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Materials, Volume 14, Issue 10 (May-2 2021) – 229 articles

Cover Story (view full-size image): The background is wastewater in nature, showing the application of thin films as photocatalysts. In the upper part, the films containing the most Ti3O5 and Ti2O3 (revealed by the two crystal models) were prepared by adjusting the oxygen flow rate and voltage in reactive sputtering. The following is the comparison of the photodegradation of the dye wastewater of different thin films. The films containing the most Ti2O3 and Ti3O5 exhibited the best absorbance (revealed by the color of the films), photothermal effect (revealed by the temperature), and photocatalytic activity (revealed by the color of the solution). View this paper
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11 pages, 4138 KiB  
Article
Microstructure and Mechanical Properties of NiTi-Based Eutectic Shape Memory Alloy Produced via Selective Laser Melting In-Situ Alloying by Nb
by Igor Polozov and Anatoly Popovich
Materials 2021, 14(10), 2696; https://doi.org/10.3390/ma14102696 - 20 May 2021
Cited by 15 | Viewed by 3166
Abstract
This paper presents the results of selective laser melting (SLM) process of a nitinol-based NiTiNb shape memory alloy. The eutectic alloy Ni45Ti45Nb10 with a shape memory effect was obtained by SLM in-situ alloying using a powder mixture of [...] Read more.
This paper presents the results of selective laser melting (SLM) process of a nitinol-based NiTiNb shape memory alloy. The eutectic alloy Ni45Ti45Nb10 with a shape memory effect was obtained by SLM in-situ alloying using a powder mixture of NiTi and Nb powder particles. Samples with a high relative density (>99%) were obtained using optimized process parameters. Microstructure, phase composition, tensile properties, as well as martensitic phase transformations temperatures of the produced alloy were investigated in as-fabricated and heat-treated conditions. The NiTiNb alloy fabricated using the SLM in-situ alloying featured the microstructure consisting of the NiTi matrix, fine NiTi+β-Nb eutectics, as well as residual unmelted Nb particles. The mechanical tests showed that the obtained alloy has a yield strength up to 436 MPa and the tensile strength up to 706 MPa. At the same time, in-situ alloying with Nb allowed increasing the hysteresis of martensitic transformation as compared to the alloy without Nb addition from 22 to 50 °C with an increase in Af temperature from −5 to 22 °C. Full article
(This article belongs to the Special Issue Materials, Design and Process Development for Additive Manufacturing)
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Figure 1

Figure 1
<p>(<b>a</b>) SEM-image of the NiTi-Nb powder blend and chemical distribution of the elements in the blend: (<b>b</b>) blue—Ti and red—Nb and (<b>c</b>) green—Ni and red—Nb.</p> Full article ">Figure 2
<p>Effect of VED on the density of NiTiNb samples produced by SLM using (<b>a</b>) 300 µm and (<b>b</b>) 70 µm laser spot size.</p> Full article ">Figure 3
<p>Optical images of the polished microsections for the samples produced using parameter sets (<b>a</b>) D1, (<b>b</b>) D2, (<b>c</b>) D3, (<b>d</b>) F1, (<b>e</b>) F2, (<b>f</b>) E1, and (<b>g</b>) E2.</p> Full article ">Figure 4
<p>SEM-images showing the microstructure of the NiTiNb samples produced using parameter sets (<b>a</b>,<b>b</b>) E1 and (<b>c</b>,<b>d</b>) A1.</p> Full article ">Figure 5
<p>The XRD pattern of the NiTiNb sample produced using the E1 parameter set.</p> Full article ">Figure 6
<p>(<b>a</b>) SEM-image of the microstructure of E1 sample and EDS-maps showing the distribution of (<b>b</b>) Ti, (<b>c</b>) Ni, and (<b>d</b>) Nb.</p> Full article ">Figure 7
<p>SEM-images of the NiTiNb samples after different heat treatments: (<b>a</b>,<b>d</b>) 500 °C for 2 h, (<b>b</b>,<b>e</b>) 900 °C for 30 min, and (<b>c</b>,<b>f</b>) 900 °C for 2 h.</p> Full article ">Figure 8
<p>DSC-curves of the in-situ alloyed NiTiNb samples (<b>a</b>) in the as-fabricated state and (<b>b</b>) after annealing at 900 °C for 2 h.</p> Full article ">
19 pages, 6852 KiB  
Article
Interlaminar Fracture Behavior of Carbon Fiber/Polyimide Composites Toughened by Interleaving Thermoplastic Polyimide Fiber Veils
by Bangwei Lan, Yi Liu, Song Mo, Minhui He, Lei Zhai and Lin Fan
Materials 2021, 14(10), 2695; https://doi.org/10.3390/ma14102695 - 20 May 2021
Cited by 11 | Viewed by 3151
Abstract
Carbon fiber reinforced thermosetting polyimide (CF/TSPI) composites were interleaved with thermally stable thermoplastic polyimide (TPPI) fiber veils in order to improve the interlaminar fracture toughness without sacrificing the heat resistance. Both of the mode I and mode II interlaminar fracture toughness (GIC [...] Read more.
Carbon fiber reinforced thermosetting polyimide (CF/TSPI) composites were interleaved with thermally stable thermoplastic polyimide (TPPI) fiber veils in order to improve the interlaminar fracture toughness without sacrificing the heat resistance. Both of the mode I and mode II interlaminar fracture toughness (GIC and GIIC) for the untoughened laminate and TPPI fiber veils interleaved laminates were characterized by the double cantilever beam (DCB) test and end notch flexure (ENF) test, respectively. It is found that the TPPI fiber veils interleaved laminates exhibit extremely increased fracture toughness than the untoughened one. Moreover, the areal density of TPPI greatly affected the fracture toughness of laminates. A maximum improvement up to 179% and 132% on GIC and GIIC is obtained for 15 gsm fiber veils interleaved laminate, which contributes to the existence of bicontinuous TPPI/TSPI structure in the interlayer according to the fractography analysis. The interlaminar fracture behavior at elevated temperatures for 15 gsm fiber veils interleaved laminate were also investigated. The results indicated that the introduction of thermally stable TPPI fiber veils could enhance the fracture toughness of CF/TSPI composites by exceeding 200% as compared to the untoughened one even as tested at 250 °C. Full article
(This article belongs to the Section Advanced Composites)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>The process schematic of (<b>a</b>) preparation of unidirectional CF/TSPI prepreg; (<b>b</b>) electrospinning of TPPI fiber veil; (<b>c</b>) preparation of TPPI fiber veils interleaved CF/TSPI laminates.</p> Full article ">Figure 2
<p>The geometry schematic of DCB (<b>a</b>) and ENF (<b>b</b>) test specimens.</p> Full article ">Figure 3
<p>SEM micrographs of TPPI fiber veils in low resolution (<b>a</b>) and high resolution (<b>b</b>), and the calculated fiber diameters distribution (<b>c</b>).</p> Full article ">Figure 4
<p>DSC curve (<b>a</b>) and TGA curve (<b>b</b>) of TPPI fiber veils.</p> Full article ">Figure 5
<p>DCB test results of untoughened laminate and the laminates interleaved with different areal densities of TPPI fiber veils: (<b>a</b>) Load–displacement curves and crack propagation length–displacement curves, as well as (<b>b</b>) the corresponding R-curves.</p> Full article ">Figure 6
<p>Load–displacement curves in ENF tests of untoughened laminate and the laminates interleaved with different areal densities of TPPI fiber veils.</p> Full article ">Figure 7
<p>SEM micrographs of mode I fracture surfaces of untoughened and interleaved laminates and the schematic diagrams of the illustrated interlayer structure. (<b>a</b>) untoughened laminates; (<b>b</b>) 5 gsm TPPI fiber veils interleaved laminates; (<b>c</b>) 10 gsm TPPI fiber veils interleaved laminates; (<b>d</b>) 15 gsm TPPI fiber veils interleaved laminates; (<b>e</b>) 20 gsm TPPI fiber veils interleaved laminates.</p> Full article ">Figure 8
<p>SEM micrographs of mode II fracture surfaces for laminates with different areal densities of interleaves: (<b>a</b>) Untoughened, (<b>b</b>) 5 gsm, (<b>c</b>) 10 gsm, (<b>d</b>) 15 gsm, (<b>e</b>) 20 gsm.</p> Full article ">Figure 9
<p>DCB test results of untoughened laminate and the 15 gsm fiber veils interleaved laminate measured at different temperatures: (<b>a</b>) Load–displacement curves and crack propagation length–displacement curves, as well as (<b>b</b>) the corresponding R-curves.</p> Full article ">Figure 10
<p>SEM micrographs of mode I fracture surfaces for untoughened and interleaved laminates after DCB test at different temperature. (<b>a</b>) untoughened laminate; (<b>b</b>) 15 gsm TPPI fiber veils interleaved laminate.</p> Full article ">Figure 11
<p>Load–displacement curves in ENF tests of untoughened and 15 gsm fiber veils interleaved laminates measured at different temperatures.</p> Full article ">Figure 12
<p>SEM micrographs of mode II fracture surfaces for untoughened and interleaved laminates after the ENF test at different temperature. (<b>a</b>) untoughened laminate; (<b>b</b>) 15 gsm TPPI fiber veils interleaved laminate.</p> Full article ">
12 pages, 8232 KiB  
Article
Synthesis of Copper Nitride Layers by the Pulsed Magnetron Sputtering Method Carried out under Various Operating Conditions
by Magdalena Wilczopolska, Katarzyna Nowakowska-Langier, Sebastian Okrasa, Lukasz Skowronski, Roman Minikayev, Grzegorz W. Strzelecki, Rafal Chodun and Krzysztof Zdunek
Materials 2021, 14(10), 2694; https://doi.org/10.3390/ma14102694 - 20 May 2021
Cited by 11 | Viewed by 2642
Abstract
Copper nitride shows various properties that depend on the structure of the material and is influenced by the change in technical parameters. In the present work, Cu–N layers were synthesized using the pulsed magnetron sputtering method. The synthesis was performed under different operating [...] Read more.
Copper nitride shows various properties that depend on the structure of the material and is influenced by the change in technical parameters. In the present work, Cu–N layers were synthesized using the pulsed magnetron sputtering method. The synthesis was performed under different operating conditions: direct current (DC) or alternating current (AC) power supply, and various atmospheres: pure Ar and a mixture of Ar + N2. The structural properties of the deposited layers were characterized by X-ray diffraction measurements, and Raman spectroscopy and scanning electron microscopy have been performed. Optical properties were also evaluated. The obtained layers showed tightly packed columnar grain features. The kinetics of the layer growth in the AC mode was lower than that observed in the DC mode, and the layers were thinner and more fine-grained. The copper nitride layers were characterized by the one-phase and two-phase polycrystalline structure of the Cu3N phase with the preferred growth orientation (100). The lattice constant oscillates between 3.808 and 3.815 Å for one-phase and has a value of 3.828 Å for a two-phase structure. Phase composition results were correlated with Raman spectroscopy measurements. Raman spectra exhibited a broad, diffused, and intense signal of Cu3N phase, with Raman shift located at 628–635 cm−1. Studies on optical properties showed that the energy gap ranged from 2.17 to 2.47 eV. The results showed that controlling technical parameters gives a possibility to optimize the structure and phase composition of deposited layers. The reported changes were discussed and attributed to the properties of the material layers and technology method. Full article
(This article belongs to the Special Issue Optical Characterization and Applications of Metallic Thin Films)
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Figure 1

Figure 1
<p>(<b>a</b>) Schematic diagram of the apparatus used in the experiment; (<b>b</b>) the scheme of current pulse time behavior in the AC and DC modes of pulsed power supply.</p> Full article ">Figure 2
<p>SEM images of Cu–N layers synthesized with various process parameters (<b>a</b>–<b>d</b>) cross-section; (<b>e</b>–<b>h</b>) surface morphology.</p> Full article ">Figure 3
<p>(<b>a</b>) The X-ray diffraction patterns and (<b>b</b>) Raman spectra of the Cu–N layers.</p> Full article ">Figure 4
<p>Elllipsometric azimuths (<b>a</b>) Ψ and (<b>b</b>) Δ and (<b>c</b>) transmittance spectra for A4 sample. Experimental data (circles, squares, triangles, and stars) are plotted every third (Ψ and Δ) or tenth (T) collected point. Solid lines represent the spectra calculated from the optical model of sample.</p> Full article ">Figure 5
<p>(<b>a</b>) Real part of the complex refractive index and (<b>b</b>) extinction coefficient of the Cu–N layers.</p> Full article ">Figure 6
<p>(<b>a</b>) Transmittance spectra recorded for the Cu–N layers. The data for glass are added for comparison; (<b>b</b>) The Tauc plot for the Cu–N layers.</p> Full article ">
14 pages, 5688 KiB  
Article
Enhanced Storage Stability and Rheological Properties of Asphalt Modified by Activated Waste Rubber Powder
by Weihong Liu, Yishen Xu, Hongjun Wang, Benan Shu, Diego Maria Barbieri and Jose Norambuena-Contreras
Materials 2021, 14(10), 2693; https://doi.org/10.3390/ma14102693 - 20 May 2021
Cited by 32 | Viewed by 3521
Abstract
Segregation of waste crumb rubber powder (WR) modified asphalt binders the large-scale application of WR in asphalt. The method of microwave activation combined with chemical activation (KMWR) was proposed to improve storage stability and rheological properties of WR modified asphalt in this work. [...] Read more.
Segregation of waste crumb rubber powder (WR) modified asphalt binders the large-scale application of WR in asphalt. The method of microwave activation combined with chemical activation (KMWR) was proposed to improve storage stability and rheological properties of WR modified asphalt in this work. Storage stability and rheological properties of virgin asphalt, MWR modified asphalt, and KMWR modified asphalt were comparatively studied by the standard segregation test, bending beam rheometer (BBR) test, and dynamic shear rheometer (DSR) test. The effect of composite activation on waste rubber powder particles was studied by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and Brunauer–Emmett–Teller (BET) tests. The main results showed that after the physical and chemical composite activation, the storage stability of waste rubber powder modified asphalt was significantly improved, WR modified asphalt had better crack resistance, better rutting resistance, and better fatigue performance. After physical and chemical activation, WR was desulfurized, and a large number of active groups was grafted on the WR particles. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>SEM images of waste tire crumb rubber particles under different magnifications: (<b>a</b>) ×50; (<b>b</b>) ×1000.</p> Full article ">Figure 2
<p>Stiffness and “m” values of the four kinds of asphalt.</p> Full article ">Figure 3
<p>Effect of temperature on viscosity-temperature curves (<b>a</b>) and Log relation (<b>b</b>) of the four kinds of asphalt.</p> Full article ">Figure 4
<p>Effect of temperature on complex modulus and phase angles (<b>a</b>), rutting factor, (<b>b</b>) and failure temperature (<b>c</b>) of the four kinds of asphalt.</p> Full article ">Figure 4 Cont.
<p>Effect of temperature on complex modulus and phase angles (<b>a</b>), rutting factor, (<b>b</b>) and failure temperature (<b>c</b>) of the four kinds of asphalt.</p> Full article ">Figure 5
<p>Effect of repeated loading-unloading cycles on shear strain and non-recoverable creep compliance (<b>e</b>) of virgin asphalt (<b>a</b>), WR modified asphalt (<b>b</b>), MWR modified asphalt, (<b>c</b>) and KMWR modified asphalt (<b>d</b>).</p> Full article ">Figure 5 Cont.
<p>Effect of repeated loading-unloading cycles on shear strain and non-recoverable creep compliance (<b>e</b>) of virgin asphalt (<b>a</b>), WR modified asphalt (<b>b</b>), MWR modified asphalt, (<b>c</b>) and KMWR modified asphalt (<b>d</b>).</p> Full article ">Figure 6
<p>Effect of loading cycles on complex modulus (<b>a</b>) and fatigue life (<b>b</b>) of the four kinds of asphalt.</p> Full article ">Figure 7
<p>FTIR results of the three kinds of waste rubber powder.</p> Full article ">Figure 8
<p>SEM images (<b>a</b>–<b>c</b>) and element distribution (<b>d</b>–<b>f</b>) of the three kinds of waste rubber powder.</p> Full article ">Figure 9
<p>Specific surface area of the three kinds of waste rubber powder.</p> Full article ">
26 pages, 6678 KiB  
Article
Architecture-Promoted Biomechanical Performance-Tuning of Tissue-Engineered Constructs for Biological Intervertebral Disc Replacement
by Gernot Lang, Katja Obri, Babak Saravi, Aldo R. Boccaccini, Anton Früh, Michael Seidenstücker, Bodo Kurz, Hagen Schmal and Bernd Rolauffs
Materials 2021, 14(10), 2692; https://doi.org/10.3390/ma14102692 - 20 May 2021
Cited by 5 | Viewed by 2758
Abstract
Background: Biological approaches to intervertebral disc (IVD) restoration and/or regeneration have become of increasing interest. However, the IVD comprises a viscoelastic system whose biological replacement remains challenging. The present study sought to design load-sharing two-component model systems of circular, nested, concentric elements reflecting [...] Read more.
