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Materials, Volume 12, Issue 13 (July-1 2019) – 176 articles

Cover Story (view full-size image): Ab initio calculations predict increased lithium binding energy and voltage for initial stages of lithiation of C60 substitutionally doped with one nitrogen or boron atom, but little effect on most of the voltage-capacity curve. Interestingly, voltage profiles computed with GGA and hybrid functionals are largely similar in spite of significant quantitative differences in the electronic structures. View this paper.
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16 pages, 6254 KiB  
Article
Microstructure and Abrasive Wear Resistance of Various Alloy Hardfacings for Application on Heavy-Duty Chipper Tools in Forestry Shredding and Mulching Operations
by Ladislav Falat, Miroslav Džupon, Miroslava Ťavodová, Richard Hnilica, Veronika Ľuptáčiková, Lucia Čiripová, Viera Homolová and Katarína Ďurišinová
Materials 2019, 12(13), 2212; https://doi.org/10.3390/ma12132212 - 9 Jul 2019
Cited by 16 | Viewed by 3750
Abstract
Five different alloy hardfacings on 16MnCr5 grade low-carbon ferritic–pearlitic steel were investigated in terms of their abrasive wear resistance in laboratory testing conditions. The selected hardfacing materials, namely “E520 RB”, “RD 571”, “LNM 420FM”, “E DUR 600”, and “Weartrode 62”, were individually deposited [...] Read more.
Five different alloy hardfacings on 16MnCr5 grade low-carbon ferritic–pearlitic steel were investigated in terms of their abrasive wear resistance in laboratory testing conditions. The selected hardfacing materials, namely “E520 RB”, “RD 571”, “LNM 420FM”, “E DUR 600”, and “Weartrode 62”, were individually deposited onto plain ground-finish surfaces of 10 mm thick steel plate samples. The studied hardfacings were fabricated using several different welding methods and process parameters proposed by their industrial manufacturers. In the present comparative study, the results obtained from laboratory abrasive wear tests of the investigated hardfacings were analyzed and discussed in relation to their microstructure, hardness, and wear mechanism characteristics. Regardless of great variety in microstructure and chemical composition of individual hardfacing materials, the results clearly indicated the governing factor for the wear resistance improvement to be the overall carbon content of the used hardfacing material. Thus it has been shown that the “E520 RB” hardfacing exhibited the highest abrasive wear resistance thanks to its appropriate hardness and beneficial “ledeburite-type” eutectic microstructure. Full article
(This article belongs to the Special Issue Tribology: Friction and Wear of Engineering Materials)
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Figure 1

Figure 1
<p>Testing apparatus for three-body abrasive wear test according to “ГОСТ 23.208-79” standard [<a href="#B25-materials-12-02212" class="html-bibr">25</a>]: schematic layout (<b>a</b>) and detailed photograph of the apparatus at work (<b>b</b>).</p> Full article ">Figure 2
<p>Characterization of “E520 RB” hardfacing: overall microstructure visualized by light-optical microscope (LOM) (<b>a</b>); detailed microstructure visualized by scanning electron microscope (SEM) (<b>b</b>); thermodynamic calculation of equilibrium phase composition depending on temperature (<b>c</b>); X-ray diffraction (XRD) pattern representing experimentally determined phase composition (<b>d</b>).</p> Full article ">Figure 3
<p>Characterization of “RD 571” hardfacing: overall microstructure visualized by LOM (<b>a</b>); detailed microstructure visualized by SEM (<b>b</b>); thermodynamic calculation of equilibrium phase composition depending on temperature (<b>c</b>); XRD-pattern representing experimentally determined phase composition (<b>d</b>).</p> Full article ">Figure 4
<p>Characterization of “LNM 420FM” hardfacing: overall microstructure visualized by LOM (<b>a</b>); detailed microstructure visualized by SEM (<b>b</b>); thermodynamic calculation of equilibrium phase composition depending on temperature (<b>c</b>); XRD-pattern representing experimentally determined phase composition (<b>d</b>).</p> Full article ">Figure 5
<p>Characterization of “E DUR 600” hardfacing: overall microstructure visualized by LOM (<b>a</b>); detailed microstructure visualized by SEM (<b>b</b>); thermodynamic calculation of equilibrium phase composition depending on temperature (<b>c</b>); XRD-pattern representing experimentally determined phase composition (<b>d</b>).</p> Full article ">Figure 6
<p>Characterization of “Weartrode 62” hardfacing: overall microstructure visualized by LOM (<b>a</b>); detailed microstructure visualized by SEM (<b>b</b>); thermodynamic calculation of phase composition depending on temperature (<b>c</b>); XRD-pattern representing experimentally determined phase composition (<b>d</b>).</p> Full article ">Figure 7
<p>Average surface hardness values of investigated materials: 0—16MnCr5 steel; 1—“E520 RB” hardfacing; 2—“RD 571” hardfacing; 3—“LNM 420FM” hardfacing; 4—“E DUR 600” hardfacing; 5—“Weartrode 62” hardfacing.</p> Full article ">Figure 8
<p>Average weight loss of investigated materials subjected to abrasive wear testing: 0—16MnCr5 steel; 1—“E520 RB” hardfacing; 2—“RD 571” hardfacing; 3—“LNM 420FM” hardfacing; 4—“E DUR 600” hardfacing; 5—“Weartrode 62” hardfacing.</p> Full article ">Figure 9
<p>Relative abrasive wear resistance in relation to hardness ratio: 0—16MnCr5 steel; 1—“E520 RB” hardfacing; 2—“RD 571” hardfacing; 3—“LNM 420FM” hardfacing; 4—“E DUR 600” hardfacing; 5—“Weartrode 62” hardfacing.</p> Full article ">Figure 10
<p>Typical cross-sectional profiles of wear tracks generated on the surfaces of investigated materials after abrasion wear tests: 16MnCr5 grade steel (<b>a</b>); “E520 RB” hardfacing (<b>b</b>); “RD 571” hardfacing (<b>c</b>); “LNM 420FM” hardfacing (<b>d</b>); “E DUR 600” hardfacing (<b>e</b>); “Weartrode 62” hardfacing (<b>f</b>).</p> Full article ">Figure 11
<p>Correlation between average weight loss and maximal wear track depth of investigated materials after abrasion wear testing: 0—16MnCr5 steel; 1—“E520 RB” hardfacing; 2—“RD 571” hardfacing; 3—“LNM 420FM” hardfacing; 4—“E DUR 600” hardfacing; 5—“Weartrode 62” hardfacing.</p> Full article ">Figure 12
<p>Typical wear mechanisms of selected hardfacings with significantly differing abrasive wear resistance: “E520 RB” (<b>a</b>); “Weartrode 62” (<b>b</b>); “RD 571” (<b>c</b>); “LNM 420FM” (<b>d</b>).</p> Full article ">
13 pages, 5158 KiB  
Article
Surface Roughness Characterisation and Analysis of the Electron Beam Melting (EBM) Process
by Manuela Galati, Paolo Minetola and Giovanni Rizza
Materials 2019, 12(13), 2211; https://doi.org/10.3390/ma12132211 - 9 Jul 2019
Cited by 67 | Viewed by 6399
Abstract
Electron Beam Melting (EBM) is a metal powder bed fusion (PBF) process in which the heat source is an electron beam. Differently from other metal PBF processes, today, EBM is used for mass production. As-built EBM parts are clearly recognisable by their surface [...] Read more.
Electron Beam Melting (EBM) is a metal powder bed fusion (PBF) process in which the heat source is an electron beam. Differently from other metal PBF processes, today, EBM is used for mass production. As-built EBM parts are clearly recognisable by their surface roughness, which is, in some cases, one of the major limitations of the EBM process. The aim of this work is to investigate the effects of the orientation and the slope of the EBM surfaces on the surface roughness. Additionally, the machine repeatability is studied by measuring the roughness of surfaces built at different positions on the start plate. To these aims, a specific artefact was designed. Replicas of the artefact were produced using an Arcam A2X machine and Ti6Al4V powder. Descriptive and inferential statistical methods were applied to investigate whether the surface morphology was affected by process factors. The results show significant differences between the upward and downward surfaces. The upward surfaces appear less rough than the downward ones, for which a lower standard deviation was obtained in the results. The roughness of the upward surfaces is linearly influenced by the sloping angle, while the heat distribution on the cross-section was found to be a key factor in explaining the roughness of the downward surfaces. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Artefact; and (<b>b</b>) positions of the replicas on the build plate (single job).</p> Full article ">Figure 2
<p>RTP-80 profilometer (Metrology Systems) with a TL90 drive unit and experimental setup for the acquisition of the surface roughness (<b>a</b>); and an example of roughness profiles (<b>b</b>).</p> Full article ">Figure 3
<p>Surface textures observed for the top surface (<b>a</b>), upward surfaces (<b>b</b>), and for the downward surfaces (<b>c</b>).</p> Full article ">Figure 4
<p>Analysis of the data distribution through (<b>a</b>) the Ryan–Joiner test and (<b>b</b>) a relative frequency histogram.</p> Full article ">Figure 5
<p>Linear regression model for the roughness of the upward surfaces.</p> Full article ">Figure 6
<p>Interval plot for surface roughness for the downward surfaces according to the slope (<b>a</b>) and the position on the build plate (<b>b</b>).</p> Full article ">Figure 7
<p>Melting areas at different build heights of the artefact (single replica).</p> Full article ">
13 pages, 2112 KiB  
Article
Femtosecond Laser Nano/Micro Textured Ti6Al4V Surfaces—Effect on Wetting and MG-63 Cell Adhesion
by Georg Schnell, Susanne Staehlke, Ulrike Duenow, J. Barbara Nebe and Hermann Seitz
Materials 2019, 12(13), 2210; https://doi.org/10.3390/ma12132210 - 9 Jul 2019
Cited by 45 | Viewed by 5718
Abstract
Nano- and microstructured titanium surfaces have recently attracted attention in the field of regenerative medicine because of the influence which surface characteristics such as roughness and wettability can have on cellular processes. This study focuses on the correlation of surface properties (wettability and [...] Read more.
Nano- and microstructured titanium surfaces have recently attracted attention in the field of regenerative medicine because of the influence which surface characteristics such as roughness and wettability can have on cellular processes. This study focuses on the correlation of surface properties (wettability and nano/micro texture) of laser-structured Ti6Al4V samples with pronounced cell adhesion. Samples were structured with multiple laser parameters in order to create a range of surface properties. Surface characterization was performed by contact angle measurements 1 and 7 days after laser processing. The arithmetic mean roughness of the material surface in an area (Sa) was determined by means of confocal laser scanning microscopy (CLSM). Immediately after wettability tests of the laser-structured surfaces, in vitro experiments with human MG-63 osteoblasts were carried out. For this purpose, the cell morphology and actin cytoskeleton organization were analyzed using CLSM and scanning electron microscopy. On rough microstructures with deep cavities, the cell growth and spreading were inhibited. An improved cellular adhesion and growth on nanostructured and sinusoidal microstructured surfaces could be demonstrated, regardless of hydrophilicity of the surfaces. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Surface characterization of laser-structured Ti6Al4V specimens. (<b>a</b>) Scanning electron microscope images (StereoScan360), scale bars left: 10 µm, right: 1 µm and (<b>b</b>) confocal laser scanning microscope images (LEXT OLS 4000), square side length: 256 µm, with corresponding elevation profile of laser irradiated structures and polished Ti6Al4V reference.</p> Full article ">Figure 2
<p>Cell morphology after 24 h on laser-structured samples (<b>a</b>) 1 day after laser process, and (<b>b</b>) 7 days after laser process (FE-SEM Merlin VP compact, scale bars above: 10 µm, below: 2 µm). (<b>c</b>) Cell area of osteoblasts on various nano/micro textured samples compared to planar reference (mean ± s.e.m., Kruskal–Wallis test post hoc uncorrected Dunn´s test, * <span class="html-italic">p</span> &lt; 0.001, n = 40 cells). Note that the cell growth was impaired on Micro1, which is independent of the wettability (see <a href="#materials-12-02210-t003" class="html-table">Table 3</a>).</p> Full article ">Figure 3
<p>Organization of the actin cytoskeleton in MG-63 cells cultivated for 24 h on nano/micro textured samples. (<b>a</b>,<b>b</b>) 1 day after laser structuring, and (<b>c</b>,<b>d</b>) 7 days after laser structuring (LSM780, (<b>a</b>,<b>c</b>) zoom1, scale bars: 10 µm, (<b>b</b>,<b>d</b>) zoom4, scale bars: 2 µm; red: actin, blue: nucleus). Note that the actin cytoskeleton was only cortically arranged or in short filaments inside the cells on Micro1, in contrast to all other samples, where cells exhibit long filaments through the cells.</p> Full article ">
24 pages, 9057 KiB  
Article
Generalized Softened Variable Angle Truss Model for RC Hollow Beams under Torsion
by Luís Bernardo
Materials 2019, 12(13), 2209; https://doi.org/10.3390/ma12132209 - 9 Jul 2019
Cited by 3 | Viewed by 2838
Abstract
In recent studies, a new softened truss model called Generalized Softened Variable Angle Truss Model (GSVATM) has been proposed to compute the full torsional response of reinforced concrete (RC) rectangular solid beams under pure torsion. In this article, the GSVATM is extended to [...] Read more.
In recent studies, a new softened truss model called Generalized Softened Variable Angle Truss Model (GSVATM) has been proposed to compute the full torsional response of reinforced concrete (RC) rectangular solid beams under pure torsion. In this article, the GSVATM is extended to cover RC hollow beams under torsion. The modification of the calculation procedure, in order to account for the specific behavior of RC hollow beams for low loading levels, as well as the final solution procedure, is presented. The theoretical predictions from the extended GSVATM are compared with experimental results of RC hollow beams under torsion found in the literature. Good agreement is observed between the experimental and theoretical results, for both high and low loading levels. Full article
(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Example of a RC box (hollow) beam for a bridge deck (dimensions in meters).</p> Full article ">Figure 2
<p>Beam elements modelled using the truss analogy: (<b>a</b>) thin beam, (<b>b</b>) box beam.</p> Full article ">Figure 3
<p>Strain gradient due the bending of the walls.</p> Full article ">Figure 4
<p>GSVATM flowchart for RC solid beams.</p> Full article ">Figure 5
<p>New flowchart for GSVATM for RC solid and hollow beams.</p> Full article ">Figure 6
<p>Geometrical parameters of the cross section.</p> Full article ">Figure 7
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam A095C.</p> Full article ">Figure 8
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam A120a.</p> Full article ">Figure 9
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam B065b.</p> Full article ">Figure 10
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam B080a.</p> Full article ">Figure 11
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam B110a.</p> Full article ">Figure 12
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam C065a.</p> Full article ">Figure 13
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam C100a.</p> Full article ">Figure 14
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam D075a.</p> Full article ">Figure 15
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam D090a.</p> Full article ">Figure 16
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam A2.</p> Full article ">Figure 17
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam A3.</p> Full article ">Figure 18
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam A4.</p> Full article ">Figure 19
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam A5.</p> Full article ">Figure 20
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam B2.</p> Full article ">Figure 21
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam B3.</p> Full article ">Figure 22
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam B4.</p> Full article ">Figure 23
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam B5.</p> Full article ">Figure 24
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam C2.</p> Full article ">Figure 25
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam C3.</p> Full article ">Figure 26
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam C4.</p> Full article ">Figure 27
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam C5.</p> Full article ">Figure 28
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam C6.</p> Full article ">Figure 29
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam D3.</p> Full article ">Figure 30
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam D4.</p> Full article ">Figure 31
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam T0.</p> Full article ">Figure 32
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam T1.</p> Full article ">Figure 33
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam T2.</p> Full article ">Figure 34
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam T5.</p> Full article ">Figure 35
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam VH1.</p> Full article ">Figure 36
<p><math display="inline"><semantics> <mrow> <msub> <mi>M</mi> <mi>T</mi> </msub> </mrow> </semantics></math>−θ curves for Beam VH2.</p> Full article ">
12 pages, 11437 KiB  
Article
An Experimental Study on Micro-Milling of a Medical Grade Co-Cr-Mo Alloy Produced by Selective Laser Melting
by Gabriele Allegri, Alessandro Colpani, Paola Serena Ginestra and Aldo Attanasio
Materials 2019, 12(13), 2208; https://doi.org/10.3390/ma12132208 - 9 Jul 2019
Cited by 44 | Viewed by 5016
Abstract
Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are very promising materials, in particular, in the biomedical field where their unique properties of biocompatibility and wear resistance can be exploited for surgery applications, prostheses, and many other medical devices. While Additive Manufacturing is a key technology in this [...] Read more.
