>(<b>A</b>) SEM image of the prepared Titania; (<b>B</b>) SEM image of N-Titania; (<b>C</b>) TEM image of the prepared Titania; (<b>D</b>) TEM image of the prepared N-Titania.</p> Full article ">Figure 3
<p>XRD analysis of Titania and N-Titania in addition to the locations of JCPDS card No. 21-1272. The inset figure is an overlay of the 25.05 peaks for TiO<sub>2</sub> and N-TiO<sub>2</sub> to better visualize the line broadening.</p> Full article ">Figure 4
<p>(<b>A</b>) XPS analysis of N-Titania; (<b>B</b>) XPS fine spectrum of the N-Titania in the region of nitrogen.</p> Full article ">Figure 5
<p>EIS analyses of DSCs using the prepared TiO<sub>2</sub> NFs, including experimental data and their fitting by (<b>A</b>) EQ1; (<b>B</b>) EQ2; (<b>C</b>) EQ3; (<b>D</b>) utilized equivalent circuits.</p> Full article ">Figure 6
<p>(<b>A</b>) Bode phase and total impedance data; (<b>B</b>) the estimated R<sub>s</sub> and R<sub>ct</sub> errors (%).</p> Full article ">Figure 7
<p>EIS analyses of DSCs using the prepared N-TiO<sub>2</sub> NFs, including experimental data and their fitting by (<b>A</b>) EQ1; (<b>B</b>) EQ2; (<b>C</b>) EQ3; (<b>D</b>) total impedance and bode phase data before and after equivalent circuit fitting.</p> Full article ">Figure 8
<p>(<b>A</b>) EIS analyses of DSCs without and after N-doping of TiO<sub>2</sub> photoanode; (<b>B</b>) Bode phase and total impedance data N-doping of TiO<sub>2</sub> photoanode.</p> Full article ">
14 pages, 3146 KiB  
Article
Iodine-Doped Graphene Oxide: Fast Single-Stage Synthesis and Application as Electrocatalyst
by Adriana Marinoiu, Daniela Ion-Ebrasu, Amalia Soare and Mircea Raceanu
Materials 2022, 15(17), 6174; https://doi.org/10.3390/ma15176174 - 5 Sep 2022
Cited by 4 | Viewed by 2582
Abstract
Iodine-doped graphene oxide is attracting great attention as fuel cell (FC) electrocatalysts with a high activity for the oxygen reduction reaction (ORR). However, most of the reported preparation techniques for iodine-doped graphene (I/rGO) could be transposed into practice as multiple step procedures, a [...] Read more.
Iodine-doped graphene oxide is attracting great attention as fuel cell (FC) electrocatalysts with a high activity for the oxygen reduction reaction (ORR). However, most of the reported preparation techniques for iodine-doped graphene (I/rGO) could be transposed into practice as multiple step procedures, a significant disadvantage for scale-up applications. Herein, we describe an effective, eco-friendly, and fast technique for synthesis by a microwave-tuned one-stage technique. Structural and morphological characterizations evidenced the obtaining of nanocomposite sheets, with iodine bonded in the graphene matrix. The ORR performance of I/rGO was electrochemically investigated and the enhancement of the cathodic peak was noted. Based on the noteworthy electrochemical properties for ORR activity, the prepared I/rGO can be considered an encouraging alternative for a more economical electrode for fuel cell fabrication and commercialization. In this perspective, the iodine-based catalysts synthesis can be considered a step forward for the metal-free electrocatalysts development for the oxygen reduction reaction in fuel cells. Full article
(This article belongs to the Special Issue Materials for Electrochemical Energy Systems)
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Full article ">Figure 1
<p>SEM microstructure and energy dispersive X-ray spectroscopy spectrum of prepared I-doped graphene oxide.</p> Full article ">Figure 2
<p>Detailed XPS high resolution survey for I/rGO sample: (<b>a</b>) carbon C1s; (<b>b</b>) oxygen O1s; and (<b>c</b>) iodine I3d.</p> Full article ">Figure 3
<p>BET isotherms and BJH curves corresponding to graphene oxide.</p> Full article ">Figure 4
<p>BET isotherms and BJH curves corresponding to iodine−doped graphene.</p> Full article ">Figure 5
<p>TGA/DTGA plots corresponding to: (<b>a</b>) r−GO and (<b>b</b>) I/rGO.</p> Full article ">Figure 6
<p>Overlaid ATR−FTIR rGO and I/rGO spectra with the fingerprint zone in the inset.</p> Full article ">Figure 7
<p>(<b>a</b>) Cycling voltammograms of reduced graphene oxide (rGO) and iodine−doped rGO (I/rGO) recorded between 0.4–0.7 V vs. Ag/AgCl, in oxygen atmosphere, scanned with 50 mV/s; (<b>b</b>) cycling voltammograms of I/rGO at different sweeping rates.</p> Full article ">Figure 8
<p>Linear sweep voltammograms for I/rGO at various rotation speeds (250 to 1000 rpm) on RDE.</p> Full article ">Figure 9
<p>Fitted K–L plots for I/rGO determined from linear sweep voltammograms.</p> Full article ">
28 pages, 8262 KiB  
Article
Measuring the Effect of Pack Shape on Gravel’s Pore Characteristics and Permeability Using X-ray Diffraction Computed Tomography
by Jiayi Peng, Zhenzhong Shen and Jiafa Zhang
Materials 2022, 15(17), 6173; https://doi.org/10.3390/ma15176173 - 5 Sep 2022
Cited by 1 | Viewed by 2185
Abstract
Particle shape is one of the critical parameter factors that affect gravel’s pore structure and permeability. However, few studies have considered its effects on engineering applications due to the difficulty of conducting laboratory tests. To overcome these difficulties, new methods of estimating the [...] Read more.
Particle shape is one of the critical parameter factors that affect gravel’s pore structure and permeability. However, few studies have considered its effects on engineering applications due to the difficulty of conducting laboratory tests. To overcome these difficulties, new methods of estimating the gravel pack shape that involve manual work and measuring the surface area of particles and pores based on support vector machine segmentation and the reconstruction of X-ray diffraction computed tomography (CT) images were proposed. Under the same conditions, CT tests were carried out on gravel packs and two other regular-shaped particle packs to investigate the influence of particle shape on the fractal dimension of gravel’s pore–particle interface and the specific surface area of the pore network. Additionally, permeability tests were performed to study the effect of particle shape on gravel’s hydraulic conductivity. The results showed that a gravel pack with a larger aspect ratio and a smaller roundness had a larger specific pore network surface area and a more complex pore structure, leading to lower permeability. This kind of gravel had a more significant length, quantity, and tortuosity of the seepage path when seepage occurred in a two-dimensional seepage field simulation. Therefore, we suggest that the filter materials of hydraulic projects should preferably use blasting gravel with a larger aspect ratio and smaller roundness to achieve better anti-seepage properties. In addition, projects can increase pores’ specific surface area using our method as a control factor in filter construction. Full article
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<p>Materials used.</p> Full article ">Figure 2
<p>Experimental process.</p> Full article ">Figure 3
<p>Constant-head permeability test system.</p> Full article ">Figure 4
<p>A CT image of S1.</p> Full article ">Figure 5
<p>Numerical simulation model. (<b>a</b>) Schematic of the computational domain and the boundary. (<b>b</b>) The corresponding CT section of S1. (<b>c</b>) Schematic representation of the model’s cut location.</p> Full article ">Figure 6
<p>Box plots of the shape parameters. (<b>a</b>) The box plot of the aspect ratios. (<b>b</b>) The box plot of the roundnesses.</p> Full article ">Figure 7
<p>Particle size distributions of the gravel. (<b>a</b>) D<sub>Ⅰ</sub>, size range was 2–5 mm. (<b>b</b>) D<sub>Ⅱ</sub>, size range was 5–10 mm. (<b>c</b>) D<sub>Ⅲ</sub>, size range was 10–20 mm. (<b>d</b>) D1, D2, and D3 particle size distributions in the laboratory test.</p> Full article ">Figure 8
<p>The porosities of the packs. (<b>a</b>) The porosities of the glass ball packs. (<b>b</b>) The porosities of the gravel packs. (<b>c</b>) The porosities of the plastic octahedron packs.</p> Full article ">Figure 9
<p>Image segmentation based on the SVM. (<b>a</b>) The original CT scanning image. (<b>b</b>) The image after segmentation.</p> Full article ">Figure 10
<p>Results of the segmentation of the same CT image of O1 via different methods. (<b>a</b>) The SVM method. (<b>b</b>) The gray-scale morphology method. (<b>c</b>) The histogram segmentation method.</p> Full article ">Figure 11
<p>Box dimensions of the pore–particle interfaces. (<b>a</b>) The box plot of the box dimensions of single particles’ pore–particle interfaces. (<b>b</b>) The bar graph of the packs’ average box dimensions. The figure’s error lines were based on the standard deviation.</p> Full article ">Figure 12
<p>The relationship between the particle pack shape and the average box dimension of the pore–particle interfaces. The error lines in the figures were based on the standard deviation. (<b>a</b>) The relationship between the average box dimension of the pore–particle interface and the aspect ratio of the packs. (<b>b</b>) The relationship between the average box dimension of the pore–particle interface and the roundness of the packs.</p> Full article ">Figure 13
<p>Contact markers on CT images. (<b>a</b>) CT middle section of B1. (<b>b</b>) CT middle section of S1. (<b>c</b>) CT middle section of O1.</p> Full article ">Figure 14
<p>The pore network model of the packs. All models were cut in the middle to show their internal structure.</p> Full article ">Figure 15
<p>Specific surface area of the pore network (<span class="html-italic">A</span>) values of the different packs.</p> Full article ">Figure 16
<p>The relationship between the particle pack shape and the specific surface area of the pore network of the pack. (<b>a</b>) The relationship between the specific surface area of the pore network and the aspect ratio of the pack. (<b>b</b>) The relationship between the specific surface area of the pore network and the roundness of the pack.</p> Full article ">Figure 17
<p>Permeability test results of the packs. (<b>a</b>) The relationship between the hydraulic gradient and the flow velocity of the pack. (<b>b</b>) The hydraulic conductivity of the pack. The error bars in the figure were based on the standard deviations.</p> Full article ">Figure 18
<p>The relationship between the hydraulic conductivity and the pore characteristics of packs. (<b>a</b>) The relationship between the aspect ratio of the pack and the hydraulic conductivity. (<b>b</b>) The relationship between the roundness of the pack and the hydraulic conductivity. (<b>c</b>) The relationship between the average box dimension of the pore–particle interface and the hydraulic conductivity. (<b>d</b>) The relationship between the specific surface area of the pore network and the hydraulic conductivity.</p> Full article ">Figure 19
<p>Partial flow field diagrams obtained from the simulation. The left column graphs are the velocity field diagrams with a hydraulic gradient of 0.1, and the right column graphs are the streamline diagrams with a velocity greater than 0.09 cm/s, flowing from the inlet to the outlet with the same hydraulic gradient.</p> Full article ">Figure 20
<p>Box plot of the tortuosity of the traces in the flow field from the simulation.</p> Full article ">
3 pages, 401 KiB  
Editorial
New Frontiers in Materials Design for Laser Additive Manufacturing
by Silja-Katharina Rittinghaus, Eric A. Jägle, Manfred Schmid and Bilal Gökce
Materials 2022, 15(17), 6172; https://doi.org/10.3390/ma15176172 - 5 Sep 2022
Cited by 5 | Viewed by 2306
Abstract
Laser-based additive manufacturing (LAM) in all its variations is now being established as a technique for manufacturing components from various material types and alloys [...] Full article
(This article belongs to the Special Issue New Frontiers in Materials Design for Laser Additive Manufacturing)
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<p>(<b>a</b>) Schematic of interactive physical phenomena during a stable LPBF process [<a href="#B2-materials-15-06172" class="html-bibr">2</a>]. (<b>b</b>) scanning electron microscopy (SEM) picture of 1.2709 at 10,000× <span class="html-italic">g</span> magnification coated with 1 vol.% SiC [<a href="#B3-materials-15-06172" class="html-bibr">3</a>]. (<b>c</b>) Illustration of the surface coverage by micro powders with increasing nanoparticle loading (vol%) [<a href="#B4-materials-15-06172" class="html-bibr">4</a>].</p> Full article ">
18 pages, 11653 KiB  
Article
PBF-LB/M of Low-Alloyed Steels: Bainite-like Microstructures despite High Cooling Rates
by Dominic Bartels, Tobias Novotny, Andreas Mohr, Frank van Soest, Oliver Hentschel, Carsten Merklein and Michael Schmidt
Materials 2022, 15(17), 6171; https://doi.org/10.3390/ma15176171 - 5 Sep 2022
Cited by 9 | Viewed by 2320
Abstract
Laser-based powder bed fusion of metals (PBF-LB/M) is an emerging technology with enormous potential for the fabrication of highly complex products due to the layer-wise fabrication process. Low-alloyed steels have recently gained interest due to their wide potential range of applications. However, the [...] Read more.
