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Materials, Volume 14, Issue 2 (January-2 2021) – 237 articles

Cover Story (view full-size image): A graphene oxide aerogel (GOA) was formed inside a melamine sponge (MS) framework. After reduction with hydrazine at 60 °C, the electrical conductive nitrogen-enriched rGOA-MS composite material with a specific density of 20.1 mg/cm3 was used to fabricate an electrode, which proved to be a promising electrocatalyst for the oxygen reduction reaction. The rGOA-MS composite material was characterized by elemental analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. It was found that nitrogen in the material is presented by different types with the maximum concentration of pyrrole-like nitrogen. By using Raman scattering it was established that the rGOA component of the material is graphene-like carbon with an average size of the sp2-domains of 5.7 nm. This explains a quite high conductivity of the composite obtained. View this paper
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15 pages, 2199 KiB  
Article
Assembling Surface Linker Chemistry with Minimization of Non-Specific Adsorption on Biosensor Materials
by Jack Chih-Chieh Sheng, Brian De La Franier and Michael Thompson
Materials 2021, 14(2), 472; https://doi.org/10.3390/ma14020472 - 19 Jan 2021
Cited by 10 | Viewed by 2681
Abstract
The operation of biosensors requires surfaces that are both highly specific towards the target analyte and that are minimally subject to fouling by species present in a biological fluid. In this work, we further examined the thiosulfonate-based linker in order to construct robust [...] Read more.
The operation of biosensors requires surfaces that are both highly specific towards the target analyte and that are minimally subject to fouling by species present in a biological fluid. In this work, we further examined the thiosulfonate-based linker in order to construct robust and durable self-assembling monolayers (SAMs) onto hydroxylated surfaces such as silica. These SAMs are capable of the chemoselective immobilization of thiol-containing probes (for analytes) under aqueous conditions in a single, straightforward, reliable, and coupling-free manner. The efficacy of the method was assessed through implementation as a biosensing interface for an ultra-high frequency acoustic wave device dedicated to the detection of avidin via attached biotin. Fouling was assessed via introduction of interfering bovine serum albumin (BSA), IgG antibody, or goat serum. Improvements were investigated systematically through the incorporation of an oligoethylene glycol backbone employed together with a self-assembling diluent without a functional distal group. This work demonstrates that the incorporation of a diluent of relatively short length is crucial for the reduction of fouling. Included in this work is a comparison of the surface attachment of the linker to Si3N4 and AlN, both materials used in sensor technology. Full article
(This article belongs to the Special Issue Advanced Designs of Materials, Devices and Techniques for Biosensing)
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Figure 1
<p>General mechanism of the reaction between a thiosulfonate and a thiol.</p> Full article ">Figure 2
<p>Structures of S–(11–trichlorosilyl-undecenyl) benzenethiosulfonate (TUBTS), S–(2–(2–(2–(3–trichlorosilyl–propyloxy)–ethoxy)–ethoxy)–ethyl) benzenethiosulfonate (OEG–TUBTS), trifluoroacetic acid 2–(3–trichlorosilyl–propyloxy)–ethyl ester (7–OEG–TFA), trifluoroacetic acid 2–(2–(3–trichlorosilyl–propyloxy)–ethoxy)–ethyl ester (10–OEG–TFA), trifluoroacetic acid 2–(2–(2–(3–trichlorosilyl-propyloxy)–ethoxy)––ethoxy)–ethyl ester (13–OEG–TFA), and biotinthiol.</p> Full article ">Figure 3
<p>Surface attachment of TUBTS to quartz followed by immobilization of biotinthiol.</p> Full article ">Figure 4
<p>Surface attachment of 7–OEG–TFA and 13–OEG–TFA followed by cleavage of the protecting TFA Group. An identical protocol was employed for 10–OEG–TFA.</p> Full article ">Figure 5
<p>EMPAS frequency shifts measured with TUBTS and biotinylated TUBTS self-assembling monolayers (SAMs), using 0.1 mg mL<sup>−1</sup> BSA, IgG, and avidin solutions in PBS buffer solution.</p> Full article ">Figure 6
<p>EMPAS measured with OEG–TUBTS and biotinylated OEG–TUBTS SAMs, using 0.1 mg mL<sup>−1</sup> BSA, IgG, and avidin solutions in PBS buffer solution.</p> Full article ">Figure 7
<p>EMPAS response profiles for (<b>a</b>) OEG–TUBTS SAM and (<b>b</b>) biotinylated OEG–TUBTS SAM using a 0.1 mg mL<sup>−1</sup> avidin solution.</p> Full article ">Figure 8
<p>EMPAS non-specific adsorption frequency shifts measured with undiluted goat serum using a cleaned quartz crystal and 7–OEG, 10–OEG, 13–OEG SAMs.</p> Full article ">Figure 9
<p>EMPAS frequency shifts measured with OEG–TUBTS/7–OEG and biotinylated OEG–TUBTS/7–OEG SAMs, using 0.1 mg mL<sup>−1</sup> BSA, IgG, and avidin solutions in PBS buffer solution.</p> Full article ">Figure 10
<p>EMPAS frequency shifts measured with 45.1 mg mL<sup>−1</sup> BSA and 45 mg mL<sup>−1</sup> BSA with 0.1 mg mL<sup>−1</sup> avidin solutions in PBS, using biotinylated TUBTS, OEG–TUBTS, and OEG–TUBTS/7–OEG SAMs.</p> Full article ">
24 pages, 8000 KiB  
Article
Estimating a Stoichiometric Solid’s Gibbs Free Energy Model by Means of a Constrained Evolutionary Strategy
by Constantino Grau Turuelo, Sebastian Pinnau and Cornelia Breitkopf
Materials 2021, 14(2), 471; https://doi.org/10.3390/ma14020471 - 19 Jan 2021
Cited by 2 | Viewed by 2510
Abstract
Modeling of thermodynamic properties, like heat capacities for stoichiometric solids, includes the treatment of different sources of data which may be inconsistent and diverse. In this work, an approach based on the covariance matrix adaptation evolution strategy (CMA-ES) is proposed and described as [...] Read more.
Modeling of thermodynamic properties, like heat capacities for stoichiometric solids, includes the treatment of different sources of data which may be inconsistent and diverse. In this work, an approach based on the covariance matrix adaptation evolution strategy (CMA-ES) is proposed and described as an alternative method for data treatment and fitting with the support of data source dependent weight factors and physical constraints. This is applied to a Gibb’s Free Energy stoichiometric model for different magnesium sulfate hydrates by means of the NASA9 polynomial. Its behavior is proved by: (i) The comparison of the model to other standard methods for different heat capacity data, yielding a more plausible curve at high temperature ranges; (ii) the comparison of the fitted heat capacity values of MgSO4·7H2O against DSC measurements, resulting in a mean relative error of a 0.7% and a normalized root mean square deviation of 1.1%; and (iii) comparing the Van’t Hoff and proposed Stoichiometric model vapor-solid equilibrium curves to different literature data for MgSO4·7H2O, MgSO4·6H2O, and MgSO4·1H2O, resulting in similar equilibrium values, especially for MgSO4·7H2O and MgSO4·6H2O. The results show good agreement with the employed data and confirm this method as a viable alternative for fitting complex physically constrained data sets, while being a potential approach for automatic data fitting of substance data. Full article
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<p>Fitting of the heat capacity for the substance MgSO<sub>4</sub>·1H<sub>2</sub>O using the Levenberg-Marquardt algorithm.</p> Full article ">Figure 2
<p>Comparison of fit results from a standard LM-algorithm and the addition of weight factors (red) for: (<b>a</b>) Anhydrous magnesium sulfate; (<b>b</b>) magnesium sulfate monohydrate.</p> Full article ">Figure 3
<p>Example of two-dimensional spherical optimization problem. Points are individuals, the blue area is the solution area, and the dashed line is the dispersion calculated with the covariance matrix. Generation 1 shows the initial random distribution. Generations 2–3 show the population moving towards the detected favorable direction of the solution due to the ranking of the individuals. Higher random dispersion is expected as the algorithm looks for other possible minima in the vicinity by “mutation”. In generations 4–6, after the individuals are sufficiently dispersed, with the information of the covariance matrix, the global minimum is pinpointed and all the individuals, regardless of their initial position, converge to the final solution area.</p> Full article ">Figure 4
<p>Qualitative curve of the Debye model, the three regions indicate the application of the different established conditions.</p> Full article ">Figure 5
<p>Comparison of the different fit results of MgSO<sub>4</sub> showing: (<b>a</b>) literature points region; (<b>b</b>) extended range until 2000 K.</p> Full article ">Figure 6
<p>Comparison of the different fit results of MgSO<sub>4</sub>·1H<sub>2</sub>O showing: (<b>a</b>) literature points region; (<b>b</b>) extended range until 2000 K.</p> Full article ">Figure 7
<p>Comparison of the different fit results of MgSO<sub>4</sub>·2H<sub>2</sub>O showing: (<b>a</b>) literature points region; (<b>b</b>) extended range until 2000 K.</p> Full article ">Figure 8
<p>Comparison of the different fit results of MgSO<sub>4</sub>·4H<sub>2</sub>O showing: (<b>a</b>) literature points region; (<b>b</b>) extended range until 2000 K.</p> Full article ">Figure 9
<p>Comparison of the different fit results of MgSO<sub>4</sub>·5H<sub>2</sub>O showing: (<b>a</b>) literature points region; (<b>b</b>) extended range until 2000 K.</p> Full article ">Figure 10
<p>Comparison of the different fit results of MgSO<sub>4</sub>·6H<sub>2</sub>O showing: (<b>a</b>) literature points area; (<b>b</b>) extended range until 2000 K.</p> Full article ">Figure 11
<p>Comparison of the different fit results of MgSO<sub>4</sub>·7H<sub>2</sub>O showing: (<b>a</b>) literature points region; (<b>b</b>) extended range until 2000 K.</p> Full article ">Figure 12
<p>Comparison of the different fit results, showing the literature data in green (mean of the values) with the 95% confidence interval boundaries of: (<b>a</b>) MgSO<sub>4</sub>; (<b>b</b>) MgSO<sub>4</sub>·1H<sub>2</sub>O.</p> Full article ">Figure 13
<p>Comparison of the different fit results, showing the literature data in green (mean of the values) with the 95% confidence interval boundaries of: (<b>a</b>) MgSO<sub>4</sub>·2H<sub>2</sub>O; (<b>b</b>) MgSO<sub>4</sub>·4H<sub>2</sub>O.</p> Full article ">Figure 14
<p>Comparison of the different fit results, showing the literature data in green (mean of the values) with the 95% confidence interval boundaries of: (<b>a</b>) MgSO<sub>4</sub>·6H<sub>2</sub>O; (<b>b</b>) MgSO<sub>4</sub>·7H<sub>2</sub>O.</p> Full article ">Figure 15
<p>Fitted results of the enthalpy curve in the literature points region for: (<b>a</b>) MgSO<sub>4</sub>; (<b>b</b>) MgSO<sub>4</sub>·1H<sub>2</sub>O.</p> Full article ">Figure 16
<p>Fitted results of the entropy curve in the literature points region for: (<b>a</b>) MgSO<sub>4</sub>; (<b>b</b>) MgSO<sub>4</sub>·1H<sub>2</sub>O.</p> Full article ">Figure 17
<p>Fitted results of the entropy curve in the literature points region for MgSO<sub>4</sub>·2H<sub>2</sub>O.</p> Full article ">Figure 18
<p>Comparison between the fitted heat capacity with the CMA-ES method and the experimental output from the DSC setup.</p> Full article ">Figure 19
<p>Temperature—vapor pressure comparison of MgSO<sub>4</sub>·7H<sub>2</sub>O between experimental data from Steiger et al. [<a href="#B37-materials-14-00471" class="html-bibr">37</a>], Van’t Hoff curves, and the calculation of this work taking the MgSO<sub>4</sub>·7H<sub>2</sub>O as the fixed composition (black lines): (<b>a</b>) for a limited range to show literature points for the dehydration of MgSO<sub>4</sub>·7H<sub>2</sub>O and MgSO<sub>4</sub>·6H<sub>2</sub>O; (<b>b</b>) extended range to show further curves and the dehydration of MgSO<sub>4</sub>·1H<sub>2</sub>O.</p> Full article ">
19 pages, 43847 KiB  
Article
Experimental and Numerical Investigation of AA5052-H32 Al Alloy with U-Profile in Cold Roll Forming
by Mohanraj Murugesan, Muhammad Sajjad and Dong Won Jung
Materials 2021, 14(2), 470; https://doi.org/10.3390/ma14020470 - 19 Jan 2021
Cited by 14 | Viewed by 3835
Abstract
The cold roll forming process is broadly used to produce a specific shape of cold-roll formed products for their applications in automobiles, aerospace, shipbuilding, and construction sectors. Moreover, a proper selection of strip thickness and forming speed to avoid fracture is most important [...] Read more.
The cold roll forming process is broadly used to produce a specific shape of cold-roll formed products for their applications in automobiles, aerospace, shipbuilding, and construction sectors. Moreover, a proper selection of strip thickness and forming speed to avoid fracture is most important for manufacturing a quality product. This research aims to investigate the presence of longitudinal bow, the reason behind flange height deviation, spring-back, and identification of thinning location in the cold roll-forming of symmetrical short U-profile sheets. A room temperature tensile test is performed for the commercially available AA5052–H32 Al alloy sheets using Digital Image Correlation (DIC) technique, which allows complete displacement and strain data information at each time-step. The material properties are estimated from the digital images using correlation software for tested samples; the plastic strain ratios are also calculated from samples at 0°, 45°, and 90° to the rolling direction. The tested sample’s surface morphology and the elemental analysis are conducted using scanning electron microscopy (SEM) method and energy-dispersive X-ray spectroscopy (EDS) analytical technique combined with element mapping analysis, respectively. The cold roll forming experiments are systematically carried out, and then finite element analysis is utilized to correlate the experiment with the model. The performed cold roll forming numerical model outcome indicates a good agreement with the experimental measurements. Overall, the presented longitudinal strain was observed to influence the geometry profile. The spring-back is also noticed at the profile tail end and is more pronounced at high forming speed with lower strip thickness. Conversely, while the forming speed is varied, the strain and stress variations are observed to be insignificant, and the similar results also are recognized for the thinning behavior. Full article
(This article belongs to the Special Issue Recent Advances in Metal Forming Technology)
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<p>Field emission scanning electron microscopy (FESEM) analysis (<b>a</b>) Microstructure observation at initial state; (<b>b</b>) Microstructure observation after fracture; (<b>c</b>) Tested samples.</p> Full article ">Figure 2
<p>Energy dispersive X–ray spectroscopy (EDS) analysis (<b>a</b>) Element spectrum corresponding to AA5052-H32 material; (<b>b</b>) EDS elemental mapping images showing the distribution of chemical elements.</p> Full article ">Figure 3
<p>(<b>a</b>) Experimental setup used for the uniaxial tension test with Aramis; (<b>b</b>) Yield and tensile strength data at 0<math display="inline"><semantics> <msup> <mrow/> <mo>°</mo> </msup> </semantics></math>, 45<math display="inline"><semantics> <msup> <mrow/> <mo>°</mo> </msup> </semantics></math> and 90<math display="inline"><semantics> <msup> <mrow/> <mo>°</mo> </msup> </semantics></math> to the RD ; (<b>c</b>) Major strain measurements by Digital Image Correlation (DIC) just before and after fracture.</p> Full article ">Figure 4
<p>(<b>a</b>) Schematic representation of cold roll forming; (<b>b</b>) cold roll forming experimental set–up; (<b>c</b>) measurement procedures on finished part, such as bow, height, cross-section and spring-back, after forming process.</p> Full article ">Figure 5
<p>Roll forming process reduced mesh models for the constant arc length method.</p> Full article ">Figure 6
<p>Strip before entering the first forming station defining boundary conditions and illustrating meshes considered.</p> Full article ">Figure 7
<p>Sheet blank deformation during the roll forming process considering solid and shell elements (<b>a</b>) numerical results of solid and shell elements; (<b>b</b>) sheet deformation at each forming stage.</p> Full article ">Figure 8
<p>(<b>a</b>) Formed U-profile at real-time experiment; (<b>b</b>) spring-back of U-profile; (<b>c</b>) deformed 2D U-profile coordinates of front section from experiment and simulation; (<b>d</b>) deformed 2D U-profile coordinates of back section from experiments.</p> Full article ">Figure 9
<p>Section views of formed short U-profiles at different forming speed.</p> Full article ">Figure 10
<p>(<b>a</b>) Plastic strain obatined along predefined bend-line paths at roll speed of 60 <math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math> <math display="inline"><semantics> <msup> <mi mathvariant="normal">s</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>; (<b>b</b>) plastic strain obatined from chosen element at roll speed of 60 <math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math> <math display="inline"><semantics> <msup> <mi mathvariant="normal">s</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>; (<b>c</b>) stage-wise peak strain comparison with forming speed of 60 <math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math> <math display="inline"><semantics> <msup> <mi mathvariant="normal">s</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math> and 90 <math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math> <math display="inline"><semantics> <msup> <mi mathvariant="normal">s</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>; (<b>d</b>) comparison of stress and strain in chosen bend-line elements.</p> Full article ">Figure 11
<p>Effective stress contours on the formed part at roll speed of 90 <math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math> <math display="inline"><semantics> <msup> <mi mathvariant="normal">s</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math>.</p> Full article ">Figure 12
<p>Thickness distribution in cold formed parts at 90 <math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math> <math display="inline"><semantics> <msup> <mi mathvariant="normal">s</mi> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </semantics></math> forming speed.</p> Full article ">
24 pages, 10127 KiB  
Article
Residual Mechanical Properties and Constitutive Model of High-Strength Seismic Steel Bars through Different Cooling Rates
by Xianhua Yao, Peiqiao Qin, Junfeng Guan, Lielie Li, Min Zhang and Yongwei Gao
Materials 2021, 14(2), 469; https://doi.org/10.3390/ma14020469 - 19 Jan 2021
Cited by 5 | Viewed by 2063
Abstract
In this study, the high-temperature test (i.e., temperature to 1000 °C) is conducted on 600 MPa seismic steel bars, and its residual mechanical properties and constitutive relations are investigated though three cooling rates, i.e., under air, furnace, and water-cooling conditions. Results show that [...] Read more.
In this study, the high-temperature test (i.e., temperature to 1000 °C) is conducted on 600 MPa seismic steel bars, and its residual mechanical properties and constitutive relations are investigated though three cooling rates, i.e., under air, furnace, and water-cooling conditions. Results show that three cooling methods have significant effects on the apparent characteristics of 600 MPa steel bars, when the heating temperature is greater than 600 °C. In addition, the ultimate and yield strength of steel bars have been significantly affected by different cooling methods, with increasing heating temperature. However, the elastic modulus is significantly not affected by temperature. Furthermore, the elongation rate after fracture and the total elongation rate at the maximum force do not change significantly, when the heating temperature is less than 650 °C. The elongation rate, after fracture, and the total elongation rate, at the maximum force, have different changes for three cooling methods. The degeneration of the stress–strain curves occurs when the heating temperature is high. The two-fold line, three-fold line, and Ramberg–Osgood models are developed based on the stress–strain curve characteristics of steel bars after cooling. The fire resistance of 600 MPa steel bars of reinforced concrete structure is analyzed, which provides a basis for post-disaster damage assessment, repair, and reinforcement of the building structure. Full article
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Figure 1
<p>Three ways of cooling.</p> Full article ">Figure 2
<p>Schematic diagram of heating temperature and cooling system. (<span class="html-italic">T</span>c denotes target temperature; <span class="html-italic">T</span><sub>A</sub> is ambient temperature; <span class="html-italic">T</span><sub>w</sub> represents water temperature).</p> Full article ">Figure 3
<p>Tensile test.</p> Full article ">Figure 4
<p>High-precision extensometer.</p> Full article ">Figure 5
<p>Appearance of steel bar after air cooling. (<b>a</b>) The surface color of 14 mm diameter steel bars changing with temperature after high-temperature cooling; (<b>b</b>) the tensile fracture sections of 14 mm diameter steel bars under air cooling, both show significant necking and fractures in the shape of a silver cup cone; (<b>c</b>) the surface color of 18 mm diameter steel bars changing with temperature after high-temperature cooling; (<b>d</b>) the tensile fracture sections of 18 mm diameter steel bars under air cooling, both show significant necking and fractures in the shape of a silver cup cone.</p> Full article ">Figure 5 Cont.