Cobalt-chromium-molybdenum (Co-Cr-Mo) alloys are very promising materials, in particular, in the biomedical field where their unique properties of biocompatibility and wear resistance can be exploited for surgery applications, prostheses, and many other medical devices. While Additive Manufacturing is a key technology in this field, micro-milling can be used for the creation of micro-scale details on the printed parts, not obtainable with Additive Manufacturing techniques. In particular, there is a lack of scientific research in the field of the fundamental material removal mechanisms involving micro-milling of Co-Cr-Mo alloys. Therefore, this paper presents a micro-milling characterization of Co-Cr-Mo samples produced by Additive Manufacturing with the Selective Laser Melting (SLM) technique. In particular, microchannels with different depths were made in order to evaluate the material behavior, including the chip formation mechanism, in micro-milling. In addition, the resulting surface roughness (Ra and Sa) and hardness were analyzed. Finally, the cutting forces were acquired and analyzed in order to ascertain the minimum uncut chip thickness for the material. The results of the characterization studies can be used as a basis for the identification of a machining window for micro-milling of biomedical grade cobalt-chromium-molybdenum (Co-Cr-Mo) alloys. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Figure 1

Figure 1
<p>CoCr alloy equilibrium diagram with the microstructural changes (under thermodynamic equilibrium conditions) [<a href="#B10-materials-12-02208" class="html-bibr">10</a>].</p> Full article ">Figure 2
<p>Minimum Uncut Chip Thickness (MUCT): (<b>a</b>) relation between specific cutting force and feed per tooth; (<b>b</b>) plowing and shearing in one tool revolution. Kc: specific cutting force; fz: feed per tooth.</p> Full article ">Figure 3
<p>The three-axis milling machine used for the preliminary tests.</p> Full article ">Figure 4
<p>Microchannels for the layered effect test: (<b>a</b>) test design; (<b>b</b>) microchannels image after the machining.</p> Full article ">Figure 5
<p>Experimental configuration: (<b>a</b>) sample fixed in the micro-milling machine; (<b>b</b>) machined microchannels; (<b>c</b>) scheme of the micro-milling tests.</p> Full article ">Figure 6
<p>Force analysis for the layered effect test.</p> Full article ">Figure 7
<p>Microchannel A (fz = 10 µm)—Forces in a single spindle rotation: (<b>a</b>) Fx; (<b>b</b>) Fy; (<b>c</b>) Fz and (<b>d</b>) Fc (cutting force). fz: feed per tooth; Fx: force component along X axis; Fy: force component along Y axis; Fz: force component along Z axis.</p> Full article ">Figure 7 Cont.
<p>Microchannel A (fz = 10 µm)—Forces in a single spindle rotation: (<b>a</b>) Fx; (<b>b</b>) Fy; (<b>c</b>) Fz and (<b>d</b>) Fc (cutting force). fz: feed per tooth; Fx: force component along X axis; Fy: force component along Y axis; Fz: force component along Z axis.</p> Full article ">Figure 8
<p>Specific cutting force (Kc).</p> Full article ">Figure 9
<p>Roughness behavior when fz increases: (<b>a</b>) Ra (profile roughness) and (<b>b</b>) Sa (surface roughness).</p> Full article ">Figure 10
<p>Chip analysis: (<b>a</b>) chip formation fz = 0.5 µm/tooth/rev, global view—magnification equal to 100; (<b>b</b>) chip analysis fz = 0.5 µm/tooth/rev—magnification equal to 1000; (<b>c</b>) chip formation fz = 10 µm/tooth/rev, global view—magnification equal to 100; (<b>d</b>) chip analysis fz = 10 µm/tooth/rev—magnification equal to 1000. fz: feed per tooth.</p> Full article ">Figure 11
<p>Chip length analysis. fz: feed per tooth.</p> Full article ">Figure 12
<p>Microhardness: increasing trend when fz (feed per tooth) increases.</p> Full article ">
8 pages, 3312 KiB  
Article
Analysis of the Basal Plane Dislocation Density and Thermomechanical Stress during 100 mm PVT Growth of 4H-SiC
by Johannes Steiner, Melissa Roder, Binh Duong Nguyen, Stefan Sandfeld, Andreas Danilewsky and Peter J. Wellmann
Materials 2019, 12(13), 2207; https://doi.org/10.3390/ma12132207 - 9 Jul 2019
Cited by 19 | Viewed by 5125
Abstract
Basal plane dislocations (BPDs) in 4H silicon carbide (SiC) crystals grown using the physical vapor transport (PVT) method are diminishing the performance of SiC-based power electronic devices such as pn-junction diodes or MOSFETs. Therefore, understanding the generation and movement of BPDs is crucial [...] Read more.
Basal plane dislocations (BPDs) in 4H silicon carbide (SiC) crystals grown using the physical vapor transport (PVT) method are diminishing the performance of SiC-based power electronic devices such as pn-junction diodes or MOSFETs. Therefore, understanding the generation and movement of BPDs is crucial to grow SiC suitable for device manufacturing. In this paper, the impact of the cooldown step in PVT-growth on the defect distribution is investigated utilizing two similar SiC seeds and identical growth parameters except for a cooldown duration of 40 h and 70 h, respectively. The two resulting crystals were cut into wafers, which were characterized by birefringence imaging and KOH etching. The initial defect distribution of the seed wafer was characterized by synchrotron white beam X-ray topography (SWXRT) mapping. It was found that the BPD density increases with a prolonged cooldown time. Furthermore, small angle grain boundaries based on threading edge dislocation (TED) arrays, which are normally only inherited by the seed, were also generated in the case of the crystal cooled down in 70 h. The role of temperature gradients inside the crystal during growth and post-growth concerning the generation of shear stress is discussed and supported by numerical calculations. Full article
(This article belongs to the Special Issue Silicon Carbide and Related Materials for Energy Saving Applications—Select Papers from E-MRS 2019—Symposium “Silicon Carbide and Related Materials for Energy Saving Applications")
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Figure 1

Figure 1
<p>Calculated resolved shear stress distribution inherent to grown wafers at 2250 °C.</p> Full article ">Figure 2
<p>(<b>a</b>) Synchrotron white beam x-ray topography (SWXRT) mapping from a wafer cut from crystal A, recorded in back-reflection geometry in 0004 reflection; (<b>b</b>) section of the wafer exhibiting a network of dense basal plane dislocations (BPDs) distributed in a similar manner to shear stress presented in <a href="#materials-12-02207-f001" class="html-fig">Figure 1</a>, marked by dotted circles; (<b>c</b>) section of the wafer exhibiting a BPD network next to a zone defined by strain fields caused by domain boundaries.</p> Full article ">Figure 3
<p>(<b>a</b>) Birefringence scan of sample B0, the seed utilized to grow crystal B; (<b>b</b>) birefringence scan of sample B2, cut near the crystal growth interface; (<b>c</b>) birefringence scan of sample C0, the seed utilized to grow crystal C; (<b>d</b>) birefringence scan of sample C2, cut near the crystal growth interface. The increased strain and tilt is clearly visible for sample C2, cooled within 70 h.</p> Full article ">Figure 4
<p>Differential interference contrast (DIC) optical microscope images of the (0001)-surface of 4° off-axis wafers etched with KOH; (<b>a</b>) Subdomain boundaries consisting of threading edge dislocations (TEDs) arranged along the &lt;1<math display="inline"><semantics> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> </semantics></math>00&gt; direction, taken from sample C2 in the center area of the wafer; (<b>b</b>) array of basal plane dislocations (BPDs) lined up in the &lt;11<math display="inline"><semantics> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> </semantics></math> 0&gt; direction, taken from sample C2 in the middle between the center and the edge of the wafer. Both images are aligned according to the directions depicted in the middle; (<b>c</b>) defect density of BPDs derived from etched wafers, where samples B1 and C1 correspond to wafers cut next to the seed from crystal B and crystal C, respectively, while samples B2 and C2 correspond to wafers cut near the growth interface of crystal B and crystal C, respectively.</p> Full article ">Figure 4 Cont.
<p>Differential interference contrast (DIC) optical microscope images of the (0001)-surface of 4° off-axis wafers etched with KOH; (<b>a</b>) Subdomain boundaries consisting of threading edge dislocations (TEDs) arranged along the &lt;1<math display="inline"><semantics> <mover accent="true"> <mn>1</mn> <mo>¯</mo> </mover> </semantics></math>00&gt; direction, taken from sample C2 in the center area of the wafer; (<b>b</b>) array of basal plane dislocations (BPDs) lined up in the &lt;11<math display="inline"><semantics> <mover accent="true"> <mn>2</mn> <mo>¯</mo> </mover> </semantics></math> 0&gt; direction, taken from sample C2 in the middle between the center and the edge of the wafer. Both images are aligned according to the directions depicted in the middle; (<b>c</b>) defect density of BPDs derived from etched wafers, where samples B1 and C1 correspond to wafers cut next to the seed from crystal B and crystal C, respectively, while samples B2 and C2 correspond to wafers cut near the growth interface of crystal B and crystal C, respectively.</p> Full article ">
7 pages, 1729 KiB  
Letter
A New Broadband and Strong Absorption Performance FeCO3/RGO Microwave Absorption Nanocomposites
by Wei Huang, Shicheng Wei, Yujiang Wang, Bo Wang, Yi Liang, Yuwei Huang and Binshi Xu
Materials 2019, 12(13), 2206; https://doi.org/10.3390/ma12132206 - 9 Jul 2019
Cited by 23 | Viewed by 3203
Abstract
A novel composite of FeCO3 nanoparticles, which are wrapped with reduced graphene oxide (RGO), is fabricated using a facile one-spot solvothermal method. The composite consists of a substrate of RGO and FeCO3 nanoparticles that are embedded in the RGO layers. The [...] Read more.
A novel composite of FeCO3 nanoparticles, which are wrapped with reduced graphene oxide (RGO), is fabricated using a facile one-spot solvothermal method. The composite consists of a substrate of RGO and FeCO3 nanoparticles that are embedded in the RGO layers. The experimental results for the FeCO3/RGO composite reveal a minimum refection loss (−44.5 dB) at 11.9 GHz when the thickness reaches 2.4 mm. The effective bandwidth is 7.9 GHz between 10.1 and 18 GHz when the refection loss was below −10 dB. Compared to GO and RGO, this type of composite shows better microwave absorption thanks to improved impedance matching. Overall, this thin and lightweight FeCO3/RGO composite is a promising candidate for absorbers that require both strong and broad absorption. Full article
(This article belongs to the Special Issue Carbon Based Functional Microwave Shields)
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<p>(<b>a</b>) XRD patterns for graphene oxide, (GO), reduced graphene (RGO), and FeCO<sub>3</sub>/RGO; XPS spectra of FeCO<sub>3</sub>/RGO; (<b>b</b>) wide scan; (<b>c</b>) C1s spectrum; (<b>d</b>) Fe2p spectrum.</p> Full article ">Figure 2
<p>(<b>a</b>) SEM; (<b>b</b>) TEM; (<b>c</b>) HRTEM images of FeCO<sub>3</sub>/reduced graphene oxide (RGO).</p> Full article ">Figure 3
<p>(<b>a</b>) <span class="html-italic">ε</span>′; (<b>b</b>) <span class="html-italic">ε</span>″; (<b>c</b>) <span class="html-italic">μ</span>′; (<b>d</b>) <span class="html-italic">μ</span>″ for graphene oxide (GO), reduced graphene oxide (RGO), and FeCO<sub>3</sub>/RGO.</p> Full article ">Figure 4
<p>3D <span class="html-italic">R</span><sub>L</sub> plots of (<b>a</b>) graphene oxide (GO); (<b>b</b>) reduced graphene oxide (RGO) and (<b>c</b>) FeCO<sub>3</sub>/RGO; (<b>d</b>) <span class="html-italic">R</span><sub>L</sub> curves of FeCO<sub>3</sub>/RGO with 2~3 mm.</p> Full article ">
19 pages, 6823 KiB  
Article
Complex Study of Eutectoidal Phase Transformation of 2507-Type Super-Duplex Stainless Steel
by István Mészáros and Bálint Bögre
Materials 2019, 12(13), 2205; https://doi.org/10.3390/ma12132205 - 9 Jul 2019
Cited by 16 | Viewed by 3743
Abstract
The aim of this work was to study expansively the process of the eutectoidal phase transformation of 2507-type super-duplex stainless steel. Three sample sets were prepared. The first sample set was made to investigate the effect of the previous cold rolling and heat [...] Read more.
The aim of this work was to study expansively the process of the eutectoidal phase transformation of 2507-type super-duplex stainless steel. Three sample sets were prepared. The first sample set was made to investigate the effect of the previous cold rolling and heat treatment for the eutectoidal phase transformation. Samples were cold rolled at seven different rolling reductions which was followed by heat treatment at five different temperatures. The second sample set was prepared to determine the activation energy of the eutectoidal decomposition process using the Arrhenius equation. Samples were cold rolled at seven different rolling reductions and were heat treated at the same temperature during eight different terms. A third sample set was made to study how another plastic-forming technology, beside the cold rolling, can influence the eutectoidal decomposition. Samples were elongated by single axis tensile stress and were heat treated at the same temperature. The results of the first and the third sample sets were compared. The rest δ-ferrite contents were calculated using the results of AC and DC magnetometer measurements. DC magnetometer was used as a feritscope device in this work. Light microscope and electron back scattering diffraction (EBSD) images demonstrated the process of the eutectoidal decomposition. The thermoelectric power and the hardness of the samples were measured. The results of the thermoelectric power measurement were compared with the results of the δ-ferrite content measurement. The accurate value of the coercive field was determined by a Foerster-type DC coercimeter device. Full article
(This article belongs to the Special Issue Advances in Duplex Stainless Steels)
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<p>Typical precipitations of duplex stainless steel.</p> Full article ">Figure 2
<p>G. Herbstleb and P. Schwaab’s simplified precipitation diagram for duplex stainless steel.</p> Full article ">Figure 3
<p>Kinetics of the eutectoidal decomposition of δ-ferrite in DSS.</p> Full article ">Figure 4
<p>Directions of the manufacturing hot rolling and the experimental cold rolling.</p> Full article ">Figure 5
<p>Set-up of the AC magnetometer.</p> Full article ">Figure 6
<p>δ-ferrite contents in function of the heat treatment temperature measured by the AC magnetometer.</p> Full article ">Figure 7
<p>Set-up of the DC magnetometer.</p> Full article ">Figure 8
<p>δ-ferrite contents vs. the heat treatment temperature measured by the DC magnetometer.</p> Full article ">Figure 9
<p>Microscope images of 2507-type SDSS in the magnification of 1000×: (<b>a</b>) Base microstructure of the 2507-type SDSS; (<b>b</b>) heat-treated sample at 850 °C without deformation; (<b>c</b>) ε = 61.9% deformed sample without heat treatment; (<b>d</b>) ε = 61.9% deformed sample and heat treated at 850 °C.</p> Full article ">Figure 10
<p>Phase maps made by EBSD: (<b>a</b>) The original phase ration of the 2507-type SDSS; (<b>b</b>) heat-treated sample at 850 °C without deformation; (<b>c</b>) ε = 22.3% deformed sample and heat treated at 850 °C; (<b>d</b>) ε = 61.9% deformed sample and heat treated at 850 °C. (Color marking: red area—δ-ferrite; green area—austenite; yellow area—σ-phase).</p> Full article ">Figure 11
<p>Sematic illustration of the TEP instrument.</p> Full article ">Figure 12
<p>Values of the TEP in function of the heat treatment temperature.</p> Full article ">Figure 13
<p>Values of the TEP in function of the rolling reduction.</p> Full article ">Figure 14
<p>Set-up of the Foerster-type DC coercimeter: (<b>a</b>) First step of the measuring; (<b>b</b>) second step of the measuring.</p> Full article ">Figure 15
<p>Values of the coercive field in function of the heat treatment temperature.</p> Full article ">Figure 16
<p>Hardness of the samples in function of the heat treatment temperature.</p> Full article ">Figure 17
<p>Avrami curves.</p> Full article ">Figure 18
<p>Arrhenius plot of the ε = 61.9% deformed original sample series.</p> Full article ">Figure 19
<p>Activation energy in function of the rolling reduction.</p> Full article ">Figure 20
<p>Volume division of the sample before the elongation.</p> Full article ">Figure 21
<p>The equivalent deformation in function of the δ-ferrite content.</p> Full article ">
17 pages, 1920 KiB  
Article
Methanol Dehydration to Dimethyl Ether on Zr-Loaded P-Containing Mesoporous Activated Carbon Catalysts
by José Palomo, José Rodríguez-Mirasol and Tomás Cordero
Materials 2019, 12(13), 2204; https://doi.org/10.3390/ma12132204 - 9 Jul 2019
Cited by 25 | Viewed by 4242
Abstract
Activated carbons have been prepared by the chemical activation of olive stones with phosphoric acid and loaded with Zr. The addition of Zr to the phosphorus-containing activated carbons resulted in the formation of zirconium phosphate surface groups. Gas phase methanol dehydration has been [...] Read more.