Laser-based powder bed fusion of metals (PBF-LB/M) is an emerging technology with enormous potential for the fabrication of highly complex products due to the layer-wise fabrication process. Low-alloyed steels have recently gained interest due to their wide potential range of applications. However, the correlation between the processing strategy and the material properties remains mostly unclear. The process-inherent high cooling rates support the assumption that a very fine martensitic microstructure is formed. Therefore, the microstructure formation was studied by means of scanning electron microscopy, hardness measurements, and an analysis of the tempering stability. It could be shown that additively manufactured Bainidur AM samples possess a bainitic microstructure despite the high process-specific cooling rates in PBF-LB/M. This bainitic microstructure is characterized by an excellent tempering stability up to temperatures as high as 600 °C. In contrast to this, additively manufactured and martensitic-hardened specimens are characterized by a higher initial hardness but a significantly reduced tempering stability. This shows the potential of manufacturing products from Bainidur AM for high-temperature applications without the necessity of a post-process heat treatment for achieving the desired bainitic microstructure. Full article
(This article belongs to the Special Issue Research and Development of Additive Manufacturing Technology)
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Full article ">Figure 1
<p>Morphology of the powder materials used (<b>a</b>) with a nominal size from 15 to 45 µm and (<b>b</b>) an exemplary design of the build job on the AconityMINI.</p> Full article ">Figure 2
<p>Experimental approach for (<b>a</b>) sample preparation for analysis of the relative part density and hardness measurements and (<b>b</b>) measurement pattern for determining the material hardness.</p> Full article ">Figure 3
<p>Results of the optical density analysis for the different processing parameters on the AconityMINI machine. The scale is magnified exemplary only once (225 W–850 mm/s–100 µm). Red indicates a lower relative part density, green indicates a higher relative part density.</p> Full article ">Figure 4
<p>Exemplary (<b>a</b>,<b>c</b>) cross-sections and (<b>b</b>,<b>d</b>) magnified regions for determining the relative part density in the worst apparent regions of the specimen for (<b>a</b>,<b>b</b>) 275 W–550 mm/s–100 µm and (<b>c</b>,<b>d</b>) 275 W–700 mm/s–110 µm.</p> Full article ">Figure 5
<p>Mean hardness of test cubes manufactured on the AconityMINI systems using the different process parameters. The hardness of additively manufactured 16MnCr5 according to [<a href="#B15-materials-15-06171" class="html-bibr">15</a>] is provided as a reference. Information on the respective standard deviations can be found in <a href="#app1-materials-15-06171" class="html-app">Appendix A</a>.</p> Full article ">Figure 6
<p>Etched cross-sections for samples manufactured using a (<b>a</b>,<b>b</b>) low (36.8 J/mm<sup>3</sup>), (<b>c</b>,<b>d</b>) medium (54.1 J/mm<sup>3</sup>), and (<b>e</b>,<b>f</b>) high VED (75.8 J/mm<sup>3</sup>).</p> Full article ">Figure 7
<p>Different microstructural regions of PBF-LB/M specimens (<b>a</b>) in the core with the fusion zone (i) and heat-affected zone (ii) and (<b>b</b>) in case (iii), manufactured using a medium VED of 54.1 J/mm<sup>3</sup>.</p> Full article ">Figure 8
<p>SEM images of the (<b>a</b>) fusion zone and the heat-affected zone within the core of the specimen as well as corresponding magnification of the (<b>b</b>) fusion zone and (<b>c</b>) the heat-affected zone. Exemplary illustrations of the apparent microstructure according to [<a href="#B26-materials-15-06171" class="html-bibr">26</a>].</p> Full article ">Figure 9
<p>Material hardness for different tempering temperatures in the as-built as well as quenched and tempered states. The specimens were manufactured using a medium VED (54.1 J/mm<sup>3</sup>).</p> Full article ">Figure 10
<p>Etched cross-section of (<b>top</b>) as-built and tempered as well as (<b>bottom</b>) quenched and tempered specimens. The specimens were manufactured using a medium VED (54.1 J/mm<sup>3</sup>).</p> Full article ">Figure 11
<p>SEM images of the center region of the specimens in (<b>top</b>) as-built and tempered as well as (<b>bottom</b>) quenched and tempered states. The specimens were manufactured using a medium VED (54.1 J/mm<sup>3</sup>).</p> Full article ">Figure A1
<p>Cross-sections of the specimens manufactured with a hatch distance of 100 µm.</p> Full article ">Figure A2
<p>Cross-sections of the specimens manufactured with a hatch distance of 110 µm.</p> Full article ">Figure A3
<p>Cross-sections of the specimens manufactured with a hatch distance of 120 µm.</p> Full article ">Figure A4
<p>SEM images (from <a href="#materials-15-06171-f011" class="html-fig">Figure 11</a>) of the as-built and tempered as well as quenched and tempered specimens.</p> Full article ">
14 pages, 1039 KiB  
Article
Experimental Studies on Adaptive-Passive Symmetrical Granular Damper Operation
by Mateusz Żurawski and Robert Zalewski
Materials 2022, 15(17), 6170; https://doi.org/10.3390/ma15176170 - 5 Sep 2022
Cited by 2 | Viewed by 1654
Abstract
This paper presents experimental studies on a controllable granular damper, whose dissipative properties are provided by the friction phenomenon occuring between loose granular material. In addition, in order to adjust to the current trends in vibration suppression, we built a semi-active device, controlled [...] Read more.
This paper presents experimental studies on a controllable granular damper, whose dissipative properties are provided by the friction phenomenon occuring between loose granular material. In addition, in order to adjust to the current trends in vibration suppression, we built a semi-active device, controlled by a single parameter—underpressure. Such granular structures subjected to underpressure are called Vacuum-Packed Particles. The first section presents the state of the art. A brief description of the most often used intelligent and smart materials for the manufacture of dampers is presented. The main advantages of the proposed device are a simple structure, low construction cost, symmetrical principle of operation, and the ability to change the characteristics of the damper by quickly and suddenly changing the negative pressure inside the granular core. The second section provides a detailed description of the construction and operation principles of the original symmetrical granular damper. A description of its application in the laboratory research test stand is also provided. The third section presents the results of the experimental studies including the recorded damping characteristics of the investigated damper. The effectiveness of the ethylene–propylene–diene grains’ application is presented. The two parameters of underpressure and frequency of excitation were considered during the empirical tests. The influence of the system parameters on its global dissipative behavior is discussed in detail. The damper operation characteristics are close to linear, which is positive information from the point of view of the potential adaptive-passive control process. Brief conclusions and the prospective application of vacuum-packed particle dampers are presented in the final section. Full article
(This article belongs to the Special Issue Advanced Materials Structures for Sound and Vibration Damping)
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<p>Scheme 1 of the symmetrical granular damper.</p> Full article ">Figure 2
<p>Scheme 2 of the symmetrical granular damper.</p> Full article ">Figure 3
<p>Scheme of the principle of the operation—initial stage.</p> Full article ">Figure 4
<p>Scheme of the principle of the operation—operating stage.</p> Full article ">Figure 5
<p>Test stand.</p> Full article ">Figure 6
<p>AGA Labor vacuum pump.</p> Full article ">Figure 7
<p>SVPP damper with EPDM grains.</p> Full article ">Figure 8
<p>Force/displacement curve for frequency <math display="inline"><semantics> <msub> <mi>f</mi> <mn>1</mn> </msub> </semantics></math>.</p> Full article ">Figure 9
<p>Force/displacement curves for various frequencies <math display="inline"><semantics> <msub> <mi>f</mi> <mn>2</mn> </msub> </semantics></math>→<math display="inline"><semantics> <msub> <mi>f</mi> <mn>5</mn> </msub> </semantics></math>.</p> Full article ">Figure 10
<p>Force/displacement characteristics for various rotational speeds for up00 underpressure.</p> Full article ">Figure 11
<p>Force/displacement characteristics for various rotational speeds for up01 underpressure.</p> Full article ">Figure 12
<p>Force/displacement characteristics for various rotational speeds for up02 → up09 underpressure.</p> Full article ">Figure 12 Cont.
<p>Force/displacement characteristics for various rotational speeds for up02 → up09 underpressure.</p> Full article ">Figure 13
<p>Force/underpressure characteristics for <math display="inline"><semantics> <msub> <mi>f</mi> <mn>2</mn> </msub> </semantics></math> rotational speed.</p> Full article ">
14 pages, 20270 KiB  
Article
Strength Characteristics and Microstructure Analysis of Alkali-Activated Slag–Fly Ash Cementitious Material
by Chenhui Zhu, Yuanyuan Wan, Lei Wang, Yuchen Ye, Houjun Yu and Jie Yang
Materials 2022, 15(17), 6169; https://doi.org/10.3390/ma15176169 - 5 Sep 2022
Cited by 10 | Viewed by 2427
Abstract
Modifying the admixture of alkali-activated cementitious materials using components such as fly ash and fine sand may reduce CO2 emissions and conserve natural resources and energy. This study adopted strength testing, scanning electron microscopy, and mercury intrusion porosimetry to investigate the influence [...] Read more.