<p>Appearance of steel bar after air cooling. (<b>a</b>) The surface color of 14 mm diameter steel bars changing with temperature after high-temperature cooling; (<b>b</b>) the tensile fracture sections of 14 mm diameter steel bars under air cooling, both show significant necking and fractures in the shape of a silver cup cone; (<b>c</b>) the surface color of 18 mm diameter steel bars changing with temperature after high-temperature cooling; (<b>d</b>) the tensile fracture sections of 18 mm diameter steel bars under air cooling, both show significant necking and fractures in the shape of a silver cup cone.</p> Full article ">Figure 6
<p>Appearance of steel bar after furnace cooling. (<b>a</b>) The surface color of 14 mm diameter steel bars changing with temperature after high-temperature furnace cooling; (<b>b</b>) the tensile fracture sections of 14 mm diameter steel bars under furnace cooling, both show significant necking and fractures in the shape of a silver cup cone; (<b>c</b>) the surface color of 18 mm diameter steel bars changing with temperature after high-temperature furnace cooling; (<b>d</b>) the tensile fracture sections of 18 mm diameter steel bars under furnace cooling, both show significant necking and fractures in the shape of a silver cup cone.</p> Full article ">Figure 7
<p>Appearance of steel bar after water cooling. (<b>a</b>) The surface color of 14 mm diameter steel bars changing with temperature after high-temperature water cooling; (<b>b</b>) the tensile fracture sections of 14 mm diameter steel bars under water cooling, both show significant necking and fractures in the shape of a silver cup cone; (<b>c</b>) the surface color of 18 mm diameter steel bars changing with temperature after high-temperature water cooling; (<b>d</b>) the tensile fracture sections of 18 mm diameter steel bars under water cooling, both show significant necking and fractures in the shape of a silver cup cone.</p> Full article ">Figure 7 Cont.
<p>Appearance of steel bar after water cooling. (<b>a</b>) The surface color of 14 mm diameter steel bars changing with temperature after high-temperature water cooling; (<b>b</b>) the tensile fracture sections of 14 mm diameter steel bars under water cooling, both show significant necking and fractures in the shape of a silver cup cone; (<b>c</b>) the surface color of 18 mm diameter steel bars changing with temperature after high-temperature water cooling; (<b>d</b>) the tensile fracture sections of 18 mm diameter steel bars under water cooling, both show significant necking and fractures in the shape of a silver cup cone.</p> Full article ">Figure 8
<p>Stress–strain curves of 14 mm diameter steel bars under different cooling conditions after heating.</p> Full article ">Figure 9
<p>Stress–strain curves of 18 mm diameter steel bars under different cooling conditions after heating.</p> Full article ">Figure 10
<p>Curves of mechanical indices changing with temperature for 14 mm diameter steel bars under different cooling modes after heating.</p> Full article ">Figure 11
<p>Curves of mechanical indices changing with temperature for 18 mm diameter steel bars under different cooling modes after heating.</p> Full article ">Figure 12
<p>Comparison of experimental results and predicted curves for the mechanical properties of steel bar samples under air cooling.</p> Full article ">Figure 13
<p>Comparison of experimental results and predicted curves for the mechanical properties of steel bar samples under furnace cooling.</p> Full article ">Figure 14
<p>Comparison of experimental results and predicted curves of the mechanical properties of steel bar samples under water cooling.</p> Full article ">Figure 15
<p>Comparison of the constitutive models of typical steel bars under air cooling.</p> Full article ">Figure 16
<p>Comparison of the constitutive models of typical steel bars under furnace cooling.</p> Full article ">Figure 17
<p>Comparison of the constitutive models of typical steel bars under water cooling.</p> Full article ">
18 pages, 11893 KiB  
Article
Determination of the Shear Modulus of Pine Wood with the Arcan Test and Digital Image Correlation
by Piotr Bilko, Aneta Skoratko, Andrzej Rutkiewicz and Leszek Małyszko
Materials 2021, 14(2), 468; https://doi.org/10.3390/ma14020468 - 19 Jan 2021
Cited by 12 | Viewed by 2691
Abstract
Arcan shear tests with digital image correlation were used to evaluate the shear modulus and shear stress–strain diagrams in the plane defined by two principal axes of the material orthotropy. Two different orientation of the grain direction as compared to the direction of [...] Read more.
Arcan shear tests with digital image correlation were used to evaluate the shear modulus and shear stress–strain diagrams in the plane defined by two principal axes of the material orthotropy. Two different orientation of the grain direction as compared to the direction of the shear force in specimens were considered: perpendicular and parallel shear. Two different ways were used to obtain the elastic properties based on the digital image correlation (DIC) results from the full-field measurement and from the virtual strain gauges with the linear strains: perpendicular to each other and directed at the angle of π/4 to the shearing load. In addition, the own continuum structural model for the failure analysis in the experimental tests was used. Constitutive relationships of the model were established in the framework of the mathematical multi-surface elastoplasticity for the plane stress state. The numerical simulations done by the finite element program after implementation of the model demonstrated the failure mechanisms from the experimental tests. Full article
(This article belongs to the Special Issue Testing of Materials and Elements in Civil Engineering)
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Figure 1

Figure 1
<p>The wood material axes on a log view (<b>a</b>); scanning electron microscope photograph of a RT plane at 746 times magnitude (<b>b</b>); and scanning electron microscope photograph of a LR plane at 533 times magnitude (<b>c</b>).</p> Full article ">Figure 2
<p>The standard shear modulus test specimen-strain gauge T-rosette and a way of measurement of the shear angle (<b>a</b>); and a state of pure shear (<b>b</b>). All dimensions are in millimeters (mm) unless otherwise noted.</p> Full article ">Figure 3
<p>The specimens: (<b>a</b>) dimensions subjected to variation; (<b>b</b>) LR,L orientation; (<b>c</b>) LR,R orientation; (<b>d</b>) geometry of specimen used for shear tests; and (<b>e</b>,<b>f</b>) stress distributions in the middle section for LR,L specimens. All dimensions are in millimeters (mm) unless otherwise noted.</p> Full article ">Figure 4
<p>The Arcan fixture: (<b>a</b>) scheme; (<b>b</b>) the explanation of measuring points/sections; (<b>c</b>) physical fixture; (<b>d</b>) distances and tooth plates; and (<b>e</b>) experimental setup with the DIC system.</p> Full article ">Figure 5
<p>The shear angle maps just before the failure for each LR,L-type specimen: (<b>a</b>–<b>f</b>) for each of the samples from L1 to L6 respectively.</p> Full article ">Figure 6
<p>The shear angle plots along critical sections for LR,L-type specimens: (<b>a</b>) Specimen L3; and (<b>b</b>) Specimen L2.</p> Full article ">Figure 7
<p>The shear angle maps just before the failure for each LR,R-type specimen: (<b>a</b>–<b>f</b>) for each of the samples from R1 to R6 respectively.</p> Full article ">Figure 8
<p>The shear angle plots along critical sections for LR,R-type specimens: (<b>a</b>) Specimen R2; and (<b>b</b>) Specimen R6.</p> Full article ">Figure 9
<p>Charts of the relationship of shear stress–shear angle at the central point for LR,L specimens with their linear approximation: (<b>a</b>–<b>f</b>) for each of the samples from L1 to L6 respectively.</p> Full article ">Figure 10
<p>Charts of the relationship of shear stress–shear angle at the central point for LR,R specimens with their linear approximation: (<b>a</b>–<b>f</b>) for each of the samples from R1 to R6 respectively.</p> Full article ">Figure 10 Cont.
<p>Charts of the relationship of shear stress–shear angle at the central point for LR,R specimens with their linear approximation: (<b>a</b>–<b>f</b>) for each of the samples from R1 to R6 respectively.</p> Full article ">Figure 11
<p>Contours of orthotropic strength criteria: (<b>a</b>) in the principal stress space; and (<b>b</b>) in the axes of orthotropy (I) and (II) are Rankine-type criterion for tension and compression regime and (III) is the Mohr–Coulomb shear failure criterion.</p> Full article ">Figure 12
<p>Distributions of the shear stress for different configurations of the specimens: (<b>a</b>) the finite element mesh; (<b>b</b>) Specimen LR,L; and (<b>c</b>) Specimen LR,R.</p> Full article ">Figure 13
<p>Graphs of the responses obtained from the numerical tests-description in the text: (<b>a</b>) load vs. displacement graphs; and (<b>b</b>) stress–strain curves for the middle point of the specimen.</p> Full article ">Figure 14
<p>Comparison of the maps of the maximum principal strains <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mn>1</mn> </msub> </mrow> </semantics></math> obtained numerically (<b>a</b>–<b>c</b>) and calculated from displacements measured by the DIC method (<b>d</b>–<b>f</b>) for LR,L orientation.</p> Full article ">Figure 15
<p>Comparison of the maps of the maximum principal strains <math display="inline"><semantics> <mrow> <msub> <mi>ε</mi> <mn>1</mn> </msub> </mrow> </semantics></math> obtained numerically (<b>a</b>–<b>c</b>) and calculated from displacements measured by the DIC method (<b>d</b>–<b>f</b>) for LR,R orientation.</p> Full article ">
18 pages, 5260 KiB  
Article
Short-Term Flexural Stiffness Prediction of CFRP Bars Reinforced Coral Concrete Beams
by Lei Wang, Jin Yi, Jiwang Zhang, Wu Chen and Feng Fu
Materials 2021, 14(2), 467; https://doi.org/10.3390/ma14020467 - 19 Jan 2021
Cited by 16 | Viewed by 2689
Abstract
FRP (Fiber Reinforced Polymer) Bar reinforced coral concrete beam is a new type of structural member that has been used more and more widely in marine engineering in recent years. In order to study and predict the flexural performance of CFRP reinforced coral [...] Read more.
FRP (Fiber Reinforced Polymer) Bar reinforced coral concrete beam is a new type of structural member that has been used more and more widely in marine engineering in recent years. In order to study and predict the flexural performance of CFRP reinforced coral concrete beams, the flexural rigidity, crack morphology and failure mode of concrete were studied in detail. The results show that under the condition of similar reinforcement ratio, the flexural rigidity of CFRP reinforced coral concrete beam is significantly lower than that of ordinary reinforced concrete beam. Increasing the cross-section reinforcement ratio within a certain range can increase the bending stiffness of the test beam or reduce the deflection, but the strength utilization rate of CFRP reinforcement is greatly reduced. The short-term bending stiffness of the CFRP reinforced coral concrete beam calculated by the existing standard formula is obviously higher. This paper proposes a modified formula for introducing the strain inhomogeneity coefficient (ψ) of CFRP bars and considers the relative slip between CFRP bars and coral concrete to predict the short-term flexural stiffness of coral concrete beams reinforced by CFRP bars. The formula was verified with the test results, and it was proved that the formula has a good consistency with the test results. Full article
(This article belongs to the Section Advanced Materials Characterization)
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<p>Coral debris.</p> Full article ">Figure 2
<p>CFRP bars.</p> Full article ">Figure 3
<p>(<b>a</b>) Test specimen: geometry and reinforcement detail (dimensions in mm); (<b>b</b>) Actual loading condition of test beam.</p> Full article ">Figure 4
<p>Effect of reinforcement ratio of CFRP bars on load-deflection curves.</p> Full article ">Figure 5
<p>Comparison of crack width of specimen beams: (<b>a</b>) Average Crack width; (<b>b</b>) Maximum Crack width.</p> Full article ">Figure 6
<p>Effect of reinforcement ratio of CFRP bars on strain curve.</p> Full article ">Figure 7
<p>Relative slip curve of CFRP bars and coral concrete.</p> Full article ">Figure 8
<p>Failure pattern of specimen beams: (<b>a</b>) S-16-1 concrete crashing failure; (<b>b</b>) C-12-2 concrete crashing failure; (<b>c</b>) C-10-1 CFRP bar slip failure.</p> Full article ">Figure 8 Cont.
<p>Failure pattern of specimen beams: (<b>a</b>) S-16-1 concrete crashing failure; (<b>b</b>) C-12-2 concrete crashing failure; (<b>c</b>) C-10-1 CFRP bar slip failure.</p> Full article ">Figure 9
<p>Crack distribution and development of the test beams: (<b>a</b>) S-16-1; (<b>b</b>) C-12-2; (<b>c</b>) C-10-1; (<b>d</b>) C-8-2.</p> Full article ">Figure 9 Cont.
<p>Crack distribution and development of the test beams: (<b>a</b>) S-16-1; (<b>b</b>) C-12-2; (<b>c</b>) C-10-1; (<b>d</b>) C-8-2.</p> Full article ">Figure 10
<p>Comparison of calculated and experimental deflection of CFRP bars: (<b>a</b>) C-8; (<b>b</b>) C-10; (<b>c</b>) C-12.</p> Full article ">Figure 11
<p>Relationship between tensile strength and strain inhomogeneity coefficient of concrete [<a href="#B14-materials-14-00467" class="html-bibr">14</a>].</p> Full article ">Figure 12
<p>Comparison between result of the proposed formula and that of test results. (<b>a</b>) C-8; (<b>b</b>) C-10; (<b>c</b>) C-12.</p> Full article ">
15 pages, 6501 KiB  
Article
Sustainable Additive Manufacturing: Mechanical Response of Polyamide 12 over Multiple Recycling Processes
by Nectarios Vidakis, Markos Petousis, Lazaros Tzounis, Athena Maniadi, Emmanouil Velidakis, Nikolaos Mountakis and John D. Kechagias
Materials 2021, 14(2), 466; https://doi.org/10.3390/ma14020466 - 19 Jan 2021
Cited by 79 | Viewed by 5139
Abstract
Plastic waste reduction and recycling through circular use has been critical nowadays, since there is an increasing demand for the production of plastic components based on different polymeric matrices in various applications. The most commonly used recycling procedure, especially for thermoplastic materials, is [...] Read more.
Plastic waste reduction and recycling through circular use has been critical nowadays, since there is an increasing demand for the production of plastic components based on different polymeric matrices in various applications. The most commonly used recycling procedure, especially for thermoplastic materials, is based on thermomechanical process protocols that could significantly alter the polymers’ macromolecular structure and physicochemical properties. The study at hand focuses on recycling of polyamide 12 (PA12) filament, through extrusion melting over multiple recycling courses, giving insight for its effect on the mechanical and thermal properties of Fused Filament Fabrication (FFF) manufactured specimens throughout the recycling courses. Three-dimensional (3D) FFF printed specimens were produced from virgin as well as recycled PA12 filament, while they have been experimentally tested further for their tensile, flexural, impact and micro-hardness mechanical properties. A thorough thermal and morphological analysis was also performed on all the 3D printed samples. The results of this study demonstrate that PA12 can be successfully recycled for a certain number of courses and could be utilized in 3D printing, while exhibiting improved mechanical properties when compared to virgin material for a certain number of recycling repetitions. From this work, it can be deduced that PA12 can be a viable option for circular use and 3D printing, offering an overall positive impact on recycling, while realizing 3D printed components using recycled filaments with enhanced mechanical and thermal stability. Full article
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<p>2020 recycled plastics market and parameters affecting plastics circular economy (market volume data source: Technavio. Global Recycled Plastics Market 2020–2022 (IRTNTR21968).</p> Full article ">Figure 2
<p>Flow chart with the methodology followed for the PA12 recycling in the current study.</p> Full article ">Figure 3
<p>Parameters employed in the study for the construction of the FFF 3D printed specimens.</p> Full article ">Figure 4
<p>Tensile tests: (<b>a</b>) device experimental setup and specimens after the test, (<b>b</b>) stress strain graphs from the no 2 specimen of each recycle course, (<b>c</b>) comparison of the tensile strength average values along with the calculated deviation from each recycle course studied, and (<b>d</b>) comparison of the tensile modulus of elasticity average values along with the calculated deviation from each recycle course studied.</p> Full article ">Figure 5
<p>Flexural tests: (<b>a</b>) device experimental setup and specimens after the test, (<b>b</b>) stress strain graphs from the no 2 specimen of each recycle course, (<b>c</b>) comparison of the flexural strength average values along with the calculated deviation from each recycle course studied, and (<b>d</b>) comparison of the flexural modulus of elasticity average values along with the calculated deviation from each recycle course studied.</p> Full article ">Figure 6
<p>Impact tests: (<b>a</b>) comparison of the impact strength average values along with the calculated deviation from each recycle course studied and (<b>b</b>) device experimental setup and specimens after the test.</p> Full article ">Figure 7
<p>Micro-hardness Vickers tests: (<b>a</b>) comparison of the Vickers micro-hardness average values along with the calculated deviation from each recycle course studied and (<b>b</b>) device experimental setup and specimens after the test.</p> Full article ">Figure 8
<p>(<b>a</b>) TGA graphs for pure PA12 1st recycling course versus 6th recycling course; (<b>b</b>) magnified TGA temperature window for the material’s thermal degradation region.</p> Full article ">Figure 9
<p>(<b>a</b>) DSC 2nd heat/cool cycle curves for PA12 1st, 3rd, and 6th recycling courses and (<b>b</b>) magnified temperature window of the DSC curves.</p> Full article ">Figure 10
<p>Specimens’ side surface SEM images: (<b>a</b>) 1st recycling course, (<b>b</b>) 2nd recycling course, (<b>c</b>) 3rd recycling course, (<b>d</b>) 4th recycling course, (<b>e</b>) 5th recycling course and (<b>f</b>) 6th recycling course.</p> Full article ">Figure 11
<p>Tensile specimens’ fracture surface SEM images: (<b>a</b>) 1st recycling course, (<b>b</b>) 2nd recycling course, (<b>c</b>) 3rd recycling course, (<b>d</b>) 4th recycling course, (<b>e</b>) 5th recycling course and (<b>f</b>) 6th recycling course.</p> Full article ">Figure 12
<p>Virgin and recycled in the 6 recycle courses studied in this work PA12 mechanical properties summary.</p> Full article ">
18 pages, 5431 KiB  
Article
CuWO4 with CuO and Cu(OH)2 Native Surface Layers for H2S Detection under in-Field Conditions
by Simona Somacescu, Adelina Stanoiu, Ion Viorel Dinu, Jose Maria Calderon-Moreno, Ovidiu G. Florea, Mihaela Florea, Petre Osiceanu and Cristian E. Simion
Materials 2021, 14(2), 465; https://doi.org/10.3390/ma14020465 - 19 Jan 2021
Cited by 5 | Viewed by 2691
Abstract
The paper presents the possibility of detecting low H2S concentrations using CuWO4. The applicative challenge was to obtain sensitivity, selectivity, short response time, and full recovery at a low operating temperature under in-field atmosphere, which means variable relative humidity [...] Read more.