Background: Biological approaches to intervertebral disc (IVD) restoration and/or regeneration have become of increasing interest. However, the IVD comprises a viscoelastic system whose biological replacement remains challenging. The present study sought to design load-sharing two-component model systems of circular, nested, concentric elements reflecting the nucleus pulposus and annulus fibrosus. Specifically, we wanted to investigate the effect of architectural design variations on (1) model system failure loads when testing the individual materials either separately or homogeneously mixed, and (2) also evaluate the potential of modulating other mechanical properties of the model systems. Methods: Two sets of softer and harder biomaterials, 0.5% and 5% agarose vs. 0.5% agarose and gelatin, were used for fabrication. Architectural design variations were realized by varying ring geometries and amounts while keeping the material composition across designs comparable. Results: Variations in the architectural design, such as lamellar width, number, and order, combined with choosing specific biomaterial properties, strongly influenced the biomechanical performance of IVD constructs. Biomechanical characterization revealed that the single most important parameter, in which the model systems vastly exceeded those of the individual materials, was failure load. The model system failure loads were 32.21- and 84.11-fold higher than those of the agarose materials and 55.03- and 2.14-fold higher than those of the agarose and gelatin materials used for system fabrication. The compressive strength, dynamic stiffness, and viscoelasticity of the model systems were always in the range of the individual materials. Conclusions: Relevant architecture-promoted biomechanical performance-tuning of tissue-engineered constructs for biological IVD replacement can be realized by slight modifications in the design of constructs while preserving the materials’ compositions. Minimal variations in the architectural design can be used to precisely control structure–function relations for IVD constructs rather than choosing different materials. These fundamental findings have important implications for efficient tissue-engineering of IVDs and other load-bearing tissues, as potential implants need to withstand high in situ loads. Full article
(This article belongs to the Special Issue Recent Advances in Novel Biomaterials for Tissue Repair and Tissue Engineering)
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Figure 1
<p><b>Architectural design variations, fabrication, and mechanical characterization of load-sharing, two-component composite model systems</b>. (<b>A</b>) Illustration of the three architectural designs A1, A2, and A3. Dark gray illustrates elements fabricated from stiffer biomaterials, namely 5% agarose or caffeic acid-crosslinked gelatin. White illustrates elements fabricated from the softer biomaterial, 0.5% agarose. (<b>B</b>) Diameters of the central elements and inner and outer diameters of the central element-surrounding rings. The central element diameters were 3.5 mm and 5.5 mm of architectures 1 and 2 (for a soft biomaterial), the outer diameters of the first ring were 7.5 mm and 9.5 mm (for a hard biomaterial), those of the second ring were 11.5 mm and 14.5 mm (for a soft biomaterial), and those of the third ring were 15.5 mm and 18.5 mm (for a hard biomaterial). Thus, the widths of the rings intended for a hard material remained constant at 4 mm. For architecture 3, the central element diameter was 6.5 mm (for a hard biomaterial), the outer diameter of the first ring (for a soft biomaterial) was 12.5 mm and of the second ring (for a hard biomaterial) was 16.5 mm. (<b>C</b>) Three cylindrical metal punches used for model system fabrication and the 5% agarose used for punching. The punches were fabricated by gluing cylindrical metal rings in a concentric fashion onto a Petri dish. (<b>D</b>) For model system fabrication fabricated from 0.5% agarose (the soft biomaterial) and 5% agarose (the hard biomaterial), solidified 5% agarose filling the entire Petri dish with a height of 3 mm was punched, and the rings intended as space for the soft biomaterial were manually removed. The remaining space was then filled with a softer biomaterial, namely 0.5% agarose. (<b>E</b>) The rings removed from (<b>D</b>) were used as a mold for gelatin elements. After removing these rings, the empty space within the gelatin was filled with the softer biomaterial, 0.5% agarose. (<b>F</b>) illustrates the displacement over time used for mechanical characterization of the model systems, using an incubator-housed loading device IncuDyn CA2008 in displacement control and custom-made software. The sinusoidal displacement is shown enlarged. X-axis label: time (s). Y-axis label: displacement (µm).</p> Full article ">Figure 2
<p><b>Mechanical characterization of the failure loads of the tested model systems, controls, and materials used for fabrication.</b> (<b>A</b>) Failure loads of the architectures 1, 2, and 3 of the 0.5% and 5% agarose model system and of the biomaterials used for fabrication. (<b>B</b>) Failure loads of the architectures 1, 2, and 3 of the 0.5% agarose gelatin model system and of the biomaterials used for fabrication. (<b>C</b>) Failure loads of the best-performing architecture of both agarose model systems and agarose gelatin model systems determined in (<b>A</b>,<b>B</b>) as well as their associated homogeneously mixed controls and open controls. Those were fabricated by cutting the stiff rings of architecture 1 into pieces and distributing them within the softer biomaterial, leading to an unconfined situation. (<b>D</b>) Failure loads of all individual materials used for model system fabrication. The box plots give the median and the 25th and 75th percentiles, the whiskers give the 10th and 90th percentiles, and the round symbols, if present, indicate outliers. The dark gray lines and the asterisks (*) indicate differences at <span class="html-italic">p</span> &lt; 0.05 identified in ANOVA or ANOVA on ranks and pairwise multiple comparison procedures, such as the Newman–Keuls or Dunn’s method. Light gray lines and the asterisk (*) indicate differences at <span class="html-italic">p</span> &lt; 0.05 that were identified with the same statistical tests, in which only architectures 1, 2, and 3 were compared. Number of 0.5% and 5% agarose homogeneous controls: <span class="html-italic">n</span> = 5, number of all other 0.5% and 5% agarose samples: <span class="html-italic">n</span> = 6, number of gelatin material samples: <span class="html-italic">n</span> = 10, number of all other 0.5% agarose and gelatin samples: <span class="html-italic">n</span> = 6.</p> Full article ">Figure 3
<p><b>Mechanical characterization of the compressive strengths of the tested model systems, controls, and materials used for fabrication</b>. (<b>A</b>) Compressive strengths of the architectures 1, 2, and 3 of the 0.5% and 5% agarose model system and of the biomaterials used for fabrication. (<b>B</b>) Compressive strengths of the architectures 1, 2, and 3 of the 0.5% agarose gelatin model system and of the biomaterials used for fabrication. (<b>C</b>) Compressive strengths of the best-performing architecture of both agarose model systems and agarose gelatin model systems determined in (A) and (B) as well as their associated homogeneously mixed controls and open controls. Those were fabricated by cutting the stiff rings of architecture 1 into pieces and distributing them within the softer biomaterial, leading to an unconfined situation. (D) Compressive strengths of all individual materials used for model system fabrication. The asterisk (*) indicates a significant difference (<span class="html-italic">p</span> &lt; 0.05). The box plots give the median and the 25th and 75th percentiles. The whiskers give the 10th and 90th percentiles, and the round symbols indicate outliers if present. The dark gray lines and the asterisks (*) indicate differences at <span class="html-italic">p</span> &lt; 0.05 identified in ANOVA or ANOVA on ranks and pairwise multiple comparison procedures, such as the Newman–Keuls or Dunn’s method. Light gray lines and asterisks (*) indicate differences at <span class="html-italic">p</span> &lt; 0.05 that were identified with the same statistical tests. Only architectures 1, 2, and 3 were compared. Number of 0.5% and 5% agarose architecture 1 model systems: <span class="html-italic">n</span> = 5, number of 0.5% and 5% agarose architecture 2 model systems: <span class="html-italic">n</span> = 4, number of 0.5% and 5% agarose architecture 3 model systems: <span class="html-italic">n</span> = 6, number of 0.5% and 5% agarose homogeneous controls: <span class="html-italic">n</span> = 5, number of 0.5% and 5% agarose open controls: <span class="html-italic">n</span> = 5, number of 0.5% agarose material samples: <span class="html-italic">n</span> = 5, number of 5% agarose material samples: <span class="html-italic">n</span> = 4, number of all 0.5% agarose and gelatin samples: <span class="html-italic">n</span> = 6 each.</p> Full article ">Figure 4
<p><b>Mechanical characterization of the dynamic stiffness of the tested model systems, controls, and materials used for fabrication</b>. (<b>A</b>) Dynamic stiffness of the architectures 1, 2, and 3 of the 0.5% and 5% agarose model system and of the biomaterials used for fabrication. (<b>B</b>) Dynamic stiffness of the architectures 1, 2, and 3 of the 0.5% agarose gelatin model system and of the biomaterials used for fabrication. (<b>C</b>) Dynamic stiffness of the best-performing architecture of both agarose model systems and agarose gelatin model systems determined in (<b>A</b>,<b>B</b>) as well as their associated homogeneously mixed controls and open controls. Those were fabricated by cutting the stiff rings of architecture 1 into pieces and distributing them within the softer biomaterial, leading to an unconfined situation. (<b>D</b>) Dynamic stiffness of all individual materials used for model system fabrication. The box plots give the median and the 25th and 75th percentiles, the whiskers give the 10th and 90th percentiles, and the round symbols if present indicate outliers. The dark gray lines and the asterisks (*) indicate differences at <span class="html-italic">p</span> &lt; 0.05 identified in ANOVA or ANOVA on ranks and pairwise multiple comparison procedures, such as the Newman–Keuls or Dunn’s method. Light gray lines and the asterisk (*) indicate differences at <span class="html-italic">p</span> &lt; 0.05 that were identified with the same statistical tests, in which only architectures 1, 2, and 3 were compared. Number of 0.5% and 5% agarose architecture 1 model systems: <span class="html-italic">n</span> = 6, number of 0.5% and 5% agarose architecture 2 model systems: <span class="html-italic">n</span> = 7, number of 0.5% and 5% agarose architecture 3 model systems: <span class="html-italic">n</span> = 6, number of 0.5% and 5% agarose homogeneous controls: <span class="html-italic">n</span> = 5, number of 0.5% and 5% agarose open controls: <span class="html-italic">n</span> = 6, number of 0.5% agarose material samples: <span class="html-italic">n</span> = 8, number of 5% agarose material samples: <span class="html-italic">n</span> = 6, number of 0.5% agarose and gelatin architecture 1 model systems: <span class="html-italic">n</span> = 5, number of 0.5% agarose and gelatin architecture 2 model systems: <span class="html-italic">n</span> = 6, number of 0.5% agarose and gelatin architecture 3 model systems: <span class="html-italic">n</span> = 6, number of 0.5% agarose and gelatin homogeneous controls: <span class="html-italic">n</span> = 6, number of 0.5% agarose and gelatin open controls: <span class="html-italic">n</span> = 6, number of 0.5% agarose material samples: <span class="html-italic">n</span> = 8, number of gelatin material samples: <span class="html-italic">n</span> = 7.</p> Full article ">Figure 5
<p><b>Mechanical characterization of the phase shift as an indicator of the viscoelasticity of the tested model systems, controls, and materials used for fabrication</b>. (<b>A</b>) Phase shift of the architectures 1, 2, and 3 of the 0.5% and 5% agarose model system and of the biomaterials used for fabrication. (<b>B</b>) Phase shift of the architectures 1, 2, and 3 of the 0.5% agarose gelatin model system and of the biomaterials used for fabrication. (<b>C</b>) Phase shift of all architectures of both agarose model systems and agarose gelatin model systems determined in (<b>A</b>,<b>B</b>) as well as their associated homogeneously mixed controls and open controls. Those were fabricated by cutting the stiff rings of architecture 1 into pieces and distributing them within the softer biomaterial, leading to an unconfined situation. (<b>D</b>) Phase shift of all individual materials used for model system fabrication. The box plots give the median and the 25th and 75th percentiles. The whiskers give the 10th and 90th percentiles, and the round symbols indicate outliers if present. The dark gray lines and the asterisks (*) indicate differences at <span class="html-italic">p</span> &lt; 0.05 identified in ANOVA or ANOVA on ranks and pairwise multiple comparison procedures, such as the Newman–Keuls or Dunn’s method. Number of 0.5% and 5% agarose architecture 1, 2, and 3 model systems: <span class="html-italic">n</span> = 6 each, number of 0.5% and 5% agarose homogeneous controls: <span class="html-italic">n</span> = 5, number of 0.5% and 5% agarose open controls, 0.5% and 5% agarose material samples: <span class="html-italic">n</span> = 6 each, number of 0.5% agarose and gelatin architecture 1 model systems: <span class="html-italic">n</span> = 5, number of 0.5% agarose and gelatin architecture 2 and 3 model systems: <span class="html-italic">n</span> = 6 each, number of 0.5% agarose and gelatin homogeneous and open controls: <span class="html-italic">n</span> = 6 each, number of 0.5% agarose material samples: <span class="html-italic">n</span> = 6, number of gelatin material samples: <span class="html-italic">n</span> = 10.</p> Full article ">Figure 6
<p><b>Mechanical characterization of homogeneous constructs with 20 mm diameter and 5 mm height fabricated from gelatin crosslinked with caffeic acid to determine the degradation behavior at room temperature (RT) and at 37 °C over time</b>. (<b>A</b>) Compressive strength, (<b>B</b>) dynamic stiffness, (<b>C</b>) phase shift, and (<b>D</b>) failure load at different time points. The box plots give the median and the 25th and 75th percentiles. The whiskers give the 10th and 90th percentiles, and the round symbols indicate outliers if present. The dark gray lines and the asterisks (*) indicate differences at <span class="html-italic">p</span> &lt; 0.05 identified in ANOVA or ANOVA on ranks and pairwise multiple comparison procedures, such as the Newman–Keuls or Dunn’s method. Number of 0.5% and 5% agarose architecture 1 and 3 model systems: <span class="html-italic">n</span> = 6 each, number of 0.5% and 5% agarose architecture 2 model systems: <span class="html-italic">n</span> = 7, number of 0.5% and 5% agarose homogeneous controls: <span class="html-italic">n</span> = 5, number of 0.5% and 5% agarose open controls: <span class="html-italic">n</span> = 6, number of 0.5% agarose material samples: <span class="html-italic">n</span> = 8, number of 5% agarose material samples: <span class="html-italic">n</span> = 6, number of 0.5% agarose and gelatin architecture 1 model systems: <span class="html-italic">n</span> = 5, number of 0.5% agarose and gelatin architecture 2 and 3 model systems: <span class="html-italic">n</span> = 6 each, number of 0.5% agarose and gelatin homogeneous and open controls: <span class="html-italic">n</span> = 6 each, number of 0.5% agarose material samples: <span class="html-italic">n</span> = 8, number of gelatin material samples: <span class="html-italic">n</span> = 7.</p> Full article ">Figure 7
<p><b>Representative fluorescence images taken during the cytotoxicity test of gelatin crosslinked with caffeic acid and of architecture 1 fabricated from agarose and a dextran-based hydrogel seeded with human chondrons and mechanically loaded</b>. (<b>A</b>) presents images of human chondrocytes that were incubated with or without gelatin contact to assess cell survival on day 11, using live-dead imaging. Scale bar: 1000 µm. (<b>B</b>) presents a fluorescence image of human articular chondrons within architecture 1 that was fabricated from 5% agarose used as a harder biomaterial and from a dextran-based hydrogel seeded with human chondrons used as soft, cell-loaded biomaterial. The image was taken on day 8 after the model system was mechanically loaded on day 7 with a total strain ranging from 0 to 10%. Number of wells with and without gelatin contact: <span class="html-italic">n</span> = 6 each, number of mechanically loaded architectures: <span class="html-italic">n</span> = 3, number of control architectures: <span class="html-italic">n</span> = 2.</p> Full article ">
18 pages, 10349 KiB  
Article
Effect of Heat Treatment on the Microstructure and Performance of Cu Nanofoams Processed by Dealloying
by Jenő Gubicza, Péter Jenei, Gigap Han, Pham-Tran Hung, Youngseok Song, Dahye Park, Ábel Szabó, Csilla Kádár, Jae-Hun Kim and Heeman Choe
Materials 2021, 14(10), 2691; https://doi.org/10.3390/ma14102691 - 20 May 2021
Cited by 6 | Viewed by 2495
Abstract
Cu nanofoams are promising materials for a variety of applications, including anodes in high-performance lithium-ion batteries. The high specific surface area of these materials supports a high capacity and porous structure that helps accommodate volume expansion which occurs as batteries are charged. One [...] Read more.
Cu nanofoams are promising materials for a variety of applications, including anodes in high-performance lithium-ion batteries. The high specific surface area of these materials supports a high capacity and porous structure that helps accommodate volume expansion which occurs as batteries are charged. One of the most efficient methods to produce Cu nanofoams is the dealloying of Cu alloy precursors. This process often yields nanofoams that have low strength, thus requiring additional heat treatment to improve the mechanical properties of Cu foams. This paper provides the effects of heat treatment on the microstructures, mechanical properties, and electrochemical performance of Cu nanofoams. Annealing was conducted under both inert and oxidizing atmospheres. These studies ultimately reveal the underlying mechanisms of ligament coarsening during heat treatment. Full article
(This article belongs to the Special Issue New Advances in Characterization of Cellular Materials)
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<p>Scanning electron microscopy (SEM) images for Cu foams (<b>a</b>) processed by using route B and annealed at (<b>b</b>) 300 °C for 70 h and (<b>c</b>) 800 °C for 5 h.</p> Full article ">Figure 2
<p>SEM images of (<b>a</b>) Cu foam materials processed by route C and subsequently annealed at (<b>b</b>) 300 °C for 70 h, (<b>c</b>) 600 °C for 5.5 h (<b>d</b>) and 800 °C for 5 h.</p> Full article ">Figure 3
<p>A plot of <math display="inline"><semantics> <mrow> <mi>l</mi> <mi>n</mi> <mfenced close="}" open="{"> <mrow> <mfenced close="]" open="["> <mrow> <msup> <mi>d</mi> <mn>3</mn> </msup> <mo>−</mo> <msubsup> <mi>d</mi> <mn>0</mn> <mn>3</mn> </msubsup> </mrow> </mfenced> <mi>T</mi> <mo>/</mo> <mi>t</mi> </mrow> </mfenced> </mrow> </semantics></math> versus 1/T used to determine the activation energy of the mechanism behind ligament coarsening in Cu foams processed by dealloying and subsequently annealed under an inert atmosphere. The plotting was performed based on Equation (3). The grain sizes (<span class="html-italic">d</span> and <span class="html-italic">d</span><sub>0</sub>) were taken in nanometres, while the units of t and T were hours and Kelvin degrees, respectively.</p> Full article ">Figure 4
<p>SEM image illustrates several ligaments grown in the material processed by route C and subsequently annealed at 800 °C for 5 h. The yellow arrows indicate boundaries between the coalesced ligaments.</p> Full article ">Figure 5
<p>(<b>a</b>) Williamson–Hall plots for Cu foam processed by route C and the counterpart of this material, which was annealed at 600 °C for 5.5 h after dealloying. FWHM: full width at half maximum, g: magnitude of the diffraction vector (see text). (<b>b</b>) A section of the diffraction pattern evaluated by the CMWP fitting method using data obtained from a Cu foam processed by route C. The open circles represent the measured data, and the solid line reflects the fitted pattern. The difference between the data and the calculated pattern is shown as a black line at the bottom of the figure.</p> Full article ">Figure 6
<p>Comparison of (<b>a</b>) microstructural parameters and (<b>b</b>) hardness and elastic modulus obtained via indentation measurements for Cu foams processed by route C, as well as its counterpart material that was annealed at 600 °C for 5.5 h after dealloying.</p> Full article ">Figure 7
<p>Force versus penetration depth curves obtained by nanoindentation from Cu foam materials that were processed by route C (<b>a</b>) and the counterpart material that was annealed at 600 °C for 5.5 h after dealloying (<b>b</b>).</p> Full article ">Figure 8
<p>(<b>a</b>,<b>b</b>) Distributions of hardness and (<b>c</b>,<b>d</b>) Young’s modulus obtained by nanoindentation measurements conducted on Cu foams processed by (<b>a</b>,<b>c</b>) route C and (<b>b</b>,<b>d</b>) its counterpart annealed at 600 °C for 5.5 h after dealloying.</p> Full article ">Figure 9
<p>SEM images of Cu nanofoams oxidized at (<b>a</b>,<b>b</b>) 110 °C for 30 min and (<b>c</b>,<b>d</b>) at 140 °C for 30 min.</p> Full article ">Figure 10
<p>SEM images of Cu nanofoams oxidized at (<b>a</b>,<b>b</b>) 170 °C for 30 min and (<b>c</b>,<b>d</b>) 200 °C for 30 min.</p> Full article ">Figure 11
<p>Plot of <math display="inline"><semantics> <mrow> <mi>l</mi> <mi>n</mi> <mfenced close="}" open="{"> <mrow> <mfenced close="]" open="["> <mrow> <msup> <mi>d</mi> <mn>3</mn> </msup> <mo>−</mo> <msubsup> <mi>d</mi> <mn>0</mn> <mn>3</mn> </msubsup> </mrow> </mfenced> <mi>T</mi> <mo>/</mo> <mi>t</mi> </mrow> </mfenced> </mrow> </semantics></math> versus 1/<span class="html-italic">T</span> to estimate the activation energy of the causal mechanism of ligament coarsening for dealloyed Cu foams annealed under an oxidizing atmosphere. Solid squares indicate materials processed by route A from CuAl<sub>2</sub>, open down triangles reflect materials dealloyed from Cu<sub>20</sub>Zn<sub>80</sub> by using 5 wt.% HCl at RT for 72 h, solid circles indicate materials dealloyed from Cu<sub>30</sub>Al<sub>70</sub> by using 85 wt.% H<sub>3</sub>PO<sub>4</sub> at RT for 72 h, and open circles reflect materials dealloyed from Cu<sub>35</sub>Zn<sub>65</sub> by using 5 wt.% HCl at RT for 72 h. The data for the latter three types of precursor alloy were taken from Reference [<a href="#B43-materials-14-02691" class="html-bibr">43</a>].</p> Full article ">Figure 12
<p>Voltage profiles of Cu foams oxidized at (<b>a</b>) 170 °C and (<b>c</b>) 200 °C, as well as a comparison of the areal capacity of Cu foam anodes that were oxidized at (<b>b</b>) 170 °C and (<b>d</b>) 200 °C at 1 mA/cm<sup>2</sup> in 0.01–3.0 V.</p> Full article ">
23 pages, 39856 KiB  
Article
Experimental and Numerical Study of Fracture Behavior of Rock-Like Material Specimens with Single Pre-Set Joint under Dynamic Loading
by Bo Pan, Xuguang Wang, Zhenyang Xu, Lianjun Guo and Xuesong Wang
Materials 2021, 14(10), 2690; https://doi.org/10.3390/ma14102690 - 20 May 2021
Cited by 10 | Viewed by 2275
Abstract
The Split Hopkinson Pressure Bar (SHPB) is an apparatus for testing the dynamic stress-strain response of the cement mortar specimen with pre-set joints at different angles to explore the influence of joint attitudes of underground rock engineering on the failure characteristics of rock [...] Read more.