Modifying the admixture of alkali-activated cementitious materials using components such as fly ash and fine sand may reduce CO2 emissions and conserve natural resources and energy. This study adopted strength testing, scanning electron microscopy, and mercury intrusion porosimetry to investigate the influence of different admixtures on the compressive strength and flexural strength of alkali slag cementing materials and the microstructure characteristics of hardened slurry under the action of load. The flexural strength of alkali slag cement slurry and mortar was reduced by replacing slag powder with fly ash. Content of fine sand less than 20% had little effect on the strength of alkali slag cement mortar; however, when the content of fine sand exceeded 30%, the strength decreased significantly. The hydration degree at 3 d was large, and the density of slurry increased with the extension of age. Increased fly ash or fine sand content decreased the density of the slurry, and increased fly ash resulted in a large number of unhydrated fly ash particles in the cementitious materials. Addition of fine sand resulted in a large number of microcracks in the slurry, which gradually decreased with the extension of hydration age. Full article
(This article belongs to the Special Issue Convergence & Sustainable Technology in Building Materials)
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<p>SEM image of fly ash.</p> Full article ">Figure 2
<p>Effect of fly ash content on strength of alkali slag cement paste. (<b>a</b>) Compressive strength, (<b>b</b>) Flexural Strength.</p> Full article ">Figure 3
<p>Effect of fly ash content on strength of alkali slag cement mortar. (<b>a</b>) Compressive strength, (<b>b</b>) Flexural Strength.</p> Full article ">Figure 4
<p>Effect of sand content on strength of alkali slag cement mortar. (<b>a</b>) Compressive strength, (<b>b</b>) Flexural Strength.</p> Full article ">Figure 5
<p>SEM images of the alkali slag cement slurry with pure ore powder at the hydration age of 3 d. (<b>a</b>) ×1.00 k, (<b>b</b>) ×5.00 k.</p> Full article ">Figure 6
<p>SEM images of the alkali slag cement slurry with 50% fly ash at hydration age of 3 d. (<b>a</b>) ×1.00 k, (<b>b</b>) ×5.00 k.</p> Full article ">Figure 7
<p>SEM images of 80% fly ash alkali slag cement slurry at the hydration age of 3 d. (<b>a</b>) ×1.00 k, (<b>b</b>) ×5.00 k.</p> Full article ">Figure 8
<p>SEM images of alkali slag cement mortar with hydration ages of 3 d. (<b>a</b>) ×1.00 k, (<b>b</b>) ×5.00 k.</p> Full article ">Figure 9
<p>SEM images of alkali slag cement mortar with hydration ages of 28 d. (<b>a</b>) ×1.00 k, (<b>b</b>) ×5.00 k.</p> Full article ">Figure 10
<p>SEM images of alkali slag cement sand substituted with 50% fly ash at hydration ages of 3 d. (<b>a</b>) ×1.00 k, (<b>b</b>) ×5.00 k.</p> Full article ">Figure 11
<p>SEM images of alkali slag cement sand substituted with 50% fly ash at hydration ages of 28 d. (<b>a</b>) ×1.00 k, (<b>b</b>) ×5.00 k.</p> Full article ">Figure 12
<p>SEM images of alkali slag cement sand replaced by 80% ore powder with fly ash at hydration ages of 3 d. (<b>a</b>) ×1.00 k, (<b>b</b>) ×5.00 k.</p> Full article ">Figure 13
<p>SEM images of alkali slag cement sand replaced by 80% ore powder with fly ash at hydration ages of 28 d. (<b>a</b>) ×1.00 k, (<b>b</b>) ×5.00 k.</p> Full article ">
11 pages, 7658 KiB  
Article
Ultrafine-Grained Tungsten Heavy Alloy Prepared by High-Pressure Spark Plasma Sintering
by Shuaihao Zhang, Qiqi Zhu, Qiunan Li, Wei Ji, Weimin Wang and Zhengyi Fu
Materials 2022, 15(17), 6168; https://doi.org/10.3390/ma15176168 - 5 Sep 2022
Cited by 8 | Viewed by 2178
Abstract
Tungsten heavy alloy (WHA) is an ideal material employed for kinetic energy penetrators due to its high density and excellent mechanical properties. However, it is difficult to obtain ultrafine-grained tungsten alloy with excellent properties by traditional powder metallurgy method because of severe grain [...] Read more.
Tungsten heavy alloy (WHA) is an ideal material employed for kinetic energy penetrators due to its high density and excellent mechanical properties. However, it is difficult to obtain ultrafine-grained tungsten alloy with excellent properties by traditional powder metallurgy method because of severe grain growth at a high sintering temperature with a long soaking time. In this study, the sintering behavior of tungsten alloys was studied at 800 to 1300 °C, and highly dense 93W-5.6Ni-1.4Fe (wt.%) WHA was successfully fabricated at a low temperature of 950 °C with a high pressure of 150 MPa by spark plasma sintering. The as-sintered tungsten alloy possesses a high relative density (98.6%), ultrafine grain size (271 nm) and high dislocation density (2.6 × 1016 m−2), which results in excellent properties such as a high hardness (1079 HV1). The high sintering pressure is considered to support an additional driving force for the sintering and lead to a low-temperature densification, which effectively limits grain growth. Full article
(This article belongs to the Special Issue Spark Plasma Sintering of Materials: Processing and Applications)
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<p>(<b>a</b>) XRD pattern and (<b>b</b>) SEM image of the mixed powders.</p> Full article ">Figure 2
<p>XRD patterns of 93W-5.6Ni-1.4Fe tungsten alloys after SPS at 800–1300 °C under (<b>a</b>) 50 MPa and (<b>b</b>) 150 MPa.</p> Full article ">Figure 3
<p>The fracture morphologies of 93W-5.6Ni-1.4Fe tungsten alloys after SPS under 50 MPa at different temperatures: (<b>a</b>) 800 °C, (<b>b</b>) 850 °C, (<b>c</b>) 900 °C, (<b>d</b>) 950 °C, (<b>e</b>) 1000 °C, (<b>f</b>) 1050 °C, (<b>g</b>) 1100 °C, (<b>h</b>) 1150 °C, (<b>i</b>) 1200 °C, (<b>j</b>) 1250 °C, and (<b>k</b>) 1300 °C. Inserts are the magnified images.</p> Full article ">Figure 4
<p>The fracture morphologies of 93W-5.6Ni-1.4Fe tungsten alloys after SPS under 150 MPa at different temperatures: (<b>a</b>) 800 °C, (<b>b</b>) 850 °C, (<b>c</b>) 900 °C, (<b>d</b>) 950 °C, (<b>e</b>) 1000 °C, (<b>f</b>) 1050 °C, (<b>g</b>) 1100 °C, (<b>h</b>) 1150 °C, (<b>i</b>) 1200 °C, (<b>j</b>) 1250 °C, and (<b>k</b>) 1300 °C. Inserts are the magnified images.</p> Full article ">Figure 5
<p>Change in (<b>a</b>) relative density and (<b>b</b>) grain size of 93W-5.6Ni-1.4Fe tungsten alloys sintered at 800–1300 °C under different pressures.</p> Full article ">Figure 6
<p>The EBSD results of band contrast images and Inverse Pole Figure (IPF) images for tungsten alloys sintered at 950 °C under (<b>a</b>,<b>b</b>) 150 MPa and (<b>c</b>,<b>d</b>) 50 MPa, respectively.</p> Full article ">Figure 7
<p>TEM images of 93W-5.6Ni-1.4Fe alloy sintered at 950 °C under 150 MPa. (<b>a</b>,<b>b</b>) Dark field image of WHA; The element distribution of (<b>c</b>) W, (<b>d</b>) Ni and (<b>e</b>) Fe; The HRTEM images of grain boundaries within (<b>f</b>) W grains and between (<b>g</b>) W and γ phases.</p> Full article ">Figure 8
<p>The relationship between sintering temperature and hardness of 93W-5.6Ni-1.4Fe tungsten alloys sintered under different pressures.</p> Full article ">
13 pages, 1564 KiB  
Article
Construction Products between Testing Laboratory and Market Surveillance: Case study of Cementitious Ceramic Tile Adhesives
by Cristina Stancu, Dawid Dębski and Jacek Michalak
Materials 2022, 15(17), 6167; https://doi.org/10.3390/ma15176167 - 5 Sep 2022
Cited by 6 | Viewed by 2600
Abstract
This article presents the results of the interlaboratory comparison (ILC) study of the following four characteristics of ceramic tile adhesives (CTAs): initial tensile adhesion strength, tensile adhesion strength after heat ageing, tensile adhesion strength after immersion in water, and tensile adhesion strength after [...] Read more.
This article presents the results of the interlaboratory comparison (ILC) study of the following four characteristics of ceramic tile adhesives (CTAs): initial tensile adhesion strength, tensile adhesion strength after heat ageing, tensile adhesion strength after immersion in water, and tensile adhesion strength after freeze–thaw cycles. The results showed that the objective of the ILC was achieved—the z-score analysis carried out following ISO 13528 allowed for classifying all results obtained by 23 laboratories out of 27 as satisfactory. The results of the remaining four laboratories were rated worse. Despite the achieved goal, the ILC notes high heterogeneity of the results in terms of failure patterns, as well as significant differences between the lowest and the highest values of tensile adhesion strength for various measurement conditions. The results of the ILC were discussed in terms of the possibility of including them in the risk analysis conducted by the manufacturer. The results of the ILC are also valuable information for market surveillance authorities, who, in the authors’ opinion, should be more cautious about results on samples taken from the market. The ILC results for CTAs are also a valuable recommendation for a possible revision of EN 12004. Full article
(This article belongs to the Special Issue Feature Papers in Refractories and Ceramics: Microstructure, Properties and Applications)
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<p>The results of the z-score analysis for measurements of the following CTA characteristics (<b>A</b>)—initial tensile adhesion strength, (<b>B</b>)—tensile adhesion strength after heat ageing, (<b>C</b>)—tensile adhesion strength after immersion in water, and (<b>D</b>)—tensile adhesion strength after freeze–thaw cycles. Legend: (■) |z| &lt; 2 (satisfactory); (■) 2 &lt; |z| &lt; 3 (questionable); (■) |z| ≥ 3 (unsatisfactory); ( <span class="html-fig-inline" id="materials-15-06167-i001"><img alt="Materials 15 06167 i001" src="/materials/materials-15-06167/article_deploy/html/images/materials-15-06167-i001.png"/></span>) samples that were assessed by the construction supervision as meeting the requirements for CTA class C2 (&gt;1.0 N/mm<sup>2</sup> following EN 12004); ( <span class="html-fig-inline" id="materials-15-06167-i002"><img alt="Materials 15 06167 i002" src="/materials/materials-15-06167/article_deploy/html/images/materials-15-06167-i002.png"/></span>) samples that the construction supervision has assessed as not meeting the requirements for CTA class C2.</p> Full article ">
12 pages, 2985 KiB  
Article
Microstructure and Properties of a Graphene Reinforced Cu–Cr–Mg Composite
by Ruiyu Lu, Bin Liu, Huichao Cheng, Shenghan Gao, Tiejun Li, Jia Li and Qihong Fang
Materials 2022, 15(17), 6166; https://doi.org/10.3390/ma15176166 - 5 Sep 2022
Cited by 3 | Viewed by 2047
Abstract
To improve the graphene/copper interfacial bonding and the strength of the copper matrix, Cu–Cr–Mg alloy powder and graphene nanosheets (GNPs) have been used as raw materials in the preparation of a layered graphene/Cu–Cr–Mg composite through high-energy ball-milling and fast hot-pressing sintering. The microstructure [...] Read more.