The paper presents the possibility of detecting low H2S concentrations using CuWO4. The applicative challenge was to obtain sensitivity, selectivity, short response time, and full recovery at a low operating temperature under in-field atmosphere, which means variable relative humidity (%RH). Three different chemical synthesis routes were used for obtaining the samples labeled as: CuW1, CuW2, and CuW3. The materials have been fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). While CuWO4 is the common main phase with triclinic symmetry, different native layers of CuO and Cu(OH)2 have been identified on top of the surfaces. The differences induced into their structural, morphological, and surface chemistry revealed different degrees of surface hydroxylation. Knowing the poisonous effect of H2S, the sensing properties evaluation allowed the CuW2 selection based on its specific surface recovery upon gas exposure. Simultaneous electrical resistance and work function measurements confirmed the weak influence of moisture over the sensing properties of CuW2, due to the pronounced Cu(OH)2 native surface layer, as shown by XPS investigations. Moreover, the experimental results obtained at 150 °C highlight the linear sensor signal for CuW2 in the range of 1 to 10 ppm H2S concentrations and a pronounced selectivity towards CO, CH4, NH3, SO2, and NO2. Therefore, the applicative potential deserves to be noted. The study has been completed by a theoretical approach aiming to link the experimental findings with the CuW2 intrinsic properties. Full article
(This article belongs to the Special Issue Advanced Materials for Gas Sensors)
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<p>Gas mixing station with accessories for the metal oxide semiconductors (MOX) gas sensors evaluation.</p> Full article ">Figure 2
<p>XRD patterns for CuW1, CuW2, and CuW3 materials.</p> Full article ">Figure 3
<p>SEM micrographs of CuW1 showing mixed states of aggregation (<b>a</b>) and different regions of the sample with distinct particle sizes (<b>b</b>–<b>d</b>) with a higher magnification inset in (<b>b</b>).</p> Full article ">Figure 4
<p>SEM micrographs of CuW2: (<b>a</b>) Secondary emission (SE) and (<b>b</b>) back-scattered electrons (BSE) images taken simultaneously from the same region and higher resolution, (<b>c</b>) SE, (<b>d</b>) BSE micrographs, and (<b>e</b>) higher magnification images.</p> Full article ">Figure 5
<p>SEM micrographs of CuW3: (<b>a</b>) SE and (<b>b</b>) BSE images taken simultaneously from the same region; (<b>c</b>,<b>d</b>) higher resolution SEM micrographs showing the CuWO<sub>4</sub> platelets size and shape.</p> Full article ">Figure 6
<p>The short-range structural ordering in the lattice of our samples analyzed via Raman spectroscopy.</p> Full article ">Figure 7
<p>Cu2p and W4f high resolution superimposed spectra of CuW1, CuW2, and CuW3 in the “as received” stage (<b>a</b>,<b>c</b>), after a gentle surface Ar ion etching (<b>b</b>), and W4f deconvoluted spectrum for the CuW1 sample (<b>d</b>). The formation of CuOH on the top of the surface is marked with symbol *.</p> Full article ">Figure 8
<p>The superimposed O1s of CuW1, CuW2, and CuW3 in the “as received” stage and after a gentle Ar ion etching (<b>a</b>) and the singlet O1s deconvoluted spectrum for the CuW1 sample in the “as received” stage (<b>b</b>).</p> Full article ">Figure 9
<p>Sensor signal dependence with respect to the operating temperature after 10 ppm H<sub>2</sub>S exposure under 50 % relative humidity (RH) background (<b>a</b>); raw data of CuW1, CuW2, and CuW3 operated at 150 °C for one pulse of 10 ppm H<sub>2</sub>S (<b>b</b>).</p> Full article ">Figure 10
<p>Potential changes at the CuW2 surface induced by RH variations.</p> Full article ">Figure 11
<p>Sensor signal behavior with respect to the H<sub>2</sub>S concentrations.</p> Full article ">Figure 12
<p>Selective sensitivity aspects for CuW2 towards different gas interfering.</p> Full article ">Figure 13
<p>The changes in band bending depending on the sensor signal.</p> Full article ">Figure 14
<p>Surface band bending with respect to the depth z<sub>0</sub> measured from the surface to the bulk of the sensitive material.</p> Full article ">
18 pages, 3625 KiB  
Article
Propolis and Organosilanes as Innovative Hybrid Modifiers in Wood-Based Polymer Composites
by Majka Odalanowska, Magdalena Woźniak, Izabela Ratajczak, Daria Zielińska, Grzegorz Cofta and Sławomir Borysiak
Materials 2021, 14(2), 464; https://doi.org/10.3390/ma14020464 - 19 Jan 2021
Cited by 16 | Viewed by 3187
Abstract
The article presents characteristics of wood/polypropylene composites, where the wood was treated with propolis extract (EEP) and innovative propolis-silane formulations. Special interest in propolis for wood impregnation is due to its antimicrobial properties. One propolis-silane formulation (EEP-TEOS/VTMOS) consisted of EEP, tetraethyl orthosilicate (TEOS), [...] Read more.
The article presents characteristics of wood/polypropylene composites, where the wood was treated with propolis extract (EEP) and innovative propolis-silane formulations. Special interest in propolis for wood impregnation is due to its antimicrobial properties. One propolis-silane formulation (EEP-TEOS/VTMOS) consisted of EEP, tetraethyl orthosilicate (TEOS), and vinyltrimethoxysilane (VTMOS), while the other (EEP-TEOS/OTEOS) contained EEP, tetraethyl orthosilicate (TEOS), and octyltriethoxysilane (OTEOS). The treated wood fillers were characterized by Fourier transform infrared spectroscopy (FTIR), atomic absorption spectrometry (AAS), and X-ray diffraction (XRD), while the composites were investigated using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and optical microscopy. The wood treated with EEP and propolis-silane formulations showed resistance against moulds, including Aspergillus niger, Chaetomium globosum, and Trichoderma viride. The chemical analyses confirmed presence of silanes and constituents of propolis in wood structure. In addition, treatment of wood with the propolis-silane formulations produced significant changes in nucleating abilities of wood in the polypropylene matrix, which was confirmed by an increase in crystallization temperature and crystal conversion, as well as a decrease in half-time of crystallization parameters compared to the untreated polymer matrix. In all the composites, the formation of a transcrystalline layer was observed, with the greatest rate recorded for the composite with the filler treated with EEP-TEOS/OTEOS. Moreover, impregnation of wood with propolis-silane formulations resulted in a considerable improvement of strength properties in the produced composites. A dependence was found between changes in the polymorphic structures of the polypropylene matrix and strength properties of composite materials. It needs to be stressed that to date literature sources have not reported on treatment of wood fillers using bifunctional modifiers providing a simultaneous effect of compatibility in the polymer-filler system or any protective effect against fungi. Full article
(This article belongs to the Special Issue Application of Natural Polymers in Bio-Based Products)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Spectra of wood (A), wood treated with: EEP (B), EEP-TEOS/OTEOS (C) and TEOS/OTEOS (D).</p> Full article ">Figure 2
<p>Spectra of wood (A), wood treated with: EEP (B), EEP-TEOS/VTMOS (C) and TEOS/VTMOS (D).</p> Full article ">Figure 3
<p>Diffractograms of wood and wood impregnated with EEP, EEP-TEOS/VTMOS and EEP-TEOS/OTEOS.</p> Full article ">Figure 4
<p>DSC exotherms of WPC.</p> Full article ">Figure 5
<p>Crystal conversion of PP and WPC.</p> Full article ">Figure 6
<p>PLM images registered at 136 °C for (<b>A</b>) PP + wood, (<b>B</b>) PP + EEP, (<b>C</b>) PP + EEP-TEOS/OTEOS, (<b>D</b>) PP + EEP-TEOS/VTMOS after (<b>a</b>) 0 min, (<b>b</b>) 3 min, (<b>c</b>) 6 min.</p> Full article ">Figure 7
<p>X-ray diffraction pattern of composite materials.</p> Full article ">
16 pages, 3032 KiB  
Article
Ecotoxicity and Essential Properties of Fine-Recycled Aggregate
by Diana Mariaková, Klára Anna Mocová, Kristina Fořtová, Pavla Ryparová, Jan Pešta and Tereza Pavlů
Materials 2021, 14(2), 463; https://doi.org/10.3390/ma14020463 - 19 Jan 2021
Cited by 11 | Viewed by 2455
Abstract
This article deals with the possibility of utilization of secondary-raw materials as a natural sand replacement in concrete. Four types of waste construction materials were examined—recycled aggregate from four different sources. The natural aggregate was examined as well as used as the reference [...] Read more.
This article deals with the possibility of utilization of secondary-raw materials as a natural sand replacement in concrete. Four types of waste construction materials were examined—recycled aggregate from four different sources. The natural aggregate was examined as well as used as the reference sample. All the samples were tested to evaluate the water absorption, particle size distribution, and particle density. The basic chemical reactions in the view of ecotoxicology are investigated and measured based on Czech standards. Chemical analysis, Lemna growth inhibition test, freshwater algae, daphnia acute, and mustard germination toxicity test were made and discussed in this paper. Based on the physical and geometrical properties and ecotoxicology of examined waste materials, this work evaluated them as suitable for utilization in concrete as a sand replacement. Full article
(This article belongs to the Special Issue Environmentally Friendly Materials in Construction)
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<p>Tested waste materials recycled concrete aggregate (RCA): (<b>a</b>) NA; (<b>b</b>) RA 1; (<b>c</b>) RA 4.</p> Full article ">Figure 2
<p>Oven-dry density and water absorption of aggregate according to CSN EN 1097-6.</p> Full article ">Figure 3
<p>The particle size distributions of natural aggregate (NA) and RCA (grain size 0/4 mm) according to CSN EN 933-1.</p> Full article ">Figure 4
<p>The results of ecotoxicity experiments: (<b>a</b>) Daphnia immobilization, (<b>b</b>) algae growth rate, (<b>c</b>) algae chlorophyll content, (<b>d</b>) mustard root elongation, (<b>e</b>) <span class="html-italic">Lemna</span> growth rate, (<b>f</b>) <span class="html-italic">Lemna</span> chlorophyll content. X—not determined, 0—zero values, 100 + s—leachates amended with nutrient salts.</p> Full article ">Figure 4 Cont.
<p>The results of ecotoxicity experiments: (<b>a</b>) Daphnia immobilization, (<b>b</b>) algae growth rate, (<b>c</b>) algae chlorophyll content, (<b>d</b>) mustard root elongation, (<b>e</b>) <span class="html-italic">Lemna</span> growth rate, (<b>f</b>) <span class="html-italic">Lemna</span> chlorophyll content. X—not determined, 0—zero values, 100 + s—leachates amended with nutrient salts.</p> Full article ">Figure 5
<p>Test plants photo-documentation: (<b>a</b>) control, (<b>b</b>) NA—100%, (<b>c</b>) NA—salts, (<b>d</b>) RA 1—100%, (<b>e</b>) RA 2—12.5%, (<b>f</b>) RA 2—1.56%, (<b>g</b>) RA 3—100 + s, (<b>h</b>) RA 3—12.5 %, (<b>i</b>) RA 4—100%.</p> Full article ">
14 pages, 3123 KiB  
Article
An Analytical Model for Estimating the Bending Curvatures of Metal Sheets in Laser Peen Forming
by Yunxia Ye, Zeng Nie, Xu Huang, Xudong Ren and Lin Li
Materials 2021, 14(2), 462; https://doi.org/10.3390/ma14020462 - 19 Jan 2021
Viewed by 2459
Abstract
Laser peen forming (LPF) is suitable for shaping sheet metals without the requirement for die/mold and without causing high temperatures. An analytical model for estimating the bending curvatures of LPF is convenient and necessary for better understanding of the physical processes involved. In [...] Read more.
Laser peen forming (LPF) is suitable for shaping sheet metals without the requirement for die/mold and without causing high temperatures. An analytical model for estimating the bending curvatures of LPF is convenient and necessary for better understanding of the physical processes involved. In this paper, we describe a new analytical model based on internal force balance and the energy transformation in LPF. Experiments on 2024 aluminum alloy sheets of 1–3 mm thickness were performed to validate the analytical model. The results showed that for 1 mm and 3 mm thick–thin plates, the curvature obtained by the analytical model changes from −14 × 10−4 mm−1 and −1 × 10−4 mm−1 to 55 × 10−4 mm−1 and −21 × 10−4 mm−1, respectively, with the increase of laser energy, which is consistent with the experimental trend. So, when either the stress gradient mechanism (SGM) or the shock bending mechanism (SBM) overwhelmingly dominated the forming process, the analytical model could give relatively accurate predicted curvatures compared with the experimental data. Under those conditions where SGM and SBM were comparable, the accuracy of the model was low, because of the complex stress distributions within the material, and the complex energy coupling process under these conditions. Full article
(This article belongs to the Special Issue Metal Forming and Forging)
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<p>Bending mechanisms of laser peen forming: (<b>a</b>) SGM (<b>b</b>) SBM.</p> Full article ">Figure 2
<p>An illustration of deformation scheme for convex bending in laser peen formation.</p> Full article ">Figure 3
<p>Schematic of concave deformation in laser shock forming. (<b>a</b>) polar coordinates (<b>b</b>) concave deformation.</p> Full article ">Figure 4
<p>Schematic of laser-induced shock wave pressure vs. time.</p> Full article ">Figure 5
<p>(<b>a</b>) Processing strategies of laser peen forming and (<b>b</b>) the typical results.</p> Full article ">Figure 6
<p>Geometrical schematic of a curvature.</p> Full article ">Figure 7
<p>Curvatures of 3 mm 2024 aluminum alloy vs. laser pulse energies.</p> Full article ">Figure 8
<p>Stresses measured along the depth of 3 mm target for laser energies of 4 J and 6 J.</p> Full article ">Figure 9
<p>Curvatures of 1 mm 2024 aluminum alloy vs. laser pulse energies.</p> Full article ">Figure 10
<p>Curvatures of 2 mm 2024 aluminum alloy vs. laser pulse energies: (<b>a</b>) experiment (<b>b</b>) analytical model.</p> Full article ">
13 pages, 1546 KiB  
Article
Characterization of GaAs Solar Cells under Supercontinuum Long-Time Illumination
by Nikola Papež, Rashid Dallaev, Pavel Kaspar, Dinara Sobola, Pavel Škarvada, Ştefan Ţălu, Shikhgasan Ramazanov and Alois Nebojsa
Materials 2021, 14(2), 461; https://doi.org/10.3390/ma14020461 - 19 Jan 2021
Cited by 8 | Viewed by 3427
Abstract
This work is dedicated to the description of the degradation of GaAs solar cells under continuous laser irradiation. Constant and strong exposure of the solar cell was performed over two months. Time-dependent electrical characteristics are presented. The structure of the solar cells was [...] Read more.
This work is dedicated to the description of the degradation of GaAs solar cells under continuous laser irradiation. Constant and strong exposure of the solar cell was performed over two months. Time-dependent electrical characteristics are presented. The structure of the solar cells was studied at the first and last stages of degradation test. The data from Raman spectroscopy, reflectometry, and secondary ion mass spectrometry confirm displacement of titanium and aluminum atoms. X-ray photoelectron spectroscopy showed a slight redistribution of oxygen bonds in the anti-corrosion coating. Full article
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<p>Light I–V curves from supercontinuum laser irradiation. In subfigure (<b>a</b>), I–V characteristics are indicated as maximum power points (MPPs). In subfigure (<b>b</b>), the power characteristics show a slight increase in performance may be observed during 42th day.</p> Full article ">Figure 2
<p>Dark I–V curves from supercontinuum laser irradiation in (<b>a</b>) semi-logarithmic and (<b>b</b>) loglog scale. Slight relaxation and improvement during 20 to 42th day is observed.</p> Full article ">Figure 3
<p>Raman spectroscopy from specimen processed by supercontinuum laser irradiation. Due to the height of the transverse-optical mode of GaAs, in order to preserve detail, the peak was plotted in a separate graph. Differences in relative intensities of AlAs phonons indicates possible displacements at As sites. Exposed area is measured after SL illumination of 67 days.</p> Full article ">Figure 4
<p>Reflectance measurement from supercontinuum laser irradiation. There is a significant change, especially in the near-infrared (NIR) region. These interference fringes indicate a differences in thin-films. Exposed area is measured after SL illumination of 67 days.</p> Full article ">Figure 5
<p>Wide X-ray Photoelectron Spectroscopy (XPS) spectra of exposed and unexposed area from supercontinuum laser irradiation. Four significant peaks are marked: O1s, C1s, Al2p, and Al2s. These regions were then examined in high resolution. Al2p and Al2s peaks are associated with thin anti-reflection layers.</p> Full article ">Figure 6
<p>High resolution of C1s region from XPS (<b>a</b>) before and (<b>b</b>) after SL irradiation of 67 days. Binding energy value for C − C is 284.6 eV, for C − O − C is 285.6 eV, and for O − C − O is 288.6 eV. An increase of last two mentioned bonds is visible.</p> Full article ">Figure 7
<p>High resolution of O1s region from XPS (<b>a</b>) before and (<b>b</b>) after SL irradiation of 67 days. Binding energy value for O − C is 531.7 eV, for metal oxide is 530.7 eV, and for O = C is 533 eV. It can be seen there is an increase in the exposed area, compared to the C1s region, where is a slight decrease.</p> Full article ">Figure 8
<p>High resolution of Al2p region from XPS (<b>a</b>) before and (<b>b</b>) after SL irradiation of 67 days. Binding energy value for Al<sup>3+</sup> is 74.1 eV and for Al<sup>x+</sup> is 74.6 eV. Displacement of the Al peak indicates the degradation of the thin layer.</p> Full article ">Figure 9
<p>High resolution of Al2s region from XPS (<b>a</b>) before and (<b>b</b>) after SL irradiation of 67 days. Binding energy value of deconvoluted oxidation states for Al<sup>3+</sup> is 119.1 eV and for Al<sup>x+</sup> is 119 eV. The relative change in energy is indicated by a difference in the structure composition of anti-reflection coating elements.</p> Full article ">Figure 10
<p>The whole etching process using SIMS in time dependence. The graph is in semi-logarithmic representation. The etched was exposed (illumination of 67 days, dashed line) and unexposed area. The graph is represented for a basic idea of the etching process where the etching depth was up to 8 <math display="inline"><semantics> <mi mathvariant="sans-serif">μ</mi> </semantics></math><math display="inline"><semantics> <mi mathvariant="normal">m</mi> </semantics></math>. On the contrary, the second graph in <a href="#materials-14-00461-f011" class="html-fig">Figure 11</a> is used to recognize the main differences in thin-films between the exposed and unexposed areas.</p> Full article ">Figure 11
<p>The first few etched tens of nanometers of the solar cell surface in detail using SIMS. The change in Al is especially visible. The difference is visible before and after illumination of 67 days.</p> Full article ">Figure 12
<p>Declared power spectral density from manufacturer of the SL.</p> Full article ">Figure 13
<p>Simplified model structure of the single-junction GaAs solar cell. Essential layers are GaAs/AlGaAs, which create a pn junction, where AlGaAs is only thin layer of 20 nm. An important function of protection and anti-reflection against the adverse effects performs <math display="inline"><semantics> <mrow> <msub> <mi>Al</mi> <mn>2</mn> </msub> <msub> <mi mathvariant="normal">O</mi> <mn>3</mn> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <msub> <mi>TiO</mi> <mn>2</mn> </msub> </semantics></math> thin-films.</p> Full article ">
24 pages, 2534 KiB  
Article
Stress-Based FEM in the Problem of Bending of Euler–Bernoulli and Timoshenko Beams Resting on Elastic Foundation
by Zdzisław Więckowski and Paulina Świątkiewicz
Materials 2021, 14(2), 460; https://doi.org/10.3390/ma14020460 - 19 Jan 2021
Cited by 7 | Viewed by 3071
Abstract
The stress-based finite element method is proposed to solve the static bending problem for the Euler–Bernoulli and Timoshenko models of an elastic beam. Two types of elements—with five and six degrees of freedom—are proposed. The elaborated elements reproduce the exact solution in the [...] Read more.