The Split Hopkinson Pressure Bar (SHPB) is an apparatus for testing the dynamic stress-strain response of the cement mortar specimen with pre-set joints at different angles to explore the influence of joint attitudes of underground rock engineering on the failure characteristics of rock mass structure. The nuclear magnetic resonance (NMR) has also been used to measure the pore distribution and internal cracks of the specimen before and after the testing. In combination with numerical analysis, the paper systematically discusses the influence of joint angles on the failure mode of rock-like materials from three aspects of energy dissipation, microscopic damage, and stress field characteristics. The result indicates that the impact energy structure of the SHPB is greatly affected by the pre-set joint angle of the specimen. With the joint angle increasing, the proportion of reflected energy moves in fluctuation, while the ratio of transmitted energy to dissipated energy varies from one to the other. NMR analysis reveals the structural variation of the pores in those cement specimens before and after the impact. Crack propagation direction is correlated with pre-set joint angles of the specimens. With the increase of the pre-set joint angles, the crack initiation angle decreases gradually. When the joint angles are around 30°–75°, the specimens develop obvious cracks. The crushing process of the specimens is simulated by LS-DYNA software. It is concluded that the stresses at the crack initiation time are concentrated between 20 and 40 MPa. The instantaneous stress curve first increases and then decreases with crack propagation, peaking at different times under various joint angles; but most of them occur when the crack penetration ratio reaches 80–90%. With the increment of joint angles in specimens through the simulation software, the changing trend of peak stress is consistent with the test results. Full article
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<p>Schematic diagram of instability zone of cracked rock mass.</p> Full article ">Figure 2
<p>Specimen preparation process.</p> Full article ">Figure 3
<p>The specimens’ fragmentation under different impact pressure.</p> Full article ">Figure 4
<p>Schematic diagram of the experimental procedures.</p> Full article ">Figure 5
<p>Stress–strain curves of specimens with joint angles.</p> Full article ">Figure 6
<p>Proportion of energy with joint angles.</p> Full article ">Figure 7
<p>Relationship between energy density per unit time and joint angles.</p> Full article ">Figure 8
<p>A schematic diagram of crack propagation of jointed rock mass.</p> Full article ">Figure 9
<p>MRI effect, crack morphology, and T<sub>2</sub> distribution of specimen with different joint angles.</p> Full article ">Figure 9 Cont.
<p>MRI effect, crack morphology, and T<sub>2</sub> distribution of specimen with different joint angles.</p> Full article ">Figure 10
<p>Numerical model of SHPB systems and specimen.</p> Full article ">Figure 11
<p>Stress isograms and numerical simulation effect of specimens.</p> Full article ">Figure 11 Cont.
<p>Stress isograms and numerical simulation effect of specimens.</p> Full article ">Figure 11 Cont.
<p>Stress isograms and numerical simulation effect of specimens.</p> Full article ">Figure 12
<p>Relationship between joint angle and crack initiation angle.</p> Full article ">Figure 13
<p>Relation diagram of crack penetration rate and real-time stress.</p> Full article ">Figure 14
<p>Relation diagram of stress value of numerical simulation and test stress in test.</p> Full article ">
21 pages, 7018 KiB  
Article
Thermal and Mechanical Characterization of Carbides for High Temperature Nuclear Applications
by Mattia Manzolaro, Stefano Corradetti, Michele Ballan, Riccardo Salomoni, Alberto Andrighetto and Giovanni Meneghetti
Materials 2021, 14(10), 2689; https://doi.org/10.3390/ma14102689 - 20 May 2021
Cited by 10 | Viewed by 2395
Abstract
In the facilities for the production of Radioactive Ion Beams (RIBs) according to the Isotope Separation On-Line (ISOL) technique, a production target is typically impinged by a high-power primary beam, generating radioactive isotopes for basic research and technological applications. With the aim to [...] Read more.
In the facilities for the production of Radioactive Ion Beams (RIBs) according to the Isotope Separation On-Line (ISOL) technique, a production target is typically impinged by a high-power primary beam, generating radioactive isotopes for basic research and technological applications. With the aim to guarantee an efficient extraction of the aforementioned isotopes, the production target must work in a high vacuum environment, at temperatures that are usually between 1600 °C and 2200 °C. Its main components are often characterized by intense temperature gradients and consequently by severe thermal stresses. Carbides are widely used for target manufacturing, and in this work a specific method for their thermal and mechanical characterization is presented and discussed. It is based on the comparison between experimental measurements and numerical simulations, with the introduction of the novel Virtual Thermoelastic Parameters approach for the structural verification procedure. High-performance silicon carbides (SiC) are taken as a reference to describe the method. Measured emissivity and thermal conductivity data are presented and discussed, together with the experimental estimation of material limitations for both temperature and stress fields. The aforementioned results can be promptly used for the design process of high-power ISOL targets. Full article
(This article belongs to the Special Issue Advanced Techniques for Materials Characterization)
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<p>The SPES target architecture; (<b>a</b>) CAD view with indication of the main components; (<b>b</b>) picture of the open box.</p> Full article ">Figure 2
<p>Schematic representation of the analysis of particle transport and interactions with matter.</p> Full article ">Figure 3
<p>Thermal and structural analyses: inputs, outputs and material properties.</p> Full article ">Figure 4
<p>The experimental apparatus adopted for both emissivity and thermal conductivity estimations; (<b>a</b>) general CAD view of the whole apparatus; (<b>b</b>) detailed CAD view of the sample area; (<b>c</b>) picture of the sample area at high temperature.</p> Full article ">Figure 5
<p>The experimental apparatus used to determine the temperature limit of target materials; (<b>a</b>) picture of the opened hot zone; (<b>b</b>) picture of the closed hot zone; (<b>c</b>) picture of the water-cooled vacuum chamber and of the temperature measurement setup.</p> Full article ">Figure 6
<p>Stress components characterizing the disc-shaped test specimen and picture of two reconstructed discs evidencing the typical crack paths and crack path branches characterizing SiC SA and SiC SP samples.</p> Full article ">Figure 7
<p>Thermal–structural design of ISOL targets making use of the RTPs and VTPs approaches.</p> Full article ">Figure 8
<p>SEM images of the fracture surface in proximity of the disc periphery for six different SiC SP test specimens.</p> Full article ">Figure 9
<p>Measured emissivity values for SiC SA samples.</p> Full article ">Figure 10
<p>Measured emissivity values for SiC SP samples.</p> Full article ">Figure 11
<p>Measured thermal conductivity values for SiC SA samples and comparison with data obtained by Munro [<a href="#B19-materials-14-02689" class="html-bibr">19</a>], Hexoloy<sup>®</sup> datasheets [<a href="#B25-materials-14-02689" class="html-bibr">25</a>] and the inverse estimation (with linear interpolation) by Manzolaro et al. [<a href="#B15-materials-14-02689" class="html-bibr">15</a>].</p> Full article ">Figure 12
<p>Measured thermal conductivity values for SiC SP samples and comparison with SiC SA data.</p> Full article ">Figure 13
<p>Sample mass (%) monitored at the end of every specific test (24 h at constant temperature).</p> Full article ">Figure 14
<p>Weibull plot of strength data for SiC SA (RTPs approach).</p> Full article ">Figure 15
<p>Weibull plot of strength data for SiC SP (RTPs approach).</p> Full article ">Figure 16
<p>Critical stress versus temperature plot (RTPs approach) for both SiC SA and SP (T<sub>AV_Ci</sub> is calculated as the arithmetic average of T<sub>max</sub> and T<sub>min</sub> values reported in <a href="#materials-14-02689-t004" class="html-table">Table 4</a> and <a href="#materials-14-02689-t005" class="html-table">Table 5</a>).</p> Full article ">
13 pages, 4628 KiB  
Article
On the Use of Paper Sludge as Filler in Biocomposites for Injection Moulding
by Vito Gigante, Patrizia Cinelli, Marco Sandroni, Roberto D’ambrosio, Andrea Lazzeri and Maurizia Seggiani
Materials 2021, 14(10), 2688; https://doi.org/10.3390/ma14102688 - 20 May 2021
Cited by 10 | Viewed by 2550
Abstract
The potential use of paper sludge (PS) as filler in the production of bio-composites based on poly lactic acid (PLA) and polybutylene adipate terephthalate (PBAT) was investigated. PS/PLA/PBAT composites, with addition of acetyl tributyl citrate (ATBC) as biobased plasticizer, were produced with PS [...] Read more.
The potential use of paper sludge (PS) as filler in the production of bio-composites based on poly lactic acid (PLA) and polybutylene adipate terephthalate (PBAT) was investigated. PS/PLA/PBAT composites, with addition of acetyl tributyl citrate (ATBC) as biobased plasticizer, were produced with PS loadings up to 30 wt.% by twin-screw extrusion followed by injection moulding. The composites were characterized by rheological measurements, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and mechanical tests (tensile and impact resistance) to study the effect of PS on the processability, thermal stability, crystallinity and mechanical performance of polymeric matrix. The optimized composites at higher PS content were successfully processed to produce pots for horticulture and, in view of this application, preliminary phytotoxicity tests were conducted using the germination test on Lepidium sativum L. seeds. Results revealed that developed composites up to 30 wt.% PS had good processability by extrusion and injection moulding showing that PS is a potential substitute of calcium carbonate as filler in the production of bio-composites, and the absence of phytotoxic effects showed the possibility of their use in the production of pots/items for applications in floriculture and/or horticulture. Full article
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<p>(<b>a</b>) Haake MiniLab mini-extruder equipped with Haake MiniJet II injection moulding (<b>b</b>) granules of Matrix1; (<b>c</b>) granules of Matrix1_20 (<b>d</b>) dog bone specimens containing 10, 20 and 30 % wt. of the PS (Matrix1 series).</p> Full article ">Figure 2
<p>Set-up of the <span class="html-italic">L. sativum</span> seed germination test and germinated seeds after 72 h.</p> Full article ">Figure 3
<p>SEM images of pulverised PS at various magnifications: ×500 (<b>left</b>) and ×1600 (<b>right</b>).</p> Full article ">Figure 4
<p>TG and DTG curves of the paper industry residue.</p> Full article ">Figure 5
<p>Tensile properties of Matrix1 and Matrix1c composites.</p> Full article ">Figure 6
<p>Rotational rheometer measurements at different temperatures.</p> Full article ">Figure 7
<p>DSC Thermogram of Matrix1 series compared with pure PLA.</p> Full article ">Figure 8
<p>Injection molding pots of Matrix1_30 formulations.</p> Full article ">Figure 9
<p>(<b>a</b>) Set-up for the preparation of the eluates and (<b>b</b>) the eluates obtained from PS and graules containing 30 wt.% PS (Matrix1_30).</p> Full article ">
23 pages, 8182 KiB  
Article
Recycling Blast Furnace Ferronickel Slag as a Replacement for Paste in Mortar: Formation of Carboaluminate, Reduction of White Portland Cement, and Increase in Strength
by Qingfeng Guan, Jingliang Xia, Jing Wang, Faguang Leng, Yongxiang Zhou and Changwei Cao
Materials 2021, 14(10), 2687; https://doi.org/10.3390/ma14102687 - 20 May 2021
Cited by 4 | Viewed by 2486
Abstract
Blast furnace ferronickel slag (BFFS) is generated in the production of ferronickel alloys and is used as cement replacement in concrete or mortar. The effectivity in reducing cement consumption and improving performance are limited. By referring to the paste replacement method, this work [...] Read more.
Blast furnace ferronickel slag (BFFS) is generated in the production of ferronickel alloys and is used as cement replacement in concrete or mortar. The effectivity in reducing cement consumption and improving performance are limited. By referring to the paste replacement method, this work used BFFS to replace an equal volume of the white Portland cement paste to obtain greater performance enhancement. BFFS was used with five levels of replacement (0%, 5%, 10%, 15%, 20%) and four water-to-cement ratios (0.40, 0.45, 0.50, 0.55) were designed. Fluidity, mechanical strength, hydration products, and pore structure of every mixture were measured. The results showed that the workability of the mortars decreased due to the reduced volume of water, but the 28-day compressive strength of the mortars increased, and the cement content of the mortars was also reduced by 33 wt %. The X-ray diffraction (XRD) patterns revealed that there existed a carboaluminate phase, and the presence of the ettringite was stabilized, indicating that the accumulating amount of the hydration products of the mortar increased. Furthermore, the BFFS could consume the portlandite and free water to form a higher amount of chemically bound water due to its pozzolanic activity. A high degree of hydration and a large volume of the hydration products refined the porosity of the hardened mortars, which explained the enhancement of the strength of the mortars. Compared to the cement replacement method, the paste replacement method was more effective in preparing eco-friendly mortar or concrete by recycling BFFS for reducing the cement content of the mortar while improving its strength. Full article
(This article belongs to the Special Issue Mix-Design and Behavior of Special Concrete)
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<p>The SEM image of the blast furnace ferronickel slag.</p> Full article ">Figure 2
<p>The particle size distributions of the white Portland cement, the blast furnace ferronickel slag, and the fine aggregate; DD: differential distribution; CV: cumulative volume.</p> Full article ">Figure 3
<p>The X-ray diffraction pattern of the BFFS powder.</p> Full article ">Figure 4
<p>The variation in the dosage of the superplasticizer of the mortar with the volume of the BFFS at various volumes of the replaced paste (PRB) and the replaced cement (CRB).</p> Full article ">Figure 5
<p>The variation in the slump flow of the mortar.</p> Full article ">Figure 6
<p>The percentage of the change in the 3-day strength of the mortar versus the volume of the BFFS: (<b>a</b>) flexural strength; (<b>b</b>) compressive strength.</p> Full article ">Figure 7
<p>The percentage of the change in the 28-day strength of the mortar versus the volume of the BFFS: (<b>a</b>) flexural strength; (<b>b</b>) compressive strength.</p> Full article ">Figure 8
<p>The XRD patterns of the paste containing the BFFS after 28 days of hydration: (<b>a</b>) the pastes produced by the paste replacement method at a water-to-cement ratio of 0.40 and different volumes of the BFFS; (<b>b</b>) the pastes produced by the paste replacement method with 20 vol% of the BFFS at different water-to-cement ratios; (<b>c</b>) the pastes produced by different replacement methods with 20 vol% of the BFFS.</p> Full article ">Figure 9
<p>The differential thermal analysis curves of the pastes after 28 days of hydration: (<b>a</b>) the pastes produced by the paste replacement method with different volumes of the BFFS; (<b>b</b>) the pastes produced by adding 20 vol% of the BFFS to replace an equal volume of the paste at different water-to-cement ratios; (<b>c</b>) the pastes produced by different replacement methods with 20 vol% of the BFFS; CSH: calcium silicate hydrates; Et: ettringite; Hc: hemicarboaluminate; Mc: monocarboaluminate; Ms: monosulfate; Ht: hydrotalcite; CH: Portlandite; CO<sub>3</sub><sup>2−</sup>: carbonate.</p> Full article ">Figure 10
<p>The amounts of the portlandite and bound water of the samples produced by the paste replacement method or the cement replacement method with different volumes of the BFFS, at various water-to-cement ratios, and at a curing period of 28 days.</p> Full article ">Figure 11
<p>The TGA and DTA curves of pastes PRB-0.40-20 and PRB-0.55-20 at a curing period of 28 days.</p> Full article ">Figure 12
<p>The pore size distribution of the pastes after 28 days of hydration.</p> Full article ">Figure 13
<p>The porosity of the pastes after 28 days of hydration.</p> Full article ">Figure 14
<p>The statistical results of the porosity and pore size distribution of the pastes after 28 days of hydration.</p> Full article ">Figure 15
<p>The flexural strength of the PRB mortars versus the cement content of the mortar at various water-to-cement ratios and a curing period of: (<b>a</b>) 3 days; (<b>b</b>) 28 days.</p> Full article ">Figure 16
<p>The compressive strength of the PRB mortars versus the cement content of the mortar at various water-to-cement ratios and a curing period of: (<b>a</b>) 3 days; (<b>b</b>) 28 days.</p> Full article ">Figure 17
<p>The flexural strength of the PRB and CRB mortars versus the cement content of the mortar at various water-to-cement ratios and a curing period of: (<b>a</b>) 3 days; (<b>b</b>) 28 days.</p> Full article ">Figure 18
<p>The compressive strength of the PRB and CRB mortars versus the cement content of the mortar at various water-to-cement ratios and a curing period of: (<b>a</b>) 3 days; (<b>b</b>) 28 days.</p> Full article ">Figure 19
<p>The ratio of the cement content to the compressive strength of the PRB mortars versus the volume of the BFFS at various water-to-cement ratios and a curing period of: (<b>a</b>) 3 days; (<b>b</b>) 28 days.</p> Full article ">Figure 20
<p>The ratio of the cement content to the flexural strength of the PRB mortars versus the volume of the BFFS at various water-to-cement ratios and a curing period of: (<b>a</b>) 3 days; (<b>b</b>) 28 days.</p> Full article ">Figure 21
<p>The ratio of the cement content to the compressive strength of the PRB and CRB mortars versus the volume of the BFFS at various water-to-cement ratios and a curing period of: (<b>a</b>) 3 days; (<b>b</b>) 28 days.</p> Full article ">Figure 22
<p>The ratio of the cement content to the flexural strength of the PRB and CRB mortars versus the volume of the BFFS at various water-to-cement ratios and a curing period of: (<b>a</b>) 3 days; (<b>b</b>) 28 days.</p> Full article ">
20 pages, 4301 KiB  
Article
Viscoelastic Properties of Epoxidized Natural Rubber/Poly(lactic acid) PLA/ENR Blends Containing Glycidyl-POSS and Trisilanolisooctyl-POSS as Functional Additives
by Magdalena Lipińska, Klaudia Toczek and Magdalena Stefaniak
Materials 2021, 14(10), 2686; https://doi.org/10.3390/ma14102686 - 20 May 2021
Cited by 6 | Viewed by 2481
Abstract
The glycidyl-POSS (Polyhedral Oligomeric Silsesquioxanes, Polysilsesquioxane, POSS) (Gly-POSS) and trisilanolisooctyl-POSS (HO-POSS) were applied as functional additives influencing on the viscoelastic properties of the dynamic vulcanized PLA/ENR (poly(lactic acid)/epoxidized natural rubber) blends. The plasticizing effect of HO-POSS on PLA/ENR melt, leading to the decrease [...] Read more.