Activated carbons have been prepared by the chemical activation of olive stones with phosphoric acid and loaded with Zr. The addition of Zr to the phosphorus-containing activated carbons resulted in the formation of zirconium phosphate surface groups. Gas phase methanol dehydration has been studied while using the prepared Zr-loaded P-containing activated carbons as catalysts. Carbon catalysts showed high steady-state methanol conversion values, which increased with Zr loading up to a limit that was related to P content. The selectivity towards dimethyl ether was higher than 95% for all Zr loadings. Zirconium phosphate species that were present on catalysts surface were responsible for the catalytic activity. Full article
(This article belongs to the Special Issue Advanced Carbon Materials For Catalytical Applications)
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Graphical abstract
Full article ">Figure 1
<p>Nitrogen adsorption–desorption isotherms at −196 °C of (<b>a</b>) Chemically activated carbon (ACP2800) before and after different Zr loads. (<b>b</b>) Physically activated carbon (AC800) before and after a Zr load of 5.25% (<span class="html-italic">w/w</span>).</p> Full article ">Figure 2
<p>(<b>a</b>) Normalized P2p XPS spectra for ACP2800 and the 5.25% Zr loaded phosphorus containing samples; (<b>b</b>) Normalized O1s XPS spectra for ACP2800, AC800 and the 5.25% Zr loaded samples; and, (<b>c</b>) Normalized Zr3d XPS spectra for the 5.25% Zr loaded samples.</p> Full article ">Figure 3
<p>Amount of CO that evolved as a function of temperature during temperature programmed desorption (TPD) for (<b>a</b>) ACP2800, ACP2800Zr2.25, ACP2800Zr5.25 and ACP2800Zr7.50. (<b>b</b>) AC800, AC800Zr5.25 and, ACP2800 and ACP2800Zr5.25 after 4 hours on reaction at 400 °C, P<sub>MeOH</sub> = 0.02 atm, W/F<sub>MeOH</sub> = 0.1 g.s/μmol.</p> Full article ">Figure 4
<p>Ammonia TPD of the samples ACP2800, ACP2800Zr5.25, and AC2800Zr5.25.</p> Full article ">Figure 5
<p>Steady-state methanol conversion and selectivity to dimethyl ether (DME) as a function of Zr loading for the sample ACP2800 (400 °C, P<sub>MeOH</sub> = 0.02 atm, W/F<sub>MeOH</sub> = 0.1 g.s/μmol).</p> Full article ">Figure 6
<p>Methanol conversion and selectivity to DME as a function of the temperature for the catalyst ACP2800ZR5.25 (P<sub>MeOH</sub> = 0.02 atm, W/F<sub>MeOH</sub> = 0.1 g.s/μmol).</p> Full article ">Figure 7
<p>Methanol conversion as a function of time-on-stream (TOS) for ACP2800, ACP2800Zr5.25m and AC800Zr5.25 (400 °C, P<sub>MeOH</sub> = 0.02 atm, W/F<sub>MeOH</sub> = 0.1 g.s/μmol).</p> Full article ">Figure 8
<p>Methanol conversion and selectivity towards DME as a function of TOS for the ACP2800Zr5.25 sample (350 °C, P<sub>MeOH</sub> = 0.04 atm, W/F<sub>MeOH</sub> = 0.1 g.s/μmol).</p> Full article ">Figure 9
<p>Effect of water vapor in the feed on methanol conversion at 350 °C (W/F<sub>MeOH</sub> = 0.1 g.s/μmol).</p> Full article ">
13 pages, 4880 KiB  
Article
Effect of CNTs in Copper Matrix on Mechanical Characteristics and Tribological Behavior under Dry Sliding and Boundary Lubrication Conditions
by Lin Zhao, Pingping Yao, Haibin Zhou, Taimin Gong, Minwen Deng, Zhongyi Zhang, Yelong Xiao, Hui Deng, Yang Li and Fenghua Luo
Materials 2019, 12(13), 2203; https://doi.org/10.3390/ma12132203 - 9 Jul 2019
Cited by 10 | Viewed by 3376
Abstract
In the present work, the mechanical and tribological properties of carbon nanotube (CNT)-reinforced Cu matrix composites featuring 0–1.8 vol% CNTs prepared by spark plasma sintering under dry sliding and boundary lubrication conditions were investigated. The results of microstructure revealed that the bonding interface [...] Read more.
In the present work, the mechanical and tribological properties of carbon nanotube (CNT)-reinforced Cu matrix composites featuring 0–1.8 vol% CNTs prepared by spark plasma sintering under dry sliding and boundary lubrication conditions were investigated. The results of microstructure revealed that the bonding interface in Cu/CNT composites was very well established. Additionally, the addition of CNTs has a positive effect on improving the hardness and tensile strength of the composites, while the stress–strain response quasi-static tensile test confirms the same results. CNTs are proved to lead to certain self-lubrication. The addition of CNTs could result in decreased coefficient of friction (COF) and wear rates by reducing adhesive wear under dry sliding conditions, while the oil lubricating film was the major reason for decreased COF under boundary lubrication conditions. Full article
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<p>Schematic illustration of the fabrication process of Cu/carbon nanotube (CNT) composite.</p> Full article ">Figure 2
<p>Schematic illustration of ball-on-block tribometer.</p> Full article ">Figure 3
<p>Typical metallographs of (<b>a</b>) pure Cu and (<b>b</b>) Cu/0.6 CNTs and (<b>c</b>) relative density of Cu/CNT composite.</p> Full article ">Figure 4
<p>TEM images of Cu/CNT composite: (<b>a</b>) interface bonding of Cu and CNTs, (<b>b</b>) high-resolution TEM (HRTEM) image of highlighted region A, (<b>c</b>) HRTEM image of highlighted region C, and (<b>d</b>) energy-dispersive x-ray spectroscopy (EDS) line-scanning results of region B.</p> Full article ">Figure 5
<p>Mechanical properties of pure Cu and Cu/CNT composites: (<b>a</b>) typical quasi-static stress–strain curves and (<b>b</b>) tensile strength and Vickers hardness.</p> Full article ">Figure 6
<p>SEM micrographs of fractured surfaces of Cu/CNT composites containing (<b>a</b>,<b>b</b>) 0.3, (<b>c</b>,<b>d</b>) 0.6, (<b>e</b>,<b>f</b>) 1.2, and (<b>g</b>,<b>h</b>) 1.8 vol.% CNTs after tensile tests.</p> Full article ">Figure 7
<p>Coefficient of friction (COF) and wear rates of pure Cu and Cu/CNT composites with a pressure of 10 N under dry sliding conditions.</p> Full article ">Figure 8
<p>SEM images of worn surface under dry friction conditions of Cu/CNT composites containing: (<b>a</b>) 0, (<b>b</b>) 0.3, (<b>c</b>) 0.6, (<b>d</b>) 1.2, and (<b>e</b>) 1.8 vol.% CNTs and (<b>f</b>) highly magnified image of worn surface.</p> Full article ">Figure 9
<p>Average COF of pure Cu and Cu/CNT composites under different loading pressures and boundary lubrication conditions.</p> Full article ">Figure 10
<p>SEM images of worn surface under boundary lubrication conditions of Cu/CNT composites containing: (<b>a</b>) 0, (<b>b</b>) 0.3, (<b>c</b>) 0.6, (<b>d</b>) 1.2, and (<b>e</b>) 1.8 vol.% CNTs under a load of 40 N and (<b>f</b>) highly magnified image of typical grooves.</p> Full article ">Figure 11
<p>Schematic illustration of wear mechanism: (<b>a</b>) dry friction condition and (<b>b</b>) boundary lubrication condition.</p> Full article ">
18 pages, 17966 KiB  
Article
Obtaining Nanoparticles of Chilean Natural Zeolite and its Ion Exchange with Copper Salt (Cu2+) for Antibacterial Applications
by Judith Vergara-Figueroa, Serguei Alejandro-Martín, Héctor Pesenti, Fabiola Cerda, Arturo Fernández-Pérez and William Gacitúa
Materials 2019, 12(13), 2202; https://doi.org/10.3390/ma12132202 - 9 Jul 2019
Cited by 22 | Viewed by 4723
Abstract
This article describes the production of nanoparticles of Chilean natural zeolite, using three size reduction methods: Ball mill, microgrinding, and microfluidization. Morphological characterization of samples indicated an average diameter of 37.2 ± 15.8 nm of the zeolite particles. The size reduction and chemical [...] Read more.
This article describes the production of nanoparticles of Chilean natural zeolite, using three size reduction methods: Ball mill, microgrinding, and microfluidization. Morphological characterization of samples indicated an average diameter of 37.2 ± 15.8 nm of the zeolite particles. The size reduction and chemical treatments did not affect the morphology or integrity of the zeolite. An increase of the zeolite samples’ Si/Al ratio was observed after the acid treatment and was confirmed by SEM-EDX analysis. Moreover, the effectiveness of the copper salt ion exchange (Cu2+) to the zeolite nanoparticles was analyzed by SEM-EDX. XRD analysis indicated that clinoptilolite and mordenite are the main phases of Chilean natural zeolite, and the crystalline structure was not affected by the modification processes. The FTIR characterization showed the presence of chemical bonds of copper with the zeolite nanoparticle framework. The ion-exchanged zeolite nanoparticles were evaluated for antibacterial behavior by the disc diffusion method. Additionally, the minimum inhibitory concentration and minimum bactericidal concentration were obtained. Microbiological assays with copper-exchanged nanozeolites showed an antimicrobial activity with a bactericidal effect against Escherichia coli and Staphylococcus aureus, which are the primary pathogens of food and are also resistant to multiple drugs. In this study, a new application for natural nanozeolites is demonstrated, as the incorporated copper ions (Cu2+) in nanozeolites registered a productive antibacterial activity. Full article
(This article belongs to the Collection Porous Materials and Nanozeolites)
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<p>SEM and AFM images of natural zeolite particles after different size reduction processes. (<b>a</b>) SEM. Zeolite microparticles after the ball mill process; (<b>b</b>) SEM. Zeolite microparticles after the grinding process in a SUPER MASSCOLLOIDER; (<b>c</b>) AFM. nZ after the microfluidization process; (<b>d</b>) nZ histogram. (<b>e</b>) AFM. nZH-Cu; (<b>f</b>) nZH-Cu histogram.</p> Full article ">Figure 2
<p>SEM-EDX. EDX analysis of the nZ sample without treatment.</p> Full article ">Figure 3
<p>SEM-EDX. EDX analysis to nZ after acid treatment (nZH sample).</p> Full article ">Figure 4
<p>SEM-EDX. EDX analysis to nZ after the ion exchange process (nZH-Cu sample).</p> Full article ">Figure 5
<p>XRD to samples of natural zeolite. (<b>a</b>) Z without grinding; (<b>b</b>) Z first grinding; (<b>c</b>) Z second grinding; (<b>d</b>) nZ; (<b>e</b>) nZH; (<b>f</b>) nZH-Cu.</p> Full article ">Figure 6
<p>FTIR spectra of samples of natural zeolite. (<b>a</b>) nZH; (<b>b</b>) nZH-Cu.</p> Full article ">Figure 7
<p>Disc diffusion assay against <span class="html-italic">E. coli</span> and <span class="html-italic">S. aureus</span>. (<b>a</b>) Using 1 and 3 mg/mL of nZH-Cu as an antimicrobial agent. (<b>b</b>) Using 1 and 3 mg/mL of nZH, <span class="html-italic">n</span> = 3.</p> Full article ">Figure 8
<p>Seeding from the halos of inhibition for the strains of <span class="html-italic">E. coli</span> and <span class="html-italic">S. aureus</span> against nZH-Cu.</p> Full article ">Figure 9
<p>Determination of the MIC by double serial dilution against <span class="html-italic">E. coli</span> and <span class="html-italic">S. aureus</span>. (<b>a</b>) Using 3 and for 1 mg/mL of nZH-Cu. (<b>b</b>) Using 3 and 1 mg/mL of nZH.</p> Full article ">Figure 10
<p>Sowing from the tubes with strains of <span class="html-italic">E. coli</span> and <span class="html-italic">S. aureus</span> at concentrations of 3, 0.75, and 1 mg/mL of nZH-Cu.</p> Full article ">Figure 11
<p>Bacterial count by the microdrop technique and determination of the antibacterial activity of nZH-Cu against reference strains of <span class="html-italic">E. coli</span> and <span class="html-italic">S. aureus</span>.</p> Full article ">
19 pages, 5840 KiB  
Article
SEM Image Analysis in Permeable Recycled Concretes with Silica Fume. A Quantitative Comparison of Porosity and the ITZ
by Manuel J. Chinchillas-Chinchillas, Carlos A. Rosas-Casarez, Susana P. Arredondo-Rea, José M. Gómez-Soberón and Ramón Corral-Higuera
Materials 2019, 12(13), 2201; https://doi.org/10.3390/ma12132201 - 8 Jul 2019
Cited by 48 | Viewed by 6169
Abstract
Recycled aggregates (RA) from construction and demolition can be used in permeable concretes (PC), improving the environment. PCs have a significant porous network, their cement paste and the interaction between the paste and the RA establishing their strength. Therefore, it is important to [...] Read more.
Recycled aggregates (RA) from construction and demolition can be used in permeable concretes (PC), improving the environment. PCs have a significant porous network, their cement paste and the interaction between the paste and the RA establishing their strength. Therefore, it is important to evaluate the porosity in the interfacial transition zones. The porosity of the cement paste, the aggregate and the interfacial transitional zones (ITZ) of a PC with recycled coarse aggregates (RCA) and silica fume (SF) is measured by means of image analysis–scanning electron microscope (IA)-(SEM) and by mapping the chemical elements with an SEM-EDS (energy dispersive spectrometer) detector microanalysis linked to the SEM and, as a contrast, the mercury intrusion porosimetry technique (MIP). In the IA process, a “mask” was created for the aggregate and another for the paste, which determined the porosity percentage (for the anhydrous material and the products of hydration). The results showed that using SF caused a reduction (32%) in the cement paste porosity in comparison with the PC with RA. The use of RA in the PC led to a significant increase (190%) in the porosity at different thicknesses of ITZ compared with the reference PC. Finally, the MIP study shows that the use of SF caused a decrease in the micropores, mesopores and macropores. Full article
(This article belongs to the Special Issue Properties and Novel Applications of Recycled Aggregates)
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Full article ">Figure 1
<p>General scheme of the test samples. (<b>a</b>) real photo of the specimen beam and (<b>b</b>) areas of study for analysis of scanning electron microscope (SEM) and mercury intrusion porosimetry (MIP).</p> Full article ">Figure 2
<p>RCA 50 SF embedded in epoxy resin with a polished surface. (<b>a</b>–<b>c</b>) “areas of interest" for study in IA-SEM.</p> Full article ">Figure 3
<p>Elemental mapping of the RCA 50 SF sample between the natural coarse aggregate (NCA) and the new paste.</p> Full article ">Figure 4
<p>Preparation of the aggregate mask for the RCA 50 C sample (<b>a</b>) image after the operating instructions and (<b>b</b>) after the morphological filters.</p> Full article ">Figure 5
<p>Elaboration of the mask of the paste for the sample RCA 50 C (<b>a</b>) image after the operating instructions and (<b>b</b>) after the morphological filters.</p> Full article ">Figure 6
<p>The total porosity of the image (<b>a</b>) initial image and (<b>b</b>) segmentation and binarization of image after application of threshold segregation.</p> Full article ">Figure 7
<p>(<b>a</b>) Porosity of the aggregate, (<b>b</b>) porosity of the paste and (<b>c</b>) anhydrous material.</p> Full article ">Figure 8
<p>Images resulting from the sectors of the ITZ with the porosities determined at different theoretical thicknesses.</p> Full article ">Figure 9
<p>Mercury intrusion porosimetry, (<b>a</b>) intrusion and (<b>b</b>) extrusion.</p> Full article ">Figure 10
<p>Porosity, anhydrous material and pH of the cement paste in the PC.</p> Full article ">Figure 11
<p>The porosity of the samples analyzed in the ITZ with several theoretical thicknesses.</p> Full article ">Figure 12
<p>Anhydrous material of the samples analyzed in the IZT with various theoretical thicknesses.</p> Full article ">Figure 13
<p>Hydration products of the samples analyzed in the IZT with various theoretical thicknesses.</p> Full article ">
17 pages, 6904 KiB  
Article
Evolution of Power Losses in Bending Rolled Fully Finished NO Electrical Steel Treated under Unconventional Annealing Conditions
by Ivan Petryshynets, František Kováč, Ján Füzer, Ladislav Falat, Viktor Puchý and Peter Kollár
Materials 2019, 12(13), 2200; https://doi.org/10.3390/ma12132200 - 8 Jul 2019
Cited by 3 | Viewed by 3161
Abstract
Currently, the non-oriented (NO) iron-silicon steels are extensively used as the core materials in various electrical devises due to excellent combination of their mechanical and soft magnetic properties. The present study introduces a fairly innovative technological approach applicable for fully finished NO electrical [...] Read more.