The stress-based finite element method is proposed to solve the static bending problem for the Euler–Bernoulli and Timoshenko models of an elastic beam. Two types of elements—with five and six degrees of freedom—are proposed. The elaborated elements reproduce the exact solution in the case of the piece-wise constant distributed loading. The proposed elements do not exhibit the shear locking phenomenon for the Timoshenko model. The influence of an elastic foundation of the Winkler type is also taken into consideration. The foundation response is approximated by the piece-wise constant and piece-wise linear functions in the cases of the five-degrees-of-freedom and six-degrees-of-freedom elements, respectively. An a posteriori estimation of the approximate solution error is found using the hypercircle method with the addition of the standard displacement-based finite element solution. Full article
(This article belongs to the Special Issue Modeling and Analysis of Static, Dynamic, and Thermal Behavior of Shell, Plate, and Beam Structures)
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<p>Equilibrium of bending moments and lateral forces at the interelement node.</p> Full article ">Figure 2
<p>Three-node, five-degrees-of-freedom stress-based beam element.</p> Full article ">Figure 3
<p>Stress-based beam element with two nodes and six degrees of freedom (2M2f).</p> Full article ">Figure 4
<p>Bending problem for the Timoshenko beam.</p> Full article ">Figure 5
<p>Comparison of section forces obtained by displacement-based models with the exact solution reproduced precisely by the equilibrium model.</p> Full article ">Figure 6
<p>Comparison of deflections at nodes and section forces at central points of elements.</p> Full article ">Figure 7
<p>Strain energy and solution error.</p> Full article ">Figure 8
<p>Beam on elastic foundation, problem definition.</p> Full article ">Figure 9
<p>(<b>Left diagrams</b>): the deflection, shear force, and bending moment, the exact solution. The approximation solution errors for the deflection, shear force, and bending moment obtained by the 2M1f element (<b>middle diagrams</b>), and the 2M2f and the displacement-based element 2d3r (<b>right diagrams</b>).</p> Full article ">Figure 10
<p>The lower and upper bounds for the strain energy (<b>left diagram</b>) and the errors of the approximate solutions (<b>right diagram</b>).</p> Full article ">Figure 11
<p>The reference solution: the deflection, shear force, and bending moment (<b>left diagrams</b>); comparison of these quantities obtained with 12 element meshes with the reference solution: for 2M1f, 3d2r, and 2d2r models (<b>right diagrams</b>). <math display="inline"><semantics> <mrow> <msub> <mi>K</mi> <mi>s</mi> </msub> <mo>=</mo> <mn>1.0714</mn> <mo>·</mo> <msup> <mn>10</mn> <mn>9</mn> </msup> </mrow> </semantics></math> N.</p> Full article ">Figure 12
<p>Comparison of errors for the deflections, shear forces and bending moments obtained with 12 element meshes: for 2d3r (<b>left diagrams</b>) and 2M2f (<b>right diagrams</b>). <math display="inline"><semantics> <mrow> <msub> <mi>K</mi> <mi>s</mi> </msub> <mo>=</mo> <mn>1.0714</mn> <mo>·</mo> <msup> <mn>10</mn> <mn>9</mn> </msup> </mrow> </semantics></math> N.</p> Full article ">Figure 13
<p>The strain energy and the errors of the approximate solutions in relations with the element length; <math display="inline"><semantics> <mrow> <msub> <mi>K</mi> <mi>s</mi> </msub> <mo>=</mo> <mn>1.0714</mn> <mo>·</mo> <msup> <mn>10</mn> <mn>9</mn> </msup> </mrow> </semantics></math> N.</p> Full article ">Figure 14
<p>The reference solution: the deflection, shear force and bending moment (<b>left diagrams</b>); comparison of these quantities obtained with 12 element meshes with the reference solution: for 2M1f, 3d2r and 2d2r models (<b>right diagrams</b>). <math display="inline"><semantics> <mrow> <msub> <mi>K</mi> <mi>s</mi> </msub> <mo>=</mo> <mn>0.2</mn> <mo>·</mo> <msup> <mn>10</mn> <mn>9</mn> </msup> </mrow> </semantics></math> N.</p> Full article ">Figure 15
<p>Comparison of errors for the deflections, shear forces and bending moments obtained with 12 element meshes: for 2d3r (<b>left diagrams</b>) and 2M2f (<b>right diagrams</b>). <math display="inline"><semantics> <mrow> <msub> <mi>K</mi> <mi>s</mi> </msub> <mo>=</mo> <mn>0.2</mn> <mo>·</mo> <msup> <mn>10</mn> <mn>9</mn> </msup> </mrow> </semantics></math> N.</p> Full article ">Figure 16
<p>The strain energy and the errors of the approximate solutions in relations with the element length; <math display="inline"><semantics> <mrow> <msub> <mi>K</mi> <mi>s</mi> </msub> <mo>=</mo> <mn>0.2</mn> <mo>·</mo> <msup> <mn>10</mn> <mn>9</mn> </msup> </mrow> </semantics></math> N.</p> Full article ">
13 pages, 2225 KiB  
Article
Structure of Plasma (re)Polymerized Polylactic Acid Films Fabricated by Plasma-Assisted Vapour Thermal Deposition
by Zdeněk Krtouš, Lenka Hanyková, Ivan Krakovský, Daniil Nikitin, Pavel Pleskunov, Ondřej Kylián, Jana Sedlaříková and Jaroslav Kousal
Materials 2021, 14(2), 459; https://doi.org/10.3390/ma14020459 - 19 Jan 2021
Cited by 6 | Viewed by 2374
Abstract
Plasma polymer films typically consist of very short fragments of the precursor molecules. That rather limits the applicability of most plasma polymerisation/plasma-enhanced chemical vapour deposition (PECVD) processes in cases where retention of longer molecular structures is desirable. Plasma-assisted vapour thermal deposition (PAVTD) circumvents [...] Read more.
Plasma polymer films typically consist of very short fragments of the precursor molecules. That rather limits the applicability of most plasma polymerisation/plasma-enhanced chemical vapour deposition (PECVD) processes in cases where retention of longer molecular structures is desirable. Plasma-assisted vapour thermal deposition (PAVTD) circumvents this limitation by using a classical bulk polymer as a high molecular weight “precursor”. As a model polymer in this study, polylactic acid (PLA) has been used. The resulting PLA-like films were characterised mostly by X-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR) spectroscopy. The molecular structure of the films was found to be tunable in a broad range: from the structures very similar to bulk PLA polymer to structures that are more typical for films prepared using PECVD. In all cases, PLA-like groups are at least partially preserved. A simplified model of the PAVTD process chemistry was proposed and found to describe well the observed composition of the films. The structure of the PLA-like films demonstrates the ability of plasma-assisted vapour thermal deposition to bridge the typical gap between the classical and plasma polymers. Full article
(This article belongs to the Special Issue Innovative Plasma-Based Deposition Techniques for the Production of Functional Materials)
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<p>(<b>a</b>) Experimental set-up used for PAVTD of PLA-like coatings and (<b>b</b>) chemical structure of conventional PLA with the assignment of C, O and H that corresponds to different spectral peaks detectable by XP) and NMR, respectively.</p> Full article ">Figure 2
<p>Variation of the O/C ratio in the PLA-lie films as a function of plasma power. O/C ratio of original PLA, PLA evaporated with plasma switched off (0 W) and range of O/C ratios reachable by the PECVD technique according to [<a href="#B31-materials-14-00459" class="html-bibr">31</a>,<a href="#B33-materials-14-00459" class="html-bibr">33</a>] are provided for comparison.</p> Full article ">Figure 3
<p>High-resolution spectra of C 1s and O 1s peaks for evaporated PLA (0 W) and PLA-like films deposited at 10 W, 30 W and 100 W (normalised). Red: C=O (C2/O2 in <a href="#materials-14-00459-f001" class="html-fig">Figure 1</a>b); Blue: O–(C=O)–C (C3/O1 in <a href="#materials-14-00459-f001" class="html-fig">Figure 1</a>b); Green: C–C (C1 in <a href="#materials-14-00459-f001" class="html-fig">Figure 1</a>b); Black: C–O–C ether (not present in original PLA). For details of the fitting, see <a href="#app1-materials-14-00459" class="html-app">Supplementary Information Figure S3</a>.</p> Full article ">Figure 4
<p>Dependence of the fraction of (<b>a</b>) carbon- and (<b>b</b>) oxygen-containing functional groups on discharge power. All corresponding XPS spectra of C 1s and O 1s XPS peaks are provided as <a href="#app1-materials-14-00459" class="html-app">Supporting Information Figure S3</a>.</p> Full article ">Figure 5
<p><b>(a</b>) <sup>1</sup>H NMR spectra of PLA, evaporated PLA (0 W) and PLA-like coatings deposited by PAVTD of PLA at various discharge powers (<b>b</b>) changes in the composition of the films with the discharge power.</p> Full article ">Figure 6
<p>The fraction of carbon atoms bonded in different chemical groups in dependence on the discharge power as measured by XPS and NMR.</p> Full article ">Figure 7
<p>Proposed simplified reaction scheme of plasma polymerisation during the PAVTD deposition of PLA.</p> Full article ">Figure 8
<p>(<b>a</b>) Comparison of a model of PAVTD of PLA with experimental data. (<b>b</b>) Comparison of the evolution of the average length of undisturbed PLA units with discharge power and experimentally obtained data according to Equation (1).</p> Full article ">
21 pages, 33034 KiB  
Article
Development of Bacterial Cellulose Biocomposites Combined with Starch and Collagen and Evaluation of Their Properties
by Silmar Baptista Nunes, Katharine Valéria Saraiva Hodel, Giulia da Costa Sacramento, Pollyana da Silva Melo, Fernando Luiz Pellegrini Pessoa, Josiane Dantas Viana Barbosa, Roberto Badaró and Bruna Aparecida Souza Machado
Materials 2021, 14(2), 458; https://doi.org/10.3390/ma14020458 - 19 Jan 2021
Cited by 12 | Viewed by 3414
Abstract
One of the major benefits of biomedicine is the use of biocomposites as wound dressings to help improve the treatment of injuries. Therefore, the main objective of this study was to develop and characterize biocomposites based on bacterial cellulose (BC) with different concentrations [...] Read more.
One of the major benefits of biomedicine is the use of biocomposites as wound dressings to help improve the treatment of injuries. Therefore, the main objective of this study was to develop and characterize biocomposites based on bacterial cellulose (BC) with different concentrations of collagen and starch and characterize their thermal, morphological, mechanical, physical, and barrier properties. In total, nine samples were produced with fixed amounts of glycerol and BC and variations in the amount of collagen and starch. The water activity (0.400–0.480), water solubility (12.94–69.7%), moisture (10.75–20.60%), thickness (0.04–0.11 mm), water vapor permeability (5.59–14.06 × 10−8 g·mm/m2·h·Pa), grammage (8.91–39.58 g·cm−2), opacity (8.37–36.67 Abs 600 nm·mm−1), elongation (4.81–169.54%), and tensile strength (0.99–16.32 MPa) were evaluated and defined. In addition, scanning electron microscopy showed that adding biopolymers in the cellulose matrix made the surface compact, which also influenced the visual appearance. Thus, the performance of the biocomposites was directly influenced by their composition. The performance of the different samples obtained resulted in them having different potentials for application considering the injury type. This provides a solution for the ineffectiveness of traditional dressings, which is one of the great problems of the biomedical sector. Full article
(This article belongs to the Special Issue Advanced Biomaterials for Medical Applications)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>The main steps of the methodology used for bacterial cellulose (BC) and BC–collagen–starch biocomposite production and characterization. Created via <a href="http://BioRender.com" target="_blank">BioRender.com</a>.</p> Full article ">Figure 2
<p>Visual appearance of the pure bacterial cellulose (BC; control) and BC–collagen–starch biocomposites. (<b>a</b>) F1, (<b>b</b>) F2, (<b>c</b>) F3, (<b>d</b>) F4, (<b>e</b>) F5, (<b>f</b>) F6, (<b>g</b>) F7, (<b>h</b>) F8, and (<b>i</b>) F9.</p> Full article ">Figure 3
<p>Physical and barrier properties of pure bacterial cellulose (BC, F1) and BC–collagen–starch biocomposites (F2–F9). (<b>a</b>) Water activity (a<sub>w</sub>) content; (<b>b</b>) Water solubility; (<b>c</b>) Moisture content; (<b>d</b>) Total solids content; (<b>e</b>) Thickness; (<b>f</b>) Water vapor permeability; (<b>g</b>) Grammage and (<b>h</b>) Opacity. Bars followed by the same letters were not significantly different at <span class="html-italic">p</span> &lt; 0.05 according to Tukey’s test with 95% confidence.</p> Full article ">Figure 4
<p>Characterization of pure bacterial cellulose (BC,F1) and BC–collagen–starch biocomposites (F2–F9). (<b>a</b>) Swelling rate and (<b>b</b>) water retention rate.</p> Full article ">Figure 5
<p>Mechanical properties of pure bacterial cellulose (BC,F1) and BC–collagen–starch biocomposites (F2–F9). (<b>a</b>) Elongation (%) and (<b>b</b>) tensile strength (MPa).</p> Full article ">Figure 6
<p>Scanning electron microscopy (SEM) surface micrographs of the surfaces of the pure bacterial cellulose (BC, F1) and BC–collagen–starch biocomposite (F2–F9). (<b>a</b>) F1, (<b>b</b>) F2, (<b>c</b>) F3, (<b>d</b>) F4, (<b>e</b>) F5, (<b>f</b>) F6, (<b>g</b>) F7, (<b>h</b>) F8, and (<b>i</b>) F9.</p> Full article ">Figure 7
<p>Thermal analysis of pure bacterial cellulose (BC,F1) and BC–collagen–starch biocomposites (F2–F9). (<b>a</b>) Thermogravimetric analysis (TGA) and (<b>b</b>) differential thermogravimetry (DTG).</p> Full article ">Figure 8
<p>Scores scatter plot by principal component analysis of pure bacterial cellulose (BC,F1) and BC–collagen–starch biocomposites (F2–F9).</p> Full article ">
12 pages, 6739 KiB  
Article
Gravity-Driven Separation of Oil/Water Mixture by Porous Ceramic Membranes with Desired Surface Wettability
by Chunlei Ren, Wufeng Chen, Chusheng Chen, Louis Winnubst and Lifeng Yan
Materials 2021, 14(2), 457; https://doi.org/10.3390/ma14020457 - 19 Jan 2021
Cited by 10 | Viewed by 2900
Abstract
Porous Al2O3 membranes were prepared through a phase-inversion tape casting/sintering method. The alumina membranes were embedded with finger-like pores perpendicular to the membrane surface. Bare alumina membranes are naturally hydrophilic and underwater oleophobic, while fluoroalkylsilane (FAS)-grafted membranes are hydrophobic and [...] Read more.
Porous Al2O3 membranes were prepared through a phase-inversion tape casting/sintering method. The alumina membranes were embedded with finger-like pores perpendicular to the membrane surface. Bare alumina membranes are naturally hydrophilic and underwater oleophobic, while fluoroalkylsilane (FAS)-grafted membranes are hydrophobic and oleophilic. The coupling of FAS molecules on alumina surfaces was confirmed by Thermogravimetric Analysis and X-ray Photoelectron Spectroscopy measurements. The hydrophobic membranes exhibited desired thermal stability and were super durable when exposed to air. Both membranes can be used for gravity-driven oil/water separation, which is highly cost-effective. The as-calculated separation efficiency (R) was above 99% for the FAS-grafted alumina membrane. Due to the excellent oil/water separation performance and good chemical stability, the porous ceramic membranes display potential for practical applications. Full article
(This article belongs to the Section Materials Chemistry)
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<p>(<b>a</b>) Schematic illustration of the tape casting method, (<b>b</b>) alumina green tape after phase-inversion and drying, and (<b>c</b>) green samples after cutting.</p> Full article ">Figure 2
<p>Scanning electron microscope (SEM) images of the as-prepared alumina membrane. (<b>a</b>) Cross-section before polishing, (<b>b</b>) cross-section after polishing, (<b>c</b>) top surface, and (<b>d</b>) bottom surface.</p> Full article ">Figure 3
<p>Wetting behavior of water and oil on alumina membranes (top surface). (<b>a</b>) Droplets of water (dyed blue, 50 μL) and oil (octane, dyed red, 50 μL) on a bare alumina membrane. (Inset) A photograph of an oil droplet (octane, 5 μL) underwater on a bare alumina membrane. (<b>b</b>) Droplets of water (dyed blue) and oil (octane, dyed red) on a fluoroalkylsilane (FAS)-grafted alumina membrane.</p> Full article ">Figure 4
<p>(<b>a</b>) Illustration of the calculation of theoretical water intrusion pressure of FAS-grafted membrane. <span class="html-italic">θ<sub>w</sub></span> and <span class="html-italic">θ</span><sub>0</sub> are the apparent water contact angle on a porous hydrophobic surface and a flat hydrophobic surface, respectively. (<b>b</b>) Photographs of a water droplet (5 μL) on the as-prepared porous hydrophobic surface (polished, FAS-grafted) and flat hydrophobic surface (unpolished, FAS-grafted). <span class="html-italic">θ<sub>w</sub></span> was ~146° and <span class="html-italic">θ</span><sub>0</sub> was ~131° in our case.</p> Full article ">Figure 5
<p>DRIFTS spectrum of the alumina powders before and after grafting with FAS.</p> Full article ">Figure 6
<p>TG analysis of the alumina powder without grafting and the FAS-grafted alumina powder at different times. G1-24 h, G2-48 h, and G3-72 h, respectively.</p> Full article ">Figure 7
<p>Change of water contact angle of FAS-grafted alumina membrane after exposure to air, water, and ethanol, respectively, as a function of exposure time (days).</p> Full article ">Figure 8
<p>XPS spectra of F 1s on FAS-grafted alumina membrane before and after ultrasonic cleaning in ethanol.</p> Full article ">Figure 9
<p>Schematic setup for the octane or water permeation tests.</p> Full article ">Figure 10
<p>Water and octane flux of (<b>a</b>) a bare alumina membrane and (<b>b</b>) a FAS-grafted alumina membrane.</p> Full article ">Figure 11
<p>Oil/water separation equipment. (<b>a</b>) Octane/water mixture (30/70 <span class="html-italic">v</span>/<span class="html-italic">v</span>) above a porous alumina membrane and water was poured into the beaker. (<b>b</b>) Water selectively permeated through the bare membrane, while the octane was repelled and remained in the upper glass tube. (<b>c</b>) Separation of octane/water mixture (70/30 <span class="html-italic">v</span>/<span class="html-italic">v</span>) using the FAS-grafted membrane; octane easily passed through the membrane and flowed into a beaker. (<b>d</b>) Water was repelled by the FAS-grafted membrane and flowed into another beaker.</p> Full article ">
14 pages, 8531 KiB  
Article
Microstructure and Mechanical Properties of Laser-Welded DP Steels Used in the Automotive Industry
by Hanbing He, Farnoosh Forouzan, Joerg Volpp, Stephanie M. Robertson and Esa Vuorinen
Materials 2021, 14(2), 456; https://doi.org/10.3390/ma14020456 - 19 Jan 2021
Cited by 18 | Viewed by 3949
Abstract
The aim of this work was to investigate the microstructure and the mechanical properties of laser-welded joints combined of Dual Phase DP800 and DP1000 high strength thin steel sheets. Microstructural and hardness measurements as well as tensile and fatigue tests have been carried [...] Read more.