To improve the graphene/copper interfacial bonding and the strength of the copper matrix, Cu–Cr–Mg alloy powder and graphene nanosheets (GNPs) have been used as raw materials in the preparation of a layered graphene/Cu–Cr–Mg composite through high-energy ball-milling and fast hot-pressing sintering. The microstructure of the composite after sintering, as well as the effect of graphene on the mechanical properties and conductivity of the composite, are also studied. The results show that the tensile strength of the composite material reached a value of 349 MPa, which is 46% higher than that of the copper matrix, and the reinforcement efficiency of graphene is as large as 136. Furthermore, the electrical conductivity of the composite material was 81.6% IACS, which is only 0.90% IACS lower than that of the copper matrix. The Cr and Mg elements are found to diffuse to the interface of the graphene/copper composite during sintering, and finely dispersed chromium carbide particles are found to significantly improve the interfacial bonding strength of the composite. Thus, graphene could effectively improve the mechanical properties of the composite while maintaining a high electrical conductivity. Full article
(This article belongs to the Special Issue Advanced Manufacturing of Metals and Composites: Effect of Processes on Microstructure and Mechanical Properties)
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<p>Preparation process of the GNPs /Cu–Cr–Mg composite.</p> Full article ">Figure 2
<p>SEM images of GNPs/Cu–Cr–Mg composite powders; (<b>a</b>) gas atomized Cu–Cr–Mg alloy powder, (<b>b</b>) raw GNPs, (<b>c</b>) GNPs/Cu–Cr–Mg mixture powder, and (<b>d</b>) EDS results of spot 1.</p> Full article ">Figure 3
<p>SEM images of a GNPs/Cu–Cr–Mg composite and the Cu–Cr–Mg matrix; (<b>a</b>) low magnification SEM image of the composite, (<b>b</b>) high magnification SEM image of the composite, (<b>c</b>) low magnification SEM image of the Cu–Cr–Mg matrix, and (<b>d</b>) high magnification SEM image of the Cu–Cr–Mg matrix.</p> Full article ">Figure 4
<p>XRD patterns of a GNPs/Cu–Cr–Mg composite.</p> Full article ">Figure 5
<p>EPMA of a GNPs/Cu–Cr–Mg composite material; (<b>a</b>) SEM of a GNPs/Cu–Cr–Mg composite, (<b>b</b>) elemental mapping of Cu in (<b>a</b>), (<b>c</b>) elemental mapping of C in (<b>a</b>), (<b>d</b>) element mapping of Cr in (<b>a</b>) and, (<b>e</b>) elemental mapping of Mg in (<b>a</b>).</p> Full article ">Figure 6
<p>Raman spectrum of a GNPs/Cu–Cr–Mg composite.</p> Full article ">Figure 7
<p>Mechanical properties of a GNPs/Cu–Cr–Mg composite; (<b>a</b>) tensile stress-strain curves, (<b>b</b>) obtained values of yield strength, tensile strength, and elongation of the composite and matrix material, and (<b>c</b>) the strengthening efficiency (R) obtained in this study in comparison with those reported in the literature [<a href="#B4-materials-15-06166" class="html-bibr">4</a>,<a href="#B12-materials-15-06166" class="html-bibr">12</a>,<a href="#B13-materials-15-06166" class="html-bibr">13</a>,<a href="#B15-materials-15-06166" class="html-bibr">15</a>,<a href="#B16-materials-15-06166" class="html-bibr">16</a>,<a href="#B18-materials-15-06166" class="html-bibr">18</a>,<a href="#B19-materials-15-06166" class="html-bibr">19</a>,<a href="#B22-materials-15-06166" class="html-bibr">22</a>,<a href="#B24-materials-15-06166" class="html-bibr">24</a>,<a href="#B31-materials-15-06166" class="html-bibr">31</a>,<a href="#B33-materials-15-06166" class="html-bibr">33</a>,<a href="#B34-materials-15-06166" class="html-bibr">34</a>,<a href="#B35-materials-15-06166" class="html-bibr">35</a>].</p> Full article ">Figure 8
<p>Tensile fracture of GNPs/Cu–Cr–Mg Composites. (<b>a</b>) Cu–Cr–Mg matrix material; (<b>b</b>) GNPs/Cu–Cr–Mg composites.</p> Full article ">
17 pages, 4370 KiB  
Article
High-Energy Computed Tomography as a Prospective Tool for In Situ Monitoring of Mass Transfer Processes inside High-Pressure Reactors—A Case Study on Ammonothermal Bulk Crystal Growth of Nitrides including GaN
by Saskia Schimmel, Michael Salamon, Daisuke Tomida, Steffen Neumeier, Tohru Ishiguro, Yoshio Honda, Shigefusa F. Chichibu and Hiroshi Amano
Materials 2022, 15(17), 6165; https://doi.org/10.3390/ma15176165 - 5 Sep 2022
Cited by 3 | Viewed by 2899
Abstract
For the fundamental understanding and the technological development of the ammonothermal method for the synthesis and crystal growth of nitrides, an in situ monitoring technique for tracking mass transport of the nitride throughout the entire autoclave volume is desirable. The feasibility of using [...] Read more.
For the fundamental understanding and the technological development of the ammonothermal method for the synthesis and crystal growth of nitrides, an in situ monitoring technique for tracking mass transport of the nitride throughout the entire autoclave volume is desirable. The feasibility of using high-energy computed tomography for this purpose was therefore evaluated using ex situ measurements. Acceleration voltages of 600 kV were estimated to yield suitable transparency in a lab-scale ammonothermal setup for GaN crystal growth designed for up to 300 MPa operating pressure. The total scan duration was estimated to be in the order of 20 to 40 min, which was sufficient given the comparatively slow crystal growth speed in ammonothermal growth. Even shorter scan durations or, alternatively, lower acceleration voltages for improved contrast or reduced X-ray shielding requirements, were estimated to be feasible in the case of ammonoacidic growth, as the lower pressure requirements for this process variant allow for thinned autoclave walls in an adapted setup designed for improved X-ray transparency. Promising nickel-base and cobalt-base alloys for applications in ammonothermal reactors with reduced X-ray absorption in relation to the maximum operating pressure were identified. The applicability for the validation of numerical simulations of the growth process of GaN, in addition to the applicability of the technique to further nitride materials, as well as larger reactors and bulk crystals, were evaluated. Full article
(This article belongs to the Special Issue Wide and Ultra-Wide Bandgap Semiconductor Materials for Power Devices)
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<p>Calculated total X-ray transmission of an exemplary ammonothermal growth setup in two variants differing by the autoclave wall thickness <span class="html-italic">t</span> as a function of X-ray photon energy. The absence of data below 50 keV originates from calculating data at an interval of 50 keV starting at 50 keV. Total transmission would approach zero for photon energies approaching zero.</p> Full article ">Figure 2
<p>Calculated X-ray transmission of Inconel 718 for different values of the wall thickness <span class="html-italic">t</span> (i.e., a radiographed thickness of 2<span class="html-italic">t</span>) as a function of photon energy.</p> Full article ">Figure 3
<p>Calculated ratio of yield strength <span class="html-italic">R</span><sub><span class="html-italic">p</span>0.2</sub> at 650 °C and linear attenuation coefficient <span class="html-italic">µ</span> as a function of photon energy for different alloys with high mechanical strength at high temperatures. Insofar as the alloys show significant precipitation hardening, the yield strengths of the precipitation-hardened condition were used. The absence of data below 50 keV is because data were calculated at an interval of 50 keV starting at 50 keV. The ratio <span class="html-italic">R</span><sub><span class="html-italic">p</span>0.2</sub>/<span class="html-italic">µ</span> would approach zero for photon energies approaching zero, as <span class="html-italic">µ</span> will become large for very low photon energies.</p> Full article ">Figure 4
<p>Yield strength of the different alloys as a function of temperature. The dashed lines represent the lowest temperature of the heat treatment.</p> Full article ">Figure 5
<p>Computed tomography measurements obtained ex situ with an ammonothermal setup containing all typical elements except for the reaction medium. The material of the crucible was Inconel 718 in all cases. The material of the autoclave wall was Inconel 718 in (<b>a</b>–<b>c</b>), whereas an autoclave made of Haynes 282 was used in (<b>d</b>). Different acceleration voltages were tested: (<b>a</b>) 300 kV; (<b>b</b>) 550 kV; (<b>c</b>) 600 kV; (<b>d</b>) 590 kV. The autoclave wall thickness was <span class="html-italic">t</span> = 14.5 mm in all cases. Subfigure (<b>e</b>) shows a photograph of the setup placed inside the autoclave, consisting of the Inconel 718 crucible, Inconel 718 wire standoffs, and GaN crystal pieces hung using a molybdenum wire.</p> Full article ">Figure 6
<p>Ex situ computed tomography measurements obtained at 590 kV, 1 mA, and 2.5 s exposure time for each single projection image (all autoclave walls were Inconel 718). Left: vertical section through the setup with reduced autoclave wall thicknesses. Center: horizontal sections for each wall thickness. Right: vertical section of an established Inconel 718 autoclave designed for maximum operating conditions of 300 MPa and 600 °C. In the lower half, a 1.5 mm Ag tube shows the impact of a liner. The thin, lengthy, unlabeled objects in the vertical sections (also visible as a pair of dots in the horizontal sections) are Cu wires used as a standoff for hanging the GaN crystals.</p> Full article ">Figure 7
<p>Linear attenuation coefficient of selected binary and ternary nitride materials. Data from the Photon Cross Sections Database XCOM of the National Institute of Standards and Technology (NIST) [<a href="#B21-materials-15-06165" class="html-bibr">21</a>].</p> Full article ">Figure 8
<p>Wall thickness for a maximum operating pressure of 120 MPa estimated using Equation (1), with <span class="html-italic">R</span><sub><span class="html-italic">p</span>0.2</sub> of the different alloys at 650 °C and a safety factor of 1.5 (i.e., <span class="html-italic">p</span> = 180 MPa). For better readability of the data for the remaining alloys, the values for Inconel 625 were excluded from the plot because the low mechanical strength would cause dissimilarly large wall thicknesses. The lowest inner diameter represents the experimentally studied geometry with 21 mm inner diameter.</p> Full article ">Figure 9
<p>Wall thickness for a maximum operating pressure of 300 MPa estimated using Equation (1), with <span class="html-italic">R</span><sub><span class="html-italic">p</span>0.2</sub> of the different alloys at 650 °C and a safety factor of 1.5 (i.e., <span class="html-italic">p</span> = 450 MPa). For better readability of the data for the remaining alloys, the values for Inconel 625 were excluded from the plot because the low mechanical strength would cause dissimilarly large wall thicknesses. The lowest inner diameter was represented by the experimentally studied geometry with 21 mm inner diameter.</p> Full article ">Figure 10
<p>Considered options for the arrangement of seeds in a large reactor (top view of cross-section through the interior of an autoclave). Seeds are represented by yellowish rectangles. Dashed lines indicate mirror planes. (<b>a</b>) Example for conventional seed arrangement; (<b>b</b>) Proposed seed arrangement to reduce the length of radiographed path through GaN for improving X-ray transparency.</p> Full article ">
16 pages, 3345 KiB  
Article
Effect of Cu Modified Textile Structures on Antibacterial and Antiviral Protection
by Małgorzata Cieślak, Dorota Kowalczyk, Małgorzata Krzyżowska, Martyna Janicka, Ewa Witczak and Irena Kamińska
Materials 2022, 15(17), 6164; https://doi.org/10.3390/ma15176164 - 5 Sep 2022
Cited by 13 | Viewed by 2428
Abstract
Textile structures with various bioactive and functional properties are used in many areas of medicine, special clothing, interior textiles, technical goods, etc. We investigated the effect of two different textile woven structures made of 90% polyester with 10% polyamide (PET) and 100% cotton [...] Read more.