Currently, the non-oriented (NO) iron-silicon steels are extensively used as the core materials in various electrical devises due to excellent combination of their mechanical and soft magnetic properties. The present study introduces a fairly innovative technological approach applicable for fully finished NO electrical steel before punching the laminations. It is based on specific mechanical processing by bending and rolling in combination with subsequent annealing under dynamic heating conditions. It has been revealed that the proposed unconventional treatment clearly led to effective improvement of the steel magnetic properties thanks to its beneficial effects involving additional grain growth with appropriate crystallographic orientation and residual stress relief. The philosophy of the proposed processing was based on employing the phenomena of selective grain growth by strain-induced grain boundary migration and a steep temperature gradient through the cross-section of heat treated specimens at dynamic heating conditions. The stored deformation energy necessary for the grain growth was provided by plastic deformation induced within the studied specimens during the bending and rolling process. The magnetic measurements clearly show that the specimens treated according to our approach exhibited more than 17% decrease in watt losses in comparison with the specimens treated by conventional heat treatment leading only to stress relief without additional grain growth. Full article
(This article belongs to the Collection Magnetoelastic Materials)
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<p>Three-roller bending system for mechanical treatment of experimental samples.</p> Full article ">Figure 2
<p>Cross-sectional nano-hardness dependence of experimental steel in its initial fully finished state (R1) and after subsequent bending deformation (R4).</p> Full article ">Figure 3
<p>Microstructural variation of individual experimental samples of investigated non-oriented (NO) electrical steel corresponding to different material states: R1 (<b>a</b>); R2 (<b>b</b>); R3 (<b>c</b>); R4 (<b>d</b>); R5 (<b>e</b>); and R6 (<b>f</b>).</p> Full article ">Figure 4
<p>Grain size distribution characteristics of individual microstructures of investigated NO electrical steel corresponding to different material states: R1 (<b>a</b>); R2 (<b>b</b>); R3 (<b>c</b>); R4 (<b>d</b>); R5 (<b>e</b>); and R6 (<b>f</b>).</p> Full article ">Figure 4 Cont.
<p>Grain size distribution characteristics of individual microstructures of investigated NO electrical steel corresponding to different material states: R1 (<b>a</b>); R2 (<b>b</b>); R3 (<b>c</b>); R4 (<b>d</b>); R5 (<b>e</b>); and R6 (<b>f</b>).</p> Full article ">Figure 5
<p>Average grain size of studied fully finished electrical steel in individual material states according to <a href="#materials-12-02200-t001" class="html-table">Table 1</a>.</p> Full article ">Figure 6
<p>IPF representation of grain crystallographic orientations of investigated NO electrical steel in initial fully finished state—sample R1 (<b>a</b>) and after bending rolling and subsequent dynamic heat treatment—sample R6 (<b>b</b>). The key for the identification of crystallographic orientation is located on the right (<b>c</b>).</p> Full article ">Figure 7
<p>ODF sections taken at φ<sub>2</sub> = 45° representing the through-thickness textures evolved in investigated samples R1 (<b>a</b>) and R6 (<b>b</b>).</p> Full article ">Figure 8
<p>The variation of orientation density along θ-fibre (<b>a</b>) and γ-fibre (<b>b</b>) in NO electrical steel in fully finished material state—sample R1 (blue curve) and after bending deformation followed by dynamic annealing—sample R6 (red curve).</p> Full article ">Figure 9
<p>The measured coercivity of fully finished electrical steel in individual material states according to <a href="#materials-12-02200-t001" class="html-table">Table 1</a>.</p> Full article ">Figure 10
<p>The B-H hysteresis loops recorded for the studied samples at 50Hz in the first quadrant.</p> Full article ">Figure 11
<p>Power losses as a function of magnetizing frequency in studied samples at B<sub>max</sub> = 1.5 T.</p> Full article ">
16 pages, 5793 KiB  
Article
Friction Behavior of Silver Perrhenate in Oil as Lubricating Additive for Use at Elevated Temperatures
by Junhai Wang, Ting Li, Tingting Yan, Xiaoyi Wei, Xin Qu and Shuai Yuan
Materials 2019, 12(13), 2199; https://doi.org/10.3390/ma12132199 - 8 Jul 2019
Cited by 5 | Viewed by 3153
Abstract
In this study, we use an aqueous solution synthesis method to prepare silver perrhenate powders and suspend them into a poly alpha olefin (PAO) base oil with polyoxyethylene octylphenyl ether. Four ball tests and ball-on-disk reciprocating mode are performed to determine how silver [...] Read more.
In this study, we use an aqueous solution synthesis method to prepare silver perrhenate powders and suspend them into a poly alpha olefin (PAO) base oil with polyoxyethylene octylphenyl ether. Four ball tests and ball-on-disk reciprocating mode are performed to determine how silver perrhenate performs tribologically as a lubricating additive over a wide range of temperatures. The physical and chemical properties, as well as the lubricating mechanisms of the silver perrhenate additive, are characterized via X-ray diffraction, scanning electron microscope, Fourier transformation infrared spectroscopy, Raman spectrum, and X-ray photoelectron spectroscopy. The four-ball test results demonstrate that the oil added with silver perrhenate additive is more effective than the base oil in reducing friction and improving wear resistance, and provides the best lubricating performance when at a concentration of 0.5 wt%. The reciprocating mode findings indicate that the hybrid lubricant exhibits distinctively better tribological properties than the base oil at high temperatures, and its low shear strength and chemical inertness allow for low friction at elevated temperatures. The resulting silver perrhenate layer that incorporates native superalloy oxides on the worn surface can provide lubrication by serving as a barrier that prevents direct contact between the rubbing surfaces at elevated temperatures. Full article
(This article belongs to the Special Issue Tribology: Friction and Wear of Engineering Materials)
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<p>The schematic diagram of reciprocal sliding friction device.</p> Full article ">Figure 2
<p>The XRD pattern, Raman spectra, and Thermogravimetric (TG) curve of as-synthesized product. (<b>a</b>) XRD pattern; (<b>b</b>) Raman spectra; (<b>c</b>) TG curve.</p> Full article ">Figure 3
<p>The SEM micrograph of as-synthesized product.</p> Full article ">Figure 4
<p>The FTIR spectra of base oil with and without added surfactant.</p> Full article ">Figure 5
<p>The transmittances of base oil containing various concentrations of AgReO<sub>4</sub> additive with the help of SA.</p> Full article ">Figure 6
<p>The average friction coefficients and wear scar diameter (WSD) values of varying lubricating samples.</p> Full article ">Figure 7
<p>The SEM images of wear scars lubricated by different lubricating samples under four-ball test condition. (<b>a</b>) PAO; (<b>b</b>) PAO + SA + 0.3 wt% AgReO<sub>4</sub>; (<b>c</b>) PAO + SA + 0.5 wt% AgReO<sub>4</sub>; (<b>d</b>) PAO + SA + 1.0 wt% AgReO<sub>4</sub>.</p> Full article ">Figure 8
<p>The friction coefficient curves and average friction coefficient value of worn surface lubricated by different oil mixtures at varying temperatures. (<b>a</b>) PAO; (<b>b</b>) PAO + SA; (<b>c</b>) PAO + SA + 0.5 wt% AgReO<sub>4</sub>; (<b>d</b>) average friction coefficient value.</p> Full article ">Figure 9
<p>The SEM micrographs of worn surface of GH4169 alloy after 10 min sliding tests lubricated by various lubricating samples at elevated temperatures. (<b>a</b>) 300 °C, PAO; (<b>b</b>) 400 °C, PAO; (<b>c</b>) 300 °C, PAO + SA + 0.5 wt% AgReO<sub>4</sub>; (<b>d</b>) 400 °C, PAO + SA + 0.5 wt% AgReO<sub>4</sub>.</p> Full article ">Figure 10
<p>The mean width values of worn tracks lubricated by different lubricants at various temperatures.</p> Full article ">Figure 11
<p>The XPS spectra of typical elements on the worn track after friction test lubricated by oil with 0.5 wt% AgReO<sub>4</sub> additive at 400 °C. (<b>a</b>) Survey; (<b>b</b>) C1s; (<b>c</b>) O1s; (<b>d</b>) Ag3d; (<b>e</b>) Re4f; (<b>f</b>) Ni2p; (<b>g</b>) Fe2p; (<b>h</b>) Cr2p.</p> Full article ">Figure 12
<p>The XPS analysis of some elements on the worn track after friction test lubricated by pure PAO oil at 400 °C. (<b>a</b>) Survey; (<b>b</b>) C1s; (<b>c</b>) O1s; (<b>d</b>) Ni2p; (<b>e</b>) Fe2p; (<b>f</b>) Cr2p.</p> Full article ">Figure 13
<p>The Raman spectra of the worn surface after sliding friction test lubricated with oil containing 0.5 wt% AgReO<sub>4</sub> additive at 400 °C.</p> Full article ">Figure 14
<p>The XRD patterns of silver perrhenate powder after heat treatment for 15 min at different temperatures.</p> Full article ">
22 pages, 3927 KiB  
Article
An Efficient Beam Element Based on Quasi-3D Theory for Static Bending Analysis of Functionally Graded Beams
by Hoang Nam Nguyen, Tran Thi Hong, Pham Van Vinh and Do Van Thom
Materials 2019, 12(13), 2198; https://doi.org/10.3390/ma12132198 - 8 Jul 2019
Cited by 38 | Viewed by 4024
Abstract
In this paper, a 2-node beam element is developed based on Quasi-3D beam theory and mixed formulation for static bending of functionally graded (FG) beams. The transverse shear strains and stresses of the proposed beam element are parabolic distributions through the thickness of [...] Read more.
In this paper, a 2-node beam element is developed based on Quasi-3D beam theory and mixed formulation for static bending of functionally graded (FG) beams. The transverse shear strains and stresses of the proposed beam element are parabolic distributions through the thickness of the beam and the transverse shear stresses on the top and bottom surfaces of the beam vanish. The proposed beam element is free of shear-looking without selective or reduced integration. The material properties of the functionally graded beam are assumed to vary according to the power-law index of the volume fraction of the constituents through the thickness of the beam. The numerical results of this study are compared with published results to illustrate the accuracy and convenience rate of the new beam element. The influence of some parametrics on the bending behavior of FGM beams is investigated. Full article
(This article belongs to the Special Issue Advances in Structural Mechanics Modeled with FEM)
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<p>The FG beam model.</p> Full article ">Figure 2
<p>The comparison of the nondimensional transverse displacement <math display="inline"> <semantics> <mrow> <msup> <mi>w</mi> <mo>*</mo> </msup> <mo stretchy="false">(</mo> <mi>L</mi> <mo>/</mo> <mn>2</mn> <mo>,</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> </semantics> </math> across the depth of FG SS beams subjected to a uniform load with <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>/</mo> <mi>h</mi> <mo>=</mo> <mn>5</mn> </mrow> </semantics> </math>.</p> Full article ">Figure 3
<p>The comparison of the nondimensional shear stress <math display="inline"> <semantics> <mrow> <msubsup> <mi>τ</mi> <mrow> <mi>x</mi> <mi>z</mi> </mrow> <mo>*</mo> </msubsup> </mrow> </semantics> </math> across the depth of FG SS beams subjected to a uniform load for different values of <math display="inline"> <semantics> <mi>p</mi> </semantics> </math> with <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>/</mo> <mi>h</mi> <mo>=</mo> <mn>5</mn> </mrow> </semantics> </math>.</p> Full article ">Figure 3 Cont.
<p>The comparison of the nondimensional shear stress <math display="inline"> <semantics> <mrow> <msubsup> <mi>τ</mi> <mrow> <mi>x</mi> <mi>z</mi> </mrow> <mo>*</mo> </msubsup> </mrow> </semantics> </math> across the depth of FG SS beams subjected to a uniform load for different values of <math display="inline"> <semantics> <mi>p</mi> </semantics> </math> with <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>/</mo> <mi>h</mi> <mo>=</mo> <mn>5</mn> </mrow> </semantics> </math>.</p> Full article ">Figure 4
<p>The comparison of the nondimensional axial stress <math display="inline"> <semantics> <mrow> <msubsup> <mi>σ</mi> <mi>x</mi> <mo>*</mo> </msubsup> </mrow> </semantics> </math> across the depth of FG SS beams subjected to a uniform load for different values of <math display="inline"> <semantics> <mi>p</mi> </semantics> </math> with <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>/</mo> <mi>h</mi> <mo>=</mo> <mn>5</mn> </mrow> </semantics> </math>.</p> Full article ">Figure 5
<p>Nondimensional maximum transverse deflection <math display="inline"> <semantics> <mrow> <msubsup> <mi>w</mi> <mrow> <mi>max</mi> </mrow> <mo>*</mo> </msubsup> </mrow> </semantics> </math> depends on the power-law index and length-to-thickness ratio of FG beams subjected to a uniform load, (<b>a</b>) SS beams, (<b>b</b>) CC beams, (<b>c</b>) CS beams and (<b>d</b>) CF beams.</p> Full article ">Figure 6
<p>Nondimensional maximum transverse deflection <math display="inline"> <semantics> <mrow> <msubsup> <mi>w</mi> <mrow> <mi>max</mi> </mrow> <mo>*</mo> </msubsup> </mrow> </semantics> </math> as a function of the power-law index and length-to-thickness ratio of FG beams subjected to a uniform load, (<b>a</b>) SS beams, (<b>b</b>) CC beams, (<b>c</b>) CS beams and (<b>d</b>) CF beams.</p> Full article ">Figure 6 Cont.
<p>Nondimensional maximum transverse deflection <math display="inline"> <semantics> <mrow> <msubsup> <mi>w</mi> <mrow> <mi>max</mi> </mrow> <mo>*</mo> </msubsup> </mrow> </semantics> </math> as a function of the power-law index and length-to-thickness ratio of FG beams subjected to a uniform load, (<b>a</b>) SS beams, (<b>b</b>) CC beams, (<b>c</b>) CS beams and (<b>d</b>) CF beams.</p> Full article ">Figure 7
<p>Nondimensional axial stress <math display="inline"> <semantics> <mrow> <msubsup> <mi>σ</mi> <mi>x</mi> <mo>*</mo> </msubsup> <mo stretchy="false">(</mo> <mi>L</mi> <mo>/</mo> <mn>2</mn> <mo>,</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> </semantics> </math> through the thickness of FG beams subjected to a uniform load with <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>/</mo> <mi>h</mi> <mo>=</mo> <mn>5</mn> </mrow> </semantics> </math>, (<b>a</b>) SS beams and (<b>b</b>) CC beams.</p> Full article ">Figure 8
<p>Nondimensional shear stress <math display="inline"> <semantics> <mrow> <msubsup> <mi>τ</mi> <mrow> <mi>x</mi> <mi>z</mi> </mrow> <mo>*</mo> </msubsup> <mo stretchy="false">(</mo> <mn>0</mn> <mo>,</mo> <mi>z</mi> <mo stretchy="false">)</mo> </mrow> </semantics> </math> across the depth of FG beams subjected to a uniform load with <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>/</mo> <mi>h</mi> <mo>=</mo> <mn>5</mn> <mo>,</mo> </mrow> </semantics> </math> (<b>a</b>) SS beams and (<b>b</b>) CC beams.</p> Full article ">Figure 9
<p>The distribution across the thickness of nondimensional vertical displacement of FG beam subjected to a uniform load with <math display="inline"> <semantics> <mrow> <mi>L</mi> <mo>/</mo> <mi>h</mi> <mo>=</mo> <mn>5</mn> <mo>,</mo> </mrow> </semantics> </math> (<b>a</b>) SS beams and (<b>b</b>) CC beams.</p> Full article ">Figure 10
<p>The deflection ratio of FG beams subjected to uniform load, (<b>a</b>) SS beams and (<b>b</b>) CC beams.</p> Full article ">
20 pages, 5791 KiB  
Review
New Perspectives in the Use of Biomaterials for Periodontal Regeneration
by Federico Ausenda, Giulio Rasperini, Raffaele Acunzo, Angelina Gorbunkova and Giorgio Pagni
Materials 2019, 12(13), 2197; https://doi.org/10.3390/ma12132197 - 8 Jul 2019
Cited by 45 | Viewed by 11484
Abstract
Periodontitis is a disease with a high prevalence among adults. If not treated, it can lead to loss of teeth. Periodontal therapy aims at maintaining patient’s teeth through infection control and correction of non-maintainable anatomies including—when possible—regeneration of lost periodontal tissues. The biological [...] Read more.