The aim of this work was to investigate the microstructure and the mechanical properties of laser-welded joints combined of Dual Phase DP800 and DP1000 high strength thin steel sheets. Microstructural and hardness measurements as well as tensile and fatigue tests have been carried out. The welded joints (WJ) comprised of similar/dissimilar steels with similar/dissimilar thickness were consisted of different zones and exhibited similar microstructural characteristics. The trend of microhardness for all WJs was consistent, characterized by the highest value at hardening zone (HZ) and lowest at softening zone (SZ). The degree of softening was 20 and 8% for the DP1000 and DP800 WJ, respectively, and the size of SZ was wider in the WJ combinations of DP1000 than DP800. The tensile test fractures were located at the base material (BM) for all DP800 weldments, while the fractures occurred at the fusion zone (FZ) for the weldments with DP1000 and those with dissimilar sheet thicknesses. The DP800-DP1000 weldment presented similar yield strength (YS, 747 MPa) and ultimate tensile strength (UTS, 858 MPa) values but lower elongation (EI, 5.1%) in comparison with the DP800-DP800 weldment (YS 701 MPa, UTS 868 MPa, EI 7.9%), which showed similar strength properties as the BM of DP800. However, the EI of DP1000-DP1000 weldment was 1.9%, much lower in comparison with the BM of DP1000. The DP800-DP1000 weldment with dissimilar thicknesses showed the highest YS (955 MPa) and UTS (1075 MPa) values compared with the other weldments, but with the lowest EI (1.2%). The fatigue fractures occurred at the WJ for all types of weldments. The DP800-DP800 weldment had the highest fatigue limit (348 MPa) and DP800-DP1000 with dissimilar thicknesses had the lowest fatigue limit (<200 MPa). The fatigue crack initiated from the weld surface. Full article
(This article belongs to the Special Issue Advances in Laser Processing)
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<p>Setup for the laser welding experiments of tubes showing the large view with all components (<b>left</b>) and the detailed view of the clamped work piece (<b>right</b>).</p> Full article ">Figure 2
<p>(<b>a</b>) Top view of a laser-welded joint on tubes with dissimilar materials; (<b>b</b>) Welding sequence visualization.</p> Full article ">Figure 3
<p>Dimensions of test specimens for tensile- and fatigue-tests, with welds in the center of L-gauge.</p> Full article ">Figure 4
<p>Crosssections of the different types of WJs. (<b>a</b>) DP800/1.3-DP800/1.3; (<b>b</b>) DP1000/1.3-DP1000/1.3; (<b>c</b>) DP800/1.3-DP1000/1.3; (<b>d</b>) DP800/2.1-DP800/2.1; (<b>e</b>) DP800/2.1-DP1000/1.3.</p> Full article ">Figure 5
<p>(<b>a</b>) Different zones in DP800/1.3-DP800/1.3 WJ, and (<b>b</b>) microhardness across the different zones.</p> Full article ">Figure 6
<p>Measurement points of microhardness at the welded joints across the BM, SZ, HZ and FZ. BM: base metal, SZ: softening zone, HZ: hardening zone, and FZ: fusion zone.</p> Full article ">Figure 7
<p>Optical microscope images of WJ (<b>a</b>), BM (<b>b</b>), SZ (<b>c</b>), HZ (<b>d</b>) and FZ (<b>e</b>) in the DP800/1.3-DP800/1.3 WJ.</p> Full article ">Figure 8
<p>Optical microscope images of WJ (<b>a</b>), BM (<b>b</b>), SZ (<b>c</b>), HZ (<b>d</b>) and FZ (<b>e</b>) in the DP1000/1.3-DP1000/1.3 WJ.</p> Full article ">Figure 9
<p>Stress-strain curves of the tensile tested weldments.</p> Full article ">Figure 10
<p>Fatigue test results of the welded DP800/1.3, DP800/2.1, DP1000/1.3, DP1000/1.3-DP800/1.3 and DP800/2.1-DP1000/1.3 samples, tested at R = 0.1, 20 Hz, and RT.</p> Full article ">Figure 11
<p>Typical fatigue failure locations.</p> Full article ">Figure 12
<p>SEM images of the fatigue fracture surface of a DP800/1.3-DP800/1.3 weldment under the maximum stress of 626 MPa. (<b>a</b>) Overall morphology of fatigue fracture, (<b>b</b>) crack initiation region, (<b>c</b>) crack propagation region, and (<b>d</b>) final fast crack propagation region.</p> Full article ">Figure 13
<p>SEM images of a fatigue fracture surface of a DP1000/1.3-DP1000/1.3 weldment under stress 282 MPa. (<b>a</b>) Overall morphology of the fatigue fracture, (<b>b</b>) crack initiation region, (<b>c</b>) crack propagation region, and (<b>d</b>) final fast crack propagation region.</p> Full article ">
12 pages, 2187 KiB  
Article
Enhancement of Gingival Tissue Adherence of Zirconia Implant Posts: In Vitro Study
by Alexandra Zühlke, Michael Gasik, Khalil Shahramian, Timo Närhi, Yevgen Bilotsky and Ilkka Kangasniemi
Materials 2021, 14(2), 455; https://doi.org/10.3390/ma14020455 - 19 Jan 2021
Cited by 7 | Viewed by 2529
Abstract
Prevention of bacterial inflammation around dental implants (peri-implantitis) is one of the keys to success of the implantation and can be achieved by securing the gingival tissue-abutment interface preventing penetration of bacteria. Modern dental practice has adopted zirconia abutments in place of titanium, [...] Read more.
Prevention of bacterial inflammation around dental implants (peri-implantitis) is one of the keys to success of the implantation and can be achieved by securing the gingival tissue-abutment interface preventing penetration of bacteria. Modern dental practice has adopted zirconia abutments in place of titanium, but the adhesion of gingival tissue to zirconia is inferior to titanium. The aim of this study was to assess and improve the adhesion of mucosal tissues to zirconia posts using sol-gel derived TiO2 coating following dynamic mechanical testing. The posts were cultivated with porcine bone-gingival tissue specimens in vitro for 7 and 14 days and then subjected to dynamic mechanical analysis simulating physiological loading at 1 Hz up to 50 μm amplitude. In parallel in silico analysis of stresses and strains have been made simulating “the worst case” when the fixture fails in osseointegration while the abutment still holds. Results show treatment of zirconia can lead to double interface stiffness (static shear stiffness values from 5–10 to 17–23 kPa and dynamic from 20–50 to 60–125 kPa), invariant viscostiffness (from 5–35 to 45–90 kPa·sα) and material memory values (increased from 0.06–0.10 to 0.17–0.25), which is beneficial in preventing bacterial contamination in dental implants. This suggests TiO2-coated zirconia abutments may have a significant clinical benefit for prevention of the bacterial contamination. Full article
(This article belongs to the Special Issue Translational Research on Dental Materials)
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<p>Experimental setup: (<b>a</b>) arrangement of the abutment post and tissues for cultivation; (<b>b</b>) mechanical setup of the specimen in the dynamic mechanical analysis (DMA) sample holder; (<b>c</b>) photo of the actual specimen in the sample holder.</p> Full article ">Figure 2
<p>The median differences for two comparisons (static and dynamic stiffness) are shown in the above Cumming estimation plot. The raw data are plotted on the upper axes; each mean difference is plotted on the lower axes as a bootstrap sampling distribution. Mean differences are depicted as dots; 95% confidence intervals are indicated by the ends of the vertical error bars.</p> Full article ">Figure 3
<p>Data on dynamic viscostiffness and memory values for treated (coated) and control (uncoated) posts.</p> Full article ">Figure 4
<p>The Cohen’s d-value between control (uncoated) and treated (coated) samples viscostiffness (kPa·s<sup>α</sup>) shown in the Gardner–Altman estimation plot. Both groups are plotted on the left axes; the mean difference is plotted on floating axes on the right as a bootstrap sampling distribution. The mean difference is depicted as a dot; the 95% confidence interval is indicated by the ends of the vertical error bar.</p> Full article ">Figure 5
<p>Snapshot of the simulation at 180 s from test start time with vertical loading along the Z–axis on the post surface (the post is not shown). Color scale shows shear stress τ<sub>RZ</sub> and color contours third principal logarithmic (true) strain ε<sub>3</sub>. It is seen that most of the strain and stress accumulate at the top and the bottom of the post.</p> Full article ">Figure 6
<p>Pressure in the gingival tissue along the post interface. Color scale indicated respective times from the start of the experiment.</p> Full article ">Figure 7
<p>Shear stress τ<sub>RZ</sub> in the gingival tissue along the post interface. Color scale indicated respective times from the start of the experiment.</p> Full article ">
16 pages, 12794 KiB  
Article
Material Model Development of Magnesium Alloy and Its Strength Evaluation
by Wenjia Huang, Ninshu Ma, Yunwu Ma, Toshiro Amaishi, Kenji Takada and Takayuki Hama
Materials 2021, 14(2), 454; https://doi.org/10.3390/ma14020454 - 19 Jan 2021
Cited by 3 | Viewed by 2692
Abstract
A new material model of magnesium alloys, combining both Hill’48 yield function and Cazacu’06 yield function, was developed and programmed into LS-DYNA using user subroutine, in which both slip dominant and twinning/untwinning dominant hardening phenomena were included. First, a cyclic load test was [...] Read more.
A new material model of magnesium alloys, combining both Hill’48 yield function and Cazacu’06 yield function, was developed and programmed into LS-DYNA using user subroutine, in which both slip dominant and twinning/untwinning dominant hardening phenomena were included. First, a cyclic load test was performed, and its finite element analysis was carried out to verify the new material model. Then, the deformation behaviors of the magnesium crash box subjected to the compressive impact loading were investigated using the developed material model. Compared with the experimental results, the new material model accurately predicted the deformation characteristics of magnesium alloy parts. Additionally, the effect of the thickness distribution, initial deflection and contact friction coefficient in simulation models on deformation behaviors were investigated using this validated material model. Full article
(This article belongs to the Special Issue Assessment of Metallurgical and Mechanical Properties of Welded Joints via Numerical Simulation and Experiments)
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<p>Asymmetry of stress-strain curves: (<b>a</b>) tension to compression; (<b>b</b>) compression to tension.</p> Full article ">Figure 2
<p>Validation of the newly implemented material model: (<b>a</b>) normalized yield surface; (<b>b</b>) cyclic stress-strain history.</p> Full article ">Figure 3
<p>Dimensions of crash box.</p> Full article ">Figure 4
<p>Experiment device and results: (<b>a</b>) loading device; (<b>b</b>) deformed crash box; (<b>c</b>) reaction force verse stroke curves.</p> Full article ">Figure 5
<p>FEA model of the crash box: (<b>a</b>) Isometric view; (<b>b</b>) front view.</p> Full article ">Figure 6
<p>Thickness measurement: (<b>a</b>) physical image of the test piece; (<b>b</b>) locations of the measured points.</p> Full article ">Figure 7
<p>Results with different values for <math display="inline"><semantics> <mi>β</mi> </semantics></math>.</p> Full article ">Figure 8
<p>Results with different values for C.</p> Full article ">Figure 9
<p>Input stress–strain (SS) curves for slip deformation and twinning deformation.</p> Full article ">Figure 10
<p>Von Mises effective stress: (<b>a</b>) standard model; (<b>b</b>) designed model.</p> Full article ">Figure 11
<p>Effective plastic strain: (<b>a</b>) standard model; (<b>b</b>) designed model.</p> Full article ">Figure 12
<p>Experiment result: (<b>a</b>) deformation mode; (<b>b</b>) force-stroke curves.</p> Full article ">Figure 13
<p>Deformation modes under different wall thickness: (<b>a</b>) 2.00 mm; (<b>b</b>) 1.96 mm; (<b>c</b>) 1.90 mm; (<b>d</b>) 1.80 mm.</p> Full article ">Figure 14
<p>Force-stroke curves under different wall thickness.</p> Full article ">Figure 15
<p>Comparison of slide degree under different friction condition: (<b>a</b>) = 0.05; (<b>b</b>) = 0.10; (<b>c</b>) = 0.20.</p> Full article ">Figure 16
<p>Force-stroke cruves under different friction conditions.</p> Full article ">Figure 17
<p>Two types of initial deflection: (<b>a</b>) arched type; (<b>b</b>) wavy type.</p> Full article ">Figure 18
<p>Simulation results: (<b>a</b>) Von-Mises (V-M) effective stress of type 1; (<b>b</b>) effective plastic strain of type 1; (<b>c</b>) V-M effective stress of type 2; (<b>d</b>) effective plastic strain of type 2.</p> Full article ">Figure 19
<p>Force-stroke curves under different types.</p> Full article ">
11 pages, 3418 KiB  
Article
Impact of Zr-Doped Bi2O3 Radiopacifier by Spray Pyrolysis on Mineral Trioxide Aggregate
by Tzu-Yu Peng, May-Show Chen, Ya-Yi Chen, Yao-Jui Chen, Chin-Yi Chen, Alex Fang, Bo-Jiun Shao, Min-Hua Chen and Chung-Kwei Lin
Materials 2021, 14(2), 453; https://doi.org/10.3390/ma14020453 - 19 Jan 2021
Cited by 3 | Viewed by 2492
Abstract
Mineral trioxide aggregates (MTA) have been developed as a dental root repair material for a range of endodontics procedures. They contain a small amount of bismuth oxide (Bi2O3) as a radiopacifier to differentiate adjacent bone tissue on radiographs for [...] Read more.
Mineral trioxide aggregates (MTA) have been developed as a dental root repair material for a range of endodontics procedures. They contain a small amount of bismuth oxide (Bi2O3) as a radiopacifier to differentiate adjacent bone tissue on radiographs for endodontic surgery. However, the addition of Bi2O3 to MTA will increase porosity and lead to the deterioration of MTA’s mechanical properties. Besides, Bi2O3 can also increase the setting time of MTA. To improve upon the undesirable effects caused by Bi2O3 additives, we used zirconium ions (Zr) to substitute the bismuth ions (Bi) in the Bi2O3 compound. Here we demonstrate a new composition of Zr-doped Bi2O3 using spray pyrolysis, a technique for producing fine solid particles. The results showed that Zr ions were doped into the Bi2O3 compound, resulting in the phase of Bi7.38Zr0.62O12.31. The results of materials analysis showed Bi2O3 with 15 mol % of Zr doping increased its radiopacity (5.16 ± 0.2 mm Al) and mechanical strength, compared to Bi2O3 and other ratios of Zr-doped Bi2O3. To our knowledge, this is the first study of fabrication and analysis of Zr-doped Bi2O3 radiopacifiers through the spray pyrolysis procedure. The study reveals that spray pyrolysis can be a new technique for preparing Zr-doped Bi2O3 radiopacifiers for future dental applications. Full article
(This article belongs to the Special Issue Advances in Dental Composite Materials and Biomaterials)
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<p>Characterization of Bi<sub>2</sub>O<sub>3</sub> particles. (<b>a</b>) XRD pattern; and (<b>b</b>) TGA/ DTA analysis.</p> Full article ">Figure 2
<p>Characterization of Bi<sub>2</sub>O<sub>3</sub> particles. (<b>a</b>,<b>b</b>) TEM images; (<b>c</b>) crystal lattice planes; and (<b>d</b>) the diffraction pattern.</p> Full article ">Figure 3
<p>XRD patterns of Bi<sub>2</sub>O<sub>3</sub>; Zr (10 mol %): Bi<sub>2</sub>O<sub>3</sub>; Zr (15 mol %): Bi<sub>2</sub>O<sub>3</sub>; and Zr (20 mol %): Bi<sub>2</sub>O<sub>3</sub>.</p> Full article ">Figure 4
<p>SEM images of (<b>a</b>) Bi<sub>2</sub>O<sub>3</sub>; (<b>b</b>) Zr (10 mol %): Bi<sub>2</sub>O<sub>3</sub>; (<b>c</b>) Zr (15 mol %): Bi<sub>2</sub>O<sub>3</sub>; and (<b>d</b>) Zr (20 mol %): Bi<sub>2</sub>O<sub>3</sub>.</p> Full article ">Figure 5
<p>Characterization of Zr (15 mol %): Bi<sub>2</sub>O<sub>3</sub> particles. (<b>a</b>,<b>b</b>) TEM images; (<b>c</b>) crystal lattice planes; and (<b>d</b>) the diffraction pattern.</p> Full article ">Figure 6
<p>The radiopacity of Portland cement (PC) mixed with different Zr-doping ratios of Bi<sub>2</sub>O<sub>3</sub> particles. (<span class="html-italic">n</span> = 5, * <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01).</p> Full article ">Figure 7
<p>Diametral tensile strengths of PC mixed with different Zr-doping ratios of Bi<sub>2</sub>O<sub>3</sub> particles. (<span class="html-italic">n</span> = 5, ** <span class="html-italic">p</span> &lt; 0.01).</p> Full article ">Figure 8
<p>(<b>a</b>) Initial setting time; and (<b>b</b>) final setting time of PC mixed with spray pyrolysis-derived of Bi<sub>2</sub>O<sub>3</sub> and Zr-doped Bi<sub>2</sub>O<sub>3</sub> particles. Bi<sub>2</sub>O<sub>3</sub>* represents the sample from commercial sol-gel derived Bi<sub>2</sub>O<sub>3</sub> powder. (<span class="html-italic">n</span> = 12, * <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01).</p> Full article ">
22 pages, 56259 KiB  
Article
Evaluation Method of the Vibration Reduction Effect Considering the Real Load- and Frequency-Dependent Stiffness of Slab-Track Mats
by Zeming Zhao, Kai Wei, Wenhao Ding, Fang Cheng and Ping Wang
Materials 2021, 14(2), 452; https://doi.org/10.3390/ma14020452 - 18 Jan 2021
Cited by 9 | Viewed by 2381
Abstract
The purpose of this research was to investigate and improve the accuracy of the existing slab-track mat (STM) specifications in the evaluation of the vibration reduction effect. The static nonlinearity and dynamic mechanical characteristics of three types of STMs were tested, and then [...] Read more.