The glycidyl-POSS (Polyhedral Oligomeric Silsesquioxanes, Polysilsesquioxane, POSS) (Gly-POSS) and trisilanolisooctyl-POSS (HO-POSS) were applied as functional additives influencing on the viscoelastic properties of the dynamic vulcanized PLA/ENR (poly(lactic acid)/epoxidized natural rubber) blends. The plasticizing effect of HO-POSS on PLA/ENR melt, leading to the decrease of complex viscosity at 160 °C, was observed. After the incorporation of Gly-POSS into PLA/ENR blends the complex viscosity increased confirming that the epoxy groups of Gly-POSS were able to react with the functional groups of ENR and the groups present at the end of PLA chains. The incorporation of Gly-POSS into 40:60 PLA/ENR blend provided significant enhancement of the storage shear modulus G’ at 30 °C. Furthermore, the glass transition temperatures Tg of ENR phase for PLA/ENR/Gly-POSS blends were shifted to higher values of temperature as compared with blends modified by HO-POSS. Strong reduction of the elongation at break Eb for 40:60 PLA/ENR/Gly-POSS blend indicated that Gly-POSS particles acted as multifunctional cross-links reducing elasticity of the material. The modification of 40:60 PLA/ENR blend by HO-POSS molecules led to lower values of composting coefficient KC indicating stronger deterioration of the mechanical properties that resulted from more intense degradation processes occurring during disposal in soil. Full article
(This article belongs to the Special Issue Advanced Polymer Composites: Auxiliaries and Additives)
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<p>The complex viscosity η* as a function of time at processing temperature 160 °C at constant strain and angular frequency, equivalent of 1 s<sup>−1</sup> oscillation strain rate (<b>a</b>). The storage modulus G’ and loss modulus G’’ as a function of time at processing temperature of 160 °C (<b>b</b>).</p> Full article ">Figure 2
<p>Influence of thermal treatment during 15 and 30 min of compression molding at 160 °C on the viscoelastic properties of molten PLA/ENR formulations, the storage modulus G’, loss modulus G’’ for: 20:80 PLA/ENR (<b>a</b>); 30:70 PLA/ENR (<b>b</b>); 40:60 PLA/ENR (<b>c</b>); and complex viscosity η* of PLA/ENR blends (<b>d</b>).</p> Full article ">Figure 3
<p>Complex viscosity η* as a function of time at processing temperature 160 °C at constant strain and angular frequency, equivalent of 1 s<sup>−1</sup> oscillation strain rate for POSS modified 20:80 PLA/ENR (<b>a</b>) and 40:60 PLA/ENR blend (<b>b</b>).</p> Full article ">Figure 4
<p>Influence of compression molding during 15 min at 160 °C on the viscoelastic properties of molten PLA/ENR/Gly-POSS blends. Storage shear G’ modulus (<b>a</b>); loss shear G’’ modulus (<b>b</b>).</p> Full article ">Figure 5
<p>Influence of compression molding during 15 min at 160 °C on the viscoelastic properties of molten PLA/ENR/HO-POSS formulations. Storage shear G’ modulus (<b>a</b>); loss shear G’’ modulus (<b>b</b>).</p> Full article ">Figure 6
<p>SEM images of 20:80 PLA/ENR (<b>a</b>); 30:70 PLA/ENR (<b>b</b>,<b>c</b>); 40:60 PLA/ENR (<b>d</b>).</p> Full article ">Figure 7
<p>Storage shear modulus G’ as a function of oscillation strain at angular frequency of 10 rad s<sup>−1</sup> (1.59 Hz) at 30 °C for ENR/PLA (<b>a</b>) and POSS modified blends (<b>b</b>).</p> Full article ">Figure 8
<p>Damping properties, the loss tan δ as a function of oscillation strain at 30 °C and angular frequency of 20 Hz for various PLA/ENR (<b>a</b>) and PLA/ENR/POSS formulations (<b>b</b>).</p> Full article ">Figure 9
<p>Storage shear modulus G’ and loss shear modulus G’’ as a function of angular frequency at 30 °C for PLA/ENR blends.</p> Full article ">Figure 10
<p>Influence of POSS on the storage shear modulus G’ and loss shear modulus G’’ as a function of angular frequency at 30 °C for 20:80 PLA/ENR (<b>a</b>) and 40:60 PLA/ENR (<b>b</b>) blend.</p> Full article ">Figure 11
<p>Loss tan δ (−) as a function of temperature (°C) for PLA/ENR (<b>a</b>) and POSS modified blends (<b>b</b>).</p> Full article ">Figure 12
<p>TGA curves of ENR and PLA/ENR blends.</p> Full article ">Scheme 1
<p>The structures of used polyhedral oligomeric silsesquioxanes POSS additives: (<b>a</b>)—glycidyl-POSS, (<b>b</b>)—trisilanolisooctyl-POSS.</p> Full article ">
10 pages, 20839 KiB  
Article
High Temperature Electrical Properties of Co-Substituted La4BaCu5O13+δ Thin Films Fabricated by Sputtering Method
by Woosuck Shin, Akihiro Tsuruta, Toshio Itoh, Takafumi Akamatsu and Ichiro Terasaki
Materials 2021, 14(10), 2685; https://doi.org/10.3390/ma14102685 - 20 May 2021
Viewed by 2036
Abstract
The high-temperature conductivity of the perovskite oxides of a La4BaCu5O13+δ (LBCO) thin film prepared by RF sputtering deposition and thermal annealing has been studied. While the bulk LBCO compound was metallic, the LBCO film deposited on a [...] Read more.
The high-temperature conductivity of the perovskite oxides of a La4BaCu5O13+δ (LBCO) thin film prepared by RF sputtering deposition and thermal annealing has been studied. While the bulk LBCO compound was metallic, the LBCO film deposited on a Si substrate by sputtering and a post annealing process showed semiconductor-like conduction, which is considered to be due to the defects and poor grain connectivity in the LBCO film on the Si substrate. The LBCO film deposited on a SrTiO3 substrate was of high film quality and showed metallic conduction. When the cation site Cu was substituted by Co, the electrical conductivity of the LBCO film increased further and its temperature dependence became smaller. The transport properties of LBCO films are investigated to understand its carrier generation mechanism. Full article
(This article belongs to the Special Issue Thin Films for Energy Production and Storage)
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<p>Crystal structure of La<sub>4</sub>BaCu<sub>5</sub>O<sub>13+δ</sub>. (The figure was drawn using VESTA [<a href="#B8-materials-14-02685" class="html-bibr">8</a>]. Red is Cu; blue is Ba, which is shaded in the pyramid; green is La; and black is O).</p> Full article ">Figure 2
<p>The chips of Co<sub>3</sub>O<sub>4</sub> were placed on the surface of the LBCO sputtering target of 100 mm in diameter.</p> Full article ">Figure 3
<p>XRD pattern of the LBCO and Co-substituted LBCO films, (<b>a</b>) with different thermal annealing temperatures on the SiO/Si substrate, and (<b>b</b>) the LBCO films (the peaks of red index) compared with the SrTiO<sub>3</sub> single crystal substrate (the peaks of black index) with the different concentrations of Co-substitution.</p> Full article ">Figure 4
<p>High-temperature thermoelectric properties of the LBCO films.</p> Full article ">Figure 5
<p>High-temperature thermoelectric properties of the Co-substituted LBCO films.</p> Full article ">Figure 6
<p>AFM and FESEM micrographs showing the surface morphology of the prepared LBCO films on (<b>a</b>)SiO/Si, (<b>b</b>) SrTiO<sub>3</sub>, and (<b>c</b>) Co-substituted film on SrTiO<sub>3</sub>. SEM observation of the LBCO films on Si wafers showed a high crack concentration (<b>d</b>) in the film with a thickness of 0.5 μm, and (<b>e</b>) greatly reduced cracking in the thicker, 1 μm, film. The SEM observation of the film on SrTiO<sub>3</sub> showed just a smooth surface and is not shown here.</p> Full article ">Figure 7
<p>(<b>a</b>) Hall carrier concentration and (<b>b</b>) Hall mobility of La<sub>4</sub>BaCu<sub>5</sub>O<sub>13+δ</sub> thin film on the substrate of SrTiO<sub>3</sub> measured from room temperature to 300 °C. A single carrier model is assumed.</p> Full article ">
12 pages, 11054 KiB  
Article
Nanoparticles of Bioactive Glass Enhance Biodentine Bioactivity on Dental Pulp Stem Cells
by Camila Corral Nunez, Diego Altamirano Gaete, Miguel Maureira, Javier Martin and Cristian Covarrubias
Materials 2021, 14(10), 2684; https://doi.org/10.3390/ma14102684 - 20 May 2021
Cited by 9 | Viewed by 3423
Abstract
This study aimed to investigate the cytotoxicity and bioactivity of a novel nanocomposite containing nanoparticles of bioactive glass (nBGs) on human dental pulp stem cells (hDPSCs). nBGs were synthesized by the sol–gel method. Biodentine (BD) nanocomposites (nBG/BD) were prepared with 2 and 5% [...] Read more.
This study aimed to investigate the cytotoxicity and bioactivity of a novel nanocomposite containing nanoparticles of bioactive glass (nBGs) on human dental pulp stem cells (hDPSCs). nBGs were synthesized by the sol–gel method. Biodentine (BD) nanocomposites (nBG/BD) were prepared with 2 and 5% wt of nBG content; unmodified BD and glass ionomer cement were used as references. Cell viability and attachment were evaluated after 3, 7 and 14 days. Odontogenic differentiation was assessed with alkaline phosphatase (ALP) activity after 7 and 14 days of exposure. Cells successfully adhered and proliferated on nBG/BD nanocomposites, cell viability of nanocomposites was comparable with unmodified BD and higher than GIC. nBG/BD nanocomposites were, particularly, more active to promote odontogenic differentiation, expressed as higher ALP activity of hDPSCs after 7 days of exposure, than neat BD or GIC. This novel nanocomposite biomaterial, nBG/BD, allowed hDPSC attachment and proliferation and increased the expression of ALP, upregulated in mineral-producing cells. These findings open opportunities to use nBG/BD in vital pulp therapies. Full article
(This article belongs to the Special Issue Bioactive Dental Materials)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Representative SEM images (accelerating voltage of 20 kV, working distance of 10.3–10.6 mm, magnification of 1000×) and EDX elemental analysis of BD, 2% nBG/BD, 5% nBG/BD and GIC set cement surfaces.</p> Full article ">Figure 2
<p>Cell viability of hDPSCSs cultured with BD, 2% nBG/BD, 5% nBG/BD and GIC at different culture times as determined by the MTS assay. Values are combined from 2 experiments (<span class="html-italic">n</span> = 4/experiment), standard deviations are represented by vertical bars. *: Statistically significant difference compared with BD (<span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 3
<p>Representative SEM images (accelerating voltage of 20 kV, working distance of 10.0–11.4 mm, magnification 100× and 1000×) of hDPSCs cultured with BD, 2% nBG/BD, 5% nBG/BD and GIC after 7 and 14 days of incubation.</p> Full article ">Figure 4
<p>ALP activity of hDPSCs cultured with BD, 2% nBG/BD, 5% nBG/BD and GIC at different times. Values are means combined from 2 experiments (<span class="html-italic">n</span> = 4/experiment), standard deviations are represented by vertical bars. #: Statistically significant difference compared with control (<span class="html-italic">p</span> &lt; 0.05). *: Statistically significant difference compared with BD (<span class="html-italic">p</span> &lt; 0.05).</p> Full article ">
29 pages, 10256 KiB  
Article
Impact of Sulphate Ions Content on Performance of Maleic and Acrylic Superplasticizers in Cement Paste
by Elżbieta Janowska-Renkas
Materials 2021, 14(10), 2683; https://doi.org/10.3390/ma14102683 - 20 May 2021
Cited by 4 | Viewed by 2121
Abstract
The paper presents test results of the impact of sulphate ions from calcium sulphates: Hemihydrate, dihydrate and anhydrite, on rheological properties and hydration heat of cement pastes with, and without, superplasticizers, derivatives of maleic (SP-2) and acrylic (SP-1) acids. It is demonstrated that [...] Read more.
The paper presents test results of the impact of sulphate ions from calcium sulphates: Hemihydrate, dihydrate and anhydrite, on rheological properties and hydration heat of cement pastes with, and without, superplasticizers, derivatives of maleic (SP-2) and acrylic (SP-1) acids. It is demonstrated that cement pastes fluidity depends on superplasticizer chemical structure, and its effect is expressed by a hydrophilic coefficient. As maleic superplasticizers have flexible comb-like structure composed of a shorter backbone chain containing COO− carboxylate groups and very long side chains, cement pastes showed higher fluidity than with acrylic superplasticizer with ladder-like structure, longer backbone chains with shorter side chains. SP-1 showing lower hydrophilicity coefficient and fewer COO− groups was found to be less sensitive to increased sulphate ion content in pastes. However, with SP-2 with higher hydrophilicity, a gradual fluidity loss (increased paste viscosity) was observed. Plastic viscosity was approximately at the same level in SP-1-containing pastes. Tests showed that sulphates definitely changed polycarboxylate superplasticizers performance. A high concentration of sulphate ions reduced maleic superplasticizer efficiency. Under these conditions, SP-1 is more effective and therefore more suitable for fluidity of pastes containing higher SO42− ions content. Thus, sulphate ions concentration in the paste should be considered when selecting superplasticizer. Full article
(This article belongs to the Special Issue Advances in Cement-Based Materials: Mechanical Behavior, Rheology, and Radiology)
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<p>GPC chromatograms of superplasticizers specimens (SP-1, SP-2), [based on results published in [<a href="#B41-materials-14-02683" class="html-bibr">41</a>]].</p> Full article ">Figure 2
<p>Results of the GPC chromatographic analysis of superplasticizer polymer fractions (SP-1, SP-2), [based on results published in [<a href="#B41-materials-14-02683" class="html-bibr">41</a>]].</p> Full article ">Figure 3
<p>Selected function groups: Aliphatic, ether and carbonyl groups identified by means of IR testing), (based on results published in [<a href="#B41-materials-14-02683" class="html-bibr">41</a>]).</p> Full article ">Figure 4
<p>Approximate chemical structures of superplasticizers: ladder-shaped (SP-1) and comb-shaped (SP-2) determined based on mathematical calculation of molar masses.</p> Full article ">Figure 5
<p>Results of FTIR spectral analysis of superplasticizer samples (based on results published in [<a href="#B41-materials-14-02683" class="html-bibr">41</a>]).</p> Full article ">Figure 6
<p>Flow curves of cement pastes with addition of CaSO<sub>4</sub>·0.5H<sub>2</sub>O, CaSO<sub>4</sub>, CaSO<sub>4</sub>·2H<sub>2</sub>O, after 10 min.</p> Full article ">Figure 7
<p>Flow curves of cement pastes with addition of CaSO<sub>4</sub>·0.5H<sub>2</sub>O, CaSO<sub>4</sub>, CaSO<sub>4</sub>·2H<sub>2</sub>O, after 60 min.</p> Full article ">Figure 8
<p>Flow curves of cement pastes with addition of CaSO<sub>4</sub>·0.5H<sub>2</sub>O, CaSO<sub>4,</sub> CaSO<sub>4</sub>·2H<sub>2</sub>O in presence of SP-1 superplasticizer, after 10 min.</p> Full article ">Figure 9
<p>Flow curves of cement pastes with addition of CaSO<sub>4</sub>·0.5H<sub>2</sub>O, CaSO<sub>4</sub>, CaSO<sub>4</sub>·2H<sub>2</sub>O in presence of SP-1 superplasticizer, after 60 min.</p> Full article ">Figure 10
<p>Flow curves of cement pastes with addition of CaSO<sub>4</sub>·0.5H<sub>2</sub>O, CaSO<sub>4</sub>, CaSO<sub>4</sub>·2H<sub>2</sub>O in presence of SP-2 superplasticizer, after 10 min.</p> Full article ">Figure 11
<p>Flow curves of cement pastes with addition of CaSO<sub>4</sub>·0.5H<sub>2</sub>O, CaSO<sub>4</sub>, CaSO<sub>4</sub>·2H<sub>2</sub>O in presence of SP-2 superplasticizer, after 60 min.</p> Full article ">Figure 12
<p>Flow curves of pastes of C1, C2 and C3 cements containing K<sub>2</sub>SO<sub>4</sub> in presence of SP-1 in 1% by mass, after 10 and 60 min.</p> Full article ">Figure 13
<p>Two states of polymer in the solution: a freely unfolded chain and chain condensed under the stimulus impact-attraction of chain segments based on [<a href="#B52-materials-14-02683" class="html-bibr">52</a>].</p> Full article ">Figure 14
<p>Flow curves of cementitious pastes containing 5% by mass of CaSO<sub>4</sub>·0.5H<sub>2</sub>O and CaSO<sub>4</sub> in quantity from 20 to 80% by mass, after 10 min.</p> Full article ">Figure 15
<p>Flow curves of cementitious pastes containing 5% by mass of CaSO<sub>4</sub>·0.5H<sub>2</sub>O and CaSO<sub>4</sub> in quantity from 20 to 80% by mass, after 60 min.</p> Full article ">Figure 16
<p>Flow curves of cementitious pastes containing 5% by mass of CaSO<sub>4</sub>·0.5H<sub>2</sub>O and CaSO<sub>4</sub> in quantity from 20 to 80% by mass in presence of SP-1 type superplasticizer, 1% by mass, after 10 min.</p> Full article ">Figure 17
<p>Flow curves of cement pastes containing 5% by mass of CaSO<sub>4</sub>·0.5H<sub>2</sub>O and CaSO<sub>4</sub> in quantity from 20 to 80% by mass in presence of SP-1 type superplasticizer, 1% by mass, after 60 min.</p> Full article ">Figure 18
<p>Flow curves of cementitious pastes containing 5% by mass of CaSO<sub>4</sub>·0.5H<sub>2</sub>O and CaSO<sub>4</sub> in quantity from 20 to 80% by mass in presence of SP-2 type superplasticizer, 1% by mass, after 10 min.</p> Full article ">Figure 19
<p>Flow curves of cement pastes containing 5% by mass of CaSO<sub>4</sub>·0.5H<sub>2</sub>O and CaSO<sub>4</sub> in quantity from 20 to 80% by mass in presence of SP-2 type superplasticizer, 1% by mass, after 60 min.</p> Full article ">Figure 20
<p>Plastic viscosity η<sub>pl</sub> of pastes from cements C1, CM1, CM2, CM3 and C2 containing calcium sulphate anhydrite without and with 1% by mass of SP-1 and SP-2 superplasticizer, determined after 10 min.</p> Full article ">Figure 21
<p>Hydration heat evolution rate curves for C1 cement without and with 1% by mass of SP-1 and SP-2 superplasticizers.</p> Full article ">Figure 22
<p>Hydration heat evolution rate curves for C2 cement without and with 1% by mass of SP-1 and SP-2 superplasticizers.</p> Full article ">Figure 23
<p>Hydration heat evolution rate curves for C3 cement without and with 1% by mass of SP-1 and SP-2 superplasticizers.</p> Full article ">Figure 24
<p>Hydration heat evolution rate curves for CM2 and CM3 cements with 1% by mass of SP-1 and SP-2 superplasticizers.</p> Full article ">Figure 25
<p>Hydration heat evolution rate curves for CM1 cement without and with SP-1 and SP-2 superplasticizers.</p> Full article ">Figure 26
<p>Hydration heat evolution rate curves for CM4 cement without and with SP-1 and SP-2 superplasticizers.</p> Full article ">
41 pages, 7300 KiB  
Review
Metallic Material Selection and Prospective Surface Treatments for Proton Exchange Membrane Fuel Cell Bipolar Plates—A Review
by Tereza Bohackova, Jakub Ludvik and Milan Kouril
Materials 2021, 14(10), 2682; https://doi.org/10.3390/ma14102682 - 20 May 2021
Cited by 23 | Viewed by 5911
Abstract
The aim of this review is to summarize the possibilities of replacing graphite bipolar plates in fuel-cells. The review is mostly focused on metallic bipolar plates, which benefit from many properties required for fuel cells, viz. good mechanical properties, thermal and electrical conductivity, [...] Read more.