Periodontitis is a disease with a high prevalence among adults. If not treated, it can lead to loss of teeth. Periodontal therapy aims at maintaining patient’s teeth through infection control and correction of non-maintainable anatomies including—when possible—regeneration of lost periodontal tissues. The biological regenerative potential of the periodontium is high, and several biomaterials can be utilized to improve the outcome of periodontal therapy. Use of different natural and synthetic materials in the periodontal field has been studied for many years. The main materials used today in periodontology analyzed in this review are: Resorbable and non-resorbable barrier membranes; autogenous, allogeneic, xenogeneic, and alloplastic bone substitutes; biological agents, such as amelogenins; platelet-derived growth factor; bone morphogenic proteins; rh fibroblast growth factor 2; teriparatide hormone; platelet concentrates; and 3D scaffolds. With the development of new surgical techniques some concepts on periodontal regeneration that were strictly applied in the past seem to be not so critical today. This can have an impact on the materials that are needed when attempting to regenerate lost periodontal structures. This review aims at presenting a rationale behind the use of biomaterials in modern periodontal regeneration Full article
(This article belongs to the Special Issue Biomaterials and Biological Mediators for Periodontal and Bone Regeneration)
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<p>Evolution of flap designs for periodontal regeneration in relation to biological and clinical concepts.</p> Full article ">Figure 2
<p>Visual representation of the surgical incisions according to surgical technique.</p> Full article ">Figure 3
<p>Visual representation of the suturing technique according to surgical technique.</p> Full article ">Figure 4
<p>Choice of flap design and biomaterials according to defect morphology. SFA: Single flap approach, M-MIST: Modified minimally invasive surgical technique, EPP: Entire papilla preservation, MIST: Minimally invasive surgical technique.</p> Full article ">
14 pages, 3350 KiB  
Article
Field Test of Self-Cleaning Zr-Modified-TiO2-SiO2 Films on Glass with a Demonstration of Their Anti-Fogging Effect
by Andraž Šuligoj, Olena Pliekhova, Nives Vodišek, Mohor Mihelčič, Angelja K. Surca, Roman Kunič, Barbara Šubic, Jernej Starman, Aleš Ugovšek and Urška Lavrenčič Štangar
Materials 2019, 12(13), 2196; https://doi.org/10.3390/ma12132196 - 8 Jul 2019
Cited by 9 | Viewed by 3632
Abstract
The number of commercial products claiming self-cleaning properties is rising and testing of long-term activity and durability of such coatings needs to be addressed more. The time-dependent changes of different characteristics like haze, transparency, and color are essential for transparent glazing materials. Herein, [...] Read more.
The number of commercial products claiming self-cleaning properties is rising and testing of long-term activity and durability of such coatings needs to be addressed more. The time-dependent changes of different characteristics like haze, transparency, and color are essential for transparent glazing materials. Herein, we aimed to examine whether the laboratory results obtained on the Zr-modified-titania-silica (TiZr) self-cleaning materials would translate to larger-scale outdoor-exposed testing. TiZr thin films were deposited via spraying onto float glass window surfaces and exposed into three different environments for 20 months. For comparison, a commercially available active SGG BIOCLEANTM glass and standard float glass were simultaneously exposed in the same conditions. It was shown that the self-cleaning property of either a commercial product or TiZr-coated float glass was not considerably effective in real field test conditions, although the previous laboratory tests showed pronounced photocatalytic activity of TiZr thin films. The inclination angle; however, was shown to have a considerable effect on the self-cleaning ability of samples, as did the rain patterns during the testing period. On the other hand, the anti-fogging effect of our TiZr material was very well expressed in controlled laboratory conditions (measuring droplet formation time) as well as in the real outdoor environment. Full article
(This article belongs to the Special Issue Self-Cleaning Surfaces)
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<p>Atomic force microscopy (AFM) (<b>a</b>,<b>b</b>) and scanning electron microscopy (SEM) (<b>c</b>,<b>d</b>) images of the TiZr coating obtained with the dip-coating (<b>a</b>,<b>c</b>) and spray-coating method (<b>b</b>,<b>d</b>).</p> Full article ">Figure 2
<p>X-ray diffraction (XRD) pattern of dried TiZr sol (<b>A</b>) and UV-vis total (Total T) and diffuse transmittance (Diffuse T) of the three tested surfaces (<b>B</b>). The solid (—) and dashed (---) lines in (<b>B</b>) represent fresh and used (20 months of exposure) 90° samples averaged across all three locations, respectively.</p> Full article ">Figure 3
<p>Results of field testing of the surfaces; change in light transmittance is expressed as change in transmittance (1-R) according to lux meter (<b>a</b>), color changes (ΔE*) (<b>b</b>), and changes in haze (<b>c</b>). The blue and yellow columns represent the average monthly rainfall and the number of days with storms in one month on the three locations, respectively, and are valid for all panels. The gray lines in the top-left panel represent the number of hours of sun per day and are valid for this location only (Ljubljana). Results are faceted by areas (vertical facets) and angles of exposure (horizontal facets).</p> Full article ">Figure 4
<p>The averaged results from the three locations of field testing of the surfaces; change in light transmittance expressed as 1-R according to lux meter (<b>a</b>), changes in ΔE* values; (<b>b</b>) and changes in haze (<b>c</b>). The pale blue bars represent the average monthly rainfall in mm across all locations. The dashed lines represent the maximum value as measured in the dataset, and are shown to guide the reader’s eye, and the gray-filled arrow represents the difference from the maximum values (measured at 45° inclination).</p> Full article ">Figure 4 Cont.
<p>The averaged results from the three locations of field testing of the surfaces; change in light transmittance expressed as 1-R according to lux meter (<b>a</b>), changes in ΔE* values; (<b>b</b>) and changes in haze (<b>c</b>). The pale blue bars represent the average monthly rainfall in mm across all locations. The dashed lines represent the maximum value as measured in the dataset, and are shown to guide the reader’s eye, and the gray-filled arrow represents the difference from the maximum values (measured at 45° inclination).</p> Full article ">Figure 5
<p>Dependence of time of formation of water droplets (condensation) on the relative humidity across samples (<b>a</b>), dependence on the orientation of the sample (<b>b</b>) and water contact angles of the pristine samples (<b>c</b>). Solid lines in (<b>a</b>) represent the linear correlation fitting to data.</p> Full article ">Figure 6
<p>The anti-fogging effect of the TiZr coating on the office window. The picture was taken on 20 October 2017 after one month of exposure time.</p> Full article ">
9 pages, 2496 KiB  
Article
Porous Open-Сell UHMWPE: Experimental Study of Structure and Mechanical Properties
by Alexei I. Salimon, Eugene S. Statnik, Michael Yu. Zadorozhnyy, Fedor S. Senatov, Dmitry D. Zherebtsov, Alexander A. Safonov and Alexander M. Korsunsky
Materials 2019, 12(13), 2195; https://doi.org/10.3390/ma12132195 - 8 Jul 2019
Cited by 16 | Viewed by 4872
Abstract
Ultra-high molecular weight polyethylene (UHMWPE) is a bioinert polymer that is widely used as bulk material in reconstructive surgery for structural replacements of bone and cartilage. Porous UHMWPE can be used for trabecular bone tissue replacement, and it can be used in living [...] Read more.
Ultra-high molecular weight polyethylene (UHMWPE) is a bioinert polymer that is widely used as bulk material in reconstructive surgery for structural replacements of bone and cartilage. Porous UHMWPE can be used for trabecular bone tissue replacement, and it can be used in living cell studies as bioinert 3D substrate permeable to physiological fluids. It is important to develop techniques to govern the morphology of open-cell porous UHMWPE structures (pore size, shape, and connectivity), since this allows control over proliferation and differentiation in living cell populations. We report experimental results on the mechanical behavior of porous open-cell UHMWPE obtained through sacrificial removal (desalination) of hot-molded UHMWPE-NaCl powder mixtures with pore sizes in the range 75 µm to 500 µm. The structures were characterized using SEM and mechanically tested under static compression and dynamic mechanical analysis (DMA), bending, and tensile tests. Apparent elastic modulus and complex modulus were in the range of 1.2 to 2.5 MPa showing a weak dependence on cell size. Densification under compression caused the apparent elastic modulus to increase to 130 MPa. Full article
(This article belongs to the Special Issue Bone Biomaterials)
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<p>The appearance of the as-supplied powders of (<b>a</b>) ultra-high molecular weight polyethylene (UHMWPE); (<b>b</b>) rock salt; (<b>c</b>) The histogram of particle size distribution after sieving. Red bars—UHMWPE, blue bars—salt.</p> Full article ">Figure 2
<p>The schematic illustration of the three-point bending experiment (<b>a</b>) and tensile testing (<b>b</b>) Dimensions in millimeters. The stress–strain curves recorded during the three-point bending load application (<b>c</b>) and tensile testing (<b>d</b>), respectively.</p> Full article ">Figure 3
<p>The scanning electron microscopy (SEM) images of porous UHMWPE uniform (<b>a</b>, <b>b</b>, <b>c</b>) and hybrid (<b>d</b>) structure fabricated from a powder having different average particle size, (<b>e</b>) a stack of optical images and deep focus pseudo-3D reconstructed image.</p> Full article ">Figure 4
<p>The porosity analysis of the prepared porous structures.</p> Full article ">Figure 5
<p>The static (<b>a</b>) and dynamic (<b>b</b>) mechanical properties of porous open-cell UHMWPE (fabricated from 75 to 150 µm powder fraction).</p> Full article ">
12 pages, 7975 KiB  
Article
Fabrication of 50.0 μm Ultra-Fine Pure Rhodium Wire, Using a Multi-Pass Wire Drawing Process, for Probe Card Pins
by Sang-Kon Lee, In-Kyu Lee, Sung-Yun Lee and Sun-Kwang Hwang
Materials 2019, 12(13), 2194; https://doi.org/10.3390/ma12132194 - 8 Jul 2019
Cited by 5 | Viewed by 3584
Abstract
Rhodium is a rare material that is widely used in electrical and electronic components due to its excellent mechanical and electrical properties. Ultra-fine rhodium wires in particular are widely used in electronic components. In this study, a multi-pass wire drawing process was designed [...] Read more.
Rhodium is a rare material that is widely used in electrical and electronic components due to its excellent mechanical and electrical properties. Ultra-fine rhodium wires in particular are widely used in electronic components. In this study, a multi-pass wire drawing process was designed to fabricate ultra-fine pure rhodium wire with a diameter of 50.0 µm from an initial diameter of 80.0 µm, which is used as probe card pins. An elastic–plastic finite element (FE) analysis was performed to validate the pass schedule that was designed for this study. A fine wire drawing experiment was also carried out to verify the effectiveness of the designed process. As a result, the ultra-fine rhodium wire was fabricated using the design process without wire breaks and the diameter of the final drawn wire was 47.80 µm. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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<p>Representative applications of very fine wire.</p> Full article ">Figure 2
<p>Photos of (<b>a</b>) probe card and (<b>b</b>) card pin.</p> Full article ">Figure 3
<p>Flow stress curve of the initial rhodium wire.</p> Full article ">Figure 4
<p>Initial model of the elastic–plastic analysis.</p> Full article ">Figure 5
<p>Equipment (Instron 5566A) for measuring the drawing load.</p> Full article ">Figure 6
<p>Wire drawing dies. (<b>a</b>) structure; (<b>b</b>) manufactured drawing die. ND, natural diamond.</p> Full article ">Figure 7
<p>Precision fine wire drawing machine.</p> Full article ">Figure 8
<p>Distribution of the effective stain in the drawn wire.</p> Full article ">Figure 9
<p>Drawing load.</p> Full article ">Figure 10
<p>Drawing stress at the die exit.</p> Full article ">Figure 11
<p>Wire drawing dies.</p> Full article ">Figure 12
<p>SEM image of the initial wire. (<b>a</b>) <math display="inline"><semantics> <mrow> <mo>×</mo> <mn>1000</mn> </mrow> </semantics></math>; (<b>b</b>) <math display="inline"><semantics> <mrow> <mo>×</mo> <mn>5000</mn> </mrow> </semantics></math>.</p> Full article ">Figure 13
<p>Final drawn wire.</p> Full article ">Figure 14
<p>SEM image (<math display="inline"><semantics> <mrow> <mo>×</mo> <mn>1000</mn> </mrow> </semantics></math>) of the drawn wire at each pass.</p> Full article ">Figure 15
<p>SEM image (<math display="inline"><semantics> <mrow> <mo>×</mo> <mn>2500</mn> </mrow> </semantics></math>) of the final drawn wire.</p> Full article ">Figure 16
<p>Shape of the probe card pin after press forming.</p> Full article ">
14 pages, 8671 KiB  
Article
Numerical Simulation, Machining and Testing of a Phase Change Heat Sink for High Power LEDs
by Jianhua Xiang, Haoxing Zheng, Yipin Wang, Chunliang Zhang, Chao Zhou and Conggui Chen
Materials 2019, 12(13), 2193; https://doi.org/10.3390/ma12132193 - 8 Jul 2019
Cited by 2 | Viewed by 3162
Abstract
Thermal management is crucial to guarantee the normal operation of light-emitting diodes (LEDs) Phase change heat sink is superior to traditional metal solid heat sink due to very small thermal resistance. In this study, a new type of phase change heat sink for [...] Read more.