The purpose of this research was to investigate and improve the accuracy of the existing slab-track mat (STM) specifications in the evaluation of the vibration reduction effect. The static nonlinearity and dynamic mechanical characteristics of three types of STMs were tested, and then a modified fractional derivative Poynting–Thomson (FDPT) model was used to characterize the preload and frequency dependence. A modified vehicle–floating slab track (FST) coupled dynamic model was established to analyze the actual insertion loss. The insertion loss error evaluated by the frequency-dependent tangent stiffness increased with the increase in STM nonlinearity, and the error obtained by the third preload tangent stiffness was usually greater than that of the second preload. Compared with the secant stiffness, the second preload frequency-dependent tangent stiffness was more suitable for evaluating STMs with high-static–low-dynamics (HSLD) stiffness. In order to reflect the frequency dependence effect and facilitate engineering applications, it is recommended that second preload tangent stiffness corresponding to the natural frequency of the FST be used for evaluation. Furthermore, the insertion loss of the STMs with monotonically increased stiffness decreased as the axle load increased, and the opposite was true for the STMs with monotonically decreased stiffness. The vibration isolation efficiency of the STMs with HSLD stiffness was both stable and better than that of the STMs with monotonic stiffness. Full article
(This article belongs to the Section Construction and Building Materials)
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<p>Modified fractional derivative Poynting–Thomson (FDPT) model for slab-track mats (STMs).</p> Full article ">Figure 2
<p>Testing samples: (<b>a</b>) STM-I; (<b>b</b>) STM-II; (<b>c</b>) STM-III.</p> Full article ">Figure 3
<p>Dynamic test equipment system: (<b>a</b>) from left to right are the industrial personal computer, dynamic mechanical tester machine with a temperature control box, and hydraulic power pack; (<b>b</b>) from top to bottom are the supporting steel plate, STM, and loading steel plate.</p> Full article ">Figure 4
<p>Finite element model of the vehicle–floating slab track (FST).</p> Full article ">Figure 5
<p>Test and fitting results: (<b>a</b>) nonlinear force–displacement curve; (<b>b</b>) Nonlinear stiffness–force curve.</p> Full article ">Figure 6
<p>Dynamic hysteresis loop of (<b>a</b>) STM-I; (<b>b</b>) STM-II; (<b>c</b>) STM-III.</p> Full article ">Figure 7
<p>Test data and fitting result: dynamic storage stiffness of (<b>a</b>) STM-I; (<b>b</b>) STM-II; (<b>c</b>) STM-III.</p> Full article ">Figure 8
<p>Predicted storage stiffness of STMs under different frequencies and various preloads at 20 °C: (<b>a</b>) STM-I; (<b>b</b>) STM-II; (<b>c</b>) STM-III.</p> Full article ">Figure 9
<p>Vertical vehicle–damping pad floating slab track (DPFST) coupled dynamic model.</p> Full article ">Figure 10
<p>Vertical dynamic displacement: (<b>a</b>) rail; (<b>b</b>) slab in Cases 1–5.</p> Full article ">Figure 11
<p>Vertical vibration acceleration: (<b>a</b>) slab; (<b>b</b>) concrete base in Cases 1–5.</p> Full article ">Figure 12
<p>Vibration acceleration levels: (<b>a</b>) slab; (<b>b</b>) concrete base in Cases 1–5.</p> Full article ">Figure 13
<p>The supporting force of STM-I under (<b>a</b>) no load and (<b>b</b>) full load of the vehicle.</p> Full article ">Figure 14
<p>Vertical vibration acceleration: (<b>a</b>) slab; (<b>b</b>) concrete base in Cases 6–10.</p> Full article ">Figure 15
<p>Vibration acceleration levels: (<b>a</b>) slab; (<b>b</b>) concrete base in Cases 6–10.</p> Full article ">Figure 16
<p>Vertical vibration acceleration: (<b>a</b>) slab; (<b>b</b>) concrete base in Cases 11–15.</p> Full article ">Figure 17
<p>Vibration acceleration levels: (<b>a</b>) slab; (<b>b</b>) concrete base in Cases 11–15.</p> Full article ">Figure 18
<p>Vibration acceleration levels of the concrete base: (<b>a</b>) STM-I; (<b>b</b>) STM-II; (<b>c</b>) STM-III.</p> Full article ">
12 pages, 4041 KiB  
Article
Acousto-Optic Cells with Phased-Array Transducers and Their Application in Systems of Optical Information Processing
by Vladimir Balakshy, Maxim Kupreychik, Sergey Mantsevich and Vladimir Molchanov
Materials 2021, 14(2), 451; https://doi.org/10.3390/ma14020451 - 18 Jan 2021
Cited by 16 | Viewed by 3021
Abstract
This paper presents the results of theoretical and experimental studies of anisotropic acousto-optic interaction in a spatially periodical acoustic field created by a phased-array transducer with antiphase excitation of adjacent sections. In this case, contrary to the nonsectioned transducer, light diffraction is absent [...] Read more.
This paper presents the results of theoretical and experimental studies of anisotropic acousto-optic interaction in a spatially periodical acoustic field created by a phased-array transducer with antiphase excitation of adjacent sections. In this case, contrary to the nonsectioned transducer, light diffraction is absent when the optical beam falls on the phased-array cell at the Bragg angle. However, the diffraction takes place at some other angles (called “optimal” here), which are situated on the opposite sides to the Bragg angle. Our calculations show that the diffraction efficiency can reach 100% at these optimal angles in spite of a noticeable acousto-optic phase mismatch. This kind of acousto-optic interaction possesses a number of interesting regularities which can be useful for designing acousto-optic devices of a new type. Our experiments were performed with a paratellurite (TeO2) cell in which a shear acoustic mode was excited at a 9∘ angle to the crystal plane (001). The piezoelectric transducer had to nine antiphase sections. The efficiency of electric to acoustic power conversion was 99% at the maximum frequency response, and the ultrasound excitation band extended from 70 to 160 MHz. The experiments have confirmed basic results of the theoretical analysis. Full article
(This article belongs to the Special Issue Acousto-Optical Spectral Technologies)
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<p>Two variants of flat phased-array transducers with antiphase excitation of adjacent sections: (<b>a</b>) Sectioning by partitioning the internal and external electrodes; (<b>b</b>) Sectioning by means of transducer cuts.</p> Full article ">Figure 2
<p>Radiation patterns of four-sectioned (red line) and one-sectioned (green line) transducers.</p> Full article ">Figure 3
<p>Statement of the problem of acousto-optic (AO) interaction in the field of the phased-array transducer.</p> Full article ">Figure 4
<p>AO interaction in a paratellurite crystal: (<b>a</b>) Frequency dependencies of the Bragg angles in the case of light scattering in the +1st and –1st diffraction orders at different polarizations of incident optical radiation; (<b>b</b>) The area of AO interaction when the optical beam with extraordinary polarization diffracts into +1st order.</p> Full article ">Figure 5
<p>AO interaction areas for branch <span class="html-italic">+1e</span> in the case of <span class="html-italic">m</span> = 4 and different width of individual sections: (<b>a</b>) <span class="html-italic">l</span> = 0.4 mm; (<b>b</b>) <span class="html-italic">l</span> = 0.15 mm; (<b>c</b>) <span class="html-italic">l</span> = 0.11 mm; (<b>d</b>) <span class="html-italic">l</span> = 0.07 mm.</p> Full article ">Figure 6
<p>Characteristics of low-selective area shown in <a href="#materials-14-00451-f005" class="html-fig">Figure 5</a>c: (<b>a</b>) Operating frequency <math display="inline"> <semantics> <mrow> <msub> <mi>f</mi> <mn>0</mn> </msub> </mrow> </semantics> </math>, period of transducer structure <span class="html-italic">d</span> and figure of merit <span class="html-italic">M</span> as functions of crystal cut angle <math display="inline"> <semantics> <mi>χ</mi> </semantics> </math>; (<b>b</b>) Frequency characteristics of AO interaction at the operating frequency <math display="inline"> <semantics> <mrow> <msub> <mi>f</mi> <mn>0</mn> </msub> <mo>=</mo> <mn>21</mn> </mrow> </semantics> </math> MHz (<math display="inline"> <semantics> <mrow> <mi>χ</mi> <mo>=</mo> <mn>4</mn> <mo>°</mo> </mrow> </semantics> </math>).</p> Full article ">Figure 7
<p>AO interaction areas for branch <span class="html-italic">+1o</span> in the case of <span class="html-italic">m</span> = 4 and different width of individual sections: (<b>a</b>) <span class="html-italic">l</span> = 0.15 mm; (<b>b</b>) <span class="html-italic">l</span> = 0.07 mm.</p> Full article ">Figure 8
<p>Frequency dependences of optimal angles for branches <span class="html-italic">+1е</span> and <span class="html-italic">+1о</span>: calculation for (<b>a</b>) <span class="html-italic">d</span> = 0.22 mm, and (<b>b</b>) <span class="html-italic">d</span> = 0.2 mm.</p> Full article ">Figure 9
<p>AO deflector of nonpolarized light: (<b>a</b>) Combined areas of AO interaction for +<span class="html-italic">1e</span> (red color) and +<span class="html-italic">1o</span> (blue color) diffraction branches, the overlap area is shown by yellow color; (<b>b</b>) Frequency characteristics of the AO deflector in the case of unpolarized light.</p> Full article ">Figure 10
<p>Experimental results: (<b>a</b>) AO cell with a nine-section transducer; (<b>b</b>) Angular characteristics of the AO diffraction for different number of connected sections: <span class="html-italic">m</span> = 9 (red), 5 (blue) and 2 (green).</p> Full article ">
24 pages, 5466 KiB  
Article
Multi-Scale Analyses and Modeling of Metallic Nano-Layers
by Zara Moleinia and David F. Bahr
Materials 2021, 14(2), 450; https://doi.org/10.3390/ma14020450 - 18 Jan 2021
Cited by 2 | Viewed by 1899
Abstract
The current work centers on multi-scale approaches to simulate and predict metallic nano-layers’ thermomechanical responses in crystal plasticity large deformation finite element platforms. The study is divided into two major scales: nano- and homogenized levels where Cu/Nb nano-layers are designated as case studies. [...] Read more.
The current work centers on multi-scale approaches to simulate and predict metallic nano-layers’ thermomechanical responses in crystal plasticity large deformation finite element platforms. The study is divided into two major scales: nano- and homogenized levels where Cu/Nb nano-layers are designated as case studies. At the nano-scale, a size-dependent constitutive model based on entropic kinetics is developed. A deep-learning adaptive boosting technique named single layer calibration is established to acquire associated constitutive parameters through a single process applicable to a broad range of setups entirely different from those of the calibration. The model is validated through experimental data with solid agreement followed by the behavioral predictions of multiple cases regarding size, loading pattern, layer type, and geometrical combination effects for which the performances are discussed. At the homogenized scale, founded on statistical analyses of microcanonical ensembles, a homogenized crystal plasticity-based constitutive model is developed with the aim of expediting while retaining the accuracy of computational processes. Accordingly, effective constitutive functionals are realized where the associated constants are obtained via metaheuristic genetic algorithms. The model is favorably verified with nano-scale data while accelerating the computational processes by several orders of magnitude. Ultimately, a temperature-dependent homogenized constitutive model is developed where the effective constitutive functionals along with the associated constants are determined. The model is validated by experimental data with which multiple demonstrations of temperature effects are assessed and analyzed. Full article
(This article belongs to the Section Materials Simulation and Design)
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Graphical abstract
Full article ">Figure 1
<p>Demonstration of adaptive boosting technique where base classifiers with simple thresholds are trained according to the assigned weighted function acquired relative to the precision of the previous classifier in data allocation. Each sample shows the number of classifiers, <span class="html-italic">m</span>, trained up to that point. The solid and dashed lines in the domains are the decision made and revised choices, respectively, based on the weight of the misplaced data illustrated with expanded boundaries.</p> Full article ">Figure 2
<p>Schematic representation of a microcanonical ensemble with equal probability of state, <math display="inline"><semantics> <msub> <mi>p</mi> <mi>i</mi> </msub> </semantics></math>, and energy, <math display="inline"><semantics> <msub> <mi>E</mi> <mi>i</mi> </msub> </semantics></math>, of each subsystem in the total volume, <math display="inline"><semantics> <mo>Λ</mo> </semantics></math>, with the average velocity of <math display="inline"><semantics> <mrow> <mo>〈</mo> <mi mathvariant="bold">v</mi> <mo>〉</mo> </mrow> </semantics></math> and energy <span class="html-italic">U</span>.</p> Full article ">Figure 3
<p>(<b>a</b>) A high resolution scanning electron microscopy image of a metallic nano-layer. (<b>b</b>) A generalized representative structure of a metallic nano-layer with <span class="html-italic">n</span> elements/layers. (<b>c</b>) A 3-dimensional Cu/Nb nano-layer unit cell discretized into (<b>d</b>) eight-node hexahedral elements with eight integration points and the local coordinate system of <math display="inline"><semantics> <mrow> <mo>(</mo> <mi>ξ</mi> <mspace width="0.222222em"/> <mo>,</mo> <mspace width="0.222222em"/> <mi>η</mi> <mspace width="0.222222em"/> <mo>,</mo> <mspace width="0.222222em"/> <mi>ζ</mi> <mo>)</mo> </mrow> </semantics></math>.</p> Full article ">Figure 4
<p>The verification of the size-dependent constitutive model and deep-learning SLC results plotted by “SIM” and solid lines with the experimental data [<a href="#B49-materials-14-00450" class="html-bibr">49</a>,<a href="#B50-materials-14-00450" class="html-bibr">50</a>] designated by “EXP” and symbolic points.</p> Full article ">Figure 5
<p>(<b>a</b>) True stress-strain curves for four thickness combinations of 34 nm and 63 nm as well as 48.5 nm Cu/Nb multi-layers illustrating the effect of layer combinations on the plastic deformation and flow strength. (<b>b</b>) Equivalent plastic strain versus true strain curves for the cases in (<b>a</b>) clarifying the size and layer geometrical order effects. (<b>c</b>) True stress-strain curves of 34 nm, 40 nm, and 63 nm Cu/Nb multi-layers demonstrating the effects of transverse (TRANS) and longitudinal (LONGL) loading directions plotted with solid and dash lines, respectively.</p> Full article ">Figure 6
<p>The variation of flow and yield strength (<b>left vertical axis</b>) as well as transition strain (<b>right vertical axis</b>), respectively, with respect to layer thickness in the range of 25 nm to 400 nm. The true stress-strain curves in this range is attached to the top right corner to clarify the overall constitutive behavior.</p> Full article ">Figure 7
<p>Variations of effective parameters in homogenized constitutive model with layer thicknesses where one layer thickness is fixed while the other one changes. Symbolic points signify simulation (SIM) results and solid lines the best fitted equivalent curves (EQ). Variations of <math display="inline"><semantics> <msub> <mi>τ</mi> <mi>sat</mi> </msub> </semantics></math>, for (<b>a</b>) fixed Cu layer spacing, d_Cu, and (<b>b</b>) fixed Nb layer spacing, d_Nb. Variations of <math display="inline"><semantics> <msub> <mi>h</mi> <mn>0</mn> </msub> </semantics></math>, for (<b>c</b>) fixed Cu layer spacing, d_Cu, and (<b>d</b>) fixed Nb layer spacing, d_Nb.</p> Full article ">Figure 8
<p>The comparison of the results obtained through the homogenized and nano-scale size-dependent constitutive model on 25 nm, 40 nm, 48.5 nm, 75 nm, and 300 nm Cu/Nb laminates. Symbolic points denote homogenized (HM) and solid lines the nano-scale (NS) model results.</p> Full article ">Figure 9
<p>(<b>a</b>) The validation of the temperature-dependent constitutive model with 34 nm, 60 nm, and 63 nm Cu/Nb laminates at 25 °C, 400 °C, and 500 °C. Symbolic points are the experimental (EXP) [<a href="#B49-materials-14-00450" class="html-bibr">49</a>,<a href="#B55-materials-14-00450" class="html-bibr">55</a>] and solid lines the simulation (SIM) data. (<b>b</b>) Flow strength versus temperature curves of 25 nm, 50 nm, 75 nm, and 100 nm Cu/Nb laminates at 25 °C up to 700 °C demonstrating the nonlinear effects of temperature growth on flow strength.</p> Full article ">
37 pages, 7570 KiB  
Article
Dependence of Heat Transport in Solids on Length-Scale, Pressure, and Temperature: Implications for Mechanisms and Thermodynamics
by Anne M. Hofmeister
Materials 2021, 14(2), 449; https://doi.org/10.3390/ma14020449 - 18 Jan 2021
Cited by 9 | Viewed by 3272
Abstract
Accurate laser-flash measurements of thermal diffusivity (D) of diverse bulk solids at moderate temperature (T), with thickness L of ~0.03 to 10 mm, reveal that D(T) = D∞(T)[1 − exp(−bL)]. [...] Read more.