The aim of this review is to summarize the possibilities of replacing graphite bipolar plates in fuel-cells. The review is mostly focused on metallic bipolar plates, which benefit from many properties required for fuel cells, viz. good mechanical properties, thermal and electrical conductivity, availability, and others. The main disadvantage of metals is that their corrosion resistance in the fuel-cell environment originates from the formation of a passive layer, which significantly increases interfacial contact resistance. Suitable coating systems prepared by a proper deposition method are eventually able to compensate for this disadvantage and make the replacement of graphite bipolar plates possible. This review compares coatings, materials, and deposition methods based on electrochemical measurements and contact resistance properties with respect to achieving appropriate parameters established by the DOE as objectives for 2020. An extraordinary number of studies have been performed, but only a minority of them provided promising results. One of these is the nanocrystalline β-Nb2N coating on AISI 430, prepared by the disproportionation reaction of Nb(IV) in molten salt, which satisfied the DOE 2020 objectives in terms of corrosion resistance and interfacial contact resistance. From other studies, TiN, CrN, NbC, TiC, or amorphous carbon-based coatings seem to be promising. This paper is novel in extracting important aspects for future studies and methods for testing the properties of metallic materials and factors affecting monitoring characteristics and parameters. Full article
(This article belongs to the Special Issue Advances in Manufacturing and Recycling of Battery Materials)
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<p>Proton exchange membrane fuel cell model.</p> Full article ">Figure 2
<p>Serpentine flow fields. Reprinted from [<a href="#B26-materials-14-02682" class="html-bibr">26</a>], copyright (2016), with permission from Elsevier.</p> Full article ">Figure 3
<p>Outputs of assembled fuel cells with different bipolar plates. Reprinted from [<a href="#B26-materials-14-02682" class="html-bibr">26</a>] copyright (2016), with permission from Elsevier.</p> Full article ">Figure 4
<p>MEA cross section for in situ measurement according to Makkus (Au wire placed between membrane and E-tek backing plus electrode). Reprinted from [<a href="#B64-materials-14-02682" class="html-bibr">64</a>] copyright (2000), with permission from Elsevier.</p> Full article ">Figure 5
<p>Scheme of method for in situ contact resistance measurement according to Makkus. Reprinted from [<a href="#B64-materials-14-02682" class="html-bibr">64</a>] copyright (2000), with permission from Elsevier.</p> Full article ">Figure 6
<p>In situ contact resistance measurement according to Lædre [<a href="#B65-materials-14-02682" class="html-bibr">65</a>].</p> Full article ">Figure 7
<p>Principle of contact resistance measurement; stainless steel plate as a sample. Reprinted from [<a href="#B70-materials-14-02682" class="html-bibr">70</a>] copyright (2018), with permission from Elsevier.</p> Full article ">Figure 8
<p>Contact resistance dependence on contact force. Reprinted from [<a href="#B45-materials-14-02682" class="html-bibr">45</a>] copyright (2010), with permission from Elsevier.</p> Full article ">Figure 9
<p>Principle of Cr-interlayer effect for amorphous carbon coating. Reprinted from [<a href="#B26-materials-14-02682" class="html-bibr">26</a>] copyright (2016), with permission from Elsevier.</p> Full article ">Figure 10
<p>Effect of pH on the polarization curve of 310S stainless steel in 0.05 M H<sub>2</sub>SO<sub>4</sub> with 2 ppm F<sup>−</sup>. Reprinted from [<a href="#B52-materials-14-02682" class="html-bibr">52</a>] copyright (2008), with permission from Elsevier.</p> Full article ">Figure 11
<p>Influence of electrolyte pH (0.05 M SO<sub>4</sub><sup>2−</sup> with 2 ppm HF) on open-circuit potential of Ti-Al6-V4. Reprinted from [<a href="#B31-materials-14-02682" class="html-bibr">31</a>] copyright (2016), with permission from Elsevier.</p> Full article ">Figure 12
<p>Influence of electrolyte pH (0.05 M SO<sub>4</sub><sup>2−</sup> with 2 ppm HF) on current density of Ti-Al6-V4 and Ta<sub>2</sub>N coating at potentiostatic polarization. Reprinted from [<a href="#B31-materials-14-02682" class="html-bibr">31</a>] copyright (2016), with permission from Elsevier.</p> Full article ">Figure 13
<p>(<b>a</b>) Ta<sub>2</sub>N coated Ti-Al6-V4 alloy before and after PST test in 0.05 M H<sub>2</sub>SO<sub>4</sub> with 2 ppm HF. Reprinted from [<a href="#B31-materials-14-02682" class="html-bibr">31</a>] copyright (2016), with permission from Elsevier. (<b>b</b>) Effect of pH and temperature on contact resistance- 310S steel on 0.05 M H<sub>2</sub>SO<sub>4</sub> with 2 ppm HF. Reprinted from [<a href="#B52-materials-14-02682" class="html-bibr">52</a>] copyright (2008), with permission from Elsevier.</p> Full article ">Figure 14
<p>Comparison of corrosion behavior of steel in 0.5 M H<sub>2</sub>SO<sub>4</sub> at 80 °C without (<b>a</b>) and with 2 ppm HF (<b>b</b>). Reprinted from [<a href="#B77-materials-14-02682" class="html-bibr">77</a>] copyright (2007), with permission from Elsevier.</p> Full article ">Figure 15
<p>Influence of fluoride addition on corrosion behavior of Ti-Al6-V4 alloy and ZrCN coating. Reprinted from [<a href="#B66-materials-14-02682" class="html-bibr">66</a>] copyright (2015), with permission from Elsevier.</p> Full article ">Figure 16
<p>Comparison of SS 316 behavior at 25 °C and 80 °C in 0.5M sulfuric acid, pH = 4 and oxygen bubbled. Reprinted from [<a href="#B183-materials-14-02682" class="html-bibr">183</a>] copyright (2007), with permission from Elsevier.</p> Full article ">Figure 17
<p>The amount of ions released after 500 h of exposure of AISI 316L depending on the applied potential (BA = bright annealing state). Reprinted from [<a href="#B16-materials-14-02682" class="html-bibr">16</a>] copyright (2015), with permission from Elsevier.</p> Full article ">Figure 18
<p>Current density dependence on applied potential for 316L steel with TiN coating in 1 mM H<sub>2</sub>SO<sub>4</sub>. Reprinted from [<a href="#B23-materials-14-02682" class="html-bibr">23</a>] copyright (2010), with permission from Elsevier.</p> Full article ">Figure 19
<p>Effect of applied potential on current density of 316L steel coated with amorphous carbon with chromium interlayer. Reprinted from [<a href="#B24-materials-14-02682" class="html-bibr">24</a>] copyright (2017), with permission from Elsevier.</p> Full article ">Figure 20
<p>Potential impact on 316L steel contact resistance in sulfuric acid, pH = 3. Reprinted from [<a href="#B185-materials-14-02682" class="html-bibr">185</a>] copyright (2014), with permission from Elsevier.</p> Full article ">Figure 21
<p>Effect of exposure time on contact resistance values for TiN coating on 316L steel before and after potentiostatic test in 1 mM H<sub>2</sub>SO<sub>4</sub>. Reprinted from [<a href="#B23-materials-14-02682" class="html-bibr">23</a>] copyright (2015), with permission from Elsevier.</p> Full article ">
16 pages, 14593 KiB  
Article
Selective Laser Melted M300 Maraging Steel—Material Behaviour during Ballistic Testing
by Ireneusz Szachogłuchowicz, Bartosz Fikus, Krzysztof Grzelak, Janusz Kluczyński, Janusz Torzewski and Jakub Łuszczek
Materials 2021, 14(10), 2681; https://doi.org/10.3390/ma14102681 - 20 May 2021
Cited by 6 | Viewed by 3202
Abstract
Significant growth in knowledge about metal additive manufacturing (AM) affects the increase of interest in military solutions, where there is always a need for unique technologies and materials. An important section of materials in the military are those dedicated to armour production. An [...] Read more.
Significant growth in knowledge about metal additive manufacturing (AM) affects the increase of interest in military solutions, where there is always a need for unique technologies and materials. An important section of materials in the military are those dedicated to armour production. An AM material is characterised by different behaviour than those conventionally made, especially during more dynamic loading such as ballistics testing. In this paper, M300 maraging steel behavior was analysed under the condition of ballistic testing. The material was tested before and after solution annealing and ageing. This manuscript also contains some data based on structural analysis and tensile testing with digital image correlation. Based on the conducted research, M300 maraging steel was found to be a helpful material for some armour solutions after pre- or post-processing activities. Conducted solution annealing and ageing increased the ballistic properties by 87% in comparison to build samples. At the same time, the material’s brittleness increased, which affected a significant growth in fragmentation of the perforated plate. According to such phenomena, a detailed fracture analysis was made. Full article
(This article belongs to the Special Issue Microstructural and Mechanical Properties Investigation of Alloy Prepared by Additive Manufacturing Technology)
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<p>SEM image of M300 powder grains.</p> Full article ">Figure 2
<p>Explanation of layer thickness, hatching distance values, and sample plate dimension.</p> Full article ">Figure 3
<p>Sample panel on the SLM 125 HL’s substrate plate.</p> Full article ">Figure 4
<p>Experimental stand for terminal ballistics tests: (<b>a</b>) investigated specimen mount, (<b>b</b>) high-speed camera, (<b>c</b>) light source, (<b>d</b>) protective box with bullet catcher, (<b>e</b>) intelligent light screen, (<b>f</b>) electromagnetic muzzle device, and (<b>g</b>) barrel launching system, calibre 5.56 mm.</p> Full article ">Figure 5
<p>Servo-hydraulic pulsator for tensile tests Instron 8802 (<b>a</b>) with digital image correlation system DIC (<b>b</b>).</p> Full article ">Figure 6
<p>Sample dimensions basing on the ASTM E466 96 standard.</p> Full article ">Figure 7
<p>Microstructure of the AM M300 steel in BHT (<b>a</b>) and AHT (<b>b</b>) conditions.</p> Full article ">Figure 8
<p>Microstructure of the AM M300 in BHT condition with marked crack (red circle) from non-melted grain (yellow circle) and visible melt-pool boundary (blue arrow).</p> Full article ">Figure 9
<p>Tensile test results of M300 steel in AHT and BHT conditions.</p> Full article ">Figure 10
<p>DIC of M300 steel in BHT condition during tensile testing, (<b>a</b>) a reference sample before the tensile testing, (<b>b</b>) Rp 0.2% proof strength, (<b>c</b>) the ultimate tensile strength (UTS) point, (<b>d</b>) breaking point, and (<b>e</b>) a sample after a fracture.</p> Full article ">Figure 11
<p>DIC of M300 steel in AHT condition during tensile testing, (<b>a</b>) a reference sample before the tensile testing, (<b>b</b>) Rp 0.2% proof strength, (<b>c</b>) the ultimate tensile strength (UTS) point, (<b>d</b>) breaking point, and (<b>e</b>) a sample after a fracture.</p> Full article ">Figure 12
<p>High-speed camera images captured during plates perforation: (<b>a</b>) BHT condition, 936m/s impact velocity; (<b>b</b>) AHT condition, 918m/s impact velocity; (<b>c</b>) BHT condition, 746m/s impact velocity; (<b>d</b>) AHT condition, 743m/s impact velocity.</p> Full article ">Figure 13
<p>Fractures of projectile entry and exit of both penetrated plates: (<b>a</b>) BHT (<b>b</b>) AHT.</p> Full article ">Figure 14
<p>Perforation channel surface with visible deformed areas (<b>a</b>) and cracks (<b>b</b>) of the BHT plate.</p> Full article ">
12 pages, 2938 KiB  
Communication
Dynamic Covalent Bonds of Si-OR and Si-OSi Enabled A Stiff Polymer to Heal and Recycle at Room Temperature
by Ping Fan, Can Xue, Xiantai Zhou, Zujin Yang and Hongbing Ji
Materials 2021, 14(10), 2680; https://doi.org/10.3390/ma14102680 - 20 May 2021
Cited by 8 | Viewed by 2641
Abstract
As stiff polymers are difficult to self-heal, the balance between polymers’ self-healing ability and mechanical properties is always a big challenge. Herein, we have developed a novel healable stiff polymer based on the Si-OR and Si-OSi dynamic covalent bonds. The self-healing mechanism was [...] Read more.
As stiff polymers are difficult to self-heal, the balance between polymers’ self-healing ability and mechanical properties is always a big challenge. Herein, we have developed a novel healable stiff polymer based on the Si-OR and Si-OSi dynamic covalent bonds. The self-healing mechanism was tested and proved by the small molecule model experiments and the contrast experiments of polymers. This polymer possesses excellent tensile, bending properties as well as room temperature self-healing abilities. Moreover, due to the sticky and shapeable properties under wetting conditions, the polymer could be used as an adhesive. Besides, even after four cycles of recycling, the polymer maintains its original properties, which meets the requirements of recyclable materials. It was demonstrated that the polymer exhibits potential application in some fields, such as recyclable materials and healable adhesives. Full article
(This article belongs to the Section Carbon Materials)
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<p>(<b>a</b>) The reaction route of <b>P(AamKH550)</b> (polymer of N-(4-(triethoxysilyl)butyl)acrylamide) and <b>PVA</b> (polyvinyl alcohol). (<b>b</b>) Proposed mechanism for self-healing of <b>P(AamKH550)/PVA</b> (polymer blends of P(AamKH550) and PVA).</p> Full article ">Figure 2
<p>Differential scanning calorimetry (DSC) curve of <b>P(AamKH550)/PVA</b>.</p> Full article ">Figure 3
<p>Mechanical properties of <b>P(AamKH550)/PVA</b> strips. (<b>a</b>) Mechanical tensile-stress curves of <b>P(AamKH550)/PVA</b> samples tested under ambient conditions (25 °C, 45H%). The illustration shows the average and the error bar of tensile Young’s modulus of the tested four samples. (<b>b</b>) Mechanical bending-stress curves of <b>P(AamKH550)/PVA</b> samples tested under ambient conditions (25 °C, 45H%). The illustration shows the average and error bar of bending Young’s modulus of the measured three samples. (<b>c</b>) The image of tensile-stress tests of <b>P(AamKH550)/PVA</b>. (<b>d</b>) The image of bending-stress tests of <b>P(AamKH550)/PVA</b>. (<b>e</b>) The image of 0.2612 g strip of <b>P(AamKH550)/PVA</b> withstanding a 1 kg hook weight (sample size: 40 mm length × 5 mm width × 2 mm height).</p> Full article ">Figure 4
<p>Self-healing properties of <b>P(AamKH550)/PVA</b> strips. (<b>a</b>) Mechanical tensile-stress curves of the pristine <b>P(AamKH550)/PVA</b> samples and healed samples at 25 °C and 23H% for 1 h, 3 h, 6 h, 12 h and 24 h, respectively. (<b>b</b>) Mechanical tensile-stress curves of the pristine <b>P(AamKH550)/PVA</b> samples and <b>P(AamKH550)/PVA</b> samples healed for 24 h at 23H% and 25 °C, 50 °C, 60 °C and 70 °C, respectively. (<b>c</b>) Optical microscopic image of a damaged <b>P(AamKH550)/PVA</b> strip under ambient conditions. (<b>d</b>) Optical microscopic image of the <b>P(AamKH550)/PVA</b> strip healed for 1 h under ambient conditions. (<b>e</b>) Photographs of original <b>P(AamKH550)/PVA</b> disks in 25 mm diameter (left) and healed <b>P(AamKH550)/PVA</b> disks (right) after healing (25 °C, 23H%) for 1 h withstanding 1 kg of weight. (<b>f</b>) Comparison of the healable materials in this work and recent reports on the self-healing efficiency and ultimate strength.</p> Full article ">Figure 5
<p>Self-healing mechanism studies of <b>P(AamKH550)/PVA</b>. (<b>a</b>) Schemes of <sup>1</sup>H NMR (1), In-Situ IR (2), ESI-MS (3). (<b>b</b>) <sup>1</sup>H NMR spectra of 3-aminopropyltriethoxysilane in CDCl<sub>3</sub> (spectrum a) and the exchange reaction of 3-aminopropyltriethoxysilane with ethanol-D<sub>6</sub> in CDCl<sub>3</sub> (spectrum b). The amplified insets show integral area of –Si-O-CH<sub>2</sub>- of spectrum a and b, respectively. (<b>c</b>) In-Situ IR spectra of the reaction between aminopropyltriethoxysilane (KH550) and ethylene glycol. (<b>d</b>) The three-dimensional in-situ IR spectra of the reaction between KH550 and ethylene glycol. (<b>e</b>) ESI-MS spectra of exchange reaction between 3-aminopropyltrimethoxysilane (KH540) and KH550 at 25 °C. (<b>f</b>) Healing properties of <b>P(AamKH550)/PVA</b>, <b>P(AamKH550-Aam)/PVA</b>, <b>PAam/PVA</b> strips healed at 25 °C and 23H% for 24 h.</p> Full article ">Figure 6
<p>Recycling properties of <b>P(AamKH550)/PVA</b>. (<b>a</b>) Tensile-stress curves of the pristine <b>P(AamKH550)/PVA</b> strips and reprocessing <b>P(AamKH550)/PVA</b> strips after the 1st, 2nd, 3rd and 4th generation. (<b>b</b>) Photographs of the reprocessing method of the <b>P(AamKH550)/PVA</b> strips.</p> Full article ">Figure 7
<p>Adhesion tests of P(AamKH550)/PVA.</p> Full article ">
23 pages, 6996 KiB  
Review
RE-Based Inorganic-Crystal Nanofibers Produced by Electrospinning for Photonic Applications
by Alessandra Toncelli
Materials 2021, 14(10), 2679; https://doi.org/10.3390/ma14102679 - 20 May 2021
Cited by 6 | Viewed by 2651
Abstract
Electrospinning is an effective and inexpensive technique to grow polymer materials in nanofiber shape with exceptionally high surface-area-to-volume ratio. Although it has been known for about a century, it has gained much interest in the new millennium thanks to its low cost and [...] Read more.