Textile structures with various bioactive and functional properties are used in many areas of medicine, special clothing, interior textiles, technical goods, etc. We investigated the effect of two different textile woven structures made of 90% polyester with 10% polyamide (PET) and 100% cotton (CO) modified by magnetron sputtering with copper (Cu) on bioactive properties against Gram-positive and Gram-negative bacteria and four viruses and also on the some comfort parameters. PET/Cu and CO/Cu fabrics have strong antibacterial activity against Staphylococcus aureus and Klebsiella pneumonia. CO/Cu fabric has good antiviral activity in relation to vaccinia virus (VACV), herpes simplex virus type 1 (HSV-1) and influenza A virus H1N1 (IFV), while its antiviral activity against mouse coronavirus (MHV) is weak. PET/Cu fabric showed weak antiviral activity against HSV-1 and MHV. Both modified fabrics showed no significant toxicity in comparison to the control medium and pristine fabrics. After Cu sputtering, fabric surfaces became hydrophobic and the value of the surface free energy was over four times lower than for pristine fabrics. The modification improved thermal conductivity and thermal diffusivity, facilitated water vapour transport, and air permeability did not decrease. Full article
(This article belongs to the Special Issue Bioactive and Functional Materials)
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<p>Schematic diagram of DC magnetron sputtering system.</p> Full article ">Figure 2
<p>The SEM images of textile materials used in the study: (<b>a</b>) woven fabrics, (<b>b</b>) longitudinal and (<b>c</b>) cross section views of the fibers.</p> Full article ">Figure 3
<p>Photos and the microscopic 3D images (magnification × 100) and surface roughness parameters of the Cu modified fabrics.</p> Full article ">Figure 4
<p>Results of SEM/EDS analysis: SEM images (<b>A</b>), exemplary maps of Cu distribution (blue) (<b>B</b>) and sum spectra (<b>C</b>).</p> Full article ">Figure 5
<p>Toxicity of tested samples with MTT method (Cell viability versus control).</p> Full article ">Figure 6
<p>The values of air and water vapour permeability for pristine and Cu modified textile structures.</p> Full article ">
15 pages, 4102 KiB  
Article
Chemical Distributions of Different Sodium Hydroxide Molarities on Fly Ash/Dolomite-Based Geopolymer
by Wan Mastura Wan Ibrahim, Mohd Mustafa Al Bakri Abdullah, Romisuhani Ahmad, Andrei Victor Sandu, Petrica Vizureanu, Omrane Benjeddou, Afikah Rahim, Masdiyana Ibrahim and Ahmad Syauqi Sauffi
Materials 2022, 15(17), 6163; https://doi.org/10.3390/ma15176163 - 5 Sep 2022
Cited by 20 | Viewed by 2539
Abstract
Geopolymers are an inorganic material in an alkaline environment that is synthesized with alumina–silica gel. The structure of geopolymers consists of an inorganic chain of material and a covalent-bound molecular system. Currently, Ordinary Portland Cement (OPC) has caused carbon dioxide (CO2) [...] Read more.
Geopolymers are an inorganic material in an alkaline environment that is synthesized with alumina–silica gel. The structure of geopolymers consists of an inorganic chain of material and a covalent-bound molecular system. Currently, Ordinary Portland Cement (OPC) has caused carbon dioxide (CO2) emissions which causes greenhouse effects. This analysis investigates the impact on fly ash/dolomite-based-geopolymer with various molarities of sodium hydroxide solutions which are 6 M, 8 M, 10 M, 12 M and 14 M. The samples of fly ash/dolomite-based-geopolymer were prepared with the usage of solid to liquid of 2.0, by mass and alkaline activator ratio of 2.5, by mass. After that, the geopolymer was cast in 50 × 50 × 50 mm molds before testing after 7 days of curing. The samples were tested on compressive strength, density, water absorption, morphology, elemental distributions and phase analysis. From the results, the usage of 8 M of NaOH gave the optimum properties for the fly ash/dolomite-based geopolymer. The elemental distribution analysis exposes the Al, Si, Ca, Fe and Mg chemical distribution of the samples from the selected area. The distribution of the elements is related to the compressive strength and compared with the chemical composition of the fly ash and dolomite. Full article
(This article belongs to the Special Issue New Geopolymers Used in Civil Engineering)
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<p>Fly ash/dolomite geopolymer compressive strength.</p> Full article ">Figure 2
<p>Ion balance and dissolution process in the dolomite/fly ash based geopolymer.</p> Full article ">Figure 3
<p>Density of fly ash/dolomite geopolymer.</p> Full article ">Figure 4
<p>Rate of water absorption for fly ash/dolomite geopolymer.</p> Full article ">Figure 5
<p>Porosity of fly ash/dolomite geopolymer.</p> Full article ">Figure 6
<p>Fly ash/dolomite morphology for (<b>a</b>) 8 M and (<b>b</b>) 14 M NaOH Molarity.</p> Full article ">Figure 7
<p>The morphology of (<b>a</b>) reaction between fly ash and dolomite and (<b>b</b>) gelation process of the geopolymer.</p> Full article ">Figure 8
<p>Schematic diagram of the reaction between fly ash and dolomite geopolymer.</p> Full article ">Figure 9
<p>Si and Al elemental distribution for 8 M of NaOH fly ash/dolomite geopolymer.</p> Full article ">Figure 10
<p>Ca and Fe elemental distribution for 8 M of NaOH fly ash/dolomite geopolymer.</p> Full article ">Figure 11
<p>Mg elemental distribution for 8 M of NaOH fly ash/dolomite geopolymer.</p> Full article ">Figure 12
<p>XRD patterns of fly ash, dolomite and fly ash/dolomite geopolymer.</p> Full article ">
19 pages, 650 KiB  
Article
Resistance of 3D-Printed Components, Test Specimens and Products to Work under Environmental Conditions—Review
by Marcin Głowacki, Adam Mazurkiewicz, Małgorzata Słomion and Katarzyna Skórczewska
Materials 2022, 15(17), 6162; https://doi.org/10.3390/ma15176162 - 5 Sep 2022
Cited by 18 | Viewed by 3116
Abstract
The development of additive manufacturing methods known as “3D printing” started in the 1980s. In these methods, spatial models are created from a semi-finished product such as a powder, filament or liquid. The model is most often created in layers, which are created [...] Read more.
The development of additive manufacturing methods known as “3D printing” started in the 1980s. In these methods, spatial models are created from a semi-finished product such as a powder, filament or liquid. The model is most often created in layers, which are created from the semi-finished product, which is most often subjected to thermal treatment or using light or ultraviolet rays. The technology of additive manufacturing has both advantages and disadvantages when compared to the traditionally used methods of processing thermoplastic materials, such as, for example, injection or extrusion. The most important advantages are low cost, flexibility and speed of manufacturing of elements with different spatial shapes. From the point of view of the user of the product, the most important disadvantages are the lower mechanical properties and lower resistance to environmental factors that occur during the use of the manufactured products. The purpose of this review is to present current information and a compilation of features in the field of research on the effects of the interactions of different types of environments on the mechanical properties of 3D-manufactured thermoplastic products. Changes in the structure and mechanical properties of the material under the influence of factors such as humidity, salt, temperature, UV rays, gasoline and the environment of the human body are presented. The presented article enables the effects of environmental conditions on common materials used in 3D printing technology to be collated in one place. Full article
(This article belongs to the Special Issue Polish Achievements in Materials Science and Engineering)
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<p>The range of subjects discussed in the review, along with the materials.</p> Full article ">
11 pages, 13098 KiB  
Article
Internal and Marginal Adaptation of Adhesive Resin Cements Used for Luting Inlay Restorations: An In Vitro Micro-CT Study
by Linah M. Ashy and Hanadi Marghalani
Materials 2022, 15(17), 6161; https://doi.org/10.3390/ma15176161 - 5 Sep 2022
Cited by 8 | Viewed by 2185
Abstract
Adequate internal adaptation and marginal sealing of resin luting cements are of particular importance for the success of cemented ceramic inlays. The purpose of this study was to investigate the initial adaptation of different resin cements at the tooth-inlay restoration interface at enamel [...] Read more.
Adequate internal adaptation and marginal sealing of resin luting cements are of particular importance for the success of cemented ceramic inlays. The purpose of this study was to investigate the initial adaptation of different resin cements at the tooth-inlay restoration interface at enamel versus dentin surfaces. Thirty-two extracted human molars were allocated to four groups. One Class II cavity was prepared in each tooth. In each group, half of the cavities’ gingival floors were on enamel while the other halves were on cementum. Lava Ultimate CAD/CAM inlays were luted to the cavities using the following adhesive systems: RelyX Unicem, RelyX Ultimate, eCement, and Variolink Esthetic DC. After staining teeth with silver nitrate solution, marginal and internal gap volumes were determined using micro-CT images. Statistical analyses were conducted by independent t test and one-way ANOVA followed by post hoc Tukey test (p < 0.05). The internal and marginal gap volume values were the highest for Variolink Esthetic DC at the dentin surface (0.629 ± 0.363) and (2.519 ± 1.007), respectively, and the lowest for RelyX Unicem at the enamel surface (0.005 ± 0.004) and (0.009 ± 0.003), respectively. The internal and marginal adaptation on the enamel surface for RelyX Unicem and RelyX Ultimate resin cements were comparable to each other and to eCement but significantly better than Variolink Esthetic DC cement. Regardless of the adhesive resin system used, adaptation on enamel is superior to that on dentin surfaces. Full article
(This article belongs to the Special Issue Polymeric Materials for Oral and Maxillofacial Reconstructive Treatment)
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<p>Micro-CT images of internal and marginal gap at the gingival floor of a Class II Lava Ultimate inlay luted with RelyX Unicem resin cement on (<b>a</b>) enamel and (<b>b</b>) cementum/dentin. Inl, inlay; E, enamel; D, dentin.</p> Full article ">Figure 2
<p>Micro-CT images of internal and marginal gap at the gingival floor of a Class II Lava Ultimate inlay luted with RelyX Ultimate resin cement on (<b>a</b>) enamel and (<b>b</b>) cementum/dentin. Inl, inlay; E, enamel; D, dentin.</p> Full article ">Figure 3
<p>Micro-CT images of internal and marginal gap at the gingival floor of a Class II Lava Ultimate inlay luted with <span class="html-italic">e</span>Cement resin cement on (<b>a</b>) enamel and (<b>b</b>) cementum/dentin. Adhesive layer contains: solid arrow, silver deposits; dotted arrow, void.</p> Full article ">Figure 4
<p>Micro-CT images internal and marginal gap at the gingival floor of a Class II Lava Ultimate inlay luted with Variolink esthetic DC resin cement on (<b>a</b>) enamel and (<b>b</b>) cementum/dentin. Adhesive layer contains: solid arrow, silver deposits; dotted arrow, void.</p> Full article ">Figure 5
<p>Mean internal gap volume (mm<sup>3</sup>) of inlay restoration associated with different resin cements on enamel vs. cementum/dentin surfaces.</p> Full article ">Figure 6
<p>Mean marginal gap volume (mm<sup>3</sup>) of inlay restoration associated with different resin cements on enamel vs. cementum/dentin surfaces.</p> Full article ">
9 pages, 2342 KiB  
Article
Quantum Cutting in Ultraviolet B-Excited KY(CO3)2:Tb3+ Phosphors
by Dechuan Li and Guangping Zhu
Materials 2022, 15(17), 6160; https://doi.org/10.3390/ma15176160 - 5 Sep 2022
Cited by 5 | Viewed by 1651
Abstract
Highly efficient quantum cutting KY(CO3)2:Tb3+ phosphors excited by ultraviolet B (UVB) and ultraviolet C (UVC) were investigated. The structural and spectroscopic properties were characterized by XRD analysis and fluorescence spectrophotometry, respectively. The results showed that the monoclinic crystal [...] Read more.