Thermal management is crucial to guarantee the normal operation of light-emitting diodes (LEDs) Phase change heat sink is superior to traditional metal solid heat sink due to very small thermal resistance. In this study, a new type of phase change heat sink for high power LEDs is first designed. Then, the fabrication process of boiling structures at the evaporation surface of the phase change heat sink is discussed and analyzed. To make a comparison and deep discussion, the machining process is simulated through the FEM (finite element analysis) software, DEFORM-3D. Last but not least, heat transfer performance of the fabricated phase change heat sink is tested. Results have shown that the designed new type of phase change heat sink has superior heat transfer performance and is suitable for heat dissipation of high-power LEDs. Full article
(This article belongs to the Special Issue Advanced Materials and Devices in Solid State Lighting)
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<p>The schematic to the packaging of high-power LED with phase-change heat sink.</p> Full article ">Figure 2
<p>The schematic to the sealing of main-body and end-cover.</p> Full article ">Figure 3
<p>The schematic to form spiral grooves by P-E ploughing-extrusion processing.</p> Full article ">Figure 4
<p>The schematic to form radial boiling structures.</p> Full article ">Figure 5
<p>Mixed structures of V-grooves and U-grooves by P-E processing. (<b>a</b>) <span class="html-italic">d</span><sub>ph</sub> = 0.80 mm, <span class="html-italic">a</span><sub>ph</sub> = 0.20 mm; (<b>b</b>) <span class="html-italic">d</span><sub>ph</sub> = 0.40 mm, <span class="html-italic">a</span><sub>ph</sub> = 0.20 mm.</p> Full article ">Figure 6
<p>V-grooves by P-E processing. (<b>a</b>) <span class="html-italic">d</span><sub>ph</sub> = 0.20 mm, <span class="html-italic">a</span><sub>ph</sub> = 0.20 mm; (<b>b</b>) <span class="html-italic">d</span><sub>ph</sub> = 0.16 mm, <span class="html-italic">a</span><sub>ph</sub> = 0.20 mm.</p> Full article ">Figure 7
<p>Geometry model of the workpiece and the cutting tool in simulation.</p> Full article ">Figure 8
<p>Finite element mesh model of the workpiece.</p> Full article ">Figure 9
<p>Deformation zones in the process of fin forming.</p> Full article ">Figure 10
<p>The flow vector of the metal during the process.</p> Full article ">Figure 11
<p>Tri-axial stress distribution in the process.</p> Full article ">Figure 12
<p>The morphology of microgrooves under different feedings in simulation. (<b>a</b>) <span class="html-italic">A</span><sub>ph</sub> = 0.1 mm, <span class="html-italic">f</span><sub>h</sub> = 0.05 mm; (<b>b</b>) <span class="html-italic">a</span><sub>ph</sub> = 0.1 mm, <span class="html-italic">f</span><sub>h</sub> = 0.1 mm; (<b>c</b>) <span class="html-italic">a</span><sub>ph</sub> = 0.1 mm, <span class="html-italic">f</span><sub>h</sub> = 0.2 mm; (<b>d</b>) <span class="html-italic">a</span><sub>ph</sub> = 0.1 mm, <span class="html-italic">f</span><sub>h</sub> = 0.5 mm.</p> Full article ">Figure 13
<p>SEM section images of microgrooves under different <span class="html-italic">d</span><sub>ph</sub> in experiment. (<b>a</b>) <span class="html-italic">a</span><sub>ph</sub> = 0.1 mm, <span class="html-italic">d</span><sub>ph</sub> = 0.21 mm; (<b>b</b>) <span class="html-italic">a</span><sub>ph</sub> = 0.1 mm, <span class="html-italic">d</span><sub>ph</sub> = 0.31 mm; (<b>c</b>) <span class="html-italic">a</span><sub>ph</sub> = 0.1 mm, <span class="html-italic">d</span><sub>ph</sub> = 1.24 mm.</p> Full article ">Figure 14
<p>The phase change heat sink specimens.</p> Full article ">Figure 15
<p>The heat transfer performance testing system.</p> Full article ">Figure 16
<p>Heat transfer performance of phase change heat sink vs. metal solid heat sink.</p> Full article ">Figure 17
<p>Heat transfer performance of phase change heat sink under the input power of 10 W.</p> Full article ">
24 pages, 11692 KiB  
Article
Effective Design of the Graded Strut of BCC Lattice Structure for Improving Mechanical Properties
by Long Bai, Changyan Yi, Xiaohong Chen, Yuanxi Sun and Junfang Zhang
Materials 2019, 12(13), 2192; https://doi.org/10.3390/ma12132192 - 8 Jul 2019
Cited by 82 | Viewed by 6757
Abstract
In order improve the poor mechanical properties of the body-centred cubic (BCC) lattice structure, which suffers from the stress concentration effects at the nodes of the BCC unit cell, a graded-strut design method is proposed to increase the radii corner of the BCC [...] Read more.
In order improve the poor mechanical properties of the body-centred cubic (BCC) lattice structure, which suffers from the stress concentration effects at the nodes of the BCC unit cell, a graded-strut design method is proposed to increase the radii corner of the BCC nodes, which can obtain a new graded-strut body-centred cubic (GBCC) unit cell. After the relative density equation and the force model of the structure are obtained, the quasi-static uniaxial compression experiments and finite element analysis (FEA) of GBCC samples and BCC samples are performed. The experimental results show that for the fabricated samples with the same relative density, the GBCC can increase the initial stiffness by at least 38.20%, increase the plastic failure strength by at least 34.12%, compared with the BCC. Coupled experimental and numerical results not only suggest that the GBCC has better mechanical and impact resistance properties than the BCC, but also indicate that as the radii corner increases, the stress concentration effect at the node and the mechanical properties will be improved, which validates the proposed design method for graded-strut unit cells and can provide guidance for the design and future research on ultra-light lattice structures in related fields. Full article
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<p>(<b>a</b>) 3D model of the BCC unit cell, (<b>b</b>) 3D model of the GBCC unit cell, (<b>c</b>) the schematic of the BCC unit cell sections, (<b>d</b>) the schematic of the GBCC unit cell sections.</p> Full article ">Figure 2
<p>Schematic of the GBCC unit cell strut and cross section: (<b>a</b>) GBCC unit cell strut, (<b>b</b>) cross-sectional dimensions of a graded-density strut.</p> Full article ">Figure 3
<p>Schematic of the strut with boundary conditions of the GBCC graded-strut unit cell: (<b>a</b>) strut with boundary conditions; (<b>b</b>) cutaway view of the strut; (<b>c</b>) section size of the strut; (<b>d</b>) decomposition diagram of the graded strut; (<b>e</b>) equivalent schematic of both ends of the strut; (<b>f</b>) schematic of the equivalent part size of the strut.</p> Full article ">Figure 4
<p>Diagram of the relationship between theoretical relative density and <span class="html-italic">R</span><sub>1</sub>, <span class="html-italic">R</span><sub>2</sub>, <span class="html-italic">L</span>.</p> Full article ">Figure 5
<p>Schematic of the GBCC unit cell and strut under force: (<b>a</b>) unit cell under force; (<b>b</b>) space force and deformation of the strut; (<b>c</b>) displacement of <span class="html-italic">S</span><sub>7</sub> in the plane coordinate system <span class="html-italic">o</span>′<span class="html-italic">x</span>′<span class="html-italic">y</span>′; (<b>d</b>) force and deformation of the strut in the plane coordinate system <span class="html-italic">o</span>″<span class="html-italic">x</span>″<span class="html-italic">y</span>″.</p> Full article ">Figure 6
<p>Boundary conditions of a lattice structure sample.</p> Full article ">Figure 7
<p>Samples fabricated by SLM.</p> Full article ">Figure 8
<p>Surface topography of unit cell strut, (<b>a</b>) unit cell strut, (<b>b</b>) partial enlargement of unit cell strut (×300).</p> Full article ">Figure 9
<p>The electron micrographs of the sample unit cells.</p> Full article ">Figure 10
<p>The <span class="html-italic">ϕ</span><sub>0</sub> and <span class="html-italic">ϕ</span><sub>1</sub> values of samples.</p> Full article ">Figure 11
<p>The FEA failure process diagram of Group 1.</p> Full article ">Figure 12
<p>The FEA failure process diagram of Group 2.</p> Full article ">Figure 13
<p>The FEA failure process diagram of Group 3.</p> Full article ">Figure 14
<p>The sample failure process diagram of (<b>a</b>) (<b>b</b>) and (<b>c</b>).</p> Full article ">Figure 14 Cont.
<p>The sample failure process diagram of (<b>a</b>) (<b>b</b>) and (<b>c</b>).</p> Full article ">Figure 15
<p>Stress-strain curve of three groups of samples.</p> Full article ">Figure 16
<p>Energy analysis of the GBCC and BCC samples.</p> Full article ">
9 pages, 2523 KiB  
Communication
Loading Graphene Quantum Dots into Optical-Magneto Nanoparticles for Real-Time Tracking In Vivo
by Yu Wang, Nan Xu, Yongkai He, Jingyun Wang, Dan Wang, Qin Gao, Siyu Xie, Yage Li, Ranran Zhang and Qiang Cai
Materials 2019, 12(13), 2191; https://doi.org/10.3390/ma12132191 - 8 Jul 2019
Cited by 13 | Viewed by 3562
Abstract
Fluorescence imaging offers a new approach to visualize real-time details on a cellular level in vitro and in vivo without radioactive damage. Poor light stability of organic fluorescent dyes makes long-term imaging difficult. Due to their outstanding optical properties and unique structural features, [...] Read more.
Fluorescence imaging offers a new approach to visualize real-time details on a cellular level in vitro and in vivo without radioactive damage. Poor light stability of organic fluorescent dyes makes long-term imaging difficult. Due to their outstanding optical properties and unique structural features, graphene quantum dots (GQDs) are promising in the field of imaging for real-time tracking in vivo. At present, GQDs are mainly loaded on the surface of nanoparticles. In this study, we developed an efficient and convenient one-pot method to load GQDs into nanoparticles, leading to longer metabolic processes in blood and increased delivery of GQDs to tumors. Optical-magneto ferroferric oxide@polypyrrole (Fe3O4@PPy) core-shell nanoparticles were chosen for their potential use in cancer therapy. The in vivo results demonstrated that by loading GQDs, it was possible to monitor the distribution and metabolism of nanoparticles. This study provided new insights into the application of GQDs in long-term in vivo real-time tracking. Full article
(This article belongs to the Special Issue Advanced Materials in Drug Release and Drug Delivery Systems)
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<p>Morphology and elemental analysis of graphene quantum dots (GQDs) loaded nanoparticles: (<b>a</b>~<b>c</b>) high resolution tranmission electron microscopy (HRTEM) images at different magnifications (bright field image); (<b>d</b>~<b>i</b>) energy dispersive spectroscopy (EDS) analysis of the nanocomposite; (<b>d</b>) graph representation, (<b>e</b>) EDS analysis of the nanocomposite (merged), (<b>f</b>) EDS C elemental map, (<b>g</b>) EDS O elemental map, (<b>h</b>) EDS Fe elemental map, (<b>i</b>) EDS N elemental map.</p> Full article ">Figure 2
<p>Properties of GQD-nanoparticles (NPs): (<b>a</b>) X-ray diffraction (XRD) patterns; (<b>b</b>) Raman spectrum, the ordered G band and disordered D band were indicated; (<b>c</b>) X-ray photoelectron spectrum (XPS); (<b>d</b>–<b>g</b>) XPS analysis of C, O, N and Fe, respectively; (<b>h</b>) Photoluminescence (PL) spectra with the pulsed laser excitations at 490 nm; (<b>i</b>) Magnetizing curve, magnetization (M), magnetic field strength (H).</p> Full article ">Figure 3
<p>Cell viability of L929 cells incubated with GQD-NPs. The experiments were carried out in triplicate. Data were presented as mean ± standard deviation (SD) (<span class="html-italic">n</span> = 3). The cell viability values were all normalized to control groups (untreated cells after incubation for 24 h or 48 h). Asterisk (*) and double asterisks (**) refer to statistical significance of <span class="html-italic">p</span> &lt; 0.05 and <span class="html-italic">p</span> &lt; 0.01, respectively, compared with control groups between the cell viability values after co-incubation for 24 h; double pounds (##) refer to a statistical significance of <span class="html-italic">p</span> &lt; 0.01 compared with control groups between the cell viability values after co-incubation for 48 h.</p> Full article ">Figure 4
<p>Fibered confocal fluorescence microscopic (FCFM) images of GQD-NPs (imaged under 488 nm excitation, green) and blood vessels (imaged by tail vein injection of Evans blue under 660 nm excitation, red) in tumor tissues over time.</p> Full article ">
15 pages, 2285 KiB  
Review
Effects of Hot Sterilization on Torsional Properties of Endodontic Instruments: Systematic Review with Meta-Analysis
by Mario Dioguardi, Diego Sovereto, Riccardo Aiuto, Luigi Laino, Gaetano Illuzzi, Enrica Laneve, Bruna Raddato, Vito Carlo Alberto Caponio, Antonio Dioguardi, Khrystyna Zhurakivska, Giuseppe Troiano and Lorenzo Lo Muzio
Materials 2019, 12(13), 2190; https://doi.org/10.3390/ma12132190 - 8 Jul 2019
Cited by 10 | Viewed by 3806
Abstract
Sterilization is a fundamental step in the reuse of endodontic instruments. The sterilization procedure involves disinfection, cleaning, washing, drying, packaging, and sterilization by heat. Heat sterilization can lead to changes in the physical and mechanical properties of dental instruments. These changes can affect [...] Read more.
Sterilization is a fundamental step in the reuse of endodontic instruments. The sterilization procedure involves disinfection, cleaning, washing, drying, packaging, and sterilization by heat. Heat sterilization can lead to changes in the physical and mechanical properties of dental instruments. These changes can affect the external surfaces via micropitting, corrosion, a reduction in cutting capacity, and/or an influence on the resistance to cyclic fatigue or to torsional fatigue. In this study, we examined the modification of the torsional properties of endodontic instruments after hot sterilization, and compared the properties with instruments not subjected to hot sterilization cycles in terms of resistance to torsional fatigue and deflection angle in NiTi and steel instruments. The following work was performed based on the PRISMA indications. Studies were identified through bibliographic research using electronic databases. A total of 725 records were identified in the PubMed and Scopus databases. A total of 685 records remained after exclusion by year of publication (1979 to 2019). With the application of the eligibility criteria (all articles pertaining to the issue of sterilization in endodontics), we found 146 articles, which decreased to 130 articles after elimination of duplications. There were 45 articles that studied the influences of sterilization procedures on the physical and mechanical characteristics of the instruments, and 12 that measured parameters related to resistance to torsional fatigue. Applying the inclusion and exclusion criteria resulted in a total of eight articles for quantitative analysis. The meta-analysis results show a pejorative effect of torsional fatigue for NiTi instruments subjected to heat sterilization compared to the non-sterilized control. Full article
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<p>Forest plot of the random effects model of the meta-analysis of the primary outcome.</p> Full article ">Figure 2
<p>Forest plot of the random effects model of the meta-analysis of the secondary outcome.</p> Full article ">Figure 3
<p>Forest plot of the fixed effects model of the meta-analysis of the tertiary outcome.</p> Full article ">Figure 4
<p>Forest plot of the fixed effects model of the meta-analysis of the quaternary outcome.</p> Full article ">Figure 5
<p>Flow chart of the different phases of the systematic review.</p> Full article ">Figure 6
<p>Funnel plots of the evaluation of heterogeneity for the (<b>A</b>) first, (<b>B</b>) second, (<b>C</b>) third, and (<b>D</b>) fourth outcomes.</p> Full article ">
14 pages, 3319 KiB  
Article
Graphene Quantum Dots as Nanozymes for Electrochemical Sensing of Yersinia enterocolitica in Milk and Human Serum
by Sumeyra Savas and Zeynep Altintas
Materials 2019, 12(13), 2189; https://doi.org/10.3390/ma12132189 - 8 Jul 2019
Cited by 85 | Viewed by 6653
Abstract
The genus Yersinia contains three well-recognized human pathogens, including Y. enterocolitica, Y. pestis, and Y. pseudotuberculosis. Various domesticated and wild animals carry Yersinia in their intestines. Spread to individuals arises from eating food or water contaminated by infected human or [...] Read more.