Accurate laser-flash measurements of thermal diffusivity (D) of diverse bulk solids at moderate temperature (T), with thickness L of ~0.03 to 10 mm, reveal that D(T) = D∞(T)[1 − exp(−bL)]. When L is several mm, D∞(T) = FT−G + HT, where F is constant, G is ~1 or 0, and H (for insulators) is ~0.001. The attenuation parameter b = 6.19D∞−0.477 at 298 K for electrical insulators, elements, and alloys. Dimensional analysis confirms that D → 0 as L → 0, which is consistent with heat diffusion, requiring a medium. Thermal conductivity (κ) behaves similarly, being proportional to D. Attenuation describing heat conduction signifies that light is the diffusing entity in solids. A radiative transfer model with 1 free parameter that represents a simplified absorption coefficient describes the complex form for κ(T) of solids, including its strong peak at cryogenic temperatures. Three parameters describe κ with a secondary peak and/or a high-T increase. The strong length dependence and experimental difficulties in diamond anvil studies have yielded problematic transport properties. Reliable low-pressure data on diverse thick samples reveal a new thermodynamic formula for specific heat (∂ln(cP)/∂P = −linear compressibility), which leads to ∂ln(κ)/∂P = linear compressibility + ∂lnα/∂P, where α is thermal expansivity. These formulae support that heat conduction in solids equals diffusion of light down the thermal gradient, since changing P alters the space occupied by matter, but not by light. Full article
(This article belongs to the Special Issue High-Pressure Materials)
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Figure 1
<p>Thermal evolution in LFA (raw data) for thin samples: (<b>a</b>) Temperature-time curve of copper foil at 298 K, which initially heats due to the laser pulse (solid curve) and then cools to the surroundings. Raw data (grey) are fit with Cowan’s model. Black dot = position of <span class="html-italic">t</span><sub>½</sub>. (<b>b</b>) Schematic of initial conditions in two parallel bars. Heavy dots represent application of a pulse. (<b>c</b>) Schematic of initial conditions for a blended bar, where <span class="html-italic">Q</span> = <span class="html-italic">Q</span><sub>1</sub> + <span class="html-italic">Q</span><sub>2</sub>. (<b>d</b>) Operation essentials of LFA. Dashed box indicates the furnace enclosing the sample. Speckled rectangle depicts the edge-on the sample of thickness <span class="html-italic">L.</span> Grey shows graphite coatings. Arrows indicate arrival of laser energy and departure of emissions. Dashed arrows show fast ballistic transfer. Squiggle arrows indicate slow diffusive travel of heat across the sample. (<b>e</b>) Temperature–time curve of quartz at 298 K, showing a small amount of ballistic transfer, addressed by modeling (<a href="#sec3dot1dot2-materials-14-00449" class="html-sec">Section 3.1.2</a>). Schematics after Figure 5a and Figure 21a,b from Criss and Hofmeister [<a href="#B9-materials-14-00449" class="html-bibr">9</a>], which is open access.</p> Full article ">Figure 2
<p>Cowan’s model for LFA contrasted with DAC laser heating experiments: (<b>a</b>) Theoretical dimensionless cooling curves that assume small temperature changes and a narrow laser pulse (spike at <span class="html-italic">Dt</span>/<span class="html-italic">L</span><sup>2</sup> = 0) as in LFA experiments. Small radiative losses (℘ &lt; 1) are calculated using Equation (16) without modification, whereas <span class="html-italic">T</span>-<span class="html-italic">t</span> curves for large losses (℘ = 2, 5, or 10) from (16) are rescaled with maximum temperature set near unity. Scaling provides a visual curve more like LFA data (<a href="#materials-14-00449-f001" class="html-fig">Figure 1</a>) and better shows the downshifting of the halftime. Dots = <span class="html-italic">t</span><sub>½</sub> and its multiples. (<b>b</b>) Temperatures (squares) ascertained by Beck et al. [<a href="#B30-materials-14-00449" class="html-bibr">30</a>] from fitting emissions from laser heating the rear side of a 0.1 μm thick foil of iridium sandwiched between thin MgO slices in a DAC. Data were digitized and a polynomial fit was made to emissions processed at two different pressures. Unlike LFA, the laser serves as an unsteady furnace that provides a large surge in <span class="html-italic">T,</span> rather than adding an increment of heat. (<b>c</b>) Schematic of diamond anvil experiments on uncoated metal films. (<b>d</b>) Schematic of heat generated as the laser pulse penetrates and attenuates as it crosses an uncoated sample. Part (<b>b</b>) is modified after Beck et al. [<a href="#B30-materials-14-00449" class="html-bibr">30</a>] with permission from AIP.</p> Full article ">Figure 3
<p>Temperature–time curves revealing fast electronic transport: (<b>a</b>) Raw data collected over a short time from a Fe-Ni meteorite with <span class="html-italic">L</span> = 4.59 mm at moderate <span class="html-italic">T</span>. Blue curves from [<a href="#B9-materials-14-00449" class="html-bibr">9</a>], which is open access, used a holder and cap with apertures permitting laser light to reach the detector and/or to directly heat the thin graphite cap. Orange and green curves, offset for clarity, record emissions only from the meteorite and show electronic heat transport. (<b>b</b>) Long sample of electrolytic iron at high <span class="html-italic">T</span>. Purple curve shows a long duration where the sample is first heated by electrons, then cools radiatively to the surroundings, and next warms by vibrational transport. Long durations provide instabilities at long times. Both electronic <span class="html-italic">T</span>-<span class="html-italic">t</span> (inset) and vibrational evolution are fit to Cowan’s model. Pink curve shows data collected over a brief duration. Software used a large gain to meet a 1 Volt minimum signal strength, producing white noise. For long durations, wide spacing of points (inset) also produces noise. Similar <span class="html-italic">D</span><sub>ele</sub> was obtained in [<a href="#B9-materials-14-00449" class="html-bibr">9</a>] for other metals using short and long durations.</p> Full article ">Figure 4
<p>Log-log plot of thermal diffusivity vs. temperature for metals and single-crystal insulators with nearly end-member compositions, as labeled. Structures are various. Thickness, fits, and data sources are shown in <a href="#materials-14-00449-t001" class="html-table">Table 1</a>. Because synthetic sapphire is thin, low <span class="html-italic">T</span> data points were not used in fitting (see below). Components of the fit for KTaO<sub>3</sub> perovskite are shown in thick aqua solid and dotted curves.</p> Full article ">Figure 5
<p>Correlation of fitting coefficients F and G obtained using (21) for all 173 measurements compiled in [<a href="#B4-materials-14-00449" class="html-bibr">4</a>] (Table 7.2) plus metals (<a href="#materials-14-00449-t001" class="html-table">Table 1</a>; also [<a href="#B9-materials-14-00449" class="html-bibr">9</a>,<a href="#B11-materials-14-00449" class="html-bibr">11</a>,<a href="#B24-materials-14-00449" class="html-bibr">24</a>,<a href="#B25-materials-14-00449" class="html-bibr">25</a>]). Thicknesses exceed ~1 mm. Fits for anisotropic substances are made to each orientation explored. Exponential fits are provided for the various bonding types. Grainy samples (e.g., brucite, Mg(OH)<sub>2</sub>, and ceramics) fall slightly lower on the curves than similar crystals, due to porosity reducing <span class="html-italic">D</span>. Salts lie slightly below the curve for the silicates, which have ionic-covalent bonding. AgCl and metal Ti measurements were over small <span class="html-italic">T</span>-ranges, so F and G are less well constrained. Modified after Figure 7.5 in Hofmeister [<a href="#B4-materials-14-00449" class="html-bibr">4</a>] with permissions.</p> Full article ">Figure 6
<p>Data on metals: (<b>a</b>) Non-adherence to the Wiedemann–Franz law. Grey = Sommerfeld’s Lorenz number for the ratio of measured κ to electrical conductivity (σ) times T, is low by a factor of 3, stemming from ETKG describing fluctuations, not heat flow down a thermal gradient [<a href="#B6-materials-14-00449" class="html-bibr">6</a>]. Black symbols and curves = data on 7 elements from [<a href="#B45-materials-14-00449" class="html-bibr">45</a>] (Table 14.2). These elements had at least 4 temperatures where κ and σ were independently measured. (<b>b</b>) Correlation of κele (obtained from measured D and electronic heat capacity) with the number of nearly free electrons. Part (<b>b</b>) is modified after Figure 20b in Criss and Hofmeister [<a href="#B9-materials-14-00449" class="html-bibr">9</a>], which is open access.</p> Full article ">Figure 7
<p>Dependence of <span class="html-italic">D</span><sub>heat</sub> at 298 K on thickness. Fits are least squares to (22): (<b>a</b>) High <span class="html-italic">D</span> samples. Not shown is a point for MgO at 17.5 mm<sup>2</sup> s<sup>−1</sup> for <span class="html-italic">L</span> = 10.0 mm. Open plus = MgO. Circles = corundum, with black dots representing (1120) orientations. Grey dots = ceramic Al<sub>2</sub>O<sub>3</sub>. Squares = two orientations of quartz. X = Ge124 silica glass. (<b>b</b>) Expanded view showing low <span class="html-italic">D</span> and emphasizing thin samples. Triangles = yttrium stabilized cubic zirconia. These samples are fairly hard, permitting the preparation of sections approaching <span class="html-italic">L</span> = 0.1 mm at 5–6 mm across. Soft materials (alkali halides and micas), shown previously [<a href="#B4-materials-14-00449" class="html-bibr">4</a>], are omitted due to difficulties in preparing very thin sections with parallel faces. Modified after Figure 7.9 in Hofmeister [<a href="#B4-materials-14-00449" class="html-bibr">4</a>], with permission from Elsevier.</p> Full article ">Figure 8
<p>Dependence of <span class="html-italic">D</span> at 298 K on thickness for various elements and alloys: (<b>a</b>) Linear plot, showing fits to (22) for elements with &gt;4 measurements over a wide range of <span class="html-italic">L</span>. Parker et al. [<a href="#B11-materials-14-00449" class="html-bibr">11</a>] used an adiabatic model, rather than Cowan’s model used here. (<b>b</b>) Expanded view on logarithmic scales showing additional materials, mostly foils, and some single crystals. The power law fit is to brass and only for <span class="html-italic">L</span> &lt; 0.5 mm. The steels are non-magnetic. Foils were obtained from Alfa/Aesar, the Washington U. Physics Department machine shop, and various other sources.</p> Full article ">Figure 9
<p>Logarithmic plot of fitting parameters in <a href="#materials-14-00449-t002" class="html-table">Table 2</a>. Fused quartz and steel were not used in fitting because these measurements did not include very thin samples. High <span class="html-italic">T</span> data are shown only for MgO and YSZ.</p> Full article ">Figure 10
<p>Thermal diffusivity of cubic insulators vs. temperature for various thicknesses. Insets list samples from different sources and their thicknesses, plus fits: (<b>a</b>) MgO, where surface hydration is possible. Some datasets with similar thickness were merged, as indicated in the inset. The ~0.5 mm samples diverge from the power law but are still reasonably fit. (<b>b</b>) Yt-stabilized cubic zirconia. Colorless samples with <span class="html-italic">L</span> &lt; 1 mm are from MTI Corp., whereas thick samples are from Morion Company. Lower <span class="html-italic">D</span> for brown colored YSZ from Pretty Rock Inc. is attributed to additional impurities. Solid lines are least squares fits to the high-<span class="html-italic">T</span> datasets using Equation (21). Data on the thinnest section is more uncertain, due to lateral size. However, even with an uncertainty of 20%, these <span class="html-italic">D</span>-values remain below trends for larger samples.</p> Full article ">Figure 11
<p>Thermal diffusivity of MgO and YSZ as a function of thicknesses at various temperatures. Insets list fits. Samples are described in <a href="#materials-14-00449-f010" class="html-fig">Figure 10</a> and previously in [<a href="#B4-materials-14-00449" class="html-bibr">4</a>,<a href="#B10-materials-14-00449" class="html-bibr">10</a>].</p> Full article ">Figure 12
<p>Spectra in the visible (grey rectangle) and near-IR (white background) wavelength ranges relevant to laser heating of foils. Thin patterned black curves = blackbody emissions with <span class="html-italic">T</span> as labeled. Green, blue or orange curves = metal spectral properties calculated from indices of refraction tabulated in [<a href="#B83-materials-14-00449" class="html-bibr">83</a>]. Pink vertical line = the laser wavelength. Purple horizontal bar = range of the detector used in [<a href="#B30-materials-14-00449" class="html-bibr">30</a>,<a href="#B81-materials-14-00449" class="html-bibr">81</a>,<a href="#B82-materials-14-00449" class="html-bibr">82</a>]: (<b>a</b>) Comparison with high-<span class="html-italic">T</span> emission data (red curve) from [<a href="#B84-materials-14-00449" class="html-bibr">84</a>] to 1-<span class="html-italic">r</span>, which is reasonable for metals, due to opacity; (<b>b</b>) Comparison of mean free paths (=1/<span class="html-italic">A</span>) to blackbody curves for temperatures commonly explored in laser-heating DAC studies.</p> Full article ">Figure 13
<p>Temperatures calculated in two-laser DAC experiments: (<b>a</b>) Example from [<a href="#B81-materials-14-00449" class="html-bibr">81</a>], digitized and rescaled. Squares represent the front surface which absorbs the laser pulse and circles represent the rear. Conditions and <span class="html-italic">T</span> differences are listed. Y-axes limits were chosen so each <span class="html-italic">T</span>-<span class="html-italic">t</span> profile fills the graph. Platinum experiments [<a href="#B81-materials-14-00449" class="html-bibr">81</a>] began with the rear surface being hotter (grey rectangle), which prohibits the diffusion of heat from the front to the rear but permits the travel of the laser beam. Thin black curve = laser pulse profile [<a href="#B81-materials-14-00449" class="html-bibr">81</a>]. Since the relationship of data collection to the pulse was not specified, the laser profile was placed where the front surface began warming. Part (<b>a</b>) was modified after <a href="#materials-14-00449-f003" class="html-fig">Figure 3</a>d,f of McWilliams et al. [<a href="#B81-materials-14-00449" class="html-bibr">81</a>], with permissions from Elsevier. (<b>b</b>) Temperature differences across the ~3 μm foil of Pt compared to those in experiments on iron [<a href="#B82-materials-14-00449" class="html-bibr">82</a>], obtained from digitizing and subtracting temperature curves in [<a href="#B81-materials-14-00449" class="html-bibr">81</a>,<a href="#B82-materials-14-00449" class="html-bibr">82</a>]. Grey rectangle shows times where the rear surface is undesirably hotter than the front. Average <span class="html-italic">T</span> differences are rough.</p> Full article ">Figure 14
<p>Graphical representation of data compiled in <a href="#materials-14-00449-t003" class="html-table">Table 3</a>. Metals and Si (red crosses) are included in the fits: (<b>a</b>) Comparison of values from Equation (24) to measurements of <span class="html-italic">κ</span> as a function of pressure. RbF was excluded due to uncertainites in <span class="html-italic">c<sub>P</sub></span> [<a href="#B68-materials-14-00449" class="html-bibr">68</a>]; (<b>b</b>) Dependence of ∂ln(<span class="html-italic">κ</span>)/∂<span class="html-italic">P</span> on compressibility (<span class="html-italic">B<sub>T</sub></span><sup>−1</sup>), excluding fused quartz where bonds bend rather than contract. In both panels, hard solids cluster. These involve small, difficult to measure, changes during compression. Soft halides have large changes, but deform and absorb water, producing systematic errors. Halides with <span class="html-italic">B<sub>T</sub></span> &lt; 15.5 GPa, which is accompanied by ∂ln<span class="html-italic">κ</span>/∂<span class="html-italic">P</span> &gt; 60% GPa<sup>−1</sup> and phase transformations at very low <span class="html-italic">P</span>, were excluded from these plots.</p> Full article ">Figure 15
<p>Calculations using (42) compared to measured transport data at pressure from <a href="#materials-14-00449-t003" class="html-table">Table 3</a>. KBr exemplifies the soft, hydroscopic alkali halides (<span class="html-italic">B<sub>T</sub></span> &lt; 16 GPa). Reliable data on ∂<span class="html-italic">B</span>/∂<span class="html-italic">T</span> or δ<sub>T</sub> were not found for Ni, Sn, or Gd.</p> Full article ">Figure 16
<p>Fits to various metals using the radiative diffusion model with two mechanisms. We assumed <span class="html-italic">A</span>~<span class="html-italic">ν</span><sup>2</sup> for the infrared region and <span class="html-italic">A</span>~<span class="html-italic">ν</span> for the near-IR. Parameters are listed in the inserted table. If <span class="html-italic">κ</span> had been non-dimensionalized, only 3 parameters would be needed. Fits are in black. Data (grey) are from Hust and Lackford [<a href="#B24-materials-14-00449" class="html-bibr">24</a>], except for Al from Bradley and Radebaugh [<a href="#B106-materials-14-00449" class="html-bibr">106</a>]. Al-1100 is an alloy with about 1% impurities, usually Si or Fe. Tungsten is sintered, with non-negligible porosity. Modified after Figure 11.10 in Hofmeister [<a href="#B4-materials-14-00449" class="html-bibr">4</a>], with permission from Elsevier.</p> Full article ">
14 pages, 5612 KiB  
Article
Impact of Particle Size on Performance of Selective Laser Sintering Walnut Shell/Co-PES Powder
by Yueqiang Yu, Minzheng Jiang, Suling Wang, Yanling Guo, Ting Jiang, Weiliang Zeng and Yu Zhuang
Materials 2021, 14(2), 448; https://doi.org/10.3390/ma14020448 - 18 Jan 2021
Cited by 5 | Viewed by 2126
Abstract
The agricultural and forestry waste walnut shell and copolyester hot-melt adhesives (Co-PES) powder were selected as feedstock. A kind of low-cost, low-power consumption, and environmentally friendly walnut shell/Co-PES powder composites (WSPC) was used for selective laser sintering (SLS). Though analyzing the size and [...] Read more.
The agricultural and forestry waste walnut shell and copolyester hot-melt adhesives (Co-PES) powder were selected as feedstock. A kind of low-cost, low-power consumption, and environmentally friendly walnut shell/Co-PES powder composites (WSPC) was used for selective laser sintering (SLS). Though analyzing the size and morphology of walnut shell particle (≤550 μm) as well as performing an analysis of surface roughness, density, and mechanical test of WSPC parts with different particle sizes, results showed that the optimal mechanical performance (tensile strength of 2.011 MPa, bending strength of 3.5 MPa, impact strength of 0.718 KJ/m2) as walnut shell powder particle size was 80 to 120 μm. When walnut shell powder particle diameter was 120 to 180 μm, the minimum value of surface roughness of WSPC parts was 15.711 μm and density was approximately the maximum (0.926 g/cm3). Full article
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<p>Morphologies of powder particles: (<b>a</b>) walnut shell powder particles (<b>b</b>) Co-PES powder particles.</p> Full article ">Figure 2
<p>Process of WSPC for SLS: (<b>a</b>) AFS-360 rapid prototyping equipment (<b>b</b>) schematic diagram of SLS (<b>c</b>) sintering method (<b>d</b>) sintering state.</p> Full article ">Figure 3
<p>Particle size distribution of walnut shell powder: (<b>a</b>) type I (<b>b</b>) type II (<b>c</b>) type III (<b>d</b>) type V (<b>e</b>) type IV (<b>f</b>) type VI.</p> Full article ">Figure 4
<p>Microscopic morphology of walnut shell powder particle: (<b>a</b>) type I, (<b>b</b>) type II, (<b>c</b>) type III, (<b>d</b>) type IV, (<b>e</b>) type V and (<b>f</b>) type VI.</p> Full article ">Figure 5
<p>Micro-morphologies and three-dimensional morphologies of WSPC parts with different walnut shell powder particle sizes. (<b>a</b>) and (<b>b</b>) type I, (<b>c</b>) and (<b>d</b>) type II, (<b>e</b>) and (<b>f</b>) type III, (<b>g</b>) and (<b>h</b>) type IV, (<b>i</b>) and (<b>j</b>) typeV.</p> Full article ">Figure 5 Cont.
<p>Micro-morphologies and three-dimensional morphologies of WSPC parts with different walnut shell powder particle sizes. (<b>a</b>) and (<b>b</b>) type I, (<b>c</b>) and (<b>d</b>) type II, (<b>e</b>) and (<b>f</b>) type III, (<b>g</b>) and (<b>h</b>) type IV, (<b>i</b>) and (<b>j</b>) typeV.</p> Full article ">Figure 6
<p>SEM figures of sections of WSPC parts with different walnut shell powder particle sizes: (<b>a</b>) type I, (<b>b</b>) type II, (<b>c</b>) and (<b>d</b>) type III, (<b>e</b>) type IV and (<b>f</b>) type V.</p> Full article ">Figure 7
<p>Histograms of density of powder particles and parts.</p> Full article ">Figure 8
<p>The mechanical properties change curves of WSPC parts with different walnut shell powder particle sizes: (<b>a</b>) tensile strength, (<b>b</b>) bending strength and (<b>c</b>) impact strength.</p> Full article ">
13 pages, 2117 KiB  
Article
Experimental Investigation into the Effect of Pyrolysis on Chemical Forms of Heavy Metals in Sewage Sludge Biochar (SSB), with Brief Ecological Risk Assessment
by Binbin Li, Songxiong Ding, Haihong Fan and Yu Ren
Materials 2021, 14(2), 447; https://doi.org/10.3390/ma14020447 - 18 Jan 2021
Cited by 32 | Viewed by 3224
Abstract
Experimental investigations were carried out to study the effect of pyrolysis temperature on the characteristics, structure and total heavy metal contents of sewage sludge biochar (SSB). The changes in chemical forms of the heavy metals (Zn, Cu, Cr, Ni, Pb and Cd) caused [...] Read more.