Highly efficient quantum cutting KY(CO3)2:Tb3+ phosphors excited by ultraviolet B (UVB) and ultraviolet C (UVC) were investigated. The structural and spectroscopic properties were characterized by XRD analysis and fluorescence spectrophotometry, respectively. The results showed that the monoclinic crystal structure of KY(CO3)2:Tb3+ remained in the Tb3+ doping range of 0~100%. In the excitation spectrum, two intense excitation peaks were observed in the ultraviolet range. Under the excitation of 283 nm, the maximum quantum efficiency of KY(CO3)2:0.7Tb3+ could reach 119%. However, the most efficient quantum cutting occurred at the 5K8 excited state in the cross-relaxation of 5K8 + 7F65D4 + 5D4. The Tb3+ content could be selected arbitrarily in the KY(CO3)2 host without any concentration quenching. Optimal quantum cutting concentrations of Tb3+ in KY(CO3)2 were 0.7 and 0.3 for the excitation of UVB and UVC, respectively. UVB-excited phosphors are more popular with high transparency in products such as glass or resin. A quick response code was fabricated by resin to show the hidden information clearly. Therefore, the highly efficient phosphor could be a candidate material for the application in information identification technology. Full article
(This article belongs to the Special Issue Inorganic Luminescent Materials: Recent Years of Research and Application)
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<p>X-ray diffraction spectra of KYC:xTb<sup>3+</sup> (<span class="html-italic">x</span> = 0, 0.1, 0.3, 0.5, 0.7, 1).</p> Full article ">Figure 2
<p>(<b>a</b>–<b>f</b>) Morphologies of KYC:xTb<sup>3+</sup>(<span class="html-italic">x</span> = 0.01, 0.1, 0.3, 0.5, 0.7, 1); (<b>g</b>) Selected area of KYC:0.5Tb<sup>3+</sup>; (<b>h</b>–<b>k</b>) Element mapping of K, Y, Tb, and O; (<b>l</b>) Energy dispersive spectroscopy analysis.</p> Full article ">Figure 3
<p>Luminescence spectra of KYC:<span class="html-italic">x</span>Tb<sup>3+</sup>: (<b>a</b>) excitation spectra; (<b>b</b>) emission spectra of KYC:0.001Tb<sup>3+</sup>; (<b>c</b>) emission spectra excited at 283 nm; (<b>d</b>) emission spectra excited at 351 nm.</p> Full article ">Figure 4
<p>Energy level diagram of KYC:Tb<sup>3+.</sup></p> Full article ">Figure 5
<p>Decay curves (<b>a</b>) and energy level lifetimes (<b>b</b>) of KYC:<span class="html-italic">x</span>Tb<sup>3+.</sup></p> Full article ">Figure 6
<p>(<b>a</b>) Chromaticity point of phosphor; (<b>b</b>) Quick response code; (<b>c</b>) Quick response code excited by 365 nm LED.</p> Full article ">
13 pages, 20829 KiB  
Article
Effect of Dynamic Preheating on the Thermal Behavior and Mechanical Properties of Laser-Welded Joints
by Linyi Xie, Wenqing Shi, Teng Wu, Meimei Gong, Detao Cai, Shanguo Han and Kuanfang He
Materials 2022, 15(17), 6159; https://doi.org/10.3390/ma15176159 - 5 Sep 2022
Cited by 4 | Viewed by 2274
Abstract
The high cooling rate and temperature gradient caused by the rapid heating and cooling characteristics of laser welding (LW) leads to excessive thermal stress and even cracks in welded joints. In order to solve these problems, a dynamic preheating method that uses hybrid [...] Read more.
The high cooling rate and temperature gradient caused by the rapid heating and cooling characteristics of laser welding (LW) leads to excessive thermal stress and even cracks in welded joints. In order to solve these problems, a dynamic preheating method that uses hybrid laser arc welding to add an auxiliary heat source (arc) to LW was proposed. The finite element model was deployed to investigate the effect of dynamic preheating on the thermal behavior of LW. The accuracy of the heat transfer model was verified experimentally. Hardness and tensile testing of the welded joint were conducted. The results show that using the appropriate current leads to a significantly reduced cooling rate and temperature gradient, which are conducive to improving the hardness and mechanical properties of welded joints. The yield strength of welded joints with a 20 A current for dynamic preheating is increased from 477.0 to 564.3 MPa compared with that of LW. Therefore, the use of dynamic preheating to reduce the temperature gradient is helpful in reducing thermal stress and improving the tensile properties of the joint. These results can provide new ideas for welding processes. Full article
(This article belongs to the Topic Advanced Processes in Metallurgical Technologies)
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<p>HLAW system.</p> Full article ">Figure 2
<p>Tensile sample showing dimensions (in millimeters).</p> Full article ">Figure 3
<p>FEM simulation framework.</p> Full article ">Figure 4
<p>Gauss heat source model: (<b>a</b>) LW; (<b>b</b>) HLAW.</p> Full article ">Figure 5
<p>Mesh of FEM.</p> Full article ">Figure 6
<p>Temperature distribution of the arc with currents of (<b>a</b>) 20 A and (<b>b</b>) 40 A.</p> Full article ">Figure 7
<p>Comparison of experimental temperature verification. (<b>a</b>) Temperature curve at point A (30,30,1). (<b>b</b>) Comparison of cross-section molten pool morphology with a 0 A current. (<b>c</b>) Comparison of cross-section molten pool morphology with a 20 A current.</p> Full article ">Figure 8
<p>Temperature distribution at 2.5 s with currents of (<b>a</b>) 0 A and (<b>b</b>) 20 A. (<b>c</b>,<b>d</b>) Magnified views of the central region taken from the central areas in (<b>a</b>,<b>b</b>), respectively.</p> Full article ">Figure 9
<p>Temperature distribution with different currents at special points. (<b>a</b>) Maximum temperature gradients at special points (50, 0, 1). (<b>b</b>) Maximum cooling rate at special points (50, 0, 1). (<b>c</b>) Maximum temperature gradients at special points (<span class="html-italic">x</span>, 0, 1). (<b>d</b>) Maximum cooling rate at special points (<span class="html-italic">x</span>, 0, 1).</p> Full article ">Figure 10
<p>Microhardness distribution in the weld section. (<b>a</b>) Microhardness test position. (<b>b</b>) Microhardness test results.</p> Full article ">Figure 11
<p>Microstructural images obtained from the optical microscope for the WMs. (<b>a</b>–<b>e</b>) 0 A, 10 A, 20 A, 30 A, and 40 A currents, respectively.</p> Full article ">Figure 12
<p>Tensile mechanical properties.</p> Full article ">Figure 13
<p>Scanning electron microscope images of the fracture for (<b>a</b>) 20 A and (<b>b</b>) 40 A cases. (<b>c</b>) and (<b>d</b>) Higher magnification micrographs taken from the central areas in (<b>a</b>) and (<b>b</b>), respectively.</p> Full article ">
17 pages, 4382 KiB  
Article
Free Vibration Analysis of a Graphene-Platelet-Reinforced, Porous, Two-Cylindrical-Panel System
by Xianguang Sun, Weichao Chi and Jia Luo
Materials 2022, 15(17), 6158; https://doi.org/10.3390/ma15176158 - 5 Sep 2022
Cited by 4 | Viewed by 2080
Abstract
In this study, a novel, dynamic model of a graphene-platelet-reinforced, porous (GPLRP) double-cylindrical-panel system is proposed. The material properties of a graphene-platelet-reinforced, porous, double-cylindrical-panel system were determined by the Halpin–Tsai micromechanics model and the typical mechanical properties of open-cell metal foams. Different types [...] Read more.
In this study, a novel, dynamic model of a graphene-platelet-reinforced, porous (GPLRP) double-cylindrical-panel system is proposed. The material properties of a graphene-platelet-reinforced, porous, double-cylindrical-panel system were determined by the Halpin–Tsai micromechanics model and the typical mechanical properties of open-cell metal foams. Different types of porosity distribution and graphene platelet (GPL) distribution patterns were considered. Love’s shell theory was utilized to derive the theoretical formulation, and the Rayleigh–Ritz method was used to calculate the natural frequencies of the system. The proposed model was validated by several comparison studies with the natural frequencies in the existing literature. Finally, the effects of stiffness of Winkler springs, boundary condition, porosity coefficient, porosity distribution, GPL distribution pattern, and GPL weight fraction on the free vibration characteristics of the system were evaluated. Full article
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<p>Schematic diagram of the GPLRP, two-cylindrical-panel system. (<b>a</b>) two-cylindrical-panel system; (<b>b</b>) single-cylindrical-panel.</p> Full article ">Figure 2
<p>Cross-section of a single GPLRP, cylindrical panel for different porosity distributions. (<b>a</b>) Porosity-I; (<b>b</b>) Porosity-II; (<b>c</b>) Porosity-III.</p> Full article ">Figure 3
<p>Three types of GPL distribution patterns. (<b>a</b>) GPL A; (<b>b</b>) GPL B; (<b>c</b>) GPL C.</p> Full article ">Figure 4
<p>The influences of spring stiffness on first six dimensionless natural frequencies of the GPLRP, two-cylindrical-panel system (Porosity-I, GPL A, <span class="html-italic">e</span><sub>1</sub> = 0.5). (<b>a</b>) SSSS; (<b>b</b>) CCCC.</p> Full article ">Figure 5
<p>The influences of porosity coefficient on dimensionless fundamental frequencies of the GPLRP, two-cylindrical-panel system (SSSS). (<b>a</b>) Porosity-I; (<b>b</b>) Porosity-II; (<b>c</b>) Porosity-III.</p> Full article ">Figure 6
<p>The influences of porosity coefficient on dimensionless fundamental frequencies of the GPLRP, two-cylindrical-panel system (CCCC). (<b>a</b>) Porosity-I; (<b>b</b>) Porosity-II; (<b>c</b>) Porosity-III.</p> Full article ">Figure 7
<p>The influences of porosity coefficient on dimensionless fundamental frequencies of the GPLRP, two-cylindrical-panel system (SSSS). (<b>a</b>) GPL A; (<b>b</b>) GPL B; (<b>c</b>) GPL C.</p> Full article ">Figure 8
<p>The influences of porosity coefficient on dimensionless fundamental frequencies of the GPLRP, two-cylindrical-panel system (CCCC). (<b>a</b>) GPL A; (<b>b</b>) GPL B; (<b>c</b>) GPL C.</p> Full article ">Figure 9
<p>The influences of GPL weight fraction on dimensionless fundamental frequencies of the GPLRP, two-cylindrical-panel system (SSSS). (<b>a</b>) Porosity-I; (<b>b</b>) Porosity-II; (<b>c</b>) Porosity-III.</p> Full article ">
19 pages, 6051 KiB  
Article
Statistical Assessment of Fracture Toughness Results from the HAZ of X80 Pipeline FCAW Girth Weld
by Hongyuan Chen, Qingshan Feng, Ying Bi, Xiongxiong Gao, Lianshuang Dai and Qiang Chi
Materials 2022, 15(17), 6157; https://doi.org/10.3390/ma15176157 - 5 Sep 2022
Cited by 2 | Viewed by 2094
Abstract
Due to the wide application of flux-cored arc welds (FCAW) susceptible to significant scatter in weld and Heat Affected Zone (HAZ) fracture toughness, there is an interest in methods for evaluating the reliability of welds containing defects. The mechanical properties of the FCAW [...] Read more.