The genus Yersinia contains three well-recognized human pathogens, including Y. enterocolitica, Y. pestis, and Y. pseudotuberculosis. Various domesticated and wild animals carry Yersinia in their intestines. Spread to individuals arises from eating food or water contaminated by infected human or animal faeces. Interaction with infected pets and domestic stock may also lead to infection. Yersinia is able to multiply at temperatures found in normal refrigerators; hence, a large number of the bacteria may be present if meat is kept without freezing. Yersinia is also rarely transmitted by blood transfusion, because it is able to multiply in stored blood products. Infection with Yersinia can cause yersiniosis, a serious bacterial infection associated with fever, abdominal pain and cramps, diarrhea, joint pain, and symptoms similar to appendicitis in older children and adults. This paper describes a novel immunosensor approach using graphene quantum dots (GQDs) as enzyme mimics in an electrochemical sensor set up to provide an efficient diagnostic method for Y. enterecolitica. The optimum assay conditions were initially determined and the developed immunosensor was subsequently used for the detection of the bacterium in milk and human serum. The GQD-immunosensor enabled the quantification of Y. enterocolitica in a wide concentration range with a high sensitivity (LODmilk = 5 cfu mL−1 and LODserum = 30 cfu mL−1) and specificity. The developed method can be used for any pathogenic bacteria detection for clinical and food samples without pre-sample treatment. Offering a very rapid, specific and sensitive detection with a label-free system, the GQD-based immunosensor can be coupled with many electrochemical biosensors. Full article
(This article belongs to the Special Issue Nanomaterials in Health Care Diagnostics)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>A</b>) Illustration of electrodes. (<b>B</b>) A picture of electrodes. (<b>C</b>) Electrochemical measurement set up of Keithley-4200 semi-conductor parameter analyzer KTE I version (V9.1).</p> Full article ">Figure 2
<p><b>(A)</b> Real-time measurement curves obtained with six different GQD concentrations. (<b>B</b>) Overall results of GQD optimization assays in a concentration range of 0.5–50,000 ppm (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 3
<p>Characterization of GQDs using TEM at 1 µm (<b>A</b>) and 50 nm (<b>B</b>) scales.</p> Full article ">Figure 4
<p>AFM analysis of bare (<b>A</b>), GQD-laminated (<b>B</b>), and antibody-immobilized (<b>C</b>) sensor surfaces.</p> Full article ">Figure 5
<p>(<b>A</b>) The real-time measurement curves obtained for different concentrations of <span class="html-italic">Y. enterocolitica</span> in PBS buffer, using 5000 ppm GQDs as enzyme mimics. (<b>B</b>) Overall results of <span class="html-italic">Y. enterocolitica</span> detection in a concentration range of 6.23 × 10<sup>2</sup>–6.23 × 10<sup>8</sup> cfu mL<sup>−1</sup> with an R<sup>2</sup> value of 0.98 (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 6
<p>Optimization of GQD concentration for milk (<b>A</b>, <b>B</b>) and serum (<b>C</b>, <b>D</b>) assays by testing two different concentrations (6 and 6.23 × 10<sup>8</sup> cfu mL<sup>−1</sup>) of <span class="html-italic">Y. enterecolitica</span> (<span class="html-italic">n</span> = 3).</p> Full article ">Figure 7
<p>(<b>A</b>) The real-time measurement curves obtained for different concentrations of <span class="html-italic">Y. enterocolitica</span> in milk, using 5000 ppm GQDs as enzyme mimics. (<b>B</b>) The quantification of <span class="html-italic">Y. enterocolitica</span> in milk; inset: Regression analysis resulting in R<sup>2</sup> value 0.98 (<span class="html-italic">n</span> = 6). (<b>C</b>) Overall results of <span class="html-italic">Y. enterocolitica</span> detection in human serum; inset: Regression analysis resulting in R<sup>2</sup> value of 0.98 (<span class="html-italic">n</span> = 6). The bacterium was measured in a concentration range of 1<tt>‒</tt>6.23×10<sup>8</sup> cfu mL<sup>−1</sup> for both assays.</p> Full article ">Figure 7 Cont.
<p>(<b>A</b>) The real-time measurement curves obtained for different concentrations of <span class="html-italic">Y. enterocolitica</span> in milk, using 5000 ppm GQDs as enzyme mimics. (<b>B</b>) The quantification of <span class="html-italic">Y. enterocolitica</span> in milk; inset: Regression analysis resulting in R<sup>2</sup> value 0.98 (<span class="html-italic">n</span> = 6). (<b>C</b>) Overall results of <span class="html-italic">Y. enterocolitica</span> detection in human serum; inset: Regression analysis resulting in R<sup>2</sup> value of 0.98 (<span class="html-italic">n</span> = 6). The bacterium was measured in a concentration range of 1<tt>‒</tt>6.23×10<sup>8</sup> cfu mL<sup>−1</sup> for both assays.</p> Full article ">Scheme 1
<p>Principle of the graphene quantum dots (GQDs)-based immunosensor for <span class="html-italic">Y. enterocolitica</span> detection.</p> Full article ">
13 pages, 9943 KiB  
Article
Mechanical Properties and Microstructures of Laser–TIG Welded ME21 Rare Earth Mg Alloy
by Taotao Li, Gang Song, Zhaodong Zhang and Liming Liu
Materials 2019, 12(13), 2188; https://doi.org/10.3390/ma12132188 - 8 Jul 2019
Cited by 8 | Viewed by 3160
Abstract
The microstructural and mechanical properties of laser–tungsten inert gas (TIG) hybrid welding of Mg alloy sheets for automobiles are investigated in the present work, including AZ31 and ME21, AZ31 and AZ31, ME21 and ME21, and corresponding comparisons were carried out. The results show [...] Read more.
The microstructural and mechanical properties of laser–tungsten inert gas (TIG) hybrid welding of Mg alloy sheets for automobiles are investigated in the present work, including AZ31 and ME21, AZ31 and AZ31, ME21 and ME21, and corresponding comparisons were carried out. The results show that columnar crystals appear in the ME21/ME21 and ME21/AZ31 heat-affected zones, and no columnar crystals formed in the AZ31/AZ31 fusion zone under a constant heat ratio of arc to laser. Heat accumulation in a narrow area and the undercooling degree are the two main factors for the formation of columnar crystal. The ME21/ME21 joint has a tensile strength of up to 185.2 MPa, which is about 81.8% of that of the ME21 base metal (BM-ME21). The tensile strength of the ME21/AZ31 joint (158.8 MPa) is lower than that of the ME21/ME21 joint. The fracture of the ME21/ME21 and ME21/AZ31 joints occurs at the junction of the columnar crystal and the heat-affected zone. The microhardness of the ME21/AZ31 joint presents a low–high–low–high trend from BE-ME21 to BE-AZ31, and the distribution of the ME21/AZ31 welded joint microhardness in the cross-section presents a low–high–low trend. The ME21/ME21 weld seam is composed of an AlCe3 intermetallic compound, Mn particles, and α-Mg, and the ME21/AZ31 weld seam is composed of a α-Mg, Mg17Al12, and AlCe3 intermetallic compound. Full article
(This article belongs to the Special Issue Laser Materials Fabrication and Joining)
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<p>(<b>a</b>) Schematic diagram of Mg alloy welding process; (<b>b</b>,<b>c</b>) the cross-section of Mg alloy plates and welding fixture.</p> Full article ">Figure 2
<p>Bead surface appearances of welded joints.</p> Full article ">Figure 3
<p>Microstructure of the base metal (<b>a</b>) AZ31 Mg alloy; (<b>b</b>) ME21 Mg alloy.</p> Full article ">Figure 4
<p>Micrographs of the joint cross-sections (<b>a</b>) ME21/ME21 joint; (<b>b</b>) AZ31/AZ31 joint; (<b>c</b>) ME21/AZ31 joint.</p> Full article ">Figure 5
<p>Microstructures of different joints (<b>a</b>) zone I in <a href="#materials-12-02188-f004" class="html-fig">Figure 4</a>a; (<b>b</b>) zone II in <a href="#materials-12-02188-f004" class="html-fig">Figure 4</a>a; (<b>c</b>) zone III in <a href="#materials-12-02188-f005" class="html-fig">Figure 5</a>c; (<b>d</b>) zone IV in <a href="#materials-12-02188-f004" class="html-fig">Figure 4</a>c; (<b>e</b>) zone V in <a href="#materials-12-02188-f004" class="html-fig">Figure 4</a>c; (<b>f</b>) zone VI in <a href="#materials-12-02188-f004" class="html-fig">Figure 4</a>c.</p> Full article ">Figure 6
<p>Microstructures of ME21/AZ31 joint by electron probe micro-analyzer (EPMA).</p> Full article ">Figure 7
<p>(<b>a</b>) Secondary electron image by EPMA; (<b>b</b>–<b>f</b>) elements distribution of Zn, Mg, Al, Mn, and Ce in (<b>a</b>).</p> Full article ">Figure 8
<p>XRD spectra of ME21 and weld seam: (<b>a</b>) XRD phase analysis location; (<b>b</b>) ME21 base metal; (<b>c</b>) ME21/ME21; (<b>d</b>) AZ31/AZ31; and (<b>e</b>) ME21/AZ31.</p> Full article ">Figure 9
<p>(<b>a</b>) Tensile strength of different joints; (<b>b</b>) Engineering stress–strain curve of different joints.</p> Full article ">Figure 10
<p>The fracture location of Mg alloys joints: (<b>a</b>) ME21/ME21; (<b>b</b>) AZ31/AZ31; (<b>c</b>) ME21/AZ31.</p> Full article ">Figure 11
<p>SEM morphologies of fracture surfaces at high magnifications: (<b>a</b>) ME21/ME21 at the top half of the weld; (<b>b</b>) ME21/ME21 at the bottom half of the weld; (<b>c</b>) AZ31/AZ31 at the top half of the weld; (<b>d</b>) AZ31/AZ31 at the bottom half of the weld; (<b>e</b>) ME21/AZ31 at the top half of the weld; (<b>f</b>) ME21/AZ31 at the bottom half of the weld.</p> Full article ">Figure 12
<p>Microhardness map of ME21/ME21 joint and ME21/AZ31 joint.</p> Full article ">
12 pages, 1059 KiB  
Article
Effectiveness of Low-Level Laser Therapy during Tooth Movement: A Randomized Clinical Trial
by Gaetano Isola, Marco Matarese, Francesco Briguglio, Vincenzo Grassia, Giacomo Picciolo, Luca Fiorillo and Giovanni Matarese
Materials 2019, 12(13), 2187; https://doi.org/10.3390/ma12132187 - 8 Jul 2019
Cited by 37 | Viewed by 5070
Abstract
The present study evaluated the effects of low-level laser therapy (LLLT) by means of a diode laser in accelerating orthodontic tooth movement (OTM). After extraction of the first upper premolars for orthodontic purpose, 82 maxillary canines which needed distalization were analyzed in 41 [...] Read more.
The present study evaluated the effects of low-level laser therapy (LLLT) by means of a diode laser in accelerating orthodontic tooth movement (OTM). After extraction of the first upper premolars for orthodontic purpose, 82 maxillary canines which needed distalization were analyzed in 41 enrolled patients (21 males, 20 females, mean age 13.4 ± 2.1 years). On all experimental sites, an orthodontic force of 50/N was applied by a nickel-titanium (NiTi) closed coil spring (G&H, Franklin, IN, USA) in order to obtain the space closure. Using a split mouth randomized design, the test side was treated using a diode laser (Wiser Laser Doctor Smile, Brendola, Italy) operating at 810 nm wavelength in continuous wave mode at both the buccal and palatal side on three points/side (distal, medial and mesial) (1 W output power, continuous wave of 66.7 J/cm2, energy density of 8 J) at baseline and at 3, 7, and 14 days and every 15 days until the space closed. On the control side, the opposite selected canine was treated only using orthodontic traction. The primary outcome chosen was the overall time needed to complete the levelling and closing space, measured on a study cast. The secondary outcome chosen was the evaluation of pain levels related to tooth traction, using a Visual Analogue Scale (VAS), recorded at 3, 7, and 14 days after treatments. The mean space closures of the maxillary canines were comparable between groups [Test, 4.56 mm (95% CI 3.9–4.8); Control, 4.49 mm (95% CI 3.8–4.7), p = 0.456]. The laser group yielded less mean time [84.35 ± 12.34 days (95% CI 79.3–86)] to accomplish space closure compared to the control group [97.49 ± 11.44 days (91.7–102.3)] (p < 0.001). The test side showed a significant reduction in the average range of dental pain at 3 [Test, 5.41 (95% CI 5.1–5.6); Control, 7.23 (95% CI 6.9–7.6), p < 0.001], 7 [Test, 4.12 (95% CI 3.8–4.7); Control, 5.79 (95% CI 5.4–5.8), p < 0.001], and at 14 days [Test, 2.31 (95% CI 1.8–2.3); Control, 3.84 (95% CI 3.3–4.2), p < 0.001] after treatment (p < 0.001). This study demonstrates that the use of LLLT therapy was effective in accelerating tooth movement and reducing pain levels related to OTM. Full article
(This article belongs to the Special Issue Advanced Materials for Oral and Dentofacial Surgery)
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Figure 1
<p>Flowchart of the study.</p> Full article ">Figure 2
<p>(<b>a</b>) The closed NiTi coil spring of 9 mm used for the study; (<b>b</b>) The NiTi coil spring activated with a force of 50/N.</p> Full article ">Figure 3
<p>The results of the pain levels experienced in diode laser and control groups at each follow-up session (3, 7, and 14 days). Error bars represent the Standard Deviation (±SD). *, <span class="html-italic">p</span> &lt; 0.001, comparison between groups at each follow-up session.</p> Full article ">
20 pages, 5329 KiB  
Article
Hot Deformation Behavior of Q345 Steel and Its Application in Rapid Shear Connection
by Mengwei Wu, Shuangjie Zhang, Shibo Ma, Huajun Yan, Wei Wang and Qiang Li
Materials 2019, 12(13), 2186; https://doi.org/10.3390/ma12132186 - 7 Jul 2019
Cited by 9 | Viewed by 3198
Abstract
The high-temperature deformation behavior of Q345 steel is detected by a Gleeble-3800 thermal simulator. The Arrhenius constitutive equation for high-temperature flow stress and the dynamic recrystallization model are constructed. With the secondary development technology, customized modifications are made on existing Deform-3D software. The [...] Read more.
The high-temperature deformation behavior of Q345 steel is detected by a Gleeble-3800 thermal simulator. The Arrhenius constitutive equation for high-temperature flow stress and the dynamic recrystallization model are constructed. With the secondary development technology, customized modifications are made on existing Deform-3D software. The constructed constitutive model and dynamic recrystallization model are embedded into Deform-3D to realize the secondary development of Deform-3D. The grain size and volume percentage distribution of dynamic recrystallization are obtained by simulating the shear connection process at high temperature and high speed. The results show that the constitutive equation and the dynamic recrystallization model constructed in this paper can be used to predict the evolution of the microstructure. The difference between the prediction results and the experimental data is about 3%. The accuracy of Arrhenius constitutive equation, dynamic recrystallization model and the feasibility of software secondary development are verified. Full article
(This article belongs to the Special Issue Development of the Rolling Process in Metallic Materials)
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Figure 1

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<p>Shear connection diagram.</p> Full article ">Figure 2
<p>Technological process.</p> Full article ">Figure 3
<p>True stress-strain relationship curves of Q345 steel: (<b>a</b>) <math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math> = 0.01 s<sup>−1</sup>; (<b>b</b>) <math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math> = 0.1 s<sup>−1</sup>; (<b>c</b>) <math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math> = 1.0 s<sup>−1</sup>; (<b>d</b>) <math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math> = 10 s<sup>−1</sup>.</p> Full article ">Figure 4
<p>Correlation coefficient fitting: (<b>a</b>) In <math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math>-In<span class="html-italic">σ</span>; (<b>b</b>) In <math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math>-<span class="html-italic">σ</span>; (<b>c</b>) In <math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math>-In[sinh(<span class="html-italic">ασ</span>)]; (<b>d</b>) In[sinh(<span class="html-italic">ασ</span>)]-1/<span class="html-italic">T</span>; (<b>e</b>) In<span class="html-italic">Z</span>-In[sinh(<span class="html-italic">ασ</span>)].</p> Full article ">Figure 5
<p>Critical strain and peak strain solution curve: (<b>a</b>) In<span class="html-italic">θ</span>-ε (<math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math> = 0.01 s<sup>−1</sup>); (<b>b</b>) In<span class="html-italic">θ</span>-ε (<math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math> = 0.1 s<sup>−1</sup>); (<b>c</b>) In<span class="html-italic">θ</span>-ε (<math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math> = 0.01 s<sup>−1</sup>); (<b>d</b>) In<span class="html-italic">θ</span>-ε (<math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math> = 0.1 s<sup>−1</sup>).</p> Full article ">Figure 6
<p>Material constant linear regression solution: (<b>a</b>) Inε<sub>p</sub>-In <math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math>; (<b>b</b>) Inε<sub>p</sub>-1/<span class="html-italic">T</span>; (<b>c</b>) ε<sub>p</sub>-<span class="html-italic">Z</span><sup><span class="html-italic">m</span>1</sup>.</p> Full article ">Figure 7
<p>Dynamic recovery and dynamic recrystallization curve. (<b>a</b>) Dynamic recovery curve; (<b>b</b>) Dynamic recrystallization curve.</p> Full article ">Figure 8
<p>Linear regression results of dynamic recrystallization equation: (<b>a</b>) lnε<sub>p</sub>-ln <math display="inline"><semantics> <mover accent="true"> <mi>ε</mi> <mo>˙</mo> </mover> </semantics></math>; (<b>b</b>) lnε<sub>p</sub>-1/T.</p> Full article ">Figure 9
<p>Process of cut connection: (<b>a</b>) before cutting the connection; (<b>b</b>) after cutting the connection.</p> Full article ">Figure 10
<p>Q345 steel prior austenite structure.</p> Full article ">Figure 11
<p>Dynamic recrystallized grain size: (<b>a</b>) L = 100%; (<b>b</b>) L = 125%; (<b>c</b>) L = 150%.</p> Full article ">Figure 12
<p>Dynamic recrystallization volume percentage: (<b>a</b>) L = 100%; (<b>b</b>) L = 125%; (<b>c</b>) L = 150%.</p> Full article ">Figure 13
<p>Tracking point location.</p> Full article ">Figure 14
<p>Dynamic recrystallized grain size at each tracking point: (<b>a</b>) L = 100%; (<b>b</b>) L = 125%; (<b>c</b>) L = 150%.</p> Full article ">Figure 14 Cont.