Experimental investigations were carried out to study the effect of pyrolysis temperature on the characteristics, structure and total heavy metal contents of sewage sludge biochar (SSB). The changes in chemical forms of the heavy metals (Zn, Cu, Cr, Ni, Pb and Cd) caused by pyrolysis were analyzed, and the potential ecological risk of heavy metals in biochar (SSB) was evaluated. The conversion of sewage sludge into biochar by pyrolysis reduced the H/C and O/C ratios considerably, resulting in stronger carbonization and a higher degree of aromatic condensation in biochar. Measurement results showed that the pH and specific surface area of biochar increased as the pyrolysis temperature increased. It was found that elements Zn, Cu, Cr and Ni were enriched and confined in biochar SSB with increasing pyrolysis temperature from 300–700 °C; however, the residual rates of Pb and Cd in biochar SSB decreased significantly when the temperature was increased from 600 °C to 700 °C. Measurement with the BCR sequential extraction method revealed that the pyrolysis of sewage sludge at a suitable temperature transferred its bioavailable/degradable heavy metals into a more stable oxidizable/residual form in biochar SSB. Toxicity of heavy metals in biochar SSB could be reduced about four times if sewage sludge was pyrolyzed at a proper temperature; heavy metals confined in sludge SSB pyrolyzed at about 600 °C could be assessed as being low in ecological toxicity. Full article
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<p>Diagram of self-made pyrolysis device. 1: Nitrogen, 2: Rotor flow, 3: Tube furnace, 4: Heating tube, 5: Sand bath, 6: Particle sampler, 7: Quartz filter, 8: Wash gas bottles.</p> Full article ">Figure 2
<p>FTIR spectrum of the SS and its biochars. SS, sewage sludge; SSB-X, biochar prepared by pyrolysis of sewage sludge at X temperature (°C).</p> Full article ">Figure 3
<p>SEM images of sewage sludge and its biochar SSB. (<b>a</b>) SS(10,000×), (<b>b</b>) SS(20,000×), (<b>c</b>) SSB-300(10,000×), (<b>d</b>) SSB-300(20,000×), (<b>e</b>) SSB-400(10,000×), (<b>f</b>) SSB-400(20,000×) (<b>g</b>) SSB-500(10,000×), (<b>h</b>) SSB-500(20,000×), (<b>i</b>) SSB-600(10,000×), (<b>j</b>): SSB-600(20,000×), (<b>k</b>) SSB-700(10,000×), (<b>l</b>) SSB-700(20,000×).</p> Full article ">Figure 4
<p>Residual rate of heavy metals in biochar at different pyrolysis temperatures.</p> Full article ">Figure 5
<p>Chemical forms of heavy metals in SS and biochar.</p> Full article ">Figure 6
<p>C<sub>f</sub>, E<sub>r</sub>, RI of SS and biochar. (<b>a</b>) Decrease of metals contamination/pollution factor with increase of pyrolysis temperatures (<b>b</b>) Decrease of metals ecological risk as pyrolyzed at rising temperature (<b>c</b>) Overall ecological risk index of various pyrolyzed biochar SSB.</p> Full article ">
18 pages, 6755 KiB  
Article
Synthesis and Investigation of Cryogenic Mechanical Properties of Chopped-Glass-Fiber-Reinforced Polyisocyanurate Foam
by Jeong-Dae Kim, Jeong-Hyeon Kim, Dong-Ha Lee, Dong-Ju Yeom and Jae-Myung Lee
Materials 2021, 14(2), 446; https://doi.org/10.3390/ma14020446 - 18 Jan 2021
Cited by 10 | Viewed by 2849
Abstract
Polyisocyanurate foam (PIF) has been adopted as a liquefied natural gas (LNG) insulating material owing to its various mechanical merits such as high structural stability and mechanical strength, and excellent insulating ability. In an attempt to increase the mechanical strength of PIF, chopped-glass-fiber-reinforced [...] Read more.
Polyisocyanurate foam (PIF) has been adopted as a liquefied natural gas (LNG) insulating material owing to its various mechanical merits such as high structural stability and mechanical strength, and excellent insulating ability. In an attempt to increase the mechanical strength of PIF, chopped-glass-fiber-reinforced polyisocyanurate foam (CGR-PIF) was synthesized by adding chopped glass fibers to polyol and isocyanate, which are the raw materials used in the polymerization process for producing PIF. The main objective is to closely observe the compression material characteristics of PIF and CGR-PIF in terms of the cryogenic temperature. Therefore, compressive tests were conducted at cryogenic temperature including low temperatures, and microscopic images were obtained to analyze the cell size and distribution that affects the mechanical and thermal properties of the foam. Furthermore, recovery ratio and weight loss which are important factors of brittle fracture were evaluated, and the applicability of the foams to a cryogenic environment was evaluated. Finally, thermal conductivity, an important parameter of insulation, was evaluated. The obtained results confirm that the compressive strength of CGR-PIF significantly increases at cryogenic temperatures; moreover, a relatively higher thermal conductivity was observed in the case of CGR-PIF as compared to that of PIF owing to the chopped glass fibers. Full article
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<p>Schematic of the liquefied natural gas (LNG) insulation system. (<b>a</b>) cross-section of LNG insulation system (<b>b</b>) polymeric foam used in system (<b>c</b>) molecular structure of polyurethane foam (PUF) and polyisocyanurate foam (PIF).</p> Full article ">Figure 2
<p>Photograph of chopped glass fibers.</p> Full article ">Figure 3
<p>Manufacturing process of chopped-glass-fiber-reinforced polyisocyanurate foam (CGR-PIF).</p> Full article ">Figure 4
<p>(<b>a</b>) Schematic of sample for compression tests and (<b>b</b>) machined specimens for compression test of PIF and CGR-PIF.</p> Full article ">Figure 5
<p>Photographs and schematic of test apparatus. (<b>a</b>) Universal testing machine equipped with cryogenic chamber. (<b>b</b>) Laser flash analysis.</p> Full article ">Figure 6
<p>Cell morphologies of the PIF and CGR-PIF along the surface perpendicular to the foaming direction for (<b>a</b>) PIF and (<b>b</b>) CGR-PIF.</p> Full article ">Figure 7
<p>Cell morphologies of the PIF and CGR-PIF along the surface parallel to the foaming direction for (<b>a</b>) PIF and (<b>b</b>) CGR-PIF.</p> Full article ">Figure 8
<p>Typical compression stress–strain curves for polymeric foam.</p> Full article ">Figure 9
<p>Stress–strain curve of the PIF and CGR-PIF at (<b>a</b>) 20, (<b>b</b>) −40, (<b>c</b>) −100, and (<b>d</b>) −163 °C.</p> Full article ">Figure 10
<p>Compressive properties: (<b>a</b>) yield stress, (<b>b</b>) young’s modulus and (<b>c</b>) specific energy of PIF and CGR-PIF at various temperatures.</p> Full article ">Figure 11
<p>Definition of maximum deformation height and recovery height.</p> Full article ">Figure 12
<p>(<b>a</b>) Maximum deformation ratio and (<b>b</b>) recovery ratio for PIF and CGR-PIF.</p> Full article ">Figure 13
<p>Photograph of permanently deformed specimen after compressive test for (<b>a</b>) PIF at 20 °C, (<b>b</b>) CGR-PIF at 20 °C, (<b>c</b>) PIF at −163 °C, and (<b>d</b>) CGR-PIF at −163 °C.</p> Full article ">Figure 13 Cont.
<p>Photograph of permanently deformed specimen after compressive test for (<b>a</b>) PIF at 20 °C, (<b>b</b>) CGR-PIF at 20 °C, (<b>c</b>) PIF at −163 °C, and (<b>d</b>) CGR-PIF at −163 °C.</p> Full article ">Figure 14
<p>Weight loss ratio for PIF and CGR-PIF.</p> Full article ">Figure 15
<p>Typical curve of temperature change on the rear surface of the specimen measured by IR detector.</p> Full article ">
17 pages, 9920 KiB  
Article
Effect of the Notch-to-Depth Ratio on the Post-Cracking Behavior of Steel-Fiber-Reinforced Concrete
by José Valdez Aguilar, César A. Juárez-Alvarado, José M. Mendoza-Rangel and Bernardo T. Terán-Torres
Materials 2021, 14(2), 445; https://doi.org/10.3390/ma14020445 - 18 Jan 2021
Cited by 7 | Viewed by 2737
Abstract
Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically [...] Read more.
Concrete barely possesses tensile strength, and it is susceptible to cracking, which leads to a reduction of its service life. Consequently, it is significant to find a complementary material that helps alleviate these drawbacks. The aim of this research was to determine analytically and experimentally the effect of the addition of the steel fibers on the performance of the post-cracking stage on fiber-reinforced concrete, by studying four notch-to-depth ratios of 0, 0.08, 0.16, and 0.33. This was evaluated through 72 bending tests, using plain concrete (control) and fiber-reinforced concrete with volume fibers of 0.25% and 0.50%. Results showed that the specimens with a notch-to-depth ratio up to 0.33 are capable of attaining a hardening behavior. The study concludes that the increase in the dosage leads to an improvement in the residual performance, even though an increase in the notch-to-depth ratio has also occurred. Full article
(This article belongs to the Special Issue Concrete and Construction Materials)
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Figure 1
<p>Tensile bending test in prismatic specimens. (<b>a</b>) Measurement of the crack-mouth opening by means of extensometer clip-type Epsilon brand. (<b>b</b>) Measurement of the deflection at midspan of specimen through a linear variable differential transformer (LVDT), VISHAY brand.</p> Full article ">Figure 2
<p>Configuration of the 3-point bending test, dimensions in mm. (<b>a</b>) Measurement of the crack-mouth opening. (<b>b</b>) Measurement of the displacement at midspan by an LVDT.</p> Full article ">Figure 3
<p>Experimental behavior at the proportional limit.</p> Full article ">Figure 4
<p>General behavior at the proportional limit.</p> Full article ">Figure 5
<p>Curves of bending tensile test for the ratio (a/d) = 0: (<b>a</b>) Series 1 and (<b>b</b>) Series 2.</p> Full article ">Figure 6
<p>Curves of bending tensile test for the ratio (a/d) = 0.08: (<b>a</b>) Series 1 and (<b>b</b>) Series 2.</p> Full article ">Figure 7
<p>Curves of bending tensile test for the ratio (a/d) = 0.16, (<b>a</b>) Series 1, (<b>b</b>) Series 2.</p> Full article ">Figure 8
<p>Curves of bending tensile test for the ratio (a/d) = 0.33: (<b>a</b>) Series 1 and (<b>b</b>) Series 2.</p> Full article ">Figure 9
<p>Residual normal stresses for both series with fibers and for each of the studied (a/d) ratios (<b>a</b>) 0, (<b>b</b>) 0.08, (<b>c</b>) 0.16, and (<b>d</b>) 0.33.</p> Full article ">Figure 10
<p>Characteristic residual strength for each (a/d) ratio: (<b>a</b>) Series 1 and (<b>b</b>) Series 2.</p> Full article ">Figure 11
<p>Curve fit for the computation of the fracture energy by the slope fracture work model 2: (<b>a</b>) Series 1 and (<b>b</b>) Series 2.</p> Full article ">
8 pages, 10264 KiB  
Article
Fabrication of Highly Transparent Y2O3 Ceramics with CaO as Sintering Aid
by Danlei Yin, Jun Wang, Meng Ni, Peng Liu, Zhili Dong and Dingyuan Tang
Materials 2021, 14(2), 444; https://doi.org/10.3390/ma14020444 - 18 Jan 2021
Cited by 24 | Viewed by 3089
Abstract
Highly transparent Y2O3 ceramics were successfully fabricated with CaO as sintering aid. The microstructure evolution, optical transmittance, hardness and thermal conductivity of the Y2O3 ceramics were investigated. It was found that doping a small amount (0.01–0.15 wt.%) [...] Read more.
Highly transparent Y2O3 ceramics were successfully fabricated with CaO as sintering aid. The microstructure evolution, optical transmittance, hardness and thermal conductivity of the Y2O3 ceramics were investigated. It was found that doping a small amount (0.01–0.15 wt.%) of CaO could greatly improve the densification rate of Y2O3. With an optimized CaO dosage of 0.02 wt.% combined with the low temperature vacuum sintering plus hot isostatic pressing (HIP-ing), Y2O3 ceramics with in-line transmittance of 84.87% at 1200 nm and 81.4% at 600 nm were obtained. Full article
(This article belongs to the Special Issue Novel Laser Ceramic Materials and Applications)
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Figure 1
<p>Relative density versus vacuum sintering temperature of the Y<sub>2</sub>O<sub>3</sub> samples with different CaO contents.</p> Full article ">Figure 2
<p>Average grain size versus vacuum sintering temperature of Y<sub>2</sub>O<sub>3</sub> samples with different CaO contents.</p> Full article ">Figure 3
<p>SEM images of 0.02 wt.% CaO-doped (<b>a</b>,<b>c</b>,<b>e</b>) and 0.15 wt.% CaO-doped samples (<b>b</b>,<b>d</b>,<b>f</b>), vacuum sintered at 1450 °C, 1550 °C and 1650 °C, respectively.</p> Full article ">Figure 4
<p>SEM images of the ceramics after vacuum sintering 1550 °C and HIP-ing at 1510 °C with CaO concentration of (<b>a</b>) 0.02 wt.% and (<b>b</b>) 0.15 wt.%.</p> Full article ">Figure 5
<p>In-line transmission of the Y<sub>2</sub>O<sub>3</sub> ceramics with different CaO contents vacuum sintered at 1550 °C and HIP-ed at 1510 °C.</p> Full article ">Figure 6
<p>Thermal conductivity of the Y<sub>2</sub>O<sub>3</sub> ceramics with different contents of CaO versus temperature.</p> Full article ">
18 pages, 5571 KiB  
Article
Conformational Stability of Poly (N-Isopropylacrylamide) Anchored on the Surface of Gold Nanoparticles
by Runmei Li, Cong Cheng, Zhuorui Wang, Xuefan Gu, Caixia Zhang, Chen Wang, Xinyue Liang and Daodao Hu
Materials 2021, 14(2), 443; https://doi.org/10.3390/ma14020443 - 18 Jan 2021
Cited by 6 | Viewed by 2766
Abstract
To verify the temperature sensitive failure of poly (N-isopropylacrylamide) (PNIPAM) anchored on the surface of gold nanoparticles (AuNPs), the UV-Vis spectra with temperature variations of the following aqueous solutions respectively containing AuNPs-PNIPAM, Au-PNIPAM/PNIPAM, PNIPAM, in different media (including salt, ethanol, HCl and cetyltrimethylammoniumbromide [...] Read more.
To verify the temperature sensitive failure of poly (N-isopropylacrylamide) (PNIPAM) anchored on the surface of gold nanoparticles (AuNPs), the UV-Vis spectra with temperature variations of the following aqueous solutions respectively containing AuNPs-PNIPAM, Au-PNIPAM/PNIPAM, PNIPAM, in different media (including salt, ethanol, HCl and cetyltrimethylammoniumbromide (CTAB)), were systematically determined. The results indicated that the UV-Vis spectrum of AuNPs-PNIPAM suspension hardly changed even above the Lower Critical Solution Temperature (LCST) of PNIPAM, but that of Au-PNIPAM/PNIPAM sharply increased only in absorbance intensity. A possible mechanism of the failed temperature sensitivity of PNIPAM anchored on the surface of AuNPs was proposed. Being different from free PNIPAM molecules, a strong interaction exists among PNIPAM molecules anchored on the surface of AuNPs, restraining the change in conformation of PNIPAM. The temperature sensitivity of Au-PNIPAM/PNIPAM originates from the free PNIPAM molecules rather than the anchored PNIPAM one. The changing electrostatic interaction could effectively regulate the aggregation behavior of AuNPs-PNIPAM and enhance its sensitivity to temperature. Full article
(This article belongs to the Special Issue Advances in Metal-Based Nanoparticles)
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<p>The TEM images for gold nanoparticles (AuNPs) (<b>A</b>) and AuNPs-poly (N-isopropylacrylamide) (PNIPAM) (<b>B</b>), and size distribution for AuNPs (<b>C</b>) and AuNPs-PNIPAM (<b>D</b>). High magnification TEM image for Au-PNIPAM (<b>E</b>). TEM EDS mapping images for the Au element (<b>F</b>) and N element (<b>G</b>) and corresponding spectrum (<b>H</b>).</p> Full article ">Figure 2
<p>The change in the UV-Vis spectra with temperature for AuNPs-PNIPAM (<b>A</b>) and AuNPs (<b>B</b>).</p> Full article ">Figure 3
<p>The change in the UV-Vis spectra with temperature for AuNPs-PNIPAM/PNIAM (<b>A</b>) and the supernatant from centrifugation of AuNPs-PNIPAM/PNIAM (<b>B</b>,<b>C</b>).</p> Full article ">Figure 4
<p>The change in the UV-Vis spectra with temperature under a lower salt concentration (3.2 mM) for AuNPs-PNIPAM (<b>A</b>) and AuNPs (<b>B</b>), and under a higher salt concentration (16.9 mM) for AuNPs-PNIPAM (<b>C</b>) and AuNPs (<b>D</b>).</p> Full article ">Figure 5
<p>The change in the UV-Vis spectra with temperature for AuNPs-PNIPAM/PNIAM (<b>A</b>) and the supernatant from centrifugation of AuNPs-PNIPAM/PNIAM (<b>B</b>,<b>C</b>) in the presence of 16.9 mM of NaCl.</p> Full article ">Figure 6
<p>The possible mechanisms on the dispersive behavior of AuNPs-PNIPAM with change in temperature. (<b>A</b>) AuNPs-PNIPAM in absence of salt medium. The networks of hydrogen bonds formed among PNIPAM molecules restraining the thermo-sensitivity conformational change of PNIPAM; (<b>B</b>) AuNPs-PNIPAM in the presence of salt medium. The dispersive behavior of AuNPs-PNIPAM affected by the temperature dependent electrostatic interactions (including NaCl electrostatic screening, the negative charge increase due to Cl<sup>−1</sup> adsorption and enhancing dehydration of PNIPAM chains due to Cl<sup>−1</sup> polarization).</p> Full article ">Figure 7
<p>The change in the UV-Vis spectra with time for AuNPs-PNIPAM after addition of HCl (0.002 M) (<b>A</b>,<b>B</b>), the corresponding change in λ<sub>max</sub> with time (<b>C</b>), and acid titration curves for pure water and PNIPAM solution (3.47 × 10<sup>−6</sup> mg/L mM) (<b>D</b>).</p> Full article ">Figure 8
<p>A possible mechanism on the variation of AuNPs-PNIPAM Zeta potential with time in HCl medium. In this process, protons slowly enter into PNIPAM palisades due to protons binding on amide O of PNIPAM, which results in the aggregation of AuNPs-PNIPAM caused by a decrease in Zeta potential. Further increase of protons in PNIPAM palisades makes negatively charged AuNPs-PNIPAM positive, forming the hydrated PNIPAM shell to inhibit the aggregation.</p> Full article ">Figure 9
<p>The change in Uv-vis spectra of Au-PNIPAM in the presence of 0.018 M HCl with heating-and-cooling cycles (<b>A</b>), and change of λ<sub>max</sub> with heating-and-cooling cycles (<b>B</b>).</p> Full article ">Figure 10
<p>The change in Uv-vis spectra with time for AuNPs (<b>A</b>) and Au-PNIPAM (<b>B</b>) in ethanol medium.</p> Full article ">Figure 11
<p>The change in UV-Vis spectra with time for AuNPs (<b>A</b>) and Au-PNIPAM (<b>B</b>) in 0.025 mM of CTAB solution.</p> Full article ">
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