Due to the wide application of flux-cored arc welds (FCAW) susceptible to significant scatter in weld and Heat Affected Zone (HAZ) fracture toughness, there is an interest in methods for evaluating the reliability of welds containing defects. The mechanical properties of the FCAW girth weld of an X80 pipeline are tested and then analyzed. By obtaining fracture toughness results from a statistically significant number of SENB specimens, with notches positioned in different HAZ locations, the effect of variation within the results can be evaluated. The results of the fracture toughness tests were analyzed using statistical methods, to compare both the difference in behavior between HAZ microstructures and the variation when a similar microstructure has been sampled. The range of different characteristic toughness values was analyzed using a postulated ECA case to illustrate the sensitivity of the results to how toughness is defined. The analyses supported recommendations to be made on the optimum approach to characterizing HAZ fracture toughness for reliable pipeline assessments in multi-pass girth welds with complex HAZ microstructure distributions. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Pipeline Steel)
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<p>Schematic diagrams showing specimen location in the girth weld.</p> Full article ">Figure 2
<p>Macro section W01-04 of the 12 o’clock region of the FCAW girth weld.</p> Full article ">Figure 3
<p>Microstructure in the location of the ICGCHAZ identified in <a href="#materials-15-06157-f001" class="html-fig">Figure 1</a>.</p> Full article ">Figure 4
<p>Microstructure in the location of the ICGCHAZ from <a href="#materials-15-06157-f002" class="html-fig">Figure 2</a> at higher magnification, showing coarse grains decorated with second phase precipitates around the grain boundaries.</p> Full article ">Figure 5
<p>Microstructure in the location of the ICGCHAZ from <a href="#materials-15-06157-f003" class="html-fig">Figure 3</a> at highest magnification, showing coarse grains decorated with second phase precipitates around the grain boundaries.</p> Full article ">Figure 6
<p>Stress–strain curves generated from round tensile specimen from the parent metal, and from two all-weld metal round tensile specimens, tested at room temperature.</p> Full article ">Figure 7
<p>Charpy impact energy ductile-to-brittle transition curves for weld centerline notched specimens.</p> Full article ">Figure 8
<p>Charpy percent shear area ductile-to-brittle transition curves for weld centerline notched specimens.</p> Full article ">Figure 9
<p>Charpy impact energy ductile-to-brittle transition curves for HAZ notched specimens.</p> Full article ">Figure 10
<p>Charpy impact energy ductile-to-brittle transition curves for HAZ notched specimens.</p> Full article ">Figure 11
<p>Example of post-test metallography from specimen W01-40, characterizing the distance of the crack tip from the fusion line, in terms of s1 and s2.</p> Full article ">Figure 12
<p>Example of post-test metallography from specimen W01-31, characterizing the distance of the crack tip from the fusion line, in terms of s1 and s2.</p> Full article ">Figure 13
<p>Frequency distribution of the valid fracture toughness results from the quasi-static SENB specimens notched to sample the weld fusion line, showing the range and scatter.</p> Full article ">Figure 14
<p>Results of quasi-static SENB specimens HAZ notched at the fusion line, plotted to show the fracture toughness, J against the shortest distance of the crack tip to the fusion line. The results to the left of the dotted line are ‘valid’.</p> Full article ">Figure 15
<p>Failure Assessment Diagram (FAD) showing example pipe girth weld assessments with sensitivity cases for a range of fracture toughness values based on interpretation of these experimental results listed in <a href="#materials-15-06157-t008" class="html-table">Table 8</a>.</p> Full article ">
24 pages, 4589 KiB  
Article
Hybrid Ti6Al4V/Silk Fibroin Composite for Load-Bearing Implants: A Hierarchical Multifunctional Cellular Scaffold
by Simone Murchio, Matteo Benedetti, Anastasia Berto, Francesca Agostinacchio, Gianluca Zappini and Devid Maniglio
Materials 2022, 15(17), 6156; https://doi.org/10.3390/ma15176156 - 5 Sep 2022
Cited by 8 | Viewed by 2774
Abstract
Despite the tremendous technological advances that metal additive manufacturing (AM) has made in the last decades, there are still some major concerns guaranteeing its massive industrial application in the biomedical field. Indeed, some main limitations arise in dealing with their biological properties, specifically [...] Read more.
Despite the tremendous technological advances that metal additive manufacturing (AM) has made in the last decades, there are still some major concerns guaranteeing its massive industrial application in the biomedical field. Indeed, some main limitations arise in dealing with their biological properties, specifically in terms of osseointegration. Morphological accuracy of sub-unital elements along with the printing resolution are major constraints in the design workspace of a lattice, hindering the possibility of manufacturing structures optimized for proper osteointegration. To overcome these issues, the authors developed a new hybrid multifunctional composite scaffold consisting of an AM Ti6Al4V lattice structure and a silk fibroin/gelatin foam. The composite was realized by combining laser powder bed fusion (L-PBF) of simple cubic lattice structures with foaming techniques. A combined process of foaming and electrodeposition has been also evaluated. The multifunctional scaffolds were characterized to evaluate their pore size, morphology, and distribution as well as their adhesion and behavior at the metal–polymer interface. Pull-out tests in dry and hydrated conditions were employed for the mechanical characterization. Additionally, a cytotoxicity assessment was performed to preliminarily evaluate their potential application in the biomedical field as load-bearing next-generation medical devices. Full article
(This article belongs to the Special Issue Development of Bioactive Materials and Coatings for Biomedical Applications)
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<p>A 3D model of the L-PBF Ti6Al4V simple cubic lattice structure (on the <b>left</b>) and the simple cubic lattice unit (on the <b>right</b>). T0 is the diameter of the strut (670 µm), R is the radius of the fillet at the junction (600 µm), and L represents the side of the cell unit (4 mm).</p> Full article ">Figure 2
<p>An illustration and image of the electrowetting setup, composed of a DC power supply, a siphon, a counter-electrode chamber in aluminum, and the Ti6Al4V cage, acting as the anode of the electrophoretic chamber. A close-up image of an electrowetted composite system is reported in the lower-right corner of the figure.</p> Full article ">Figure 3
<p>The workflow of the pore analysis in Fiji. Starting from the SEM initial image (<b>a</b>), thresholding was applied with the percentile method (<b>b</b>). Subsequent artifact cleaning (<b>c</b>) and binary mask inversion (<b>d</b>) were applied before the segmentation process (<b>e</b>). Detected porosity along the frame edges was excluded.</p> Full article ">Figure 4
<p>(<b>A</b>) The bar plots of the mean gelation temperatures with respect to the solution composition are reported along with the error bars. The dotted line indicates the trend connection line of the temperature mean values. The investigated solutions were pure gelatin (G) and the mixture of gelatin/silk fibroin in different volume ratios, respectively, of 1:2, 1:3, and 1:4. (<b>B</b>) The ξ-potential interval plot showing the mean value and the SD error bar of pure gelatin (G), G/SF 1:4, and pure silk fibroin (SF) is reported with the mean trend line.</p> Full article ">Figure 5
<p>A representative close-up of the FE-SEM images of the four composite specimens at the metal-polymer interface were attached with a representative 3D reconstruction of a single strut of the LPBF Ti6Al4V lattice structure. The four FE-SEM images represent the silk fibroin foamed (SF) composite specimens (top-left), the silk fibroin electrowet (SF_EW) composite specimens (top-right), the silk fibroin/gelatin foamed (SFG) composite specimens (bottom-left), and the silk fibroin/gelatin electrowet (SFG_EW) composite specimens (bottom-right). Scale bars were set to 2 µm for all four images.</p> Full article ">Figure 6
<p>Sketches of the proposed mechanisms related to the foaming and the electrowetting processes. (<b>A</b>) The drawing depicts a comparison between the foaming and electrowetting of a pure silk fibroin solution, highlighting the electrodeposition of SF and its reorganization into a more ordered structure and β-sheets enriched the coating of the outermost titanium surface. Possible different fracture location lines, ascribable to the role of hydrolysis-induced porosity, are reported. (<b>B</b>) The sketch reports the main possible driving mechanisms of the SFG electrowetting. The intermolecular interactions of SF and G in the blend solution generated polyelectrolyte complexes, which were reordered along the electric field lines and reorganized in dipole configurations. The latter exposed the negative chains toward the titanium surface, while the positive side faced the counter-electrode. (<b>C</b>) The SFG foaming sketch highlighting the role of gelatin in possibly creating a gel nanolayer at the liquid–gas interface, wrapping the N20 particles. Combined with the G/SF complexes, this can help hinder Ostwald ripening or coalescence phenomena.</p> Full article ">Figure 7
<p>(<b>A</b>) Example of FE-SEM images of the four different foams involved in the porosity analysis. The scale bar was set to 100 µm. (<b>B</b>) Box plots with the distribution histograms for the four porosity parameters investigated, namely, the area (μm<sup>2</sup>), the equivalent diameter (μm), the circularity C, and the aspect ratio AR. The box charts report the IQR, mean, and median values. The upper and lower bounds were set at 1.5 IQR. (<b>C</b>) Multi-comparison bar plots with the <span class="html-italic">p</span>-value significance were reported for the area, equivalent diameter, circularity, and aspect ratio (AR).</p> Full article ">Figure 8
<p>The averaged force–displacement curves pull-out curves for dry (<b>A</b>) and wet (<b>B</b>) conditions for the four investigated classes of specimens. Scatter bands are also represented. (<b>C</b>) Comparative boxplots, depicting the interfacial shear strength values against the four different classes of specimens for the two different testing conditions (dry and wet). Boxplots show the IQR, mean, and median values. The upper and lower bounds were set at 1.5 IQR. Dotted and dashed lines represent the mean trend line for dry specimens and the mean trend line for wet specimens, respectively. (<b>D</b>) The FE-SEM images of the pull-out failure surfaces for the dry (<b>a</b>–<b>d</b>) and wet (<b>e</b>–<b>h</b>) specimens. The scale bars were set to 100 μm. (<b>E</b>) Close-up FE-SEM images of the pull-out failure surfaces for the dry (<b>a</b>–<b>d</b>) and wet (<b>e</b>–<b>h</b>) specimens. Scale bars were set to 10 μm.</p> Full article ">Figure 9
<p>The bar plots reporting the %LDH values against the different conditions tested. Two controls, positive (CTRL+) and negative (CTRL−), were also reported. The evaluated conditions are the bare titanium cage (Ti), the four previously investigated composite conditions (herein classified as Ti + SF, Ti + SF_EW, Ti + SFG, and Ti + SFG_EW), and two stand-alone foams, namely one of pure silk fibroin (SF) and one of the blended compositions at a volume ratio of gelatin-silk fibroin 1:4 (SFG). The dashed line indicates the threshold limit below which the sample is not considered cytotoxic.</p> Full article ">
20 pages, 4058 KiB  
Review
Steel Fiber-Reinforced Concrete: A Systematic Review of the Research Progress and Knowledge Mapping
by Muhammad Nasir Amin, Waqas Ahmad, Kaffayatullah Khan and Ayaz Ahmad
Materials 2022, 15(17), 6155; https://doi.org/10.3390/ma15176155 - 5 Sep 2022
Cited by 20 | Viewed by 4311
Abstract
This study performed a scientometric-based examination of the literature on steel fiber-reinforced concrete (SFRC) to identify its key elements. Typical review papers are limited in their capacity to link distinct segments of the literature in an organized and systematic method. The most challenging [...] Read more.