<p>Dynamic recrystallized grain size at each tracking point: (<b>a</b>) L = 100%; (<b>b</b>) L = 125%; (<b>c</b>) L = 150%.</p> Full article ">Figure 15
<p>Dynamic recrystallization volume percentage of each tracking point: (<b>a</b>) L = 100%; (<b>b</b>) L = 125%; (<b>c</b>) L = 150%.</p> Full article ">Figure 16
<p>Temperature changes during the shear connection process: (<b>a</b>) L = 100%; (<b>b</b>) L = 125%; (<b>c</b>) L = 150%.</p> Full article ">Figure 17
<p>Microscopic morphology at different pressure amounts: (<b>a</b>) L = 100%; (<b>b</b>) L = 125%; (<b>c</b>) L = 150%.</p> Full article ">
23 pages, 9485 KiB  
Review
Graphene Oxide and Its Inorganic Composites: Fabrication and Electrorheological Response
by Yu Zhen Dong, Joo Nyeon Kim and Hyoung Jin Choi
Materials 2019, 12(13), 2185; https://doi.org/10.3390/ma12132185 - 7 Jul 2019
Cited by 18 | Viewed by 4595
Abstract
Composite particles associated with graphene oxide (GO) and inorganic materials provide the synergistic properties of an appropriate electrical conductivity of GO with the good dielectric characteristics of inorganic materials, making them attractive candidates for electrorheological (ER) materials. This review paper focuses on the [...] Read more.
Composite particles associated with graphene oxide (GO) and inorganic materials provide the synergistic properties of an appropriate electrical conductivity of GO with the good dielectric characteristics of inorganic materials, making them attractive candidates for electrorheological (ER) materials. This review paper focuses on the fabrication mechanisms of GO/inorganic composites and their ER response when suspended in a non-conducting medium, including steady shear flow curves, dynamic yield stress, On-Off tests, and dynamic oscillation analysis. Furthermore, the morphologies of these composites, dielectric properties, and sedimentation of the ER fluids are covered. Full article
(This article belongs to the Special Issue Graphene Oxide: Synthesis, Reduction, and Frontier Applications)
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<p>(<b>a</b>) SEM image of GO/TiO<sub>2</sub> [<a href="#B53-materials-12-02185" class="html-bibr">53</a>], (<b>b</b>) TEM image of GO wrapped Al<sub>2</sub>O<sub>3</sub> [<a href="#B54-materials-12-02185" class="html-bibr">54</a>].</p> Full article ">Figure 2
<p>TEM images of (<b>a</b>) GO-wrapped TiO<sub>2</sub> microspheres [<a href="#B56-materials-12-02185" class="html-bibr">56</a>] and (<b>b</b>) core-shell structured TiO<sub>2</sub>/GO [<a href="#B58-materials-12-02185" class="html-bibr">58</a>].</p> Full article ">Figure 3
<p>TEM images of (<b>a</b>) nSiO<sub>2</sub>, (<b>b</b>) p1SiO<sub>2</sub>, (<b>c</b>) p2SiO<sub>2</sub>, (<b>d</b>) epSiO<sub>2</sub>, (<b>e</b>) GO/nSiO<sub>2</sub>, (<b>f</b>) GO/p1SiO<sub>2</sub>, (<b>g</b>) GO/p2SiO<sub>2</sub>, and (<b>h</b>) GO/epSiO<sub>2</sub>. [<a href="#B59-materials-12-02185" class="html-bibr">59</a>].</p> Full article ">Figure 4
<p>TEM images of GO-wrapped silica sphere (<b>a</b>) and GO-wrapped silica spheres rod with an aspect ratio of 5.0 (<b>b</b>), rod with an aspect ratio of 20 (<b>c</b>) [<a href="#B60-materials-12-02185" class="html-bibr">60</a>].</p> Full article ">Figure 5
<p>TEM images (<b>a</b>) Fe<sub>3</sub>O<sub>4,</sub> (<b>b</b>) Fe<sub>3</sub>O<sub>4</sub>/SiO<sub>2,</sub> and (<b>c</b>) Fe<sub>3</sub>O<sub>4</sub>/SiO<sub>2</sub>/GO [<a href="#B65-materials-12-02185" class="html-bibr">65</a>].</p> Full article ">Figure 6
<p>(<b>a</b>) SEM and (<b>b</b>) TEM images of Si-GO [<a href="#B66-materials-12-02185" class="html-bibr">66</a>].</p> Full article ">Figure 7
<p>TEM images of (<b>a</b>) silica and (<b>b</b>) GO coated silica [<a href="#B68-materials-12-02185" class="html-bibr">68</a>].</p> Full article ">Figure 8
<p>Optical microscopy images of GO/TiO<sub>2</sub>-based ER fluid in the absence of an electric field (<b>a</b>) and under an applied electric field (<b>b</b>) [<a href="#B53-materials-12-02185" class="html-bibr">53</a>].</p> Full article ">Figure 9
<p>Dielectric properties of ER fluids based on (<b>a</b>,<b>b</b>) GO-wrapped silica with different aspect ratios [<a href="#B59-materials-12-02185" class="html-bibr">59</a>] and (<b>c</b>,<b>d</b>) GO/SiO<sub>2</sub> spheres with different densities [<a href="#B59-materials-12-02185" class="html-bibr">59</a>].</p> Full article ">Figure 10
<p>Shear stress of GO/SiO<sub>2</sub> [<a href="#B67-materials-12-02185" class="html-bibr">67</a>] based ER fluid (3 vol.%) under (<b>a</b>) DC electric fields and (<b>b</b>) AC electric fields (1 kHz), and (<b>c</b>) shear stress, (<b>d</b>) shear viscosity curves of Si-GO based ER fluid (9 wt.%) [<a href="#B66-materials-12-02185" class="html-bibr">66</a>].</p> Full article ">Figure 11
<p>Dynamic yield stress as a function of the electric field strength for (<b>a</b>) Si-GO based ER fluid (9 wt.%) [<a href="#B66-materials-12-02185" class="html-bibr">66</a>], (<b>b</b>) Fe<sub>3</sub>O<sub>4</sub>/GO based ER fluid (15 wt.%) [<a href="#B55-materials-12-02185" class="html-bibr">55</a>].</p> Full article ">Figure 12
<p>Effect of switching the applied electric field for (<b>a</b>) GO-coated silica based ER fluid (15 wt.%) [<a href="#B68-materials-12-02185" class="html-bibr">68</a>], (<b>b</b>) series of ER fluids based on GO-coated silica with different aspect ratios [<a href="#B60-materials-12-02185" class="html-bibr">60</a>].</p> Full article ">Figure 13
<p>(<b>a</b>) Strain amplitude sweep test and (<b>b</b>) angular frequency sweep test for Fe<sub>3</sub>O<sub>4</sub>/GO-based ER fluid (15 wt.%) [<a href="#B55-materials-12-02185" class="html-bibr">55</a>].</p> Full article ">Figure 14
<p>Sedimentation properties of (<b>a</b>) Fe<sub>3</sub>O<sub>4</sub> and Fe<sub>3</sub>O<sub>4</sub>/SiO<sub>2</sub>/GO-based ER fluids (25 vol.%) [<a href="#B64-materials-12-02185" class="html-bibr">64</a>], (<b>b</b>) TiO<sub>2</sub>, TiO<sub>2</sub>/urea and TiO<sub>2</sub>/GO-based ER fluids (37 vol.%) [<a href="#B58-materials-12-02185" class="html-bibr">58</a>].</p> Full article ">Scheme 1
<p>Schematic diagram of the preparation process of Fe<sub>3</sub>O<sub>4</sub>/GO [<a href="#B55-materials-12-02185" class="html-bibr">55</a>].</p> Full article ">Scheme 2
<p>Synthetic pathway of core-shell typed TiO<sub>2</sub>/GO [<a href="#B58-materials-12-02185" class="html-bibr">58</a>].</p> Full article ">Scheme 3
<p>Schematic diagram of the synthetic route of GO-coated silica [<a href="#B68-materials-12-02185" class="html-bibr">68</a>].</p> Full article ">
18 pages, 5278 KiB  
Article
Durability of Steel Fiber-Reinforced Concrete Containing SiO2 Nano-Particles
by Peng Zhang, Qingfu Li, Yuanzhao Chen, Yan Shi and Yi-Feng Ling
Materials 2019, 12(13), 2184; https://doi.org/10.3390/ma12132184 - 7 Jul 2019
Cited by 86 | Viewed by 4806
Abstract
An experimental study was conducted to investigate the effect ofnano-SiO2 and steel fiber content on the durability of concrete. Five different dosages of nano-SiO2 particles and five volume dosages of steel fiber were used. The durability of concretes includes permeability resistance, [...] Read more.
An experimental study was conducted to investigate the effect ofnano-SiO2 and steel fiber content on the durability of concrete. Five different dosages of nano-SiO2 particles and five volume dosages of steel fiber were used. The durability of concretes includes permeability resistance, cracking resistance, carbonation resistance, and freezing-thawing resistance, and these were evaluated by the water permeation depth, number of cracks, total cracking area per unit area of the specimens, carbonation depth of the specimens, and the relative dynamic elastic modulus of the specimens after freezing-thawing cycles, respectively. The results indicate that the addition of nano-SiO2 particles significantly improves the durability of concrete when the content of nano-SiO2 is limited within a certain range. With the increase of nano-SiO2 content, the durability of concrete first increases and then decreases. An excessive number of nano-SiO2 particles could have an adverse effect on the durability of the concrete. The addition of the correct amount of steel fibers improves the carbonation resistance of concrete containing nano-particles, but excessive steel fiber reduces the carbonation resistance. Moreover, the addition of steel fibers reduces the permeability resistance of concrete containing nano-particles. The incorporation of steel fiber enhanced the freezing-thawing resistance and cracking resistance of concrete containing nano-particles. With increasing steel fiber content, the freezing-thawing resistance of the concrete containing nano-particles increases, and the cracking resistance of the concrete decreases gradually. Full article
(This article belongs to the Section Construction and Building Materials)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Raw materials used in study: (<b>a</b>) Class I fly ash, (<b>b</b>) Milling steel fiber, (<b>c</b>) Nano-SiO<sub>2</sub>, and (<b>d</b>) water reducing agent.</p> Full article ">Figure 2
<p>Carbonation test setup.</p> Full article ">Figure 3
<p>Anti-permeability test setup: (<b>a</b>) Anti-permeability machine, and (<b>b</b>) Measuring water permeability depth.</p> Full article ">Figure 4
<p>Freeze-thaw cycle test setup: (<b>a</b>) Freeze-thaw cycle test machine, (<b>b</b>) Measurement of dynamic modulus of elasticity.</p> Full article ">Figure 5
<p>Cracking resistance test setup.</p> Full article ">Figure 6
<p>Effect of nano-particle content on carbonation depth.</p> Full article ">Figure 7
<p>Effect of steel fiber fraction on carbonation depth.</p> Full article ">Figure 8
<p>Effect of nano-particle content on length of water permeability.</p> Full article ">Figure 9
<p>Effect of steel fiber fraction on length of water permeability.</p> Full article ">Figure 10
<p>Effect of nano-particle content on relative dynamic elastic modulus.</p> Full article ">Figure 11
<p>Effect of steel fiber fraction on relative dynamic elastic modulus.</p> Full article ">Figure 12
<p>Effect of nano-particle content on total cracking area on per area of specimen.</p> Full article ">Figure 13
<p>Effect of nano-particle content on crack number.</p> Full article ">Figure 14
<p>Effect of steel fiber fraction on total cracking area on unit area of specimen.</p> Full article ">Figure 15
<p>Effect of steel fiber fraction on crack number.</p> Full article ">
15 pages, 10232 KiB  
Article
Comparison of Mechanical Properties and Energy Absorption of Sheet-Based and Strut-Based Gyroid Cellular Structures with Graded Densities
by Dawei Li, Wenhe Liao, Ning Dai and Yi Min Xie
Materials 2019, 12(13), 2183; https://doi.org/10.3390/ma12132183 - 7 Jul 2019
Cited by 148 | Viewed by 9280
Abstract
Bio-inspired functionally graded cellular materials (FGCM) have improved performance in energy absorption compared with a uniform cellular material (UCM). In this work, sheet-based and strut-based gyroid cellular structures with graded densities are designed and manufactured by stereo-lithography (SLA). For comparison, uniform structures are [...] Read more.
Bio-inspired functionally graded cellular materials (FGCM) have improved performance in energy absorption compared with a uniform cellular material (UCM). In this work, sheet-based and strut-based gyroid cellular structures with graded densities are designed and manufactured by stereo-lithography (SLA). For comparison, uniform structures are also designed and manufactured, and the graded structures are generated with different gradients. The mechanical behaviors of these structures under compressive loads are investigated. Furthermore, the anisotropy and effective elastic modulus of sheet-based and strut-based unit gyroid cellular structures are estimated by a numerical homogenization method. On the one hand, it is found from the numerical results that the sheet-based gyroid tends to be isotropic, and the elastic modulus of sheet-based gyroid is larger than the strut-based gyroid at the same volume fraction. On the other hand, the graded cellular structure has novel deformation and mechanical behavior. The uniform structure exhibits overall deformation and collapse behavior, whereas the graded cellular structure shows layer-by-layer deformation and collapse behavior. Furthermore, the uniform sheet-based gyroid is not only stiffer but also better in energy absorption capacity than the uniform strut-based gyroid structure. Moreover, the graded cellular structures have better energy absorption capacity than the uniform structures. These significant findings indicate that sheet-based gyroid cellular structure with graded densities have potential applications in various industrial applications, such as in crashworthiness. Full article
(This article belongs to the Section Advanced Materials Characterization)
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<p>Characteristic compressive stress-strain curve of a cellular structure.</p> Full article ">Figure 2
<p>(<b>a</b>) Gyroid structure derived from bionic butterfly wings; gyroid surface (<b>b</b>) close to be strut-based gyroid structure (<b>c</b>) and double gyroid surface (<b>d</b>) close to be sheet-based gyroid structure (<b>e</b>); (<b>f</b>) is the relationship between relative density and parameter <span class="html-italic">t</span> of the two types gyroid cellular structures.</p> Full article ">Figure 3
<p>3D models of the (<b>a</b>) and (<b>b</b>) are the uniform gyroid-based cellular structures; (<b>c</b>) and (<b>d</b>) are the graded gyroid-based cellular structure structures with gradient-1 and (<b>e</b>) and (<b>f</b>) with gradient-2.</p> Full article ">Figure 4
<p>The fabricated gyroid uniform and graded cellular structures with different design parameters.</p> Full article ">Figure 5
<p>Anisotropy of strut-based gyroid (<b>a</b>) and sheet-based gyroid (<b>b</b>). (If <span class="html-italic">A<sup>H</sup></span> is close to unity, the structure could be treated as isotropic).</p> Full article ">Figure 6
<p>Deformation stages of Strut-Gyroid-U (<b>a</b>) and Sheet-Gyroid-U; (<b>b</b>) cellular structures in the presence of 0%, 15%, 30%, 45%, and 60% compression strain from the video capture.</p> Full article ">Figure 7
<p>Compressive stress-strain curves of strut-based (<b>a</b>,<b>c</b>) and sheet-based (<b>b</b>,<b>d</b>) gyroid with different gradient.</p> Full article ">Figure 8
<p>Deformation stages of layer-by-layer collapses of Strut-Gyroid-G1 (<b>a</b>) and Sheet-Gyroid-G1 (<b>b</b>) cellular structures from the video frames.</p> Full article ">Figure 9
<p>Deformation stages of layer-by-layer collapses of Strut-Gyroid-G2 (<b>a</b>) and Sheet-Gyroid-G2 (<b>b</b>) cellular structures from the video frames.</p> Full article ">Figure 10
<p>Energy absorption per unit volume for strut-based (<b>a</b>) and sheet-based (<b>b</b>) gyroid uniform and graded cellular structures.</p> Full article ">Figure 11
<p>Normalized energy absorption of strut-based and sheet-based gyroid uniform and graded cellular structures.</p> Full article ">
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