Electrospinning is an effective and inexpensive technique to grow polymer materials in nanofiber shape with exceptionally high surface-area-to-volume ratio. Although it has been known for about a century, it has gained much interest in the new millennium thanks to its low cost and versatility, which has permitted to obtain a large variety of multifunctional compositions with a rich collection of new possible applications. Rare-earth doped materials possess many remarkable features that have been exploited, for example, for diode pumped bulk solid-state lasers in the visible and near infrared regions, or for biomedical applications when grown in nanometric form. In the last few decades, electrospinning preparation of rare-earth-doped crystal nanofibers has been developed and many different materials have been successfully grown. Crystal host, crystal quality and nanosized shape can deeply influence the optical properties of embedded rare earth ions; therefore, a large number of papers has recently been devoted to the growth and characterization of rare earth doped nanofibers with the electrospinning technique and an up-to-date review of this rapidly developing topic is missing; This review paper is devoted to the presentation of the main results obtained in this field up to now with particular insight into the optical characterization of the various materials grown with this technique. Full article
(This article belongs to the Special Issue Feature Papers in Materials Physics)
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<p>Trend of the annual number of scientific publications in the new millennium as obtained from the Scopus database using the search term “electrospinning” in April 2021.</p> Full article ">Figure 2
<p>Schematic diagram of the electrospinning setup.</p> Full article ">Figure 3
<p>Evolution of PVP–oil Taylor cone geometry. Outer and inner flow rates are: (<b>a</b>) 0.4–0.04 mL/h; (<b>b</b>) 0.4–0.2 mL/h; (<b>c</b>) 0.4–0.5 mL/h. Inner needle OD is 0.5 mm. (<b>d</b>) Oil covered microfibers as a result of <span class="html-italic">Q</span>out/<span class="html-italic">Q</span> in ≈ 1. Scale bar: 20 μm. Reprinted with permission from [<a href="#B28-materials-14-02679" class="html-bibr">28</a>]. Copyright © 2006 WILEY–VCH Verlag GmbH &amp; Co. KGaA, Weinheim.</p> Full article ">Figure 4
<p>Schematic of the process to grow YF<sub>3</sub>:Eu<sup>3+</sup> hollow nanofibers. Reprinted with permission from [<a href="#B29-materials-14-02679" class="html-bibr">29</a>]. Copyright © 2012 Elsevier B.V.</p> Full article ">Figure 5
<p>X-ray diffraction patterns for CaMoO<sub>4</sub>:5 mol% Ln<sup>3+</sup> nanofibers: (<b>a</b>) as-formed precursor fibers; (<b>b</b>) the CaMoO<sub>4</sub>:5 mol% Tb<sup>3+</sup> fibers annealed at 800 °C, (<b>c</b>) CaMoO<sub>4</sub>:5 mol%Eu<sup>3+</sup> annealed at 800 °C, (<b>d</b>) CaMoO<sub>4</sub>:5 mol% Dy<sup>3+</sup> annealed at 800 °C; and the JCPDS card 29-0351 of CaMoO<sub>4</sub> for comparison. Reprinted with permission from [<a href="#B30-materials-14-02679" class="html-bibr">30</a>]. Copyright © 2009 American Chemical Society.</p> Full article ">Figure 6
<p>Approximate peak emission lines of the rare earth ions in the visible region.</p> Full article ">Figure 7
<p>Excitation (<b>A</b>) and emission (<b>B</b>) spectra of NaGdF<sub>4</sub>:x%Eu<sup>3+</sup> (x = 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 5, 7, 9, 11, 13, 15) nanofibers. Reprinted with permission from [<a href="#B13-materials-14-02679" class="html-bibr">13</a>]. Copyright © 2017 John Wiley and Sons.</p> Full article ">Figure 8
<p>Up-conversion emission spectra of (<b>a</b>) β -NaYF<sub>4</sub>:Yb<sup>3+</sup>, Er<sup>3+</sup>@precursor fibers and (<b>b</b>) α -NaYF<sub>4</sub>:Yb<sup>3+</sup>, Er<sup>3+</sup>@silica fibers excited by 980 nm NIR laser. [<a href="#B102-materials-14-02679" class="html-bibr">102</a>]. Copyright © 2011 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.</p> Full article ">
7 pages, 375 KiB  
Communication
Reversible Barrier Switching of ZnO/RuO2 Schottky Diodes
by Philipp Wendel, Dominik Dietz, Jonas Deuermeier and Andreas Klein
Materials 2021, 14(10), 2678; https://doi.org/10.3390/ma14102678 - 20 May 2021
Cited by 5 | Viewed by 2482
Abstract
The current-voltage characteristics of ZnO/RuO2 Schottky diodes prepared by magnetron sputtering are shown to exhibit a reversible hysteresis behavior, which corresponds to a variation of the Schottky barrier height between 0.9 and 1.3 eV upon voltage cycling. The changes in the barrier [...] Read more.
The current-voltage characteristics of ZnO/RuO2 Schottky diodes prepared by magnetron sputtering are shown to exhibit a reversible hysteresis behavior, which corresponds to a variation of the Schottky barrier height between 0.9 and 1.3 eV upon voltage cycling. The changes in the barrier height are attributed to trapping and de-trapping of electrons in oxygen vacancies. Full article
(This article belongs to the Special Issue Advances on Oxide Semiconductor Transistors and Related Materials)
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<p>Current-voltage behaviour of AZO/ZnO:Ar/ZnO:O<math display="inline"><semantics> <msub> <mrow/> <mn>2</mn> </msub> </semantics></math>/RuO<math display="inline"><semantics> <msub> <mrow/> <mn>2</mn> </msub> </semantics></math> layer structures. The sign of voltage refers to the polarity at the top contact. A typical IV curve obtained by cycling the voltage between <math display="inline"><semantics> <mrow> <mo>−</mo> <mn>3</mn> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <mo>+</mo> <mn>3</mn> </mrow> </semantics></math> V is shown in (<b>b</b>). The indicated barrier heights, <math display="inline"><semantics> <msub> <mi mathvariant="sans-serif">Φ</mi> <mi mathvariant="normal">B</mi> </msub> </semantics></math>, and diode quality factors, <span class="html-italic">n</span>, were extracted from the 0 V intercept and the slope of the linear parts of the curves. The forward biased current obtained with a stepwise increasing voltage is shown in (<b>d</b>). The corresponding sequence of voltage for the curves shown in (<b>d</b>) and additional sequences are shown together with the extracted current densities at <math display="inline"><semantics> <mrow> <mi>V</mi> <mo>=</mo> <mn>1.2</mn> <mtext> </mtext> </mrow> </semantics></math>V (dashed lines) in (<b>e</b>). The proposed model to explain the switching behaviour is shown in (<b>a</b>,<b>c</b>).</p> Full article ">
17 pages, 6295 KiB  
Article
Influence of Laser Energy Input and Shielding Gas Flow on Evaporation Fume during Laser Powder Bed Fusion of Zn Metal
by Yu Qin, Jinge Liu, Yanzhe Chen, Peng Wen, Yufeng Zheng, Yun Tian, Maximilian Voshage and Johannes Henrich Schleifenbaum
Materials 2021, 14(10), 2677; https://doi.org/10.3390/ma14102677 - 20 May 2021
Cited by 16 | Viewed by 3430
Abstract
Laser powder bed fusion (LPBF) of Zn-based metals exhibits prominent advantages to produce customized biodegradable implants. However, massive evaporation occurs during laser melting of Zn so that it becomes a critical issue to modulate laser energy input and gas shielding conditions to eliminate [...] Read more.
Laser powder bed fusion (LPBF) of Zn-based metals exhibits prominent advantages to produce customized biodegradable implants. However, massive evaporation occurs during laser melting of Zn so that it becomes a critical issue to modulate laser energy input and gas shielding conditions to eliminate the negative effect of evaporation fume during the LPBF process. In this research, two numerical models were established to simulate the interaction between the scanning laser and Zn metal as well as the interaction between the shielding gas flow and the evaporation fume, respectively. The first model predicted the evaporation rate under different laser energy input by taking the effect of evaporation on the conservation of energy, momentum, and mass into consideration. With the evaporation rate as the input, the second model predicted the elimination effect of evaporation fume under different conditions of shielding gas flow by taking the effect of the gas circulation system including geometrical design and flow rate. In the case involving an adequate laser energy input and an optimized shielding gas flow, the evaporation fume was efficiently removed from the processing chamber during the LPBF process. Furthermore, the influence of evaporation on surface quality densification was discussed by comparing LPBF of pure Zn and a Titanium alloy. The established numerical analysis not only helps to find the adequate laser energy input and the optimized shielding gas flow for the LPBF of Zn based metal, but is also beneficial to understand the influence of evaporation on the LPBF process. Full article
(This article belongs to the Special Issue Monitoring and Control in Additive Manufacturing Processes)
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<p>LPBF processing chamber with customized gas circulation system.</p> Full article ">Figure 2
<p>Numerical model of the LPBF processing chamber with a gas circulation system, (<b>a</b>) geometrical model; (<b>b</b>) after meshing.</p> Full article ">Figure 3
<p>Pure Zn plates (<b>a</b>) before laser scanning and (<b>b</b>) after laser scanning.</p> Full article ">Figure 4
<p>Penetration shape and temperature contour of the Zn plates, as obtained by the experiment and calculation, for laser powers of (<b>a</b>) 70 W, (<b>b</b>) 80 W, and (<b>c</b>) 90 W.</p> Full article ">Figure 5
<p>Dimensional values of the penetration shape of pure Zn plates.</p> Full article ">Figure 6
<p>Flow behavior inside the molten pool, as determined by calculation for <span class="html-italic">P</span> = 90 W <span class="html-italic">V</span> = 500 mm/s, (<b>a</b>) TC4, (<b>b</b>) pure Zn.</p> Full article ">Figure 7
<p>Saturated vapor pressure (<b>a</b>) and evaporation flux (<b>b</b>) based on the Langmuir model.</p> Full article ">Figure 8
<p>Velocity distribution of shielding gas flow obtained by simulation.</p> Full article ">Figure 9
<p>Effect of shielding gas flow on the evaporation fume, (<b>a</b>) no shielding gas flow; (<b>b</b>) insufficient shielding gas flow; (<b>c</b>) adequate shielding gas flow.</p> Full article ">Figure 10
<p>Evaporation fume captured during the LPBF of pure Zn, (<b>a</b>) insufficient shielding gas flow; (<b>b</b>) adequate shielding gas flow.</p> Full article ">Figure 11
<p>Surface quality of pure Zn by the LPBF; (<b>a</b>,<b>b</b>) single track, (<b>c</b>) top surface of a cube [<a href="#B28-materials-14-02677" class="html-bibr">28</a>].</p> Full article ">Figure 12
<p>Processing windows of pure Zn and TC4 produced by the LPBF.</p> Full article ">
14 pages, 3282 KiB  
Article
New Low-Melting Triply Charged Homoleptic Cr(III)-Based Ionic Liquids in Comparison to Their Singly Charged Heteroleptic Analogues
by Tim Peppel and Martin Köckerling
Materials 2021, 14(10), 2676; https://doi.org/10.3390/ma14102676 - 20 May 2021
Cited by 3 | Viewed by 2044
Abstract
A series of new low-melting triply charged homoleptic Cr(III)-based ionic liquids of the general formula (RMIm)3[Cr(NCS)6] (R = methyl, ethyl, n-butyl, benzyl) is reported. Their syntheses and properties are described in comparison to their singly [...] Read more.
A series of new low-melting triply charged homoleptic Cr(III)-based ionic liquids of the general formula (RMIm)3[Cr(NCS)6] (R = methyl, ethyl, n-butyl, benzyl) is reported. Their syntheses and properties are described in comparison to their singly charged heteroleptic analogues of the general formula (RMIm)[Cr(NCS)4L2] (R = methyl, ethyl, n-butyl, benzyl; L = pyridine, γ-picoline). In total, sixteen new Reineckate related salts with large imidazolium cations are described. Out of these, five compounds were crystallized, and their structures determined by single-crystal X-ray structure analyses. They all consisted of discrete anions and cations with octahedrally coordinated Cr(III) ions. In the structures, various hydrogen contacts interconnect the entities to build up hydrogen bonded networks. Thermal investigations showed relatively low melting points for the homoleptic complexes. The compounds with the [Cr(NCS)6]3− anion melt without decomposition and are stable up to 200 K above their melting points. The complex salts with the [Cr(NCS)4L2]− anion, in contrast, start to decompose and lose L molecules (Pyr or Pic) already at the melting point. Full article
(This article belongs to the Special Issue New Advances in Ionic Liquids)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>UV/Vis spectra of solid samples (solid lines) and acetonic solutions (dashed lines) of samples of (EMIm)<sub>x</sub>[Cr(NCS)<sub>4</sub><span class="html-italic">L</span><sub>2</sub>] (x = 3: <span class="html-italic">L</span> = NCS; x = 1: <span class="html-italic">L</span> = Pyr, Pic).</p> Full article ">Figure 2
<p>Thermogravimetric (black) and DSC (red) results of samples of (EMIm)<sub>x</sub>[Cr(NCS)<sub>4</sub><span class="html-italic">L</span><sub>2</sub>] (x = 3: <span class="html-italic">L</span> = NCS; x = 1: <span class="html-italic">L</span> = Pyr, Pic) in a N<sub>2</sub> atmosphere.</p> Full article ">Figure 3
<p>Structure of the cation–anion pair in (DMIm)<sub>3</sub>[Cr(NCS)<sub>6</sub>] with atom labeling scheme depicting the shortest C–H···S contact (thermal ellipsoids are drawn at the 30% probability level).</p> Full article ">Figure 4
<p>Structure of the cation–anion pair in (BMIm)[Cr(NCS)<sub>4</sub>(Pyr)<sub>2</sub>] with atom labeling scheme depicting the shortest C–H···S contact (thermal ellipsoids are drawn at the 30% probability level; hydrogen atoms at the disordered n-butyl chain omitted for clarity).</p> Full article ">Figure 5
<p>Anion–anion pairing in (EMIm)[Cr(NCS)<sub>4</sub>(Pic)<sub>2</sub>] via short hydrogen contacts with atom labeling scheme depicting the shortest C–H···S contact (thermal ellipsoids are drawn at the 30% probability level; disordered cation omitted for clarity).</p> Full article ">Figure 6
<p>Anion–cation pairing in (EMIm)<sub>3</sub>[Cr(NCS)<sub>6</sub>] via short hydrogen contacts depicting the shortest C–H···S contact (thermal ellipsoids are drawn at the 30% probability level).</p> Full article ">Figure 7
<p>Anion–cation pairing in (BenzMIm)<sub>3</sub>[Cr(NCS)<sub>6</sub>] via short hydrogen contacts depicting the shortest C–H···S contact (thermal ellipsoids are drawn at the 30% probability level).</p> Full article ">Scheme 1
<p>The two general synthetic approaches for the syntheses of complexes of the general formula (<span class="html-italic">R</span>MIm)<sub>3</sub>[Cr(NCS)<sub>6</sub>] (<span class="html-italic">R</span> = methyl, ethyl, n-butyl, benzyl; MIm = methylimidazolium).</p> Full article ">Scheme 2
<p>Multi-step synthetic approach to generate complexes with the general formula (<span class="html-italic">R</span>MIm)[Cr(NCS)<sub>4</sub><span class="html-italic">L</span><sub>2</sub>] (<span class="html-italic">R</span> = ethyl, n-butyl; MIm = <span class="html-italic">N</span>-methylimidazolium; <span class="html-italic">L</span> = pyridine, γ-picoline).</p> Full article ">
11 pages, 2125 KiB  
Article
Bio-Based Crosslinked Polymers Synthesized from Functionalized Soybean Oil and Squalene by Thiol–Ene UV Curing
by Sigita Grauzeliene, Deimante Valaityte, Greta Motiekaityte and Jolita Ostrauskaite
Materials 2021, 14(10), 2675; https://doi.org/10.3390/ma14102675 - 20 May 2021
Cited by 17 | Viewed by 3082
Abstract
The development of polymers photopolymerized from renewable resources are extensively growing as fulfills green chemistry and green engineering principles. With the rapid growth of consumerism, research on innovative starting materials for the preparation of polymers may help to reduce the negative impact of [...] Read more.