This study performed a scientometric-based examination of the literature on steel fiber-reinforced concrete (SFRC) to identify its key elements. Typical review papers are limited in their capacity to link distinct segments of the literature in an organized and systematic method. The most challenging aspects of current research are knowledge mapping, co-occurrence, and co-citation. The Scopus search engine was used to search for and obtain the data required to meet the goals of the study. During the data evaluation, the relevant publication sources, keyword assessment, productive authors based on publications and citations, top papers based on citations received, and areas vigorously involved in SFRC studies were recognized. The VOSviewer software tool was used to evaluate the literature data from 9562 relevant papers, which included citation, abstract, bibliographic, keywords, funding, and other information. Furthermore, the applications and constraints related to the usage of SFRC in the construction sector were examined, as well as potential solutions to these constraints. It was determined that only 17 publication sources (journals/conferences) had published at least 100 articles on SFRC up to June 2022. Additionally, the mostly employed keywords by authors in SFRC research include steel fibers, fiber-reinforced concrete, concrete, steel fiber-reinforced concrete, and reinforced concrete. The assessment of authors revealed that 39 authors had published at least 30 articles. Moreover, China, the United States, and India were found to be the most active and participating countries based on publications on SFRC research. This study can assist academics in building collaborative initiatives and communicating new ideas and techniques because of the quantitative and graphical depiction of participating nations and researchers. Full article
(This article belongs to the Special Issue Fiber-Reinforced Concrete: Design, Characterization, and Applications)
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<p>Documents’ subject area in the research of SFRC.</p> Full article ">Figure 2
<p>Types of documents published on the SFRC research up to June 2022.</p> Full article ">Figure 3
<p>Documents published annually on the SFRC research up to June 2022.</p> Full article ">Figure 4
<p>Mapping of publication sources with at least 100 publications: (<b>a</b>) Network map; (<b>b</b>) Density map.</p> Full article ">Figure 4 Cont.
<p>Mapping of publication sources with at least 100 publications: (<b>a</b>) Network map; (<b>b</b>) Density map.</p> Full article ">Figure 5
<p>Mapping keywords in the subject topic: (<b>a</b>) Scientific map; (<b>b</b>) Density map.</p> Full article ">Figure 6
<p>Scientific collaboration of authors: (<b>a</b>) Map of authors with minimum 30 publications; (<b>b</b>) Density of authors based on their contribution.</p> Full article ">Figure 6 Cont.
<p>Scientific collaboration of authors: (<b>a</b>) Map of authors with minimum 30 publications; (<b>b</b>) Density of authors based on their contribution.</p> Full article ">Figure 7
<p>Knowledge map of documents: (<b>a</b>) Map of documents with at least 150 citations; (<b>b</b>) Connected documents based on citations.</p> Full article ">Figure 8
<p>Mapping of countries with minimum 50 publications: (<b>a</b>) Scientific map; (<b>b</b>) Density.</p> Full article ">Figure 8 Cont.
<p>Mapping of countries with minimum 50 publications: (<b>a</b>) Scientific map; (<b>b</b>) Density.</p> Full article ">
20 pages, 21476 KiB  
Article
Dynamic Compressive Mechanical Properties of UR50 Ultra-Early-Strength Cement-Based Concrete Material under High Strain Rate on SHPB Test
by Wei Wang, Zhonghao Zhang, Qing Huo, Xiaodong Song, Jianchao Yang, Xiaofeng Wang, Jianhui Wang and Xing Wang
Materials 2022, 15(17), 6154; https://doi.org/10.3390/ma15176154 - 5 Sep 2022
Cited by 11 | Viewed by 2011
Abstract
UR50 ultra-early-strength cement-based self-compacting high-strength material is a special cement-based material. Compared with traditional high-strength concrete, its ultra-high strength, ultra-high toughness, ultra-impact resistance, and ultra-high durability have received great attention in the field of protection engineering, but the dynamic mechanical properties of impact [...] Read more.
UR50 ultra-early-strength cement-based self-compacting high-strength material is a special cement-based material. Compared with traditional high-strength concrete, its ultra-high strength, ultra-high toughness, ultra-impact resistance, and ultra-high durability have received great attention in the field of protection engineering, but the dynamic mechanical properties of impact compression at high strain rates are not well known, and the dynamic compressive properties of materials are the basis for related numerical simulation studies. In order to study its dynamic compressive mechanical properties, three sets of specimens with a size of Φ100 × 50 mm were designed and produced, and a large-diameter split Hopkinson pressure bar (SHPB) with a diameter of 100 mm was used to carry out impact tests at different speeds. The specimens were mainly brittle failures. With the increase in impact speed, the failure mode of the specimens gradually transits from larger fragments to small fragments and a large amount of powder. The experimental results show that the ultra-early-strength cement-based material has a greater impact compression brittleness, and overall rupture occurs at low strain rates. Its dynamic compressive strength increases with the increase of strain rates and has an obvious strain rate strengthening effect. According to the test results, the relationship curve between the dynamic enhancement factor and the strain rate is fitted. As the impact speed increases, the peak stress rises, the energy absorption density increases, and its growth rate accelerates. Afterward, based on the stress–strain curve, the damage variables under different strain rates were fitted, and the results show that the increase of strain rate has a hindering effect on the increase of damage variables and the increase rate. Full article
(This article belongs to the Special Issue Mechanical Research of Reinforced Concrete Materials)
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<p>Physical image of processed specimens.</p> Full article ">Figure 2
<p>An SHPB device separated by 100 mm. (<b>a</b>) Physical map of the SHPB device. (<b>b</b>) Schematic diagram of the SHPB device.</p> Full article ">Figure 3
<p>Physical photos of the test process.</p> Full article ">Figure 4
<p>Original stress wave. (<b>a</b>) SHPB test collection wave. (<b>b</b>) The three waves graph.</p> Full article ">Figure 5
<p>Stress–strain curve of 5 m/s.</p> Full article ">Figure 6
<p>Stress–strain curve of 10 m/s.</p> Full article ">Figure 7
<p>Stress–strain curve of 15 m/s.</p> Full article ">Figure 8
<p>Dynamic stress–strain curve at different strain rates.</p> Full article ">Figure 9
<p>Relationship between DIF and strain rate.</p> Full article ">Figure 10
<p>Energy absorption density–strain curve. (<b>a</b>) Impact velocity of 5 m/s. (<b>b</b>) Impact velocity of 10 m/s. (<b>c</b>) Impact velocity of 15 m/s. (<b>d</b>) Average value.</p> Full article ">Figure 10 Cont.
<p>Energy absorption density–strain curve. (<b>a</b>) Impact velocity of 5 m/s. (<b>b</b>) Impact velocity of 10 m/s. (<b>c</b>) Impact velocity of 15 m/s. (<b>d</b>) Average value.</p> Full article ">Figure 11
<p>Damage evolution variable. (<b>a</b>) Impact velocity of 5 m/s. (<b>b</b>) Impact velocity of 10 m/s. (<b>c</b>) Impact velocity of 15 m/s. (<b>d</b>) Average value.</p> Full article ">Figure 12
<p>Comparison of damage variable fitting results.</p> Full article ">Figure 13
<p>The relationship between elastic modulus and strain rate.</p> Full article ">Figure 14
<p>Comparison of fitting results with test results.</p> Full article ">
20 pages, 5062 KiB  
Article
Comprehensive Evaluation of the Sustainability of Waste Concrete towards Structural Concrete Application in Freeze-Thaw Environment
by Da Wei, Pinghua Zhu, Shan Gao, Xiancui Yan, Hui Liu and Haifeng Fan
Materials 2022, 15(17), 6153; https://doi.org/10.3390/ma15176153 - 5 Sep 2022
Cited by 7 | Viewed by 1561
Abstract
To promote the in-situ and structural application of waste concrete in cold regions, the sustainable application potential of waste concrete in a freeze-thaw (F-T) environment was comprehensively evaluated from three aspects of performance, environmental load, and economic benefit. The recycled aggregate concrete (RAC) [...] Read more.
To promote the in-situ and structural application of waste concrete in cold regions, the sustainable application potential of waste concrete in a freeze-thaw (F-T) environment was comprehensively evaluated from three aspects of performance, environmental load, and economic benefit. The recycled aggregate concrete (RAC) was produced by recycled coarse aggregate (RCA), which was obtained from the crushing of natural aggregate concrete (NAC) after every F-T 150 cycles until F-T failure. The effects of F-T damage of parent concrete on the physical properties of RCA and mechanical and frost resistance of RAC under 35% flexural stress were studied. Besides, the sustainability of NAC and RAC was compared and analyzed by emergy theory. The results suggested that the physical properties of RCA deteriorated gradually with the accumulation of F-T damage to parent concrete. The RCA obtained from parent concrete that suffered F-T damage could be used as coarse aggregate for structural concrete when F-T damage is smaller than 0.367. The F-T damage of parent concrete had an adverse effect on the mechanical properties and frost resistance of RAC. The frost resistance of RAC obtained from parent concrete with larger F-T damage was worse. The RAC prepared from parent concrete without F-T failure can serve 50 years in cold regions, while that with F-T failure can only serve 30 years. The F-T damage microelements were dispersed in the adhesive mortar of RCA and transferred to RAC, resulting in the reduction of the mechanical properties and frost resistance of RAC. Emergy analysis showed that the reuse of waste concrete after F-T failure required higher economic input, higher environment load, lower output efficiency, and sustainability. The performance, environmental load and economic benefit of RAC prepared by using waste concrete after F-T failure were inferior to that of waste concrete without F-T failure. Waste concrete after F-T failure is not recommended to be used as coarse aggregate for structural concrete. Full article
(This article belongs to the Special Issue Cement-Based Materials Applied in Sustainable Construction)
►▼ Show Figures

Figure 1

Figure 1
<p>Loading procedure diagram.</p> Full article ">Figure 2
<p>Temperature variation during F-T cycles.</p> Full article ">Figure 3
<p>Experimental process.</p> Full article ">Figure 4
<p>The variations of <span class="html-italic">f<sub>c</sub></span> (<b>a</b>) and <span class="html-italic">f<sub>f</sub></span> (<b>b</b>) of NAC after F-T cycles.</p> Full article ">Figure 5
<p>The variations of MLR (<b>a</b>) and RDME (<b>b</b>) of NAC after F-T cycles.</p> Full article ">Figure 6
<p>The variation of D<sub>(n)</sub> of NAC during F-T cycles [<a href="#B18-materials-15-06153" class="html-bibr">18</a>,<a href="#B42-materials-15-06153" class="html-bibr">42</a>].</p> Full article ">Figure 7
<p>The particle size proportions of RA-<span class="html-italic">i</span>.</p> Full article ">Figure 8
<p>Variation law of apparent density (<b>a</b>) crushing value (<b>b</b>) water absorption (<b>c</b>) and adhesive mortar content (<b>d</b>) of RCA with F-T damage of parent concrete.</p> Full article ">Figure 8 Cont.
<p>Variation law of apparent density (<b>a</b>) crushing value (<b>b</b>) water absorption (<b>c</b>) and adhesive mortar content (<b>d</b>) of RCA with F-T damage of parent concrete.</p> Full article ">Figure 9
<p>The variations of <span class="html-italic">f<sub>c</sub></span> (<b>a</b>) and <span class="html-italic">f<sub>f</sub></span> (<b>b</b>) of RAC-<span class="html-italic">i</span>.</p> Full article ">Figure 10
<p>The variations of MLR (<b>a</b>) and RDME (<b>b</b>) of RAC-<span class="html-italic">i</span>.</p> Full article ">Figure 11
<p>The variations of F-T damage of RAC-<span class="html-italic">i</span>.</p> Full article ">Figure 12
<p>The variations of porosity of RAC-<span class="html-italic">i</span>.</p> Full article ">Figure 13
<p>Micro morphology (<b>a</b>) NAC-0 (<b>b</b>) NAC-300 (<b>c</b>) NAC-600 (<b>d</b>) RAC1 (<b>e</b>) RAC3 (<b>f</b>) RAC5.</p> Full article ">Figure 14
<p>Effect mechanism of NAC F-T damage on properties of RAC.</p> Full article ">Figure 15
<p>The flow mode of energy in concrete production is (<b>a</b>) NAC; (<b>b</b>) RAC.</p> Full article ">
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