The development of polymers photopolymerized from renewable resources are extensively growing as fulfills green chemistry and green engineering principles. With the rapid growth of consumerism, research on innovative starting materials for the preparation of polymers may help to reduce the negative impact of petroleum-based plastic materials on the global ecosystem and on animal and human health. Therefore, bio-based crosslinked polymers have been synthesized from functionalized soybean oil and squalene by thiol–ene ultra-violet (UV) curing. First, thiol–ene UV curing of squalene was performed to introduce thiol functional groups. Then, hexathiolated squalene was used as a crosslinker in click UV curing of acrylated epoxidized soybean oil. Two photoinitiators, 2-hydroxy-2-methylpropiophenone and ethylphenyl (2,4,6-trimethylbenzoyl) phosphinate, were tested in different quantities. Rheological properties of the resins were monitored by real-time photorheometry. The characterization of obtained polymers was performed by differential scanning calorimetry, thermogravimetry, and Shore A hardness measurements. Polymers possessed higher storage modulus, thermal characteristics, Shore A hardness, and lower swelling value when ethylphenyl (2,4,6-trimethylbenzoyl) phosphinate was used as photoinitiator. Full article
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<p>Chemical structures of acrylated epoxidized soybean oil (AESO), hexathiolated squalene (SQ6SH), 2-hydroxy-2-methylpropiophenone (HMP), and ethylphenyl (2,4,6-trimethylbenzoyl) phosphinate (TPOL).</p> Full article ">Figure 2
<p>(<b>a</b>) Curves of storage modulus G′ versus irradiation time of the compositions with different photoinitiators, (<b>b</b>) Gel point of AESO thiol–ene resins.</p> Full article ">Figure 3
<p>FT-IR spectra of AESO, SQ6SH, and 3TPOL.</p> Full article ">Figure 4
<p>(<b>a</b>) Swelling value versus time curves of the polymers in acetone, (<b>b</b>) Swelling value versus time curves of the polymers in toluene.</p> Full article ">Figure 5
<p>DSC curve (<b>a</b>) and thermogravimetric curves (<b>b</b>) of polymer 3TPOL.</p> Full article ">Figure 6
<p>(<b>a</b>) Shore A hardness of AESO thiol–ene polymers, (<b>b</b>) Photograph of polymer 3TPOL.</p> Full article ">
11 pages, 14889 KiB  
Communication
Using TOF-SIMS Spectrometry to Study the Kinetics of the Interfacial Retro Diels–Alder Reaction
by Lilia Hassouna, Sachin Kumar Enganati, Florence Bally-Le Gall, Grégory Mertz, Jérôme Bour, David Ruch and Vincent Roucoules
Materials 2021, 14(10), 2674; https://doi.org/10.3390/ma14102674 - 20 May 2021
Viewed by 2028
Abstract
In this work, the use of Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was explored as a technique for monitoring the interfacial retro Diels–Alder (retro DA) reaction occurring on well-controlled self-assembled monolayers (SAMs). A molecule containing a Diels–Alder (DA) adduct was grafted [...] Read more.
In this work, the use of Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) was explored as a technique for monitoring the interfacial retro Diels–Alder (retro DA) reaction occurring on well-controlled self-assembled monolayers (SAMs). A molecule containing a Diels–Alder (DA) adduct was grafted on to the monolayers, then the surface was heated at different temperatures to follow the reaction conversion. A TOF-SIMS analysis of the surface allowed the detection of a fragment from the molecule, which is released from the surface when retro DA reaction occurs. Hence, by monitoring the decay of this fragment’s peak integral, the reaction conversion could be determined in function of the time and for different temperatures. The viability of this method was then discussed in comparison with the results obtained by 1H NMR spectroscopy. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Scheme representing amine-terminated SAMs (<b>a</b>) on to which a molecule containing a DA adduct was grafted to give surface (<b>b</b>). Retro DA reaction occurred on the adduct to give a furan terminated surface (<b>c</b>) liberating one BMI and FGE molecules.</p> Full article ">Figure 2
<p>Decrease of the peak area representing the maleimide-containing fragment as SAMs-Add surface is heated up to 363 K for 0 min, 30 min, 1 h, 3 h, 5 h, and 7 h.</p> Full article ">Figure 3
<p>Evolution of retro DA reaction conversion on SAMs with time, at different temperatures. The lines were drawn only to guide the eyes of the reader.</p> Full article ">Figure 4
<p>Linearization according to a first order of retro DA reaction of the adduct performed at different temperatures.</p> Full article ">Figure 5
<p>Determination of interfacial retro DA activation energy by linearization of the Arrhenius equation: ln k<sub>rDA</sub> = −8472.2 × 1/T + 14.004; R<sup>2</sup> = 0.99.</p> Full article ">Figure 6
<p>Decrease of the adduct peaks at 5.35 ppm and 5.20 ppm in <sup>1</sup>H NMR spectra of DA-containing molecule performed in deuterated DMSO at 363 K after (<b>a</b>) 0 min, (<b>b</b>) 15 min, (<b>c</b>) 30 min, (<b>d</b>) 45 min, and (<b>e</b>) 120 min.</p> Full article ">Figure 7
<p>Determination of retro DA activation energy in solution by linearization of the Arrhenius law equation: ln k<sub>rDA(s)</sub> = −15998 × 1/T + 36; R<sup>2</sup> = 0.99.</p> Full article ">Figure 8
<p>Schematic representation of retro DA reaction occurring (<b>a</b>) in solution and (<b>b</b>) on SAMs.</p> Full article ">
20 pages, 5961 KiB  
Article
Physical Properties, Spectroscopic, Microscopic, X-ray, and Chemometric Analysis of Starch Films Enriched with Selected Functional Additives
by Maciej Combrzyński, Tomasz Oniszczuk, Karol Kupryaniuk, Agnieszka Wójtowicz, Marcin Mitrus, Marek Milanowski, Jakub Soja, Iwona Budziak-Wieczorek, Dariusz Karcz, Daniel Kamiński, Sławomir Kulesza, Karolina Wojtunik-Kulesza, Kamila Kasprzak-Drozd, Marek Gancarz, Iwona Kowalska, Lidia Ślusarczyk and Arkadiusz Matwijczuk
Materials 2021, 14(10), 2673; https://doi.org/10.3390/ma14102673 - 20 May 2021
Cited by 16 | Viewed by 3284
Abstract
Biodegradable materials are used in the manufacture of packaging and compostable films and various types of medical products. They have demonstrated a large number of potential practical applications in medicine and particularly in the treatment of various cardiac, vascular, and orthopedic conditions in [...] Read more.
Biodegradable materials are used in the manufacture of packaging and compostable films and various types of medical products. They have demonstrated a large number of potential practical applications in medicine and particularly in the treatment of various cardiac, vascular, and orthopedic conditions in adults as well in children. In our research, the extrusion-cooking technique was applied to prepare thermoplastic starch (TPS), which was then utilized to obtain environmentally friendly starch-based films. Potato starch was the basic raw material exploited. Polyvinyl alcohol and keratin were used as functional additives in amounts from 0.5 to 3%, while 20% of glycerol was harnessed as a plasticizer. The processing of the thermoplastic starch employed a single screw extruder-cooker with an L/D ratio of 16. The film blowing process was carried out using a film-blowing laboratory line with L/D = 36. FTIR Spectroscopy was applied for the assignment of the prominent functional groups. The results showed that the processing efficiency of thermoplastic starch with functional additives varied depending on the level of polyvinyl alcohol and keratin addition. Moreover, the FTIR data correlated with the changes in the physical properties of the tested films. The analysis of FTIR spectra revealed several changes in the intensity of bands originating from stretching vibrations characteristic of the –OH substituent. The changes observed depended on the presence/lack of the hydrogen bonding occurring upon interactions between the starch molecules and the various additives used. In addition, notable changes were observed in bands assigned to glycoside bonds in the starch. Full article
(This article belongs to the Special Issue Bioactive Compounds and Complexes: Synthesis, Structural and Physicochemical Studies)
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<p>Starch-based film with functional substances blowing in laboratory.</p> Full article ">Figure 2
<p>Film-blowing laboratory line.</p> Full article ">Figure 3
<p>Example results of AFM nanomechanical mapping of both sides of the SGAK-I polymer foil: surface topography (Height), pseudo-Young’s modulus (DMTModulus), tip–surface adhesion force (Adhesion). Scan area is 1 × 1 µm<sup>2</sup>. Side (<b>A</b>) internal structure of foil; Side (<b>B</b>) external structure of foil.</p> Full article ">Figure 4
<p>ATR-FTIR absorption spectra for the analyzed films: SGA-I (<b>A</b>) and SGA-II (<b>B</b>) and SGA-III (<b>C</b>). Numbers next to peaks are the wavenumbers for each component. Different lines indicate various screw speeds (rpm) during film blowing processing.</p> Full article ">Figure 5
<p>ATR-FTIR absorption spectra for the analyzed films: SGAK-I (<b>A</b>), SGAK-II (<b>B</b>), and SGAK-III (<b>C</b>). Numbers next to peaks are the wavenumbers for each component. Different lines indicate various screw speeds (rpm) during film blowing processing.</p> Full article ">Figure 6
<p>Scree plots (eigenvalues from principal components): (<b>A</b>) for the section 1800–600 cm<sup>−1</sup>, (<b>B</b>) for the section 3700–600 cm<sup>−1</sup>.</p> Full article ">Figure 7
<p>Results of PCA analysis: (<b>A</b>) Score plot (numbers on graph are rpm during film blowing); (<b>B</b>) Loadings plot for region 1800–600 cm<sup>−1</sup>.</p> Full article ">Figure 8
<p>HCA analysis for region 1800–600 cm<sup>−1</sup>. Linkage criteria—Ward method. Clustering metric—Pearson correlation. Different colors indicate similarity clusters.</p> Full article ">Figure 9
<p>Results of PCA analysis: (<b>A</b>) Score plot (numbers on graph are rpm during film blowing); (<b>B</b>) Loadings plot for region 3700–600 cm<sup>−1</sup>.</p> Full article ">Figure 10
<p>HCA analysis for region 3700–600 cm<sup>−1</sup>. Linkage criteria—average linkage. Clustering metric—Pearson correlation. Different colors indicate similarity clusters.</p> Full article ">Figure 11
<p>Experimental points (blue) of SGAK-I/50 rpm and model curves (grey). The curve with FWHM (full width at half maximum) of 11° describes the amorphous phase.</p> Full article ">
20 pages, 2088 KiB  
Review
Clinical Performance of CAD/CAM All-Ceramic Tooth-Supported Fixed Dental Prostheses: A Systematic Review and Meta-Analysis
by Babak Saravi, Andreas Vollmer, Maja Hartmann, Gernot Lang, Ralf-Joachim Kohal, Martin Boeker and Sebastian B. M. Patzelt
Materials 2021, 14(10), 2672; https://doi.org/10.3390/ma14102672 - 20 May 2021
Cited by 27 | Viewed by 4410
Abstract
Although CAD/CAM ceramics present a promising alternative to metal-ceramic fixed dental prostheses, little is known about their mid- and long-term clinical performance. This systematic review aims to estimate the survival and success rates and describes the underlying complication characteristics for CAD/CAM tooth-supported zirconia- [...] Read more.
Although CAD/CAM ceramics present a promising alternative to metal-ceramic fixed dental prostheses, little is known about their mid- and long-term clinical performance. This systematic review aims to estimate the survival and success rates and describes the underlying complication characteristics for CAD/CAM tooth-supported zirconia- and lithium disilicate-based fixed dental prostheses (FDPs). We systematically searched MEDLINE and Web of Science to find relevant prospective studies with a follow-up of at least one year. We estimated pooled 1-, 5-, and 10-year survival and success rates by combining the collected data in a Poisson regression model. Descriptive statistics were conducted to evaluate the distribution of failures and complications in the included studies. Risk of bias for the included studies was assessed with an adapted checklist for single-arm trials. Pooled estimated 1-, 5-, and 10-year survival rates ranged from 93.80% to 94.66%, 89.67% to 91.1%, and 79.33% to 82.20%, respectively. The corresponding success rates excluding failures, but including any other types of intervention were 94.53% to 96.77%, 90.89% to 94.62%, and 81.78% to 89.25%. Secondary caries was the most frequent cause of failure, followed by chipping of the veneering. The most common cause of complication excluding failures but requiring intervention was chipping of the veneering. Risk of bias was generally acceptable for the included studies, with seven studies associated with low risk of bias, eight studies with a moderate risk of bias, and three studies with serious risk of bias. The current meta-analysis on CAD/CAM-supported FDPs revealed satisfying survival and success rates for up to 10 years of exposure. More prospective studies focusing on long-term performance are needed to strengthen the evidence currently available in the literature. Full article
(This article belongs to the Special Issue Ceramic Materials for Dental Implant and CAD-CAM Prostheses)
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<p>Search strategy.</p> Full article ">Figure 2
<p>PRISMA flow diagram of the selection process.</p> Full article ">Figure 3
<p>Distribution of complications (<b>A</b>) and failures (<b>B</b>) stratified by follow-up time frames. Group 1: follow-up from 18 to 46 months; Group 2: follow-up from 60 to 84 months; Group 3: follow-up from 116.4 to 120 months.</p> Full article ">Figure 4
<p>Risk of bias assessment for the included studies.</p> Full article ">
15 pages, 41920 KiB  
Article
Influence of Shielding Gas on Microstructure and Properties of GMAW DSS2205 Welded Joints
by Xin-Yu Zhang, Xiao-Qin Zha, Ling-Qing Gao, Peng-Hui Hei and Yong-Feng Ren
Materials 2021, 14(10), 2671; https://doi.org/10.3390/ma14102671 - 20 May 2021
Cited by 14 | Viewed by 2413
Abstract
In the present study, the microstructures and properties of DSS 2205 solid wire MIG welded samples prepared in different shielding gases (pure Ar gas, 98%Ar + 2%O2 and 98%Ar + 2%N2) were investigated for improving the weldability of DSS 2205 [...] Read more.
In the present study, the microstructures and properties of DSS 2205 solid wire MIG welded samples prepared in different shielding gases (pure Ar gas, 98%Ar + 2%O2 and 98%Ar + 2%N2) were investigated for improving the weldability of DSS 2205 welded joint. The work was conducted by mechanical property tests (hardness and tensile test) and corrosion resistance property tests (immersion and electrochemical tests). The results show that adding 2%O2 into pure Ar gas as the shielding gas decreases crystal defects (faults) and improves the mechanical properties and corrosion resistance of the welded joints. Phase equilibrium and microstructural homogeneity in welded seam (WS) and heat-affected zone (HAZ) can be adjusted and the strength and corrosion resistance of welded joints increased obviously by adding 2%N2 to pure Ar gas as the shielding gas. Compared with DSS 2205 solid wire MIG welding in 98%Ar + 2%O2 mixed atmosphere, the strength and corrosion resistance of welded joints are improved more obviously in 98%Ar + 2%N2 mixed atmosphere. Full article
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<p>Hardness point location.</p> Full article ">Figure 2
<p>Schematic diagram of plate tensile specimen.</p> Full article ">Figure 3
<p>Metallographic structure of DSS 2205 solid wire MIG welding joints prepared in different shielding gases. (<b>a</b>,<b>b</b>) WS and welding joints region (pure Ar gas); (<b>c</b>,<b>d</b>) WS and welding joints region (98%Ar + 2%O<sub>2</sub>); (<b>e</b>,<b>f</b>) WS and welding joints region (98%Ar + 2%N<sub>2</sub>); (1) BM (2) HAZ (3) WS.</p> Full article ">Figure 4
<p>TEM images of DSS 2205 solid wire MIG welding joints prepared in different shielding gases. (<b>a</b>) Ar; (<b>b</b>) 98%Ar + 2%O<sub>2</sub>; (<b>c</b>) 98%Ar + 2%N<sub>2</sub>; (<b>d</b>) ferrite diffraction pattern; (<b>e</b>) austenite diffraction pattern.</p> Full article ">Figure 5
<p>Hardness distribution chart.</p> Full article ">Figure 6
<p>Fracture position of flat tensile specimens of DSS 2205 solid wire MIG welding joints prepared in different shielding gases. 1#-Ar; 2#-98%Ar + 2%O<sub>2</sub>; 3#-98%Ar + 2%N<sub>2</sub>.</p> Full article ">Figure 7
<p>Pitting corrosion rate of welded joint under different shielding gases.</p> Full article ">Figure 8
<p>Polarization curves of DSS 2205 solid wire MIG welding joints under three different shielding gases.</p> Full article ">Figure 9
<p>Intergranular corrosion rate of the welded joints under different shielding gases.</p> Full article ">Figure 10
<p>Cross section morphology of intergranular corrosion for the welded joints under different shielding gases. (<b>a</b>) 1#-Ar; (<b>b</b>) 2#-98%Ar + 2%O<sub>2</sub>; (<b>c</b>) 3#-98%Ar + 2%N<sub>2</sub>.</p> Full article ">Figure 11
<p>DL-EPR test for the welded joints under different shielding gases.</p> Full article ">Figure 12
<p>Metallographic structure of the welded joints under different shielding gases after DL-EPR test (<b>a</b>) 1#-Ar; (<b>b</b>) 2#-98%Ar + 2%O<sub>2</sub>; (<b>c</b>) 3#-98%Ar + 2%N<sub>2</sub>.</p> Full article ">
15 pages, 5651 KiB  
Article
Deterioration of Portland Cement Pervious Concrete in Sponge Cities Subjected to Acid Rain
by Longxin Gao, Yong Lai, Mohammad Rashadul Islam Pramanic and Wuman Zhang
Materials 2021, 14(10), 2670; https://doi.org/10.3390/ma14102670 - 20 May 2021
Cited by 13 | Viewed by 3002
Abstract
The deterioration of Portland cement pervious concrete (PCPC) subjected to wet-dry cycles in the simulated acid rain solution was investigated; 4% silica fume (SF) and 8% fine aggregate (FAG) were used to replace part of cement and the coarse aggregates (weight by weight), [...] Read more.
The deterioration of Portland cement pervious concrete (PCPC) subjected to wet-dry cycles in the simulated acid rain solution was investigated; 4% silica fume (SF) and 8% fine aggregate (FAG) were used to replace part of cement and the coarse aggregates (weight by weight), respectively. The wear resistance, the compressive, and flexural strength of PCPC were measured. The results show that after 12 wet-dry cycles in acid rain solution the compressive strength and the flexural strength of control PCPC are decreased by 30.7% and 40.8%. The final compressive strength of PCPC with 4% SF and PCPC with 8% FAG is increased by 6.9% and 30.3%, and the final flexural strength is increased by 25.4% and 72.3%, respectively. The wear loss of PCPC is decreased by 58.8% and 81.9% when 4% SF and 8% FAG is added to PCPC, respectively. The microstructures of PCPC with wet-dry cycles are also discussed. Full article
(This article belongs to the Collection Concrete and Building Materials)
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<p>Schematic diagram of permeability measurement setup.</p> Full article ">Figure 2
<p>The relative weight of PCPC with wet-dry cycles.</p> Full article ">Figure 3
<p>Strength of control PCPC.</p> Full article ">Figure 4
<p>Strength of 4% SF PCPC.</p> Full article ">Figure 5
<p>Water permeability of PCPC without wet-dry cycles.</p> Full article ">Figure 6
<p>Strength of PCPC with 8% FAG.</p> Full article ">Figure 7
<p>Wear loss of PCPC after the abrasion test.</p> Full article ">Figure 8
<p>Surface changes of control PCPC after abrasion test. (<b>a</b>) Without wet-dry cycles, (<b>b</b>) 12 wet-dry cycles in water, and (<b>c</b>) 12 wet-dry cycles in acid rain.</p> Full article ">Figure 9
<p>Surface changes of 4% SF PCPC after abrasion test. (<b>a</b>) Without wet-dry cycles, (<b>b</b>) 12 wet-dry cycles in water, and (<b>c</b>) 12 wet-dry cycles in acid rain.</p> Full article ">Figure 10
<p>Surface changes of 8% FAG PCPC after abrasion test. (<b>a</b>) Without wet-dry cycles, (<b>b</b>) 12 wet-dry cycles in water, and (<b>c</b>) 12 wet-dry cycles in acid rain.</p> Full article ">Figure 11
<p>Microstructures of control PCPC. (<b>a</b>) Without wet-dry cycle and (<b>b</b>) with 12 wet-dry cycles in acid rain solution.</p> Full article ">Figure 12
<p>Microstructures of 4% SF PCPC. (<b>a</b>) Without wet-dry cycle and (<b>b</b>) with 12 wet-dry cycles in acid rain solution.</p> Full article ">Figure 13
<p>Microstructures of 8% FAG PCPC. (<b>a</b>) Without wet-dry cycle and (<b>b</b>) with 12 wet-dry cycles in acid rain solution.</p> Full article ">
28 pages, 13855 KiB  
Article
Factorial Analysis of Fiber Laser Fusion Cutting of AISI 304 Stainless Steel: Evaluation of Effects on Process Performance, Kerf Geometry and Cut Edge Roughness
by Achim Mahrle, Madlen Borkmann and Peer Pfohl
Materials 2021, 14(10), 2669; https://doi.org/10.3390/ma14102669 - 19 May 2021
Cited by 10 | Viewed by 3780
Abstract
Factorial Design-of-Experiment analyses were applied for conventional and beam oscillation fiber laser cutting of 10 mm thick AISI 304 stainless steel. Considered factors in case of the conventional process with a static beam involve both laser and cutting gas parameters, in particular the [...] Read more.
Factorial Design-of-Experiment analyses were applied for conventional and beam oscillation fiber laser cutting of 10 mm thick AISI 304 stainless steel. Considered factors in case of the conventional process with a static beam involve both laser and cutting gas parameters, in particular the laser power, the focal plane position, the cutting gas pressure, the nozzle stand-off distance as well as the nozzle diameter. The conducted trials were evaluated with respect to the achievable cutting speed, the cut kerf geometry and the cut edge roughness. Noticeable correlations between cut edge roughness and cut kerf geometry stimulated the development of a corresponding Computational Fluid Dynamics (CFD) model of the cutting gas flow through the kerf. A specific approach of data synchronization revealed that the experimentally determined roughness values do well correlate with numerically computed values of the backward directed component of the gas-induced shear stress and that the cut kerf geometry as internal process-inherent boundary condition influences relevant cutting characteristics more than controllable external cutting gas parameters. Finally, effects of circular beam oscillation were investigated by an additional factorial analysis considering the laser power, the focal plane position, the oscillation frequency and the oscillation amplitude as factors. The results demonstrate the potential of beam oscillation techniques for quality improvements in laser cutting. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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<p>Schematic illustration of the laser fusion cutting process.</p> Full article ">Figure 2
<p>Experimental setup for the conducted cutting trials (<b>a</b>), measured beam caustics (<b>b</b>) and schematic of the produced cutting probes (<b>c</b>).</p> Full article ">Figure 3
<p>Geometrical model of the cutting gas flow.</p> Full article ">Figure 4
<p>Different cut edge categories for different parameter sets. Category I—Run 07, Category II—Run 01, and Category III—Run 12.</p> Full article ">Figure 5
<p>Correlation between R<sub>a</sub> and R<sub>Z</sub> roughness values at the top (<b>a</b>), the middle (<b>b</b>) and the bottom (<b>c</b>) measurement positions. Correlation between R<sub>a</sub> roughness values of the left and right cutting edge at the top (<b>d</b>), the middle (<b>e</b>) and the bottom (<b>f</b>) measurement positions. The data points are colored by value of focal plane position (Blue: 2.5 mm, Green: 5.0 mm, Red: 7.5 mm).</p> Full article ">Figure 6
<p>Distribution of raw data of maximum cutting speed (<b>a</b>), top kerf width (<b>b</b>), bottom kerf with (<b>c</b>), top roughness R<sub>a</sub> (<b>d</b>), middle roughness R<sub>a</sub> (<b>e</b>) and bottom roughness (<b>f</b>) versus experimental run for laser beam cutting with a static beam. The data points are colored by value of focal plane position (Blue: 2.5 mm, Green: 5.0 mm, Red: 7.5 mm).</p> Full article ">Figure 7
<p>Analysis results of maximum cutting speed for laser beam cutting with a static beam. Half-normal probability plot of cutting speed limit (<b>a</b>) and corresponding model graph (<b>b</b>).</p> Full article ">Figure 8
<p>Correlation plot, effect plot and model graph of spot energy (<b>a</b>–<b>c</b>) and severance energy (<b>d</b>–<b>f</b>).</p> Full article ">Figure 9
<p>Results of cut kerf geometry analysis for laser cutting with a static beam. Half-normal probability plots of kerf width w<sub>K,Top</sub> (<b>a</b>), kerf width w<sub>K,Bottom</sub> (<b>b</b>) and aspect ratio (<b>c</b>), and corresponding model graphs (<b>d</b>–<b>f</b>). Parameters for model graph (<b>e</b>): gas pressure = 1.6 MPa, Nozzle stand-off distance = 0.75 mm, Nozzle diameter = 3.0 mm.</p> Full article ">Figure 10
<p>Relation between laser beam size and kerf width at the top surface of the sheet. (<b>a</b>) Geometrical conditions for different experimental trials: Run 08 with d<sub>Beam</sub> = 718 µm and v<sub>C,Max</sub> = 0.7 m/min, Run 14 with d<sub>Beam</sub> = 282 µm and v<sub>C,Max</sub> = 1.6 m/min. (<b>b</b>) Kerf/Beam ratio vs. beam intensity with a correlation coefficient of C = 0.964.</p> Full article ">Figure 11
<p>Results of roughness analysis for laser cutting with a static beam. Half-normal probability plots of surface roughness RA-Top (<b>a</b>), surface roughness RA-Middle (<b>b</b>) and surface roughness RA-Bottom (<b>c</b>), and corresponding model graphs (<b>d</b>–<b>f</b>).</p> Full article ">Figure 12
<p>Correlation between roughness values and aspect ratio. (<b>a</b>) RA-Top vs. aspect ratio; (<b>b</b>) RA-Middle vs. aspect ratio; (<b>c</b>) RA-Bottom vs. aspect ratio.</p> Full article ">Figure 13
<p>Computed velocity distribution in the symmetry plane for different experimental runs. Parameter constellations are given in <a href="#materials-14-02669-t002" class="html-table">Table 2</a>.</p> Full article ">Figure 14
<p>Computed shear stress distribution for different experimental runs. Parameter constellations are given in <a href="#materials-14-02669-t002" class="html-table">Table 2</a>.</p> Full article ">Figure 15
<p>Shear stress data distribution and correlation analysis with respect to the experimentally determined kerf ratio. Data points are colored by the value of the focal plane position (blue: 2.5 mm, green: 5.0 mm, red: 7.5 mm). (<b>a</b>) Shear stress maximum vs. run; (<b>b</b>) Backward directed shear stress component vs. run; (<b>c</b>) Shear stress ratio vs. run; (<b>d</b>) Shear stress maximum vs. kerf ratio; (<b>e</b>) Backward directed shear stress component vs. kerf ratio; (<b>f</b>) Shear stress ratio vs. kerf ratio.</p> Full article ">Figure 16
<p>Results of shear stress analysis for the simulation of the cutting gas flow. Half-normal probability plots of shear stress τ<sub>Kerf,Max</sub> (<b>a</b>), shear stress τ<sub>Kerf,X,Max</sub> (<b>b</b>) and shear stress ratio (<b>c</b>), and corresponding model graphs (<b>d</b>–<b>f</b>).</p> Full article ">Figure 17
<p>Correlation analysis between experimentally determined cut edge roughness values and computed shear stress values from the gas flow simulation: (<b>a</b>) surface roughness top vs. shear stress maximum, (<b>b</b>) surface roughness middle vs. shear stress maximum, (<b>c</b>) surface roughness bottom vs. shear stress maximum; (<b>d</b>) surface roughness top vs. backward directed shear stress component; (<b>e</b>) surface roughness middle vs. backward directed shear stress component; (<b>f</b>) surface roughness bottom vs. backward directed shear stress component; (<b>g</b>) surface roughness top vs. shear stress ratio; (<b>h</b>) surface roughness middle vs. shear stress ratio; (<b>i</b>) surface roughness bottom vs. shear stress ratio.</p> Full article ">Figure 18
<p>Distribution of raw data of maximum cutting speed (<b>a</b>), top kerf width (<b>b</b>), bottom kerf with (<b>c</b>), top roughness R<sub>a</sub> (<b>d</b>), middle roughness R<sub>a</sub> (<b>e</b>) and bottom roughness (<b>f</b>) versus experimental run for laser beam cutting with circular oscillation. The data points are colored by value of focal plane position (Blue: 2.5 mm, Green: 5.0 mm, Red: 7.5 mm).</p> Full article ">Figure 19
<p>Analysis results of maximum cutting speed for laser cutting with circular beam oscillation. Half-normal probability plot of cutting speed limit (<b>a</b>) and corresponding model graph (<b>b</b>).</p> Full article ">Figure 20
<p>Results of cut kerf geometry analysis for laser cutting with circular beam oscillation. Half-normal probability plots of kerf width w<sub>K,Top</sub> (<b>a</b>), kerf width w<sub>K,Bottom</sub> (<b>b</b>) and aspect ratio (<b>c</b>), and corresponding model graphs (<b>d</b>–<b>f</b>).</p> Full article ">Figure 21
<p>Results of roughness analysis for laser cutting with circular beam oscillation. Half-normal probability plots of surface roughness RA-Top (<b>a</b>), RA-Middle (<b>b</b>) and RA-Bottom (<b>c</b>), and corresponding model graphs (<b>d</b>–<b>f</b>).</p> Full article ">Figure 22
<p>Comparison of the best probes of the performed experimental cutting trials with a static beam ((<b>a</b>) Run 14 (<a href="#materials-14-02669-t002" class="html-table">Table 2</a>)) and with circular beam oscillation ((<b>b</b>) Run 02 (<a href="#materials-14-02669-t005" class="html-table">Table 5</a>)).</p> Full article ">Figure 23
<p>Cause–effect relationships of fiber laser fusion cutting under conditions of the performed study.</p> Full article ">
13 pages, 2609 KiB  
Article
Principal Component Analysis as a Statistical Tool for Concrete Mix Design
by Janusz Kobaka
Materials 2021, 14(10), 2668; https://doi.org/10.3390/ma14102668 - 19 May 2021
Cited by 12 | Viewed by 3257
Abstract
With the recent and rapid development of concrete technologies and the ever-increasing use of concrete, adapting concrete to the specific needs and applications of civil engineering is necessary. Due to economic considerations and care for the natural environment, improving the methods currently used [...] Read more.
With the recent and rapid development of concrete technologies and the ever-increasing use of concrete, adapting concrete to the specific needs and applications of civil engineering is necessary. Due to economic considerations and care for the natural environment, improving the methods currently used in concrete design is also necessary. In this study, the author used principal component analysis as a statistical tool in the concrete mix design process. Using a combination of PCA variables and 2D and 3D factors has made it possible to refine concrete recipes. Thirty-eight concrete mixes of different aggregate grades were analyzed using this method. The applied statistical analysis showed many interesting relationships between the properties of concrete and the content of its components such as the clustering of certain properties, showing dependence between the properties and the quantities of certain ingredients in concrete, and reducing noise in the data, which most importantly simplifies interpretation. This method of analysis can be used as an aid for concrete mix design. Full article
(This article belongs to the Special Issue Research of Structure and Properties of Concretes Based on Non-conventional Aggregates)
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Figure 1
<p>Plan of the experiment: percentage of three aggregate fractions: 0–0.5 mm, 0.5–2 mm, and 2–4 mm for 38 types of tested concrete mixes.</p> Full article ">Figure 2
<p>Compressive strength of concrete in relation to the percentage of three aggregate fraction groups. Red represents a compressive strength of 22 MPa or above, and blue represents a strength of 16 MPa or below.</p> Full article ">Figure 3
<p>Splitting tensile strength of concrete in relation to the percentage of three aggregate fraction groups. Red represents a strength over 2.5 MPa, and blue represents a strength below 2.10 MPa.</p> Full article ">Figure 4
<p>Scree plot of eigenvalues.</p> Full article ">Figure 5
<p>PCA projection of variables set in a 2D factor loading space (for the variable designations, see <a href="#materials-14-02668-t005" class="html-table">Table 5</a>).</p> Full article ">Figure 6
<p>PCA with object grouping in a two-dimensional space on the basis of concrete composition in relation to concrete properties. Compressive strength: red represents a strength of 22 MPa or above, and blue represents a strength of 16 MPa or below.</p> Full article ">Figure 7
<p>PCA with object grouping in a two-dimensional space on the basis of concrete composition in relation to concrete properties. Splitting tensile strength: red represents a strength over 2.5 MPa, and blue represents a strength below 2.10 MPa.</p> Full article ">Figure 8
<p>PCA projection of variables set in a 3D factor loading space (for the variable designations, see <a href="#materials-14-02668-t005" class="html-table">Table 5</a>).</p> Full article ">Figure 9
<p>PCA with object grouping in a three-dimensional space on the basis of concrete composition in relation to concrete properties. Compressive strength: red represents a strength of 22 MPa or above, and blue represents a strength of 16 MPa or below.</p> Full article ">Figure 10
<p>PCA with object grouping in a three-dimensional space on the basis of concrete composition in relation to properties. Splitting tensile strength: red represents a strength over 2.5 MPa, and blue represents a strength below 2.10 MPa.</p> Full article ">Figure 11
<p>PCA with object grouping in a three-dimensional space on the basis of concrete composition in relation to properties. Consistency: red represents 8.5 s or above, and blue represents 7 s or below.</p> Full article ">
16 pages, 2987 KiB  
Article
POF-Based Solar Concentrators Incorporating Dyes and Europium Chelates
by Ander Vieira, Jon Arrue, Begoña García-Ramiro, Felipe Jiménez, María Asunción Illarramendi and Joseba Zubia
Materials 2021, 14(10), 2667; https://doi.org/10.3390/ma14102667 - 19 May 2021
Cited by 2 | Viewed by 1987
Abstract
In this paper, useful models that enable time-efficient computational analyses of the performance of luminescent solar concentrators (LSCs) are developed and thoroughly described. These LSCs are based on polymer optical fibers codoped with organic dyes and/or europium chelates. The interest in such dopants [...] Read more.
In this paper, useful models that enable time-efficient computational analyses of the performance of luminescent solar concentrators (LSCs) are developed and thoroughly described. These LSCs are based on polymer optical fibers codoped with organic dyes and/or europium chelates. The interest in such dopants lies in the availability of new dyes with higher quantum yields and in the photostability and suitable absorption and emission bands of europium chelates. Time-efficiency without compromising accuracy is especially important for the simulation of europium chelates, in which non-radiative energy transfers from the absorbing ligands to the europium ion and vice versa are so fast that the discretization in time, in the absence of some simplifying assumptions, would have to be very fine. Some available experimental results are also included for the sake of comparison. Full article
(This article belongs to the Special Issue Polymer Optical Fibers: Fabrication, Characterization and Applications)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Spectral curve of the terrestrial air-mass-1.5 (AM 1.5) irradiance defined by the ASTM G-173 standard, plotted together with the responsivity curve of a typical solar cell and with the normalized absorption and emission cross sections of the dye Lumogen Orange (L).</p> Full article ">Figure 2
<p>Energy levels of the organic dyes (<b>left</b>) and of the europium chelates (<b>right</b>).</p> Full article ">Figure 3
<p>Convergence between the FDM-based simulation and the stationary-state simulation for two different POFs of 10 cm in length whose cores are doped with the dye Coumarin 6, with concentrations of 50 µm/L and 25 µm/L.</p> Full article ">Figure 4
<p>Normalized absorption (<b>a</b>) and emission (<b>b</b>) cross sections of the dopants employed.</p> Full article ">Figure 5
<p>Evolution of the output spectrum with fiber length at the end of an illuminated POF of 1 mm of diameter doped with a concentration of 49 µm/L, either (<b>a</b>) of the dye Coumarin 6, or (<b>b</b>) of the europium chelate.</p> Full article ">Figure 6
<p>Output powers against POF diameter measured and calculated with the combinations of dopants Eu/C6 and Eu/L, when the illuminated POF lengths are the saturation ones employed in [<a href="#B4-materials-14-02667" class="html-bibr">4</a>].</p> Full article ">Figure 7
<p>Output irradiances against fiber length for 1 mm POF samples doped with two different combinations of dopants in the concentrations of <a href="#materials-14-02667-t001" class="html-table">Table 1</a>, and the corresponding saturation lengths specified at 99.5% of the height of the horizontal asymptote when length <span class="html-italic">L</span> tends to infinity.</p> Full article ">Figure 8
<p>(<b>a</b>) Output powers against fiber length for various combinations of Eu concentration and fiber diameter, when the POF sample is only doped with Eu chelate. (<b>b</b>) Output powers against fiber diameter corresponding to Eu-doped POFs of 100 m, and least-square fit using Equation (31).</p> Full article ">
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